JP3623588B2 - Magnetic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor for reading information from a printed matter that has been magnetically printed.
[0002]
[Prior art]
Conventionally, a magnetic sensor for reading information from magnetically printed material is JIS.
According to C6251 (magnetic ink character reading font and printing specifications), it is taken out as an amplitude signal through a DC magnetized head, and is not particularly different from a magnetic head generally used for reading a magnetic tape. The same applies to magnetic heads for magnetic bar codes of orange cards (prepaid cards for JR Co.), which have been in circulation in recent years.
[0003]
On the other hand, in order to read pattern information from printed matter printed on magnetic ink using a special ferromagnetic material, it is considered that security is added to the specificity of the magnetic properties of the special ferromagnetic material. Thus, an AC excitation type magnetic sensor capable of both data reading and magnetic characteristic detection is used.
Such a magnetic ink uses a ferromagnetic film as a transfer material (see Japanese Patent Application No. 7-293309 “Thermal Magnetic Transfer Material” filed on Oct. 17, 1995 by the applicant of the present application).
As shown in FIG. 7, the AC excitation type magnetic sensor has a compensation coil 14 for canceling the excitation voltage generated by the excitation magnetic field generated in the detection coil 13, and detects only the detection voltage by the detected magnetic material from the detection coil 13. It has the structure to do. 11 is a magnetic core, 12 is an exciting coil.
[0004]
[Problems to be solved by the invention]
Since the method of the prior application by the applicant of the present application has such a structure, it is possible to easily measure the magnetic characteristics of the magnetic material having a small magnetization. Occurs towards. This creates two problems. For example, if a magnetic body or a metal body is present in the vicinity of the magnetic sensor, the magnetic field lines are shifted and the balance between the voltages generated by the detection coil 13 and the compensation coil 14 is lost. When the balance is lost, the voltage component of the excitation power source becomes larger than the excitation voltage component of the magnetic material to be measured, which causes the S / N ratio of the magnetic characteristic measurement to deteriorate. For this reason, when such a magnetic sensor is incorporated and used in a device having a transport system with many metal parts, there is a problem that there is a limitation on the mounting position and the like, which is very difficult to use. When there is a metal body in the vicinity of the magnetic sensor, the magnetic field density in the space changes due to the polarization action if the metal is a ferromagnetic substance, and the magnetic flux density changes due to an eddy current accompanying a change in magnetic flux other than the ferromagnetic substance. Therefore, the balance of the electromotive force with respect to the excitation magnetic field of the compensation coil 14 and the detection coil 13 is lost by the peripheral metal body.
Another problem is that when a metal conductor is present so as to surround the periphery of the exciting coil 12, the magnetic field lines of the exciting coil 12 are closed as shown by electromagnetic theory, and there is a metal body that crosses the magnetic field lines. An eddy current is generated inside the metal body, and the energy of the excitation magnetic field becomes heat or a demagnetizing field to weaken the excitation magnetic field. Accordingly, the magnetic material to be measured cannot be sufficiently excited, and a sufficient magnetic field cannot be applied to the magnetic material to be measured, so that good magnetic characteristics cannot be obtained.
Such a method of using a metal body around the sensor is general, and if this magnetic sensor cannot be used with a metal body, there is a problem that it becomes difficult to use as a limitation in use.
Therefore, such a magnetic sensor with a compensation coil has the advantage of improving sensitivity, but has the disadvantage of being easily influenced by nearby magnetic and metal bodies.
[0005]
An object of the present invention is to provide a magnetic mark or magnetic barcode data on a security protection paper such as a security printed with a magnetic ink or magnetic transfer material containing a ferromagnetic material, and a thread arranged for security purposes in the security. In order to detect the data and the magnetic characteristics, it is an object of the present invention to provide an improved magnetic sensor having the same sensitivity improvement advantage as having a compensation coil without having a compensation coil that easily causes the above-mentioned drawbacks.
[0006]
[Means for Solving the Problems]
In order to achieve this object, the magnetic sensor of the first invention of the present application has a substantial width and length for reading information printed by magnetic ink and has a U-shaped cross-sectional shape. A magnetic core, an excitation coil wound in the longitudinal direction on the U-shaped ferromagnetic core, and arranged to generate a magnetic field that intersects the gap formed in the U-shaped cross-sectional shape; A rectangular plate-like body made of a non-magnetic material provided with a rectangular groove portion in the direction and fixed to a rectangular opening formed by the gap of the U-shaped ferromagnetic material core, and the plate-like body A rectangular detection coil inserted and arranged in the groove portion so as to match the planar shape of the groove portion; and a wear prevention member provided on the installation surface of the groove portion of the plate-like body so as to cover at least the groove portion. It is a thing.
The magnetic sensor according to the second aspect of the present invention is a ferromagnetic material core having a U-shaped cross-sectional shape having a substantial width and length for reading information printed by magnetic ink, and the U-shaped strong force. An exciting coil disposed on the magnetic material core in the longitudinal direction and arranged to generate a magnetic field crossing the gap formed in the U-shaped cross-sectional shape, and two grooves in the central longitudinal direction are provided. A rectangular plate-like body fixed to a rectangular opening formed by the gap of the U-shaped ferromagnetic material core and inserted into the two groove portions of the plate-like body. Two magnetoresistive elements or Hall elements,
A wear prevention member provided to cover at least the groove part on an installation surface of the groove part of the plate-like body.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In an AC excitation type magnetic sensor, the detection sensitivity of how the weak magnetic flux density acting on the magnetic material to be detected can be detected without affecting the excitation magnetic field and with a high S / N ratio determines its performance. become. In other words, the condition for improving the performance is to increase the sensitivity of the detection coil and to remove as much as possible the voltage component caused by the AC excitation magnetic field.
[0008]
The voltage e generated in the detection coil placed in the changing magnetic field is expressed by the following equation (1) from Faraday's induction law.
[Expression 1]
e = −d / dt (∫B · dS) (1)
B: Magnetic flux density on the coil, dS: Wire segment of the coil On the other hand, the magnetic flux on the detection coil changes with time due to the excitation magnetic field generated by the excitation coil, but at a certain moment it is assumed to be uniform on the detection coil wire. For example, when the axis of the detection coil is placed parallel to the magnetic flux direction of the excitation magnetic field, the number of interlinkage magnetic fluxes ∫B · dS of the excitation magnetic field with respect to the detection coil is zero. As shown in FIG. 1A, when the surface (coil surface) including the detection coil 3 is placed in parallel with the exciting magnetic field magnetic flux direction G, it has a finite value from Faraday's induction law. As shown in FIG. 1B, in the conventional magnetic sensor with a compensation coil, the coil surface of the detection coil 3 is placed perpendicular to the magnetic flux direction G of the excitation magnetic field. Power is offset.
However, cancellation by the compensation coil tends to become more difficult as the detection sensitivity is increased. The magnetic sensor according to the present invention has an advantage that the electromotive force due to the exciting magnetic field can be canceled without the compensation coil since the coil surface of the detection coil is placed in parallel with the magnetic field. It shows that a signal can be detected by the detection coils having such an arrangement.
[0009]
FIG. 2 shows the magnetic field distribution in the vicinity of the printed portion 4 using magnetic ink containing a ferromagnetic material as a component. In the printed portion 4, the magnetic flux changes due to the influence of the ferromagnetic material.
Assuming that the right half of the detection coil 3 is S1 and the left half of the wire is S2, the following equation (2) is obtained.
e = −d / dt {∫ (B1 · dS1 + B2 · dS2)} (2)
Can be rewritten.
Assuming that the voltage due to the excitation magnetic field is e1 and the voltage due to the magnetic field change in the printed part 4 is Δe,
e = e1 + Δe−e1 = Δe
It becomes.
That is, only the change is output from the detection coil 3.
Although FIG. 2 shows an example in which the right half coil S1 is used for detection, the left half S2 can detect a similar voltage only by changing the polarity of the voltage.
Since the detected voltage is a magnetic field change due to the magnetic material of the printed portion 4, if the magnetic material has a hysteresis characteristic with a large squareness ratio, a pulse having a frequency component peculiar to the magnetic material can be detected. It can be used to provide security. In addition, since the presence or absence of magnetic ink is directly used as the amplitude value of the detection voltage, meaningful digital data can be obtained by binarization processing after a circuit (for example, a rectifier circuit) that removes an AC component.
[0010]
【Example】
Examples of the present invention will be described below. FIG. 3A is a structural diagram of the magnetic sensor 5, and FIG. 3B is a partial configuration diagram of the detection coil 3.
The U-shaped ferromagnetic magnetic core 1 has a length of 40 mm, a width of 10 mm, and a height of 15 mm. On the magnetic core 1, an exciting coil 2 in which a 0.2φ polyurethane wire is wound in the longitudinal direction for 100 turns is provided. Yes. The detection coil 3 is provided in the gap of the magnetic core 1, and a rectangular groove having a distance of 1.5 mm, a width of 0.5 mm, and a depth of 0.5 mm is cut in a 1.5 mm glass epoxy resin substrate 6. A structure in which 0.01φ polyurethane wire is wound 100 turns.
The resin substrate 6 in which the detection coil 3 is housed is mounted horizontally in the upper gap of the U-shaped ferromagnetic core 1, and the influence of the excitation magnetic field can be eliminated by slight adjustment of the left and right positions.
Further, since the surface of the resin substrate 6 is in contact with the detected object, it is covered with a thin ceramic substrate of 0.1 mm in order to prevent wear.
[0011]
FIG. 4A is a diagram for explaining how the magnetic sensor 5 is used.
FIG. 4B shows a detection signal waveform when the magnetic ink printed matter 10 containing a ferromagnetic material is read by the magnetic sensor 5 and the amplifier 8 that amplifies the detection coil output. The magnetic ink printed matter 10 is printed on Kent paper at an equal interval of 1 mm width, 10 mm length, and 3 mm interval. The magnetic ink is mainly composed of an amorphous ferromagnetic material. In this case, the frequency of the excitation alternating current of the excitation power supply 7 is 15.6 kHz.
In this embodiment, a ferrite material is used for the ferromagnetic core 1, but a material having a high magnetic permeability such as soft iron, permalloy, sendust, etc. may be used. The resin substrate 6 in which the detection coil 3 is housed can be used other than metal and ferromagnetic materials, and ceramic, glass, plastic, and bakelite material may be used.
The rectangular dimensions of the detection coil 3 are determined by the print dimensions to be read, and it is clear that the width dimension and the space between the coil lines can be narrowed if high resolution is desired.
The magnetic sensor 5 can be applied not only to detection of magnetic characteristics of printed matter using magnetic ink and magnetic transfer material and data reading but also to detection of threads and marks using ferromagnetic metal or amorphous metal.
[0012]
FIG. 5 shows an embodiment in which an MR element (magnetoresistive element) 3a, which is a magnetic detection element, is used instead of the detection coil 3.
The MR element 3a has a resistance that increases in proportion to the strength of the magnetism applied to the element, but is composed of MR1 and MR2 elements with uniform characteristics arranged in parallel.
[0013]
FIG. 6 shows an example of a detection circuit when the MR element 3a is used. Here, when a DC power supply 6a (V _in ) is applied to each of the elements MR1 and MR2 and a magnetic field H is applied, the resistance of MR1 is R1, and the resistance of MR2 is R2.
The voltage V34 between the terminals t3 and t4 is
[Expression 4]
_{V34 = R2 × V in / (} R1 + R2) ···· (3)
If the characteristics are uniform and R1 = R2, V34 is V _in / 2, and the influence of the excitation magnetic field is eliminated as in the detection coil method, and only the balance change of each element is output as the detection signal 9. A Hall element using the Hall effect may be used instead of the magnetoresistive element 3a.
[0014]
【The invention's effect】
As described above in detail, according to the present invention, the excitation type magnetic sensor for detecting the magnetic characteristics of the magnetic ink has the advantage of having a high detection capability without using a compensation coil, and is simple. This has the practical advantage of being easy to manufacture with a simple structure.
[Brief description of the drawings]
FIG. 1 is a perspective view for explaining the arrangement of detection coils used in the present invention.
FIG. 2 is a schematic perspective view for explaining the operation of a detection coil used in the present invention.
FIG. 3A is a perspective view showing an embodiment of a magnetic sensor according to the present invention, and FIG. 3B is a perspective view showing an example of the structure of a detection coil used in the embodiment.
FIG. 4 is a schematic diagram (a) for explaining the use mode of the magnetic sensor according to the present invention and a detection output waveform example diagram;
FIG. 5A is a perspective view showing another embodiment of the magnetic sensor according to the present invention, and FIG. 5B is a perspective view showing an example of the structure of a detection coil used in the embodiment.
FIG. 6 is a circuit diagram showing an example of a detection circuit used for output detection of a magnetic sensor according to the present invention.
FIG. 7 is a schematic diagram (a) showing an example of the structure of a conventional AC excitation type magnetic sensor and an equivalent circuit diagram (b) thereof.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 U type magnetic core 2 Excitation coil 3 Detection coil 3a Detection MR element 4 Print part 5 Magnetic sensor 6 Resin board 7 Excitation power supply 7a DC power supply 8 Amplifier 9 Detection signal 10 Magnetic ink printed matter 11 Magnetic core 12 Excitation coil 13 Detection coil 14 Compensation coil

Claims (2)

A ferromagnetic core having a substantial width and length for reading information printed by magnetic ink and having a U-shaped cross-sectional shape;
An exciting coil arranged to generate a magnetic field that is wound in a longitudinal direction on the U-shaped ferromagnetic material core and intersects a gap formed in the U-shaped cross-sectional shape;
A rectangular plate-like body made of a non-magnetic material provided with a rectangular groove in the central longitudinal direction, and fixed to a rectangular opening formed by the gap of the U-shaped ferromagnetic material core;
A rectangular detection coil inserted and arranged in the groove of the plate-like body so as to match the planar shape of the groove;
The magnetic sensor provided with the abrasion prevention member provided so that at least the said groove part might be covered in the installation surface of the said groove part of the said plate-shaped body . A ferromagnetic core having a substantial width and length for reading information printed by magnetic ink and having a U-shaped cross-sectional shape;
An exciting coil arranged to generate a magnetic field that is wound in a longitudinal direction on the U-shaped ferromagnetic material core and intersects a gap formed in the U-shaped cross-sectional shape;
A rectangular plate-like body made of a nonmagnetic material provided with two grooves in the central longitudinal direction, and fixed to a rectangular opening formed by the gap of the U-shaped ferromagnetic material core;
Two magnetoresistive elements or Hall elements inserted and arranged in the two groove portions of the plate,
The magnetic sensor provided with the abrasion prevention member provided so that at least the said groove part might be covered in the installation surface of the said groove part of the said plate-shaped body .

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