JPH01298535A - Actuator for optical head - Google Patents

Abstract

PURPOSE:To improve responseness by fixing a focusing drive coil on the end face of a movable part in the focusing direction. CONSTITUTION:The focusing drive coil 15 is fixed on the lower end of a cylinder part 13. Since the magnetic flux of permanent magnets 4, 5 is penetrated into the coil 15, the movable part 12 can be driven in the axial direction of a guide shaft 2 by controlling current. Since the coil 15 is arranged on the lower end face 13a of the cylinder part 13, the winding diameter of a pair coil can be reduced as compared to a case winding it around the outer periphery of the cylinder part 13, and since the coil 15 is fixed on the movable part 12 only at its upper end face, radiating efficiency is improved and a wire material with a comparatively thin diameter can be used. Thus, the responseness can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] <Industrial Application Field> The present invention relates to an actuator for an optical head for driving an objective lens in an optical head in both focusing and tracking directions.

<Prior Art> Various actuators have been proposed for driving the objective lens of an optical head used in optical disk drives, etc. For example, in Japanese Utility Model Application Publication No. 60-98120, the objective lens is moved with respect to the guide shaft. A focusing drive coil is fitted around a cylindrical coil bobbin that is integral with the movable part, and is fitted so as to be rotatable about its axis and slidable in the axial direction of the guide shaft. A shaft-sliding actuator drives the movable part in both focusing and tracking directions by magnetic action between a tracking drive coil attached to the coil and fixed magnetic units such as permanent magnets corresponding to both drive coils. Disclosed. In the above actuator, a permanent magnet or the like is arranged to partially surround the coil on the outer periphery of the bobbin, and the guide shaft is used as a part of the yoke of the fixed magnetic unit.

When using such an actuator to drive the objective lens around the guide axis, that is, in the tracking direction, it is desirable to reduce the moment of inertia of the movable part as much as possible in order to improve its responsiveness. Since the coil is wound around the outer periphery, there is a problem in that the moment of inertia of the movable part tends to increase as the outer diameter of this part increases. In addition, since the coil on the outer periphery of the bobbin generates heat when driven, the wire diameter and winding diameter of the coil should be adjusted so that the movable part, especially the sliding part between it and the guide shaft, is not affected by thermal deformation. Since it is necessary to increase the size of the movable part, the moment of inertia of the movable part tends to increase further.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main object of the present invention is to provide an optical head that has a simple structure, is as small and lightweight as possible, and has improved responsiveness. The objective is to provide actuators for

[Structure of the Invention] <Means for Solving the Problems> According to the present invention, such an object is an actuator for an optical head for driving an objective lens in an optical head in both focusing and tracking directions,
a movable part that carries the objective lens, a means for guiding the movable part in both the focusing and tracking directions, and a first magnetic means provided on the movable part to generate a driving force in the focusing direction; a second magnetic means provided in the movable part to generate a driving force in the tracking direction; and a fixed magnetic unit that supplies magnetic flux to both of the magnetic means, respectively, and the first magnetic means comprises: This is achieved by providing an actuator for an optical head, which is coupled to one end surface of the movable part in the focusing direction. especially,
The guide means includes a guide shaft that guides the movable part rotatably around the axis and slidably in the axial direction, and the first magnetic means has an annular shape and is attached to the end surface of the movable part. , may be coupled so as to surround the guide shaft.

<Function> By doing this, the winding diameter of the focusing drive coil can be reduced, and since the movable part is not affected by the heat generated by the focusing drive coil, the wire diameter of the coil can be reduced. Therefore, the moment of inertia of the movable part can be reduced.

Embodiments The present invention will now be described in detail with reference to specific embodiments with reference to the accompanying drawings.

1 to 3 show the structure of an actuator for an optical head based on the present invention. A guide shaft 2 that functions as a part of a yoke 3, which will be described later, is erected at the center of a base member 1 that is generally plate-shaped.

A 0-shaped yoke 3 is provided on both sides and the bottom of the guide shaft 2, and a pair of permanent magnets 4.5 are provided on the mutually opposing inner side surfaces of the yoke.

Further, a yoke 6 is provided on the rear end side in the longitudinal direction of the base member 1, that is, on the right side in FIG.

As clearly shown in FIG. 3, the yoke 6 is provided with an arcuate groove 7 extending laterally, so that the side surface of the yoke 6 has a 0-shape. On the inner surface of the groove 7 facing the guide shaft 2 side, a pair of permanent magnets 8.9 having a substantially complementary shape to the groove are provided laterally adjacent to each other. The yoke 6 is sandwiched between the guide shaft 2 in the base member 1.
On the opposite side, that is, on the left side in FIG. 2, a mirror member 10 having a mirror surface 10a tilting backward is provided. Four band-shaped spring members 11 made of silicone rubber are provided on the left and right sides of the base member 1 to engage with protrusions 12a provided on the side surfaces of the movable portion 12, which will be described later.

On the other hand, in the lower central part of the movable part 12 in this actuator, a cylindrical part 13 is provided in the center thereof with a through hole 14 penetrating in the vertical direction.

A focusing drive coil 15 wound annularly is provided on the lower end surface 13 a of the cylindrical portion 13 so as to surround the guide shaft 2 . A predetermined gap is defined between the inner peripheral surface of the focusing drive coil 15 and the guide shaft 2. A cylindrical lens holding section 17 for holding the objective lens 16 is provided at the front end in the longitudinal direction of the movable section 12, that is, at the left end in FIG. Here, in order to actually reduce the weight of the movable part 12 and the number of parts, the objective lens 16 and the lens holding part 17 may be integrally molded from synthetic resin.

The lens holding part 17 is inserted between the through hole 14 in the movable part 12.
An annular tracking drive coil 18 is attached to the opposite side end, that is, the curved rear end surface on the right side as shown in FIG. As clearly shown in FIGS. 2 and 3, the through hole 14 in the movable part 12 and the tracking drive coil 18
A portion thereof is cut away to form an axial through hole 20 having a generally fan-shaped cross section.

In order to assemble the movable part 12 and the base member 1, the guide shaft 2 is inserted into the through hole 14 and the yoke 6 is inserted.
By inserting the front part 6a of the movable part 1 into the through hole 2o,
2 is supported so as to be rotatable around the axis of the guide shaft 2, that is, in the tracking direction, and to be slidable in the axial direction, that is, in the casing direction. Here, the surface of the guide shaft 2 is coated with a low friction material such as Teflon resin.
The movable portion 12 can preferably slide on the shaft. Next, the ends of the spring member 11 extending from the base member 1 side are engaged with the four projecting pieces 12a provided on the sides of the movable part 12. Here, the spring member 11 is connected to the movable part 1
By using silicone rubber, which has a relatively large damping effect, it is possible to prevent unnecessary vibrations that would occur if, for example, a metal spring is used. Incidentally, in reality, this spring member may be made of any material that has a damping effect, such as an elastomer material.

The operating procedure of this embodiment will be explained below.

As clearly shown in FIG. 1, the magnetic flux formed in the magnetic gap between the guide shaft 2 as a core and the focusing permanent magnet 4.5 is transmitted to the focusing drive coil 15.
The direction and strength of the current supplied to the drive coil can be appropriately adjusted and covered to prevent the movable part 1 from passing through the drive coil.
2 can be driven and controlled in the axial direction of the guide shaft 2. Here, since the guide shaft 2 is made of a material having a high saturation magnetic flux density, such as silicon steel, it can have a smaller diameter than conventional guide shafts. Furthermore, since the focusing drive coil 15 is provided on the lower end surface 13a of the cylindrical portion 13, the winding diameter of the pair of coils can be made smaller than when it is wound around the outer periphery of the cylindrical portion 13. That is, the movable part 1
2 moments of inertia can be reduced. Furthermore, since the focusing drive coil 15 is fixed to the movable part 12 only at its upper end surface, the heat dissipation of the coil is improved, and a wire with a relatively small diameter can be used for the focusing drive coil 15. .

On the other hand, in the tracking permanent magnet (IFI'58.9), as shown in FIG. Since the magnetic flux passes through the parts 18a and 18b in opposite directions, by appropriately adjusting the direction and strength of the current supplied to the tracking drive coil 18, the movable part 12 can be moved around the axis. The drive can be controlled efficiently.Here,
The moment of inertia of the movable part 12 is reduced by providing the through hole 20 as a cutout part in the movable part 12. Further, since the tracking drive coil 18 is provided at a distance that is approximately the same as that of the guide shaft 2, the movable part 12 can be rotated with a small drive force, so the tracking drive coil 18 can be miniaturized. It is now possible.

[Effects of the Invention] As described above, according to the present invention, by providing the focusing drive coil on the end face in the focusing direction of the movable part, the winding diameter of the coil can be reduced.
Additionally, since the heat dissipation of the focusing drive coil is improved, there is no need to take unnecessary heat countermeasures, and the wire diameter of the coil can be reduced, so the moment of inertia of the moving part can be reduced as much as possible. . Therefore, the responsiveness of the actuator is improved and the access time of the optical head can be shortened, so that the effects of the present invention are great.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing the structure of an actuator for an optical head according to the present invention. FIG. 2 is a side sectional view of an actuator for an optical head according to the present invention. FIG. 3 is a plan view of an actuator for an optical head according to the present invention. 1...Base member 2...Guide shaft 3...Yoke 4.5...Permanent magnet 6...Yoke
6a...Front part 8.9...Permanent magnet 10
...Mirror member 10a...Mirror surface 11...Spring member 12...Movable part 12a...Protrusion piece 13...
...Cylindrical portion 13a...Lower end surface 14...Through hole 15...Focusing drive coil 16...Objective lens 17...Lens holding part 18...Tracking drive coil

Claims (2)

[Claims] (1) An actuator for an optical head for driving an objective lens in an optical head in both focusing and tracking directions, comprising a movable part that supports the objective lens, and a movable part that guides the movable part in both the focusing and tracking directions. a first magnetic means provided on the movable part to generate a driving force in the focusing direction; and a second magnetic means provided in the movable part to generate a driving force in the tracking direction. and a fixed magnetic unit that supplies magnetic flux to both of the magnetic means, respectively, wherein the first magnetic means is coupled to one end surface of the movable part in the focusing direction. Actuator for head. (2) The guide means includes a guide shaft that guides the movable part rotatably around the axis and slidably in the axial direction, and the first magnetic means has an annular shape and the movable part 2. The actuator for an optical head according to claim 1, wherein the actuator is coupled to the end surface so as to surround the guide shaft.