Abstract: Aimed at the problems of the frequency aliasing, frequency band overlap and derangement in wavelet packet, the reason to cause the problems is researched and an improved decomposition algorithm of redundant wavelet packet is proposed. The problem of frequency band derangement is overcome by exchanging the order of sub-nodes originated from father nodes which are sequenced in even serial numbers, and the problem of frequency band overlap is avoided by introducing two operators which can eliminate respectively the frequencies outside the pass bands of low frequency and high frequency sub-band. The simulated fault signals and endurance test datasets of a helicopter intermediate gearbox are respectively collected to certificate the improved decomposition algorithm. The simulation and analysis of the gearbox fault dataset shows that, compared with the Mallat wavelet packet algorithm and traditional redundant wavelet packet algorithm, the improved redundant wavelet packet can more expediently and effectively detects the fault feature submerged the strong interference context, owing to the elimination of frequency aliasing, frequency band overlap and derangement. So, it has much application value in fault diagnosis.

Key words: band overlap;envelope demodulation, mallat wavelet packet algorithm;redundant wavelet packet algorithm;frequency band derangement;frequency, GTAW Welder experience Measuring weld pool Laser Vision