JPH0660406A - Driving device for objective lens - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the size and performance of an objective lens driving device used in an optical disk recording / reproducing device. [Structure] A focus coil 3 and a tracking coil 4 are provided on an outer peripheral portion of a holder 2 which holds an objective lens 1.
Also, a yoke 6 composed of a base 6a and poles 6b to 6e.
When the magnets 7a and 7b are fixed to the coils, the magnetic paths of the coils 3 and 4 are formed. The surfaces of the magnetic paths of the poles 6b to 6e and the base 6a are covered with superconducting films 10a to 10d. Then, the leakage magnetic flux from this portion disappears, and the magnetic flux density in the void becomes uniform. Therefore, there is no adverse effect on the magneto-optical recording layer, and an objective lens driving device with high driving efficiency can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device used in an optical pickup section of an optical disk reproducing device.

[0002]

2. Description of the Related Art As an optical disc recording / reproducing device for recording or reproducing information on a recording surface of a disc-shaped information recording medium (hereinafter referred to as a disc), there are devices such as a compact disc, a video disc, an optical disc file and a magneto-optical disc. In recent years, a device for recording / reproducing a music signal on / from a magneto-optical disk or a phase-change type optical disk has been put into practical use, and downsizing and high performance of an objective lens driving device of an optical pickup part has become an important issue. There is.

A conventional objective lens driving device used in such an optical disk recording / reproducing device will be described. FIG. 4 is an exploded perspective view showing a configuration example of a conventional objective lens driving device. In this figure, the objective lens 1 is a focusing lens that gives a laser spot required for recording and reproduction to a recording layer of a disc (not shown). The holder 2 holds the objective lens 1, and has a structure in which the cross-sectional shape of a plane perpendicular to the optical axis of the objective lens 1 is H-shaped. The focus coil 3 is wound around the outer peripheral side surface of the holder 2. The focus coil 3 is a coil that positions the objective lens 1 by electromagnetic force so that the laser beam is focused on the recording layer of the disc, and is driven by a focus servo circuit (not shown). The tracking coil 4 is a coil fixed to both side surfaces of the focus coil 3 and precisely positions the laser spot converged by the objective lens 1 on the track of the disc.
The tracking coil 4 is driven by a tracking servo circuit (not shown).

The holder 2 wound by the focus coil 3 and the tracking coil 4 in this manner is fixed to the fixing member 6 via the four wires 5. The wire 5 is an elastic wire that holds the holder 2 so that it can be finely moved in the optical axis direction of the objective lens 1, and also serves as a conductor that supplies a drive current to the focus coil 3 and the tracking coil 4.

On the other hand, a yoke 6 is slidably provided on the chassis of an optical disk recording / reproducing apparatus (not shown).
As shown in FIG. 4, the yoke 6 is composed of a base 6a and poles 6b to 6e standing upright on the base 6a, and constitutes a magnetic circuit for generating an electromagnetic force with respect to the focus coil 3 and the tracking coil 4. A rectangular opening is provided in the center of the base 6a, and a part of an optical system (not shown) is attached to this opening. The poles 6b and 6c are magnetic bodies that form a magnetic circuit together with the base 6a, and so are the poles 6d and 6e. A magnet 7a is fixed to the surface of the pole 6b facing the pole 6c. Also pole 6d
Also, the magnet 7b is fixed to the surface facing the pole 6e. The magnets 7a and 7b are permanent magnets that give a magnetic flux to the focus coil 3 and the tracking coil 4. Magnet 7
a, a void 8a formed by the pole 6c, and a magnet 7b,
The focus coil 3 and the tracking coil 4 are inserted into the gap 8b formed by the pole 6e, respectively.

In the thus constructed objective lens driving device, laser light is emitted from the opening of the base 6a through the optical system, and is converged by the objective lens 1 to form a laser spot on the disk. Focus coil 3 at this time
A drive current is applied to the tracking coil 4 and focus servo and tracking servo are performed. The entire objective lens driving device is mounted on a feeding device (not shown), and rough track positioning control is performed in the radial direction of the disk via, for example, a rack and a pinion mechanism.

[0007]

However, in such a configuration, leakage magnetic flux is generated in two sets of magnetic circuits composed of the magnets 7a and 7b, the poles 6b to 6e, and the base 6a. FIG. 5 is an explanatory view showing a magnetic flux distribution generated in this magnetic circuit. For example, a magnetic flux distribution indicated by a solid line is generated in the air gap 8a of a set of magnetic circuits composed of the magnet 7a, the poles 6b and 6c, and the base 6a. Also, an arc-shaped leakage magnetic flux is generated above the pole 6b and the magnet 7a. Therefore, if the distance between the magnet 7a and the pole 6c is wide, a uniform magnetic flux cannot be obtained in the air gap 8a, and the magnetic resistance thereof becomes large.
Therefore, even if the magnet 7a having a large magnetomotive force is used, the efficiency of the objective lens driving device is deteriorated. When a magneto-optical recording type optical disc is used as the optical disc, a magnetic field is generated in the recording layer of the optical disc due to the magnetic flux leaking to the upper part of the magnet 7 and the yoke 6, which adversely affects the recording and reproduction of signals.

The present invention has been made in view of the above conventional problems, and makes the magnetic flux in the gap into which the tracking coil and the focus coil are inserted uniform and reduces the leakage magnetic flux to adversely affect the optical disk. With the loss
It is an object to realize an objective lens driving device having high electromechanical conversion efficiency.

[0009]

According to a first aspect of the present invention, there is provided an objective lens for converging a light beam on a recording medium, and a lens for supporting the objective lens which is finely supported by a fixing member via an elastic body. The focus coil is wound around the holder and the outer peripheral side surface of the lens holder to apply an electromagnetic force in the optical axis direction of the objective lens, and is wound around a part of the outer peripheral side surface of the lens holder in the direction perpendicular to the optical axis of the objective lens. A tracking coil that applies electromagnetic force, a yoke that forms a magnetic path between the focus coil and the tracking coil, a magnet that is fixed at a position facing the focus coil and the tracking coil of the yoke with a constant gap, and a surface of the yoke. And a superconducting film that covers the magnetic path.

According to a second aspect of the present invention, there are provided an objective lens which converges a light beam on a recording medium, a lens holder which is finely supported by a fixing member via an elastic body and holds the objective lens, and a lens holder. A magnet fixed to the outer peripheral side surface, a yoke fixed to a position facing the magnet through an air gap and forming a magnetic path, and a coil wound around the outer peripheral side surface of the yoke to apply an electromagnetic force in the optical axis direction of the objective lens. A focus coil, a tracking coil wound around a part of the outer peripheral side surface of the yoke to apply an electromagnetic force in a direction perpendicular to the optical axis of the objective lens, and a superconducting film covering a magnetic path on the surface of the yoke. It is characterized by.

[0011]

According to the present invention having such characteristics, the recording / reproducing light emitted from the outside is converged by the objective lens and is incident on the recording medium. Then, the focus coil receives an electromagnetic force in the optical axis direction of the objective lens and the tracking coil receives an electromagnetic force in the direction perpendicular to the optical axis to focus a predetermined light beam on the track of the disc. At this time, the pole of the yoke and the superconducting film that covers a part of the surface of the base do not leak the magnetic flux generated from the magnet to the outside, and give a uniform magnetic flux to the positions of the focus coil and the tracking coil. Therefore, the electromechanical conversion efficiency of the movable portion including the objective lens and the holder is improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An objective lens driving device according to a first embodiment of the present invention will be described with reference to FIGS. Figure 1
FIG. 3 is a vertical cross-sectional view showing the configuration of the objective lens driving device in the first example. Incidentally, the same parts as those in FIG. 4 showing the conventional example are designated by the same reference numerals and the description thereof is omitted. Unlike the conventional example, the yoke 6
The superconducting film 10 is coated on a part of the surface of the. The superconducting film 10 is a film having superconducting properties at a critical temperature or lower, and is made of, for example, an intermetallic compound or a ceramic. In the superconducting state, the superconducting film 10 does not have magnetic lines of force inside even if external magnetization is applied within a range not exceeding the critical magnetic field. This phenomenon occurs because the superconducting current flows on the surface of the superconducting film, and the internal magnetic field created by the superconducting current cancels the external magnetic field. This phenomenon is called the Meissner effect.

Now, as shown in FIG. 1, the outer side surfaces of the poles 6b and 6c and the bottom surface of the base 6a connecting the poles 6b and 6c are coated with a superconducting film 10a so that the cross-sectional shape becomes a U-shape.
Further, the superconducting film 10b is coated along the lower inner side surfaces of the poles 6b and 6c and the surface of the base 6a. Similarly Paul 6
The superconducting films 10c and 10d are also coated between e and 6d and the base 6a, respectively. In this way, the magnetic flux distribution becomes as shown in FIG. That is, the magnetic flux penetrating along the yoke 6 does not leak to the outside, and the magnetic flux distribution in the air gaps 8a and 8b becomes uniform.

By doing so, the magnetic flux density across the focus coil 3 and the tracking coil 4 is increased, and the efficiency of the focus servo and tracking servo of the objective lens 1 is increased. Also, as shown in FIG.
Also, the magnetic flux does not leak to the upper part of the magnet 7 and the recording layer of the optical disk is not adversely affected.

Next, an objective lens driving device according to the second embodiment of the present invention will be described with reference to FIG. The same parts as those in FIG. 1 showing the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In this figure, magnets 11a and 11b are attached to the side surface of a holder 2 that holds the objective lens 1. The magnets 11a and 11b are permanent magnets similar to the magnets 7a and 7b of the first embodiment, and also function to improve the rigidity of the holder 2. The movable portion configured in this manner is finely held by the fixed member 6 via the wire 12.

Next, the yoke 13 includes a base 13a and a pole 1.
3b, 13c. The base 13a has an opening similar to that of the conventional example, and a part of the optical system is inserted therein. The poles 13b and 13c are formed at right angles on a part of the base 13a. The poles 13b and 13c are poles which face the magnets 11a and 11b, respectively, with a constant gap therebetween, and the focus coil 14 is provided on the upper side surface thereof.
a, 14b and tracking coils 15a, 15b are wound respectively. The focus coil 14a is the pole 13
It is a coil wound in the direction perpendicular to the optical axis of the objective lens 1 along b. The tracking coil 15a is a coil wound around the surface of the focus coil 14a, and its coil shape is similar to that of the tracking coil 4 shown in FIG. Similar focus coil 14 to pole 13c
b and the tracking coil 15b are wound. The coils 14 and 15 are connected to a focus servo circuit and a tracking servo circuit, respectively, via lead wires (not shown).

The outer side surface and the bottom surface of the base 13a are covered with the superconducting film 16, and the inner surface of the base 13a and the inner side surfaces of the poles 13b and 13c are covered with the superconducting film 17. The superconducting films 16 and 17 are the superconducting films 10 of the first embodiment.
It has the same properties as.

In the objective lens driving device constructed as described above, when driving currents are respectively supplied to the fixed focus coil 14 and the tracking coil 15, the magnets 11a and 11b fixed to the holder 2 receive an electromagnetic force and the objective is moved. The lens 1 slightly moves in the optical axis of the lens 1 and in a direction perpendicular to the optical axis. In such a configuration, the tracking coil and the focus coil are fixed to the pole side, and the mass of the movable part is increased by the magnet 11. However, the structure of the movable part including the objective lens 1 is simplified, and the size of the movable part can be reduced. Further, since the focus coil 14 and the tracking coil 15 are fixed to the yoke 13, the number of windings can be increased,
A large electromagnetic force can be generated on the magnet 11.

The material development of the superconducting film has progressed in recent years, and its critical temperature tends to rise. Therefore, a material exhibiting superconductivity at room temperature can be obtained, and an objective lens driving device with high electromechanical conversion efficiency can be realized.

[0020]

As described in detail above, according to the present invention, by covering the surface of the yoke forming the magnetic circuit with the superconducting film, the magnetic flux density of the portion where the focus coil and the tracking coil are located can be increased. Can be uniform. Also, the leakage magnetic flux is reduced, and when a magneto-optical disk is used as the recording medium, it is possible to prevent the adverse effect of the magnetic field on the recording layer. Further, the electromechanical conversion efficiency of the focus coil and the tracking coil is improved, and an excellent objective lens driving device can be realized.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a configuration of an objective lens driving device in a first embodiment of the present invention.

FIG. 2 is a distribution diagram of magnetic force lines in a sectional direction of the objective lens driving device in the first example.

FIG. 3 is a vertical sectional view showing the configuration of an objective lens driving device in a second embodiment of the present invention.

FIG. 4 is an exploded perspective view showing a configuration example of a conventional objective lens driving device.

FIG. 5 is a distribution diagram of magnetic force lines in a cross-sectional direction in a conventional objective lens driving device.

[Explanation of symbols]

 1 Objective Lens 2 Holder 3, 14a, 14b Focus Coil 4, 15a, 15b Tracking Coil 5, 12 Wire 6, 13 Yoke 6a, 13a Base 6b-6e, 13b, 13c Pole 7a, 7b, 11a, 11b Magnet 10a-10d , 16,17 Superconducting film

Claims (2)

[Claims] 1. An objective lens that converges a light beam on a recording medium, a lens holder that is supported by a fixing member via an elastic body so as to be finely movable, and holds the objective lens, and a lens holder is wound around an outer peripheral surface of the lens holder. A focus coil that applies an electromagnetic force in the optical axis direction of the objective lens; a tracking coil that is wound around a part of the outer peripheral side surface of the lens holder and that applies an electromagnetic force in a direction perpendicular to the optical axis of the objective lens; A yoke forming a magnetic path of the focus coil and the tracking coil, a magnet fixed at a position facing the focus coil and the tracking coil of the yoke with a constant gap, and a magnetic path on the surface of the yoke. An objective lens driving device, comprising: a superconducting film that covers. 2. An objective lens which converges a light beam on a recording medium, a lens holder which is supported by a fixing member via an elastic body so as to be finely movable, and holds the objective lens, and is fixed to an outer peripheral side surface of the lens holder. Magnet, a yoke fixed to a position facing the magnet via an air gap and forming a magnetic path, and a focus coil wound around the outer peripheral side surface of the yoke and applying an electromagnetic force in the optical axis direction of the objective lens. A tracking coil wound around a part of the outer peripheral side surface of the yoke to apply an electromagnetic force in a direction perpendicular to the optical axis of the objective lens; and a superconducting film covering a magnetic path on the surface of the yoke. An objective lens drive device characterized by the above.