JPH0792919B2 - Objective lens drive - Google Patents

Description

The present invention relates to an objective lens driving device for driving an objective lens for focusing servo in an optical head.

2. Description of the Related Art FIG. 5 shows an example of a conventional device of this type. A ring-shaped outer cylinder 1 fixedly provided on an optical head (not shown) is provided as a whole. 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 the 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 magnet 8 and the air gap 7a, when a part of the magnetic circuit, that is, the coil 9 located in the air gap 7a is energized, the direction of the current flowing through the coil 9 and the coil A force is generated in a direction orthogonal to the magnetic flux generation direction of 9. The direction in which this force is generated is the Z-axis direction in FIG. 5, 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. In this way, 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. 5, 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 magnetic field balance due to the permanent magnet is destroyed, 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.

Means for Solving the Problems A thin plate-shaped objective lens holding plate integrally formed in a shape in which a central objective lens mounting portion is connected to a fixed portion on the outside by a flexible deformation portion, and a center of the objective lens mounting portion. And an objective lens attached with its optical axis orthogonal to each other, and having an optical path hole in the optical axis direction of the objective lens and being connected to the fixing portion, are parallel to the objective lens holding plate at a constant interval. Opposing bases, focusing servo coils provided on the bases located at portions of the bases and the objective lens mounting portion facing each other about the optical axis of the objective lens, and the objective lens mounting And a soft magnetic material provided in the part.

When a magnetic field is generated in the working focusing servo coil, a magnetic force is generated between the focusing servo coil and the soft magnetic material according to the strength of the magnetic field. For this reason,
In the objective lens holding plate, the flexible deformation portion bends, and the objective lens attached to the objective lens attachment portion is displaced in the optical axis direction. In this way, the objective lens for focusing 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. The objective lens holding plate 10 is a very thin flat plate that forms a soft magnetic body 13 by forming a thin film of a soft magnetic material such as permalloy or nickel on the surface side facing the base 11. Then, the fixing portion 10a formed in a predetermined shape by a precision press working technique or the like and formed outside and the objective lens mounting portion 10b formed in the central portion are connected to the flexible deforming portion 10c. Here, the fixing portion 10a is fixed to the spacer 12 and connected to the base 11. 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 of the objective lens 15 is oriented in the Z-axis direction in FIG. 1, that is, the direction perpendicular to the objective lens holding plate 10. In addition, Z
The axial direction is a direction in which a medium (not shown) approaches and separates.

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 serving as a magnetic field generating means is fixed in a spiral shape around the center 16. Further, a tracking servo coil 18 is similarly fixed in a spiral shape adjacent to the focusing servo coil 17. The accurate position of the tracking servo coil 18 is displaced in the X-axis direction in FIG. 1 with respect to the optical axis of the objective lens 15, and the objective lens mounting portion is
Only half of the edge of 10b is at a right angle. The X-axis direction is the media track direction.

In such a configuration, the objective lens 15 is driven for focusing servo by energizing the focusing servo coil 17, and the objective lens 15 is driven for tracking servo. , The tracking servo coil 18 is energized.

That is, when the focusing servo coil 17 is energized, a magnetic field is generated around it and a magnetic force is generated between the focusing servo coil 17 and the soft 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 focusing servo 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 tracking servo coil 18 is energized, a magnetic field is generated around it, and the tracking servo coil 18
A magnetic force is generated between the soft magnetic material 13 and the soft magnetic material 13. As a result, the flexible deformation 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 tracking servo coil 18. The displacement of the objective lens mounting portion 10b is based on the arrangement position of the tracking servo 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 FIG. In this embodiment, the focusing servo coil 17 and the tracking servo coil 18 are formed into a thin film to form a thin film coil. As a result, the base 11 and the objective lens holding plate
The spacing d between 10 and 10 can be reduced, thus allowing a smaller device.

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. In the above, since the focusing servo coil is provided on the base and the soft magnetic material is provided on the objective lens mounting portion to displace the objective lens in the optical axis direction, the mass of the member that displaces together with the objective lens becomes small. Therefore, the response of the displacement of the objective lens is improved, which contributes to the realization of a more accurate focusing servo, and the thickness of the device in the optical axis direction of the objective lens is reduced. Therefore, it has the effect of contributing to downsizing of the optical head and improvement of the degree of freedom in its 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 showing the embodiment of FIG. 10: Objective lens holding plate, 10a: Fixed part, 10b: Objective lens mounting part, 10c: Flexible deformation part, 11 ... Base, 13
...... Soft magnetic material, 15 …… Objective lens, 16 …… Optical path hole, 17 ・ ・ ・
… Coil for focusing servo

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 coil provided on the base at a position where the base and the objective lens mounting portion are opposed to each other around the optical axis of the objective lens and the objective lens mounting portion. And an objective lens driving device.