Non-destructive testing by laser scanning

• US 4,824,250 A
• Filed: 05/05/1988
• Issued: 04/25/1989
• Est. Priority Date: 11/17/1986
• Status: Expired due to Fees

• Current Assignee: John W. Newman
• Original Assignee: John W. Newman
• Inventors: Newman, John W.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Pascal, Robert J.
• Application Number:
  US07/191,744
• Time in Patent Office: 355 Days
• Field of Search: 356/32, 356/35.5, 356/237, 356/345, 250/562, 250/563, 250/572, 73/577, 73/578, 73/588, 73/598, 73/655, 73/657
• US Class Current: 356/502
• CPC Class Codes: G01N 2021/1759 Jittering, dithering, optical path modulation
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G01N 2201/104 Mechano-optical scan, i.e. object and beam moving

Abstract

The invention provides a method and apparatus for non-destructive testing of bonded structures, such as laminated or composite materials. A beam of coherent light is directed successively onto each point of the object. The reflected beam creates a speckle pattern. The pattern is observed once while the object is stationary and once while the object is mechanically excited. If the point being observed is free of defects, the speckle pattern will be substantially unaffected by the vibration of the excited object. If the point is defective, vibration will blur the speckle pattern. The entire object is scanned, point by point, and the results of the comparison of the speckle patterns obtained for each point are stored and displayed. In another embodiment, the object is made to vibrate continuously, and the apparatus determines whether the speckle pattern is sharp or blurred, for each point being scanned. The sharpness of the speckle pattern can be inferred from the measured intensity of the speckle pattern, or it can be calculated directly by a suitable algorithm. In general, if the detector has a nonlinear response characteristic, the total intensity of the speckle pattern will be lower when the pattern is blurred, and higher when the pattern is sharp. A low intensity therefore indicates that the point on the object is defective. As in the first embodiment, the results of the analysis are stored in a computer memory and displayed on a video monitor.

Claims

1. A system for non-destructive testing of an object, comprising:

(a) means for holding the object,

(b) means for vibrating the object, the vibrating means being connected to the holding means,

(c) means for directing a beam of coherent light onto a predetermined point on the object, so as to form a reflection pattern,

(d) means for detecting the reflection pattern obtained from the object,

(e) control means, the control means being adapted to energize and de-energize the vibrating means, and to control the beam directing means, wherein successive points on the object can be scanned by the beam, the control means being programmed to energize and de-energize the vibrating means while the beam is directed towards each point on the object, and

(f) display means for indicating, for each point on the object, the difference between the reflection pattern when the object is vibrating and when the object is stationary.

2. The system of claim 1, wherein the control means is a computer.

3. The system of claim 2, wherein the display means is a video monitor.

4. The system of claim 3, wherein the vibrating means includes a white noise generator and a piezoelectric shaker.

5. The system of claim 4, wherein the detecting means comprises an array of photodiodes.

6. The system of claim 5, wherein the directing means comprises at least one mirror for deflecting the beam.

7. A system for non-destructive testing of an object, comprising:

(a) means for vibrating the object, the vibrating means being connected to the object,

(b) means for directing a beam of coherent light onto a predetermined point on the object, so as to form a reflection pattern,

(c) means for detecting the reflection pattern obtained from the object,

(d) control means, the control means being adapted to actuate and deactuate the vibrating means, and to control the beam directing means, wherein successive points on the object can be scanned by the beam, the control means being programmed to actuate and deactuate the vibrating means while the beam is directed towards each point on the object, and

(e) display means for indicating, for each point on the object, the difference between the reflection pattern when the object is vibrating and when the object is not vibrating.

8. A system for non-destructive testing of an object, comprising:

(a) means for directing a beam of coherent light at a predetermined point on the object,

(b) means for detecting the intensity of the light reflected from the object,

(c) means for vibrating the object, the vibrating means comprising means for inducing vibrations having frequency components distributed across a wide bandwidth, and

(d) means for controlling the directing means and the vibrating means, such that the beam is successively directed onto a plurality of points on the object, and such that the beam is directed towards a particular point both while the object is vibrating and while the object is not vibrating.

9. The system of claim 8, wherein the controlling means is a computer, the computer being programmed to store information obtained from the detecting means when the object is vibrating and when the object is not vibrating.

10. The system of claim 8, wherein the vibrating means includes means for adjusting the amount of vibrational energy imparted to the object.

11. The system of claim 10, wherein the ibrating means includes a white noise generator.

12. The system of claim 8, wherein the detecting means includes an array of photo-diodes.

13. The system of claim 8, further comprising relay means for actuating the vibrating means.

14. A method for non-destructive testing of an object, comprising the steps of:

(a) directing a beam of coherent light at a point on the object, while the object is not vibrating,

(b) measuring the intensity of the light reflected from the non-vibrating object,

(c) directing a beam of coherent light at the same point on the object, while the object is vibrating, the object being made to vibrate by a vibrating means which contacts the object,

(d) measuring the intensity of the light reflected from the vibrating object,

(e) comparing the intensity of the light reflected from the object when the object is vibrating and when it is not vibrating, and

(f) repeating the above steps for each point on the object.

15. The method of claim 14, wherein each of the measuring steps comprises the step of observing a speckle pattern produced by the reflected light.

16. The method of claim 15, wherein the comparing step comprises comparing the intensity of each point on each speckle pattern produced.

17. The method of claim 14, further comprising the step of storing the results of each comparing step in the memory of a computer.

18. The method of claim 14, further comprising the step of displaying the results of each comparing step on a video monitor means.

19. The method of claim 18, wherein the comparing step includes the step of determining the amount by which the intensities of the light differ, and wherein the displaying step comprises the step of displaying a colored pixel corresponding to said amount.

20. A method for non-destructive testing of an object, comprising the steps of:

(a) directing a beam of coherent light at a point on the object while the object is stationary,

(b) measuring the intensity of the light reflected from the stationary object,

(c) vibrating the object, while directing a beam of coherent light at the same point on the object, the vibrating step being performed with a vibrating means which is in contact with the object,

(d) measuring the intensity of the light reflected from the vibrating object,

(e) comparing the intensity of the light reflected from the object when the object is vibrating and when it is not vibrating, and

(f) repeating the above steps for each point on the object.

21. A method for non-destructive testing of an object, comprising the steps of:

(a) directing a beam of coherent light at a point on the object, while the object is not vibrating,

(b) measuring the intensity of the light reflected from the non-vibrating object,

(c) directing a beam of coherent light at the same point on the object, while the object is vibrating, the object being made to vibrate by a vibrating means which contacts the object,

(d) measuring the intensity of the light reflected from the vibrating object, and

(e) comparing the intensity of the light reflected from the object when the object is vibrating and when it is not vibrating.

22. The method of claim 21, wherein each of the measuring steps comprises the step of observing a speckle pattern produced by the reflected light.

23. The method of claim 22, wherein the comparing step comprises comparing the intensity of each point on each speckle pattern produced.

24. A method for non-destructive testing of an object, comprising the steps of:

(a) subjecting the object to continuous vibration, the object being made to vibrate by a vibrating means which contacts the object,

(b) directing a beam of coherent light onto a point on the vibrating object,

(c) detecting a speckle pattern formed by the reflection of said beam of coherent light, from each point on the object,

(d) measuring the sharpness of the speckle pattern, and

(e) repeating the directing, detecting, and measuring steps for each point on the object.

25. The method of claim 24, wherein the detecting step comprises using a detector array having a nonlinear response characteristic, and wherein the measuring step comprises the step of measuring the intensity of the speckle pattern.

26. The method of claim 24, wherein the measuring step includes the step of displaying a pixel on a video monitor, the color of the pixel corresponding to the level of measured sharpness of the speckle pattern for a given point on the object.

27. A method for non-destructive testing of an object, comprising the steps of:

(a) subjecting the object to continuous vibration, the object being made to vibrate by a vibrating means which contacts the object,

(b) directing a beam of coherent light at a point on the vibrating object,

(c) detecting a speckle pattern formed by the reflection of said beam of coherent light, and

(d) measuring the sharpness of the speckle pattern.

28. The method of claim 27, wherein the directing, detecting, and measuring steps are performed repeatedly for each point on the object.

29. The method of claim 28, wherein the measuring step comprises the step of determining the intensity of the speckle pattern.

30. The method of claim 28, wherein the measuring step is followed by the step of displaying a pixel on a video monitor, the color of the pixel corresponding to the level of measured sharpness of the speckle pattern for a given point on the object.

31. The method of claim 30, further comprising the step of storing the information on the sharpness of the speckle pattern, for each point on the object, in the memory of a computer.