JP2000293874A - Object lens driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an object lens driving device where the occurrence of tilt of an object lens accompanied with driving of a lens holder is effectively suppressed. SOLUTION: A lens holder 4 which holds an object lens 5 which is supported through an elastically supporting member 3 so that the object lens 5 can be displaced in a prescribed direction is driven by electromagnetic driving means 2, 6, and 7. In this object lens driving device, a tilt suppression means which is provided with an other magnetic pole permanent magnet 20 having the other magnetic pole in the same face and a coil for tilt suppression which faces the other magnetic pole permanent magnet 20 and has approximately parallel segments in the vicinity of the boundary of the other magnetic pole is so constituted that the other magnetic pole permanent magnet 20 and the coil for tilt suppression can be relatively displaces by driving of the lens holder 4 to suppress the tilt of the object lens 5 accompanied with driving of the lens holder 4 by electromagnetic driving means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compact disc (CD) and a digital versatile disc (DVD).
Lens driving device for driving an objective lens used for recording and reproducing information on a recording medium such as an optical disk such as an optical disk and a magneto-optical disk such as a mini disk (MD) in a predetermined direction. It is.

[0002]

2. Description of the Related Art As a conventional objective lens driving device, for example, there is one shown in a perspective view in FIG. This objective lens driving device is a so-called four-wire supporting type moving coil system.
One end of each of the four elastic support members 3 made of a Be alloy, a Cu-P alloy, or the like is supported at a position separated by a predetermined interval, such as a vertex of a rectangle. These four elastic support members 3 extend substantially parallel from the support member 1 in the tangential (X-axis) direction of the disk-shaped recording medium (not shown), and suspend the lens holder 4 at the other end thereof. The objective lens 5 held by the lens holder 4 is supported by a tracking (Y-axis) direction crossing an information pit row (track) of the recording medium and a focusing (Z-axis) direction substantially parallel to the optical axis of the objective lens 5. And each can be displaced.

In order to drive the objective lens 5 in the tracking direction and the focusing direction, the support member 1 is made of a soft material having a substantially U-shape made of, for example, Fe, Ni, Co, or an alloy containing them, or ferrite. The magnetic yoke 8 is inserted into the opening 4 of the lens holder 4 so that the opposing legs face in the tangential direction.
a permanent magnet 2 made of, for example, an Nd-Fe-B alloy or the like is provided on the inner surfaces of both legs of the soft magnetic yoke 8 such that different magnetic pole surfaces face each other via a gap. I have. Further, the lens holder 4 has an opening 4a in which the optical axis of the objective lens 5 is positioned on the center line of a predetermined track of the recording medium.
A tracking coil 6 for driving the objective lens 5 in the tracking direction, and a focusing coil 7 for driving the objective lens 5 in the focusing direction to focus the objective lens 5 on the information pit surface. 2, a tracking coil 6 and a focusing coil 7 constitute an electromagnetic driving means.

Here, the focusing coil 7 is shown in FIG.
As shown in the partially exploded perspective view, the bobbin 11 made of resin or the like is wound around the axis in the focusing direction, and the tracking coil 6 is wound around the bobbin 11 around the axis in the tangential direction. Have been. The bobbin 11 on which the tracking coil 6 and the focusing coil 7 are mounted has a drive line segment 7 on one side extending in the tracking direction of the focusing coil 7.
a and a drive line segment 6 a extending in the focusing direction of the tracking coil 6 are fitted and fixed to the opening 4 a of the lens holder 4 so that the two drive permanent magnets 2 are located in the gaps facing each other. I have.

When the tracking coil 6 is energized in this way, the interaction between the current flowing through the driving line segment 6a and the magnetic flux in the tangential direction of the driving permanent magnet 2 causes the tracking direction to be applied to the tracking coil 6. Apply the directed Lorentz force to the objective lens 5
Is displaced in a tracking direction, that is, a direction crossing a track of a recording medium (not shown).

Similarly, by energizing the focusing coil 7, the interaction between the current flowing through the driving line segment 7a and the magnetic flux in the tangential direction of the driving permanent magnet 2 causes the focusing coil 7 to move in the focusing direction. By applying the applied Lorentz force, the objective lens 5 is displaced in the focusing direction, that is, in the optical axis direction substantially perpendicular to the recording surface of a recording medium (not shown).

[0007]

The objective lens driving device described above is a suspension support structure with an elastic support member 3, and is a lens holder like a shaft sliding type objective lens driving device which is another typical support structure. Since no friction occurs with the shaft portion at the time of displacement of 4, the drive with smooth and high resolution can be performed. However, on the other hand, since there is no stable guide like an axis, the structure is easy to rotate around an axis parallel to the X axis.

That is, for example, due to the accuracy or assembling accuracy of the tracking coil 6, the focusing coil 7, and other components, or the displacement of the driving permanent magnet 2, the driving force of the tracking coil 6 or the focusing coil 7 is reduced. If the center is displaced from the center of support by the elastic support member 3 including the objective lens 5 or the position of the center of gravity of the entire lens holder 4, the driving force in the tracking direction or focusing direction and the restoring force of the elastic support member 3 A rotation moment is generated by gravity, and the lens holder 4 rotates around an axis parallel to the X axis. Even if the tracking coil 6, the focusing coil 7, or the position of the driving permanent magnet 2 in the neutral state is accurately assembled, the lens holder 4 is moved from the neutral position by applying a driving force in the tracking direction or the focusing direction. Since the relative position between the driving permanent magnet 2 and the tracking coil 6 or the focusing coil 7 changes, the position of the center of the driving force moves in the lens holder 4, and similarly the driving force in the tracking direction or the focusing direction. The restoring force of the elastic support member 3 generates a rotational moment, and the lens holder 4 rotates around an axis parallel to the X axis.

When the lens holder 4 rotates around an axis parallel to the X axis, the objective lens 5 held by the lens holder 4 also rotates, so that a so-called dynamic radial tilt in which the optical axis is inclined occurs. Various aberrations such as coma occur on the wavefront of the laser beam. For this reason, side lobes are formed in the spot of the laser beam irradiated on the disk-shaped recording medium, so that crosstalk from an adjacent track is likely to occur, track offset occurs, and proper tracking control becomes impossible, and furthermore, reflection occurs. Phenomena such as a decrease in the intensity and a decrease in the information reading signal level occur, which causes a problem that the S / N as the performance of the optical head decreases.

SUMMARY OF THE INVENTION An object of the present invention is to provide an objective lens driving apparatus in which occurrence of tilt of an objective lens due to driving of a lens holder is effectively suppressed. It is in.

[0011]

According to the first aspect of the present invention, there is provided a lens holder for holding an objective lens which is supported to be displaceable in a predetermined direction via an elastic supporting member by electromagnetically driving the lens holder. A multi-pole permanent magnet having multiple magnetic poles in the same plane, and a tilt having a substantially parallel line segment near the boundary between the multiple magnetic poles facing the multiple magnetic pole permanent magnet. A tilt suppressing means comprising a coil for suppressing, the multi-pole permanent magnet and the coil for tilt suppressing are provided so as to be relatively displaceable by driving the lens holder, and the electromagnetic driving means is used to move the lens holder. The tilt of the objective lens due to driving is suppressed.

According to a second aspect of the present invention, in the objective lens driving device according to the first aspect, the multi-pole permanent magnet has three magnetic poles which are alternately different along a driving direction of the lens holder. The tilt suppressing coil includes a driving coil of the electromagnetic driving means.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 show a first embodiment of the present invention. FIG. 1 is a perspective view, FIG. 2 is a detailed view of a main part, and FIG. 3 is an operation explanatory view. Here, the same parts as those in the conventional example are denoted by the same reference numerals. This objective lens driving device is a so-called four-wire supporting type moving coil system similar to that described in the conventional example, and the supporting member 1 includes, for example, a Cu—Be alloy, a Cu—P
One end of each of the four elastic support members 3 made of an alloy or the like is supported at a position separated by a predetermined interval such as a vertex of a rectangle. These four elastic support members 3
Is an object which is extended substantially parallel to the tangential (X-axis) direction of a disc-shaped recording medium (not shown), supports the lens holder 4 at the other end thereof, and holds the objective held by the lens holder 4. A lens (5) that moves in a tracking (Y-axis) direction across an information pit row (track) of the recording medium;
Focusing almost parallel to the optical axis of the objective lens 5 (Z
(Axis) direction.

In order to drive the objective lens 5 in the tracking direction and the focusing direction, a base member 1 is provided.
B, a soft magnetic yoke 8 having a substantially U-shape made of, for example, Fe, Ni, Co, or an alloy containing them, or ferrite, and a lens holder such that both opposing legs face in the tangential direction. The soft magnetic yoke 8 is provided so as to penetrate the opening 4a of the soft magnetic yoke 8 so that different magnetic pole surfaces face each other via a gap.
For example, a driving permanent magnet 2 made of an Nd-Fe-B alloy or the like
Are provided. Further, the opening 4 of the lens holder 4
a includes a tracking coil 6 for driving the objective lens 5 in the tracking direction in order to position the optical axis of the objective lens 5 on the center line of a predetermined track of the recording medium.
In order to focus the objective lens 5 on the information pit surface,
A bobbin 11 made of resin or the like is provided with a focusing coil 7 for driving the objective lens 5 in the focusing direction. The driving permanent magnet 2, the tracking coil 6 and the focusing coil 7 constitute an electromagnetic drive unit. I do. The bobbin 11 has a driving line segment 7a on one side extending in the tracking direction of the focusing coil 7 and a driving line segment extending in the focusing direction of the tracking coil 6, as described in the conventional example. The two permanent magnets 2 for driving are fitted and fixed in the opening 4a of the lens holder 4 so as to be located in the gaps facing each other.

Further, as shown in detail in FIG. 2, the supporting member 1 is opposed to the line segment 7b on the opposite side of the driving line segment 7a of the focusing coil 7, and the surface magnetic poles are mutually inverted to perform focusing. Two element magnet pieces 2 adjacent in the direction
1 and 22, that is, multi-pole permanent magnets 20 are provided. A tilt suppressing coil 71 is wound around the focusing coil 7 around an axis parallel to the Z axis so that the coil line segment faces the vicinity of the boundary between the element magnet pieces 21 and 22. It is provided so as to be rotated and energized so that a current flows in the tilt suppressing coil 71 in a predetermined direction.

In this configuration, when the tracking coil 6 is energized, an interaction between a current flowing in the focusing direction of the tracking coil 6 and a magnetic flux in the tangential direction from the driving permanent magnet 2 facing the tracking coil 6 causes the tracking coil 6 to interact. Is applied with a Lorentz force directed in the tracking direction, so that the objective lens 5 can be displaced in the tracking direction, that is, in the direction crossing the track of the recording medium (not shown).

Similarly, when the focusing coil 7 is energized, the interaction between the current flowing in the tracking direction and the magnetic flux directed in the tangential direction by the driving permanent magnet 2 causes the Lorentz force in the focusing direction to act on the focusing coil 7. Works, the objective lens 5 can be displaced in the focusing direction, that is, the optical axis direction substantially orthogonal to the recording surface of the recording medium (not shown).

As shown in FIGS. 3A and 3B, for example, the magnetic poles of the element magnet pieces 21 and 22 facing the tilt suppressing coil 71 are defined as N poles and S poles, respectively. When the current coil i is energized so that the current i flows from left to right in the figure,
As shown in (a), when the tilt suppression coil 71 rotates clockwise, the leftward portion of the tilt suppression coil 71 faces the N magnetic pole surface of the element magnet piece 21 and the rightward portion is the element magnet piece. 22 so as to face the S magnetic pole face,
The direction of the magnetic flux to which the leftward and rightward portions of the tilt suppressing coil 71 are exposed is reversed, so that a downward Lorentz force FL acts on the leftward portion and an upward Lorentz force FR acts on the rightward portion. As a whole, a counterclockwise moment is generated, and the clockwise rotation of the tilt suppressing coil 71 can be pushed back.

Conversely, when the tilt suppressing coil 71 rotates counterclockwise as shown in FIG. 3 (b), the leftward portion of the tilt suppressing coil 71 faces the S magnetic pole surface of the element magnet piece 22. Since the rightward portion faces the N magnetic pole surface of the element magnet piece 21, an upward Lorentz force FL acts on the leftward portion of the tilt suppressing coil 71, and a downward Lorentz force FR acts on the rightward portion. Acting, a clockwise moment is generated as a whole, and the tilt suppressing coil 7
The counterclockwise rotation of 1 can be pushed back.

As described above, when the tilt suppressing coil 71 rotates around the axis parallel to the X axis and becomes non-parallel with respect to the boundary between the element magnet pieces 21 and 22, the rotation is stopped. Since a rotational moment can be generated in the pushing-back direction, the tilt suppressing coil 71 can always be directed in a predetermined direction, and the dynamic radial tilt of the objective lens 5 can be effectively suppressed.

FIGS. 4A and 4B show a second embodiment of the present invention.
It is a figure for explaining an important section of an embodiment. In this embodiment, in the configuration described in the first embodiment,
As shown in FIG. 4A, a multi-pole permanent magnet 20 is formed by crossing an element magnet piece 21 having a cross shape whose surface magnetic poles protrude in four directions in a focusing direction and a tracking direction, and a projecting portion of the element magnet piece 21. The element magnet pieces 22 formed by inverting the surface magnetic poles at the four corners are formed so as to have a rectangular surface magnetic pole as a whole. Further, on the lens holder 4 side, as shown in FIG. 4 (b), the tilt suppressing coils 61 and 71 are arranged such that the coil line segments face the vicinity of the respective boundaries between the element magnet pieces 21 and 22. In this case, the winding width is increased and each of the windings is wound a plurality of turns. The tilt suppressing coil 61 is connected in series to, for example, the tracking coil 6, and supplies a current in a direction corresponding to the driving direction of the tracking coil 6 and the size thereof in conjunction with the energizing condition to the tracking coil 6. The tilt suppressing coil 71 is connected in series to, for example, the focusing coil 7, and supplies a current in a direction corresponding to the driving direction of the focusing coil 7 and its size in conjunction with the energizing condition to the focusing coil 7.

In such a configuration, the tilt suppressing coil 71 is driven by, for example, driving in the focusing direction as shown in FIG.
When it moves upward in (b), the left and right portions of the coil segment are opposed to the upper element magnet piece 22. For this reason, when the tilt suppressing coil 71 is rotated by the rotation of the lens holder 4, the Lorentz force directed downward is increased on the side where the coil segment facing the element magnet piece 22 is increased, and the rotation is pushed back. A moment is generated in the direction.
Conversely, when the tilt suppressing coil 71 moves downward in FIG. 4B, the left and right portions of the coil line in which the current direction is reversed face the lower element magnet piece 22. Therefore, when the tilt suppressing coil 71 is rotated by the rotation of the lens holder 4, the Lorentz force directed upward is increased on the side where the coil segment facing the element magnet piece 22 is increased, and the rotation is pushed back. A moment is generated in the direction.

When the tilt suppressing coil 61 is moved to the right in FIG. 4B by driving in the tracking direction, the upper and lower portions of the coil line are opposed to the right element magnet piece 22. When the tilt suppressing coil 61 is rotated by the rotation of the lens holder 4, the Lorentz force directed to the left increases on the side where the coil line segment facing the element magnet piece 22 is increased, and the rotation is increased. Moment is generated in the direction of pushing back. Conversely, the tilt suppressing coil 71
However, when the lens holder moves to the left in FIG. 4B, the upper and lower portions of the coil segment in which the current direction is reversed come to face the element magnet piece 22 on the left side. When the tilt suppressing coil 61 is rotated by the movement, the Lorentz force directed to the right is increased on the side where the coil segment facing the element magnet piece 22 is increased, so that a moment is generated in the direction of pushing back the rotation. Become.

As described above, according to this embodiment, currents are supplied to the tilt suppressing coils 61 and 71 in a direction corresponding to their moving directions, and these currents are supplied to the tracking coil 6 and the focusing coil. 7 in conjunction with the increase or decrease of the rotation angle due to the increase or decrease of the movement amount, and a moment having a strength corresponding thereto can be generated. When the amount is large, the rotation of the lens holder 4 can be suppressed with a strong moment. Therefore,
The stability of the orientation of the objective lens 5 held by the lens holder 4 can be improved, and dynamic radial tilt can be effectively suppressed.

FIGS. 5 and 6 show a third embodiment of the present invention. FIG. 5 is a perspective view and FIG. 6 is an operation explanatory view. In the objective lens driving device, in the configuration described in the first embodiment, the multi-pole permanent magnet 20 includes three element magnet pieces 22, 21, and 22 whose surface magnetic poles are alternately reversed and are adjacent in the focusing direction. In addition to the configuration, instead of providing the tilt suppressing coil 71, the coil line segment 7b of the focusing coil 7 on the side of the multi-pole permanent magnet 20 acts as the tilt suppressing coil. The width of the intermediate element magnet piece 21 constituting the multi-pole permanent magnet 20 in the focusing direction is substantially equal to the width of the focusing coil 7 in the focusing direction. The other configuration is the same as that of the first embodiment, and a duplicate description will be omitted.

According to this embodiment, similarly to the first embodiment, by energizing the tracking coil 6, the objective lens 5 can be displaced in the tracking direction, that is, in the direction crossing the track of the recording medium (not shown). it can. In addition, when the focusing coil 7 is energized, the objective lens 5 can be displaced in the focusing direction, that is, in the optical axis direction orthogonal to the recording surface of the recording medium. In this embodiment, for example, the driving in the focusing direction is performed. FIG. 6 shows the focusing coil 7
When it moves upward as shown in (a), the coil line segment 7b comes to face the upper element magnet piece 22. Therefore, when the focusing coil 7 is rotated clockwise, for example, by the rotation of the lens holder 4, the area facing the element magnet piece 22 is increased in the left portion of the coil segment 7b, and the Lorentz force FL facing downward is increased. Increases, and a moment is generated in the direction of pushing back the rotation. FIG.
As shown in (b), when the direction of the supply current i to the focusing coil 7 is reversed and the focusing coil 7 moves downward, the coil segment 7b comes to face the lower element magnet piece 22. Therefore, when the focusing coil 7 is rotated clockwise, for example, by the rotation of the lens holder 4, the element magnet piece 2 is located at the right side of the coil segment 7b.
Since the area facing 2 increases, the upwardly directed Lorentz force FR increases, and a moment is generated in the direction of pushing back the rotation.

As described above, according to the present embodiment, the current corresponding to the moving direction is supplied to the focusing coil 7 which also serves as the tilt suppressing coil, and the magnitude of the current depends on the increase or decrease of the rotation angle according to the amount of movement. Since it is compatible, it is possible to generate a moment having a strength corresponding thereto. Therefore, with a simple structure, the rotation of the lens holder 4 can be suppressed by a small moment when the movement amount is small and by a strong moment when the movement amount is large, so that the orientation of the objective lens 5 held by the lens holder 4 can be suppressed. Can be improved, and dynamic radial tilt can be effectively suppressed.

It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified or changed. For example, the present invention can be effectively applied to an objective lens driving device having a structure in which a focusing coil 7 is wound around an objective lens 5 via a lens holder 4 as shown in FIG. In addition, a multi-pole permanent magnet 2
0 is, for example, as shown in FIG.
Can also be configured as a permanent magnet for driving. Further, in the third embodiment, the focusing coil 7 is also used as a tilt suppressing coil. However, the tracking coil 6 may be also used as a tilt suppressing coil. Furthermore, in the above-described embodiment, the dynamic radial tilt is suppressed. However, when a dynamic tangential tilt occurs, it may be configured to suppress the dynamic tangential tilt. Further, the present invention is not limited to the moving coil type objective lens driving device, but can be effectively applied to a moving magnet type objective lens driving device.

[0029]

As described above, according to the objective lens driving device of the present invention, by energizing the tilt suppressing coil, the tilt suppressing coil and the multi-pole permanent magnet are rotated by the rotation of the lens holder. Is non-parallel to the multi-pole boundary, a moment can be applied to the lens holder in a direction of pushing back the rotation of the lens holder by the electromagnetic action of the tilt suppressing coil and the multi-pole permanent magnet. Moreover,
By linking the current supplied to the tilt suppression coil with the drive coil of the tracking coil and focusing coil, a moment of strength corresponding to the increase or decrease of the rotation angle accompanying the increase or decrease of the drive amount of the lens holder is given to the lens holder. The direction of the objective lens can be stabilized with a small moment when the driving amount is small and with a strong moment when the driving amount is large. Therefore, since the occurrence of tilt of the objective lens can be effectively suppressed, various aberrations generated on the wavefront of the laser beam irradiated on the disk-shaped recording medium can be reduced, and the S / N as the performance of the optical head can be reduced. It can be effectively avoided.
Further, when the drive coil constituting the electromagnetic drive means of the lens holder is also used as the tilt suppression coil,
The configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is also a detailed view of a main part.

FIG. 3 is an operation explanatory diagram, similarly.

FIG. 4 is a diagram for explaining a main part of a second embodiment of the present invention.

FIG. 5 is a perspective view showing a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of the operation.

FIG. 7 is a perspective view showing a main part of a modification of the present invention.

FIG. 8 is a perspective view showing a conventional example.

9 is a partially exploded perspective view of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 support member 2 drive permanent magnet 3 elastic support member 4 lens holder 5 objective lens 6 tracking coil 7 focusing coil 8 soft magnetic yoke 20 multi-pole permanent magnet 21, 22 element magnet piece 61, 71 tilt suppression coil

Claims (2)

[Claims] 1. An objective lens driving device in which a lens holder holding an objective lens supported to be displaceable in a predetermined direction via an elastic support member is driven by electromagnetic driving means, wherein a plurality of lens holders are provided on the same plane. A multi-pole permanent magnet having magnetic poles, and a tilt suppressing unit including a tilt suppressing coil having a line segment substantially parallel to the boundary of the multi-pole opposed to the multi-pole permanent magnet. The tilt suppressing coil is provided so as to be relatively displaceable by driving the lens holder, so as to suppress tilt of the objective lens accompanying the driving of the lens holder by the electromagnetic driving means. Objective lens driving device. 2. The multi-pole permanent magnet includes three magnetic poles that are alternately different along a driving direction of the lens holder, and the tilt suppressing coil includes a driving coil of the electromagnetic driving unit. The objective lens driving device according to claim 1, wherein: