Fuzzy Self-adjusting PID Control Strategy for 3-RRR Parallel Robots Considering Joint Clearance

Due to the relative movement of the adjacent rigid body and the wear of materials, etc., the joint clearance in the mechanism is inevitably present. Collision and friction in the clearance joints are highly nonlinear external disturbances so that traditional control strategies will fail to achieve satisfactory control effect. In this study, the control strategy which can reduce the negative effects of clearance joints is proposed in the perspective of control. In this paper, a planar 3-RRR parallel mechanism with three clearance joints is taken as the research object. A fuzzy controller that can realize adaptive compensation of clearance force is designed to make up the lack of fixed compensation method. Specifically, fuzzy control rules of this mechanism are established, and a novel fuzzy self-adjusting PID control strategy for the mechanism with clearance joints is proposed. Aiming at the common problems of the joint clearance and against its defects of the mechanism, the design of the controller is of great theoretical and practical significance.