JPH10255291A - Objective lens-driving apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens-driving apparatus in which a force necessary for driving an objective lens upward and a force necessary for driving the objective lens downward are made nearly equal in characteristic, thereby facilitating positional control of the objective lens. SOLUTION: A lens holder 4 to which an objective lens 5 and a magnetic element 3 are fixed is set on a supporting shaft 6 in a movable fashion in the direction of an optical axis of the objective lens 5. A magnet 2 in a fixed relation to the supporting shaft 6 is arranged to face the magnetic element 3. The objective lens 5 is held at a neutral position in a direction in which the objective lens 5 can move by magnetic attraction force acting between the magnetic element 3 and magnet 2. Moreover, the direction of the optical axis of the objective lens 5 is set in parallel to the direction of gravitation when the apparatus is used. A distance between the magnetic element 3 and magnet 2 is reduced in accordance with the fall of the objective lens 5 in the moving direction. Accordingly, an asymmetry because of the influence of gravitation in the movement in an up-down direction of the objective lens 5 and a driving force characteristic holding the objective lens at the position where the objective lens is moved is improved in the up-down direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention condenses a light beam emitted from a light source such as a semiconductor laser on a recording medium,
The present invention relates to an objective lens driving device used for an optical recording / reproducing device for recording / reproducing a signal.

[0002]

2. Description of the Related Art Generally, an optical pickup used in an optical recording / reproducing apparatus accurately focuses a light beam emitted from a semiconductor laser on a recording medium in order to record or reproduce an information signal on the recording medium. Therefore, an objective lens driving device is used. As a mechanism for holding a neutral position of an objective lens in this objective lens driving device, a mechanism utilizing magnetic attraction between a magnet and a magnetic piece has been proposed. The present invention relates to an objective lens driving device used in such a manner that the direction of the optical axis of the objective lens and the direction of gravity are parallel.

FIG. 9 schematically shows an example of a conventional objective lens driving device of this type. FIG. 9 shows an objective lens driving device generally referred to as a shaft sliding type, in which a lens holder 4 is rotatable about a support shaft 6 and is movably mounted along the support shaft 6. Have been. An objective lens 5 is attached to the lens holder 4 such that its optical axis and the support shaft 6 are parallel. Further, magnetic pieces 3 are mounted on the outer peripheral surface of the lens holder 4 at positions symmetrical with respect to the support shaft 6. The support shaft 6 is fixed to the center of a member constituting the yoke 1, and the magnet 2 is mounted inside the yoke 1. Generally, the surface of the magnet 2 facing the magnetic piece 3 is parallel to the movable direction of the lens holder 4.

By disposing the yoke 1 and the lens holder 4 such that the magnetic piece 3 faces the magnet 2, a magnetic attraction is generated between the magnet 2 and the magnetic piece 3, and the lens holder 4 is moved in the movable direction. Held in neutral position. The operation held in the neutral position will be described with reference to FIG. In FIG. 10, the lens holder 4 to which the objective lens is attached as described above receives a downward force due to the action of the gravity 10, and the position of the magnetic piece 3 with respect to the magnet 2 is smaller than when the gravity 10 is ignored. Shift down. Hereinafter, the relative position between the magnet 2 and the magnetic piece 3 when the gravity 10 is neglected, that is, the relative position between the yoke 1 and the lens holder 4 is set to the magnetic neutral point. The relative position between the magnet 2 and the magnetic piece 3 when the position is shifted downward, that is, the relative position between the yoke 1 and the lens holder 4 at this time may be simply referred to as a neutral point.

The magnetic attraction 7 between the magnetic piece 3 and the magnet 2 in the state shown in FIG. 10 includes a component 8 perpendicular to the direction in which the lens holder 4 moves and a component 9 parallel to the direction in which the lens holder 4 moves. The component force 9 acts as a restoring force to the magnetic neutral point, and the position of the lens holder 4 is held as described above when the gravity 9 is balanced. That is, the neutral point of the objective lens is lower than the magnetic neutral point due to the influence of gravity. 9 and 10 show a configuration in which the magnetic piece 3 is attached to the lens holder 4 and the magnet 2 is attached to the yoke 1.
As shown in FIGS. 13 and 14, there is a lens holder having a magnet 2 attached to a lens holder 4 and a magnetic piece 3 attached to a yoke 1. In these figures, the same reference numerals as those in FIGS. 9 and 10 denote the same parts. In the case of FIGS. 13 and 14,
Of the magnetic attraction 7 between the magnet 2 and the magnetic piece 3 at a position lower than the magnetic neutral point, a component force 9 parallel to the movable direction of the lens holder 4 acts as a restoring force to the magnetic neutral point, This balances with gravity 10.

[0006]

In the case of the above-described objective lens driving device in which the neutral point of the objective lens is lower than the magnetic neutral point due to the effect of gravity, the neutral point of the objective lens is As a criterion, the force required to move the objective lens upwards from there will be much greater than the force required to move the objective lens downwards. This is illustrated in FIGS. 11 and 12 by taking the objective lens driving device described in FIGS. 9 and 10 as an example.
This will be described with reference to FIG. FIG. 11 shows a case where the objective lens is further moved downward from the neutral point of the objective lens shown in FIG. FIG. 12 shows a case where the objective lens is moved upward by the same amount as in FIG. 11 in the opposite direction from the neutral point of the objective lens shown in FIG.

In FIG. 11, a magnetic piece 3 and a magnet 2
Considering the vector direction of the magnetic attraction 7 during the period, since the neutral point of the objective lens shown in FIG. 10 is already at a position lower than the magnetic neutral point as described above, the amount of change in the vector direction of the magnetic attraction 7 Is smaller than in the case of FIG. 12 in which the objective lens moves upward. As a result, FIG.
In the case of FIG. 11, the component force 9 with respect to the magnetic attraction 7 is larger than the case of FIG. And in FIG.
Since the magnetic piece 3 is farther from the magnetic neutral point than in the case of FIG. 10, the magnitude of the magnetic attraction 7 is reduced. Therefore, the position of the objective lens is changed from the state of FIG.
When moving downward as shown in FIG. 1, the amount of change in the component force 9 of the magnetic attraction 7 parallel to the movable direction of the lens holder 4 is the change in the vector direction of the magnetic attraction 7 and the magnitude of the magnetic attraction 7 Are offset and hardly increase, and the driving force 11 required to maintain the position in FIG. 11 becomes small.

In the state of FIG. 12, since the magnetic piece 3 is close to the magnetic neutral point, the magnitude of the magnetic attraction 7 increases, but the amount of change in the vector direction of the magnetic attraction 7 from the state of FIG. 10 is extremely large. Since it is large, the component force 9 with respect to the magnetic attraction 7 is smaller than in the case of FIG. 10, and the force for canceling the gravity 10 due to this is reduced. As a result, in the state shown in FIG. 12, the amount of reduction of the component force 9 of the magnetic attractive force 7 parallel to the movable direction of the lens holder 4 becomes larger than the case shown in FIG. The driving force 12 required for holding is also increased.

FIG. 15 shows an example of a calculation result of this phenomenon. It can be seen that a larger driving force is required when moving the objective lens upward than when moving the objective lens downward and holding the objective lens in that position. This difference in the driving force is not only for maintaining the position of the objective lens, but also for the driving force moving to that position.

As described above, in the conventional objective lens driving device, when the objective lens is driven in the upward direction and when the objective lens is driven in the downward direction, the characteristics of the force required for driving do not match. There was a problem that position control became difficult. The present invention solves the above-described problems, makes the characteristics of the force required for driving when the objective lens is driven upward and when it is driven downward substantially equal, and facilitates position control of the objective lens. It is an object of the present invention to provide an objective lens driving device.

[0011]

In order to solve the above-mentioned problems and to achieve the above object, an objective lens driving device according to the present invention provides a lens holder having a surface of a magnet arranged opposite to the above-mentioned magnetic piece. And the distance between the magnetic piece and the magnet becomes narrower as the objective lens moves downward.

[0012]

The objective lens driving device of the present invention having the above-described structure improves the asymmetry of the vertical driving force characteristic of the objective lens due to the influence of gravity without adding special parts or complicated mechanisms. It is possible to easily control the position of the objective lens.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied to an objective lens driving device called a shaft sliding type.
In this figure, a lens holder 4 is mounted so as to be rotatable about a support shaft 6 and movable along the support shaft 6. An objective lens 5 is attached to the lens holder 4 so that its optical axis and the support shaft 6 are parallel. Further, the magnetic piece 3 is mounted on the outer peripheral surface of the lens holder 4 at a position symmetrical with respect to the support shaft 6. The support shaft 6 is fixed to the center of a member constituting the yoke 1, and a magnet 2 is provided inside the yoke 1.
However, they are arranged so as to be inclined such that the distance between the surface of the magnet 2 and the support shaft 6 becomes smaller as going down. By arranging the yoke 1 and the lens holder 4 such that the magnetic piece 3 faces the magnet 2, magnetic attraction is generated between the magnet 2 and the magnetic piece 3, and the lens holder 4 is held at a neutral position in the movable direction. Is done.

The principle of operation of the present invention is shown in FIG. 2 when the objective lens 5 in FIG. 1 is at the neutral position, FIG. 3 when the objective lens 5 is located below the neutral position, and FIG. FIG. 4 showing a state in which is positioned above the neutral position.
This will be described with reference to FIG. 2 to 4, the same reference numerals as those in FIG. 1 indicate the same components. In FIG. 2, the lens holder 4 on which the objective lens is attached receives a downward force due to the action of gravity 10, and the position of the magnetic piece 3 with respect to the magnet 2 is shifted downward from the above-described magnetic neutral point. At this time, the magnetic attractive force 7 between the magnetic piece 3 and the magnet 2 is divided into a component force 8 perpendicular to the movable direction of the lens holder 4 and a component force 9 parallel to the movable direction of the lens holder 4. Component 9
Works as a restoring force to the magnetic neutral point, and this is the gravity 1
The neutral position of the lens holder 4 is held at the point where it is balanced with 0.

FIG. 3 shows a case where the position of the objective lens is further moved downward from the state shown in FIG. 2, but the distance between the magnetic piece 3 and the magnet 2 is reduced by inclining the surface of the magnet 2. As a result, the magnetic attraction 7 can be prevented from decreasing due to the magnetic piece 3 moving away from the magnetic neutral point. Therefore, when the position of the objective lens moves downward from the position of FIG. 2 to the position of FIG.
Changes in the vector direction of the magnetic attraction 7 directly affect the amount of change in the component force 9 of the magnetic attractive force 7 that is parallel to the movable direction of the lens holder 4, and the driving force 11 required to maintain the position in FIG. Will also grow as such.

FIG. 4 shows a case where the objective lens in the state of FIG. 2 is moved upward in the opposite direction by the same amount as in FIG. Since the surface of the magnet 2 is inclined, the distance between the magnetic piece 3 and the magnet 2 is widened, and an increase in the magnetic attraction 7 due to the magnetic piece 3 approaching the magnetic neutral point is suppressed. Therefore, when the position of the lens holder 4 having the objective lens moves upward from the state of FIG. 2 to the state of FIG. The driving force 12 necessary for the lens holder 4 to hold the position shown in FIG.

FIG. 8 shows a calculation result example of the relationship between the position of the objective lens and the driving force in the embodiment of the present invention as described above. When compared with FIG. 15 which is the calculation result of the conventional example, the effect of tilting the magnet as described above is due to the fact that the position at which the objective lens is moved downward is compared with the case where the position at which the objective lens is moved upward is maintained. It can be seen that the difference in driving force characteristics between the case of holding upward and the case of holding downward is significantly improved when is held.
In addition, not only the driving force in the case of holding, but also the difference in driving force characteristics between when moving upward and when moving downward is also greatly improved.

Another embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the magnetic piece 3 is attached to the lens holder 4 and the magnet 2 is attached to the yoke 1. The distance between the surface and the magnetic piece 3 is changed. In FIG. 5, except for the matters described above, the configuration is the same as that of FIG. 1, and the same reference numerals indicate the same components.

As still another embodiment of the present invention, FIG. 6 shows an example in which a magnet 2 is attached to a lens holder 4 and a magnetic piece 3 is attached to a yoke 1, and the magnet 2 is inclined. FIG. 7 shows an example in which is tapered. In any case, it is important to arrange the distance between the surface of the magnet 2 and the magnetic piece 3 so as to become narrower as the objective lens 5 goes down, and to move the objective lens 5 up and down and maintain its position. The asymmetry of the driving force characteristics can be improved. In FIGS. 6 and 7,
The same reference numerals as those in FIG. 13 denote the same parts unless otherwise specified.

[0020]

As described above, according to the present invention, the lens holder 4 holding the objective lens 5 and the fixing member to which the lens holder 4 is movably attached in the optical axis direction of the objective lens 5 are provided. Magnetic piece 3 in one of them,
On the other side, the magnet 2 is fixed, and the magnetic piece 3 and the magnet 2 are disposed so as to face each other.
The objective lens 5 is held at a neutral position in the movable direction by a magnetic attractive force 7 acting between the objective lens 5 and the magnet 2, and the optical axis direction of the objective lens 5 becomes parallel to the direction of gravity 10. In the objective lens driving device used as described above, as the objective lens 5 descends along the movable direction, the distance between the magnetic piece 3 and the magnet 2 arranged to face each other as described above becomes narrow. Thus, the vertical asymmetry of the vertical movement of the objective lens 5 caused by the influence of the gravity 10 and the driving force characteristic held at the moved position can be improved, and therefore the position of the objective lens 5 can be improved. Control can be easier.

[Brief description of the drawings]

FIG. 1 schematically shows an embodiment of the present invention, in which (a) is a plan view and (b) is a longitudinal sectional front view.

FIG. 2 is a schematic enlarged vertical sectional front view of a main part for explaining the operation of the apparatus shown in FIG.

FIG. 3 is a schematic enlarged vertical sectional front view of a main part for explaining another operation of FIG. 1;

FIG. 4 is a view for explaining still another operation of the apparatus shown in FIG. 1;
It is a schematic enlarged longitudinal front view of a main part.

5A and 5B schematically show another embodiment of the present invention, wherein FIG. 5A is a plan view and FIG.

FIGS. 6A and 6B schematically show still another embodiment of the present invention, wherein FIG. 6A is a plan view, and FIG. 6B is a longitudinal sectional front view.

FIGS. 7A and 7B schematically show still another embodiment of the present invention, wherein FIG. 7A is a plan view, and FIG. 7B is a longitudinal sectional front view.

FIG. 8 is a characteristic diagram showing an example of a calculation result of a relationship between an objective lens position and a driving force in the objective lens driving device of the present invention.

FIGS. 9A and 9B schematically show a conventional example, in which FIG. 9A is a plan view and FIG. 9B is a longitudinal sectional front view.

FIG. 10 is a schematic enlarged vertical sectional front view of a main part for explaining the operation of the apparatus shown in FIG. 9;

FIG. 11 is a schematic enlarged vertical sectional front view of a main part for explaining another operation of FIG. 9;

FIG. 12 is a schematic enlarged vertical sectional front view of a main part, for explaining still another operation of the apparatus shown in FIG. 9;

FIG. 13 schematically shows another conventional example,
(A) is a plan view, (b) is a longitudinal sectional front view.

FIG. 14 is a schematic enlarged vertical sectional front view of a main part for explaining the operation of the apparatus shown in FIG.

FIG. 15 is a characteristic diagram showing an example of a calculation result of a relationship between an objective lens position and a driving force in a conventional objective lens driving device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Yoke 2 Magnet 3 Magnetic piece 4 Lens holder 5 Objective lens 6 Support shaft 7 Magnetic attraction between magnetic piece and magnet 8 Component force perpendicular to lens holder moving direction 9 Component force parallel to lens moving direction 10 Gravity 11 Driving force for positioning the objective lens below the neutral point 12 Driving force for positioning the objective lens above the neutral point

Claims (2)

[Claims] A lens holder holding an objective lens;
A magnetic piece is fixed to one of the lens holder and a fixing member movably attached in the optical axis direction of the objective lens, and a magnet is fixed to the other, and the magnetic piece and the magnet face each other. The objective lens is held at a neutral position in the movable direction by a magnetic attractive force acting between the magnetic piece and the magnet, and the optical axis direction of the objective lens is parallel to the direction of gravity. In the objective lens driving device used in such a manner, as the objective lens descends along the movable direction, the distance between the magnetic piece and the magnet arranged so as to face each other as described above decreases. An objective lens driving device characterized in that: 2. The shaft slide, wherein the lens holder holding the objective lens is movable as described above along an axis provided on the fixing member, and is rotated about this axis. 2. A moving type.
An objective lens driving device according to claim 1.