JPH06338003A - Magnetic field application device - Google Patents

Abstract

(57) [Summary] [Purpose] The heat generation amount of the magnetic field application device can be significantly reduced without requiring a large-capacity power supply. In a magnetic field applying device used in a magneto-optical disk device or the like, a residual magnetic field is generated in the magnetic core by flowing an overcurrent when the polarity of the magnetic core is reversed, and the current value when energized is reduced. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field applying device used in a magneto-optical recording device such as a magneto-optical disk device.

[0002]

2. Description of the Related Art Conventionally, as a magnetic field applying device used in a magneto-optical disk device or the like, one using a permanent magnet and one using an electromagnet are known. The one using a permanent magnet has a drawback that it takes a long time to switch the polarity and the device becomes large.

Therefore, as a magnetic field applying device using an electromagnet, there is, for example, a device disclosed in Japanese Patent Publication No. 4-56362. That is, an optical information recording / reproducing apparatus adapted to record or erase information by condensing a light beam from a light source such as a semiconductor laser with an optical lens and projecting the light spot on a magneto-optical disk to which a bias magnetic field is applied. The bias magnetic field applying means is composed of a magnetic core formed of a semi-hard magnetic material and having a sufficient distance between the N and S poles, an exciting coil capable of reversing the polarities of the magnetic poles, and a pulse exciting current power supply. Is a bias magnetic field applying device.

[0004]

However, in the above-mentioned conventional magnetic field applying device, a current is applied to magnetize the coil once, and then the current is set to 0, and the magnetic field is applied to the magneto-optical disk by the coercive force of the semi-hard magnetic material. Since it is applied, there is an advantage that the current consumption is small, but it is necessary to momentarily supply a large amount of current in order to increase the coercive force, and the magnetic field application power source becomes large, which is not preferable for component mounting. There is.

The present invention has been made in view of the above points, and it is an object of the present invention to significantly reduce the amount of heat generated by a magnetic field applying device without requiring a large-capacity power source.

[0006]

The present invention has been made to achieve the above-mentioned object, and a light beam from a light source is condensed by an objective lens to form a spot on the magneto-optical recording medium. In a magnetic field applying device for applying a bias magnetic field to the magneto-optical recording medium for recording or erasing information on the magneto-optical recording medium, a magnetic core formed of a semi-hard magnetic material or a soft magnetic material, and the magnetic core. Is provided with an exciting coil capable of reversing the polarity, a normal current supplying means for supplying a normal current to the exciting coil, and an overcurrent supplying means for supplying an overcurrent to the exciting coil at the time of polarity reversal. It is a magnetic field applying device. Further, the overcurrent supply means supplies an overcurrent smaller than the magnetic saturation current value of the magnetic core to the exciting coil. Further, it has a magnetic sensor arranged in the vicinity of the magneto-optical recording medium, and a control circuit for controlling a current flowing through the exciting coil based on an output signal from the magnetic sensor.

[0007]

According to the present invention, at the time of polarity reversal, a residual magnetic field is generated by causing a current larger than that during energization, that is, an overcurrent, to be momentarily applied to the exciting coil. It is possible to reduce the current value. Also,
By supplying an overcurrent smaller than the saturation current value to the exciting coil, the load on the power supply is reduced. Further, the residual magnetic field of the magnetic core is detected by the magnetic sensor, and the amount of current flowing through the exciting coil is accurately controlled based on the detected signal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the accompanying drawings. 1 in the figure is H-shaped in cross section (sideways)
In this bobbin, the exciting coil 2 is wound around the central portion 1a of the bobbin 1, and the central portion 1a of the bobbin 1 is formed with a hole. A magnetic core 3 is inserted into this hole, and a cover 4 covering the outer periphery of the bobbin 1 is formed continuously with the magnetic core 3. The magnetic field generating means A composed of these is arranged above the medium 5 at a predetermined interval.

Here, as the material of the magnetic core 3, a soft magnetic material having a coercive force Hc of about 1 to 10 [Oe] (for example, pure iron, mild steel, cast iron, silicon steel, etc.) or semi-hard material is used. A material (Hc of about 10 to 100 [Oe]) is preferable. If a hard material is used, the coercive force Hc will increase, but since the magnetic permeability is small, the current required to obtain a predetermined magnetic field must be extremely large, and the area of the hysteresis loop is large. This is because the energy loss at the time of reversing is also large.

The magnetic field generating means A is connected to a magnetic field generating means drive circuit 8 which supplies a current to the exciting coil 2 in order to magnetize the magnetic core 3. Here, the magnetic field generated in the exciting coil 2 will be described with reference to FIGS. 2 and 3.
FIG. 2 is a diagram showing the relationship between the current flowing through the coil and time,
In the figure, a is a curve showing the characteristic when the normal current IA is passed, and b is a curve showing the characteristic when the overcurrent IB is passed according to the present invention. FIG. 3 is a diagram showing the relationship between the coil magnetic field (H) and the magnetic flux density (B). When the normal current IA is passed through the exciting coil 2, a coil magnetic field HA is generated, which causes a magnetic flux density BA. Further, the coil magnetic field HB is generated by causing the overcurrent IB to flow through the exciting coil 2, thereby generating the magnetic flux density BB.

Therefore, if the overcurrent IB is temporarily made to flow at the moment of reversing the direction of the magnetic field or at the moment of raising the magnetic field, as shown in FIG. 2B, as shown in FIG. The magnetic field generated in the magnetic core 3 can be strengthened by the amount of the residual magnetism (BA'-BA). That is, the current required to obtain the predetermined magnetic field can be reduced as compared with the case where the rising manner as shown in FIG. In addition, an overcurrent as shown in FIG.
It is more preferable to let it flow to (1) because the settling time becomes longer than that of (b).

The magnetic field generating means drive circuit 8 can use a known current control circuit as shown in FIG. 4, for example. By inputting a step input from the arithmetic processing unit 12 described later to the magnetic field generating means drive circuit 8. , Excitation coil 2
In addition, an overcurrent IB such as b shown in FIG. 2 can flow.

By the way, generally, magnetic materials cannot be magnetized infinitely, and saturation occurs at a certain point. Therefore, even if a large amount of current is passed to increase the remanence, the remanence cannot be increased beyond a certain limit. Further, if too much overcurrent is passed, the time until the current returns to a steady value becomes long, and the timing for writing information to the medium 5 must be delayed by the semiconductor laser drive circuit 11 during that time, so the performance as a drive device is improved. It is not preferable.

Therefore, as shown in FIG. 5, by using the drive circuit in which the adjusting means 8a, 8b such as the volume is provided to the resistors R1, R2 in the magnetic field generating means drive circuit 8 shown in FIG. The current flowing through the coil 2 is the magnetic core 3
It is possible to adjust the constant of the circuit so that the current value is smaller than the current value required for saturation.

On the other hand, below the medium 5, a carriage 7 having an objective lens 6 and the like mounted thereon is arranged so as to face the magnetic field generating means A. The objective lens position detecting means 9 is connected to the carriage 7, and is also connected to a drive circuit 10 for moving the objective lens 6. The semiconductor laser drive circuit 11, the magnetic field generation means drive circuit 8, the objective lens position detection means 9, and the drive circuit 10 described above are connected to an arithmetic processing unit 12, and these respective circuits and the like are connected to the arithmetic processing unit 12. Controlled by.

Next, an embodiment of the apparatus according to this embodiment will be described. When writing information to media 5,
When the arithmetic processing unit 12 receives the designated target track information, the arithmetic processing unit 12 gives a drive signal to the drive circuit 10. Thereby, the drive circuit 10 moves the carriage 7 to the target track. Then, when the objective lens position detecting means 9 detects that the target track has been reached, the detection signal is transmitted to the arithmetic processing unit 12.
A drive command is sent from the arithmetic processing unit 12 to the magnetic field generating means drive circuit 8. Then, the magnetic field generator driving circuit 8 supplies the exciting coil 2 with the overcurrent IB as shown in FIG. 2B, and the magnetic field B applied to the medium 5 by this overcurrent is BB as shown in FIG. To BA '. In consideration of this timing, the arithmetic processing unit 12 sends a lighting command to the semiconductor laser drive circuit 11, and the information is recorded on the medium 5.

Next, another embodiment will be described with reference to FIG. In the embodiment shown in FIG. 6, the same parts as those in the embodiment shown in FIG. 1 described above are designated by the same reference numerals. The difference from the previous embodiment is that a magnetic sensor 13 including a Hall element for detecting magnetism is arranged in the vicinity of the medium 5, and a gain variable to which a signal obtained from the magnetic sensor 13 is input. That is, the amplifier 14 is interposed between the arithmetic processing unit 12 and the magnetic field generating means drive circuit 8.

Therefore, the output from the magnetic sensor 13 is sent to the magnetic field generating means drive circuit 8 via the variable gain amplifier 14. The variable gain amplifier 14 uses the output of the magnetic sensor 13 to drive the magnetic field generating means 8
The gain input to is changed, and the waveform of the current flowing through the exciting coil 2 is changed according to the gain. With such a configuration, the residual magnetic field of the magnetic core 3 can be detected by the magnetic sensor 13 and an optimum current waveform can always be created.

[0019]

As described above, according to the present invention,
Since more current is instantaneously applied when the polarity is reversed than when the current is applied, the current value required when the current is applied to create a predetermined magnetic field can be reduced by the amount of residual magnetism. Therefore, current consumption is reduced, and heat generation in the device can be suppressed. Moreover, since only the minimum current for generating the residual magnetism is passed, the power supply can be downsized and the cost can be reduced. Furthermore, since the amount of residual magnetism remaining in the magnetic core is detected and the amount of current flowing through the exciting coil is controlled, the accuracy of the current set value is improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an apparatus showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing characteristics of a current flowing through an exciting coil.

FIG. 3 is an explanatory diagram showing a relationship between a coil magnetic field and a magnetic flux density.

FIG. 4 is an explanatory diagram showing a magnetic field generation unit drive circuit.

FIG. 5 is an explanatory diagram showing another magnetic field generating means drive circuit.

FIG. 6 is an explanatory view of an apparatus showing another embodiment.

[Explanation of symbols]

 1 Bobbin 2 Excitation Coil 3 Magnetic Core 4 Cover 5 Media 6 Objective Lens 7 Carriage 8 Magnetic Field Generation Means Driving Circuit 8a, 8b Adjusting Means 9 Objective Lens Position Detecting Means 10 Driving Circuit 11 Semiconductor Laser Driving Circuit 12 Arithmetic Processor 13 Magnetic Field Sensor 14 Variable gain amplifier

Claims (3)

[Claims] 1. A light beam from a light source is condensed by an objective lens to form a spot on the magneto-optical recording medium, and a bias is applied to the magneto-optical recording medium to record or erase information on the magneto-optical recording medium. In a magnetic field applying device for applying a magnetic field, a magnetic core formed of a semi-hard magnetic material or a soft magnetic material, an exciting coil capable of reversing the polarity of the magnetic core, and a normal current usually supplied to this exciting coil A magnetic field applying device comprising: a current supply means; and an overcurrent supply means for supplying an overcurrent to the exciting coil when the polarity is reversed. 2. The magnetic field applying apparatus according to claim 1, wherein the overcurrent supplying means supplies an overcurrent smaller than a magnetic saturation current value of the magnetic core to the exciting coil. 3. A magnetic sensor arranged near the magneto-optical recording medium, and a control circuit for controlling a current flowing through the exciting coil based on an output signal from the magnetic sensor. Alternatively, the magnetic field applying device according to claim 2.