Kineto-static Mechanical Synthesis for Nonlinear Profile Design of Passive Stiffness Using Closed Kinematic Chain and Its Application to Landing Mechanism for Impact Absorption

Abstract

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.