JP4128652B2 - Magnetic sensor for discriminating magnetic characteristics of magnetic material and characteristic discriminating apparatus using the magnetic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor for discriminating the magnetic characteristics of a magnetic material and a characteristic discriminating apparatus using the magnetic sensor.
[0002]
[Prior art]
Conventional measures to prevent counterfeiting of securities and cards include those using special printing technology that is generally difficult to forge, such as holographic printing, barcodes and designs printed with magnetic ink, ultraviolet rays, infrared rays, etc. There are known information recording media in which printing is performed with special ink that reacts, and resin pieces, threads, or metal pieces are embedded in paper or resin.
In order to determine the authenticity of such specially printed information recording media, a visual comparison with authentic products, a method of detecting reflection and absorption from ink by ultraviolet and infrared irradiation, and reflection by radio waves , A method for detecting the amount of absorption and a method for detecting a magnetic amount or pattern applied by a magnetic sensor are known.
[0003]
In such a case, the structure of a magnetic head (for example, Model SST-80HPT Saneitech Co., Ltd.) generally used for detecting minute magnetism is shown in FIG. Here, 21a, 21b and 21c are magnetic cores, 22 is an exciting coil wound on the central magnetic core 21a, 23 is a sense coil wound on the outer magnetic core 21b, and 24 is on the outer magnetic core 21c. A compensation coil 25 is wound around a head gap formed between the central magnetic core 21a and the outer magnetic core 21b.
Fig. 9 shows the magnetic head gap (width I gap) and the magnetic field intensity distribution in the vicinity (reference: digital magnetic recording by Makoto Kizawa, Shokodo).
Since the gap width I of the magnetic head is about 0.1 to 0.4 mm, it is narrower than the size of the magnetic material to be detected. Therefore, as a magnetic field necessary for obtaining the magnetic characteristics, only a magnetic field in which the region occupied by the leakage magnetic flux is narrow and the strength of the magnetic field varies greatly depending on the position within the region can be obtained. For this reason, when an attempt is made to detect a change in magnetic flux due to a change in the magnetic field strength, the magnetic field strength acting on the magnetic material is not uniform, and the integration of the magnetic flux of the magnetic material excited by a different magnetic field strength. Can only be obtained as a value.
[0004]
Here, when V is the detection voltage, B is the magnetic flux density, H is the magnetic field strength, and μ is the magnetic permeability of the magnetic material (however, it is non-linear), the detection voltage V and the magnetic flux density B are expressed by the following equations (1) and (2). It is expressed in
[Expression 1]
V = dB / dt (1)
B = μH (2)
(1) From the equation (2), considering the effects of the partial magnetic field strengths dH ₁ , dH ₂ , and dH ₃ ,
[Expression 2]
V = μd (H ₁ + H ₂ + H ₃ ...) / Dt (3)
It is. For this reason, this magnetic head has a drawback that the difference in the holding force Hc cannot be clearly separated.
[0005]
FIG. 10 is an example of characteristics measured with a narrow gap magnetic head, and FIG. 10A shows BH characteristics I and II of magnetic materials having different holding forces Ha and Hb. FIG. 10B shows the detection voltage (V = dB / dt) detected from each material when a uniform magnetic field acts on the entire magnetic material. When excited with an intensity greater than the holding forces Ha and Hb, a ferromagnetic material having a large squareness ratio generates a pulse voltage. If the holding force values are different, two pulses having a phase difference are detected. . Since the intensity of the magnetic field acting on each part of the magnetic material is different in FIG. 10C, the detection pulse becomes an integral value from each part as shown in Equation (3), and a clear phase difference can be detected. Can not.
[0006]
Next, a magnetic head having a wide gap has the disadvantages that the influence of the periphery of the head cannot be ignored because the magnetic path is wide, and that it is difficult to generate a strong magnetic field due to an increase in magnetic resistance. In addition, when there is metal around the head, the balance between the sense signal and the compensation signal is lost, and it becomes difficult to cancel the excitation signal component in the detection output. become unable.
[0007]
In general, when the gap length is increased, the magnetic resistance in the magnetic circuit is increased, and it is difficult to obtain a strong magnetic field strength. The reason is as follows.
Assuming that the relative permeability of the magnetic head is μs, the length of the axis of the magnetic head is L, the gap length is La, the total number of turns is N, and the current to be applied is I, the magnetic field generated in the gap is
[Equation 3]
H = μsN1 / (L + μsLa) (4)
Since this expression (4) is established when L <μsLa, μs is about 2000 when a ferrite material is taken as an example. Therefore, when L is 100 mm, La is 100/20000 = 0. It is not established unless it is less than 05.
[0008]
Next, for authenticity determination of information recording media, a safety line is used to store safety assurance data using ferromagnetic foils and threads, and a certain kind of ferromagnetic material has a peculiarity. There is a method previously proposed by the applicant of the present application that uses a magnetic property to determine the authenticity of a safety-protective paper (see Japanese Patent Application No. 5-196688, “Safety-Protective Paper and Its Authenticity Determination Device”).
Furthermore, when a ferromagnetic material is used as a part of an information recording material, a change in magnetic strength or a change in magnetic characteristics due to heat, slit width, etc. is detected by a magnetic head or a magnetic coil, and the change is meaningful. It has been used as data (see Japanese Patent Application No. 6-291994, “Safety Protective Paper and its Authenticity Determination Device”).
Also, as one of the methods for discriminating the unique magnetic properties of the ferromagnetic material, there is a true / false discrimination method using the magnetic history properties of the ferromagnetic material due to the change of the excitation magnetic field strength (Japanese Patent Application No. Hei 07-018343). No. “Safety Protective Paper and its Authenticator”).
[0009]
[Problems to be solved by the invention]
As presented in Japanese Patent Application No. 5-196688 "Safety Protective Paper and its Authenticity Judgment Device", it is determined that a ferromagnetic material having magnetic properties that cannot be easily counterfeited by the alloy ratio and manufacturing method is the material itself. As a technique for this, it is shown that even a slight difference in magnetic characteristics can be easily discriminated by examining magnetic hysteresis characteristics due to changes in the excitation magnetic field strength.
However, in order to discriminate a large amount of small pieces attached to paper or a plastic card at a high speed, the discriminating apparatus tends to be large.
For example, when cards with a 1 mm width magnetic material piece are passed through a discrimination device at a speed of 10 m / s, it is necessary to detect magnetic history characteristics by means such as modulating the excitation signal within 100 μs. Therefore, there are drawbacks such as an increase in excitation frequency.
[0010]
Further, when processing a large amount in a non-contact manner, the magnetic characteristics (coercive force Hc, magnetic flux density Bm, squareness ratio, etc.) of the magnetic material to be detected are detected and compared as absolute values. Since it is difficult to apply the magnetic material to a magnetic material, it has been difficult with a conventional magnetic sensor.
[0011]
A first object of the present invention is to provide a magnetic sensor that can easily detect magnetic characteristics of a magnetic material used in an information recording medium.
A second object of the present invention is to provide an apparatus for discriminating magnetic properties of a magnetic material that has a simple structure and high discrimination ability.
[0012]
[Means for Solving the Problems]
In order to achieve the first object of the present application, a magnetic sensor for discriminating magnetic characteristics of a magnetic material according to the present invention comprises:
A soft magnetic core having an E-shaped longitudinal section;
An exciting coil wound on the central arm of the soft magnetic core;
A sensing coil wound on one of the two outer arms of the soft magnetic core;
A compensation coil wound on the other of the two outer arms of the soft magnetic core;
Provided with a guide path that guides the magnetic body to be detected, arranged so as to bridge the end of the central arm of the soft magnetic material magnetic core and the end of the outer arm around which the detection coil is wound. A non-magnetic hard material guide plate formed as follows:
A comparative magnetic material of known magnetic properties disposed on or in the guide plate along the guide path of the guide plate and located in the bridging portion;
With
When the detection target magnetic body travels along the guide path, a detection output indicating the magnetic characteristics of the detection target magnetic body is obtained from the detection coil.
[0013]
In order to achieve the second object of the present application, the magnetic property discrimination device for a magnetic material according to the present invention comprises:
A soft magnetic core having an E-shaped longitudinal section;
An exciting coil wound on the central arm of the soft magnetic core;
A sensing coil wound on one of the two outer arms of the soft magnetic core;
A compensation coil wound on the other of the two outer arms of the soft magnetic core;
Provided with a guide path that guides the magnetic body to be detected, arranged so as to bridge the end of the central arm of the soft magnetic material magnetic core and the end of the outer arm around which the detection coil is wound. A non-magnetic hard material guide plate formed as follows:
A comparative magnetic material of known magnetic properties disposed on or in the guide plate along the guide path of the guide plate and located in the bridging portion;
An excitation power source for supplying an excitation current to the excitation coil;
A differential amplifier that takes out the difference between the detection output from the detection coil and the compensation output from the compensation coil and takes out the differential detection output that suppresses the influence of the excitation magnetic field due to the excitation current;
A phase comparison circuit for extracting phase information corresponding to a phase difference between the differential detection output by the magnetic material for comparison from the differential amplifier and the differential detection output by the magnetic material to be detected;
A determination circuit that compares the phase information from the phase comparison circuit with previously stored standard information to determine the magnetic characteristics of the magnetic material to be detected;
It has the composition provided with.
Here, the excitation current from the excitation power supply can be a sine wave of at least one wavelength that oscillates intermittently or a sine wave modulated so as to have a small distortion component.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In a magnetic sensor, when the gap length is long, the magnetoresistance is determined by the path of the leakage magnetic field from the gap, and the strength of the magnetic field cannot be uniquely determined, and an experimental or simulation method is used.
In the present invention, a magnetic path is formed on the same surface close to the detection signal in order to obtain a compensation signal by making the shape of the magnetic core E type. For this reason, even if the metal approaches, the detection side and the compensation side are affected by the same effect, so that they can be canceled out and a minute change in magnetic flux can be detected.
In the magnetic head according to the present invention, ferrite is used for the magnetic core, and the maximum magnetic field strength is about five times that of the central magnetic field of a finite-length air-core coil having the same number of turns.
That is, in order to obtain a strong magnetic field with a magnetic head having a wide gap, there is a limit to the contribution due to the magnetic permeability of the magnetic core, and it is necessary to increase the total number of turns and the current. When the total number of turns is increased, the self-inductance is increased and the excitation frequency cannot be increased, and the conveyance speed of the discriminating object is limited.
When the current is increased, the generation of heat due to the resistance value of the winding cannot be ignored, and the excitation power source becomes large.
[0015]
(A) Ease of discriminating magnetic characteristics The wide gap magnetic sensor according to the present invention can have a uniform magnetic field sufficiently larger than the size of the magnetic material to be discriminated. Equations (1), (2) to (5) The detection voltage V shown in FIG.
[Expression 4]
V = dμH / dt (5)
However, it is difficult to accurately measure the phase information with respect to the excitation magnetic field strength change of the detected pulse waveform as an absolute value for the following reason.
"Phase variation of sensor and amplifier system"
It is difficult to make the magnetic field excitation magnetic field strength and phase variations of the magnetic sensor, detection amplifier, etc. constant.
Therefore, there is a drawback that phase information cannot be compared with absolute values when authenticity determination is performed. In this case, if a magnetic material whose magnetic properties are known in advance is incorporated in the magnetic sensor, the degree of opening between peaks with the measured material is measured even if the excitation magnetic field strength or the phase of the amplifier system changes. Therefore, it is possible to easily determine authenticity.
[0016]
(B) Advantages of a sensor incorporating a magnetic material Although a wide gap type magnetic sensor can produce a uniform magnetic field in a wide area, there is a limit. FIG. 1 shows the magnetic field strength produced by the magnetic sensor of the embodiment of the present invention. The portion that can be regarded as uniform is a portion of 10 mm 2 in the center of the gap, and the peripheral portion gradually becomes smaller.
This means that when it is necessary to continuously determine the authenticity of the object to be measured, such as a card, it passes through the part where the magnetic intensity is different. It becomes difficult to deal with.
If there is a reference pulse having a reference phase and amplitude, it is possible to easily determine the difference in magnetic characteristics. The pulse from the moving magnetic material of the previous example is detected as a moving pulse as indicated by a dotted arrow in FIG. Since the movement pulse moves to a certain position and moves in the opposite direction, it is only necessary to compare the position changed to the maximum with the reference pulse.
[0017]
In the magnetic characteristic discriminating apparatus, the magnetic characteristic has complicated elements such as magnetic permeability, saturation magnetic flux density, squareness ratio, and initial magnetic permeability to express the characteristic. For example, even if only the magnetic permeability is taken, it is generally non-linear in ferromagnetic materials, and the non-linearity also depends on conditions such as excitation frequency, excitation intensity, temperature, etc., so there are subtle differences. Discriminating is disadvantageous in increasing the burden on the discriminating device.
In the present invention, when the direct display method is used, if the same magnetic material as the reference magnetic material is used as the reference magnetic material, it can be easily discriminated simply by checking whether the detection pulse and the reference pulse overlap at all. Therefore, a simple discrimination device can be manufactured.
In the characteristic determination apparatus according to the present invention, a pulse having a reference phase and amplitude is always present on the display surface by incorporating a magnetic material having similar magnetic characteristics and a known magnetic characteristic into the magnetic sensor. Therefore, authenticity can be easily and accurately determined by comparing the magnitudes of the phase differences.
[0018]
【Example】
FIG. 3 shows an embodiment of the magnetic sensor of the present invention. Reference numeral 1 denotes a magnetic core of a magnetic sensor, which uses a ferrite material having an E-shaped longitudinal section and a relative permeability of about 2400. In addition, the magnetic core force material may be a material with high magnetic permeability such as permalloy or sendust. Reference numeral 2 denotes an exciting coil wound on the central arm of the magnetic core 1 and winds a lead wire of 0.3φ about 2500 turns. Reference numeral 3 denotes a sense coil wound on one of the two outer arms of the magnetic core 1, and winds a 0.075φ lead wire for about 100 turns. Reference numeral 4 denotes a compensation coil wound on the other of the two outer arms of the magnetic core 1 and winds a 0.075φ lead wire for about 100 turns. The compensation coil 4 is for canceling the excitation signal component generated in the sense coil 3. Reference numeral 5 is a guide plate arranged so as to bridge the end of the central arm of the magnetic core 1 and the end of the outer arm around which the detection coil 3 is wound, and is made of hard plastic or ceramic material. It is formed to have a guide path that guides the detected object. Other than non-magnetic metal materials, non-metallic materials such as hard ceramics that can withstand contact wear on the guide path of the object to be detected are not preferable because the magnetic flux balance is lost due to the eddy current effect caused by the excitation magnetic field. Use. Reference numeral 6 is a magnetic material for comparison, and a magnetic material having a clear magnetic characteristic equivalent in shape to the comparative material is attached to or embedded in the guide plate 5 in the bridge portion where the magnetic field of the magnetic sensor is uniform. Keep it.
When authenticity determination is performed, an authentic material can be used as the comparative magnetic material 6, and the determination circuit is simplified. Further, instead of fixing and sticking the comparative magnetic material 6, for example, the guide plate 5 can be replaced so that it can be easily replaced.
[0019]
FIG. 4 shows a block diagram of the characteristic determination apparatus. Here, reference numeral 7 denotes an excitation power source that applies a sine wave of 10 Vp-p and a frequency of 5 KHz to the excitation coil. A differential amplifier 8 obtains a difference between signals from the sense coil 3 and the compensation coil 4.
Although omitted here, the signals from the sense coil 3 and the compensation coil 4 are somewhat different in amplitude and phase, and include a circuit for changing the amplitude and phase in order to minimize the influence of the excitation magnetic field. Reference numeral 9 denotes a phase comparison circuit that compares the signal pulse from the comparison magnetic material 6 with the signal pulse from the magnetic material to be measured, and sends a value corresponding to the phase difference as a digital value to the discrimination circuit.
10 is a discriminating circuit, which compares the phase difference information from the phase comparison information with the information of the true material stored in advance, and if it matches, it is a genuine product, and if it does not match, it is a counterfeit. The display device or other control device is notified as being present. A microcomputer is generally used as the display / control / device.
The discriminating circuit 10 can take into account the amplitude, shape, history characteristics, noise characteristics, etc. of the pulse in addition to the phase difference information, and the accuracy of the true / false judgment is further improved.
[0020]
FIG. 5 is a specific example of the phase comparison circuit 9, and FIG. 6 is a signal timing chart showing the operation of the circuit. Here, 11 is a comparator, which compares the detected pulse with a set comparison voltage and compares it with a reference level of an input signal, for example, 0-5V, and binarizes it. In order to measure the time between pulses, a state that is “1” only between pulses is created. For example, 12 is a J-K flip-flop, and each time the pulse shown in (a) is input, a waveform shaping pulse that takes the 1/0 state shown in (b) is created. According to the state 1/0 of the flip-flop 12 shown in (c), the count clock CK is gated by the NAND gate 13 to generate a count lock as shown in (d). The binary counter 14 counts this gated clock. The count value is always set to 0 when the excitation start timing signal RESET shown in (e) is reset and excitation is started. After the excitation is completed, the count value is temporarily stored in the data buffer 15 in synchronization with the SET pulse shown in (f). The stored data is compared with a true value by the discriminating circuit 10, and if it is correct, it is determined to be true, and if it is different, it is determined to be false and sent to a display device or another control device.
[0021]
In order to eliminate the disadvantage that the excitation power source of the magnetic sensor in the present invention tends to be large, according to the intermittent excitation method, if the ratio of the intermittent period to the whole period is small, the heat is reduced by that ratio and the supply of excitation power There is a merit that power capacity can be increased, and the disadvantage can be compensated practically. FIG. 7 is an example of an intermittent excitation waveform.
Of course, the intermittent excitation waveform is not a rectangular wave containing a distortion component, but a sine wave or a waveform that rises smoothly, such as (Sinx) / x, in order to minimize the distortion caused by the magnetic material forming the circuit system and the magnetic core. Is preferred.
[0022]
【The invention's effect】
As described above in detail, according to the present invention, the apparatus for determining authenticity based on the difference in the magnetic properties of the ferromagnetic material generates a sufficiently large uniform magnetic field compared to the size of the magnetic material to be determined. It is possible to make true / false judgments easily and accurately by discriminating from the magnetic sensor in which a genuine product or a magnetic material to be used as a reference for comparison is preliminarily embedded, and discrimination from the phase information of the reference pulse and detection pulse obtained from the sensor. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a magnetic sensor according to an embodiment of the present invention and its exciting magnetic field strength.
FIG. 2 is a waveform diagram showing detection pulses that accompany the movement of an object to be detected in the apparatus of the present invention.
FIG. 3 is a perspective view showing an embodiment of a magnetic sensor according to the present invention.
FIG. 4 is a block diagram illustrating an example of a true / false determination apparatus according to the present invention.
FIG. 5 is a block diagram showing a specific example of a phase comparison circuit used in the present invention.
6 is a timing chart showing signal waveforms in the phase comparison circuit of FIG. 5;
FIG. 7 is an example of an intermittent excitation waveform used in the present invention.
FIG. 8 is a schematic view showing a structural example of a conventional narrow gap type magnetic sensor.
FIG. 9 is a characteristic diagram showing a magnetic field distribution example of a narrow gap head.
FIG. 10 is a BH characteristic diagram of a magnetic material showing an example of a waveform detected by a narrow gap type magnetic sensor, an example of a detection signal from a magnetic material in a uniform magnetic field (b), and a case where the magnetic field is not uniform. It is a detection signal example figure (c).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Magnetic core 2 Excitation coil 3 Sense coil 4 Compensation coil 5 Guide board 6 Magnetic block for comparison 7 Excitation power supply 8 Differential amplifier 9 Phase comparison circuit 10 Discrimination circuit 11 Comparator 12 JK flip-flop 13 NAND gate 14 Binary counter 15 Data buffer 21a, 21b, 21c Magnetic core 22 Excitation coil 23 Sense coil 24 Compensation coil 25 Head gap

Claims (3)

A soft magnetic core having an E-shaped longitudinal section;
An exciting coil wound on the central arm of the soft magnetic core;
A sensing coil wound on one of the two outer arms of the soft magnetic core;
A compensation coil wound on the other of the two outer arms of the soft magnetic core;
Provided with a guide path that guides the magnetic body to be detected, arranged so as to bridge the end of the central arm of the soft magnetic material magnetic core and the end of the outer arm around which the detection coil is wound. A non-magnetic hard material guide plate formed as follows:
A comparative magnetic material of known magnetic properties disposed on or in the guide plate along the guide path of the guide plate and located in the bridging portion;
With
A magnetic sensor for discriminating magnetic characteristics of a magnetic material configured to obtain a detection output indicating the magnetic characteristics of the detection target magnetic body from the detection coil when the detection target magnetic body travels along the guide path. . A soft magnetic core having an E-shaped longitudinal section;
An exciting coil wound on the central arm of the soft magnetic core;
A sensing coil wound on one of the two outer arms of the soft magnetic core;
A compensation coil wound on the other of the two outer arms of the soft magnetic core;
Provided with a guide path that guides the magnetic body to be detected, arranged so as to bridge the end of the central arm of the soft magnetic material magnetic core and the end of the outer arm around which the detection coil is wound. A non-magnetic hard material guide plate formed as follows:
A comparative magnetic material of known magnetic properties disposed on or in the guide plate along the guide path of the guide plate and located in the bridging portion;
An excitation power source for supplying an excitation current to the excitation coil;
A differential amplifier that takes out the difference between the detection output from the detection coil and the compensation output from the compensation coil and takes out the differential detection output that suppresses the influence of the excitation magnetic field due to the excitation current;
A phase comparison circuit for extracting phase information corresponding to a phase difference between the differential detection output by the magnetic material for comparison from the differential amplifier and the differential detection output by the magnetic material to be detected;
A determination circuit that compares the phase information from the phase comparison circuit with previously stored standard information to determine the magnetic characteristics of the magnetic material to be detected;
An apparatus for discriminating magnetic properties of magnetic materials. 3. The magnetic characteristic of the magnetic material according to claim 2, wherein the exciting current from the exciting power source is a sinusoidal wave having at least one wavelength that oscillates intermittently or a sine wave modulated so as to have a small distortion component. Discriminator.

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