JPS61292786A - Fingerprint sensor - Google Patents

Abstract

PURPOSE:To improve the image resolution of a fingerprint sensor with the image pickup of only a limited area by detecting the difference between the center position of a subject image and that of an image pickup element and obtaining coincidence between both center positions by means of an XY stage. CONSTITUTION:The fingerprint image of a subject 1 set closely to a transparent flat plate 21 is led to the outside through a hologram diffraction gratings 31 and 41 and photographed by an image pickup element 32 and at the same time detected by a quartered photodetector 42 consisting of four photodiodes. A position detecting circuit 43 performs comparison among the output voltages of those photodiodes and measures the distance between the center of the subject 1 and that of a contact surface 2. Then a stage control circuit 52 drives an XY stage 51 in the XY direction so as to secure coincidence between the center of the element 32 set on the stage 51 and the center of the subject 1 detected by the detector 42.

Description

[Detailed Description of the Invention] [Summary] In a fingerprint sensor that matches and identifies individuals, the subject and the image sensor are aligned, improving the resolution of the imaging pattern, improving the performance of the device, and shortening the matching time. This is what I did.

[Industrial application field]

The present invention relates to a personal verification system, and more particularly to a total reflection filtering type fingerprint sensor that improves the performance of the device and shortens verification time.

BACKGROUND OF THE INVENTION As the information society progresses, various technologies related to maintaining the confidentiality of information processing systems are being developed. For example, in place of conventional ID cards, which are often lost or stolen, for controlling entry into computer rooms, personal verification systems are being introduced in which each individual's fingerprints are registered in advance and verified upon entering the room. However, since it is aimed at particularly important equipment, there is a desire to develop a device with even higher performance.

[Conventional technology]

FIG. 6 is a principle diagram showing a conventional total reflection filtering type fingerprint sensor.

In the figure, the fingerprint sensor includes a transparent flat plate 21 that closely contacts the subject 1 and propagates reflected light, a fingerprint input unit 2 that includes a light source 22 that illuminates the subject through the transparent flat plate, and a lower surface of the transparent flat plate 21. A fingerprint imaging section 3 includes an optical element, for example, a hologram diffraction grating 31, which is disposed in the transparent flat plate 21 to derive the fingerprint image of the subject 1 to the outside, and an image pickup element 32 to photograph the fingerprint image led to the outside. It is made up of.

Even if the subject (finger) l is brought into close contact with the transparent flat plate 21 with an appropriate pressing force, the subject will have unevenness such as fingerprints, and the convex portions 11 will directly contact the transparent flat plate 21, but the concave portions 12 will not allow air space. The transparent flat plate 21 is contacted through the transparent plate 21 .

Light that passes through the transparent flat plate 21 from the light source 22 and reaches the recess 12 is scattered by the recess 12, enters the transparent flat plate 21 again, and then exits to the air layer below the transparent flat plate 21 according to Snell's law.

On the other hand, the light that reaches the surface that the convex portion 11 abuts from the light source 22 is scattered at the contact surface and a part of it is emitted to the air layer below the transparent flat plate 21. The remaining light incident on the interface of the air layer is totally reflected at the interface, propagates inside the transparent flat plate 21, and is guided to the outside by the hologram diffraction grating 31.

The image led out to the outside by the hologram diffraction grating 31 is an image representing the convex portion 11, that is, a fingerprint image, and the fingerprint image is detected by photographing the image led out to the outside by the image sensor 32 and inputting the output voltage to the device. can do.

[Problem that the invention seeks to solve]

FIG. 2 is a diagram showing problems in the conventional fingerprint sensor.

In a personal verification system, the area IA of fingerprints etc. is several meters long.
A width of approximately m square is sufficient. However, as shown in FIG. 2, the contact surface 2A of the subject in a conventional fingerprint sensor is made sufficiently wider than the required width, for example, by several times, taking into account the tolerance to the size of the subject and the deviation of the contact position. 10m
The size is about 0 m square, and the image processing is performed over the entire area of the contact surface.

Therefore, when attempting to identify fine patterns in the wide area, there are problems in that the equipment becomes expensive and it becomes difficult to ensure resolution.

[Means for solving problems]

FIG. 1 is a block diagram showing the basic configuration of the present invention.

The above-mentioned problem is caused by the fingerprint input unit 2, which is equipped with a transparent flat plate 21 that brings the subject 1 into close contact with the subject 1 and propagates reflected light, and a light source 22 that irradiates the subject through the transparent flat plate, as shown in FIG. A fingerprint imaging section 3 includes an optical element 31 that guides the fingerprint image of the subject 1 that has been brought into close contact with the transparent flat plate to the outside, and an image sensor 32 that photographs the fingerprint image that has been led out to the outside, and a fingerprint imaging unit 3 that is in close contact with the transparent flat plate 21. An optical element 41 that guides the image of the subject 1 to the outside from a transparent flat plate, a 4-split photodetector 42 that detects the image of the subject 1 that has been guided to the outside, and a 4-split photodetector 42 that detects the subject from the output signal of the 4-split photodetector. A position detection unit 4 includes a position detection circuit 43 for detecting the center position of the image of the object, an XY stage 51 on which an image sensor is loaded, and an output signal from the position detection circuit 43 to move the XY stage, and to detect the image of the subject and Stage control circuit 5 that matches the center position of the image sensor
This problem is solved by the fingerprint sensor of the present invention, which is provided with an image sensor moving section 5 having an image sensor moving section 2.

[Effect]

In FIG. 1, the position detection unit 4 detects the difference between the center position of the image of the subject and the center position of the image sensor, and the XY stage 51 and stage control circuit 52 detect the center position of the image of the subject and the center of the image sensor. By matching the positions, even if the contact surface of the subject 1 is sufficiently wide compared to the required imaging area, it is possible to image only the necessary limited area without imaging the entire surface of the contact surface. , it becomes possible to easily improve the resolution of imaging, and it is also possible to shorten the time required for verification.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 3 is a block diagram showing one embodiment of the present invention, and Fig. 4 is a block diagram showing an embodiment of the present invention.
FIG. 5, which is a diagram showing a divided photodetector, is an example of a fingerprint image obtained by the fingerprint sensor of the present invention, and the same object is represented by the same symbol throughout the diagram.

The difference between the fingerprint sensor according to the present invention shown in FIG. 3 and the conventional fingerprint sensor shown in FIG. 4 and an image sensor moving section 5.

In FIG. 3, the fingerprint image of the subject brought into close contact with the transparent flat plate 21 propagates inside the transparent flat plate 21 and is led out through optical elements such as hologram diffraction gratings 31 or 41 disposed at both ends of the transparent flat plate 21. Ru.

The fingerprint image led out to the outside through the hologram diffraction grating 31 is photographed by the imaging device 32, and the fingerprint image led out to the outside through the hologram diffraction grating 41 is detected by the 4-split photodetector 42.

The four-division photodetector 42 consists of four photodiodes 44 as shown in FIG.
The photodiodes 44 are configured to detect the light reflected by the respective photodiodes 44. For example, when the test portion IA is brought into contact with the center of the contact surface 2A, the amount of light reflected in each quadrant of the contact surface is approximately equal, and the output voltages output from the four photodiodes 44 are also equal. However, when the test portion IA deviates from the center of the contact surface 2A, the amount of light reflected in each quadrant differs, and a corresponding difference occurs in the output voltage of the photodiode 44.

The position detection circuit 43 includes a circuit that compares the output voltages of the respective photodiodes 44, and by comparing the output voltages, it is possible to determine the distance from which the center of the test portion IA deviates from the center of the contact surface 2A, that is, Δ, , ΔY can be detected. Signals indicating the distance between the center of the test portion IA and the center of the contact surface 2A, that is, ΔX and ΔY, are input to the stage control circuit 52, and the stage control circuit 52 uses the above signals to control the The XY stage 51 is driven in the X direction or the Y direction so that the center of the image sensor 32 and the center of the subject IA detected by the 4-split photodetector 42 match.

The fingerprint image photographed by such a fingerprint sensor has no wasted parts as shown in FIG. 5, making it possible to easily improve the imaging resolution and shorten the time required for verification.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a fingerprint sensor that improves the resolution of an imaged pattern, improves the performance of the device, and shortens the matching time.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of the present invention, Fig. 2 is a diagram showing problems in conventional fingerprint sensors, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is divided into four parts. FIG. 5 is a diagram showing a photodetector. FIG. 5 is an example of a fingerprint image produced by the fingerprint sensor of the present invention. FIG. 6 is a principle diagram showing a conventional fingerprint sensor. In the figure, 1 is a finger (subject), IA is a test part, 2 is a fingerprint input part, 2A is a contact surface, 3 is a fingerprint imaging part, 4 is a position detection part, 5 is an image sensor moving part, and 21 is transparent Flat plate, 22 is a light source, 31.
41 is a hologram diffraction grating (optical element), 32 is an image sensor, 42 is a 4-split photodetector, 43 is a position detection circuit, 44 is a photodiode, and 51 is an XY
The stage, 52, is a stage control circuit.
Diagram showing T drawing 2 Diagram showing θF4 Tsuji-Usho 1 Force 7 Fuku mouth/So 2 Circle 3

Claims (1)

[Claims] A fingerprint input unit (2) comprising a transparent flat plate (21) that closely contacts the subject (1) and propagates reflected light, and a light source (22) that illuminates the subject through the transparent flat plate; (21), an optical element (31) for guiding a fingerprint image of the subject (1) in close contact with the transparent flat plate to the outside, and an imaging device (32) for photographing the fingerprint image led out to the outside. an optical element (41) that guides an image of the subject (1) brought into close contact with a transparent flat plate (21) to the outside from the transparent flat plate; a position detection unit (4) comprising a four-division photodetector (42) that detects an image; and a position detection circuit (43) that detects the center position of the image of the subject from the output signal of the four-division photodetector; , an XY stage (51) on which the image sensor is mounted, and a stage that moves the XY stage according to the output signal of the position detection circuit (43) to match the image of the subject with the center position of the image sensor. A fingerprint sensor comprising: an image sensor moving section (5) equipped with a control circuit (52).