This paper describes development and experimental evaluation of a hydraulic actuator leakage fault detector based on the extended Kalman filtering (EKF). Identification of external leakage at either side of the actuator as well as the internal leakage between the two chambers is examined. The present work is built upon previous work by the authors, but incorporates a significant improvement in that the new scheme is capable of detecting leakage faults for actuators that are also subject to unknown loading and/or significant friction. Experiments on a laboratory-based hydraulic actuator, using both structured (sinusoidal) and unstructured (pseudorandom) test signals show that: (i) under normal (no-fault) operating condition, the EKF-based state estimator closely predicts the states of the system and the external load, including actuator friction, using only a few measurements, (ii) in the presence of leakage faults, the level of residual errors between the estimated and the measured line pressures increase indicating the occurrence of faults and (iii), different leakage fault types and levels can be identified by tracking the pattern of the residual errors and without a need to model leakage faults. The present work lays a foundation for developing on-line leakage monitoring systems for hydraulic actuators.

Keywords: fault detection and isolation, extended kalman filtering, leakage, hydraulic actuators, friction, environmental interaction.