The main bearing is the core mechanical equipment of shield machine, known as the heart of the shield machine, mainly applied to support the rotation of cutterhead system. The health status of main bearing has significant impact on the stable and safe construction for shield machine. However, main bearing has very low rotational speed of only 1 rpm to 5 rpm, and the structure is very complex, with a diameter even exceeding 10 m. The fault features for main bearing vibration signals are relatively weak. Therefore, the main bearing fault diagnosis is a challenging task. To tackle the problem, we develop a novel generalized envelope nonlinear Gini index-gram guided two-stage chirp mode decomposition (GENGI-TSCMD) for fault diagnosis of shield machine main bearing in this article. The proposed method consists of optimized demodulated frequency band (ODFB) selection and fault frequency extraction two key parts. We firstly developed GENGI-gram for ODFB extraction, which adopting stepwise increasing segmentation and signal frequency spectrum trend to divide the signal’s frequency bands, and obtain two grams. A new GENGI fault pulse identifier was constructed to select ODFB in these two grams. GENGI can availably characterize fault pulse features and suppress noise interference by combining generalized envelope and nonlinear weights based on Gini index. For fault frequency extraction, we proposed TSCMD by establishing bandwidth guided adaptive chirp mode decomposition (BACMD) and fault frequency extraction mode decomposition (FEMD). BACMD is adopted to extract sub-signals in each demodulation frequency band of GENGI-gram. FEMD is applied to decompose each order fault frequency sub-signals of ODFB signal’s envelope. In this way, the main bearing’s fault type can be precisely diagnosed. BACMD derives the bandwidth calculation formula for sub-signal, which can extract sub-signals with specific frequency bandwidth. FEMD constructs a novel adaptive signal decomposition model, which can effectively decompose each order fault frequency sub-signal with narrow frequency band. Then we use actual main bearing fault vibration signals to verify the proposed method. The experimental results show that proposed GENGI-TSCMD can availably filter out various types of strong noise disturbance, and precisely extract each order fault frequency component. Moreover, proposed method has superior performance than current signal processing fault diagnosis methods.
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