Early detection of gear tooth cracking using the resonance demodulation technique

The resonance demodulation technique has been extensively used for rolling bearing diagnostics. This paper presents a scheme of using the resonance demodulation technique for early detection of gear tooth cracks. The objective is to supplement the current techniques of gearbox fault diagnosis based on the synchronous signal averaging technique. The proposed scheme focuses on the fact that gear tooth crack will produce vibration impacts that would excite the structural resonances when the cracked tooth is engaged. Using this scheme, the regular gear meshing harmonics are first removed from the synchronous signal average to generate the residual signal. The residual signal is then band-pass filtered around a structural resonance within the range of gear meshing harmonics. The bandpassed residual signal is demodulated to extract the features related to the crack-induced sudden change in a complete revolution of the gear of interest. A number of statistical measures can then be used on the demodulated signal as an indicator on the existence and status of the crack. In this paper. an analytic signal model is also proposed to describe the gear meshing signal and its processing, the resonance demodulation technique is presented based on the signal model. The method is validated using numerically simulated data, test data from a gear rig, and helicopter in-flight vibration data. The results show that the resonance demodulation technique is an effective tool for the early detection of gear tooth cracks. (C) 2001 Academic Press.