THE POSITION CONTROL OF ELECTROHYDRAULIC SERVOMECHANISM VIA A NOVEL VARIABLE-STRUCTURE CONTROL

There are many distinct advantages of a hydraulic control system, such as a higher speed of response with fast motions and possible speed reversals, a higher torque stiffness and a continuous operation. The hydraulic control system is becoming the most common form of precise manipulation system. However, some nonlinear phenomena, such as the relationship between input current and output flow, the fluid compressibility and the deadband due to internal leakage and hysteresis, make the control of the hydraulic system difficult. A novel variable structure control (VSC) with a time-varying switching gain, a second-order relation between sliding surface and uncertainties, and a boundary layer for the sliding surface, is employed to deal with the position control of the electrohydraulic servomechanism which is subjected to parameter uncertainties and external disturbances. Furthermore, the robust stability of the system is verified by a Lyapunov stability criterion. Finally, the simulations show that the proposed appraoch can achieve an accurate and robust tracking performance.