JP2692684B2 - Uneven shape detection method - Google Patents

Description

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

A fingerprint matching method is used as one of individual identification methods. In this fingerprint collation, since the fingerprint is usually handled as an image, an input device for converting the fingerprint into image data is necessary.

[Conventional technology]

A fingerprint is an uneven pattern, and the basic principle of detecting the uneven pattern that has been conventionally performed is shown in FIG. When the finger (10) is pressed against the one surface 13 of the transparent flat plate (light guide plate) 11, the convex parts (fingerprint ridges) come into contact, but the concave parts do not come into contact.

As shown in FIG. 7A, when the light r0 is radiated from below through the transparent body 11 so that total reflection does not occur on the flat surface 13 against which the finger (10) is pressed, the light is emitted from the transparent flat plate 11. The light that hits the recess P is scattered in all directions, but they all pass through the flat plate again and disappear in the distance (ray r1). On the other hand, the light striking the convex portion Q is scattered in all directions in the flat plate 11 and part of the light exits from the flat plate (ray r2), but part of the light propagates inside the flat plate by total reflection (ray r3). By forming an image of this total reflection component with an appropriate optical meter, a pattern (fingerprint image) of the convex portion can be obtained.

By the way, as shown in FIG. 7B, the plane on which the finger 10 is pressed.
Light from inside the flat plate is set so that the condition for total reflection is satisfied for
When r0 is irradiated, the concave portion P is not irradiated with light, and only the convex portion Q is selectively irradiated. However, in the case of a human finger, light is partially transmitted, so that the light radiated to the convex portion Q propagates inside the finger as shown by r4 and goes around to the concave portion P, resulting in the concave portion P.
Also emit light. Therefore, in the case of FIG. 7B, r1, r2, and r3 components are generated as in the case of FIG. 7A. Therefore, the convex pattern can be obtained by constructing an optical system that images only the r3 component.

In any of the above cases, both the concave portion P and the convex portion Q of the finger act as a light emitter. As described above, in order to obtain a fingerprint image (concavo-convex image), illumination means for irradiating light to a finger is required.

[Problems to be solved by the invention]

However, conventionally, the light source is generally placed under the transparent flat plate, that is, on the side opposite to the finger. Further, in the case shown in FIG. 7B, the light source is incorporated in the side portion or inside of the transparent flat plate 11.

In any case, these device configurations are factors that hinder the thinning and simplification of the device.

The object of the present invention is to arrange the light source on the same side as the object (finger) to be inspected, thereby making the apparatus compact, simple, and particularly thin.
Is to try.

Since the object to be inspected occupies a certain space on one side of the transparent flat plate, if the light source is arranged in the same space as the object to be inspected, the space accompanying the arrangement of the light source is not substantially increased and the device can be made thinner.

[Means for solving the problem]

When the uneven object is transparent or partially transparent to the illumination light and has a light scattering property (a human finger is also applicable), the uneven object 10 is irradiated with the illumination light r0 from outside as shown in FIG. Then, a part of the light r4 propagating inside the object can be emitted from the concave portion P and the convex portion Q. When an uneven object illuminated in this way is brought into contact with the light guide plate (transparent plate) 11, r1, r2, r3 components are generated and the r3 component is imaged, as in the case shown in FIGS. 7A and 7B. Thus, a convex pattern can be obtained.

The present invention is based on such an idea. According to the present invention, an object to be inspected which transmits light at least partially and has a light scattering property is brought into contact with one surface of the light guide plate, and the object to be inspected is In the method of detecting the uneven shape of the object by optically identifying the signal light scattered from the concave portion and the convex portion of the object surface when the light is irradiated on the object to be inspected, other than the contact surface with the light guide plate, A structural feature is that light emitted from a surface is used and light propagating inside the object to be inspected is used as scattered signal light from concave portions and convex portions on the object surface.

Further, in order to carry out this method, it is preferable to use a positioning guide for positioning the object to be inspected on a predetermined contact surface of the light guide plate. An illumination light source is embedded inside the positioning guide.

Preferably, the invention is used to detect fingerprints.

Preferably, the positioning guide has a positioning space for inserting a finger, and a living body detection photodetector including a light emitting element and a light receiving element facing each other across the positioning space is provided.

The illumination light source can also serve as the light emitting element of the living body detection photodetector.

(Operation)

When the uneven object is illuminated from a surface other than the contact surface with the light guide plate 11, the optical system including the light guide plate, the imaging optical system, and the like can be separated from the illumination system, so that the size can be reduced. The position where the concave-convex object is brought into contact with the light guide plate is specified by using a positioning guide or the like, but if an illumination system is integrally formed inside this guide, the volume increment due to the illumination system can be substantially eliminated.

In particular, when the invention is used as a fingerprint sensor, the device itself is embedded, for example, in the entrance door of a computer room. Therefore, a thinner device is required. In this case, if the light source is arranged on the same side as the finger, that portion is originally the space in front of the door and does not contribute to the thickness of the light guide plate.

〔Example〕

Hereinafter, as an embodiment of the present invention, a case where a finger is brought into contact with a light guide plate to obtain a fingerprint image will be described with reference to FIG. The process of emitting light from the convex portion of the fingerprint, propagating in the light guide plate 11 by total reflection, and capturing as an image by the imaging optical system is not directly related to the present invention, and therefore omitted.

The surface 13 of the light guide plate 11 with which the finger 10 contacts forms a part of the imaging system. Therefore, the position where the finger comes into contact (the position where the finger is placed) is limited to within a predetermined area. Therefore, in order to ensure that the finger can be placed at the designated position, a guide 21 that is hollowed out into a substantially U shape corresponding to the shape of the finger is used as shown in FIG.

The outer shape of the guide 21 is not particularly limited, but is formed as a rectangular plate having a substantially U-shaped positioning space 22 as shown in FIG. 3, for example. The guide 21 is fixed at a predetermined position on the light guide plate 11.

An LED 23 is arranged in the guide 21 as a light source for illuminating a finger from both sides with a place 22 interposed therebetween.

The LED 23 is fixed in a groove 24 formed on both sides of the guide 21, and is exposed to an opening connected to the groove 24, preferably an opening 26 that widens toward the end to widen the irradiation range.
The LEDs 23 may be one pair or plural pairs (FIG. 3).
In principle, the light source may be a light bulb, a mini lamp, etc. instead of the LED.

Light from LED 23 enters part of the inside of the finger from the side of the finger (composition
r4), and propagates to the contact surface 13 with the light guide plate 11. As a result, the finger itself becomes a light emitter, and the information of the convex portion Q can be propagated in the light guide plate 11. The wavelength used by the LED 23 should be selected in a band where absorption inside the finger is as small as possible (for example, red or near infrared is preferable). The LED 23 evenly illuminates the contact surface of the finger from both sides of the finger. As the LED 23, an LED array 25 extending in the longitudinal direction of the finger as shown in FIG. 4 can be used.

When the present invention is used as a fingerprint sensor, it is also possible to perform biometric detection in parallel to determine whether a finger is a living human, not a rubber replica, for example. FIG. 5 shows an embodiment of such a living body detection method.
When the finger 10 is illuminated with r0 from one side surface, a part r5 passes through the inside and is emitted from the opposite side surface. As is well known, the emitted light r6 is amplitude-modulated by the periodical change of the red blood cell distribution due to the pulse, and therefore, if this period is within a predetermined range (frequency band of human pulse), it is regarded as a living body. Such a living body detection method itself is known. In order to detect this living body, it is necessary to provide a light source light emitting element and a light receiving element on both sides of the finger. Therefore, the light source for detecting the living body can be used also as the light source (LED 23) for detecting the fingerprint image described above.
Can be mounted at the position of the LED 23 on the right side shown in FIG.

In FIG. 5, only one side of the finger of the light source 23 is arranged. In this case, the symmetry of the illumination is broken but the light components r1, r2, r3 shown in FIG. 1 are generated. Therefore, there is basically no inconvenience in carrying out the present invention.

The light receiving element 28 is connected to a photodetecting device 30 known per se. The living body detection method itself by the light detection device 30 is not the subject of the present invention, and will be omitted.

The above description is directed to the case where the image forming optical system is formed by using the transparent light guide plate (parallel plate) 11, but the case where a prism which is conventionally used is used instead of the plate as the light guide plate. Of course, the same can be applied.

(Effect)

As described above, according to the present invention, the illumination system of the uneven object to be inspected and the optical system (including the light guide plate) for forming the image of the convex pattern are independent, so that the optical system can be further downsized. In particular, the light guide plate can be made thinner.

Further, by embedding the illumination system in the contact position designation guide of the uneven object to be inspected, it is possible to virtually eliminate the volume occupied by the illumination system.

Further, if the present invention is used for fingerprint detection, the light source for illuminating the object to be inspected can be used also as the light source for detecting the living body, and can be made compact and have multiple functions.

[Brief description of the drawings]

FIG. 1 is a diagram showing the basic principle of the present invention, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3 is a plan view showing a guide for input position designation, and FIG. 4 is a diagram showing an illumination light source. FIG. 5 is a perspective view showing an LED array, FIG. 5 is a view showing an embodiment in the case of being applied to the living body detection of the present invention, FIG. 6 is a view showing the basic principle of a known fingerprint input device, FIGS. 7A and 7B. The figure shows a conventional illumination system for separating uneven information light. 10 ... Object to be inspected, 11 ... Light guide plate, 13 ... Contact surface, 21 ... Guide, P ... Recessed portion, Q ... Convex portion.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Ikeda, 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Fumio Yamagishi 1015, Kamikodanaka, Nakahara-ku, Kawasaki, Kanagawa, Fujitsu Limited

Claims (6)

(57) [Claims] 1. A flat surface (1) of a light guide plate (11) is provided with a test object (10) which transmits light at least partially and has a light scattering property.
By detecting the scattered signal light from the concave portion (P) and the convex portion (Q) on the surface of the object when the object is irradiated with light, the uneven shape of the object is detected. In the method, irradiating the object to be inspected from a surface other than the contact surface with the light guide plate, and utilizing light (r4) propagating in the object to be inspected as scattered signal light from concave portions and convex portions of the object surface. A method of detecting uneven shapes, which is a feature. 2. A predetermined contact surface (1
3) The uneven shape detecting method according to claim 1, wherein a positioning guide (21) which is positioned above and has an irradiation light source (23) embedded therein is used. 3. The uneven shape detecting method according to claim 1, which is used for detecting a human fingerprint. 4. The uneven shape detecting method according to claim 2, wherein the positioning guide is provided with a positioning space (22) for inserting a finger. 5. A light-emitting element (23) and a light-receiving element (28) which face each other with the positioning space therebetween in the positioning guide.
The uneven shape detecting method according to claim 4, further comprising: a photodetector for detecting a living body, which comprises 6. The uneven shape detecting method according to claim 5, wherein the light source for illumination constitutes a light emitting element of a photodetector for detecting a living body.