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.
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.
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.
To prevent the human injury or breakage of the robot caused by interaction or collision between the robot and its environment, it is an important issue to introduce robot softness. However, because not only softness but also stiffness is required for precise task execution, the simultaneous realization of softness and stiffness using time varying stiffness is required in the real environment. We focus on that the robot is accompanied by motion, and propose a realization method of time varying stiffness using robot motion and nonlinear passive stiffness. To realize the purpose-oriented profile of the time dependent stiffness, the nonlinear profile of the passive stiffness has to be arbitrary designed considering the robot dynamics. In this paper, we propose a nonlinear profile design method of passive stiffness based on kineto-statics with closed kinematic chain. The mechanism is synthesized based on the optimization of the generative force or torque, and the purpose-oriented stiffness is realized. The proposed method is evaluated by simulations and experiments using a prototype of landing mechanism.
We developed the robot Babyloid for the purpose that psychological distresses in elderly people and the people requiring a nursing care are decreased by taking care of Babyloid. Babyloid is not all-arounder and cannot do anything, except expressions of physiological and psychological states for the self-sufficiency such as whimpering, becoming grumpy and so on. Through interaction with expressions of self-sufficiency, we considered that mental condition of elderly people is improved by building up trusting relationships between the people and Babyloid. In this paper, we explain concept, design, and specifics of Babyloid.
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.