Dynamic feed-forward control of a parallel kinematic machine

This paper deals with the dynamic feed-forward control of a 6-UPS parallel kinematic machine (PKM). The control system consists of the closed-loop control subsystem and the dynamic control subsystem. The closed-loop control subsystem is constructed by using the PD control and low-pass filter. Moreover, zero phase error tracking control (ZPETC) is introduced to the closed-loop control subsystem to improve its response capability. Based on the rigid-body dynamic model of the PKM, the dynamic control subsystem is designed by using the computed torque control and feed-forward control. Since the phase lag of the closed-loop control subsystem is almost eliminated by ZPETC and PD control, the motion precision of the closed-loop control subsystem is improved largely. The influence of the dynamic characteristic of the PKM on the motion precision is decreased due to the introduction of rigid-body dynamic model into the control system. As a result, the motion precision of the moving platform is greatly improved.