JPH09138958A - Objective lens driving device for optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens driving device in which it is easy to make center points of driving forces of a focus direction (the optical axis direction of an objective lens) and a tracking direction (the radial direction of a disk) coincide and which is suitable for miniaturizing and thining a device. SOLUTION: This objective lens driving device has a movable part to which a focus coil 1 for driving an objective lens in the focus direction and tracking coils 2a, 2b for driving the lens in the tracking direction and a fixing part having a single magnetic circuit and the movable part is elastically supported from the fixing part. At this time, the center points of driving forces and the center of gravity of the movable part are made to coincide by making the whole of or one part of parts of the focus coil traversing the inside of the gap of the magnetic circuit non-parallel with the tracking direction and by arranging two pieces of tracking coils 2a, 2b arranged symmetrically with respect to the center line dividing the coils in the tracking direction parallel with the tracking direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device for driving an objective lens in an optical disc device which optically projects information by projecting a light spot on the optical disc.

[0002]

2. Description of the Related Art An objective lens driving device of an optical disc device is a device for moving an objective lens according to surface wobbling or eccentricity of a disc for projecting a light spot on a recording medium to optically read information. The driving force for moving the movable part including the objective lens is generated by the electromagnetic action of the magnetic flux generated in the gap of the magnetic circuit composed of the magnet and the yoke and the current flowing through the focus coil and the tracking coil fixed to the movable part. To do.

Here, the driving force in the optical axis direction (focusing direction) of the objective lens is obtained by the focus coil, and the driving force in the direction intersecting with the track of the optical disk (tracking direction) is obtained by the tracking coil. Further, the movable part is elastically supported by a fixed part including a magnetic circuit by an elastic member, and a mechanism for determining the position of the movable part is determined by the balance between the supporting force of the elastic member and the driving force by the electromagnetic action. There is.

Conventionally, the objective lens driving device is shown in FIGS.
As shown in FIG. 4, in order to reduce the size and the thickness, the magnetic circuit including the permanent magnets 3a and 3b and the yoke 4 is unified,
The focus coil 1 and the tracking coils 2a and 2b are arranged so as to intersect the magnetic flux generated in the gap. Since the direction of the current flowing through the focus coil 1 and the direction of the current flowing through the tracking coils 2a and 2b are different, a driving force in the focus direction acts on the focus coil 1 and the tracking coils 2a and 2b move in the tracking direction. Driving force of.

However, in the objective lens driving device shown in FIGS. 7 and 8, the center point of the driving force in the focusing direction by the focus coil 1 and the tracking coils 2a, 2b.
Since the center point of the driving force in the tracking direction due to does not match, if the center of gravity of the movable part matches the center point of one of the driving forces, the center point of the other driving force will shift from the center of gravity of the movable part. However, there is a problem in that a moment is generated in accordance with the amount of deviation and unnecessary resonance (rolling resonance, pitching resonance and yawing resonance) occurs.

As a means for solving this problem, the objective lens driving device disclosed in JP-A-5-290395 and JP-A-6-124467 is known.

In the objective lens driving device disclosed in Japanese Patent Laid-Open No. 5-290395, as shown in FIG. 9, a portion of the focus coil 1 that intersects with the magnetic field generated in the gap of the magnetic circuit (in the gap of the magnetic circuit, , The crossing part)
Is made non-parallel to the tracking direction, and by attaching the tracking coils 2a and 2b to the non-parallel portion,
The center points of the driving forces in the focus direction and the tracking direction are matched.

In the objective lens driving device disclosed in Japanese Patent Application Laid-Open No. 6-124467, as shown in FIG. 10, the focus coils 1a and 1b are arranged so as to sandwich the tracking coils 2a and 2b, or in FIG. As shown, the tracking coil 2 sandwiches the focus coil 1.
By disposing a, 2b, 2c, and 2d, the center points of the driving forces in the focus direction and the tracking direction are made to coincide with each other.

[0009]

However, in the objective lens driving device disclosed in Japanese Patent Laid-Open No. 5-290395, since the tracking coil is mounted on the non-parallel portion of the focus coil, the focusing direction and the tracking direction are different from each other. It was not easy to match the center points of the driving forces. That is, in the tracking coil, the center points of the driving forces generated in the portion on the center side (side A in FIG. 9) and the portion on the outside (side B in FIG. 9) of the gap of the magnetic circuit are parallel to the tracking direction. It was not easy to determine the center point of the driving force in the tracking direction, which is not on the same straight line and acts on the entire tracking coil.

On the other hand, in the objective lens driving device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-124467, the thickness of the coil portion composed of the focus coil and the tracking coil in the focusing direction increases, and the device can be made smaller and thinner. There are problems such as not being present and the number of parts being increased, and the assembling process being complicated.

Therefore, it is an object of the present invention to provide an objective lens driving device for an optical disk device, which makes it easy to match the center points of the driving forces in the focus direction and the tracking direction, and which is suitable for making the device small and thin. And

[0012]

According to a first aspect of the present invention, there is provided an objective lens driving device for an optical disc device, wherein a first lens holder for holding the objective lens is driven in the optical axis direction (focusing direction) of the objective lens. Coil (focus coil), and a movable part to which two second coils (tracking coils) for driving the optical disc in the radial direction (tracking direction) are fixed, and a yoke provided with a pair of permanent magnets. A fixed part including one magnetic circuit, wherein the movable part is supported from the fixed part by an elastic member, in a gap of the magnetic circuit of the first coil, All or part of the crossing portion is made non-parallel to the radial direction of the optical disc, and the first coil is arranged symmetrically with respect to a center line dividing the first coil in the radial direction of the optical disc. The two second coils are arranged in parallel with the radial direction of the optical disk, and the center point of the driving force of the objective lens in the optical axis direction and the center point of the driving force of the optical disk in the radial direction are arranged at the movable portion. It is characterized by matching the center of gravity.

According to a second aspect of the present invention, there is provided an objective lens driving device for an optical disc device according to the first aspect, wherein the focus coil fixing portion of the lens holder is fixed to the first coil of the first coil. It is characterized in that it is in contact with the outer circumference of the magnetic circuit other than the portion that crosses the gap, and the whole or part of the outer circumference of the portion that crosses the gap of the magnetic circuit.

According to a third aspect of the present invention, there is provided an objective lens driving device for an optical disc device, wherein the first coil and the two second coils are respectively provided in the objective lens driving device for the optical disc device. It is characterized in that it is directly fixed to the lens holder.

An objective lens driving device for an optical disc device according to a fourth aspect is the objective lens driving device for an optical disc device according to any one of the first to third aspects, wherein the yoke is provided on the outer peripheral side of the focus coil. Only the permanent magnet is provided.

According to a fifth aspect of the present invention, there is provided an objective lens driving device for an optical disc device according to any one of the first to third aspects, wherein the yoke is provided on the inner peripheral side of the focus coil. The permanent magnet is provided only on the outer circumference of the focus coil, and the width of the yoke on the outer peripheral side of the focus coil in the radial direction of the optical disc is made wider than the width of the inner yoke of the focus coil in the radial direction of the optical disc.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The objective lens driving device according to the present invention has an improved structure of a coil portion composed of a focus coil and a tracking coil in the conventional objective lens driving device, and has an optical axis direction (focusing direction) of the objective lens. The center point of the driving force of) and the center point of the driving force in the direction (tracking direction) intersecting the track of the optical disc are matched, and the mechanism for driving the movable part including the objective lens is the same as the conventional objective lens drive. It is similar to the device.

Here, the operation of the objective lens driving device will be described with reference to FIG. In the objective lens driving device shown in the figure, a focus coil and a tracking coil (here, the focus coil 1 is attached to the lens holder 6).
The tracking coils 2a and 2b are fixed to the lens holder 6 as shown in FIG. 1 (b), and the objective lens 5 is fixed (hereinafter, the lens holder 6,
A portion including the focus coil 1, the tracking coils 2a and 2b, and the objective lens 5 is referred to as a movable portion). On the other hand, the magnetic circuit including the permanent magnets 3a and 3b and the yoke 4 is fixed to the base 8 (hereinafter, the magnetic circuit and a portion including the base 8 are referred to as a fixing portion).

The movable portion is elastically supported by the elastic member 7 from the fixed portion. Therefore, when a driving force acts on the movable portion, the movable portion moves to a position where the elastic supporting force and the driving force are balanced. A conductive metal wire is used for the elastic member 7, and a current is passed through the focus coil 1 and the tracking coils 2a and 2b through the conductive metal wire.

In the lens driving device having the above-described structure, when a current is applied to the focus coil 1, the movable part moves along the focus direction (z-axis direction in the drawing), and the tracking coil 2a, When a current is applied to 2b, the movable part moves along the tracking direction (y-axis direction in the figure).

In the present description, the focus direction, which is the optical axis direction of the objective lens, is the z-axis direction, and the direction of the magnetic flux in the gap of the magnetic circuit (the normal direction of the permanent magnet surface).
Is the x-axis direction, and the tracking direction perpendicular to the x-axis and the z-axis is the y-axis direction.

Next, the focus coil 1 and the tracking coils 2a and 2b in the objective lens driving device according to the present invention will be described with reference to FIG.

FIG. 1A shows only the focus coil 1 and the tracking coils 2a and 2b. In an actual lens driving device, as shown in FIG. Coils 2a, 2b
Is fixed to the lens holder 6.

In the focus coil 1, a portion intersecting with a magnetic flux generated in a gap of the magnetic circuit (hereinafter referred to as a gap magnetic flux) (a portion that crosses the gap of the magnetic circuit) is not at right angles to the gap magnetic flux. It is composed of two intersecting sides (these two sides are not parallel to the tracking direction (y-axis direction) when viewed from the z-axis direction). On the other hand, the tracking 2a and 2b are arranged so that the direction of the magnetic flux generated at the center of the annular coil when a current is applied to them is parallel to the X axis (that is,
The tracking coils 2a and 2b are arranged in the racking direction (y
Axial direction) is arranged parallel to).

In the conventional objective lens driving device, the focus coil 1 has the tracking coils 2a and 2a.
Although b is directly fixed, in the present invention, the tracking coils 2a and 2b are fixed to the lens holder 6. Therefore, the tracking coils 2a and 2b can be easily arranged at appropriate positions by providing the convex portions and the concave portions in the portions of the lens holder 6 where the tracking coils 2a and 2b are fixed.

Further, as compared with the conventional objective lens driving device, a portion where the periphery of the focus coil 1 and the lens holder 6 are in contact with each other is increased (more portions around the focus coil 1 are surrounded by the lens holder 6). The deformation of the focus coil 1 can be suppressed. That is,
In the present invention, since it is not necessary to fix the tracking coils 2a and 2b to the portion that intersects with the magnetic flux in the gap portion of the focus coil 1 (the portion that crosses the gap of the magnetic circuit), the focus coil 1 and the tracking coil 2a, 2b can be placed separately, so that
The whole or part of the side intersecting the gap magnetic flux can be surrounded by the lens holder 6 to suppress the deformation of the part (conventionally, only the side of the focus coil 1 other than the portion intersecting the gap magnetic flux is It was surrounded by the lens holder 6).

FIG. 2 shows the relationship between the focus coil 1 and the tracking coils 2a and 2b and the magnetic circuit. As shown in the figure, the tracking coil 2a,
As for 2b, as in the conventional case, a portion that intersects with the magnetic flux in the gap portion at a right angle, but intersects with the magnetic flux in the gap portion of the focus coil 1 (a portion that crosses the gap of the magnetic circuit).
For, intersect at non-right angles.

Next, a method for making the center point of the driving force in the focus direction (z-axis direction) coincide with the center point of the driving force in the tracking direction (y-axis direction) will be described with reference to FIG.

FIG. 3A shows the focus coil 1, the tracking coils 2a, 2b and the magnetic circuit shown in FIG. 2 as seen from the z-axis direction, and FIG. 3B shows the tracking coil 2a, 2b shows the view of 2b from the x-axis direction. Here, L1 is a center line when the focus coil 1 is viewed from the z-axis direction (the focus coil 1 is symmetrical with respect to L1 when viewed from the z-axis direction), and the tracking coil 2a and the tracking coil 2a The coil 2b is arranged symmetrically with respect to L1.
Further, L2 is a center line of the tracking coils 2a and 2b intersecting with L1 at a right angle (thickness center line when the tracking coils 2a and 2b are viewed from the z-axis direction). Note that L
1 is parallel to the x-axis and L2 is parallel to the y-axis.

Focus coil 1 shown in FIG.
Is S1, S2, S3, S4, when viewed from the z-axis direction,
It is composed of 5 sides of S5, and S1 and S5 intersecting with the magnetic flux in the gap portion are non-perpendicular to the magnetic flux in the gap portion. Therefore, the center point P1 of the driving force in the focus direction due to the electromagnetic action of the current flowing through the focus coil 1 and the magnetic flux in the gap portion is on L1, and is closer to the center point Q of the thickness of the portion where L1 and the focus coil 1 intersect. Also shifts to the inner circumference side of the focus coil 1.

On the other hand, the tracking coil 2a shown in FIG. 3B is composed of four sides Sa, Sb, Sc, Sd, and the tracking coil 2b is Se, Sf, Sg, S.
It is composed of four sides of h. Here, since the driving force generated by the current flowing through the sides Sb and Sd of the tracking coil 2a is canceled, the driving force in the tracking direction is equal to the side S.
It is caused by the current flowing through a and Sc. Further, also in the tracking coil 2b, the driving force generated by the currents flowing through the sides Sf and Sh is canceled as in the tracking coil 2a, so that the driving force in the tracking direction is equal to the sides Se and S.
It is caused by the current flowing through g.

In the objective lens driving device according to the present invention, the center points P2 and P3 of the driving force generated by the currents flowing through the sides Sa and Sc of the tracking coil 2a and the currents flowing through the sides Se and Sg of the tracking coil 2b are used. The tracking coils 2a and 2b are arranged so that the center points P4 and P5 of the generated driving force are located on L2. By arranging the tracking coils 2a and 2b in this way, the directions of the driving forces acting on P2, P3, P4, and P5 are all the same, and the center of the driving force in the tracking direction, which is the driving force of the entire tracking coils 2a and 2b. Points
It is matched with the center point P1 of the driving force in the focus direction.

Also, as shown in FIG. 4, when the portion of the focus coil 1 that intersects with the magnetic flux in the gap portion is formed by the sides S1, S5, and S6, the electromagnetic action between the current flowing through the focus coil 1 and the magnetic flux in the gap portion. The center point P1 of the driving force in the focus direction due to is shifted to the inner circumference side of the focus coil 1 from the center point Q of the thickness of the portion where L1 and the focus coil 1 intersect. Then, as in the case of FIG. 3, the center points P2 and P3 of the driving force generated by the currents flowing through the sides Sa and Sc of the tracking coil 2a and the center points of the driving force generated by the current flowing through the sides Se and Sg of the tracking coil 2b. By arranging the tracking coils 2a and 2b so that P4 and P5 are located on L2,
The directions of the driving forces acting on P2, P3, P4, and P5 are all the same, and the center point of the driving force in the tracking direction, which is the driving force of the entire tracking coils 2a and 2b, coincides with the center point P1 of the driving force in the focusing direction. I am letting you. In the present invention, when P1 is set, that is, when L2 is set, it is necessary to set the magnetic fluxes at P2, P3, P4, and P5 on L2 to be parallel. A case in which the permanent magnet 3a forming the magnetic circuit is provided only on the outer peripheral yoke 4 of the annular focus coil 1 will be described with reference to FIG.

In FIG. 5A, the focus coil 1 is
As in the case of FIG. 3, the yoke 4 is composed of five sides, the yoke 4 on the side where the permanent magnet is not provided is located on the inner peripheral side, and the yoke 4 on the side where the permanent magnet is provided is located on the outer peripheral side. It is located in. Also in this case, as in the case of FIG. 3, the center point P1 of the driving force in the focus direction is displaced to the inner circumference side of the focus coil 1 from the center point Q of the thickness of the portion where L1 and the focus coil 1 intersect. Then, as in the case of FIG. 3, the center points P2, P3, P4, and P5 of the driving force are L2.
By arranging the tracking coils 2a and 2b so as to be located above, the directions of the driving forces acting on P2, P3, P4, and P5 are all the same, and the tracking coils 2a and 2b are aligned.
The center point of the driving force in the tracking direction, which is the driving force of the whole b, is made to coincide with the center point P1 of the driving force in the focusing direction.

Further, since the permanent magnet 3a is provided only on the yoke 4 on the outer peripheral side of the focus coil 1, in the portion of the focus coil 1 that intersects with the magnetic flux in the gap portion, at the Q point portion closest to the permanent magnet 3a. The driving force becomes maximum, and the driving force acting on the portion decreases as the distance from the driving force becomes maximum.
Therefore, when the movable part is radially shifted (a state in which the movable part is moved by several tracks in the y-axis direction which is the tracking direction), the deviation between the center of gravity of the movable part and the center point of the driving force in the focus direction is reduced. be able to. That is,
When the portion of the focus coil 1 that intersects with the magnetic flux in the gap portion (the portion that crosses the gap of the magnetic circuit) as shown in FIG. 8 is parallel to the surface of the permanent magnet, the movement thereof occurs when the radial shift is performed. The center of gravity of the movable part and the center point of the driving force in the focus direction were deviated by an amount, but Fig. 5 (a)
In this case, the shift between the center of gravity of the movable portion and the center point of the driving force in the focus direction is smaller than the movement amount when the radial shift is performed. As a result, the occurrence of rolling resonance and the tilt of the objective lens can be made smaller than in the conventional case. or,
Since the permanent magnet is not provided in the yoke 4 on the inner peripheral side of the focus coil, the reaction force in the focus direction generated by the electromagnetic action of the leakage flux from the gap flux and the current flowing through the side S3 of the focus can be made extremely small. .

Further, as shown in FIG. 5B, the focus coil 1 is composed of 6 sides as in the case of FIG. 4, and the permanent magnet is provided only on the outer peripheral side yoke.
As in the case of (a), it is possible to reduce the deviation between the center of gravity of the movable portion and the center point of the driving force in the focus direction when the movable portion is radially shifted. In this case, the shorter the side S6 of the focus coil shown in FIG. 4, the smaller the deviation between the center of gravity of the movable portion and the center point of the driving force in the focus direction.

Next, using FIG. 6, the permanent magnet 3a forming the magnetic circuit is provided only on the yoke 4 on the inner peripheral side of the annular focus coil 1, and the width W2 of the yoke on the outer peripheral side is set on the inner peripheral side. A case where the width is larger than the width W1 of the yoke 4 will be described.

As shown in FIG. 6, the width W2 of the yoke 4 without the permanent magnet on the outer peripheral side is equal to the width W of the yoke on the inner peripheral side.
By making it larger than 1, the magnetic flux in the gap becomes parallel (parallel to the x-axis) in a wider range with respect to the width direction (y-axis direction) of the yoke 4. Therefore, the tracking coil 2
It becomes easier to set the directions of the driving forces acting on P2, P3, P4, and P5 of a and 2b to be the same. Since only the width of the yoke on the outer peripheral side is widened, the mechanical margin U1 in the tracking direction (y-axis direction) is not reduced.

When the permanent magnet is provided only on one side of the yoke and the objective lens is arranged on the lens holder on the side where the permanent magnet is not provided, leakage flux from the magnetic circuit in the objective lens portion And the writing characteristics of the magneto-optical disk are improved.

[0040]

As described above, in the objective lens driving device according to the present invention, the portion of the focus coil which crosses the gap of the magnetic circuit is moved in the tracking direction (y
The tracking coil is arranged in parallel with the tracking direction (y-axis direction) so as to coincide with the center point of the driving force of the focus coil. Therefore, it is easy to match the center points of the driving forces in the focus direction and the tracking direction, and it is possible to provide an objective lens driving device of an optical disc device which is suitable for downsizing and thinning of the device.

That is, the center points of the driving forces in the focusing direction and the tracking direction are the same as those in which the tracking coil is mounted on the side that is not parallel to the tracking direction (y-axis direction) that crosses the gap of the magnetic circuit of the focus coil. It becomes easy to let.

In addition, the lens driving device is smaller and thinner, and the number of parts is reduced, as compared with a device in which the focus coil and the tracking coil are stacked in the focus direction, or a device in which the tracking coil is embedded in the focus coil. Easy to assemble.

Further, since it is not necessary to fix the tracking coil to the focus coil, it is possible to dispose the focus coil and the tracking coil separately, and as a result, all or part of the side of the portion intersecting the magnetic flux in the gap portion can be arranged. The lens holder 6 is surrounded and the deformation of the part can be suppressed.

When the permanent magnet is provided only on the outer peripheral yoke of the focus coil, the shift between the center of gravity of the movable portion and the center point of the driving force in the focusing direction is reduced when the movable portion is radially shifted. be able to. Further, when a permanent magnet is provided only on the inner circumference side yoke of the focus coil and the width of the outer circumference side yoke is made larger than the width of the inner circumference side yoke, the gap magnetic flux becomes parallel in a wide range, It becomes easier to match the center points of the driving forces in the focus direction and the tracking direction. Also, when the permanent magnet is provided on only one side of the yoke, if the objective lens is placed on the lens holder on the side where the permanent magnet is not provided, the leakage magnetic flux from the magnetic circuit in the objective lens part decreases. The write characteristics of the magneto-optical disk are improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a focus coil and a tracking coil in an objective lens driving device according to the present invention. Incidentally, (a) shows only the focus coil and the tracking coil, and (b) shows the state of being fixed to the lens holder.

FIG. 2 is a perspective view showing a positional relationship between a focus coil and a tracking coil and a magnetic circuit in the objective lens driving device according to the present invention.

FIG. 3 is a diagram for explaining a method of matching the center points of the driving forces in the focus direction and the tracking direction in the objective lens driving device according to the present invention (when a focus coil having five sides is used). .

FIG. 4 is a diagram for explaining a method of matching the center points of the driving forces in the focus direction and the tracking direction in the objective lens driving device according to the present invention (when a focus coil having 6 sides is used). .

FIG. 5 shows an objective lens driving device according to the present invention,
It is drawing which shows the case where a permanent magnet is provided only in the inner peripheral side yoke of a focus coil.

FIG. 6 shows an objective lens driving device according to the present invention,
It is a drawing showing a case where a permanent magnet is provided only on the inner peripheral side yoke of the focus coil, and the width of the outer peripheral side yoke is made larger than the width of the inner peripheral side yoke.

FIG. 7 is a perspective view showing an objective lens driving device.

FIG. 8 is a perspective view showing a positional relationship between a focus coil and a tracking coil and a magnetic circuit in a conventional objective lens driving device.

FIG. 9 is a perspective view showing a focus coil and a tracking coil in a conventional objective lens driving device.

FIG. 10 is a perspective view showing a focus coil and a tracking coil in a conventional objective lens driving device.

FIG. 11 is a perspective view showing a focus coil and a tracking coil in a conventional objective lens driving device.

[Explanation of symbols]

 1 Focus Coil 2a, 2b Tracking Coil 3a, 3b Permanent Magnet 4 Yoke 5 Objective Lens 6 Lens Holder 7 Elastic Member 8 Base

Claims (5)

[Claims] 1. A lens holder for holding an objective lens, a first coil for driving the objective lens in the optical axis direction, and a second coil for driving the objective lens in the radial direction of the optical disk.
And a fixed part including a single magnetic circuit including a yoke provided with a pair of permanent magnets. The movable part is supported by the elastic member from the fixed part. In the objective lens driving device described above, all or part of the portion of the first coil that crosses the gap of the magnetic circuit is made non-parallel to the radial direction of the optical disc, and the first coil of the optical disc is The two second coils, which are symmetrically arranged with respect to a center line divided in the radial direction, are arranged in parallel with the radial direction of the optical disc, and the center point of the driving force of the objective lens in the optical axis direction and the optical disc. 2. The objective lens driving device of the optical disk device, wherein the center point of the driving force in the radial direction of the above and the center of gravity of the movable portion are matched. 2. The objective lens driving device for an optical disk device according to claim 1, wherein an outer periphery of a fixed portion of the focus coil of the lens holder other than a portion of the first coil that crosses a gap of a magnetic circuit. , And an objective lens driving device of an optical disk device, which is in contact with all or part of the outer circumference of a portion that crosses the gap of the magnetic circuit. 3. The objective lens driving device of the optical disk device according to claim 1, wherein the first coil and the two second coils are directly fixed to the lens holder. And an objective lens driving device for an optical disk device. 4. The objective lens driving device of the optical disk device according to claim 1, wherein a permanent magnet is provided only on the outer peripheral yoke of the focus coil. Objective lens driving device of the device. 5. The objective lens driving device for an optical disk device according to claim 1, wherein a permanent magnet is provided only on a yoke on an inner peripheral side of the focus coil, and an outer periphery of the focus coil is provided. An objective lens driving device of an optical disc device, wherein a width of the side yoke in the radius direction of the optical disc is made wider than a width of the inner yoke in the radius direction of the optical disc.