JPH08249689A - Objective lens driving device - Google Patents

Abstract

PURPOSE: To provide an objective lens driving device in which miniaturization and cost reduction are achieved by simplifying the structure. CONSTITUTION: A lens holder 1 to which an objective lens 3 is fitted is formed of a plastic magnet and has a polarizing part 1b in which at least a pair of magnetic poles are polarized. Focusing coils 5 and tracking coils 6 which are disposed in a fixing member are respectively opposed with each other in the predetermined places of the polarizing part 1b, and the lens holder 1 is accurately track-servoed in two-dimension of the focusing and tracking directions by electromagnetic interaction between both coils and the polarizing part 1b of the lens holder 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical disc device such as a magneto-optical disc device or a compact disc (CD) device, and an objective lens driving device in an optical head.

[0002]

2. Description of the Related Art An optical pickup (optical head) is used in an optical disc apparatus for reading information recorded on an optical disc or writing / reading information on the optical disc. This optical pickup is required to accurately focus the laser light on the information pits of the optical disc in order to record / reproduce information on / from the optical disc without any error. However, since the optical disk has surface wobbling or eccentricity during rotation, the optical pickup must always control the position of the objective lens by the objective lens driving device according to the change of the optical disk. That is, in order to keep the objective lens at an appropriate interval with respect to the optical disc, the objective lens is set in the focusing direction and the tracking direction.
The servo precisely follows the dimension.

In such a driving device, various structures are put into practical use as a supporting system for displacing the objective lens two-dimensionally. As an example, a so-called shaft sliding system will be described with reference to FIG. To do.

In FIG. 4, a cylindrical portion for mounting an objective lens 13 is formed on one side of a lens holder 11 formed of a synthetic resin or the like in a substantially cylindrical shape, and a support shaft 12 is provided at a central portion. A shaft hole for insertion is formed. The lens holder 11 has a support shaft 12 whose one end is fixed to a frame (not shown) and the objective lens 1 described above.
3 is slidable in a direction parallel to the optical axis direction, and is rotatably supported around the support shaft 12. further,
The objective lens 13 is provided on the other side of the lens holder 11.
A counterweight 14 is attached to balance the weight with the one side on which is mounted. Further, a pair of yokes 19 made of a magnetic metal plate are embedded on both sides of the lens holder 11, and the lens holder 1 on the outer side thereof is embedded.
A focusing coil 15 and a tracking coil 16 are arranged on the outer peripheral surface of No. 1 by adhesion or the like.

On the other hand, the focusing coil 15 and the tracking coil 16 have a magnet yoke 1 which is integral with the frame and is made of a magnetic metal plate formed in an arc shape.
The arc-shaped magnets 17 fixed to the inner surface of 8 are face-to-face with each other with a minute gap. A magnetic circuit that constitutes a driving device for position control is formed by the magnet 17, the focusing coil 15 and the tracking coil 16, and a movable portion including the focusing coil 15 and the tracking coil 16 arranged in the lens holder 11 is formed. , Driving force is obtained by electromagnetic interaction with a fixed portion composed of the magnet 17 and the yokes 18 and 19. By this driving force, the relative position of the objective lens 13 can be adjusted in the focusing direction and the tracking direction. As described above, the structure of the drive device in which the coil is arranged in the movable portion is generally used because it is generally easy to reduce the weight.

[0006]

However, in the structure in which the focusing coil and the tracking coil are arranged in the movable portion such as the lens holder as described above, the lead wire for supplying power to both coils is used as the movable portion. Since it is necessary to movably provide between the fixed parts, the structure becomes complicated and the presence of the lead wire hinders the position control of the movable part. Further, when the number of turns of the coil is increased in order to increase the driving force, the weight of the movable portion increases, so that the driving force does not increase. Therefore, according to the present invention, the lens holder for mounting the objective lens is formed of a plastic magnet, and the electromagnetic interaction between the plastic magnet and the drive coil installed in the fixed portion controls the lens position in the focusing direction and the tracking direction. It is an object of the present invention to provide an objective lens driving device for an optical pickup / optical head having a simple structure and suitable for downsizing / cost reduction.

[0007]

An objective lens driving device according to the present invention is a lens holder which holds an objective lens and is movable in a focusing direction parallel to the optical axis of the objective lens and in a tracking direction orthogonal to the optical axis. When,
A fixing member facing the outer surface of the lens holder, a focusing coil and a tracking coil are arranged on the fixing member, and the coils are energized to drive the lens holder in the focusing direction and the tracking direction. In the objective lens driving device described above, the lens holder is made of a plastic magnet, at least a pair of magnetic poles are magnetized to the plastic magnet, and a focusing coil and a tracking coil disposed on the fixing member at predetermined positions of the magnetized portion. The coils for use are facing each other.

[0008]

When the lens holder is formed of a plastic magnet and the focusing coil and the tracking coil disposed on the fixing member are opposed to the lens holder, the movable portion including the lens holder is a magnet, and thus the lead wire and the like are not formed. No wiring is required, the structure is simplified and the assembly process is greatly simplified. Also,
In order to increase the driving force, it is possible to arbitrarily increase the number of turns of the focusing coil and the tracking coil.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a plan view showing an embodiment of the objective lens driving device of the present invention, and the lens holder 1 is formed by injection molding a plastic magnet into a substantially elliptical plane. As the plastic magnet, a material in which a rare earth magnetic powder such as Nd-Fe-B system or Sm-Co system is mixed as a binder, which has been remarkably reduced in weight due to the progress of material technology in recent years, is used. To be

A cylindrical portion 1a for mounting the objective lens 3 is formed on one side of the lens holder 1, and a support shaft 2 is inserted through the central portion of the lens holder 1, so that the lens holder 1 is attached to the support shaft 2. On the other hand, it is slidable in a direction parallel to the optical axis direction of the objective lens 3 and is rotatably supported around the support shaft 2. Further, a counterweight 4 is attached to the other side of the lens holder 1 to balance the weight with the one side on which the objective lens 3 is attached.

On the other hand, on the left and right in the figure with the support shaft 2 of the lens holder 1 as the center, there are provided magnetized portions 1b in which a pair of N and S magnetic poles are magnetized. A focusing coil 5 and a tracking coil 6 are opposed to the magnetized portion 1b. Further, a pair of first yoke 7 and second yoke 8 are integrally projectingly provided on a fixing member made of a magnetic metal material such as a frame (not shown) to which the base end of the support shaft 2 is fixed, so as to integrally project the first yoke 7 and the second yoke 8. A focusing coil 5 around which a self-welding electric wire is wound is inserted around the yoke 7. Further, the tracking coil 6 is fixedly arranged on the inner surface of the second yoke 8 formed in an arc shape with an adhesive or a double-sided adhesive tape.

Next, the operation of the above-described embodiment will be described. FIG. 2 is a schematic diagram showing a magnetic relationship between the magnetizing portion 1b for driving the lens holder 1 in the focusing direction and the focusing coil 5. That is, the focusing coil 5 is the magnetized portion 1b of the lens holder 1.
It is disposed so as to face one of the magnetic poles, and is wound around the first yoke 7 so that the central axis of the focusing coil 5 is parallel to the optical axis of the objective lens 3. As a result, the magnetic flux indicated by the arrow in the figure from the magnetized portion 1b to the yoke 7 is linked to one long side of the focusing coil 5, and a predetermined current is applied to the focusing coil 5 to cause the lens holder to pass. 1 generates a driving force in the vertical direction (optical axis direction) in which 1 slides on the support shaft 2.

FIG. 3 is a schematic diagram showing the magnetic relationship between the magnetizing portion 1b for driving the lens holder 1 in the tracking direction and the tracking coil 6. That is, the tracking coil 6 is wound in a substantially rectangular shape,
It is arranged on the second yoke 8 so as to face the boundary portion between the N and S poles of the magnetized portion 1b of the lens holder 1. Further, the tracking coil 6 is fixed such that the central axis of the coil is orthogonal to the optical axis and the long side of the substantially rectangular shape of the coil is parallel to the optical axis. As a result, the magnetic flux shown by the arrow in the figure from the N pole of the magnetized portion 1b to the S pole via the yoke 8 is linked to the two sides of the tracking coil 6 and a predetermined current is applied to the tracking coil 6. As a result, a driving force is generated in the tracking direction in which the lens holder 1 rotates with respect to the support shaft 2 (which is a direction substantially orthogonal to the optical axis because it is rotation, but this is also an orthogonal direction in the present application). Incidentally, in the supporting method using an elastic member described later, the tracking direction is orthogonal to the optical axis.

In the above structure, in order to increase the driving force for the lens holder 1, at least one of the focusing coil 5 and the tracking coil 6 may be increased in the number of turns. However, even in this case, the weight of the movable portion does not change, and only the driving force for the lens holder 1 is increased.

In the above embodiment, the entire lens holder 1 is made of plastic magnet.
In order to improve dimensional accuracy and mechanical strength,
A metal plate or the like may be integrally molded inside the lens holder 1 at the time of injection molding. For example, in order to improve the dimensional accuracy of the cylindrical portion 1a for mounting the objective lens 3, this cylindrical portion 1a
It is desirable that a substantially cylindrical metal body is integrally molded at the position a so that the inner surface is exposed, and the objective lens 3 is appropriately attached to the metal body. Further, in order to smooth the sliding movement and the turning movement of the shaft hole through which the support shaft 2 is inserted and the support shaft 2, a cylindrical bearing metal is integrally molded at the position of the shaft hole so that the inner surface is exposed. It is desirable to arrange by. As a result, a well-known bearing structure is formed between the bearing metal and the support shaft 2, and it becomes possible to reduce friction and improve wear resistance performance.

Further, the counterweight 4 attached to the other side of the lens holder 1 may be integrally molded. Furthermore, in the above-mentioned embodiments, the objective lens driving device of which the objective lens supporting system is the so-called axial sliding system is explained, but other known elastic members such as a leaf spring system, a four wire system or a hinge system are used. Needless to say, the supporting type lens driving device can be similarly configured.

[0017]

As described above, in the objective lens driving device according to the present invention, the lens holder is formed of a plastic magnet, and the focusing coil and tracking provided on the magnetizing portion of the lens holder are fixed to the fixing member. Since the coils for use face each other, there is no need for wiring such as lead wires to the movable part consisting of the lens holder,
The structure is simplified, the assembly process is greatly simplified, and the size and cost can be easily reduced. Further, since the focusing coil and the tracking coil are provided in the fixed portion, the number of turns of both coils can be arbitrarily increased without considering the weight of the movable portion in order to increase the driving force.

[0018]

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of an objective lens driving device according to the present invention.

FIG. 2 is a schematic view showing a magnetic circuit in a focusing direction in the embodiment of FIG.

FIG. 3 is a schematic diagram showing a magnetic circuit in a tracking direction in the embodiment of FIG.

FIG. 4 is a plan view showing a conventional objective lens driving device.

[Explanation of symbols]

 1 Lens Holder 1a Cylindrical Part 1b Magnetized Part 2 Support Shaft 3 Objective Lens 4 Counterweight 5 Focusing Coil 6 Tracking Coil 7 First Yoke 8 Second Yoke

Claims (4)

[Claims] 1. A lens holder that holds an objective lens and is movable in a focusing direction parallel to the optical axis of the objective lens and in a tracking direction orthogonal to the optical axis, and a fixing member facing the outer surface of the lens holder. When,
In an objective lens driving device in which a focusing coil and a tracking coil are arranged on the fixed member and the coils are energized to drive the lens holder in the focusing direction and the tracking direction, the lens holder is a plastic magnet. Consists of
At least a pair of magnetic poles are magnetized to the plastic magnet, and a focusing coil and a tracking coil arranged on the fixing member are opposed to the magnetized portion, respectively. 2. The lens holder made of the plastic magnet is held so as to be rotatable and slidable along a support shaft parallel to the optical axis of the objective lens and at a position displaced from the optical axis. The objective lens driving device according to claim 1, wherein the objective lens is held on one side of the support shaft and a counterweight is installed on the other side. 3. The lens holder made of the plastic magnet is movably supported by an elastic member made of a leaf spring or the like in a focusing direction parallel to the optical axis of the objective lens and in a tracking direction orthogonal to the optical axis. 1. The objective lens driving device according to item 1. 4. The objective lens driving device according to claim 1, wherein the plastic magnet is made of a rare earth magnetic material as a main component and injection molded using a synthetic resin as a binder.