JPS588570B2 - Permanent magnet magnetization/demagnetization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a permanent magnet magnetization/demagnetization circuit, and is particularly useful for magnetic sensors using magnetoelectric conversion elements.

Recently, magnetoelectric conversion elements, such as indium antimonide InSb, are used to read characters and symbols written with magnetic ink.
Magnetic sensors using magnetoresistive elements have been developed.

This has advantages such as low impedance, no inductance L component, and high sensitivity, and is expected to be put into practical use.

FIG. 1 shows a conventional example of this kind of magnetic sensor, in which 1 is a permanent magnet, 2 is a package fixed to one magnetic pole surface of this permanent magnet 1, and inside this package 2, a pellet 3 is placed on a pellet 3. Two fixed magnetoresistive elements M1 and M2 are housed.

4 covers the element storage part of the package 2 and covers the elements M1 and M
2, on which a magnetic piece 5 slides.

6 is an envelope in which the package 2 and the permanent magnet 1 are molded.

The magnetoresistive elements M1 and M2 are connected in series, a constant voltage Eo is applied to one end, the other end is grounded, and an output signal is taken out from the connection point between the two elements M1 and M2.

Now, with a bias magnetic field being applied by the permanent magnet 1, the minute magnetic piece 5 moves from one element M1 to the other element M2.
When moving in the direction of
/2Eo±△E.

By measuring this voltage change, the presence and moving direction of the magnetic piece 5 can be detected.

In such a magnetic sensor, a permanent magnet or an electromagnet as described above is used as a magnet that generates a magnetic field, and usually a ferrite magnet, a cast magnet, or the like is used.

However, when permanent magnets are used, floating magnetic particles adhere to the pole faces of the permanent magnets, and these magnetic particles adversely affect the elements M1 and M2, causing noise or malfunction.

On the other hand, if an electromagnet is used to generate a magnetic field only during use in order to avoid the influence of such stray magnetic particles, when a magnetic field of about IKG required to drive a magnetoresistive element is obtained, Joule heat due to the coil winding resistance will be generated. This caused the temperature of the magnetic sensor to rise, causing it to malfunction.

The present invention solves the above-mentioned drawbacks by using a permanent magnet while being magnetized and demagnetized by a coil.

That is, the permanent magnet is magnetized only when the magnetoresistive element is driven, and is demagnetized during the rest period of the magnetoresistive element to avoid adhesion of stray magnetic particles to the magnet.

In this way, the current flowing through the magnetizing and demagnetizing coils is only for a short period of time, so temperature rise due to Joule heat can be avoided.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a magnetizing circuit for a permanent magnet, where 7 is a commercial AC power supply, 8 and 9 are coils and diodes connected in series with this power supply 7 via a switch 10, and the coil 8 is a magnetizing circuit for a permanent magnet. It is wound around a permanent magnet 1 shown in FIG.

In this circuit, when the switch 10 is turned on, a rectified current rectified by the diode 9 (FIG. 4B) flows through the coil 8, thereby magnetizing the permanent magnet.

Figure 3A shows a permanent magnet degaussing circuit, 7, 10, 8
are the aforementioned AC power supply, switch, coil, and 11, respectively.
is a single-phase bridge rectifier circuit in which four diodes 12, 13, 14, and 15 are assembled into a bridge, and a coil 8 is connected in series to the AC input terminals A and A', and the DC output terminal B is connected to the rectifier circuit.
, B' are connected to a load 16 that decays over time.

Therefore, when the switch 10 is on, a damping current shown in FIG. 4B flows through the coil 8, and the permanent magnet is demagnetized.

Here, a capacitor can be used as the load 16, but in this case, the capacitance of the capacitor needs to be sufficiently large, and there is a risk that the capacitor will deteriorate due to excessive peak charging current.

FIG. 4A shows a degaussing circuit that takes this point into account, in which a capacitor 17 and a resistor 18 are connected in parallel to the DC output terminals B and B' of the bridge rectifier circuit 11 as loads.

In this circuit, the magnetizing current attenuates logarithmically during the initial to time, and then becomes approximately constant, as shown at the beginning of the figure.

This constant current is caused by the resistor 18 and is thought to make demagnetization incomplete, but the magnetic field generated in the coil 8
If the initial magnetic permeability is kept within the range of the magnet to be demagnetized, almost no residual magnetism will remain.

The resistor 18 also serves to increase the peak current flowing through the coil 8, thereby ensuring complete demagnetization of the magnet.

According to experiments conducted by the inventors, when a 4φ x 17mm cast magnet is demagnetized using a coil with an outer diameter of 10φ, an inner diameter of 4φ, a length of 15mm, and a number of windings of 1800 turns, the capacitance of the capacitor 17 is If the resistance value of the resistor 18 was selected to be 100 μF and the resistance value of the resistor 18 to be 3 KΩ, complete demagnetization could be performed.

Furthermore, when the resistor 18 was removed, complete demagnetization could not be achieved even with the use of a 500 μF capacitor.

Using the above results, magnetization and demagnetization can be performed using a simple circuit as shown in FIG.

In FIG. 5, diodes 12, 13, 14, and 15 form a bridge rectifier circuit 11, and a capacitor 17 and a resistor 18 are connected in parallel to DC output terminals B and B' of the bridge rectifier circuit 11. .

The coil 8 is used to magnetize and demagnetize the permanent magnet.

19 and 20 are first and second circuits for switching the magnetizing/demagnetizing circuit.
The first switch 19 performs on/off control between the terminals of the coil 8 and the AC input terminal A and DC output terminal B of the bridge rectifier circuit 11, while the second switch 20 performs on/off control between the terminals of the coil 8 and the AC input terminal A and DC output terminal B of the bridge rectifier circuit 11. On/off control is performed between one end of the parallel circuit of the resistor 18 and the DC output terminals B, B of the bridge rectifier circuit 11.

The switch 10 connects the 100V commercial AC power supply 7.

The permanent magnet is magnetized when the magnetoelectric conversion element is driven by the switch 19.
20 are connected to the B and B' sides, respectively, and a 100V commercial power source is connected by the switch 10.

At this time, a current flows through the diode 13, and a current as shown in FIG. 2B flows through the coil 8 to effect magnetization.

At the same time, the current charged in the capacitor 17 is completely discharged because both ends are short-circuited.

When the operation of the magnetic transducer is completed, the switches 19 and 20 are connected to A and B, respectively, and the switch 10 is turned on to 100V.
When connected to a commercial power supply, a current as shown in FIG. 4B flows through the coil 8, and demagnetization is performed.

As described above, by utilizing the present invention, magnetization and demagnetization can be reliably performed with a very simple circuit configuration.

Furthermore, the adhesion of stray magnetic particles on the magnet surface is avoided, and the temperature rise of the magnet due to magnetization and demagnetization is kept to a minimum.

The main point of the present invention is to connect a capacitor and a resistor in parallel as a load in a degaussing circuit using a bridge rectifier circuit,
An alternating current demagnetizing current that attenuates during the time to shown in Fig. 4B and then becomes constant is passed through the coil to completely demagnetize it using the hysteresis of the permanent magnet. The purpose is to utilize and perform this with a simple configuration.

Therefore, if the present invention is used, the permanent magnet used in the magnetoelectric conversion element can be magnetized and demagnetized with a very simple circuit configuration, which is economical.

Furthermore, since the permanent magnet is used while being repeatedly magnetized and demagnetized, it is possible to avoid floating magnetic particles from adhering to the magnetic pole surface.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a magnetic sensor using a magnetoresistive element,
FIG. 2A is a magnetizing circuit diagram explaining an embodiment of the present invention, FIG. The waveform diagram and FIG. 5 are circuit diagrams of the same embodiment. 1...Permanent magnet, 2...Package,
3... Pellet, Ml, M2... Magnetoresistive element, 5... Magnetic piece, 7... AC power supply, 8... Coil , 11... Rectifier circuit, 16... Load, A, A'... AC input terminal, B, B'... DC output terminal,
19...First switch, 20...Second
switch.

Claims (1)

[Claims] 1. an AC power source, a coil wound around a permanent magnet that is magnetized or demagnetized and one end of which is connected to the AC power source, and a rectifier circuit to which the AC power is applied via the coil and a first switch; The next stage of the rectifier circuit includes a capacitor and a resistor connected in parallel via a second switch, and the first switch connects the other end of the coil to the AC input terminal or DC output terminal of the rectifier circuit. and the second switch turns on and off between one end of the parallel circuit of the capacitor and the resistor and two DC output terminals of the rectifier circuit. circuit.