Planetary gear fault diagnosis based on instantaneous angular speed analysis

Planetary Gears (PG) are widely used in many important transmission systems such as helicopters and wind turbines due to its advantages of high power-weight ratio, self-centering and high transmission ratio. Vibration based condition monitoring of PG has received extensive researches for ensuring safe operations of these critical systems. However, due to the moving mesh gears and noise influences, the diagnostics of planet gear faults by conventional vibration measurements needs intensive signal processing but provides less satisfactory performance. This study investigates Instantaneous Angular Speed (IAS) based diagnostics which associates more directly with gear dynamics and is not influenced by the moving mesh gears. A pure torsional dynamic model of a PG is developed to gain the characteristics of IAS under different fault cases. Then experiments are performed to evaluate this IAS based diagnostics. Particularly, IAS signatures obtained by demodulating the frequency modulated pulse trains produced by two in-house made encoder wheels mounted at both the input and output of the PG. In addition, order spectrum analysis is applied to IAS signals to highlight fault components. IAS order spectra exhibit clear changes in the spectral amplitudes associating with different fault frequencies, showing consistent and efficient diagnostics. Besides, both the measurement system and signal processing computation for IAS based monitoring are more cost-effective and easier to be implemented online, compared with conventional vibration based methods.