System or method for detecting defect within a semi-opaque enclosure

• US 6,134,343 A
• Filed: 04/07/1999
• Issued: 10/17/2000
• Est. Priority Date: 09/24/1996
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Nichani, Sanjay
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Dang, Duy M.
• Application Number:
  US09/287,352
• Time in Patent Office: 559 Days
• Field of Search: 382/141-143, 382/147-149, 382/176, 382/194, 382/270, 382/294, 382/224, 382/180, 348/87, 348/92, 348/127, 356/237, 250/223.13, 250/219, 250/559.05
• US Class Current: 382/141
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G01N 21/909 in opaque containers or opaque container parts, e.g. cans, tins, caps, labels
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80

Abstract

A method and system detect for the presence of a defect or a non-conforming object of unknown shape, configuration, and location within a semi-opaque enclosure. The semi-opaque enclosure has a pattern which is visible on at least a first of its external surfaces. The semi-opaque enclosure may comprise, for example, a labeled plastic or glass bottle, and the visible pattern may be print and graphical information provided on the bottle'"'"'s label. A first digital image is captured from first channel light reflected off the first external surface of the enclosure; and a second digital image is captured from second channel light navigating the object inside the enclosure and emanating from the first external surface of the enclosure. A difference image is formed substantially devoid of information representing the visible pattern on the first external surface, by subtracting one of the first and second digital images from the other. Additional segmentation processing may be performed on the difference image in order to better identify the presence of a defect or non-conforming object within the semi-opaque enclosure.

Claims

1. A method for detecting an object located within a semi-opaque enclosure having a semi-opaque first side portion having first internal and external surfaces and a semi-opaque second side portion having second internal and external surfaces, said first side portion being different from and opposing said second side portion, said first external surface having a pattern visible externally to said enclosure, said object being located between said first and second side portions, said method comprising:

directing first channel light toward and onto said first external surface of said semi-opaque enclosure;

capturing, from portions of said first channel light reflected off said first external surface but not having passed through said first internal surface, a first digital image comprising data representing said pattern;

directing second channel light toward and onto said object and toward and onto said first side portion of said enclosure;

capturing, from portions of said second channel light emanating from said first external surface after first traveling along side and around said object inside said enclosure and passing through said first internal surface, a second digital image comprising a silhouette of said object; and

forming a difference image representing the object and substantially devoid of information representing said visible pattern by subtracting one of said first and second digital images from the other.

2. The method according to claim 1, further comprising generating said first channel light with front lighting.

3. The method according to claim 2, further comprising generating said second channel light with back lighting.

4. The method according to claim 1, further comprising generating said first channel light by directing first light from a location external said enclosure toward and onto said first external surface, whereby said first light hits said first external surface before passing through said first internal surface, said first light being generally orthogonal to said first external surface.

5. The method according to claim 4, further comprising generating said second channel light by directing second light from a location external said enclosure toward and onto said second external surface, whereby said second light hits said second external surface before passing through said second internal surface, said second light being generally orthogonal to said second external surface.

6. A method for detecting an object of unknown shape, configuration, and location on an inner wall surface of a rigid semi-opaque enclosure having a semi-opaque first side portion having first internal and external surfaces and a semi-opaque second side portion having second internal and external surfaces, said first side portion being different from and opposing said second side portion, said first external surface having a pattern visible externally to said enclosure, said method comprising:

directing first channel light toward and onto said first external surface of said semi-opaque enclosure;

capturing, from portions of said first channel light reflected off said first external surface but not having passed through said first internal surface, a first digital image comprising data representing said pattern;

directing second channel light toward and onto said object and toward and onto said first side portion of said enclosure;

capturing, from portions of said second channel light emanating from said first external surface after first traveling along side and around said object inside said enclosure and then passing through said first internal surface, a second digital image comprising a silhouette of said object; and

forming a difference image representing said object and substantially devoid of information representing said visible pattern by subtracting one of said first and second digital images from the other.

7. The method according to claim 6, wherein said rigid semi-opaque enclosure comprises a bottle and a semi-opaque label attached to and covering a substantial portion of an outer side-wall surface of said bottle, said substantial portion of said outer side-wall surface including said first external surface.

8. The method according to claim 7, further comprising generating said first channel light with front lighting.

9. The method according to claim 8, further comprising generating said second channel light with back lighting.

10. The method according to claim 7, further comprising generating said first channel light by directing first light from a location external said enclosure toward and onto said first external surface, whereby said first light hits said first external surface before passing through said first internal surface, said first light being generally orthogonal to said first external surface.

11. The method according to claim 10, further comprising generating said second channel light by directing second light from a location external said enclosure toward and onto said second external surface, whereby said second light hits said second external surface before passing through said second internal surface, said second light being generally orthogonal to said second external surface.

12. The method according to claim 10, further comprising generating said second channel light with back lighting.

13. The method according to claim 7, further comprising generating said second channel light by directing second light from a location external said enclosure toward and onto said second external surface, whereby said second light hits said second external surface before passing through said second internal surface, said second light being generally orthogonal to said second external surface.

14. The method according to claim 7, wherein said step of forming a difference image comprises subtracting said second digital image from said first digital image.

15. The method according to claim 7, wherein said first and second digital images comprise two-dimensional gray level images represented with respective two-dimensional light intensity function f₁ (x, y) and f₂ (x, y), wherein x and y denote spatial coordinates and f₁ and f₂ are values proportional to the gray level of the respective image at a point x, y.

16. The method according to claim 15, wherein said different image comprises a two-dimensional gray level image, said method further comprising performing a resegmentation operation on said difference image, said resegmentation operation comprising forming a two-dimensional binary image from said difference image.

17. The method according to claim 16, wherein said forming of a two-dimensional binary image from said difference image comprises performing a thresholding operation on said difference image, said thresholding operation comprising forming a two-dimensional binary thresholded image g (x, y) in accordance with the following:

##EQU1## where x and y are spatial coordinates of a point (x, y) of said difference image, d (x, y) is the gray level of said point (x, y), and p (x, y) is a local threshold control variable corresponding to said point (x, y).

18. The method according to claim 17, wherein p (x, y) represents a gray level local threshold image defined as a function of at least one of said first and second digital images f₁ (x, y) and f₂ (x, y).

19. A system for detecting an object of unknown shape, configuration, and location within a semi-opaque enclosure having a semi-opaque first side portion having first internal and external surfaces and a semi-opaque second side portion having second internal and external surfaces, said first side portion being different from and opposing said second side portion, said first external surface having a pattern visible externally to said enclosure, said object being located between said first and said second side portions, said system comprising:

a first light director directing first channel light toward and onto said first external surface of said enclosure;

a first image acquisition subsystem capturing, from portions of said first channel light reflected off said first external surface but not having passed through said first internal surface, a first digital image comprising data representing said pattern;

a second light director directing second channel light toward and onto said object and said first side portion of said enclosure;

a second image acquisition subsystem capturing, from portions of said channel light emanating from said first external surface after first traveling along side and around said object inside said enclosure and then passing through said first internal surface, a second digital image comprising a silhouette of said object; and

a processor for forming a difference image representing said object and substantially devoid of information representing said visible pattern by subtracting one of said first and second digital images from the other.

20. The system according to claim 19, wherein said rigid semi-opaque enclosure comprises a bottle and a semi-opaque label attached to and covering a substantial portion of an outer side-wall surface of said bottle, said substantial portion of said outer side-wall surface including said first external surface.

21. The system according to claim 20, wherein said first light director comprises a front light for generating said first channel light.

22. The system according to claim 20, wherein said first light director comprises a first light directed from a location external said enclosure toward and onto said first external surface, whereby said first light hits said first external surface before passing through said first internal surface, said first light directing light in a direction generally orthogonal to said first external surface.

23. The system according to claim 21, wherein said second light director comprises a back light generating said second channel light.

24. The system according to claim 22, wherein said second light director comprises a second light directed from a location external said enclosure toward and onto said second external surface, whereby said second light hits said second external surface before passing through said second internal surface, said second light directing light generally orthogonal to said second external surface.

25. The system according to claim 20, further comprising a vision control and processing computer system, said processor being included in said vision control and processing computer system.

26. The system according to claim 25, wherein said vision control and processing computer system comprises a central processing unit, at least one co-processor, a computer memory device, and an image digitizing device.