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

Grasping an unknown object is difficult for robot hands. When the characteristics of the object are unknown, knowing how to plan the speed at and width to which the fingers are narrowed is difficult. In this letter, we propose a method to realize the three functions of simultaneous finger contact, impact reduction, and contact force control, which enable effective grasping of an unknown object. We accomplish this by using a control framework called multiple virtual dynamics-based control, which was proposed in a previous study. The advantage of this control is that multiple functions can be realized without switching control laws. The previous study achieved two functions, impact reduction and contact force control, with a two layers of impedance control which was applied independently to individual fingers. In this letter, a new idea of virtual dynamics that treats multiple fingers comprehensively is introduced, which enables the function of simultaneous contact without compromising the other two functions. This research provides a method to achieve delicate grasping by using proximity sensors.

DOI： 10.1109/LRA.2024.3497726

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Detecting contact when fingers are approaching an object and estimating the magnitude of the force the fingers are exerting on the object after contact are important tasks for a multi-fingered robotic hand to stably grasp objects. However, for a linkage-based under-actuated robotic hand with a self-locking mechanism to realize stable grasping without using external sensors, such tasks are difficult to perform when only analyzing the robot model or only applying data-driven methods. Therefore, in this paper, a hybrid of previous approaches is used to find a solution for realizing stable grasping with an under-actuated hand. First, data from the internal sensors of a robotic hand are collected during its operation. Subsequently, using the robot model to analyze the collected data, the differences between the model and real data are explained. From the analysis, novel data-driven-based algorithms, which can overcome noted challenges to detect contact between a fingertip and the object and estimate the fingertip forces in real-time, are introduced. The proposed methods are finally used in a stable grasp controller to control a triple-fingered under-actuated robotic hand to perform stable grasping. The results of the experiments are analyzed to show that the proposed algorithms work well for this task and can be further developed to be used for other future dexterous manipulation tasks.

DOI： 10.1186/s40648-024-00273-3

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Other Link： https://link.springer.com/article/10.1186/s40648-024-00273-3/fulltext.html

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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Publisher：2024 IEEE/SICE International Symposium on System Integration, SII 2024  

Precision grasping is an important skill for robotic hands to master so that they can be utilized in various manipulation tasks. To control the robotic hand precisely, modeling the kinematics and statics behavior of the robotic hand is one of the active areas of robotic research. While becoming popular because of their self-adaptability in robust power grasping, linkage-based under-actuated hands are difficult to model analytically for precision fingertip grasping, due to the stochastic and nonlinear dynamical behavior caused by the use of passive mechanisms inside each finger. In this paper, we proposed a fingertip force/position estimation framework, which detects in real-time using internal sensors data whether the passive locking mechanism is in action or not and uses the kinematics and statics models with gravity compensation in each case to compute the estimation. Using the proposed framework, an example of a precision grasping task is carried out to evaluate its reliability and show its potential to be used for future dexterous manipulation tasks.

DOI： 10.1109/SII58957.2024.10417552

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

This paper proposes a control method for a snake robot to move between two planes amidst changing environmental conditions. The proposed approach uses a proximity sensor affixed to the robot to estimate its position and orientation relative to the plane. When the robot's wheels become ungrounded due to environmental fluctuations, the control mode seamlessly transitions from propulsion control to recovery control. During recovery control, the robot is controlled to ensure that the ungrounded wheels regain contact with the plane. The integration of sensor information, propulsion control, and recovery control enables the snake robot to effectively adapt to the dynamically changing environment and maintain locomotion. The effectiveness of the proposed methodology was confirmed through experiments employing a snake robot. The results validate the robot's capability to traverse variable planes by utilizing the estimated information of plane. Moreover, the snake robot successfully regained ground contact through recovery control, even when encountering instances of ungrounded wheels during propulsion. Thus, the findings substantiate the robot's ability to sustain propulsion by maintaining the wheels grounded.

DOI： 10.1109/ACCESS.2024.3382205

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Publisher：2024 IEEE/SICE International Symposium on System Integration, SII 2024  

Upon grasping a fragile object, small grasping force and gripper compliance are required to avoid large deformation or damage to the object. In this study, linear servomotor based mechanism is used to construct a parallel gripper which is able to achieve small gripping force and compliance without using external force sensors. The linear motor mechanism has low friction and no reduction gear. Therefore, it can produce small thrust force with high back-drivability. The proposed parallel gripper consists of two linear motor mechanisms, a guide rail, a frame, and two fingers. The thrust force of the linear motor can be controlled through a driver. The components of the gripper were manufactured using metal machining and 3D printing, and they were carefully assembled to ensure good axial alignments. Force calibration was conducted and the minimum grasping force was confirmed as a value of 0.076 N. The friction force of the guide rail was also experimentally measured and it was confirmed to be 0.090 N. Finally, grasping experiments were conducted on potato chips and tofu. Results suggested that the proposed parallel gripper is able to handle fragile objects with sub-Newton level force.

DOI： 10.1109/SII58957.2024.10417646

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>This paper proposes cooperative control using multiple Twisted and Coiled Polymeric Fiber Actuator (TCPFA) as a method to improve the response characteristics of TCPFA. The force output of the entire system is controlled by switching the TCPFA that are heated and driven. We report that the force output can be kept constant even when multiple TCPFA are switched, and that the response characteristics can be improved by adjusting the number of TCPFA and the ratio of driving time.</p>

DOI： 10.1299/jsmermd.2024.2p1-k09

CiNii Research

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

Soft robots have high adaptability and safety due to their softness and are therefore widely used in human society. However, the controllability of soft robots to perform dexterous behaviors is insufficient when considering soft robots as alternative laborers for humans. Model-based control methods are effective for achieving dexterous behaviors. To build a suitable control model, problems based on specific properties, such as creep behavior and variable motions, must be addressed. In this paper, a lumped parameterized model for soft fingers with viscoelastic joints is established to address creep behavior. The parameters are expressed as distributions, which allows the model to account for motion variability. Furthermore, stochastic analyzes are performed based on the parameter distributions. The model results are consistent with the experimental results, and the model enables the investigation of the effects of various parameters related to robot variability.

DOI： 10.1080/01691864.2023.2279600

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Language：Others   Publishing type：Research paper (other academic)   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：The Robotics Society of Japan  

Antagonistic Total Torque Control of Rotational Straight Twisted Polymeric Fiber Actuator

DOI： 10.7210/jrsj.41.573

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

This paper proposes a novel optical proximity sensor skin that can cover entire robot links and has high responsiveness, wire-saving properties, and suitability for covering narrow surfaces. Moreover, it can extract information that can help to control robots. Although implementing these characteristics simultaneously has been problematic for sensor skins covering links, the proposed sensor skin achieves this using a newly developed analog computing circuit. This analog computing circuit only consists of several resistors and diodes and is based on the splitting ratio of photocurrents variation based on the design of the resistance values. If the output from the proximity sensing element is interpreted as a virtual force, the processed output denotes its magnitude and the location of the point of action. Even if multiple objects are detected, the outputs are associated with the resultant virtual force because photocurrents are merged. Therefore, the characteristics such as high responsiveness are maintained. This work fabricated a prototype to evaluate the proposed sensor skin. Then, collision avoidance experiments against human hands were conducted to validate the efficiency of the proposed sensor skin for generating robot motions. These results verified that the proposed sensor skin is suitable for robots reacting quickly to unknown environments.

DOI： 10.1080/01691864.2023.2239320

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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：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/tro.2023.3286045

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

The moment a legged robot touches the ground, the tip of its toe can experience a significant impact force. It is preferable to keep the landing impact force small because it causes imbalance and damage to the frame, motors, gears, and other components of the robot legs. In this paper, we propose a control method to mitigate the landing impact force by preliminary motion based on the proximity information of the tiptoe before landing. A proximity sensor is mounted on the tiptoe to detect the ground before landing, and feedback control is applied according to the sensor output to reduce the impact force. In landing experiments using a one-legged robot equipped with a proximity sensor on a tiptoe, we evaluated the effects of changing the sensor offset distance and the feedback gains on impact force mitigation. The results show that the landing impact force was mitigated by reducing the relative velocity of the tiptoe and the ground using the proposed proximity feedback control.

DOI： 10.1109/access.2022.3153127

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

DOI： 10.1080/01691864.2020.1848622

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

Real-time Motion Planning Using Proximity Information for Bipedal Walking on Sloped Terrain

DOI： 10.7210/jrsj.38.401

Language：Others  

Motion planning method of bipedal walking using partial-circular feet imitating wheel motion

Language：Japanese  

2足歩行安定性を向上する足裏実装型非接触センサの開発
For bipedal robots walking on uneven terrain, lack of information about a terrain may cause serious reduction of the stability. To solve the problem, the purpose of this paper is to develop a sensor which can be mounted on robot's soles and propose methods which can increase the stability of bipedal walk with the sensor. The sensor should detect information including relative posture and relative distance between the sole of the swing leg and the floor, when the robot execute the walk by ZMP-based control. In this paper, the sensor has been designed based on Net-Structure Proximity Sensor (NSPS) and a prototype has been developed. The developed sensor is with thin structure, light weight, less wirings (four wires only) and fast response (<1[ms]). Experimental results show that the sensor can output necessary relative posture and positon between the sole and the floor for walk control. Besides, the sensor has been mounted to the soles of a hobby robot and its feasibility is shown by controlling robot so that its sole can land on a tilted floor with maximum contacting area to improve the stability.

DOI： 10.7210/jrsj.35.669

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

We have developed a net-structure proximity sensor that detects the azimuth and elevation to a nearby object. This information can be used by robots to avoid obstacles or to respond to human behavior. We propose detection principles where the azimuth is detected by arranging two one-dimensional net-structure proximity sensors along orthogonal axes, and the elevation is detected by arranging two one-dimensional net-structure proximity sensors in a stacked ring. We also experimentally demonstrate the feasibility of these detection principles. The experimental result shows the sensor can detect azimuth at all peripheral angles and elevation from side to top up.

DOI： 10.1109/IROS.2013.6696420

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Sensorless Angular Position Estimation of Rotational Type Twisted Polymeric Fiber Artificial Muscles

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触・近接覚統合型ヒューマンインタフェース用入力デバイスの開発

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非接触型ヒューマンインタフェースデバイスの開発–独立多点センシング方式の導入とモジュール化–

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超音波式ネット状近接覚センサが検出可能な対象物情報について

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超音波式ネット状近接覚センサの構成方法に関する検討

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抵抗ネットワークを持つ光学式センサアレイにおける回路設計の検討と三次元入力インタフェースへの応用

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物体までの方位・仰角を検出可能な光学式近接覚センサの開発

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