*Article* **A New Universal Domain Adaptive Method for Diagnosing Unknown Bearing Faults**

**Zhenhao Yan 1, Guifang Liu 1,\*, Jinrui Wang 1, Huaiqian Bao 1, Zongzhen Zhang 1,2, Xiao Zhang <sup>1</sup> and Baokun Han <sup>1</sup>**


**Abstract:** The domain adaptation problem in transfer learning has received extensive attention in recent years. The existing transfer model for solving domain alignment always assumes that the label space is completely shared between domains. However, this assumption is untrue in the actual industry and limits the application scope of the transfer model. Therefore, a universal domain method is proposed, which not only effectively reduces the problem of network failure caused by unknown fault types in the target domain but also breaks the premise of sharing the label space. The proposed framework takes into account the discrepancy of the fault features shown by different fault types and forms the feature center for fault diagnosis by extracting the features of samples of each fault type. Three optimization functions are added to solve the negative transfer problem when the model solves samples of unknown fault types. This study verifies the performance advantages of the framework for variable speed through experiments of multiple datasets. It can be seen from the experimental results that the proposed method has better fault diagnosis performance than related transfer methods for solving unknown mechanical faults.

**Keywords:** fault diagnosis; rotating machinery; transfer learning; domain adaptation
