Thanagasundram S., Ram Gurung K., Feng Y., Schlindwein F.

In this paper a novel approach is proposed for vibration-based fault detection studies by the tracking of pole movements in the complex z domain. Vibration signals obtained from the ball bearings from a High Vacuum (HV) and Low Vacuum (LV) ends of a dry vacuum pump run in normal and fault conditions are modelled as time variant AR (autoregressive) series. The positions of the poles, which are the roots of the AR coefficient polynomial, vary for every frame of vibration data. It is a known fact that as defects such as spalls and cracks start to appear on the ball bearings, the amplitude of the vibrations of characteristic defect frequencies increase. Faults can be predicted by movement of poles in the complex plane as the pole positions move closer to the unit circle as the severity of the defect increases. The area of the region swept by the migratory poles loci and their distances from the unit circle can be useful fault indicators. From the position of the poles inside the unit circle, classification and quantification of the main spectral peaks of defect frequencies can be performed, leading to the possibility of having frame to frame monitoring of spectral parameters of interest. The pole representation facilitates the understanding of the spectral characteristics of the process because of the one-to-one correspondence between the poles and the AR spectral peaks. This method has interesting potential applications in condition monitoring and diagnostic applications. The description of the movement of the poles was shown to be a particularly elegant way to study the harmonic components of the signal. This analysis has been validated with actual data obtained from the pump and initial results obtained suggest that this technique might be useful for fault prediction.