JPH08320919A - Image pickup device for finger print - Google Patents

Abstract

PURPOSE: To easily reduce the size and thickness of this image pickup device for a finger print by specifying the shape of a prism having a contact face for sampling a finger print and arranging an image pickup means parallel with the contact face. CONSTITUTION: A prism 101 is a quadrangle prism constituted so that the extended face of the contact face 102 and the extended face of a 1st plane 105 intersect with each other on a vertex 206 at an angle X of 14 deg. and the face 102 and a 2nd plane 106 intersect with each other on a vertex 207 at an angle Y of 120 deg. and consists of glass with refractive index (n) of 1.5. Light irradiating from an illuminating light source 201 is made incident on the prism 101 from the face 105 and a finger print depressed to the face 102 is irradiated with the incident light. On each finger print ridge line part 110, the incident light is discharged from the finger print as scattered light. On the other hand, light is totally reflected from a finger print trough line part 110 at an outgoing angle which is the same as the incident angle upon the face 102. The reflected light is discharged from the face 106 at a prescribed refractive angle and made incident upon a CCD camera 202 whose optical axis 205 is set up in parallel with the face 102 and a finger print image is formed on the face 204.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fingerprint image pickup device,
Especially, the small size of the fingerprint image pickup device with the new prism shape
The present invention relates to a technology effectively applied to thinning.

[0002]

2. Description of the Related Art Conventionally, a fingerprint image pickup device is a device for picking up a fingerprint image and supplying a good fingerprint image to an image processing / identification device in a personal identification system by fingerprint collation. With the increasing importance of personal identification to limit the number of users, it is expected that a personal identification system using fingerprint collation will become popular as a simple personal identification method, and in order to enable installation on portable devices, There is a demand for downsizing and thinning of a personal identification system including an image pickup device.

FIG. 4 is a diagram showing a schematic structure of a conventional fingerprint image pickup device, which includes an LED (Light Emitting).
The light emitted from the illumination light source 201 composed of a diode enters the rectangular prism 401 and reaches the contact surface 102 as incident light.

The incident light reaching the contact surface 102 is reflected by the contact surface 1
Fingerprint valley portion (recess) 111 of finger 103 pressed against 02
In the background portion, the light is totally reflected by the contact surface 102, and the reflected light is formed by the imaging lens of the rectangular prism 401 and the area CCD (Charge Coupled Device).
e: CCD camera 20 including charge coupled device) 204
It is radiated from the surface 402 on the second side.

On the other hand, the incident light that reaches the fingerprint ridge portion (convex portion) 110 pressed against the contact surface 102 enters the living body through the skin and is emitted as scattered light from the living body.

As a result, area C of the CCD camera 202
On the surface of the CD 204, the fingerprint ridge 110 is dark and the fingerprint valley 111 is bright, so the fingerprint valley 111 and the fingerprint ridge 110 pressed against the contact surface 102 form a CCD image as a grayscale fingerprint image. The image is taken by the camera 202.

[0007]

The present inventor has found the following problems as a result of examining the above-mentioned prior art.

In the conventional fingerprint image pickup device, the CCD camera 2
The image pickup direction of 02 is required to be opposed to the contact surface 102 of the right-angle prism 401 so as to form an angle of 45 degrees, and even if the optical system is configured as short as possible, The effective length of the surface 102 is about 30 mm, CCD
Since the focal length of the image forming lens of the camera 202 is required to be about 10 mm, the area CCD 204 from the contact surface 102.
A distance of up to about 40 mm was required only in the optical system part.

Further, if the length of the CCD camera 202 body and the dimensions of mechanical structures such as an assembly frame (not shown) are taken into consideration, the depth d (thickness) of the fingerprint image pickup device.
Required 40 to 50 cm from the contact surface 413.

Therefore, there is a problem that it is difficult to make the fingerprint image pickup device small and thin.

An object of the present invention is to provide a technique capable of miniaturization and thinning.

Another object of the present invention is to provide a technique capable of picking up a fingerprint image of good contrast with a small and thin device.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0014]

Of the inventions disclosed in the present application, a representative one will be briefly described below.
It is as follows.

(1) A contact surface for pressing a fingerprint of a finger, a first plane forming a first angle X with the contact surface or an extension surface thereof, and the contact surface or an extension surface thereof and a first surface. A prism having a second plane forming an angle Y of 2, and an illuminating means for illuminating a fingerprint of a finger pressed against the contact surface,
A fingerprint image pickup device comprising: an image pickup unit that picks up a fingerprint of a finger illuminated by the illumination unit as a fingerprint image,
The image capturing unit captures the fingerprint image reflected by the first plane through the second plane.

(2) The critical angle at the interface of the prism is θ
₀ , the angle of refraction of the prism is n, an angle formed by a straight line connecting the fingerprint of the finger on the contact surface and the fingerprint image reflected on the first plane and imaged with the perpendicular of the contact surface is θ, When the angle between the ray of the fingerprint image emitted from the second plane and picked up by the image pickup means and the optical axis of the lens of the image pickup means is φ, θ and X are θ ₀ ≦ θ, X ≦ 90 °. −θ ₀ and φ is COS (Y−φ) = nSIN (180-2X−
Y-θ) is satisfied.

Here, the image pickup principle of the fingerprint image pickup device according to the present invention will be described with reference to FIG.

In FIG. 1, the contact surface 102 and the first plane 1
The angle made by 05 is X, the angle made by the contact surface 102 and the second plane is Y, and the light reflected at any one point 109 on the contact surface 102 passes through the first plane 105 and the second plane 106. The contact surface 102 when the optical path 113 reaching the image pickup means 107 is taken
Is an emission angle, that is, an angle formed by the optical path 113 and a perpendicular line of the contact surface 102 passing through an arbitrary point 109, and the contact surface 1
If the critical angle of 02 is θ ₀ , in order to obtain an image with high contrast, it is well known that it is necessary to image a fingerprint at an emission angle θ larger than the critical angle θ ₀ .

That is, the light scattered from the fingerprint ridge 110 into the skin and emitted from the fingerprint valley 111 is again imaged by the image pickup means 107 from the first plane 105 of the prism 101 through the second plane 106. Need to be prevented.

For this purpose, it is necessary to set θ so that θ ≧ θ ₀ is satisfied on all the pressed fingerprint surfaces.

On the other hand, since X is X ≦ 90 ° −θ ₀ ,
To obtain a good image with high contrast, θ ₀ ≦
It is necessary to set θ so as to satisfy θ ≦ 90 ° −X.

The optical path 113 of the light satisfying the condition of θ is
After being totally reflected by the first plane 105, it is refracted by the second plane 106 and emitted from the prism 101.

At this time, the angle of incidence on the second plane, that is, the angle formed by the optical path 113 of the light reflected by the first plane 105 and the perpendicular of the second plane 106 is α, and the refraction angle of the second plane 106, that is, the first plane. Assuming that the angle formed by the optical path 113 of the light emitted from the two planes with the perpendicular of the second plane 106 is β, α and β and X, Y, θ, and the refractive index n of the prism 101 are:

[0024]

## EQU1 ## α = 180-2X-Y-θ

[0025]

[Formula 2] n = SINβ / SINα holds.

When the angle between the contact surface 102 and the light emitted from the second plane 106 is δ, δ is

[0027]

(3) β = 90−Y + δ. On the other hand, if the optical axis of the image pickup means 107 can be set parallel to the contact surface 102, the thickness of the fingerprint image pickup device will be the prism 1.
It is regulated by the height of 01 and is extremely effective for thinning.

Therefore, in Equation 3, δ is taken as the image pickup means 10
If the angle φ is smaller than the maximum angle of view of 7, the image pickup means 10
A good fingerprint image can be captured within the angle of view when 7 is installed parallel to the contact surface 102. From number 3,

[0029]

## EQU4 ## Since β = 90-Y + φ, Equation 2 is

[0030]

(Equation 5)

It becomes Where SIN (90-Y + φ)
= COS (Y-φ)

[0032]

## EQU6 ## COS (Y-.phi.) = NSIN (180-2X-Y-.theta.).

That is, by setting X and Y so as to satisfy the equation 6, the image pickup means 10 in which the optical axis of the fingerprint pressed against the contact surface 102 is set parallel to the contact surface 102.
At 7, it can be captured as a fingerprint image.

[0034]

According to (1) of the above-mentioned means, it is only necessary to set φ and θ so as to satisfy the above-mentioned equation 6, for example, φ = 0 °, that is, the fingerprint image incident on the image pickup means. So that the incident angle of the reflected light including is parallel to the contact surface,
By setting the emission angle θ depending on the position of the illuminating means and determining the position of the illuminating means, the image pickup means can be installed parallel to the contact surface.

In this way, the fingerprint pressed against the contact surface 102 is imaged from the second plane through the first plane, whereby the optical axis of the image pickup means 107, that is, the image pickup means 107.
Since the optical axis of 1 can be set parallel to the contact surface 102, the thickness of the fingerprint imaging device can be reduced to the height of the prism 101.

According to item (2) of the above-mentioned means, the light radiated to the fingerprint valley portion and the background portion is totally reflected at the reflection surface at the reflection angle θ, passes through the optical path 113 and enters the image pickup means 107. To do.

On the other hand, the light applied to the fingerprint ridges is scattered in the living body, but a part of the light is emitted as scattered light from the fingerprint valleys, and the prism 10 is again irradiated from the contact surface.
It will be incident on 1.

However, since the exit angle θ of the optical path 113 at the contact surface is set to be larger than the critical angle θ _{0 of the} contact surface, the scattered light incident from the contact surface does not enter the imaging means. It is emitted from the second plane.

That is, since only the light radiated to the fingerprint valley portion and the background portion is imaged by the image pickup means, the image pickup means can obtain a good fingerprint image with high contrast.

On the other hand, the angle φ formed by the light beam of the fingerprint image which is emitted from the second plane and is picked up by the image pickup means and the optical axis of the lens of the image pickup means satisfies the equation 6, so that the contact surface and the image are picked up. The fingerprint image can be picked up by the image pickup means installed so that the optical axis of the lens of the means is parallel.

Thus, θ ≧ θ ₀ , X ≦ 90 ° −θ ₀ ,
In addition, the prism 101 of the fingerprint image pickup device, the illumination unit, and the image pickup unit are set so as to satisfy Expression 6, so that the contact surface and the optical axis of the lens of the image pickup unit are parallel to each other. However, the image pickup means can pick up a good fingerprint image with high contrast.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments.

In all the drawings for explaining the embodiments, parts having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted.

FIG. 1 is a cross-sectional view showing a schematic configuration of an embodiment of a fingerprint image photographing apparatus of the present invention, 101 is a prism (transparent contact body), 102 is a contact surface, 103 is a finger, 201
Is a light source for illumination (illumination means), 105 is a first plane, 106
Is a second plane, 202 is a CCD camera (imaging means), 20
3 is an imaging lens, 204 is an area CCD, and 205 is C
The optical axis of the CD camera 202, 110 is the fingerprint ridge (convex), 111 is the fingerprint valley (concave), 114 is the point closest to the CCD camera 202 in the fingerprint imaging range, and 113 is the reflection at the point 114. The optical path of the reflected light toward the CCD camera 202, 206 is the apex where the extension surface of the contact surface 102 and the extension surface of the first plane 105 intersect, and 207 is the apex where the contact surface 102 and the second plane 106 intersect.

However, the alternate long and short dash line represents a perpendicular line which intersects each plane of the prism 101 at right angles.

In FIG. 1, the prism 101 has a vertex 2
At 06, the extension surface of the contact surface 102 and the extension surface of the first plane 105 intersect at an angle X = 14 °, and the contact surface 10 at the apex 207.
2 and the second plane 106 are square prisms that intersect at an angle Y = 120 °, and are made of glass having a refractive index n = 1.5.

The prism 101 is fixed to a frame (not shown) by a support mechanism (not shown).

The illumination light source 201 is a light source for illuminating the fingerprint pressed against the contact surface 102 from the first plane 105, and is composed of an LED.

The illumination light source 201 is fixed to a frame (not shown) by an instruction mechanism (not shown).

The CCD camera 202 is an area CCD 204 which is an image pickup device for converting the intensity of light into the intensity of an electric signal.
And an image forming lens 203 for forming an image of incident light on the area CCD 204.
It is fixed to a frame (not shown) by a support mechanism (not shown) at a position where an optical axis 205 connecting the center of 204 and the center of the imaging lens 203 becomes parallel to the contact surface 102.

In the fingerprint image pickup apparatus of this embodiment, the light emitted from the illumination light source 201 enters the prism 101 from the first plane 105 and illuminates the fingerprint pressed against the contact surface 102.

At this time, light is incident on the fingerprint ridge 110 from the skin, and the incident light is emitted from the living body as scattered light. On the other hand, in the fingerprint valley portion 111, the light is in contact surface 1
The light is totally reflected at an exit angle that is the same as the incident angle that is incident on 02.

For example, the light totally reflected at the emission angle θ = 45 ° at the point 114 travels along the optical path 113, is totally reflected again at the point where it intersects with the first plane 105, and is emitted from the second plane 106 at a predetermined refraction angle. Then, the incident angle φ = 15 is set on the CCD camera 202 installed so that the optical axis 205 is parallel to the facing surface 102.
It is incident at an angle of ° and a fingerprint image is formed on the surface of the area CCD 204.

At this time, since the prism 101 is made of glass, the critical angle θ ₀ of the contact surface 102 is 41.5 ° which is the critical angle between air and glass.

On the other hand, in this fingerprint image pickup device, since the emission angle θ at the point 114 closest to the CCD camera 202 within the image pickup range of the fingerprint pressed against the contact surface 102 is set to 45 °, the fingerprint image is picked up. Θ ≧ 41.5 ° over the entire range
(Θ ≧ θ ₀ ) will be satisfied.

Therefore, the light scattered from the ridge portion 110 of the fingerprint into the living body is emitted from the valley portion 111 of the fingerprint, enters the prism 101 again from the contact surface 102, and then is reflected by the first plane. Then, although the scattered light is emitted from the second plane 106, the scattered light does not enter the CCD camera 202, and thus the emitted light of a favorable fingerprint image having high contrast is emitted from the second plane.

The CCD camera 202 has an optical axis 205.
And the angle φ formed by the optical path 113 of the emitted light emitted from the second plane is smaller than the maximum angle of view of the CCD camera 202,
Since it is set to 15 ° which satisfies the above-mentioned conditional expression 6, the area CCD 204 surface of the CCD camera 202 is
The fingerprint ridge 110 is dark and the fingerprint valley 111 is bright.
A high-contrast gray-scale fingerprint image is formed.

In FIG. 3, θ = 45 °, φ = 15 °, X ≦ 4
6 is a graph showing the relationship between the angle X of the apex 206 and the angle Y of the apex 207, which satisfies the equation 6 when 8.5 °, where θ = 45 °, φ = 15 °, and X ≦ 48.5 °. The set fingerprint imaging device is the first at the angle X corresponding to the curve 301.
By using a glass prism having a plane 105 and a second plane 106 at an angle Y, the abutting surface 102
And the optical axis 205 of the CCD camera 202 are installed parallel to each other, and a good fingerprint image with high contrast can be obtained.

In the fingerprint image pickup apparatus according to the present embodiment, when the height to the ridgeline where the first plane 105 and the second plane 106 intersect with each other with the contact surface 102 as a reference is the thickness of the prism 101, the thickness thereof is set. Is about 40% of the length of the contact surface 102 shown in the left-right direction in FIG.

As a result, the contact surface 10 required for picking up the fingerprint is shown.
When the length of 2 is 20 mm, the thickness of the prism 101 is about 8 mm.

Although the present embodiment has been described only when the emission angle θ of the irradiation light on the contact surface is θ = 45 °, if the emission angle θ is set too large, the trapezoid of the fingerprint image obtained by oblique imaging will be described. There is a problem that the distortion becomes remarkable and the focal point is partially defocused on the surface of the area CCD 204 which is the imaging surface. Therefore, practically, the emission angle θ is 60 ° ≧ θ ≧ θ.
_It is preferably set to ₀ .

As described above, according to this embodiment,
Within the imaging range of the fingerprint pressed against the contact surface 102, the most C
The emission angle (reflection angle) θ of the light emitted at the point 114 close to the CD camera 202 is θ = 45 °, the angle of view (incident angle) φ of the CCD camera 202 is φ = 15 °, and the contact surface 102 is The angle X formed by the first plane 105 is X = 14 °, and the contact surface 1
The angle Y formed by 02 and the second plane 106 is Y = 120 °
And θ ≧ θ ₀ , X ≦ 90 ° −θ ₀ , and COS (Y−
Since φ) = nSIN (180-2X-Y-θ) is satisfied, the light is emitted from the illumination light source 201 and the valley line portion 1
The light reaching 11 or the background portion is totally reflected by the contact surface 102, and then is reflected again by the first plane 105 to be reflected by the second plane 10.
It is incident on the CCD camera 202 via 6.

On the other hand, the light reaching the ridge portion 110 is scattered inside the living body from the ridge portion 110, and a part of the light is scattered in the valley portion 11.
The light is emitted from No. 1 and again enters the prism 101 as scattered light, but the emission angle θ is the critical angle θ ₀ = 41.5.
Since it is set to 45 °, which is larger than °, the scattered light is C
The light does not enter the CD camera 202 but exits outside the prism again.

Therefore, a good fingerprint image with high contrast can be picked up, and the fingerprint pick-up device can be made compact and thin.

In this embodiment, the angle of view φ is φ =
Although it is set as 15 °, it goes without saying that φ may be arbitrarily set as long as it is equal to or less than the maximum angle of view of the CCD camera 202.

In the present embodiment, the optical axis 205 of the CCD camera 202 is set to be parallel to the contact surface 102, but the fingerprint image reflected by the first plane 105 is incident within the angle of view. If so, be sure to set the optical axis 205 to the facing surface 1
Needless to say, it does not need to be parallel to 02.

As described above, the invention made by the present inventor is
Although the present invention has been specifically described based on the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

[0068]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) Since the image pickup means can be installed parallel to the contact surface, the fingerprint image pickup device can be made compact and thin.

(2) Scatter from the ridges of the fingerprint onto the skin,
Since the light emitted again from the valley line portion can be prevented from entering the image pickup means, a fingerprint image with good contrast can be obtained with a small and thin fingerprint image pickup device.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an imaging principle of a fingerprint imaging device of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of a fingerprint image pickup apparatus which is an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between an angle X and an angle Y that satisfies Expression 6 when θ = 45 °, φ = 15 °, and X ≦ 48.5 °.

FIG. 4 is a cross-sectional view showing a schematic configuration of a conventional fingerprint imaging device.

[Explanation of symbols]

101 ... Prism, 102 ... Face to face, 103 ... Finger, 10
4 ... Illuminating means, 105 ... First plane, 106 ... Second plane,
107 ... Image pickup means, 110 ... Fingerprint ridge line portion, 111 ... Fingerprint valley line portion, 113 ... Optical path, 114 ... Point on contact surface closest to CCD camera in fingerprint image pickup range, 201 ... Illumination light source, 202 ... CCD camera, 203 ... Imaging lens, 2
04 ... Area CCD, 205 ... Optical axis of CCD camera, 2
06 ... Apex where the extension surface of the facing surface and the extension surface of the first plane intersect, 207 ... Apex where the facing surface and the second plane intersect, 401
... right angle prism.

Claims (2)

[Claims] 1. A contact surface for pressing a fingerprint of a finger, a first plane forming a first angle X with the contact surface or an extension surface thereof, and the contact surface or an extension surface thereof and a second surface. A prism having a second flat surface forming an angle Y, an illuminating unit that illuminates a fingerprint of the finger pressed against the facing surface, and an imaging unit that captures the fingerprint of the finger illuminated by the illuminating unit as a fingerprint image. A fingerprint image pickup device comprising: a fingerprint image pickup device, wherein the image pickup unit picks up the fingerprint image reflected by the first plane through the second plane. 2. The critical angle at the interface of the prism is θ ₀ ,
The refractive index of the prism is n, the angle formed by a straight line connecting the fingerprint of the finger on the contact surface and the fingerprint image reflected and imaged on the first plane to the perpendicular of the contact surface is θ, and the second When the angle between the light beam of the fingerprint image emitted from the plane and picked up by the image pickup means and the optical axis of the lens of the image pickup means is φ, θ and X are θ ₀ ≦ θ and X ≦ 90 ° −θ. ₀ , φ is COS (Y−φ) = nSIN (180-2X−
The fingerprint image pickup device according to claim 1, wherein Y-θ) is satisfied.