Robust output feedback control for electro-hydraulic servo system with error constraint based on high-order sliding mode observer

In this paper, a robust output feedback controller with error constraint is proposed to improve the position tracking performance of the electro-hydraulic servo system. Since only the position signal of the system is available, a high-order sliding mode observer is designed to estimate the unobtainable system states. The new state observer can not only avoid the influence of sensor measurement noise but also reduce the chattering of traditional sliding mode observer. To cope with the modeling error, parameter uncertainty, and external disturbance, a robust controller based on backstepping method is designed. In addition, barrier Lyapunov function is introduced to limit the maximum tracking error to a preset range. Finally, comparative experiments are carried out on the asymmetric hydraulic cylinder test bench. The experimental result shows that the proposed controller has a satisfied tracking performance.