COMPACT SYSTEM FOR REGISTERING PAPILLARY RIDGE PATTERNS

Abstract

The invention relates to the field of biometric identification. The technical result consists in decreasing the overall dimensions and increasing the reliability of a system for registering papillary ridge patterns, while providing for reduced cost, high image quality, rapid operating speed and reduced energy consumption. The present system comprises a light source, an element which defines the position of a reading surface, an optical system, and a multi-element image receiver, wherein the reading surface is optically linked to the image receiver by rays passing through a guiding optical element, comprising a refractive surface and a reflective surface, by means of consecutive refraction on the refractive surface, reflection on the reflective surface and total internal reflection on the refractive surface

Claims

1. The present system for recording ridge pattern comprises a light source, an element which defines the position of a reading surface, an optical system, and a multi-element image receiver, wherein the reading surface is optically linked to the image receiver by rays passing through a guiding optical element, comprising a refractive surface and a reflective surface, by means of consecutive refraction on the refractive surface, reflection on the reflective surface and total internal reflection on the refractive surface.

2. The system of claim 1 wherein the optical system further comprises an optical wedge.

3. The system of claim 2 wherein the optical wedge is located in the optical path between the reading surface and objective lens forming the image on the image receiver.

4. The system of claim 1 wherein between the photosensitive surface of the image receiver and the objective lens that forms the image on this surface, a transparent plate is located, the surfaces of which are deflected from the normal line to the axis of the objective lens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a typical schematic diagram of the design of a ridge pattern recording system.

[0018] FIG. 2 is a schematic diagram of a ridge pattern recording system having small dimensions owing to the use of a guiding element between the reading surface and the objective lens forming the image on the image receiver.

DETAILED DESCRIPTION OF THE INVENTION

[0019] An exemplary embodiment of the invention may be seen in the layout shown in FIG. 2. A source of light, taking the form of a light panel 1 constructed as light-emitting diodes, shines on prism 2 made from optically transparent material. Passing through the input leg face of the prism 21, the light is incident at an angle of total internal reflection on the hypotenuse face 3, itself determining the ridge pattern scanning surface. The subject to be recorded, such as the fingerprint or the palm of the hand, is placed on this surface. At the points corresponding to the peaks of the ridge pattern, the luminous flux from the light source is partially absorbed by the object to be recorded; in the remaining areas it is fully reflected by the hypotenuse face of the prism. In this way the luminous flux becomes a carrier of the image of the ridge pattern to be recorded. The light subsequently passes through the exit leg face 22 of the prism in the direction of the guiding element 4 in the form of prisms. Refracting at surface 41 light is reflected on surface 42, which is having a mirror coating and again arrives to surface 41. Since the light reflected on surface 42 falls on surface 41 at an angle of total internal reflection, it reflects without loss and leaves the guiding element through surface 43. Along with this, the working light areas on surface 41 intersect during the passage and reflection what is impossible when using a mirror system. Then the light passes through the optical wedge 5 that compensates for the chromaticity that occurs after passing the guiding element. The objective lens 6 forms an image of the subject to be recorded on the light-sensitive surface 7 of the monochrome camera constructed as a matrix of transistors in a metal oxide semiconductor.

[0020] In another embodiment of the system, for all subject beams coming from the reading surface to the image receiver, the condition of total internal reflection on the surface 42 is satisfied. In this case, application of a mirror coating on the surface is not required.

[0021] In yet another variant embodiment of the invention, the subject beams coming from the reading surface to the image receiver pass through surfaces 22, 41 and 43 at an angle that is close to normal. In this case, there is no significant chromatic aberration at the output of the guiding element and the residual chromaticity can be compensated for by the objective lens forming the image on the image receiver. For this purpose, the objective lens uses a lens in the form of meniscus of considerable thickness or an achromatic component consisting of two lenses with opposite signs of optical power and made of different materials. Another option to compensate for the chromaticity that occurs in the optical system is to arrange between the photosensitive surface of the image receiver and the objective lens that forms the image on this surface a transparent plate, the surfaces of which are deflected from the normal line to the axis of the objective lens.

[0022] The applicants have manufactured several specimen ridge pattern scanners with a reading surface size of 82×82 mm and with a resolution on this surface equivalent to 500 dots per inch while the overall height of the device was less than 50 mm. A device with said parameters was the first known portable scanner of ridge pattern of four fingers, which has been able to produce an image quality complying with the FBI EBTS Appendix F standard. Experimental data confirmed that using the above-described guiding element, it is possible to produce systems for recording ridge patterns that significantly surpass the analogues in terms of overall dimensions.

[0023] Because of the fact that the guiding element represents a single structural component in which all the working surfaces are rigidly interconnected, the system improves image quality and reliability of operation in comparison to the systems in which reciprocal displacements of components can lead to deterioration of image characteristics.

[0024] Due to decreasing number of system components, reducing consumption of materials through decrease in overall dimensions, simplifying assembly and adjustment, leads to cost reduction of the devices.

[0025] Because of the fact that the system does not require to perform any software processing to combine several images from different channels into one output, the performance is increased and the power consumption of devices is reduced.