Kineto-static mechanical synthesis for nonlinear property design of passive stiffness using closed kinematic chain

To prevent the human injury or breakage of the robot caused by interaction or collision with 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 the robot motion, and propose a realization method of time varying stiffness using robot motion and nonlinear passive stiffness. To realize the purpose-designed property of the time dependent stiffness, the nonlinear property of the passive stiffness has to be arbitrary designed considering the robot dynamics. In this paper, we propose the nonlinear property 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 purpose-designed stiffness is realized. The proposed method is evaluated by simulations and experiments using the prototype of the landing mechanism.