Technical Note: Gearbox Health Monitoring through Multiresolution Fourier Transform of Vibration and Current Signals

The multistage helical transmission gearbox in the present study is driven by an induction motor and is coupled to a DC generator, which is connected to an electrical resistance bank for loading purposes. One and two teeth are artificially removed in one gear of the gearbox to simulate actual fault condition. When the gearbox is operated under several loads, the vibration signals are acquired from the tail-end bearing of the gearbox, and simultaneously the current drawn by the induction motor is acquired and monitored. For signal analysis, discrete wavelet transform is applied to the current and vibration signal. Subsequently, short-time Fourier transform (STFT) was applied to the level that contains information of the gear mesh frequencies and their sidebands of rotating shaft frequencies. This is a corrected multiresolution Fourier transform (MFT), which helps in further characterization of the signals. It is inferred that MFT coefficients of vibration and current signals can predict a consistent trend in the energy level possessed by the gear mesh frequencies with an increase in the severity of defects, and hence can be a useful tool in gearbox health monitoring.