RU2190352C1 - Device for recording papillary pattern - Google Patents

Abstract

FIELD: medical engineering. SUBSTANCE: device has finger imprint reading surface, projective optical system, light source, deflecting optical system and system of photodetector members connected to each other and synchronously movable and unit for image processing electrically connected to photodetector member system The deflecting optical system is plunged into immersion fluid filling a cell unit one side of which is the finger imprint reading surface. Beside that, projective optical system, light source and system of photodetector members are placed in the same module with the deflecting optical system. The deflecting optical system is a prism having equilateral trapezoid cross-section. EFFECT: wide range of functional applications; small size and low cost. 3 cl, 2 dwg

Description

The invention relates to the field of optical imaging using computer technology, in particular to devices for fingerprint cards used by law enforcement agencies
Known analogues of the invention, for example, a system for forming an image of a fingerprint during its rolling on the surface of the prism (US patent 3482498, IPC G 03 B 29/00, publ. 1969). In such schemes, to monitor the movements of the finger along the surface of the prism, electromechanical devices are used that adjust the position of the light source to ensure the optimal illumination angle. The fixtures are driven by mechanical finger rest.

 The described circuit did not find application due to the complexity of the mechanical part. In addition, more importantly, there is no control over image quality in this circuit.

 A fingerprint registration device is also known (RF application 93002977/14, IPC 6 A 61 B 5/117), containing a prism, one of its faces illuminated at an angle of total internal reflection by a light source, a projection optical system in the form of a telescopic system, a photodetector made in a rectangular matrix of photocells, and an image processing unit. This device is selected as a prototype as the closest to the claimed.

 The disadvantage of the prototype is that it has limited functionality, since it allows you to register only fingerprints and fragments of the palm. A standard fingerprint card should contain fingerprints of the first phalanx of all fingers, rolled along the receiving surface from nail to nail, and control prints of both hands, formed by simultaneously pressing 4 fingers (from index to little finger) of one hand. Currently, fingerprint registration along with control fingerprints is gradually also being included in the requirements for dactylocardiography.

The prototype allows you to register full rolling and control fingerprints, as well as obtaining handprints in only a few steps. This is due to the limited size of the prism receiving surface. At the same time, difficulties arise in “stitching” of individual fragments of the obtained fingerprints into a single image, which requires the development of special programs and techniques that lead to a rise in the cost of the process of taking fingerprints and loss of image quality. The requirements for the uniformity of the material of the prism (glass) are high, therefore, the use of large prisms, on the receiving surface of which the palm would fit completely, leads to significant technological difficulties and the cost of construction. In addition, since the object (palm) is located at an angle close to 45 ^o to the direction of observation and to the output face of the prism, significant perspective image distortions and optical aberrations arise, such as astigmatism and field curvature, etc. To compensate for them, it is necessary to use expensive projection optics and lengthen the optical path, which leads to a significant increase in the size of the device.

 The problem solved by the present invention is to expand the functionality of the device, reducing its size and cost.

This is achieved by the fact that:
- the surface perceiving fingerprints of the palm elements is a fragment of a flat transparent plate;
- a deflecting optical system is introduced into the circuit, which ensures that the light from the source enters at an optimal angle, the light is incident on the receiving surface at an angle close to the angle of total internal reflection, and the light is output to the photodetectors at an optimal angle, immersed in an immersion liquid filling the cuvette with one from the sides of which is the perceiving surface;
- a deflecting optical system has the ability to synchronously move with a light source and a system of photodetector elements;
- the surface perceiving fingerprints for the best fit of the palm can be made in the form of a fragment of a curved shell, for example spherical;
- the light source and the system of photodetector elements can be placed both outside the cell and inside it. In the latter case, the source and receivers can be made in a single unit with a deflecting optical system.

 The essence of the invention is illustrated by drawings, where in Fig.1 shows a General view of the device, in Fig. 2 is an embodiment of a deflecting optical system.

 A device for registering a papillary pattern (see Fig. 1) contains a fingerprint surface 1 made in the form of a fragment of a flat plate, a projection optical system 2, a light source 3, a system of photodetector elements 4, a deflecting optical system 5, which is immersed in immersion liquid 6 filling the cuvette 7, one of the sides of which is the receiving surface 1. The cuvette 7 is made of optically transparent material. The deflecting system 5 has the ability to move synchronously with the light source 3 by the projection system 2 and the photodetector system 4. The direction of movement is shown in FIG. 1 by arrows, and the movement mechanism is not shown for simplicity.

 The axis of the light beam is shown in FIG. 1 by a dash-dot line. The light beam from the source 3 enters the cell 7 through one of its sides at an angle that ensures minimal loss (perpendicular). A deflecting optical system 5 rotates the axis of the beam so that light falls on the receiving surface 1 at an angle close to the angle of total internal reflection. The refractive index of the immersion liquid 6 is close to the refractive index of the material of the sensing surface, therefore, the refraction and reflection from the inner surface of the plate 1 are negligible, and light without loss reaches the outer (sensing) surface of the plate 1 and undergoes total internal reflection on it. The deflecting optical system 5 rotates the reflected light so that it leaves the cell 7 without loss. The projection system 2 forms an image of a part of the receiving surface on the plane where the photodetector system 4 is located. At those points of the receiving surface 1 that are in contact with the papillary lines of the palm 9, the total internal reflection is disturbed (the light goes into the skin and is absorbed), which leads to the appearance of a black-and-white picture in the plane of the photodetector elements that repeats the lines of the papillary narrow a. With the joint movement of the source 3, the deflecting system 5, the projection system 2 and the system of photodetector elements 4 parallel to the receiving surface 1, the image is sequentially read by the photodetectors. An electrical signal from the photodetectors is input to block 8 (computer) for further processing.

 Depicted in FIG. 2 embodiment of the deflecting system 5 is a prism, which in cross section has the shape of an isosceles trapezoid. A mirror coating 10 is applied to the lateral (inclined) faces of the prism 10. The axis of propagation of the light beam is shown by a dash-dot line. Due to the proximity of the refractive indices of the material (glass) of the prism 5, the receiving plate 1 and the refractive index of the immersion liquid 6, the refraction at the glass-liquid interface is negligible and is not shown in FIGS.

 Additionally, for the best fit of the palm of the hand to the receiving surface 1, the latter can be made in the form of a curved shell, for example spherical. In addition, for compactness of the device, the light source 3, the projection system 2 and the system of photodetector elements 4 can be made in a single unit with a deflecting optical system 5 (not shown).

 Since the receiving surface (plate) has a relatively small thickness, the requirements for the uniformity of the material and the quality of its processing can be reduced in comparison with the prototype.

 Thus, the applicants proposed a fairly simple and reliable device that allows you to get high-quality fingerprints, control prints and handprints used in fingerprinting. The device can also be used to register foot prints, which can also be used for identification. To date, obtaining complete fingerprints (and especially feet) on known fingerprints has been a significant challenge.

 The applicant company begins the development of working documentation and the creation of a prototype device with a implementation period in 2001.

Claims (3)

 1. A device for registering a papillary pattern, comprising a fingerprint-receiving surface, a projection optical system optically coupled to each other, a light source deflecting the optical system and a photodetector system configured to synchronously move. and an image processing unit, electrically connected to the photodetector system, characterized in that the deflecting optical system is immersed in an immersion liquid filling the cell, one of the sides of which is a fingerprint sensing surface.  2. The device for registering a papillary pattern according to claim 1, characterized in that the light source, the projection optical system and the photodetector system are made in a single unit with a deflecting optical system.  3. The device for registering a papillary pattern according to claim 1, characterized in that the deflecting optical system is made in the form of a prism, which in cross section has the shape of an isosceles trapezoid.

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