Method and apparatus for extending operating range of bar code scanner

• US 6,547,139 B1
• Filed: 06/15/2000
• Issued: 04/15/2003
• Est. Priority Date: 07/10/1998
• Status: Expired due to Term

• Current Assignee: Welch Allyn Incorporated
• Original Assignee: Welch Allyn Incorporated
• Inventors: Havens, William H., Hammond, Charles M.
• Primary Examiner(s): Frech, Karl D.
• Assistant Examiner(s): Sanders, Allyson
• Application Number:
  US09/594,870
• Time in Patent Office: 1,034 Days
• Field of Search: 235/454, 235/459, 235/461, 235/462.22, 235/462.21, 235/462.26, 235/462.37
• US Class Current: 235/454
• CPC Class Codes: G02B 27/0075 with means for altering, e.g. increasing, the depth of field or depth of focus
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: H04N 1/4092 Edge or detail enhancement

Abstract

The operating depth of field for a bar code scanner, preferably a laser scanner, is increased by placing a cubic phase mask (CPM) in the scanning beam. The masked beam is then scanned and reflected off a bar code and received by a photodetector. The received signal is then processed to recover the original unperturbed representation of the bar code pattern. The processed signal has an increased depth of field over an unmasked scanner signal.

Claims

1. An imaging system for imaging an object located in a target region, comprising:

an illumination source;

an optical path between said illumination source and said object;

a first optics assembly in said optical path;

phase masking means in said optical path for receiving light and modifying a phase thereof as a function of position within said phase masking means, thereby creating phase modified light having known effects therein;

means for traversing said phase modified light across said object in said target region;

image sensing means for receiving light reflected from said object and producing an intermediate image signal therefrom;

said intermediate image signal including at least a misfocus error that is dependent upon a distance between said first optics assembly and said object; and

processing means for correcting for said known effects of said phase modified light to produce a final image signal of said object.

2. An imaging system according to claim 1, wherein said means for traversing includes a scanning mechanism.

3. An imaging system according to claim 1, wherein said phase masking means is between said illumination source and said first optics assembly.

4. An imaging system according to claim 1, wherein said phase masking means is between said first optics assembly and said target region.

5. An imaging system according to claim 1, further including amplitude masking means, in said optical path between said phase masking means and said object, for varying an attenuated amplitude as a function of position within said amplitude masking means, said function being substantially free of discontinuities.

6. An imaging system according to claim 5, wherein at least two of said amplitude masking means, said first optics assembly, and said phase masking means comprise different parts of a single element.

7. An imaging system according to claim 1, further including a second optics assembly in a second optical path between said object and said image sensing means.

8. An imaging system according to claim 1, wherein said illumination source is a laser light source.

9. An imaging system according to claim 8, wherein said means for traversing is a telocentric scanning mechanism.

10. An imaging system according to claim 8, wherein said phase masking means is a cubic phase mask which is shaped so that it corrects approximately for said misfocus error.

11. An imaging system according to claim 8, wherein said phase masking means includes at least one phase mask for receiving light incident thereon and modifying a phase thereof to cause an Optical Transfer Function (OTF) of said first optics assembly to be approximately invariant over a predetermined depth of field.

12. An imaging system according to claim 8, wherein said processing means includes a digital signal processor.

13. An imaging system according to claim 8 in which said processing means is adapted to calculate a transform and inverse transform of signals generated during operation of said imaging system, and in which said transform and inverse transform include at least a discrete fast Fourier transform and an inverse discrete Fast Fourier transform.

14. An imaging system according to claim 8, wherein said processing means includes a generalized recovery function including a finishing function which is adapted to optimize performance of said imaging system for bar code reading applications.

15. An imaging system according to claim 14, wherein said image sensing means is a photodetector, and in which said generalized recovery function is a generalized 1 D recovery function.

16. An imaging system according to claim 14, wherein said image sensing means is a photodetector, and in which said generalized recovery function is a generalized 2D recovery function.

17. An imaging system according to claim 14, wherein said generalized recovery function further includes a finishing function which takes into account at least one of (a) an effect of non-uniform illumination across said target region, (b) aliasing effects, and (c) diffusion effects.

18. An imaging system according to claim 1, wherein said illumination source is a light emitting diode.

19. An imaging system according to claim 18, further comprising amplitude masking means for receiving light from said phase masking means and transmitting light to said means for traversing, said amplitude masking means having an attenuated amplitude that varies as a function of position within said amplitude masking means, said function being substantially free of discontinuities.

20. An imaging system according to claim 19, wherein at least two of said amplitude masking means, said first optics assembly, and said phase masking means comprise different parts of a single element.

21. An imaging system according to claim 19, wherein said scanning mechanism is a telocentric scanning mechanism.

22. An imaging system according to claim 19, wherein said phase masking means is a cubic phase mask which is shaped so that it corrects approximately only for said misfocus error.

23. An imaging system according to claim 19, wherein said phase masking means includes at least one phase mask for receiving light incident thereon and modifying a phase thereof to cause an Optical Transfer Function (OTF) of said first optics assembly to be approximately invariant over a predetermined depth of field.

24. An imaging system according to claim 19, wherein said processing means includes a digital signal processor.

25. An imaging system according to claim 19 in which said processing means is adapted to calculate a transform and inverse transform of signals generated during operation of said imaging system, and in which said transform and inverse transform include at least a discrete fast Fourier transform and an inverse discrete Fast Fourier transform.

26. An imaging system according to claim 19, wherein said processing means includes a generalized recovery function including a finishing function which is adapted to optimize performance of said imaging system for bar code reading applications.

27. An imaging system according to claim 26, wherein said image sensing means is a photodetector, and in which said generalized recovery function is a generalized 1D recovery function.

28. An imaging system according to claim 26, wherein said image sensing means is a photodetector, and in which said generalized recovery function is a generalized 2D recovery function.

29. An imaging system according to claim 26, wherein said generalized recovery function further includes a finishing function which takes into account at least one of (a) an effect of non-uniform illumination across said target region, (b) aliasing effects, and (c) diffusion effects.

30. An imaging system for imaging an object located in a target region, comprising:

a laser illumination source;

a first optical path between said laser illumination source and said object;

a first optics assembly in said first optical path;

a cubic phase mask in said first optical path between said first optics assembly and said object within 0.5 inches of said first optics assembly for receiving light and modifying a phase thereof as a function of position within said cubic phase mask, thereby creating phase modified light having known effects therein;

an amplitude mask in said first optical path;

means for moving said phase modified light across said object;

a photodetector for receiving light reflected from said object and producing an intermediate image signal therefrom;

said intermediate image signal including at least a misfocus error that is dependent upon a distance between said first optics assembly and said object;

a second optics assembly in a second optical path between said object and said photodetector; and

processing means for correcting for said known effects of said phase modified light to produce a final image signal of said object.

31. A method of scanning for a laser scanning system suited for reading indicia located in a target region, comprising steps of:

generating an illumination beam for illuminating an indicia located in an operational depth of field;

changing locally a phase of said illumination beam as a function of position before said beam illuminates said indicia;

changing locally an amplitude of said illumination beam as a function of position before said beam illuminates said indicia;

receiving light reflected from said indicia;

converting the received light to an intermediate image signal; and

processing said intermediate image signal such that said operational depth of field is extended.

32. A method of modifying a laser beam to maximize the system resolving ability as a bar code indicia is moved throughout an operational depth of field, comprising steps of:

generating a laser illumination beam;

modifying a phase of said illumination beam a function of position in said beam;

modifying an amplitude of said illumination beam as a function of position in said beam;

scanning said phase and amplitude-modified beam across said bar code indicia;

receiving light reflected from said bar code indicia;

converting the received light to an intermediate image signal; and

processing said intermediate image signal using a precalculated recovery function to reduce effects of a position of said bar code indicia.

33. A method of scanning a barcode indicia, said indicia containing information encoded therein, comprising steps of:

illuminating said indicia in an operating range with light;

modifying an amplitude and phase of said light to reduce variations in a localized illumination distribution of said light over said operating range before said light illuminates said indicia;

directing said light to said operating range;

scanning said light across said indicia;

receiving light scattered from said indicia;

converting said scattered light to an intermediate image signal; and

processing said intermediate image signal to recover said information encoded in said indicia.

34. A method of increasing an operating depth of field, comprising:

providing illumination;

distorting a phase of said illumination in a predetermined manner at a specific distance from an object;

directing said distorted illumination to said object;

receiving light scattered from said object;

converting said received light to an intermediate image signal; and

processing said intermediate image signal using a precalculated recovery function to reduce effects of said specific distance.