Planetary gear vibration monitoring using synchronous demodulation

Condition monitoring of planetary gearboxes is crucial for their safe operation in critical applications such as helicopters. For this purpose the Defense Science and Technology Group (DSTG) of the Department of Defense of the Australian Government released in the frames of a scientific competition a vibration dataset on the issue of planetary gear rim cracking in planetary gearboxes. This work proposes a signal processing based indicator based on the synchronous demodulation of the gear mesh frequency. The synchronous demodulation is proposed for this purpose due to it demodulating only a single specified frequency. The final indicator is shown to have a clear trend with respect to the fault and allows for early detection of the fault. The proposed indicator outperforms a baseline based on Hilbert transform based demodulation of the full signal, showing the importance of demodulating specific gear mesh frequencies for gear crack monitoring. Additionally, the temperature effects are also considered, showing the importance of taking into account the gearbox oil temperature when using vibration based condition monitoring.