JP2807154B2 - Objective lens drive - Google Patents

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.

[0002]

2. Description of the Related Art In an optical disk device using an optical disk as a recording medium, an information signal is written on the disk,
An optical pickup is used to read the data. In this optical pickup, an objective lens driving device for accurately focusing a laser beam on information pits of a disk is used. Therefore, in this objective lens driving device, it is necessary to precisely control the position of the objective lens two-dimensionally in the focusing direction and the tracking direction.
In order to accurately perform the two-dimensional tracking servo, a structure for holding the objective lens at a predetermined neutral point is an important factor that determines the performance of the optical pickup.

As means for holding the objective lens at a predetermined neutral point, Japanese Patent Laid-Open Publication No. Heisei 1 (1994) discloses a method in which the objective lens is held at the neutral point by giving a magnetic restoring force.
No. 317234.

In the objective lens driving device described in Japanese Patent Application Laid-Open No. 1-317234, a magnet opposed to a driving coil is polarized and magnetized, for example, in a focusing direction.
In the magnetic circuit of this focusing magnet, FIG.
As shown in FIG. 1, one vertically long thin magnetic piece 30 is arranged, and a magnetic attraction force acting on the magnetic piece 30 generates a two-dimensional restoring force in a focusing direction and a tracking direction to generate an objective. The lens is held at a neutral point.

Here, the resonance frequency of the actuator is represented by f
_{If 0} , f ₀ is the width x, length y, and thickness t of the magnetic piece 30.
Therefore, the optimum resonance frequency f ₀ can be obtained by changing the width x, length y, and thickness t of the magnetic piece 30.

[0006]

By the way, in recent years,
In quadruple-speed CD-ROMs and the like, there is an increasing need to increase the track f ₀ (the resonance frequency of the actuator in the tracking direction) while suppressing the change in the focus f ₀ (the resonance frequency of the actuator in the focusing direction). However, since the magnetic piece 30 is disposed in the magnetic circuit of the focusing magnet, if the shape of the magnetic piece 30 is changed, that is, if the width x, length y, or thickness t of the magnetic piece 30 is changed, the track f _The focus f ₀ changes together with ₀ , so that there is a problem that the need to increase the track f ₀ while suppressing the change in the focus f ₀ cannot be satisfied.

Accordingly, an object of the present invention is to provide an objective lens driving device capable of increasing the track f ₀ while suppressing a change in the focus f ₀ .

[0008]

In order to achieve the above object, the objective lens driving device of the present invention has a driving coil on one of a lens holder holding an objective lens and a fixing member, and a magnet on the other. An objective lens driving device that is disposed so that the drive coil and the magnet are opposed to each other and the drive coil is energized to drive the lens holder in a focusing direction and a tracking direction. Polarized and magnetized at least in the focusing direction, a magnetic piece is arranged in the magnetic circuit of the focusing magnet,
An objective lens driving device configured to generate a two-dimensional restoring force in a focusing direction and a tracking direction by a magnetic attraction force acting on the magnetic piece to hold the objective lens at a neutral point. The focusing magnets are arranged in parallel with each other in a direction perpendicular to the polarization direction of the magnets.

[0009]

According to the objective lens driving device of the above-mentioned means, two magnetic pieces arranged side by side in the direction perpendicular to the direction of polarization of the focusing magnet are spaced apart from each other by the track f while suppressing the change of the focus f _0. Work to increase ₀ .

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a magnetic piece applied to an objective lens driving device according to an embodiment of the present invention.

The difference between the objective lens driving device of this embodiment and that described in Japanese Patent Application Laid-Open No. 1-317234 is that two magnetic pieces are provided in the magnetic circuit of the focusing magnet, and these two magnetic pieces are used. 10 and 10 are arranged side by side at a predetermined distance a in a direction (horizontal direction in FIG. 1) orthogonal to the polarization direction of the focusing magnet.

Hereinafter, the objective lens driving device of the present embodiment will be described in more detail. 2 to 5, reference numeral 1 denotes a lens holder. The lens holder 1 is supported so as to be rotatable around a fixed shaft 7 and movable along the shaft 7. An objective lens 2 is attached to the lens holder 1 with its optical axis parallel to the axis 7. Lens holder 1
Also, a balancer 8 is fixed to the opposite side of the objective lens 2 about the axis 7. A pair of focusing driving coils 4 and tracking driving coils 3 are fixed to the outer peripheral surface of the lens holder 1 at symmetrical positions with respect to the shaft 7. The outer peripheral surface of the lens holder 1 to which the focusing drive coil 4 and the tracking drive coil 3 are fixed is a common continuous arc surface centered on the shaft 7, and each coil 4, 3 extends along the arc surface. And is fixed to the lens holder 1.

The shaft 7 has a boss 9a formed by burring the center of an outer yoke 9 as a fixing member.
Is fixed by means such as press-fitting or bonding. The outer yoke 9 is formed in a fan shape on both sides with the shaft 7 interposed therebetween, and the outer peripheral edge of the fan shape is bent at a right angle and rises so as to face the coils 4 and 3. Each rising portion of the outer yoke 9 is formed along an arc centered on the shaft 7, and an arc-shaped magnet 6 is fixed to the inner surface of the rising portion. The magnet 6 is integrally molded with, for example, a resin binder or the like. As shown in FIG. 6, the magnet 6 has a groove 6 in a direction parallel to the shaft 7 in the middle part.
c is formed, and is divided into a focusing magnet portion 6a and a tracking magnet portion 6b with the groove 6c as a boundary. The focusing magnet portion 6a is polarized and magnetized so that the N and S poles are aligned in the direction of the axis 7, while the tracking magnet portion 6b is polarized and magnetized in a direction perpendicular to the magnetizing direction of the focusing magnet portion 6a. As a result, the N pole and the S pole are formed in the circumferential direction. Thus, each magnet part 6a,
6b are integrally formed, so that they are arranged on a continuous common surface.

As shown in FIG. 7, the focusing drive coil 4 is formed in a horizontally long rectangular shape, and is disposed such that its long side faces each magnetic pole of the focusing magnet portion 6a. . Further, the tracking drive coil 3 is formed to be a vertically long rectangle, and is disposed such that its long side faces each magnetic pole of the tracking magnet section 6b.

The inner yoke 5 is superimposed on the outer yoke 9 and is fixed with reference to the outer diameter of the boss 9a. Like the outer yoke 9, the inner yoke 5 is formed in a fan shape on both sides of the shaft 7, and the outer peripheral edge of the fan shape is bent at a right angle and rises. The rising portion is formed along an arc centered on the axis 7.
The rising portion penetrates the window hole 1a formed in the lens holder 1 with a sufficient space, and faces the magnet portions 6a and 6b with the coils 4 and 3 interposed therebetween.
As described above, the inner yoke 5, the drive coils 3 and 4, the magnet 6, and the outer yoke 9 are sequentially mounted on the shaft 7 from the inside.
Are arranged along an arc centered at the center, and a substantially closed magnetic path passing therethrough is formed.

Two magnetic pieces 10 characteristic of the present embodiment are fixed to the outer peripheral edge of the sector of the lens holder 1 at a position facing the center of the magnetic pole of the focusing magnet 6a. As described above, these magnetic pieces 10, 10 are arranged side by side at a predetermined distance a in a direction perpendicular to the polarization magnetization direction of the focusing magnet 6a (direction substantially along the circumference in FIG. 8). The magnetic piece 1
As shown in FIGS. 1, 8 and 9, reference numerals 0 and 10 each have a thin plate shape and have a width x in a circumferential direction around the shaft 7.
Is considerably smaller than the circumferential dimension of the focusing magnet portion 6a, and the length dimension y in the axial direction 7 is formed shorter than the dimension of the focusing magnet portion 6a in the axial direction. When the width of the magnetic piece 10 is x, the overall length is y, the thickness is t, and the distance between the magnetic pieces 10 and 10 is a, x = 0.5 mm (2/3 of the conventional product). ) Y = 6.4 mm t = 0.1 mm a = 3.0 mm.

Next, the operation of the objective lens driving device thus configured will be described. First, basic operations of focusing and tracking will be described. When a drive power is supplied to the focusing drive coil 4, a thrust is generated by the drive current and the magnetic flux in the magnetic circuit, and the objective lens 2 moves in the optical axis direction together with the lens holder 1 to perform a focusing operation. When a drive current is supplied to the tracking drive coil 3, a thrust is generated by the drive current and the magnetic flux in the magnetic circuit, and the objective lens 2 is driven together with the lens holder 1 in the tracking direction to perform a tracking operation. .

Next, the focusing magnet section 6a
The relationship between the magnetic flux and the magnetic pieces 10, 10 will be described. Although the focusing magnet portion 6a is polarized and magnetized in the direction of the axis 7, as shown in FIG. It decreases as it gets closer to. Since the magnetic pieces 10, 10 are arranged in the gap, the magnetic pieces 10, 10 receive a magnetic attraction force by the focusing magnet portion 6a, and are stably held at the maximum point of the magnetic flux. The same restoring force acts as the elastic restoring force. This restoring force holds the lens holder 1 at the neutral point in the circumferential direction, and thus holds the objective lens 2 at the neutral point in the tracking direction. The restoring force is proportional to the gradient of the magnetic flux distribution and the area of the magnetic piece 10. Since the magnetic flux gradient changes approximately linearly in the normal movable range of the objective lens 2 in the tracking direction, the restoring force can be obtained substantially uniformly in the normal movable range of the objective lens 2.

On the other hand, as shown in FIG. 9, in the section of the focusing magnet section 6a in the direction of the axis 7, the magnet pieces 6a are polarized and magnetized in the direction of the axis 7, so that the magnetic pieces 10, 10 The gradient of the magnetic flux in the arranged gap is reversed at the middle part in the vertical direction. Here, the magnetic pieces 10 and 10 act as a part of a magnetic path, and the magnetic pieces 10 and 10 are magnetically attracted to the central part of the polarization magnetization. This suction force acts as a restoring force, and the lens holder 1
Is held at a predetermined position in the direction of the axis 7, so that the objective lens 2
Is held at the neutral point in the focusing direction. Further, as described above, since the magnetic pieces 10, 10 act as magnetic paths of the magnetic flux from the magnet portion 6a, the magnetic flux density is improved, which contributes to the improvement of the sensitivity of the objective lens driving device, and the magnetic restoration. Power is obtained stably over a wide range.

Here, the inventor measured the resonance frequency f ₀ of the movable part in the focusing direction and the tracking direction by experiments. As a result, the focus f ₀ was about 1.1 times (compared to the conventional art), and the track f ₀ was about 2.5 times (compared to the conventional art).

Further, the present inventor has proposed that the magnetic pieces 10, 1
When the focus f0 and the track f0 were measured while changing the distance a between 0, the results shown in FIGS. 10 and 11 were confirmed . As is clear from the experimental results, the track f0 increases as the distance a between the magnetic pieces 10, 10 increases, while the focus f0 increases as the magnetic piece 1 increases.
Even if the distance a between 0 and 10 becomes long, it hardly changes. This
This is because the value of the resonance frequency f0 depends on the magnitude of the restoring force.
Based on the so-called magnetic spring constant
It is based on That is, as described above, the two magnetic pieces 1
The distance a between 0 and 10 is longer in the tracking direction
Then, the moving range of the two magnetic pieces 10, 10 becomes
Both ends of the magnetic field generated by the focusing magnet 6a
It will be expanded to. Both ends in the tracking direction
Minute, the change in magnetic flux is large,
A large restoring force can be obtained using the magnetic flux gradient.
You. As a result, a so-called magnetic spring in the tracking direction
The constant increases, which causes the track f0 to
It is thought to be higher. On the other hand, both magnetic pieces 10, 10
Even if the distance a between them is increased in the tracking direction,
The magnetic flux gradient used as the restoring force in the sing direction is almost
There is no change, so-called magnetic in the focusing direction
The dynamic spring constant is also maintained at approximately the same value.
As a result, it is considered that the focus f0 does not change. This
If the magnetic pieces 10, 10 are arranged side by side in the direction perpendicular to the direction of polarization of the focusing magnet 6a, two tracks are separated from each other as described above, it is possible to increase the track f0 while suppressing the change in the focus f0, and to increase the magnetic field. By changing the distance a between the pieces 10, a desired track f0 can be obtained.

As described above, in the present embodiment, the magnetic pieces 10, 10 are arranged side by side in the direction perpendicular to the polarization magnetization direction of the focusing magnet 6a with two magnetic pieces separated from each other.
The change in focus f ₀ is suppressed and the track f ₀
It is possible to meet the needs of increasing the track f ₀ while suppressing the change in the focus f ₀ required for, for example, recent 2 to 4 × -speed CD-ROMs.

Further, as described above, the above-mentioned needs can be met only by arranging two magnetic pieces 10, 10, so that the configuration is extremely simple.

If the parameter width x, length y, and thickness t other than the distance a between the magnetic pieces 10, 10 are changed, the focus f ₀ and the track f ₀ can be further changed. It is also possible to obtain a predetermined focus f ₀ and track f ₀ . In this way, the actuator can be designed more finely.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the invention. Needless to say.

[0026]

As described above, according to the objective lens driving device of the present invention, two magnetic pieces are arranged side by side in the direction perpendicular to the polarization magnetization direction of the focusing magnet. change now track f0 is enhanced with is suppressed, the two magnetic pieces
By adjusting the distance between the two
The track f0 can be obtained, and it is possible to respond to the need to increase the track f0 while suppressing the change in the focus f0 required for , for example, recent 2- to 4-times-speed CD-ROMs.

[Brief description of the drawings]

FIG. 1 is a perspective view of a magnetic piece applied to an objective lens driving device according to an embodiment of the present invention.

FIG. 2 is a plan view of the objective lens driving device.

FIG. 3 is a longitudinal sectional view of FIG. 2;

FIG. 4 is a longitudinal sectional view of an objective lens portion.

FIG. 5 is an enlarged plan view of a magnet and a coil part.

FIG. 6 is a perspective view of a magnet.

FIG. 7 is a front view of the coil.

FIG. 8 is a plan view of a main part of the same device showing a state of a magnetic flux of a magnetic piece.

FIG. 9 is a longitudinal sectional view of a main part of the same device showing a state of a magnetic flux of a magnetic piece.

FIG. 10 is a diagram illustrating a relationship between a track f ₀ and a distance between magnetic pieces.

FIG. 11 is a diagram illustrating a relationship between a focus f ₀ and a distance between magnetic pieces.

FIG. 12 is a perspective view of a magnetic piece showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens holder 2 Objective lens 3, 4 Drive coil 6 Magnet 6a Focusing magnet 9 Fixing member 10 Magnetic piece

Claims (1)

(57) [Claims] 1. A driving coil is arranged on one of a lens holder holding an objective lens and a fixing member, and a magnet is arranged on the other, and the driving coil and the magnet are opposed to each other to energize the driving coil. By doing
An objective lens driving device configured to drive the lens holder in a focusing direction and a tracking direction, wherein the magnet is polarized and magnetized at least in a focusing direction, and a magnetic piece is disposed in a magnetic circuit of the focusing magnet. An objective lens driving device configured to generate a two-dimensional restoring force in a focusing direction and a tracking direction by a magnetic attractive force acting on the magnetic piece to hold the objective lens at a neutral point; An objective lens driving device, wherein two pieces are arranged side by side in a direction perpendicular to the polarization magnetization direction of the focusing magnet.