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

• Current Assignee: S.P.M. Instrument AB
• Original Assignee: S.P.M. Instrument AB
• Inventors: Hedin, Lars-Olov Elis
• Primary Examiner(s): Le, John H
• Application Number:
  US14/949,317
• Publication Number:
  US 20160342148A1
• Time in Patent Office: 1,093 Days
• Field of Search: 702 34, 702 35, 702 56, 702145, 702182, 702185, 702190, 700110, 700265, 73587, 73593, 340540
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G01H 17/00 Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves, not provided for in the preceding groups see provisionally also G01H1/00
• CPC Class Codes: G01M 13/045 Acoustic or vibration analysis
• CPC Class Codes: G05B 19/4069 Simulating machining process on screen G05B19/4068 takes precedence
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/37228 Tool inspection, condition, dull tool
• CPC Class Codes: G06F 15/00 Digital computers in general details G06F1/00 – G06F13/00; Data processing equipment in general

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.

Claims

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 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.

2. The apparatus according to claim 1, wherein said evaluator delivers an output signal indicative of at least one bearing condition selected from a group comprising:

an inner race bearing surface damage, and an outer race bearing surface damage.

3. The apparatus according to claim 1, wherein said vibration sensor is a mechanically resonant vibration sensor.

4. The apparatus according to claim 1, wherein said enhancer interacts with said decimator to produce said autocorrelated envelope signal sequence such that said evaluator detects said bearing condition when the variable rotational speed of the shaft is lower than 50 revolutions per minute.

5. The apparatus according to claim 1,

wherein said decimated digital envelope signal has a first signal-to-noise ratio value in respect of said periodic signal signature,

wherein said autocorrelated envelope signal sequence has a second signal-to-noise ratio value in respect of said periodic signal signature, and

wherein said enhancer is adapted to produce said autocorrelated envelope signal sequence so that said second signal-to-noise ratio value is higher than said first signal-to-noise ratio value such that said evaluator detects said bearing condition when the variable rotational speed of the shaft is lower than 50 revolutions per minute.

6. The apparatus according to claim 1, further comprising:

a user interface for setting a signal-to-noise ratio improver value,

wherein said decimated digital envelope signal has a first signal-to-noise ratio value in respect of said periodic signal signature,

wherein said autocorrelated envelope signal sequence has a second signal-to-noise ratio value in respect of said periodic signal signature,

wherein said enhancer is adapted to produce said autocorrelated envelope signal sequence so that said second signal-to-noise ratio value is higher than said first signal-to-noise ratio value, and

wherein said enhancer is adapted to produce said autocorrelated envelope signal sequence so that said second signal-to-noise ratio depends on said signal-to-noise ratio improver value.

7. The apparatus according to claim 1, wherein said evaluator delivers an output signal indicative of whether said bearing condition is any of normal, deteriorated, and abnormal.

8. The apparatus according to claim 1, wherein said enhancer is configured to deliver said autocorrelated envelope signal sequence as a time domain signal.

9. The apparatus according to claim 1, wherein said enhancer is configured to achieve said correlation by a method for producing autocorrelation data by performing successive Fourier Transform operations on said decimated digital envelope signal to provide said autocorrelated envelope signal.

10. The apparatus according to claim 1,

wherein said enhancer is adapted to receive a first plurality of samples of said decimated digital envelope signal, said decimated digital envelope signal representing mechanical vibrations emanating from rotating the shaft so far as to cause occurrence of a vibration having a period of repetition,

wherein said enhancer is adapted to divide said decimated digital envelope signal into a first signal portion and a second signal portion, and

wherein said enhancer is adapted to generate said autocorrelated envelope signal sequence so that it has a second plurality of samples, said second plurality being a positive integer and lower than said first plurality, said autocorrelated envelope signal sequence being generated based on the first signal portion and the second signal portion.

11. The apparatus according to claim 1, wherein said decimator comprises

a first decimator for performing a first decimation of the digital envelope signal so as to achieve a first digital signal having a first reduced sampling frequency, the first reduced sampling frequency being reduced by an integer factor as compared to the first sampling frequency, and

a second decimator for performing a second decimation of said first digital signal so as to generate said decimated digital envelope signal.

12. The apparatus according to claim 11, wherein said integer factor is settable to a value adapted for measuring conditions in a measuring session, said integer factor being kept constant for the duration of a measuring session.

13. The apparatus according to claim 1, wherein said periodicity of the periodic signal signature is expressed as a factor value, said factor value being a positive, real number not limited to integer numbers.

14. The apparatus according to claim 13, wherein said factor value reflects the number of repetitions of said periodic signal signature per revolution of the shaft as a real number not limited to integer numbers.

15. The apparatus according to claim 1, wherein said vibration sensor has a substantially linear response in a frequency range up to 10 kHz.

16. A method for detecting a condition of a bearing associated with a shaft of a machine, the method comprising the steps of:

(I) providing the apparatus according to claim 1;

(II) applying the vibration sensor to a measuring point on the machine; and

(III) generating the bearing condition from the evaluator,

wherein variable rotational speed of the shaft is less than 50 revolutions per minute.

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:

(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.

18. The apparatus according to claim 17, wherein said evaluator delivers an output signal indicative of a teeth engagement error.

19. The apparatus according to claim 17, wherein said periodicity of the periodic signal signature is expressed as a factor value, said factor value being a positive, real number not limited to integers.

20. The apparatus according to claim 19, wherein said factor value reflects the number of repetitions of said periodic signal signature per revolution of the shaft as a real number not limited to integer numbers.

21. The apparatus according to claim 17,

wherein the gear system further comprises a bearing associated with said shaft, said bearing including 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 moves between said outer and inner race bearing surfaces, thereby causing mechanical vibration, and

wherein said evaluator, based on said periodicity, delivers an output signal indicative of at least one deteriorated condition selected from a group comprising:

a Bearing Inner Race damage, a Bearing Outer Race damage, and a teeth engagement error.

22. The apparatus according to claim 17, wherein said enhancer interacts with said decimator to produce said autocorrelated envelope signal sequence such that said evaluator detects said gear system condition even when the variable rotational speed of the shaft is lower than 50 revolutions per minute.