A velocity synchrosqueezing transform for fault diagnosis of planetary gearboxes under nonstationary conditions

Time-frequency analysis is widely used in the field of machinery condition monitoring and fault diagnosis under nonstationary conditions. Among the time-frequency methods synchrosqueezing transform outperforms others in providing fine-resolution time-frequency representation. However, it suffers from time-frequency smear when analysing nonstationary signals. To address this issue, this paper proposes a new synchrosqueezing-transform-based method which works by (1) mapping the raw nonstationary vibration signal into a corresponding stationary angle domain signal to meet the stationarity requirement of the synchrosqueezing transform, (2) performing the synchrosqueezing transform of the corresponding signal and (3) restoring the time-frequency representation of the raw signal from the synchrosqueezing transform result of the corresponding signal. As the synchrosqueezing transform is applied to the stationary corresponding signal, the time-frequency smear is eliminated in the synchrosqueezing transform result of the corresponding signal and the final signal time-frequency representation. As such the proposed method can generate a smear-free time-frequency representation with fine time-frequency resolution and thus provide more reliable diagnosis decisions. A fast implementation algorithm is also developed to simplify the implementation of the proposed method. The effectiveness of the proposed method is validated using both simulated and experimental vibration signals of planetary gearboxes.