Influence des fluctuations de vitesse sur le cepstre

International audienceVibratory analysis is a very popular tool to perform diagnostic of rotating machinery due to its non-intrusive nature. Nevertheless, the effect of rotation speed on the vibration became significant when the speed is non-stationary. In this case, instantaneous speed could be measured by using a tachometer signal and use to take account the speed for diagnostic. The rotating machine instantaneous speed provided by the tacho is also a very useful information. It could be sensitive to mechanical faults [1] and be used for diagnostic. It is also requested for computed order tracking [2].Since, a tachometer speed signal is not always available, instantaneous speed have to be estimated from other signal like the accelerometric signal. Some instantaneous speed extraction methods are described in the MSSP Special Issue on Instantaneous Angular Speed (IAS) Processing and Angular Applications of [3]. These methods use analytic signal, parametric approach, ...Another approach based on cepstrum was proposed in the Surveillance 8 Contest. A cepstrum (echo detector) [4, 5] is used to estimate the instantaneous speed. This method is derived from an cepstral order tracking method presented (only in French) in [6]. Unfortunately, the cepstrum is known to be sensitive to speed fluctuation.In this paper it is proposed to study the influence of speed fluctuation on the cepstrum. A first part, recall the classic cepstrum properties and study the influence of speed fluctuation. In a second part, a time quefrency-representation is introduced and speed fluctuation influence is discussed by using some samples signals