Planar light illumination and imaging device with modulated coherent illumination that reduces speckle noise induced by coherent illumination

• US 20030089779A1
• Filed: 06/27/2002
• Published: 05/15/2003
• Est. Priority Date: 11/24/2000
• Status: Active Grant

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Good, Timothy A., Knowles, C. Harry, Giordano, Patrick, Colavito, Stephen, Jankevics, Andrew, Tsikos, Constantine J., Wirth, Allan, Svedas, William
• Granted Patent: US 7,140,543 B2
• Time in Patent Office: Days
• US Class Current: 235/454
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G06K 2207/1018 Source control
• CPC Class Codes: G06K 7/10594 Beam path
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10752 Exposure time control
• CPC Class Codes: G06V 20/62 Text, e.g. of license plates, overlay texts or captions on TV images
• CPC Class Codes: G06V 30/144 using a slot moved over the image; using discrete sensing elements at predetermined points; using automatic curve following means

Abstract

An imaging device including at least one imaging array and image formation optics that provide a field of view corresponding to the imaging array. At least one illumination module (which includes at least one source of coherent illumination) produces planar light illumination that substantially overlaps the field of view corresponding to the imaging array. Illumination control circuitry modulates the power level of illumination produced by the source of coherent illumination during each photo-integration time period of the imaging array to thereby reduce speckle noise in images captured by the imaging array. The illumination control circuitry preferably modulates the power level of illumination by controlling the number and/or duration of time periods corresponding to different power levels of illumination produced by the source of coherent illumination during each photo-integration time period of the imaging array. Moreover, the illumination control circuitry preferably controls number and/or duration of the time periods such that substantially constant energy is produced by the source of coherent illumination over the time periods (thereby enabling the different speckle patterns produced over the timer periods to optimally cancel each other out).

Claims

1. An imaging device comprising:

at least one imaging array and image formation optics that provide a field of view corresponding to said at least one imaging array;

at least one illumination module that produces planar light illumination that substantially overlaps the field of view corresponding to said imaging array, said at least one illumination module including at least one source of coherent illumination; and

illumination control circuitry that modulates the power level of illumination produced by said source of coherent illumination during each photo-integration time period of the imaging array to thereby reduce speckle noise in images captured by said at least one image array.

2. The imaging device of claim 1, wherein said illumination control circuitry controls number and/or duration of time periods corresponding to different power levels of illumination produced by said source of coherent illumination during each photo-integration time period of said imaging array.

3. The imaging device of claim 2, wherein said illumination control circuitry controls number and/or duration of said time periods such that substantially constant energy is produced by said source of coherent illumination over said time periods.

4. The imaging device of claim 2, wherein said illumination control circuitry controls number and/or duration of said time periods such that total energy produced by said source of coherent illumination during each said photo-integration time period does not exceed a maximum value.

5. The imaging device of claim 1, wherein said at least one source comprises at least one visible laser diode.

6. The imaging device of claim 1, wherein said at least one source comprises a plurality of visible laser diodes.

7. The imaging device of claim 1, wherein said at least one illumination module comprises a laser illumination source, at least one focusing lens element, and at least one cylindrical lens element integrated into a modular housing.

8. The imaging device of claim 1, comprising a plurality of illumination modules each comprising a laser illumination source, at least one focusing lens element, and at least one cylindrical lens element integrated into a modular housing.

9. The imaging device of claim 1, wherein said imaging array comprises a linear imaging array.

10. The imaging device of claim 1, wherein said imaging array comprises an area array.

11. The imaging device of claim 1, wherein said illumination control circuitry includes feedback circuitry operably coupled between a monitor photodiode and a dynamic current source, said dynamic current source providing current to said source of coherent illumination, and said feedback circuitry controlling power level of illumination produced by said source of coherent illumination to provide a plurality of power levels during each photo-integration time period of the imaging array in response to timing signals and the output of said monitor photodiode provided thereto.

12. A method for illuminating at least one imaging array and reducing speckle noise in images captured by said at least one image array, the method comprising the steps of:

providing said at least one imaging array and image formation optics that provide a field of view corresponding to said at least one imaging array;

providing at least one illumination module that produces planar light illumination that substantially overlaps the field of view corresponding to said imaging array, said at least one illumination module including at least one source of coherent illumination; and

modulating the power level of illumination produced by said source of coherent illumination during each photo-integration time period of the imaging array to thereby reduce speckle noise in images captured by said at least one image array.

13. The method of claim 12, further comprising the step of controlling number and/or duration of time periods corresponding to different power levels of illumination produced by said source of coherent illumination during each photo-integration time period of said imaging array.

14. The method of claim 13, wherein the controlling step controls number and/or duration of said time periods such that substantially constant energy is produced by said source of coherent illumination over said time periods.

15. The method of claim 13, wherein the controlling step controls number and/or duration of said time periods such that total energy produced by said source of coherent illumination during each said photo-integration time period does not exceed a maximum value.

16. The method of claim 12, wherein said at least one source comprises at least one visible laser diode.

17. The method of claim 12, wherein said at least one source comprises a plurality of visible laser diodes.

18. The method of claim 12, wherein said at least one illumination module comprises a laser illumination source, at least one focusing lens element, and at least one cylindrical lens element integrated into a modular housing.

19. The method of claim 12, wherein said at least one illumination module comprises a plurality of illumination modules each comprising a laser illumination source, at least one focusing lens element, and at least one cylindrical lens element integrated into a modular housing.

20. The method of claim 12, wherein said imaging array comprises a linear imaging array.

21. The method of claim 12, wherein said imaging array comprises an area array.

22. The method of claim 12, further comprising the step of:

providing a monitor photodiode and a dynamic current source, said dynamic current source providing current to said source of coherent illumination;

controlling said dynamic current source to vary power level of illumination produced by said source of coherent illumination to provide a plurality of power levels during each photo-integration time period of the imaging array in response to timing signals and the output of said monitor photodiode.