RI-MAN

Language：Others   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Dexterous manipulation using an under-actuated hand has been a challenging task due to its non-linear dynamical characteristics. For a linkage-based under-actuated hand designed to be used to grasp and manipulate large, heavy, and rigid objects stably, precision grasping is necessary, which makes the task even more difficult to deal with. While approaches based on external sensors have been introduced throughout the years, to create a robotic hand that can be used for various tasks in unstructured environments, this paper takes the standpoint that control techniques that do not fully depend on utilizing additional sensing elements need to be further developed. This paper applies the hybrid method using analytics models and data-driven-based approaches to analyze internal sensors' data during the operation of the robot and introduces novel data-driven-based techniques to compensate for the limitations of controlling a linkage-based under-actuated hand with a self-locking mechanism. Then, a within-hand object position manipulation framework with proposed methodologies is presented and experimented with to show its effectiveness.

DOI： 10.1109/iros55552.2023.10341517

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

This paper presents a novel approach for controlling variable end-point viscoelasticity in musculoskeletal robots to reduce contact forces during contact tasks. This is achieved by adjusting the desired end-point viscoelasticity in response to environmental contact, and by controlling the end-point viscoelasticity in muscle space. The musculoskeletal system of living bodies can adapt to the mechanical impedance of joints via the nonlinear properties of muscles, which are a significant factor in enhancing flexibility and safety during contact tasks. To take advantage of the characteristics of the musculoskeletal structure, we introduce nonlinear viscous properties into muscles and control the end-point viscosity by modulating the internal force. Numerical simulations are conducted to evaluate the proposed method, which demonstrates that the method successfully reduces contact forces during the crank-turning task while maintaining tracking performance. Overall, the proposed approach promises to achieve safer and more flexible interactions between robots and their environment.

DOI： 10.1080/01691864.2023.2239880

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.7210/jrsj.41.573

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1109/tro.2023.3286045

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

This article proposes novel control methods that lower impact force by preemptive movement and smooth transition to conventional contact-based impedance control. These techniques are suggested for application in force-control-based robots and position/velocity-control-based robots. Strong impact forces have a negative influence on multiple robotic tasks. Recently, preemptive impact reduction techniques that expand conventional contact impedance control using proximity sensors have been examined. However, a seamless transition from impact reduction to contact impedance control has yet to be demonstrated. It has, therefore, been necessary to switch control strategies or perform complicated parameter tuning. In contrast, our proposed methods utilize a serial combined impedance control framework to solve these problems. The preemptive impact reduction feature can be added to an already-implemented impedance controller because the parameter design is divided into impact reduction and contact impedance control. There is no discontinuity or abrupt alteration in the contact force, nor are there any excessively large contact forces that exceed the intended repulsive force established by the contact impedance control during the transition. Furthermore, although the preemptive impact reduction uses a crude optical proximity sensor, the influence of reflectance is minimized by employing a virtual viscous force. Analyses and real-world experiments with a 1-D mass model confirm these features, which are useful for many robots performing contact tasks.

DOI： 10.1109/TRO.2023.3286045

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Authorship：Last author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Robotics Society of Japan  

<p>A Straight Twisted Polymeric Fiber Actuator (STPFA) has attracted attention as a new rotational actuator because it is soft, lightweight, silent, and inexpensive. It can rotate when heating, and be back when cooling. However, it is difficult to improve the response, especially in the cooling phase when using natural cooling. In order to improve the response in natural cooling, antagonistical actuation is one of the effective methods. However, the diactivated-side actuator generates a disturbance-like torque when the other-side actuator is activated due to its passive torsional spring-like characteristics. In order to realize the antagonistical actuating module using a pair of rotational-type STPFA, in this paper, the models are constructed that can estimate the torque generated at both ends of an antagonistically arranged rotational STPFA from the change in heater resistance. A sensorless output torque control method is proposed for the total torque obtained as the difference between the torques at the two ends using the proposed STPFA models. The effectiveness of the proposed method is demonstrated through fundamental experiments using a prototype module. </p>

DOI： 10.7210/jrsj.41.573

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROBOMECH Journal  

To control a robot performing cooperative work between a human and robot, not only the position but also the force must be controlled from the viewpoint of human–robot contact. In addition, when a robot is used for fitting and handling, tasks that are conventionally performed by experienced humans, controlling the grasping force and the force exerted by the joints can produce motions similar to those of humans and contribute to improving the success rate of the work. In the field of force control, in addition to direct force control, admittance control and impedance control are modes based on the relationship between position and force, which are known to be robust and safe. However, admittance control often becomes unstable when the robot comes into contact with a rigid body, and the performance of impedance control is degraded by friction. In this study, we aim to realize safe and accurate force control in cooperative work with humans. As a precursor, we propose admittance and impedance control, which is a series connection of conventional admittance control and impedance control. We show that the proposed force control is more robust, stable, and accurate than impedance control and admittance controls alone, or at least as good as them, when in contact with an unknown environment. Its basic effectiveness and practical usefulness are demonstrated through numerical simulations and experimental results.

DOI： 10.1186/s40648-022-00237-5

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Robotics Society of Japan  

<p>This paper proposes a grasping stiffness control method using a multi-fingered robot hand. This method does not need any information of a grasped object, such as geometry and attitude. The grasping stiffness is derived from geometrical constraints including rolling contact between a multi-fingered robot hand and a grasped object. To estimate the grasping stiffness without the use of external sensors, a contact point position of each fingertip is estimated by a relative relationship between the initial contact position and a virtual object frame. The proposed method is designed so that the desired grasping stiffness optimally transforms into a joint stiffness, and the desired joint stiffness is realized through each joint angle control. Finally, the usefulness of the proposed method is demonstrated through several numerical simulation results. </p>

DOI： 10.7210/jrsj.40.928

CiNii Research

Authorship：Last author,　Corresponding author  

J-GLOBAL

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Robotics Society of Japan  

<p>In this paper, a new force controller that connects admittance and impedance controllers in series is verified experimentally. Until now, the serially combined admittance impedance controller has been proposed and its effectiveness has been demonstrated through only numerical simulations, whereas its practical use has not yet been shown. First, the control law of the proposed force controller is shown compared with the conventional force controllers. Next, to experiment with the proposed method in the simplest case, the 1DoF experimental setup is introduced, and conduct experiments to compare with the performance of the proposed method and present methods under several situations. Finally, Its practical usefulness is demonstrated through these experimental results. </p>

DOI： 10.7210/jrsj.40.355

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

This study proposes a novel twisted and coiled polymer fiber (TCPF) actuator fabricated from a polymer-coated optical fiber. The TCPF actuator is a soft actuator that is driven by heating; the TCPF actuator in combination with a cooling system has been widely studied for applications in robotics. Sensing is a major issue in such units; in particular, temperature sensing is important for the safe usage of the TCPF. To achieve this, the electrical properties of the heating wire are typically utilized. However, this method is affected by the input voltage noise because the circuit used for actuation is the same as that used for sensing. To separate these circuits, this study developed a temperature-sensing method for the TCPF based on an optical fiber. For propagating only the heat of the polymer to the optical fiber, we embedded the optical fiber in the TCPF. This study experimentally demonstrated that the TCPF actuator fabricated using the polymer-coated optical fiber can be driven by heating. Furthermore, using the developed sensing method, we achieved temperature and force control under isometric conditions.

DOI： https://doi.org/10.1109/LRA.2021.3070247

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

© 2020, The Author(s). In this paper, a novel visual-tactile sensor is proposed; additionally, an object manipulation method for a multi-fingered robotic hand grasping an object is proposed by detecting a contact position using the visual-tactile sensor. The visual-tactile sensor is composed of a hemispheric fingertip made of soft silicone with a hollow interior and a general USB camera located inside the fingertip to detect the displacement of the many point markers embedded in the silicone. The deformation of each point marker due to a contact force is measured, and a contact position is estimated reliably through a novel method of creating virtual points to determine the point clouds. The aim is to demonstrate both the estimation performance of the new visual-tactile sensor and its usefulness in a grasping and manipulation task. By using the contact position obtained from the proposed sensor and the position of each fingertip obtained from kinematics, the position and orientation of a grasped object are estimated and controlled. The effectiveness of the method is illustrated through numerical simulation and its practical use is demonstrated through grasping and manipulating experiments.

DOI： 10.1186/s40648-020-00162-5

Language：Others   Publishing type：Research paper (scientific journal)  

© 2016 IEEE. A twisted polymeric fiber (TPF) actuator often referred to as a fishing line/sewing thread artificial muscle, is one of the soft actuators which is made by twisting and heating a nylon fishing line. There are mainly two types of the TPF actuator, one is to make a contraction motion, which is sometimes called a twisted and coiled polymeric fiber actuator, and the other is to make a rotational motion, called simply a TPF actuator. This letter focuses on the latter one and proposes an estimated temperature feedback control method to regulate a torsional angle of the TPF actuator. The TPF actuator is very lightweight and low cost, but the advantage would be lost if some external sensors, such as a thermal sensor or encoder is used. In order to control the torsional angle without the use of the external sensors, a temperature of the actuator is estimated by measuring the change in the Ohm resistance of a heater wrapping around the actuator. By feedbacking the estimated temperature, the torsional angle can be regulated indirectly. First, the two types of models are proposed. One is to derive a desired temperature of the actuator from the desired angle. The other is to estimate the actuator&#039;s temperature from a change of the resistance of the actuator&#039;s heater. Next, the temperature feedback control law is composed using these two models. Finally, experiments of the torsional angle regulation are conducted using a prototype of the actuation module, which consists of antagonistically embedded two TPF actuators to demonstrate the usefulness of the proposed controller.

DOI： 10.1109/lra.2019.2901982

Language：Others   Publishing type：Research paper (scientific journal)  

© 2016 IEEE. In this letter, an angular trajectory tracking controller for a twisted polymeric fiber (TPF) actuator by the combination of a model-based feed-forward and estimated temperature feedback is proposed. TPF actuator is one of the soft actuators that can produce a rotational motion, which is made by twisting a nylon yarn and thermally treating it. Adding a feed-forward controller with a feedback controller makes it possible to reduce a phase lag and realizes a higher frequency response compared with using only the feedback controller when performing a time-dependent trajectory tracking. First, temperature-angle, resistance-temperature, and voltage-temperature models are composed, respectively, and then combined in order to design a feedforward controller. Next, parameter estimation is performed through experiments using the prototype of a rotational actuation module. Finally, trajectory-tracking experiments are conducted using a prototype to demonstrate that the proposed method can improve the tracking performance by reducing the phase lag.

DOI： 10.1109/lra.2019.2908484

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Robust Motor Control Strategy against Time-delays and Noises -Motor Intelligence on Open Environments-

DOI： 10.7210/jrsj.36.616

Language：English   Publishing type：Research paper (scientific journal)  

Feedforward control of twisted and coiled polymer actuator based on a macroscopic nonlinear model focusing on energy
© 2016 IEEE. This letter proposes a feedforward (FF) controller for the twisted and coiled polymer actuator (TCPA), the so-called fishing line/sewing thread artificial muscle, based on its macroscopic nonlinear model. TCPA is an artificial muscle, and it contracts up to 50&#37; in response to heating. Although several methods considering Joule heating as the input have been proposed to control the TCPA displacement, the FF controller based on the linear model shows the nonnegligible offset error. Therefore, the FF controller should be designed based on a nonlinear model, e.g., the model constructed by the authors. However, computing the inverse of the nonlinear model for the FF controller is difficult. Even if the inverse can be computed under static conditions, the problem of how to compensate the dynamics still remains. For this problem, we compensate the dynamics based on the idea of the Hammerstein model, namely we divide the inverse dynamics into the nonlinear transformation part and linear dynamics part. The former part consists of a converter from the displacement to temperature and a ratio adjuster for the squared voltage. Meanwhile, the latter is represented by the linear model of TCPA temperature. Through experiments, it is verified that the proposed FF controller can reduce the offset error of the displacement compared with the linear controller.

DOI： 10.1109/LRA.2018.2801884

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Brief Survey on Control of Multi-fingered Robotic Hand

DOI： 10.7210/jrsj.36.306

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a new set-point control method for a musculoskeletal arm by combining muscular internal force feedforward control with feedback control including a large time delay. The proposed method accomplishes robust and rapid positioning with a relatively small muscular force. In the positioning by the muscular internal force feedforward controller, a large muscular force is required to achieve good performance. On the other hand, in the positioning by the feedback controller including the large time delay, the system can easily fall into an unstable state. A simple linear combination of these two controllers makes it possible to improve the control performance and to overcome the drawbacks of each controller in a complementary manner. First, a two-link six-muscle arm model is considered as a musculoskeletal system in this study. Second, the new set-point control method, which consists of the feedforward control signal and the feedback control signal including the time delay, is designed. Third, the stability of the proposed method is investigated using the Lyapunov–Razumikhin method. Finally, the results of numerical simulations and experiments are presented to demonstrate the advantages of the proposed method.

DOI： 10.1080/01691864.2018.1453375

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a new set-point control method for a musculoskeletal arm by combining muscular internal force feedforward control with feedback control including a large time delay. The proposed method accomplishes robust and rapid positioning with a relatively small muscular force. In the positioning by the muscular internal force feedforward controller, a large muscular force is required to achieve good performance. On the other hand, in the positioning by the feedback controller including the large time delay, the system can easily fall into an unstable state. A simple linear combination of these two controllers makes it possible to improve the control performance and to overcome the drawbacks of each controller in a complementary manner. First, a two-link six-muscle arm model is considered as a musculoskeletal system in this study. Second, the new set-point control method, which consists of the feedforward control signal and the feedback control signal including the time delay, is designed. Third, the stability of the proposed method is investigated using the Lyapunov–Razumikhin method. Finally, the results of numerical simulations and experiments are presented to demonstrate the advantages of the proposed method.

DOI： 10.1080/01691864.2018.1453375

Language：English   Publishing type：Research paper (scientific journal)  

Reliable physical interaction is essential for many important challenges in robotic manipulation. In this paper, we consider Constrained Object Manipulations tasks (COM), i.e. tasks for which constraints are imposed on the grasped object rather than on the robot’s configuration. To enable robust physical interaction with the environment, this paper presents a manifold learning approach to encode the COM task as a vector field. This representation enables an intuitive task-consistent adaptation based on an object-level impedance controller. Simulations and experimental evaluations demonstrate the effectiveness of our approach for several typical COM tasks, including dexterous manipulation and contour following.

DOI： 10.1007/s10514-017-9643-z

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, a nonlinear dynamics model of the twisted and coiled polymer actuator (TCPA) driven by Joule heating is proposed. TCPA is an actuator based on the phenomenon that the twisted and coiled polymer contracts by heating. TCPA has received considerable research attention after the discovery of this phenomenon. Although several conventional models were proposed to explain TCPA behavior, they do not address several characteristics of a real TCPA, namely, the delay of the displacement to the temperature, temperature behavior to the input (Joule heating), and effect of the convective heat transfer on the relationship between the displacement and temperature. The macroscopic modeling framework presented herein explains these properties. The main ideas of the proposed model are (1) the energy relating to TCPA, and (2) the temperature and velocity dependence of the convective heat transfer coefficient. Experiments were conducted for three kinds of TCPA. It was verified that the proposed model is more viable than a conventional model. In particular, the proposed model reduced the prediction errors of the displacement by more than 50&#37; compared with the conventional model. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sna.2017.10.016

Language：English   Publishing type：Research paper (scientific journal)  

Manipulation is one of the most important fields in robotics. Nevertheless, even given the long history of manipulation research, technologies for multi-fingered robotic hands are still in development. This paper investigates past research studies on control systems of multi-fingered robotic hands for grasping and manipulation.

DOI： 10.1080/01691864.2017.1365011

Language：Japanese   Publishing type：Research paper (scientific journal)  

むだ時間を含む感覚フィードバックと筋内力フィードフォワードの相補的組み合わせによる筋骨格アームの位置制御
In this paper, a new set-point control method for a musculoskeletal system by combining a feedback control including a large time-delay with a muscular internal force feedforward control is proposed to accomplish a robust and rapid positioning with relatively low muscular contraction forces. It is known that feedback control under the existence of a large time-delay owns a drawback that there is a serious trade-off between a control performance and its stability. On the other hand, the muscular internal force feedforward control, which we have already proposed, also owns a drawback that it requires a large muscular contraction forces to make a good performance in a wide range. A simple linear combination of these two controllers makes it possible to improve the control performance and to complement each drawbacks each other. Firstly a two-link six-muscle arm model is given as a specific musculoskeletal system treated in this study. Secondly the new control law, which is composed of the feedback control signal including the time-delay and the internal force feedforward control signal, is constructed by only using a kinematic information of the musculoskeletal arm model. Next, a stability of the proposed method is discussed using Lyapunov-Razumikhin method. After that, results of several numerical simulations are shown to demonstrate several advantages of the proposed method.

DOI： 10.7210/jrsj.34.143

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a novel dynamic stable grasping method of an arbitrary polyhedral object for a hand-arm system with hemispherical fingertips. This method makes it possible to satisfy the force/torque equilibrium condition for the immobilization of the object without knowledge of the object. Two control signals are proposed which generate grasping forces normal and tangential to an object surface in a final state. The dynamics of the overall system is modeled and analyzed theoretically. We demonstrate the stable grasping of an arbitrary polyhedral object using the proposed controller through numerical simulations and experiments using a newly developed mechanical hand-arm system.

DOI： 10.1017/S0263574712000525

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Sensory Feedback for Stable Grasping and Posture Control by using a Pair of Minimum-DOF Robot Fingers with Soft Tips
This paper firstly derives and analyzes non-linear dynamics of pinch motions generated by a pair of robot fingers (1 D.O.F. and 2 D.O.F.) with soft tips and finds a feedback control signal for stable grasping and posture control of a rigid object based on passivity analysis. It is shown that measurements of rotation angle of the object by means of optical devices play a crucial role in construction of such feedback signals. Secondly, results of computer simulation by using the derived non-linear differencial equations with geometric constraints and results of experiments by using such robot fingers are presented. Then, usefulness of this control method is discussed from the practical viewpoint.

DOI： 10.7210/jrsj.21.763

Language：Japanese   Publishing type：Research paper (scientific journal)  

Dynamic Stable Pinching and Orientation Control by a Pair of Robot Fingers
This paper firstly shows Lagrange's equation of a pair of robot fingers with hemishperical tips pinching a rigid object under four geometric constraints. In derivation of the equation, it is assumed that the rigid object has two parallel flat surfaces, motion of the overall system is confined to a horizontal plane and the effect of gravity is ignored. It is then shown that there exists a sensory feedback signal not only for secure pinching with the desired contact force but also for control the object orientation at a specified rotational angle. It is also shown that the method of computer simulation based on the non-linear differential equation with four geometric constraints is discussed together with presenting some computational results.

DOI： 10.5687/iscie.16.253

Authorship：Last author   Language：English  

DOI： 10.48550/arXiv.2409.12564

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Robotics Society of Japan  

<p>State estimation is one of the key techniques to control soft robots, which is difficult to use sensors like traditional robots. Though modeling is an important process to achieve this, that of soft robots is challenging because of their highly nonlinear and uncertain behaviors. Many models were proposed, and we also proposed the one which contained stochastic distributed parameters for their uncertainty. In this study, we propose the state estimation method of a soft finger by using Kalman Filter framework. Stochastic parameters are suitable for constructing an appropriate estimator. Through an experimental validation, the performance of proposed estimator is discussed. </p>

DOI： 10.7210/jrsj.42.402

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Publisher：2024 IEEE 7th International Conference on Soft Robotics, RoboSoft 2024  

Pyshical flexibility is one of the good aspects of soft robotic hands when grasping an unknown-shaped object stably or interacting with around environment safely. On the other hand, considering controlling them dexterously, their flexibility can cause nonlinear and uncertain behaviors and this will be the barrier to accurate control. Furthermore, they deform continuously and entirely, which makes it difficult to use some sensors and to control by direct sensor feedback. For such a soft robot system, state estimation is the key to realizing accurate control. It is necessary to improve the accuracy of a model for good state estimation. Recently, probabilistic models have been proposed to represent uncertainties in soft robots, and this method can overcome traditional deterministic models that sometimes exhibit good but sometimes undesirable behaviors in terms of soft robots. We also have proposed the dynamic model of a soft finger with stochastic parameters. Because this model is the extension of the traditional dynamics, it is easy to apply the traditional state estimation method. In this paper, the state estimation method that uses the stochastic characteristics of the model is proposed. Through experiments, the efficiency of the proposed estimation is investigated.

DOI： 10.1109/ROBOSOFT60065.2024.10522025

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Language：Japanese   Publisher：Japanese Society for Engineering Education  

DOI： 10.20549/jseeja.2024.0_222

CiNii Research

Publisher：Advanced Robotics  

DOI： 10.1080/01691864.2023.2292318

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Fuji Technology Press Ltd.  

<p>Muscles in the musculoskeletal system can only transmit forces in the tensile direction, thereby resulting in redundant actuation. This redundancy creates an internal force among the muscles. The musculoskeletal potential method uses a potential field generated by the internal force among muscles and performs a step input of the muscle tension balanced at the desired posture to achieve the point-to-point (PTP) position. This method is extremely simple and does not require any sensory feedback or complex real-time calculations, as long as the target muscle tension is achieved. However, it is known that convergence to a desired posture is strongly influenced by muscular arrangement. In a previous study, we limited our analysis to a specific structure with two joints and six muscles and explained the conditions for convergence to a desired posture. However, when the structure of the target system, number of joints, and number of muscles are different, the convergence conditions cannot be clarified using the previous method. In this study, we extend the previous method to a musculoskeletal system with multiple one degrees-of-freedom (DOF) joints driven by monoarticular and biarticular muscles. In this study, we clarify the conditions that must be satisfied by the muscular arrangement to converge to a desired posture in the musculoskeletal potential method and verify the results through simulation.</p>

DOI： 10.20965/jrm.2023.p0751

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Flow Measurement and Instrumentation  

This paper describes the use of a high-speed streaming camera combined with in-house image processing for real-time particle tracking velocimetry (PTV) above 1 kHz. The proposed system is evaluated by measuring the diameter and velocity of multiple free-falling droplets in a simultaneous manner. Two existing particle tracking methods are examined: median flow (MF) and four-frame best estimate (4BE). Area-limiting processing is newly added to MF and 4BE to reduce the region of interest (ROI) in which particles are detected in the next image, resulting in area-limiting MF (AMF) and area-limiting 4BE (A4BE). Except for MF, the rest three methods of AMF, 4BE, and A4BE are capable of 1-kHz real-time PTV for 1246 pixel × 600 pixel images, with 4BE and A4BE achieving even at 10 kHz for 1246 pixel × 100 pixel images. The processing times for tracking and image preparation are measured, and the bottleneck is found to be the image acquisition and preparation, rather than the tracking. AMF achieves faster processing times than MF in all conditions, showing the effectiveness of the limited ROI, while 4BE and A4BE exhibit comparable performance. The measurement error is confirmed to be approximately 1% for droplet velocity and diameter, demonstrating the high accuracy of the first in-situ real-time PTV exceeding 1 kHz.

DOI： 10.1016/j.flowmeasinst.2023.102361

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DOI： 10.1186/s40648-023-00242-2

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>The authors have previously proposed an admittance control that uses the output of a proximity sensor as a virtual force as an impact force reduction control method for realizing safe robot contact and demonstrated its effectiveness through experiments. In this study, we discuss the parameter determination method and its effectiveness under various conditions of this control by modeling sensor output and analyzing the motion equarion of virtual object. As a result, we were able to formulate the position and velocity after convergence under the assumption that the velocity converges to a constant solution. By using this result, it is possible to determine the gain of the virtual force from the speed and position at the time of the collision. It is also possible to confirm the velocity and position at the time of the collision in advance.</p>

DOI： 10.1299/jsmermd.2023.2p1-e02

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>This paper proposes a novel method to control contact transitions. The proposed method uses an optical reflective proximity sensor and reduces impact forces during a collision. The smooth contact transition achieved by the proposed method will be helpful for many robot tasks, such as grasping a fragile object, soft landing, and human interaction. There exist three fundamental points underlying our approach. The first is to utilize the proximity sensor as a virtual force sensor. The second pertains the regulation of the virtual elastic force magnitude to gevern the contact state. The third is to use the virtual force as an input for our serial-combined impedance controller. We confirmed the usefulness of the proposed method through an experiment.</p>

DOI： 10.1299/jsmermd.2023.2p2-e02

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Until now, we have proposed a new force controller that connects admittance and impedance controller in series. In this paper, we experimentally verify the collision force reduction effect of the series admittance impedance control. By experiment with the proposed controller or conventional impedance control and a 1DOF linear mechanical system, it was found that the proposed method can reduce the collision force while keeping the same trajectory tracking performance as the conventional impedance control.</p>

DOI： 10.1299/jsmermd.2023.2a2-e02

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>This paper proposes a soft and silent robotic finger driven by the Twisted and Coiled Polymeric Fiber Actuator (TCPFA), which is one of the flexible and silent polymeric actuators. In order to overcome the narrow movable area and slow responsiveness, which are the typical drawback of the TCPFA, the proposed finger configures that a pair of TCPA is arranged to imitate intrinsic and extrinsic muscles of a human finger, and an oil-cooling system is introduced. Several fundamental experiments are conducted and through these results, the increase in the range of motion and the improvement in responsiveness are verified.</p>

DOI： 10.1299/jsmermd.2023.2a2-e07

CiNii Research

Publisher：2023 IEEE/SICE International Symposium on System Integration, SII 2023  

This paper proposes a data-driven-based stable object grasping method to grasp and realize object force/torque equilibrium for a triple-fingered under-actuated robotic system. Controlling the fingertip force of an under-actuated hand for precision grasp has been a challenging task in the robotic field due to the high nonlinearity of the under-actuated system as well as the inaccuracy in model-based controllers. By attaching a force sensor to the suitable location inside the robotic hand, necessary information for stable grasping, which is the detection of contact between fingertip and object and the magnitude of the fingertip force, is obtained using the proposed data-driven methods on internal sensor data in real-time. The obtained information is then used as feedback for the stable grasp controller to realize grasped object force/torque equilibrium.

DOI： 10.1109/SII55687.2023.10039475

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Language：Others   Publishing type：Research paper (scientific journal)  

In a musculoskeletal system, the musculoskeletal potential method utilizes the potential property generated by the internal force between muscles; posture control can be achieved by the step input of muscular tension balancing at the desired posture. The remarkable aspect of this method is that neither sensory feedback nor complicated real-time calculation is required at all. However, previous studies addressed only point-to-point control as motion control. In other words, with the focus on the convergence to the desired posture, path tracking has not been discussed. Extending the previous studies, this paper proposes a path tracking control based on a sensorless feedforward approach. The proposed method first finds the optimal set of muscular forces that can form the potential field to the desired potential shape realizing the desired path; next, inputting the obtained muscular forces into the system achieves path tracking. For verification, this paper demonstrates a case study of a musculoskeletal system with two joints and six muscles. In this case study, a constrained nonlinear programming method is used to find the optimal muscular force, and the path trackability is verified by numerical simulation.

DOI： 10.1186/s40648-023-00242-2

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

A twisted and coiled polymer fiber (TCPF) is a soft thermal actuator increasingly used in current robotics applications. When implementing TCPF in robotics applications, amplifying the TCPF strain and force is necessary to obtain the desired performance. Therefore, this study proposes a mechanism to amplify the strain and force of a TCPF. Considering the TCPF as a wire, the fixed and movable pulley mechanisms are available to amplify the TCPF strain and force, respectively. However, the amplification mechanism becomes bulky when the fixed pulleys are installed separately from the movable pulleys; thus, the TCPF utility reduces. This study focuses on two characteristics of the pantograph to design a compact amplification mechanism. The first characteristic is that the pulleys on the pantograph diagonal axes can be used as a movable pulley mechanism. The other characteristic is that the pantograph circumference can be a fixed pulley mechanism, as the circumference is always invariant. Based on these characteristics, the proposed mechanism can amplify both the TCPF strain and force. The experiments show that the force is amplified based on the number of loops around the diagonal axes. Although the load and temperature affect the strain amplification, the experiments confirm that the strain is amplified. In particular, depending on the loop number, the strain becomes 5.8 times the TCPF strain while maintaining the force level. Furthermore, changing the loop number, the strain and force are amplified 2.8 times and 2 times, respectively.

DOI： 10.1109/LRA.2022.3197268

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1109/LRA.2022.3197268

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1117/12.2612843

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Until now, many types of bipedal leg-wheeled mobile robots have been proposed. However, a compound locomotion, which combines wheeled locomotion and walking simultaneously, have not yet been studied enough. In this paper, the compound locomotion method is proposed in 2D sagittal plane using an optimization technique based on quadratic programming and the effectiveness is demonstrated through numerical simulation results.</p>

DOI： 10.1299/jsmermd.2022.2a1-p12

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>The soft gripper is possible to fit in the shape of grasped objects and realize safe handling due to its softness. On the other hand, modeling and control of the grasping force by the soft gripper has not been focused yet on so far even though it is also important for not injuring them. In this study, a sensorless tip force estimation of the cable-driven soft gripper is proposed because of the difficulty of implementing sensors to the soft body generally. The model to estimate the tip force is derived from the dynamics of the soft gripper based on the lumped parameterized system. Its effectiveness and limitation are demonstrated through numerical simulation results.</p>

DOI： 10.1299/jsmermd.2022.2a1-r06

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>In order to achieve high positional accuracy with force control, To use admittance control is one of the possible candidates. However, there is a trade-off between positional accuracy and responsiveness and stability due to contact, and especially the viscosity of the virtual object contributes significantly to the stability. In this paper, we propose to expand the stability region of the above force control using series admittance impedance control through experiments.</p>

DOI： 10.1299/jsmermd.2022.2a2-k10

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Conventional industrial manipulators use additional sensors to ensure the safety for collaborating workers and environment. However, if an error occurs in the sensors or the power is not turned on, it is dangerous for the environment, so a manipulator which has structural back-drivability is desirable. As one of the candidates, Tahara et al. developed a high back-drivable parallel-link manipulator with continuously variable transmission(CVT). The high back-drivable shaft motor has a small output force compared with the motor which used conventional gear reducer, so the output force that resists a large external force makes it saturated. In this paper, we propose a method to expand the range in which reaction force can be output against external force by constructing the algorithm to change reduction ratio. The performance of the proposed method is evaluated by simulation.</p>

DOI： 10.1299/jsmermd.2022.2p1-l06

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Twisted and Coiled Polymer Fiber (TCPF) actuators can generate relatively large force, however, they have a disadvantage of slow response due to their thermal actuation. This paper proposes a method to drive TCPF at high speed by using the resonance phenomenon of an elastic beam. Experimental results show that a TCPF with a slow thermal response of approximately 0.04 Hz can even excite vibration of approximately 7 Hz by using the resonance mechanism.</p>

DOI： 10.1299/jsmermd.2022.2a2-m02

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>This paper proposes a pantograph mechanism that amplifies both the strain and force of the twisted and coiled polymer fiber (TCPF). In the proposed mechanism, the TCPF is stored in the pantograph and forms several loops around the circumference and inside of pantograph. The outer loop works as the fixed pulley that amplify the TCPF strain. On the other hand, the inner loop amplifies the TCPF force by working as the movable pulley Through experiments when setting the number of outer and inner loops to 1, it was validated that the force by the proposed mechanism can output approximately double of the TCPF force. Furthermore, it was demonstrated that the strain can be amplified simultaneously.</p>

DOI： 10.1299/jsmermd.2022.2a1-m04

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Fiber Science and Technology, Japan  

DOI： 10.2115/fiber.78.192

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Language：Japanese   Publisher：The Robotics Society of Japan  

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DOI： 10.7210/jrsj.40.414

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

<p>Detecting the contact of Multi-fingered robotic hand’s fingertip and an object plays an important role in grasping the object stably. However, there remained considerable difficulties due to non-ideal external factors, in which for an under-actuated finger with force sensor located at the link far from the fingertip, each contact position cannot be determined using only the kinematic model and tactile information. In this paper, the Density-based clustering method to the force sensor and position encoder data is introduced to realize real-time contact detection. In our approach, data of the finger’s joint sensor during operation when not in contact with object is collected and analyzed using Density-based clustering algorithm. Learned information and collected data are then used to perform real-time contact detection.</p>

DOI： 10.1299/jsmermd.2022.2a1-n01

CiNii Research

Publisher：IEEE International Conference on Intelligent Robots and Systems  

This study focuses on replicating the muscu-loskeletal system of human arms for mimicking its movement. Muscle redundancy is critical for regulating the mechanical impedance of arms and legs. However, when implementing muscle redundancy on robots, making an ill-posed problem that cannot determine the muscle forces uniquely. In this paper, first, a method for controlling end-point stiffness in the muscle space for the joint and muscle redundant system is described. Next, the muscle model imitating the nonlinear viscosity characteristic of human muscles is introduced. Then, a method to control the joint viscosity by adjusting the internal forces of muscles adequately without affecting the stiffness control directly is proposed. Finally, numerical simulations are performed to investigate the effectiveness of the proposed method.

DOI： 10.1109/IROS47612.2022.9981712

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Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Direct Drive (DD) motors have high back drivability because no reduction gears are used, and are possible to improve the flexibility if used at robotic joint. Accordingly, on the other hand, the output joint becomes easily influenced by disturbances and thus high gain feedback control is needed for accurate position control. However, there is a limitation of the value of velocity gain (D gain) because D gain is increased, a high-frequency mechanical vibration would occur due to the amplification of a discretization noise. In this study, we focus on the viscoelasticity of polymers and propose a new viscoelastic module using polymers to add adequate mechanical viscoelasticity to the DD motor. The prototype mechanism of the module is proposed and its effectiveness is shown through basic experiments.</p>

DOI： 10.1299/jsmermd.2022.2a1-m03

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3389/frobt.2021.699792

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/LRA.2021.3070247

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.snb.2021.130262

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.20965/jrm.2021.p0619

Language：English   Publishing type：Research paper (scientific journal)  

This paper discusses a new model and experimental characterization for thermal responses of straight twisted polymer fiber (TPF) actuators in blocked torsion. The proposed model is derived from combining the fiber stiffness matrix with Shafer's model of free torsion. The derived model predicts that the blocking torque increases as the initial twist increases. Although it is not widely recognized, the tension of a straight TPF decreases as the initial torsion increases, and this paper explains this fact. The proposed model predicts the decrease in tension by using Shafer's kinematic model that considers the effect of radial thermal expansion. Experimental characterization and model verification are performed using nylon 6 (polyamide 6) fiber samples with ten different initial twists, ranging from weak to strong. The results indicate that as the initial twist increases, the torque increases and the tension decreases. The tension fluctuates with respect to time. The experimental results show that the shear modulus increases as the initial twist increases. The predictions of the proposed model are reasonably consistent with the experimental thermal responses of straight TPFs in blocked torsion when the constants obtained by experimental characterization are used.

DOI： 10.1088/1361-665X/abfc1a

Language：Others   Publishing type：Research paper (other academic)  

© 2020 IEEE. This paper proposes a planar tendon-driven joint with a soft cylinder contacting a rigid plane and its modelbased controller. In previous studies of planar tendon-driven joints with soft materials, those angles were only controlled despite the position displacement due to material deformation. Concurrently, position and angle displacements are addressed in the field of the robotic hand. Although some of the studies designed controllers using soft rolling contact models, their models cannot be applied in practical cases simply due to the effect of the property of the soft material. Even if it can be modeled, their feedback controllers also cannot be applied to the joint if the model is different from theirs. Although a controller design based on the obtained model is required, this realization is difficult because a constraint due to the soft rolling contact becomes a non-holonomic one. To resolve those problems, we set the soft rolling contact as a gray-box model and design the controller based on this modeled constraint. In the controller, the modeled constraint is used to generate a reference path. A soft rolling contact model is constructed through experiments, and then we validate the proposed controller by simulation using the modeled constraint.

DOI： 10.1109/AIM43001.2020.9158848

Language：Others   Publishing type：Research paper (other academic)  

© 2020 SPIE. Fishing-line artificial muscles can exhibit various motions. Twisted Polymer Fiber (TPF) actuators, which are a class of fishing-line artificial muscle actuators, generate torsional motion by applying heat. In general, untwisted fiber contracts by heating. However, measuring the blocking thermal tensile force of a TPF, we have discovered that the tensile force decreased and fluctuated depending on the initial number of twists in the TPF. This suggests that a TPF expands depending on the initial number of twists. Furthermore, the tensile force does not decrease monotonically but fluctuates during heating.

DOI： 10.1117/12.2557783

Language：English   Publishing type：Research paper (scientific journal)  

© 2020, The Author(s). In a musculoskeletal system, internal tensile forces are generated among the muscles because it is a redundant system. The balancing of the internal tensile forces for a given posture generates a potential field in the system. Therefore, the potential field is utilized for the sensorless feedforward position control and improvement of stability based on the feedback method. However, the stability of the internal tensile forces is strongly influenced by the muscular arrangement. Previous studies showed that a stable condition can be identified through the minimization of the potential at a desired posture, and the sufficient condition has been theoretically established; however, the geometric condition of the muscular arrangement has not been determined. To effectively exploit the characteristics of the internal tensile forces, the geometric condition must be elucidated in the design of a musculoskeletal system. This paper aims to clarify the geometric condition to generate stable internal tensile forces. Based on the conditions generating the potential that is minimum at the desired posture, the paper analyzes that the geometric condition on a musculoskeletal structure with two-link and six-muscle. Additionally, the identified condition is assessed based on simulations. As a result, we revealed the geometric condition of the muscular arrangement to generate stable internal tensile forces. By designing the muscular arrangement to satisfy the condition, the stability of the internal tensile forces is ensured, and consequently, a control method utilizing the characteristics of the internal tensile force is stably implemented.

DOI： 10.1186/s40648-020-00164-3

Language：Others   Publishing type：Research paper (scientific journal)  

Experiment verification and stability analysis of iterative learning control for shape memory alloy wire
© 2019, Fuji Technology Press. All rights reserved. To achieve the control of a small-sized robot manipulator, we focus on an actuator using a shape memory alloy (SMA). By providing an adjusted voltage, an SMA wire can itself generate heat, contract, and control its length. However, a strong hysteresis is generally known to be present in a given heat and deformation volume. Most of the control methods developed thus far have applied detailed modeling and model-based control. However, there are many cases in which it is difficult to determine the parameter settings required for modeling. By contrast, iterative learning control is a method that does not require detailed information on the dynamics and realizes the desired motion through iterative trials. Despite pioneering studies on the iterative learning control of SMA, convergence has yet to be proven in detail. This paper therefore describes a stability analysis of an iterative learning control to mathematically prove convergence at the desired length. This paper also details an experimental verification of the effect of convergence depending on the variation in gain.

DOI： 10.20965/jrm.2019.p0583

Language：Others   Publishing type：Research paper (scientific journal)  

Set-point control of a musculoskeletal system under gravity by a combination of feed-forward and feedback manners considering output limitation of muscular forces
© 2019, Fuji Technology Press. All rights reserved. This paper proposes a new control method for musculoskeletal systems, which combines a feed-forward input with a feedback input, while considering an output limit. Our previous research proposed a set-point control that used a complementary combination of feedback using a time delay and a muscular internal force feed-forward; it achieved robust and rapid positioning with relatively low muscular contraction forces. However, in that control method, the range of motion of the musculoskeletal system was limited within a horizontal plane. In other words, that system did not consider the effect of gravity. The controller proposed in this paper can achieve the reaching movement of the musculoskeletal system without requiring accurate physical parameters under gravity. Moreover, the input of the proposed method can be prevented from becoming saturated with the output limit. This paper describes the design of the proposed controller and demonstrates the effectiveness of the proposed method based on the results of numerical simulations.

DOI： 10.20965/jrm.2019.p0603

Language：Japanese  

Language：Japanese  

人工筋肉の開発とソフトロボティクスへの展開 釣糸人工筋肉のモデルベースド制御に向けた巨視的モデリング

Language：Others   Publishing type：Research paper (scientific journal)  

Choice of muscular forces for motion control of a robot arm with biarticular muscles
© 2019, Fuji Technology Press. All rights reserved. The contribution of biarticular muscles to the control of robotic arms and legs has recently attracted great interest in the field of robotics. The advantages of using biarticular muscles under kinetic interaction with the external environment have been well studied; however, the contribution of the muscles to the motion control of articulated robot arms under no kinetic interaction appears to remain an unclear issue, especially for robot arms of which the muscles are directly anchored to their links, which induces a change in the moment arms to allow the muscles to generate joint torques and permit point-to-point motion control to their desired postures in a feedforward manner with constant muscular forces. This paper presents a case study in which the role of biarticular muscles in the motion control of an articulated robot arm was investigated, focusing on the feature of its redundancy actuation, which allows an arbitrary choice from infinite combinations of muscular forces, realizing motion control to a desired posture. The numerical analysis in this paper addresses three typical combination choices. Mappings from muscular forces to desired postures are calculated in the analysis of the three choices. The simulation results of motion control executed according to the three mappings are also analyzed. The analysis indicates the interesting results that biarticular muscles do not contribute to the desired postures and that a very weak dependence property of monoarticular muscles on the desired postures exists for a particular choice. The simulation results also demonstrate that the implementation of one choice results in a degraded motion control performance as compared with that of the two other choices.

DOI： 10.20965/JRM.2019.P0143

Language：English   Publishing type：Research paper (scientific journal)  

3-DOF planar parallel-wire driven robot with an active balancer and its model-based adaptive control
© 2018, © 2018 Taylor & Francis and The Robotics Society of Japan. This paper has proposed a parallel-wire driven robot (PWDR) with an active balancer, which is notably useful for such applications as ceiling maintenance and object conveyance near a ceiling in a factory. Because this robot is an under-actuated system, the uncertainty of the inertial parameters of the load strongly affects the resultant motion and reduces the control accuracy because of the dynamics interference. However, to date, the dynamics of this robot has not been thoroughly elucidated. Thus, this study analyzes the dynamics of a PWDR that controls three degree-of-freedom using two wires and an active balancer. Moreover, based on the dynamic analysis, a model-based adaptive controller for the parameter uncertainty of a load is proposed, and its effectiveness is demonstrated through simulation.

DOI： 10.1080/01691864.2018.1493397

Language：English   Publishing type：Research paper (other academic)  

Two-types force controllers for a prismatic actuation module redundantly driven by multiple sheet-type dielectric elastomer actuators

DOI： 10.1109/AIM.2018.8452275

Language：English   Publishing type：Research paper (other academic)  

© 2018 IEEE. In this paper, an iterative learning control scheme for a trajectory tracking task using a one-DOF joint manipulator which is driven by multiple antagonistic fishing line artificial muscle actuators is proposed. The fishing line actuator is one of the soft actuators made by coiling and heating a twisted polymer fiber. It has attracted attention from those who would develop soft robotic devices because it is soft, light, and low-cost. It, however, has several drawbacks, e.g. output force limitation, strong nonlinearity, or energy efficiency, etc. To cope with these drawbacks, firstly a one-DOF manipulator driven by multiple antagonistic actuators is proposed to enhance its output force, and the energy efficiency is analyzed to investigate the relationship between the energy consumption and a number of activated fishing line actuator. Next, an iterative learning control scheme to accomplish a trajectory tracking task by the one-DOF manipulator is proposed to improve its control performance even though under the existence of unknown nonlinearities. The effectiveness of the proposed control scheme is demonstrated through several experiments.

DOI： 10.1109/ROBOSOFT.2018.8405370

Language：English  

Visual sensing information is useful for acquiring an object's position and orientation when a robot grasps and manipulates an object. However, it is still difficult to obtain such information accurately in real time. This is because visual sensing information generally includes a considerable time delay due to the low sampling rate of the sensing system, the computational cost of image processing, and the latency of data transmission from the sensor to the processor. It also includes noise, which generally originates from ambient light conditions as well as the object's color, texture, pattern, and light reflection characteristics, among other sources. Furthermore, the most important concern is that such time delay and noise sometimes induce unstable behavior of the system as a whole when the information is used directly in a real-time servo controller. One practical way to avoid such unstable behavior is to choose each feedback gain to be sufficiently low, and many visual servo controllers have been designed in this way. This approach, however, introduces another problem; namely, it sacrifices control performance. In this chapter, we present a robust grasping and manipulation controller based on finger-thumb opposability. This approach can effectively employ visual sensing information even when it includes considerable time delay or noise without any performance sacrifice. First, a control scheme for object manipulation using a virtual-object frame is designed. Next, numerical simulations conducted to verify the effectiveness of the control scheme are reported. Finally, the practical usefulness of the proposed scheme is illustrated through experimental results, which emphasize that the proposed scheme is an effective way to exploit visual sensing information that includes considerable time delay and noise in a manipulation controller.

DOI： 10.1016/B978-0-12-813385-9.00009-1

Language：English   Publishing type：Research paper (other academic)  

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. This paper focuses on the torsional motion of a torsional type fishing-line artificial muscle actuator, so to speak, Twisted Polymer Fiber (TPF) actuator. TPFs are expected as limited rotation motors or limited angle motors for mechatronic applications. Aiming to construct a gray-box model for TPF actuators, this paper derives the first-order transfer function as the model from the applied electrical power to the generated torque of an actuator. The relation from the temperature to the generated torsional torque is simply assumed as a linear function of which coefficient is the torsional rigidity. In the experiment, the validity of the obtained model is evaluated, and then the blocked torque of the TPF actuator is controlled.

DOI： 10.1117/12.2295899

Language：English   Publishing type：Research paper (scientific journal)  

There is a large gap between reality and grasp models that are currently available because of the static analysis that characterizes these approaches. This work attempts to fill this need by proposing a control law that, starting from an initial contact state which does not necessarily correspond to an equilibrium, achieves dynamically a stable grasp and a relative finger orientation in the case of pinching an object with arbitrary shape via rolling soft fingertips. Controlling relative finger orientation may improve grasping force manipulability and allow the appropriate shaping of the composite object consisted of the distal links and the object, for facilitating subsequent tasks. The proposed controller utilizes only finger proprioceptive measurements and is not based on the system model. Simulation and experimental results demonstrate the performance of the proposed controller with objects of different shapes.

DOI： 10.1017/S0263574717000303

Language：English   Publishing type：Research paper (other academic)  

This paper focuses on the torsional motion of a torsional type fishing-line artificial muscle actuator, so to speak, Twisted Polymer Fiber (TPF) actuator. TPFs are expected as limited rotation motors or limited angle motors for mechatronic applications. Aiming to construct a gray-box model for TPF actuators, this paper derives the first-order transfer function as the model from the applied electrical power to the generated torque of an actuator. The relation from the temperature to the generated torsional torque is simply assumed as a linear function of which coefficient is the torsional rigidity. In the experiment, the validity of the obtained model is evaluated, and then the blocked torque of the TPF actuator is controlled.

DOI： 10.1117/12.2295899

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a new tendon-driven robot with variable joint stiffness mechanisms. The tendon-driven robot is able to vary the stiffness of joints by sliding variable stiffness mechanisms over the link by wire tensions. As a reason for that structure and moment arms of the tendon-driven robot are changed depending on the position of the variable mechanism. Thus in this paper, the tendon-driven robot with variable stiffness mechanisms is designed, and the stiffness of the tendon-driven robot is evaluated by using a stiffness ellipsoid.

DOI： 10.1109/HUMANOIDS.2017.8246877

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel dynamics model of the twisted and coiled polymer actuator (TCPA) which is one of the artificial muscles recently discovered. It can be driven by Joule heating and can contract up to 25&#37;. Most of the conventional works employed the linear model of TCPA which represents the relationships between the input voltage, the temperature, and the displacement, but the real TCPA shows the nonlinearity. Although a nonlinear model was proposed based on the curve fitting, it is difficult to apply the model to the various TCPAs. Additionally, the conventional works cannot explain the effect of the convective heat transfer condition on the displacement behavior of TCPA. This paper aims to construct a general nonlinear model of TCPA based on the following two ideas: (1) The energy balance of TCPA and (2) the temperature and velocity dependence of the heat transfer coefficient. The temperature model is obtained from the time derivative of the energy balance, and the displacement model is derived as Lagrange's equation of motion with the dissipation function. Through experiments, it is verified that the proposed model is closer to the real dynamics than the conventional linear model.

DOI： 10.1109/AIM.2017.8014112

Language：English   Publishing type：Research paper (scientific journal)  

Tendon-driven robot utilizes only tensile force (i.e. tension) for motion generation. Therefore, a redundant actuation is characteristically necessary, and then it yields the internal force among tendons. Given the internal force for balance at a desired posture, the musculoskeletal tendon-driven manipulator has the inherent possibility of point-to-point position control without any sensory feedback. However, the motion convergence is strongly governed by the arrangement of tendons.This study analyzes the mathematical conditions of convergence for this sensorless position control by use of a Lyapunov function. Subsequently, targeting the two-link musculoskeletal structure with six tendons, the sufficient conditions for the convergence at desired posture are further defined by employing an approximation of the tendon-length based on a Taylor expansion. Finally, the convergent conditions are verified through simulation and validated via experimental results.

DOI： 10.1080/01691864.2017.1372212

Language：English   Publishing type：Research paper (scientific journal)  

Tendon-driven robot utilizes only tensile force (i.e. tension) for motion generation. Therefore, a redundant actuation is characteristically necessary, and then it yields the internal force among tendons. Given the internal force for balance at a desired posture, the musculoskeletal tendondriven manipulator has the inherent possibility of point-to-point position control without any sensory feedback. However, the motion convergence is strongly governed by the arrangement of tendons. This study analyzes the mathematical conditions of convergence for this sensorless position control by use of a Lyapunov function. Subsequently, targeting the two-link musculoskeletal structurewith six tendons, the sufficient conditions for the convergence at desired posture are further defined by employing an approximation of the tendon-length based on a Taylor expansion. Finally, the convergent conditions are verified through simulation and validated via experimental results.

DOI： 10.1080/01691864.2017.1372212

Language：Japanese  

An actuator unit consisting of multiple twisted and coiled polymer actuators (TCPA) with the feedforward controller is proposed. TCPA is made by two methods: 1) overtwisting the fiber and 2) winding the twisted fiber around the mandrel. The former output the larger force than the latter, while the former shows the smaller stroke. In order to realize the coexistence of large stroke and large output force, we combine multiple TCPAs fabricated by the latter method. The performance of the actuator unit is investigated through the experiment. Additionally, it is verified that the feedforward controller based on the authors' nonlinear displacement model can reduce the offset error compared with that based on the linear model.

DOI： 10.1299/jsmermd.2017.2A1-A02

Language：Japanese  

Recently, soft actuators have been paid attention to make robots lighter and more flexible than especially present industrial robots. Above all, the dielectric elastomer actuator is useful for the robot because of its relatively high output force and voltage driving. However, the dielectric elastomer actuator has several drawbacks that its stroke is small, and a characteristic that is extended when inputting a voltage. In this paper, by combining a joint system driven by antagonistic dielectric elastomer actuators and four-bar linkage, a 1 DOF manipulator which a has large range of motion is developed. In addition, the joint angle and force controllers of this manipulator are introduced, and those performance is verified experimentally.

DOI： 10.1299/jsmermd.2017.2A1-B06

Language：Japanese  

A fishing line actuator is one of the soft actuators made by coiling a twisted polymer fiber. In this paper, we propose 2 DOF manipulator driven by the multiple fishing line actuators to realize a joint angle control and a variable stiffness independently. The effectiveness of the proposed mechanism is evaluated experimentally.

DOI： 10.1299/jsmermd.2017.2A1-A03

Language：Japanese  

A novel displacement model of the twisted and coiled polymer actuator (TCPA) is proposed. In order to explicitly deal with the effect of the convective heat transfer on the displacement behavior, we focus on the temperature and velocity dependence of the convective heat transfer and regard the convective heat transfer as one of the dissipation function. Through some experiments for three TCPAs, it is verified that the proposed model is more plausible than the conventional linear model.

DOI： 10.1299/jsmermd.2017.2A1-A01

Language：Japanese  

Fishing-line artificial muscle is one of the soft actuators attracting a lot of attention. It is made of commercially available polymer fiber. It is heat-driven actuator, so that its efficiency and responsiveness are low. However it is a low-cost, light-weight, large-force, large-stroke, quiet actuator and can be easily made. It is roughly divided into the contract type actuator and the torsional type actuator. In this study, we focus on the torsional type actuator and aim at black-box modeling and controlling it. Torsional type fishing-line actuator generates torsional torque and limited rotation angle. In this paper, we assume first-order transfer function as the model of the torque from the electrical power applied the actuator. In the experiment, we measure the torque and identify the system. Then we control the torque of it with PI control, and validate the model and design of control system.

DOI： 10.1299/jsmermd.2017.2A1-A04

Language：English   Publishing type：Research paper (other academic)  

Recently, artificial muscles made of fishing lines or sewing threads, namely twisted and coiled polymer actuators (TCPAs), have been proposed by Haines et al. A TCPA contracts by applying heat and returns to its initial length by cooling. A TCPA can be driven by voltage if the TCPA is plated by metal or if conductive wire such as nichrome is wound around it. Compared with the conventional electroactive polymers, advantages of TCPAs are low cost, simple structure, large actuation strain, and large force. However, a big disadvantage of TCPAs is slow response due to heat transfer. The problem becomes apparent during cooling, although the response of heating can be improved by feedback control. This paper proposes a control method of switching heating and cooling. In the proposed method, a TCPA is cooled by an electric cooling fan. When the TCPA is heating, the cooling fan is stopped. In a previous report, the response speed can be improved by keeping cooling fan always on; however, unnecessary energy consumption is required even during heating. In the proposed method, energy consumption during heating does not increase and the response speed can be improved using fan only during cooling. The proposed control law is as follows. Firstly, the desired control input is determined by PI-D control with respect to the length of the actuator. Then, the control inputs to the heater and to the cooling fan are switched according to the sign of the PI-D controller output. The effectiveness of the proposed control method is demonstrated by comparing the cases with and without the cooling fan in the experiments.

DOI： 10.1117/12.2259766

Language：English   Publishing type：Research paper (scientific journal)  

Control of articulated robots by biarticular actuation has recently attracted great attention in the research field of robotics. Although many of studies concerned with this issue deal with legged robots or robot arms kinetically interacting with environment such as a floor or an object, motion control of an articulated robot arm with no kinetic interaction is also an interesting topic of biarticular actuation. In the motion control, a major issue is how it is possible for biarticular actuation to contribute to improvement of control
however, showing a clear finding for this issue seems to be considerably difficult. This paper considers a study for exploring that issue. Biarticular actuation usually constitutes a redundant actuation system
therefore, control of a robot arm to a desired posture can be achieved by many combinations of actuator forces. Based on this feature, this paper considers three typical combinations of actuator forces. Point-to-point control of the robot is performed for each of the combinations in simulation, and control performances of the combinations are compared with each other. In addition, the performances are compared with that of monoarticular actuation. In those comparisons, two of the three combinations show similar control performances, which suggests possibility of major contribution of biarticular actuators to motion control of a robot arm. On the other hand, control performance of the other combination is similar to that of monoarticular actuation, rather than those of other two combinations.

DOI： 10.1007/s10015-016-0322-5

Language：English   Publishing type：Research paper (other academic)  

Recently, artificial muscles made of fishing lines or sewing threads, namely twisted and coiled polymer actuators (TCPAs), have been proposed by Haines et al. A TCPA contracts by applying heat and returns to its initial length by cooling. A TCPA can be driven by voltage if the TCPA is plated by metal or if conductive wire such as nichrome is wound around it. Compared with the conventional electroactive polymers, advantages of TCPAs are low cost, simple structure, large actuation strain, and large force. However, a big disadvantage of TCPAs is slow response due to heat transfer. The problem becomes apparent during cooling, although the response of heating can be improved by feedback control. This paper proposes a control method of switching heating and cooling. In the proposed method, a TCPA is cooled by an electric cooling fan. When the TCPA is heating, the cooling fan is stopped. In a previous report, the response speed can be improved by keeping cooling fan always on; however, unnecessary energy consumption is required even during heating. In the proposed method, energy consumption during heating does not increase and the response speed can be improved using fan only during cooling. The proposed control law is as follows. Firstly, the desired control input is determined by PI-D control with respect to the length of the actuator. Then, the control inputs to the heater and to the cooling fan are switched according to the sign of the PI-D controller output. The effectiveness of the proposed control method is demonstrated by comparing the cases with and without the cooling fan in the experiments.

DOI： 10.1117/12.2259766

Language：English   Publishing type：Research paper (other academic)  

In this paper, our previously proposed set-point control method for a musculoskeletal system is improved to reduce required muscular forces and to avoid a saturation of muscular forces during movement. The previous method is robust against a considerable time-delay in sensory information, but it still requires large muscular forces to accomplish a desired position, and the maximum exertable muscular force has not yet been taken into consideration. To cope with these two issues, two variable parameters are newly introduced. One is for changing the combination ratio of feed-forward and feedback controllers to reduce necessary muscular forces. The other is for avoiding the saturation of muscular forces during movement The effectiveness of the proposed controller is demonstrated through several numerical simulation results.

DOI： 10.1109/IECON.2016.7793411

Language：English   Publishing type：Research paper (other academic)  

In this paper, our previously proposed set-point control method for a musculoskeletal system is improved to reduce required muscular forces and to avoid a saturation of muscular forces during movement. The previous method is robust against a considerable time-delay in sensory information, but it still requires large muscular forces to accomplish a desired position, and the maximum exertable muscular force has not yet been taken into consideration. To cope with these two issues, two variable parameters are newly introduced. One is for changing the combination ratio of feed-forward and feedback controllers to reduce necessary muscular forces. The other is for avoiding the saturation of muscular forces during movement. The effectiveness of the proposed controller is demonstrated through several numerical simulation results.

DOI： 10.1109/IECON.2016.7793411

Language：English   Publishing type：Research paper (other academic)  

Recently, fishing line artificial muscle has been developed and is paid much attention due to the properties such as large contraction, light weight and extremely low cost. Typical fishing line artificial muscle is made from Nylon thread and made by just twisting the polymer. In this paper, because of the structure of the actuator, such actuators may be named as coiled polymer actuators (CPAs). In this paper, a CPA is fabricated from commercial Nylon fishing line and Ni-Cr alloy (Nichrome) wire is wound around it. The CPA contracts by the Joule heat generated by applied voltage to the Nichrome wire. For designing the control system, a simple model is proposed. According to the physical principle of the actuator, two first-order transfer functions are introduced to represent the actuator model. One is a system from the input power to the temperature and the other is a system from the temperature to the deformation. From the system identification result, it is shown that the dominant dynamics is the system from the input power to the temperature. Using the developed model, position control of the voltage-driven CPA is discussed. Firstly, the static nonlinearity from the voltage to the power is eliminated. Then, a 2-DOF PID controller which includes an inversion-based feed forward controller and a PID controller are designed. In order to demonstrate the proposed controller, experimental verification is shown.

DOI： 10.1117/12.2218850

Language：Japanese   Publishing type：Research paper (scientific journal)  

2リンク6筋を有する筋骨格システムにおけるフィードフォワード位置決めのための筋配置条件
This paper focuses on the feedforward position control for a musculoskeletal system which has two links, two joints and six muscles. This feedforward control method utilizes resultant torque generated by inputting the internal force among muscles balancing at a desired posture. The motion convergence of this control method is extremely sensitive to the muscular arrangement. Using the approximation of Taylor expansion, the previous study clarified the sufficient condition of the muscular lengths for converging at a desired posture. This paper expands this discussion to clarify the geometric conditions of the muscular arrangement.

DOI： 10.7210/jrsj.34.133

Language：Japanese  

筋骨格構造の持つ特性を利用した位置制御に関する考察

Language：Japanese  

アクティブバランサを用いたパラレルワイヤ駆動ロボット

Language：English   Publishing type：Research paper (other academic)  

This paper considers experimental investigation of an antagonistically actuated robot manipulator. The focus of the investigation is how biarticular actuation contributes to control of the manipulator. Based on the feature that antagonistically robot manipulators can be controlled by feedforward control with constant inputs, this paper treats the case of PTP (point-to-point) control of robot postures. Due to expectation of difficulty for analytical approach, this paper takes experimental methodology of acquiring mappings between sensory and motor spaces by ANNs (artificial neural networks). Based on the idea that contribution of biarticular actuation may be influenced by choice of a sensory space, this paper considers not only joint angles of a manipulator but also Cartesian coordinate and angles in binocular visual space at the hand of the manipulator as sensory spaces. For each of them, the mappings obtained from trained ANNs are compared for the cases with and without biarticular actuation, based on interpolation performance of the ANNs examined through PTP control of the manipulator. The results of the comparison shows that choice of a sensory space is less effective to the interpolation performance in the case of biarticular actuation.

DOI： 10.1109/IECON.2015.7392655

Language：English   Publishing type：Research paper (other academic)  

An Experimental Study on Effect of Biarticular Muscles in an Antagonistically Actuated Robot Arm

Language：English   Publishing type：Research paper (other academic)  

The human body possesses a musculoskeletal structure in which muscles exist around the bones and joints. The musculoskeletal tendon-driven robot utilizes this structure. This robotic system uses sets of mechanical tendons, such as wire-cables and actuators instead of the vital muscles. The redundant actuation is necessary for the system when it does not actively use any external force nor a tensioner because the mechanical tendon can transmit only a tensile force. This structural characteristic enables feedforward motion-generation that does not need any sensory feedback. However, the convergent posture strongly depends on the tendon-arrangement. Targeting the tendon-driven manipulator, which has two links and six tendons, this paper expands the mathematical conditions for the convergence into the geometric conditions of tendon-arrangement. Based on the geometric conditions, a design method of the tendon-arrangement is discussed.

DOI： 10.1109/IECON.2015.7392248

Language：Japanese   Publishing type：Research paper (scientific journal)  

Muscular Arrangement Conditions of Musculoskeletal System with Two Joints and Six Muscles for Feedforward Position Control

DOI： 10.7210/jrsj.34.133

Language：Japanese   Publishing type：Research paper (scientific journal)  

Set-point Control for a Musculoskeletal System using Complementary Combination of a Sensory Feedback Including a Time-delay and a Muscular Internal Force Feedforward

DOI： 10.7210/jrsj.34.143

Language：English   Publishing type：Research paper (other academic)  

Recently, fishing line artificial muscle has been developed and is paid much attention due to the properties such as large contraction, light weight and extremely low cost. Typical fishing line artificial muscle is made from Nylon thread and made by just twisting the polymer. In this paper, because of the structure of the actuator, such actuators may be named as coiled polymer actuators (CPAs). In this paper, a CPA is fabricated from commercial Nylon fishing line and Ni-Cr alloy (Nichrome) wire is wound around it. The CPA contracts by the Joule heat generated by applied voltage to the Nichrome wire. For designing the control system, a simple model is proposed. According to the physical principle of the actuator, two first-order transfer functions are introduced to represent the actuator model. One is a system from the input power to the temperature and the other is a system from the temperature to the deformation. From the system identification result, it is shown that the dominant dynamics is the system from the input power to the temperature. Using the developed model, position control of the voltage-driven CPA is discussed. Firstly, the static nonlinearity from the voltage to the power is eliminated. Then, a 2-DOF PID controller which includes an inversion-based feed forward controller and a PID controller are designed. In order to demonstrate the proposed controller, experimental verification is shown.

DOI： 10.1117/12.2218850

Language：English   Publishing type：Research paper (other academic)  

We propose an evaluation method of grasp stability which takes into account the elastic deformation of fingertips from the viewpoint of energy. An evaluation value of grasp stability is derived as the minimum energy which causes slippage of a fingertip on its contact surface. To formulate the evaluation value, the elastic potential energy of fingertips and the gravitational potential energy of a grasped object are considered. It is ensured that fingertips do not slip on grasped object surfaces if the external energy applied to the object is less than the evaluation value. Since our evaluation value explicitly considers the deformation values of fingertips, grasp stability is evaluated by taking into consideration the contact forces generated by the deformation. The effectiveness of our method is verified through numerical examples.

DOI： 10.1109/IROS.2015.7353688

Language：English   Publishing type：Research paper (other academic)  

Determination Method of Tendon Arrangement Using Genetic Algorithm for Feedforward Positioning of Musculoskeletal System

DOI： 10.1109/IECON.2015.7392248

Language：English   Publishing type：Research paper (other academic)  

We propose an evaluation method of grasp stability which takes into account the elastic deformation of fingertips from the viewpoint of energy. An evaluation value of grasp stability is derived as the minimum energy which causes slippage of a fingertip on its contact surface. To formulate the evaluation value, the elastic potential energy of fingertips and the gravitational potential energy of a grasped object are considered. It is ensured that fingertips do not slip on grasped object surfaces if the external energy applied to the object is less than the evaluation value. Since our evaluation value explicitly considers the deformation values of fingertips, grasp stability is evaluated by taking into consideration the contact forces generated by the deformation. The effectiveness of our method is verified through numerical examples.

DOI： 10.1109/IROS.2015.7353688

Language：Japanese  

This paper proposes a set-point control method for a musculoskeletal system considering maximum muscular force. In our previous work, the set-point control method for a musculoskeletal system was proposed which combines a feedforward control with a sensory feedback control including a considerable time-delay. However, the maximum output force of each muscle have not been considered though it sometimes induces a wind-up phenomenon because of the saturation of the muscular force. The ratio function to determine the ratio of feedforward and feedback control inputs is newly introduced in this paper to prevent such a wind-up phenomenon without the saturation of muscular force, and generate more sophisticated reaction motion even if disturbances are added on the end-point during movement. Numerical simulation results are shown to demonstrate the effectiveness of the proposed method.

Language：Japanese  

This paper proposes a wearable walking assist device using a linear actuator for people who feel that walking is slightly painful in everyday life, and numerical walking simulation is conducted to evaluate the effectiveness of proposed devices, and construct an effective control method. The linear actuator intrinsically owns enough back driverbility because there is no reduction gear. Namely, it is possible to prevent tumble of a people who wears this device even if the device suddenly makes unexpected motion. This is because the people can easily resist against an output force of the actuator due to high backdrivability. A joint torque controller to assist a swing leg which is designed, and a numerical walking simulation is conducted to verify the effectiveness of assistance of the proposed device. From these simulation results, an effective feedback controller in terms of energy consumption is designed.

Language：Japanese  

This paper proposes a new object manipulation method by means of a multi-fingered hand using a particle filter to estimate a position and attitude of an object. In our previous work [1], the object virtual frame has been presented instead of an actual frame to manipulate an object without any external sensing information. A desired position and attitude of the object, however, has not been necessarily realized using the method because of no external sensing information. In order to cope with that, a new virtual frame is proposed based on a 3D laser range sensor data including considerable noise and time-delay in this paper. Firstly a particle filter is designed to estimate the position and attitude of the object from the sensing information. Then the new virtual frame is designed based on estimations of the particle filter.

Language：English   Publishing type：Research paper (other academic)  

This paper considers experimental investigation of an antagonistically actuated robot manipulator. The focus of the investigation is how biarticular actuation contributes to control of the manipulator. Based on the feature that antagonistically robot manipulators can be controlled by feedforward control with constant inputs, this paper treats the case of PTP (point-to-point) control of robot postures. Due to expectation of difficulty for analytical approach, this paper takes experimental methodology of acquiring mappings between sensory and motor spaces by ANNs (artificial neural networks). Based on the idea that contribution of biarticular actuation may be influenced by choice of a sensory space, this paper considers not only joint angles of a manipulator but also Cartesian coordinate and angles in binocular visual space at the hand of the manipulator as sensory spaces. For each of them, the mappings obtained from trained ANNs are compared for the cases with and without biarticular actuation, based on interpolation performance of the ANNs examined through PTP control of the manipulator. The results of the comparison shows that choice of a sensory space is less effective to the interpolation performance in the case of biarticular actuation.

DOI： 10.1109/IECON.2015.7392655

Language：English   Publishing type：Research paper (other academic)  

The human body possesses a musculoskeletal structure in which muscles exist around the bones and joints. The musculoskeletal tendon-driven robot utilizes this structure. This robotic system uses sets of mechanical tendons, such as wire-cables and actuators instead of the vital muscles. The redundant actuation is necessary for the system when it does not actively use any external force nor a tensioner because the mechanical tendon can transmit only a tensile force. This structural characteristic enables feedforward motion-generation that does not need any sensory feedback. However, the convergent posture strongly depends on the tendon-arrangement. Targeting the tendon-driven manipulator, which has two links and six tendons, this paper expands the mathematical conditions for the convergence into the geometric conditions of tendon-arrangement. Based on the geometric conditions, a design method of the tendon-arrangement is discussed.

DOI： 10.1109/IECON.2015.7392248

Language：Japanese   Publishing type：Research paper (scientific journal)  

Muscular internal force determination method using reinforcement learning for feedforward positioning of musculoskeletal system
The purpose of this paper is to present solution to an ill-posed problem for a muscular internal force feedforward positioning method of a musculoskeletal system. In our previous research, the muscular internal force feedforward positioning method of the musculoskeletal system has been proposed. In the method, the position regulation of the system can be accomplished by inputting a desired internal force balancing at a desired position. However, this control method has the ill-posed problem that the muscular internal force balancing at the desired position cannot be uniquely determined because the musculoskeletal system has muscular redundancy. A determination method of the muscular internal force is an important problem because a convergence and responsiveness of the system are influenced by the muscular internal force. Therefore, this study proposes a new determination method of the muscular internal force using reinforcement learning technique in order to determine the muscular internal force uniquely by considering control performance of the system. The proposed method numerically determines the muscular internal force that can converge at a desired position smaller than a conventional method. Its effectiveness is shown through numerical simulations for reaching movements of the musculoskeletal system.

DOI： 10.1299/transjsme.14-00313

Language：English   Publishing type：Research paper (other academic)  

We propose a grasp stability index which takes into account the elastic deformation of fingertips. In this index, an evaluation value of grasp stability is derived as the minimum energy which causes slippage of a fingertip on a grasped object surface. Elastic potential energy of the fingertips and gravitational potential energy of the object are considered in this index. It is ensured that any fingertip does not slip on a grasped object surface if the external energy added to the object is less than the evaluation value. This index has good features as follows. (i) Contact forces corresponding to the grasping state are taken into account. (ii) It is possible to derive a condition of stable grasp including the kinetic energy of a grasped object. The effectiveness of this index is verified through several numerical examples.

DOI： 10.1109/SII.2014.7028081

Language：English   Publishing type：Research paper (other academic)  

This paper proposed a concept of flexible wing-mechanism for the underwater fishlike robots. The proposed system consists of a fishlike body and a pair of flexible wing. The flexible wing mechanism utilizes a Shape Memory Alloy (SMA) actuator to realize small and lightweight system with high output/weight ratio. The SMA actuator can be controlled to adjust the shape. In the flow of water, shape of the wings is controlled and then the fluid resistance will be changed. Then, we can control the posture of the robot. The wing mechanism is constructed mainly from flexible materials. Thus, range of the fluid resistance becomes different between the high speed flow and low speed flow. In the fast flow condition, flexible wing mechanism is compressed and the range of the shape control becomes low. Then, the mechanism can control the posture of the robot under the various flow speeds.

DOI： 10.1109/ROBIO.2014.7090746

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel two-link planar manipulator with continuously variable transmission (CVT) mechanism by means of plural linear shaft motors. In our previous works, we have proposed the parallel-link manipulator with the CVT mechanism which has two orthogonal DOFs. However, its configuration is not useful for a practical field because only one main link can be rotated around two joints like a joystick. In order for this mechanism to be more useful, the two-link planar type manipulator with the CVT is newly modeled and developed. Firstly, the proposed manipulator is modeled, and its control signals are designed. Next, the output force of the end-point of the manipulator is evaluated by using both the Manipulating-Force Ellipsoid and the Dynamic Manipulability Ellipsoid. After that, several fundamental experiments are performed to evaluate the CVT mechanism and show the effectiveness of the proposed manipulator.

DOI： 10.1109/AIM.2014.6878147

Language：English   Publishing type：Research paper (other academic)  

Object-level impedance control is of great importance for object-centric tasks, such as robust grasping and dexterous manipulation. Despite the recent progress on this topic, how to specify the desired object impedance for a given task remains an open issue. In this paper, we decompose the object's impedance into two complementary components-the impedance for stable grasping and impedance for object manipulation. Then, we present a method to learn the desired object's manipulation impedance (stiffness) using data obtained from human demonstration. The approach is validated in two tasks, for robust grasping of a wine glass and for inserting a bulb, using the 1 6 degrees of freedom Allegro Hand mounted with the SynTouch tactile sensors.

DOI： 10.1109/ICRA.2014.6907861

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel set-point control method of a musculoskeletal system by combining a feedforward and feedback manner to complement each drawback each other. In our previous work, a feedforward positioning method of the musculoskeletal arm model was proposed which does not need any realtime sensory information. Its performance, however, depends on a muscular arrangement and an attitude of the arm, and thereby a large initial muscular internal force is necessary to make a good performance. On the other hand, it is well-known that a visual servoing is effective and versatile for the set-point control. However, there is a considerable time-delay due to a computational burden to acquire useful information from an image and an insufficient sampling period to capture each image when using a video frame rate camera. Thus in this paper, the feedforward and feedback signal are linearly combined into one in order to mutually complement each drawback. The combined control signal is newly designed and then numerical simulation results are shown to demonstrate the effectiveness and usefulness of the proposed method.

DOI： 10.1109/ICRA.2014.6907729

Language：Japanese   Publishing type：Research paper (scientific journal)  

Analysis of Quasistatic Convergent Condition for Feedforward Position Control of Musculoskeletal System by Use of Approximation of Muscular Lengths
This paper focuses on the feedforward position control for a musculoskeletal system which has two links, two joints and six muscles. This feedforward control method utilizes the resultant torque generated by inputting the internal force among muscles balancing at a desired posture. Therefore, any sensory feedback is not necessary for positioning. The motion convergence is extremely sensitive, namely it strongly depends on muscular arrangement of a musculoskeletal system. Focusing on the potential filed generated by the input of internal force, this paper analyzes the motion convergence from the quasistatic viewpoint. In this analysis, the muscular lengths along with the joint angles are approximated by Taylor expansion. After demonstration of the reliability of the approximation, Hessian matrix of the potential field is assessed to clarify the quasistatic condition of the motion convergence at a desired posture.

DOI： 10.7210/jrsj.32.372

Language：English   Publishing type：Research paper (other academic)  

This paper proposed a concept of flexible wing-mechanism for the underwater fishlike robots. The proposed system consists of a fishlike body and a pair of flexible wing. The flexible wing mechanism utilizes a Shape Memory Alloy (SMA) actuator to realize small and lightweight system with high output/weight ratio. The SMA actuator can be controlled to adjust the shape. In the flow of water, shape of the wings is controlled and then the fluid resistance will be changed. Then, we can control the posture of the robot. The wing mechanism is constructed mainly from flexible materials. Thus, range of the fluid resistance becomes different between the high speed flow and low speed flow. In the fast flow condition, flexible wing mechanism is compressed and the range of the shape control becomes low. Then, the mechanism can control the posture of the robot under the various flow speeds.

DOI： 10.1109/ROBIO.2014.7090746

Language：Japanese  

フィードフォワード位置決め制御における収束条件を満たす筋骨格構造の決定法

Language：Japanese  

触覚情報に基づく仮想物体情報を用いた物体把持・操作

Language：Japanese  

筋内力フィードフォワードと視覚フィードバックによる相補的複合位置制御

Language：English   Publishing type：Research paper (other academic)  

We propose a grasp stability index which takes into account the elastic deformation of fingertips. In this index, an evaluation value of grasp stability is derived as the minimum energy which causes slippage of a fingertip on a grasped object surface. Elastic potential energy of the fingertips and gravitational potential energy of the object are considered in this index. It is ensured that any fingertip does not slip on a grasped object surface if the external energy added to the object is less than the evaluation value. This index has good features as follows. (i) Contact forces corresponding to the grasping state are taken into account. (ii) It is possible to derive a condition of stable grasp including the kinetic energy of a grasped object. The effectiveness of this index is verified through several numerical examples.

DOI： 10.1109/SII.2014.7028081

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel two-link planar manipulator with continuously variable transmission (CVT) mechanism by means of plural linear shaft motors. In our previous works, we have proposed the parallel-link manipulator with the CVT mechanism which has two orthogonal DOFs. However, its configuration is not useful for a practical field because only one main link can be rotated around two joints like a joystick. In order for this mechanism to be more useful, the two-link planar type manipulator with the CVT is newly modeled and developed. Firstly, the proposed manipulator is modeled, and its control signals are designed. Next, the output force of the end-point of the manipulator is evaluated by using both the Manipulating-Force Ellipsoid and the Dynamic Manipulability Ellipsoid. After that, several fundamental experiments are performed to evaluate the CVT mechanism and show the effectiveness of the proposed manipulator.

DOI： 10.1109/AIM.2014.6878147

Language：English   Publishing type：Research paper (scientific journal)  

In a musculoskeletal system like a tendon-driven robot, redundant actuation is necessary because muscles (or mechanical parts such as tendons) can transmit tension only unidirectionally. This redundancy yields internal force among muscles, which has a particular field of potential energy. Using internal force as a feedforward input, a musculoskeletal system can achieve feedforward position control with no sensory feedback. This paper studies the feedforward position control coming from the redundancy for a non-pulley musculoskeletal system. Targeting a planar two-link system with six muscles as a case study, the motion convergence depending on the muscular arrangement is examined quasi-statically. The results point out that the convergence is extremely sensitive to the muscular arrangement, and adding small offsets for the muscular connected points can remarkably improve the positioning performance.

DOI： 10.1080/01691864.2013.824133

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a robust visual servoing method for object manipulation against temporary loss of sensory information. It is known that visual information is useful for reliable object grasping and precise manipulation. Visual information becomes unavailable, however when occlusion occurs or a grasped object disappears during manipulation. In that case, the behavior of the visual servoing system becomes unstable. Our proposed method enables an object to be grasped and manipulated stably even if visual information is temporarily unavailable during manipulation. This method is based on dynamic stable object grasping and manipulation proposed in our previous work and the concept of virtual object information. A dynamic model of the overall system is first formulated. A new controller using both actual and virtual object information is proposed next. The usefulness of this method is finally verified through both numerical simulation and experiments using a triple-fingered mechanical hand.

DOI： 10.20965/jrm.2013.p0125

Language：English   Publishing type：Research paper (other academic)  

Linear Combination of Feedforward and Feedback Manners to a Musculoskeletal System for Robust Set-Point Control

Language：English   Publishing type：Research paper (scientific journal)  

In a musculoskeletal system like a tendon-driven robot, redundant actuation is necessary because muscles (or mechanical parts such as tendons) can transmit tension only unidirectionally. This redundancy yields internal force among muscles, which has a particular field of potential energy. Using internal force as a feedforward input, a musculoskeletal system can achieve feedforward position control with no sensory feedback. This paper studies the feedforward position control coming from the redundancy for a non-pulley musculoskeletal system. Targeting a planar two-link system with six muscles as a case study, the motion convergence depending on the muscular arrangement is examined quasi-statically. The results point out that the convergence is extremely sensitive to the muscular arrangement, and adding small offsets for the muscular connected points can remarkably improve the positioning performance.

DOI： 10.1080/01691864.2013.824133

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a novel dynamic stable grasping method of an arbitrary polyhedral object for a hand-arm system with hemispherical fingertips. This method makes it possible to satisfy the force/torque equilibrium condition for the immobilization of the object without knowledge of the object. Two control signals are proposed which generate grasping forces normal and tangential to an object surface in a final state. The dynamics of the overall system is modeled and analyzed theoretically. We demonstrate the stable grasping of an arbitrary polyhedral object using the proposed controller through numerical simulations and experiments using a newly developed mechanical hand-arm system.

DOI： 10.1017/S0263574712000525

Language：Japanese   Publishing type：Research paper (scientific journal)  

Robotic Manipulator with Continuously Variable Transmission Mechanism

DOI： 10.7210/jrsj.31.564

Language：English   Publishing type：Research paper (other academic)  

The human body has a musculoskeletal system with the muscles which exist around the bones and joints. Taking notice of the structural characteristics that a human possesses inherently, this paper analyzes feedforward position control for the musculoskeletal system. The feedforward positioning does not need any sensory feedback by use of internal force balancing at a desired posture. Targeting a non-pulley musculoskeletal system with two links and six muscles, this paper clarifies mathematical conditions of the feedforward positioning to converge at a desired posture. In the analysis, muscular length is approximated by Taylor expansion. Based on quasi-statical approach, the convergent conditions are clarified. The verification of the conditions is conducted through simulation.

DOI： 10.1109/ARSO.2013.6705497

Language：English   Publishing type：Research paper (other academic)  

This paper studies the feedforward position control induced by the redundancy in a non-pulley-musculoskeletal system. Targeting a planar two-link musculoskeletal system with six muscles as a case study, the motion convergence depending on the muscular arrangement is examined. The results indicate that the motion convergence is extremely sensitive to the muscular arrangement and that adding small offsets for the points of muscle connection can remarkably improve the positioning performance. © 2013 Springer Science+Business Media Dordrecht.

DOI： 10.1007/978-94-007-6996-0-86

Language：Japanese   Publishing type：Research paper (scientific journal)  

Object Manipulation based on the Dynamic Stability

DOI： 10.7210/jrsj.31.364

Language：Japanese  

区分的な二次曲面近似に基づく把持姿勢候補の生成

Language：Japanese  

筋骨格システムにおけるフィードフォワード位置決め制御の収束性と筋配置の関係

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a robust visual servoing method for object manipulation against temporary loss of sensory information. It is known that visual information is useful for reliable object grasping and precise manipulation. Visual information becomes unavailable, however when occlusion occurs or a grasped object disappears during manipulation. In that case, the behavior of the visual servoing system becomes unstable. Our proposed method enables an object to be grasped and manipulated stably even if visual information is temporarily unavailable during manipulation. This method is based on dynamic stable object grasping and manipulation proposed in our previous work and the concept of virtual object information. A dynamic model of the overall system is first formulated. A new controller using both actual and virtual object information is proposed next. The usefulness of this method is finally verified through both numerical simulation and experiments using a triple-fingered mechanical hand.

DOI： 10.20965/jrm.2013.p0125

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a new feed-forward positioning method for a musculoskeletal-like robotic system considering a muscle-like nonlinear viscosity, and a new determination method of the internal force using the reinforcement learning scheme. In our previous works, a feed-forward positioning method for the musculoskeletal-like robotic systems has been proposed. In the method, the position regulation of the system can be accomplished by inputting a desired internal force balancing at a desired position. It has been quite effective for the muscle-like driven mechanism because no sensor is necessary to regulate the position. However, this method often induces an overshoot phenomenon when performing a set-point control. In addition, there is another intrinsic problem that musculoskeletal-like redundant-driven mechanisms own the ill-posed problems that the internal force is unable to determine uniquely. In this paper, for the farmer problem, a muscle-like nonlinear viscosity is newly added to the controller to reduce such an overshoot phenomenon and then to expand the stable region of the manipulator. For the latter problem, a determination method of the internal force using a reinforcement learning scheme is newly proposed. In what follows, firstly a new feed-forward controller which considers the muscle-like viscosity is introduced, and shows its effectiveness through numerical simulations. Next, the determination method of the internal force using a reinforcement learning scheme is proposed and its effectiveness is also shown through numerical simulations. © 2013 IEEE.

DOI： 10.1109/ARSO.2013.6705498

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a new feed-forward positioning method for a musculoskeletal-like robotic system considering a muscle-like nonlinear viscosity, and a new determination method of the internal force using the reinforcement learning scheme. In our previous works, a feed-forward positioning method for the musculoskeletal-like robotic systems has been proposed. In the method, the position regulation of the system can be accomplished by inputting a desired internal force balancing at a desired position. It has been quite effective for the muscle-like driven mechanism because no sensor is necessary to regulate the position. However, this method often induces an overshoot phenomenon when performing a set-point control. In addition, there is another intrinsic problem that musculoskeletal-like redundant-driven mechanisms own the ill-posed problems that the internal force is unable to determine uniquely. In this paper, for the farmer problem, a muscle-like nonlinear viscosity is newly added to the controller to reduce such an overshoot phenomenon and then to expand the stable region of the manipulator. For the latter problem, a determination method of the internal force using a reinforcement learning scheme is newly proposed. In what follows, firstly a new feed-forward controller which considers the muscle-like viscosity is introduced, and shows its effectiveness through numerical simulations. Next, the determination method of the internal force using a reinforcement learning scheme is proposed and its effectiveness is also shown through numerical simulations.

DOI： 10.1109/ARSO.2013.6705498

Language：English   Publishing type：Research paper (other academic)  

The human body has a musculoskeletal system with the muscles which exist around the bones and joints. Taking notice of the structural characteristics that a human possesses inherently, this paper analyzes feedforward position control for the musculoskeletal system. The feedforward positioning does not need any sensory feedback by use of internal force balancing at a desired posture. Targeting a non-pulley musculoskeletal system with two links and six muscles, this paper clarifies mathematical conditions of the feedforward positioning to converge at a desired posture. In the analysis, muscular length is approximated by Taylor expansion. Based on quasi-statical approach, the convergent conditions are clarified. The verification of the conditions is conducted through simulation.

DOI： 10.1109/ARSO.2013.6705497

Language：English   Publishing type：Research paper (other academic)  

This paper studies the feedforward position control induced by the redundancy in a non-pulley-musculoskeletal system. Targeting a planar two-link musculoskeletal system with six muscles as a case study, the motion convergence depending on the muscular arrangement is examined. The results indicate that the motion convergence is extremely sensitive to the muscular arrangement and that adding small offsets for the points of muscle connection can remarkably improve the positioning performance.

DOI： 10.1007/978-94-007-6996-0-86

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel object manipulation method by a multifingered robotic hand with torsional fingertip joints. By using the unique joint configuration effectively, a dynamic object manipulation can be achieved without the use of any external sensing. Firstly, a dynamic equation of motion of the overall system considering contact models between each fingertip and objectsurface is given. Secondly, an externally sensorless control signal to grasp and manipulate the object is designed. A numerical simulation and an experiment using a prototype are performed, and then finally the effectiveness of proposed method is illustrated through a simulation and an experiment. © 2011 IEEE.

DOI： 10.1109/MHS.2011.6102234

Language：English   Publishing type：Research paper (other academic)  

In this paper, a new iterative learning control method which uses multiple space variables for a musculoskeletal-like arm system is proposed to improve the robustness against noises being included in sensory information. In our previous works, the iterative learning control method for the redundant musculoskeletal arm to acquire a desired end-point trajectory simultaneous with an adequate internal force was proposed. The controller was designed using only muscle space variables, such as a muscle length and contractile velocity. It is known that the movement of the musculoskeletal system can be expressed in a hierarchical three-layered space which is composed of the muscle space, the joint space and the task space. Thus, the new iterative learning control input is composed of multiple space variables to improve its performance and robustness. Numerical simulations are conducted and their result is evaluated from the viewpoint of the robustness to noises of sensory information. An experiment is performed using a prototype of musculoskeletal-like manipulator, and the practical usefulness of the proposed method is demonstrated through the result.

DOI： 10.1109/IROS.2012.6385628

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a new visual servoing method for object manipulation robust to considerable time-delays of visual information. There still remain several problems in visual servoing methods although they are quite useful and effective for dexterous object manipulation. For instance, time-delays to obtain necessary information for object manipulation from visual images induce unstable behavior. The time-delays are mainly caused by low sampling rate of visual sensing system, computational cost for image processing, and latency of data transmission from visual sensor to processor. The method makes it possible to avoid such unstable behavior of the systems due to considerable time-delays using virtual object frame defined by only each joint angle. Firstly, a new control scheme for object manipulation using the virtual object frame is designed. Next, numerical simulations are conducted to verify the effectiveness of the control scheme. Finally, experimental results are shown to demonstrate the practical usefulness of proposed method.

DOI： 10.1109/IROS.2012.6385589

Language：English   Publishing type：Research paper (other academic)  

This paper proposed a type of tendon driven system using V-shaped SMA (shape-memory-alloy) actuator. In the proposed system, SMA actuators are bended at the end effector and the bended angles are controllable. Thus, the stiffness of the system can be adjusted by the bended angles. In addition, to control the end effector to the desired position, we developed a position control method based on the internal force using only the geometric constraints of the system. The validity of the proposed method was examined by some experiments.

Language：English   Publishing type：Research paper (other academic)  

This paper presents an improvement of our previously proposed dynamic object grasping and manipulation method. This method, which utilizes a dual-fingered hand of which each soft and hemispheric fingertip owns a torsional joint, has performed novel 3-dimensional dynamic object grasping and manipulation stably without the use of any external sensing device. However, several limitation and weakness have still remained in terms of dexterity and robustness. In order to improve it, firstly a triple-fingered hand is newly introduced instead of the dual-fingered hand to perform regrasping. Next, the previously proposed stable object grasping controller is adequately modified to perform dynamic regrasping during manipulation. Additionally, the virtual object attitude controller is also modified to improve its performance. Finally, several experiments are conducted by using a prototype, and the usefulness of proposed controller is demonstrated through these results.

DOI： 10.1109/ICRA.2012.6224681

Language：Japanese   Publishing type：Research paper (scientific journal)  

Sensory Feedback Attitude Control for an Arbitrary Polyhedral Object by a Multi-Fingered Hand-Arm System
This paper proposes a novel control method for stable grasping and attitude regulation of an object using a multi-fingered hand-arm system. This method is based on a task space sensory-feedback control using real time information of an object attitude. A unified control signal is designed for a whole hand-arm system. Firstly, nonholonomic rolling constraints between a multi-fingered hand-arm system and a grasped object are formulated. Secondly, a novel control signal to accomplish stable grasping and attitude regulation of the grasped object is proposed. To design the control signal, it is assumed that sensory information of the attitude of the grasped object is available in real time through some external sensors, such as vision, force, tactile sensors, and so on. Next, stability of the overall closed-loop dynamics and convergence of the object attitude to a desired attitude are given based on the passivity theory. Finally, several numerical simulations are conducted, and it is demonstrated that an arbitrary polyhedral object can be grasped, and its attitude converges to the desired one stably using proposed method.

DOI： 10.7210/jrsj.30.72

Language：Japanese   Publishing type：Research paper (scientific journal)  

Sensory Feedback Attitude Control for an Arbitrary Polyhedral Object by a Multi-Fingered Hand-Arm System

DOI： 10.7210/jrsj.30.72

Language：English   Publishing type：Research paper (other academic)  

This paper presents an improvement of our previously proposed dynamic object grasping and manipulation method. This method, which utilizes a dual-fingered hand of which each soft and hemispheric fingertip owns a torsional joint, has performed novel 3-dimensional dynamic object grasping and manipulation stably without the use of any external sensing device. However, several limitation and weakness have still remained in terms of dexterity and robustness. In order to improve it, firstly a triple-fingered hand is newly introduced instead of the dual-fingered hand to perform regrasping. Next, the previously proposed stable object grasping controller is adequately modified to perform dynamic regrasping during manipulation. Additionally, the virtual object attitude controller is also modified to improve its performance. Finally, several experiments are conducted by using a prototype, and the usefulness of proposed controller is demonstrated through these results.

DOI： 10.1109/ICRA.2012.6224681

Language：Japanese   Publishing type：Research paper (scientific journal)  

High-Backdrivable Parallel-Link Manipulator with Continuously Variable Transmission Mechanism
This paper proposes a novel high-backdrivable parallel-link manipulator with Continuously Variable Transmission (CVT) mechanism using several shaft actuators. The backdrivability is quite important and necessary for robots working around our living space to ensure the safety of us and environment. As for such robots, using a rotational actuator with a high reduction ratio reducer which has been commonly used is not adequate to realize the high backdrivability from the viewpoint of mechanical configuration. In this study, several high-backdrivable linear shaft actuators are utilized instead of it. Furthermore, the CVT mechanism which is provided by a novel configuration of the parallel mechanism is employed effectively. Using multiple linear shaft actuators and the CVT mechanism is able to surmount a drawback of the linear shaft actuator whose output force is relatively small compared with that of commonly used geared motors. As the first step of the study, a simple 1 DOF manipulator is proposed, and its kinematic and dynamic models are given. Next, a PD type feedback control signal to regulate both the arm's angle and its force/velocity ratio simultaneously is designed. A statical relation between the end-point output force of the manipulator and the CVT mechanism is illustrated. Finally, several fundamental experiments are performed using a prototype to demonstrate the effectiveness of proposed mechanism.

DOI： 10.7210/jrsj.30.99

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel object manipulation method by a multifingered robotic hand with torsional fingertip joints. By using the unique joint configuration effectively, a dynamic object manipulation can be achieved without the use of any external sensing. Firstly, a dynamic equation of motion of the overall system considering contact models between each fingertip and objectsurface is given. Secondly, an externally sensorless control signal to grasp and manipulate the object is designed. A numerical simulation and an experiment using a prototype are performed, and then finally the effectiveness of proposed method is illustrated through a simulation and an experiment.

DOI： 10.1109/MHS.2011.6102234

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a new visual servoing method for object manipulation robust to considerable time-delays of visual information. There still remain several problems in visual servoing methods although they are quite useful and effective for dexterous object manipulation. For instance, time-delays to obtain necessary information for object manipulation from visual images induce unstable behavior. The time-delays are mainly caused by low sampling rate of visual sensing system, computational cost for image processing, and latency of data transmission from visual sensor to processor. The method makes it possible to avoid such unstable behavior of the systems due to considerable time-delays using virtual object frame defined by only each joint angle. Firstly, a new control scheme for object manipulation using the virtual object frame is designed. Next, numerical simulations are conducted to verify the effectiveness of the control scheme. Finally, experimental results are shown to demonstrate the practical usefulness of proposed method.

DOI： 10.1109/IROS.2012.6385589

Language：English   Publishing type：Research paper (other academic)  

This paper proposed a type of tendon driven system using V-shaped SMA (shape-memory-alloy) actuator. In the proposed system, SMA actuators are bended at the end effector and the bended angles are controllable. Thus, the stiffness of the system can be adjusted by the bended angles. In addition, to control the end effector to the desired position, we developed a position control method based on the internal force using only the geometric constraints of the system. The validity of the proposed method was examined by some experiments.

Language：English   Publishing type：Research paper (other academic)  

In this paper, a new iterative learning control method which uses multiple space variables for a musculoskeletal-like arm system is proposed to improve the robustness against noises being included in sensory information. In our previous works, the iterative learning control method for the redundant musculoskeletal arm to acquire a desired endpoint trajectory simultaneous with an adequate internal force was proposed. The controller was designed using only muscle space variables, such as a muscle length and contractile velocity. It is known that the movement of the musculoskeletal system can be expressed in a hierarchical three-layered space which is composed of the muscle space, the joint space and the task space. Thus, the new iterative learning control input is composed of multiple space variables to improve its performance and robustness. Numerical simulations are conducted and their result is evaluated from the viewpoint of the robustness to noises of sensory information. An experiment is performed using a prototype of musculoskeletal-like manipulator, and the practical usefulness of the proposed method is demonstrated through the result.

DOI： 10.1109/IROS.2012.6385628

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The present paper investigates pinching movements using an index finger and a thumb actuated by redundant nonlinear digitorum muscles mimicking the configuration of human fingers. A dual-finger model with 2-d.o.f. joints for each finger and redundant nonlinear digitorum muscles is formulated to mimic the structure of human fingers. First, the kinematics and dynamics of the overall finger-object system, as well as the nonlinear muscular dynamics, are derived in accordance with the results of physiological studies. Next, a sensory-motor control law is proposed to enable stable pinching simultaneously with orientation regulation of an object. This control law includes an internal force term generated by co-construction of the redundant muscles. It is shown that the internal force term can modulate the damping factor in the joint space by its nonlinearity. Based on this effect, it is then shown by numerical simulation that our sensory-motor control law with co-contraction of each digitorum muscle makes it possible to realize pinching movements. Therefore, the pinching movements may be realized by means of a musculo-skeletal dual-finger system with the sensory-motor control law and co-contraction of redundant digitorum muscles. (C) Koninklijke Brill NV, Leiden and The Robotics Society of Japan, 2011

DOI： 10.1163/016918610X538543

Language：Japanese  

動的物体操作における指間相対姿勢拘束を用いた把持領域の拡張

Language：Japanese   Publishing type：Research paper (scientific journal)  

Externally Sensorless Position and Attitude Control of a Grasped Object Using a Virtual Frame by a Triple Soft-Fingered Hand
This paper proposes a novel object manipulation method to regulate the position and attitude of a rigid object of parallelepiped with maintaining stable grasping by a triple soft-fingered hand without use of any external sensing. In the authors' previous works, "the Blind Grasping" control scheme was proposed for a pair of soft-fingered hand to accomplish dynamic object grasping without use of any external sensing. However, it has just achieved a stable object grasping, and a simultaneous object position and attitude control has not yet been treated, so far. To this end, a ternary finger in addition to a pair of fingers is introduced in order to enhance the Blind Grasping manner to "the Blind Manipulation" manner. Since the Blind Grasping control input has been designed for a pair of fingers, in this paper it is renewed to install it into the triple-fingered robotic hand. Moreover, both the virtual object position and attitude are utilized by defining a virtual frame instead of real information of the object position and attitude in order to achieve the Blind Manipulation. First, the overall dynamics, which considers rolling contact constraints between each fingertip and object surface, is derived. Second, a control signal to regulate the virtual object position and attitude without use of any external sensing, "the Blind Manipulation", is designed. Next, the stability of the system is discussed briefly, and finally the usefulness of our proposed manipulation method is demonstrated through a numerical simulation.

DOI： 10.7210/jrsj.29.89

Language：English   Publishing type：Research paper (other academic)  

In this paper, an enhancement of a dynamic object grasping and manipulation method, which has been proposed by us previously, is presented. This enhancement makes it possible to grasp more various shaped objects which could not have been grasped by our previous method. In our previous method, a force/torque equilibrium condition to satisfy stable object grasping has been realized by only using grasping forces normal to an object surfaces. It is because each fingertip is soft and hemispheric and then rolling constraints arise during movement, and these phenomena cannot be stopped while existing the rolling constraint forces. Therefore, satisfying the dynamic force/torque equilibrium condition depends not only on a configuration of the multi-fingered hand system, but also on the shape of the grasped object. In this paper, a class of satisfying the force/torque equilibrium condition is expanded by generating counter tangential forces to suspend the rolling motion of each fingertip. In order to generate the counter tangential force, a relative attitude constraint between each finger is introduced. Firstly, a rolling constraint between each fingertip and object surface is given. Then, a relative attitude constraint control signal to generate constantly-produced tangential forces is designed. Finally, it is demonstrated through numerical simulations that the proposed control method accomplishes to grasp arbitrary shaped polyhedral objects and regulate its position and attitude, simultaneously.

DOI： 10.1109/ICAR.2011.6088574

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel vision-based grasping and manipulation scheme of a multi-fingered hand-arm system robust for a temporary lack of sensory information. Visual information is one of the fundamental components for reliable grasping and manipulation by a multi-fingered hand-arm system. However, in case that visual information such as position and attitude of an object comes to be unavailable due to the occlusion or if the object goes out-of-sight temporarily, unstable and unfavorable behavior is often induced. The proposed method, which utilizes the stable grasping control and the concept of virtual frame, enables to grasp and manipulate an object stably even if the visual information becomes suddenly and temporarily unavailable during manipulation. Firstly, a dynamical model of object grasping using a multi-fingered hand-arm system is formulated. Next, a new control scheme for robust object grasping and manipulation using the virtual frame is proposed. Finally, numerical simulations are performed to verify the usefulness of the proposed method.

DOI： 10.1109/IROS.2011.6048102

Language：English   Publishing type：Research paper (other academic)  

This paper proposes an iterative learning control scheme for a redundant manipulator to acquire a skilled hand writing motion of its end-point specified on an arbitrary smooth surface. Firstly, the existence of a unique solution to the Lagrange equation of motion of the robot, whose end-point motion is coincident with a given desired end-point trajectory described in Cartesian coordinate system, is shown theoretically. Second, the iterative learning control signal that enables the robot end-point to trace a desired trajectory specified on an arbitrary smooth surface with fulfilling a desired contact force is designed. Next, a numerical simulation for the iterative learning scheme is conducted to show the effectiveness of the proposed controller, and its result is compared to a theoretically derived desired joint angle trajectory. This comparison shows that there exists a unique solution of the desired joint angle trajectory when an initial pose of the manipulator and a desired end-point trajectory on the constraint surface are given, even under the existence of holonomic constraint and joint redundancy.

DOI： 10.1109/ICRA.2011.5979700

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel high-backdrivable parallel-link manipulator with Continuously Variable Transmission (CVT) mechanism using several shaft actuators. The backdrivability is important and necessary for robots that operate around our life space to guarantee the safety of us, themselves and environments. A rotational actuator with a high reduction ratio reducer has been commonly used in traditional robotics field, but it cannot realize the high-backdrivability without any sensory feedback. In this study, several high-backdrivable shaft actuators are used instead of it. Moreover, the CVT mechanism which is brought by a novel configuration of the parallel mechanism is employed effectively. To utilize multiple shaft actuators with the CVT mechanism is able to surmount a drawback of the shaft actuator whose output force is relatively weak. A simple 1 DOF manipulator is proposed as the first step of this study. Firstly, its kinematic and dynamic models are given. Next, a PD type feedback control signal to regulate the arm's angle and the CVT simultaneously is designed. A static relation between an output end-point force and the CVT mechanism is analyzed. Finally, several fundamental experiments are conducted to show the effectiveness of proposed mechanism.

DOI： 10.1109/IROS.2011.6048069

Language：Japanese   Publishing type：Research paper (scientific journal)  

手指の筋骨格と巧みさの源泉

DOI： 10.7210/jrsj.28.682

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents a proposal of an iterative learning control method for a musculoskeletal arm to acquire adequate internal force in order to realize human-like natural movements. Additionally, a dynamic damping ellipsoid at the end-point is introduced to evaluate internal forces obtained through the iterative learning scheme. Our previous works presented that a human-like smooth reaching movement using a musculoskeletal redundant arm model can be achieved by introducing a nonlinear muscle model and 'the virtual spring-damper hypothesis'. However, to date, the internal forces have been determined heuristically. As described in this paper, to determine internal forces more systematically, an iterative learning control method is used for acquisition of an adequate dynamic damping ellipsoid according to a given task. It is presented that the learning control method can perform effectively to realize given tasks, even though strong nonlinear characteristics of the muscles exist. After acquiring a given task, the dynamic damping ellipsoid is introduced to evaluate the relation between a damping effect generated by the acquired internal forces and a trajectory of the end-point. Some numerical simulations are performed and the usefulness of the learning control strategy, despite strong nonlinearity, is demonstrated through these results.

DOI： 10.1163/016918610X493615

Language：English  

DOI： 10.1155/2010/217867

Language：Japanese  

多指ハンドアームシステムを用いたセンソリーフィードバックによる把持物体の姿勢制御

Language：English   Publishing type：Research paper (other academic)  

This paper describes a tactile sensing to estimate the position and orientation of a joint-axis of a linked object. This tactile sensing is useful when a multi-jointed multi-fingered robotic hand manipulates a tool which has a joint. This estimation requires sensing of the location of a contact point and the direction of an edge of the tool as contact information measured by a robotic fingertip. A conventional hard fingertip with a force sensor can measure only the location of a contact point. In contrast, we have already developed a robotic fingertip with a force sensor and a soft skin, and it can measure not only the location of a contact point but also the direction of an edge of an object. The estimation of a joint-axis of a linked object is demonstrated by using the soft fingertip.

DOI： 10.1109/IROS.2010.5649899

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel method for stable grasping and attitude regulation of an object using a multi-fingered hand-arm system. The proposed method is based on a simple sensory-feedback control using the information of an object attitude, and any mathematically complicated computation, such as calculation of inverse dynamics and kinematics, are not required. In addition, the stability of the overall system applied this method is verified. Firstly, nonholonomic rolling constraints between a multi-fingered hand-arm system and an object are formulated. Then, a novel control method for stable grasping and attitude regulation of the grasped object is proposed. It is assumed that information of the attitude of the object is available in real time by external sensors, such as vision, force, tactile sensors, and so on. Next, the stability of the overall system is verified by analyzing the closed-loop dynamics. Finally, it is demonstrated through numerical simulations that our proposed method enables to grasp the object with arbitrary shape, and regulate the attitude of the object stably.

DOI： 10.1109/ROBIO.2010.5723559

Language：English   Publishing type：Research paper (other academic)  

This paper proposes an iterative learning control scheme in a task space for a musculoskeletal redundant planar arm model to accomplish a desired time dependent trajectory tracking task. In our previous work, we have proposed the iterative learning control scheme in a muscle length space for a two-link six-muscle planar arm model. This proposed method has been effective for performing a time dependent desired trajectory tracking task even under the existence of strong nonlinearity of muscles dynamics. However in the previous work, a muscle redundancy only treated, and a joint redundancy has not yet been considered. Also a solution of inverse kinematics from the task space to the joint angle space must be calculated in real-time. This paper considers both muscle and joint redundancies, and the task space iterative learning scheme is newly exploited. By introducing the task space controller, it is unnecessary to compute inverse kinematics from the task space to the joint space in real-time. Firstly, a three-joint nine-muscle redundant planar arm is modeled. Secondly, the task space iterative learning control signal is designed. Then finally, the effectiveness of our proposed controller is illustrated through some numerical simulation results even under the existence of both redundancies and the nonlinear muscle dynamics.

DOI： 10.1109/BWCCA.2010.168

Language：English   Publishing type：Research paper (other academic)  

This paper presents a proposal of an iterative learning control method for a musculoskeletal arm to acquire adequate internal force to realize human-like natural movements. Additionally, a dynamic damping ellipsoid at the end-point is introduced to evaluate internal forces obtained through the iterative learning. In our previous works, we have presented that a human-like smooth reaching movement using a musculoskeletal redundant arm model can be obtained by introducing a nonlinear muscle model and "the Virtual spring-damper hypothesis". However, the internal forces have been determined heuristically, so far. In this paper, an iterative learning control method is used for acquisition of an adequate dynamic damping ellipsoid according to a given task, in order to determine internal forces more systematically. It is presented that the learning control scheme can perform effectively to realize given desired tasks, even under the existence of strong nonlinear characteristics of the muscles. After acquiring a given task, the dynamic damping ellipsoid is introduced to evaluate the relation between a damping effect generated by the acquired internal forces and a trajectory of the end-point. Some numerical simulations are performed and the usefulness of the learning control strategy, despite strong nonlinearity of the muscles, is demonstrated through these results.

DOI： 10.1109/IROS.2010.5650071

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel object manipulation method by using a dual soft-fingered robotic hand system, in which each fingertip has a torsional joint. By using the torsional motion of the fingertips, a novel 3-dimensional dynamic object manipulation without use of any external sensing can be achieved even though the hand system has only two fingers. Firstly, our proposed system, which includes contact models between each fingertip and surfaces of an object, is modeled. A rolling contact between each fingertip and the object surfaces can be allowed because our proposed system has soft and deformable hemispheric fingertips. Moreover, a torsional contact model between each fingertip and the object surfaces is newly proposed. It is based on an assumption that the torsional motion induces an elastic strain potential. Secondly, a dynamic object manipulation control method is designed. The control signal is composed of four parts, the one is for grasping the object stably, the second one is for controlling a position of the object, the third one is for controlling an attitude of the object, and the last one is for the torsional fingertip motion. A numerical simulation based on our model is performed, and a manipulation experiment by using our developed setup is performed. The usefulness of our proposed method is demonstrated through these results.

DOI： 10.1109/ROBOT.2010.5509816

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel object manipulation method to regulate the position and attitude of an object in the task space with dynamic stability by using a triple soft-fingered robotic hand system. In our previous works, a dynamic object grasping method without use of any external sensing, called "the Blind Grasping", has been proposed. Although stable grasping in a dynamic sense has been realized by the method, a simultaneous object position and attitude control has not yet been treated, so far. In this paper, instead of using any information of the real object position and attitude, virtual data of object position and attitude are introduced by defining a virtual frame. By using the virtual information, a control signal to regulate the virtual object position and attitude without use of any external sensing is designed. The usefulness of our proposed control method even under the existence of nonholonomic rolling constraints is illustrated through a numerical simulation result.

DOI： 10.1109/ROBOT.2010.5509372

Language：English   Publishing type：Research paper (other academic)  

In a musculoskeletal structure, a set of internal force among muscles plays an important role. The internal force has the particular potential field. Using this property, we can control the position of a musculoskeletal system without any sensory feedback. However, the internal force can not be selected uniquely due to the muscular redundancy. This paper proposes a decision method of the internal force for the feedforward positioning. The usefulness of the proposed method is demonstrated through numeral analysis.

DOI： 10.1109/BWCCA.2010.163

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a stable object grasping method to realize dynamic force/torque equilibrium by using a triple robotic fingers system with soft and deformable hemispherical fingertips. In the authors' previous works, "Blind Grasping" control scheme, which realizes stable object grasping without use of any external sensing such as vision, force, or tactile sensing in the case of using a pair of robot fingers, has been proposed. This control methodology is based on a unique configuration of human hand, called "Fingers-Thumb Opposability". In this paper, a ternary finger in addition to a pair of fingers is introduced not only to expand a stable region of grasping, but also to enhance dexterity and versatility of the multi-fingered robotic hand system. To this end, a "Blind Grasping" manner is modified in order to install it in the triple fingers system. First, dynamics of the triple robotic fingers system and a grasped object with considering rolling constraints is modeled, and a control input based on the blind grasping manner is designed. Next, the closed-loop dynamics is derived and a stability analysis is shown briefly. Finally, its usefulness is discussed through numerical simulation results.

DOI： 10.1109/IROS.2009.5354563

Language：English  

Manipulation of 2D object with arbitrary shape by robot finger under rolling constraint
Contact of two contours of a pinched object and a robot finger tip, with arbitrary shape, is expressed in terms of differential geometry. The overall finger-object dynamics with rolling and contact constraints is derived as Euler-Lagrange&#039; equation of motion and the first differential equation with curvatures of the contours is derived for updating the length parameters. Despite the complicated mathematical structure, a control input signal is proposed, which can be constructed without using object geometrical information or external sensing, and it is shown that it is effective to stabilize rotation of the object. Consequently, numerical simulations are carried out in order to demonstrate the practicality of the proposed model and control signal. © 2009 SICE.

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a segmentation method of human manipulation task based on measurement of contact force imposed by a human hand on a grasped object. We define an index measure for segmenting a human manipulation task into primitives. The indices are calculated from the set of the contact forces measured at all the contact points during a manipulation task. Then, we apply the EM algorithm to the set of the indices in order to segment the manipulation task into primitives. These primitives are mapped onto the robotic hand to impose appropriate contact forces on a grasped object. In the experiments, manipulation tasks performed in daily human life have been successfully segmented.

DOI： 10.1109/IROS.2009.5354069

Language：English   Publishing type：Research paper (other academic)  

Modeling of pinching an object with arbitrary shape by a pair of robot fingers with hemispherical ends in a horizontal plane is proposed in a mathematical and computational manner. Since the curvature of an object contour with an arbitrary curve is variable according to the change of the contact point between the object surface and the rigid finger tip, the arclength paremeter "s" explicitly appears in the overall fingers-object dynamics. It is shown that the overall fingers-object system should be accompanied with the first-order differential equation of the parameter "s" that includes the curvatures of both the object contour and finger-tip curve. A control input, which is of the same category as the control input called "blind grasping" appeared in our former papers, is utilized for the realization of stable grasp. The control input does neither need to use the kinematic information of the object nor use any external sensing. Finally, numerical simulations are carried out in order to confirm the effectiveness of our proposed model and control input.

DOI： 10.1109/IROS.2009.5354836

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel control method for stable grasping using a multi-fingered hand-arm system with soft hemispherical finger tips. The proposed method is simple but easily achieves stable grasping of an arbitrary polyhedral object using an arbitrary number of fingers. Firstly, we formulate nonholonomic constraints between a multi-fingered hand-arm system and an object constrained by rolling contact with finger tips, and derive a condition for stable grasping by stability analysis. A new index for evaluating the possibility of stable grasping is proposed and efficient initial relative positions between finger tips and the object for realizing stable grasping are analyzed. The stability of the proposed system and the validity of the index are verified through numerical simulations.

DOI： 10.1109/IROS.2009.5354174

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Generally, point-to-point control for a completely restrained (CR) parallel-wire-driven system requires a balancing internal force to prevent slackening of wires, along with a feedback term based on some displacement sensor. This paper specifically describes CR systems' internal force properties, then presents the possibility of motion convergence at a desired position when the internal force balancing at a position is given as sensorless feedforward input. Subsequently, we use the property of internal force positively for sensorless position control. This positioning method is applicable for low-cost manipulation, which does not require high accuracy, and for emergency positioning of systems when sensors malfunction.

DOI： 10.1109/TRO.2009.2013495

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1155/2009/892801

Language：Japanese  

3本指ロボットを用いた物体把持における動的力/トルク平衡の実現

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

This paper focuses on a dynamic sensory-motor control mechanism of reaching movements for a musculo-skeletal redundant arm model. The formulation of a musculo-skeletal redundant arm system, which takes into account non-linear muscle properties obtained by some physiological understandings, is introduced and numerical simulations are perfomed. The non-linear properties of muscle dynamics make it possible to modulate the viscosity of the joints, and the end point of the arm converges to the desired point with a simple task-space feedback when adequate internal forces are chosen, regardless of the redundancy of the joint. Numerical simulations were performed and the effectiveness of our control scheme is discussed through these results. The results suggest that the reaching movements can be achieved using only a simple task-space feedback scheme together with the internal force effect that comes from non-linear properties of skeletal muscles without any complex mathematical computation such as an inverse dynamics or optimal trajectory derivation. In addition, the dynamic damping ellipsoid for evaluating how the internal forces can be determined is introduced. The task-space feedback is extended to the 'virtual spring-damper hypothesis' based on the research by Arimoto et al. (2006) to reduce the muscle output forces and heterogeneity of convergence depending on the initial state and desired position. The research suggests a new direction for studies of brain-motor control mechanism of human movements.

DOI： 10.1080/11762320902789848

Language：English   Publishing type：Research paper (other academic)  

A Riemannian-geometry approach for control and stabilization of dynamics of object manipulation under holonomic or non-holonomic (but Pfaffian) constraints is presented. First, position/force hybrid control of an endeffector of a multijoint redundant (or nonredundant) robot under a nonholonomic constraint is reinterpreted in terms of "submersion" in Riemannian geometry. A force control signal constructed in the image space spanned from the constraint gradient can be regarded as a lifting in the direction orthogonal to the kernel space. By means of the Riemannian distance on the constraint submanifold, stability on a manifold for a redundant system under holonomic constraints is discussed. Second, control and stabilization of dynamics of two-dimensional object grasping and manipulation by using a pair of multi-joint robot fingers are tackled, when a rigid object is given with arbitrary shape. Then, it is shown that rolling contact constraint induce the Euler equation of motion in an implicit function form, in which constraint forces appear as wrench vectors affecting on the object. The Riemannian metric can be introduced in a natural way on a constraint submanifold induced by rolling contacts. A control signal called "blind grasping" is defined and shown to be effective in stabilization of grasping without using the details of information of object shape and parameters or external sensing. The concept of stability of the closedloop system under constraints is renewed in order to overcome the degrees-of-freedom redundancy problem. An extension of Dirichlet-Lagrange's stability theorem to a system of DOFredundancy under constraints is presented by using a Morse- Lyapunov function.

DOI： 10.1109/ROBOT.2009.5152414

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a novel control method for stable object grasping and orientation control using a dual-arm manipulator with multi-fingered hands. The control signal of the proposed method is simple but it can easily achieve stable grasping without external sensors and an orientation control of a grasped object. Firstly, holonomic constraints between a dual-arm manipulator with multi-fingered hands and the object surfaces are formulated, and the stability of the system is discussed through its convergence analysis. Next, it is shown that the relationship between a final orientation of an object and initial contact positions of finger tips becomes quasi-linear. Using this quasi-linear relationship, an orientation control method utilizing regrasping of the object is derived. It is verified that the proposed method enables to perform simple orientation control of the object without real-time external sensing through numerical simulations.

Language：English   Publishing type：Research paper (scientific journal)  

Modeling, control, and stabilization of dynamics of two-dimensional object grasping by using a pair of multi-joint robot fingers are investigated under rolling contact constraints and arbitrariness of the geometry of the object and fingerends. First, a fundamental testbed problem of modeling and control of rolling motion between 2-D rigid bodies with arbitrary shape is treated under the assumption that the two contour curves coincide at the contact point and share the same tangent. The rolling constraint induces the Euler equation of motion that is parameterized by a common arclength parameter and constrained onto the kernel space as an orthogonal complement to the image space spanned from the constraint gradient. By extending the analysis to the problem of stable grasp of a 2D-object with arbitrary shape, the Euler- Lagrange equation of motion of the overall fingers/object system parametrized by arclength parameters is derived, and shown to be accompanied with a couple of first-order differential equations that express evolutions of contact points in terms of the second fundamental form. Further, it is shown that rolling contact constraints are integrable in the sense of Frobenius and hence regarded as being holonomic. A control signal called "blind grasping" is defined and shown to be effective in stabilization of grasping without using the details of object shape and parameters or external sensing.

DOI： 10.3182/20090909-4-JP-2010.00066

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a method of directly measuring static constraints imposed by a human hand on a grasped object.Based on the analysis of the demonstration data of the human grasp, the static constraints are expressed as a combination of frictional force and normal force generated by the human hand.The static constraints are an important property to be mapped to robotic hands in the programming-by-demonstration.Measured static constraints are to be generated to robotic hands to establish the stable grasp.In the experiments, we have successfully measured the static constraints appeared in various different grasps used in the daily human life.

Language：English   Publishing type：Research paper (other academic)  

Contact of two contours of a pinched object and a robot finger tip, with arbitrary shape, is expressed in terms of differential geometry. The overall finger-object dynamics with rolling and contact constraints is derived as Euler-Lagrange' equation of motion and the first differential equation with curvatures of the contours is derived for updating the length parameters. Despite the complicated mathematical structure, a control input signal is proposed, which can be constructed without using object geometrical information or external sensing, and it is shown that it is effective to stabilize rotation of the object. Consequently, numerical simulations are carried out in order to demonstrate the practicality of the proposed model and control signal.

Language：English   Publishing type：Research paper (other academic)  

In a musculoskeletal structure, the internal force among muscles plays an important role. Changing the internal force enables to control not only joint angles but also impedance, so that vertebrate animals can produce a motion according to a situation. Focusing on a musculoskeletal system with two links and six muscles, this paper investigate the effect of biarticular muscles when feedforward position control is inputted. This control gives the constant internal force balancing at desired posture as feedforward input, based on the EP hypothesis in physiology. From the result, we point out that the biarticular muscles can reduce the convergent time of the motion, and theyalso can stabilize the system.

DOI： 10.1109/ROBOT.2009.5152196

Language：Japanese   Publishing type：Research paper (scientific journal)  

Proprioceptive Touching Control Using a Soft Robotic Thumb with 3-D Rolling Contact

DOI： 10.9746/ve.sicetr1965.44.532

Language：Japanese   Publishing type：Research paper (scientific journal)  

人体を外側から扱うロボットの設計‐人と接するロボットRI‐MANの研究開発を通して得られた知見‐

DOI： 10.7210/jrsj.26.247

Language：Japanese   Publishing type：Research paper (scientific journal)  

On Dynamic Pinching Movements of Redundant Musculo-Skeletal Dual Finger Model
The final goal of this research is to clarify and obtain the fundamental control strategy of human's pinching movements by using a redundant musculo-skeletal dual finger model. First, a mathematical model of a 3 D.O.F. musclo-skeletal dual finger in which each finger is actuated by six nonlinear redundant muscles is formulated. Next, the kinematics and dynamics considering geometrical constraints for the finger-object system are described, and a sensory-motor coordinated feedback control law is designed to realize stable pinching simultaneously with posture and position regulation. Then, some numerical simulations are performed and the results suggest that the co-contraction of the digitorum muscles makes it possible to realize human-like pinching movements. Also the convergence of the closed-loop dynamics is proved by using a concept of "Stability theory on a manifold."

DOI： 10.7210/jrsj.26.57

Language：English   Publishing type：Research paper (other academic)  

This paper deals with dynamic object grasping and position control by using a triple-fingered robotic hand with hemispherical soft finger tips. In the authors' previous works, a dynamic object grasping method by using a pair of robotic fingers, called "Blind Grasping", which does not need to use any external sensing, was proposed. However, it is so far assumed that spinning motion around the opposite axis for the object does not occur during the overall movement, because there are only two opposite fingers and thereby the spinning is uncontrollable. By introducing a surplus finger in addition to a pair of robotic fingers, this spinning can be inhibited and it becomes controllable. In this paper, a triple-fingered robotic hand system with nonholonomic constraints is modeled, and a control input to realize stable grasping with object position control is proposed. Its usefulness and effectiveness are illustrated through some numerical simulation results.

DOI： 10.1109/IROS.2008.4650702

Language：English   Publishing type：Research paper (other academic)  

This paper proposes an iterative learning control method for simultaneous force/position tracking tasks by using a 5 D.O.F. robotic thumb under non-holonomic rolling constraints. In our previous works, "blind touching", which is defined as a point-to-point control scheme for the robot to realize a desired contact position and a contact force simultaneously without any external sensing, have proposed. In this paper, an iterative learning control manner to realize a desired continuous trajectory of the center of the contact point together with a desired contact force on the task plane is proposed. The usefulness of this learning control method is demonstrated by showing results of computer simulations.

DOI： 10.1109/ROBOT.2008.4543606

Language：English   Publishing type：Research paper (other academic)  

Recently, active researches have been performed to increase a robot's intelligence so as to realize the dexterous tasks in complex environment such as in the street or homes. However, since the skillful human-like task ability is so difficult to be formulated for the robot, not only the analytical and theoretical control researches but also the direct human motion mimetic approach is necessary. In this paper, we propose that to realize the environmental interactive tasks, such as human care tasks, it is insufficient to replay the human motion along. We show a novel motion generation approach to integrate the cognitive information into the mimic of human motions so as to realize the final complex task by the robot.

DOI： 10.1109/ROBOT.2007.363950

Language：Japanese  

Development and Evaluation of a Human‐interactive Robot Platform “RI‐MAN”
The ultimate goal of this research is to develop a robot that is able to perform physical tasks such as nursing care skillfully and safely in complex environment of our home and/or hospitals. In order to realize such a robot, the design criteria and approach should be different from that of traditional industrial robots. Specifically, considering the physical interactions between the robot and human subjects, the safety, ease and affinity are more important in addition to the robot's high power, speed and accuracy. Towards this objective, "RI-MAN" is developed in RIKEN BMC which demonstrated the high ability to carry up and hold a doll softly and safely. This paper first discusses the problems on the design of a human-interactive robot, and proposes original key technologies and system integration to solve the problems including the soft and whole body interaction. The details and basic performance of RI-MAN are then introduced together with some experimental results. The further research subjects are also pointed.

DOI： 10.7210/jrsj.25.554

Language：Japanese  

完全拘束型パラレルワイヤ駆動における目標内力を用いたフィードフォワード位置決め:第2報 摩擦補償の考察

Language：English   Publishing type：Research paper (other academic)  

Human can pinch or grasp and manipulate an object stably and dexterously. Accomplishment of such tasks is contributed from human hand's configuration, called "Fingers-thumb opposability". This opposability of the thumb against other digits is specific and granted to only human among primates. When we use a cell phone, or change a TV's channel using a remote controller, we grasp it by a palm and digits other than the thumb, and push buttons using the thumb quickly, without looking the buttons. These kinds of thumb's movement seem to be one of the most intelligent movements in a human. Therefore, execution of such touching tasks without visual or tactile sensing is called in this paper "Blind Touching". The goal of this research is to realize human-like "Blind Touching" by means of a 5 D.O.F. thumb robot model with soft and hemispherical finger-tip. To do this, we formulate a simultaneous contact position and touching force control by using 3-Dimensional rolling contact with the task plane. First, dynamics of the 5 D.O.F. thumb robot model with hemispherical soft finger-tip under rolling constraints is derived. Then, a sensory-motor control law without vision, force or tactile sensing is proposed. Some numerical simulations show that the desired contact position and touching force can be attained by the proposed control scheme. A theoretical proof of convergence to the desired state is also presented.

DOI： 10.1109/ROBOT.2007.363051

Language：Japanese   Publishing type：Research paper (scientific journal)  

Human-Like Reaching Movements of a Redundant Musculo-Skeletal System with Nonlinear Muscle Dynamics
This paper studies a sensory-motor control mechanism of human's reaching movements from the perspective of robotics aspect. By formulating the musculo-skeletal redundant system which takes into account a nonlinear muscle property obtained by some physiological understandings, we suggest that the human-like reaching movements can be realized by using only simple task-space feedback scheme together with the internal force effect which comes from mechanical property of muscles without any complex mathematical computation such as an inverse dynamics or some optimal trajectory derivation. Firstly, we introduce both kinematics and dynamics of a three-link serial manipulator with six single-joint muscles and three double-joint muscles model whose movements are confined within a horizontal plane. Secondly, the nonlinear muscle property, which comes from several physiological understandings based on Hill's muscle model, is taken into consideration and illustrated by some numerical simulations that the end-point of the manipulator can converge to the desired point smoothly using only simple task-space feedback scheme by considering the muscle property and internal forces induced by the redundancy of muscles, which makes it possible to modulate the damping factors in joint-space, even if the system owns both kinematic and dynamic redundancies. Then we discuss the effectiveness of our control scheme, and suggest it as one direction to study brain-motor control mechanism of human movements.

DOI： 10.5687/iscie.19.301

Language：English   Publishing type：Research paper (other academic)  

This paper focuses on a sensory-motor control mechanism in human reaching movements from the perspective of robotics. By formulating a musculo-skeletal redundant system which takes into account a nonlinear muscle property and performing numerical simulations, we suggest that the human-like reaching movements can be realized by using only simple task-space feedback scheme together with the internal force effect coming from nonlinear property of muscles without any complex mathematical computation such as an inverse dynamics or some optimal trajectory derivation. Firstly, we introduce both kinematics and dynamics of a three-link serial manipulator with six monoarticular muscles and three biarticular muscles model whose movements are limited within a horizontal plane. Secondly, the nonlinear muscle property coming from a physiological study based on Hill's muscle model, is taken into consideration. This nonlinearity makes it possible to modulate the damping effect in joint-space by considering the internal force generated by the redundant muscles. By utilizing this feature, the end-point converges to the desired point using only simple task-space feedback control scheme, even thought the system owns both the joint and muscle redundancies. Finally, we illustrate numerical simulations to show the effectiveness of the control scheme, and suggest one of the direction to study brain-motor control mechanism of human movements.

DOI： 10.1109/IROS.2006.281931

Language：English  

This chapter deals with modeling of human-like reaching and pinching movements. For the reaching movements, we construct a two-link planar arm model with six redundant muscles. A simple task-space feedback control scheme, taking into account internal forces induced by the redundant and nonlinear muscles, is proposed for this model. Numerical simulations show that our sensory-motor control can realize human-like reaching movements. The effect of gravity is also studied here and a method for the gravity compensation on the muscle input signal level is introduced. The stability of this method is proved and its effectiveness is shown through numerical simulations. For the pinching movements, realized by the index finger and the thumb, the co-contraction between the flexor and extensor digitorum muscles is analyzed. It is shown that an internal force term can be generated by the redundant muscles to modulate a damping factor in the joint space. Numerical simulations show that the co-contraction of each digitorums makes it possible to realize human-like pinching movements. Our results suggest that the central nervous system (CNS) does not need to calculate complex mathematical models based on the inverse dynamics or on the planning of optimal trajectories. Conversely, the human motor functions can be realized through the sensory-motor control by exploiting the passivity, nonlinearity and the redundancy of the musculo-skeletal systems.

DOI： 10.1007/978-3-540-37347-6_11

Language：English   Publishing type：Research paper (scientific journal)  

This paper studies the human arm's sensory-motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two-link planar arm model with six redundant muscles. The nonlinear muscle dynamics is modeled based on several biological understandings. We then show the stability of the overall system and perform some numerical simulations. By considering the internal forces induced by the redundant muscles, we show that the damping factors in each joint can be regulated, and as the result, it can realize humanlike quasistraight line reaching movements. In addition, we also propose the gravity compensation method at the muscle input level and present the result of numerical simulation to verify the usefulness of this method. (C) 2005 Wiley Periodicals, Inc.

DOI： 10.1002/rob.20089

Language：English   Publishing type：Research paper (scientific journal)  

This paper studies the human arm's sensory-motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two-link planar arm model with six redundant muscles. The nonlinear muscle dynamics is modeled based on several biological understandings. We then show the stability of the overall system and perform some numerical simulations. By considering the internal forces induced by the redundant muscles, we show that the damping factors in each joint can be regulated, and as the result, it can realize humanlike quasistraight line reaching movements. In addition, we also propose the gravity compensation method at the muscle input level and present the result of numerical simulation to verify the usefulness of this method.

DOI： 10.1002/rob.20089

Language：English   Publishing type：Research paper (scientific journal)  

The essential motion of the ionic polymer-metal composite (IPMC) is bending, therefore some mechanisms are expected to transform from the bending to other required motions. Motivated by the motion of a spiral spring, we discovered that the bending of the ionic polymer could be directly transformed to the limited angle rotation. We introduce the model of the rotary actuator, which consists of mechanical, electrical and electromechanical dynamics. The motion of the rotary actuator is demonstrated in the experiment. The stationary properties are measured and the parameters of the dynamical model are identified, which are also validated by experiments.

DOI： 10.1117/12.599503

Language：English   Publishing type：Research paper (other academic)  

-In this paper, we study the sensory motor control mechanism in human reaching movements by considering the redundant muscle dynamics. We first formulate the kinematics and dynamics of a two-link arm model with six muscles, and introduce the nonlinear muscle dynamics based on the biological understanding. Secondly, we show the stability of the system by using intrinsic muscle characteristics and La Salle's invariance theorem. From this result and the numerical simulations, we propose that the reaching movement can be regulated by the internal forces of the redundant muscles, in detail, the muscle's internal forces can be used to control the damping of the joints. In addition, human can compensate the gravity by using antigravity muscles. To realize this effect in the arm, we propose the gravity compensation method at the muscle input level from the viewpoint of robotics. We present the result of numerical simulation to verify the usefulness of this compensation method.

DOI： 10.1109/IROS.2005.1545411

Language：English   Publishing type：Research paper (other academic)  

It is well-known that a human musculo-skeletal body is redundant in terms of both kinematics and dynamics. The former means that the degree of freedom in joint space is larger than that in task space, and the latter means that a joint is driven by a number of muscles. All human skillful movements can be performed by using both redundancies. However, these redundancies induce the underlying ill-posedness problem that each joint angle and muscle's output forces cannot be uniquely determined. These ill-posedness problems are known as "Bernstein's problem" and are important to understand how human multi-joint movements are produced. In this study, we address the latter redundancy problem on how muscle's output forces can be determined from the viewpoint of robotics. In this paper, we consider a reaching movement by means of a two-link planar arm with six muscles and show that both damping and elastic properties coming from nonlinear dynamics of the muscles play a crucial role. By using a simple task space feedback control input together with an additional term to control the internal force to regulate damping and elasticity in joint space, we show some simulation results which exhibit human-like quasi-straight line movement.

DOI： 10.1109/ROBOT.2005.1570123

Language：English   Publishing type：Research paper (scientific journal)  

This paper studies modeling and biomimetic control of a 3D 8-dof whole arm cooperative manipulation system using sensitive skin. The control law is designed based on integration of voluntary movement and reflex considering the system's redundancy. The voluntary task for holding the object is realized by impedance control at four contact points with the object using the contact force information from the sensitive skin. The reflection on the other hand is introduced as a regulation problem of the direction between the points of end-effectors and elbows. We then investigate the exact solutions for the combined motion and their solvable conditions. The validity of the proposed method is investigated by numerical simulations.

Language：English   Publishing type：Research paper (other academic)  

This paper studies modeling and bio-mimetic control of a 3D 8-dof whole arm cooperative manipulation system using sensitive skin. A sphere is considered here as a manipulated object. The control law is designed based on integration of voluntary and reflex movements considering the system's redundancy. The voluntary task for holding the object is realized by impedance control at the four contact points with the object using the contact force information from the sensitive skin. The reflection on the other hand is introduced as a regulation problem of the direction between the points of end-effectors and elbows. The solution for the redundant control is formulated and derived from the optimization point of view. The validity of the proposed method is investigated by numerical simulations.

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a dynamic human motion simulator to clarify and obtain the natural movement as human carries out. This system consists of a 3D motion capturing system, which has 6 high-speed cameras, 8 force plates, 10 3-axis accelerometers and 32 EMG sensors. To reconstruct the human's complex movement in VR space, a dynamic simulation model of human muscle-skeletal body is constructed. This model has 100 segments of born and has totally 105 D.O.F. in whole body, and also 300 muscles are included in this model. These muscles have the properties of stiffness, damping and contractive force generation. This platform makes it possible for construct human dynamic motion control functions more precisely and is thus useful for biomimetic robots. By using the super-redundant human body model, we are studying the brain motor control functions through the dynamic simulations.

Language：English   Publishing type：Research paper (scientific journal)  

It is well known that three frictionless fingers suffice to immobilize any 2D object with triangular shape but four fingers are necessary for a parallelepiped. However, it has been recently shown that only two fingers are enough to realize secure grasp of a rigid object with parallel flat surfaces in a dynamic sense if finger ends have a hemispherical shape with appropriate radius and thereby rollings; are induced between finger ends and object surfaces. This paper focuses on the two problems: (1) dynamic force/torque balance of 2D polygonal objects under the effect of gravity force by means of a pair of rolling contacts and (2) concurrent realization of dynamically secure grasp and orientation control of 2D polygonal objects by using a pair of multi-fingered hands with hemispherical ends and sensory feedback signals without knowing object kinematics and mass center. It is shown that the force/torque balance can be attained by controlling both the contact positions and inducing adequate forces in both normal and tangential directions at each of contact points indirectly through finger joints without knowing object mass center and other kinematic parameters. (C) 2003 Wiley Periodicals, Inc.

DOI： 10.1002/rob.10102

Language：English   Publishing type：Research paper (scientific journal)  

This paper is concerned with a stability theory of motion, governed by Lagrange's equation for a pair of multi-degrees of freedom robot fingers with hemi-spherical finger ends grasping a rigid object under rolling contact constraints. When a pair of dual two d.o.f. fingers is used and motion of the overall fingers-object system is confined to a plane, it is shown that the total degree of freedom of the fingers-object system is redundant for realization of stable grasping though there arise four algebraic constraints. To resolve the redundancy problem without introducing any other extra and artificial performance index, a concept of stability of motion starting from a higher dimensional manifold to a lower-dimensional manifold, expressing a set of states of stable grasp with prescribed contact force, is introduced and thereby it is proved in a rigorous way that stable grasp in a dynamic sense is realized by a sensory feedback constructed by means of measurement data of finger joint angles and the rotational angle of the object. Further, it is shown that there exists an additional sensory feedback that realizes not only stable grasp but also orientation control of the object concurrently. Results of computer simulation based on Baumgarte's method are presented, which show the effectiveness of the proposed concept and analysis.

DOI： 10.1017/S026357470200468X

Language：English   Publishing type：Research paper (scientific journal)  

This paper is concerned with a stability theory of motion governed by Lagrange's equation for a pair of multi-degrees of freedom robot fingers with hemi-spherical finger ends grasping a rigid object under rolling contact constraints. When a pair of dual two d.o.f. fingers is used and motion of the overall fingers-object system is confined to a plane, it is shown that the total degree of freedom of the fingers-object system is redundant for realization of stable grasping though there arise four algebraic constraints. To resolve the redundancy problem without introducing any other extra and artificial performance index, a concept of stability of motion starting from a higher dimensional manifold to a lower-dimensional manifold, expressing a set of states of stable grasp with prescribed contact force, is introduced and thereby it is proved in a rigorous way that stable grasp in a dynamic sense is realized by a sensory feedback constructed by means of measurement data of finger joint angles and the rotational angle of the object. Further, it is shown that there exists an additional sensory feedback that realizes not only stable grasp but also orientation control of the object concurrently. Results of computer simulation based on Baumgarte's method are presented, which show the effectiveness of the proposed concept and analysis.

DOI： 10.1017/S026357470200468X

Language：English   Publishing type：Research paper (scientific journal)  

It is well known that three frictionless fingers suffice to immobilize any 2D object with triangular shape but four fingers are necessary for a parallelepiped. However, it has been recently shown that only two fingers are enough to realize secure grasp of a rigid object with parallel flat surfaces in a dynamic sense if finger ends have a hemispherical shape with appropriate radius and thereby rollings are induced between finger ends and object surfaces. This paper focuses on the two problems: 1) realization of secure grasp of rigid objects with non-parallel flat surfaces (including triangular objects) by dual muIti-degrees-of-freedom rigid fingers with hemispherical ends and 2) concurrent realization of secure grasp and orientation control of polygonal objects under the effect of gravity. It is shown that stable grasp is realized by a sensory feedback constructed on the basis of measurements of finger joint angles and angles of the object surfaces relative to finger links without knowing object kinematics and mass center. Further, it is shown that there exists an additional sensory feedback that can regulate orientation angle of the object simultaneously.

DOI： 10.1016/S1474-6670(17)33417-1

Language：English   Publishing type：Research paper (other academic)  

This paper is concerned with experimental analysis of pinching motion by a pair of multi-degrees of freedom robot fingers with rigid hemispherical tips. The experiments were carried out in the case that a parallelepiped object is placed on a non-slippery plate in a horizontal plane and motion of the fingers and the object is confined to the plane. As predicted from the theoretical analyses, experimental results show that stable grasping in a dynamic sense is realized by a sensory feedback constructed by using measurement data of finger joint angles and the rotational angle of the object. Further, it is shown from the experiments that an additional sensory feedback works well in realizing concurrent stable grasp and orientation control of the object.

DOI： 10.1109/CIRA.2003.1222161

Language：English   Publishing type：Research paper (scientific journal)  

It is well known that three frictionless fingers suffice to immobilize any 2D object with triangular shape but four fingers are necessary for a parallelepiped. However, it has been recently shown that only two fingers are enough to realize secure grasp of a rigid object with parallel flat surfaces in a dynamic sense if finger ends have a hemispherical shape with appropriate radius and thereby rollings are induced between finger ends and object surfaces. This paper focuses on the two problems: (1) dynamic force/torque balance of 2D polygonal objects under the effect of gravity force by means of a pair of rolling contacts and (2) concurrent realization of dynamically secure grasp and orientation control of 2D polygonal objects by using a pair of multi-fingered hands with hemispherical ends and sensory feedback signals without knowing object kinematics and mass center. It is shown that the force/torque balance can be attained by controlling both the contact positions and inducing adequate forces in both normal and tangential directions at each of contact points indirectly through finger joints without knowing object mass center and other kinematic parameters.

DOI： 10.1002/rob.10102

Language：English   Publishing type：Research paper (other academic)  

This paper is concerned with computer simulation of concurrent grasp and orientation control of an object with two parallel flat surfaces by a pair of multi-degrees of freedom robot fingers that have rigid hemispherical ends. Firstly, geometrical relationships in the overall fingers-object system are discussed through four algebraic constraints between the finger tips and surfaces of the object. Then, differential algebraic equations expressing dynamics of the overall system are derived. Secondly, a sensory feedback signal for concurrent grasp and orientation control of the object is proposed and a full description of matrix form for numerically solving the closed-loop differential algebraic equation of the overall fingers-object system on the basis of the CSM (constraint stabilization method) is presented. Thirdly, simulation results of grasping and orientation control of the object are shown and then, the effects of each term of the proposed control input signal on the system performances are discussed. Finally, a guidance of gain tuning is suggested on the basis of well-known force-velocity characteristics of human muscle in muscle physiology.

DOI： 10.1109/CIRA.2003.1222171

Language：English   Publishing type：Research paper (scientific journal)  

This paper is concerned with a stability theory of motion governed by Lagrange's equation for a pair of multi-degrees of freedom robot fingers with hemispherical finger ends grasping a rigid object under rolling contact constraints. When a pair of two d.o.f. fingers is used and motion of the overall fingers-object system is confined to a plane, it is shown that the total degree of freedom of the fingers-object system is redundant for realization of stable grasping though there arise four algebraic constraints. To resolve the redundancy problem without introducing extra performance specifications, a concept of stability of motion starting from a higher dimensional manifold to a lower-dimensional manifold expressing a set of states of stable grasp with prescribed contact force is introduced and thereby it is proved in a rigorous way that stable grasp in a dynamic sense is realized by a sensory feedback constructed on the basis of measurement data of finger joint angles and the rotational angle of the object. Further, it is shown that there exists an additional sensory feedback that realizes not only stable grasp but also orientation control of the object concurrently. These results can be extended to other two cases that 1) motion of the overall system is confined to a vertical plane and therefore it is affected directly by the gravity and 2) the object has non-parallel but flat surfaces.

Language：English   Publishing type：Research paper (scientific journal)  

This paper analyzes the dynamics and control of pinch motions generated by a pair of two multi-degrees-of-freedom robot fingers with soft and deformable tips pinching a rigid object. It is shown firstly that passivity analysis leads to an effective design of a feedback control signal that realizes dynamic stable pinching (grasping), even if extra terms of Lagrange's multipliers arise from holonomic constraints of tight area-contacts between soft finger-tips and surfaces of the rigid object and exert torques and forces on the dynamics. It is shown secondly that a principle of superposition is applicable to the design of additional feedback signals for controlling both the posture (rotational angle) and position (some of task coordinates of the mass center) of the object provided that the number of degrees of freedom of each finger is specified for satisfying a condition of stationary resolution of controlled position state variables. The details of feedback signals are presented in the case of a special setup consisting of two robot fingers with two degrees of freedom.

DOI： 10.1017/S0263574700002939

Language：English   Publishing type：Research paper (scientific journal)  

This paper analyzes the dynamics and control of pinch motions generated by a pair of two multi-degrees-of-freedom robot fingers with soft and deformable tips pinching a rigid object. It is shown firstly that passivity analysis leads to an effective design of a feedback control signal that realizes dynamic stable pinching (grasping), even if extra terms of Lagrange's multipliers arise from holonomic constraints of tight area-contacts between soft finger-tips and surfaces of the rigid object and exert torques and forces on the dynamics. It is shown secondly that a principle of superposition is applicable to the design of additional feedback signals for controlling both the posture (rotational angle) and position (some of task coordinates of the mass center) of the object provided that the number of degrees of freedom of each finger is specified for satisfying a condition of stationary resolution of controlled position state variables. The details of feedback signals are presented in the case of a special setup consisting of two robot fingers with two degrees of freedom.

DOI： 10.1017/S0263574700002939

Language：English   Publishing type：Research paper (other academic)  

This paper derives lumped-parameter dynamics of motion of a pair of robot fingers with soft and deformable tips pinching a rigid object. The dynamics of the system in which area contacts between the finger-tips and the surfaces of the object arise are compared with those of a pair of rigid robot fingers with rigid contacts with an object. It is then shown that even in the simplest case of dual single degree-of-freedom fingers there exists a sensory feedback from measurement of finger joint angles and the rotational angle of the object to command inputs to joint actuators and this feedback connection from sensing to action eventually realizes stable grasping of the object, provided that the object is a rectangular parallelepiped and motion is confined to a horizontal plane. It is further shown that in the case of a pair of one d.o.f. and two d.o.f. fingers with soft tips there exists a sensory feedback that realizes not only stable grasping but also regulating the posture of the object at a specified rotational angle.

Language：English   Publishing type：Research paper (other academic)  

This paper proposes a pair of single or multi D.O.F. robot fingers with soft and deformable tips that can pinch an object stably in a dynamic sense with the aid of real-time sensory feedback. To realize dynamic stable pinching, a practical method of using optical devices is proposed for measuring both the maximum displacement of finger-tip deformation and the relative angle between the object surface and each of finger links. It is shown theoretically and by computer simulation that the overall closed-loop system of a pair of two single-D.O.F. fingers with soft tips with real-time sensory feedback of the difference between centers of two area-contacts at both sides of the object becomes asymptotically stable. This means that the pair achieves dynamic stable grasping (pinching). In the case of a pair of 1 D.O.F. and 2 D.O.F. fingers with soft tips, it is shown that the proposed method of closed-loop feedback of the difference between centers of two area-contacts and the rotational angle of the object can establish not only dynamic stable grasping but also regulation of the posture of the object.

DOI： 10.1109/ROBOT.2001.932536

Language：English   Book type：Scholarly book

Language：Others  

Soft Actuators: Materials, Modeling, Applications, and Future Perspectives, 2nd Ed.

Language：Others  

Human Inspired Dexterity in Robotic Manipulation, 1st Ed.

Language：Others  

Language：Japanese   Book type：Scholarly book

Language：Others  

Language：Others  

Language：Japanese   Book type：Scholarly book

Responsible for pages：総ページ数：vi, 193p   Language：Japanese  

Language：Others  

Language：Others  

Advances in Robot Control: From Everyday Physics to Human-Like Movements

Language：Others  

Human Friendly Mechatronics: Selected Papers of the International Conference on Machine Automation

Language：English   Book type：Scholarly book

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台市   Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：南紀白浜   Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：南紀白浜   Country：Japan  

Event date： 2023.1

Language：English   Presentation type：Oral presentation (general)  

Venue：Atlanta   Country：United States  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2022.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：English   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2021.12

Language：Japanese  

Venue：鹿児島（オンライン）   Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長野（オンライン）   Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長野（オンライン）   Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪（オンライン）   Country：Japan  

Sensorless Torque Control for Antagonistically Arranged Rotational-Type Twisted Polymeric Fiber Actuators

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪（オンライン）   Country：Japan  

End-Point Stiffness Control for a Tendon-Driven Redundant Manipulator with Musculoskeletal Structure

Event date： 2021.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Xi'an (Online)   Country：China  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡（オンライン）   Country：Japan  

Transition Movement Control between Wheel and Walking Movement for a Biped Robot with Hemispheric Feet

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡（オンライン）   Country：Japan  

Environmental Adaptability of Admittance and Impedance Control with Independent Anisotropic Rigidity

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡（オンライン）   Country：Japan  

External sensorless object-orientation control using contact position estimation by the multi-fingered robot hand

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

A Twisted Polymeric Fiber Actuator (TPFA) has been attracting attention as a new actuator　that is silent, inexpensive, and can directly extract a rotational motion. Until now, we have proposed a　sensorless rotational angle controller using estimated temperature feedback in order to take advantage　of the low cost of TPFA. In order to construct a sensorless torque control method as an expansion of　the utility of the TPFA, the relationship between output torque and change in temperature is modeled　and the sensorless torque controller is designed. The proposed method is eventually verified through　experiments.

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神戸市産業振興センター, 兵庫   Country：Japan  

Event date： 2020.5 - 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Yale University, USA   Country：United States  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：湯の川温泉, 函館   Country：Japan  

Event date： 2020.1

Language：English   Presentation type：Oral presentation (general)  

Venue：Honolulu   Country：United States  

In this paper, a novel visual-tactile sensor is proposed and an object manipulation method of a grasped object by a multi-fingered robotic hand is proposed by detecting a contact position using the visual-tactile sensor. The visual-tactile sensor is composed of a hemispheric fingertip part made of soft silicone with hollow inside and a general USB camera located at the inside of the fingertip to detect the displacement of many point markers embedded in the silicone. The deformation of each point marker due to a contact force is measured and a contact position is estimated in stable through a novel method of creating virtual points in figuring out the point clouds. Not only to demonstrate the estimation performance of the new visual-tactile sensor itself, but its practical usefulness in a grasping and manipulation task is also illustrated as well. By using a contact position obtained from the proposed sensor and the position of each fingertip obtained from kinematics, the position and orientation of a grasped object are estimated and controlled. Its performance is demonstrated through numerical simulation results.

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：サンポート高松, 香川   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：サンポート高松, 香川   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：サンポート高松, 香川   Country：Japan  

Event date： 2017.11

Language：English  

Venue：Birmingham   Country：United Kingdom  

This paper proposes a new tendon-driven robot with variable joint stiffness mechanisms. The tendon-driven robot is able to vary the stiffness of joints by sliding variable stiffness mechanisms over the link by wire tensions. As a reason for that structure and moment arms of the tendon-driven robot are changed depending on the position of the variable mechanism. Thus in this paper, the tendon-driven robot with variable stiffness mechanisms is designed, and the stiffness of the tendon-driven robot is evaluated by using a stiffness ellipsoid.

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：川越   Country：Japan  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：川越   Country：Japan  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：川越   Country：Japan  

Event date： 2017.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Munich   Country：Germany  

This paper proposes a novel dynamics model of the twisted and coiled polymer actuator (TCPA) which is one of the artificial muscles recently discovered. It can be driven by Joule heating and can contract up to 25&#37;. Most of the conventional works employed the linear model of TCPA which represents the relationships between the input voltage, the temperature, and the displacement, but the real TCPA shows the nonlinearity. Although a nonlinear model was proposed based on the curve fitting, it is difficult to apply the model to the various TCPAs. Additionally, the conventional works cannot explain the effect of the convective heat transfer condition on the displacement behavior of TCPA. This paper aims to construct a general nonlinear model of TCPA based on the following two ideas: (1) The energy balance of TCPA and (2) the temperature and velocity dependence of the heat transfer coefficient. The temperature model is obtained from the time derivative of the energy balance, and the displacement model is derived as Lagrange's equation of motion with the dissipation function. Through experiments, it is verified that the proposed model is closer to the real dynamics than the conventional linear model.

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福島   Country：Japan  

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福島   Country：Japan  

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福島   Country：Japan  

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福島   Country：Japan  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Florence   Country：Italy  

In this paper, our previously proposed set-point control method for a musculoskeletal system is improved to reduce required muscular forces and to avoid a saturation of muscular forces during movement. The previous method is robust against a considerable time-delay in sensory information, but it still requires large muscular forces to accomplish a desired position, and the maximum exertable muscular force has not yet been taken into consideration. To cope with these two issues, two variable parameters are newly introduced. One is for changing the combination ratio of feed-forward and feedback controllers to reduce necessary muscular forces. The other is for avoiding the saturation of muscular forces during movement The effectiveness of the proposed controller is demonstrated through several numerical simulation results.

Event date： 2016.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Las Vegas   Country：United States  

Event date： 2015.11

Language：English   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2015.11

Language：English   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2015.9 - 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Hamburg   Country：Germany  

Event date： 2014.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Besancon   Country：France  

This paper proposes a novel two-link planar manipulator with continuously variable transmission (CVT) mechanism by means of plural linear shaft motors. In our previous works, we have proposed the parallel-link manipulator with the CVT mechanism which has two orthogonal DOFs. However, its configuration is not useful for a practical field because only one main link can be rotated around two joints like a joystick. In order for this mechanism to be more useful, the two-link planar type manipulator with the CVT is newly modeled and developed. Firstly, the proposed manipulator is modeled, and its control signals are designed. Next, the output force of the end-point of the manipulator is evaluated by using both the Manipulating-Force Ellipsoid and the Dynamic Manipulability Ellipsoid. After that, several fundamental experiments are performed to evaluate the CVT mechanism and show the effectiveness of the proposed manipulator.

Event date： 2014.5 - 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong Kong   Country：China  

Event date： 2014.5 - 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong Kong   Country：China  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Vilamoura   Country：Portugal  

Event date： 2012.6

Language：English   Presentation type：Oral presentation (general)  

Venue：St. Paul   Country：United States  

Event date： 2011.9

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2011.9

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2011.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Shanghai   Country：China  

Event date： 2010.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2010.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2010.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Anchorage   Country：United States  

Event date： 2010.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Anchorage   Country：United States  

Event date： 2009.10

Language：English   Presentation type：Oral presentation (general)  

Venue：St. Louis   Country：United States  

Event date： 2009.10

Language：English   Presentation type：Oral presentation (general)  

Venue：St. Louis   Country：United States  

Event date： 2009.10

Language：English   Presentation type：Oral presentation (general)  

Venue：St. Louis   Country：United States  

Event date： 2009.10

Language：English   Presentation type：Oral presentation (general)  

Venue：St. Louis   Country：United States  

Event date： 2009.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Event date： 2009.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Event date： 2009.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Event date： 2008.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Nice   Country：France  

Event date： 2008.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Pasadena   Country：United States  

Event date： 2007.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Rome   Country：Italy  

Event date： 2007.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Rome   Country：Italy  

Event date： 2006.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Beijing   Country：China  

Event date： 2006.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Beijing   Country：China  

Event date： 2006.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Orlando   Country：United States  

Event date： 2005.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Edmonton   Country：Canada  

Event date： 2005.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Barcelona   Country：Spain  

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟市   Country：Japan  

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟市   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台市   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2022.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Long Beach, CA   Country：United States  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島（オンライン）   Country：Japan  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島（オンライン）   Country：Japan  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島（オンライン）   Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪（オンライン）   Country：Japan  

On the modeling for position control of fishing-line artificial muscle with switching between heating and forced air cooling

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪（オンライン）   Country：Japan  

On the Feed-forward control to improve contraction speed of Twisted and Coiled Polymer Fiber actuator and temperature limit

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡（オンライン）   Country：Japan  

A Stbout temperature dependence of viscoelasticity of twisted coiled polymer fiber (TCPF)

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Boston, MA   Country：United States  

Event date： 2020.4 - 2020.5

Language：English  

Venue：None   Country：United States  

Fishing-line artificial muscles can exhibit various motions. Twisted Polymer Fiber (TPF) actuators, which are a class of fishing-line artificial muscle actuators, generate torsional motion by applying heat. In general, untwisted fiber contracts by heating. However, measuring the blocking thermal tensile force of a TPF, we have discovered that the tensile force decreased and fluctuated depending on the initial number of twists in the TPF. This suggests that a TPF expands depending on the initial number of twists. Furthermore, the tensile force does not decrease monotonically but fluctuates during heating.

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：サンポート高松, 香川   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：サンポート高松, 香川   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：サンポート高松, 香川   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学, 東京   Country：Japan  

Event date： 2019.8 - 2020.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

間の運動知能は未だロボットのそれと比較して圧倒的に洗練されており，その乖離はまだ大きい．その理由は数多く考えらえるが，その一つに制御構造が挙げられる．例えば視覚から得た情報を元にフィードバックを行い，自身の運動に反映させる場合，人の視覚フィードバックにおいては，鍛え上げられたアスリートでさえ150～200[ms]の時間的な遅れがあると言われている．ロボットのフィードバック制御において人と同様の運動を実現する事を目標とした場合，200[ms]の遅れは致命的であり，遅れがあるフィードバックのみで人と同様の運動を実現する事はほぼ不可能に近い．すなわち，感覚情報からのフィードバックの遅れを感じさせない運動生成能力は，フィードバックだけでなく，体性感覚や学習などによって獲得したフィードフォワード系が大きく寄与していると言われている．工学的に言い換えれば，時間遅れに対して非常に頑健な制御構造を有していると言える．これまで，フィードバックとフィードフォワードを組み合わせた制御構造は，運動生理学やロボティクスなどの分野でいくつか提案されているが，決定打はまだない．
本講演では，人間の特徴的な身体構造である筋骨格構造に注目し，講演者がこれまで行ってきた筋骨格構造特有の制御手法により，簡便な手法でありながらセンサ情報の遅れに対して頑健なフィードバックとフィードフォワードの組み合わせによる制御構造について紹介する．本手法では，動力学の逆モデルを必要としない筋内力フィードフォワードと，むだ時間を含む手先フィードバックを線形結合することで，センサ情報に遅れがある場合でもロバストに手先を目標値へ収束させることが可能となる．いくつかの数値シミュレーション結果を元に提案手法の有効性を示す．

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇奈月   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇奈月   Country：Japan  

Event date： 2019.3