EP3474242B1

EP3474242B1 - Ultraviolet fluorescent color detection device and ultraviolet fluorescent color detection method

Info

Publication number: EP3474242B1
Application number: EP17754594.4A
Authority: EP
Inventors: Tsutomu Nanao
Original assignee: Vienex Corp
Current assignee: Vienex Corp
Priority date: 2017-03-23
Filing date: 2017-03-23
Publication date: 2020-11-04
Anticipated expiration: 2037-03-23
Also published as: WO2018173210A1; CN109155091A; KR101825339B1; EP3474242A1; CN109155091B; EP3474242A4; JP6235765B1; JPWO2018173210A1

Description

TECHNICAL FIELD

The present invention relates to an optical line sensor unit and more particularly, to an optical line sensor unit for discriminating securities or banknotes. Furthermore, the present invention relates to a UV ray fluorescence color detection device for accurately detecting a fluorescence color emitted from a phosphor contained in the securities or banknote during UV ray irradiation, and a method for detecting a UV ray fluorescence color.

BACKGROUND ART

Due to remarkable improvement in printing technique and copying technique, forgery of the banknote or securities has become more sophisticated, and it is very important to accurately determine a forged paper sheet and eliminate it to maintain social order in a country. Especially, a device for dealing with the banknote such as an ATM or paper money processor strongly requires a discrimination system capable of discriminating authenticity at high speed with high performance.
As a method for discriminating the banknote or securities (hereinafter, referred to as "medium"), a close contact optical line sensor unit using an equal magnification optical system such as SELFOC lens array (registered trademark: manufactured by Nippon Sheet Glass Company, Limited) has been widely used.
In the optical line sensor unit, a high precision discrimination method is required because the forgery of the medium has become more sophisticated, and the medium is discriminated from images taken with a light source which emits a visible light or infrared light from three directions of front, back, and transmission of the target medium, with respect to each of a plurality of wavelengths.
Therefore, a light source portion of the optical line sensor unit includes a plurality of LEDs so that lights having the respective wavelengths can be emitted, and the light is emitted while the LEDs are sequentially switched with respect to each observation line. Thus, image data is obtained by combining optical output signals in the respective observation lines, in the light receiving portion, and the medium is discriminated based on the image data.
Furthermore, due to an improvement in performance of a UV LED, a new method is employed in which the UV LED is mounted in a reflection light source to discriminate a fluorescence image of the medium and printing ink on a surface of the medium, formed by UV excitation.
The present invention relates to a sensor for discriminating a fluorescence emitted from the medium by a UV ray.
According to a conventional method for discriminating the medium with the UV ray, the UV light is emitted, and then an optical sensor receives a visible light or infrared light in a reflected image of a fluorescent medium surface while the UV ray is blocked, and an output of the optical sensor is determined. However, in this discrimination method, since the output is detected in a monotone, the output is largely different in image from a case where the fluorescence is actually discriminated by the naked eye, and due to inhibition by a fluorescence of a medium base material, the problem is that the target fluorescence cannot be obtained with enough contrast.
In order to solve the above problem, it has been proposed by the inventors of the present invention that at least one visible light color filter film is provided on a pixel of a line sensor, and the fluorescence color of the medium is directly detected. Thus, when the medium is irradiated with the UV light, the fluorescence color of the medium can be directly detected, so that discrimination precision is expected to be further improved.
However, it has been found that there are various problems in the above method in detecting reading precision of the fluorescence color from the medium during the UV ray irradiation at the same color balance as the discrimination by naked eye.
That is, in the conventional discrimination sensor, monochromatic visible LEDs such as red, green, and blue LEDs are sequentially turned on, and their output images of the medium can be synthesized into an appropriate color output image after their contrast balance have been corrected, respectively but when the color filter is provided with respect to each sensor pixel to detect the fluorescence color, an output balance with respect to each color filter cannot be corrected, so that the problem is that the desired contrast of the fluorescence color emitted during the UV ray irradiation cannot be accurately detected.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: Unexamined Japanese Patent Publication No. 2006-39996
Patent Document 2: Unexamined Japanese Patent Publication No. 2001-229722
Patent Document 3: US 2012/0318961 proposes an image sensor module that includes: a sensor IC having light receivers arranged in a main scanning direction; a lens unit configured to form an image on the sensor IC with light transferred from a read target; a first light source unit having a first output surface extending along the main scanning direction and outputting a first linear light extending along the main scanning direction from the first output surface toward the read target, the first output surface being placed at a position spaced apart from the lens unit in a sub-scanning direction; and a second light source unit having a second output surface extending along the main scanning direction and outputting a second linear light extending along the main scanning direction from the second output surface toward the read target, the second output surface being placed between the lens unit and the first output surface in the sub-scanning direction.
Patent Document 4: US 2013/0038913 proposes an image sensor unit that includes a reflection reading light guide that emits light from a reflection reading light source toward the bill, a transmission reading light guide that emits light from a transmission reading light source toward the bill, an imaging element that focuses light from the bill, and a light receiving element that receives light that is collected by the imaging element. The transmission reading light source and the transmission reading light guide are disposed on the opposite side of a conveyance path through which the bill can pass, for the reflection reading light source and the reflection reading light guide, and a light blocking member that blocks a part of the light from the reflection reading light guide is disposed between the reflection reading light guide and the transmission reading light guide..

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

The present invention provides a new method achieved after every effort has been made to solve the above problem.
When an optical line sensor unit characterized by having a color filter on a pixel of a sensor is used, a fluorescence color emitted from a medium during UV light irradiation can be detected, but the following problems arise in a case where an accurate color tone is to be obtained.
For example, like the conventional technique, in the case where the fluorescence color of the medium is detected by sequentially turning on the visible light sources such as red, green, and blue LEDs and also by turning on the UV LED, a white balance is corrected by adjusting output signals of the visible LEDs having the respective wavelengths, so that a realistic visible light image can be obtained, but since the white balance of the color filter cannot be detected, so that accurate information about the color tone of the fluorescence emitted during the UV light irradiation cannot be obtained unless another method is employed. Furthermore, it has been considered that a contrast balance of the color filter is corrected by simultaneously turning on the red, green, and blue LEDs as the white color source, but it has been found that it is difficult to correct a temperature-output characteristic and temporal change of each element and to correct a transmission characteristic of the color filter used for a narrow wavelength range of the LED light emission, with respect to each of the red, green, and blue LEDs.
The present invention was made in view of the above circumstances, and it is an object to provide a UV ray fluorescence color detection device capable of simply and accurately detecting reading precision of a visible fluorescence color of a medium emitted during the UV light irradiation, and a method for detecting the UV ray fluorescence color.

MEANS FOR SOLVING THE PROBLEMS

The inventors of the present invention have made various studies and found that with a white light source which emits an output covering an entire visible light range, a white reference output is detected with respect to each color filter, and this is used to correct sensitivity with respect to each color filter, so that a fluorescence color of a medium emitted during the UV light irradiation can be detected with a proper color balance.
Furthermore, it has been found that in the sensor, instead of using LEDs each having a visible-light single wavelength of R, B, or G, as the visible light source (each of the RGB LEDs varies in temperature characteristic and temporal change, and it is difficult to stabilize the color balance), by using a specific white LED in which the LED is covered with a phosphor, a white medium is detected by this light source as a reference, and an output is corrected with respect to each color filter, so that reading precision of the visible fluorescence color of the medium emitted during the UV light irradiation can be simply and accurately detected.
A UV ray fluorescence color detection device according to the present invention is set out in claim 1.
In this configuration, when the white light is emitted from the white LED light source by emitting the fluorescence from the phosphor, and the white light illuminates the white reference object, the light emitted from the white reference object enters into the plurality of light receiving elements through the visible light color filter. The output signal obtained from each of the light receiving elements is used as a reference pixel output value, so that the reading precision of the visible fluorescence color of the medium emitted during the UV light irradiation can be simply and accurately detected.
More specifically, when the medium such as securities or banknote is discriminated, the UV light is emitted from the UV light source to the medium, and the fluorescence is emitted from the medium and enters into the plurality of light receiving elements through the visible color filter, so that the output signal can be obtained from each of the light receiving elements. When the output signal is corrected with the reference pixel output value, the fluorescence color emitted during the UV light irradiation can be appropriately balanced. Thus, a high-quality image achieving a desired color balance can be obtained.
The UV light source emits the UV light having the wavelength of 400 nm or less and more preferably in the wavelength range of 300 nm to 400 nm. The UV light source is not limited in composition and structure, but it is preferable that its light emission efficiency and output are high, and there is no visible light complementary wavelength which becomes a disincentive factor. For example, a semiconductor-based UV LED mainly composed of gallium nitride is preferably used as the UV light source.
It is preferable that a time taken for an output of the white LED light source to rise from 10% to 90%, and a time taken for the output to fall from 90% to 10% are each 2 µsec or less. In general, the LED for illumination normally uses perovskite-based phosphor, and as illustrated in FIG. 9 as a comparison example, the phosphor is low in response speed, and each of a rising time Tr2 and a falling time Tf2 is 1 msec or more in some cases, so that it is necessary to previously evaluate the response speed.
In this configuration, when the white LED light source having the high responsiveness is used, higher image quality having a desired color balance can be obtained during the UV light irradiation. That is, the medium needs to be read at high speed to be determined in short time, and since the many wavelengths are switched in short time, the white LED light source having high responsiveness is preferably used.
For example, the reflection and transmission on a front surface and a back surface of the medium need to be read in a reading time of 100 µsec or less per wavelength and more preferably 50 µsec or less per wavelength, in multiple wavelength. Therefore, it is preferable that a time taken for an output of the white LED light source to rise from 10% to 90%, and a time taken for the output to fall from 90% to 10% are each 2 µsec or less, and more preferably 0.5 µsec or less.
For example, the violet or blue LED element (not illustrated) is used, and the element is covered with the phosphor. When the phosphor is composed of yellow-emitting YAG: Ce (cerium-doped yttrium oxide-aluminum-garnet sintered compact), the white LED light source can be high in response speed.
The plurality of light receiving elements may be linearly arranged in a main scanning direction. In this configuration, the visible fluorescence color of the medium emitted from the one observation line during the UV light irradiation can be detected at high speed.
A method for detecting a UV ray fluorescence color according to the present invention is set out in claim 4.

EFFECT OF THE INVENTION

According to the present invention, the output signal obtained from each of the light receiving elements when the white light is emitted from the white LED light source by emitting the fluorescence from the phosphor, and the white reference object is irradiated with the white light is used as the reference pixel output value, so that the reading precision of the visible fluorescence color of the medium at the time of the UV light irradiation can be simply and accurately detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a configuration of an optical line sensor unit in an embodiment of the present invention.
FIG. 2 is a cross-sectional view schematically illustrating an additional configuration of an optical line sensor unit.
FIG. 3 is a perspective view of a line light source.
FIG. 4 is a perspective exploded view illustrating component members of the line light source.
FIG. 5 is a side view of the line light source.
FIG. 6 is a schematic view illustrating an element arrangement in a light receiving portion.
FIGS. 7(a) to 7(c) are views illustrating arrangement examples of light receiving elements and color filters in the light receiving portion.
FIG. 8 is a schematic view for describing a manner in which a correction is made by a correction processor.
FIG. 9 is a view illustrating an example and a comparison example of response speed of a white LED light source.

MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic cross-sectional view illustrating a configuration of an optical line sensor unit in an embodiment of the present invention.
The optical line sensor unit includes a housing 16, a line light source 10 for lighting a paper sheet, a lens array 11 for guiding a light emitted from the line light source 10 to a focal plane 20 and reflected by the paper sheet, and a light receiving portion 12 mounted on a substrate 13 for receiving a transmitted light after being guided by the lens array 11. The paper sheet is transferred in a direction x (sub scanning direction) along the focal plane 20.
The housing 16, the line light source 10, the light receiving portion 12, and the lens array 11 extend in a y direction (main scanning direction), that is, a direction perpendicular to a sheet surface in FIG. 1, and FIG. 1 illustrates their cross-sectional surfaces.
The line light source 10 is a unit for emitting a light toward the paper sheet on the focal plane 20. The kind of the emitted light includes a visible light, a white light, and a UV light, and also may include an infrared light.
The UV light has a wavelength peak of 300 nm to 400 nm, and the infrared light may have a wavelength peak of 1500 nm.
At least the UV light is emitted so as not to temporally overlap with another light (that is, so as to temporally shift from another light). The infrared light may be emitted so as to temporally overlap or so as not to temporally overlap with the visible light in some cases.
The light emitted from the line light source 10 passes through a protection glass 14 and is collected to the focal plane 20. The protection glass 14 is not necessarily required and may be omitted, but it is desirably provided to protect the line light source 10 and the lens array 11 from being covered with dust (such as paper powder generated when the paper sheet is transferred) or being damaged while in use (at the time of being used).
The material of the protection glass 14 is required to be able to transmit the light emitted from the line light source 10 and may be a transparent resin such as acrylic resin or cycloolefin-based resin. However, in this embodiment of the present invention, the material which transmits the UV light especially, such as white sheet glass or borosilicate glass is preferably used.
A substrate 5 is disposed to face a bottom surface of the line light source 10 to fix a second light source portion 3 and a first light source portion 4 disposed at both ends of the line light source 10 (refer to FIGS. 4 and 5). The substrate 5 is a thin insulating plate made of phenol or epoxy glass, and its back surface has a wiring pattern composed of copper foil. Terminals of the second light source portion 3 and the first light source portion 4 are inserted into holes formed in various places of the substrate 5 and bonded to the wiring pattern with solder on the back surface of the substrate, so that the second light source portion 3 and the first light source portion 4 can be mounted on and fixed to the substrate 5, and a power is supplied from a predetermined drive power supply (not illustrated) to the second light source portion 3 and the first light source portion 4 through the wiring pattern on the substrate back surface to drive and control the light emission.
The lens array 11 is an optical element to form an image of the light reflected by the paper sheet, in the light receiving portion 12, and it may be a rod lens array such as SELFOC lens array (registered trademark: manufactured by Nippon Sheet Glass Company, Limited). In this embodiment of the present invention, the magnification of the lens array 11 is set to 1 (upright).
A UV light blocking filter film 15 is preferably provided in an arbitrary position between the focal plane 20 and the light receiving portion 12, as a "third optical filter" which reflects or absorbs a UV light to prevent the UV light from entering into the light receiving portion 12. According to this embodiment of the present invention, the UV light blocking filter film 15 is mounted on a surface of the lens array 11 to function to block the UV light. In this specification, the term "to block the light" means that the light is reflected or absorbed so as not to pass through.
The UV light blocking filter film 15 is not limited in particular and may be made of any material and have any structure as long as it can prevent the UV light from entering into the light receiving portion 12. For example, as a preferable filter film, a UV light absorbing film may be provided by mixing or coating an organic UV light absorbing agent in or on a transparent film, or an interference filter (bandpass filter) may be provided by forming multi-layer thin films by vapor deposition with metal oxide having different transmittances or refractive indexes, such as titanium oxide or silicon oxide, or dielectric substance, on a glass surface.
Furthermore, the UV light blocking filter film 15 is mounted on the output surface of the lens array 11 in the above, but it may be mounted on an input surface or a middle portion of the lens array 11, or may be directly vapor-deposited or applied to an inner surface of the protection glass 14. The point is that the UV light reflected by the paper sheet is to be prevented from entering into the light receiving portion 12.
The light receiving portion 12 is mounted on the substrate 13 and includes a light receiving element which receives the reflected light and reads an image as an electric output by performing photoelectric conversion. The material and the structure of the light receiving element are not limited in particular, and the light receiving element may be provided by disposing a photodiode or phototransistor made of amorphous silicon, crystalline silicon, CdS, or CdSe. Furthermore, it may be a CCD (charge coupled device) linear image sensor. In addition, the light receiving portion 12 may be a multi-chip type linear image sensor provided by arranging a plurality of ICs (integrated circuits) each integrally having a photodiode, a phototransistor, a driver circuit, and an amplifier circuit. Furthermore, as necessary, an electric circuit such as driver circuit or amplifier circuit, or a connector for externally extracting a signal may be mounted on the substrate 13. In addition, when an A/D converter, various kinds of correction circuits, an image processing circuit, a line memory, and an I/O control circuit are also mounted on the substrate 13, the signal can be externally extracted as a digital signal.
In addition, the above-described optical line sensor unit is the reflective type optical line sensor unit which receives the light emitted from the line light source 10 toward the paper sheet and reflected by the paper sheet, but as illustrated in FIG. 2, it may be a transmissive type optical line sensor unit which receives a light emitted from the line light source 10 toward the paper sheet and passed through the paper sheet, in which the line light source 10 is set opposite to the light receiving portion 12 so as to be the focal plane 20 as a reference. In this case, other than the structure in which the line light source 10 is positioned under the focal plane 20, the structure of the line light source 10 itself is the same as that described above in FIG. 1. Furthermore, the reflective type optical line sensor unit and the transmissive type optical line sensor unit may be both provided.

FIG. 3 is a perspective view schematically illustrating an appearance of the line light source 10 in the optical line sensor unit illustrated in FIG. 1. FIG. 4 is an exploded perspective view of component members of the line light source 10, and FIG. 5 is a side view of the line light source 10. In addition, a cover member 2 is not illustrated in FIG. 5.
The line light source 10 includes a transparent light guide 1 extending along a longitudinal direction L, the second light source portion 3 provided in the vicinity of one end surface in the longitudinal direction L, the first light source portion 4 provided in the vicinity of the other end surface in the longitudinal direction L, the cover member 2 for holding side surfaces (bottom side surface 1a and right and left side surfaces 1b and 1c) of the light guide 1, and a light diffusion pattern P which is formed on a light diffusion pattern formation surface 1g obliquely provided between the bottom side surface 1a and the right and left side surface 1b so that the lights emitted from the second light source portion 3 and the first light source portion 4 to end surfaces 1e and If of the light guide 1, respectively traveling in the light guide 1 are diffused and refracted and emitted from a light exit surface 1d of the light guide 1. In addition, preferably, the line light source 10 further includes a second optical filter 6 and a first optical filter 7 formed at the end surfaces 1e and 1f of the light guide 1, respectively.
The light guide 1 may be made of resin having high transmittance of light such as acrylic resin, or optical glass, but in the embodiment of the present invention, since the first light source portion 4 which emits the UV light is used, the light guide 1 is preferably made of fluorine-based resin or cycloolefin-based resin which is relatively small in attenuation due to the UV light (refer to Patent Document 2).
The light guide 1 is in the form of a thin and long cylinder, and its cross-sectional surface perpendicular to the longitudinal direction L has substantially the same shape and the same dimension at any cut point in the longitudinal direction L. Furthermore, a proportion of the light guide 1, that is, a ratio of a length of the light guide 1 in the longitudinal direction L, to a height H of the cross-sectional surface perpendicular to the longitudinal direction L is more than 10 and preferably more than 30. That is, when the length of the light guide 1 is 200 mm, the height H of the cross-sectional surface perpendicular to the longitudinal direction L is about 5 mm, for example.
The side surfaces of the light guide 1 are composed of five side surfaces, that is, the light diffusion pattern formation surface 1g (corresponding to the obliquely cut surface of the light guide 1 in FIG. 4), the bottom side surface 1a, the right and left side surfaces 1b and 1c, and the light exit surface 1d (corresponding to the upper surface of the light guide 1 in FIG. 4). The bottom side surface 1a and the right and left side surfaces 1b and 1c have a planar shape, while the light exit surface 1d has an outwardly convex and smoothly curved shape in order to achieve a light converging effect of the lens. However, the light exit surface 1d is not necessarily required to have the convex curved shape, and it may have a planar shape. In this case, the condenser lens for the light emitted from the light guide 1 is to be disposed so as to face the light exit surface 1d.
The light diffusion pattern P on the light diffusion pattern formation surface 1g linearly extends along the longitudinal direction L of the light guide 1 with widths equally spaced. A dimension of the light diffusion pattern P along the longitudinal direction L is set so as to be longer than a length of a reading portion of the image sensor (that is, a width of a reading region of the light receiving portion 12).
The light diffusion pattern P is composed of a plurality of V-shaped grooves in the light diffusion pattern formation surface 1g of the light guide 1. Each of the plurality of V-shaped grooves is formed so as to extend in a direction perpendicular to the longitudinal direction L of the light guide 1, and has the same length. The plurality of V-shaped groove may have a shape of an isosceles triangle in a cross-section, for example.
By the light diffusion pattern P, the light introduced from the end surfaces 1e and 1f of the light guide 1 and traveling in the light guide 1 in the longitudinal direction L can be refracted and diffused, and then emitted from the light exit surface 1d along the longitudinal direction L with uniform brightness. Thus, the light can almost uniformly illuminate the paper sheet along the longitudinal direction L of the light guide 1 as a whole, so that brightness unevenness is not caused.
Furthermore, the V-shape of the groove in the light diffusion pattern P is one example, and the shape may be changed to a U-shape, for example instead of the V-shape as long as the brightness unevenness is kept unnoticeable. The width of the light diffusion pattern P is not necessarily equally spaced, and the width may vary along the longitudinal direction L of the light guide 1. A depth of the groove and an opening width of the groove may be also appropriately changed.
The cover member 2 has a thin and long shape along the longitudinal direction L of the light guide 1 and has a bottom surface 2a facing the light diffusion pattern formation surface 1g of the light guide 1, a right side surface 2b facing the right side surface 1b of the light guide 1, and a left side surface 2c facing the left side surface 1c of the light guide 1 so as to cover the bottom side surface 1a and the right and left side surfaces 1b and 1c of the light guide 1. Each of these three side surfaces is a planar surface, and three inner surfaces of them make an almost U-shaped recessed portion in cross-sectional view, so that the light guide 1 can be inserted in this concave portion. When the light guide 1 is inserted, the bottom surface 2a of the cover member 2 adheres to the bottom side surface 1a of the light guide 1, the right side surface 2b of the cover member 2 adheres to the right side surface 1b of the light guide 1, and the left side surface 2c adheres to the left side surface 1c of the light guide 1. Therefore, the light guide 1 can be protected by the cover member 2.
In addition, the cover member 2 is not limited to a transparent cover, and it may be translucent or opaque cover. For example, the cover member 2 may be a member molded with highly reflective white resin or may be a resin molded member coated with white resin in order to reflect the light leaked from the side surface other than the light exit surface of the light guide 1, back into the light guide 1. Alternatively, the cover member 2 may be made of metal such as stainless steel or aluminum.
The second light source portion 3 includes a light source 3a for emitting a visible light or a light in a wavelength range from visible to infrared lights, and a light source 3b for emitting a white light. The light source 3a has a plurality of LEDs (light emitting diodes) which emit near-infrared, red, green, and blue lights having respective wavelengths. The light source 3b is a white light LED light source for emitting the white light by emitting a fluorescence from a phosphor, or the white LED light source may emit the white light by emitting the fluorescence from the phosphor with a blue or violet LED, and the white LED light source may emit the white light by emitting the fluorescence from the phosphor with a UV-region LED. In the white LED light source, the phosphor is applied to the LED element or mixed in a sealing agent, and the fluorescence from the phosphor is combined with the light from the LED so that its output can cover the entire visible light range.
The light source 3b serving as the white light LED light source is preferably high in responsiveness, and as described in FIG.9 as an example, a response time (rising time Tr1) taken for an output (relative light emission intensity) to rise from 10% to 90%, and a response time (falling time Tf1) taken for the output to fall from 90% to 10% are 2 µsec or less, and more preferably 0.5 µsec or less. The responsiveness of the white light LED light source which emits the white light by emitting the fluorescence from the phosphor is deteriorated because the phosphor is used, so that it is preferable to use a specific phosphor. For example, the light source 3b has the structure in which the violet or blue LED element (not illustrated) is used and covered with the phosphor. When the phosphor is composed of yellow light emitting YAG: Ce (cerium-doped yttrium oxide-aluminum-garnet sintered compact), the white LED light source can be high in response speed.
The first light source portion 4 is a UV light source which emits a UV light to the light guide 1, and it may be a UV LED light source which emits a UV light having a wavelength of 300 nm to 400 nm. Preferably, it may be a UV light emitting diode which emits a UV light having a peak light emission wavelength in the range of 330 nm to 380 nm.
Each of the second light source portion 3 and the first light source portion 4 has a terminal 31 to be used when it is mounted on the substrate 5, and after the terminal 31 is inserted in the substrate 5 and bonded with solder, each of them is electrically connected to a drive power supply (not illustrated). The drive power supply has a circuit configuration which can drive the second light source portion 3 and the first light source portion 4 at the same time or at a temporally shifted time to emit light by selecting an electrode terminal for applying a voltage to the second light source portion 3 and an electrode terminal for applying a voltage to the first light source portion 4. Furthermore, among the plurality of LEDs incorporated in the second light source portion 3, any LEDs can be selected to emit lights at the same time or a temporally shifted time.
Thus, with the above-described compact configuration, the visible light or the light in the wavelength range from the visible light to the infrared light can enter from the second light source portion 3 (light source 3a) into the light guide 1 through the end surface 1e, and the UV light can enter from the first light source portion 4 into the light guide 1 through the end surface 1f. Thus, the light emitted from the first light source portion 4 or the light emitted from the second light source portion 3 can exit from the light exit surface 1d of the light guide 1. Furthermore, the white light can enter from the light source 3b into the light guide 1 through the end surface 1e where the light source 3a is disposed and exits from the light exit surface 1d of the light guide 1.
Preferably, the second optical filter 6 is provided at the end surface 1e of the light guide 1 where the second light source portion 3 is disposed, to transmit the infrared light and the visible light having a wavelength of 420 nm or more and to block the UV light having a wavelength less than 400 nm by reflecting or absorbing the UV light. In addition, the first optical filter 7 is disposed at the end surface 1f to which the first light source portion 4 of the light guide 1 is disposed, to transmit the UV light having the wavelength less than 400 nm and to block the infrared light and the visible light having the wavelength of 420 nm or more by reflecting or absorbing those lights.
The second optical filter 6 and the first optical filter 7 are not limited in particular, and any material and any structure can be used for them as long as they can block the intended wavelength range. For example, in the case of a reflective optical filter, it is preferably an interference filter (bandpass filter) which is obtained by forming multi-layer thin films by vapor deposition with metal oxide having different transmittances or refractive indexes, or dielectric substance, on a glass surface.
As for the reflective interference filter, multi-layer films having adjusted transmittances, refractive indexes, and film thicknesses are formed by vapor deposition with silicon oxide and tantalum pentoxide, for example to obtain desired bandpass filter characteristics. In addition, as a matter of course, a bandpass filter which has been conventionally produced for usual optical industries may be used as long as required performance is satisfied.
In the case where the interference filter is used as the second optical filter 6 and the first optical filter 7, when the intended transmission range cannot be adjusted only with the interference filter, a thin film formed of metal, or its oxide, nitride, or fluoride is to be further applied to ensure the desired wavelength characteristics.
When the second optical filter 6 is an optical filter which absorbs the UV light, the UV light absorbing film may be formed by mixing or coating an organic UV light absorbing agent in or on a transparent film. Furthermore, it may be the interference filter in which multi-layer films having adjusted transmittances, refractive indexes, and film thicknesses are formed by vapor deposition with silicon oxide and titanium oxide, for example to obtain desired wavelength characteristics which block the UV light by both functions of reflection and absorption.
Furthermore, when the first optical filter 7 is an optical filter which absorbs the visible light and the infrared light, a substance which transmits the UV light and blocks the visible light and the infrared light may be added to the film.
Furthermore, the second optical filter 6 and the first optical filter 7 can be disposed for the light guide 1 by any method, and the end surfaces 1e and 1f of the light guide 1 may be covered with them by coating or vapor deposition. Alternatively, the film-like or plate-like second optical filter 6 and first optical filter 7 may be prepared and set so as to adhere to the end surfaces 1e and 1f of the light guide 1, or to be apart from the end surfaces 1e and 1f by a certain distance, respectively.
Furthermore, the second optical filter 6 and the first optical filter 7 may be disposed at the second light source portion 3 and the first light source portion 4, respectively instead of being disposed at the end surfaces 1e and 1f of the light guide 1. In this case, the light source portions 3 and 4 may be covered with the optical filters 6 and 7 by coating or vapor deposition, respectively, or the film-like or plate-like optical filters 6 and 7 may be prepared and disposed so as to adhere to the light source portions 3 and 4, respectively. Still alternatively, the second optical filter 6 may be configured such that a substance which transmits the visible light or the light in the wavelength range from the visible light to the infrared light and blocks the UV light is added to a sealing agent of the second light source portion 3. Similarly, the first optical filter 7 may be configured such that a substance which transmits the UV light and blocks the visible light or the light in the wavelength range from the visible light to the infrared light is added to a sealing agent of the first light source portion 4.
When the first optical filter 7 is the optical filter which transmits the UV light and reflects or absorbs the infrared light and the visible light, the following merits are provided. First, assumption is made that the first light source portion 4 consists of a mounting base made of material such as aluminum oxide ceramics sintered body which emits fluorescence having a wavelength of around 690 nm when the UV light illuminates it. When the UV light is emitted from the first light source portion 4 and illuminates the mounting base of the first light source portion 4, the fluorescence having the wavelength of around 690 nm is secondarily emitted and this secondarily emitted fluorescence needs to be prevented from entering into the light guide 1. Thus, since the first optical filter 7 is designed to reflect or absorb the infrared light and the visible light, the secondarily emitted fluorescence is prevented from entering into the light guide 1, so that unnecessary fluorescence can be prevented from being emitted from the light exit surface 1d of the light guide 1. As a result, contrast of UV fluorescence of the paper sheet can be improved. Furthermore, other than the aluminum oxide ceramics sintered body which emits fluorescence from the UV light, in a case where fluorescence is emitted from a sealing resin, secondary emission can be similarly prevented.
When the second optical filter 6 is the optical filter which transmits the infrared light and the visible light and reflects or absorbs the UV light, the following merits are provided. First, assumption is made that the second light source portion 3 consists of a mounting base made of material such as aluminum oxide ceramics sintered body which emits fluorescence having a wavelength of around 690 nm when the UV light illuminates it. When the UV light emitted from the first light source portion 4 passes through the end surface 1e of the light guide 1 and illuminates the second light source portion 3, the fluorescence in the vicinity of 690 nm is secondarily emitted from the second light source portion 3 and this secondarily emitted fluorescence needs to be prevented from entering into the light guide 1. Thus, when the second optical filter 6 is designed to reflect or absorb the UV light and prevent the UV light from going out of the end surface 1e of the light guide 1, the UV light never illuminates the second light source portion 3. Therefore, unnecessary fluorescence can be prevented from being emitted from the light exit surface 1d of the light guide 1. As a result, contrast of UV fluorescence of the paper sheet is improved.
According to the embodiment of the present invention, the second optical filter 6 preferably transmits the infrared light and the visible light and reflects the UV light, and the following merits are provided. That is, since the UV light emitted from the first light source portion 4 into the light guide 1 is reflected by the second optical filter 6 and returned to the light guide 1, an amount of the UV light is increased, so that an amount of the UV light emitted from the light exit surface 1d of the light guide 1 can be increased. In this case, the second optical filter 6 transmits the infrared light and the visible light emitted from the second light source portion 3, so that the infrared light and the visible light from the second light source portion 3 are not prevented from entering into the light guide 1.
Furthermore, when the first optical filter 7 transmits the UV light and reflects the visible light and the infrared light, since the visible light and the infrared light emitted from the second light source portion 3 into the light guide 1 are reflected by the first optical filter 7 and returned to the light guide 1, an amount of the lights is increased, so that an amount of the visible light and infrared light emitted from the light exit surface 1d of the light guide 1 can be increased. In addition, since the first optical filter 7 transmits the UV light emitted from the first light source portion 4, the UV light can be emitted from the light exit surface 1d of the light guide 1.
The UV light emitted from the first light source portion 4 enters into the light guide 1 through the first optical filter 7 and is diffused and refracted by the light diffusion pattern formation surface 1g and then exits from the light exit surface 1d and illuminates the paper sheet (medium) on the focal plane 20. Thus, a fluorescence is emitted from the paper sheet and the emitted fluorescence color is detected by the light receiving portion 12, so that the paper sheet can be discriminated with the UV light.
The visible light or the light in the wavelength range from the visible light to the infrared emitted from the light source 3a of the second light source portion 3 enters into the light guide 1 through the second optical filter 6 and is diffused and refracted by the light diffusion pattern formation surface 1g, and then exits from the light exit surface 1d and illuminates the paper sheet (medium) on the focal plane 20. Thus, the paper sheet can be discriminated with the visible light or the infrared light.

FIG. 6 is a schematic view illustrating an element arrangement of the light receiving portion 12. The light receiving portion 12 has a sensor IC chip integrally including a plurality of light receiving elements (each composed of a photodiode or phototransistor) linearly arranged in the y direction, a signal processor 21, and a driver 22, and each light receiving element is covered with a color filter and mounted on the substrate. The driver 22 is a circuit portion for producing and supplying a bias current to drive the light receiving element, and the signal processor 21 is a circuit portion for reading and processing a light detection signal of the light receiving element. The kind of the light receiving element is not limited in particular, but a silicon PN diode or PIN diode is used.
While the paper sheet is moved in the x direction (sub scanning direction), the linearly arranged light receiving elements are exposed to light and an observation line having a predetermined width can be set on the paper sheet along the y direction (main scanning direction). An exposure time for reading line information of the paper sheet (that is, an optical reading time) can be optionally set depending on the intensity of the light source, sensor wavelength sensitivity, or the like. For example, moving speed of the paper sheet in the x direction is 1500 mm to 2000 mm/sec in an ATM or bill processing machine, so that when 0.5 msec to 1.0 msec is employed as the optical reading time, the width of the observation line in the x direction is 0.75 mm to 2 mm.
In this embodiment of the present invention, as illustrated in FIG. 6, one pixel (the pixel means a spatial unit for reading and processing image data) in the light receiving portion 12 is composed of the plurality of, such as four linearly arranged light receiving elements. In FIG. 6, among the four light receiving elements, the first light receiving element is covered with a red (R) color filter, the second light receiving element is covered with a green (G) color filter, and the third light receiving element is covered with a blue (B) color filter. Thus, the fourth light receiving element is covered with a transparent (W) filter or not covered with a color filter. In addition, the color filters (R, G, B) are normally not transparent to the UV light having the wavelength in the range of 300 nm to 400 nm, and transmit the infrared light having the wavelength of 800 nm or more.
Thus, in the light receiving portion 12, each pixel includes the visible light color filters (R, G, B), and the light enters into each of the light receiving elements through the color filter.
Furthermore, the one element is covered with the same color filter in FIG. 6, but two or more light receiving elements may be covered with the same color filter.
The transparent (W) filter is a "transparent" filter having no color. For example, it desirably has light transmittance equal to total light transmittance of all of the color filters. For example, when an envelope curve is made by connecting a light transmission band of the R filter, a light transmission band of the G filter, and a light transmission band of the B filter, the W filter desirably has the light transmittance similar to the envelope curve. The film material of the "transparent filter" is selected from transparent acrylic resin, cycloolefin-based resin, silicone resin, and fluorine-based resin in a case of an organic material, and selected from silicon nitride film and silicon oxide film in a case of an inorganic material.
The color filter material is transparent to the UV light having the wavelength in the range of 300 nm to 400 nm. The optical filter material also transmits the infrared light having the wavelength of 800 nm or more.
Furthermore, as for the organic material, transparent material containing a UV light absorbent to be used for liquid crystal is not preferably used because it is not transparent to the UV light.
Thus, the one pixel in the light receiving portion 12 has the plurality of light receiving elements and the color filters covering them, so that by simultaneously turning on the plurality of light emitting elements each of which can emit the light having the desired wavelength range, the color information of the paper sheet in the one observation line can be obtained at once without the need to switch the wavelength of the light source.
The light detection signal of the light receiving portion 12 having the above configuration is a signal obtained from the light detection signals of all the light receiving elements at the same time and sent to the signal processor 21. The signal processor 21 determines the color information of the paper sheet, based on signal intensity of the light receiving element which has passed through the R, G, and B color filters of the light receiving portion 12 and calculates a total light amount transmitted to the pixel, based on signal intensity which passed through the transparent (W) filter or not passed through the color filters. As a result, image data can be obtained based on the accurate light amount of each color signal with the total light amount used as a denominator (reference).
The signal from the signal processor 21 is sent to a control unit 100. For example, the control unit 100 includes a central processing unit (CPU) and when the CPU executes a program, the control unit 100 functions as a determination unit 101 and a correction processor 102.
The determination unit 101 determines authenticity, denomination, and defacement by comparing the image data of the paper sheet obtained by the light receiving elements, with master data. The correction processor 102 corrects the signal from the signal processor 21 and generates corrected image data. The determination unit 101 makes a determination based on the image data which has been corrected by the correction processor 102.
Here, the element arrangement of the light receiving portion 12 is not limited to that above arrangement. For example, the light receiving elements of the light receiving portion 12 are arranged in a row such as RGBWRGBW ··· as illustrated in FIG. 7(a), but instead of the above, they may be arranged in two or more columns. FIG. 7(b) illustrates a case where the light receiving elements are arranged 2 × 2 in each pixel, and the second light receiving element having the transparent (W) filter or having no color filter is arranged in a corner of one column (lower column, for example) of the two columns. FIG. 7(c) illustrates a case where the light receiving elements are arranged in four columns in each pixel, and the second light receiving element having the transparent (W) filter or having no color filter is arranged in one column (lowest column, for example) of the four columns. In any case, the light signal detected by the light receiving element having the transparent (W) filter or having no filter is recorded, and the signal intensity of the light receiving elements having the color filters (R, G, B) can be detected, in each pixel.
Furthermore, instead of the transparent (W) filter, the green (G) color filter may be provided and arranged like RGBGRGBG ···. Thus, the kind and the number of the color filters in each pixel are not limited and each pixel only needs to have at least one visible color filter.

FIG. 8 is a schematic view to describe a manner in which the correction is made by the correction processor 102. In this embodiment of the present invention, the white light emitted from the light source 3b of the second light source portion 3 is used to correct the signal, so that a proper color balance can be obtained in the fluorescence color emitted during the UV light irradiation.
More specifically, a white reference object 200 is transferred along the focal plane 20 in the x direction. The white reference object 200 is a white sheet having high reflectivity, for example. While the white reference object 200 is transferred, the white light is emitted from the light source 3b of the second light source portion 3, and the white light exits from the light exit surface 1d of the light guide 1 and illuminates the white reference object 200. A light is reflected from the white reference object 200 illuminated with the white light, reaches the light receiving portion 12 through the lens array 11, and is received by the plurality of light receiving elements through the respective color filters in the light receiving portion 12. Thus, the signal intensity of the output signal from each light receiving element is detected.
Thus, values of the signal intensity corresponding to RGB colors are obtained with the white light in each pixel and divided by a smallest value in the pixel, so that a ratio (Rn : Gn : Bn) of normalized output of each color of RGB is calculated as a reference pixel output value in each pixel.
After that, the paper sheet (medium) is transferred along the focal plane 20 in the x direction. While the paper sheet is transferred, the UV light is emitted from the first light source portion 4 and the UV light exits from the light exit surface 1d of the light guide 1 and illuminates the paper sheet. The fluorescence is generated from the paper sheet illuminated with the UV light, reaches the light receiving portion 12 through the lens array 11, and is received by the plurality of light receiving elements through the respective color filters in the light receiving portion 12. Thus, signal intensity Rf, Gf, Bf of the output signals from the light receiving elements are detected.
Thus, the signal intensity values Rf, Gf, Bf corresponding to the colors RGB in each pixel are obtained with the fluorescence and divided by the normalized output ratio (Rn : Gn : Bn) of the colors RGB which has been previously calculated in each pixel, whereby corrected signal intensity values Rfc, Gfc, Bfc are calculated in each pixel.
More specifically, the corrected signal intensity value Rfc corresponding to red (R) in each pixel is calculated by the following formula (1), the corrected signal intensity value Gfc corresponding to green (G) in each pixel is calculated by the following formula (2), and the corrected signal intensity value Bfc corresponding to blue (B) in each pixel is calculated by the following formula (3). $Rfc = Rf / Rn$
$Gfc = Gf / Gn$
$Bfc = Bf / Bn$

In this embodiment of the present invention, in the white LED light source (light source 3b of the second light source portion 3) in the present invention, that is, in the excitation light source, the white light is generated such that the violet or blue LED is covered with the phosphor, and the light emitted from the LED element is combined with the fluorescence from the phosphor. Thus, when the white light illuminates the white reference object 200, the light is emitted from the white reference object 200 and enters into the plurality of light receiving elements through the visible light color filters. Thus, the output signals are obtained from the light receiving elements and used as the reference pixel output values Rn, Gn, Bn, whereby it is possible to simply and accurately detect reading precision of the visible fluorescence color emitted from the paper sheet during the UV light irradiation.
More specifically, when the paper sheet (medium) such as securities or banknote is discriminated, the UV light is emitted from the UV light source (first light source portion 4) to the paper sheet, and the fluorescence is emitted from the paper sheet and enters into the plurality of light receiving elements through the visible light color filters, whereby the output signals Rf, Gf, Bf are obtained from the respective light receiving elements. The output signals Rf, Gf, Bf are corrected with the reference pixel output values Rn, Gn, Bn by the above formulas (1) to (3). Thus, the fluorescence color emitted during the UV light irradiation can be balanced, so that a high quality image having the desired color balance can be obtained.
Especially, since the above embodiment employs the white LED light source (light source 3b of the second light source portion 3) which is short in rising time and falling time and high in responsiveness, a higher quality image having the desired color balance can be obtained during the UV light irradiation. That is, it is preferable to use the while LED light source having the high responsiveness because it is necessary to read the paper sheet at high speed (reading speed for one line needs to be 100 µsec or less) in order to distinguish the paper sheet in a short time and many wavelengths are switched in a short time.
Furthermore, in the embodiment of the present invention, the plurality of light receiving elements are linearly arranged in the y direction (main scanning direction) in the light receiving portion 12. Thus, the visible fluorescence color of the paper sheet on the one observation line can be detected at high speed during the UV light irradiation.

<Non-limiting examples>

In the above, the embodiment of the present invention has been described according to the invention. Other non-limiting examples of the method and apparatus are provided. For example, the light source 3a of the second light source portion 3 is the light source which emits the visible light or the light having the wavelength range of the visible to infrared lights in the above embodiment, but it may be the light source which emits only the visible light. The light source 3a of the second light source portion 3 may be omitted and only the light source 3b may be provided as the white LED light source. Furthermore, the formation surface of the light diffusion pattern P may be disposed in any surface except for the light exit surface 1d of the light guide 1. For example, the light diffusion pattern may be formed on the bottom side surface 1a, and this may serves as the formation surface of the light diffusion pattern P (in this case, it is not necessary to form a slant surface between the bottom side surface 1a and the right and left side surface 1b).
In the correction process, instead of correcting the output signal from the light receiving element obtained when the UV light is emitted from the first light source portion 4 and the fluorescence is emitted from the paper sheet and enters into the light receiving portion 12, the output signal from the light receiving element obtained when the visible light or the light having the wavelength range of the visible to infrared lights and is emitted from the light source 3a of the second light source portion 3, and a light is emitted the light from the paper sheet and enters into the light receiving portion 12 may be corrected with the reference pixel output values Rn, Gn, Bn.
The line light source 10 does not necessarily have the configuration in which the light is emitted from the one or both end surfaces of the light guide 1 in the longitudinal direction L, and is diffused and refracted by the light diffusion pattern P, and it may have a configuration in which the light is directly emitted from the bottom side surface 1a of the light guide 1 toward the focal plane 20 through the light exit surface 1d (that is, direct type). In this case, even when the LEDs which are inexpensive and relatively small in output are used as the light source, the desired light amount can be ensured by arranging the line light source 10 to be the direct type. In this direct type arrangement, the light guide 1 can be omitted.
Furthermore, the observation line is not limited to the one line, and a plurality of observation lines each extending along the y direction (main scanning direction) may be arranged in the x direction (sub scanning direction). In this case, an average value of the output signals in the pixels in the same line in the x direction is calculated and the correction process may be performed with the average value.

DESCRIPTION OF REFERENCE SIGNS

1: light guide
2: cover member
3: second light source portion
3a: light source
3b: light source (white LED light source)
4: first light source portion
6: second optical filter
7: first optical filter
10: line light source
11: lens array
12: light receiving portion
20: focal plane
100: control unit
101: determination unit
102: correction processor
200: white reference object

Claims

A UV ray fluorescence color detection device for detecting a fluorescence color emitted from a medium and received by a light receiving portion (12) when a UV light is emitted from a UV light source (4) to the medium, the UV ray fluorescence color detection device comprising:
a white LED light source (3b) for emitting a white light by emitting a fluorescence from a phosphor;

a plurality of pixels provided in the light receiving portion (12), each pixel having a plurality of light receiving elements, for receiving a light passing through at least one red (R) color filter, at least one green (G) color filter and at least one blue (B) color filter in each pixel; and

a correction processor (102) for correcting a color balance of an output signal from each of the light receiving elements obtained when the UV light is emitted from the UV light source (4) and a fluorescence is emitted from the medium and enters into each of the plurality of light receiving elements through the visible light color filter, based on normalized RGB color output ratios for the pixels calculated from an output signal from each of the light receiving elements obtained when the white light is emitted from the white LED light source (3b), illuminates a white reference object (200), is emitted from the white reference object (200) and enters into each of the plurality of light receiving elements of each pixel through the RGB color filters;

wherein the correction processor (102) is configured to calculate each normalized RGB color output ratio from values of the signal intensity corresponding to RGB colors obtained with the white light in each pixel and divided by a smallest value of the signal intensity corresponding to RGB colors obtained with the white light in the pixel;

wherein such corrected output signal of the light receiving elements is used to discriminate the medium.
The UV ray fluorescence color detection device according to claim 1, wherein
a time taken for an output of the white LED light source (3b) to rise from 10% to 90%, and a time taken for the output to fall from 90% to 10% are each 2 µsec or less.
The UV ray fluorescence color detection device according to claim 1 or 2, wherein
the plurality of light receiving elements are linearly arranged in a main scanning direction (y).
A method for detecting a UV ray fluorescence color with a UV ray fluorescence color detection device according to claim 1.
The method for detecting a UV ray fluorescence color according to claim 4, wherein
a time taken for an output of the white LED light source (3b) to rise from 10% to 90%, and a time taken for the output to fall from 90% to 10% are each 2 µsec or less.
The method for detecting a UV ray fluorescence color according to claim 4 or 5, wherein
the plurality of light receiving elements are linearly arranged in a main scanning direction (y).