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| Frequency Demodulation Based on Delayed Autocorrelation and Its Application to Gear Fault Diagnosis |
| He Wei Jiang Zhinong |
| ((Diagnosis ＆Self-Recovery Engineering Research Center，Beijing University of Chemical Engineering, Beijing 100029 China) |
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Abstract When a gear has a local fault, the vibration signal of the gearbox usually is amplitude-modulated (AM) and frequency-modulated (FM). The demodulation analysis has been extensively used for gear diagnosis. However, traditional demodulation methods are mainly applicable to amplitude demodulation, while frequency modulation is usually ignored. Although Hilbert transform can be used for frequency demodulation, it is liable to be affected by noise which often taints the gear vibration signal seriously. Due to the excellent anti-noise property of the delayed autocorrelation function, the delayed autocorrelation demodulation method has been applied to amplitude demodulation in low SNR by some researchers, but is rarely used for frequency demodulation. By derivation, it is found that the autocorrelation function of the FM signal is amplitude-modulated and that of the AM-FM signal is amplitude-modulated and frequency-modulated. Moreover, the modulation frequencies of both are unchanged. Therefore, the delayed autocorrelation demodulation method is applicable not only to amplitude demodulation but also to frequency demodulation. The simulation experiments and gear vibration signal analysis verify this conclusion and show that the delayed autocorrelation demodulation method is robust to noise.
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Received: 10 September 2008
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Corresponding Authors:
He Wei
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2009, Vol. 28 
