JP2002366939A - Device for detecting fingerprint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fingerprint detecting device capable of detecting a fingerprint without being affected by moisture, oil, etc., on a finger surface. SOLUTION: This fingerprint detecting device is provided with a flat plate 1, a thin film layer 2 that shows a different color in accordance with a temperature distribution of the finger surface placed and pressed against one surface of the flat plate 1, a light source 4 that emits light to the flat plate 1 and makes the light go through the flat plate 1 to be made incident on the thin film layer 2, and an imaging part 5 arranged in front of light absorbed and reflected by the thin film layer 2 for picking-up the light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fingerprint detection device used for personal authentication using, for example, a fingerprint collation system or a fingerprint authentication system.

[0002]

2. Description of the Related Art As conventional optical fingerprint detection devices, there are known a total reflection fingerprint detection device using a prism as shown in FIG. 3 and an optical path separation fingerprint detection device as shown in FIG. ing. In the total reflection type fingerprint detection device shown in FIG. 3, the prism 9 is illuminated from the light source 4 so as to satisfy the condition of total reflection inside the inclined surface of the prism 9. Then, the light from the light source 4 is totally reflected as shown by an arrow a. On the other hand, since the refractive index of moisture or the like on the surface of the finger 3 is different from the refractive index of air in the fingerprint convex portion 6, total reflection does not occur, and light from the light source 4 is scattered as indicated by arrow B. Therefore, a contrast fingerprint image can be obtained by receiving the difference in brightness between the total reflection light of the fingerprint concave portion 7 and the scattered light of the fingerprint convex portion 6 by the imaging section 5 such as a CCD. Fingerprint matching and personal authentication.

In the fingerprint detecting device having the above structure, when acrylic is used as the material of the prism 9, the refractive index of the optical path from acrylic to air is about 0.67,
The refractive index of the light path from acrylic to water is about 0.89.
In this case, the condition that the incident light is totally reflected at the interface between acrylic and air is 42 degrees or more, and the condition that the incident light is totally reflected at the interface between acrylic and water is 63 degrees or more. When the angle of incidence of light on the side is 45 degrees, the light is totally reflected at the fingerprint concave portion 7 at 42 degrees or more, which is the condition for total reflection. Therefore, light is transmitted and scattered without being totally reflected.

In the fingerprint detection device shown in FIG. 4, the light from the light source 4 is incident on the prism 9 having one surface coated with black, but the imaging unit 5 is arranged in an area where the light from the fingerprint recess 7 does not reach. As shown by the arrow C, the imaging unit 5 receives only the scattered light from the fingerprint convex part 6, thereby obtaining a fingerprint image with contrast.

[0005]

However, the fingerprint sensor of the total reflection type shown in FIG. That is, when the surface is dry, the surface of the fingerprint convex portion 6 has almost the same condition as when the air is interposed similarly to the fingerprint concave portion 7, and the incident light of the prism 9 is totally reflected by the fingerprint convex portion 6 as well. There is a problem that the imaging unit 5 may not be able to obtain a fingerprint image with contrast. Conversely, if the fingerprint convex portion 6 has excessive moisture or oil content, a residual fingerprint is likely to remain on the surface of the detection surface, which is the prism main surface 8, which adversely affects the acquisition of a fingerprint image of the target finger. There were also problems. Further, even in the optical path separation type fingerprint detection device invented for the purpose of reducing these effects, the scattered light is not stabilized due to the surface condition of the fingerprint convex portion 6, and the imaging unit for imaging the scattered light is not provided. 5, there was also a problem that a fingerprint image with high contrast could not be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide a fingerprint detecting device capable of detecting a finger without being affected by the condition of the finger surface.

[0007]

According to the present invention, there is provided a fingerprint detecting apparatus comprising: a transparent body; a thin film layer which shows a different color in accordance with a temperature distribution on a surface of the finger which is adhered to and pressed against one side of the transparent body; A light source that irradiates the transparent body with light and passes light through the transparent body to make light incident on the thin film layer, and an imaging unit that is provided in front of the light absorbed and reflected by the thin film layer and captures light, It is provided.

[0008] In the fingerprint detection device according to the present invention, the transparent body is formed of a flat plate.

In the fingerprint detecting device according to the present invention, the transparent body is a prism.

[0010] In the fingerprint detection device according to the present invention, the thin film layer is made of cholesteric liquid crystal.

In the fingerprint detecting device according to the present invention, the transparent body is made of a material having a low thermal conductivity.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. The same or corresponding members and portions as those in FIGS. 3 and 4 are denoted by the same reference numerals. Embodiment 1 FIG. FIG. 1 is an explanatory view of a fingerprint detection device according to a first embodiment of the present invention. In this fingerprint detection device, a thermochromism phenomenon is applied to a main surface 8 of a flat plate 1 made of an acrylic transparent material having a low thermal conductivity. A thin film layer 2 composed of cholesteric liquid crystal is applied. This cholesteric liquid crystal has a property that its color changes in accordance with a change in ambient temperature. On the opposite side of the main surface 8 of the flat plate 1, a light source 4 for irradiating light and an imaging unit 5 for obtaining reflected light indicated by an arrow d from the main surface 8 are arranged.

In this fingerprint detection device, the temperature distribution on the surface of the finger 3 is transmitted to the thin film layer 2 by pressing the finger 3 against the thin film layer 2. The transmitted temperature distribution appears as a color change in the thin film layer 2, for example, from low temperature to high temperature, black →
A color distribution such as red → orange → yellow → green → blue is formed. That is,
High-temperature side discolored portion 11 with which fingerprint convex portion 6 of thin film layer 2 is in contact
Shows the color on the high-temperature side, and shows the color on the low-temperature side in the low-temperature side discoloration portion 12 facing the fingerprint concave portion 7 of the thin film layer 2. The light from the light source 4 is absorbed and reflected by the color-distributed thin film layer 2,
The color distribution pattern that appears due to the temperature difference between the fingerprint convex portion 6 and the fingerprint concave portion 7 of the finger 3 is captured on the image capturing section 5, and the fingerprint pattern is detected. Then, for example, fingerprint collation is performed based on this information, and personal authentication can be performed. In this fingerprint detection device, when a flat plate made of a material having a relatively high thermal conductivity is used, the heat distribution transmitted to the thin film layer 2 is easily diffused to the periphery, and the boundary of each color distribution in the thin film layer 2 is determined. Is blurred and the fingerprint pattern is blurred, so that acrylic, which is a material having low thermal conductivity, is used. Of course, the present invention is not limited to this, and may be, for example, glass having a low thermal conductivity.

Embodiment 2 FIG. FIG. 2 is an explanatory diagram of a fingerprint detection device according to Embodiment 2 of the present invention. In this fingerprint detection device, a thin film layer 2 composed of a cholesteric liquid crystal utilizing a thermochromism phenomenon is formed on a main surface 8 of a prism 9 which is a transparent member made of acrylic having a low thermal conductivity. On the opposite side of the main surface 8 of the prism 8, a light source 4 and an imaging unit 5 that obtains reflected light emitted from the light source 4 and reflected by the main surface 8 as indicated by an arrow E are arranged. The light source 4 is arranged so as to be totally reflected by the main surface 8. Also in this fingerprint detection device, in order to prevent the boundaries of the respective color distributions in the thin film layer 2 from being blurred and the fingerprint pattern from being blurred, acrylic, which is a material having low thermal conductivity, is used for the prism 9. However, it may be glass.

In this fingerprint detection device, a color distribution is formed in the thin film layer 2 by pressing a finger 3 against the thin film layer 2 as in the fingerprint detection device of the first embodiment. The light from the light source 4 is absorbed and totally reflected in the color-distributed thin film layer 2, and a color distribution pattern appearing due to a temperature difference between the fingerprint convex portion 6 and the fingerprint concave portion 7 of the finger 3 is imaged by the imaging section 5. A fingerprint pattern is detected. In the above embodiments, the thin film layer is made of cholesteric liquid crystal. However, the present invention is not limited to this, and any thin film layer may be used as long as it changes color in response to a temperature change.

[0016]

As described above, according to the fingerprint detection device of the present invention, different colors are displayed in accordance with the temperature distribution of the transparent body and the surface of the finger pressed against the transparent body. A thin film layer, a light source that irradiates the transparent body with light and passes light through the transparent body to cause light to enter the thin film layer, and is provided in front of the light absorbed and reflected by the thin film layer to capture light. Since the image pickup unit is provided, the fingerprint can be detected based on the temperature distribution information on the finger surface, and is not affected by moisture, oil, drying, or the like on the finger surface. In addition, the imaging unit captures the color distribution pattern and processes the color information at the same time to detect the fingerprint with higher accuracy.

Further, according to the fingerprint detecting apparatus of the present invention, since the transparent body is formed of a flat plate, the transparent body can be easily processed and compact, and the fingerprint detecting apparatus can be made small and inexpensive. can do.

According to the fingerprint detecting device of the present invention, since the transparent body is a prism, for example, when a total reflection method in which light from a light source is totally reflected by a thin film layer is adopted, the light from the light source is reflected by the prism. Efficiently incident on

Further, according to the fingerprint detection device of the present invention, since the thin film layer is made of cholesteric liquid crystal, a delicate temperature change can be regarded as a color change.
Fingerprints can be detected with high accuracy.

According to the fingerprint detecting device of the present invention, since the transparent body is made of a material having a low thermal conductivity,
Diffusion of the heat distribution on the finger surface thermally transferred to the thin film layer is suppressed, sharpness at the boundary of each color distribution in the thin film layer is secured, and a fingerprint can be detected with higher accuracy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a fingerprint detection device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a fingerprint detection device according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional total reflection type fingerprint detection device.

FIG. 4 is an explanatory diagram of a conventional light separation type fingerprint detection device.

[Explanation of symbols]

1 flat plate (transparent), 2 thin film layers, 3 fingers, 4 light sources,
5 imaging part, 6 fingerprint convex part, 7 fingerprint concave part, 9 prism (transparent body).

Claims (5)

[Claims] 1. A transparent body, a thin film layer having a different color according to the temperature distribution of the surface of a finger pressed and adhered to one surface of the transparent body, and irradiating the transparent body with light to pass through the transparent body. A fingerprint detection device comprising: a light source for causing light to enter the thin film layer; and an imaging unit provided in front of the light absorbed and reflected by the thin film layer to capture light. 2. The fingerprint detection device according to claim 1, wherein the transparent body is a flat plate. 3. The fingerprint detection device according to claim 1, wherein the transparent body is a prism. 4. The fingerprint detecting device according to claim 1, wherein the thin film layer is made of a cholesteric liquid crystal. 5. The fingerprint detecting device according to claim 1, wherein the transparent body is made of a material having low thermal conductivity.