Synchronized electronic shutter system and method for thermal nondestructive evaluation

• US 6,712,502 B2
• Filed: 04/10/2002
• Issued: 03/30/2004
• Est. Priority Date: 04/10/2002
• Status: Expired due to Fees

• Current Assignee: National Aeronautics and Space Administration (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Zalameda, Joseph N., Winfree, William P.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): PRUCHNIC, STANLEY J
• Application Number:
  US10/120,225
• Publication Number:
  US 20030193987A1
• Time in Patent Office: 720 Days
• Field of Search: 374/4, 374/5, 374/6, 374/7, 374/124, 374/43, 374/44, 374/120, 374/121, 374/130, 374/137, 374/126, 250/330, 250/332, 250/341.6
• US Class Current: 374/5
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/0805 Means for chopping radiation
• CPC Class Codes: G01N 25/72 Investigating presence of flaws

Abstract

The invention is a synchronized electronic shutter system (SESS) and method for same side and through transmission thermal analysis and inspection of a material for finding defects, corrosion, disbond defects, integrity of a weld and determination of paint thickness. The system comprises an infrared detector that acquires background images of the sample. A shutter then covers the detector and lamps rapidly heat the sample above ambient temperature. Shutters cover all lamps at the same time the shutter over the infrared detector is opened. The infrared detector acquires a series of temperature images over time radiated from the sample as the sample cools down. After collecting a series of temperature images taken by the SESS, a processed image is developed using one of the group comprising time derivative calculation, temperature normalization data reduction routine, thermal diffusivity curve fitting and averaging the series of temperature images.

Claims

1. A method for thermal inspection of a sample of material, said method comprising the steps of:

pointing an infrared detector having a lens at a surface of said sample to acquire background data;

covering said lens with a first shutter;

firing a lamp having a reflector pointed at said sample to heat said sample above an ambient temperature;

covering said lamp with a second shutter; and

opening said first shutter to expose said lens to enable said detector to acquire temperature measurements of said sample over time as said sample cools down.

2. The method of claim 1, further comprising the step of opening said second shutter to expose said lamp while covering said lens with said first shutter.

3. The method of claim 1, wherein said step of covering said lamp with said second shutter occurs at the same time as said step of opening said first shutter to expose said lens of said infrared detector.

4. The method of claim 1, further comprising the step of receiving a signal from a computer to start said method before covering said lens of said infrared detector.

5. The method of claim 1, wherein said lamp and said infrared detector are on the same side of said sample.

6. The method of claim 5, wherein a second lamp resides on said same side of said sample as said first lamp and said infrared detector, said second lamp having a third shutter that covers said second lamp when said second shutter covers said first lamp and said third shutter uncovers said second lamp when said second shutter uncovers said first lamp, both said first lamp and said second lamp being pointed at a same surface of said sample as said infrared detector.

7. The method of claim 6, wherein one electronic input signal is input from a computer having a central processing unit that generates 4 electronic output signals, the first output signal being used for operating said first shutter, the second output signal being used for operating said second shutter, the third output signal being used for operating said third shutter, and the fourth output signal being used for triggering the firing of flashes from both said lamps simultaneously.

8. The method of claim 1, wherein said lamp is on an opposite side of said sample from said infrared detector.

9. The method of claim 1, wherein said first lamp has a duration of firing of approximately 0.002 seconds to raise a temperature of said sample approximately 10 degrees Celsius above an ambient temperature.

10. The method of claim 1, wherein said temperature measurements comprise a plurality of temperature images of said sample over time, said method further comprises the step of creating a processed image from said plurality of temperature images by a method selected from the group consisting of curve fitting for thermal diffusivity, time derivative calculations, normalization data reduction routine, and averaging.

11. An apparatus for thermally inspecting a sample of a material, comprising:

an infrared detector having a lens pointed at a surface of said sample;

means for heating said sample to a temperature above an ambient temperature;

a first shutter to cover and uncover said lens of said infrared detector;

a second shutter to cover and uncover said means for heating;

shutter electronics, operatively connected to said first shutter and said second shutter, for controlling synchronization of the opening and closing of each shutter and a timing of a firing of said means for heating;

a computer, electrically connected to said shutter electronics, for generating a trigger signal to initiate a thermal inspection process.

12. The apparatus of claim 11, wherein said means for heating is a flash heat lamp.

13. The apparatus of claim 12, further comprising a second flash heat lamp having a third shutter that moves in tandem to said second shutter.

14. The apparatus of claim 13, wherein said first and second flash heat lamps are both pointed at the same surface of said sample as said lens.

15. The apparatus of claim 11, wherein said shutter electronics cause said first shutter to uncover said infrared detector lens at the same time said second shutter covers said means for heating.

16. The apparatus of claim 11, wherein said shutter electronics cause said first shutter to cover said infrared detector lens at the same time said second shutter uncovers said means for heating.

17. The apparatus of claim 11, wherein said means for heating is pointed at a surface of said sample that is opposite to the surface said lens is pointed towards.

18. The apparatus of claim 11, wherein said shutter electronics comprise a pair of dual monostable muitivibrators.

19. The apparatus of claim 18, wherein each one of said pair of dual monostable multivibrators comprise Schmitt-trigger inputs.

20. The apparatus of claim 11, wherein said computer collects a plurality of temperature images over time taken by said infrared detector of said sample, said plurality of temperature images being used to construct a processed image by using a method selected from the group consisting of curve fitting for thermal diffusivity, time derivative calculations, normalization data reduction routine, and averaging.

21. A method for thermally inspecting a thin sample having a first surface and a second surface opposite to said first surface, said method comprising the steps of:

opening a shutter to an infrared detector, said detector being pointed toward said first surface, to measure reference infrared radiation emanating from said first surface when said sample is at an ambient temperature;

closing said shutter to said detector while opening a shutter of a lamp that is pointed at said sample;

firing said lamp to heat said sample to a temperature above said ambient temperature;

closing said shutter of said lamp to cover said lamp while opening said shutter to said infrared detector;

acquiring a plurality of temperature images of said sample over time from said infrared detector; and

producing a processed image from said plurality of temperature images.

22. The method of claim 21, wherein said processed image indicates a location where said first surface has a defect.

23. The method of claim 21, wherein said processed image is formed by a normalization data reduction routine performed on said plurality of temperature images and wherein said lamp is on a same side of said sample as said infrared detector.

24. The method of claim 23, further comprising the step of pointing said lamp at said first surface of said sample.

25. The method of claim 24, further comprising the step of pointing a second lamp toward said first surface, said second lamp comprising a shutter that operates in tandem to said shutter of said first lamp and said second lamp being fired at the same time said first lamp is fired.

26. The method of claim 21, wherein said processed image is formed by curve fitting said plurality of temperature images to a theoretical model for thermal diffusivity.

27. The method of claim 22, wherein said processed image is formed by applying a temperature normalization data reduction routine to said plurality of temperature images.

28. The method of claim 21, wherein said lamp is pointed at said second surface of said sample.

29. The method of claim 21, wherein said step of firing said lamp lasts for a duration of approximately 0.008 seconds and heats said sample approximately 10 Celsius degrees above said ambient temperature.

30. An apparatus for thermally inspecting a thin sample having a first surface and a second surface opposite to said first surface, comprising:

an infrared detector having a lens pointed at said first surface, said detector having a first shutter;

a lamp for heating said thin sample, said lamp having a reflector and having a second shutter, said lamp being pointed at one of said first surface and said second surface of said thin sample; and

shutter electronics, operatively connected to said first shutter and said second shutter, for controlling synchronization of the opening and closing of each shutter to enable thermal inspection of said sample upon actuation of a trigger signal.

31. The apparatus of claim 30, said shutter electronics comprising a pair of dual monostable multivibrators with Schmitt-trigger inputs.

32. The apparatus of claim 30, said shutter electronics actuating said first and said second shutter in complement to one another.

33. The apparatus of claim 30, wherein said lamp is pointed at said second surface.

34. The apparatus of claim 30, further comprising a second lamp being pointed at said first surface, wherein said first lamp is also pointed at said first surface.

35. The apparatus of claim 30, further comprising a computer electrically connected to both an image processor and said shutter electronics, said computer actuating said trigger, said image processor receiving a plurality of temperature images of said sample taken over time by said infrared detector and applying one of a curve fitting routine for thermal diffusivity, a time derivative calculation, a normalization data reduction routine, and an averaging routine to produce a processed image that has the capability of illustrating locations of defects on said sample.

36. A method for thermal inspection of a sample of material, said method comprising the steps of:

pointing an infrared detector having a lens at a surface of said sample to acquire background data;

covering said lens with a shutter;

firing a lamp having a reflector pointed at said sample to heat said sample above an ambient temperature; and

opening said shutter from said lens to enable said infrared detector to acquire temperature measurements of said sample over time as said sample cools down.

37. The method of claim 36, wherein said step of firing said lamp to heat said sample occurs at the same time as the step of covering said lens with said shutter.

38. The method of claim 36, further comprising the step of receiving a signal from a computer to start said method before covering said lens of said infrared detector.

39. The method of claim 36, wherein said lamp and said infrared detector are on the same side of said sample.

40. The method of claim 39, wherein a second lamp resides on said same side of said sample as said first lamp and said infrared detector, said second lamp firing to heat said sample at the same time as the step of covering said lens with said shutter, both said first lamp and said second lamp being pointed at a same surface of said sample as said infrared detector.

41. The method of claim 40, wherein one electronic input signal is input from a computer having a central processing unit that generates two electronic outputs, the first output signal for operating said shutter, the second output signal for triggering the firing of flashes from both said lamps simultaneously.

42. The method of claim 36, wherein said lamp is on an opposite side of said sample from said infrared detector.

43. The method of claim 36, wherein said lamp has a duration of firing of approximately 0.008 seconds to raise a temperature of said sample approximately 10 degrees Celsius above an ambient temperature.

44. The method of claim 36, wherein said temperature measurements comprise a plurality of temperature images of said sample over time, said method further comprising the step of creating a processed image from said plurality of temperature images by a method selected from the group consisting of curve fitting for thermal diffusivity, time derivative calculations, normalization data reduction routine, and averaging.

45. An apparatus for thermally inspecting a sample of a material, comprising:

an infrared detector having a lens pointed at a surface of said sample;

means for heating said sample to a temperature above an ambient temperature;

a shutter to cover and uncover said lens of said infrared detector;

shutter electronics, operatively connected to said shutter, for controlling synchronization of the opening and closing of said shutter and a timing of a firing of said means for heating; and

a computer, electrically connected to said shutter electronics, for generating a trigger signal to initiate a thermal inspection process.

46. The apparatus of claim 45, wherein said means for heating is a flash heat lamp.

47. The apparatus of claim 46, further comprising a second flash heat lamp that fires in tandem with said first flash lamp.

48. The apparatus of claim 47, wherein said first and second flash heat lamps are both pointed at the same surface of said sample as said lens.

49. The apparatus of claim 45, wherein said shutter electronics cause said shutter to cover said infrared detector lens during said time of firing of said means for heating.

50. The apparatus of claim 45, wherein said shutter electronics cause said shutter to open after said time of firing said means for heating to enable said infrared detector to detect the infrared energy emanating from said heated sample.

51. The apparatus of claim 45, wherein said means for heating is pointed at a surface of said sample that is opposite to the surface said lens is pointed towards.

52. The apparatus of claim 45, wherein said shutter electronics comprise a pair of dual monostable multivibrators.

53. The apparatus of claim 52, wherein each one of said pair of dual monostable multivibrators comprise Schmitt-trigger inputs.

54. The apparatus of claim 45, wherein said computer collects a plurality of temperature images of said sample taken over time by said infrared detector, said plurality of temperature images being used to construct a processed image by using a method selected from the group consisting of curve fitting for thermal diffusivity, time derivative calculations, normalization data reduction routine, and averaging.

55. A method for thermally inspecting a thin sample having a first surface and a second surface opposite to said first surface, said method comprising the steps of:

pointing an infrared detector having a lens at said first surface of said thin sample to measure reference infrared radiation emanating from said first surface when said sample is at an ambient temperature;

covering said lens with a shutter;

firing a lamp that is pointed at said sample to heat said sample to a temperature above said ambient temperature;

opening said shutter to said lens of said infrared detector;

acquiring a plurality of temperature images of said sample over time by using said infrared detector; and

producing a processed image from said plurality of temperature images.

56. The method of claim 55, wherein said processed image indicates a location where said first surface has a defect.

57. The method of claim 55, wherein said processed image is formed by a normalization data reduction routine performed on said plurality of temperature images and wherein said lamp is on a same side of said sample as said infrared detector.

58. The method of claim 57, further comprising the step of pointing said lamp at said first surface of said sample.

59. The method of claim 58, further comprising the step of pointing a second lamp toward said first surface, said second lamp being fired at the same time said first lamp is fired.

60. The method of claim 55, wherein said processed image is formed by curve fitting said plurality of temperature images to a theoretical model for thermal diffusivity.

61. The method of claim 55, wherein said processed image is formed by applying a temperature normalization data reduction routine to said plurality of temperature images.

62. The method of claim 55, wherein said lamp is pointed at said second surface of said sample.

63. The method of claim 55, wherein said step of firing said lamp lasts for a duration of approximately 0.008 seconds and heats said sample approximately 10 degrees Celsius above said ambient temperature.

64. An apparatus for thermally inspecting a thin sample having a first surface and a second surface opposite to said first surface, comprising:

an infrared detector having a lens pointed at said first surface;

a shutter to cover and uncover said lens of said infrared detector;

a lamp for heating said thin sample, said lamp having a reflector that is pointed at said sample, said lamp being pointed at one of said first surface and said second surface of said thin sample; and

shutter electronics, electrically connected to said shutter and said lamp, for synchronizing the opening and closing of said shutter with a firing of said lamp such that said shutter covers said lens of said infrared detector during the time of firing of said lamp and said shutter opens when said lamp is not fired to enable thermal inspection of said sample.

65. The apparatus of claim 64, wherein said shutter electronics comprise a pair of dual monostable multivibrators with Schmitt-trigger inputs.

66. The apparatus of claim 64, said lamp being pointed at said second surface.

67. The apparatus of claim 64, further comprising a second lamp being pointed at said first surface, said first lamp also being pointed at said first surface.

68. The apparatus of claim 64, further comprising a computer electrically connected to both an image processor and said shutter electronics, said computer actuating a trigger signal from said shutter electronics to fire said lamp, said image processor receiving a plurality of temperature images of said sample taken over time by said infrared detector and applying one of a curve fitting routine for thermal diffusivity, a time derivative calculation, a normalization data reduction routine, and an averaging routine to produce a processed image that has the capability of illustrating locations of defects on said sample.