High-Gain Observer-Based Sliding Mode Force Control for the Single-Rod Electrohydraulic Servo Actuator

A high-gain observer based sliding mode force control system for the single-rod servo actuator is presented in this paper. In order to track the desired force, full states for feedback are needed. Since only the output force is measured, a high-gain observer with easy implementation and calibration is designed for the estimation of the unavailable states. Then the sliding mode controller is proposed and a continuously varying function instead of the traditional sign function is used to constitute the switching term of the control input which takes the distance of the system states from the sliding surface into account. So the chattering phenomena are eliminated. The stability of the closed-loop force control system is analyzed by the singular perturbation method and simulations show the effectiveness of the proposed force control method for the single-rod electrohydraulic servo actuator.