Method and apparatus for loosening of fasteners on structures

• US 8,229,680 B2
• Filed: 04/29/2009
• Issued: 07/24/2012
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Acellent Technologies, Inc.
• Original Assignee: Acellent Technologies, Inc.
• Inventors: Liu, Bao, Ouyang, Lien, Beard, Shawn J., Li, Irene, Chang, Fu-Kuo
• Primary Examiner(s): TSAI, CAROL S W
• Application Number:
  US12/432,659
• Publication Number:
  US 20090276168A1
• Time in Patent Office: 1,182 Days
• Field of Search: 702/33, 702/56, 737/61, 737/99, 735/87, 735/94, 737/69, 324/242, 324/225, 324/235, 324/240, 324/241, 324/243, 324/658, 324/659
• US Class Current: 702/33
• CPC Class Codes: G01H 1/00 Measuring characteristics of vibrations in solids by using direct conduction to the detector G01H9/00, G01H11/00 take precedence

Abstract

Methods and apparatuses for detecting fastener loosening. Sensors query a structure at a baseline value of an environment variable, such as temperature, and this baseline signal is stored for later use. Subsequently, users can query the structure remotely and at any time, and the signals from these queries are compared to the stored baseline signal. In some embodiments, an index is calculated, and the system determines that one or more fasteners have come loose if the calculated index exceeds a predetermined threshold value. It is desirable to select a time window within which the query signal is most sensitive to fastener loosening but least sensitive to variations in the environment variable. Accordingly, embodiments of the invention include methods and apparatuses for determining an optimal time window for use in calculating the above described index.

Claims

1. A method of detecting a loosening of a fastener on a structure, comprising:

retrieving a first set of data corresponding to a first signal transmitted through a structure having a fastener;

determining a second set of data corresponding to a second signal transmitted through the structure;

calculating a value of an index according to the first set of data and the second set of data;

comparing the calculated index value to a predetermined threshold value; and

determining the loosening of the fastener according to the comparing;

wherein the first signal is a baseline signal corresponding to a first degree of loosening of the fastener, and wherein the second signal is a subsequent signal transmitted through the structure subsequent to transmission of the first signal so as to facilitate determination of the loosening of the fastener subsequent to the transmission of the first signal.

2. The method of claim 1, wherein the first and second sets of data represent magnitude values of, respectively, a received signal corresponding to the first signal, and a received signal corresponding to the second signal.

3. The method of claim 2, wherein the first set of data represents an envelope of the received signal corresponding to the first signal, and wherein the second set of data represents an envelope of the received signal corresponding to the second signal.

4. The method of claim 3, wherein the index compares a difference between the first and second sets of data to a sum of one or more elements of the first and second sets of data.

5. The method of claim 4, wherein the index I is at least approximately:

6. The method of claim 1, wherein the threshold value is between approximately 0.1 and approximately 0.2.

7. The method of claim 1, wherein the fastener is a bolt.

8. The method of claim 1, wherein the calculating further comprises determining an optimal time window for use in determining the index.

9. The method of claim 8, wherein the determining an optimal time window further comprises:

determining a third set of data corresponding to signals transmitted through the structure at different values of an environment variable;

determining a fourth set of data corresponding to signals transmitted through the structure at different loosenings of the fastener;

determining values of an objective function for various time windows, the objective function comparing a sensitivity of signals transmitted through the structure to the loosening of the fastener, to a sensitivity of signals transmitted through the structure to the environment variable; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum value of the objective function.

10. The method of claim 9, wherein:

the determining a third set of data further comprises determining a third set of data corresponding to M signals transmitted through the structure at different values of an environment variable;

the determining a fourth set of data further comprises determining a fourth set of data corresponding to N signals transmitted through the structure at different loosenings of the fastener; and

the objective function I_j is at least approximately;

11. The method of claim 9, wherein the environment variable is a temperature of the structure.

12. The method of claim 8, wherein the determining an optimal time window further comprises:

determining a third set of data corresponding to signals transmitted through the structure at different values of an environment variable;

determining values of an objective function for various time windows, the objective function measuring a sensitivity of signals transmitted through the structure to the environment variable; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum value of the objective function.

13. The method of claim 12, wherein:

the determining a third set of data further comprises determining a third set of data corresponding to M signals transmitted through the structure at different values of an environment variable; and

the objective function I_j is at least approximately;

14. The method of claim 12, wherein the environment variable is a temperature of the structure.

15. A method of detecting a loosening of a fastener on a structure, comprising:

querying a structure by transmitting first signals through the structure;

receiving first data corresponding to the transmitted first signals;

retrieving second data corresponding to second signals transmitted through the structure;

calculating a value of an index at least partially according to the first data and the second data;

comparing the calculated index value to a threshold value; and

determining a loosening of the fastener on the structure when the calculated index value exceeds the threshold value;

wherein the second data is data representative of baseline signals corresponding to a first degree of loosening of the fastener, and wherein the first data is data representative of a subsequent signal transmitted through the structure subsequent to transmission of the second signals, so as to facilitate determination of the loosening of the fastener subsequent to the transmission of the second signals.

16. The method of claim 15, wherein the second signals are the baseline signals transmitted at a baseline value of an environment variable.

17. The method of claim 16, wherein the environment variable is a temperature of the structure.

18. The method of claim 15, wherein the first and second data represent, respectively, magnitude values of received signals corresponding to the transmitted first signals, and magnitude values of received signals corresponding to the transmitted second signals.

19. The method of claim 18, wherein the first data represents envelope values of the received signals corresponding to the transmitted first signals, and wherein the second data represents envelope values of the received signals corresponding to the transmitted second signals.

20. The method of claim 19, wherein the index compares a difference between the first and second data to a sum of one or more elements of the first and second data.

21. The method of claim 20, wherein the index I is at least approximately:

22. The method of claim 15, wherein the threshold value is between approximately 0.1 and approximately 0.2.

23. The method of claim 15, wherein the fastener is a bolt.

24. The method of claim 15, wherein the calculating further comprises determining an optimal time window for use in determining the index.

25. The method of claim 24, wherein the determining an optimal time window further comprises:

determining third data corresponding to signals transmitted through the structure at different values of an environment variable;

determining fourth data corresponding to signals transmitted through the structure at different loosenings of the fastener;

determining values of an objective function for various time windows, the objective function comparing a sensitivity of signals transmitted through the structure to the loosening of the fastener, to a sensitivity of signals transmitted through the structure to the environment variable; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum value of the objective function.

26. The method of claim 25, wherein:

the determining third data further comprises determining third data corresponding to M signals transmitted through the structure at different values of an environment variable;

the determining fourth data further comprises determining fourth data corresponding to N signals transmitted through the structure at different loosenings of the fastener; and

the objective function I_j is at least approximately;

27. The method of claim 25, wherein the environment variable is a temperature of the structure.

28. The method of claim 24, wherein the determining an optimal time window further comprises:

determining third data corresponding to signals transmitted through the structure at different values of an environment variable;

determining values of an objective function for various time windows, the objective function measuring a sensitivity of signals transmitted through the structure to the environment variable; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum value of the objective function.

29. The method of claim 28, wherein:

the determining third data further comprises determining third data corresponding to M signals transmitted through the structure at different values of an environment variable; and

the objective function I_j is at least approximately;

30. The method of claim 28, wherein the environment variable is a temperature of the structure.

31. A method of determining an optimal time window for facilitating detection of a loosening of a fastener on a structure, comprising:

determining a first set of data corresponding to first signals transmitted through the structure, differing ones of the first signals transmitted through the structure at differing values of an environment variable;

determining values of an objective function for various time windows, wherein the respective values are determined at least partially according to a portion of the first set of data corresponding to the respective time window; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum one of the values.

32. The method of claim 31, wherein:

the determining a first set of data further comprises determining a first set of data corresponding to M signals transmitted through the structure at different values of the environment variable; and

the objective function I_j is at least approximately;

33. The method of claim 31:

further comprising determining a second set of data corresponding to second signals transmitted through the structure, differing ones of the second signals transmitted through the structure at differing loosenings of the fastener;

wherein the respective values are determined at least partially according to a portion of the first set of data corresponding to the respective time window and a portion of the second set of data corresponding to the respective time window.

34. The method of claim 33, wherein:

the determining a first set of data further comprises determining a first set of data corresponding to M signals transmitted through the structure at different values of the environment variable;

the determining a second set of data further comprises determining a second set of data corresponding to N signals transmitted through the structure at different loosenings of the fastener; and

the objective function I_j is at least approximately;

35. The method of claim 31, wherein the environment variable is a temperature of the structure.

44. The non-transitory computer-readable medium of claim 34, wherein the determining an optimal time window further comprises:

determining a third set of data corresponding to signals transmitted through the structure at different values of an environment variable;

determining a fourth set of data corresponding to signals transmitted through the structure at different loosenings of the fastener;

determining values of an objective function for various time windows, the objective function comparing a sensitivity of signals transmitted through the structure to the loosening of the fastener, to a sensitivity of signals transmitted through the structure to the environment variable; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum value of the objective function.

45. The non-transitory computer-readable medium of claim 44, wherein:

the determining a third set of data further comprises determining a third set of data corresponding to M signals transmitted through the structure at different values of an environment variable;

the determining a fourth set of data further comprises determining a fourth set of data corresponding to N signals transmitted through the structure at different loosenings of the fastener; and

the objective function I_j is at least approximately;

46. The non-transitory computer-readable medium of claim 44, wherein the environment variable is a temperature of the structure.

36. A non-transitory computer readable medium containing computer instructions stored therein for causing a computer processor to perform a method of detecting a loosening of a fastener on a structure, the method comprising:

retrieving a first set of data corresponding to a first signal transmitted through a structure having a fastener;

determining a second set of data corresponding to a second signal transmitted through the structure;

calculating a value of an index according to the first set of data and the second set of data;

comparing the calculated index value to a predetermined threshold value; and

determining the loosening of the fastener according to the comparing;

wherein the first signal is a baseline signal corresponding to a first degree of loosening of the fastener, and wherein the second signal is a subsequent signal transmitted through the structure subsequent to transmission of the first signal so as to facilitate determination of the loosening of the fastener subsequent to the transmission of the first signal.

37. The non-transitory computer-readable medium of claim 36, wherein the first and second sets of data represent magnitude values of, respectively, a received signal corresponding to the first signal, and a received signal corresponding to the second signal.

38. The non-transitory computer-readable medium of claim 37, wherein the first set of data represents an envelope of the received signal corresponding to the first signal, and wherein the second set of data represents an envelope of the received signal corresponding to the second signal.

39. The non-transitory computer-readable medium of claim 38, wherein the index compares a difference between the first and second sets of data to a sum of one or more elements of the first and second sets of data.

40. The non-transitory computer-readable medium of claim 39, wherein the index I is at least approximately:

41. The non-transitory computer-readable medium of claim 36, wherein the threshold value is between approximately 0.1 and approximately 0.2.

42. The non-transitory computer-readable medium of claim 36, wherein the fastener is a bolt.

43. The non-transitory computer-readable medium of claim 36, wherein the calculating further comprises determining an optimal time window for use in determining the index.

47. The non-transitory computer-readable medium of claim 43, wherein the determining an optimal time window further comprises:

determining a third set of data corresponding to signals transmitted through the structure at different values of an environment variable;

determining values of an objective function for various time windows, the objective function measuring a sensitivity of signals transmitted through the structure to the environment variable; and

determining the optimal time window according to a one of the various time windows corresponding to a maximum value of the objective function.

48. The non-transitory computer-readable medium of claim 47, wherein:

the determining a third set of data further comprises determining a third set of data corresponding to M signals transmitted through the structure at different values of an environment variable; and

the objective function I_j is at least approximately;

49. The non-transitory computer-readable medium of claim 47, wherein the environment variable is a temperature of the structure.