JPH08110967A - Metal thread detector for paper sheets - Google Patents

Abstract

PURPOSE: To generate a stable detection output level by arranging electrode plates of a detection capacitor on the same plane so that the electrode plates with the same polarity are opposed to each other at a prescribed interval and driving the opposed electrode plates with the same polarity by respective in- phase oscillation outputs. CONSTITUTION: A capacitor part C86a consisting of a detecting electrode plate 8a and a ground electrode plate 6a arranged on the same plane and a capacitor C86b consisting of a detecting electrode plate 8b and a ground electrode plate 6b arranged on the same plane are arranged so that respective plates 8a, 8b and 6a, 6b respectively having the same polarity are arranged at a prescribed interval so as to hold a paper sheet 2 between them. The opposed electrode plates 8a, 8b and 6a, 6b are connected to a tuning circuit in an electrostatic sensor circuit 12 and driven by in-phase oscillation outputs. A detection output from the circuit 12 is inputted to a thread judging circuit 16 including a microprocessor or the like in its inside through an A/D conversion means 14, the existence of a thread is judged and outputted to the outside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a metal thread detecting device for paper sheets having a built-in metal thread.

[0002]

2. Description of the Related Art In order to prevent counterfeiting of paper sheets such as banknotes, securities, cash cards, and checks, so-called thread-embedded paper sheets in which metal or plastic is inserted between paper sheets are used in Europe and the like. in use. In these paper sheets,
The presence / absence of a thread is detected to determine whether the bill is a genuine bill or a counterfeit bill. As a device for automatically making a genuine / counterfeit determination, a device using a magnetic sensor, or Japanese Patent Laid-Open No. 4-5 is used.
A device using the electrostatic sensor described in Japanese Patent No. 4693 is known. A configuration example of a conventional metal sled detection device using such an electrostatic sensor will be described with reference to FIG. 9. The sled detection device includes an electrode detection unit 10, an electrostatic sensor circuit 12, an AD conversion unit 14, and a sled. Judgment circuit 1
6, the electrode detection unit 10 includes a detection electrode 8 formed of a conductor plate or a conductor needle, and a ground electrode 6 of the conductor plate. The ground electrode 6 and the detection electrode 8 pass the bill 2 containing the thread 4. They are arranged at the upper and lower positions with the path 18 in between, that is, facing each other with a passage gap of the paper sheet 2 interposed therebetween. In this specification, "paper sheets" include not only banknotes but also securities such as checks, tickets and bills, and the "paper" of banknotes is used in a broad concept including not only pulp but also films such as plastics. Has been done.

In such a structure, when the paper sheet 2 passes through the electrode detection section 10, it is more than when the paper sheet portion without the thread 4 passes between the detection electrode 8 and the ground electrode 6.
When the thread 4 passes, the dielectric constant between the electrodes 6-8 changes, and the change in the electrode capacitance significantly appears in the thread 4, and a signal corresponding to the change in the capacitance is output by the electrostatic sensor circuit 12. Was detected in step S3 and input to the thread determination circuit 16 via the AD conversion means 14 to determine the presence or absence of a thread.

[0004]

In such a conventional thread detecting apparatus, in order to shorten the detection time by the sensor and increase the number of processed sheets per unit time, the paper sheet is conveyed in the lateral direction and the presence or absence of the thread is detected. When I tried to judge, the following problems occurred. That is, FIG. 10 (A) corresponding to FIG. 9 shows the sheet 2a or 2b in the lateral direction.
FIG. 3 is an enlarged cross-sectional view of the electrode detection unit 10 when the sheet is conveyed, and the sheet conveyance paths 20a, 20b and 2 before and after the electrode detection unit 10 are shown.
0c and 20d are composed of good conductors such as metal, and these good conductors are grounded together with the ground electrode 6, and the electrode 8-6 is grounded to the resonator 22. When the paper sheet 2a is brought close to the detection electrode and conveyed to the conventional electrode detection unit 10 having such a configuration, an output level v1 as shown in FIG. Is high, and when the paper sheet 2b is brought close to the ground electrode 6 and conveyed, an output level v2 as shown in FIG. 10C is obtained, and it is found that the paper sheet detection level is relatively low. did. Thus, the conventional electrode detector 10 as shown in FIG.
In the above configuration, the detection levels of the paper sheet 2 and the thread 4 fluctuate greatly according to the distance between the paper sheet 2 and the detection electrode 8, and it is extremely difficult to set a stable thread detection level, and it is a short hand. In the case of conveyance, the presence or absence of a thread has to be determined by the magnitude of the absolute value of the detection level, and there is a problem that the influence of the fluctuation of the detection output depending on the conveyance position is extremely large. When a sheet without threads is passed through the electrode detection unit 10, the output level v as shown in FIG.
3 waveforms were obtained, and it was found that this output level was generally lower than the output level v2 when the sled 4 was brought close to the ground electrode 6 and conveyed. In addition, in the configuration of the conventional electrode output unit 10, the paper sheet 2 is attached to the electrode detection unit 10
At the time point t1 when the paper sheet 2 enters the sheet and the time point t2 when the paper sheet 2 leaves the electrode detection unit 10, the electric field distribution between the electrode plates 8-6 as shown in FIG. The large peak waveform that was exceeded is shown in Fig. 10 (B).
Observed as shown in (D) to (D), this peak waveform makes the difference in the detection level in the absence of the thread more unstable, and the above-mentioned spike-like peak variation in the variation in the thread detection level due to the variation in the passing position. However, there is a problem in that it is difficult to judge whether a thread is present or not.

The present invention has been made under the circumstances described above, and an object of the present invention is to eliminate the above-mentioned peak noise and to provide a stable detection output level which is not affected by the distance between the paper sheet and the electrode. An object is to provide a metal thread detection device for paper sheets that can be generated.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a metal thread detection device for paper sheets, and the above object of the present invention is to provide a paper thread in a passage path in which a metal thread is built. One set or a plurality of sets of detection electrodes and ground electrode plates, which are arranged on the same plane that form the capacitor section, are respectively brought close to the front and back surfaces of the leaves, and each electrode plate having the same polarity faces each other. Arranged at intervals,
Achieved by driving these facing electrode plates of the same polarity with oscillation outputs of the same phase to form an electrostatic sensor and analyzing the signal from this electrostatic sensor to detect the presence or absence of the metal thread. To be done.

[0007]

According to the present invention, the detection electrode plate and the ground electrode plate are arranged on the same plane to form a capacitor section, and these electrode plates are arranged at predetermined intervals so that the electrode plates having the same polarity face each other. At the same time, these opposed electrode plates of the same polarity are driven by oscillation outputs of the same phase to form an electrostatic sensor, so that the electric field distribution between the opposed electrode plates is symmetrical and has the same strength. An electric field can be generated, and a detection output that is not affected by the paper sheet passage position can be generated. In addition, the capacitor is not formed between the facing electrode plates, but is formed between the electrode plates arranged on the same plane, so the electric field is disturbed when the paper enters or leaves the electrode detection unit. Therefore, it is possible to prevent the generation of the peak waveform when the paper enters and leaves the electrode detection unit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the sheet metal thread detecting device of the present invention will be described with reference to FIGS. First,
FIG. 1 corresponding to FIG. 9 is a diagram showing an example of the configuration of the metal thread detecting device of the present invention, in which the detection electrode plate 8 is provided in the passage path for short-side conveyance of the paper sheet 2 having the thread 4 built therein.
a and the ground electrode plate 6a, which are arranged on the same plane, and the capacitor portion C86a, the detection electrode plate 8b, and the ground electrode plate 6
and a capacitor C86b arranged on the same plane, which is composed of b, and electrode plates 8a- having the same polarity so as to sandwich the paper sheet 2.
8b, 6a-6b are arranged at a predetermined interval so that they face each other, and these facing electrode plates of the same polarity are input to the tuning circuit of the electrostatic sensor circuit 12, and the detection output thereof is fed to the AD conversion means 14. It is adapted to be input to a thread determination circuit 16 having a built-in microprocessor or the like via the above, to determine the presence or absence of a thread, and output it to the outside.

Therefore, as shown in FIG. 4, the electrostatic sensor circuit 12 drives the external tuning circuit 30 with a high frequency oscillator circuit 24 for generating a high frequency bias sine wave of several tens of kHz to several tens of MHz and a high frequency bias output. Amplifier circuit 2 that also functions as an impedance converter to amplify the signal into a signal sufficient for
6, a tuning circuit 30 including an inductance element L and capacitor portions C86a and C86b, and an output of the tuning circuit 30 is a diode D1.
The output is detected by a capacitor C3 and a resistor R1.
The amplifier Q1 is smoothed through a low-pass filter and is output to the outside as a sensor, and the resonance sensitivity adjusting circuit 40 that monitors the detection output and adjusts the resonance sensitivity of the tuning circuit 30.

Incidentally, the above-mentioned capacitor portions C86a and C8
6b is preferably formed on the capacitor substrate 7 having a pattern as shown in FIG. 2A or 2B, and the substrate material is preferably a glass epoxy substrate having low hygroscopicity. or,
The high frequency oscillating circuit 24 is not specially provided, and in the case of the frequency in the above range, it is also possible to generate by dividing the basic clock of the microprocessor. In the present invention, an oscillating frequency of around 300 KHz is generated. I am using.

The operation of the above structure will be described with reference to FIGS. 3 and 5. Between the electrode plates 8a-6a and 8b-6b forming the capacitor section of the tuning circuit 30, there are opposed electrode plates. Since they are driven by oscillation outputs having the same phase, an electric field as shown in FIG. 3 (A) is usually formed, and these are formed by capacitors C86a and C86b with respect to the signal source as shown in FIG. 3 (B). Since it is equivalent to the case of being inserted in parallel, the equivalent circuit is shown in Fig. 3.
It becomes like (C). Therefore, the resonance frequency of this tuning circuit is expressed by the following equation.

[0012]

## EQU1 ## fr = 1 / 2π√ (L * ((C86a + C86
b) + ΔC)); L: Inductance of the inductance element L C86a, C86b: Capacitance of the electrode plate capacitor ΔC: Change capacitance caused by movement of paper sheet and sled In equation 1, ΔC is a capacitance change component caused by movement of paper sheet. Therefore, ΔC = 0 in the idle state where there are no paper sheets, ΔC = ΔC1 in the case of a paper sheet without threads, and ΔC = ΔC2 in the case of a paper sheet with a built-in thread.
C1 <ΔC2. Then, when the paper sheet 2 enters the capacitor parts C86a and C86b, as shown in FIG. 3 (A), symmetrical repulsive electric fields are generated between the ground electrodes 6a and 6b and the detection electrodes 8a and 8b. Since E1 is generated, unlike the electric field E3 in one direction shown in FIG. 11,
Symmetrical fluctuating electric fields are generated. Therefore, paper sheet 2
Is conveyed at a distance close to the detection electrode plate 8a or is far away from the detection electrode plate 8a, the capacitor C86
The total capacitance change of a and C86b is almost constant at any position, and in the case of a paper sheet with a built-in sled, the output waveform of the electrostatic sensor circuit 12 is an output at a constant level v10 as shown in FIG. 5 (A). Was done. Further, in the case of a paper sheet that does not include a thread, the output waveform of the electrostatic sensor circuit 12 is as shown in FIG. Further, in these output waveforms, the entry of paper sheets as shown in FIGS. 10 (B) and (C),
No peak disturbance noise was observed at the time of exit, and it was confirmed that the effect of driving the electrode plates of the capacitors on the same plane and driving the opposing electrode plates with the same phase oscillation output was well exhibited.

In the case of the electrostatic sensor circuit 12 having the detection capacitor having such a configuration, the output waveform thereof is digitized by the AD conversion means 14, and the thread determination circuit 16 determines that the output level is within a predetermined allowable setting range. From the waveforms of FIGS. 5A and 5B, it can be easily and accurately / stably executed to judge that there is a thread and to judge that there is no thread if it is outside the above-mentioned allowable setting range and output it to the outside. it is obvious.

It will be apparent to those skilled in the art that the AD conversion means 14 and the thread determination circuit described above can all be configured by analog circuits using analog comparators and the like. Further, the detection capacitor with a ground electrode plate as shown in FIG. 1 is more effective when the paper sheet conveyance path is provided on the conveyance path formed of a defective conductor such as synthetic resin.

FIG. 6 shows the output waveform of the electrostatic sensor circuit 12 when the sheet 2 is conveyed in the longitudinal direction.

FIG. 7 corresponding to FIG. 1 is a diagram showing another configuration example of the metal thread detecting device of the present invention,
The devices with the same number respectively perform the same function, and the paper entrance and exit ports 20a and 20b and the paper exit and exit ports 20c and 20d are respectively made of aluminum,
The ground electrode plate 6a is made of a good conductor such as stainless steel or brass.
6 to 6b are omitted, and the ground electrode plate is made of these good conductors. Therefore, the detection capacitor C8a is composed of the detection electrode plate 8a and the conveyance paths 20a and 20c, the detection capacitor C8b is composed of the detection electrode plate 8b and the conveyance paths 20b and 20d, and the capacitor substrate 7 is shown in FIG. The patterns shown in A) and (B) are formed.

Even when the detection capacitor having such a structure is used, there is a gap between the capacitors C8a and C8b as shown in FIG.
Since a symmetrical electric field as shown in FIG.
Output waveforms of the electrostatic sensor as shown in (A) and (B) can be generated, and the presence / absence of a thread can be determined easily and accurately / stablely.

[0018]

As described above, according to the metal thread detecting device for paper sheets of the present invention, the electrode plates of the detecting capacitors are arranged on the same plane, and the electrode plates of the same polarity are opposed to each other and have a predetermined shape. They are arranged so as to face each other at intervals, and the electrode plates of the same polarity, which are opposed to each other, are driven by the oscillation outputs of the same phase, so that the electric field distribution between the opposed electrode plates is symmetrical and of the same intensity. An electric field can be generated, and a detection output that is not affected by the passing position for conveying the sheet in the lateral direction can be generated. In addition, because the capacitor is not formed between the electrode plates facing each other but between the electrode plates arranged on the same plane, the disturbance of the electric field when the paper enters or leaves the electrode detection unit. Can be prevented
It is also possible to suppress the generation of a peak waveform when a paper sheet enters or leaves the electrode detection unit. Therefore, the presence or absence of the thread can be stably and accurately detected even when the paper sheet is conveyed in the lateral direction, and the processing time of the detection device can be significantly shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an embodiment configuration of a metal thread detecting device of the present invention.

FIG. 2 is an example of a sensing capacitor electrode pattern of the present invention.

FIG. 3 is a diagram showing an electric field distribution of the detection capacitor of the present invention and its equivalent circuit.

FIG. 4 is a circuit diagram showing a configuration example of an electrostatic sensor circuit of the present invention.

FIG. 5 is an output waveform example for explaining the operation.

FIG. 6 is an example of an output waveform of an electrostatic sensor when a sheet is conveyed in the longitudinal direction.

FIG. 7 is a diagram showing another configuration example of the metal thread detecting device of the present invention.

FIG. 8 is a diagram showing an example of a detection capacitor electrode pattern.

FIG. 9 is a diagram showing a configuration of a conventional sled detecting electrostatic sensor circuit.

FIG. 10 is a diagram showing a structure of a detection capacitor section and an example of a sensor output waveform.

FIG. 11 is a diagram showing an electric field distribution of a conventional detection capacitor unit.

[Explanation of symbols]

 2 paper sheet 4 thread 6,6a, 6b, 6c, 6d ground electrode plate 7 substrate 8, 8a, 8b detection electrode plate 12 electrostatic sensor circuit 14 AD conversion means 16 thread determination circuit 22 oscillation circuit 30 tuning circuit

Claims (4)

[Claims] 1. A detection electrode and a ground electrode plate, which are arranged on the same plane constituting a capacitor part, so as to approach a front surface and a back surface of the paper sheet, respectively, to a passage path of the paper sheet containing a metal thread. One or a plurality of sets are arranged at a predetermined interval so that the electrode plates of the same polarity face each other, and the electrode plates of the same polarity which face each other are driven by oscillation outputs of the same phase, respectively, and electrostatically generated. Configure the sensor,
A metal thread detecting device for banknotes, wherein the presence or absence of the metal thread is detected by analyzing a signal from the electrostatic sensor. 2. The detection device for a metal thread of a sheet according to claim 1, wherein the detection electrode plate is arranged in the center, and the detection electrode plate is surrounded by the ground electrode plate. 3. The metal thread detecting device for paper sheets according to claim 1, wherein the ground electrode plate is also used as a good conductor of the paper path. 4. The metal thread detecting device for a paper sheet according to claim 1, wherein the paper sheet is conveyed in a short side direction.