Motion control for a redundantly actuated parallel electrohydraulic mechanism

In this paper, a motion controller for a redundantly actuated parallel electrohydraulic mechanism (RA-PEHM) is developed that includes a position tracking loop and an internal force rejecting loop. Electrohydraulic and rigid body models are built. The structure of internal force space is analyzed. Model-based position control for rigid-body degrees of freedom (DOF) is proposed, using a fast inner force loop to track programming desired generalized forces thereby reproducing desired position. Force control based on real-time solution of the basis of the internal force space for redundant DOF is used to reject internal forces, which are usually caused by some factors, such as inconsistent dynamic behavior of drive units, zero drift of servovalves and measuring error of sensors. Simulation results show the proposed control scheme has good position tracking performance and effectively reduces the internal force simultaneously.