JPH02297081A - Magnetic head - Google Patents

Abstract

PURPOSE:To detect a minute magnetic pattern with high sensitivity by providing a detection coil in which one end each is connected and fixed magnetically to each magnetic pole, and an end face of the other end each is wound round to one of cores opposed at a small gap. CONSTITUTION:A magnetic head 1 becomes an open magnetic path in a part in which a magnetic pattern 21 of a bill 20 is not formed, a magnetic flux phipassing through the inside of cores 3, 4 is not varied, and no electromotive force is generated in a magnetic coil 5. When the bill 20 moves in the direction as indicated with an arrow A, and passes through a front end gap G of the pattern 21, when the gap G is connected magnetically by the pattern 21, the head 1 becomes a closed magnetic path, the magnetic flux passing through the inside of the cores 3, 4 is varied, and electromotive force is generated in the coil 5. Simultaneously, when the rear end of the pattern 21 passes through the gap G, pulsative electromotive force is generated in its front end and rear end. This electromotive force is amplified by an amplifier 7, and outputted as a detecting signal. As a result, S/N of the coil 5 is improved, and a minute magnetic pattern can be detected.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a magnetic head.

(Prior Art and Problems to be Solved) In recent years, detection means using magnetic media have been widely used, and are also used, for example, to identify banknotes in automatic vending machines. The magnetic head 10 shown in FIG. 2 is a magnetic head used to identify magnetic patterns on banknotes, and has a core 11 wound with a coil 12 and a constant current source 13 (FIG. 4).
The DC excitation current I is supplied to magnetize the core 11, and the terminal voltage of the coil 12 is taken out and amplified by the amplifier 14.

In areas of the banknote 20 where the magnetic pattern 21 is not formed, the core 11 forms an open magnetic path due to the gap G, and the magnetic flux Φ interlinking with the coil 12 does not change. When it reaches the position of the gap G, the core 11 becomes a closed magnetic path, and the magnetic flux Φ passing through the core 11 changes. The impedance of the coil 12 changes as the magnetic flux Φ changes, and the terminal voltage ■ changes accordingly. This voltage V is taken out and amplified by an amplifier 14 to obtain a detection signal corresponding to the change Δ■.

However, the amount of change in the voltage of the coil 12 is 10~lOO
The direct current (μ) is extremely small, and moreover, the direct current (2) output from the constant current source 13 is not a perfect direct current and has a slight ripple. For this reason, there is a problem in that the S/N ratio of the detection signal deteriorates, making it difficult to detect fine magnetic patterns.

The present invention has been made in view of the above points, and an object of the present invention is to provide a magnetic head that can detect fine magnetic patterns with good accuracy.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a permanent magnet, each one end of which is magnetically connected and fixed to each magnetic pole of the permanent magnet, and the end surface of each other end slightly The sensor includes a pair of cores facing each other with a gap between them, and a detection coil wound around at least one of these cores.

(Function) When the magnetic pattern of the object to be detected passes through the gap between the cores, the gap between the cores is magnetically connected by the magnetic pattern, and the magnetic head becomes a closed loop. At this time, the magnetic flux interlinking with the detection coil wound around the core changes,
An electromotive force is generated in the detection coil. This electromotive force is caused only by changes in the magnetic flux of the permanent magnet. This allows detection of minute magnetic patterns.

(Example) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, a magnetic head 1 is composed of a permanent magnet 2, a pair of cores 3.4, and a detection coil 5.
The end faces 2a and 2b of the permanent magnet 2 have magnetic poles, for example, N and S poles. Each one end (base end) 3a, 4a of the core 3.4
are closely fixed and magnetically connected to the magnetic poles 2a and 2b of the permanent magnet 2, and the other ends (tips) 3b and 4b are bent inward, with a slight gap G between each end surface. They are facing each other.

The detection coil 5 is wound approximately around the middle of the core 3.4, and one end is connected to the amplifier 7 (FIG. 2), and the other end is grounded. The detection coil 5 may be wound around at least one of the cores 3.4, and the portion where the magnetic pattern 21 of the banknote 20 is formed is connected to the opposing tips 3b, 3b, and 3b of the core 3.4, respectively. 4b and moves at a constant speed in the direction of arrow A, crossing the gap G. The magnetic pattern 21 of the banknote 20 is a character or the like printed with magnetic ink.

The action will be explained below.

In FIGS. 1 and 2, the magnetic helad 1 has a banknote 20
The area where the magnetic pattern 21 is not formed is an open magnetic path, and the magnetic flux Φ passing through the core 3.4 is
The magnetic flux Φ interlinking with the detection coil 5 does not change. Therefore,
No electromotive force is generated in the detection coil 5.

When the banknote 20 moves in the direction of arrow A and the front end of the magnetic pattern 21 passes through the gap G, the magnetic pattern 21
When the gap G is magnetically connected by e occurs. Similarly, when the rear end of the magnetic pattern 21 passes through the gap G, an electromotive force e is applied to the detection coil 5.
occurs. That is, the detection coil 5 has the magnetic pattern 2
1 passes through the gap G, a pulse-like electromotive force e is generated at its front end and rear end.

This electromotive force e is amplified by an amplifier 7 and output as a detection signal.

The magnetic field of the permanent magnet 2 is a complete DC magnetic field, and moreover, the permanent magnet 2 and the detection coil 5 are electrically unrelated. Therefore, the detection coil 5 can detect only magnetic changes caused by the magnetic pattern 21. As a result, the S/N ratio of the detection coil 5 is greatly improved by several times compared to the conventional one, and it becomes possible to detect minute magnetic patterns.

(Effects of the Invention) As explained above, according to the present invention, a pair of permanent magnets, each one end of which is magnetically connected and fixed to each magnetic pole of the permanent magnet, and the end faces of each other end facing each other with a slight gap are provided. Since the configuration includes a core and a detection coil wound around at least one of these cores, it is possible to detect only magnetic changes, and as a result, the S/N ratio is significantly increased. This makes it possible to detect fine magnetic patterns with high precision. It is also possible to detect patterns printed on the back side. Moreover, the structure of the magnetic head is simple.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a magnetic head according to the present invention;
2 is an equivalent circuit diagram of FIG. 1, FIG. 3 is a block diagram of a conventional magnetic head, and FIG. 4 is an equivalent circuit diagram of FIG. 3. ■... Magnetic head, 2... Permanent magnet, 3.4...
Core, 5...Detection coil, 7...Amplifier, G...
Gap, 20...Banknote, 21...Magnetic pattern. Applicant Minerva Co., Ltd. Agent Patent Attorney Kanji Nagado 2nd

Claims (1)

[Claims] A permanent magnet, a pair of cores having one end magnetically connected and fixed to each magnetic pole of the permanent magnet, and the end faces of each other end facing each other with a slight gap, and a detection device wound around at least one of these cores. A magnetic head characterized by being equipped with a coil.