Rolling Element Bearing Fault Diagnosis Using Laplace-Wavelet Envelope Power Spectrum
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Research Article Rolling Element Bearing Fault Diagnosis Using Laplace-Wavelet Envelope Power Spectrum Khalid F. Al-Raheem,1 Asok Roy,2 K. P. Ramachandran,1 D. K. Harrison,2 and Steven Grainger2 1 Department 2 School
of Mechanical and Industrial Engineering, Caledonian College of Engineering, P.O. Box 2322, CPO Seeb, PC 111, Oman of Engineering Science and Design, Glasgow Caledonian University, Glasgow G40BA, UK
Received 1 July 2006; Revised 19 December 2006; Accepted 1 April 2007 Recommended by Alex Kot The bearing characteristic frequencies (BCF) contain very little energy, and are usually overwhelmed by noise and higher levels of macro-structural vibrations. They are difficult to find in their frequency spectra when using the common technique of fast fourier transforms (FFT). Therefore, Envelope Detection (ED) has always been used with FFT to identify faults occurring at the BCF. However, the computation of the ED is suffering to strictly define the resonance frequency band. In this paper, an alternative approach based on the Laplace-wavelet enveloped power spectrum is proposed. The Laplace-Wavelet shape parameters are optimized based on Kurtosis maximization criteria. The results for simulated as well as real bearing vibration signal show the effectiveness of the proposed method to extract the bearing fault characteristic frequencies from the resonant frequency band. Copyright © 2007 Khalid F. Al-Raheem et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
The predictive maintenance philosophy of using vibration information to lower operating costs and increase machinery availability is gaining acceptance throughout industry. Since most of the machinery in a predictive maintenance program contains rolling element bearings, it is imperative to establish a suitable condition monitoring procedure to prevent malfunction and breakage during operation. The hertzian contact stresses between the rolling elements and the races are one of the basic mechanisms that initiate a localized defect. When a rolling element strikes a localized defect, an impulse occurs which excites the resonance of the structure. Therefore, the vibration signature of the damaged bearing consists of exponentially decaying sinusoid having the structure resonance frequency. The duration of the impulse is extremely short compared with the interval between impulses, and so its energy is distributed at a very low level over a wide range of frequency and hence, can be easily masked by noise and low-frequency effects. The periodicity and amplitude of the impulses are governed by the bearing operating speed, location of the defect, geometry of the bearing, and the type of the bearing load. The theoretical estimations of these frequencies are denoted as bearing characteristics frequencies (BCF); see the appendix.
The rolling elements experience some slippage as the rolling
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