Force/Position Hybrid Control of 6PUS-UPU Redundant Driven Parallel Manipulator Based on 2-DOF Internal Model Control

To improve control performance of parallel manipulator, servo control is optimized according to 2-DOF control with Internal Model Control. Position loop of the controller is redesigned based on the original current loop and speed loop. The hybrid force/position control strategy on the basis of cross-coupling is proposed. With mechatronic cosimulation system, it is proved that the force/position hybrid control on the basis of 2-DOF Internal Model Control has better stability and position precision compared with the traditional PID control. The control precision and stability of the parallel manipulator are improved effectively in actual experiment. Two types of compliance operation including peg in hole and surface tracking are realized in 6PUS-UPU parallel manipulator and both have good applicable effect. 1. Introduction Parallel manipulator is becoming increasingly popular in a large number of applications. It is a complex system with characteristics of multidegree of freedom, multi-input multioutput, high nonlinearity and strong coupling, and so forth. Control of parallel manipulator is very complex and researches mostly focus on kinematic and dynamic control. Dynamic control can meet the demands of high performance more than kinematic control. Dynamic feed forward control and computed torque control are common dynamic control methods [1–3]. Müller and Hufnagel [4] proposed the adaptive and singularity-free inverse dynamics models for control of parallel manipulators, Achim and Matthias [5] used the dynamics model as a feed forward on a handheld parallel mechanism to reduce the disturbance, and Farhadmanesh and Rastin [6] designed a new fuzzy model-based controller for complex dynamical systems with application to a 3-RRR spherical parallel manipulator. Classic PID controller is widely used in various kinds of industrial fields for its simple structure and strong robustness. However, classic PID controller cannot meet the different performance requirements simultaneously. 2-DOF control and Internal Model Control are introduced to improve the performance of parallel manipulator [7–10]. First, the servo control strategy of 6PUS-UPU parallel manipulator is analyzed. The PID control is combined with 2-DOF and Internal Model Control to redesign servo control loops of the parallel manipulator. Next the hybrid force/position control of parallel manipulator is proposed. Then the entire model of the 6PUS-UPU parallel manipulator is established, and the mechatronic cosimulation is carried out. Finally the control method is verified by actual prototype