JPH0478980A - Uneven shape detector - Google Patents

Abstract

PURPOSE:To reduce assembly error by emitting fully reflected scattered beams to the outside of a transparent light transmission body, forming a spherical face or a non-spherical image formation mirror, where the image is formed, on one part of the transparent light transmission body and arranging an image sensor at a position where the image is formed by the image formation mirror. CONSTITUTION:A spherical mirror is formed by deposition, etc., while being spherically shaped on one end face of a transparent light transmission body 20, and an image sensor 4 is arranged at the image forming position of the spherical mirror 8. When an uneven object 10 gets contact with one face of the transparent light transmission body 20, scattered beams 11 generated from projecting parts P as the result of lighting a contact face S are propagated in the transparent light transmission body 20 while being fully reflected. The scattered beams 11 fully reflected from the projecting parts P are emitted to the outside of the transparent light transmission body 20 by the spherical mirror 8 and image-formed on the image sensor 4 and therefore, the uneven pattern image of the uneven object 10 is converted to a picture data. Thus, since the spherical mirror 8 is formed on one face of the transparent light transmission body 20, an optical system is integrally formed and assembly error is reduced.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an uneven shape detection device for detecting uneven pattern images such as fingerprints, and aims to provide an optical system with less assembly error and improved durability. A concave-convex object is brought into contact with one surface of a transparent light guide, and the scattered light generated as a result of illuminating the contact surface is totally reflected at least once within the transparent light guide, and the totally reflected scattered light is imaged to form an image. In an uneven shape detection device for obtaining an uneven pattern image of an uneven object, a spherical or aspherical imaging mirror is attached to the transparent light guide to emit the totally reflected scattered light to the outside of the transparent light guide and form an image. An image sensor is arranged at a position where an image is formed by the imaging mirror.

[Industrial application field]

The present invention relates to an improvement in an uneven shape detection device for detecting an uneven pattern image such as a fingerprint.

There is a system that performs fingerprint matching as a personal identification method.

This system usually handles the fingerprint as an image, and requires an input device (an uneven shape detection device, hereinafter referred to as a fingerprint image input device) that detects the uneven pattern image of the fingerprint and converts it into image data.

For this reason, an optical system is used that irradiates the finger with light, removes the scattered light generated from the concave parts of the scattered light generated by the fingerprint, and forms an image of the scattered light generated from the convex parts. It is required to be easy and to have few assembly errors.

[Conventional technology]

FIG. 4 is a sectional view of a conventional example (part 1) of a fingerprint image input device, and FIG. 5 is a sectional view of a conventional example (part 2) of a fingerprint image input device. Note that FIG. 4 shows the imaging state of scattered light emitted from each point on the finger, and FIG. 5 shows the imaging state of the light beam emitted from one point on the finger.

FIG. 4 shows an example of a fingerprint image input device that detects convex portions (ridges) of a fingerprint and converts them into image data.

In the figure, the transparent light guide 2 is, for example, a processed glass plate, and the left end surface in the figure has a flat mirror 6 formed by vapor deposition of aluminum or the like.
is formed, and a lens 3 is bonded to the right end surface corresponding to the plane mirror 6. An image sensor 4 is placed at the position where the image is formed by the lens 3, and a light source 5 is placed below the transparent light guide 2.

In such a fingerprint image input device, when the finger 1 is pressed against the upper surface (contact surface) of the transparent light guide 2, the convex part P of the finger 1 comes into contact, but the concave part Q does not come into contact. Therefore, the reflected/scattered light from the concave portion Q of the finger passes through the air through the transparent light guide 2.
Therefore, there is no component that transmits downward through the transparent light guide 2 as shown by the broken line in the figure and propagates through the transparent light guide 2 while being totally reflected.

On the other hand, the reflected/scattered light from the convex portion P directly enters the transparent light guide 2 from the finger 1 as a spherical wave, and a part of it satisfies the condition of total reflection in the transparent light guide 2 and becomes transparent. The light propagates through the light guide 2 through repeated total reflection.

Then, this total reflection component is reflected by the plane mirror 6, exits from the right end surface (output surface), is imaged by the lens 3 on the image sensor 4, and is converted into image data.

Note that the reflected and scattered light from the convex portion is a spherical wave, so when using a single spherical lens to form an image with little aberration, the center of curvature of the lens 3 should be centered as shown in Figure 5. An aperture stop 7 is required.

[Problems to be Solved by the Invention] When manufacturing the optical system of the fingerprint image input device described above,
A plane mirror 6 and an aperture stop 7 are formed on the end face of the transparent light guide 2 by vapor deposition or bonding, and a lens 3 is bonded thereto.

As described above, the manufacturing process of conventional optical systems is complicated and costly, and there are problems such as assembly errors caused by adhesion of lenses and durability.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an uneven shape detection device with improved assembly errors and durability.

[Means to solve the problem]

The principle components will be extracted from the configuration diagram of the first embodiment in FIG. 1 and explained.

20 is a transparent light guide, 4 is an image sensor, and 5 is a light source.

8 is a spherical imaging mirror (or aspherical imaging mirror, hereinafter referred to as spherical mirror) formed on one surface of the transparent light guide 20
Then, the scattered light 11 from the convex portion that has been reflected at least once in the transparent light guide 20 is emitted to the outside and is imaged on the image sensor 4.

[Effect]

(1) When the uneven object 10 is brought into contact with one surface of the transparent light guide 20, the scattered light 11 from the convex portion P generated as a result of illuminating the contact surface is totally reflected inside the transparent light guide 20. propagate.

The scattered light 11 totally reflected from this convex portion P is transferred to the spherical mirror 8
The light is emitted to the outside of the transparent light guide 20 and formed into an image on the image sensor 4.

As a result, the uneven pattern image of the uneven object 10 is converted into image data.

By forming the spherical mirror 8 on one surface of the transparent light guide 20 in this manner, a lens for image formation becomes unnecessary.

Note that the spherical mirror 8 is formed by shaping one surface of the transparent light guide 20 into a spherical surface and performing aluminum vapor deposition on the spherical surface, so the optical system can be integrally molded, improving assembly errors and improving durability. sexual improvement is achieved.

(2) In the above configuration, if an aperture stop is provided on the exit surface, imaging aberrations are improved.

(3) Furthermore, if the inclination of the spherical mirror 8 is set, for example, so that the difference in path length of the scattered light emitted from each convex portion to the imaging plane is minimized, trapezoidal distortion is improved by the so-called tilting effect. .

(4) Furthermore, among the scattered light emitted from the center of the contact surface,
If the scattered light emitted from the center of the spherical mirror 8 is set as the optical axis, and the forward axis and the normal line of the light receiving surface of the image sensor 4 are set to form a predetermined angle, the difference in the optical path length of the scattered light to the spherical mirror 8 is determined. The tilt of the image plane is corrected.

〔Example〕

Embodiments of the present invention will be described in detail with reference to the drawings.

(First example) FIG. 1 is a block diagram of the first embodiment.

The transparent light guide 20 is, for example, a glass plate with a predetermined thickness, one end surface of which is shaped into a spherical surface, and a spherical mirror 8 is formed by vapor deposition or the like.

Further, the image sensor 4 is a two-dimensional sensor, and is arranged at the imaging position of the spherical mirror 8.

Here, the curvature of the spherical surface is determined so that the totally reflected scattered light 11 forms an image outside the transparent light guide 20, and the center of the curvature is the optical axis 12 (the scattered light emitted from the center of the contact surface S). Of these, the light beam emitted from the center of the spherical mirror 8 is determined to be parallel to the contact surface S (optical axis 12).

Touch the contact surface S of the transparent light guide 20 formed in this way with a finger 1 (
When the uneven object 10) is pressed and irradiated with light by the light source 5, the light is reflected and scattered on the finger surface and inside.

Among these, the scattered light from the concave portion Ω of the finger passes through the air and enters the transparent light guide 20, so there is no component that is totally reflected and propagated through the transparent light guide 20.

However, the reflected/scattered light from the convex portion P directly enters the transparent light guide 20 from the finger as a spherical wave, and a part of it satisfies the condition for total reflection in the transparent light guide 20.

Up to this point, it is the same as the conventional example shown in FIGS. 4 and 5, but the imaging of reflected and scattered light from the convex portion P is performed as follows.

Of the light scattered by the convex part P of the fingerprint, the transparent light guide 20
The scattered light 11 that satisfies the total internal reflection condition and propagates through the transparent light guide 20 is reflected by the spherical mirror 8 formed on the end face of the transparent light guide, and is emitted into the air from one end face (output face) 9. It is taken out.

Since the spherical mirror 8 also serves as an imaging optical system (concave mirror), the scattered light 11 extracted into the air is focused.

Strictly speaking, the set of images from each convex portion P is a curved surface (field curvature)
However, by approximating it with a plane and placing the two-dimensional image sensor 4 on this approximate plane, image data of a convex pattern image (fingerprint ridge pattern image) can be obtained.

Incidentally, although the imaging plane is tilted due to the difference in the optical path length from each part to the spherical mirror 8, it can be corrected by adjusting the angle between the normal n of the image sensor 4 and the optical axis 12.

(Second example) FIG. 2 is a block diagram of the second embodiment.

The second embodiment is an example in which an aperture stop 7 is provided on the exit surface 9 in the first embodiment.

That is, the aperture diaphragm 7 is glued or glued so that the light (optical axis 12) emitted from the center of the contact surface S (finger 1) and from the center of the spherical mirror 8 passes vertically at the center of the aperture diaphragm 7. Formed by printing. This makes it possible to reduce the aberration of the image formed by the spherical mirror 8.

(Third example) FIG. 3 is a block diagram of the third embodiment.

In the third embodiment, a so-called tilting effect is provided in order to correct the trapezoidal distortion based on the difference in path length of the scattered light of each copy to the imaging plane.

For this reason, for example, the inclination of the spherical mirror 8 is set so that the difference in optical path length between the scattered light emitted from each convex portion and the imaging plane is minimized. As a result, the optical axis 12 has an angle with respect to the axis R parallel to the contact surface S. Therefore, when the aperture stop 7 is provided, it is offset from the center of the exit surface 9 so that the shaft 12 passes through the aperture stop 7.

In addition, the second. In the third embodiment, as described in the first embodiment, if a certain angle is set between the normal n of the image sensor 4 and the optical axis 12, the difference in the optical path length to the spherical mirror 8 will be The inclination of the approximate plane based on this can be corrected.

As described above, by forming the spherical mirror or aspherical mirror 8 with an imaging function in a part of the transparent light guide 20, the lens can be omitted.

Therefore, the optical system can be integrally molded, and assembly errors and durability are improved.

[Effects of the Invention] As explained above, in the present invention, a mirror formed on a transparent light guide has an imaging function, and the transparent light guide can be integrally molded. As a result, it is no longer necessary to bond optical parts during the production of the optical system, resulting in the following effects: (1) reduction in manufacturing man-hours, (2) reduction in assembly errors, and (2) improvement in durability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the first embodiment, Fig. 2 is a block diagram of the second embodiment, Fig. 3 is a block diagram of the third embodiment, and Fig. 4 is a block diagram of the conventional example (part 1). FIG. 5 is a sectional view of a conventional example (No. 2) of the device. In the figure, ■ is a finger, 2 and 20 are transparent light guides, 34 is an image sensor, 5 is a light source, 6 is a flat surface Mi is an aperture stop, 8 is a spherical mirror, aspherical surface Mi is an uneven object, 11 is scattered light, 12 is the optical axis, P
Q is the concave portion, 0 is the center of curvature, n is the normal, and S is the normal. The fingerprint image input is the lens, ra, 7 ra, 10 is the convex part, and is the contact surface

Claims (4)

[Claims] (1) The uneven object (10) is brought into contact with one surface of the transparent light guide (20), and the scattered light generated as a result of illuminating the contact surface is totally reflected at least once within the transparent light guide, and the total reflection In the unevenness shape detection device for imaging the scattered light (11) to obtain an uneven pattern image of the uneven object, the totally reflected scattered light (11) is emitted to the outside of the transparent light guide (20), In addition, a spherical or aspherical imaging mirror (8
) is formed on a part of the transparent light guide (20),
An image sensor (
4) An uneven shape detection device characterized by arranging the above. (2) The uneven shape detection device according to claim 1, wherein an aperture stop is formed on the light emitting surface of the transparent light guide. (3) The uneven shape detecting device according to claim (1), wherein the imaging mirror is formed so that the difference in optical path length of each scattered light to the imaging surface is reduced. (4) Of the scattered light emitted from the center of the contact surface, the scattered light emitted from the center of the mirror is defined as the optical axis, and the angle formed between this optical axis and the normal to the light-receiving surface of the image sensor is determined by the curvature of field. 2. The uneven shape detection device according to claim 1, wherein the angle is set to a predetermined angle that reduces defocus.