Enhanced spectral coherence and its application to bearing fault diagnosis

Spectral coherence (SCoh) is one of the most dedicated methods for characterizing the second-order cyclostationarity of bearing faults. Under the assumption of second-order cyclostationarity, the SCoh of the bearing vibration signal is expected to have non-zero values along lines–determined by fault-related cyclic frequencies. However, the bearing vibration signal produced by a complex mechanical system always exhibits mixed cyclostationarity–a combination of several orders of cyclostationarity, rather than pure second-order cyclostationarity. The fault-unrelated cyclic frequencies exhibiting a series of non-zero elements on the bivariate plane are served as a tricky problem to interfere with the fault identification. To address this issue, an enhanced SCoh is proposed by combining two basic operators designed by using median filtering and autocorrelation, respectively. Analysis of simulated signals, vibration datasets obtained from artificial fault bearing experiments, and accelerated bearing degradation tests are conducted to verify and compare the performance of the improved SCoh.