Nonlinear Motion Control of a Hydraulic Press Based on an Extended Disturbance Observer

This paper focuses on high-performance motion control of the electro-hydraulic system of hydraulic presses. A detailed mathematical model of the system was constructed. An electro-hydraulic system of hydraulic presses is a kind of nonlinear system with parametric uncertainties, uncertain nonlinearities, and external disturbances. To attenuate the above effects, a nonlinear robust motion controller based on an extended disturbance observer was developed. The outer position tracking loop was designed with a sliding mode control to compensate for disturbance estimation error, while the inner pressure control loop using the backstepping method can realize accurate output force control. The stability of the overall closed-loop system based on the Lyapunov approach can be proven to be effective. Both simulation and experiment results showed that the proposed controller has a good transient-response and provides accurate position tracking in the presence of parametric uncertainties, uncertain nonlinearities, and external disturbances.