Detection of Fatigue Cracks in Gears with the Continuous Wavelet Transform


Under ideal operating conditions, gearboxes generate vibration signals with frequency components that are pure harmonics of the gear meshing frequency. Developing tooth fatigue cracks introduce short-time amplitude and phase modulations of the gear meshing vibration signal. Traditional techniques for gear fault detection have focused on either the time domain or the frequency domain. The newly developed wavelet transform enables one to look at the evolution in time of a signal's frequency content. This property is very well suited for the analysis of localized transients that are generated by the operation of faulty gears. In this study, magnitude wavelet maps of the vibration signal are calculated and used to assess the condition of an instrumented gear test rig. A key finding is that the wavelet map of the residual vibration signal offers a better indicator to the presence of cracks than the map of the actual signal. The results obtained are also compared against those of the well-accepted phase demodulation approach.
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