Imaging engine and method for code readers

• US 6,340,114 B1
• Filed: 06/12/1998
• Issued: 01/22/2002
• Est. Priority Date: 06/12/1998
• Status: Expired due to Fees

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Stankelis, Thomas M., Gelles, Rubin, Patel, Mehul, He, Duanfeng, Joseph, Eugene, Correa, Mark, Li, Yajun
• Primary Examiner(s): Frech, Karl D.
• Application Number:
  US09/096,578
• Time in Patent Office: 1,320 Days
• Field of Search: 235/462.01, 235/472.01, 235/470, 235/456, 235/462.22, 235/462.23, 235/462.24, 235/462.06
• US Class Current: 235/462.22
• CPC Class Codes: G06K 2207/1011 Aiming
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10811 Focalisation

Abstract

An imaging engine and signal processing devices and methods are disclosed for reading various kinds of optical codes. The compact structure may include a two dimensional image sensor, apparatus for focusing images at different focal disclosures, an aiming system, a hi-low beam illumination system and related signal processing circuits.

Claims

1. An imaging and aiming apparatus for an optical code reader comprising:

an image sensor, including an array of photo sensor cells for producing electronic signals corresponding to a two-dimensional array of pixel information for a target image;

a lens assembly for focusing light incident on the reader from at least two different fields of view, corresponding to at least two different focal distances;

means for controlling the lens assembly to select a field of view; and

an aiming pattern projector for projecting at least two different aiming frames, each indicating a field of view of the lens assembly.

2. The apparatus of claim 1, further comprising power supply, decoding circuitry and video controller circuitry and wherein the apparatus is less than 2 cubic inches in volume and is dimensioned to replace a moving laser beam scanning engine in a handheld barcode scanner.

3. The apparatus of claim 2, wherein the apparatus can read both high and low density barcodes, and has a total working range of between 1½

and 18 inches.

4. The apparatus of claim 1, wherein the aiming frames have different, partially overlapping angular dimensions corresponding to the different fields of view of the lens assembly and wherein the aiming pattern includes a centrally located marker.

5. The apparatus of claim 4, wherein each aiming frame consists of four corner markers each comprising a plurality of illuminated spots.

6. The apparatus of claim 5, wherein the aiming pattern projector comprises at least one laser and at least one diffractive optical element.

7. The apparatus of claim 4, wherein the principal optical axes of said aiming pattern projector and the lens assembly are offset from one another, but by no more than 1″

, and wherein the image sensor obtains an image of at least a portion of the aiming pattern.

8. The apparatus of claim 7, further comprising means for obtaining pixel information of a target field of view both with and without an image of the centrally located marker and means for determining the distance of a target code based on the apparent location of the centrally located marker in the field of view.

9. The apparatus of claim 8, wherein the aiming pattern projector is periodically turned off during which time pixel information of the target field is obtained without an image of the centrally located marker.

10. The apparatus of claim 1, further comprising frame grabbing circuitry for providing video signals for displaying images produced by the apparatus on a terminal monitor.

11. The apparatus of claim 10, further comprising means for selectively turning off the aiming pattern projector when the apparatus is used to obtain pixel information for image display.

12. The apparatus of claim 11, wherein the means for selectively turning off the aiming pattern projector is an electrical switch.

13. The apparatus of claim 12, wherein the moving optical element is a moving mirror which folds the optical path of at least one of the lens.

14. The apparatus of claim 13, wherein the means for controlling the lens assembly is an electronic servo for flipping the mirror.

15. The apparatus of claim 1, wherein the lens assembly comprises a first lens, a second lens having a different field of view than the first lens, and a moving optical element for selectively providing an image to the image sensor through one of the first or the second lens.

16. The apparatus of claim 1, further comprising an illumination source for illuminating a target of the optical code reader, the illumination source having at least a first and a second illumination fields corresponding to first and second fields of view of the lens assembly, respectively.

17. The apparatus of claim 1, wherein the lens assembly has an aperture less than {fraction (1/10)}″

in diameter and includes two lenses, each having two concave-convex plastic lens elements with spherical convex surfaces and diameters less than ½

″

; and

snap fitting means for aligning the lens elements along a common optical axis in back-to-back relationship.

18. An imaging engine for a handheld optical code reader for reading optical codes located at various distances from the imaging engine comprising:

a solid state device for producing a signal corresponding to a two-dimensional image,

a solid state device lens assembly having a principal input optical axis for focusing light on the solid state device, said lens assembly being switchable between at least two different focal distances;

an optical element for projecting an aiming pattern in a field of view of the solid state device lens assembly, the pattern having an angular dimension related to the size of the fields of view of the solid state device lens assembly at the at least two different focal distances;

an illumination source which is switchable to provide a first illumination field adapted to illuminate a target code at one of said focal distances and a second illumination field adapted to illuminate a target code at another of said focal distances;

decoding circuitry for selecting a portion of an image of the field for decoding; and

control circuitry for switching said solid state device lens assembly and illumination source.

19. An imaging lens system for a solid state device optical code reader comprising:

an imaging lens assembly having a first angular field of view and a second angular field of view, wherein the lens assembly includes two objective lenses and switching means including mirror selectively positionable in a beam path of the solid state device to provide incident light from said first or said second lenses to the solid state device; and

means for rapidly switching between said first and said second fields of view in response to detected distance between the reader and a target barcode, at which the reader is aimed.

20. The system of claim 19, wherein the mirror is a flip mirror.

21. The system of claim 20, wherein the flip mirror is servo controlled responsive a signal from a microprocessor of said reader.

22. An optical code reader comprising:

a solid state device imaging system having at least two different fields of view;

a laser; and

a diffractive optical element for diffracting light from the laser and producing at least two different aiming pattern frames corresponding to the at least two different scanning fields of the solid state device imaging system.

23. The optical code reader of claim 22, wherein said diffractive optical element produces arrays of spots indicating the corners of the aiming pattern frames and a center marker.

24. The optical code reader of claim 23, wherein the two aiming patterns are nested aiming frames and wherein the center marker is a cross-hair pattern of spots located at the center of the two aiming frames.

25. An optical code reader comprising:

a solid state device imaging system having at least one field of view;

an aiming pattern projector for projecting an aiming pattern in the direction of a target barcode;

a means for decoding a target optical code located in a field of view of the solid state device imaging system; and

means for locating at least a portion of an aiming pattern in an image produced by the solid state device imaging system and for providing feedback to the decoding means to identify an image area in which the target barcode is located.

26. The optical code reader of claim 25, wherein a principal optical axis of said solid state device imaging system and a principal optical axis of the two aiming patterns are parallel and offset by a distance less than ½

inch.

27. The optical code reader of claim 26, wherein the location of at least a portion of at least one of said aiming patterns within an image produced by the solid state device is employed to determine the distance from the target to the reader.

28. The optical code reader of claim 26, wherein an image produced by the solid state device imaging system includes a center marker of said aiming patterns.

29. The optical code reader of claim 28, further comprising:

a switchable illumination source; and

means for analyzing the position of the center marker relative to the field of view of the reader to select an illumination level for a subsequent image to be decoded.

30. The optical code reader of claim 28, further comprising means for analyzing the position of the center marker relative to the field of view of the reader to select an exposure level for a subsequent image to be decoded.

31. The optical code reader of claim 28, further comprising:

means for changing the focal distance of the CCD imaging system, and

means for analyzing the position of the center marker relative to the field of view of the reader to select a focal distance for a subsequent image to be decoded.

32. A method for reading a target barcode comprising:

projecting an aiming pattern from a handheld optical code reader in the direction of the target barcode;

producing a signal corresponding to a two dimensional image with a field including at least a portion of the aiming pattern and the target barcode;

identifying the location of at least a portion of the pattern within the two-dimensional image; and

selecting a portion of an image of the field for decoding, relative to the identified location.

33. The method of claim 32, wherein the aiming pattern is projected by directing a laser beam through a diffractive optical element of a handheld scanner.

34. The method of claim 32, wherein the pattern includes a peripheral field frame.

35. The method of claim 32, wherein the two dimensional image includes the central marker.

36. The method of claim 32, wherein the aiming pattern is projected from a handheld scanner and wherein the signal corresponding to the two dimensional image is produced by a solid state device imaging system having a principal optical axis parallel to and offset from a principal optical axis of the aiming pattern.

37. The method of claim 36, further comprising the step of locating at least a portion of the aiming pattern within a two-dimensional image from said solid state device imaging system and producing a signal corresponding to the distance between the optical code reader and the target barcode based on the location of the position of the aiming pattern.

38. The method of claim 37, further comprising the step of switching a focal distance of the solid state device imaging system in response to the determined distance of the barcode.

39. The method of claim 38, further comprising the steps of illuminating the target barcode and selecting the amount of illumination based on the determined distance of the barcode.

40. The method of claim 32, wherein the aiming pattern is periodically projected and wherein two dimensional images of the field are produced, a first image being produced when the aiming pattern is being projected, and a second image being produced when the aiming pattern is not being projected, and wherein a portion of the second image is selected for decoding on the basis of the identified location in the first image.

41. An apparatus for determination of the distance between an imaging engine and a target barcode comprising:

means for projecting an aiming pattern from an optical code reader in the direction of the target barcode, said aiming pattern having a principal optical axis;

electro-optical means for producing a signal corresponding to a two dimensional image with a field including at least a portion of the aiming pattern and the target barcode, wherein the electro-optical means has a principal optical axis generally parallel and offset from the principal optical axis of the projecting means; and

means for locating at least a portion of the aiming pattern within a two dimensional image detected by said electro-optical means and for producing a signal corresponding to the distance between the imaging engine and the target barcode based on the location of the position of the at least a portion of the aiming pattern.

42. The apparatus of claim 41, wherein the means for projecting projects a second aiming pattern from the optical code reader, the aiming pattern being associated with a first distance from the imaging engine and the second aiming pattern being associated with a second distance from the imaging engine.

43. The apparatus of claim 41, further comprising:

a lens assembly means being switchable between at least two different focal distances; and

an illumination means which is switchable to provide a first illumination field adapted to illuminate the target barcode at one of the focal distances and a second illumination field adapted to illuminate the target barcode at another of the focal distances.

44. A target illumination source for a handheld optical code reader comprising:

means for producing a broad beam of low output intensity to illuminate a target barcode close to the optical code reader; and

means for producing a narrower beam of higher output intensity to illuminate a target barcode far from the optical code reader.

45. The illumination source of claim 44, adapted for use with the reader which is switchable between a relatively larger and a relatively smaller field of view and wherein the beam of illumination is selected to correspond with the field of view of the reader.

46. The illumination source of claim 44, wherein the means for producing the lower output intensity illumination beam is one or more light emitting elements with a wide divergence pattern located relatively near a principal optical axis of the reader;

and

wherein the means for producing the higher output intensity illumination beam is one or more light emitting elements with a narrow divergence pattern located relatively farther from a principal optical axis of the reader.

47. The illumination source of claim 44, wherein the means for producing the higher intensity, relatively narrower illumination beam is plural light emitting diodes each associated with a focusing lenslet located in a front face of the reader.

48. The illumination source of claim 44,

wherein the beam producing means are plural light emitting elements, which emit light from a forward face of the reader;

and further comprising

an image sensor for producing electronic signals corresponding to a two dimensional array of pixel information for a field view; and

image processing means for compensating said signals for known variations in illumination of the beam producing means.

49. A method for determining a distance between an imaging engine and a target barcode comprising the steps of:

projecting an aiming pattern from an optical code reader in a direction of the target barcode, the aiming pattern having a principal optical axis;

producing, by electro-optical means, a signal corresponding to a two dimensional image with a field including at least a portion of the aiming pattern and the target barcode, wherein the electro-optical means has a principal optical axis generally parallel and offset from the principal optical axis of the aiming pattern; and

locating at least a portion of the aiming pattern within the two dimensional image; and

generating a signal corresponding to the distance between the imaging engine and the target barcode based on the location of the position of the at least a portion of the aiming pattern.

50. A method for determining a distance between an imaging engine and a target barcode comprising the steps of:

projecting a first and second aiming pattern from an optical code reader in the direction of the target barcode, wherein the first and second aiming patterns are associated with a first and second focal distance;

capturing an image of the first and second aiming patterns;

correlating an offset between the first projected aiming pattern and the second projected aiming pattern with the first and second focal distances;

calibrating the imagining engine using said correlation;

illuminating the target barcode using either the first or second aiming pattern; and

determining a distance of the between the imaging engine and the target barcode using an offset of a portion of either the first or second aiming pattern.

51. The method of claim 50, wherein the portion of either the first or second aiming pattern is a central marker of either the first or second aiming pattern.

52. An apparatus for determining a distance between a barcode reader and a target barcode comprising:

means for projecting a first aiming pattern onto a first target plane and for projecting a second aiming pattern onto a second target plane, wherein a portion of the first aiming pattern is offset from a portion of the second aiming patterns with respect to an axis;

means for correlating the offset of the portion of the first aiming pattern with a distance of the first target plane and for correlating the offset of the portion of the second aiming pattern with a distance of the second target plane; and

means for determining the distance between the barcode reader and the target barcode as a function of an offset of a portion of either the first or second aiming patterns.