Abstract: The control strategy of a 4-DOF parallel kinematic machine (PKM) with actuation redundancy, which is created by adding a redundant link with active actuator to a corresponding non-redundant PKM, is studied. Based on the position control of the corresponding non-redundant PKM, the redundant chain is controlled by using force mode to control the internal force of the redundant chain, and other kinematic chains are controlled by using position mode to ensure the motion precision of the redundant PKM. Based on the transfer function of the control system, the stability, anti-disturbance capability and response performance are studied. Further, the control strategy is applied to the numerical control system and the experiment is carried out. The contour test with the PKM moving along a circular trajectory shows that the contour error of the redundant PKM is similar to that of the corresponding non-redundant one. In addition, the clearance in the non-redundant extendible chain is reduced due to the existence of the redundant chain. Thus, the engineering effectiveness and feasibility of the control strategy are verified.

Key words: Actuation redundancy, Force control, Parallel kinematic machine