Method and apparatus for structural integrity monitoring

• US 5,195,046 A
• Filed: 07/30/1990
• Issued: 03/16/1993
• Est. Priority Date: 01/10/1989
• Status: Expired due to Fees

• Current Assignee: Innovative Dynamics, Inc.
• Original Assignee: Gail A. Hickman, Joseph J. Gerardi
• Inventors: Gerardi, Joseph J., Hickman, Gail A.
• Primary Examiner(s): Cosimano, Edward R.
• Application Number:
  US07/559,482
• Time in Patent Office: 960 Days
• Field of Search: 73/579, 73/583, 73/602, 73/659, 73/768, 73/771, 73/775, 364/506, 364/507, 364/508, 364/550
• US Class Current: 702/35
• CPC Class Codes: B64D 15/16 by mechanical means
• CPC Class Codes: B64D 15/20 Means for detecting icing or initiating de-icing
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0066 by exciting or detecting vibration or acceleration vibration testing of structures G01M7/00
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 29/2437 Piezoelectric probes
• CPC Class Codes: G01N 29/2475 Embedded probes, i.e. probes incorporated in objects to be inspected
• CPC Class Codes: G08B 19/02 Alarm responsive to formation or anticipated formation of ice

Abstract

A system is disclosed for monitoring a structure and detecting disturbances and faults associated with such structure. The system includes an actuation device for mechanically exciting the structure, a sensing device for transducing vibrations experienced by the structure, and digital signal processing means for processing signals output by the sensing device. The response of the structure due to the mechanical excitation is analyzed and a baseline or normal response is determined. Vibrations of the structure are then analyzed and compared to the normal response of the structure and the nature of disturbances identified. Another aspect of the invention relates to a system for monitoring cracks, strains and the like and includes a continuity/strain sensor having a piezoelectric layer, and first and second low resistance layers. By suitably monitoring sensors in accordance with the invention, the magnitude as well as the location of a force can be determined.

Claims

1. An apparatus for monitoring and identifying disturbances to a structure comprising:

a) first processing means for processing signals so as to monitor and identify disturbances to said structure;

b) switch means controlled by said first processing means for gating a voltage signal;

c) actuation means for applying a physical impulse to said structure upon receiving said voltage signal gated by said switch means, wherein the application of said physical impulse to said structure by said actuation means results in said structure experiencing an initial force of magnitude "F" in a first direction followed by a plurality of reactive forces in a direction opposite said first direction and having a total magnitude of "F" wherein said plurality of forces are applied to said structure at positions away from where said force of magnitude "F" was applied;

d) sensor means for detecting the effects of said physical impulse on said structure and outputting an analog signal, said effects of said physical impulse indicative of said disturbances on said structure;

e) second processing means for converting said analog signal into a digital signal; and

f) means for providing said digital signal to said first processing means so as to monitor and identify disturbances to said structure.

2. The apparatus of claim 1 further comprising a high voltage power supply coupled to said switch means wherein said first processing means causes said switch means to gate said voltage signal from said high voltage power supply to said actuation means.

3. The apparatus of claim 1 further comprising pattern recognition means for determining the nature of said disturbance applied to said structure.

4. The apparatus of claim 3 further comprising display means for graphically indicating said disturbance applied to the structure.

5. The apparatus of claim 1 wherein said forces produce a surface wave of wavelength "L" on said structure, "L" being twice the distance separating where said initial force was applied and where an average force of said plurality of reactive forces was applied.

6. The apparatus of claim 5 wherein each of said actuation means has associated therewith two sensor means placed on opposite sides of said actuation means at a distance of "L" from a center of said actuation means.

7. The apparatus of claim 6 wherein said actuation means is circular in shape.

8. The apparatus of claim 1 wherein said first processing means is a microprocessor and said second processing means is an amplifier/conditioner circuit which amplifies and digitizes said analog signal to produce a digital signal.

9. The apparatus of claim 8 further comprising:

g) a host central processing unit for performing signature pattern analysis; and

h) a plurality of said apparatuses, each being connected to said host central processing unit and being controlled by said host central processing unit.

10. The apparatus of claim 9 wherein said host central processing unit is connected to each of said apparatuses by a digital signal bus.

11. The apparatus of claim 10 wherein said digital signal bus comprises:

1) a power line;

2) a power ground line;

3) a serial-in communication line;

4) a serial-out communication line;

5) a serial ground line;

6) a reset line; and

7) an address line.

12. The apparatus of claim 8 further comprising:

g) an energy storage means for supplying said voltage signal gated by said switch means to said actuation means; and

h) means for charging said energy storage means to a voltage level greater than a voltage level of a power supply which powers said charging means.

13. The apparatus of claim 12 wherein said charging means is a DC-DC converter.

14. The apparatus of claim 12 wherein said actuation means comprises a pair of electromagnetic coils separated by a gap and configured such that application of said voltage signal causes said gap to change in size thereby applying said physical impulse to said structure.

15. The apparatus of claim 14 wherein each of said coils comprises a flat spiral metalization layer.

16. The apparatus of claim 12 wherein said sensor means comprises a piezoelectric sensor.

17. The apparatus of claim 16 wherein said piezoelectric sensor comprises a polarized polyvinylidene fluoride layer, a first low resistance contact on one side of said layer, and a second low resistance contact on another side of said layer.

18. The apparatus of claim 16 further comprising a housing in which said apparatus is embedded.

19. A method of monitoring and identifying icing on and fatigue to a structure comprising the steps of:

a) acquiring and storing at least one of time and frequency domain signatures of known failure modes of said structure; and

b) forming a database of patterns which are correlated to icing conditions, wherein said step of forming employs pattern recognition software, said software being employed to perform the steps of;

i) generating features;

ii) analyzing histograms; and

iii) classifying signals,

so as to enable a processor to make icing and fatigue measurements on said structure by correlating at least one of said time and frequency domain signatures of said known failure modes with at least one of time and frequency domain signals obtained from said structure.

20. An apparatus for monitoring and identifying disturbances to a structure comprising:

a) first processing means for processing signals so as to monitor and identify disturbances to said structure;

b) a plurality of switch means each separately controlled by said first processing means for gating a voltage signal;

c) a plurality of actuation means each coupled to one of said plurality of switch means for applying a physical impulse to said structure upon receiving a voltage signal gated by the switch means to which it is coupled, each of said plurality of actuation means having a pair of electromagnetic coils separated by a gap and configured such that an application of said voltage signal causes said gap to change, thereby applying said physical impulse to said structure;

d) a plurality of sensor means attached to various portions of said structure, search for detecting the effects of said physical impulse on said structure and outputting an analog signal, said effects of said physical impulse indicative of disturbances of said structure;

e) second processing means for converting any one of said analog signals into a corresponding digital signal;

f) multiplexer means for selectively applying any of said analog signals to said second processing means; and

g) means for providing any one of said digital signals to said first processing means so as to monitor and identify disturbances to said structure.

21. The apparatus of claim 20 wherein each of said coils comprises a flat spiral metallization layer.

22. The apparatus of claim 20 wherein each of said sensor means comprises a piezoelectric sensor and wherein each of said pairs of coils has associated therewith a plurality of said piezoelectric sensors.

23. The apparatus of claim 20 wherein each of said sensor means comprises a piezoelectric sensor.

24. The apparatus of claim 23 wherein said piezoelectric sensor comprises a polarized polyvinylidene fluoride layer, a first low resistance contact on one side of said layer, and a second low resistance contact on another side of said layer.

25. A method of monitoring and identifying faults and physical disturbance to a structure comprising the steps of:

a) mechanically exciting said structure so as to induce vibration of said structure;

b) transducing said vibration so as to produce a first analog signal corresponding to said vibration;

c) deriving a baseline vibration signal from said first analog signal, said baseline vibration signal representing a baseline or normal response of said structure;

d) monitoring said structure by transducing said physical disturbances so as to produce a second analog signal corresponding to said faults and physical disturbances;

e) deriving another vibration signal from second analog signal, said another vibration signal representing a response of said structure due to said faults and physical disturbances;

f) obtaining a first plurality of features from said baseline vibration signal, said feature being influenced by the nature of said structure;

g) obtaining a second plurality of features from said another vibration signal, said features being influenced by the nature of said structure; and

h) analyzing said first plurality and said second plurality of features so as to monitor and identify the nature and extent of said faults and physical disturbances, wherein said step of analyzing is performed in a pattern space of a plurality of known features which are known to be indicative of specific disturbances and faults.

26. The method of claim 25 wherein said analyzing comprises analyzing in a frequency domain and in a time domain.

27. The method of claim 25 wherein said disturbances and faults comprise at least some of the group of ice accretion, fatigue, stress, corrosion, structural damage and cracks.

28. The apparatus of claim 25 wherein said known features are selected from the group of amplitude ratios of power spectrum signals, frequencies of signals, frequency differences of signals, partial energies, ratio of partial energies, number of power spectrum peaks exceeding a threshold, frequencies at which various percentages of total energy are observed, damping numbers, a percentage of a demodulation period, standard deviation, kurtosis, skewness, decay time, mode shapes and total energy.

29. An apparatus for monitoring and detecting faults in a structure comprising:

a) a continuity sensor comprising a first low resistance layer, said first low resistance layer being in the form of at least one elongated low resistance path having a first electrode and having first and second ends; and

b) a dynamic strain sensor adapted for attachment to a surface of said structure and having;

i) a first piezoelectric layer; and

ii) said first low resistance layer, said first

electrode being attached to one side of said piezoelectric layer and electrically insulated from said structure, wherein an opposite side of said piezoelectric layer is adapted for attachment to said structure which forms a second low resistance layer, and continuity faults are detected by monitoring electrical resistance between said first and second ends, and strains are detected by monitoring said first low resistance layer and said second low resistance layer for electrical signals, wherein a capacitance value of said dynamic strain sensor is determined by a dielectric constant of said piezoelectric layer, a distance separating said first electrode from said second low resistance contact, and a surface area of said first electrode attached to said piezoelectric layer, and wherein the measured electrical resistance, strain, and capacitance vary in accordance with the nature and extent of the faults in the structure to be monitored and detected.

30. The apparatus of claim 29 further comprising a plurality of such apparatuses connected in series wherein a location of a continuity fault in said first low resistance layer may be determined by measuring a capacitance value of the series connection of said apparatuses.

31. An apparatus for monitoring and detecting faults in a structure comprising:

a) a continuity sensor comprising a first low resistance layer, said first low resistance layer being in the form of at least one elongated low resistance path having a first electrode and having first and second ends; and

b) a dynamic strain sensor adapted for attachment to a surface of said structure and having;

i) a piezoelectric layer attached to said first low resistance layer; and

ii) a second low resistance layer attached to an opposite side of said piezoelectric layer and adapted for attachment to said structure,

wherein continuity faults are detected by monitoring electrical resistance between said first and second ends, strains and detected by monitoring said first low resistance layer and said second resistance layer for electrical signals, and a capacitance value of said dynamic strain sensor is determined by a dielectric constant of said piezoelectric layer, a distance separating said first electrode from said second low resistance contact, and surface area of said first electrode attached to said piezoelectric layer, and wherein the measured electrical resistance, strain, and capacitance vary in accordance with the nature and extent of the faults in the structure to be monitored and detected.

32. The apparatus of claim 31 further comprising a plurality of such apparatuses connected in series wherein a location of a continuity fault in said first low resistance layer may be determined by measuring a capacitance value of the series connection of said apparatuses.

33. An apparatus for monitoring strains in a structure comprising:

a) a piezoelectric layer which produces electrical signals in response to application of a dynamic force to said layer; and

b) a first low resistance layer attached on one side to a first side of said piezoelectric layer, and adapted for attachment to said structure on another side;

c) a second low resistance layer attached to a second side of said piezoelectric layer; and

d) means for monitoring said first and second low resistance layers for electrical signals so as to determine the existence and extent of strains experienced by said structure.

34. The apparatus of claim 33 wherein said monitoring means comprises a digital signal processor and pattern recognition means for identifying the cause of said strains.

35. An apparatus for monitoring strains in a structure comprising:

a) a piezoelectric layer which produces electrical signals in response to application of a dynamic force to said layer; and

b) a first low resistance layer attached on one side to a first side of said piezoelectric layer, and adapted for attachment to said structure on another side;

c) a second low resistance layer attached to a second side of said piezoelectric layer; and

d) means for detecting a capacitance value of said piezoelectric layer by determining the capacitance between said first and second low resistance layers so as to determine the existence and extent of strains experienced by said structure.

36. An apparatus for monitoring and identifying disturbances to a structure comprising:

a) first processing means for processing signals so as to monitor and identify disturbances to said structure;

b) switch means controlled by said first processing means for gating a voltage signal;

c) actuation means for applying a physical excitation to said structure upon receiving said voltage signal gated by said switch means, wherein the application of said physical excitation to said structure by said actuation means results in said structure experiencing an initial force of magnitude "F" in a first direction followed by a plurality of reactive forces in a direction opposite said first direction and having a total magnitude of "F" wherein said plurality of forces are applied to said structure at positions away from where said force of magnitude "F" was applied;

d) sensor means for detecting the effects of said physical excitation on said structure and outputting an analog signal, said effects of said physical excitation indicative of said disturbances on said structure;

e) second processing means for converting said analog signal into a digital signal; and

f) means for providing said digital signal to said first processing means so as to monitor and identify disturbances to said structure.