System and method for providing diffuse illumination in a symbology reader

• US 7,614,563 B1
• Filed: 12/29/2005
• Issued: 11/10/2009
• Est. Priority Date: 12/29/2005
• Status: Active Grant

• Current Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Original Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Inventors: Nunnink, Laurens, Equitz, William H., Gerst, Carl W.
• Primary Examiner(s): Koyama; Kumiko C
• Application Number:
  US11/321,702
• Time in Patent Office: 1,412 Days
• Field of Search: 235/462.06, 235/462.2, 235/462.21, 235/462.22, 235/462.35, 235/462.42, 235/472.01, 235/473, 362/27
• US Class Current: 235/473
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10831 Arrangement of optical elements, e.g. lenses, mirrors, prisms optical elements per se G02B
• CPC Class Codes: G06K 7/10881 constructional details of hand-held scanners

Abstract

An illumination system and method for use in a handheld symbology reader that employs a grid of reflecting elements applied to a transparent plate adapted to project a highly diffuse and uniform illumination on a subject. The grid defines a geometry with a large number of transparent spaces between grid elements through which an image of the subject can be acquired. A light source array is configured to project light into the grid at a right angle via a light pipe having a distal beveled edge or side projecting light sources. Another light source may be employed to illuminate second light pipe with a chamfered edge to create low-angle illumination.

Claims

1. A handheld symbology reader having a reader imager that acquires images of subjects comprising:

a housing constructed and arranged to be held by and operated by a hand;

a first light source array constructed and arranged to direct light in a radial direction inward toward and approximately normal to an optical axis of the reader imager;

the array including a first light pipe having an axial portion that receives light projecting in an axial direction approximately parallel with the optical axis and a bevel edge that internally reflects the light into the radial direction;

an illumination grid assembly including a transparent plate having an imager-facing side and a subject-facing side, the imager-facing side including, applied thereon, a plurality of grid elements with transparent spaces therebetween, each of the grid elements including a surface with a reflective center and a non-reflective edge facing toward the subject and a non-reflective surface facing toward the reader image; and

wherein the transparent plate is constructed and arranged to internally reflect light in the radial direction and cause light from the array to reflect from the reflective center of each grid element and exit through the subject-facing side toward the subject as highly diffuse light while image light is returned to the imager from the subject through the transparent spaces.

2. The handheld symbology reader as set forth in claim 1 wherein the transparent plate is operatively and unitarily connected to the axial portion and the bevel edge of the first light pipe.

3. The handheld symbology reader as set forth in claim 1 further comprising a second light pipe having a edge at a distal end that generates dark field light, the chamfered edge being located axially remote from and external of the first light pipe.

4. The handheld symbology reader as set forth in claim 3 wherein the second light pipe defines an interior opening and wherein the illumination grid assembly is constructed and arranged to project the highly diffuse light through the interior opening.

5. The handheld symbology reader as set forth in claim 4 further comprising a second light source array arranged to project light to the second light pipe, the first light source array being remote from the second light source array.

6. The handheld symbology reader as set forth in claim 5 wherein the first light source array projects light in a first direction and the second light source projects light in a second direction opposite the first direction.

7. The handheld symbology reader as set forth in claim 6 wherein the first light pipe is located between a proximal end of the second light pipe and the reader imager.

8. The handheld symbology reader as set forth in claim 7 further comprising a reflector that receives light from a third array of light sources and a conical diffuser nested within the interior opening of the second light pipe tapering from a widened opening adjacent to the distal end of the second light pipe to a narrowed aperture adjacent to the illumination grid assembly, the illumination grid assembly spanning the aperture and the reflector projecting light into the conical diffuser.

9. The handheld symbology reader as set forth in claim 5 wherein each of the first light source array and the second light source array project light in a first direction.

10. The handheld symbology reader as set forth in claim 9 wherein the first light source array is located radially inward of the second light source and the light pipe is nested within the interior opening of the second light pipe adjacent to side walls of the second light pipe.

11. The handheld symbology reader as set forth in claim 5 wherein each of the first light source array and the second light source array are located together on an illumination circuit board.

12. The handheld symbology reader as set forth in claim 5 wherein the first light source array projects light having a first wavelength and the second light source array projects light having a second wavelength, different than the first wavelength.

13. The handheld symbology reader as set forth in claim 12 wherein each wavelength defines a discrete visible color.

14. The handheld symbology reader as set forth in claim 1 wherein the light pipe includes an inner edge adapted to retain the transparent plate, the transparent plate being a separate non-unitary component relative to the light pipe, inner edge and a confronting perimeter edge of the transparent plate being constructed and arranged to transmit light therebetween.

15. The handheld symbology reader as set forth in claim 1 wherein each grid element defines a circular outline shape.

16. The handheld symbology reader as set forth in claim 1 wherein the first light source array comprises a plurality of side-projecting LEDs mounted on a circuit board, the transparent plate including a perimeter edge facing the array and receiving transmitted light therefrom.

17. The handheld symbology reader as set forth in claim 16 wherein the perimeter edge includes a lens shape for collimating the light from the array.

18. The handheld symbology reader as set forth in claim 1 wherein the reader imager includes a lens having an aperture defining a polygonal aperture shape and wherein the grid elements are spaced from each other in accordance with an arrangement that is substantially aligned with respect to the polygonal aperture shape.

19. The handheld symbology reader as set forth in claim 18 wherein the polygonal aperture shape comprises a square shape.

20. The handheld symbology reader as set forth in claim 19 wherein the reader imager includes a lens having an aperture and wherein the imager side of the transparent plate is located coincident with the aperture.

21. The handheld symbology reader as set forth in claim 20 wherein the imager side of the transparent plate includes, in the transparent spaces external of the aperture an opaque coating.

22. A method for reading symbology on a subject with a handheld reader comprising the steps of:

aiming a distal end of a housing having a hand grip at the subject at a predetermined working distance;

diffusely illuminating the subject with a diffuse light provided by a diffuse illumination grid assembly within the housing, the grid assembly receiving light from a first array of light sources around a perimeter thereof and internally reflecting the light between a subject-facing face and an imager-facing face of a transparent plate, the internally reflected light striking grid elements on the imager-facing side, each of the grid elements having a reflective center and a non-reflective edge and transparent spaces between the grid elements, wherein the internally reflected light is emitted from the grid elements, through the subject-facing face and toward the subject as highly diffuse light;

illuminating the subject at a predetermined time using a light pipe that receives light from a second array of light sources and that internally reflects the light into an end that produces dark field illumination; and

acquiring an image of the subject from the highly diffuse light reflected from the subject through the transparent spaces based upon the reflection of the highly diffuse light off the subject.

23. The method as set forth in claim 22 wherein the step of diffusely illuminating includes projecting light through a conical diffuser nested within the light pipe and having a aperture aligned with an imager and which is spanned by a portion of the grid assembly.

24. The method as set forth in claim 22 further comprising providing a diffuse illuminator light pipe that bends light from the first array of light sources from an axial orientation into a radially inward direction into the transparent plate.

25. The method as set forth in claim 22 wherein the step of diffusely illuminating includes projecting light from a plurality of side-projecting LEDs located adjacent to a perimeter edge of the transparent plate.

26. A handheld symbology reader having a reader imager that acquires images of subjects comprising:

a housing constructed and arranged to be held by and operated by a hand;

a first light source array constructed and arranged to direct light in a radial direction inward toward and approximately normal to an optical axis of the reader imager;

an illumination grid assembly including a transparent plate having an imager-facing side and a subject-facing side, the imager-facing side including, applied thereon, a plurality of grid elements with transparent spaces therebetween, each of the grid elements including a surface with a reflective center and a non-reflective edge facing toward the subject and a non-reflective surface facing toward the reader image;

a lens having an aperture defining a polygonal aperture shape and where the grid elements are spaced from each other in accordance with an arrangement that is substantially aligned with respect to the polygonal aperture shape; and

wherein the transparent plate is constructed and arranged to internally reflect light in the radial direction and cause light from the array to reflect from the reflective center of each grid element and exit through the subject-facing side toward the subject as highly diffuse light while image light is returned to the imager from the subject through the transparent spaces.

27. The handheld symbology reader as set forth in claim 26 wherein the polygonal aperture shape comprises a square shape.

28. The handheld symbology reader as set forth in claim 27 wherein the reader imager includes a lens having an aperture and wherein the imager side of the transparent plate is located coincident with the aperture.

29. The handheld symbology reader as set forth in claim 28 wherein the imager side of the transparent plate includes, in the transparent spaces external of the aperture an opaque coating.