JPH10104442A - Image input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a clear body image corresponding to the uneven pattern on the surface of a body by projecting illumination light at an angle other than a stray light permissible angle to an incidence surface. SOLUTION: A holding member 200 holds a light source 3 so that a vertical incidence angle component θv on a plane orthogonal to a reference end 220 on the incidence surface which prescribes a slant angle θo among components of the angle of incidence between luminous flux emitted by the light sources 3 and incidence surface 22 is set within a range off an area of an angle X at which stray light can be made incident. The angle X (stray light permissible angle) at which the stray light can be made incident is within a range represented as (Xc-Θ)<=X<=(Xc+Θ). In the expression, Xc is a stray light permissible center angle given by (90 deg.-sin<-1> (ncore .sin(90 deg. -30θo))), ncore is a refractive index of the core in an optical fiber, Θ is a total reflection critical angle in air given by (sin<-1> (ncore .sin(90 deg.-Sc-ϕ)99, and Sc and ϕ are a stray light permissible center angle and a total reflection critical angle in the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input device for obtaining an object image such as a fingerprint or a rubber stamp having irregularities.

[0002]

2. Description of the Related Art An image input apparatus of this type is disclosed in, for example, U.S. Pat.
Apparatus described in Japanese Patent Publication No. 300930 (first conventional example)
It has been known. As shown in FIG. 26, these image input devices irradiate a fiber optical plate (FOP) B in which a number of optical fibers A are bundled and integrated, and an incident surface C of the fiber optical plate B. And a device for outputting an image such as a fingerprint having irregularities. According to these image input devices, when the finger C1 or the like is brought into contact with the incident surface C of the fiber optical plate B, light from the light source D enters the fiber optical plate B only from the convex portion directly in contact with the incident surface C. Incident. Then, the incident light propagates through the fiber optical plate B and is output from the emission surface E, and an image E1 (an image of a fingerprint or the like) corresponding to an uneven pattern such as a fingerprint is obtained.

However, in these image input devices, if light enters from a portion where the finger C1 or the like does not contact the incident surface C, the contrast of the image E1 to be output is reduced, and the image E1 is unclear. It will be something.
For this reason, the incidence surface C of the fiber optical plate B is generally inclined by a predetermined angle with respect to the optical axis (coincident with the optical axis direction of the internal optical fiber). Note that the fiber optical plate (first conventional example) in which the incident surface C is inclined with respect to the optical axis is particularly called a slant FOP, and the inclination angle θ ₀ is called a slant angle. In the fiber optical plate B of the first conventional example, unnecessary light incident from a portion that is not in contact with the incident surface C (a concave portion such as a finger that is not in contact with the incident surface C) is emitted from the optical fiber A.
The slant angle θ ₀ and the numerical aperture NA of the optical fiber A are matched so as not to propagate through the inside (so as not to satisfy the total reflection condition). Therefore, the unnecessary light (stray light) described above is not theoretically output from the emission surface E.

[0004] For example, Japanese Patent Application Laid-Open No. 7-174947 discloses a fiber optical plate of a second conventional example.
A structure in which a light absorber is provided between optical fibers constituting the structure is disclosed. The arrangement of the light absorber prevents light from entering and exiting between adjacent optical fibers, and the object C1
Unnecessary light incident from a non-contact portion between the optical fiber and the incident surface C is efficiently attenuated in the fiber optical plate. Therefore, in the fiber optical plate having such a structure, the contrast of an output image can be improved.

[0005]

However, when light enters and exits between adjacent optical fibers in the above-mentioned fiber optical plate, the output image (image of an object having unevenness on the surface) has an inferior contrast. It will be clear. For example, as described in JP-A-7-17494 described above.
Even if a light absorber is arranged between adjacent optical fibers as in the fiber optical plate of JP-A-7, it is difficult to completely absorb light, and light is incident from a non-contact portion between the object and the incident surface. Light propagates to the adjacent optical fiber.
Then, as shown in FIG. 27, when such light is reflected on the side surface F and / or the incident surface C of the fiber optical plate B, the light is guided in the direction of total reflection in the optical fiber, and There is a possibility that the light will propagate through the inside and be output from the emission surface E. In such a case, as described above, the image to be output is affected by the output of unnecessary light (stray light) and becomes unclear.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide an image input device for obtaining a clear image of an object having an uneven surface. I have.

[0007]

SUMMARY OF THE INVENTION In order to obtain a clear image, a light beam from a light source is transmitted from a fiber optical plate (hereinafter referred to as a FOP) from a direction deviating from an angle region in which stray light can enter. The light source is provided with a special structure for holding the light source at a predetermined position so as to be incident on the incident surface. That is, the image input device according to the present invention includes:
At least a plurality of optical fibers are bundled and integrated into a first
A housing for accommodating the first FOP, a plurality of light sources for illuminating an incident surface of the first FOP, and the plurality of light sources form at least a part of an opening of the housing. And a holding member having a holding portion for holding the plurality of light sources so as to surround the light source. Note that the first F
OP is a predetermined slant angle θ with respect to the optical axis of the optical fiber.
_{It has} an incident surface inclined by ₀ (0 ° <θ ₀ <90 °) and an exit surface facing the incident surface. Further, the housing is
An upper surface having an opening for exposing the incident surface is provided. Further, the holding portion of the holding member is provided on the upper surface of the housing and is arranged so as to sandwich the opening of the housing.

In particular, in the image input apparatus according to the present invention, the holding member is provided on the incident surface defining the slant angle θ ₀ among the incident angle components between the light beam emitted from the light source and the incident surface. The light source is held in a state where the vertical incident angle component θ _V on a plane orthogonal to the reference end is set in a range outside the angle region in which stray light can enter.

Note that an angle X at which stray light can enter (hereinafter referred to as a stray light allowable angle) is within a range given by the following equation.

(X _c -Θ) ≦ X ≦ (X _c + Θ) In other words, the holding member has a vertical incidence component θ _V of the light beam from the light source in a range of 0 ° to (X _c -Θ). , And / or (X _c + Θ) to 180 °,
Holds the light source.

Note that X _C is given by the formula (90 ° −sin ⁻¹ (n
_core · sin (90 ° −3θ ₀ ))), the stray light allowable central angle, n _core is the refractive index of the core in the optical fiber, θ
₀ is the slant angle and Θ is the equation (sin ^-1 (n _core · sin
(90 ° −S _C −φ))), the critical angle for total reflection in air, S _C, is represented by the formula (sin ⁻¹ ((1 / n _core ))
· SinX _C )), the stray light allowable central angle in the optical fiber, φ, is given by the formula (sin ^-1 (n _clad /
The critical angle for total reflection in the optical fiber, given by n _core )), and n _clad is the refractive index of the cladding in the optical fiber.

Further, in the image input device according to the present invention, the holding member is orthogonal to the incident surface, out of the incident angle component between the light beam emitted from the light source and the incident surface.
Holds the light source in a state where the horizontal incident angle component θ _H on a plane parallel to the reference end on the incident surface defining the slant angle θ ₀ is set within a range of 0 ° or more and 20 ° or less. doing. More preferably, the holding member holds the light source such that, of the light beams emitted from the light source, the center light beam and the incident surface are parallel (θ _H = 0 °). In this case, in the holding member, the component on the incident surface of the directional vector component of the central light beam travels from the auxiliary end on the incident surface facing the reference end toward the reference end. Thus, it is preferable to hold the light source.

[0013] In addition, the holding member may include a structure for adjusting a spread angle of a light beam emitted from the light source. Further, the holding member may include a light blocking member that covers the incident surface of the first FOP via a gap. In addition, the first
Is preferably in the range of 25 ° to 40 °.

Further, the image input device according to the present invention is
An image sensor having a light receiving surface is provided so as to face the emission surface of the first FOP, and various structures can be realized.

Specifically, a second FOP may be provided between the first FOP and the image sensor. The second FOP may be a tapered FOP whose cross-sectional area decreases from the first FOP toward the image sensor, and the exit surface and the entrance surface of the first FOP are:
They may be parallel to each other. In addition, the first FOP
An optical system may be provided between the second FOP and the image sensor or between the second FOP and the image sensor.

With the above-described holding structure, the irradiation direction of the light source can be easily controlled, and the irradiation of the light beam within the area of the stray light allowable angle X can be suppressed. For this reason, only the desired light component can be reliably output from the exit surface, and a clearer image (with no decrease in contrast due to stray light) can be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image input device according to the present invention will be described with reference to FIGS. In each of the drawings, the same elements are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is an assembly process diagram for explaining the structure of the image input apparatus according to the present invention. An image input device according to the present invention includes an FOP2 (first FOP) which is integrated by bundling a plurality of optical fibers. This FOP2 is
An incident surface 22 inclined by a predetermined slant angle θ ₀ (0 ° <θ ₀ <90 °) with respect to the optical axis of the optical fiber;
2 and is housed in the housing 100. An image sensor 6 (CCD or the like) is provided on the emission surface 23 side of the FOP 2 and a pedestal 300 having an engagement groove 301 provided on its main surface.
Supported by The pedestal 300 forms a dark room for housing the FOP 2 by engaging with the housing 100. Further, the housing 100 is provided with the incident surface 22 of the FOP2.
Upper surface 150 provided with opening 101 for exposing
Having. The light source 3 (illuminating means) that illuminates the incident surface 22 of the FOP 2 is held at a predetermined position by a holding member 200. The holding member 200 is connected to the opening 1 of the housing 100.
The light sources 3 are accommodated in holes 201 provided in the holding portions 250 and 260, respectively.

Further, the image input device according to the present invention is
A control system 400 is provided. The control system 400 takes in an electric signal (video signal) from the image sensor 6, performs predetermined image processing, and also controls driving of the light source 3.

FIG. 2 is a diagram showing a structure of a main part of the image input apparatus according to the present invention. As shown in FIG. 2, the image input device 1 includes at least a FOP 2 and an LED 3 as a light source. The FOP 2 is obtained by bundling and integrating a large number of optical fibers 21 directed substantially in the same direction, and an incident surface 22 and an exit surface 23 are provided at both ends of the optical fiber 21, respectively. From the output surface 23. Within the FOP2, adjacent optical fibers 21
As shown in FIG. 3 and FIG.
Is desirably provided. The light absorber 24 is for achieving optical insulation between the adjacent optical fibers 21, and emits and enters light between the adjacent optical fibers 21 by absorbing light leaked from the optical fibers 21. Function to prevent The optical fiber 21 includes a core 21b having a predetermined refractive index n _core and a clad 21a provided on the outer periphery of the core 21b and having a lower refractive index n _clad than the core 21b.

The incident surface 22 is a surface for allowing light to enter the optical fiber 21 through the convex portion of the object 4 to be contacted, and is inclined by a predetermined angle with respect to the optical axis direction of the optical fiber 21. (Non-parallel and non-orthogonal directions). The inclination angle θ ₀ (slant angle) of the incident surface 22 is such that unnecessary light (reflected light from the concave portion) incident from a concave portion (non-contact portion) not in contact with the incident surface 22 of the object 4 does not propagate through the optical fiber 21. It is desirable to set as follows. Slant angle of such incident surface 22, as shown in FIG. 3, is determined according to the refractive index of the cladding 21a and a core 21b of the optical fiber 21, the refractive index of the clad 21a n _clad, the core 21b Assuming that the refractive index is n _core and the refractive index of air is 1, the inclination angle θ ₀ is smaller than the angle θ _M that satisfies the following equations (1) to (3).

N _core · sin β = n _clad · sin 90 ° (condition of total reflection propagation) ‥‥ (1) n _core · sin α = sin 90 ° (condition of incident angle 0 °) ‥‥ (2) θ _M + (90) (Α + α) + (90 ° −β) = 180 ° (3) That is, the slant angle θ ₀ is such that the light incident substantially parallel to the incident surface 22 is totally reflected in the optical fiber 21 at an angle close to the critical angle. By making the slant angle θ ₀ smaller than θ _M, even if light is incident at any angle from the air, light is theoretically totally reflected and propagated at the boundary between the cladding 21a and the core 21b. I will not do it. Specifically, for example, the refractive index of the cladding 21a of the optical fiber 21 is set to n
_clad = 1.45, the refractive index of the core 21b is n _core = 1.50
Then, the theoretical inclination angle θ _M is about 36 °, and the slant angle θ ₀ may be an angle smaller than 36 °, for example, about 30 °. Since the theoretical inclination angle θ _M depends on the refractive indices n _core and n _clad of the core 21b and the cladding 21a of the optical fiber 21, the slant angle θ ₀ should be set independently of the material of the optical fiber 21 used. Although not possible, it is generally set within the range of about 20 ° to 40 °.

On the other hand, the emission surface 23 is an output surface for emitting the light that has entered from the incidence surface 22 and propagates through the optical fiber 21, and is substantially orthogonal to the optical axis direction of the optical fiber 21. Thus, light is easily output from the optical fiber 21.

According to such FOP2, the incident surface 22
By setting a predetermined optical path length between the object 4 and the exit surface 23, light incident from a non-contact portion (such as in the air) between the object 4 and the entrance surface 22 is attenuated during propagation in the optical fiber 21,
Theoretically, there is no output from the emission surface 23.

However, it is difficult to completely avoid the emission and incidence of light between the optical fibers 21 by the light absorber 24 provided between the optical fibers 21 in the FOP. Light may be guided through the light absorber 24 to the adjacent optical fiber 21 in some cases. Such light is applied to the cladding 2 of FOP2 as shown in FIG.
When the light is reflected on a boundary surface such as 1a, the core 21b, the light absorber 24 or the side surface 25 of the FOP 2 (reflected on the side surface 25 in FIG. 5), and further reflected on the incident surface 22 toward the inside of the FOP, light The light propagates while being totally reflected in the fiber 21 (travels along the optical axis direction of the optical fiber 21).
The light is output from the emission surface 23.

Therefore, the range of the stray light allowable angle with respect to the incident surface 22 of the FOP 2 (the incident angle of the stray light that can reach the exit surface 23)
The LED 3 as the light source is held by the holding member 200 so that the light from the light source is incident in a range outside the range. As shown in FIG. 2, the LED 3 is a unit for irradiating an object 4, for example, a finger, which comes into contact with the incident surface 22 with light of a predetermined wavelength, and comes into contact with the incident surface 22 by irradiating the light. This is for effectively increasing the amount of light incident from the object 4. As this LED3,
It is desirable to use one that emits light with high directivity characteristics. That is, by using such an LED 3, it becomes easy to control the direction of light irradiation (the traveling direction of the light beam emitted from the light source), and it is possible to prevent light from being irradiated at the stray light allowable angle. It should be noted that the light source is not limited to the LED 3, and other light emitters such as a laser and a lamp may be used as long as the light can be emitted at an angle other than the stray light allowable angle. Also, an optical system such as a lens is provided between the light source and the entrance
Irradiated collimated light may be applied.

In this specification, the incident angle component of the light beam illuminating the incident surface 22 of the FOP 2 is divided into a vertical incident angle component θ _V and a horizontal incident angle component θ _H as shown in FIG. I do.

In FIG. 6, the incidence plane 22 of the FOP 2 is xy.
The plane on the plane and the normal to the xy plane are defined as the z-axis. Therefore, the x-axis is an axis on the xy plane, and the reference end 2 that defines the slant angle θ ₀ (the acute angle)
20 and the auxiliary end 230 facing the reference end 220 via the incident surface 22. The y-axis is an axis on the xy plane, and is an axis orthogonal to at least the reference end 220. Here, the reference end 220
Is a line segment that is a boundary line between the side surface 25 and the incident surface 22 and includes a slant angle θ ₀ (a sharp angle). The auxiliary end 230 is also a boundary line between the side surface 25 and the incident surface 22, and is a reference end 220.
Are the line segments facing each other.

Therefore, the vertical incident angle component θ _V is obtained by calculating the incident light beam component on the yz plane and the y axis when the incident light beam directed to the incident surface 22 is mapped on the yz plane in the drawing. (0 ° to 180 °). The horizontal incident angle component θ _H is the angle formed between the incident light beam component on the xz plane and the x axis when the incident light beam directed to the incident surface 22 is mapped on the xz plane in the drawing. Ingredients (0 ~ 90
゜). Note that for the vertical incident angle component θ _V ,
0 ° indicates the reference end 220 side as viewed from the origin O on the incident surface 22, and 180 ° indicates the auxiliary end 230 side as viewed from the origin O. For the horizontal incident angle component θ _H , 0 ° is
It is shown that they coincide with the x-axis in FIG.
Indicates that it is aligned with the axis.

Further, the stray light means that the FOP
2, transmitted through the light absorber 24 and passed through the optical fiber 2.
Unnecessary light propagating irrespective of one optical axis. The stray light allowable angle X is an angle of incidence of an unnecessary light beam incident on the incident surface 22 (an angle on the yz plane similar to the above-described vertical incident angle component where the slant angle side of FOP2 is 0 °). As shown in FIG. 5, the light incident from the incident surface 22 into the FOP 2 is irregularly reflected at the boundary surface such as the side surface 25 or the incident surface 22, and as a result, the optical fiber The angle refers to an angle which is totally reflected inside, propagates, and is output from the exit surface 23. Then, the stray light allowable angle X is given by the following equation (4).
Within the range given by

(X _C −Θ) ≦ X ≦ (X _C + Θ) ‥‥ (4) where X _C is expressed by the formula (90 ° −sin ⁻¹ (n _core · sin
(90 ° -3θ ₀ ))) the stray light allowable central angle given by:
n _core is the refractive index of the core in the optical fiber, θ ₀ is the slant angle, and Θ is the equation (sin ⁻¹ (n _core · sin (90 ° −S
_C −φ))), the critical angle for total reflection in air, S _C, is given by the formula (sin ⁻¹ ((1 / n _core ) · sin).
X _C )), the stray light allowable central angle in the optical fiber, φ is given by the formula (sin ⁻¹ (n _clad / n _core )), and the critical angle of total reflection in the optical fiber, and
n _clad is the refractive index of the cladding in the optical fiber (see FIG. 7).
reference).

That is, in FIG. 5, if the refraction angle of light that enters the FOP 2 having the refractive index n _core with respect to the incident surface 22 at an angle X _C (perpendicular incident angle component) is γ, the following equation (5) ) Holds.

Sin (90 ° −X _C ) = n _core · sin γ ‥‥ (5) Further, as shown in FIG. 5, light propagating through the optical fiber 21 from the incident surface 22 at an angle γ is a side surface 25. Let δ be the refraction angle when the light is totally reflected by the light source and ε be the refraction angle when the light is totally reflected by the light incident surface 22. The following equation (6) holds from the sum of the interior angles of the triangles connecting the reflection points.

(90 ° −γ) + 2δ + ε = 180 ° (6) In FIG. 5, the slant angle θ ₀ of the FOP and the side surface 2
The following equation (7) is established from the sum of the internal angles of the triangles connecting the reflection point No. 5 and the reflection point on the incident surface 22.

Θ ₀ + (90 ° + δ) + ε = 180 ° (7) Here, the light reflected into the FOP 2 at the incident surface 22 propagates at an angle ε with respect to the incident surface 22. When the angle ε of the light coincides with θ ₀ which is the optical axis direction of the FOP 2, the light reaches the emission surface 23. That is, when the following equation (8) holds, the stray light incident at the incident angle X _C (the angle component corresponding to the vertical incident angle component) propagates in parallel with the optical axis of the FOP 2.

Ε = θ ₀ ‥‥ (8) Therefore, δ is eliminated by the equations (6) to (8), and γ
Is expressed as a function of θ ₀ , and is substituted into Expression (5) to eliminate γ, whereby the stray light allowable center angle X _C is given as in the following Expression (9).

X _C = 90 ° −sin ⁻¹ (n _core · sin (90 ° −3θ ₀ )) ‥‥ (9) The stray light allowable center angle X _C is determined by the following formula: This is an angle component on the yz plane corresponding to the vertical incident angle component of the light beam when it is parallel to the direction. At this time, the stray light propagates in the optical fiber 21 by total reflection, and
FIG. 7 shows a possible range of the stray light allowable angle X output from FIG.
As shown in (2), the angle range is obtained by adding or subtracting the total reflection critical angle と し て about the stray light allowable center angle X _C. The critical angle of total reflection refers to the minimum angle of incidence from the core 21b to the cladding 21a when light propagates while totally reflecting inside the optical fiber 21. Therefore, the stray light allowable angle X is (X _C −
Θ) to (X _C + Θ), which is represented by equation (4). In FIG. 7, theta _- the stray light admissible center angle means the total reflection critical angle of the reference end 220 side (theta) from X _C, theta ₊ the total reflection critical supplementary end 230 side from the stray light admissible center angle X _C Means angle (Θ).

Next, an experiment for measuring the output of the FOP 2 (output from the exit surface 23) with respect to the vertical incident angle component θ _V and the horizontal incident angle component θ _H which are the incident angle components of the light beam emitted from the light source will be described. .

First, as for the vertical incident angle component θ _V , as shown in FIG.
2, the horizontal incident angle component θ _H is 15 °, 30 °, 90 °
With the angle of incidence fixed at ゜, the amount of output light from the exit surface 23 was measured while changing the vertical incident angle component θ _V from 0 ° to 180 °. Specifically, the horizontal incident angle component θ
_{With H} fixed at predetermined angles (15 °, 30 °, 90 °), the LED 3 is shown by an arrow L1 in FIG. 8A together with an optical system (lens) that collimates the light emitted from the LED 3. The measurement was performed while moving in the specified direction.

FIG. 8B shows the vertical incident angle component θ _V and the exit surface 2 measured by the measuring method shown in FIG.
3 is a graph showing a relationship with the light amount of light output from No. 3; In the graph, the vertical axis is a value normalized by setting the maximum output to 100.

As can be seen from this graph, the permissible stray light angle X does not depend much on the horizontal incident angle component θ _H.
It is in the range of about 70 ° to 110 °. Conversely, light source 3
The light source 3 is installed at a position where the light beam emitted from the light source is incident on the incident surface 22 from a range other than the range (70 ° to 110 °) where the vertical incident angle component θ _V is concerned, so that the stray light FOP 2 Can be suppressed.

On the other hand, as for the horizontal incident angle component θ _H , as shown in FIG.
With respect to No. 2, while the vertical incident angle component θ _V was fixed at 90 °, the output light amount from the exit surface 23 was measured while changing the horizontal incident angle component θ _H from 0 ° to 90 °. Specifically, in a state where the vertical incident angle component θ _V is fixed at a predetermined angle (90 °), the LED 3 is coupled with an optical system (lens) for collimating the light emitted from the LED 3 by an arrow in FIG. The measurement was performed while moving in the direction indicated by L2.

FIG. 9B shows the horizontal incident angle component θ _H and the exit surface 2 measured by the measuring method shown in FIG. 9A.
3 is a graph showing a relationship with the light amount of light output from No. 3; In the graph, the vertical axis is a value normalized by setting the maximum output to 100.

As can be seen from this graph, the horizontal incident angle component θ _H is preferably as close to 0 ° as possible, and is preferably set to at least 20 ° or less.

The light source 3 preferably uses a directional light emitting body. However, as shown in FIG. 10, it is also possible to use a light source having a predetermined divergence angle around the central light beam 30. It is. However, when such a light source 3 is used, as shown in FIG. 11, each of the holding portions 250 and 260 of the holding member 200 having a thickness h.
The central light beam 30 and the incident surface 2
Even when each light source 3 is fixed so that 2 is parallel to each other, the light beam from each light source 3 irradiates the incident surface 22 with a certain spread angle. Therefore, the spread angle of the light beam emitted from such a light source 3 is as shown in FIG.
As shown in (c), the light is emitted from the light source 3 by adjusting the distance from the opening 202 of the fixing hole 201 provided in each of the holding portions 250 and 260 to the emission end face of the light source 3. The spread angle of the light beam can be adjusted.
Of course, it is also possible to provide an optical system (lens) as collimating means in the opening 202.

As described above, since the horizontal incident angle component θ _H of the light beam irradiated on the incident surface 22 is preferably closer to 0 °, each light source 3 is held as shown in FIG. In the state of being held by the member 200 (the center light beam 30 and the incident surface 22 are parallel), the light beam is based on a line connecting the origin O on the incident surface 22 and the reference end 220 as shown in FIG. It can be seen that it is preferable to irradiate the incident surface 22 from the range of + 120 ° to + 180 ° or the range of -120 ° to -180 °. The fact that the traveling direction of the central light beam 30 is within this range means that at least a component on the incident surface 22 of the direction vector component of the central light beam 30 travels from the auxiliary end 230 toward the reference end 220. Means

From the above considerations, in the image input device according to the present invention, the holding member 200 allows the central light beam 30 from the light source 3 to be parallel to the incident surface 22 and the reference end 22.
Each light source 3 is positioned at an angle of 125 ° with respect to an axis (coincident with the y-axis) on the entrance surface 22 perpendicular to 0.
(See FIG. 14).

The stray light is not limited to unnecessary light from the light source 3. Therefore, as shown in FIG. 15, by providing the light blocking member 270 that covers the incident surface 22 on the holding member 200, it is possible to more reliably prevent the incidence of stray light (first application example).

Next, FIGS. 17 and 18 show photographs of halftone images in which the emission surface 23 of the FOP 2 is displayed on a display when the vertical incident angle component θ _V is actually changed.

The slant angle θ ₀ of the FOP 2 used for photographing is 30 ° and the horizontal incident angle component θ _H is 90 °. As shown in FIG. 16, the light source 3 is moved in the direction indicated by the arrow L3. Is moved so that the vertical incident angle component θ _V becomes 0 ° (FIG. 17).
(A)), 30 ° (FIG. 17 (b)), 60 ° (FIG.
(C)), 90 ° (FIG. 18 (a)), 120 ° (FIG.
(B)) and at 150 ° (FIG. 18 (c)), the exit surface 23 (the exit surface 23 of FOP2 on the left side of each photograph) was photographed.

As can be seen from these photographs, when the vertical incident angle component θ _V is around 60 ° or 120 ° or more, the incidence of stray light can be effectively suppressed. on the other hand,
When the vertical incident angle component θ _V is 0 ° and 30 °, it is not very effective in suppressing stray light incidence. Further, when the vertical incident angle component θ _V is 90 °, the effect of suppressing stray light incidence is reduced. Cannot be obtained. Note that the fingerprint pattern shown in the photographs of FIGS. 17A and 17B is the incident surface 2 of FOP2.
2 is the remaining fat. Also, this photographing result is shown in FIG.
Results of the graph shown in (b) (when θ _H = 90 °)
Is consistent with the trend.

As described above, the core refractive index n of FOP2
_core is 1.50, the cladding refractive index n _{cl ad} is 1.45 (N
If A = 0.35), the critical angle 全 for total reflection in the air is about 20 °, and if the slant angles θ _{0 of} FOP2 are 20 ° and 30 °, respectively, the range of the stray light allowable angle X is
According to the equation (4), 21 ° (= 41 ° −20 °) respectively
61 ° (= 41 ° + 20 °) and 70 ° (= 90 ° −
20 °) to 110 ° (= 90 ° + 20 °). Therefore, by irradiating the light from the LED 3 to the incident surface 22 from an area other than the stray light allowable angle X within the range given in this way, stray light is emitted from the emission surface 2 of the FOP 2.
3, only the light incident from the portion in contact with the incident surface 22 is clearly output from the exit surface 23.

In order to further verify such a value of the stray light allowable angle X, the inventors used an actual FOP2 to determine the characteristics of the incident angle component (vertical incident angle component θ _V ) of the incident light beam and the output intensity of the stray light. Was measured using the measuring device shown in FIG. FIG. 20 shows measurement data obtained from the measurement device shown in FIG. The prepared FOP2 has slant angles θ ₀ of 20 ° and 30 °, respectively.
Further, in each FOP2, the refractive index n _{core of the core} is 1.
50, cladding refractive index n _clad is 1.45 (NA = 0.
35). And for each FOP2,
With the horizontal incident angle component θ _H fixed at 90 °, the output surface 23 is changed while the vertical incident angle component θ _V with respect to the incident surface 22 is changed from 5 ° to 180 ° (the reference end side of the FOP 2 is set to 0 °). The change in the output intensity of the stray light output from was measured. As the light source 3, a semiconductor laser 51 (LN9R manufactured by Matsushita Electric Industrial, 35 mW, 680 nm) was used. As an output intensity measuring means, a CCD 52 (BS7259, manufactured by Matsushita Electronics) was attached to the emission surface 23, and the output was taken into an output detection device 53 (DVS3000, manufactured by Hamamatsu Photonics), and stray light output intensity was measured by area integration.

Referring to the graph of FIG.
° FOP2, the vertical incident angle component θ of the incident light beam
_{When V} is 30 °, the output intensity of stray light becomes maximum, and the output intensity decreases as the incident angle increases or decreases from that angle. Further, in the FOP2 having a slant angle of 30 °, the stray light output intensity becomes maximum when the vertical incident angle component θ _V is 90 °, and the output intensity decreases as the vertical incident angle component θ _V increases or decreases from that angle. , Incident angle 20 °
There was a tendency for the output intensity to increase even at around. In addition,
In the graph of FIG. 20, the vertical axis is a value normalized by setting the maximum value of the stray light output intensity to 1.

As a result of such a measurement, the value of the theoretical stray light allowable angle X described above and the incident angle component (vertical incident angle component θ _V ) at which the actual stray light output intensity becomes maximum become the slant angle θ ₀ . It can be seen that they almost match as dependent functions. Further, it can be seen that light incident on the incident surface 22 within the range of the stray light allowable angle X shown in the above equation (4) becomes stray light and is output from the emission surface 23. For this reason, by emitting a light beam from the light source 3 at an incident angle other than the stray light allowable angle X with respect to the incident surface 22, the output of stray light can be suppressed, and only desired light can be output clearly.

Next, the method of use and operation of the image input apparatus 1 according to the present invention will be described with reference to the drawings.

In FIG. 2, the LED 3 is installed with its light beam emitting surface facing the incident surface 22 of the FOP 2, and the light beam is irradiated on the incident surface 22 at an angle other than the stray light allowable angle X.
The output surface 23 of the FOP 2 is provided with a photoelectric conversion unit 6 such as a CCD so that an image of light output from the output surface 23 can be converted into an electric signal and output. In this state, when an object having an uneven surface, for example, a finger 4 is brought into contact with the incident surface 22 of the FOP 2, FIG.
As shown in the dashed circle in the middle, only the convex portion 41 of the fingerprint of the finger comes into contact with the incident surface 22.

On the other hand, the finger 4 is irradiated with light from the LED 3, and the light enters the optical fiber 21 through the convex portion 41 of the finger 4. At this time, since the light from the LED 3 irradiates the incident surface 22 at an angle other than the stray light allowable angle X, even if the light enters the optical fiber 21 directly from the air without passing through the finger 4, the stray light And is not output from the emission surface 23.

The light incident on the optical fiber 21 via the finger 4 propagates in the respective optical fibers 21 by total reflection and reaches the emission surface 23, where the light (fingerprint pattern) of the finger 4 is obtained.
Is output as an image corresponding to. At this time, the incident surface 2
Since there is no output of stray light incident from the non-contact portion between the finger 2 and the finger 4, portions other than the fingerprint image on the exit surface 23 (recesses not in contact with the incident surface 22) become dark, and the fingerprint light image Is a clear image with clear contrast. Then, this clear image is input to the photoelectric conversion means 6 and processed as an electric signal.

As described above, according to the image input device 1 according to the present invention, an object image can be clearly output according to the uneven shape in contact with the incident surface 22. For this reason,
It will be very useful if used for an identification device with an uneven shape such as fingerprint detection.

Next, the above-described image input apparatus 1
As the P2, a trapezoidal cross section in which the entrance surface 22 and the exit surface 23 are not parallel is used, but this FOP2 may be a parallelogram in cross section having the entrance surface 22 and the exit surface 23 parallel to each other (second). Application example). That is, as shown in FIG. 21, the image input device 1 a according to the second application example includes at least the light source 3, the entrance surface 22 and the exit surface 2 that are parallel to each other.
3 having FOP2. Even with such an image input device 1a, as described above, the light source 3
By irradiating the incident surface 22 with the light flux from the incident surface 22 at an angle other than the stray light allowable angle X, an image corresponding to the convex portion contacting the incident surface 22 can be clearly output from the exit surface 23.

Furthermore, the image input device according to the present invention
As shown in FIG. 22 to FIG. 25, it can be realized by various configurations.

That is, in the third application example shown in FIG. 22, between the slant FOP 500 having the incident surface 501 and the image sensor 601, the cross-sectional area decreases from the slant FOP 500 toward the image sensor 601. The tapered FOP 600 is provided. Even with this structure, the stray light allowable angle X described above
When irradiating the incident surface 22 with a light beam from other sources, the propagation of stray light in the optical fiber can be effectively suppressed.

In the fourth application example shown in FIG. 23, a slant F in which the entrance surface 511 and the exit surface 512 are parallel to each other.
OP510, image sensor 601, and slant FO
An optical system 602 (lens) provided between the P510 and the image sensor 601 is provided. Note that a scattering process is performed on the emission surface 512 of the slant FOP 510.

In the fifth application example shown in FIG. 24, the slant F in which the entrance surface 521 and the exit surface 522 are parallel to each other.
An OP 520 and an image sensor 601 are provided, and a taper FOP 600 is provided between the slant FOP 520 and the image sensor 601 as in the third application example (FIG. 22).

Further, the sixth application example shown in FIG.
An image sensor 601 includes a slant FOP 520 in which the entrance surface 521 and the exit surface 522 are parallel to each other, and a slant FOP 530 in which the entrance surface 531 and the exit surface 532 are parallel to each other between the slant FOP 520 and the image sensor 601. , An optical system 602 provided between the slant FOP 530 and the image sensor 601. In any of the fourth to sixth application examples having the above-described structure, the luminous flux from the stray light allowable angle X other than the above-described angle
2, the propagation of stray light through the optical fiber can be effectively suppressed.

[0067]

As described above, according to the present invention, light for illuminating the incident surface at an angle other than the stray light allowable angle with respect to the incident surface is emitted, so that the convex portion of the object that is in contact with the incident surface. Only the light incident from the object is output from the output surface, and the light incident from the concave portion of the object that is not in contact with the incident surface is not output from the output surface. Therefore, a clear object image corresponding to the concavo-convex pattern on the object surface can be obtained.

Further, by using a light source having a high directivity characteristic as the light source or by providing a structure for limiting the spread angle of the light beam from the light source, the irradiation direction of the light from the light source (the light beam emitted from the light source) It is easy to control the direction of travel, and it is possible to prevent light from being emitted at an allowable stray light angle.
For this reason, only desired light can be reliably output from the exit surface.

[Brief description of the drawings]

FIG. 1 is an assembly process diagram for explaining a configuration of an image input device according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of an image input device according to the present invention.

FIG. 3 is a diagram for explaining light propagation in a fiber optical plate.

FIG. 4 is a diagram showing a cross-sectional structure of a fiber optical plate in the image input device according to the present invention.

FIG. 5 is a diagram for explaining a mechanism of stray light generation in the fiber optical plate.

FIG. 6 is a diagram for explaining an incident angle of a light beam incident on the fiber optical plate.

FIG. 7 is a diagram for explaining an allowable range of stray light.

FIG. 8A is a diagram for explaining a method for measuring a stray light allowable range for a vertical incident angle component, and FIG. 8A shows a relationship between the vertical incident angle component and the amount of emitted light measured by the method shown in FIG. It is a graph (b) which shows a relationship.

9A is a diagram for explaining a method of measuring a stray light allowable range with respect to a horizontal incident angle component, and FIG. 9A is a graph showing the relationship between the horizontal incident angle component and the amount of emitted light measured by the method shown in FIG. It is a graph (b) which shows a relationship.

FIG. 10 is a diagram for explaining the spread of a light beam emitted from a light source.

FIG. 11 is a diagram showing a structure of a holding member for holding a light source at a predetermined position.

FIGS. 12A to 12C are diagrams showing a structure for adjusting a spread angle of a light beam emitted from a light source.

FIG. 13 is a diagram showing an optimum range in which a light source is installed in the image input device according to the present invention.

FIG. 14 is a diagram for explaining an installation state of a light source in the image input device according to the present invention.

FIG. 15 is a diagram showing a schematic structure of a first application example of the image input device according to the present invention.

FIG. 16 is a diagram for describing a method for capturing an image of an incident surface of a fiber optical plate with respect to a vertical incident angle component.

FIG. 17 is a photograph showing the halftone image displayed on the display on the output surface of the fiber optic plate by the method shown in FIG. 16 (part 1). (A) is a vertical incident angle component = 0 °, (b) is a vertical incident angle component = 30 °,
(C) is a photograph of each exit surface at a vertical incident angle component of 60 °.

FIG. 18 is a photograph showing the halftone image displayed on the display on the output surface of the fiber optical plate by the method shown in FIG. 16 (part 2). (A) is a vertical incident angle component = 90 °, and (b) is a vertical incident angle component = 120.
゜ and (c) are photographs of the respective exit surfaces when the vertical incident angle component is 150 °.

FIG. 19 is a diagram showing a schematic structure of an apparatus for measuring a stray light output when a vertical incident angle component is changed for fiber optical plates having different slant angles.

FIG. 20 is a graph showing a relationship between a vertical incident angle component and a stray light output measured by the device shown in FIG. 19;

FIG. 21 is a diagram showing a schematic structure of a second application example of the image input apparatus according to the present invention.

FIG. 22 is a diagram showing a schematic structure of a third applied example of the image input device according to the present invention.

FIG. 23 is a diagram showing a schematic structure of a fourth applied example of the image input device according to the present invention.

FIG. 24 is a diagram showing a schematic structure of a fifth application example of the image input apparatus according to the present invention.

FIG. 25 is a diagram showing a schematic structure of a sixth application example of the image input device according to the present invention.

FIG. 26 is a diagram illustrating a configuration of a conventional image input device.

FIG. 27 is a diagram for explaining a problem of a conventional image input device.

[Explanation of symbols]

1 ... Image input device, 2,500,510,520,53
0, 600: fiber optical plate, 21: optical fiber, 22: incident surface, 23: emission surface, 3: LED (light source), 100: housing, 200: holding member, 220: reference end, 230: auxiliary end, 250, 260 ... holding part.

Claims (9)

[Claims] Claims: 1. A plurality of optical fibers are bundled and integrated,
And a predetermined slant angle θ _{0 with} respect to the optical axis of the optical fiber.
A first fiber optical plate having an incident surface inclined only by the angle of incidence, and an exit surface facing the incident surface; a light source for illuminating the incident surface of the first fiber optical plate; A holding member for holding the slant angle θ ₀ of the incident angle component between the light beam emitted from the light source and the incident surface. In a state where the vertical incident angle component θ _V on a plane orthogonal to the reference end on the incident surface that has been defined is set to a range deviated from the stray light allowable angle X given by the range of the following equation, An image input device characterized by being held. (X _c −Θ) ≦ X ≦ (X _c + Θ) X _C : Equation (90 ° −sin ⁻¹ (n _core · sin (90
° -3θ ₀ ))) The stray light allowable center angle given by n _core : refractive index of the core in the optical fiber θ ₀ : slant angle ：: formula (sin ⁻¹ (n _core · sin (90 ° −S _C))
−φ))), the critical angle for total reflection in air S _C : Equation (sin ⁻¹ ((1 / n _core ) · sin)
Given by X _C)), stray light admissible center angle in the optical fiber phi: Formula (given by ^{_{sin -1 (n clad / n core}} )), total reflection critical angle n _clad in the optical fiber: in the optical fiber Refractive index of cladding 2. The incident member, which is orthogonal to the incident surface and defines the slant angle θ ₀ , of the incident angle component between the light beam emitted from the light source and the incident surface. The light source is held in a state where a horizontal incident angle component θ _H on a plane parallel to a reference end on a surface is set within a range of 0 ° or more and 20 ° or less. The image input device according to the above. 3. A plurality of optical fibers are bundled and integrated,
And a predetermined slant angle θ _{0 with} respect to the optical axis of the optical fiber.
A first fiber optical plate having an incident surface inclined only by the angle, and an exit surface facing the incident surface; and housing the first fiber optical plate.
A housing having an upper surface with an opening for exposing the light incident surface, at least one pair of light sources for illuminating the light incident surface of the first fiber optic plate, and And at least one pair of light sources arranged to sandwich the opening of the housing and holding each of the light sources such that the pair of light sources surrounds at least a part of the opening of the housing. And a holding member having a holding portion. 4. The holding member, wherein a component on the incident surface of the directional vector component of the central luminous flux from the light source faces a reference end on the incident surface defining the slant angle θ _0. The image input device according to any one of claims 1 to 3, wherein the light source is held so as to advance from the auxiliary end on the incident surface toward the reference end. 5. The light source according to claim 1, wherein the holding member holds the light source such that a center light beam of the light beams emitted from the light source is parallel to the incident surface. 5. The image input device according to claim 4. 6. The image input device according to claim 1, wherein the holding member includes a light shielding member that covers an incident surface of the first fiber optical plate via a gap. apparatus. 7. The image sensor according to claim 1, further comprising an image sensor having a light receiving surface arranged to face the light exit surface of the first fiber optical plate. Image input device. 8. The image input device according to claim 7, further comprising a second fiber optical plate between said first fiber optical plate and said image sensor. 9. An optical system further comprising an optical system between the first fiber optical plate and the image sensor or between the second fiber optical plate and the image sensor. 9. The image input device according to 7 or 8.