JPH02240795A - Recognizing method for magnetic ink printing pattern - Google Patents

Abstract

PURPOSE:To improve the accuracy in the case of recognizing a magnetic ink printing pattern by detecting a magnetic field from the magnetic ink printing pattern, while applying a feeble bias magnetic field in the direction opposite to an initial magnetization to an MR element pattern. CONSTITUTION:An MR element chip in which a ferromagnetic magneto- resistance element (MR element) 1 is formed is provided, and with respect to a current pattern 3, a magnetic field is applied in the longitudinal direction of a pattern of an MR element 1. That is, by allowing an initial magnetization instantaneous current Iini to flow to the current pattern 3, the MR element 1 is brought to initial magnetization in the Hini direction in advance, and subsequently, a current of Ib is allowed to flow to the current pattern 3 and a bias magnetic field of Hb is applied to the extent that the initial magnetization is not inverted. In such a way, since the internal magnetization of the MR element pattern comes to rotate easily against the external magnetic field Hex, the sensitivity is improved.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for recognizing a magnetic ink print pattern using magnetic ink, for the purpose of improving the sensitivity of magnetic ink print pattern recognition, the detection magnetic field direction and A current pattern is provided that generates a bias magnetic field in a perpendicular direction, and an instantaneous current is passed through the pattern to perform initial magnetization, and then a magnetic ink printed pattern is recognized.
In addition to the initial magnetizing instantaneous current, the current pattern is configured to constantly flow a weak current in the opposite direction to the instantaneous current to apply a weak bias magnetic field to the magnetoresistive element while detecting the magnetic field from the magnetic ink printed pattern. do.

[Industrial application field]

The present invention relates to a method for recognizing magnetic ink print patterns using magnetic ink.

Printed patterns using magnetic ink (magnetic patterns) are used for various things, and accurate recognition of the magnetic patterns is important in identifying counterfeit products and the like.

Therefore, in order to obtain a large amount of recognition information from the magnetic pattern, it is necessary to recognize the magnetic pattern over a wider range than before, and to make it possible to recognize even minute patterns. Therefore, a recognition device is required that has a plurality of magnetic detectors arranged in an array and accurately detects the magnetic patterns.

Conventionally, a semiconductor magnetoresistive element such as [nSb] was used as a method to realize the above recognition device, but recently a ferromagnetic thin film magnetoresistive element (hereinafter referred to as M
A sensor using an R element (referred to as an R element) has been developed. M.R.
The element utilizes the fact that when the internal magnetization aligned in the longitudinal direction of the MR element pattern is rotated by an external magnetic field, the resistance value changes.

[Conventional technology]

A conventional method for recognizing a magnetic printed pattern using an MR element is to magnetize the magnetic printed pattern in advance and then apply a weak magnetic field generated from the magnetic printed pattern to an MR element made of a ferromagnetic thin film as shown in FIG. Detection is performed using the fact that the resistance R of the MR element depends on the relative angle θ between the direction of magnetization M due to the magnetic field from the magnetic print pattern and the direction of the current 2 flowing through the MR element 1. It is something. At this time, before recognizing the magnetic print pattern, the MR element 1 momentarily applies a magnetic field in the longitudinal direction of the pattern to perform initial magnetization, but when recognizing the magnetic print pattern, no bias magnetic field is applied.

[Problem to be solved by the invention]

Since the magnetic field generated by the magnetic ink print pattern is extremely weak, it is necessary to increase the sensitivity of the MR element to detect it. A highly sensitive MR element can be realized by reducing the sensitivity S of the MR element with respect to the width W and film thickness t of the MR element pattern. However, increasing the thickness of W increases the area of the MR element, and t needs to be 300 Å or more to maintain the properties of the film, so each has a limit value and is infinite. The problem is that sensitivity cannot be improved.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide a method for recognizing magnetic ink print patterns that makes it possible to improve the sensitivity of magnetic ink print pattern recognition.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention.

In the same figure, 2 is a ferromagnetic magnetoresistive element (MR element) 1
3 is a current pattern that can apply a magnetic field in the longitudinal direction of the pattern of the MR element l.

[For production]

An instantaneous initial magnetization current 1i old is passed through the current pattern 3 to initialize the MR element l in the 1old direction, and then a current Ib is passed through the current pattern 3 so that the initial magnetization does not reverse.
By applying the bias magnetic field b, the internal magnetization of the MR element pattern becomes easier to rotate with respect to the external magnetic field Hex, so that the sensitivity is improved.

〔Example〕

FIG. 2 shows an apparatus with which the method of the invention can be carried out. This device includes a conveying means 12 consisting of a plurality of rollers 11 for conveying a recording medium 10, a magnetizing means 13 for magnetizing a magnetic pattern printed on the recording medium 10, and a magnetizing means 13 for detecting the magnetized magnetic pattern. A magnetic sensor 14 and a signal processing circuit 15 that processes signals from the magnetic sensor 14
It is configured with the following.

FIG. 3 is an enlarged sectional view of section A in FIG. 2, showing a magnetic sensor that detects a magnetic pattern.

In the figure, reference numeral 20 denotes a magnetoresistive element (MR element), which is mounted on a protective plate 21 with a flexible printed board 22 for applying a bias magnetic field sandwiched therebetween. 23 is a flexible printed board for driving the MR element 20, one end of which is wire-bonded to the electrode of the MR element 20 with a wire 24, and the other end connected to a printed board 25 equipped with a drive circuit (not shown). . 26 is a resin or non-magnetic metal cover for protecting the MR element.

FIG. 4 is an enlarged view of the pattern of the MR element 20 shown in FIG. This MR element has a structure in which a resistor pattern 27 formed on a silicon substrate on which an oxide film is grown and external connection terminals 28, 29, and 30 are integrally connected. The resistor pattern 27 is made of a ferromagnetic thin film such as permalloy formed in a zigzag pattern, and a conductive material (for example, gold) 3 in inclined stripes.
1 was formed.

Resistor pattern 2 generally equipped with such a conductor pattern
7 is called a barber pole type, and after initial magnetization in the longitudinal direction of the pattern 27, a predetermined current is applied to the terminals 28 and 30, and an external magnetic field Hex perpendicular to the longitudinal direction of the pattern 27 is applied. Then, the resistance change of the first block and the second block is detected from the terminal 29, and the presence or absence of the external magnetic field Hex can be detected from the resistance value change.

FIG. 5 shows the relationship between the magnetic field strength in the detection magnetic field direction of the MR element shown in FIG. 4 and the change in resistance value. In the figure, the horizontal axis represents the external magnetic field strength,
The vertical axis represents the resistance change, and curves A and B show the relationship between the external magnetic field and the resistance change. Note that the width of the MR element pattern dimension is 1507 mm, and the thickness of the permalloy film is 300 mm.

The figure shows that when a bias magnetic field Hb=20e is applied (shown by the curve), the resistance change for the same external magnetic field is larger in the micromagnetic field range than when Hb=Q (shown by the curve B), that is, the output is larger. I understand. Therefore, in this embodiment, a constant current of -40 mA is applied to the current pattern 3 provided on the back surface of the MR element (formed on the flexible printed board 22 in FIG. 3) as shown in FIG.
The magnetic ink print pattern is detected while a bias magnetic field of Hb=-20e, which is opposite to the initial magnetization, is generated in the element section. On the other hand, the MR element requires an initial magnetization step to align the magnetization in the MR element pattern in the same direction before detecting the magnetic ink print pattern.
When the switch is turned on, an instantaneous current of 200 mA is passed through the current pattern 3 as shown in FIG. 7, and a magnetic field of approximately 100 e is generated to perform initial magnetization.

According to the present embodiment described above, the internal magnetization of the MR element pattern can be easily rotated, so that the sensitivity to a minute magnetic field is improved.

〔Effect of the invention〕

As explained above, according to the present invention, by detecting the magnetic field from the magnetic ink print pattern while applying a weak bias magnetic field in the opposite direction to the initial magnetization to the MR element pattern, the magnetic ink print pattern It is possible to improve the accuracy when recognizing.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a diagram showing an apparatus capable of implementing the method of the present invention, Fig. 3 is an enlarged sectional view of section A in Fig. 2, and Fig. 4 is Fig. 3. Figure 5 is a diagram showing the output characteristics of the MR element, Figure 6 is a diagram showing a flexible printed board with a current pattern for applying a bias magnetic field, and Figure 7 is a diagram showing the current flowing through the current pattern. FIG. 8 is a diagram showing a conventional MR element. In the figure, 1.20 is a magnetoresistive element (MR element), 2 is an MR element chip, 3 is a current pattern, 1O is a recording medium, 11 is a roller, 12 is a conveying means, 14 is a magnetic sensor, 15 is a signal processing circuit shows. Fig. 2 is an enlarged sectional view of section A in Fig. 2; Fig. 9 is an enlarged pattern of the MR element in Fig. 3; Fig. 2 shows an apparatus capable of carrying out the method of the invention; Fig. 15... Figure 7 shows the output characteristics of the 31-circuit MR element; Figure 7 shows the current pattern; Figure 7 shows the current flow;

Claims (1)

[Claims] 1. A current pattern (3) that generates a bias magnetic field in a direction perpendicular to the direction of the detected magnetic field is provided on the front or back surface of the magnetoresistive element chip (2), and an instantaneous current is applied to the pattern (3). In the method of recognizing the printed pattern of magnetic ink after initial magnetization is carried out by passing current, in addition to the instantaneous current for initial magnetization, a weak current is constantly passed in the opposite direction to the instantaneous current in the current pattern (3) to increase magnetic resistance. A method for recognizing a magnetic ink print pattern, characterized in that the magnetic field from the magnetic ink print pattern is detected while applying a weak bias magnetic field to the element (1).