Internal Leakage Diagnosis in Hydraulic Actuators Using Wavelet Transforms

This paper describes experimental evaluation of applying wavelet transform to detect internal leakage in hydraulic actuators due to seal damage. The method analyses pressure signal at one side of the actuator in response to periodic step inputs to the control valve. It is shown that the detailed version of decomposed pressure signal, using discrete wavelet transform, establishes feature patterns that can effectively detect internal leakage and its severity. The method is also capable of detecting changes in the friction property of the actuator, another problem associated with actuator seal damage. Specifically, the root mean square (RMS) of level two detail coefficients, obtained from the measured pressure signal, is used to detect internal leakage. The degree of changes of the RMS value from the one obtained under normal operating condition indicates the severity of leakage fault. Furthermore, it is shown that the RMS of level three detail coefficient values, is sensitive to the changes of the actuator friction. All these observations are made without a need to model the actuator, leakage or friction.