Hiroe Hashiguchi

Three-dimensional multi-joint reaching under redundancy of DOFs

A simple control method for 3-dimensional multi-joint reaching movements under redundancy of Degrees-of-Freedom is proposed, which neither need to introduce any performance index to solve inverse kinematics uniquely nor need to calculate pseudo-inverse of the Jacobian matrix of task coordinates with respect to joint coordinates. The proposed control signal is composed of linear superposition of three terms: 1) angular-velocity feedback for damping shaping; 2) task-space position feedback with a single stiffness parameter; and 3) compensation for gravity force on the basis of estimates for uncertain parameters of the potential energy. Through a variety of computer simulations by using a whole arm model with five DOFs, the importance of synergistic adjustments of damping factors as well as its relation to selection of the stiffness parameter is pointed out. It is shown that if damping factors are chosen synergistically corresponding to the inertia matrix at the initial time and the stiffness parameter then the endpoint converges asymptotically to the target position and reaches it smoothly without incurring any self-motion.

Control of a Handwriting Robot with DOF Redundancy Based on Feedback in Task Coordinates

In order to enhance dexterity of a robot hand, it is said that the robot should be designed to have a redundant number of degrees-of-freedom(DOF). However, in redundant robotic systems, the inverse kinematics from task-description space to joint space becomes ill-posed. Therefore the problem of determination of joint motions becomes difficult. In order to avoid this ill-posedness, many methods have been proposed, most of which introduce an additional input term calculated from some intentionally artificial index of performance. This paper treats a 4-DOF redundant handwriting robot by using a novel and simple control method for resolving the problem of such illposedness based on feedback in task-coordinates. The effectiveness of the proposed control method is demonstrated through computer simulation.

Natural resolution of DOF redundancy in execution of robot tasks under the gravity: a challenge to Bernstein's problem and applications to handwriting robots

In order to enhance dexterity in execution of robot tasks, a redundant number of degrees-of-freedom (DOF) is adopted for design of robotic mechanisms like robot arms and multi-fingered robot hands. Associated with such redundancy in DOFs relative to the number of physical variables necessary and sufficient for description of a given task, an extra performance index is introduced for controlling such a redundant robot in order to avoid ill-posedness of inverse kinematics from task space to joint space. This paper shows that such ill-posedness of DOF redundancy can be resolved in a natural way without introducing any artificial performance index or calculating any pseudo-inverse. Instead, a sensory feedback composed with a term of task space position feedback and another term of adequate joint dampings together with gravity compensation based on estimates on unknown parameters is shown to be in effect to carry out the target task without incurring self-motion

Stability of zero-moment-manifold control for a family of under-actuated robots

This paper proposes a novel control scheme called the ZMM control for generating any desired motion for a family of under-actuated robots with instability such as gymnastics robots and robotic puppets having a single leg pivoted at the floor. This pivotal ankle joint can not be actuator-driven but is passive with a rotary damper. Therefore these robots are intrinsically unstable under the effect of gravity and considered to be under-actuated and nonholonomically constrained. This paper first introduces an (n

Generation of Large Gymnastic Motions for a Family of Under-Actuated Robots by Zero-Moment-Manifold Control

1)-dimensional configuration manifold for such robots with n joints, which is called the ZMM (zero moment manifold) and defined as a set of joint angle vectors that satisfy zero of the rotational moment around the first ankle joint. It is shown theoretically that any motion starting from any given posture on a subset of the ZMM and targeting to a desired form of motion can be stabilized by using a coordinated control composed of gravity compensation for other joints except the ankle and PD feedback despite of the existence of a nonholonomic constraint. The effectiveness of the proposed control scheme is verified by numerical simulation and experimental results using a gymnastics robot with four joints.

Physiologically Inspired Robot Control: A Challenge to Bernstein’s Degrees-of-Freedom Problem

This paper is concerned with a novel control method to generate any desired motion for a family of under-actuated robots such as gymnastics robots and acrobots having a single lower leg pivoted at the floor. This pivotal ankle joint can not be actuator-driven but may have only a passive viscous device such as a rotary damper. Therefore these robots are intrinsically unstable under the effect of gravity. In order to maneuver such an under-actuated robot with n joints under non-holonomic constraint without loosing stability of motion, we have proposed a zero moment manifold (ZMM) control method by introducing an (n - 1)-dimensional configuration manifold, on which a set of joint angle vectors satisfies zero of the rotational moment around the ankle joint. It could be shown theoretically that any motion starting from any initial posture on a subset of the ZMM and moving to a desired posture can be stabilized by using a coordinated control composed of gravity compensation and PD feedback. Though the theoretical proof can guarantee only stability of movements of joint angles in a narrow range, it has been observed that the robot can move in a wider range through preliminary numerical simulation results. Notwithstanding such a conservative result of theory, this paper shows that the ZMM control with constant PD gains can generate global gymnastics movements for a class of under-actuated robots by verifying through a variety of numerical simulations that most of given attractors (target postures) have corresponding large attraction regions. This is also verified experimentally by using a real gymnastics robot with four joints and a series of large movements can be produced consecutively as programmed by selecting several target postures enough separated each other and combining them

Generation of 3-D motion of under-actuated gymnastics robots having two free joints

This paper explores what are the fundamentals of physiologically inspired robot control through investigating two interesting but difficult problems of robot control: 1) robotic hand-writing and 2) human-like multi-joints reaching with surplus DOFs (Degrees-of-Freedom). Noteworthy characteristics in control of these systems are a) redundancy in DOF, b) dexterity in execution of a target task, and c) indispensability of sensory motor coordination, though d) their dynamics are nonlinear and governed by geometric constraints in the former system. Due to these inherent characteristics, both the conventional control-theoretic approaches originated from the linear system theory and Lyapunov’s direct method are likely to fail. By gaining physical insights into these nonlinear dynamics with redundancy in DOFs and physical descriptions of target tasks, this article claims that a symbiosis of “robotics” and “neuro-physiology” is quite effective in finding a simpler sensory-motor coordination principle in each case that leads to accomplishment of each imposed task regardless of annoying characteristics of its motion dynamics with nonlinearity and DOF-redundancy.

Why does surplus DOF of robot fingers enhance dexterity of object manipulation: analysis and simulation of overall fingers-object dynamics

In the previous paper, a zero moment manifold (ZMM) control method effective for control of a class of under- actuated robots has been proposed and some experimental results have been presented. However, those robots can exercise only in the sagittal plane. This paper extends this control method to generate three-dimensional motion for gymnastics robots having an ankle joint pivoted at the floor. This ankle joint has two orthogonal axes and can not be actuator-driven. In order to maneuver intrinsically unstable robots, we propose an extended ZMM method by redefining the ZMM as a (n-2)- dimensional configuration manifold for such robots with n joints. It is shown theoretically that any motion toward the target pose starting from any given posture on a subset of the ZMM can be stabilized by using this extended ZMM control. Some simulation results of a 10-DOF gymnastics robot model show the effectiveness of the proposed method.

A sensory feedback method for a handwriting robot with D.O.F. redundancy

In order to enhance dexterity in execution of robot tasks, a redundant number of degrees-of-freedom (DOF) is adopted for design of robotic mechanisms like robot arms and multi-fingered robot hands. However, it is said that surplus DOF of such a robotic mechanism incurs a problem of illposedness of inverse kinematics from task space to joint space. This paper attempts to show that, in the case of a pinching task (grasping in 2D space), by using a pair of robot fingers with hemispherical finger ends, 1) the ill-posedness of inverse kinematics can be resolved in a natural and dynamic way by means of sensory feedback signals from task space to joint space and 2) surplus DOF of fingers enhances dexterity of pinching tasks by remarkably accelerating the speed of convergence toward target object manipulation.

Supervisory Control Strategies in a Multi-Fingered Robotic Hand System

In order to enhance dexterity of a robot hand, it is said that the robot should be designed to have a redundant number of degrees-of-freedom(D.O.F.). However, in redundant robotic systems, the inverse kinematics from task-description space to joint space becomes ill-posed. Therefore the problem of determination of joint motions becomes difficult. In order to avoid this ill-posedness, many methods have been proposed, most of which introduce an additional input term calculated from minimization of some intentionally introduced artificial index of performance. This paper treats a 4-D.O.F. redundant handwriting robot by using a novel and simple control method and resolving the problem of such ill-posedness based on sensory feedback in task-coordinates. The effectiveness of the proposed control method is demonstrated through computer simulation and a preliminary experiment.