Command smoothing-proxy sliding mode control of hydraulic servo system considering structural flexibility

In this study, a command smoothing-disturbance observer-based proxy sliding mode control (CS-DPSMC) method is proposed for a class of hydraulic servo systems with structural flexibility. First, to alleviate the influence of residual vibration due to structural flexibility, command smoothing method (CS) is used to modify the desired trajectory; Then, a nonlinear disturbance observer-based proxy sliding mode controller (DPSMC) is developed so as to make the hydraulic actuator track the desired trajectory. Besides, the control signal is continuous because the discontinuous sign function is theoretically canceled. Therefore, high-frequency unmodeled dynamics of flexible structures will not be excited. According to the passivity theory and Lyapunov theory, the stability of the control system is proven. The effectiveness of the proposed algorithm is verified by comparative numerical analysis.