Abstract
Realization of mechanical softness is an important issue for a safe and adaptive control of robots in the real world. However, because the robot also requires stiffness for task execution, the simultaneous realization of softness and stiffness is necessary. In this paper, we design a nonlinear passive stiffness using closed kinematic chain. Because the proposed mechanism utilizes linear spring and nonlinearity of the closed kinematic chain, we can easily design the nonlinearity of the stiffness by changing the link parameters of members. The proposed mechanism is used for the leg of a robot and the mechanical parameters (length of members) are optimized so that the impact force on landing is reduced. The effectiveness of the proposed mechanism and optimization method are evaluated by simulations and experiments.
