Nonlinear motion control of the hydraulic press based on an extended piecewise disturbance observer

Abstract

This article presents a nonlinear motion controller based on an extended piecewise disturbance observer to track desired motion trajectory for the hydraulic press. The proposed extended piecewise disturbance observer accounts for external load by applying the double-drive parameter adaptation. Considering the special work principle of the separate meter-in separate meter-out drive system adopted in the hydraulic press, the nonlinear cascade controller is extended to synthesize the motion controller. The outer motion tracking loop uses the sliding mode control to compensate for load estimation error with desired driving force as control output. The inner pressure control loop is designed based on the backstepping technique. The minimum equivalent load criterion is proposed to function as the bridge linking the outer and inner loops. The stability of the overall close-loop system is proved based on the Lyapunov theory. Both simulation and experiment results demonstrate that the proposed nonlinear cascade controller, together with the extended piecewise disturbance observer, provides an excellent motion tracking performance for the hydraulic press in the presence of complex external load, which typically consists of the deformation force and the friction.