Dynamics and control of a planar 3-DOF parallel manipulator with actuation redundancy

This paper deals with the dynamics and control of a planar 3-DOF parallel manipulator with actuation redundancy. According to the kinematics of the redundant manipulator, the inverse dynamics is derived by using the virtual work principle, and the driving force is optimized by utilizing the least-square method. Based on the dynamic model, a position and force switching control strategy is proposed for the parallel manipulator. In this control strategy, two extendible links are controlled by position and force modes, respectively. Moreover, in the whole workspace, their control modes are switched. The critical angles for switching control modes are planned and the position compensation method is investigated. The control tests show that the contour error of the redundantly actuated parallel manipulator is similar to that of its corresponding non-redundant parallel manipulator without one extendible link. However, the redundant parallel manipulator has a larger orientation workspace and higher stiffness. The redundantly actuated parallel manipulator is incorporated into a 4-DOF hybrid machine tool which also includes a feed worktable.