JPH0250782A - Uneven shape detector - Google Patents

Abstract

PURPOSE:To have an optical system whose stray light shielding effect is excellent and to obtain a small-sized, thin uneven shape detector for fingerprint, etc. by providing a pin hole for an aperture diaphragm at the shielding box of a picture sensor. CONSTITUTION:When a finger 2 with an uneven shape of a fingerprint, etc. is mounted on a face 52 of a light leading body 5, it is lighted from the internal part of the light leading body 5 by incident illuminating light A from the face 51, and the one part of scattered light from a projecting part repeats total reflection at parallel faces 51 and 52, mirror-reflects at a mirror face 53 and propagates in a left edge face direction approximately parallel with the parallel faces 51 and 52 of the light leading body. Then, it outgoes from a curved face through a pin hole 62 and image-forms on a picture sensor 3. The picture sensor 3 is connected with an external optical system optically only through the open hole of the fine diameter of a pin hole shape, since the other face is covered with a shielding box completely, electromagnetic shielding to the picture sensor and stray light eliminating can be executed at the same time, and the title device can be miniaturized and simplified.

Description

[Detailed Description of the Invention] [1 Already Required] An uneven shape detection device for detecting an uneven pattern such as a fingerprint, which has an optical system with good electromagnetic shielding characteristics for an image sensor and an excellent stray light shielding effect, and is compact.・Aiming to provide a thin uneven shape detection device, an uneven object to be detected is placed on one side of a transparent light guide having two mutually parallel surfaces, and an uneven object is detected from the outside of the other side. The incident light is scattered by the contact surface between the light guide and the object, and a portion of the scattered light is imaged on the image sensor via a curved surface for light beam focusing formed at one end of the light guide. In a device that detects the uneven shape of an object, a shield box is installed to surround the image sensor.
A pinhole is formed in a part of the shield box, and the pinhole is positioned at the center of curvature of the curved surface to serve as an aperture stop for the curved surface.

[Industrial application field]

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

Fingerprint matching is used as one of the methods for identifying individuals. In this fingerprint verification, since the fingerprint is usually handled as image data, an input device is required to convert the fingerprint into image data.

[Conventional technology]

In order to use a fingerprint image input device, for example, to control entry by attaching it to a door, or to limit the number of people who can access a database by attaching it to an information system terminal, it is necessary to attach the device to a door or a keyboard. It is necessary to make the device smaller and thinner so that it can be embedded, and proposals for this purpose have been made.

FIG. 2 is a diagram showing a conventional device for this purpose, in which (a) is a diagram showing the basic configuration, and (b) is a diagram showing an image sensor section.

In this method, an uneven object 2 such as a fingerprint to be detected is placed on one surface 12 of a transparent light guide 1 having two parallel surfaces, and light A is incident from outside on the other surface 11. and light guide 1
The contact surface between the object 2 and the object 2 is illuminated.

Then, the illumination light is reflected in all directions within the light guide l at the convex parts 3 such as the ridges of the fingerprint that are in contact with the surface 12, and since there is an air layer in the middle of the troughs 4 of the fingerprint, the light is reflected by the air layer. get into the
It is reflected at a predetermined location and scattered in all directions, but most of it re-enters vertically from the surface 12, re-emits from the other surface 11, and disappears into the distance. (R+) On the other hand, part of the scattered light from the convex portion 3 (
R2) is total reflection P l + P z on parallel plane 11.12
, P Emit to the outside of 1. Then, an image is formed on an image sensor 3 such as a CCD provided at the focal point of the roughly curved surface 14.

This aperture stop 14 is an imaging system based on a single spherical surface (for example, -
It uses only a portion of the spherical surface of a convex lens (a convex lens) for image formation to reduce the effect of image blurring due to aberrations and improve resolution. There is.

Since the image sensor 3 uses a highly sensitive two-dimensional photoelectric conversion element such as a CCD, it is necessary to shield electromagnetic noise from the surrounding environment. It was surrounded by shield box 4. In addition, in order to improve the contrast of the detected image on the imaging plane, it is necessary to remove stray light that enters from directions other than the signal light, so it is necessary to limit the solid angle of the incident light with a hood 41 etc. to prevent stray light. was going on.

[Problem to be solved by the invention]

By the way, although the above-mentioned conventional device can be made smaller and thinner, there is a problem that electromagnetic shielding and stray light countermeasures are insufficient. That is, in an optical system using the light guide described above, an opening is required to ensure a contact surface between the finger and the light guide plate, and it is not possible to provide sufficient electromagnetic shielding by covering the entire optical system with a conductor.

Therefore, the image sensor is electromagnetically shielded by itself, but in order to receive the entire fingerprint image that spreads and forms an image, it is not possible to cover the light-receiving surface of the image sensor. requires a wide aperture and is not a sufficient countermeasure against stray light.

The present invention was created in view of the above-mentioned problems, and an object of the present invention is to provide a compact and thin uneven shape detection device that has an optical system that has good electromagnetic shielding characteristics for an image sensor and an excellent stray light shielding effect. purpose.

[Means to solve the problem]

In order to solve the above problems, the uneven shape detection device of the present invention places an uneven object to be detected on one surface of a transparent light guide having two parallel surfaces, and detects an uneven object on the outside of the other surface. The light incident from the light guide is scattered by the contact surface between the light guide and the object, and a portion of the approximately scattered light is imaged on the image sensor via a curved surface for light beam focusing formed at one end of the light guide. In a device that detects the uneven shape of an object, a shield box is installed to surround the image sensor.
A pinhole is formed in a part of the shield box, and the pinhole is positioned at the center of curvature of the curved surface to serve as an aperture stop for the curved surface, and further, light propagating inside the transparent light guide The structure is such that the light is totally reflected at least once by a transparent light guide, and then an image is formed on the image sensor.

[Effect]

The aperture stop formed inside the light guide is used as part of the shield box, and the pinhole of the shield box is positioned at the point where the effective signal light is most focused, so the aperture area can be reduced and the electromagnetic shielding effect can be improved. It is possible to increase it.

In addition, only the light that has passed in a predetermined direction through the aperture stop provided to improve the resolution of the optical system is incident on the sensor surface, so stray light can be suppressed as much as possible.

〔Example〕

The present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing the main configuration of an uneven shape detection device according to the present invention.

In the figure, 5 is a light guide, 6 is a shield box, and 3 is an image sensor.

The light guide 4 is made of a transparent object having parallel surfaces 51 and 52, and has an inclined mirror surface 53 formed at one end, an aperture stop 54 embedded in the other end, and a light beam focusing surface such as a spherical surface on the end surface. A curved surface 55 is formed.

The aperture stop 54 is formed, for example, as follows.

That is, when the light beam propagating from the center Q of the finger contact surface is selected to be along the optical axis, a surface S perpendicular to the tip axis is formed on the end surface of the light guide. Next, a metal plate 61 constituting one side of the shield box 6 with a pinhole 62 formed therein which serves as an aperture diaphragm is placed on the surface S so that the pinhole 62 is at the position of the optical axis.
Further, a plano-convex lens 56 is bonded thereon via a transparent plate 57 such that the pinhole 62 is located at the center of curvature of the plano-convex lens. Optical adhesives are used as these adhesives in order not to hinder the propagation of light.

The image sensor 3 is a photoelectric conversion element such as a CCD mounted on a printed circuit board 31, and its light-receiving surface is tilted at a predetermined angle with respect to the optical axis. is attached to the focal plane) and led out to the outside by a cable 31. Note that this inclination of the light-receiving surface is such that the fingerprint input surface (finger contact surface) is inclined with respect to the optical axis, so that the focal plane is also inclined accordingly.

By covering the shield box 6 with the metal plate 61, the image sensor 3 is surrounded by the shield box.

In the device configured in this way, when the finger 2 having an uneven shape such as a fingerprint is placed on the surface 52 of the light guide 5, the surface 51
The light guide 5 is illuminated from inside by the incident light A, and a part of the scattered light from the convex portion undergoes total reflection on the parallel surfaces 51 and 52 and is specularly reflected on the mirror surface 53 to illuminate the light guide 5. It propagates toward the left end surface substantially parallel to the parallel planes 51 and 52 of.

Then, it passes through a pinhole and exits from the curved surface, and the image sensor 3
image on top.

The image sensor 3 is optically connected to the external optical system only through a pinhole-like micro-diameter opening, and the other surfaces are completely covered with a shield box, which provides electromagnetic shielding and stray light removal for the image sensor. can be performed at the same time, and the device can be realized with a small size and simple configuration.

[Effects of the Invention] According to the present invention, since the pinhole for the aperture stop is provided in the shield box of the image sensor, it is possible to improve the electromagnetic shielding characteristics and the stray light suppressing effect with a compact configuration. Therefore, when applied to a fingerprint verification system, it can be easily embedded into a device without damaging its appearance.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the main configuration of an uneven shape detection device of the present invention, and FIG. 2 is a diagram showing a conventional device. In the figure,

Claims (1)

[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 outside on the other surface is guided. Scattered at the contact surface between the body and the object,
In a device that detects the uneven shape of an object by focusing a portion of the roughly scattered light onto an image sensor through a curved surface for focusing a light beam formed at one end of a light guide, a shield box is installed to surround the image sensor. established,
An uneven shape detecting device characterized in that a pinhole is formed in a part of the shield box, and the pinhole is positioned at the center of curvature of the curved surface to serve as an aperture stop for the curved surface. 2. The detection device according to claim 1 is configured such that the light propagating inside the transparent light guide is subjected to at least one total reflection by the transparent light guide before being imaged on the image sensor. Characteristic uneven shape detection device.