Fault detection in a multistage gearbox by time synchronous averaging of the instantaneous angular speed

The paper deals with an instantaneous angular speed (IAS) based algorithm for fault detection in a multistage gearbox. Fast Fourier transform (FFT) is a well established technique for analysis of a stationary signal. However, the IAS signal from the multistage gearbox is a combination of periodic signal and structure borne noise. This structure borne noise makes the IAS signal non stationary. Hence, FFT is no longer suitable for this non stationary signal analysis. Therefore in this paper, the IAS signal is time synchronously averaged with respect to lay shaft speed and then followed by FFT reveals the gear mesh frequency and rotational frequencies which are synchronous with the gearbox's rotating speed. Thus, the algorithm can accurately and reliably detect the fault in multistage gearbox using the IAS. The paper also investigated the behavior of IAS signal for three different gearboxes (healthy, one tooth and two teeth broken) under two different speeds and three different loading conditions.