JPH03254403A - Bias magnetic field generator for magneto-optical recording - Google Patents

Abstract

PURPOSE:To improve the generation efficiency of a magnetic flux density in the vicinity of the surface of a core top by surrounding a side face of a coil with a side yoke, covering the upper face of the coil with a top yoke and forming a prescribed magnetic gap between an end face in the broadwise direction of the core top and an end face of the top yoke. CONSTITUTION:A couple of side yokes 4 are arranged on both sides of a core 2 along the lengthwise direction of a core top 1, a side yoke 4 surrounds the side face of a coil 3 and is linked magnetically to the core 2 and a top yoke 5 is arranged on the upper part of a couple of side yokes 4 incorporated in the coil 3. Then a prescribed gap is specified between the side face in the broadwise direction of the core top 1 placed to surround the core top 1 and the side face of the core top. That is, since the core top 1 and the top yoke 5 are arranged closely via a prescribed gap, the magnetic flux easily passes through the gap. Thus, the magnetic reluctance of the magnetic circuit is reduced and the total magnetic flux quantity is increased. Thus, the effective magnetic flux density in the vicinity of the surface of the core top 1 is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bias magnetic field generating device for magneto-optical recording, and more particularly to a magnetic circuit configuration of an electromagnetic type bias magnetic field generating device.

[Conventional technology]

So-called magneto-optical recording records information based on the direction of magnetization of a magnetic film. The coercive force required to reverse the magnetization of the magnetic film decreases as the temperature rises. By utilizing this phenomenon, a laser beam is focused on a magnetic film to perform magnetization reversal and record information. The direction of magnetization is determined by the direction of an externally applied bias magnetic field, and the direction of the bias magnetic field is reversed when erasing and recording information.

Electromagnets have conventionally been used to generate such bias magnetic fields. FIG. 7 shows a conventional electromagnetic type bias magnetic field generating device for magneto-optical recording. To illustrate, the conventional device includes a core formed with a top having a predetermined length and width;
It consists of a coil that is wound around the core and generates magnetic flux from the top of the core when energized. The top portion of the core is arranged to face the magneto-optical disk, which is an information recording medium, along the radial direction, and applies a bias magnetic field to the surface of the magneto-optical disk. In magneto-optical recording, since it is necessary to switch between recording and erasing information at high speed, the current direction of the coil is synchronously reversed to reverse the magnetic field.

In this case, the magnetic flux that effectively acts on the magneto-optical disk is a perpendicular component generated near the top plane of the core.

[Problem that the invention seeks to solve]

In an electromagnetic bias magnetic field generator, a coil is constantly energized to continuously generate magnetic flux. For this reason, it has the disadvantage of generating a large amount of heat. In order to suppress heat generation, it is necessary to increase the efficiency of magnetic flux generation near the top of the core and reduce the amount of current applied. However, the conventional example shown in FIG. 7 has a problem in that sufficient magnetic flux generation efficiency cannot be obtained because the magnetic resistance of the magnetic circuit that guides the magnetic flux is large. By the way, in order to increase the magnetic flux generation efficiency, it is possible to increase the number of turns of the coil. However, in this case, the inductance of the coil increases, making it difficult to reverse the magnetic field at high speed. Furthermore, if the amount of current is increased in order to increase the total amount of magnetic flux generated by the electromagnet, the amount of heat generated by the coil will inevitably increase. Furthermore, in order to increase the bias magnetic field without lowering the magnetic field reversal speed or increasing the amount of heat generated by the coil, it may be possible to increase the overall size of the electromagnet. However, when the size of the electromagnet is increased, it becomes difficult to incorporate it into a magneto-optical recording device.

[Means for solving problems]

In view of the above-mentioned problems of the conventional technology, the present invention improves the magnetic flux generation efficiency, concentrates the magnetic flux, and improves the magnetic flux density of the bias magnetic field necessary for recording and erasing information, thereby reducing the amount of heat generated by the coil. With the goal.

In order to achieve the above object, a bias magnetic field generating device for magneto-optical recording according to the present invention has the configuration shown in FIG. FIG. 1 is an exploded perspective view of the device according to the invention. As shown, the device has a core 2 formed with a top 1 having a predetermined length and width. A coil 3 is arranged around the core 2 and generates magnetic flux from the top 1 of the core when energized. A pair of side yokes 4 are arranged on both sides of the core 2 along the length direction of the core top 1.

The side yoke 4 surrounds the side surface of the coil 3 and the core 2.
is magnetically connected to. A top yoke 5 is arranged above the pair of side yokes 4 in which the coil 3 is incorporated. The top yoke 5 is magnetically connected to each side yoke 4 and is arranged to cover the upper surface 6 of the coil 3. Then, it is placed so as to surround the core top 1, and a predetermined gap is defined between the core top 1 and the side surface of the core top 1 along the width direction of the core top 1. The width of this gap is set so as to optimize the magnetic flux distribution near the surface of the core top 1.

The core 2 and the pair of side yokes 4 are connected via a bottom portion 7 and are integrally formed of a ferromagnetic material, such as iron. Further, the top yoke 5 is made of a ferromagnetic plate made of iron or the like and has a long hole 8 formed therein which is aligned with the top part 1 of the core through a predetermined gap.

[For production]

In the bias magnetic field generating device according to the present invention, a magnetic circuit is configured by a core, a side yoke, and a top yoke. Since the top of the core and the top yoke are placed close to each other with a predetermined gap in between, the magnetic flux can easily pass through this gap. Therefore, the magnetic resistance of the magnetic circuit decreases and the total amount of magnetic flux increases.

Therefore, the effective magnetic flux density near the top surface of the core increases. However, if the width of the gap is reduced too much, the magnetic flux generated at the top of the core will be pulled by the top yoke, which will reduce the effective magnetic flux component acting on the magneto-optical disk, which is not preferable.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a schematic cross-sectional view showing a state in which the bias magnetic field generating device according to the present invention is incorporated into a magneto-optical recording device. The bias magnetic field generator 9 is mounted on the housing IO. This device 9 includes a core 2 on which a top portion 1 having a predetermined length and width is formed, a coil 3 wound around the core 2, a pair of side yokes 4 surrounding the sides of the coil 3, and a coil 3. and a top yoke 5 that covers the end face of the core and defines a predetermined gap between it and the core top 1. A head 11 is arranged to face the magnetic field generator 9. The head 11 is the base 1 of the magneto-optical recording device.
2, and has an objective lens 13 for focusing the laser beam. A magneto-optical disk I4 can be mounted between the magnetic field generator 9 and the head 11. The magneto-optical disk 14 is composed of a disk-shaped transparent carrier 15 and a magneto-optical recording medium 16 formed on the surface of the carrier 15.

The core top portion 1 is arranged along the radial direction of the disk 14, and its length is set to, for example, 16 degrees. Further, the width dimension is set to, for example, one inch in consideration of installation errors in the magneto-optical recording device. The core top portion 1 is disposed close to the recording medium 16 of the disk 14, and has a structure in which a magnetic field is efficiently applied. Therefore, the magnetic flux effective for recording and erasing information is a vertical component generated near the surface of the core top 1. Furthermore, an objective lens 13 is connected to a portion of the recording medium 16 to which the magnetic field is applied via a transparent carrier 15.
This allows the laser beam to be focused.

With this configuration, information is selectively recorded and erased by reversing the bias magnetic field.

Next, the operation of the bias magnetic field generating device according to the present invention will be explained in detail with reference to FIG. FIG. 3 is a schematic cross-sectional view taken along the width direction of the top of the core of the magnetic field generator, showing the distribution of magnetic flux. As shown in the figure, the core, top yoke, and side yokes form a magnetic circuit, and the magnetic flux generated from the top of the core flows to the side yokes via the top yoke and returns to the core. In the present invention, since a predetermined gap is formed between the top yoke and the top of the core, a considerable portion of the magnetic flux flowing out of the core passes through this gap and flows toward the top yoke.

Therefore, the magnetic resistance of the magnetic circuit decreases and the total magnetic flux increases. Therefore, the magnetic flux protruding from the gap also increases, and the efficiency of magnetic flux generation improves. In particular, the magnetic flux density near the top surface of the core, which effectively acts on the magneto-optical disk, is extremely high, and an effective bias magnetic field can still be generated even if the amount of current applied to the coil is reduced.

On the other hand, FIG. 4 is a schematic cross-sectional view of a conventional bias magnetic field generating device, showing its magnetic flux distribution state. The magnetic flux flows out from the central core, passes through the air, and returns to the bottom of the core. Therefore, the magnetic resistance is high and the total amount of magnetic flux is low compared to the bias magnetic field generating device according to the present invention. As a result, the magnetic flux density near the surface of the top of the core is also lower than in the present invention.

Therefore, in order to generate the same bias magnetic field, a larger amount of current is required, resulting in an increase in the amount of heat generated by the electromagnet.

Next, FIG. 5 shows the distribution of magnetic flux density in the vicinity of the core top surface using the gap distance between the core top and the side yoke as a parameter. In the illustrated graph, the horizontal axis indicates the distance in the width direction with the center of the top of the core as the origin, and the vertical axis indicates the magnetic flux density.

The unit of distance is millimeter and the unit of magnetic flux density is 1O-
It is 2 Tesla. However, the magnetic flux density shows the distribution of the perpendicular component that effectively acts on the magneto-optical disk. The measurement results shown in the graph were obtained under the conditions shown in the table below.

In the table graph, curve 1 shows the width direction distribution of magnetic flux density when the gap size is about 0.5, and curve 2 shows the width direction distribution of the magnetic flux density when the gap size is about 1. Curve 3 shows the magnetic flux density distribution when the gap size is 1.5 mm. Curve 4 shows the magnetic flux density distribution in a conventional structure for reference. As is clear from the graph, when a top yoke is used and a gap is formed between the top yoke and the top of the core, the effective magnetic flux density can be significantly improved compared to the conventional method. It can be seen that the smaller the gap size, the higher the level of magnetic flux density. However, if the gap size is excessively reduced, the magnetic flux emitted from the top of the core will be excessively pulled by the top yoke edge, which is undesirable because the effective vertical component of the magnetic flux density will decrease. Also, curve 1.
As is clear from comparing 2 and 3, the smaller the gap size within the allowable range, the higher the magnetic flux density level.
On the other hand, the peak width of the magnetic flux density distribution is narrowed. In other words, the narrower the gap, the steeper the edge of the peak, and the narrower the flat peak area becomes, creating the possibility that the installation tolerance for the magneto-optical recording device cannot be accommodated. Therefore, it is preferable to set the gap size so that the peak level and peak width of the magnetic flux density are optimized according to the specifications of each magneto-optical recording device.

In the example shown in FIG. 5, for example, the gap size is 15
When m1 is set, the generation efficiency of magnetic flux density can be improved approximately twice as compared to the conventional example. As a result, in order to obtain the same level of magnetic flux density as in the conventional example, the current flowing through the coil can be reduced to about 50%. Therefore, it is possible to significantly reduce the amount of heat generated compared to the conventional method.

Finally, FIG. 6 shows the relationship between the gap amount and the total magnetic flux amount.

In the illustrated graph, the horizontal axis represents the amount of gap between the top of the core and the top yoke, and the vertical axis represents the total amount of magnetic flux generated by the electromagnet.

The total amount of magnetic flux is expressed as a relative value based on the gap amount of 5.0, that is, the case where the top yoke is not disposed between the core and the side yokes. The total amount of magnetic flux increases as the gap amount or gap size becomes smaller. For example, when the gap amount is 1.0 m, the total magnetic flux amount is 2.3 times as much as when there is no top yoke. however,
Since the inductance of the electromagnet is proportional to the total amount of magnetic flux, the inductance also increases by about two or three times. Therefore, if left as is, a side effect of providing the gap would be that the high-speed switching characteristics of the bias magnetic field would deteriorate. However, as a countermeasure to this problem, the inductance can be lowered by adjusting the number of turns of the coil and the coil current while keeping the magnetomotive force, or ampere turns, of the coil constant. For example, if the number of coil turns is halved and the coil current is doubled, the inductance can be reduced to 1/4 while keeping the ampere turns constant. In other words, there is no problem because only the inductance can be adjusted without changing the power consumption.

〔Effect of the invention〕

As described above, according to the present invention, the side surface of the coil is surrounded by the side yoke, the top surface of the coil is covered by the top yoke, and a predetermined magnetic gap is formed between the widthwise end surface of the top of the core and the end surface of the top yoke. By doing so, it is possible to lower the magnetic resistance and increase the total amount of magnetic flux. As a result, the efficiency of generating magnetic flux density near the surface of the top of the core is improved.

Therefore, when such a bias magnetic field generating device is incorporated into a magneto-optical recording device, there is an effect that the amount of current applied to the coil can be lowered compared to the conventional method, and the amount of heat generated can be kept low.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of a bias magnetic field generating device for magneto-optical recording according to the present invention, FIG. 2 is a schematic cross-sectional view showing the device shown in FIG. 1 incorporated into a magneto-optical recording device, and FIG. The figure is a schematic cross-sectional view showing the magnetic flux distribution of the magnetic field generator shown in Figure 1, Figure 4 is a schematic cross-sectional view showing the magnetic flux distribution of the conventional bias magnetic field generator, and Figure 5 is the core of the bias magnetic field generator. Figure 6 is a graph showing the magnetic flux density distribution near the top, Figure 6 is a graph showing the relationship between the gap between the top of the core and the end face of the top yoke and the total magnetic flux in a magnetic field generator, and Figure 7 is a graph showing the relationship between the total amount of magnetic flux and the magnetic flux density distribution in the vicinity of the top of the magnetic field generator. FIG. 1 is a schematic perspective view showing the structure of a recording bias magnetic field generating device. 1... Core top 3... Coil 5... Top yoke 9... Bias magnetic field generator 10... Housing 13... Objective lens 15... Transparent carrier

Claims (4)

[Claims] 1. a core having a top portion having a predetermined length and width;
A coil is wound around the core to generate magnetic flux from the top of the core when energized, and a coil is placed on both sides of the core along the length of the top of the core to surround the sides of the coil and to be magnetically connected to the core. a pair of side yokes, which are magnetically connected to each side yoke and arranged to cover the upper surface of the coil, and are arranged along the width direction of the core top through a predetermined gap with the side surface of the core top. A bias magnetic field generating device for magneto-optical recording consisting of a top yoke arranged in the top yoke. 2. 2. The bias magnetic field generating device for magneto-optical recording according to claim 1, wherein the dimensions of the gap are set to optimize the magnetic flux distribution near the top of the core. 3. 2. The bias magnetic field generating device for magneto-optical recording according to claim 1, wherein the core and the pair of side yokes are integrally formed from a magnetic material. 4. 2. The bias magnetic field generating device for magneto-optical recording according to claim 1, wherein said top yoke is comprised of a magnetic plate in which an elongated hole is formed which is aligned with the top of said core through a predetermined gap.