Speed/Force Control of Plane Type Parallel Mechanism by Using Internal Force with Redundant Degree of Freedom

Abstract

This paper describes speed/force control of a plane-type parallel link mechanism with redundant degree of freedom (DOF). Parallel mechanisms have problems of singular points and joint clearances. Motion transmissibility of parallel mechanisms decreases at singular points in working space, which make it difficult to realize stable control. Joint clearances cause to reduce stiffness of the mechanism, and errors of control accuracy when external forces are applied. We propose utilization of internal force in order to overcome these problems. We apply the proposed method to plane-type parallel link mechanism composed of a couple of 2-DOF link with a rotary actuator and a linear actuator. The internal force can reduce errors caused by joint clearance and improve the stiffness of mechanism. This paper proves the effectiveness of the proposed method by experiments of the speed control under sudden load and of speed/force hybrid control.