Amplitude and phase wavelet maps for the detection of cracks in geared systems

The newly developed wavelet transform enables one to look at the evolution in time of a signal's frequency content. This property makes it very suitable for the detection of vibration transients generated by developing localised faults in gear trains. Recent applications of the wavelet technique have focused on the use of the amplitude map only. In this study, both the amplitude and phase maps of the wavelet transform are used in conjunction to assess the condition of an instrumented gear test rig. The phase wavelet map is found to display distinctive features in the presence of a cracked tooth. Another key finding is that the amplitude wavelet map of the residual vibration signal offers a better indicator to the presence of faults than the map of the actual signal. A new polar representation is also introduced that makes pinpointing the precise location of a crack an easy task. The cases studied include a healthy gear, one with a simulated fatigue crack, and one with a simulated chipped tooth. (C) 1999 Academic Press.