Envelope Cepstrum Based Method for Rolling Bearing Diagnostics

The task of identifying a faulty roller element bearing has been so far faced through the use of envelope analysis. As it is well known the main issue linked to such approach is related to the definition of the optimal band-pass filter which can enhance the defect characteristics when the vibration signal is affected by severe noise. The Kurtogram has overcome this limit by letting the optimal band-pass filter be selected in a semi-automatic way, that is by exploiting the potentials of the Spectral Kurtosis. This paper aims at presenting an alternative algorithm which is able to cope with faults characterised by an impulsive-periodic nature. It is well known that faults characterised by periodic-impulsive nature are identifiable by means of cepstral analysis while damages inducing modulation effects are usually assessed via envelope processing. The presented algorithm combine two instruments, since it is based on the Fourier spectrum of the cepstrum squared envelope. Such spectrum allows to isolate the modulation effect by centring the modulating frequency around the DC component. In this paper the algorithm is applied to both synthesized data reproducing typical damaged rolling bearing signals and experimental data. Results achieved by exploiting the proposed algorithm are compared to the ones obtained by applying conventional envelope analysis based on Spectral Kurtosis.