A compound control strategy for the digital valve based hydraulic position tracking system

Digital valve based hydraulic system seems to be a potential alternative to the traditional servo system in industrial applications, where performance-price ratio and reliability are considered more important than control accuracy. Compared to servo and proportional valves, digital valve constituted by on/off valves is inexpensive and reliable, which is more suitable for equipment used in harsh environment such as rolling, forging and engineering machinery. This paper presents a compound control strategy for a digital valve based position tracking system, the idea is to use a cost function based open-loop control strategy as a feed-forward term to improve the accuracy of the position tracking system. It is shown that the presented strategy is feasible for low-frequency position tracking of the cylinder. Besides, simultaneous control of the velocity and downstream pressure is achieved using the compound control strategy. The tracking error is within 2mm when the frequency of the reference signal is 0.1 Hz, which is tolerable in low precision engineering applications.