JPS59148159A - Optical pickup device - Google Patents

Abstract

PURPOSE:To prevent the recording medium of a magnetized thin film from exerting an evil effect due to leaked magnetic flux on it by driving electromagnetically the optical element of an optical beam system and at the same time cutting off the leaked magnetic flux. CONSTITUTION:An object lens 2, etc. of the optical beam system of an optical pickup are driven electromagnetically by a driving coil 6, permanent magnet 8, etc. which are set within a housing 4. Thus the focus control, etc. are performed to a disk 1. A magnetic shielding member 13 is provided to the housing 4 to cut off the leaked magnetic flux. Thus an evil effect due to the leaked magnetic flux is prevented from exerting on the magnetized thin film of the disk 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical pickup device for recording and reproducing information by optical means on a recording medium made of a magnetic thin film.

Conventional technology In general, information signals are recorded by irradiating a light beam onto a -axis anisotropic magnetic thin film, such as GdTbFe, in a spot shape and heating it to a temperature near the Curie point to form a magnetization reversal region. There are known methods for doing this. When reproducing information, a light beam for reading information is irradiated onto the recording medium, and the Kerr rotation angle of reflected light or transmitted light of the light beam is different between areas where magnetization has been reversed and areas where magnetization has not been reversed. You can obtain a playback signal by doing this.

In conventional optical pickup devices, in order to focus a light beam onto a recording medium, the entire optical system or a part of the optical system, such as an objective lens, is driven by a driving device that uses electromagnetic force.

Here, a specific example of an optical pickup device is shown in FIGS. 1 and 2. The optical pickup device shown in FIG. 1 includes an objective lens 2 that focuses a light beam onto a recording body 1-1-
A lens barrel 3 that supports the objective lens 2. An elastic support 5A that supports the lens barrel 3 on the housing 4 so as to be movable in the direction perpendicular to the recording medium 1.
and 5B, a drive coil 6 fixed to the lens barrel 3, a magnetic circuit consisting of yokes 7A and 7B that apply a magnetic field to the drive coil 6, and a permanent magnet 8, and a galvanometer mirror that moves the light beam on the surface of the recording medium 1. -9. When recording information, the optical pickup device records information in a track while moving relatively parallel to the recording medium 1, and when reproducing information, it reproduces while following the already formed information track. At this time, the relative distance between the recording medium 1 and the optical pickup changes depending on the unevenness of the surface of the recording medium 1, vertical movement during movement, external vibrations, and the like. Therefore, in order to ensure that the light beam is always focused on the recording medium 1, a separate detector (not shown) detects the error signal of the defocus, and the driving coil 6 is connected to the magnetic circuit. Focus control of the objective lens 2 is performed by driving by a drive device composed of A, 7B, and 8.

Further, in order to prevent the light beam from deviating from the information track once grasped, a separate detector (not shown) detects the amount of track deviation, and the galvano mirror 9 is rotationally driven to perform tracking control.

In the example of the optical pickup device shown in FIG. 2, focus control is performed in the same manner as in FIG.
This is performed by electromagnetically driving in a direction perpendicular to the optical axis using a coil 11 fixed to the objective lens 2 and a magnetic circuit 12 that applies a magnetic field.

In the optical pickup device configured as shown in FIG. 1 or 2, the focal length of the objective lens 2 is as short as several millimeters, and the optical pickup device is close to the recording medium 1, so that focus control and A magnetic circuit installed for tracking control? A, 7B.

There is a drawback that the leakage magnetic flux from 8 acts on the recording medium 1, which is a uniaxially anisotropic magnetized thin film, and has an adverse effect on information recording and reproduction.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical pickup device which eliminates the above-mentioned drawbacks and prevents leakage magnetic flux generated from the optical pilaf pickup device from having an adverse effect on a magnetic thin film recording medium during information recording and reproduction. It's about doing.

In order to achieve this object, the present invention provides magnetic shielding by disposing a member with high magnetic permeability between the main body of the optical pickup device and the recording medium.

Example Hereinafter, the present invention will be explained in detail with reference to the drawings.

First, a first embodiment of the present invention will be described with reference to FIG.

In Fig. 3, 1 is a recording medium made of a uniaxially anisotropic magnetic thin film, 2 is an objective lens fixed to a lens barrel 3, and 5A and 5B.
6 is an elastic support that supports the lens barrel 3 so as to be movable in the optical axis direction with respect to the housing 4; 6 is a yoke 7 that is fixed to the lens barrel 3;
A driving coil inserted into a magnetic circuit consisting of A and 7B and a permanent magnet 8, and 9 is a galvanometer mirror. Furthermore,
13 is a magnetic barrier member made of a material with high magnetic permeability, such as permalloy, provided with a hole 13A through which the light beam passes;
The elastic support 5B side of the casing 4 is surrounded and fixed to the casing 4, the hole 13A is coaxial with the lens barrel 3, and a galvano mirror is attached.
The reflected light from the lens barrel 3 passes through the objective lens 2 and the hole 13.
The light is made to enter the recording medium 1 through A.

In such a device, when recording/reproducing information, the optical pickup device is moved relatively parallel to the recording medium 1, and focus control is performed to drive the objective lens 2 in the optical axis direction, and the light beam is focused on the information track. Tracking control is performed using a galvanometer mirror 9 to prevent it from slipping off. At that time, leakage magnetic flux from the magnetic circuit consisting of the yokes 7A and 7B and the permanent magnet 8 may act on the recording medium 1 and cause unnecessary magnetization reversal, or the recording conditions by the light beam may change and the information In order to avoid incomplete recording and reproduction, the present invention provides a hole 1 through which the light beam passes.
A magnetic barrier member 13 with an opening of 3A is provided between the housing 4 and the recording medium 1 to reduce the influence of leakage magnetic flux.

Next, a second embodiment of the present invention is shown in FIG.

Here, 1 is a recording medium of a uniaxially anisotropic magnetic thin film, 14 is an optical pickup device main body equipped with an electromagnetic objective lens drive mechanism, and 15 is a high-transparent device provided with a slit portion 15A through which the light beam from the main body 14 passes. The magnetic material 11 is a magnetic material such as permalloy. The TfJ distraction member 15 is fixed to the frame of the recording device main body in which the optical pickup device main body 14 and the recording medium 1 are housed, and the optical pickup device main body 14 follows the information track when recording and reproducing information. At the same time, it is moved along the slit portion 15A in the direction of the arrow shown in the figure. With this configuration, the influence of leakage magnetic flux can be reduced as in the first embodiment described above.

Next, a third embodiment of the present invention is shown in FIGS. 5(A) to 5(C). FIG. 5(A) shows the configuration of the optical pickup device of this example, where 2 is an objective lens for receiving a light beam;
Reference numeral 17 indicates a main body of the optical pickup device, and 17 indicates a magnetic barrier member having a hole 17A through which the light beam from the objective lens 2 passes, and is rotatably supported by a rotating shaft 18. The direction of the magnetic field of the leakage magnetic flux from the optical pickup device main body 18 is
As shown in Figure (A), it is configured to be opposite to the magnetization direction of the recording medium 1. When recording information, leakage magnetic flux is used as a bias magnetic field so that magnetization reversal is likely to occur when a light beam is irradiated as shown in Figure 6 (B), and the influence of leakage magnetic flux is ignored except when recording information. To avoid this, please use magnetic protection.

For this purpose, as shown in FIG. 5(A), the magnetic shielding member 17 is constructed so as to be movable and removable from the front surface of the objective lens 2, and the magnetic shielding member 17 is configured to be movable and removed from the front surface of the objective lens 2, as shown in FIG. like,
A magnetic shielding member 17 is moved in front of the objective lens 2 so that the light beam passage hA is at the position of the objective lens 2, so that leakage magnetic flux does not act on the recording medium 1.

Further, when recording information, as shown in FIG. 5(C), the magnetic shielding member 17 is removed from the front surface of the objective lens 2 so that the leakage magnetic flux acts as a bias magnetic field.

Effects Although one embodiment of the present invention has been described above, according to the present invention, it is possible to reduce the influence of leakage magnetic flux leaking from an optical pickup device on a uniaxially anisotropic magnetic thin film recording medium, thereby making it possible to record information. reliability can be improved.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing two examples of the configuration of a conventional optical pickup device, FIG. 3 is a cross-sectional view showing a first embodiment of the optical pickup device of the present invention, and FIG. 4 is a cross-sectional view showing a first embodiment of the optical pickup device of the present invention. Second
FIG. 5(A) is a plan view showing a third embodiment of the present invention, FIGS. 5(B) and (C) are side views for explaining its operation, and FIG. (A) and (Japanese) are also explanatory diagrams of the leakage magnetic flux. l...recording medium, 2...objective lens, 3...lens barrel, 4...casing. 5^, 5B... Elastic support body, 6... Drive coil, 7
...Yoke, 8...Permanent magnet, 9...Galvanometer mirror-510...Parallel spring, 11.
... Drive coil, 12... Magnetic circuit, 13.15.1
7... Magnetic first member, 13A, 17A... Hole through which the light beam passes, 14, Ift... Optical pickup device main body, 15A... Slit portion, 18... Rotating shaft. Patent applicant: Canon Co., Ltd. Figure 5 (A) CB) Figure 6

Claims (1)

[Scope of Claims] 1) In an optical pickup device that optically records or reproduces information by irradiating a light beam onto a recording medium made of a magnetic thin film, the light beam is guided to the recording medium, and an optical element and an optical system including a mechanism for electromagnetically driving at least a portion of the optical element; and a magnetic barrier member disposed between the recording medium and the optical system so as to shield leakage magnetic flux from the mechanism. An optical pickup device characterized by comprising: 2. In the optical pickup device according to claim 1, the magnetic blocking member is moved so as to be removable from between the optical system and the recording medium when recording, reproducing or erasing information. An optical pickup device characterized by having a mechanism for.