A study on vibration component separation of a rotor system during startup and its application in fault diagnosis

Rotating machinery usually works under conditions of variable speed. The vibration signals extracted from such equipment contain more fault information than those operating in steady-state conditions, therefore harmonic component extraction on this occasion becomes a hot issue. However, some harmonics still cannot be extracted effectively by traditional signal processing methods, i.e. how to separate the components that are too close to each other in the time-frequency plane, and how to separate the cross-coupled components around a critical speed during rotor startup or shut down. To solve these problems, a new method is developed based on improved variational mode decomposition (VMD) by generalized demodulation technology (GDT) and a zero-phase shift filter (ZPSF) in this paper. After obtaining the instantaneous frequency of the main dominant component, GDT and the ZPSF are used as preprocessing methods to enhance the signal-to-noise ratio (SNR) and to extract separable components, and the wide-band component is improved in the form of a tractable narrowband. Finally, VMD is used to enhance the SNR of the separable components and reduce the coupling effect between the crossed components. Compared with conventional methods, the stimulation signal and the experimental signal analysis obtained from the rotor kit show that this hybrid approach is able to effectively compromise the speed fluctuation and thus extract all the useful vibration components from the rotor system during startup; therefore, it can effectively be applied to fault diagnosis.