JP2011158395A - Detection method and detector of information on cross-sectional structure of paper sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect information on the cross-sectional structure of sheets through the use of Optical Coherence Tomography (henceforth, OCT). <P>SOLUTION: Sheets to be detected 10 set in a transfer mechanism 20 are irradiated with low-coherence light from an OCT signal detector 30 to receive light reflected from the sheets 10 and to detect the intensity of interfering light (to detect OCT raw signals) acquired inbetween with reference light. Acquired OCT raw signals are provided for a data processing and determiner 50 to perform profile computation processing in the depth direction of reflectance (S1), profile analysis processing in the depth direction of reflectance (S2), and determination processing (S3) as data processing and determination processing. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for detecting cross-sectional structure information of paper sheets, and more particularly, non-destructive of cross-sectional structure information of paper sheets using an optical coherence tomography (OCT) technique. The present invention relates to a method and an apparatus for detection.

  Optical coherence tomography (OCT) is a tomographic (cross-section) measurement method that uses the principle of low-coherence interference of light. This measurement method is a technique that has been put into practical use as a diagnostic device for eyes, skin, and the like in the medical field, and as a prior patent (application) relating to such a technique, Patent Document 1 (Japanese Patent Laid-Open No. 2007-101264) and Patent Document 2 (US Pat. No. 5,565,986).

In the techniques described in Patent Document 1 and Patent Document 2, a measurement object is a biological object such as a human body, and has a configuration mainly used in the medical field. For this reason, the techniques described in Patent Document 1 and Patent Document 2 cannot be applied to detection of the cross-sectional structure information of paper sheets as they are.
On the other hand, regarding the technology for detecting the cross-sectional structure information of paper sheets, for example, Patent Literature 3 (Japanese Patent Laid-Open No. Hei 8-110967) discloses a technology for detecting the presence or absence of metal threads embedded in paper sheets. ing. The technique described in Patent Document 3 is to pass a paper sheet between opposing capacitor electrodes and detect the presence or absence of a metal thread based on a capacitance change during the passage. With this technique, the presence or absence of a metal thread can be detected, but there is a problem that the structural characteristics of the metal thread cannot be detected.

  Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-285507) discloses a paper authenticity determination method using a cross-sectional shape of a thread insertion paper having a unique paper cross-sectional shape. In the authenticity determination of the paper disclosed in Patent Document 4, it is necessary to see the cross-sectional shape. If the paper does not clearly show the cross-sectional shape, the paper must be cut to check the cross-section. There is a problem that structural information may not be obtained by nondestructive measurement.

  In Patent Document 5 (Japanese Patent Laid-Open No. 2002-269616), by detecting the magnetic amount of the magnetic pigment present in the printed matter and the image marking amount, and collating them with those values of the genuine bill, A technique for performing authenticity determination is disclosed. Although this technique is an intaglio printed material and is effective when a magnetic component is used in ink, there is a problem that determination cannot be performed when a magnetic component is not used in ink.

JP 2007-101264 A US Pat. No. 5,565,986 JP-A-8-110967 JP 2004-285507 A JP 2002-269616 A

When detecting the cross-sectional structure information of a paper sheet, it is necessary to detect the thread even if it is non-contact and the shape of the thread embedded in the paper sheet is not clear at the end of the paper sheet . Moreover, even when the magnetic ink component is not piled up on the surface of paper sheets, it is necessary to be able to confirm the presence or absence of intaglio printing.
In the prior art, a technique for correctly detecting the sectional structure information of paper sheets has not been established.

The present invention has been made based on such a technical background, and a detection method and a detection method for detecting cross-sectional structure information of paper sheets using an optical coherence tomography (hereinafter referred to as “OCT”) technique. The main purpose is to provide a device.
Another object of the present invention is to provide a method and apparatus for obtaining the cross-sectional structure information of a paper sheet by using the OCT method and determining the authenticity of the paper sheet.

Said subject can be solved by the structure as described in each claim of a claim of this application.
Prior to the description of the configuration of the present invention for solving the above problems, an outline of the present invention will be described.
(1) Detection object of the present invention The detection object of the present invention is a paper sheet, particularly a paper sheet that has been subjected to anti-counterfeit processing such as banknotes and securities.

FIG. 1 schematically shows the configuration of the target paper sheet.
Referring to FIG. 1, a paper sheet 10 that is an object of detection of the invention has a security thread 11 embedded therein and an intaglio ink 12 printed on the surface thereof. A characteristic of the security thread 11 is that it is buried in the paper sheet 10 and is difficult to confirm from the outside. The feature of the intaglio ink 12 is that the ink 12 is slightly raised on the surface of the paper sheet 10. This invention is an invention for detecting a feature (cross-sectional structure information) on the cross-sectional structure in the thickness direction of the paper sheet 10.

Here, the security thread 11 is, for example, an elongated band (often made of transparent plastic with a metal film deposited on the surface) embedded in the paper sheet 10. The presence of these security threads 11 gives certain characteristics regarding the cross-sectional structure of the paper sheet 10.
The intaglio ink 12 is one in which the ink 12 is stacked and printed higher than usual, and the height of the ink stack is, for example, about 50 μm. The intaglio ink 12 can be printed by intaglio printing.

Even if the paper sheet 10 as shown in FIG. 1 is to be duplicated by a copying machine or an OA printer, it is impossible to duplicate the structure in the thickness direction of the paper sheet 10 by the security thread 11 or the intaglio ink 12. is there. Therefore, by detecting the feature (information) of the cross-sectional structure of the paper sheet 10, it is possible to determine the authenticity of the paper sheet with high accuracy. In the present invention, as will be described below, the cross-sectional structure information of paper sheets is detected by nondestructive measurement using an OCT technique.
(2) Outline of the Invention of the Present Application FIG. 2 shows a configuration block of a detection apparatus for the sectional structure information of paper sheets according to the present invention.

With reference to FIG. 2, the detection device of the present invention irradiates the paper 10 that is a detection target set in the transport mechanism unit 20 with low coherence light from the OCT signal detection unit 30, The reflected light from the paper sheet 10 is received, and the intensity of the interference light obtained with the reference light is detected (detection of the OCT raw signal). The OCT raw signal obtained by the OCT signal detection unit 30 is given to the data processing and determination unit 50 for data processing and determination. The contents of the data processing and determination are classified into “reflectance depth direction profile calculation processing” (S1), “reflectance depth direction profile analysis processing” (S2), and “determination processing” (S3). Can do.
(3) Description of OCT Method As a configuration for obtaining the OCT raw signal in the OCT signal detection unit 30, the method of measuring the depth direction structure information of the paper sheet 10 differs depending on the type of the OCT method.

As an OCT method,
a. a time domain OCT (see FIG. 3A), and b. a Fourier domain OCT, the Fourier domain OCT is further b-1. a frequency domain OCT (using a spectroscope for the detection unit, see FIG. 3B), and
b-2. Wavelength swept OCT (using a wavelength swept light source as a light source, see FIG. 3C).

The basic configuration for each OCT technique is the configuration shown in FIGS.
Any type of OCT technique may be used in the present invention, and in the description of the embodiment below, the frequency domain OCT technique will be described as an example.
The basic configuration of the three types of OCT methods shown in FIGS. 3A to 3C will be briefly described.

3A and 3B, reference numeral 31 denotes a low coherence light source, such as an LED, an SLD (super luminescent diode), a halogen lamp, or the like. In FIG. 3C, reference numeral 31 denotes a wavelength scanning light source, which is a light source capable of changing the emission wavelength.
In each figure, the light emitted from the light source 31 is converted into parallel light by, for example, a collimating lens 32, is given to a beam splitter 33, and is divided into detection light 34 and reference light 35. Then, the detection light 34 is condensed by the objective lens 36 and applied to the paper sheet 10 to be detected. Then, the reflected light is converted into parallel light by the objective lens 36 and is incident on the beam splitter 33 again.

  On the other hand, the reference light 35 is reflected by the reference mirror 37 and returns to the beam splitter 33. The reference mirror 35 is movable so as to scan the optical path length in FIG. 3A, but is fixedly arranged in FIGS. 3B and 3C. Then, the light reflected and returned by the paper sheet 10 by the beam splitter 33 and the light reflected and returned by the reference mirror 37 are recombined, and the photodetector 38 (FIGS. 3A and 3C) or the spectroscope 40 (FIG. 3B). In FIGS. 3A and 3C, reference numeral 39 denotes a detection condenser lens.

3B, the spectroscope 40 includes a diffraction grating 41, a detection condensing lens 42, and a linear CCD 43.
In FIG. 3B, the spectral interference signal measured by the linear CCD 43 using the spectroscope 40 is Fourier transformed.
On the other hand, in FIG. 3C, the time-varying signal output from the photodetector 38 measured while sweeping the wavelength of the light source 31 is Fourier transformed.
(4) Configuration of the Invention The specific configuration of the present invention is the following configuration as described in the claims.

  When viewed from a certain aspect, the present invention divides the low-coherence light into detection light and reference light, irradiates the detection paper with the detection light, and obtains reflected light from the paper, The reference mirror is irradiated with the reference light to obtain reflected light reflected by the reference mirror, and interference light is obtained by causing interference between the reflected light from the paper sheet and the reflected light from the reference mirror. The paper is received by the light receiving element according to the intensity of the light and converted into an electrical signal, a signal in the depth direction of the paper is obtained from the converted signal, and the signal in the depth direction is analyzed to obtain the paper A method for detecting the cross-sectional structure information of a paper sheet, wherein the cross-sectional structure information in the depth direction of the paper sheet and the cross-sectional structure information in a direction raised from the surface of the paper sheet are obtained with reference to the surface of the paper It is.

The paper sheet is partially intaglio-printed on the surface thereof, and the raised cross-sectional structure information based on the surface of the paper sheet includes position information indicating the ink swell by intaglio printing. It is desirable that
In addition, a security thread is embedded in a predetermined position inside the paper sheet, and the cross-sectional structure information in the depth direction of the paper sheet based on the surface of the paper sheet includes the security sheet. Depth position and reflectance information based on the reflected signal reflected by the sled may be included.

Further, it is a method for performing authenticity determination as to whether or not the paper sheet is a predetermined type of paper sheet from the cross-sectional structure information obtained by the detection method, wherein the authenticity determination includes a security thread embedded. The determination may be made based on the difference signal of the detection signal between the remaining area and the unembedded area.
Alternatively, it is a method for determining whether or not a paper sheet is a predetermined type of paper sheet from the cross-sectional structure information obtained by the detection method, wherein the authenticity determination includes a security thread embedded. You may determine based on the ratio of the detection signal of an area | region and the area | region which is not embedded.

  From another aspect, the present invention divides the low-coherence light emitted from the light source into the detection light and the reference light in two, and the detection light is detected. Irradiate the leaves to obtain the reflected light from the paper sheet, and irradiate the reference mirror to the reference mirror to obtain the reflected light from the reference mirror, and interfere the two reflected lights to generate interference light. An optical unit; a light receiving element for receiving the interference light output from the optical unit and converting it into an electrical signal; and a signal obtained by receiving the light from the light receiving element in a depth direction of the paper sheet A signal processing means for obtaining a signal, and a depth direction component of the signal obtained by the signal processing means, thereby analyzing the cross-sectional structure information in the depth direction of the paper sheet based on the surface of the paper sheet; Cross-sectional structure in the direction raised from the surface of the paper Characterized in that it comprises a signal analyzing means for obtaining a distribution, and a detecting apparatus of a cross-sectional structure information of the sheet.

The paper sheet is partially intaglio-printed on the surface thereof, and the raised cross-sectional structure information based on the surface of the paper sheet includes position information indicating the ink swell by intaglio printing. It is desirable that
A security thread is embedded in a predetermined position inside the paper sheet, and the cross-sectional structure information in the depth direction with respect to the surface of the paper sheet is reflected by the security thread. Position information and reflectance information based on the signal may be included.

  The detection device further includes a storage unit that stores information on at least one of intaglio printing and a security thread regarding a predetermined type of paper sheet, and a signal obtained by the signal analysis unit is stored in the storage unit. It may be configured to include authenticity determination means for determining the authenticity of the sheet to be inspected by comparing with the stored information.

  According to this invention, it is possible to obtain the characteristics of the reflectance distribution in the depth direction of the paper sheet that is the detection target. Thereby, it is possible to determine the presence or absence of the security thread embedded in the paper sheet and the presence or absence of the intaglio ink on the surface of the paper sheet. Then, the authenticity of the paper sheet can be determined.

It is an illustration figure of the paper sheet 10 which is a detection object of this invention, (a) is the plane of the paper sheet 10, (b) has shown the cross section of the paper sheet 10 illustratively. 1 is a configuration block diagram showing an outline of a cross-sectional structure information detection device of the present invention. It is a basic composition block diagram of time domain OCT. It is a basic block diagram of OCT of a frequency domain. It is a basic lineblock diagram of wavelength sweep OCT. 1 is a configuration block diagram of a cross-sectional structure information detection apparatus for paper sheets using an OCT technique according to an embodiment of the present invention. A (1) is a diagram illustrating an example of an interference spectrum signal when a reflection surface exists only at a position of depth Z = Z ₁ obtained by processing the detected OCT raw signal, and B (1 ) Is a diagram illustrating an example of an interference spectrum signal in the case where the reflection surface exists only at the position of depth Z = Z ₂ (> Z ₁ ), and A (2) and B (2) are respectively A (1) and B (1) are the results of discrete Fourier transform of the interference spectrum signal, and each signal peak position and signal peak corresponding to the reflection surface existing at the depths Z = Z ₁ and Z = Z ₂ , respectively. Each value is shown. It is a flowchart for demonstrating the processing content performed in the data processing and determination part 50 (refer FIG. 2). It is a graph of the depth direction profile of a reflectance. It is a graph showing the difference between the part with and without the security thread. It is a graph showing the difference of the signal in an intaglio ink part and its peripheral part. 3 is a schematic plan view of a paper sheet 10 in which a security thread 11 is embedded in a predetermined area. FIG. It is an example of the signal obtained by performing the depth direction profile calculation process of a reflectance. It is a graph of the difference signal between the thread area | region (thread part) obtained by the thread detection determination process by a difference signal, and its adjacent area | region (thread non-part). It is a graph of the signal ratio which calculated | required ratio (ratio signal) of a thread | seat non-part and a thread | sled part from a reflectance profile.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 4 is a block diagram showing the configuration of a cross-sectional structure information detecting apparatus for paper sheets using the OCT technique according to an embodiment of the present invention. This configuration is a configuration block diagram in the case of using a spectrum domain interference method (frequency domain OCT). Therefore, the configuration shown in FIG. 4 is basically the same as the configuration of FIG. 3B.

  In FIG. 4, 31 is an SLD (super luminescent diode) as a light source, which emits low coherence light. The low coherence light emitted from the SLD 31 is converted into parallel light by the collimator lens 32 and given to the beam splitter (BS) 33. The beam splitter 33 divides the given light into detection light 34 and reference light 35 and emits the light toward the paper sheet 10 and the reference mirror 37 that are detection targets, respectively. The detection light 34 is collected by the objective lens 36 and irradiated to the reference plane (this reference plane is Z = 0 plane) of the transport mechanism 20 (see FIG. 2) on which the paper sheet 10 is mounted. The The irradiated detection light is reflected on the surface of the paper sheet 10 and enters the inside of the paper sheet 10 having a depth in the Z direction from the reference plane Z = 0, and the reflected light reflected inside is reflected The light reflected by the surface enters the beam splitter 33 via the objective lens 36.

On the other hand, the reference light 35 divided by the beam splitter 33 is reflected by the reference mirror 37. In the reference mirror 37, the optical path length viewed from the beam splitter 33 is fixed at a position equidistant from the reference plane Z = 0 plane of the paper sheet 10. Then, the reference light reflected by the reference mirror 37 is again incident on the beam splitter 33.
In the beam splitter 33, the reflected light reflected by the paper sheet 10 and the reflected light reflected by the reference mirror 37 are recombined. This recombined light is interference light in which light of a plurality of wavelengths where the reflected light reflected by the paper sheet 10 and the reference light reflected by the reference mirror 37 interfere with each other is mixed. The recombined light 44 is reflected by the diffraction grating 41 to become interference fringe light 45, and is condensed by a condenser lens 46 onto a line-shaped light receiving element, for example, a linear CCD 43. Therefore, the linear CCD 43 detects the intensity of the interference fringe light.

The detected light intensity of the interference fringes, that is, the OCT raw signal, is viewed from the Z-axis direction (depth direction) of the paper sheet 10 with respect to the reflection surface existing at the position of Z = Z _1. For example, an interference spectrum signal shown in FIG. 5A (1) is obtained. That is, when Z = Z ₁ , the phase difference between the reflected light of the paper sheet 10 and the reflected light of the reference mirror 37 is
nkZ ₁ (where n is the refractive index of the object to be detected (paper sheets), k is the wave number)
Thus, an interference spectrum signal having a period inversely proportional to the depth position Z ₁ of the reflection surface of the paper sheet 10 is obtained.

For the reflection surface existing at the position of Z = Z ₂ (> Z ₁ ), for example, an interference spectrum signal shown in FIG. 5B (1) is obtained. That is, when Z = Z ₂ , the phase difference between the reflected light of the paper sheet 10 and the reflected light of the reference mirror 37 is
nkZ ₂ (where n is the refractive index of the detection object (paper sheet), k is the wave number)
An interference spectrum signal having a period inversely proportional to the magnitude of the depth position Z ₂ is obtained.

Then, when the obtained interference spectrum signal is subjected to discrete Fourier transform (DFT), the depth position of the reflection surface can be obtained from the signal peak position, and the amplitude reflectance of the reflection surface can be obtained from the signal peak value.
The respective signal peak positions and signal peak values for the respective reflecting surfaces existing at the depths Z = Z ₁ and Z = Z ₂ of the reflecting surface of the paper sheet 10 are shown in (2) and (B) of FIG. 2).

In this embodiment, the OCT signal detection unit 30 shown in FIG. 2 has the configuration shown in FIG. 4, and the data processing and determination unit 50 shown in FIG. A three-stage process shown in FIG.
FIG. 6 is a flowchart for explaining the processing contents performed in the data processing and determination unit 50 (see FIG. 2).

When the OCT raw signal detected by the OCT signal detection unit 30 (see FIG. 2) is given to the data processing and determination unit 50 (step S0), the data processing and determination unit 50 performs the depth direction profile calculation processing of the reflectance. (Step S1), the reflectance depth direction profile analysis processing (Step S2), and the determination processing (Step S3) are sequentially executed.
The reflectance depth direction profile calculation process of (Step S1) includes a discrete Fourier transform (hereinafter referred to as “DFT”) process, a filtering process for removing noise, and an interval data averaging process. ing.

By performing these processes on the detected OCT raw signal, a graph of the reflectance profile in the depth direction as shown in FIG. 7 is obtained.
In FIG. 7, the horizontal axis represents the position [μm] of the optical path length in the depth direction, and the vertical axis represents the signal [dB] normalized by the peak value.
From the graph of FIG. 7, the largest signal appears at the surface position in the thickness direction of the paper sheet to be detected, and light scatters in the paper sheet as the depth increases in the thickness direction of the paper sheet. It can be understood that the signal gradually weakens.
In the depth direction profile analysis processing of the reflectance in (Step S2), the position detection processing of the signal peak (first peak) corresponding to the outermost surface of the measurement unit, and the presence or absence of the second signal peak inside the paper sheet And confirmation processing. When the second signal peak is present inside the paper sheet, the peak position detection process is also included. The processing related to the second signal peak can be performed based on the ratio or difference of detection signals between the area where the security thread is embedded and the area where the security thread is not embedded.

By performing the depth direction profile analysis processing of the reflectance, a graph representing the difference between the presence and absence of the security thread as shown in FIG. 8 is obtained.
In the graph of FIG. 8, the horizontal axis represents the position [μm] of the optical path length in the depth direction, and the vertical axis represents the signal [dB] normalized by the peak value. According to the graph of FIG. 8, the first peak of the signal appears when the optical path length in the depth direction is about 100 μm, and the second peak of the signal appears when the optical path length in the depth direction is about 150 μm. Appears.

From this signal characteristic, the position of the first peak (the optical path length in the depth direction is 100 μm) is the surface of the paper sheet, and the security thread is embedded at a position of about 50 μm (150-100) from the surface. Understandable.
The intaglio ink can be subjected to detection processing based on ink swell information by intaglio printing, that is, ink position information.

  FIG. 9 is a graph showing the difference in signal between the intaglio ink part and its peripheral part. In the graph of FIG. 9 as well, the horizontal axis is the depth direction optical path length position [μm], and the vertical axis is the peak value. Represents the converted signal [dB]. A peak appears at the position where the optical path length in the depth direction is about 40 μm in the ink portion where the intaglio ink is printed on the surface of the paper sheet. On the other hand, a peak appears at a position where the optical path length in the depth direction is about 120 μm in the vicinity of the ink portion (the portion without the intaglio ink).

From this graph, it is understood that the surface of the paper sheet is at a position where the optical path length in the depth direction is 120 μm, and the surface of the paper sheet is printed with an ink volume of about 80 μm by printing intaglio ink. it can. That is, it is shown that the ink surface is in front of the paper surface.
The determination process in (Step S3) includes (1) presence determination of intaglio ink and true / false determination based thereon, and (2) presence determination of security thread and true / false determination based thereon.

Next, these two determination processes will be specifically described.
(1) Intaglio ink presence determination and true / false discrimination based thereon In this determination and discrimination, a predetermined position on the surface of the paper sheet and the state of its vicinity are detected, and the difference ΔH1 in the first signal peak generation position is evaluated. To do. A) If ΔH1 ≧ (predetermined threshold 1), it is determined that the paper sheet is genuine (with intaglio ink).

b) If ΔH1 <(predetermined threshold value 1), it is determined that the paper sheet is duplicated or counterfeit (no intaglio ink).
(2) Security thread existence determination and true / false determination based on the determination,
A. If the second signal peak is not detected when the predetermined position of the paper sheet is detected, it is determined that the copy or forgery (no security thread) is detected.

I. When the second signal peak is detected at a predetermined position on the paper sheet, the difference ΔH2 between the first signal peak generation position and the second signal peak generation position is evaluated. And the evaluation is
a) In the case of (predetermined threshold 2) ≦ ΔH2 ≦ (predetermined threshold 3), it is determined as authentic (with security thread).

b) If ΔH2 <(predetermined threshold 2) or ΔH2> (predetermined threshold 3), it is determined that the sheet is suspected of being duplicated or forged.
That is, when the second signal peak generation position corresponding to the security thread is in a predetermined depth position in relation to the first signal peak (the surface of the paper sheet), it is determined to be authentic. If the depth position of the second signal peak is not the embedded depth position of the security thread, the second signal peak may not be a signal peak based on the authentic security thread, so I am suspicious that it is not a good paper sheet.

Next, data processing and determination unit 50 that performs security thread detection S1: Reflectance depth direction profile calculation processing,
S2: Reflection depth direction profile analysis processing,
and,
S3: The process steps of the determination process will be described more specifically.

Specifically, two types of methods can be applied to the processing steps S1, S2, and S3 performed in the data processing and determination unit 50.
(1) Thread detection determination processing using a difference signal, and (2) Thread detection determination processing using a ratio signal.
Each of these two types of processing will be described.

(1) Thread detection determination process based on difference signal In this process, the sheet 10 to be detected is set in the transport mechanism 20 (see FIG. 2), and the surface of the set sheet 10 is exposed to the detection light 34. In this way, the paper sheet 10 is transported in the X direction by the transport mechanism unit 20. At that time, both the area where the predetermined security thread should be embedded in the paper sheet 10 and the adjacent area (area where the security thread is not embedded) are scanned with the detection light.

More specifically, as shown in FIG. 10, a security thread 11 is embedded in a predetermined area of the paper sheet 10.
Therefore, for example, the paper sheet 10 is transported in the X direction by the transport mechanism unit 20, and the scanning portion indicated by the horizontal line A <b> 1 is exposed to the detection light 34 and is scanned with the detection light 34.
In FIG. 10, the paper sheet 10 is scanned from left to right. As a result, an area without a thread, an area where a thread is embedded, and an area without a thread are sequentially scanned, and the signal is obtained. The signal shown in FIG. 11 is obtained by performing the depth direction profile calculation process of the reflectance of step S1 on the obtained signal.

In FIG. 11, the horizontal axis represents the depth position [μm], and the vertical axis represents the detection signal level [dB]. In FIG. 11, the solid line A2 represents the detection result of the thread area, and the broken line A3 represents the detection result of the non-thread area.
In any case, a high detection signal level is obtained on the surface of the paper sheet 10 as the first peak. This is because the detection light 34 is largely reflected on the surface of the paper sheet 10.

In the thread region, a second peak appears at a depth of about 55 μm. That is, in the thread area, the detection light irradiated by the security thread 11 is reflected by the security thread 11 embedded at a depth of about 55 μm from the surface of the paper sheet 10 to increase the detection signal level. It appears as a peak.
In the thread detection determination process using the difference signal, a difference signal between the thread area (thread-containing part) and the adjacent area (thread-free part) is obtained. That is, the graph shown in FIG. 12 is obtained. In FIG. 12, the horizontal axis is the depth position [μm], and the vertical axis is the differential signal level [dB].

In FIG. 12, the characteristic of the reflectance (difference between profile signals) between the threaded part and the threadless part is obtained.
A predetermined threshold level is set for the difference signal F (Z).
A section in which the difference signal F (Z) is equal to or greater than the set threshold value, that is, a signal total value S1 (a hatched portion) in (Z: Za to Zb) in FIG. 12 is calculated. The signal sum value S1 is expressed by the following equation.

Then, the signal total value S1 is compared with a preset threshold value,
S1 ≧ (set threshold)
In this case, it is determined that the security thread 11 is present.
In the case of the paper sheet 10 as shown in FIG. 10, scanning is performed by applying detection light from the left to the right of the paper sheet 10, and the first peak value and the second peak value based on the reflected light are Are continuously collected, position information, depth information, and width information of the security thread 11 can be obtained. Therefore, it can be determined whether or not the security thread 11 is embedded at the normal position, depth, and width.

Further, since the reflection intensity by the security thread 11 is also related to the material of the thread, it is also determined whether the security thread 11 made of a predetermined material is embedded depending on whether or not it has a regular reflectance. It is possible.
(2) Thread Detection Judgment Process Using Ratio Signal Next, a process for performing the detection judgment of the security thread 11 by taking the signal ratio will be described.

In this process, the reflectance profile calculation process is the same as the security thread detection determination process using the difference signal, and a reflectance profile as shown in FIG. 11 is obtained.
Next, a ratio (ratio signal) between the thread-free part and the thread-equipped part is obtained from the obtained reflectance profile.
A graph of the obtained signal ratio is shown in FIG.

In FIG. 13, the horizontal axis is the depth position [μm], and the vertical axis is the signal ratio R (Z).
The graph of FIG. 13 is obtained by calculating the ratio of the reflectance profile signal between adjacent regions (threaded part and threadless part).
Then, a threshold level is set for the obtained ratio signal R (Z).
Then, a signal sum value S2 in a section (Z: Za to Zb) in which the obtained ratio signal R (Z) is equal to or greater than a threshold value is calculated.

  The signal sum value S2 can be expressed by the following equation.

The signal total value S2 is compared with a preset threshold value,
If S2 = ≧ (setting threshold), it is determined that there is a security thread.
For example, when the present invention is applied to the determination of the authenticity of banknotes, information on security threads and intaglio inks determined in advance according to the type of banknotes is registered in the storage means (memory table), and at the time of authenticity determination The information in the memory table may be referred to.

That is, the detection apparatus further includes storage means for storing information on at least one of the intaglio printing and the security thread for a predetermined type of paper sheet, and stores the signal obtained by the signal analysis means in the storage means. It may be configured to include authenticity determination means for determining the authenticity of the sheet to be inspected by comparing with the information thus obtained.
In this case, the conveyance mechanism unit 20 (see FIG. 2) controls the conveyance of the banknote 10, and reads and consults appropriate information from the memory table by linking the detection position of the banknote surface and the detection signal. Can do.

  In addition, various design changes can be made within the scope of matters described in the claims.

DESCRIPTION OF SYMBOLS 10 Paper sheet 11 Security thread 12 Intaglio ink 20 Conveyance mechanism part 30 OCT signal detection part 31 Light source 32 Collimating lens 33 Beam splitter 34 Detection light 35 Reference light 37 Reference mirror 41 Diffraction grating 43 Linear CCD
50 Data processing and judgment unit

Claims (10)

The low-coherence light is divided into detection light and reference light, and the detection light is applied to the paper sheet to be measured to obtain reflected light from the paper sheet, and the reference light is applied to the reference mirror to Obtain the reflected light reflected by the reference mirror, interfer the reflected light from the paper sheet and the reflected light from the reference mirror to obtain the interference light,
The interference light is received by the light receiving element according to the intensity of the interference light and converted into an electrical signal,
Obtain the depth direction signal of the paper from the converted signal,
By analyzing the signal in the depth direction, it is possible to obtain the cross-sectional structure information in the depth direction of the paper sheet and the cross-sectional structure information in the direction raised from the surface of the paper sheet, based on the surface of the paper sheet. A method for detecting cross-sectional structure information of a paper sheet, which is characterized. The paper sheets are partially intaglio printed on the surface,
The sectional structure of the paper sheet according to claim 1, wherein the sectional structure information of the bulge based on the surface of the paper sheet includes position information indicating the bulge of ink by intaglio printing. Information detection method. A security thread is embedded in a predetermined position inside the paper sheet,
The cross-sectional structure information in the depth direction of the paper sheet based on the surface of the paper sheet includes depth position and reflectance information based on a reflection signal reflected by the security thread. The method for detecting the cross-sectional structure information of a paper sheet according to claim 1 or 2. A method of performing authenticity determination as to whether or not a paper sheet is a predetermined type of paper sheet from the cross-sectional structure information obtained by the detection method according to claim 1,
The method of determining whether the authenticity determination is based on a difference signal of detection signals between an area where a security thread is embedded and an area where the security thread is not embedded. A method of performing authenticity determination as to whether or not a paper sheet is a predetermined type of paper sheet from the cross-sectional structure information obtained by the detection method according to claim 1,
The method is characterized in that the authenticity determination is performed based on a ratio of detection signals between a region where a security thread is embedded and a region where a security thread is not embedded. A method of performing authenticity determination as to whether or not the paper sheet is a predetermined type of paper sheet from the cross-sectional structure information obtained by the detection method of claim 2,
The authenticity determination is based on the fact that the ink swell information by intaglio printing is position information based on the reflection signal of the surface of the paper sheet, and is determined based on the fact that it is in the front position from the position information of the surface of the paper sheet A method characterized by. A light source for irradiating low coherence light;
The low-coherence light emitted from the light source is divided into detection light and reference light, and the reflected light from the paper is obtained by irradiating the detection light to the paper to be detected, and the reference light is used as the reference light. An optical unit that irradiates the reference mirror to obtain reflected light from the reference mirror, and interferes with both reflected light to generate interference light;
A light receiving element for receiving the interference light output from the optical unit and converting it into an electrical signal;
A signal processing means for obtaining a signal in the depth direction of the paper sheet from a signal obtained by receiving light by the light receiving element;
By analyzing the depth direction component of the signal obtained by the signal processing means, the sectional structure information in the depth direction of the paper sheet and the surface of the paper sheet were raised with reference to the surface of the paper sheet. Signal analysis means for obtaining direction sectional structure information;
An apparatus for detecting the cross-sectional structure information of a paper sheet. The paper sheets are partially intaglio printed on the surface,
8. The cross-sectional structure of a paper sheet according to claim 7, wherein the cross-sectional structure information of the swell based on the surface of the paper sheet includes position information indicating the swell of ink by intaglio printing. Information detection device. A security thread is embedded in a predetermined position inside the paper sheet,
The cross-sectional structure information in the depth direction based on the surface of the paper sheet includes position information and reflectance information based on a reflection signal reflected by the security thread. The detection apparatus of the cross-section structure information of paper sheets of 6 or 7. The detection apparatus further includes a storage unit that stores information on at least one of intaglio printing and a security thread regarding a predetermined type of paper sheet,
The apparatus according to claim 1, further comprising: a true / false determining unit that determines whether the paper sheet to be inspected is true or false by comparing a signal obtained by the signal analyzing unit with information stored in the storage unit. The detection apparatus of the cross-sectional structure information of paper sheets in any one of 7-9.

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