System and process for detecting and monitoring surface defects

• US 5,359,416 A
• Filed: 10/19/1992
• Issued: 10/25/1994
• Est. Priority Date: 10/19/1992
• Status: Expired due to Fees

• Current Assignee: Alliant Techsystems Incorporated (Northrop Grumman Corporation)
• Original Assignee: Thiokol Corporation (Howmet Aerospace, Inc.)
• Inventors: Mueller, Mark K.
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US07/963,572
• Time in Patent Office: 736 Days
• Field of Search: 356/371, 356/237, 356/446, 250/562, 250/572
• US Class Current: 356/600
• CPC Class Codes: G01N 2021/8864 Mapping zones of defects
• CPC Class Codes: G01N 2021/8887 based on image processing techniques
• CPC Class Codes: G01N 2021/9518 using a surface follower, e.g. robot
• CPC Class Codes: G01N 21/9515 Objects of complex shape, e.g. examined with use of a surface follower device measuring contours and curvatures G01B11/24
• CPC Class Codes: G01N 2201/102 Video camera
• CPC Class Codes: G01N 2201/1085 Using optical fibre array and scanner

Abstract

A system and process for detecting and monitoring defects in large surfaces such as the field joints of the container segments of a space shuttle booster motor. Beams of semi-collimated light from three non-parallel fiber optic light panels are directed at a region of the surface at non-normal angles of expected incidence. A video camera gathers some portion of the light that is reflected at an angle other than the angle of expected reflectance, and generates signals which are analyzed to discern defects in the surface. The analysis may be performed by visual inspection of an image on a video monitor, or by inspection of filtered or otherwise processed images. In one alternative embodiment, successive predetermined regions of the surface are aligned with the light source before illumination, thereby permitting efficient detection of defects in a large surface. Such alignment is performed by using a line scan gauge to sense the light which passes through an aperture in the surface. In another embodiment a digital map of the surface is created, thereby permitting the maintenance of records detailing changes in the location or size of defects as the container segment is refurbished and re-used. The defect detection apparatus may also be advantageously mounted on a fixture which engages the edge of a container segment.

Claims

1. A process for detecting defects in a surface, comprising the steps of:

positioning a light source relative to the surface;

generating positional information about the position of the light source relative to the surface by using positioning indicia located on the surface;

directing a plurality of beams of light from the light source onto a region of the surface;

detecting a portion of the light which is reflected from the surface at an angle other than the angle of expected reflectance;

generating reflectance information corresponding to the light detected during said detecting step; and

analyzing the reflectance information and the positional information to discern and identify the location of defects in the surface.

2. The process of claim 1, further comprising maintaining a record of surface defects discerned during said analyzing step.

3. The process of claim 1, further comprising the steps of repositioning the light source relative to the surface such that the beams of light may be directed onto a different region of the surface and repeating the preceding steps whereby defects in multiple regions of the surface may be detected.

4. The process of claim 3, wherein said repositioning step further comprises:

sensing a portion of light which passes through an aperture in the surface, said sensing being performed by a light sensor;

generating aperture-positional signals corresponding to the light sensed during said sensing step; and

analyzing the aperture-positional signals to determine the present position of the light sensor relative to the aperture.

5. The process of claim 4, wherein said sensing step comprises introducing a portion of light which passes through the aperture in the surface into a line scan gauge.

6. The process of claim 1, wherein said directing step comprises directing a plurality of beams of light at non-normal angles of expected incidence onto a region of the surface.

7. The process of claim 6, wherein said directing step includes directing beams of light which are arranged in at least two groups, with each group positioned in a substantially non-parallel relationship with at least one other such group.

8. The process of claim 6, wherein said detecting step comprises introducing a portion of the reflected light into a video camera.

9. The process of claim 6, wherein said analyzing step comprises processing the reflectance information by computer.

10. The process of claim 6, wherein said step of generating reflectance information comprises introducing signals into an output device producing a human-readable form of output.

11. A process for detecting defects in a surface, comprising the steps of:

positioning a light source relative to the surface;

directing semi-collimated light generated by the light source at non-normal angles of expected incidence onto a region of the surface;

generating positional information about the position of the light source relative to the surface by using positioning indicia located on the surface;

detecting a portion of the light which is reflected from the surface at an angle other than the angle of expected reflectance;

generating signals which correspond to the light detected during said detecting step;

filtering the signals generated during said generating step through a noise filter to produce arithmetic filter outputs;

analyzing the arithmetic filter outputs to discern defects in the surface; and

analyzing the positional information to identify the location of defects in the surface.

12. A system for detecting defects in a surface, comprising:

a light source capable of directing a plurality of beams of light onto a region of the surface;

a positioning indicia locator in communication with said light source, said positioning indicia locator capable of determining the position of said light source relative to positioning indicia located on the surface;

a light detector capable of detecting light reflected from the surface and of generating signals corresponding to the presence of such reflected light;

a reflectance signal convertor in communication with said light detector, said convertor capable of converting the signals generated by said light detector into analyzable reflectance signals; and

an analyzer in communication with said reflectance signal convertor, said analyzer capable of analyzing the analyzable reflectance signals to discern defects in the surface.

13. The system of claim 12, further comprising a positioning apparatus capable of altering the position of the surface relative to said light source such that defects in multiple regions of the surface may be detected.

14. The system of claim 12, wherein said positioning indicia locator comprises:

a light sensor capable of sensing a portion of light which passes through an aperture in the surface, and of generating signals corresponding to the presence of such sensed light;

a surface position analyzer in communication with said light sensor capable of analyzing the aperture-positional signals to determine the present position of said light sensor relative to the aperture.

15. The system of claim 14, wherein said light sensor comprises a line scan gauge.

16. The system of claim 12, further comprising a record-keeping apparatus in communication with said analyzer, said record-keeping apparatus capable of maintaining a record of surface defects discerned by said analyzer.

17. The system of claim 12, wherein said light source is further configured to direct a plurality of beams of light at non-normal angles of expected incidence onto a region of the surface.

18. The system of claim 12, wherein said light source comprises more than one light source positioned to generate beams of light, said light sources positioned such that the beams of light are arranged in at least two groups, with each group positioned in a substantially non-parallel relationship with at least one other such group.

19. The system of claim 12, wherein said light detector comprises a video camera.

20. The system of claim 12, wherein said analyzer comprises a computer.

21. The system of claim 12, wherein said reflectance signal convertor comprises an output device producing a human-readable form of output.

22. The system of claim 12, further comprising a mounting fixture for use in inspecting regions on the surface of a substantially cylindrical member, said mounting fixture including a chord beam configured to slidably engage an edge of the cylindrical member.

23. The system of claim 22, wherein said mounting fixture further comprises compensation means permitting full rotation of said fixture when said fixture is engaged with the edge of a cylindrical member which is not perfectly circular.

24. A system for detecting defects in a surface, comprising:

a light capable of directing semi-collimated light at non-normal angles of expected incidence onto a region of the surface;

a positioning indicia locator in communication with said light source, said positioning indicia locator capable of determining the position of said light source relative to positioning indicia located on the surface;

a light detector capable of detecting a portion of the light which is reflected from the surface at an angle other than the angle of expected reflectance and of generating signals which correspond to such detected light;

a noise filter capable of filtering the signals generated by said light detector to produce arithmetic filter outputs; and

an analyzer capable of analyzing the arithmetic filter outputs to discern defects in the surface.

25. The system of claim 24, wherein said light source comprises at least one fiber optic light panel.

26. The system of claim 24, wherein said analyzer comprises a defect locator capable of determining the location of a detected defect relative to a predetermined point on the surface.

27. The system of claim 24, wherein said analyzer comprises an estimator capable of determining the location and extent of a detected surface defect.

28. The system of claim 24, wherein said convertor comprises an output device producing a human-readable form of output.