Journal of the Robotics Society of Japan

A robust numerical solution to the inverse kinematics is proposed based on Levenberg-Marquardt method, where the squared norm of the residual with a small bias is used for the damping factor. A rather simple idea remarkably improves numerical stability and convergence performance even in unsolvable cases. The discussion is done through an investigation of the condition number of coefficient matrix. Comparison tests with the conventional methods show that only the proposed method succeeds in all cases. It frees operators from being careful about the target position-orientation assignment of effectors, so that it facilitates easy robot motion designs and remote operations.

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This paper presents a fast method of evaluating grasp stability when a multi-fingered hand grasps objects. Different from previous methods, we consider approximating the friction cone by using a few ellipsoids. By using this method, the total force/moment set applied to the grasped object can be obtained by a common set of multiple ellipsoids. This method is not conservative but effective since approximated force closure is tested by simply calculating the inequalities of quadratic form. Moreover, by using the ellipsoidal approximation, we propose an easy method of evaluating the grasp stability. We show that the grasp stability can be easily calculated by using simple equations. The effectiveness of the proposed method is verified by several numerical examples where we show that the proposed method has practical accuracy for real applications and evaluates the grasp stability much faster than conventional methods.

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This paper answers the question on indeterminate contact force posed by Makita, Oda, and Maeda in Vol.27, No.4. Introduction of an elastic contact model is a reasonable solution to their question and it was already solved in our subsequent researches. This paper introduces our two computation methods based on the elastic contact model and poses questions to their analysis from the physical point of view.

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This paper proposes a design concept for renovating a legged robot to a hybrid mobile robot with minimal degrees of freedom (4DOFs) and its motion analysis for switching locomotion from leg-type to wheel-type and vice versa. For the leg-type locomotion, specifically in the transitional state of sitting or standing, we show the control method based on minimization of total energy cost considering the distribution of a motor power payload in hip and knee joints using a motor specification. Also, we discuss robot configurations for switching between the two types under such environmental factors like walking gaits, ground inclination angle and traveling direction. Knee joint position of a pivotal foot determines knee ahead and knee behind gaits. Then we find three beneficial switching types aiming for moderate use of motor, rider's comfort, and energy saving. Moreover, we clarify the control method for changing traveling direction within a switching period. Finally, we demonstrate the switching and verify that the results of the analysis become useful for enabling the switch on demand. Also, the demonstration verifies that the robot can generate a steering function while it switches between the two types of locomotion.

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