System and method for employing color illumination and color filtration in a symbology reader

• US 8,061,610 B2
• Filed: 10/24/2005
• Issued: 11/22/2011
• Est. Priority Date: 10/24/2005
• Status: Active Grant

• Current Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Original Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Inventors: Nunnink, Laurens
• Primary Examiner(s): HESS, DANIEL A
• Application Number:
  US11/257,410
• Publication Number:
  US 20070091332A1
• Time in Patent Office: 2,220 Days
• Field of Search: 235/454, 235/462.01, 235/462.24, 358/3.01, 358/518
• US Class Current: 235/454
• CPC Class Codes: G06K 7/10732 Light sources

Abstract

This invention provides a system and method for employing and analyzing images that are illuminated in different colors depending upon the type of illumination being employed. In an illustrative embodiment, a color image sensor is used to acquire images of subjects of interest, and each of the direct bright field, dark field and diffuse illumination are transmitted to the surface simultaneously (concurrently with each other) in a discrete illumination color that is discretely discernable by the sensor. For example, direct bright field and dark field may be red, while diffuse may be blue. Pixels of the same sensitivity (for example, red and blue) in the image sensor receive only the image generated by that color of illumination. The reader of this invention includes processing components that independently assemble images from red and blue pixel addresses to create, in effect two simultaneous images (one image generated using a combination dark field and direct bright field and the other image generated using diffuse illumination) that overlap (are registered with respect to each other) perfectly. The best image is determined using conventional image analysis tools, and meaningful data (the code of the read symbol, for example) is derived from that best image.

Claims

1. A system for scanning a surface comprising:

an imager having image sensor pixels that each acquire images in each of at least a first image color and a second image color;

a focuser that varies focus of the imager with respect to the surface;

an illumination assembly constructed and arranged to simultaneously provide a first illumination type in a first illumination color recognized by the imager as the first image color and a second illumination type in a second illumination color recognized by the imager as the second image color, and a focus pattern, projected on the surface, in a focus illumination color recognized by the imager as the focus image color; and

a focus process that reads image pixel data from the imager in the focus illumination color and that controls the focuser based upon the image pixel data in the focus illumination color.

2. The system as set forth in claim 1 wherein the first illumination type comprises dark field illumination and the second illumination type comprises direct diffuse illumination.

3. The system as set forth in claim 2 wherein the illumination assembly includes a light pipe having a chamfered end that projects the first illumination color onto the surface and a diffuser mounted within the light pipe that projects the second illumination color onto the surface.

4. The system as set forth in claim 3 wherein the diffuser includes an optical filter that prevents reflection therefrom of the first illumination color.

5. The system as set forth in claim 4 wherein the first illumination color is red and the second illumination color is blue.

6. The system as set forth in claim 4 wherein each of the first illumination color and the second illumination color are each produced by a plurality of respective first LED transmitters and second LED transmitters that, respectively, emit the first illumination color and the second illumination color.

7. The system as set forth in claim 6 wherein each of the first illumination color and the second illumination color are defined by wavelengths that are visible light.

8. The system as set forth in claim 2 wherein at least one of the first illumination color and the second illumination color is produced by white light transmitted from LEDs and passed through a filter that transmits the at least one of the first illumination color and the second illumination color respectively.

9. The system as set forth in claim 1 wherein the image sensor pixels each acquire images in a least a third image color, the illumination assembly is constructed and arranged to provide, simultaneously with the first illumination color and the second illumination color, a third illumination type in a third illumination color recognized by the imager as the third image color.

10. The system as set forth in claim 9 wherein the first illumination type comprises dark field illumination, the second illumination type comprises direct diffuse illumination, and the third illumination type comprises direct bright field illumination.

11. The system as set forth in claim 1, further comprising a best image process that determines whether a best image for pattern recognition is provided in one of either the first image color or the second image color.

12. The system as set forth in claim 11 further comprising a pattern recognition process that receives imager pixel data from the best image process and decodes the best image into data therefrom.

13. The system as set forth in claim 12 wherein the pixel data received by the pattern recognition process defines the best image comprising a plurality of areas, each composed of a discrete image color of the first image color and the second image color.

14. The system as set forth in claim 12 wherein the best image process determines which pixels provide the best image based at least upon contrast.

15. The system as set forth in claim 12, wherein the first illumination type comprises dark field illumination and the second illumination type comprises direct illumination.

16. The system as set forth in claim 12, wherein the image sensor pixels each acquire images in a least a third image color, the illumination assembly is constructed and arranged to provide, simultaneously with the first illumination color and the second illumination color, a third illumination type in a third illumination color recognized by the imager as the third image color and the best image process further determines whether a best image for pattern recognition is provided in one of either the first image color, the second image color or the third image color.

17. A method for scanning a surface comprising the steps of:

acquiring images with image pixels of an imager in each of at least a first image color and a second image color;

varying focus of the imager with respect to the surface;

simultaneously providing a first illumination type in a first illumination color recognized by the imager as the first image color and a second illumination type in a second illumination color recognized by the imager as the second image color, and a focus pattern, projected on the surface, in a focus illumination color recognized by the imager as the focus image color; and

reading image pixel data from the imager in the focus illumination color; and

controlling focus based upon the image pixel data in the focus illumination color.

18. The method as set forth in claim 17 wherein the first illumination type comprises dark field illumination and the second illumination type comprises direct diffuse illumination.

19. The method as set forth in claim 18 further comprising projecting the first illumination color through a light pipe having a chamfered end that projects the first illumination color onto the surface and projecting the second illumination color through a diffuser mounted within the light pipe that projects the third illumination color onto the surface.

20. The method as set forth in claim 19 further comprising providing, in conjunction with the diffuser, an optical filter that restricts reflection of light of the first illumination color.

21. The method as set forth in claim 17 wherein the first illumination color is red and the second illumination color is blue.

22. The method as set forth in claim 17 further comprising producing each of the first illumination color and the second illumination color by a plurality of respective first LED transmitters and second LED transmitters that, respectively, emit the first illumination color and the second illumination color.

23. The method as set forth in claim 22 wherein each of the first illumination color and the second illumination color are defined by wavelengths that are visible light.

24. The method as set forth in claim 17 further comprising determining whether pixels provide a best image for pattern recognition in the first image color or in the second image color.

25. The method as set forth in claim 24 further comprising receiving pixel data from the step of determining and decoding the best image into data therefrom.

26. The method as set forth in claim 25 wherein the pixel data received by the step of decoding defines the best image comprising a single image color of the first image color and the second image color.

27. The method as set forth in claim 25 wherein the pixel data received by the step of decoding defines the best image comprising a plurality of areas, each composed of a discrete image color of the first image color and the second image color.

28. The method as set forth in claim 25 wherein the step of decoding determines which pixels provide the best image based at least upon contrast.

29. The method of claim 25, wherein the first illumination type comprises dark field illumination and the second illumination type comprises direct illumination.

30. A system for scanning a surface and deriving data therefrom comprising:

an imager that receives image data in at least three discrete image colors, each of which colors is resolvable into a discrete image color data stream;

an illuminator that simultaneously projects on the surface at least three illumination colors corresponding substantially to at least three image colors, each of the three image colors respectively being projected in a first illumination type, a second illumination type and a third illumination type; and

a best image process that derives that image color stream displaying the best image from each discrete image color data stream.

31. The system as set forth in claim 30 further comprising a pattern recognition process that receives the discrete color image stream that is the best image and decodes the discrete color image stream into data represented by the surface.

32. The system as set forth in claim 30 wherein the first illumination type and the second illumination type each comprise illumination oriented to produce reflections from a surface that are directed differently from each other.

33. The system as set forth in claim 32 wherein each of the first illumination type and the second illumination type comprise dark field illumination.

34. The system as set forth in claim 30 wherein the first illumination type comprises dark field illumination and the second illumination type comprises direct diffuse illumination.

35. The system as set forth in claim 30 further comprising a pattern recognition process that receives imager pixel data from the best image process and decodes the best image into data therefrom.

36. The system of claim 35, wherein the first illumination type comprises dark field illumination and the second illumination type comprises direct illumination.