Approximate Variable Structure Control for Transient Load in Large Hydraulic Press

Transient load in large hydraulic valve spool opening seriously affects the accuracy and stability of hydraulic control system. According to characteristics of the load control system, sliding mode variable structure control strategy (VSC) is presented and an approximate variable structure controller is designed to reduce the system´s chatter. The control strategy was applied to large hydraulic press control system. Compared to PID control strategy which had good dynamic characteristics, results indicate that approximate VSC for transient load can effectively eliminate mutation, reduce system tremor, improve system robustness and control precision.