JP2807153B2 - 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, a method for holding the objective lens at the neutral point by giving a magnetic restoring force has been proposed.
These are described in JP-A-8-179635, JP-A-58-163908, JP-A-62-141646, and the like.

According to the objective lens driving device having the magnetic restoring force, the range in which the magnetic restoring force is uniform is narrow, and it is necessary to improve the use of a plurality of magnetic pieces to compensate for the narrow range. In addition, the holding of the neutral point by one magnetic piece is either one of the focusing direction and the tracking direction, and if an attempt is made to obtain the neutral point in both the focusing direction and the tracking direction, a two-phase There was a problem that a magnetic piece was required, the configuration was complicated, and the cost was high.

Therefore, the present applicant has filed Japanese Patent Application Laid-Open
In -317234, the above problem was solved. In the objective lens driving device described in Japanese Patent Application Laid-Open No. HEI 1-317234, a magnet disposed to face a driving coil is polarized, for example, in a focusing direction, and is provided in a magnetic circuit of the focusing magnet as shown in FIG. A thin thin plate-like long magnetic piece 30 is arranged in the vertical direction, and a magnetic attraction force acting on the magnetic piece 30 generates a two-dimensional restoring force in the focusing direction and the tracking direction to neutralize the objective lens. It is designed to be held at a point.

[0006]

Here, the width of the magnetic piece 30 is x, the length is y, x = 0.8 mm, y = 4.6 m.
When the resonance frequency f0 of the movable part in the focusing direction and the tracking direction was measured as m, the focus f0 was 26.6 Hz and the track f0 was 17.0 Hz. These focus f0, track f0, in the example CD or the like, both of usually about 20～30Hz, width x of the magnetic piece 30, the length y, the magnetic Ri <br/> by the appropriately adjusting the thickness t The magnetic flux passing through the piece 30 is optimized by increasing or decreasing the magnetic flux .

By the way, recent 2-4 times speed CD-ROMs
In such cases, the need to increase the track f0 is increasing. However, in order to increase the track f0 without increasing the focus f0 without changing the shape of the magnetic piece 30, the length y is increased without changing the width x of the magnetic piece 30. must Rukoto has been confirmed. This
This increases the magnetic flux that is the source of the restoring force in the focusing direction.
Without increasing the tracking direction restoring force.
Is thought to be due to the increase in magnetic flux
If the sex piece 30 is too long, there is a problem that the magnetic circuit is disturbed and linearity is deteriorated. There is also a problem that the pickup cannot be made compact because it is too thick.

Accordingly, an object of the present invention is to provide an objective lens driving device which can increase the track f0 without increasing the focus f0 while maintaining good linearity, and which can be made thinner.

[0009]

According to a first aspect of the present invention, there is provided an objective lens driving device in which a driving coil is provided on one of a lens holder holding an objective lens and a fixing member and a magnet is provided on the other. An objective lens driving device arranged 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 the focusing direction and the tracking direction. A magnetic piece is disposed in a magnetic circuit of the focusing magnet, and a magnetic attraction acting on the magnetic piece provides a two-dimensional restoring force in the focusing direction and the tracking direction. An objective lens driving device for generating and holding the objective lens at a neutral point In, a width of at least one end of the polarization direction of the magnetic pieces, and characterized by being larger than that of the central portion.

In order to achieve the above object, the objective lens driving device of the second means has a driving coil disposed on one of a lens holder holding an objective lens and a fixing member, and a magnet disposed on the other, and the driving coil is disposed on the other side. An objective lens driving device configured to drive a lens holder in a focusing direction and a tracking direction by causing a drive coil and a magnet to face each other and energizing the drive coil, wherein the magnet is polarized at least in a focusing direction. A magnetic piece is arranged in a magnetic circuit of the focusing magnet, and a two-dimensional restoring force is generated in a focusing direction and a tracking direction by a magnetic attraction force acting on the magnetic piece to generate the objective lens. In an objective lens driving device configured to hold at a neutral point, At least one of the thickness of the end portion in the direction of polarization of the sexual strip, and characterized by being larger than that of the central portion.

[0011]

According to the objective lens driving device of the first and second means, the magnetic piece focuses by suppressing the magnetic flux in the magnetic piece that is the source of the restoring force in the focusing direction by the narrow portion at the center. Do not increase f0
Ku, have work to increase the volume of the magnetic piece which is a tracking direction of the restoring force of the original increase the track f0 by, thus the length y of the magnetic pieces to be smaller than the same length or with a conventional, enhanced track f0 .

[0012]

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 JP-A-1-317234 is that the width x of both ends 10a and 10b in the direction of polarization of the magnetic piece 10 is different.
Is larger than the width xc of the central portion 10c.

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 overlaid 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.

A magnetic piece 10, which is a feature of the present embodiment, is 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 shown in FIGS. 8 and 9, the magnetic piece 10 has a thin plate shape, and the width x in the circumferential direction around the shaft 7 is the same as the circumferential size of the focusing magnet portion 6a. The length y in the direction of the axis 7 is considerably smaller than the dimension of the focusing magnet portion 6a in the direction of the axis 7. The magnetic piece 10
As shown in FIG. 1, the width x of both ends 10a and 10b in the vertical direction (polarization direction) is larger than the width xc of the center 10c. Incidentally, both ends 10a, 10
The width of b is x, the width of the central portion 10c is xc, and the entire length is y
Then, x = 1.6 mm, xc = 0.7 mm, and y = 4.4 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 piece 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 piece 10 is arranged in the gap, the magnetic piece 1
At 0, a magnetic attractive force by the focusing magnet portion 6a acts, and a restoring force equivalent to an elastic restoring force that is stably held at the maximum point of the magnetic flux acts. 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. Objective lens 2
Since the magnetic flux gradient changes approximately linearly in the normal movable range 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 portion 6a in the direction of the axis 7, the magnetic piece 10 is disposed because the magnet portion 6a is polarized and magnetized in the direction of the axis 7. The gradient of the magnetic flux in the air gap is reversed in the middle part in the vertical direction. Here, the magnetic piece 10 acts as a part of a magnetic path, and the magnetic piece 10 is magnetically attracted to the central portion of 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, whereby the objective lens 2 is held at a neutral point in the focusing direction. Also, as described above, the magnetic piece 10
Acts as a magnetic path for the magnetic flux from the magnet portion 6a, so that the magnetic flux density is improved and contributes to the improvement of the sensitivity of the objective lens driving device, and the magnetic restoring force can be stably obtained in a wide range.

Here, the inventor measured the resonance frequency f0 of the movable part in the focusing direction and the tracking direction by experiments. As a result, the focus f0 = 19.4Hz (of conventional 26.6Hz
Ri decrease) track f0 = 21.6Hz (traditional 17.0Hz
Increased ).

As described above, in this embodiment, the width x of both ends 10a and 10b in the polarization direction of the magnetic piece 10 is set.
(1.6 mm) to the width xc (0.7 m
m), the magnetic piece 10 suppresses the magnetic flux in the magnetic piece, which is the source of the restoring force in the focusing direction, by the narrow portion 10c at the center, thereby reducing the focus f0.
Together is lowered, the track is increased flux and increased volume of the magnetic piece which is a tracking direction of the restoring force of the former is f
0 are adapted to be increased, thus even if the length of the magnetic piece 10 (4.4 mm) smaller than the prior thereto (4.6 mm), it is possible to increase the track f0. In this embodiment, when increasing the track f0,
The focus f0 is lowered in the
By appropriately adjusting the width xc, the focus f0 can be adjusted.
It is also possible not to lower it.

[0024] Depending, it can increase the track f ₀ while maintaining good linearity, yet has a possible thinning. By the way, the length of the magnetic piece 10 (4.4 m
Even if m) is the same as the conventional one (4.6 mm), the same effect can be obtained.

In this embodiment, the track f ₀
And the focus f ₀ can be lowered at the same time, so that such a demand can be satisfied.

If the magnetic piece 10 is entirely widened in the width direction as it is, both the focus f ₀ and the track f ₀ can be further increased to about 25 Hz, which is required for a CD or the like, for example. It is also possible to set both f ₀ to an intermediate value in the resonance frequency range of 20 to 30 Hz.

Furthermore, if the dimensions of the details are changed,
It is also possible to track f ₀ and 30～40Hz.

FIG. 10 is a perspective view of a magnetic piece applied to an objective lens driving device according to another embodiment of the present invention. The magnetic piece 20 of this embodiment is different from the magnetic piece 10 of the previous embodiment in that both ends 20a, 20a in the polarization direction of the magnetic piece 20 are provided.
This is the point that the thickness t of b is larger than the thickness tc of the central portion 20c.

Even with this configuration, the magnetic piece 20 suppresses the magnetic flux in the magnetic piece, which is the source of the restoring force in the focusing direction, by the narrow portion at the center, and also reduces the source of the restoring force in the tracking direction. Needless to say, the volume of the magnetic piece is increased, so that the same effect as in the previous embodiment can be obtained.

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, for example, in each of the above embodiments, the width or the thickness of both ends in the polarization direction of the magnetic piece is larger than those of the central portion, but one end (the upper end or the upper end). The same effect can be obtained even if only the width or thickness of the lower end portion is larger than those of the central portion.

[0031]

As described above, according to the objective lens driving device of the first invention, the width of at least one end in the polarization direction of the magnetic piece is made larger than that of the central portion, and the second invention is improved. According to the objective lens driving device, the thickness of at least one end in the polarization direction of the magnetic piece is made larger than that of the central part, so that the magnetic piece is used as a source of the restoring force in the focusing direction. Focusing by suppressing the magnetic flux of the
The resonance frequency in the tracking direction is not increased, and the volume of the magnetic piece that is the source of the restoring force in the tracking direction is increased .
As a result, the resonance frequency in the tracking direction can be increased , and the length of the magnetic piece can be made equal to or smaller than that of the conventional art, and the track f0 can be increased. Therefore, the track f0 can be increased while maintaining good linearity, and the thickness can be reduced.

[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 perspective view of a magnetic piece applied to an objective lens driving device according to another embodiment of the present invention.

FIG. 11 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, 20 Magnetic piece 10a, 10b, 20a, 20b End part in the polarization direction of magnetic piece 10c, 20c Central part of magnetic piece t Magnetic piece Tc Thickness of the center of the magnetic piece x x Width of the end of the magnetic piece in the polarization direction xc Width of the center of the magnetic piece

Claims (2)

(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 in which the width of at least one end in the polarization direction of the piece is larger than that of the center. 2. A driving coil is disposed on one of a lens holder holding an objective lens and a fixing member, and a magnet is disposed 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 in which the thickness of at least one end in the polarization direction of the piece is larger than that of the center.