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

• US 20060028635A1
• Filed: 10/11/2005
• Published: 02/09/2006
• 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 7,119,890 B2
• Time in Patent Office: Days
• US Class Current: 356/71
• 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 surface, an illumination reflection surface, and a platen surface; and

an illumination source,

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

2. The print scanner of claim 1, further comprising a diffuser between the illumination source and the illumination injection surface.

3. The print scanner of claim 1, wherein the illumination injection surface of the prism is in the same plane as the platen surface.

4. The print scanner of claim 3, wherein the illumination source is adjacent to the illumination injection surface.

5. The print scanner of claim 3, wherein the rays of light are reflected off at least one other surface of the prism before hitting the illumination reflection surface.

6. The print scanner of claim 1, wherein the illumination reflection surface is diffusive.

7. The print scanner of claim 1, wherein the illumination injection surface is flat.

8. The print scanner of claim 1, wherein the illumination injection surface is curved.

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

an optical system; and

an image sensor,

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

10. The print scanner of claim 1, further comprising a lens disposed between the illumination source and the illumination injection surface.

11. A method for producing a print patter with a print scanner, wherein the print scanner includes a prism and an illumination source, the prism having an illumination injection surface, an illumination reflection surface, and a platen surface, the method comprising:

(a) 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 that is less than the critical angle of the illumination reflection surface;

(b) reflecting the injected rays of light with the illumination reflection surface of the prism; and

(c) illuminating the platen surface with the reflected rays of light from the illumination reflection surface of the prism.

12. The method of claim 11, further comprising:

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

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

13. The method of claim 11, wherein step (a) comprises injecting rays of light through a diffuser at the illumination injection surface.

14. The method of claim 11, wherein step (a) comprises injecting rays of light through the illumination injection surface such that the illumination injection surface is in the same plane as the platen surface.

15. The method of claim 14, further comprising between step (a) and step (b):

reflecting the rays of light off at least one other surface of the prism.