Construction of adaptive redundant multiwavelet packet and its application to compound faults detection of rotating machinery

It is significant to detect the fault type and assess the fault level as early as possible for avoiding catastrophic accidents. Due to diversity and complexity, the compound faults detection of rotating machinery under non-stationary operation turns to be a challenging task. Multiwavelet with two or more base functions may match two or more features of compound faults, which may supply a possible solution to compound faults detection. However, the fixed basis functions of multiwavelet transform, which are not related with the vibration signal, may reduce the accuracy of compound faults detection. Moreover, the decomposition results of multiwavelet transform not being own time-invariant is harmful to extract the features of periodical impulses. Furthermore, multiwavelet transform only focuses on the multi-resolution analysis in the low frequency band, and may leave out the useful features of compound faults. To overcome these shortcomings, a novel method called adaptive redundant multiwavelet packet (ARMP) is proposed based on the two-scale similarity transforms. Besides, the relative energy ratio at the characteristic frequency of the concerned component is computed to select the sensitive frequency bands of multiwavelet packet coefficients. The proposed method was used to analyze the compound faults of rolling element bearing. The results showed that the proposed method could enhance the ability of compound faults detection of rotating machinery.