An Improved Lempel–Ziv Complexity for Bearing Fault Diagnosis Based on the Time–Frequency Encoding Method

Lempel-Ziv complexity (LZC) is extensively utilized in the identification of bearing faults. The present enhancement in LZC encoding relies on time-domain information. When the magnitude of fluctuation is minimal, LZC utilizing time-domain information encoding is unable to properly differentiate signals with varying frequency components. Thus, an improved LZC based on the time-frequency encoding method is proposed. Initially, the time-domain encoding is obtained according to the quartile of the amplitude. Then, the frequency-domain encoding is calculated based on the statistic value at each frequency along the frequency direction of the Wigner Trispectrum. Finally, the ultimate encoding is derived from both time-domain encoding and frequency-domain encoding. The proposed method is validated through the actual data of bearing. The time-frequency encoding technique can significantly augment the capacity of encoding sequences to depict signal variations and boost the LZC representation of signal complexity.