JPS61143897A - Detector for sheet paper - 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 [Technical Field of the Invention] The present invention relates to a paper sheet detection device used, for example, to detect watermarks on banknotes.

[Technical background of the invention and its problems] In general, for example, watermarks on banknotes are created uniquely in each country, such as on people or buildings, by using the density and density of fibers in the process of making paper. Since the density of the fibers that make up banknotes is utilized in this way, coarse areas become brighter and denser areas become darker, making it possible for humans to identify the fibers, which is why they are used to determine the authenticity of banknotes.

By the way, when detecting such a watermark made of coarse and dense tlIIt on banknotes, since the coarse part is thin and the dense part is thick, conventional methods have been to detect it with a thickness sensor or to detect the difference in brightness between the coarse and dense parts. Detection methods using transmitted visible light or near-infrared light are known. However, although the difference in thickness is usually about ±20 μm, the former method has a problem in that sufficient resolution cannot be obtained. Also,
In the latter case, there were problems in that it was easily affected by dirt and patterns on the banknotes, and that a sufficient S/N ratio could not be obtained.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to accurately detect watermarks made of coarse Δ of m fibers on banknotes, and to determine the authenticity of banknotes. It is an object of the present invention to provide a paper sheet detection device useful for applications such as the following.

[Summary of the Invention] In order to achieve the above object, the present invention focuses on the fact that the optical absorption band of the fibers constituting banknotes is approximately 3 μm, and utilizes the optical absorption characteristics of the fiber components to utilize infrared rays. This device is designed to detect the density of the fibers that make up the banknotes.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, P represents a banknote as a paper sheet, and is conveyed in the direction of arrow a in the figure by a conveyor belt (not shown) or the like. Here, the banknote P has a thickness of 90μ
m to about 120 μm, and is printed using various inks, and the printing thickness is often 10 μm or less. Further, the banknote P is made of paper, and its main component is fibrous material (cellulose). The light absorption band of cellulose is approximately 3 μm, and it absorbs infrared rays of this wavelength well. In order to simplify the explanation, it is assumed that the banknote P has a bar watermark, such as the part b shown in FIG. 2, for example. In this bar watermark, part 0 is a dense part of fibers and 6 parts in between are coarse parts of aMt. An infrared radiator 1 having a peak of radiant energy at approximately 3 μm is disposed on one side of the banknote P to be conveyed, and an infrared radiator 1 having a peak of radiant energy at approximately 3 μm is disposed on the other side of the banknote P, facing the radiator 1 and approximately An infrared sensor 2 sensitive to a wavelength band of 3 μm is provided. The infrared radiator 1 is, for example, an infrared heater, and its surface temperature is set to about 690° C. so that the peak of radiant energy is about 3 μm.

The output signal of the infrared sensor 2 is supplied to a preamplifier 3, where it is amplified and then supplied to an amplifier 4 and a timing generation circuit 5. The output signal of the amplifier 4 is supplied together with a reference voltage (for example, -5 volts) from a reference voltage generation circuit 6 to a difference detection circuit 7, where a difference from the reference voltage is detected. The output signal of the difference detection circuit 7 is fed back to the amplifier 4, and the gain of the amplifier 4 is controlled. That is, the gain of the amplifier 4 is controlled according to the difference detected by the difference detection circuit 17, and when the output of the amplifier 4 is large, the output of the difference detection circuit 7 is made small, and the output of the amplifier 4 is always kept at a constant value (for example, +5 volts)
I try to keep it that way.

For example, when the radiator 1 deteriorates or the light emitting surface of the radiator 1 or the light receiving surface of the infrared sensor 2 becomes dirty and the amount of light decreases, this can be done by increasing the gain of the amplifier 4 that amplifies the output of the infrared sensor 2. This is to ensure that a photoelectric conversion signal of a constant value is always obtained.

In all of the above operations, the banknote P is connected to the radiator 1 and the infrared sensor 2.
This is the operation when there is no banknote P between the radiator 1 and the infrared sensor 2. However, if the banknote P is conveyed between the radiator 1 and the infrared sensor 2, the gain control for the amplifier 4 will be performed when the banknote P is between the radiator 1 and the infrared sensor 2. It is necessary to hold it at the level before it reaches the level between it and the infrared sensor 2. That is, when the banknote P is conveyed between the radiator 1 and the infrared sensor 2,
The timing generation circuit 5 detects this and generates a timing signal (Kenshōshin@) T1 as shown in FIG. 2, and stops the function of the difference detection circuit 7 with the timing signal T1.
While holding the gain control level, the timing signal T! is supplied to the amplifier 8. While the timing signal Tl is supplied to the amplifier 8 (the banknote P is
and the infrared sensor 2), the output signal of the amplifier 4 is amplified. As a result, the output signal V of the amplifier 8 has a waveform as shown in FIG.
supplied to That is, the dense part C of the bar watermark
also has a large absorption of infrared rays, so the level of the signal decreases,
Since the coarse portion d has little absorption, the level of the signal V becomes high. The signal V thus obtained is set to a threshold level VH which is lower than that level by ΔVn.
By converting it into a value, it is possible to detect the closed valve indicated by eight points. This is performed by the data acquisition setting circuit 9, and the following processing is performed starting from these eight points. That is, when the banknote P is conveyed between the radiator 1 and the infrared sensor 2, the timing generation circuit 5 uses the output signal of the amplifier 3 to generate a signal corresponding to the bar watermark part as shown in FIG. A timing signal (gate signal) T2 is generated and supplied to the data acquisition setting circuit 9. Then, the data acquisition setting circuit 9 passes the output signal of the gate width divider 8 to which the timing signal T2 is supplied, supplies it to the sample hold circuit 10, and also performs the above-mentioned 2iIff conversion. 8 points detected, 8
A sample pulse SP and an A/D conversion pulse AP as shown in FIG. Thereby, the sample and hold circuit 10 samples and holds the signal from the data acquisition setting circuit 9 according to the supplied sample pulse SP, and supplies it to the A/D conversion circuit 11. The A/D conversion circuit 11 converts the signal from the sample hold circuit 10 into a digital signal in accordance with the supplied A/D conversion pulse AP. This A
/D converted data is transferred to RAM (Random Access Memory) via the switching circuit 12 which becomes active at this time.
memory) 13 and stored there. This RAM
The number of data stored in 13 is the number K of sample pulses SP.
be equivalent to. For example, if the area where the bar watermark exists is L and the sample interval is e, then K is shown below.

K=L/e When the data K11l is stored in the RAM 13 in this way, the switching circuit 12 is put into the inhibit state, and the switching circuit 1
4 is activated, the data in the RAM 13 is transferred to the RAM 16 managed by the CPLI (Central Processing Unit) 15. When this data transfer is completed, the CPU 15 performs a pattern matching operation between the data in the RAM 16 (that is, the detected fiber density pattern) and the standard pattern in the standard pattern memory 17 to determine the authenticity of the bar watermark. It makes a judgment and outputs the judgment result. Here, if there are seven types of banknotes P to be handled and each banknote P is different, seven types of standard patterns need to be prepared. In addition, the handling direction of banknotes P is 4 types: front, back, forward, and reverse.
If the direction is permitted, 7×4=28 types of standard patterns will be prepared. In addition, by the above-mentioned processing, R
Immediately after all the data in AM13 is transferred to the RAM 16, the switching circuit 12 is activated, and at the same time the switching circuit 14 is inhibited, so that the A/D conversion data for the next banknote P can be stored in the RAM 13. It's important.

In this way, the optical absorption band of the fibers that make up banknotes is approximately 3μ.
By focusing on the fact that the fiber components are located at m, the density and density of the fibers that make up the banknotes can be detected using infrared rays by utilizing the light absorption characteristics of the fiber components. This allows for sufficient resolution compared to conventional methods, and is less susceptible to dirt and patterns on banknotes.
In addition, since the S/N ratio is sufficiently high, watermarks made of m-thick thick watermarks on banknotes can be detected reliably and accurately, making it extremely useful for determining the authenticity of banknotes.

In the above embodiment, an infrared heater is used as the infrared radiator, but the present invention is not limited to this, and an infrared lamp may be used instead. Further, although the case where the present invention is applied to a detection device for banknotes has been described, the present invention is not limited thereto, and can also be applied to a detection device for other paper sheets such as checks or stock certificates.

[Effects of the Invention] As detailed above, according to the present invention, there is provided a paper sheet detection device that can accurately detect watermarks made of the coarse and dense fibers of banknotes, and is useful for determining the authenticity of banknotes. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG. 2 is a timing chart for explaining the operation of the large-wheel example. P...Banknotes (paper sheets), 1...Infrared radiator, 2...Infrared sensor, 5...
Timing generation circuit, 9... Data acquisition setting circuit, 10... Sample hold circuit, 11...
...A/D conversion circuit, 13, 16...RA
M, 15...CPU, 17...Standard pattern memory. Agent Patent Attorney Noriyuki Chika (Kuha 122)

Claims (8)

[Claims] (1) An infrared radiation means that emits infrared rays to the paper sheets; an infrared detection means that detects the light transmitted from the paper sheets by the infrared radiation means; and an output signal of the infrared detection means that What is claimed is: 1. A paper sheet detection device comprising: a determining means for determining the density of fibers constituting the sheet. (2) The discrimination means detects the density pattern of the fibers constituting the paper sheet using the output signal of the infrared detection means, and compares the detected density pattern with a preset standard pattern to determine whether the paper sheet is 2. The paper sheet detection device according to claim 1, wherein the paper leaf detection device determines whether the fibers constituting the fibers are dense or dense. (3) The paper leaf detection device according to claim 1, wherein the infrared radiation means emits infrared radiation having a peak of radiant energy of approximately 3 μm. (4) The paper sheet detection device according to claim 1, wherein the infrared radiation means is an infrared heater. (5) The paper sheet detection device according to claim 1, wherein the infrared radiation means is an infrared lamp. (6) The paper sheet detection device according to claim 1, wherein the density of the fibers forms a watermark. (7) The paper sheet detection device according to claim 1, wherein the paper sheet is a banknote. (8) The paper sheet detection device according to claim 1, wherein the paper sheet is a check.