JPS63209033A - Objective lens driver - Google Patents

Abstract

PURPOSE:To obtain an objective lens driving device where a restoring force and a vertical drag to a sliding surface do not occur and which is easy to be controlled by setting a magnetic circuit consisting of a permanent magnet and a yoke only in a movable part and setting only parts consisting of nonmagnetic material such as a coil for control, etc., in a fixed part. CONSTITUTION:The first coil 10 for controlling difocusing and the second coil 11 for controlling off-track are provided in the fixed part 15 and the yoke 14 and a permanent magnet 5 are provided in a movable holder 2 which is the movable part, then the permanent magnet magnetically fixed to at least one of the first coil and the second coil in order to interlink fluxes whose directions of adjacent vectors are nearly reverse. Thus, since the parts consisting of the magnetic material are not set on the fixed side near to the movable holder, the distribution of flux density of the permanent magnet surface does not alter even if the device actuates and the force of a focus control direction (restoring force) does not occur in the permanent magnet. Since the parts consisting of the magnetic material do not exist on the fixed side the vertical drag (the force in a radial direction, occurring in the permanent magnet) does not occur even if the permanent magnet has the asymmetry of the distribution of flux density.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an objective lens driving device, in particular, an objective lens driving device that controls track deviation and defocus of a light spot focused on an information recording surface of an optical disk. The present invention relates to an objective lens drive device for a playback device or a recording/playback device.

[Prior Art] Fig. 9 to Fig. 12 show a conventional objective lens driving device, in which Fig. 9 is an exploded perspective view, Fig. 10 is a plan view,
Figure 11 is a sectional view taken along the line XI-XI in Figure 10;
The figure is a diagram showing a change in the restoring force as the permanent magnet of the objective lens driving device is displaced in the focal direction.

In the figure, (1) is an objective lens, (2) is a cylindrical bearing part (3) near the center, and the objective lens (1) is fixedly placed at a position eccentric from the bearing part (3) by a predetermined distance. (5) is a ring-shaped permanent magnet magnetized with four poles in the radial direction, which is fixedly held in a ring part (4) provided at the bottom of the movable holder (2). ,
(6) is a base yoke which is a fixed part, and this base yoke (6) has arc-shaped outer protrusions (7a), (7b) in the outer circumferential direction of the permanent magnet (5) and ring-shaped outer protrusions in the inner circumferential direction. It has an inner protrusion (8).

(9) is a support shaft that is fixedly erected approximately at the center of the base yoke (6), and this support shaft (9) has a movable holder (
2) is fitted so as to be slidable in the axial direction of arrow A in FIG. 9 and rotatable in the direction of arrow B.

(10) is a focus control coil fixedly disposed on the outer periphery of the inner protrusion (8) of the base yoke (6);
a), (1l b), (11c).

(lid) is the outer protrusion (7a) of the base yoke (6)
, (7b) is a track control coil disposed on the inner periphery of the base yoke (6), and (12) is the outer protrusion (7a) of the base yoke (6).
, (7b) and the inner protrusion (8) is a coil base made of a non-magnetic material fixedly provided on the base yoke (6), and this coil base (12) is equipped with a track control coil. (lla), (llb), (tic), (11
d) for storing and positioning the recess (13a), (
13b), (13c), and (13d) are provided.

The track control coil (lla), (11b),
(llc) and (lid) have a rectangular shape, and are track control coils (11a).

The recess (13a) of the coil base (12) so that the - sides of (llb), (llc), and (lid) are close to each other,
(13b), (13c), and (13d) are provided.

The permanent magnet (5) includes a focus control coil (10) and track control coils (lla) and (flb).

(llc) and (lid) with a predetermined air gap between the track control coil (llc) and (lid).
a), (llb), (lie).

The surface facing the adjacent portion of the (lid) side is magnetized so that the magnetic pole is different from that of other identical peripheral surfaces.

Next, the operation will be explained. Focus control coil (10)
By applying a control current according to the amount of defocus to the movable holder (2), the movable holder (2) slides in the direction of arrow A, and the objective lens (1
) focus control can be performed. Also, a track control coil (11&>).

(llb), (llc), and (lid), the movable holder (2
) rotates in the direction of arrow B, allowing tracking control of the objective lens (1).

[Problems to be Solved by the Invention] Since the conventional objective lens drive device is configured as described above, as shown in FIG.
As the focus is controlled, the magnetic flux on the surface of the permanent magnet (5) is reduced by moving in the direction of the arrow in Figure 9 in the base yoke (6) as shown in Figure 12 Ca), (b), and (c). The density distribution changes as shown in curves (a), (b), and (c) in FIG.
).

This restoring force F is caused by the permanent magnet (5)
By moving towards the upper end, the permanent magnet (5) gradually changes and protrudes from the upper end of the base yoke (6) (
FIG. 12(b)) The position changes rapidly as shown at point (b) of the curve.

This restoring force F causes the operation of the objective lens drive device to become nonlinear, causing control problems. In addition, if the magnetic flux density distribution of the permanent magnet (5) is not point symmetrical, the magnetic flux density distribution in the air gap will also be asymmetrical, and a radial force will be generated on the permanent magnet (5), and this force will be applied to the sliding surface. acts as a normal force on the sliding surface to increase the frictional force on the sliding surface,
There was a problem with control problems.

This invention was made to solve the above-mentioned problems.
The object of the present invention is to obtain a movable permanent magnet type objective lens drive device that is easy to control.

Means for Solving Problem c] The objective lens drive device according to the present invention includes a first coil for focus shift control and a coil for track shift control brush 2 in a fixed part, and a movable holder which is a movable part. is provided with a yoke and a permanent magnet, and this permanent magnet is connected to the first coil and the second coil.
At least one of the coils is magnetized so as to interlink magnetic fluxes whose directions of adjacent vectors are substantially opposite to each other.

[Function] In the objective lens driving device according to the present invention, since the movable holder is provided with a permanent magnet and a yoke, no component made of magnetic material is disposed on the fixed side near the movable holder.
Even when the device operates, the magnetic flux density distribution on the surface of the permanent magnet does not change, and no force (restoring force) in the focus control direction is generated on the permanent magnet.

Furthermore, since there are no parts made of magnetic material on the fixed side, no vertical force (force in the radial direction that occurs in the permanent magnet) will be generated even if there is an asymmetry in the magnetic flux density distribution in the magnet.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the objective lens driving device according to the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG. 4 is a developed view of a track control coil used in an embodiment of the objective lens driving device according to the present invention, and FIG.
FIG. 6 is a partial bottom view of the movable part seen from the back side, and FIG. 6 is a partial plan view showing the fixed part of FIG. It is attached.

In the figure, (1) is an objective lens, (2) is a cylindrical bearing part (3) near the center, and the objective lens (1) is fixedly placed at a position eccentric from the bearing part (3) by a predetermined distance. (14) is a ring-shaped movable yoke with a U-shaped cross section fixedly provided on a ring portion (4) provided in the outer circumferential direction of the movable holder (2); (5
) is a permanent magnet magnetized with 4 poles 4'J in the radial direction, which is provided on the side adjacent to the ring part (4) of the movable holder (2) inside the movable yoke (14), and (15) is the fixed part. This is a coil base made of a certain non-magnetic material.

The coil base (15) has a coil fixing part (16) that holds a focus control coil (10) and a track control coil (lla>, (llb). Track control coil (lla), (ll
b) are provided with notches (17a) and (17b) for arranging and positioning them approximately point-symmetrically about the support shaft (9).

(9) is a support shaft that is fixedly erected approximately in the center of the coil base (15), and this support shaft (9) has a movable holder (2
) is fitted so as to be slidable in the axial direction of arrow A in FIG. 2 and rotatable in the direction of arrow B in FIG. 1.

A closed magnetic path is formed by the permanent magnet (5) and the movable yoke (14), and a predetermined gap is provided in the air gap of this closed magnetic path, and a focus control coil (10) and a track control coil ( 11a) and (llb) are arranged on the coil fixing part (16) of the coil base (15).
) is provided. Further, the permanent magnet (5) is magnetized so that the magnetic poles are different between the negative side and the other side of the track control coils (lla) and (llb).

Next, the operation of one embodiment of the present invention will be explained. Focus control coil (10) and track control coil (ll
a) and (llb) are the permanent magnet (5) and the movable yoke (
14), and their effective magnetic fluxes are interlinked with each other. Therefore,
The focus control coil (10) controls the control current according to the focus shift.
The movable holder (2) slides in the direction indicated by the arrow in FIG. 2, and the focus of the objective lens (1) can be controlled.

Furthermore, by passing a control current corresponding to the track deviation to the track control coils (lla) and (llb), the movable holder (2) rotates in the direction of arrow B in FIG. can be controlled.

As described above, since the permanent magnet (5) and the movable yoke (14) are arranged on the movable holder (2), and no parts made of magnetic material are arranged on the fixed part, the permanent magnet The magnetic flux density distribution on the surface of the magnet (5) does not change,
It does not generate any resilience. Further, even if the magnetic flux density distribution of the permanent magnet (5) is asymmetrical, since the movable holder (2) is provided with a magnetic circuit, no normal force acts on the sliding surface.

In the above embodiment, a movable yoke with a U-shaped cross section is used to make the magnetic circuit a closed magnetic path, but as shown in FIGS. ), a ring-shaped movable yoke (18) is fixedly provided on the ring part (4), a permanent magnet (5) is provided on the outer circumferential surface of this movable yoke (18), and a predetermined gap is provided in the outer circumferential direction. Focus control coil (10) and track control coil (
Even if 11a) and (llb) are arranged, the same effect as in the above embodiment can be obtained.

However, in this case, the effective magnetic flux density interlinking the control coil tends to be lower than that in the above embodiment, so care must be taken at the time of design.

The second embodiment shown in FIGS. 7 and 8 is substantially the same as the first embodiment except for the magnetic circuit portion, so a detailed explanation will be omitted.

[Effects of the Invention] As described above, according to the present invention, a magnetic circuit consisting of a permanent magnet and a yoke is disposed only in the movable part, and only parts made of non-magnetic material such as a control coil are disposed in the fixed part. Since the configuration is such that the magnetic flux density distribution on the surface of the permanent magnet does not change due to the control operation, no restoring force is generated in the permanent magnet. Further, even if the magnetic flux density distribution of the permanent magnet is non-uniform, no normal force acts on the sliding surface. As a result, there is no external force, the operation becomes linear, and highly accurate control becomes easy.

Furthermore, since the movable part is provided with a yoke to form a closed magnetic path, it is possible to obtain an objective lens drive device with high drive sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an objective lens device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG.
The figure is a sectional view taken along the line ■-■ in FIG. 1, FIG. 4 is a developed view of a track control coil used in an embodiment of the objective lens drive device according to the present invention, and FIG. Figure 6 is a partial bottom view of the movable part seen from the back.
FIG. 7 is a plan view showing an objective lens drive device according to another embodiment of the present invention; FIG. 8 is a cross-sectional view taken along line ■-■ in FIG. 7; FIG. is an exploded perspective view showing a conventional objective lens drive device, FIG. 10 is a plan view of the device, FIG. 11 is a sectional view taken along the line XI-XI in FIG. 10, and FIG. 12 is a focal displacement of a permanent magnet. FIG. 3 is a diagram showing changes in restoring force with directional displacement. In the figure, (1) is an objective lens, (2) is a movable holder, (5) is a permanent magnet, (9) is a support shaft, (10) is a focus control coil, and (11a). (llb) is a track control coil, (14) is a movable yoke, and (1g) is a movable yoke. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Figure 1 1: Objective 2: Movable holder Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 (a ) (b) (c) l・Indication of the case Japanese Patent Application No. 62-041109 2, Name of the invention Objective lens drive device 3, Person making the amendment Representative Moriya Shiki 4, Agent 5, Specification subject to amendment Claims and Detailed Description of the Invention. 6. Contents of Correction Claims (1) A movable holder that is rotatably and movably fitted to a support shaft and holds an objective lens having an optical axis parallel to the axial direction of the support shaft; , an objective lens drive having a driving means for rotating and sliding the movable holder in the axial direction so as to control defocus and track deviation of the light spot focused on the disk via the objective lens; In the apparatus, the driving means includes a magnetic circuit provided on the movable holder and a first focus control circuit provided on the fixed part.
consisting of a coil and a second coil for track control,
The magnetic circuit includes a movable yoke and a permanent magnet, and the permanent magnet is configured to interlink magnetic flux in which the directions of adjacent vectors are substantially opposite to at least one of the first coil and the second coil. An objective lens drive device characterized by being magnetized. (2) The permanent magnet has a ring shape and is magnetized in the radial direction, and the first coil and the second coil are disposed facing the permanent magnet, and the second coil is arranged opposite to the permanent magnet. The coil has a rectangular shape and is arranged to have sides substantially parallel to the spindle, and the permanent magnet has one side and the other side of the side parallel to the spindle of the second coil. 2. The objective lens driving device according to claim 1, wherein the objective lens driving device is magnetized so that the directions of interlinking magnetic flux vectors are substantially opposite to each other. (3) The movable yoke has a U-shaped cross section and a ring shape, and is fixedly provided on the movable holder so that the opening faces in a direction opposite to the disk side. , the objective lens according to claim 1 or 2, wherein the permanent magnet is fixedly disposed on a circumferential surface adjacent to an outer circumference of the movable holder inside the movable yoke. Drive device. (4) The movable yoke is a ring-shaped thin cylinder,
Claim 1 or 2, wherein the permanent magnet is fixedly provided on the outer circumference of the movable holder, and the permanent magnet is fixedly provided on the outer circumferential surface of the movable yoke. objective lens drive device.

Claims (4)

[Claims] (1) A movable holder that holds an objective lens that is rotatably and movably fitted to a support shaft and has an optical axis parallel to the axial direction of the support shaft; In the objective lens driving device, the driving means includes a driving means for rotating the movable holder and sliding the movable holder in the axial direction so as to control defocus and track misalignment of the emitted light spot. The magnetic circuit includes a first coil for focus control and a second coil for track control provided on the fixed part, and the magnetic circuit includes a movable yoke and a permanent magnet. An objective lens driving device characterized in that at least one of the first coil and the second coil is magnetized so as to interlink magnetic fluxes whose directions of adjacent vectors are substantially opposite to each other. (2) The permanent magnet has a ring shape and is magnetized in the radial direction, and the first coil and the second coil are disposed to face the permanent magnet, and the second coil is magnetized in the radial direction. The permanent magnet is arranged to have a rectangular shape and have sides substantially parallel to the spindle, and the permanent magnet is interlinked with one side and the other side of the side parallel to the spindle of the second coil. 2. The objective lens driving device according to claim 1, wherein the objective lens driving device is magnetized so that the direction of the magnetic flux vector is substantially reverse. (3) The movable yoke has a U-shaped cross section and a ring shape, and is fixedly provided on the movable holder so that the opening faces in a direction opposite to the disk side. , the objective lens according to claim 1 or 2, wherein the permanent magnet is fixedly disposed on a circumferential surface adjacent to an outer circumference of the movable holder inside the movable yoke. Drive device. (4) The movable yoke is a ring-shaped thin cylinder,
Claim 1 or 2, wherein the permanent magnet is fixedly provided on the outer circumference of the movable holder, and the permanent magnet is fixedly provided on the outer circumferential surface of the movable yoke. objective lens drive device.