Transient Feature Extraction of Encoder Signal Based on Envelope Demodulation for Fault Diagnosis of RV Reducer
Dongxiao Wang, Xiaoqin Liu, Xing Wu, Tao Liu, Kai Xu, Jianlong Li
Abstract
Rotation vector (RV) reducers have been widely used as an important part of robot joints, and the health monitoring of RV reducers needs to be studied urgently. Traditional vibration analysis faces challenges due to the vibration spectral complexity introduced by time-varying transmission path and interferences of other components in reducers. The rotary encoder contains rich diagnostic information, which provides a new way for fault diagnosis of rotating machinery. This paper presents a feasible strategy for health assessment of RV reducers using encoder signal. In this algorithm, the angle sequence is firstly converted into instantaneous angular speed (IAS) by central difference method (CDM). Then, considering the amplitude modulation characteristics of the fault impact, a scheme for extracting shock transients based on envelope demodulation is determined, and a fault crest proportion index defined on the envelope power spectrum (Epfc) is designed. The optimal filtering band of IAS is determined through the proposed index and band-pass filtering is performed by utilizing Morlet wavelet. Furthermore, band-pass filtering is further implemented on the envelope of the filtered IAS to reduce noise. Finally, transient impulses are extracted by synchronous averaging (SA) to remove the interferences of random shocks. In this step, cross-correlation is employed to correct the phase deviation of the IAS signal and improve the effect of SA. The effectiveness of the proposed method is verified by the fault experiment of RV reducer.