JPH07107704B2 - Concavo-convex shape detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to an apparatus capable of easily and accurately detecting an uneven shape of an object such as a fingerprint with a thin structure. With the aim of providing a device that is thin and can accurately detect the shape, an uneven object to be detected is mounted on one surface of a transparent light guide body having two parallel surfaces. The light incident from the outside of the other surface is scattered at the contact surface between the light guide and the object, then propagates through the light guide, and the light emitted from the light guide detects the uneven shape of the object. In the device described above, a curved surface for focusing a light beam and an image sensor are provided as an imaging system for detecting the uneven shape, and the light is reflected on the surface of the light guide perpendicular to the light propagating in the longitudinal direction in the light guide. The beam converging curved surface members are arranged so as to face each other, and the light beam concentrating member is provided outside the converging curved surface member. An image sensor for detecting an image of each uneven point formed by the scattered light is provided at a position where the light emitted from the bundled curved body is focused.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device capable of easily and accurately detecting an uneven shape of an object such as a fingerprint with a thin structure.

Conventionally, research has been conducted on fingerprint matching for personal identification,
At that time, the uneven shape formed by the fingerprint of the finger pressed against one surface of the parallel transparent light guide is detected after light is incident from the outside of the other surface and propagated in the light guide. At this time, since the configuration became large, it was desired to easily develop a thin device.

[Prior Art] Research has been conducted to identify an individual with a fingerprint and enable entry into a computer room or use a terminal connected to a computer. This is because fingerprints have the characteristics of being "universal" and "correction invariant". At this time, a finger is placed on the flat plate of the fingerprint sensor, the uneven shape of the fingerprint is detected as image data by the light proved from below, and collated with the data stored in advance in the data file. The uneven shape of the fingerprint sensor is detected by the device shown in FIGS. 9 and 10. In FIG. 9, reference numeral 1 denotes, for example, a finger on a fingerprint sensor as an object for detecting the uneven shape. 2 is a right-angle prism, 3 is a light source of illumination light, and 4 is an imaging system. The finger 1 is pressed against the slope of the right-angled prism 2 and illuminated from a light source 3 provided on the side. When there is unevenness like the fingerprint of the finger 1, the concave portion 5 is called the valley line of the fingerprint in the air layer, and the convex portion 6 is called the ridge line of the fingerprint. The light is reflected and goes straight to another side different from the light source of the prism 2 (solid line in FIG. 9). Also, at the ridge of the fingerprint shown as 6, the illumination light is scattered in all directions inside the prism (broken line in FIG. 9). Therefore, the light reflected from the concave portion 5 jumps out from the prism 2 and the imaging system 4
The light strongly entering the lens and reflected by the convex part weakly enters the imaging system 4. In the image pickup system 4, a lens focusing portion (not shown) is used, and a fingerprint image with contrast can be obtained by the intensity of light corresponding to the valley line and the ridge line of the fingerprint of the finger 1.

FIG. 10 shows an apparatus for obtaining an image having a higher contrast than that of FIG. In FIG. 6, reference numeral 7 denotes a light guide, whose surfaces 7-1 and 7-2 are parallel to each other, and which uses transparent glass plastic as a material, and 8
Indicates a diffraction grating including a lens. One surface 7 of light guide 7
-2 is pressed with a finger, and the illumination light is made to enter almost vertically from the other surface 7-1. There is an air layer in the recess 5 of the finger 1, and the illumination light in this case enters the recess 5, is reflected at a predetermined place, and is scattered in all directions. Most of the light re-enters the surface 7-2 in the vertical direction and travels straight in the light guide 7, while the other surface 7-
It emerges from 1 (R1) and disappears in the distance. On the other hand, the light hitting the convex portion 6 is scattered in the light guide body 7 so that the convex portion 6 is used as a new light source, and a part of the light is emitted from the light guide body 7 as indicated by R2, and Is a light guide 7 as indicated by R3 while totally reflecting
Propagates inside. An image of the component indicated by R3 is formed by the diffraction grating 8 and a fingerprint image is obtained by the image pickup system 4 provided outside the light guide 7 such as one using a CCD. The diffraction grating 8 is additionally provided with a lens function.

[Problems to be Solved by the Invention] In the devices shown in FIGS. 9 and 10, the imaging system is provided in a direction away from the light propagation path with respect to the position where the finger is applied. Therefore, even if the light guide body is used, the thickness of the device is increased due to the imaging system.

It was inconvenient because the sensor could not be embedded inside the door when it was attached to the door to control the entry into the computer room like a fingerprint collation system.

An object of the present invention is to improve the above-mentioned drawbacks and to provide a thin device capable of accurately detecting an uneven shape of an object by devising a place for providing an imaging system within the thickness of a light guide. is there.

[Means for Solving the Problems] FIG. 1 is a diagram showing a principle configuration of the present invention. In FIG. 1, an uneven object 10 to be detected is placed on one surface 7-2 of a transparent light guide 7 having two surfaces parallel to each other, and is incident from the outside of the other surface 7-2. The light thus guided is guided by the light guide 7 and the object 1.
The present invention has the following configuration in an apparatus in which light is emitted from the light guide after being scattered by a contact surface with the light guide, and is then detected by the light emitted from the light guide. That is, a curved surface body for focusing a light beam and an image sensor are provided as an imaging system for detecting the uneven shape, and the light beam is focused on the surface of the light guide body which is perpendicular to the light propagating in the longitudinal direction of the light guide body. An image for detecting an image of each uneven point formed by the scattered light at a position where the light-beam focusing curved body is focused on the outside of the focusing curved body with the curved curved bodies facing each other. A sensor is provided and configured.

[Operation] In FIG. 1, the object 10 whose concave and convex shape is to be detected is the light guide 7.
It is placed on one surface 7-2 and the illumination light is incident on the light guide 7 from the other surface 7-1. The light reflected by the convex portion 6 of the object 10 and scattered inside the light guide 7 propagates at points P1, P2, ... While repeating total reflection. Now, the curved surface for focusing the surface light beam perpendicular to the light totally reflected at point P3
11 are provided so as to face each other, and the light totally reflected outside the light guide 7 is focused. Image sensor at the focused position
Provide 12 Therefore, the image sensor 12 determines the uneven shape of the object 10. The arrangement positions of the curved surface body 11 for focusing the light beam and the image sensor 12 are present in the respective extension planes of the one surface 7-2 and the other surface 7-1 in the longitudinal direction of the light guide body 7 as shown in the figure. Therefore, the arrangement positions are within the thickness of the light guide 7.

[Embodiment] FIG. 2 shows an embodiment of the present invention in which the curved surface for focusing the light beam is a hemispherical plano-convex lens and an aperture stop is provided at the joint with the light guide 7. In FIG. 2, 13 indicates a cylindrical portion of the lens and 14 indicates a convex lens portion. 15 is the aperture stop,
16 indicates a mirror. In FIG. 2, when a finger is placed on one surface 7-2 of the light guide 7, light scattered by the ridges of the fingerprint passes through P1, P2, and P3, and at the surface M of the mirror 16. It is drawn so that it reflects. FIG. 3 shows the light guide 7 extended and expanded on the scattered light in order to explain the light of P1 to M. As shown in FIG. 3, if the optical path of the straight traveling light from the ridge which becomes the convex portion 6 is taken as the optical axis, one surface 7-2 of the light guide 7 is shown.
Since the (fingerprint input surface) is inclined, it can be seen that the surface of the image sensor 12 also needs to be inclined. In focusing the light beam by the convex lens, aberration appears remarkably, so the aperture stop 15 is provided at the position of the center of curvature of the convex lens. The aperture stop 15 is advantageously arranged on the surface of the light guide 7. In reality, since the fingerprint input surface and the optical axis are tilted, the aspect ratio of the fingerprint image changes, and the image size also changes depending on the focal length of the lens, so when processing the data captured by the image sensor. Needs to be kept in mind.

FIG. 4 further models the optical system of FIG.
When the spherical lens of 3 is used, the relationship between the fingerprint input surface and the sensor surface is shown. The center of curvature of the lens is the origin O, the optical axis direction is the z-axis, the direction of the aperture stop is the y-axis, and the x-axis is orthogonal to the y-axis and the z-axis. For example, on the fingerprint input surface (finger contact surface), take the ridge B on the z-axis extension,
Fig. 5 shows the results of calculating the change in image position on the sensor surface when the distance L1 between BOs is 90 mm, the distance between AB and BC is 10 mm, the refractive index of the light guide is 1.5, and the radius of curvature r is 10 mm. Is shown in. In Fig. 5, the distance L2 of OB 'is about 37.5 and the dotted line is the original image position (flat surface), but the calculation result is the solid line A'B'.
C ′, and the deviation at the point B ′ is less than 200 μmm in the z-axis direction. Within this range, the entire fingerprint of one finger can be focused with only a single spherical surface within the depth of focus.

Next, FIG. 6 is a diagram showing the structure of the aperture stop. Light guide 7
The thickness t is selected so that the center of curvature P of the spherical lens coincides with the other surface 7-1 of the light guide 7, and the aperture stop is formed by the antireflection film 16 having an elliptical hole. Therefore, the light ray incident on the ellipse is totally reflected, but the light ray incident on the film portion outside the ellipse is absorbed without being reflected. The reason why the ellipse is used is that the beam is obliquely incident on the reflecting surface, so that the beam effectively operates as a circular aperture stop.

Next, FIG. 7 is a diagram showing a specific example of detecting a fingerprint image according to the present invention. When fingerprint collation is used for entering room management, it is preferable to embed and mount the fingerprint input device in the door 17 of the room in terms of ease of use and aesthetics. By embedding the light guide in a bent shape near the knob 18, the fingerprint image input optical system can be installed without spoiling the appearance. The reference numerals of the respective parts in FIG. 7 are the same as those described above.

FIG. 8 is a diagram showing still another application example. When incorporating a fingerprint collation system for the purpose of limiting the number of people who can access the database in the information processing system, if a fingerprint input device is not specially provided, for example, if it can be embedded in the keyboard 19, it does not spoil the appearance. Also, the system will be easy to use. FIG. 8 shows an example in which the keyboard 19 is embedded, and 20 indicates a terminal device.

[Effects of the Invention] As described above, according to the present invention, since the curved surface for focusing the light beam is used, the optical system can be made thin. Therefore, when it is applied to a fingerprint matching system, it can be easily embedded in a device without impairing its appearance.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a diagram for explaining the operation of an optical system, and FIG. 4 is an optical system of FIG. Fig. 5 is a model diagram of Fig. 5, Fig. 5 is a diagram for explaining the calculation result of the image position, Fig. 6 is a diagram showing a configuration example of an aperture stop, and Figs. 7 and 8 are specific examples / applications for detecting a fingerprint image. FIG. 9 and FIG. 10 are diagrams showing an example of the configuration of a conventional device. 1 ... Finger, 4 ... Imaging system 5 ... Fingerprint valley line, 6 ... Fingerprint ridge line 7 ... Light guide, 10 ... Uneven object 11 ... Light beam focusing curved surface 12 ... Image sensor

Claims (3)

[Claims] 1. An uneven object to be detected is placed on one surface of a transparent light guide having two parallel surfaces, and light incident from the outside of the other surface is used as the light guide. In a device that scatters inside the light guide at the contact surface with the object, propagates through the light guide, and detects the uneven shape of the object by the light emitted from the light guide, a light beam focusing as an imaging system to detect the uneven shape A curved surface body for focusing the light beam, the curved surface body for focusing the light beam is arranged to face the surface of the light guide body which is perpendicular to the light propagating in the longitudinal direction in the light guide body. An image sensor for detecting an image of each uneven point formed by the scattered light is provided at a position for converging the light emitted from the curved body for converging the light beam on the outside of the uneven shape detection. apparatus. 2. The detecting device according to claim 1, further comprising an aperture stop at a position of a center of curvature of the curved surface, and a normal line of a light-receiving surface of the image sensor forms a predetermined angle with an optical axis from the uneven object. An unevenness shape detecting device characterized in that an image sensor is provided in the. 3. The detection device according to claim 1, wherein the light propagating in the transparent light guide is totally reflected at least once by the transparent light guide, and then is imaged on the image sensor. A concave-convex shape detecting device characterized in that