Fault detection and location in gears by the smoothed instantaneous power spectrum distribution

Time–frequency methods are effective tools for analysing diagnostics signals and have been widely used to describe machine condition. This paper introduces a time–frequency distribution, called the smoothed instantaneous power spectrum (SIPS) distribution, and demonstrates its use in the detection and location of local tooth defects in gears. The SIPS distribution is derived from the frequency domain definition of the instantaneous power spectrum (IPS) distribution, but has the added advantage that provides a considerable reduction in the ringing effect of the IPS transform, which results in a smoother and clearer time–frequency representation. A simulated gear vibration signal is used to show the capabilities of the proposed method over the IPS distribution and spectrogram. Healthy and faulty vibration signals monitored from a gear test rig are analysed, the results of which show that a local gear tooth defect can clearly be detected by the SIPS distribution.     

Determination of the cutoff frequency of an acoustic circumferential wave using a time–frequency analysis

In this article, time–frequency representation of Wigner–Ville is used to analyse the acoustic signal backscattered by a thin elastic tube of radii ratio b/a. This analysis allows to determine the reduced cutoff frequency of the circumferential antisymmetric wave A1 propagating around the tube. The evolution of this reduced cutoff frequency in function of b/a is reported. The values obtained of reduced cutoff frequency are compared to the values computed from the proper modes method.