JPH06180304A - Magnetism sensing method - Google Patents

Abstract

PURPOSE:To sense the magnetism of a specimen and the range of coercive force by making a magnetic sensor with a biased positive field pass after a magnetic specimen is saturated negative to judge whether or not the coercive force of the specimen is larger than an impressed field and then by making a magnetic sensor with a biased field close to the coercive force of the specimen pass to detect a change in output. CONSTITUTION:After a bill (magnetic substance) is moved in the arrow direction and saturated negative by a magnet 10 at position A, a coercive force of the bill is detected by a differential magnetoresistance element MR 120 with a positive field biased by a magnet 30 at position B. Further, a coercive force of the bill is detected at position C by a magnetoresistance element MR 240 with a field close to the coercive force of the bill biased by a magneto 50, so that the range of coercive forces inherit to the bill is restricted. Analyzing a saturation magnetization curve and a mode of each differential magnetoresistance element signal enables sensing of a magnetism without being affected by a presensing residual magnetization state and judgment of false and truth from a magnetism pattern and a magnetism of the bill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting magnetic properties, and more particularly to detection of magnetic properties of magnetic materials contained in printing ink such as banknotes.

[0002]

2. Description of the Related Art In recent years, the progress of copying technology has been remarkable, and there has been a problem that securities such as banknotes and checks are misused by copying.

Therefore, research for identifying such paper sheets is being rapidly advanced.

For example, for identifying bills, there are two types of identification, that is, identification by light and identification by magnetism.

Among these, the magnetic identification uses the fact that the magnetic ink is used in some form for the bill, and the bill is identified by detecting the distribution of the magnetic ink.

[0006] For example, conventionally, a magnetic field is applied to a bill in advance by using a magnet, and a magnetic pencil or a magnetic copy is used because of the residual magnetic flux density after removing the magnetic field. There is a method of determining whether or not. (Japanese Patent Laid-Open No. 52-152793) However, in the method as described above, since only the residual magnetic flux density is observed, the residual magnetic flux density becomes approximately the same as that of the magnetic ink when it is lightly painted with a magnetic pencil, which is reliable. There was a problem that it could not be identified.

[0007] In general, a magnetic measuring device can measure the residual magnetic flux density, the coercive force, etc., but the object to be measured must be stationary, and the measurement takes some time. , If you only want to determine whether or not you have a certain magnetic quality, the operation is complicated, and it is impossible to measure without a certain amount of mass, and the magnetic quality of magnetic materials such as magnetic ink of banknotes is There was a problem that it could not be measured.

Therefore, in order to provide a method for easily detecting the magnetic substance of a magnetic substance with a simple device, the inventors of the present invention arranged a magnetic sensor for measuring a change in the magnetic flux distribution and an upstream side of the magnetic sensor. A first magnet that is installed and applies a saturation magnetic field whose absolute value is larger than its coercive force to the magnetic body to be detected and that is disposed near the magnetic sensor and has a polarity opposite to that of the first magnet. And a second magnet for applying a magnetic field having a value equal to the coercive force of the magnetic substance to be detected by the magnetic sensor, so that no output from the magnetic sensor is produced when the target magnetic substance passes through. Have proposed a method of detecting whether or not the magnetic substance has a desired magnetic property.

However, the saturation magnetic field strength of a bill is about 3
Since it is as large as about 000G and is separated from the subject, a stronger magnet is required to secure this value.
Since the bias magnetic field applied to the detection magnetic sensor is strong, the sensitivity is low, and there is a problem that a detailed magnetic pattern cannot be detected.

Further, it is good if it is known beforehand what kind of coercive force a genuine note has, such as a bill, but this method cannot be used if it is not known at all.

Further, although the coercive force is small, it is not necessary to apply a too large magnetic field, and when a large magnetic field is applied, there is a problem that the sensitivity is lowered.

[0012]

As described above, since the conventional magnetic substance detecting device has low sensitivity, it can only detect the presence or absence of a magnetic pattern, that is, whether or not magnetic printing is performed, and any magnetic pattern. There is a problem in that it cannot be detected at all when it is not known what the coercive force has or the coercive force.

The present invention has been made in view of the above circumstances, and it is possible to detect a magnetic substance with high accuracy and high sensitivity, and to detect what degree of coercive force the magnetic substance has. The purpose is to provide a quality detection method.

[0014]

The first method of the present invention comprises:
The first magnetic field necessary for saturating the magnetic substance to be detected is set according to the saturation magnetic field applying step of applying the first magnetic field to the detection target and the magnetic quality of the magnetic substance to be detected. A second magnetic field having a polarity opposite to that of the first magnetic field is applied to the magnetic sensor as a bias magnetic field, and the object to which the first magnetic field is applied is passed through to detect a change in output of the magnetic sensor. No. 1 detection step, a determination step of determining whether the coercive force of the detection target object is larger than the second magnetic field based on the output change, and a determination result of the determination step. A second detection step of detecting a change in the output of the magnetic sensor by passing a third magnetic field closer to the coercive force of the detected object as a bias magnetic field to the magnetic sensor based on Including, and So that to detect whether a magnetic substance having.

According to a second method of the present invention, a saturation magnetic field applying step of applying a first magnetic field necessary for saturating a magnetic body to be detected to a detected body, and the magnetic body to be detected. A second magnetic field having a polarity opposite to that of the first magnetic field and applied to the magnetic sensor as a bias magnetic field is applied to the detected object to which the first magnetic field is applied. A first detection step of allowing the magnetic sensor to detect an output change of the magnetic sensor, and a third magnetic field different from the second magnetic field as a bias magnetic field applied to the magnetic sensor, and passing the object to be detected. A second detection step of detecting an output change of the magnetic sensor, and a range of coercive force of the detected object is calculated based on the outputs of the first and second detection steps, and To detect if it is a magnetic material with quality. There.

The device used here is, for example, in addition to the above-described improved magnetic substance detection device, a first device dedicated to saturation magnetization for applying a saturation magnetic field having a sufficiently large absolute value to a magnetic body to be detected. A magnetic sensor which is provided with a magnet and measures a change in magnetic flux distribution, and a second magnetic sensor which is provided near the magnetic sensor
A plurality of pairs of magnets are prepared, and the range of the coercive force is detected by the ratio or sign of the peak height of the output, and the size is set to give a bias magnetic field of optimum strength to the magnetic sensor. To do.

[0017]

The coercive force Hc of the magnetic substance is the intersection of the H axis and the loop in the magnetic flux density-magnetic field strength (BH) curve, as shown in FIG. Take At this time, that is, when the magnetic field strength H is Hc or -Hc,
The magnetic flux density passing through the inside of the magnetic body is zero. When a magnetic material having a residual magnetic flux density of -Br enters a magnetic field of + Hc, the absolute value of the residual magnetic flux density of the magnetic material decreases and becomes zero.

Even if this Br = 0 state moves on the differential type magnetoresistive element as shown in FIG. 7 (b), the magnetic field does not change and the differential output does not change.

On the contrary, when the magnetic substance of + Br enters the magnetic field of + Hc, the residual magnetic flux density of Br 'causes the magnetic flux distribution to change, and the differential output changes.

This is the same in the case of the magnetic flux distribution of -Hc.

When magnetic detection is performed using the differential magnetoresistive element, the output form of the signal has a correlation between the detected residual magnetization direction of the magnetic material and the bias magnetic field applied to the MR element. Focusing on, the output of the MR element is detected by applying a plurality of bias magnetic fields, and when the direction of the residual magnetization and the magnetization direction of the bias magnet are the same as shown in FIG. 8 (a), the output of the MR element is It changes as shown in b). Further, when the direction of residual magnetization is opposite to the direction of magnetization of the bias magnet as shown in FIG. 9 (a), the output of the MR element reverses and changes as shown in FIG. 9 (b).

For example, when changing the magnetization state of the magnetic material along the saturation magnetization curve as shown in FIG. 10, the phenomenon as shown in FIGS. 8 and 9 with the coercive force Hc as the boundary in the applied bias magnetic field in the positive direction. Appears. Therefore, the range of coercive force values can be detected by identifying the form of the output signal. Furthermore, by increasing the number of MR elements and bias magnets, it is possible to finely limit the coercive force value range. According to the method described above, the bias magnet may be changed according to the magnitude of the coercive force. Therefore, at the same time as the detection of the high-sensitivity magnetic substance, the magnetic pattern has the optimum strength of the magnetic sensor. Since the bias magnetic field can be set, highly accurate detection is possible.

The magnetic field may be detected and discriminated under different magnetic field strengths. Alternatively, the magnetic field may be detected and discriminated under one magnetic field strength, and then an appropriate magnetic field strength may be applied. Magnetic detection may be performed therein.

Further, the magnetic body side may be moved, the detection device side may be moved, and the magnetic body may be moved relative to the measuring device.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic explanatory view of an apparatus for realizing the coercive force detecting method of the embodiment of the present invention. FIG. 2 is a diagram showing a saturation magnetization curve of the magnetic substance at each element position.

This device is, in addition to the improved magnetic substance detecting device described above, a first magnet dedicated to saturation magnetization for applying a saturation magnetic field Hm having an absolute value larger than its coercive force to a magnetic substance to be detected. The second magnet 30 is provided in the vicinity of the first differential type magnetoresistive element 20 as a magnetic sensor for arranging 10 to measure the change in the magnetic flux distribution, and similarly measures the change in the magnetic flux distribution. A third magnet 50 arranged near the second differential type magnetoresistive element 40 as a magnetic sensor is provided, and these outputs are taken out through a signal processing circuit as shown in FIG. It was done. This signal processing circuit includes a capacitor 60 connected to the first and second differential magnetoresistive elements 20 and 40, and resistors 61 to 63.
And an operational amplifier 64.

The first magnet 10 for saturation magnetization, which is installed on the most upstream side with respect to the traveling direction a of the banknote 1, and is further sequentially arranged at a predetermined interval in the traveling direction a, and is detected. Negative magnetic field −H at the position where the magnetic material to be passed passes
1 (position A in FIG. 1) and a positive magnetic field H2 (Fig. 1) which is a magnetic field of the reverse polarity of the first magnet 10.
A second magnet 30 which emits the B position), a differential type magnetoresistive element 20 which is arranged in the vicinity of the second magnet 30 and is biased by the second magnet 30 to a positive magnetic field H2, The second differential type magnetoresistive element 40 is provided downstream of the second magnet 30 and biased to the positive magnetic field H3 (position C in FIG. 1) by the third magnet 50. Is configured to travel on a non-magnetic top metal G of the detection device main body by a transfer means (not shown). The first and second magnets are disposed on the back surface of the support substrate 60 installed below the top metal G so as to be parallel to the top metal G, and the first and second differential magnetoresistive elements 30,
50 is arranged on the surface of the support substrate 60. The first and second differential magnetoresistive elements are thin film magnetoresistive elements arranged on the surface of an insulating substrate. Here, it is assumed that the positive magnetic field Hc is the coercive force of the magnetic ink of the bill. The negative magnetic field -H1 is a saturated magnetic field whose absolute value is sufficiently larger than the absolute value of the positive magnetic field Hc.

Next, using this apparatus, the first magnetic material F1
A method for discriminating three kinds of magnetic substances, that is, 100 Oe, the second magnetic substance F2 500 Oe, and the third magnetic substance F3 900 Oe will be described.

The bill 1 is run in the direction of arrow a, and as shown in FIG. 2, first, at position A, the magnetic material to be measured by the first magnet is negatively saturated, and then at position B, the second magnet is used. The coercive force is detected by the first differential type magnetoresistive element biased by and the coercive force is detected by the magnetoresistive element biased by the third magnet at the position C. Here, the first magnet is -3000 G and the second magnet is 300
G, and the third magnet is 700G.

Since this first magnet is -3000 G, any magnetic material is sufficiently saturated. The saturation magnetization curves of the magnetic bodies F1 to F3 at this time are as shown in FIG. 4, and the form of each differential magnetoresistive element signal is shown in FIGS. 5 (a) to 5 (c).
It came to be shown in. Since the magnetic material F1 is magnetized in the + direction at both B and C positions, the output signals from the first and second differential magnetoresistive elements both have the form shown in FIG. 5 (a). It can be seen that the saturation magnetization curve of the magnetic material F1 intersects with the horizontal axis at a value smaller than the magnetic field strength of 300 G at B, that is, the coercive force exists in the range of 0 to 300 Oe.

On the other hand, since the magnetic substance F3 is magnetized in the-direction at the positions of B and C, its output signal is opposite to that of the case of F1 as shown in FIG. 5 (c), and its saturation magnetization curve. Indicates that the magnetic field strength at C intersects with the horizontal axis at a value larger than 700 G and the coercive force is 700 Oe or more.

Further, in the case of the magnetic material F2, since the magnetization directions of B and C are different, the form of the output signal from the first and second differential type magnetoresistive elements is as shown in FIG. 5 (b). Appear differently. From this, the saturation magnetization curve is
It intersects with the horizontal axis between 0 and 700G. That is, it can be seen that the coercive force is between 300 and 700G.

Therefore, if it is determined which one of FIGS. 5 (a) to 5 (c) the form of the output signal from the magnetic material having an unknown coercive force is determined, the coercive force is 0 to 300, 300 to.
It is possible to easily determine in which range the value is 700, 700 Oe or more. Further, if a pair of a magnet and a differential type magnetoresistive element is added and the horizontal axis is finely divided, the range of finer coercive force value can be limited.

Thus, according to the method of the present invention,
It is possible to detect magnetic properties without being affected by the residual magnetization state before detection.

Further, since the magnetic pattern and the magnetic quality are used for discrimination, a high degree of authenticity determination can be performed. Also, since each part is small, it is easy to make it small and thin.

Further, the present invention can be applied not only to magnetic ink and magnetic toner for forms, but also to magnetic cards and magnetic plate materials and bar materials.

Second Embodiment Next, a second embodiment of the present invention will be described.

Also in this method, an apparatus similar to the apparatus shown in the first embodiment of FIG. 1 is used. Here, the magnetic field strengths of the second and third magnets may be set according to the characteristics to be detected. FIG. 6 is a diagram showing a magnetization curve of the subject.

For example, when the outputs obtained at B and C are as shown in (a) and (b), respectively, a pseudo slope between points A and B can be found from the ratio of peak heights.

Further, if they are reversed as shown in (b) and (c), it is understood that the object has a coercive force between the magnetic fields C and D. C or D depending on the peak height ratio
You can tell which one is.

Further, by further adding one or more sets of differential type magnetoresistive elements and bias magnets, a total of three or more sets are provided, the number of measurement points on the magnetization curve of the magnetic body is increased, and the characteristics of the curves are
That is, more detailed values can be obtained by detecting the characteristic such as the squareness in addition to the holding force.

Although a permanent magnet was used as the bias magnet, the second and third magnets are composed of electromagnets, and when changing the magnetic substance to be detected, the coil current is changed to change the strength of the bias magnetic field. Adjust it.

Further, the first magnet and the yoke magnetized by the first magnet may be used, and the yoke may be replaced if necessary. Moreover, the magnetizing strength, the area, and the number of poles may be devised with one magnet. Further, the magnetoresistive element may be integrated into one chip, or a signal processing circuit may be mounted on the magnetoresistive element chip. This makes it possible to reduce the size and simplify the assembly. Further, once saturated magnetization is performed, not only magnetic property detection along the saturation magnetization curve but also detection along a minor loop may be performed.

Further, although permanent magnets are used as the first to third magnets, the bias magnetic field can be changed by attaching position adjusting means to the second and third magnets and adjusting the height. Good.

This method is a device for simply detecting the range of the coercive force value of an unknown magnetic substance, and can be easily detected even if the coercive force of the magnetic substance used in the magnetic card is changed. It can be applied to magnetic card readers, in-line sensors for magnetic quality discrimination in writing lines such as magnetic cards and floppy disks.

[0047]

As described above, according to the present invention, it is possible to easily determine the range of unknown magnetic properties.

[Brief description of drawings]

FIG. 1 is a diagram showing a magnetic substance detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a saturation magnetization curve of a magnetic body in the device.

FIG. 3 is a diagram showing a signal processing circuit in the device.

FIG. 4 is a diagram showing a saturation magnetization curve of each magnetic material in the method of the example of the present invention.

FIG. 5 is a diagram showing output in the same method.

FIG. 6 is a diagram showing a method of a second embodiment of the present invention.

FIG. 7 is an explanatory diagram of the principle of the present invention.

FIG. 8 is an explanatory diagram of the principle of the present invention.

FIG. 9 is an explanatory diagram of the principle of the present invention.

FIG. 10 is an explanatory diagram of the principle of the present invention.

[Explanation of symbols]

 10 First Magnet 20 First Differential Magnetoresistive Element 30 Second Magnet 40 Second Differential Magnetoresistive Element 50 Third Magnet 60 Substrate

Claims (2)

[Claims] 1. A saturation magnetic field applying step of applying a first magnetic field required for saturating a magnetic substance to be detected to a detection target, and setting according to the magnetic quality of the magnetic substance to be detected. The second magnetic field having a polarity opposite to that of the first magnetic field is applied as a bias magnetic field to the magnetic sensor, and the object to which the first magnetic field is applied is passed through the magnetic sensor to output the magnetic field. A first detecting step of detecting a change; a determining step of determining whether or not a coercive force of the detected object is larger than the second magnetic field based on the output change; A second magnetic field that detects a change in the output of the magnetic sensor while allowing the third magnetic field, which is closer to the coercive force of the detected object, to be applied to the magnetic sensor as a bias magnetic field based on the determination result Including the detection step, Magnetic substance detecting method for detecting whether a magnetic substance having a magnetic substance that. 2. A saturation magnetic field applying step of applying a first magnetic field necessary for saturating a magnetic substance to be detected to a detection target, and setting according to the magnetic quality of the magnetic substance to be detected. The second magnetic field having a polarity opposite to that of the first magnetic field is applied to the magnetic sensor as a bias magnetic field, and the object to which the first magnetic field is applied is passed through the magnetic field to output the magnetic sensor. A first detection step of detecting a change, and a third magnetic field different from the second magnetic field as a bias magnetic field are applied to the magnetic sensor to allow the detected object to pass therethrough, thereby changing the output of the magnetic sensor. Based on the detection results of the second detection step of detecting
A determination step of determining whether or not the coercive force of the object to be detected is larger than the second and third magnetic fields, and detecting what magnetic substance the object to be detected has Magnetic quality detection method.