JPH08249692A - Objective lens driving device - Google Patents

Abstract

PURPOSE: To enhance reliability and productivity of an objective lens driving device by increasing a degree of freedom for design, stably maintaining the posture of an objective lens and obtaining a stable lens characteristic. CONSTITUTION: An objective lens 2 is held at the respective neutral points in a focusing direction and a tracking direction by a first magnetic piece 10 disposed oppositely to a focusing magnet part 6a and a second magnetic piece 11 disposed oppositely to a tracking magnet part 6b, and the area of the second magnetic piece 11 is changed with the area of the first magnetic piece 10 being maintained just as it is. Therefore, the resonance frequency of the focusing direction is changed. The resonance frequency of only the tracking direction is independently changed, and also the balance (resultant force) between the magnetic attraction of the first magnetic piece and the magnetic attraction of the second magnetic piece is properly taken, thereby being able to set the so-called lateral pressure in an arbitrary 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 an optical pickup used in an optical disk device or the like.

[0002]

2. Description of the Related Art In an optical disc apparatus using an optical disc as a recording medium, an optical pickup is used for writing and reading an information signal on the disc. The optical pickup has an information pit of the disc. An objective lens driving device is provided for accurately focusing the laser beam. In the above-mentioned 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. The structure for maintaining the characteristics is an important factor that determines the performance of the optical pickup.

From this point of view, Japanese Patent Laid-Open No. 1-317234 discloses an objective lens driving device in which the objective lens is held at a neutral point by a magnetic restoring force. In this structure, the drive magnet arranged to face the drive coil is polarized and magnetized, for example, in the focusing direction, and magnetically applied to a thin plate-shaped magnetic piece arranged in the magnetic circuit formed by the focusing magnet portion. By applying a suction force, a restoring force is two-dimensionally generated in the focusing direction and the tracking direction, and the restoring force holds the objective lens at a neutral point in the focusing direction.

On the other hand, in the objective lens driving device, each resonance frequency (f0) in the focusing direction and the tracking direction
Since is given as an important design value,
As described above, the desired resonance frequency (f0) value is obtained by variously changing the shapes of the magnetic pieces arranged to face the focusing magnet portion.

Further, by disposing a pair of magnetic pieces so as to face a pair of focusing magnet portions arranged substantially in axial symmetry and changing the shape of each magnetic piece variously, the magnetic pieces are attached to the focusing magnet portion. A so-called “side pressure” is applied in the suction direction, and the “side pressure” stabilizes the posture of the lens to maintain the lens characteristics.

[0006]

However, as described above, when the shape of the magnetic piece opposed to the focusing magnet portion is changed, both resonance frequencies in the focusing direction and the tracking direction change at the same time. Even if one side of the resonance frequencies in the focusing direction and the tracking direction is adjusted to the target value, the value on the other side changes. That is, the conventional device has a problem that the resonance frequency in the tracking direction alone cannot be changed without changing the resonance frequency in the focusing direction.

When the "side pressure" is obtained by changing the shape of the magnetic piece arranged to face the focusing magnet section, the magnetic piece is attracted to the focusing magnet section in the "side pressure" direction. However, there is also a problem that the degree of freedom in design is small.

Therefore, according to the present invention, the resonance frequency in the tracking direction alone can be changed without changing the resonance frequency in the focusing direction.
It is an object of the present invention to provide an objective lens driving device capable of applying "side pressure" in any direction.

[0009]

To achieve the above object, the present invention provides a lens holder provided so as to reciprocate in a focusing direction and a tracking direction while holding an objective lens, and a driving force is applied to the lens holder. A drive coil and a drive magnet arranged to face each other,
A focusing magnet part and a tracking magnet part polarized and polarized in the focusing direction and the tracking direction of the drive magnet, and a magnetic piece arranged in a magnetic circuit formed by the focusing magnet part and the tracking magnet part. In the objective lens drive device configured to hold the objective lens at a neutral point by a restoring force generated in the focusing direction and the tracking direction based on the magnetic attraction force acting on the magnetic piece, The magnetic piece is configured to include a first magnetic piece opposed to the focusing magnet section and a second magnetic piece opposed to the tracking magnet section.

[0010]

According to the present invention having such a structure, by changing the shape of the second magnetic piece opposed to the tracking magnet, the resonance frequency in the focusing direction is hardly changed, and only the tracking direction is changed. The resonance frequency of the
The so-called “side pressure” is obtained by the balance (resulting force) between the magnetic attraction force of the magnetic piece and the magnetic attraction force of the second magnetic piece.
Is set in any direction.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4, the lens holder 1 is supported so as to be rotatable around a fixed shaft 7 and slidably movable in the axial direction, and the objective lens 2 has the optical axis as the above-mentioned axis. It is attached so that it is parallel to 7.
A balancer 8 is fixed to the lens holder 1 on the opposite side of the objective lens 2 about the axis 7. Further, the lens holder 1 is provided with a pair of arc-shaped outer peripheral surfaces so as to connect the objective lens 2 and the balancer 8, and the pair of arc-shaped outer peripheral surfaces are arranged at symmetrical positions with the shaft 7 interposed therebetween. A pair of focusing drive coil 4 and tracking drive coil 3 are fixed to each other. 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
It is a common continuous arc surface centered on the axis 7,
The coils 4 and 3 are bent along the arc surface and fixed to the lens holder 1.

The shaft 7 has an outer yoke 9 as a fixing member.
Boss 9a formed by burring in the center of the
Are fixed by means such as press fitting or adhesion. The outer yoke 9 has a pair of fan-shaped bottom portions on both sides of the shaft 7, and the outer peripheral edge portions of the pair of fan-shaped bottom portions are bent at right angles to form the coils 4 and 3 above. A pair of wall portions that are raised to face each other are provided. The rising wall portions of these outer yokes 9 are connected to the shaft 7
Is formed so as to form an arc shape with the center as the center, and arc-shaped drive magnets 6 are fixed to the inner surface of each rising wall portion.

Each of the magnets 6 is composed of a focusing magnet portion 6a and a tracking magnet portion 6b, which are arranged in parallel on a continuous common peripheral surface. The focusing magnet portion 6a has an N pole and an S pole in the axis 7 direction. The magnetizing portion 6b for polarization is polarized and magnetized in the direction orthogonal to the magnetizing direction of the magnet portion 6a for focusing.
A pole and an S pole are formed in the circumferential direction. The focusing magnet portion 6a and the tracking magnet portion 6b are arranged to face the focusing drive coil 4 and the tracking drive coil 3 on the lens holder 1 side in the radial direction.

That is, the focusing drive coil 4 is formed in a horizontally long rectangle as shown in FIG. 6, and its long side portion faces each magnetic pole of the focusing magnet portion 6a. Are arranged as follows. The tracking drive coil 3 is formed in a vertically long rectangle, and its long side portion is arranged so as to face each magnetic pole of the tracking magnet portion 6b.

On the other hand, the inner yoke 5 is superposed on the outer yoke 9 and is fixed on the basis of the outer diameter of the boss portion 9a. Similar to the outer yoke 9, the inner yoke 5 is formed in a fan shape on both sides with the shaft 7 interposed therebetween.
The outer peripheral edge of this fan shape is bent at a right angle and stands up. The rising portion is formed along an arc centered on the shaft 7. The rising wall is the lens holder 1
Through the window hole 1a formed in the drive magnet section 6a, with the coils 4 and 3 interposed therebetween.
It is arranged so as to face 6b. As described above, the inner yoke 5, the drive coil 3, and the inner coil 5 are sequentially arranged from the inner side in the radial direction.
4, the drive magnet 6, and the outer yoke 9 are arranged along concentric arcs centering on the shaft 7, respectively, and a substantially closed magnetic path passing through these is formed.

Further, on the arcuate outer peripheral surface of the lens holder 1, a magnetic piece 10 is fixed at a position facing the magnetic pole center of the focusing magnet portion 6a, and at the same time, facing the magnetic pole center of the tracking magnet portion 6b. The magnetic piece 11 is fixed to the position where the magnetic piece 11 is formed. As shown in FIGS. 7 and 8, each of the magnetic pieces 10 and 11 has a thin plate shape.

First, in the magnetic piece 10, the width dimension x1 in the circumferential direction about the axis 7 (see FIG. 7) is set to be considerably smaller than the circumferential dimension of the focusing magnet portion 6a. At the same time, the length dimension y1 in the axis 7 direction (see FIG. 8A) is formed shorter than the dimension in the axis 7 direction of the focusing magnet portion 6a. On the other hand, in the magnetic piece 11, the width dimension x2 (see FIG. 7) in the circumferential direction about the shaft 7 is formed to be slightly shorter than the circumferential dimension of the tracking magnet portion 6b, and the shaft 7 Direction length y2 (Fig. 8 (b)
(See) is formed to be considerably shorter than the dimension of the tracking magnet portion 6b in the axis 7 direction.

Next, the operation of the objective lens driving device configured as described above will be described. First, the basic operation of focusing and tracking will be described. By supplying a driving power to the focusing driving coil 4, a thrust is generated by the driving current and the magnetic flux in the magnetic circuit, and the objective lens 2 moves together with the lens holder 1 in the optical axis direction to perform the focusing operation. Further, when a drive current is passed through the tracking drive coil 3, thrust is generated by the drive current and the magnetic flux in the magnetic circuit, and the objective lens 2 is driven in the tracking direction together with the lens holder 1 to perform the tracking operation. .

Next, the focusing magnet portion 6a.
Also, the relationship between each magnetic flux generated by the tracking magnet portion 6b and the magnetic pieces 10 and 11 will be described. First, the focusing magnet portion 6a is polarized and magnetized in the direction of the axis 7, but in the plane orthogonal to the axis 7 as shown in FIG. It decreases as it gets closer to both ends. Since the magnetic piece 10 is arranged in the void,
A magnetic attraction force by the focusing magnet portion 6a acts on the magnetic piece 10, and a restoring force equivalent to an elastic restoring force that tends to be stably held at the maximum point of the magnetic flux distribution acts on the magnetic piece 10. This restoring force holds the lens holder 1 at a neutral point in the circumferential direction, and thus the objective lens 2 is held at a neutral point in the tracking direction. The restoring force is proportional to the magnetic flux density and the area of the magnetic piece 10. In the normal movable range of the objective lens 2 in the tracking direction,
The restoring force is obtained almost linearly in the normal movable range of the objective lens 2.

On the other hand, as shown in FIG. 8A, in the cross section of the focusing magnet portion 6a in the axis 7 direction, the magnet portion 6a is polarized and magnetized in the axis 7 direction. The gradient of the magnetic flux lines in the arranged air gap is reversed at the intermediate portion in the vertical direction. Here, the magnetic piece 10 acts as a part of the magnetic path, and the magnetic piece 1
Zero is magnetically attracted to the center of the polarized magnetization. This suction force acts as a restoring force, and the lens holder 1 is held at a predetermined position in the axis 7 direction, so that the objective lens 2 is held at a neutral point in the focusing direction. Further, as described above, since the magnetic piece 10 acts as a magnetic path of the magnetic flux emitted 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 restoring force is wide. Can be obtained stably.

On the other hand, the tracking magnet portion 6b is polarized and magnetized in the circumferential direction, but in the plane orthogonal to the axis 7 as shown in FIG. The gradient of the magnetic flux lines reverses in the middle part in the circumferential direction. Here, the magnetic piece 11 acts as a part of the magnetic path, and the magnetic piece 11 is magnetically attracted to the central portion of the polarized magnetization. This suction force acts as a restoring force, and the lens holder 1 is held at a predetermined position in the axis 7 direction, so that the objective lens 2 is held at a neutral point in the tracking direction.

As described above, in this embodiment, the first magnetic piece 10 and the second magnetic piece 11 which are arranged on one side and on the other side of the focusing magnet portion 6a and the tracking magnet portion 6b respectively provide a focusing direction and a tracking direction. The objective lens 2 is held at the neutral point, but the restoring force is the first magnetic piece 10 and the second magnetic piece 1.
Since it is proportional to each area of No. 1, it is possible to change the resonance frequency in the focusing direction and the resonance frequency in the tracking direction by changing the areas of the first magnetic piece 10 and the second magnetic piece 11.

In particular, the resonance frequency in the focusing direction is almost changed by changing the area of the second magnetic piece 11, for example, the length of the side and the plate thickness while keeping the area of the first magnetic piece 10 as it is. Without changing the resonance frequency only in the tracking direction. In addition, the magnetic attraction force in the first magnetic piece 10 and the second magnetic piece 11
The so-called "side pressure" can be set in an arbitrary direction by appropriately taking a balance (resulting force) with the magnetic attraction force in.

The invention made by the present inventor has been specifically described based on the embodiments, but the invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say, for example, by making the width or thickness of both ends in the polarization direction of the magnetic piece larger than those of the central portion, or by making only the width or thickness of one end larger than those of the central portion. , The resonance frequency and the lateral pressure can be variously set.

[0025]

As described above, in the objective lens driving device according to the present invention, the first magnetic piece arranged to face the focusing magnet section and the second magnetic piece arranged to face the tracking magnet section, By holding the objective lens at each neutral point in the focusing direction and the tracking direction and changing the area of the second magnetic piece while keeping the area of the first magnetic piece as it is, the resonance frequency in the focusing direction is almost changed. Without changing the resonance frequency only in the tracking direction, and by appropriately adjusting the balance (resulting force) between the magnetic attraction force in the first magnetic piece and the magnetic attraction force in the second magnetic piece. Since it can be set in any direction, the degree of freedom in design can be increased and the appearance of the objective lens can be improved. The can be stably maintained,
In particular, it is possible to eliminate the meandering and the like caused by the backlash of the objective lens during focusing, and to obtain stable lens characteristics, and to improve the reliability and productivity of the objective lens driving device.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing a structure of an objective lens driving device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional explanatory view of the objective lens driving device shown in FIG.

FIG. 3 is a vertical cross-sectional explanatory view showing an enlarged objective lens portion.

FIG. 4 is an enlarged plan view of a drive magnet and a drive coil portion.

FIG. 5 is an enlarged perspective view of a drive magnet.

FIG. 6 is an explanatory front view showing an enlarged drive coil.

FIG. 7 is an explanatory plan view of a main part of the same device, showing a state of magnetic flux in a magnetic piece portion.

8A and 8B show states of magnetic flux in a magnetic piece portion, where FIG. 8A is a vertical sectional view of a focusing magnet portion, and FIG. 8B is a vertical sectional view of a tracking magnet portion.

[Explanation of symbols]

 1 Lens Holder 2 Objective Lens 3,4 Drive Coil 6 Drive Magnet 6a Focusing Magnet 6b Tracking Magnet 10 First Magnetic Piece 11 Second Magnetic Piece

Claims (1)

[Claims] 1. A lens holder provided so as to reciprocate in a focusing direction and a tracking direction while holding an objective lens, and a driving coil and a driving magnet which are arranged to face each other so as to give a driving force to the lens holder, A focusing magnet part and a tracking magnet part polarized and polarized in the focusing direction and the tracking direction of the drive magnet, and a magnetic piece arranged in a magnetic circuit formed by the focusing magnet part and the tracking magnet part. In the objective lens driving device configured to hold the objective lens at a neutral point by a restoring force generated in a focusing direction and a tracking direction based on a magnetic attraction force acting on the magnetic piece, Focusing magnetic pieces An objective lens driving device, characterized in that it comprises a first magnetic piece arranged to face the magnet unit, and a second magnetic piece arranged opposite to the tracking magnet portion.