Adaptive diagnosis for electro-hydraulic servo actuator faults based on adaptive nonsingular terminal sliding mode observers

Aiming at the problem of multiple faults in the electro-hydraulic servo actuator system (EHSA), this paper proposes a novel fault diagnosis method based on a nonsingular terminal sliding mode observer (NTSMO). Three typical faults, namely servo valve stuck, hydraulic cylinder leakage, and open circuit, are modeled and injected into the EHSA based on their fault mechanisms and corresponding mathematical descriptions. The main focus of the study lies in the design of a group of NTSMOs specifically developed for fault diagnosis, supported by a more accurate AMESim model to enhance simulation reliability. Fault decision-making is further achieved through a dedicated observer strategy (DOS) combined with an adaptive threshold mechanism. Theoretical analysis verifies the stability and accuracy of the proposed observer as well as the rationality of the adaptive threshold design. Co-simulation results using AMESim/MATLAB demonstrate that the proposed method exhibits strong applicability and high diagnostic accuracy for the three typical types of faults.