Optimal demodulation subband selection for sun gear crack fault diagnosis in planetary gearbox

Envelope analysis (EA) is one of the most usually used demodulation methods for fault diagnosis of gearboxes, the main problem for EA is to find a frequency subband that contains more fault-related components. However, modulation phenomenon can be observed for both healthy and damaged situations in planetary gearboxes. And most of the traditional EA techniques cannot distinguish the fault-related modulation components from fault-unrelated modulation components, which may leads to a degradation of the fault diagnosis method for planetary gearbox. In order to overcome the problem of finding the subband that contains the most fault-related modulation components, this paper proposed a new optimal demodulation subband selection method (ODSSM) for fault diagnosis of planetary gearbox. With the proposed method, the fault-related degree of each subband is evaluated based on a new index that measuring the ratio of fault-related modulation components to fault-unrelated modulation components in envelope spectrum. The index then is employed to find the optimal demodulation subband in the entire frequency range based on genetic algorithm (GA). Finally, fault diagnosis results can be obtained based on EA method. For validation, the proposed method and other two methods are utilized to detect the sun gear crack fault in planetary gearbox. The results show that the proposed method can detect the gear fault in both simulation signals and experiment signals, and achieves improved demodulation performance than the other two methods.