Research on Fault-Tolerant Control of High-Speed on/off Valves Based on Unknown Sensor Input Observers

As the core component of digital hydraulic systems, the precise control of high-speed <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on/off</small> valves (HSVs) largely depends on current sensor monitoring and feedback. However, sensors may fail due to aging, interference, and other factors, leading to degraded system performance. This article proposes a fault-tolerant control (FTC) method for HSV current sensors based on an unknown input sliding mode observer. First, a first-order low-pass filter is introduced to equivalently transform sensor faults into actuator faults, and coordinate transformation is employed to decouple faults and disturbances. Subsequently, an unknown input sliding mode state observer is designed to simultaneously achieve system state observation and fault disturbance reconstruction. Finally, a fault-tolerant controller is designed based on the reconstructed values. Simulation and experimental results demonstrate that the proposed method achieves precise control of HSVs in the presence of both sensor faults and external disturbances. Compared with traditional methods, the proposed approach effectively suppresses high-frequency chattering phenomena, conserves computational resources, and reduces position tracking error by 72.73% in hydraulic cylinder control applications. This research provides a new technical pathway for high-precision control of digital hydraulic systems.