Application of Fast Fourier and Wavelet Transforms Towards Actuator Leakage Diagnosis: A Comparative Study

Applications of fast Fourier and wavelet transforms to detect internal leakage in hydraulic actuators are experimentally compared. By analyzing the dynamics of the actuator, it is shown that the internal leakage increases the damping characteristic of the system and decreases the Bode magnitude of pressure signal over valve displacement, around the hydraulic natural frequency. This is further confirmed, by decomposing the original pressure signal, using either transform methods, and identifying the frequency component sensitive to internal leakage. The root mean square of the processed pressure signal is used and a comparison of the two transforms is made to assess their ability to detect internal leakage fault using only pressure signal obtained from either open-loop or closed-loop systems. The results indicate that both approaches can detect internal leakage without a need to explicitly include the model of the actuator and/or the leakage. It is further shown that the wavelet transform method is found to be more sensitive to the internal leakage than the approach based on fast Fourier transform.