JPH05159331A - Objective lens actuator - Google Patents

Abstract

PURPOSE:To provide the automatic center returning means of an objective lens for which side pressure is hardly loaded to a turning center axis, the generation of bearing friction resonance damaging to a tracking control operation is extremely reduced, and the configuration is simplified concerning the sliding shaft type objective lens actuator of an optical disk device. CONSTITUTION:A rectangular magnetic board 1 is arranged in a tracking coil 2 at the outer peripheral part of a movable element 9, the movable element 9 is turned with a central axis 15 as a center until a point, where the attracting force is made equal for both driving magnets 5 and 6, by obtaining the attracting force from the focus driving magnet 5 and the tracking driving magnet 6 having reverse magnetic poles, and an objective lens 18 is returned to the center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens actuator used in a device (optical disc device) for recording or reproducing an information signal by using laser light on an information recording disc (disc) which is driven to rotate. Regarding data

[0002]

2. Description of the Related Art In recent years, an information recording / reproducing device using an optical disk has been attracting attention as a next-generation information medium.

An example of a conventional objective lens actuator used in an optical disk device will be described below with reference to the drawings. 4 and 5 are conventional objective lens actuators.
3A and 3B are a perspective view and a plan view showing an example of a printer. As shown in the figure, the sleeve 16, the focus coil 17, the tracking coil 2, and the objective lens 18 are integrally attached to the lens holder 9a to form the mover 9, which can be slid and rotated about the central axis 15. Is becoming And lens holder 9
Magnetic balls 3 are arranged in a in a position symmetrical with respect to the central axis 15, and a permanent magnet 4 for returning to the center is arranged on the yoke base 19 at a position facing the magnetic balls 3. Reference numeral 20 denotes a disk, which rotates in the direction indicated by arrow 22.

Further, the pair of focus driving magnets 5 and the pair of tracking driving magnets 6 are provided in the yoke base 19 respectively.
And a magnetic force is applied to the focusing coil 17 and the tracking coil 2 which are attached to each other and are arranged to face each other.

The operation of the conventional example thus constructed will be described. The driving force of the mover 9 is the focus coil 17
A sliding force in the direction indicated by the arrow 11 is obtained by passing a current through the coil, and a turning force in the direction indicated by the arrow 10 is obtained by passing a current through the tracking coil 2. And
By setting the sliding direction 11 to the focal direction of the objective lens 18 and the rotating direction 10 to a direction orthogonal to the track of the disc 20, the objective lens 18 focuses the laser light on the track of the disc 20. In this way, the focus control (focusing) and the track follow-up control (tracking) required for non-contact tracking can be performed at the same time.

The magnetic ball 3 has a central axis 1 in the lens holder 9a.
5, the permanent magnets 4 for returning to the center are arranged symmetrically with respect to each other.
It has a function of automatically returning to a neutral position when the movable element 9 including the objective lens 18 is rotated by receiving the suction force 21 from. As a result, when the tracking operation is performed, the center point of driving of the objective lens 18 (the neutral position when the driving force is cut off) is automatically guaranteed, and stable tracking operation can be performed.

The above-mentioned conventional example is disclosed in Japanese Examined Patent Publication No. 63-41.
This is an improvement of the configuration of claim 7 described in Japanese Patent Publication No. 136.

[0008]

However, the above-mentioned conventional structure has the following problems. That is, the center return permanent magnets 4 arranged on the left and right sides must exert a strong attractive force 21 on the magnetic balls 3 arranged on the left and right sides, and the magnetic flux density of the magnets and the mounting position are unbalanced. If there is, the imbalance in the attraction force to the magnetic ball 3 is likely to occur, and the sleeve 1 of the mover 9
A large lateral pressure is generated between 6 and the central shaft 15. In that case,
When the frictional force between the sleeve 16 and the central shaft 15 is increased and the objective lens 8 is rotated (tracking operation), the phase of displacement of the objective lens 8 is relative to the phase of the current flowing through the tracking coil 2. Large irregular delays occur, the phase margin of the tracking control system is reduced, and control stability is impaired (bearing friction resonance that is harmful to tracking control operation).

Further, a dedicated permanent magnet for returning to the center (permanent magnet 4 for returning to the center) is required, which increases the material cost.

The present invention solves the above-mentioned conventional problems and has a center returning mechanism that does not apply unnecessary lateral pressure between the objective lens movable element 9 and the center axis without using a permanent magnet dedicated to the center returning. The objective is to provide an objective lens actuator.

[0011]

In order to achieve this object, an objective lens actuator of the present invention is provided with an objective lens and an electromagnetic coil, and a movable element which is at least rotatable with respect to its central axis. A pair of first permanent magnets spaced apart from the mover and having magnetic poles facing the mover, and a pair of first permanent magnets spaced apart from the mover to be adjacent to or close to the first permanent magnets. And a pair of second permanent magnets having magnetic poles opposite in polarity to the first permanent magnet, and a pair of facing and spaced from the first and second permanent magnets and attached to the mover. And a magnetic plate.

[0012]

According to the present invention, with the above-mentioned structure, the centering force of the objective lens can be obtained by applying the attractive force from both the first and second permanent magnets to the magnetic plate. In comparison, an extremely small force is sufficient, and the unnecessary lateral pressure between the mover and the central shaft caused by the imbalance of the suction force is significantly reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, reference numeral 1 denotes a magnetic plate, which is axially symmetrically attached to the outer periphery of the cylindrical movable element 9 (inside the tracking coil 2) one by one. The magnetic ball 3 and the center-returning permanent magnet 4 in the conventional example 5 are deleted. Others have the same functions as those of the conventional example, and the same reference numerals are given to omit the description.

The operation of the objective lens actuator constructed as described above will be described with reference to FIG. The magnetic plate 1 receives attraction forces 7 and 8 from a pair of permanent magnets (the focus drive magnet 5 and the tracking drive magnet 6) arranged to face the magnetic plate 1 and automatically returns to a position where these attraction forces are balanced. The power to do is working. As a result, the objective lens is automatically returned to the center point of driving when the current of the tracking coil 2 is cut off.

The details of this operation will be described. As shown in FIG. 3, the focus driving magnet 5 and the tracking driving magnet 6 are magnetized in opposite directions with the joint surface as a boundary.
Acts like a broken line. The focus driving magnet 5 and the tracking driving magnet 6 may be close to each other instead of being joined. In FIG. 2, the maximum part of the magnetic flux passing through the magnetic plate 1 is located near the center of both magnets, and the magnetic plate 1 receives the even and maximum attraction forces (arrows 7 and 8) from both magnets and restrains them. Has been done. On the other hand, FIG. 3 shows a state in which the lens holder 9a is rotationally moved in the clockwise direction of the tracking direction 10. At this time, the magnetic plate 1 has a size of arrows 12 and 13 from both magnets 5 and 6.
Unequal forces act in both directions, receive the force of the difference, return to the original maximum passing magnetic flux position, and stand still at the position shown in FIG.

The magnetic plate 1 is a rectangular thin plate made of a magnetic material. Although a magnetic sphere may be used as in the conventional example, when a sphere is used, the position where the attractive forces 7 and 8 are balanced is sensitive to the distribution of the magnetic flux density of the permanent magnet and easily varies, and the center point position of the objective lens is It is difficult to determine uniformly. On the other hand, when a plate is used, the position where the attraction forces 7 and 8 are balanced becomes relatively insensitive to the magnetic flux density distribution, and the center position of the objective lens is likely to be uniformly set. Further, since the magnetic plate 1 has a rectangular shape, the attraction force can be further balanced.

In the case of this embodiment, the attraction forces 7 and 8 acting on the magnetic plate 1 are close to the tangential direction of rotation with respect to the central shaft 15 rather than the lateral pressure direction of the central shaft 15 (radial direction), and Since the distance from the shaft 15 (radius of rotation) is larger than that of the conventional example, when obtaining a center restoring force equivalent to that of the conventional example, the force acting on the magnetic plate 1 in the lateral pressure direction of the central axis is 10 minutes of the conventional example. The bearing friction due to the lateral pressure between the sleeve 16 and the central shaft 15 caused by the imbalance of the attraction forces of the two magnetic plates is also 1/10 or less. As a result, the allowable range of the dimensional error relating to the assembly accuracy of the bearing, the mover, the magnet, etc. can be widened as compared with the conventional one, and the workability is improved.

As described above, according to this embodiment, the mover 9
By arranging the magnetic plate 1 inside the tracking coil 2 on the outer peripheral portion of the object and obtaining the attractive force from the focus driving magnet 5 and the tracking driving magnet 6, the central axis 15 is less likely to be subjected to lateral pressure and less likely to cause friction. The function of returning the center of the lens can be realized, and the conventional magnet for returning to the center is unnecessary.

[0019]

As described above, according to the present invention, a pair of first permanent magnets having a magnetic pole facing the mover and spaced apart from the outside of the mover to which the objective lens and the electromagnetic coil are attached are movable. A pair of second permanent magnets spaced apart from the outside of the child, adjacent to or close to the first permanent magnet and having magnetic poles of opposite polarities to the first permanent magnet;
Since the permanent magnet and the pair of magnetic plates attached to the mover so as to be opposed to and separated from each other are provided, unnecessary side pressure is generated between the objective lens mover and the center axis without using the permanent magnet dedicated to the center return. It is possible to realize an excellent objective lens actuator having a center returning mechanism that does not require stable tracking control.

[Brief description of drawings]

FIG. 1 is a perspective view of an objective lens actuator according to an embodiment of the present invention.

FIG. 2 is a plan view of the same.

FIG. 3 is a plan view for similarly explaining the operation.

FIG. 4 is a perspective view showing an example of a conventional objective lens actuator.

FIG. 5 is a plan view of the same.

[Explanation of symbols]

 1 Magnetic Plate 5 Focus Driving Magnet 6 Tracking Driving Magnet 9 Mover 15 Central Axis 18 Objective Lens

Claims (3)

[Claims] 1. An objective lens and an electromagnetic coil are attached, at least a movable element rotatable about a central axis of the movable element, and a movable element arranged apart from the movable element and having a magnetic pole facing the movable element. A pair of first permanent magnets, and a pair of magnetic poles having a polarity opposite to that of the first permanent magnets, which are disposed outside the mover to be adjacent to or close to the first permanent magnets. Objective lens actuator including a second permanent magnet and a pair of magnetic plates mounted on the mover so as to face and separate from the first and second permanent magnets.
Ta. 2. The objective lens actuator according to claim 1, wherein the first and second permanent magnets also serve as permanent magnets for driving an electromagnetic coil. 3. The objective lens actuator according to claim 1, wherein the magnetic plate has a rectangular shape.