JPH0675294B2 - 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 A conventional example of this type of device is shown in FIG. 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.

Then, since the magnetic circuit is formed by the magnetic circuit forming portion 8, the permanent magnet 8 and the gap 7a, a part thereof, that is, the gap
When the coil 9 located at 7a is energized, a force is generated in the direction of the current flowing through the coil 9 and the direction orthogonal to the magnetic flux generation direction of the coil 9. The direction in which this force is generated is the Z-axis direction in FIG. 8, 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. 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.

Means for Solving Problems A thin plate-shaped objective lens holding plate integrally formed in a shape in which the central objective lens mounting portion is connected by a 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, a magnetic body and a magnetic field generating means are provided at a portion where the base and the objective lens mounting portion face each other, the magnetic bodies and the magnetic field generating portions facing each other in different facing areas with their centers aligned with the optical axis of the objective lens.

Action When a magnetic field is generated in the magnetic field generating means, a repulsive force is generated between the magnetic field generating means and the magnetic body according to the strength of the magnetic field. 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.

Further, since the facing areas of the magnetic body and the magnetic field generating means are different,
The generated magnetic flux with the smaller facing area is wrapped in the generated magnetic flux with the larger facing area. Accordingly, when the magnetic body and the magnetic field generating means repel and separate from each other, the centers of the two do not deviate from each other, and the objective lens for focusing servo can be driven without shifting the optical axis.

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 made 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 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 13 is formed in the center of the objective lens mounting portion 10b, and an objective lens 14 is fitted and fixed in the mounting hole 13. The optical axis direction is Z in FIG.
In the axial direction, that is, in the direction perpendicular to the objective lens holding plate 10. The Z-axis direction is a direction in which the medium approaches and separates from a medium (not shown). Further, the objective lens mounting portion 10b has a focusing servo coil as a magnetic field generating means centered on the mounting hole 13.
Fifteen (hereinafter referred to as FS coil) are fixed in a spiral shape. Adjacent to the FS coil 15, a tracking servo coil 16 (hereinafter referred to as TS coil) is also fixed in a spiral shape. The position of the TS coil 16 is displaced from the optical axis of the objective lens 14 in the X-axis direction in FIG. The X-axis direction is the media track direction.

Next, details of the base 11 will be described with reference to FIG. The base 11 has the objective lens 14 at the center thereof.
The optical path hole 17 is formed so that the optical axis and the central axis of the optical path coincide with each other. The optical path hole 17 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.
Focusing servo magnet 18 (hereinafter referred to as FS magnet) as a magnetic body that is a permanent magnet with 17 at the center,
Magnet 19 for tracking servo (hereinafter referred to as TS magnet)
And are fixed. The FS magnet 18 is a structure having a hole 18a having a diameter slightly larger than that of the optical path hole 17 in the central portion,
The arrangement position is a position facing the FS coil 15. In addition, the facing area of the FS magnet 18 is wider than that of the FS coil 15. One of the TS magnets 19
Is a structure having a facing area that is substantially the same as the TS coil 16 and is arranged at a position displaced by a distance s from a position facing the TS coil 16 at a right angle. This distance s is about 1/2 of the TS coil 16 in the stagger direction.
Is the length of.

In such a configuration, to drive the objective lens 14 for the focusing servo, energize the FS coil 15 and to drive the objective lens 14 for the tracking servo, use the TS This is done by energizing the coil 16.

That is, when the FS coil 15 is energized, a magnetic field is generated around it and a repulsive force is generated between the FS coil 15 and the FS magnet 18. As a result, the flexible deforming portion 10c bends, and the objective lens mounting portion 10b moves in the Z direction in accordance with the amount of current supplied to the FS coil 15.
Displace in the axial direction. Therefore, the objective lens 14 is also displaced in the Z-axis direction, that is, the optical axis direction, and is used for focusing servo.

Here, when the FS coil 15 and the FS magnet 18 repel, what kind of magnetic flux is generated and repels each other will be described based on FIGS. 4 and 5. The magnetic flux generated by the FS coil 15 will be described as a magnetic flux α, and the magnetic flux generated by the FS magnet 18 will be described as a magnetic flux β. FIG. 4 shows an example of magnetic flux generated when the FS coil 15 and the FS magnet 18 have the same facing area for convenience of description. FIG. 5 shows the FS in this embodiment.
Magnetic flux generated by the coil 15 for FS and the magnet 18 for FS. Then, when the facing areas of the FS coil 15 and the FS magnet 18 are the same, as shown in FIG. 4, the magnetic flux α and the magnetic flux β have substantially the same shape and substantially the same distribution state. Therefore, when the FS coil 15 and the FS magnet 18 are repelled, the respective axial centers which should originally be on the optical axis C of the objective lens 14 are easily displaced,
The optical axis of the driven objective lens 14 becomes difficult to be constant. On the other hand, as in this embodiment, the FS coil 15 and
When the areas facing the FS magnet 18 are different, the magnetic flux α exhibits a distribution state in which it is surrounded by the magnetic flux β, as shown in FIG. Therefore, the axes of the FS coil 15 and the FS magnet 18 do not easily change from the optical axis C of the objective lens 14, and the driven optical axis of the objective lens 14 is constant.

Next, when the TS coil 16 is energized, a magnetic field is generated around the TS coil 16, and an attractive force or a repulsive force is generated between the TS coil 16 and the TS magnet 19. 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 TS coil 16. The displacement of the objective lens mounting portion 10b is based on the arrangement position of the TS coil 16. Therefore, the objective lens 14 is also displaced in the X-axis direction, that is, the track direction of the media, and is used for the tracking servo. As in the case of the FS coil 15,
By changing the polarity of energization to the TS coil 16,
The displacement direction of the objective lens 14 on the X axis can be set in any direction.

Then, it is only the objective lens mounting portion 10b that is displaced together with the objective lens 14 due to the flexible deformation portion 10c bending. Therefore, the inertial mass of the displacement object when the objective lens 14 is displaced becomes very small, and the response of the displacement of the objective lens 14 is improved, which contributes to accurate focusing servo and tracking servo. Further, the thickness of the entire apparatus is determined by the thickness of the base 11 and the objective lens holding plate 10 and the distance d between them.
The thickness is just the sum of the above, 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 the implementation, set the facing area of the FS coil 15 to FS.
Of course, it may be formed wider than the facing area of the magnet 18 for use. Further, the FS coil 15 and the TS coil 16 formed on the objective lens holding plate 10 may be formed as thin films. In this case, the mass of the objective lens mounting portion 10b is reduced, and the movable responsiveness of the objective lens 14 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. Mount, connect the base with the optical path hole to the fixed part, and face it in parallel with the objective lens holding plate at a constant interval, and center the optical axis of the objective lens at the facing part of the base and the objective lens mounting part. Since the magnetic body and the magnetic field generating means which are matched and face each other in different facing areas are provided and both are magnetically repulsed to displace the objective lens in the optical axis direction, the magnetic body and the magnetic field generating means are arranged. Among them, since the magnetic field generated distribution is such that the generated magnetic flux of the narrower side is enclosed by the generated magnetic flux of the wider facing area, the magnetic substance and the magnetic field generating means repel each other from the optical axis of the objective lens of the mutual axial center. Gap is effective Therefore, it is possible to eliminate the deviation of the optical axis when the objective lens is driven, and the mass of the member that is displaced together with the objective lens is reduced. Therefore, the responsiveness of the displacement of the objective lens is reduced. It contributes to the realization of a more accurate focusing servo, and further, the thickness of the device in the direction of the object's optical object is reduced, thus reducing the size of the optical head and improving its design flexibility. It has the effect of contributing.

[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 magnetic body and magnetic field generation. And FIG. 5 is a vertical sectional side view of the magnetic body and the magnetic field generating means, which virtually show an example of the magnetic flux generated when the opposing area to the means is the same, and FIG. Vertical side view of
FIG. 6 is an overall vertical sectional side view showing a conventional example. 10 ... Objective lens holding plate, 10a ... Fixed part, 10b ... Objective lens mounting part, 10c ... Flexible deformation part, 11 ... Base, 14 ... Objective lens, 15 ... FS coil (magnetic field generating means), 17 ... Optical path hole, 18
… FS magnet (magnetic material)

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 one of the facing portions of the base and the objective lens mounting portion is provided, and the magnetic body and the magnetic field generating means that are aligned in the optical axis of the objective lens and face each other in different facing areas are provided. An objective lens drive device characterized by the following.