A Wavelet-Based Approach for External Leakage Detection and Isolation From Internal Leakage in Valve-Controlled Hydraulic Actuators

In this paper, the application of wavelet transform to detect external leakage fault in hydraulic actuators is described. This paper also examines the isolation of this fault from actuator internal leakage in a multiple-fault environment. The pressure signal at either chamber of a laboratory-based hydraulic actuator, in response to a periodic step input, is decomposed into discrete wavelet coefficients. An index is calculated based on the root mean square (rms) value of level-four approximate coefficient of the pressure signal. This index is shown to be sensitive to external leakage. Furthermore, in our previous work, an index was calculated based on the rms value of the level-two detail coefficient for internal leakage fault detection. In this paper, we further show that these indices are independently sensitive to external and internal leakages. Thus, by inspecting them simultaneously, one cannot only identify external and internal leakages but also isolate them even when they occur together. Experimental tests show promising results for detecting and isolating low amount of external and internal leakages without a need to model the actuator or leakage types.