JPH0690801B2 - Objective lens drive - Google Patents

Description

TECHNICAL FIELD The present invention relates to an objective lens driving device, and more particularly to a device for driving an objective lens by a ring-shaped permanent magnet and a control coil.

[Prior Art] In recent years, an optical information recording system capable of storing a large amount of information with extremely high density and stability has become widespread as an optical disc, a compact disc, or an external storage device of a computer.

In such an optical information recording system, an objective lens is indispensable for reading or writing information by condensing a light spot on an information recording surface of an optical information recording medium. The objective lens driving device plays a very important role in controlling the position of the lens and controlling the track shift and the focus shift of the light spot.

FIG. 4 shows a general objective lens driving device.

The objective lens driving device shown in the figure has a movable holder (1).
And a base yoke (2).

The movable holder (1) has a flat octagonal upper surface, and a cylindrical bearing portion (3) is formed substantially in the center thereof. Further, the objective lens (4) is held and fixed on one blade of the movable holder (1) at a position decentered from the bearing portion (3) by a predetermined distance. Furthermore, a ring-shaped protrusion (5) is formed in the lower part of the movable holder (1), and a ring-shaped permanent magnet (6) magnetized with four poles in the radial direction is fixed to the protrusion (5). To be done.

On the other hand, the base yoke (2) is formed in a substantially cylindrical shape, the outer circumference of which constitutes an outer protruding portion (7), and a spindle (8) is provided upright in the substantially central portion. Also, the outer protrusion (7)
An inner protrusion (9) is concentrically formed between the shaft and the support shaft (8).

The tracking control coils (10a) and (10b) are bonded and fixed to the inner peripheral surface of the outer protruding portion (7), and the focus control coil (11) is attached to the outer peripheral surface of the inner protruding portion (9). Adhesive fixed.

The base yoke (2) and the inner protruding portion (9) are made of a magnetic material and are joined at the bottom.

The movable holder (1) and the base yoke (2) configured as described above are bearings in which the support shaft (8) protruding in the central portion of the base yoke (2) is provided in the central portion of the movable holder (1). Inserted in the portion (3), the movable holder (1) is supported by the base yoke (2) so as to be slidable in the axial direction indicated by the arrow A and rotatable in the arrow B direction.

Here, the permanent magnet (6) is positioned with a predetermined gap between the tracking control coils (10a), (10b) and the focus control coil (11), and the tracking control coil (10a), One side of arrow (10b) in the direction of arrow A is magnetized so that its magnetic pole is different from that of the other same circumferential surface.

The objective lens driving device according to the illustrated example is configured as described above, and its operation will be described below.

A laser beam or the like is emitted from the objective lens (4) to form a light spot on the information recording surface of an optical information recording medium such as an optical disk. When a defocus occurs in the light spot, the defocus occurs. A focus control coil (11) is conducted with a control current corresponding to the amount, and the movable holder (1) is slid in the direction of arrow A through the permanent magnet (6) to control the focus of the objective lens (4). be able to.

Further, when a track shift occurs in the light spot, a control current corresponding to the track shift amount is conducted to the tracking control coils (10a) and (10b) to move through the permanent magnet (6). The holder (1) rotates in the direction of arrow B, and it becomes possible to control the track position of the objective lens (4).

[Problems to be Solved by the Invention] Since the conventional objective lens driving device is configured as described above, due to an error in each component or an assembly error,
As shown in FIG. 5, when eccentricity occurs between the permanent magnet (6) and the outer protrusion (7) and the inner protrusion (9) of the yoke (2), the movable holder (1) is supported by a spindle. There is a problem that a sliding force is deteriorated because a force (perpendicular force) in a direction orthogonal to (8) is generated and a frictional force increases.

That is, as a result of the eccentricity generated between the permanent magnet (6) and the yoke (2), the outer peripheral surface (6a) of the permanent magnet (6) and the inner peripheral surface of the outer protruding portion (7) partially come close to each other, and The inner peripheral surface (6b) of the permanent magnet (6) and the outer peripheral surface of the inner protruding portion (9) are also partially close to each other.

However, the proximity area between the outer peripheral surface (6a) of the permanent magnet (6) and the inner peripheral surface of the outer protruding portion (7), and the inner peripheral surface (6b) of the permanent magnet (6) and the inner protruding portion (9). Since the area close to the outer peripheral surface is different, the permanent magnet (6) receives a vertical drag force.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide an objective lens driving device having a good sliding characteristic by reducing a vertical drag force caused by eccentricity between a permanent magnet and a yoke. Especially.

[Means for Solving Problems] In order to achieve the above object, an objective lens driving device according to the present invention includes a ring-shaped permanent magnet, a yoke, a focus control coil, and a tracking control coil. .

The ring-shaped permanent magnet is provided in the holder that holds the objective lens.

Further, the yoke is provided on the fixed side so as to face the inner side surface and the outer side surface of the permanent magnet.

The focus control coil and the tracking control coil are fixed to the yoke side in a gap formed by the permanent magnet and the yoke.

A concave-convex groove is provided on the yoke surface corresponding to the outer side surface of the permanent magnet or on the outer side surface of the permanent magnet.

[Operation] Since the objective lens driving device according to the present invention has the above-mentioned means, the magnetic flux density is reduced in the concave portions of the concave and convex grooves formed on the outer peripheral surface of the permanent magnet or the yoke surface facing the outer peripheral surface of the permanent magnet. On the other hand, the magnetic flux density increases in the convex portion.

Here, the normal force F received by the permanent magnet is (Si: Permanent magnet inner diameter area, So: Permanent magnet outer diameter area, Bi:
(Inner diameter side magnetic flux density, Bo: Outer diameter side magnetic flux density) Therefore, by providing the concave and convex grooves on the yoke surface, the area S0 of the outer diameter part of the permanent magnet is substantially reduced, and the force received by the inner diameter side of the permanent magnet due to eccentricity etc. And the force received on the outer diameter side is almost cancelled. As a result, the normal force F is reduced and the sliding characteristics are improved.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an exploded perspective view of an objective lens driving device according to one embodiment of the present invention. The parts corresponding to those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

A feature of the present invention is that the concave and convex grooves are formed on the outer peripheral surface of the permanent magnet or the yoke surface facing the outer peripheral surface of the permanent magnet. In the present embodiment, the inner peripheral surface of the outer protruding portion (7) of the yoke is formed. A concave portion (20) and a convex portion (21) are formed on the surface.

FIG. 2 shows an enlarged state in which the ring-shaped permanent magnet (6) is inserted in the yoke (2) shown in FIG.

As is clear from the figure, the convex portion (21) formed on the outer protruding portion (7) of the yoke (2) constitutes a magnetic circuit with the permanent magnet (6), and has a high magnetic flux density. , Recess (2
On the surface facing (0), the magnetic flux density is significantly reduced as compared with the convex portion (21).

That is, the normal force F applied to the permanent magnet (6) acts on the inner peripheral surface (6b) and the outer peripheral surface (6a) of the permanent magnet (6), respectively, but protrudes outward from the concave and convex grooves (20) and (21). Equivalently the area of the inner peripheral surface (S1) by forming on the inner surface of the part (7)
By making the areas (S0) of the outer peripheral surface equal to each other, the forces cancel each other out over the entire circumference, and it becomes possible to reduce the total sum of the normal forces (F).

FIG. 3 shows a ring-shaped permanent magnet used in the objective lens driving device according to the second embodiment of the present invention. The parts corresponding to those in the first embodiment are designated by the same reference numerals and will not be described. Omit it.

The feature of this embodiment is that the concave portion (20) and the convex portion (21) are formed on the outer peripheral surface of the permanent magnet (6), and as a result, the same as in the device shown in the first embodiment. It is possible to obtain actions and effects.

If the permanent magnet (6) is made of a plastic magnet, it is possible to easily form the concave and convex grooves.

As described above, according to the present invention, since the concave and convex grooves are formed on the outer peripheral surface of the permanent magnet or the opposing surface of the yoke, the magnetic flux on the inner peripheral surface of the permanent magnet and the opposing surface of the yoke and the yoke. It is possible to equivalently set the density and the area of the part where the density is generated, to make the normal force received on the inner and outer peripheral surfaces of the permanent magnet almost equal, and to make the gap between the permanent magnet and the yoke due to partial accuracy and assembly error. It is possible to suppress the vertical drag force to an extremely low level even if an imbalance occurs.

As a result, it is possible to suppress the frictional force due to the vertical drag force to a small level, and it is possible to secure good sliding characteristics.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an objective lens driving device according to an embodiment of the present invention, FIG. 2 is a partial plan view of a permanent magnet and a yoke according to an embodiment of the present invention, and FIG. 4 is an exploded perspective view of a conventional objective lens driving device, and FIG. 5 is a plan view showing a positional relationship between a permanent magnet and a yoke of the conventional objective lens driving device. In the figure, (1) is a movable holder, (2) is a base yoke, (4) is an objective lens, (6) is a ring-shaped permanent magnet,
(7) is an outer protrusion, (8) is a support shaft, (9) is a protrusion,
(10) is a tracking control coil, (11) is a focus control coil, (20) is a concave portion, and (21) is a convex portion. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (4)

[Claims] 1. A holder, which is held so as to be rotatable around a predetermined axis and movable along the axis, an objective lens provided at a position eccentric from the axis of the holder, and the holder being provided with the axis. A driving device that rotates around and that moves along the axis; and an objective lens driving device that performs focus control and tracking control of a light spot on an optical information recording medium, the driving device including: A ring-shaped permanent magnet provided, a yoke provided on the fixed side so as to face the inner peripheral surface and the outer peripheral surface of the permanent magnet, and arranged in a gap formed by the permanent magnet and the yoke and fixed to the yoke. And an uneven groove formed on an outer peripheral surface of the permanent magnet or on a yoke surface facing the outer peripheral surface. Drive unit. 2. The objective lens driving device according to claim 1, wherein the concave and convex grooves are formed on a yoke surface facing the outer peripheral surface of the permanent magnet. 3. The objective lens driving device as claimed in claim 1, wherein the concave and convex grooves are formed on the outer peripheral surface of the ring-shaped permanent magnet. 4. The objective lens drive device according to claim 1, wherein the permanent magnet is a plastic magnet.