A method for Variable-Speed bearing fault diagnosis is proposed. The new method is based on the analysis of shocking spikes from defect positions. The shocking spikes are detected form vibration signal by an amplitude threshold. The bearing system generates impacts at a constant angle interval. If the shaft speed is variable, the inter-impact time intervals will change accordingly. By measuring the inter-impact intervals, we can get the instant frequency of impacts, which is a dimensionless tendency of shaft speed. If certain statistical information about shaft speed (for example, average speed) is given, by comparing the same kind of information between impact instant frequency and shaft speed, the fault type can be identified. The method was testified by experimental data.
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