Dynamic Decoupling Based Robust Synchronous Control for a Hydraulic Parallel Manipulator

In this paper, a novel dynamic decoupling-based robust synchronous control scheme is proposed for the high-precision motion trajectory tracking control of a hydraulic parallel manipulator. The presented controller is derived by effectively integrating joint disturbance rejection technique with a cross-coupling control (CCC) approach. The parallel manipulator is first considered as a multi-axis system with modeling uncertainties and strong nonlinear coupling dynamics. For each axis, two extended state observers are synthesized to estimate and reject both the matched uncertainties and unmatched uncertainties (e.g., external disturbances and unmodeled nonlinearities), and then the decoupled dynamic model of the system in joint space can be established. A synchronization error is developed to represent the coordination degree of multiple actuators and then coupled with the position error to form a coupling position error. Subsequently, based on the system decoupled dynamic model, a synchronous controller with the feedback of coupling position error is carried out to coordinate the motions of actuators by combining the CCC strategy with robust control via backstepping method. The proposed controller can theoretically guarantee the simultaneous convergence of both position tracking errors and synchronization errors. The stability of the system is verified via the Lyapunov method. The comparative experiment results are obtained to verify the high tracking performance nature of the proposed control strategy.