Method and apparatus for analysing the condition of a machine having a rotating part
First Claim
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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Abstract
A method analyzing a machine having a rotating shaft includes generating an electric measurement signal dependent on mechanical vibrations from the shaft rotation; sampling the measurement signal to generate a digital measurement data signal; performing a decimation of the digital measurement data signal to achieve a digital signal having a reduced sampling frequency, where the decimation includes controlling the reduced sampling frequency such that the number of sample values per revolution of the shaft is kept at a substantially constant value, and receiving the digital signal at an enhancer input performing a correlation in the enhancer so as to produce an output signal sequence where repetitive signals amplitude components are amplified in relation to stochastic signal components, and performing a condition analysis for analyzing the condition of the machine dependent on the digital signal having a reduced sampling frequency.
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Citations
22 Claims
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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:
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(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 has a 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 on said digital envelope signal, said signal indicative of the variable rotational speed of the shaft, and said 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An apparatus for detecting a condition of a gear system associated with a shaft of a machine, where the shaft rotates at a variable rotational speed during operation of the machine and the gear system includes a first gear having first teeth and a second gear having second teeth so that, when the shaft rotates, the first teeth engage with the second teeth thereby causing mechanical vibration, the apparatus comprising:
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(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 for sampling 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 for generating 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 for generating a decimated digital envelope signal having a reduced sampling frequency, where said decimator has a 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 on said digital envelope signal, said signal indicative of the variable rotational speed of the shaft, and said 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 wherein said periodic signal signature is amplified in relation to stochastic signal components; and(F) an evaluator for detecting said gear system condition based on said autocorrelated envelope signal sequence, said evaluator thereby detecting said gear system condition even when the variable rotational speed of the shaft varies during a measurement. - View Dependent Claims (18, 19, 20, 21, 22)
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Specification