TWI621998B - Fingerprint image capturing system - Google Patents

Abstract

A fingerprint imaging system includes a finger pressing member having an opposite top surface and a bottom surface. The top surface defines a first normal line, and has a light incident surface and a light exit surface on opposite sides of the finger pressing member. The light-incident surface corresponds to one light source module, and the light-emitting surface corresponds to an image capturing module. The surface light source module has a light emitting surface, and the light emitting surface is parallel to the first normal line. The vertical light emitting surface defines a second normal line, and the second normal line forms a first angle with the light incident surface, and the first angle is 30 degrees to 45 degrees.

Description

Fingerprint imaging system

An image capturing system, in particular a fingerprint image capturing system for capturing fingerprint images.

In general, the fingerprint recognition device reads a fingerprint by a method of fixing a finger to read a fingerprint, for example, by using a pressing plate for a finger contact, and then using a plurality of light-emitting elements to provide a fingerprint image of a finger that touches the contact plate. In order to meet the principle of total reflection, the fingerprint recognition device must have a certain angle between the lens, the finger and the light source in order to extract the clear and clear fingerprint, so that the conventional optical type Fingerprint identification devices generally have problems of large size and inability to be thinned, and there are disadvantages of dark areas at the edges of the fingerprint images that are taken out.

The embodiment provides a fingerprint image capturing system, which solves the problem that the fingerprint image which is easily obtained by the prior art is blurred and the edge has a clear dark area.

The fingerprint imaging system disclosed in this embodiment includes a finger pressing member having an opposite top surface and a bottom surface. The vertical top surface defines a first normal line, and has a light incident surface and a light exit surface on opposite sides of the finger pressing member. The light-incident surface corresponds to one light source module, and the light-emitting surface corresponds to an image capturing module. The surface light source module has a light emitting surface, and the light emitting surface is parallel to the first normal line. The vertical light emitting surface defines a second normal line, and the second normal line forms a first angle with the light incident surface, and the first angle is 30 degrees to 45 degrees.

The fingerprint imaging system disclosed in this embodiment includes a finger pressing member and has a phase A top surface and a bottom surface of the pair form a height between the top surface and the bottom surface. The vertical top surface defines a first normal. The opposite sides of the finger pressing member respectively have a light-incident surface and a light-emitting surface, and the light-incident surface corresponds to one light source module, and the light-emitting surface corresponds to an image capturing module. The surface light source module has a light emitting surface, and defines a length along the light emitting surface, and the length of the light emitting surface is equal to the height of the finger pressing member. The vertical light emitting surface defines a second normal line, and the second normal line forms a first angle with the light incident surface, and the first angle is 30 degrees to 45 degrees.

According to the fingerprint imaging system disclosed in the above embodiment, the length of the emitting surface is equal to the height of the finger pressing member, and the first angle between the second normal line and the light incident surface is 30 degrees to 45 degrees. The light will be evenly refracted to the top of the top surface so that the top surface is evenly received. In this way, the fingerprint image captured by the image capturing module can have uniform brightness without the problem of uneven brightness, thereby improving the image capturing quality of the fingerprint image capturing system.

The features, implementations, and effects of the present embodiment will be described in detail below with reference to the drawings.

10‧‧‧ Fingerprint imaging system

11‧‧‧ finger press

111‧‧‧ top surface

112‧‧‧ bottom

113‧‧‧Into the glossy surface

114‧‧‧Glossy surface

12‧‧‧ surface light source module

121‧‧‧ point light source

122‧‧‧Diffuser

13‧‧‧Image capture module

20‧‧‧ fingers

21‧‧‧ Fingerprint

D1‧‧‧ first normal

D2‧‧‧ second normal

1 and 2 are schematic views of a fingerprint imaging system of the present invention.

Figure 3 shows the refraction path of the light from the surface source to the finger.

FIG. 4 is a fingerprint image captured by the fingerprint imaging system of the present invention.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a fingerprint imaging system of the present invention.

The fingerprint imaging system 10 of the embodiment includes a finger pressing member 11, a light source module 12 and an image capturing module 13.

The finger pressing member 11 is a light transmissive plate body, and the material thereof may be glass (model specification: BK7) or polymethylmethacrylate (PMMA). The refractive index n1 of the finger pressing member 11 ranges from 1.49 to 1.52.

The cross section of the finger pressing member 11 has a trapezoidal shape and is composed of a top surface 111, a bottom surface 112, a light incident surface 113 and a light exit surface 114. The top surface 111 of the finger pressing member 11 is used For one finger contact, the width of the top surface 111 is greater than the width of the bottom surface 112. The light-incident surface 113 and the light-emitting surface 114 are respectively connected between the top surface 111 and the bottom surface 112 and are located on opposite sides of the finger pressing member 11.

The surface light source module 12 includes a plurality of point light sources 121 and a diffusion plate 122.

The diffusing plate 122 has a light emitting surface 1221, and the light emitting surface 1221 corresponds to the light incident surface 113. It should be noted that a top normal line D1 may be defined perpendicular to the top surface 111 of the finger pressing member 11, and the light emitting surface 1221 and the first normal line D1 may be parallel to each other. In addition, a second normal line D2 is defined perpendicular to the light emitting surface 1221, and a first angle θ1 is formed between the second normal line D2 and the light incident surface 113. This first angle θ1 is 30 degrees to 45 degrees. Preferably, the first angle θ1 is 45 degrees.

In order to achieve the optimal design of the first angle θ1 between the second normal line D2 and the light incident surface 113, a second angle θ2 is formed between the light incident surface 113 and the top surface 111 such that the second angle θ2 is 30. Degree to 45 degrees. Similarly, the third angle θ3 is also formed between the light-emitting surface 114 and the top surface 111, and the third angle θ3 is also 30 degrees to 45 degrees.

Therefore, when the point light sources 121 emit light toward the diffusion plate 122, the light emitted by the point light sources 121 can be uniformized by the diffusion plate 122, and a uniform surface light source is emitted by the light emitting surface 1221, so that the surface light sources are The light rays are all incident on the light incident surface 113 in a direction parallel to the second normal line D2, so that the light of the surface light source enters the finger pressing member 11 and can be refracted to the top surface 111 including the edges, so that the entire surface area of the top surface 111 Has the most complete light receiving state.

The image capturing module 13 corresponds to the light emitting surface 114, and the image capturing module 13 is configured to capture a fingerprint image of the light reflected from the top surface 111.

Referring to FIG. 2, it is further defined that the top surface 111 has a width W, and the top surface 111 and the bottom surface 112 have a height H therebetween. A length L is defined along the light emitting surface 1221, and the length L of the light emitting surface 1221 is equal to the height H of the finger pressing plate 11.

Referring to FIG. 3, in order to simplify the description, the upper end, the center and the lower end of the light emitting surface 1221 represent three light rays L1, L2 and L3 of the emitted surface light source as an example. When the light rays L1, L2, and L3 enter the light incident surface 113 in a direction parallel to the second normal line D2 (shown in FIG. 2), the light rays L1, L2, and L3 also form a first angle θ1 with the light incident surface 113, respectively. . For example, when the first angle θ1 is 45 degrees, it can be inferred that the incident angle θ _in of the light rays L1, L2, and L3 is 45 degrees, and if the refractive index n1 of the finger pressing member 11 is 1.5168, and the air refractive index n2 is 1, the refractive formula: sinθ _in = 1.5168 sinθ _out, can calculate θ _out is 27.78 degrees, so that the light L1, L2 and L3, respectively, the incident angle of 27.78 degrees toward the top surface 111.

Thus, from the refracting paths of the light rays L1, L2, and L3 of FIG. 3, the light ray L1 and the light ray L3 can be respectively refracted to the leftmost edge and the rightmost edge of the top surface 111. In other words, the light of the surface light source emitted by the light-emitting surface 1221 can be uniformly refracted to the periphery of the top surface 111, respectively, so that the top surface 111 can receive light uniformly and uniformly. After the top surface 111 is uniformly received, the fingerprint 21 of the finger 20 can be visualized, so that the image capturing module 13 can clearly capture the image of the fingerprint 21 reflected from the top surface 111.

Furthermore, when the light rays L1, L2, and L3 are incident on the light incident surface 113 parallel to the second normal line D2, and the first angle θ1 formed by the light beams L1, L2, and L3 and the light incident surface 113 is 30 degrees, It can be inferred that the incident angle θ _in of the light rays L1, L2, and L3 is 60 degrees. If the refractive index n1 of the finger pressing member 11 is 1.5168 and the air refractive index n2 is 1, according to the refractive formula: sin θ _in = 1.5168 sin θ _out , It is estimated that θ _out is 34.81 degrees, so that the light rays L1, L2, and L3 are respectively incident on the top surface 111 at an incident angle of 34.81 degrees.

Therefore, in order to meet the image capturing quality of the image capturing module 13, the optimum refractive angle θ _out of the light sources L1, L2, and L3 of the surface light source emitted by the surface light source module 12 is 34.81 degrees to 27.78 degrees. In addition, the length L of the light-emitting surface 1221 is equal to the height H of the finger pressing plate 11, and the optimum ratio of the width W to the height H is obtained in order to obtain the maximum image taking width (that is, the width W of the top surface 111) and the optimum image capturing angle. It is 5:2.

For example, when the thickness of the finger pressing plate 11 is 8 mm, the maximum image capturing width is 20 mm, and at the same time, the light illuminating angles θ _out of the surface light sources L1, L2, and L3 are 34.81 degrees to 27.78 degrees, so that the top surface is made. The entire area of the 111 is uniformly received by light. Thus, as shown in FIG. 4, the image capturing module 13 can obtain a uniform and clear fingerprint image, and the edge of the fingerprint image does not have obvious dark areas, which is compared with the conventional fingerprint image capturing system. The brightness of the opposite ends of the fingerprint image is significantly lower than the brightness of the central area. The fingerprint image capturing system 10 of the embodiment can solve the problem that the conventional fingerprint image is blurred and the edge is easy to generate dark areas. Although the present embodiment is disclosed above, it is not intended to limit the embodiments, and those skilled in the art, regardless of the spirit and scope of the embodiments, the shapes, structures, features, and spirits as described in the application scope. The scope of patent protection of this embodiment is subject to the definition of the scope of the patent application attached to this specification.

Claims (8)

A fingerprint image capturing system comprising a finger pressing member having a top surface and a bottom surface, wherein the top surface defines a first normal line and has a light incident surface on opposite sides of the finger pressing member And a light-emitting surface corresponding to a light source module, wherein the light-emitting surface corresponds to an image capturing module, wherein the surface light source module has a light emitting surface, the light emitting surface is parallel to the first normal line, and Vertically defining a second normal line, the second normal line and the light incident surface form a first angle, the first angle is 30 degrees to 45 degrees; and the surface light source module further comprises a diffusing plate having the light emitting surface; and a plurality of point light sources corresponding to the diffusing plate; wherein the light emitted by the point light sources forms a light source through the diffusing plate, the surface light source is incident on the light source a light incident surface of the finger pressing member, wherein the light incident surface is inclined with respect to the diffusion plate. The fingerprint image capturing system of claim 1, wherein the light incident surface and the top surface form a second angle, the second angle is 30 degrees to 45 degrees, and the light emitting surface forms a third angle with the top surface. The third angle is 30 degrees to 45 degrees. The fingerprint imaging system according to claim 1 or 2, wherein the finger pressure member is made of glass or acryl, and the refractive index of the finger pressure ranges from 1.49 to 1.52. The fingerprint imaging system of claim 3, wherein the light source of the surface light source enters the light incident surface with a refractive angle θ _out of 34.81 degrees to 27.78 degrees. A fingerprint image capturing system comprising a finger pressing member having a top surface and a bottom surface, the top surface and the bottom surface having a height, and a light entering the opposite sides of the finger pressing member And a light emitting surface corresponding to a light source module, wherein the light emitting surface corresponds to an image capturing module, wherein the surface light source module has a light emitting surface, and a length is defined along the light emitting surface, The length of the light emitting surface is equal to the height of the finger pressing member, and the light emitting surface defines a vertical a second normal line, the second normal line and the light incident surface form a first angle, the first angle is 30 degrees to 45 degrees; and the surface light source module further comprises: a diffusion plate, the diffusion The plate has the light emitting surface; and a plurality of point light sources corresponding to the diffusing plate; the light emitted by the point light sources forms a light source through the diffusing plate, and the surface light source enters the light incident surface of the finger pressing member The light incident surface is inclined with respect to the diffusion plate. The fingerprint image capturing system of claim 5, wherein the light incident surface and the top surface form a second angle, the second angle is 30 degrees to 45 degrees, and the light emitting surface forms a third angle with the top surface The third angle is 30 degrees to 45 degrees. The fingerprint imaging system of claim 5 or 6, wherein the finger pressure member is made of glass or acryl, and the finger pressure has a refractive index ranging from 1.49 to 1.52. The fingerprint image capturing system of claim 7, wherein the top mask has a width, the ratio of the width to the height is 5:2, and the light refracting angle θ _out of the surface light source into the light incident surface is 34.81. Degree to 27.78 degrees.