Method and apparatus for verifying two dimensional mark quality

• US 8,108,176 B2
• Filed: 06/29/2006
• Issued: 01/31/2012
• Est. Priority Date: 06/29/2006
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Nadabar, Sateesha, Gopalakrishnan, Venkat K., Gerst, Carl W.
• Primary Examiner(s): Lau, Tung S
• Application Number:
  US11/427,420
• Publication Number:
  US 20080004822A1
• Time in Patent Office: 2,042 Days
• Field of Search: 702/150
• US Class Current: 702/150
• CPC Class Codes: G06K 5/00 Methods or arrangements for verifying the correctness of markings on a record carrier; Column detection devices

Abstract

A method and system for applying a two dimensional mark on a first surface of a component and assessing mark quality, the method including the steps of positioning a component with a first surface at a first station, applying a two dimensional mark to the first surface at the first station wherein the applied mark is intended to codify a first information subset, obtaining an image of the applied two dimensional mark at the first station, performing a mark quality assessment on the obtained image and performing a secondary function as a result of the mark quality assessment.

Claims

1. A method for applying a two dimensional mark on a first surface of a component and assessing mark quality, the method comprising the steps of:

positioning a component with a first surface in a first position at a first station;

applying a two dimensional mark to the first surface at the first station wherein the applied mark is intended to codify a first information subset;

obtaining an image of the applied two dimensional mark while the component remains in the first position at the first station;

performing a mark quality assessment on the mark in the obtained image; and

performing a secondary function as a result of the mark quality assessment.

2. The method of claim 1 wherein the step of performing a mark quality assessment includes attempting to decode the image of the mark and when the image is successfully decoded, gleaning other mark quality characteristics from the mark in the obtained image.

3. The method of claim 1 wherein the step of performing a mark quality assessment includes attempting to decode the image of the mark and when the image is successfully decoded, unwarping the mark to at least in part compensate for mark distortion thereby generating an unwarped mark, gleaning mark quality characteristics from the unwarped mark, generating an applied mark quality value as a function of the gleaned characteristics from the unwarped mark and comparing the applied mark quality value to a baseline assessment value, the secondary function including, when the applied mark quality value is below the baseline value, indicating a low mark quality level.

4. The method of claim 1 wherein the step of performing a mark quality assessment on the obtained image includes decoding the mark in the obtained image, using the decoded information to generate a synthetic mark model, using the mark model and the mark in the obtained image to generate a difference map and using the difference map to compensate the mark obtained in the image for at least a subset of non-optimal lighting, first surface warping, lens/optical distortion, perspective distortion, and perceived background texture.

5. The method of claim 1 wherein the step of obtaining an image includes providing a stationary camera at the first station that has a field of view that is centered along a trajectory that forms an obtuse angle with at least a portion of the first surface.

6. The method of claim 1 wherein the step of obtaining an image includes using a reader to obtain the image, and wherein the reader includes a fixed mount reader.

7. The method of claim 2 wherein the step of gleaning other mark quality characteristics includes gleaning at least a subset of geometric characteristics of the mark, mark size, mark color, mark shading, symbol contrast, axial non-uniformity of the mark, grid non-uniformity of the mark, extreme reflectance, angle of distortion, dot diameter, dot ovality, dot position, image sharpness and background uniformity.

8. The method of claim 2 wherein the step of gleaning other mark quality characteristics includes obtaining information from the mark in the obtained image indicative of the degree of at least one irregularity in the obtained image the step of performing a mark quality assessment further including, where the degree of the at least one irregularity in the image exceeds a tolerable level, at least in part compensating for the irregularity thereby generating a compensated mark, gleaning mark quality characteristics from the compensated mark and generating an applied mark quality value as a function of the gleaned characteristerics from the compensated mark.

9. The method of claim 2 wherein the step of gleaning other mark quality characteristics includes obtaining information from the mark in the obtained image indicative of the degree of at least one irregularity in the obtained image and., when the degree of the at least one irregularity exceeds a tolerable level, providing a feedback signal indicating that the degree or irregularity is intolerale.

10. The method of claim 3 wherein the step of unwarping the mark thereby generating an unwarped mark includes using the decoded information from the mark to generate a synthetic mark model, comparing the synthetic mark model to the mark in the obtained image to generate a deformation map and unwarping the mark using the deformation map to generate the unwarped mark.

11. The method of claim 4 wherein the step of using decoded information to generate a mark model includes using the decoded information as well as known characteristics of the mark to generate the mark model.

12. The method of claim 4 wherein the step of generating a mark model includes generating a mark model corresponding to the specific data decoded from the imaged mark.

13. The method of claim 5 wherein the step of providing a camera includes positioning the camera so that the field of view is centered along a trajectory that forms an obtuse angle with a central portion of the first surface.

14. The method of claim 8 wherein the step of performing a mark quality assessment further includes comparing the applied mark quality value to a baseline assessment value, the secondary function including, when the applied mark quality value is below the baseline value, indicating a low mark quality level.

15. The method of claim 8 wherein the first surface may be warped, the at least one irregularity including at least a subset of non-optimal lighting, first surface warping, lens/optical distortion, perspective distortion, and perceived background texture.

16. The method of claim 8 wherein the at least one irregularity is geometric distortion, the step of compensating including using the decoded information to generate a synthetic mark model and using the mark model to compensate for the geometric distortion.

17. The method of claim 14 wherein the secondary function further includes, when the applied mark quality value is at least equal to the baseline value, indicating a high mark quality level.

18. The method of claim 16 further including the step of providing known mark characteristics, the step of generating a synthetic mark model including using both the provided known mark characteristics and the decoded information.

19. The method of claim 16 wherein the step of using the mark model includes using the mark model and the mark in the obtained image to generate a difference map and using the difference map to compensate for the irregularity in the mark in the obtained image.

20. A method for assessing quality of a two dimensional mark that is applied to a first surface, the method comprising the steps of:

obtaining an image of the applied two dimensional mark;

decoding the mark in the obtained image to generate a first information subset wherein the first information subset includes the actual information coded by the mark;

using the first information subset to generate a synthetic mark model;

comparing the synthetic mark model to the mark in the obtained image to generate a difference map;

using the difference map to at least in part compensate for at least one irregularity in the mark in the obtained image thereby generating a compensated mark; and

assessing, with a processor, the quality of the compensated mark.

21. The method of claim 20 wherein the step of using decoded information to generate a mark model includes using the decoded information as well as known characteristics of the mark to generate the mark model.

22. The method of claim 20 wherein the step of generating a mark model includes generating the mark model corresponding to specific data decoded from the imaged mark.

23. The method of claim 20 wherein the step of obtaining an image includes using a reader to obtain the image, and wherein the reader includes a fixed mount reader.

24. A method for applying a two dimensional mark on a first surface of a component and assessing mark quality, the method comprising the steps of:

positioning a component with a first surface in a first position at a first station;

applying a two dimensional mark to the first surface at the first station wherein the applied mark is intended to codify a first information subset;

obtaining an image of the applied two dimensional mark while the component remains in the first position at the first station;

performing, with a processor, a mark quality assessment on the mark in the obtained image; and

providing a signal to an external device.

25. The method of claim 24 wherein the step of performing a mark quality assessment includes attempting to decode the image of the mark and when the image is successfully decoded, gleaning other mark quality characteristics from the mark in the obtained image.

26. The method of claim 24 wherein the step of obtaining an image includes using a reader to obtain the image, and wherein the reader includes a fixed mount reader.