WO2014090750A1

WO2014090750A1 - Biometric fingerprint capture device with compact lighting

Info

Publication number: WO2014090750A1
Application number: PCT/EP2013/075958
Authority: WO
Inventors: Sylvaine Picard; Gilles Monteilliet; Michel CRUCHAGA
Original assignee: Morpho
Priority date: 2012-12-10
Filing date: 2013-12-09
Publication date: 2014-06-19
Also published as: FR2999320A1

Abstract

A biometric fingerprint capture device, comprising a frame (1) defining a capture area (2), an image sensor (3) mounted in the frame to have a field (4) covering the capture area and a lighting member (5) for lighting the capture area, the lighting member comprising at least one light source (6), the lighting member comprising at least one wave guide (7) having an input surface (7.1) extending opposite the light source and an output surface (7.2) at least partially covered by a series of microprisms arranged to direct a light wave emitted by the light source towards the capture area in a manner that is substantially uniform in intensity and direction.

Description

BIOMETRIC FOOTPRINT CAPTURE DEVICE

COMPACT LIGHTING

The present invention relates to a non-contact biometric fingerprint capture device such as fingerprints and palm prints that are formed by the ridges and furrows of the skin. These devices are used for the identification of individuals from their fingerprints for example to allow them access to a place.

A biometric fingerprint capture device generally comprises and more particularly a frame defining a capture zone materialized by a transparent sup ^¬ port on which an individual to identify must place one or more of his fingers. An image sensor is mounted in the frame to have a neck field ^¬ ering the capture zone. To illuminate the cap area ^¬ ture and thus allow capturing an image of the finger or of the individual, there is provided an illumination device comprising a light source such as a diode troluminescente electrician.

The quality of the identification depends beautiful shot ^¬ contrast of the image. In these devices, such as that of US-A-5448649, a strong con trast ^¬ is obtained that:

the parts of the transparent support which are not in contact with the finger (these parts are opposite the bottom of the furrows of the skin) reflect the light;

- The parts of the transparent support in contact with the finger (specifically with the ridges of the skin) reflect little or no light.

In the aforementioned document, the transparent support incorporates microprisms used to promote this selective reflection of light.

There are also capture devices without contact in which the capture area is a free space area in which the individual to be identified must place the lower part of the hand. Free space zone means that this zone is devoid of support (between the finger or the hand and the sensor in the zone of space captured by it, and between the finger or the hand and the lighting device ) on which the hand or finger has to be applied: it is the operator, through the operation of its muscles, which keeps his hand in the capture zone, the hand being optionally movable in cer tain ^¬ contactless capture devices . The device may include a guide against which the hand or the finger can be applied, this guide does not extend into the captured capture area for identification.

The quality of the image obtained and reliability of fingerprint authentication depend largely on the lighting to be controlled in the volume of cap ^¬ ture following criteria for orientation relative to the finger and angular intensity ( lighting lobe) in order to obtain uniform illumination on the curved surface of the finger. To ensure this, it is known to move the light source (diode) away from the capture area. This aug ^¬ mente however the size of the device and requires the use of an LED relatively high power and thus energy intensive and Neck ^¬ Teuse to purchase.

An object of the invention is to remedy at least in part the aforementioned drawbacks.

The invention aims to exploit the shadows projected on the skin because of the reliefs thereof in directional lighting. It appears that the quality of the image obtained is all the better that the directivity of the beam is homogeneous over the entire surface of the illuminated finger.

For this purpose, it is provided, according to the invention, a fingerprint capture device contactless biométri ^¬ having ridges and furrows, comprising a frame defining a capture zone, an image sensor mounted in the frame for a field covering the capture zone and a body of illumination of the cap ^¬ ture zone, the lighting member comprising at least one light source. The illumination device comprises at least one waveguide having an input surface extending in ^¬ re gard to the light source and an exit surface at least partially covered with a series of micropris ^¬ my arranged to directing a light wave emitted by the light source in a substantially uniform manner in intensity and towards the capture zone so as to bring a shadow on the footprint, bringing out the ridges and furrows.

Thus, the microprisms will orient in the same direction a maximum of light waves towards the capture zone by ensuring a uniform distribution of the light wave on the capture zone. Local variations in direction of the beam are thereby limi ^¬ tees. This provides a good quality lighting fa ^¬ vorise the formation of a shadow showing the ridges and furrows. It is therefore not necessary to use a high power light source or too far away from the light source of the capture area.

Other features and advantages of the invention will become apparent from reading the following description of non-confined particular embodiments of the invention ^¬ tive.

Reference will be made to the appended drawings, among which:

- Figure 1 is a schematic view of a dispo ^¬ sitive according to a first embodiment of the invention;

FIG. 2 is a schematic view of a device according to a second embodiment of the invention,

Figure 3 is a view similar to Figure 1 of a variant of the first embodiment, - Figure 4 is a schematic top view of another variant of the first embodiment ré¬ ^{¬ tion} .

Referring to the figures, the cap device ^¬ ture biometric fingerprint, according to the invention, is intended to capture an image of one or more fingers of an individual without the individual applies its hand on a surface. The image is intended to be processed to extract exploitable biometric characteristics to recognize these biometric characteristics and to identify the individual.

The device comprises a frame 1 defining a capture area 2. An image sensor 3 is mounted in the frame 1 to have a field 4 covering the capture area 2. The image sensor 3 is known in itself and has performances, in particular in terms of resolution, definition ^¬ tion, sensitivity, acquisition speed, depth of field, adapted to the acquisition of an image of sufficient quality to allow its processing as indicated above. The image sensor 3 can be associated with one or more lenses making it possible to magnify ^¬ ment or approaching the capture zone 2 with respect to the image sensor 3. Alternatively, the sensor 3 can be placed after a optical folding system.

The device comprises a member, generally designated 5, lighting the capture area 2. The lighting member 5 comprises light sources formed here of light emitting diodes 6 arranged in a row.

According to the invention, the lighting member 5 comprises a waveguide 7 having an entrance surface 7.1 extending opposite the light emitting diodes 6 and a 7.2 output surface at least partially re ^¬ covered with a series of microprisms 8 arranged to diri ^¬ ger substantially uniformly to cap- ture zone 2 a transmitted light wave by électrolu diodes ^¬ minescentes 6 (the light rays emerging from the series of microprisms 8 form an angle of 20 ° to 40 ° with respect to the general surface of the finger here considered substantially horizontal). The waveguide is made of a transparent material such as polymethylmethacrylate. The microprisms are known in themselves and are generally in the form of a film transpa rent ^¬, for example polyester, on one surface of which were made of very small prisms. The microprism film 8 is here fixed on the waveguide by gluing by means of an adhesive having an optical index close to that of polymethyl methacrylate. The microprism film is here represented in the form of a strong line (the reliefs of the microprism have been enlarged in FIG. 1 and have been omitted in FIG. 2).

The waveguide 7 comprises a plate having a first side facing the light-emitting diodes 6 to form the input surface 7.1 and two main surfaces, one of which forms the exit surface 7.2 and the other forms a rear surface 7.3 arranged to Refle ^¬ chir to 7.2 exit surface at least a portion of the light wave emitted by the diodes électroluminescen ^¬ your 6.

The input surface 7.1 is disposed at a predetermined distance from the light emitting diodes and the light emitting diodes 6 are selected so that the light-emitting diodes 6 have an emission cone corresponding to the thickness of the plate so that the entire light beam of the light-emitting diodes substantially between the plate by the entrance surface 7.1. The plate thus has a lar ^¬ geur slightly greater than the length of the row of light emitting diodes 6 and a thickness slightly greater than the width of the row of LEDs. Alternatively, the light emitting diodes 6 are each received in a bore in the pla ^¬ that in the lengthwise direction thereof. As a further variant, a lens is placed between the input surface 7.1 and the light-emitting diodes 6 to ensure a homogeneous light intensity distribution at the output of the microprisms 8 between the input surface 7.1 and the side of the plate opposite the entrance area 7.1.

The rear surface 7.3 is arranged to reflect toward the exit surface 7.2 prove- the light beam nant emitting diodes 6. The ar ^¬ Rière surface is for instance covered with a coating reflects ^¬ chissant such as paint or has one state on ^¬ face adapted for this purpose.

In the first embodiment shown in FIG. 1, the plate extends parallel to an ^optical axis of the image sensor 3. The plate has a second side opposite to the input surface 7.1 extending in the vicinity immediate capture area 2.

The series of microprisms 8 is here arranged to bring out the luminous flux with a light most favorable to the acquisition of the furrows (usually desig ^¬ nated by the word "ridges") of the skin. This angle will be chosen, preferably, between 20 and 40 ^¬ grés relative to the surface of the finger.

In the second embodiment shown in FIG. 2, the plate extends perpendicularly to the optical axis of the image sensor 3, between the ^cap¬ ture zone 2 and the image sensor 3.

The microprism 8, represented by a strong line, is here arranged to bring out the luminous flux at a An angle between 60 ° and 80 ° with respect to the direction of emission of the luminous flux by the light-emitting diodes 6. The microprism 8 further comprises at least one opening facing the image sensor 3 to enable the sensor image 3 to capture a clear image of the capture area 2 without the microprism 8 appears on the image. The microprism 8 is pierced by a plura lity of openings ^¬ such as microprism 8 has the appearance of a mesh facing the image sensor 3.

Of course, the invention is not limited to the embodiments described but encompasses any variant within the scope of the invention as defined by the claims.

In particular, other light sources are usable.

In addition, the micro prism and little wind ^¬ waveguide be positioned differently in the frame. Prior ^¬ ference however, they will be positioned such my ^¬ niere that the light beam output from the micro prism is oriented at an angle between 20 ° and 40 ° with rap ^¬ port to the major part of the finger surface. Mid ^¬ croprismes may have different angles in func ^¬ tion of their position relative to the light source so that the direction of outgoing light rays is substantially the same over the entire exit surface of the series of microprisms.

The device may comprise a guide against the ^¬ which the hand or finger can be applied, this guide s' not extending into the capture zone.

An embodiment may include several light guides. They will be activated simultaneously or in sequence or alternately.

In Figure 3 is shown a first will ^¬ smiling of the first embodiment in which two waveguides 7 are arranged vertical face to face to illuminate in front of and behind the area to capture.

In Figure 4 is shown a second will ^¬ smiling of the first embodiment comprising three waveguides 7 vertical, one arranged as in the pre ^¬ Mier embodiment and two are mounted face to face opposite sides of the finger .

Claims

A non-contact biometric fingerprint capture device comprising ridges and furrows, comprising a frame (1) defining a capture area (2), an image sensor (3) mounted in the frame to have a field ( 4) covering the capture area and a lighting member (5) of the capture area, the lighting member having at least one light source (6), characterized in that the lighting member comprises at least one light source (6), at least one waveguide (7) having an input surface (7.1) extending opposite the light source and an output surface (7.2) at least partially covered by a series of microprisms arranged to substantially uniform in angle and intensity towards the capture area a light wave emitted by the light source so as to carry on the footprint a shadow highlighting the ridges and furrows.

2. Device according to claim 1, wherein the waveguide (7) comprises a plate having a first side facing the light source to form the input surface (7.1) and two main surfaces of which one form the exit surface (7.2) and the other (7.3) are arranged to reflect towards the exit surface at least a part of the light wave emitted by the light source (6).

3. Device according to claim 2, wherein the plate extends parallel to an optical axis of the image sensor (3).

4. Device according to claim 3, wherein the plate has a second side opposite to the input surface (7.1) extending in the immediate vicinity of the capture zone (2).

5. Device according to claim 3, in the- a lens is placed between the input surface (7.1) and the light source (6) for a more efficient injection of the light flux into the waveguide to ensure a better controlled light rejection and distributed at the output of the series of light. microprisms (8).

6. Device according to claim 2, wherein the light source (6) is a light emitting diode positioned to have an emission cone cor ^¬ corresponding to the thickness of the plate.

The device of claim 1, wherein the series of microprisms (8) extends discontinuously on a surface of the waveguide (7).

8. Device according to claim 1, compor ^¬ as several waveguides (7) used simultaneously or alternately.

9. Device according to claims 2 or 7, wherein the plate extends perpendicularly to an optical axis of the image sensor (3).