JPH0628112B2 - Objective lens drive - Google Patents

Description

The present invention relates to an objective lens driving device, and more particularly to a track shift of a light spot focused on an information recording surface of an optical information recording medium (hereinafter referred to as a disk). And an objective lens driving device of a reproducing device or a recording / reproducing device which controls defocus.

[Prior Art] FIGS. 8 to 11 show a conventional objective lens driving device. FIG. 8 is an exploded perspective view thereof, FIG. 9 is a plan view of an assembled state thereof, and FIG. 9 is a cross-sectional view taken along the line XX, FIG. 11 (a) is a plan view showing the positional relationship between the permanent magnet and the base yoke, and FIG. 11 (b) is the angular displacement of the permanent magnet and the action on the permanent magnet. It is a figure which shows the relationship of the torque to perform. 8 to 11, (1) is an objective lens, and (2) is provided with a cylindrical bearing portion (3) near the central portion, and the objective is placed at a position decentered by a predetermined distance from the bearing portion (3). A movable holder holding the lens (1) fixedly,
(5) is a ring-shaped permanent magnet that is fixedly held by a ring portion (4) provided in the lower portion of the movable holder (2) and is magnetized in four poles in the radial direction, (5a), (5a), 5
b), (5c) and (5d) are magnetic poles of the permanent magnet (5), and the magnetic poles (5a) and (5b) and the magnetic poles (5c) and (5d) have the same polarity on the same peripheral surface. . Reference numeral (6) is a base yoke which is a fixed portion, and the base yoke (6) has an outer protruding portion (7) and an inner protruding portion (8) so as to have a predetermined gap with the permanent magnet (5). Have Notches (9a) and (9b) are provided on the outer protruding portion (7).
Are symmetrically provided so as to face the boundary (a) between the magnetic poles (5a) and (5c) and the boundary (b) between the magnetic poles (5b) and (5d) of the permanent magnet (5). Note that (C) is the boundary between the magnetic poles (5a) and (5d), and (D) is the magnetic pole (5b).
And (5c).

Reference numeral (10) is a support shaft which is fixedly erected substantially in the center of the base yoke (6), and the bearing portion (3) of the movable holder (2) is attached to the support shaft (10) by the arrow in FIG. It is fitted so as to be slidable in the direction A and rotatable in the direction of arrow B in FIG.

(11) is a focus control coil fixedly arranged on the outer periphery of the inner protrusion (8) of the base yoke (6) so as to face the permanent magnet (5), and (12a) and (12b) are back coils. This is a rectangular track control coil fixed to the yokes (13a), (13b) so as to have sides that are substantially parallel to the axis of the support shaft (10).

As shown in FIG. 10, the back yokes (13a), (13b) oppose each other substantially parallel to the peripheral surface of the permanent magnet (5), and the track control coils (12a), (12).
Fixedly arranged on the outer periphery of the outer protrusion (7) so that b) is housed in the notches (9a) and (9b) so as to have a side substantially parallel to the axis of the support shaft (10). Has been done.

The track control coils (12a) and (12b) have one side and the other side which are substantially parallel to the axis of the support shaft (10),
The magnetic poles (5
a), (5c) and magnetic poles (5b), (5d) are opposed.

Next, the operation will be described. Focus control coil (11)
When a control current corresponding to the amount of defocus is applied to the movable holder (2), the movable holder (2) slides in the direction of arrow A, and the focus control of the objective lens (1) can be performed.

Further, when a control current according to the amount of track deviation is passed through the track control coils (12a), (12b), the movable holder (2) rotates in the direction of arrow B, and the objective lens (1) is track-controlled. be able to.

In this case, as shown in FIG. 11, the boundary (a) between the magnetic poles (5a) and (5c) of the permanent magnet (5) and the cutout portion (9a) provided in the base yoke (6) and Since the boundary (b) between the magnetic poles (5b) and (5d) and the notch (9b) are arranged to face each other, when the angular displacement θ is given to the permanent magnet (5), the magnetic energy in the air gap is The permanent magnet (5) changes, and the torque (force) T as shown by the solid line in FIG. 11B acts on the permanent magnet (5), and the permanent magnet (5) tries to return to its original position. It is possible to hold the middle point in the track control direction (direction of arrow B in FIG. 9) of (2).

[Problems to be Solved by the Invention] Since the conventional objective lens driving device is configured as described above, as shown in FIG. 11 (b), it is in the middle of the track control direction of the movable holder (2). The points are held magnetically.

However, when a control current is passed through the focus control coil (11), the torque (force) acting on the permanent magnet (5) as shown by the chain line and the alternate long and short dash line in FIG. 11 (b) as an example. The angular position of the permanent magnet (5) at which is zero changes, and the midpoint holding position of the movable holder (2) changes.
That is, when a control current is passed through the focus control coil (11), an operation in the track control direction occurs in addition to an operation in the focus control direction (hereinafter abbreviated as operation interference).

This is because the static magnetic field Hm generated by the permanent magnet (5) interferes with the dynamic magnetic field Hc generated by passing a control current through the focus control coil (11), the magnetic energy in the air gap changes, and the permanent magnet is changed. This is because the force balance in the circumferential direction (θ direction) acting on (5) is lost.

The causes of this imbalance are the magnetic poles (5a), (5b), (5c), (5d) of the permanent magnet (5) and the notch (9a) provided in the base yoke (6).
This is because (9b) is point-symmetrical about the axis of the support shaft (10). That is, the degree of increase or decrease in magnetic energy due to the dynamic magnetic field Hc is also point-symmetrical about the axis of the support shaft (10), and the circumferential force acting on the permanent magnet (5) caused by this is canceled. Because they don't match. As described above, the conventional objective lens driving device has a problem that it is very difficult to control and operate it because of operational interference.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an objective lens driving device that is free from operation interference and is easy to control.

[Means for Solving the Problems] In the objective lens driving device according to the present invention, a notch portion is provided asymmetrically by displacing a fixed angle from a symmetrical position in a base yoke that is a fixed portion, or is provided in a movable portion. The permanent magnets are magnetized asymmetrically with a certain angle offset from the symmetrical position, and the positional relationship between the notch and the boundary between the magnetic poles is approximately a line centered on a straight line passing through the axis of the spindle. It is configured to be symmetrical (not including point symmetry).

[Operation] In the objective lens driving device according to the present invention, a dynamic magnetic field H generated by passing a control current through the focus control coil.
Since the increase / decrease in magnetic energy due to c occurs line-symmetrically around a straight line passing through the center of rotation in the track control direction, the torque (force) acting on the permanent magnet in the track control direction is increased / decreased as the magnetic energy increases / decreases. They cancel each other out and prevent the occurrence of motion interference.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to Figs. FIG. 1 is an exploded perspective view of an objective lens driving device according to the present invention, FIG. 2 is a plan view of its assembled state, FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2, and FIG. A plan view of the permanent magnet used in the example, FIG. 5 is a partial plan view showing a positional relationship between the permanent magnet and the base yoke, and FIG.
FIGS. 9A and 9B are a plan view and a characteristic diagram showing the relationship between the angular displacement of the permanent magnet and the torque acting on the permanent magnet.

1 to 6, the above-mentioned FIGS.
The same parts as those of the conventional apparatus shown in the figure are denoted by the same reference numerals, and the operations of focus control and track control are the same as those of the above-described conventional apparatus, and therefore the description thereof is omitted.

As shown in FIGS. 4 and 5, the present invention is particularly applicable to the boundary (c) of the magnetic poles (5d) and (5a) of the permanent magnet (5) and the boundary (b) of the magnetic poles (5b) and (5d). And the central angle φy of the notches (9a) and (9b) and the magnetic poles (5a) and (5b) so that the notches (9a) and (9b) provided in the base yoke (6) face each other. The angle θm of 1) is provided in the relationship of φy = 180−θm. In the figure, φ0 is φy /
It is 2.

Next, the operation will be described. When angular displacement θ is applied to the permanent magnet (5) as shown in FIG. 6 (a), the magnetic energy in the air gap changes, and the permanent magnet (5) shows as shown in FIG. 6 (b). Torque (force) T acting like
The permanent magnet (5) is about to return to its original position, and it becomes possible to hold the middle point of the movable holder (2) in the track control direction (direction of arrow B in FIG. 2).

Further, the increase or decrease of the magnetic energy of the air gap due to the dynamic magnetic field Hc generated by passing the control current through the focus control coil (11) occurs line-symmetrically with respect to the line YY shown in FIG. Therefore, as the magnetic energy increases and decreases, the torques (forces) in the track control direction that act on the permanent magnets (5) cancel each other out, so that operation interference does not occur.

In the above-described embodiment, the central angle of the notch provided in the base yoke (6) is asymmetrically set to φy = 180−θm so that no operation interference occurs. As shown, the magnetic energy of the air gap is increased or decreased by the dynamic magnetic field Hc by setting the central φm of the magnetic poles (5a) and (5b) of the permanent magnet (5) to φm = 180−θm. Causes line symmetry with respect to the line M-M, so that operation interference does not occur. In the figure, φ
0 is φm / 2.

[Effects of the Invention] As described above, according to the present invention, the positional relationship of the boundary portion of the magnetic poles magnetized in the notch ring-shaped permanent magnet provided in the base yoke which is the fixed portion, Since it is configured to be almost line-symmetrical (not including point-symmetrical) about a straight line passing through the axis of the support shaft that holds the movable holder in a rotatable and slidable manner, a control current is passed through the focus control coil. The increase or decrease of the magnetic energy in the magnetic circuit air gap caused by this occurs line-symmetrically with respect to the above straight line, and it is possible to prevent the occurrence of operation interference and to facilitate the control operation.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an objective lens driving device according to an embodiment of the present invention, and FIG. 2 is a plan view of its assembled state,
3 is a cross-sectional view taken along the line III-III in FIG. 2, FIG. 4 is a plan view of the permanent magnet used in this embodiment, and FIG. 5 shows the positional relationship between the permanent magnet and the base yoke. Partial plan views, FIGS. 6 (a) and 6 (b) are plan views and characteristic diagrams showing the relationship between the angular displacement of the permanent magnet and the torque acting on the permanent magnet, and FIG. 7 is according to the second embodiment of the present invention. FIG. 8 is a partial plan view showing the relationship between the permanent magnet and the base yoke, FIG. 8 is an exploded perspective view showing a conventional objective lens driving device, FIG. 9 is a plan view of the assembled state, and FIG. 11A and 11B are a plan view and a characteristic view showing the relationship between the angular displacement of the permanent magnet and the torque acting on the permanent magnet. In the figure, (1) is an objective lens, (2) is a movable holder, (5) is a permanent magnet, (5a), (5b), (5).
c) and (5d) are magnetic poles, (6) is a base yoke, and (9)
a) and (9b) are notches, (10) is a spindle, (11)
Is a focus control coil, and (12a) and (12b) are track control coils. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A movable holder, which is rotatably and slidably held by a support shaft, an objective lens provided on the movable holder at a position eccentric from the support shaft, and the movable holder being slid and rotated. In the objective lens drive device having a drive device for focus control and track control of the light spot on the optical information recording medium, the drive device is provided in the movable holder in a direction substantially orthogonal to the axis of the support shaft. A multi-pole magnetized ring-shaped permanent magnet, a base yoke that is a fixed portion provided to face the inner peripheral surface and the outer peripheral surface of the permanent magnet, and at least one position of a boundary portion between the magnetic poles of the permanent magnet. Focus control fixedly provided in the base yoke so as to be located in a notch portion provided in the base yoke so as to face each other and in a gap formed by the permanent magnet and the base yoke. And a coil for controlling a track, and the positional relationship between the boundary of the magnetic pole and the notch is substantially line-symmetrical with respect to a line passing through the axis of the support shaft. An objective lens driving device characterized by: 2. The objective lens driving device according to claim 1, wherein the permanent magnet is magnetized with four poles, and the notch portion is provided at two positions.