JPH0468693B2 - - Google Patents

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.

Prior art In general, uniaxially anisotropic magnetic thin films, e.g.
A known method is to record information signals by irradiating a thin film such as GdTbFe with a spot-like light beam and heating it to a temperature near the Curie point to form a magnetization reversal region. When reproducing information, a light beam for reading information is irradiated onto the recording medium, and the Kerr rotation angle of the reflected light or transmitted light of the light beam is different between areas where the magnetization has been reversed and areas where the magnetization has not been reversed. You can obtain a playback signal by doing this. Conventionally, in this type of optical pickup device, 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 medium 1, a lens barrel 3 that supports the objective lens 2, and a housing that allows the lens barrel 3 to be moved in a direction perpendicular to the recording medium 1. body 4
A magnetic circuit including elastic supports 5A and 5B supported on the recording medium 1, a drive coil 6 fixed to the lens barrel 3, yokes 7A and 7B that apply a magnetic field to the drive coil 6, and a permanent magnet 8, and a light beam on the recording medium 1. It is composed of a galvanometer mirror 9 that is moved on the surface of the mirror.
When recording information, the optical pickup device records information in a track shape 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) is used to detect the error signal of the defocus, and the drive coil 6 is formed of magnetic circuits 7A, 7B, and 8. It is driven by a driving device to perform focus control of the objective lens 2. Further, in order to prevent the light beam from deviating from the information track once grasped, a separately provided 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 done by electromagnetically driving in a direction perpendicular to the optical axis using a coil 11 and a magnetic circuit 12 that provides 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 focus control and tracking control are required. Magnetic circuit 7A arranged for
There was a drawback in that leakage magnetic flux from 7B and 8 acted on the recording medium 1, which was a uniaxially anisotropic magnetized thin film, and had an adverse effect on recording and reproducing information.

Therefore, an object of the present invention is to provide an optical pickup device that eliminates the above-mentioned drawbacks and prevents leakage magnetic flux generated from the optical pickup device from having an adverse effect on a magnetic thin film recording medium during information recording and reproduction. There is a particular thing.

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.

EXAMPLES Hereinafter, the present invention will be described 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 are movable lenses in the optical axis direction relative to the housing 4. An elastic support 6 is fixed to the lens barrel 3, and a driving coil 9 is a galvanometer mirror inserted into a magnetic circuit consisting of yokes 7A and 7B and a permanent magnet 8. Furthermore, 1
3 is a magnetically resistant member made of a material with high magnetic permeability, such as permalloy, provided with a hole 13A through which the light beam passes, and is fixed to the housing 4 by surrounding the elastic support 5B side of the housing 4; The hole 13A is made coaxial with the lens barrel 3, so that the reflected light from the galvano mirror 9 is directed to the lens barrel 3.
The light is made to enter the recording medium 1 through the objective lens 2 and the hole 13A.

In such a device, when recording/reproducing information, the optical pickup device is relatively moved in parallel with the recording medium 1, focus control is performed to drive the objective lens 2 in the optical axis direction, and the light beam is moved to track the information. Tracking control is performed using the galvano mirror 9 to prevent it from falling off. At that time,
The 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 information may not be recorded or reproduced. In order to avoid incompleteness, the present invention:
A magnetic shielding member 13 having a hole 13A through which the light beam passes 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,
Reference numeral 14 designates a main body of an optical pickup device equipped with an electromagnetic objective lens drive mechanism, and reference numeral 15 designates a magnetically resistant member made of a high magnetic permeability material, such as permalloy, provided with a slit portion 15A through which the light beam from the main body 14 passes. The magnetically-resistant 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 allows the optical pickup device main body 14 to follow the information track when recording and reproducing information. At the same time, it moves 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 similarly to the first embodiment described above.

Next, a third embodiment of the present invention is shown in FIGS. 5A to 5C. FIG. 5A shows the configuration of the optical pickup device of this example, where 2 is an objective lens for condensing the light beam, 16 is the main body of the optical pickup device, and 17 is a hole 17A through which the light beam from the objective lens 2 passes. have,
It is a magnetically resistant member 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 16 is configured to be opposite to the magnetization direction of the recording medium 1, as shown in FIG. 6A. 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 6B, and the influence of leakage magnetic flux is avoided except when recording information. For this purpose, magnetic shielding is performed.

To this end, as shown in FIG. 5A, the magnetically resistant member 17 is configured to be movable and removable from the front surface of the objective lens 2, and the objective lens 17 is configured to be movable and removable from the front surface of the objective lens 2, as shown in FIG. 5B. Move the magnetically resistant member 17 to the front of the lens 2 and open the light beam passage hole 17A.
is placed 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. 5C, 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 The embodiments of this explanation have 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 sectional views showing two examples of the configuration of a conventional optical pickup device, and FIG. 3 is a sectional view showing a first embodiment of the optical pickup device of the present invention.
FIG. 4 is a perspective view showing a second embodiment of the invention, FIG. 5A is a plan view showing a third embodiment of the invention, and FIGS. 5B and C are side views for explaining its operation. 6th
Figures A and B are also explanatory diagrams of the leakage magnetic flux. DESCRIPTION OF SYMBOLS 1... Recording medium, 2... Objective lens, 3... Lens barrel, 4... Housing, 5A, 5B... Elastic support body, 6
... Drive coil, 7 ... Yoke, 8 ... Permanent magnet, 9 ... Galvanometer mirror, 10 ... Parallel spring,
11... Drive coil, 12... Magnetic circuit, 13,
15, 17...Magnetic resistance member, 13A, 17
A... Hole through which the light beam passes, 14, 16... Optical pickup device main body, 15A... Slit portion, 18
……Axis of rotation.

Claims (1)

[Scope of Claims] 1. 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, comprising: an optical element that guides the light beam to the recording medium; an optical system including a mechanism for electromagnetically driving at least a portion of an element; and a magnetic shield disposed between the recording medium and the optical system to suppress leakage magnetic flux from the mechanism. An optical pickup device characterized by comprising: 2. In the optical pickup device according to claim 1, a mechanism for moving the magnetically resistant member so that it can be removed from between the optical system and the recording medium when recording, reproducing or erasing information. An optical pickup device characterized by having: