Recursive Spectral Analysis-based Diagnostic with Application to Electrohydraulic Actuators

This paper presents the diagnostic of electrohydraulic actuators. Different types of faults common in practice are considered such as a pump fault, abnormal viscous friction, oil contamination, and internal or external oil leakage. The entire diagnostic consists of two components: 1) reference tracking control; 2) recursive harmonic analysis. Firstly, the robust repetitive control is used such that the actuator position follows the harmonic reference signal. Secondly, the Fourier transforms of the control input at multiple harmonics are calculated recursively from sliding discrete Fourier transform. Instead of the raw control input, the modulated input signal is employed for better efficiency and robustness. The diagnostic decision is made based on distribution of the Fourier transforms. The effectiveness of the proposed method is demonstrated with numerical simulations. Diagnostic performance with different sizes of the sliding window is analyzed in terms of separation metrics, as a critical design parameter.