Kyushu University Academic Staff Educational and Research Activities Database
List of Presentations
Kenji Tahara Last modified date:2018.06.07

Associate Professor / Control Systems / Department of Mechanical Engineering / Faculty of Engineering


Presentations
1. H. Y. Han, S. Arimoto, Kenji Tahara, M. Yamaguchi, P. T A Nguyen, Robotic pinching by means of a pair of soft fingers with sensory feedback, 2001IEEE International Conference on Robotics and Automation (ICRA), 2001, 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..
2. S. Arimoto, Kenji Tahara, M. Yamaguchi, Existence of feedbacks from sensing to action for stable grasping and dextrous manipulation by multi-fingered robot hands, Proceedings of the 2001 IEEE International Conference on Control Applications CCA '01, 2001, 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..
3. S. Nakamura, Kenji Tahara, J. H. Bae, M. Sekimoto, S. Arimoto, Experiments of grasping and object-manipulation by a pair of multi-degrees of freedom robot fingers, 2003 IEEE International Symposium on Computational Intelligence in Robotics and Automation, CIRA 2003, 2003.01, 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..
4. J. H. Bae, Kenji Tahara, S. Nakamura, S. Arimoto, Computer simulation of grasping and object-manipulation by a pair of multi-degrees of freedom robot fingers, 2003 IEEE International Symposium on Computational Intelligence in Robotics and Automation, CIRA 2003, 2003.01, 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..
5. Fumihiko Asano, Zhi Wei Luo, Kenji Tahara, Masaki Yamakita, Shigeyuki Hosoe, Modeling and control for whole arm dynamic cooperative manipulation, 2004 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2004.12, 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..
6. Kenji Tahara, Z. W. Luo, T. Odashima, M. Onishi, S. Hosoe, A. Kato, Dynamic control and simulation of human musculo-skeletal model, SICE Annual Conference 2004, 2004.12, 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..
7. Kenji Tahara, Zhi Wei Luo, Suguru Arimoto, Hitoshi Kino, Task-space feedback control for a two-link arm driven by six muscles with variable damping and elastic properties, 2005 IEEE International Conference on Robotics and Automation, 2005, 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..
8. Kenji Tahara, Zhi Wei Luo, Suguru Arimoto, Hitoshi Kino, Sensory-motor control of a muscle redundant arm for reaching movements - Convergence analysis and gravity compensation, IEEE IRS/RSJ International Conference on Intelligent Robots and Systems, IROS 2005, 2005, -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..
9. Kenji Tahara, Zhi Wei Luo, Suguru Arimoto, On control mechanism of human-like reaching movements with musculo-skeletal redundancy, 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2006, 2006, 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..
10. Kenji Tahara, Suguru Arimoto, Zhi Wei Luo, Morio Yoshida, On control for "blind touching" by human-like thumb robots, 2007 IEEE International Conference on Robotics and Automation, ICRA'07, 2007, 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..
11. Masaki Onishi, Zhi Wei Luo, Tadashi Odashima, Shinya Hirano, Kenji Tahara, Toshiharu Mukai, Generation of human care behaviors by human-interactive robot RI-MAN, 2007 IEEE International Conference on Robotics and Automation, ICRA'07, 2007.11, 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..
12. Kenji Tahara, Suguru Arimoto, Masahiro Sekimoto, Morio Yoshida, Zhi Wei Luo, On iterative learning control for simultaneous force/position trajectory tracking by using a 5 D.O.F. robotic thumb under non-holonomic rolling constraints, 2008 IEEE International Conference on Robotics and Automation, ICRA 2008, 2008, 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..
13. Kenji Tahara, Suguru Arimoto, Morio Yoshida, Dynamic object grasping by a triple-fingered robotic hand, 2008 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS, 2008, 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..
14. Akihiro Kawamura, Kenji Tahara, Ryo Kurazume, Tsutomu Hasegawa, Simple orientation control of an object by regrasping using a dual-arm manipulator with multi-fingered hands, 2009 International Conference on Advanced Robotics, ICAR 2009, 2009, 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..
15. Kazuya Matsuo, Kouji Murakami, Tsutomu Hasegawa, Kenji Tahara, Ryo Kurazume, Measurement of static constraints imposed by a human hand on a grasped object, 2009 International Conference on Advanced Robotics, ICAR 2009, 2009, 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..
16. Morio Yoshida, Suguru Arimoto, Kenji Tahara, Manipulation of 2D object with arbitrary shape by robot finger under rolling constraint, ICROS-SICE International Joint Conference 2009, ICCAS-SICE 2009, 2009, 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..
17. H. Kino, S. Kikuchi, T. Yahiro, Kenji Tahara, Basic study of biarticular muscle's effect on muscular internal force control based on physiological hypotheses, 2009 IEEE International Conference on Robotics and Automation, ICRA '09, 2009, 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..
18. Suguru Arimoto, Morio Yoshida, Masahiro Sekimoto, Kenji Tahara, A riemannian-geometry approach for dynamics and control of object manipulation under constraints, 2009 IEEE International Conference on Robotics and Automation, ICRA '09, 2009, 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..
19. Kazuya Matsuo, Kouji Murakami, Tsutomu Hasegawa, Kenji Tahara, Ryo Kurazume, Segmentation method of human manipulation task based on measurement of force imposed by a human hand on a grasped object, 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2009, 2009.12, 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..
20. Morio Yoshida, Suguru Arimoto, Kenji Tahara, Pinching 2D object with arbitrary shape by two robot fingers under rolling constraints, 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2009, 2009.12, 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..
21. Akihiro Kawamura, Kenji Tahara, Ryo Kurazume, Tsutomu Hasegawa, Dynamic grasping for an arbitrary polyhedral object by a multi-fingered hand-arm system, 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2009, 2009.12, 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..
22. Kenji Tahara, Suguru Arimoto, Morio Yoshida, Dynamic force/torque equilibrium for stable grasping by a triple robotic fingers system, 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2009, 2009.12, 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..
23. Akihiro Kawamura, Kenji Tahara, Ryo Kurazume, Tsutomu Hasegawa, Sensory feedback attitude control for a grasped object by a multi-fingered hand-arm system, 2010 IEEE International Conference on Robotics and Biomimetics, ROBIO 2010, 2010, 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..
24. Kenji Tahara, Hitoshi Kino, Iterative learning scheme for a redundant musculoskeletal arm
Task space learning with joint and muscle redundancies, 5th International Conference on Broadband Wireless Computing, Communication and Applications, BWCCA 2010, 2010, 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..
25. Kenji Tahara, Hitoshi Kino, Iterative learning control for a redundant musculoskeletal arm
Acquisition of adequate internal force, 23rd IEEE/RSJ 2010 International Conference on Intelligent Robots and Systems, IROS 2010, 2010, 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..
26. Kenji Tahara, Keigo Maruta, Motoji Yamamoto, External sensorless dynamic object manipulation by a dual soft-fingered robotic hand with torsional fingertip motion, 2010 IEEE International Conference on Robotics and Automation, ICRA 2010, 2010, 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..
27. Kenji Tahara, Suguru Arimoto, Morio Yoshida, Dynamic object manipulation using a virtual frame by a triple soft-fingered robotic hand, 2010 IEEE International Conference on Robotics and Automation, ICRA 2010, 2010, 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..
28. Hitoshi Kino, Shiro Kikuchi, Kenji Tahara, Decision method of internal force for sensorless positioning of musculoskeletal system, 5th International Conference on Broadband Wireless Computing, Communication and Applications, BWCCA 2010, 2010, 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..
29. Kazuya Matsuo, Kouji Murakami, Katsuya Niwaki, Tsutomu Hasegawa, Kenji Tahara, Ryo Kurazume, A tactile sensing for estimating the position and orientation of a joint-axis of a linked object, 23rd IEEE/RSJ 2010 International Conference on Intelligent Robots and Systems, IROS 2010, 2010, 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..
30. Akihiro Kawamura, Kenji Tahara, Ryo Kurazume, Tsutomu Hasegawa, Robust manipulation for temporary lack of sensory information by a multi-fingered hand-arm system, 2011 IEEE/RSJ International Conference on Intelligent Robots and Systems: Celebrating 50 Years of Robotics, IROS'11, 2011, 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..
31. Kenji Tahara, Suguru Arimoto, Iterative learning scheme for a redundant manipulator
Skilled hand writing motion on an arbitrary smooth surface, 2011 IEEE International Conference on Robotics and Automation, ICRA 2011, 2011, 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..
32. Kenji Tahara, Shingo Iwasa, Shu Naba, Motoji Yamamoto, High-backdrivable parallel-link manipulator with continuously variable transmission, 2011 IEEE/RSJ International Conference on Intelligent Robots and Systems: Celebrating 50 Years of Robotics, IROS'11, 2011, 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..
33. Akihiro Kawamura, Kenji Tahara, Ryo Kurazume, Tsutomu Hasegawa, Dynamic object manipulation using a multi-fingered hand-arm system
Enhancement of a grasping capability using relative attitude constraints of fingers, IEEE 15th International Conference on Advanced Robotics: New Boundaries for Robotics, ICAR 2011, 2011, 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..
34. Akihiro Kawamura, Kenji Tahara, Ryo Kurazume, Tsutomu Hasegawa, Robust visual servoing for object manipulation with large time-delays of visual information, 25th IEEE/RSJ International Conference on Robotics and Intelligent Systems, IROS 2012, 2012, 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..
35. Ryota Ishibashi, Takahiko Oda, Kenji Tahara, Hitoshi Kino, Akira Kojima, Parallel system using V-shaped shape memory alloy actuator, 2012 51st Annual Conference on of the Society of Instrument and Control Engineers of Japan, SICE 2012, 2012, 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..
36. Kenji Tahara, Yuta Kuboyama, Ryo Kurazume, Iterative learning control for a musculoskeletal arm
Utilizing multiple space variables to improve the robustness, 25th IEEE/RSJ International Conference on Robotics and Intelligent Systems, IROS 2012, 2012, 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..
37. Kenji Tahara, Keigo Maruta, Motoji Yamamoto, Alternative dexterous object manipulation using torsional fingertip joints of multifingered hand, 22nd Annual Symp. on Micro-Nano Mechatronics and Human Science, MHS 2011, Held Jointly with the Symp. on COE for Education and Research of Micro-Nano Mechatronics, Micro-Nano GCOE 2011, Symp. on Hyper Bio Assembler for 3D Cellular System Innovation, 2012, 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..
38. Kenji Tahara, Keigo Maruta, Akihiro Kawamura, Motoji Yamamoto, Externally sensorless dynamic regrasping and manipulation by a triple-fingered robotic hand with torsional fingertip joints, 2012 IEEE International Conference on Robotics and Automation, ICRA 2012, 2012.01, 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..
39. Hitoshi Kino, Hiroaki Ochi, Kenji Tahara, Yuki Matsutani, Ryota Ishibashi, Study of human motion generation based on redundancy of musculoskeletal structure
Analysis of potential generated by internal force for two-link system, 2013 IEEE Workshop on Advanced Robotics and Its Social Impacts, ARSO 2013, 2013, 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..
40. Hitoshi Kino, Shiro Kikuchi, Yuki Matsutani, Kenji Tahara, Sensibility to muscular arrangement of feedforward position control for non-pulley-musculoskeletal system, 5th FTRA International Conference on Information Technology Convergence and Services, ITCS 2013 and the 3rd International Conference on Intelligent Robotics, Automations, Telecommunication Facilities, and Applications, IRoA 2013, 2013, 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..
41. Yuki Matsutani, Hiroaki Ochi, Hitoshi Kino, Kenji Tahara, Motoji Yamamoto, Feed-forward positioning of musculoskeletal-like robotic systems with muscular viscosity
Determination of an adequate internal force, 2013 IEEE Workshop on Advanced Robotics and Its Social Impacts, ARSO 2013, 2013, 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..
42. Tomofumi Okada, Kenji Tahara, Development of a two-link planar manipulator with continuously variable transmission mechanism, 2014 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM 2014, 2014, 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..
43. Tokuo Tsuji, Kosei Baba, Kenji Tahara, Kensuke Harada, Kenichi Morooka, Ryo Kurazume, Grasp stability analysis for elastic fingertips by using potential energy, 7th IEEE/SICE International Symposium on System Integration, SII 2014, 2014.01, 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..
44. Ryota Ishibashi, Hiroaki Ochi, Takahiko Oda, Ryuji Okuda, Katsuya Umeda, Kenji Tahara, Hitoshi Kino, Akira Kojima, A proposal of a SMA actuated wing mechanism using flexible structure for the capability of various flow speeds, 2014 IEEE International Conference on Robotics and Biomimetics, IEEE ROBIO 2014, 2014.04, 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..
45. Tokuo Tsuji, Kosei Baba, Kenji Tahara, Kensuke Harada, Kenichi Morooka, Ryo Kurazume, Grasp stability evaluation based on energy tolerance in potential field, IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2015, 2015.12, 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..
46. Takeshi Arakawa, Kentaro Takagi, Kenji Tahara, Kinji Asaka, Position control of fishing line artificial muscles (coiled polymer actuators) from nylon thread, Electroactive Polymer Actuators and Devices (EAPAD) 2016, 2016, 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..
47. Hiroaki Ochi, Hitoshi Kino, Kenji Tahara, Yuki Matsutani, Geometrie conditions for feedforward positioning of musculoskeletal tendon-driven structure, 41st Annual Conference of the IEEE Industrial Electronics Society, IECON 2015, 2016.01, 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..
48. Tetsuya Morizono, Kenji Tahara, Hitoshi Kino, Experimental investigation of contribution of biarticular actuation to mappings between sensory and motor spaces, 41st Annual Conference of the IEEE Industrial Electronics Society, IECON 2015, 2016.01, 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..
49. Kenji Tahara, Yuki Matsutani, Daisuke Nakagawa, Masataka Sato, Hitoshi Kino, Variable combination of feed-forward and feedback manners for set-point control of a musculoskeletal arm considering the maximum exertable muscular force, 42nd Conference of the Industrial Electronics Society, IECON 2016, 2016.12, 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..
50. Kentaro Takagi, Takeshi Arakawa, Jun Takeda, Ken Masuya, Kenji Tahara, Kinji Asaka, Position control of twisted and coiled polymer actuator using a controlled fan for cooling, Electroactive Polymer Actuators and Devices (EAPAD) 2017, 2017, 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..
51. Ken Masuya, Shu Ono, Kentaro Takagi, Kenji Tahara, Nonlinear dynamics of twisted and coiled polymer actuator made of conductive nylon based on the energy balance, 2017 IEEE International Conference on Advanced Intelligent Mechatronics, AIM 2017, 2017.08, 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%. 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..
52. Yuki Matsutani, Kenji Tahara, Hitoshi Kino, Hiroaki Ochi, Stiffness evaluation of a tendon-driven robot with variable joint stiffness mechanisms, 17th IEEE-RAS International Conference on Humanoid Robotics, Humanoids 2017, 2017.12, 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..
53. Ken Masuya, Shu Ono, Kentaro Takagi, Kenji Tahara, Nonlinear Dynamics of Twisted and Coiled Polymer Actuator made of Conductive Nylon based on the Energy Balance, 2017 IEEE International Conference on Advanced Intelligent Mechatronics, 2017.07.
54. Kentaro Takagi, Takeshi Arakawa, Jun Takeda, Ken Masuya, Kenji Tahara, Kinji Asaka, Position control of twisted and coiled polymer actuator using a controlled fan for cooling, SIPE, 2017.03.
55. Takeshi Arakawa, Kentaro Takagi, Kenji Tahara, Kinji Asaka, Position control of fishing line artificial muscles (coiled polymer actuators) from nylon thread, SIPE, 2016.03.
56. Kenji Tahara, Yuki Matsutani, Daisuke Nakagawa, Masataka Sato, Hitoshi Kino, Variable combination of feed-forward and feedback manners for set-point control of a musculoskeletal arm considering the maximum exertable muscular force, 42nd Annual Conf. of the IEEE Industrial Electronics Society, 2016.10.
57. Hiroaki Ochi, Hitoshi Kino, Kenji Tahara, Yuki Matsutani, Geometric conditions for feedforward positioning of musculoskeletal tendon-driven structure, 41st Annual Conf. of the IEEE Industrial Electronics Society, 2015.11.
58. Tetsuya Morizono, Kenji Tahara, Hitoshi Kino, Experimental investigation of contribution of biarticular actuation to mappings between sensory and motor spaces, 41st Annual Conf. of the IEEE Industrial Electronics Society, 2015.11.
59. Tokuo Tsuji, Kosei Baba, Kenji Tahara, Kensuke Harada, KEN'ICHI MOROOKA, Ryo Kurazume, Grasp stability evaluation based on energy tolerance in potential field, IEEE⁄RSJ Int. Conf. Intell. Robots, Syst., 2015.09.
60. Tokuo Tsuji, Kosei Baba, Kenji Tahara, Kensuke Harada, KEN'ICHI MOROOKA, Ryo Kurazume, Grasp Stability Analysis for Elastic Fingertips by Using Potential Energy, 2014 IEEE/SICE International Symposium on System Integration, 2014.12.
61. Tomofumi Okada, Kenji Tahara, Development of a two-link planar manipulator with continuously variable transmission mechanism, 2014 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, 2014.07.
62. Miao Li, Hang Yin, Kenji Tahara, Aude Billard, Learning object-level impedance control for robust grasping and dexterous manipulation, 2014 IEEE International Conference on Robotics and Automation, 2014.06.
63. Yuki Matsutani, Kenji Tahara, Hitoshi Kino, Hiroaki Ochi, Motoji Yamamoto, Set-point control of a musculoskeletal arm by the complementary combination of a feedforward and feedback Manner, 2014 IEEE International Conference on Robotics and Automation, 2014.06.
64. Kenji Tahara, Yuta Kuboyama, Ryo Kurazume, Iterative learning control for a musculoskeletal arm: Utilizing multiple space variables to improve the robustness, IEEE/RSJ Int. Conf. Intell. Robots, Syst., 2012.10.