Magnetism sensing method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a magnetic material detection method, and particularly relates to detection of magnetic material of a magnetic material contained in printing ink such as banknotes.

【0002】

[Conventional technology]

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.

【0003】

Therefore, research for the identification of such paper leaves is rapidly progressing.

【0004】

For example, two types of banknotes are used: light identification and magnetic identification.

【0005】

Of these, magnetic identification utilizes the fact that magnetic ink is used in some form for banknotes, and the banknotes are identified by detecting the distribution of the magnetic ink.

【0006】

For example, conventionally, a magnetic field is applied to a banknote using a magnet in advance, and the residual magnetic flux density after removing the magnetic field is used to determine whether the banknote is a genuine magnetic material, a magnetic pencil, or a magnetic copy. There is a way to do it. (Japanese Patent Laid-Open No. 52-152793) However, since the above-mentioned method only looks at the residual magnetic flux density, the residual magnetic flux density is about the same as that of 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 material measuring device can measure residual magnetic flux density, coercive force, etc., but the object to be measured must be stationary, and it takes a certain amount of time to measure, which is specific. If you want to judge only whether or not it has magnetic quality, the operation is complicated and it cannot be measured without a certain amount of mass, and the magnetic quality of magnetic materials such as magnetic ink on bills cannot be measured. There was a problem.

【0008】

Therefore, in order to provide a method for easily detecting the magnetic substance of a magnetic material with a simple device, the present inventors dispose of a magnetic sensor for measuring a change in magnetic flux distribution and an arrangement on the upstream side of the magnetic sensor. A first magnet that applies a saturated magnetic field with an absolute value larger than its coercive force to the magnetic material to be detected, and a magnetic sensor that is placed near the magnetic sensor and has a polarity opposite to that of the first magnet. It is desired by providing a second magnet for applying a magnetic field equal to the coercive force of the magnetic material to be used, and preventing the output from the magnetic sensor when the target magnetic material passes through. We are proposing a method for detecting whether or not the material is a magnetic material having the magnetic properties of.

【0009】

However, since the saturated magnetic field strength of banknotes is as large as about 3000 G and is separated from the subject, a stronger magnet is required to secure this value, and the bias magnetic field applied to the detection magnetic sensor is strong. However, there is a problem that the sensitivity becomes low and a detailed magnetic pattern cannot be detected.

【0010】

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

【0011】

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

【0012】

[Problems to be Solved by the Invention]

As described above, since the conventional magnetic quality detection 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 what kind of magnetic pattern it has and what kind of maintenance it has. There is a problem that it cannot be detected at all when it is unknown whether it has a magnetic force.

【0013】

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

【0014】

[Means for solving problems]

The first method of the present invention includes a step of applying a saturated magnetic field to apply a first magnetic field required for the magnetic material to be detected to be saturated, and a magnetic substance of the magnetic material 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 first magnetic field is passed through the object to be detected. Based on the first detection step of detecting the output change of the magnetic sensor and the output change, the determination to determine whether or not the coercive force of the object to be detected is larger than the second magnetic field. A third magnetic field that is closer to the coercive force of the object to be detected based on the process and the determination result of the determination process is applied to the magnetic sensor as a bias magnetic field, and is passed through the object to be detected, and the output of the magnetic sensor. It includes a second detection step of detecting a change, and detects what kind of magnetic material the object to be detected has.

【0015】

The second method of the present invention includes a saturation magnetic field application step of applying a first magnetic field required for the magnetic material to be detected to be saturated to the object to be detected, and the magnetic property of the magnetic material 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 first magnetic field is passed through the object to be detected. A magnetic sensor is passed through the object to be detected in a state where a first detection step for detecting an output change of the magnetic sensor and a third magnetic field different from the second magnetic field are applied to the magnetic sensor as a bias magnetic field. Based on the output of the second detection step for detecting the output change of the above and the outputs of the first and second detection steps, the range of the coercive force of the object to be detected is calculated, and the object to be detected has any magnetic quality. It is designed to detect whether it is a magnetic material.

【0016】

The device used here is, for example, in addition to the above-mentioned improved magnetic quality detection device, a first magnet dedicated to saturation magnetizing that applies a saturation magnetic field having a sufficiently large absolute value to the magnetic material to be detected is arranged. Prepare multiple pairs of a magnetic sensor that measures changes in the magnetic flux distribution and a second magnet that is placed in the vicinity of this magnetic sensor, and the holding force is determined by the ratio or sign of the peak height of the output. It is characterized in that it is large enough to detect a range and give a bias magnetic field of optimum strength to the magnetic sensor.

【0017】

[Action]

As shown in Fig. 7 (a), the coercive force Hc of a magnetic material is the intersection of the H axis and the loop on the magnetic flux density-magnetic field strength (BH) curve, and takes positive and negative values. 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 material is zero. When a magnetic material with 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 to 0.

【0018】

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

【0019】

Conversely, when a + Br magnetic material enters the + Hc magnetic field, the magnetic flux distribution changes due to the residual magnetic flux density of Br ́, and the differential output changes.

【0020】

This also applies to the magnetic flux distribution of -Hc.

【0021】

Then, when performing magnetic detection using a differential magnetoresistive element, pay attention to the fact that the output form of the signal correlates with the direction of the residual magnetization of the magnetic material detected and the direction of the bias magnetic field applied to the MR element. , Multiple bias magnetic fields are applied to detect the output of each MR element, and when the direction of residual magnetism and the magnetization direction of the bias magnet are the same as shown in Fig. 8 (a), the output of the MR element is shown in Fig. 8 (b). It changes as shown. When the direction of the residual magnetization and the magnetization direction of the bias magnet are opposite as shown in Fig. 9 (a), the output of the MR element is inverted and changed as shown in Fig. 9 (b).

【0022】

For example, when the magnetization state of the magnetic material is changed along the saturation magnetization curve as shown in FIG. 10, the phenomena shown in FIGS. 8 and 9 appear at the coercive force Hc in the positively applied bias magnetic field. Therefore, the range of the coercive force value 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 range of coercive force values. According to the above method, the bias magnet may be changed according to the degree of coercive force. Therefore, at the same time as detecting highly sensitive magnetic material, the magnetic pattern has the optimum strength for the magnetic sensor. Since the bias magnetic field can be set, highly accurate detection is possible.

【0023】

It should be noted that the magnetic field may be detected and discriminated under different magnetic field intensities, or after the magnetic detection is performed and discriminated under one magnetic field strength, an appropriate magnetic field strength is given closer and appropriate. Magnetic detection may be performed.

【0024】

Further, the magnetic material side may be moved, or the detection device side may be moved, and in the end, the magnetic material may be configured to move relative to the measuring device.

【0025】

[Example]

Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

【0026】

Example 1 FIG. 1 is a schematic explanatory view of an apparatus for realizing the coercive force detection method according to the embodiment of the present invention. FIG. 2 is a diagram showing a saturation magnetization curve of a magnetic material at each element position.

【0027】

In this device, in addition to the improved magnetic quality detection device described above, a first magnet 10 dedicated to saturation magnetizing that applies a saturation magnetic field Hm having an absolute value larger than its coercive force to the magnetic material to be detected is arranged. As a second magnet 30 arranged in the vicinity of the first differential magnetic resistance element 20 as a magnetic sensor to be installed and to measure the change in the magnetic flux distribution, and as a magnetic sensor to measure the change in the magnetic flux distribution in the same manner. It is equipped with a third magnet 50 arranged in the vicinity of the second differential magnetic resistance element 40 of the above, and these outputs are taken out via a signal processing circuit as shown in FIG. is there. This signal processing circuit is composed of a capacitor 60 connected to the first and second differential magnetoresistive elements 20 and 40, resistors 61 to 63, and an operational amplifier 64, respectively.

【0028】

The first magnet 10 dedicated to saturation magnetism installed on the most upstream side with respect to the traveling direction a of the bill 1 is sequentially arranged at a predetermined interval with respect to the traveling direction a, and attempts to detect the magnet. The first magnet 10 that emits a negative magnetic field-H1 (position A in Fig. 1) at the position where the magnetic material passes, and the positive magnetic field H2 (Fig. 1), which is the magnetic field of the reversal polarity of this first magnet. A second magnet 30 that emits position B), a differential magnetic resistance element 20 that is placed in the vicinity of this second magnet 30 and biased to a positive magnetic field H2 by the second magnet 30, and a second magnet. The positive magnetic field H3 is arranged on the downstream side of the magnet 30 of the third magnet 50. It is composed of a second differential magnetoresistive element 40 biased to (position C in FIG. 1), and the bill 1 travels on the non-magnetic top metal G of the detection device body by a transfer means (not shown). It is configured to do. Further, the first and second magnets are arranged 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. These first and second differential magnetoresistive elements are composed of 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 banknote. 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.

【0029】

Next, a method of discriminating between three types of magnetic materials, the first magnetic material F1 100Oe, the second magnetic material F2 500Oe, and the third magnetic material F3 900Oe, will be described using this device.

【0030】

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

【0031】

Since this first magnet is -3000G, any magnetic material is sufficiently saturated and magnetized. The saturation magnetization curves of each magnetic material F1 to F3 at this time are shown in Fig. 4, and the form of each differential magnetoresistive element signal is shown in Fig. 5 (a) to (c). Since the magnetic material F1 is magnetized in the + direction at both positions B and C, the output signals from the first and second 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 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.

【0032】

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

【0033】

In the case of the magnetic material F2, the magnetization directions of B and C are different, so the morphology of the output signals from the first and second magnetoresistive elements appears differently as shown in Fig. 5 (b). .. From this, the saturation magnetization curve intersects the horizontal axis between the magnetic field strengths of 300 to 700 G. That is, it can be seen that the coercive force is between 300 and 700 G.

【0034】

Therefore, if it is determined which of FIGS. 5 (a) to 5 (c) the form of the output signal from the magnetic material having an unknown coercive force applies, the range in which the coercive force is 0 to 300, 300 to 700, 700 Oe or more. It can be easily determined whether or not it has a value within. Further, if a pair of a magnet and a differential magnetoresistive element is added so that the horizontal axis is finely divided, the range of finer coercive force values can be limited.

【0035】

In this way, according to the method of the present invention, it is possible to detect the magnetic substance without being affected by the residual magnetization state before detection.

【0036】

Further, since the magnetic pattern and the magnetic quality are used for identification, a high degree of authenticity can be determined. Moreover, since each part is small, it is easy to make it smaller and thinner.

【0037】

Furthermore, it can be applied not only to magnetic ink and magnetic toner for forms, but also to magnetic cards and magnetic plates and bars.

【0038】

Example 2 Next, a second embodiment of the present invention will be described.

【0039】

Also in this method, the same apparatus as 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.

【0040】

For example, when the outputs obtained in B and C are shown in (a) and (b), respectively, the ratio of peak heights shows the pseudo slope between points AB.

【0041】

If it is inverted as in (b) and (c), it can be seen that the subject has a coercive force between the magnetic fields C and D. In addition, the ratio of the peak heights indicates whether it is C or D.

【0042】

In addition, one or more sets of differential magnetoresistive elements and bias magnets are added to provide a total of three or more sets, and the number of measurement points on the magnetization curve of the magnetic material is increased. In addition, more detailed values can be obtained by detecting unique characteristics such as squareness.

【0043】

A permanent magnet was used as the bias magnet, but the second and third magnets are composed of electromagnets, and when changing the magnetic material to be detected, the strength of the bias magnetic field can be adjusted by changing the coil current. Good.

【0044】

Further, it may be composed of a first magnet and a yoke magnetized by the first magnet, and the yoke may be replaced as needed. In addition, one magnet may be used to devise the magnetizing strength, area, and number of poles. 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 quality detection along the saturation magnetization curve but also detection along a minor loop may be performed.

【0045】

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

【0046】

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

【0047】

[Effect of the invention]

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

[Simple explanation of drawings]

[Figure 1]

The figure which shows the magnetic quality detection apparatus of the Example of this invention [Figure 2]

The figure which shows the saturation magnetization curve of the magnetic material in this apparatus [Fig. 3]

The figure which shows the signal processing circuit in this apparatus [Fig. 4]

The figure which shows the saturation magnetization curve of each magnetic material in the method of the Example of this invention. [Fig. 5]

Diagram showing output in the same method [Fig. 6]

The figure which shows the method of the 2nd Example of this invention [Fig. 7]

Explanatory drawing of principle of this invention [Fig. 8]

Explanatory drawing of principle of this invention [Fig. 9]

Explanatory drawing of principle of this invention [Fig. 10]

Explanatory drawing of principle of this invention [Explanation of symbols]

10 1st magnet 20 First differential magnetoresistive element 30 Second magnet 40 Second differential magnetoresistive element 50 Third magnet 60 board