A generalized instantaneous-frequency-estimation-free stepwise demodulation transform and its application in vibration signal analysis of rotating machinery

Existing generalized demodulation (GD) based methods have inherent shortcomings for the vibration signal processing of rotating machinery. A generalized instantaneous frequency (IF) synchronized stepwise demodulation transform was proposed to address such shortcomings in this work. Firstly, the frequency of the truncated signal in a short time window can be treated as a straight line with an inclination angle. The angle determination strategy was proposed, where the appropriate angle can be selected by the guidance of the kurtosis index. Then, the novel forward and backward demodulators used in generalized demodulation can be used to demodulate the truncated signal. Through sliding the window, the time-frequency representation of the analyzed signal can be obtained with the boosted readability and independence of the instantaneous frequency pre-extraction. To effectively tackle multicomponent signals, the original linear transforming kernel was improved to enable the proposed method to simultaneously enhance the multiple frequency components without iterations. The signal reconstruction of the proposed transform was theoretically derived and the results show that the proposed method allows for the reconstruction of the interested frequency components. The simulation and experimental vibration signal analyses verify the effectiveness of the proposed method in enhancing the time-frequency representation and increasing the accuracy of the feature extraction. The comparison with other time-frequency analysis methods further indicates the advantages of the proposed method. © 2021, Editorial Office of Journal of Vibration and Shock. All right reserved.