High-performance motion control of the hydraulic press based on an extended fuzzy disturbance observer

This article focuses on the high-performance motion control problem of the hydraulic press. Smooth and precise motion control of the hydraulic press is hardly achieved due to the complex external disturbances which typically consist of the deformation force and friction force. An extended fuzzy disturbance observer is first constructed to estimate and compensate the hardly modeled deformation force. The proposed extended fuzzy disturbance observer differs with the fuzzy disturbance observer on parameter adaptation; the fuzzy disturbance observer is commonly driven by the disturbance observer error, while the designed extended fuzzy disturbance observer is driven by the disturbance observer error and the motion tracking error together. The nonlinear cascade controller is further applied to synthesize the motion controller considering the particular work principle of the separate meter-in separate meter-out drive system adopted in the hydraulic press. The outer motion tracking loop of the nonlinear cascade controller is designed based on the sliding mode control with the desired driving force as control output, and the inner pressure control loop of the nonlinear cascade controller uses the backstepping technique to make the separate meter-in separate meter-out drive system track the desired driving force precisely. The minimum equivalent load criterion is proposed to act as the bridge linking the outer and inner loop. The stability of the overall closed-loop system is proved based on the Lyapunov theory. The performance of the proposed scheme is verified through the simulations and experiments. The results demonstrate that the nonlinear cascade controller together with the extended fuzzy disturbance observer provides an excellent motion tracking performance in the presence of complex external disturbances.