System for analyzing signals generated by rotating machines

• US 6,453,273 B1
• Filed: 10/09/2001
• Issued: 09/17/2002
• Est. Priority Date: 04/19/2000
• Status: Expired due to Term

• Current Assignee: National Instruments Corporation (Emerson Electric Company)
• Original Assignee: National Instruments Corporation (Emerson Electric Company)
• Inventors: Jin, Wei, Shao, Hui, Qian, Shie
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US09/974,402
• Publication Number:
  US 20020052714A1
• Time in Patent Office: 343 Days
• Field of Search: 702/190, 702/56, 702/182, 702/183, 708/400, 708/401, 340/679, 340/683
• US Class Current: 702/190
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence

Abstract

A signal analysis system and method for analyzing an input signal acquired from a mechanical system. The mechanical system may include at least one rotating apparatus. The signal analysis system may include an input for receiving samples of an input signal acquired from the mechanical system, wherein the input signal is sampled in time, and wherein the input signal comprises a plurality of order components. The signal analysis system may also include a processor coupled to the input and a memory medium coupled to the processor which stores analysis software. The processor may be operable to execute the analysis software to: (a) perform an invertible joint time-frequency transform on the input signal to produce a first array of coefficients which depend on time and frequency; (b) generate a modified array of coefficients from the first array of coefficients, wherein the modified array of coefficients corresponds to a desired subset of the plurality of order components; and (c) generate a time domain signal from the modified array of coefficients. The signal analysis system may also include a presentation device coupled to the processor which is operable to present the time domain signal to a user. The time domain signal is useable in analyzing operation of the rotating apparatus in the mechanical system.

Claims

1. A system for analyzing the operation of a rotating apparatus in a mechanical system, the system comprising:

an input for receiving samples of an input signal, wherein the input signal is acquired from the mechanical system containing the rotating apparatus, wherein the input signal is sampled in time, wherein the input signal comprises a plurality of order components;

a processor coupled to the input;

a memory medium coupled to the processor which stores analysis software;

wherein the processor is operable to execute the analysis software to;

perform an invertible joint time-frequency transform on the input signal to produce a first array of coefficients which depend on time and frequency;

generate a modified array of coefficients from the first array of coefficients, wherein the modified array of coefficients corresponds to a desired subset of the plurality of order components; and

generate a time domain signal from the modified array of coefficients; and

a presentation device coupled to the processor which is operable to present the time domain signal to a user;

wherein the time domain signal is useable in analyzing operation of the rotating apparatus in the mechanical system.

2. The system of claim 1, wherein said generating the modified array of coefficients includes selecting the desired subset of the plurality of order components.

3. The system of claim 1, wherein, in generating the modified array of coefficients, the processor is operable to:

determine coefficient positions from the first array which correspond to the desired subset of the plurality of order components in the input signal, and

set coefficients of said modified array equal to zero at positions other than said coefficient positions.

4. The system of claim 3, wherein, in generating the modified array of coefficients, the processor is operable to set coefficients of the modified array equal to coefficients of the first array at said coefficient positions.

5. The system of claim 1, further comprising a user input device coupled to the processor, wherein, in response to execution of the analysis software, the processor is operable to receive user input from the user input device, wherein the user input specifies the desired subset of the plurality of order components.

6. The system of claim 1, further comprising a user input device coupled to the processor, wherein, in response to execution of the analysis software, the processor is operable to receive user input from the user input device, wherein the user input specifies a second subset of the plurality of order components in the input signal for removal, wherein the desired subset of the plurality of order components corresponds to order components of the input signal which are not included in the second subset of the plurality of order components.

7. The system of claim 1, further comprising:

a display configured to display a visual representation of the first array of coefficients, wherein the visual representation indicates at least one of the plurality of order components;

an input device, wherein the processor is operable to receive user input from the input device, wherein the user input indicates a user'"'"'s selection of one or more points in the visual representation, wherein said user input operates to define the desired subset of the plurality of order components.

8. The system of claim 1, wherein each of the order components in the input signal comprises a rotation-periodic signal present in the input signal.

9. The system of claim 1, wherein, in generating the time domain signal from the modified array of coefficients, the processor is operable to execute the analysis software to perform an inverse joint time-frequency transform on the modified array of coefficients.

10. The system of claim 1, wherein the joint time-frequency transform comprises the Gabor transform.

11. The system of claim 1,

wherein the presentation device is a display device operable to visually display the time domain signal.

12. The system of claim 1,

wherein the presentation device is a speaker operable to audially present the time domain signal.

13. The system of claim 1, wherein the mechanical system is operable to be adjusted in response to analysis of the time domain signal.

14. The system of claim 13, wherein adjustment of the mechanical system comprises one or more of:

1) changing a design of the mechanical system;

     2) replacing one or more components of the mechanical system;

     3) predicting a failure of one or more components of the mechanical system; and

     4) adding a sound-absorbent material to one or more locations of the mechanical system.

15. The system of claim 1, wherein the input signal comprises a signal generated by a microphone proximate to the mechanical system.

16. The system of claim 1, wherein, in generating the modified array of coefficients, the processor is operable to:

determine coefficient positions from the first array which correspond to the desired subset of the plurality of order components in the input signal;

compute an instantaneous rotation frequency signal with respect to time, wherein the instantaneous rotation frequency signal corresponds to a fundamental order component of the input signal;

multiply the instantaneous rotation frequency signal by one or more order numbers to generate one or more order curves, wherein the one or more order curves determine the coefficient positions from the first array.

17. The system of claim 16, wherein said coefficient positions from the first array comprise positions of the first array which reside in the union of neighborhoods containing the one or more order curves respectively, wherein said one or more order curves define the desired subset of the plurality of order components.

18. The system of claim 16, wherein said coefficient positions from the first array comprise positions of the first array which reside in the complement of the union of neighborhoods containing the one or more order curves, wherein said one or more order curves correspond to order components of the input signal which are not in the desired subset of the plurality of order components.

19. The system of claim 16, wherein said one or more order numbers are determined in response to user input.

20. The system of claim 16, further comprising a rotation sensing device coupled to the processor, and configured to provide a first signal comprising a stream of arrival times to the processor, wherein each pair of successive arrival times in said stream indicates a constant angular displacement of said rotating apparatus;

where said processor is operable to compute the instantaneous rotation frequency signal by filtering the arrival times to determine a stream of derivative estimates, wherein the instantaneous rotation frequency signal is determined from said stream of derivative estimates.

21. The system of claim 20, wherein said processor is operable to filter with arrival times with an FIR filter;

wherein coefficients of said FIR filter are determined by operating on a linear system derived from a Taylor senes expansion of time with respect to rotation angle of the rotating element.

22. The system of claim 21, wherein matrix coefficients of the linear system have the form $\frac{{(n}^{}}{}$

 



Δ



 



θ

)kk!,

where index k ranges from 1 to an upper limit M, wherein index k ranges through a set of M distinct integer values different from zero.

23. The system of claim 22, wherein M is even and the set of M distinct integers comprises the non-zero integer values between −

M/2 and M/2 inclusive.

24. The system of claim 20, wherein, in filtering said arrival times, said processor is configured to compute the expression t_k−

2−

8t<sub>k−

1</sub>+8t_k+1−

t_k+2 for a first arrival time t_k, wherein t<sub>k−

1</sub> is a first previous arrival time, wherein t<sub>k−

2</sub> is a second previous arrival time, wherein t_k+1 is a first following arrival time, wherein t_k+2 is a second following arrival time.

25. The system of claim 20, wherein, in response to execution of the analysis software, the processor is further operable to compute the instantaneous rotation frequency by reciprocating the stream of derivative estimates.

26. The system of claim 25, wherein, in response to execution of the analysis software, the processor is further operable to interpolate the reciprocated derivative estimates to determine rotation frequency values at a series of samples times.

27. The system of claim 16, wherein, in computing the instantaneous rotation frequency signal, said processor is operable to search the first array of coefficients according to one or more search criteria.

28. The system of claim 16, wherein, in computing the instantaneous rotation frequency signal, said processor is operable to:

receive a rotation indicator signal indicative of rotations of the rotating apparatus;

operate on the rotation indicator signal to determine values of the instantaneous rotation frequency signal.