Modal control of a hydraulically driven redundant actuated fully parallel mechanism

In this paper, we consider the problem of modal-space control for the hydraulically driven fully parallel mechanism with actuation redundancy. Firstly, the mechanical-hydraulic interaction system is transformed into modal-space model. Then, independent modal decoupled systems for the redundant mechanism are obtained. According to the eigenvalue frequency characteristics, two types of modal systems – zero eigenvalue modal systems and nonzero ones – naturally result and these systems can be treated separately. For the nonzero eigenvalue modal systems, it is convenient to employ dynamic pressure feedback control to regulate damping. For the zero eigenvalue modal systems, we give a proof to show that they just lie in the null space of the Jacobian of the mechanism, then it is more appropriate to implement force control for this type of modal system. Some simulation results further explain the proposed modal-space control method.