Application of cepstrum pre-whitening for the diagnosis of bearing faults under variable speed conditions P. Borghesani a,n , P. Pennacchi a , R.B. Randall b , N. Sawalhi b,1 , R. Ricci a a Politecnico di Milano, Dipartimento di Meccanica, via la Masa 1, 20156 Milano, Italy b University of New South Wales, School of Mechanical & Manufacturing Engineering, Sydney, NSW2052, Australia article info Article history: Received 18 January 2012 Received in revised form 4 September 2012 Accepted 8 November 2012 Available online 4 December 2012 Keywords: Cepstrum Whitening Bearing diagnostics Deterministic/random separation abstract Diagnostics of rolling element bearings involves a combination of different techniques of signal enhancing and analysis. The most common procedure presents a first step of order tracking and synchronous averaging, able to remove the undesired components, synchronous with the shaft harmonics, from the signal, and a final step of envelope analysis to obtain the squared envelope spectrum. This indicator has been studied thoroughly, and statistically based criteria have been obtained, in order to identify damaged bearings. The statistical thresholds are valid only if all the deterministic components in the signal have been removed. Unfortunately, in various industrial applications, characterized by heterogeneous vibration sources, the first step of synchro- nous averaging is not sufficient to eliminate completely the deterministic components and an additional step of pre-whitening is needed before the envelope analysis. Different techniques have been proposed in the past with this aim: The most widely spread are linear prediction filters and spectral kurtosis. Recently, a new technique for pre- whitening has been proposed, based on cepstral analysis: the so-called cepstrum pre- whitening. Owing to its low computational requirements and its simplicity, it seems a good candidate to perform the intermediate pre-whitening step in an automatic damage recognition algorithm. In this paper, the effectiveness of the new technique will be tested on the data measured on a full-scale industrial bearing test-rig, able to reproduce the harsh conditions of operation. A benchmark comparison with the traditional pre- whitening techniques will be made, as a final step for the verification of the potentiality of the cepstrum pre-whitening. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction The application of condition-based maintenance on the industrial scale, as for instance in complex process plants or rail fleets, is generating a need for highly automated algorithms for the assessment of the health state of the machine components, in particular bearings. This is usually performed on the basis of vibration signals collected by accelerometers installed on the surface of the machine casings. Among the numerous techniques developed since the 1980s for the analysis of those signals, cyclostationary tools have proved to be very effective. McCormick and Nandi [1] were the first to address bearing diagnostics with a cyclostationary approach, understanding the second-order cyclostationary nature of Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ymssp Mechanical Systems and Signal Processing 0888-3270/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ymssp.2012.11.001 n Corresponding author. Tel.: þ39 2 2399 8486. E-mail address: pietro.borghesani@mail.polimi.it (P. Borghesani). 1 Now at: Mechanical Engineering Department, Prince Mohammad Bin Fahd University (PMU), P.O. Box 1664, AlKhobar 31952, Saudi Arabia. Mechanical Systems and Signal Processing 36 (2013) 370–384