System and method for illuminating a platen in a live scanner and producing high-contrast print images

• US 20040257627A1
• Filed: 06/17/2003
• Published: 12/23/2004
• Est. Priority Date: 06/17/2003
• Status: Active Grant

• Current Assignee: HID Global Corporation (Assa Abloy AB)
• Original Assignee: Cross Match Technologies Incorporated (Assa Abloy AB)
• Inventors: McClurg, George W.
• Granted Patent: US 6,954,261 B2
• Time in Patent Office: Days
• US Class Current: 358/509
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence

Abstract

Light from an illumination source is injected into a prism of a print scanner through an illumination injection surface that is not directly imaged by an optical system and an image sensor of the print scanner. This light travels across the prism and hits a highly reflective surface of the prism. When this light hits the highly reflective surface, it is scattered and becomes diffused. Some of this diffused light remains in total internal reflection (TIR) within the prism and is reflected off the inside of the platen surface of the prism. The diffused light reflected off the inside of the platen surface is imaged by the optical system and the image sensor.

Claims

1. A print scanner, comprising:

a prism having an illumination injection surface, an illumination reflection surface, and a platen surface, said illumination reflection surface of said prism having a reflective coating that diffuses incident rays of light; and

an illumination source,

wherein said illumination source injects rays of light into said prism at said illumination injection surface of said prism, the rays of light traveling internally through said prism to hit said illumination reflection surface of said prism where the rays of light are diffused, the rays of light hitting said illumination reflection surface of said prism at an angle less than the critical angle of said illumination reflection surface, the diffused rays of light traveling internally through said prism to illuminate said platen surface of said prism.

2. The print scanner of claim 1, wherein said illumination injection surface is flat.

3. The print scanner of claim 1, wherein said illumination injection surface is curved.

4. The print scanner of claim 1, wherein said illumination source comprises an array of light-emitting diodes.

5. The print scanner of claim 1, further comprising:

an optical lens located between said illumination source and said injection surface of said prism.

6. The print scanner of claim 1, wherein said illumination reflection surface of said prism is conditioned to reduce spectral reflections prior to being coated with said reflective coating.

7. The print scanner of claim 6, wherein said illumination reflection surface is ground.

8. The print scanner of claim 1, wherein said reflective coating is paint.

9. The print scanner of claim 1, further comprising:

an optical system; and

an image sensor,

wherein said optical system focuses an image of said platen surface of said prism onto an imaging portion of said image sensor, the image composed primarily of diffused rays of light totally internally reflected at said platen surface.

10. A method for producing a ridge pattern image with a print scanner, wherein the print scanner includes a prism, an illumination source, an optical system, and an image sensor, the prism having an illumination injection surface, an illumination reflection surface, and a platen surface, the illumination reflection surface having a coating that diffuses incident rays of light, the method comprising:

(1) injecting rays of light into the prism through the illumination injection surface of the prism such that the injected rays of light travel through the prism to hit the illumination reflection surface, the rays of light hitting the illumination reflection surface at an angle less than the critical angle of the illumination reflection surface;

(2) diffusing the injected rays of light with the illumination reflection surface of the prism; and

(3) illuminating the platen surface with the diffused rays of light reflected off the illumination reflection surface of the prism.

11. The method of claim 10, further comprising:

(4) collecting rays of light totally internally reflected off the platen surface of the prism; and

(5) focusing the collected rays of light onto an imaging portion of the image sensor.

12. The method of claim 11, wherein the illumination injection surface of the prism is flat.

13. The method of claim 11, wherein the illumination injection surface of the prism is curved.

14. The method of claim 11, wherein step (1) comprises:

producing the injected rays of light with a light-emitting diode.

15. The method of claim 11, wherein step (1) comprises:

producing the injected rays of light with a light-emitting diode and an optical lens.

16. The method of claim 11, wherein step (1) comprises:

producing the injected rays of light with an array of light-emitting diodes.