Fuzzy sliding mode control of hydraulic cylinders driving a quadruped robot

A quadruped robot driven by hydraulic cylinders has advantages for heavy loads, but the nonlinear and uncertain dynamics of the hydraulic actuators have to be considered. In this paper, a multi-strategy combination fuzzy sliding mode controller is adopted for the dynamic force control of a hydraulic servo system. First, a nonlinear mathematic modeling of a hydraulic actuator is given. Based on the modeling, a sliding mode controller is designed using the Lyapunov techniques. Second, a fuzzy scheduling mechanism is designed for boundary layer width tuning to reduce the chattering. Finally, a set of experiments were performed to analyze the effect of variation in given force, hydraulic parameters, supply pressure and environmental stiffness. The results show that the proposed fuzzy sliding mode controller is effective for a nonlinear hydraulic system, and makes the system response robust in presence of uncertainties.