Fault feature extraction of planetary gearboxes under nonstationary conditions based on reassigned wavelet scalogram

Planetary gearboxes often run under time-variant conditions, thus resulting in nonstationary signals. How to extract fault features from nonstationary vibration signals is a key issue of planetary gearbox fault diagnosis. Considering the merits of reassigned wavelet scalogram, i.e. fine time-frequency resolution and free from cross term interferences, it is used to analyze the vibration signals in joint time-frequency domain. The effectiveness of reassigned wavelet scalogram in planetary gearbox fault diagnosis under nonstationary conditions is validated by both lab experimental and in-situ signals. For the lab experimental signals, the gear characteristic frequencies and their time evolving features are identified. From the comparison between normal and faulty signal analysis results, the sun gear fault is diagnosed. For the in-situ signals, their time-frequency structures are also resolved. According to the presence of periodical impulses and their repeating period, the planet gear fault is detected.