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Method and apparatus for analysing the condition of a machine having a rotating part

  • US 10,133,257 B2
  • Filed: 11/23/2015
  • Issued: 11/20/2018
  • Est. Priority Date: 12/22/2008
  • Status: Active Grant
First Claim
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1. An apparatus for detecting a condition of a bearing associated with a shaft of a machine, where the shaft rotates at a variable rotational speed during operation of the machine, and where the bearing includes a rolling element placed between an outer race bearing surface and an inner race bearing surface so that, when the shaft rotates, the rolling element movable between said outer and inner race bearing surfaces thereby causing mechanical vibration, the apparatus comprising:

  • (A) a vibration sensor configured to generate an analogue vibration signal including a vibration signal component dependent on said mechanical vibration, and stochastic signal components, where the vibration signal component has a repetition frequency that depends on the variable rotational speed of the shaft;

    (B) an analogue-to-digital converter that samples said analogue vibration signal at a first sampling frequency so as to generate a digital vibration signal based on said analogue vibration signal;

    (C) a digital enveloper that generates a digital envelope signal based on said digital vibration signal, the digital envelope signal including a signal signature that is periodic with a frequency that depends on said repetition frequency;

    (D) a decimator that generates a decimated digital envelope signal having a reduced sampling frequency, where said decimator hasa first input for receiving said digital envelope signal;

    a second input for receiving a signal indicative of the variable rotational speed of the shaft; and

    a third input for receiving a signal indicative of an output sample rate setting signal;

    said decimator being adapted to generate said decimated digital envelope signal dependent onsaid digital envelope signal,said signal indicative of the variable rotational speed of the shaft, andsaid signal indicative of an output sample rate setting signal,such that the number of sample values per revolution of the shaft is kept at a substantially constant value when the variable rotational speed of the shaft varies during a measurement, thereby generating said decimated digital envelope signal so that said periodic signal signature has a periodicity in terms of repetition per revolution of the shaft;

    (E) an enhancer having an input for receiving said decimated digital envelope signal, said enhancer being adapted to perform signal processing involving autocorrelation of said decimated digital envelope signal so as to produce an autocorrelated envelope signal sequence where said periodic signal signature is amplified in relation to stochastic signal components; and

    (F) an evaluator that detects said condition of the bearing based on said autocorrelated envelope signal sequence, said evaluator thereby detecting said bearing condition even when the variable rotational speed of the shaft varies during a measurement.

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