JPH0675295B2 - Objective lens drive - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to an objective lens driving device for driving an objective lens for focusing servo and tracking servo in an optical head.

2. Description of the Related Art FIG. 8 shows a conventional example of this type of device. A ring-shaped outer cylinder 1 is fixedly provided on an optical head (not shown). The outer cylinder 1 is made of a soft magnetic material.
A ring-shaped inner cylinder 2 having a smaller diameter than the outer cylinder 1 is provided on the inner circumference of the outer cylinder 1.
Are arranged in a non-contact state. The center hole of the inner cylinder 2 is an optical path hole 2a which is a part of the optical path. The inner cylinder 2 is connected to the outer cylinder 1 by a diaphragm spring 3. Further, an objective lens 4 is provided, and this objective lens 4 is fitted and fixed to a ring-shaped iron piece 5. The iron piece 5 is connected to the inner cylinder 2 by two leaf springs 6 with the optical axis of the objective lens 4 aligned with the central axis of the optical path hole 2a.

Next, a magnetic circuit forming portion 7 is formed so as to project inward on the inner peripheral surface of the outer cylinder 1, and a permanent magnet 8 is fixed to the root portion thereof. A void 7a is formed in a part of the magnetic circuit forming portion 7, and a part of the inner cylinder 2 extends into the void 7a.
A coil 9 is wound around the extending portion of the inner cylinder 2.

Since a magnetic circuit is formed by the magnetic circuit forming portion 7, the permanent magnets 8 and the air gap 7a, a part of the magnetic circuit, that is, the direction located in the air gap 7a and the direction of the current flowing through the coil 9 when the coil 9 is energized. And a force is generated in a direction orthogonal to the magnetic flux generation direction of the coil 9. The direction of this force is
It is the Z-axis direction in the figure, that is, the optical axis direction of the objective lens 4. Therefore, when the inner cylinder 2 is displaced in the Z axis direction, the objective lens 4 is also displaced in the Z axis direction. Thus
The objective lens 4 is driven during focusing servo.

On the other hand, driving of the objective lens 4 during tracking servo is
This is performed by energizing a coil (not shown) arranged near the iron piece 5 to magnetically move the iron piece 5. The movable direction of the iron piece 5 at this time is the X-axis direction in FIG. 8, that is, the direction perpendicular to the optical axis of the objective lens 4. In particular,
A pair of permanent magnets (not shown) are arranged opposite to each other in the X-axis direction around the iron piece 5 that holds the objective lens 4. And X
Similarly, a pair of coils are arranged centering on the iron piece 5 in a direction orthogonal to the axis. Therefore, by energizing one of the coils, the balance of the magnetic field of the permanent magnet is broken, and the objective lens 4 is displaced in either direction on the X axis.

Problems to be Solved by the Invention When the objective lens 4 is displaced, members having a large mass such as the iron piece 5 and the inner cylinder 2 are also displaced. Therefore, there is a drawback that the inertial mass of the displaced object at the time of displacement becomes large and the response of displacement of the objective lens 4 deteriorates.

Further, during the tracking servo, the leaf spring 6 is bent to displace the objective lens 4. However, since the leaf spring 6 is long in the optical axis direction of the objective lens 4,
The entire apparatus also has a drawback that the thickness of the objective lens 4 in the optical axis direction becomes thick.

Means for solving the problem A thin plate-shaped objective lens holding plate integrally formed in a shape in which the central objective lens mounting portion is connected by the flexible deformation portion is provided on the outer fixing portion, and the center of the objective lens mounting portion is provided. An objective lens is attached with the optical axes orthogonal to each other, and a base having an optical path hole in the optical axis direction of the objective lens is connected to a fixing portion and arranged in parallel with the objective lens holding plate at a constant interval.
Then, in a portion of the base and the objective lens mounting portion facing each other about the optical axis of the objective lens, a focusing servo magnetic material is provided on one of them, and a focusing servo magnetic field generating means is provided on the other. . Further, in a portion where the base and the objective lens mounting portion are offset from each other and face each other, a tracking servo magnetic material is provided on either one of them and a tracking servo magnetic field generating means is provided on the other.

When a magnetic field is generated in the magnetic field generating means for focusing servo, a magnetic force or an attractive force or a magnetic force is generated between the magnetic field generating means for focusing servo and the magnetic material for focusing servo in accordance with the strength of the magnetic field. Repulsive force occurs. Therefore, in the objective lens holding plate, the flexible deforming portion is bent, and the objective lens attached to the objective lens attaching portion is displaced in the optical axis direction. In this way, the objective lens for focusing servo is driven.

Similarly, when a magnetic field is generated in the tracking servo magnetic field generating means, a magnetic force, an attractive force, or a repulsive force is generated between the tracking servo magnetic field generating means and the tracking servo magnetic body according to the strength of the magnetic field. Power is generated. Therefore, in the objective lens holding plate, the flexible deformable portion is bent,
The objective lens attached to the objective lens attachment portion is displaced in the direction perpendicular to the optical axis thereof. In this way, the objective lens for the tracking servo is driven.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. An objective lens holding plate 10 and a base 11 having the same outer dimensions are provided. These objective lens holding plates
The base 10 and the base 11 are fixed to each other via a spacer 12 at their ends, and are opposed to each other with a space d.

Details of the objective lens holding plate 10 will be described with reference to FIG. This objective lens holding plate 10 has a thin film of a soft magnetic material such as permalloy or nickel on the surface side facing the base 11 to form a magnetic material 13 as a focusing servo magnetic material and a tracking servo magnetic material. It consists of a very thin flat plate. Then, the fixing portion 10a formed on the outer side and the objective lens mounting portion 10b formed on the central portion, which are formed in a predetermined shape by a precision press working technique or the like, are connected to the flexible deforming portion 10c. Here, the fixing portion 10a is fixed to the spacer 12 and is fixed to the base 11
Are linked to. Therefore, the objective lens mounting portion 10b is displaceable in each of the three-dimensional directions by bending the flexible deformation portion 10c. A mounting hole 14 is formed in the center of the objective lens mounting portion 10b, and an objective lens 15 is fitted and fixed in the mounting hole 14. The optical axis direction is the Z axis direction in FIG. 1, that is, the objective lens holding plate.
In the direction perpendicular to 10. The Z-axis direction is a direction in which the medium approaches and separates from a medium (not shown).

Next, details of the base 11 will be described with reference to FIG. The base 11 has the objective lens 15 at the center thereof.
The optical path hole 16 is formed such that the optical axis of the optical axis and the central axis of the optical path are aligned. The optical path hole 16 becomes a part of the optical path of the optical head (not shown). On the other hand, the optical path hole is formed in the base 11.
A focusing servo coil 17 (hereinafter, referred to as an FS coil) as a focusing servo magnetic field generating means is fixed in a spiral shape around the center 16. Also this
Adjacent to the FS coil 17, a tracking servo coil 18 (hereinafter,
The coil for TS) is similarly fixed in a spiral shape.
The exact position of the TS coil 18 is determined by the objective lens
It is a position shifted in the X-axis direction in FIG. 1 with respect to the optical axis of 15, and is a position where only half of it faces the end of the objective lens mounting portion 10b at a right angle. The X-axis direction is the media track direction.

In such a configuration, to drive the objective lens 15 for focusing servo, energize the FS coil 17 and to drive the objective lens 15 for tracking servo, use TS This is done by energizing the coil 18.

That is, when the FS coil 17 is energized, a magnetic field is generated around the FS coil 17, and a magnetic force is generated between the FS coil 17 and the magnetic body 13. As a result, the flexible deformation portion 10c bends, and the objective lens mounting portion 10b is displaced in the Z-axis direction according to the amount of electricity supplied to the FS coil 17. Therefore, the objective lens 15 is also displaced in the Z-axis direction, that is, the optical axis direction, and is used for focusing servo.

On the other hand, when the TS coil 18 is energized, a magnetic field is generated around the TS coil 18, and a magnetic force is generated between the TS coil 18 and the magnetic body 13. As a result, the flexible deforming portion 10c bends, and the objective lens mounting portion 10b is displaced in the X-axis direction according to the amount of electricity supplied to the TS coil 18. The displacement of the objective lens mounting portion 10b as described above is based on the arrangement position of the TS coil 18. Therefore, the objective lens 15 is also displaced in the X-axis direction, that is, the track direction of the media, and is used for the tracking servo.

Then, it is only the objective lens mounting portion 10b that is displaced together with the objective lens 15 by the flexible deformation portion 10c bending. Therefore, the inertial mass of the displaced object when the objective lens 15 is displaced becomes very small, and the response of the displacement of the objective lens 15 is improved, which contributes to accurate focusing servo and tracking servo. Also, the thickness of the entire device is
The thickness is the same as the thickness of the base 11 and the objective lens holding plate 10 plus the distance d between them, and the structure is thin in the optical path direction. Therefore, it contributes to downsizing of the entire optical head, and the degree of freedom in designing the optical system can be improved.

In addition, in practice, the base 11 may be provided with a property as a soft magnetic material. In this case, the magnetic flux of the magnetic field generated between the base 11 and the objective lens holding plate 10 becomes stronger.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted (the same applies hereinafter). In this embodiment, the magnetic body 13 is not formed on the objective lens holding plate 10, and the FS coil 17 and the TS coil 18 are formed on such an objective lens holding plate 10. The FS coil 17 was formed in a spiral shape around the objective lens 15. The TS coil 18 is formed at the end of the objective lens mounting portion 10b which is displaced from the optical axis of the objective lens 15 in the X-axis direction. Further, on the base 11, a focusing servo magnet 20 (hereinafter referred to as an FS magnet) as a focusing servo magnetic body which is a permanent magnet, and a tracking servo magnet as a tracking servo magnetic body are provided. 21 (hereinafter referred to as a TS magnet) was fixed. The FS magnet 20 has a structure in which a hole 20a having a diameter slightly larger than that of the optical path hole 16 is provided in the central portion, and the arrangement position thereof is a position facing the FS coil 17. One of the TS magnets 21 has a structure having a facing area substantially the same as that of the TS coil 18, and its arrangement position is a position displaced by a distance s from the position facing the TS coil 18 at a right angle. The distance s is about half the length of the TS coil 18 in the shift direction.

In such a configuration, the objective lens 15 is driven in substantially the same way as in the first embodiment. That is, FS coil 17 and FS
The objective lens 15 is driven in the Z-axis direction by attraction and repulsion with the use magnet 20, and is used for focusing servo.
Further, the objective lens 15 is driven in the X-axis direction by the attraction and repulsion between the TS coil 18 and the TS magnet 21, and is used for tracking servo.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the FS coil 17 and the TS coil 18 are formed into a thin film to form a thin film coil. As a result, the distance d between the base 11 and the objective lens holding plate 10 can be narrowed, and thus a smaller device can be obtained.

Although not shown, the FS coil 17 formed on the objective lens holding plate 10 as in the structure of the second embodiment
When the TS coil 18 and the TS coil 18 are formed into a thin film, the mass of the objective lens mounting portion 10b is reduced, and the responsiveness of movement of the objective lens 15 can be further improved.

Advantageous Effects of Invention The present invention provides a thin plate-shaped objective lens holding plate integrally formed with an outer fixing portion, a central objective lens mounting portion, and a flexible deforming portion connecting the two, and the objective lens mounting portion is provided with an objective lens. And a base having an optical path hole is connected to a fixed portion so as to face the objective lens holding plate in parallel at a constant interval, and the base and the objective lens mounting portion face the optical axis of the objective lens as a center. The focusing servo magnetic material is provided on one of the two, and the focusing servo magnetic field generating means is provided on the other, and a magnetic force, an attractive force, or a repulsive force is generated between them to displace the objective lens in the optical axis direction. In addition, a magnetic material for tracking servo is provided on one of the portions of the base and the objective lens mounting portion that are offset from each other and face each other, and a magnetic field generating means for the tracking servo is provided on the other, and both are provided. Since the objective lens is displaced in the direction perpendicular to the optical axis by generating a magnetic force, an attractive force or a repulsive force, the mass of the member that is displaced together with the objective lens becomes small, and therefore the displacement of the objective lens Contributes to the realization of a more accurate focusing servo and tracking servo, and the thickness of the device in the optical axis direction of the objective lens is reduced, thus making the optical head smaller and smaller. It has the effect of contributing to the improvement of the degree of freedom of the design.

[Brief description of drawings]

FIG. 1 is an overall vertical side view showing a first embodiment of the present invention, FIG. 2 is a bottom view of an objective lens holding plate, FIG. 3 is a plan view of a base, and FIG. 4 is a second view of the present invention. FIG. 5 is a bottom view of the objective lens holding plate, FIG. 6 is a plan view of the base, and FIG. 7 is an objective lens holding plate showing the third embodiment of the present invention. FIG. 8 is a vertical sectional side view showing an example of a conventional example. 10 ... Objective lens holding plate, 10a ... Fixed part, 10b ... Objective lens mounting part, 10c ... Flexible deformation part, 11 ... Base, 13 ... Magnetic material (magnetic material for focusing servo), 13 ... Magnetic material (tracking) Servo magnetic material), 15 ... Objective lens, 16 ... Optical path hole, 17 ... FS coil (focusing servo magnetic field generating means), 18 ... TS coil (tracking servo magnetic field generating means)

Claims (1)

[Claims] 1. A thin plate-shaped objective lens holding plate integrally formed in a shape in which a central objective lens mounting portion is connected to an outer fixing portion by a flexible deformation portion, and an optical axis at the center of the objective lens mounting portion. And an objective lens mounted orthogonally to each other, and a base which has an optical path hole in the optical axis direction of the objective lens and is connected to the fixing portion so as to face the objective lens holding plate in parallel at a constant interval. And a focusing servo magnetic body provided on either one of the base and the objective lens mounting portion facing each other around the optical axis of the objective lens and a focusing servo provided on the other side. Magnetic field generating means, and a tracking servo magnetic body provided in either one of the portions of the base and the objective lens mounting portion that are offset from each other and face each other. An objective lens driving device which is characterized more becomes possible and tracking servo magnetic field generating means provided.