RU2231119C2 - Papillary pattern recording device - Google Patents

Abstract

FIELD: optical pattern shapers including fingerprinting devices.

SUBSTANCE: fingerprinting device has output surface of its prism turned relative to line of its intersection by plane formed by input beam and that reflected from pick-up surface, angle of turn being 1 to 45 deg.

EFFECT: enhanced quality of pattern, reduced size of device.

1 cl, 3 dwg

Description

The present invention relates to the field of optical imaging using computer technology, in particular to devices for fingerprint cards used by law enforcement agencies to identify a person by fingerprints.

Known analogues of the invention, for example, a fingerprint registration device (RF application No. 93002977/14, IPC 7 A 61 B 5/117 of 01/18/93) containing a prism, one of the inner surfaces of which is illuminated at an angle of total internal reflection, a light source , a projection optical system in the form of a telescopic system, a photodetector made in the form of a rectangular matrix of photocells, and an image processing unit. The main disadvantage of this device is the following: an image, for example, of a fingerprint emerging from a prism, is obtained “compressed” along one of the coordinate axes. So, when performing a prism having in the cross section the shape of an isosceles right triangle, the image “shrinks” approximately 1.4 times along one of the coordinate axes. In this case, it is necessary to take special measures with the use of algorithms that “stretch” the image, which inevitably increases the magnitude of the possible error, which ultimately reduces the probability of identifying a person by fingerprints.

A fingerprint registration device is also known (RF patent No. 2022524 dated 05/28/92, IPC 7 A 61 B 5/117), containing a sequentially located light source, a prism, the contact surface of which is placed at an angle of total internal reflection to the axis of the light beam, which corrects a prism, an optical imaging system including a positive component, an array photodetector, and an image processing system, the optical imaging system further comprising a second positive component and an aper urnuyu diaphragm, the back focus of the first positive component is combined with the front focus of the positive component and the second aperture diaphragm. This device is selected as a prototype as the closest to the claimed.

The prototype has the same drawback as the analogue (“compressed” image along one of the coordinate axes). In addition, the presence of a corrective prism, two positive components and an aperture diaphragm significantly increases the dimensions of the device, which is important when creating small-sized devices used, for example, in access restriction systems.

The problem solved by the present invention is to improve image quality and reduce the size of the device. This is achieved by the fact that the output surface of the prism is made turned relative to the line of intersection of the output surface of the prism by a plane formed by the rays that are input and reflected from the receiving surface, and the angle of rotation is 1-40 °.

The essence of the invention is illustrated by drawings in figures 1, 2 and 3, which shows a General view of the device and the prism, respectively.

A device for registering a papillary pattern (Fig. 1) contains a sequentially located light source 1, a prism 2 (prism SWR), having an input surface BC, a receiving surface EB and an output surface EC, a system of photodetector elements 3, an image processing unit 4, and an electrical connection 5 (for example, a cable) connecting the photodetector elements 3 with the image processing unit 4. Elements 1, 2 and 3 are optically connected. A finger of the hand is applied to the sensing surface of the EB 6. Rays from the light source 1 (shown by arrows) fall onto the sensing surface of the EB at an angle close to the angle of total internal reflection.

The device operates as follows.

The light beam (shown by arrows) from source 1 enters into prism 2 through the input face of the aircraft at an angle that ensures minimal loss (usually perpendicular), after which it is reflected from the surface of the EB and leaves prism 2 through the output surface of the EC, reaching the photodetector elements 3. At those points of the receiving surface of the EB prism 2 that are in contact with the papillary lines of the finger 6, the total internal reflection is impaired (light goes into the skin and is absorbed), which leads to the appearance of light in the plane of the photodetector elements shadow pattern, repeating lines fingerprint finger 6. The electrical signal from photodetector elements 3 via the cable 5 is inserted into the unit 4 (PC) for further processing.

Consider now an example of the structural implementation of prism 2, presented in figure 2 (prism KCBELC ₁ B ₁ F). It is obtained from the prism ABCDA ₁ B ₁ C ₁ D ₁ described in the prototype and analogue (for ease of perception, the prism ABCDA ₁ B ₁ C ₁ D _{1 is} depicted with a cross section in the form of an isosceles trapezoid) by rotating its output surface AA ₁ D ₁ D relative to the line of intersection of the output surface (line MN) by the POR plane formed by the input light rays and reflected from the receiving surface AA ₁ B ₁ B. Here, point R is the point of intersection of the input surface BB ₁ C ₁ C of the prism with a light beam from source 1, point O is the point of reflection of the beam from the receiving surface of the prism, and point P is the point of intersection of the output surface of the prism with the reflected beam. The angle of rotation of the output surface relative to the line MN (angle KND) is 1-40 °.

As already mentioned, in the devices described in the analogue and prototype, the image is “compressed” along one of the coordinate axes (in Fig. 1, the ratio of the distances α / α ₁ is approximately 1.4 when the prism with the cross section in the form of an isosceles right triangle or isosceles trapezoid with angles with a larger base equal to 45 degrees). The same “compression” along one of the coordinate axes occurs in the inventive device. By turning the prism exit surface by a certain angle, as was said above, it is possible to achieve a similar “compression” of the image along the other coordinate axis (in Fig. 3, where the view of the prism from the receiving surface is shown (view G), “compression” is shown along the other coordinate axis with a coefficient equal to the ratio β / β ₁ ). Selecting the rotation angle, it is possible to provide the required “compression” ratio of the image ~ 1.4.

Thus, a simple technical solution is proposed that allows to obtain an image that is equally “compressed” along two coordinate axes, which virtually eliminates the processing error inherent in the prototype device. In addition, uniformly “compressed” along two coordinate axes, the image allows you to bring the photodetector elements 3 to the output surface of the prism, thereby achieving a reduction in the dimensions of the device.

The applicant company is developing documentation for the manufacture of a prototype of the claimed device.

Claims (1)

A device for registering a papillary pattern containing a light source sequentially located and optically interconnected, a prism having an input, receiving and output surface and a system of photodetector elements, and an image processing unit electrically connected to the system of photodetector elements, characterized in that it has an output the surface of the prism is made rotated relative to the line of intersection of the output surface of the prism by a plane formed by the input and reflected from the receiving surface rays, and the angle of rotation is 1-40 °.

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