Fuzzy control of robot and compliant wrist system

Abstract

A robotic compliant wrist device which combines passive compliance and a displacement sensor for robots to facilitate various complex manipulation tasks has been developed. The wrist provides the necessary flexibility to accommodate transitions as robots make contact with the workpiece, to correct the positioning error of robots and the geometric tolerance of parts, and to avoid high impact forces normally generated in manufacturing operations. The sensing from the wrist device is used in the feedback loop for actively controlling contact forces and compensating for positioning errors during motion and contact. The authors present the design of two prototypes of the wrist device, and then propose a systematic hybrid position force control scheme for the robot and compliant wrist system. They also discuss the design of a fuzzy controller which assigns velocities for the measured forces in the corresponding directions in insertion operation. The controller is composed of four parts: fuzzification interface, knowledge base, decision-making logic, and defuzzification interface. Compared with the method of evaluating exact force zones, the fuzzy control approach presented a smoother performance, and yielded a fast process towards a full insertion.