Device for imaging the papillary lines of a finger

• US 20040114783A1
• Filed: 01/22/2004
• Published: 06/17/2004
• Est. Priority Date: 12/22/2000
• Status: Active Grant

• Current Assignee: Fingerpin AG
• Original Assignee: Fingerpin AG
• Inventors: Spycher, Martin, Roosdorp, Anne-Sophie Golsong
• Granted Patent: US 7,315,632 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: A61B 5/1172 using fingerprinting
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence

Abstract

Device has a transparent body (1) with a support surface (2). Light is incident on the surface at an angle less than that required for total internal reflection. In the areas of the fingerprint ridges evanescent fields are excited. Propagated light (12-14) is reflected from the surface (2) and incident on a detector (22) at angles within the angular range for total internal reflection.

Claims

1. An apparatus for optically recording the papillary ridges on a finger surface, the apparatus having a transparent body (1) with a support surface (2) for a finger and with a lateral surface (25), as well as comprising a light source (8) for illuminating the finger surface and an optical system for imaging the papillary ridges that lie on the support surface (2), and comprising a light detector (22)

characterized in that

the light source (8) emits a light bundle (9) that has a divergent angle that is smaller than the critical angle for total internal reflection at the support surface (2) of the transparent body (1), and the light bundle (9) leads through the transparent body (1) and falls onto the support surface (2) and irradiates the papillary ridges of the finger there, and the optical system for imaging the papillary ridges is designed such that a propagating light bundle (12) that emanates from the support surface (2) and leads through the optical system in order to image the papillary ridges and falls onto a detector surface of the light detector (22) lies in an angular range that corresponds to the angular range in which light beams that are reflected at the support surface (2) with water, lying thereupon, by total internal reflection.

2. The apparatus as claimed in claim 1,

characterized in that

the optical axis of the imaging optical system runs perpendicularly through the lateral surface (25) of the transparent body (1).

3. The apparatus as claimed in claim 2,

characterized in that

the support surface (2) of the transparent body (1) is arranged at a first angle (α

) to the optical axis of the imaging optical system, and the detector surface of the light detector (22) is arranged at a second angle (β

) to the optical axis of the imaging optical system in accordance with the Scheimpflug principle.

4. The apparatus as claimed in claim 3,

characterized in that

the imaging optical system has a diaphragm (20).

5. The apparatus as claimed in claim 4,

characterized in that

the imaging optical system has a single lens or a plurality of lenses.

6. The apparatus as claimed in claim 5,

characterized in that

the imaging optical system has a mirror for the purpose of folding it.

7. The apparatus as claimed in one of the preceding claims,

characterized in that

the light source (8) has at least one lens.

8. The apparatus as claimed in one of the preceding claims,

characterized in that

the light source (8) has at least two light-emitting diodes that are arranged in a one- or two-dimensional array.

9. The apparatus as claimed in one of the preceding claims,

characterized in that a diffuser is arranged between the light source (8) and the transparent body (1).

10. The apparatus as claimed in one of the preceding claims,

characterized in that the light detector (22) has a two-dimensional CMOS camera or a CCD camera.

11. The apparatus as claimed in one of the preceding claims,

characterized in that

the transparent body (1) consists of a high-index material with an optical reflective index of greater than 1.55.

12. The apparatus as claimed in one of the preceding claims,

characterized in that

a mirror (30) is integrated on a lateral surface (25) of the transparent body (1), this mirror (30) preferably being configured in a flat or cylindrical fashion or in a shape that permits a preferred, substantially undistorted imaging onto the light detector.

13. The apparatus as claimed in claim 12,

characterized in that

a focusing lens (32) is integrated on a further lateral surface (31) of the transparent body (1) and/or in that a diaphragm (44) is arranged outside the transparent body (1), there being arranged with particular preference outside the transparent body (1) a deflecting mirror (45) that directs the light focused by the integrated lens (32) onto a printed circuit board (50) on which the light detector (22) and the light source (8) are arranged.

14. The apparatus as claimed in one of the preceding claims,

characterized in that the light-emitting diodes (51) of the light source (8) emit light in the red wavelength region from 650 to 780 nm or in the infrared wavelength region from 780 to 930 nm.

15. A method for operating the apparatus as claimed in one of the preceding claims and in one of claims 8 and/or 14, characterized in that

the light-emitting diodes (51) are respectively driven such that the light intensity they emit, is in accordance with the length of the light path from each light-emitting diode to the light detector (22), and the light-sensitive surface (23) of the light detector (22) is thereby homogeneously illuminated.

16. The method as claimed in claim 15,

characterized in that

a first row of light-emitting diodes (51) is driven such that the light intensity they emit is 60 to 80% of the light intensity that is emitted by a second row of light-emitting diodes (51).

17. The apparatus as claimed in claim 15,

characterized in that

a middle row of light-emitting diodes (51) is driven such that the light intensity they emit is approximately 30 to 70%, preferably approximately 50% of the light intensity that is emitted by two outer rows of light-emitting diodes (51).