JPS5860203A - Method for identifying circular body - Google Patents

Abstract

PURPOSE:To identify a circular body, with regard to the identification of the circular body such as a coin, by altenately energizing a magnetic flux generator by a plurality of sine wave currents whose frequencies are different, converting the output of the magnetic flux generotor into the peak level of the signal component of each frequency, and individually obtaining the attenuating rate of respective signal component. CONSTITUTION:A signal switching device 7 sequentially switches the output of oscillators 5 and 6 of 20 and 4 kHz. A voltage-current converter 8 converts the voltage to the current, and supplies the signals having a current waveform analogous to the voltage waveform of a signal source to an exciting coil 22. The output of a magnetism-electricity converter 3, which is the magnetic flux detector in a coin detector 1, is amplified to an appropriate level by an amplifier 9. The output of a peak holder 10 is converted into a digital quantity by an A/D converter 11, and sent to a microcomputer 12, where the attenuation rate of the signal component of each frequency (20kHz and 4kHz) is individually obained. The result is applied to the corresponding tape wherein the kind of the coin 4 and the attenuation rate are stored in advance, and the passed coin is identified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for identifying circular objects such as coins, and more particularly to a method for identifying the type of circular object by reading the change in magnetic flux that occurs when the circular object passes through a passage. It is something.

Many of the coin identification methods in vending machines, currency exchange machines, etc. that have been put into practical use use mechanical or optical detectors. However, although this type of identification method can measure the external shape of a coin, it cannot qualitatively or consistently measure it, so it has the disadvantage that it cannot distinguish between genuine coins and fake coins. Therefore, an identification method that magnetically detects the passage of a coin has been proposed so that the type and quality of the coin (regular and pseudo) can be identified at the same time. One of the useful magnetic identification methods is to utilize the eddy current loss that occurs inside the coin.
That is, based on the property that the eddy current loss that occurs when a conductor is placed in an alternating magnetic field is proportional to the size of the conductor, its electromagnetic properties (especially conductivity), and the square of the alternating frequency, the size and conductivity are proportional to each other. The reason why it is possible to identify different types of coins by the magnitude of the eddy current loss is that the magnetic flux generated by the eddy current has a deterrent effect against changes in the main magnetic flux of the magnetic flux generator. This is clear from the electromagnetic principle that acts as

However, even with magnetic identification methods that utilize such characteristics, when the object to be identified is a coin, it may be inconvenient with today's coin types. This will be explained with reference to FIG. Figure (a) shows the attenuation rate-frequency characteristics of a coin made of copper (10 yen coin), and figure (b) shows the attenuation rate-frequency characteristic of a coin made of cupronickel (100 yen coin). It shows. The positional relationship between the coin detector and the coin to obtain this characteristic is shown in FIG. In the same figure, a coin detector 1 includes a pot-shaped core (A 21) with a coil 22 wound thereon, a magnetic flux generator 2 for generating magnetic flux, and a magnetic flux generator 2 which is arranged opposite to this magnetic flux generator 2 and converts the entire amount of the magnetic flux into a voltage. The coin 4 is placed between the magnetic flux generator 2 and the magnetoelectric converter 3.The characteristic curves in FIG. The output voltage of the magnetoelectric converter 3 is converted into an attenuation rate when the frequency of the excitation current applied to the coil 22 is changed for each thickness (d, -, d3).

From this figure, we can see that the frequency band where it is easy to identify copper coins (identification of thickness d) is in the low frequency range, while it is almost impossible to identify in the high frequency range above about 5.10 KHz, while it is easy to identify cupronickel coins. (Identification of thickness d) It can be seen that the frequency band is in the high range of about 10 KHz and is difficult to identify in the low range. The reason for drawing such a characteristic curve is that, as mentioned above, since the conductivity of the coins differs, the eddy current loss also differs. Therefore, it can be seen that with today's coin types, it is difficult to identify all coins with high precision without using excitation currents of multiple frequencies.

One way to solve this problem is to make the excitation current waveform a non-sinusoidal wave with harmonic components, such as a rectangular wave, and separate the output of the magnetic flux detector into fundamental wave and harmonic signal components. An identification method has been proposed in which the attenuation rate of each coin is determined and the coin identification is substantially performed using excitation currents of a plurality of frequencies. This identification method uses harmonic components as excitation currents at high frequencies, so in theory, with one non-sinusoidal current, it is possible to obtain results equivalent to identification using excitation currents in multiple frequency bands with equal constraints. This has the advantage that only one excitation coil is required.

However, in this identification method, since the frequencies of the fundamental wave and harmonics are in a fixed relationship, it is not possible to select the most suitable frequency for identification, and furthermore, the amplitude level of the harmonics is higher than that of the fundamental wave. It has the disadvantage that the output level of the harmonic component in the magnetic flux detector becomes extremely small, which is surprising because the eddy current loss is large for high-frequency harmonics. ta0pJ1chi,
The above identification method has inherent limitations in selecting multiple frequencies suitable for identification, and there is a large gap between the signal levels of the fundamental wave component and harmonic components in the magnetic flux detector.
Therefore, it was necessary to increase the dynamic range of the detector itself, and a high gain amplifier was required, making it impossible to perform efficient identification.

In order to eliminate the above-mentioned drawbacks, the present applicant has filed a patent application filed in
No. 180750 "Circular object identification method" uses a single excitation coil and uses multiple excitation currents having signal components of arbitrary frequencies and levels to achieve highly accurate and highly efficient identification. proposed a method.

To summarize this identification method, the excitation current of the magnetic flux generator is a composite current that combines multiple sinusoidal currents with different frequencies, and the output of the magnetic flux detector is separated into the original signal components of multiple frequencies through a filter. Furthermore, the attenuation rate of each signal component is determined individually, and circular objects such as coins are identified based on the results. Therefore, according to this method, before forming the composite current, it is possible to arbitrarily select the frequency and signal level for each of the plurality of sinusoidal currents that are the constituent currents of the composite current. .

However, in the identification method according to this proposal, it is necessary to separate the output of the magnetic flux detector into the original signal components of multiple frequencies through a filter, so at least a signal processing system for each frequency is required. In general, a multiplexer is required to selectively take in the signals of the processing system, which inconveniently complicates the circuit configuration of the entire device and increases cost.

The purpose of the present invention is to enable the frequency and level of each of a plurality of sine wave signals that are signal sources to be arbitrarily selected, and to enable highly accurate and highly efficient identification, as well as to simplify the circuit configuration. Another object of the present invention is to provide a method for identifying a circular object, which is inexpensive and can provide a compact device.

To summarize the invention, energizing the magnetic flux generator with a plurality of sinusoidal currents, each having a different frequency, converts the output of the magnetic flux detector to the peak level of the signal component at each frequency; The attenuation rate of each signal component is determined individually and circular objects are identified based on the results. Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a block diagram of a coin identification device to which a coin identification method according to an embodiment of the present invention is applied. Moreover, FIG. 4 shows the signal waveforms of the main parts in FIG. C).

In FIG. 3, 5 is a 20 KHz sine wave oscillator, and 6 is a 4 KHz sine wave oscillator. In this example, we will use two sine wave oscillators as signal sources,
Also, their frequency is 20KH, which is suitable for identifying cupronickel coins.
z and 2KHz, which is suitable for identifying other coins.

The signal switch 7 is a circuit that sequentially switches the outputs of the oscillators 5 and 6 to form signals with different frequencies alternately in time series. Switch the output.

The voltage-current converter 8 performs voltage-current conversion on the output signal of the signal switch 7 and supplies the converted signal to the excitation coil 22 of the magnetic flux generator 2 . The reason why the voltage-to-current converter 8 is placed before the magnetic flux generator 2 is to eliminate the influence of the rebound voltage of the excitation coil 22 that occurs when switching the output of the oscillator 5.6. That is, when a normal voltage amplifier is generally used in place of this voltage-current converter, rebound stain pressure is generated in the excitation coil 22 in the discontinuous state when the oscillator is switched by the switch 7.
The excitation current does not become a sine wave due to the influence of the rebound b voltage, but becomes a transient asymmetric wave due to the release of energy stored in the impedance of the excitation coil 22. The effect begins to appear in step 4.The identification method for detecting such changes in magnetic flux requires that the magnetic flux generated from the excitation coil be proportional to the signal source, that is, the excitation current waveform should be similar to the signal source voltage waveform. Therefore, if you use the voltage-to-current converter shown in this example instead of a normal voltage amplifier that performs voltage-to-voltage conversion, you can generate a signal with a current waveform similar to the voltage waveform of the signal source. This means that it can be supplied to the excitation coil 22.

The output of the magnetoelectric converter 3, which is a magnetic flux detector, is amplified to an appropriate level by an amplifier 9 and input to a peak holder 1°. The peak holder 1o is successively reset by a reset signal synchronized with the switching signal to the switch 7, and holds the peak value of the signal (e) during a certain delay time. The output of this peak holder 10 is converted into a digital quantity by an A/D converter 11 and then sent to a microcomputer 1.
Sent to 2. The microcomputer 12 determines how much the output of the A/D converter 11 changes between when the coin 4 is present and when the coin 4 is not present.
The attenuation rates of the signal components (0 KHz and 4 KHz) are individually determined, and the results are applied to a pre-stored correspondence table of coin types and attenuation rates to identify passing coins.

In addition, when two frequencies of 20K) Tz and 4KHz are used, according to experiments, the change in thickness d is first affected by the high frequency edge component (20KHz).
has the largest change in attenuation rate, followed by brass (5 yen coin), aluminum (1 yen coin), and copper (10 yen coin), which exhibits large attenuation almost independently of d. In contrast, for low frequency components (4KITz), copper exhibits the largest variation in attenuation rate, followed by aluminum, brass, and cupronickel, with cupronickel having almost no attenuation regardless of d.

Therefore, once the material and thickness are determined, the attenuation rate for that coin is 2.
Since it is uniquely determined by the 0 KHz component and the 4 KHz component, it is extremely easy to create a table stored in advance in the microcomputer 12 that represents the correspondence between the attenuation rate and the type of coin.

Note that it goes without saying that the amplitude levels of the signals (a) and (b) can be adjusted arbitrarily, and may be set to an appropriate value taking into consideration the degree of attenuation rate, the dynamic range of the amplifier 9, etc. In the above embodiments, a voltage-to-current converter is used, but if the transient time due to the bounce voltage of the exciting coil can be made short enough, or if the voltage can be made small enough to be ignored, a normal voltage can be used. An amplifier may also be used.

As described above, according to the identification method of the present invention, there is only one signal processing system after magnetic flux detection regardless of the number of signal sources, and the circuit configuration is extremely simple since no filters or the like are required. become. In addition, it has the advantage of having only one excitation coil, and the optimum frequency for identifying coins can be selected, and the oscillation level of each sine wave oscillator is also set to a level that allows for the most efficient identification. I can do it. Therefore,
This has the effect of further promoting miniaturization, lower cost, and higher precision of identification devices to which the present invention is applied.

Note that as the magnetoelectric transducer mentioned in the above embodiments, for example, a Hall element, a magnetoresistive element, or a magnetic diode is used. Further, the application area of the identification method according to the present invention includes identification devices for iron bars and iron pipes in addition to coins.

[Brief explanation of the drawing]

Figures 1 (a) and (b) show the attenuation rate-frequency characteristics for different coin materials, and Figure 2 shows the coin detector used to obtain the previous characteristics and the same detector and coins. Indicates the positional relationship between Further, FIG. 3 shows a block diagram of a coin identification device to which a coin identification method according to an embodiment of the present invention is applied,
FIG. 4 shows a signal waveform diagram of the main parts of the device. 1... Coin detector, 2... Magnetic flux generator, 3
... Magnetoelectric conversion element (magnetic flux detector), 4... Coin, 5
．． 6...Sine wave oscillator, 7...Switcher,
8... Voltage-current converter, 10... Peak holder, 12... Microcomputer. Applicant Kubota Iron Works Co., Ltd. Agent Patent Attorney Hisao Komori

Claims (2)

[Claims] (1) A magnetic flux generator that forms a magnetic flux that crosses a path of a circular object, and a magnetic flux detector that is interposed in a part of the magnetic path through which the magnetic flux passes, and the magnetic flux that is generated when the circular object crosses the magnetic flux. In a method for identifying a circular object, the circular object is identified by detecting the amount of change with the magnetic flux detector. The magnetic flux generator is alternately energized with a plurality of sinusoidal currents having different frequencies, and the output of the magnetic flux detector is converted to the peak level of the signal component of each frequency via a peak holder. Circular object identification method 0 in which the attenuation rate of signal components is individually determined and circular objects are identified based on their convergence. (2) The circular object identification method according to claim 1, wherein the plurality of sine wave currents are obtained by voltage-current conversion of an output signal of a sine wave oscillator.