JPH07161090A - External magnetic field generating device - Google Patents

Abstract

PURPOSE:To obtain an external magnetic field generating device whose construction is of a small-sized and a simple and capable of generating a stable external magnetic field. CONSTITUTION:This external magnetic field generating device is provided with a magnetic field impressing means impressing a magnetic field on the irradiation position of a laser beam converged by an objective lens 15 on the disk surface at the time of recording or reproducing information and a magnetic field inverting means inverting the direction of the magnetic field impressed by the magnetic field impressing means. The magnetic field impressing means is provided in the vicinity of the irradiation position of the laser beam and has at least two magnetic poles 111a, 110b opposed each other almost parallel and the magnetic field inverting means inverts the direction of the magnetic field in a state where magnetic poles 110a, 110b are energized so that magnetic fields generated from magnetic poles 110a, 110b repulse each other. Further, the magnetic field impressing means is composed of electromagnets and magnetic poles 110a,110b are opposed each other across the objective lens 15 and forms of flat planes of tip parts of magnetic poles 110a, 110b are made to be almost parallel with the moving locus of the objective lens 15 in accordance with a tracking movement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc-shaped information recording medium such as a magneto-optical disc (in this specification, "optical disc").
Alternatively, it is simply referred to as "disk". ), An external magnetic field generator provided in an optical disc device for recording, reproducing, and erasing information.

[0002]

2. Description of the Related Art In recent years, an optical disk for recording and reproducing information by converging a laser beam onto the disk surface has been provided as a large capacity information recording medium replacing a magnetic disk. An optical disk device for recording and reproducing information is provided with an external magnetic field generator for applying a magnetic field to the disk when recording, rewriting or erasing information on the disk.

As shown in FIG. 6, such a magnetic field generating device has a yoke 22 extending so as to encompass a region where information is recorded in the radial direction of the disk 17 (direction perpendicular to the paper surface of the drawing). An electromagnet constituted by a winding coil 23 wound around the disk is provided, and the electromagnet is arranged at a position symmetrical with respect to the disk 17 with respect to the objective lens 15 installed in the rotary actuator 9 for tracking. It is set up. The winding coil 23 is covered with a case 24 to secure its positioning and shield.

When information is recorded on or erased from the disk 17, the objective lens 15 focuses and irradiates the laser beam onto the disk surface, and the winding coil 23
A current is applied to the disk 17 and a magnetic field perpendicular to the disk 17 is applied. Further, in an optical disk device, recording, reproduction and erasing of information are generally performed frequently, and it is necessary to reverse the direction of the magnetic field applied to the disk in accordance with each of these operations. The reversal of this magnetic field is input to the winding coil 23. This is done by reversing the direction of the applied current.

Further, as shown in FIG. 7, a columnar permanent magnet 29 extending in the radial direction of the disk 17 (direction perpendicular to the plane of the drawing) and magnetized with two poles in the radial direction is used. Some apply a magnetic field to the disk 17. In this device, the permanent magnet 29 is arranged in a position symmetrical to the objective lens 15 with respect to the disk 17 like the winding coil 23, and is configured to be rotatable about an axis 30.

Above the permanent magnet 29, there is provided an electromagnet including a magnetic field generating yoke 25, a winding coil 26 wound around the yoke 25, and a case 27 arranged to secure the positioning and shield of these members. Winding coil 2
6 is appropriately energized, a perpendicular magnetic field is generated with respect to the permanent magnet 29, and the permanent magnet 29 is rotated by mutual attraction and repulsion action, and the direction of the magnetic field applied to the disk 17 by the permanent magnet 29 is reversed. In addition, in order to secure the shield of the magnet 29 around the permanent magnet 29,
8 are provided.

[0007]

However, in the conventional magnetic field generator shown in FIG. 6, the winding coil becomes large in size in order to secure a magnetic field of a predetermined strength, and the device becomes large accordingly. was there. Furthermore, there are problems that the generated magnetic field distribution easily varies in the radial direction of the disk, a stable magnetic field cannot be applied, the structure becomes complicated, and it is difficult to secure mechanical mounting accuracy.

On the other hand, in the magnetic field generator shown in FIG.
There are problems that the time required for magnetic field reversal becomes long and high-speed access is not possible, the device becomes large, and the structure becomes complicated including the consideration of the leakage flux of the permanent magnet. Furthermore, both devices occupy the space above the disc, which is an obstacle to making the optical disc device smaller and thinner.

The present invention has been made to solve such conventional problems, and an object thereof is to obtain an external magnetic field generator which is small in size, has a simple structure, and can generate a stable external magnetic field. To aim.

[0010]

[Means for Solving the Problems] To achieve the above object,
The invention of claim 1 of the present application is a magnetic field applying means for applying a magnetic field to an irradiation position on a disk surface of a laser beam focused by an objective lens at the time of recording or erasing information, and a magnetic field applied by the magnetic field applying means. In the external magnetic field generator having a magnetic field reversing means for reversing the direction of the magnetic field, the magnetic field applying means includes at least two magnetic poles arranged near the irradiation position of the laser beam and facing each other substantially parallel to the disk surface. The magnetic field reversing means is related to the external magnetic field generator for reversing the directions of the magnetic fields in a state of being excited so that the magnetic fields generated from the magnetic poles repel each other.

According to a second aspect of the invention, in the first aspect of the invention, the magnetic field applying means is an electromagnet,
An external magnetic field generator in which magnetic poles of the electromagnet are provided so as to face each other across the objective lens, and a planar shape of a tip of the magnetic pole is substantially parallel to a movement locus of the objective lens accompanying a tracking operation. Is.

[0012]

In the present invention, as described above, the magnetic field applying means is provided in the vicinity of the irradiation position of the laser beam and has at least two magnetic poles facing each other substantially parallel to the disk surface. Are formed by the magnetic field reversing means so as to form magnetic fields in directions repelling each other.

That is, the magnetic poles provided in the magnetic field applying means are made to be either N poles or S poles by the magnetic field reversing means at the time of recording (including rewriting) or erasing of information on the disk. The magnetic flux emitted substantially parallel to the disk or incident on each magnetic pole substantially parallel to the disk is bent in a direction intersecting with the disk surface between the magnetic poles, so that the magnetic field is applied to the disk close to the magnetic poles. A vertical magnetic field is formed.

In order to record or erase information on the optical disc, it is necessary to focus the laser beam by the objective lens and apply an external magnetic field to the focusing position on the disc. As described above, the apparatus uses a repulsive magnetic field generated by a plurality of magnetic poles provided to face each other substantially parallel to the disk surface to generate a vertical magnetic field to the disk. It becomes possible to do.

Therefore, according to the present invention, the external magnetic field generator is provided on the same side as the objective lens, unlike the conventional optical disc apparatus in which the external magnetic field has to be placed on the opposite side of the objective lens with the disc interposed therebetween. Therefore, the space in the optical disk device can be effectively used, and the optical disk device can be made smaller and thinner.

Further, according to the invention of claim 2, the plane shape of the tip of the magnetic pole is made substantially parallel to the movement locus of the objective lens accompanying the tracking operation.
A magnetic field having a constant and stable intensity can be obtained with respect to the movement trajectory of the objective lens accompanying the tracking operation.

[0017]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration of a main part of an optical disc device provided with an external magnetic field generator according to an embodiment of the present invention.
3 to 3 are a side sectional view and a plan view showing the configuration of the external magnetic field generator according to the embodiment, respectively.

Referring to FIG. 1, a base plate 1 of the apparatus is provided with positioner driving magnetic circuit yokes 2a and 2b for moving an optical head 6 in a radial direction of an optical disk 17 to coarsely position a laser beam spot. A permanent magnet 3 is provided in each of the voids of the yokes 2a and 2b.

Further, bobbins 5a and 5b for fixing and supporting the electromagnetic coil 4 are fastened to the housing of the optical head 6, and the bobbin 5a and 5b are provided with the electromagnetic coil 4 so as to surround the permanent magnet 3. Bearings 7a and 7b for supporting the head 6 with respect to guide shafts 8a and 8b for guiding the movement of the head 6 in the radial direction of the disk.

Recording and reproducing information on the disk 17,
A laser beam for erasing is emitted by an LD (laser diode) 12 provided in a fixed head 11 provided on the base plate 1, passes through an optical system provided on the fixed head 11, and then is protected from dust. It is emitted from the window 13, passes through a hole provided in the optical head 6, is reflected upward by a mirror 14 attached to the rotary actuator 9, and is guided to an objective lens 15 also attached to the upper part of the rotary actuator 9. Then, the light is focused by the objective lens 15 and focused on the surface of the disk 17 mounted on the spindle motor 16.

On the other hand, the external magnetic field generator according to the present embodiment is provided with a pair of electromagnets provided below the disk 17 so as to face each other with the objective lens 15 interposed therebetween. 2 and 3, the yokes 10a, 10b of the electromagnet made of a high magnetic permeability material are fixed to the housing of the optical head 6, and the magnetic pole tips 110a, 110b thereof are fixed.
Are positioned so as to face each other so as to sandwich the objective lens 15 in a gap lg between the objective lens 15 and the disk 17, and on the other hand, insulating members 18a and 18b are provided at the bases thereof, and winding coils 19a and 19b is wound.

Further, as shown in FIG. 3, the rotary actuator 9 for the purpose of fine movement positioning to the target track in the radial direction of the disk (up and down direction in the same figure) is provided with the head 6
By known electromagnetic action due to the rotation driving magnets 21a and 21b fixed to the back yokes 20a and 20b provided in the above, and energization of a rotation driving coil (not shown) provided on the outer periphery of the rotary actuator 9, The objective lens 15 is rotated in the range of the angle θ ₁ (movable range ab) by rotating about P.

Here, the magnetic pole tip 110 of the yoke 10a.
a has a concave planar shape along an arc of radius R ₂ centered on a point P which is the rotation center of the actuator 9, while the magnetic pole tip 110 b of the yoke 10 b has a radius R centered on the point P. _It has a convex planar shape along the arc of ₁ . The objective lens 15 attached to the rotary actuator 9 moves at the center position of the gap between the magnetic poles 110a and 110b, and the spot of the laser beam focused by the lens 15 has a radius (R ₂
-R ₁₎ and thus to move / 2 arcs above.

The winding coils 19a and 19b are energized so that the magnetic poles 110a and 110b have the same polarity. As a result, for example, when the magnetic poles 110a and 110b are both N poles, the magnetic flux lines emitted from the tips of the magnetic poles 110a and 110b collide and repel at the position directly above the objective lens 15 as shown in FIG. The magnetic field is bent to form a perpendicular magnetic field to the disk 17 by interlinking perpendicularly to the disk 17.

On the other hand, the laser beam is focused and irradiated by the objective lens 15 on the lower surface position of the disk to which the vertical magnetic field is applied, and information is recorded or erased. In order to reverse the direction of the magnetic field applied to the disk, the direction of energization to the winding coils 19a and 19b is reversed and the magnetic pole 11 is rotated.
The polarities of 0a and 110b may be reversed.

FIG. 4 is a diagram showing the magnetic flux distribution at the center position of the gap between the magnetic poles. Since each of the magnetic poles 110a and 110b has the planar shape as described above, the magnetic pole 110a
The magnetic flux distribution from is as shown in the diagram T due to the magnetic flux concentration at both ends of the recess. On the other hand, the magnetic flux distribution from the magnetic pole 110b is as shown in the diagram U because the magnetic flux is concentrated at the tip of the convex portion.
Therefore, the magnetic flux distribution on the center position of the gap between the magnetic poles, that is, on the trajectory line of the movement of the laser beam spot is as shown in the diagram V which is a combination of the diagram T and the diagram U, and the objective lens 15 (laser beam spot) A stable and uniform magnetic field distribution can be obtained between ab which is the movable range of.

As described above, according to this embodiment, unlike the conventional optical disk device in which the external magnetic field generator is forced to be placed on the opposite side of the objective lens with the disk sandwiched, the external magnetic field generator is used as the objective. Since it can be provided on the same side as the lens, the space in the optical disk device can be effectively utilized, and the optical disk device can be made compact and thin.

Further, as shown in FIG. 5, by using the present invention, it is possible to realize an optical disc device capable of recording and reproducing on both sides of the disc. That is, as shown in the figure, optical heads 56 and 66 are provided on both the upper surface side and the lower surface side of the disk 517, and these optical heads 56 and 66 are provided.
On the other hand, the same external magnetic field generator as in the above-described embodiment, that is, the yokes 510a and 510b and the coil 519a, which face the optical head 56 with the objective lens 515 in between,
519b, and the objective lens 61 for the optical head 66.
The yokes 610a and 610b and the coils 619a and 619b which face each other with 5 interposed are provided.

With this structure, it is possible to easily realize an optical disk device capable of recording / reproducing operations on both sides of the disk, and to improve the data processing speed.

[0030]

As described above, according to the present invention,
It is possible to realize an external magnetic field generator having a simple structure and a small size that can generate a stable external magnetic field.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a main part of an optical disc device provided with an external magnetic field generator according to an embodiment of the present invention.

FIG. 2 is a side sectional view showing a configuration of an external magnetic field generator according to the embodiment.

FIG. 3 is a plan view showing a configuration of an external magnetic field generator according to the embodiment.

FIG. 4 is a diagram showing a magnetic flux distribution in the external magnetic field generator of the embodiment.

FIG. 5 is a side sectional view showing a configuration of an external magnetic field generator different from that of the embodiment.

FIG. 6 is a side sectional view showing a configuration of a conventional external magnetic field generator.

FIG. 7 is a side sectional view showing a configuration of another conventional external magnetic field generator.

[Explanation of symbols]

6,56,66 optical head 9 rotary actuator for tracking 10a, 10b, 510a, 510b, 610a, 61
0b York 15 Objective lens 17,517 Optical disc 19a, 19b, 519a, 519b, 619a, 61
9b Coils 110a, 110b Magnetic poles In the drawings, the same reference numerals indicate the same or corresponding portions.

Claims (2)

[Claims] 1. A magnetic field applying means for applying a magnetic field to an irradiation position on a disk surface of a laser beam focused by an objective lens at the time of recording or erasing information, and a direction of a magnetic field applied by the magnetic field applying means is reversed. In the external magnetic field generating device including magnetic field reversing means, the magnetic field applying means has at least two magnetic poles that are arranged in the vicinity of the irradiation position of the laser beam and that face each other substantially parallel to the disk surface, The magnetic field reversing device is a device for reversing the directions of magnetic fields in a state where the magnetic fields generated from the magnetic poles are excited so as to repel each other. 2. The magnetic field applying means is composed of an electromagnet, the magnetic poles of the electromagnet are provided so as to face each other across the objective lens, and the planar shape of the tip of the magnetic pole is the locus of movement of the objective lens accompanying the tracking operation. The external magnetic field generator according to claim 1, wherein the external magnetic field generator is substantially parallel to