Combined fault frequency demodulation analysis for a planetary gearbox based on VMD

Combined fault vibration signals of a planetary gearbox with features of multi-source modulation and complex sideband structure in frequency domain. It is difficult to effectively extract gear fault features with conventional Fourier spectral analysis. However, the frequency modulation part of combined fault vibration signals contains fault information and is independent on the vibration transfer path. Here, a frequency demodulation analysis method based on the variational mode decomposition was proposed to extract combined fault features of a planetary gearbox. Firstly, the single-component number was determined according to sampling frequency and carrier one. Then, a multi-component signal was adaptively decomposed into a series of intrinsic mode functions with the variational mode decomposition. Instantaneous frequency of each intrinsic mode function was calculated, and sensitive single-component was selected according to the matching relation between central frequency and meshing one. Finally, instantaneous frequency spectrum of each sensitive single-component was analyzed to diagnose combined faults. The effectiveness of the proposed method was verified through analyzing simulated vibration signals and test ones, and combined faults of sun gear-planet one, sun gear-gear ring and planet gear-gear ring were diagnosed. © 2020, Editorial Office of Journal of Vibration and Shock. All right reserved.