Dynamic modeling and analysis for the identification of gear localized faults in planetary gearboxes under eccentricity effects

Planetary gearboxes are widely used in heavy industries such as wind power, transportation, and manufacturing, and their reliability is critical for ensuring the stable operation of mechanical systems. Fault detection and diagnosis in planetary gearboxes are important for ensuring system safety. In gear transmission systems, the features of localized faults typically manifest as sidebands around the meshing frequency in the spectrum or as gear rotation frequency in the envelope spectrum. However, factors such as gear eccentricity and shaft runout can also produce localized gear fault-like spectral features. This makes it difficult to detect localized faults based on characteristic spectral line analysis and sideband energy ratio, especially in complex systems like planetary gearboxes. Recently, the instantaneous angular speed (IAS) signal has emerged as a promising alternative, offering advantages such as eliminating the need for order tracking and being unaffected by time-varying signal transmission paths in planetary gear sets. In this work, we develop a modified planetary gearbox dynamic model and investigate the effects of gear fault and eccentricity on mesh stiffness. Utilizing the developed model, IAS signals are generated, and their waveforms and order spectra analyzed. Additionally, we propose an abnormal-preserving spectral component reconstruction method to extract and enhance abnormal components within the signal. The results indicate that localized gear fault and eccentricity exhibit the same periodicity, both generating fault-related sidebands around meshing orders in the order spectrum, and fault characteristic components in the envelope spectrum. However, after abnormal component reconstruction, gear faults exhibit distinct periodic jitters, accompanied by a significant increase in kurtosis. In contrast, the kurtosis of the reconstructed signal in the case of gear eccentricity does not show a noticeable increase. This distinction allows the accurate identification of gear localized fault in gear systems. The findings are validated experimentally on a planetary gearbox test rig.