JPS5839386A - Discrimination of paper sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a method for optically discriminating paper sheets.

Traditionally, methods such as detecting minute patterns on paper sheets or detecting the transmittance or reflectance of light in specific parts are used to optically distinguish paper sheets such as banknotes and securities. is used. However, all of these conventional methods focus on one characteristic caused by a single element among the many characteristic items of paper sheets, and detect the characteristics related to that item with a single detector. This is an attempt to distinguish between types. Therefore, it is necessary to detect the subtle features of paper sheets with extremely high precision, so it is difficult to detect disturbances.In recent years, with the spread of copying machines, it has become easier to create highly accurate counterfeit notes by copying, The discrimination method has a problem in its ability to discriminate against this type of counterfeit banknotes.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for discriminating paper sheets that can detect as a feature the integrated characteristics produced by a combination of a plurality of elements.

A feature of the present invention is to irradiate the surface of a paper sheet with light, detect the intensity of scattered light of the light at a predetermined position on the surface of the paper sheet at at least two locations, calculate the ratio of the intensities, and calculate the intensity ratio. The purpose of this method is to distinguish paper sheets.

The present invention will be explained below using examples.

1 and 2 are front views showing essential parts of a first embodiment of the present invention, in which 1 is a paper sheet, such as a banknote, and 2 is a beam-shaped light 8 directed against the paper surface. A light projector 4 and 5 project light at an angle α, and first and second photodetectors are light receiving elements such as photodiodes. In this embodiment, two photodiodes are provided in this way, and both of them are arranged with their light receiving axes facing the incidence of the above-mentioned light beam, that is, the detection, .lJp, so that the scattered light components 6 and 7 at the point P are received. .

The first photodiode 4 of these two is located within a plane that includes the light beam 3 and the normal to the surface of the banknote 1 at point P, and the angle between the light receiving axis and the surface of the banknote 1 is as described above. Let the direction be approximately equal to σ.

Since the surface of the paper used for banknotes l is relatively smooth, when the point P is in an unprinted area or in a dry offset printing pattern area, the scattered light component 6 toward the first photodiode 4 is scattered. The light intensity R1 is large, and the components directed in other directions are relatively small. Therefore, the light intensity RB of the scattered light component 7 directed toward the second photodiode 5 is small. This situation is shown in Fig. 2(a), -
When the intaglio printing pattern 8 is located at the point of emphasis P, the light incident on the point P hits the pattern 8 and is scattered in all directions as shown in the figure (to). Therefore, the intensity R1 of the scattered light component 6
' is smaller than the above R1, and conversely, the intensity R of the scattered light component 7
i is larger than R2 described above.

Since both the dry offset printing and intaglio printing described above are used for printing banknotes, the intensity ratio R1/Rg of the scattered light components 6 and 7 differs significantly depending on the location. Therefore, there is a unique relationship between the position of the detection point P and the scattered light intensity ratio R1/R2 depending on the type of banknote.

The present invention uses this relationship as a feature to discriminate paper sheets, and selects the position of the detection point P to
The type of banknote, etc. is identified by determining the .

Furthermore, in a counterfeit note that has been copied using a copying machine or the like, even if the original is a dry offset printed pattern, the copied pattern will be raised in the same way as an intaglio printed pattern. Therefore, by appropriately selecting the position of the detection point P, it is possible to make the intensity ratio R1/R2 significantly different from that of a genuine note, and therefore, counterfeit notes can also be easily discriminated by this embodiment.

FIG. 8 is a block diagram showing the arithmetic processing circuit used in this embodiment, and numerals 4 and 5 in the figure are the above-mentioned first and second photodiodes. The first and second photodiodes 4.5 receive the scattered lights 6, 7 from the detection point P at their respective positions, and convert them into electrical outputs 11+I2 corresponding to the intensities R1, R2. This: h + engineering 11 is a signal KI proportional to each logarithm by a log amplifier 10.11.
OFq 1, is converted into 6og 2, and further subtracted by the differential amplifier 12, and the difference between the two is 10 g (I
1/work 2) is output. II, Engineering 2 corresponds to R1, R2, eog < Engineering 1/IB) is Rx/Rs
The value corresponds to K.

Therefore, the above 60g (work 1/Is) at a predetermined detection point
is calculated for each type of banknote and stored as a feature value. Then, 40g (Eng/Is) of the banknote to be discriminated is obtained according to the present example, and the above-mentioned dog(
It goes without saying that the intensity ratio R1/R2) may be further converted into the intensity ratio R1/R2 and used as the feature value.

The first embodiment described above shows the basic configuration of the present invention, and the present invention can be further modified and implemented in various ways.

For example, the number of photodetectors is not limited to two, but eight or more may be provided, and the number of detection points may be two or more. In any of these cases, a plurality of feature values are used, so the discrimination accuracy increases. Furthermore, the position of the optical sensor does not need to be particularly limited, and may be selected as appropriate.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 to 6. While the detection point in the first embodiment was fixed, in this embodiment, the surface of the paper sheet is scanned by a method such as moving the paper sheet in a predetermined direction, and the intensity ratio of the scattered light is determined. R
1/R2 is determined corresponding to the position on the scanning line S. Then, an intensity ratio pattern as shown in FIG. 6 is obtained.

In this embodiment, paper sheets are discriminated using this intensity ratio pattern as a feature.

FIG. 6 is a block diagram showing the arithmetic processing circuit used in this embodiment. The circuit shown in this figure has the same basic configuration as the arithmetic processing circuit used in the first embodiment [Fig. This is an example.

In the figure, 18 is the central processing unit (CPU) of the computer.
), 14 is a storage device (memory), 15 is an analog-digital converter (ADC), 16 is a logic circuit, and 17 is a bus line. The memory 14 stores characteristic patterns for each type of paper sheet to be discriminated, for example, banknotes, as a dictionary pattern in advance. When discriminating banknotes, the surface of the banknote 1 is scanned in accordance with a command from the CPU 18, and the characteristic patterns on the scanning line S are The scattered light intensity F11.corresponds to the position. R2 is detected, and gag<work1/workg) corresponding to the intensity ratio R1/Rg is output as described above. The ADC 15 converts the command from the CPU 13 into a digital signal and sends it to the logic circuit 16 (C).

The logic circuit 16 compares the feature pattern detected in this way with various dictionary patterns stored in the memory 14 in advance, selects the one that matches or the one with the smallest difference between the two, and applies a pattern corresponding to that dictionary pattern. The type of banknote to be used is output as a recognition result.

As is clear from the above description, this embodiment performs discrimination by scanning the surface of a paper sheet and using the two-dimensional distribution of scattering characteristics caused by paper quality and printing method.

Next, an eighth embodiment of the present invention will be described (see FIG. 7). In this embodiment, a plurality of pairs of color sensors are arranged, and discrimination is performed using the scattering characteristics of each monochromatic light at a predetermined detection point. FIG. 7 is a top view showing the arrangement of the color sensor, in which a detector for red is composed of a red filament 18, photodiodes 19 and 19', and a blue filament 2o, photodiodes 21, 21' and a yellow filter are similarly arranged. 2
2 and photodiodes 23 and 28', blue respectively.
Configure a detector for yellow.

By detecting the scattered light intensity ratio for each monochromatic light at the detection point P using the eight detector pairs configured in this manner and using this as a feature, paper sheets can be discriminated.

The arithmetic processing circuit used in this example is provided with the circuit shown in FIG. 8 for each pair of detectors, and the entire CP
It may be configured to be controlled by U.

As mentioned above, both dry offset printing and intaglio printing are used to print banknotes, and many different colors are used. Therefore, according to this embodiment, it is possible to accurately detect the characteristics caused by the combination of color and printing method, and it is possible to accurately discriminate paper sheets.

The present invention is not limited to the above-described embodiments, and can be implemented with various modifications.

For example, in order to detect the scattering characteristics at a desired position, in the above embodiment, a beam of light was projected onto the detection point, but instead of this, as shown in FIG. It may be irradiated. However, in this case, the photodetector 4.5
Directing the optical axis of the lens toward the detection point P is the same as the above embodiment, but an aperture 24 and a condensing lens 2 are further provided on the optical axis.
5 is arranged so that only the scattered light components 6 and 7 at the detection point P are received. Here, point P and photodetector 4゜5
It is necessary to arrange the condenser lens 25 so that it is located at the image formation position of the condenser lens 25.

Further, although white light is used as the irradiation light in the first to eighth embodiments, monochromatic light may be used in the first and second embodiments, and in the eighth embodiment, white light is used as the irradiation light. A plurality of different light emitters may be arranged around the incident optical axis.

As explained above, according to the present invention, by using a plurality of photodetectors, it is possible to accurately detect the scattering characteristics unique to various paper sheets caused by the combination of paper, printing method, and color pattern in the paper industry. This makes it possible to distinguish paper sheets with high accuracy.

[Brief explanation of the drawing]

1 to 8 are front views and block diagrams of main parts showing the first embodiment of the present invention, and FIGS. 4 to 6 are main part block diagrams showing the first embodiment of the present invention.
Fig. 7 is a top view of main parts showing an eighth embodiment of the present invention, and Fig. 8 shows a modification of the wooden invention. It is a main part front view. In the figure, l is a paper sheet, 2 is a floodlight, 8.3' is irradiated light, 4.5.19.19', 21, 21', 28°28' is a photodetector, and 6.7 is scattered light. Components 18, 20° 22 is a filter, 24 is an aperture, and P is a detection point. 1st leap (Q) 21￥I (b) 3rd leap Figure 4 Figure 5 Figure 61'21 Figure 7 Figure 814

Claims (1)

[Claims] Irradiate the surface of the paper sheet with light, detect the intensity of the scattered light of the light at a predetermined position on the surface of the paper sheet at at least two locations, and calculate the ratio of the intensities of the scattered light detected at the at least two locations. A paper sheet discrimination method characterized by discriminating paper sheets based on the intensity ratio.