JP2000276749A - Objective lens driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make suppressible the generation of an unwanted moment at the time of driving an objective lens by sizing a magnet greater than the movable range of a focusing coil or tracking coil. SOLUTION: A magnetic circuit is formed out of magnets 21a and 21b magnetized so as to confront the same poles, outer yokes 19a and 19b on the outside of the magnets 21a and 21b, a yoke made of a magnetic substance provided so as to connect inner yokes 20a and 20b through the air-core parts of tracking coils 18a and 18b in the gap of two focusing coils 17a and 17b in an optical axis direction and a lid-shaped yoke sharing the protection of a movable part with one part of the magnetic circuit while avoiding an objective lens 15. The magnets 21a and 21b are sized greater than the movable part of the focusing coils 17a and 17b or tracking coils 18a and 18b, the density of magnetic flux to be impressed to the coils is kept almost constant regardless of the position of the objective lens 15 and a structure not to apply the unwanted moment to the movable part is formed.

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 and an optical disk device using the same.
Magneto-optical disk device, CD-ROM device, DVD-RO
The present invention relates to an objective lens driving device used for an M device, a DVD-RAM device, and the like, and an optical disk device using the same.

[0002]

2. Description of the Related Art A conventional objective lens driving device has a plate-like magnetic body arranged on a side surface of a magnetic circuit including a magnetic plate and a magnet, as shown in, for example, Japanese Patent Application Laid-Open No. 7-320278.
With this plate-shaped magnetic material, the distribution of the magnetic flux density in the magnetic gap portion in the tracking direction is made uniform, a stable driving force is generated, and the inclination of the objective lens is suppressed.

[0003]

In an optical disk device, an optical head coarsely moves a mounted objective lens driving device in a disk radial direction. The objective lens driving device includes a movable portion including the objective lens and a support member that supports the movable portion, and finely moves the objective lens with respect to a disk serving as a recording medium. The movable portion of the objective lens driving device is usually provided with a magnetic circuit formed of an objective lens, a yoke, and a magnet, a focus coil arranged in the magnetic circuit to finely move the objective lens in a focus direction, and arranged in the magnetic circuit. And a tracking coil for finely moving the objective lens in the tracking direction.

[0004] The drive center of the focus coil substantially coincides with the center of force of the magnetic circuit formed by the yoke and the magnet, regardless of the position in the tracking direction. Therefore, when the objective lens moves in the tracking direction, a difference is generated between the center of gravity of the movable portion and the drive center, and a moment is generated by the driving force of the focus coil. Due to this moment force, the objective lens is tilted, and an optical aberration and defocus occur in a spot focused by the objective lens. As a result, there have been problems such as the deterioration of the reproduction signal of the recording medium and the inability to correctly record.

It is an object of the present invention to provide an objective lens driving device and an optical disk device equipped with the same, which are provided with a magnetic circuit that does not generate an unnecessary moment when the objective lens is driven.

[0006]

According to the present invention, there is provided a movable member including an objective lens mounted on an optical head for coarsely moving a disk in a radial direction, and a support member for supporting the movable member. An objective lens driving device comprising: an objective lens; a magnetic circuit formed by a yoke and a magnet; a focus coil arranged in the magnetic circuit to finely move the objective lens in a focus direction; And a tracking coil for finely moving the objective lens in the tracking direction, the size of the magnet is a focus coil or
We propose an objective lens driving device that takes over the movable range of the tracking coil.

The magnet may have a cross shape. A part of the magnet may be in a gap between the plurality of support members in the optical axis direction. A yoke is provided on the motor side that rotates the disk,
An optical disc device may be used in which the mutual interference between the motor and the magnetic field of the objective lens driving device is suppressed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, referring to FIGS.
Embodiments of an objective lens driving device and an optical disk device equipped with the same according to the present invention will be described.

FIG. 1 is a perspective view showing a schematic structure of an embodiment of an optical disk apparatus according to the present invention. Here, the optical disk device of the present invention will be described using a CD-ROM device as an example. When the compact disk 1 is placed on the disk tray 3, the CD-ROM device sends the disk 1 into the device by a disk loading mechanism (not shown). The disk 1 is magnetically attracted and fixed to the turntable 2 of the spindle motor 13 by the clamper 4 attached to the clamper holder 5.

The disk 1 is rotated at a predetermined number of revolutions by a spindle motor 13, and information is written or read out by an optical head 9 provided in a unit mechanical chassis 6 disposed below the disk 1. .
The optical head 9 is fixed to the unit mechanical chassis 6 so as to be able to roughly move in the radial direction of the disk 1 and has an objective lens driving device 10 mounted thereon. The unit mechanical chassis 6 is attached to the mechanical base 7 via vibration isolating legs 8a to 8d made of an elastic member. Outside these mechanisms, a bottom cover 11 and a top cover 12 are attached.

FIG. 2 is a perspective view showing a schematic structure of the unit mechanical chassis 6 mounted on the optical disk device according to the present invention. The disk 1 is rotated at a predetermined rotation speed by a spindle motor 13, and an optical head 9, which can move roughly in the radial direction of the disk 1, is disposed on a unit mechanical chassis 6 disposed below the disk 1.
Is mounted with an objective lens driving device 10 for finely moving the objective lens 15 in the focusing direction and the tracking direction.

FIG. 3 is a perspective view showing the appearance of an embodiment of the objective lens driving device according to the present invention. Here, the optical axis direction of the objective lens 15, that is, the Z axis is defined as the focus direction, and the radial direction of the disk 1, that is, the Y axis direction, is defined as the tracking direction. The objective lens 15 is held at the center of gravity of the XY plane of the lens holding member 16 made of a highly rigid plastic nonmagnetic material such as polycarbonate. Air-core coil-shaped focus coils 17a, 17b
Are arranged on the lens holding member 16 in parallel with the Z-axis direction around the objective lens 15. Similarly, the tracking coils 18a and 18b having an air-core coil shape are disposed on the lens holding member 16 in parallel with the objective lens 15 interposed therebetween in the Y-axis direction.

A magnet 21 magnetized so that its poles face each other.
a, 21b, outer yokes 19a, 19b outside the magnets 21a, 21b and two focus coils 17
a, 17b at the gap in the optical axis direction.
Inner yokes 20a, 20b penetrating the air cores of a, 18b
A yoke made of a magnetic material such as iron provided so as to tie and a lid-shaped yoke, which is not shown but also protects a part of a magnetic circuit and a movable portion while avoiding the objective lens 15, Form a magnetic circuit. This focus coil 17
Since a and 17b and tracking coils 18a and 18b are air-core coil-shaped, they can be directly wound around the lens holding member 16 and have a structure that can reduce assembly costs.

The inner yokes 20a and 20b increase the efficiency of the magnetic circuit and increase the magnetic flux density between the gaps, and also absorb the magnetic flux leaking in the Z-axis direction, thereby reducing the Z-axis vertical invalid lines of the tracking coils 18a and 18b. It also has the function of changing the driving force of the layer part to the tracking driving force. In order to prevent the influence of the magnetic field from the spindle motor 13 from affecting the magnetic circuit of the objective lens driving device, or the effect of the magnetic field of the objective lens driving device from affecting the magnetic circuit of the spindle motor 13 Side yokes 25a and 25b for magnetic shielding are provided in the tracking direction of the objective lens driving device.

The lens holding member 16 and the damping holder 2
2, suspensions 24a to 24d made of a spring material such as a phosphor bronze wire having a diameter of about 0.1 mm are arranged in parallel with each other in a symmetrical manner in the ZX plane and the XY plane, and between the suspension mounting boards 23 through the lens holding member 16 side. Is fixed by an adhesive or the like, and the suspension mounting board 23 side is fixed by soldering or the like. Damping holder 2
2 is filled with a viscoelastic member such as silicon gel to give a high damping to the suspensions 24a to 24d.

The objective lens driving device according to the present embodiment includes a magnet 2
The size of the focus coils 17a, 17a
b or the movable range of the tracking coils 18a and 18b or more, regardless of the position of the objective lens 15, the magnetic flux density applied to the coil is kept substantially constant, and an unnecessary moment is not applied to the movable portion.

The present invention provides focus coils 17a, 17
b, a magnetic circuit structure having a uniform magnetic flux density distribution constituted by the tracking coils 18a and 18b, the outer yokes 19a and 19b, and the inner yokes 20a and 20b. The shape, the method of supporting the movable portion including the objective lens 15, and the like are not limited, so that various variations can be developed without departing from the technical scope of the present invention.

FIG. 4 is a view showing the principle that the objective lens 15 is tilted by moving the objective lens 15 by Δy in the tracking direction, and a moment force 30 is generated by the focus coil driving force 29. In a conventional magnetic circuit, a focus coil 26 having an air-core coil shape and a yoke 27 are arranged in the air-core portion, and the yoke 27 and the magnet 28 are arranged so that one side of the focus coil 26 has a gap.

When a current 31 is applied to the focus coil 26, the focus coil driving force 2
9 occurs. The drive center 29 is located at the center of the magnetic circuit formed by the yoke 27 and the magnet 28 regardless of the position of the focus coil 26. On the other hand, the support center 33 is determined by the support member and the objective lens 15
It moves with the position of the movable part including the focusing coil 26 and the focusing coil 26.

Therefore, a difference is generated between the support center 33 and the drive center 32, and a moment force 30 is generated with the difference being the arm length and the rotation center as the support center 33. The movable part including the objective lens 15 and the focus coil 26 is tilted by the moment force 30, and the objective lens 15 is tilted. At this time, the difference between the support center 33 and the drive center 32, that is, the arm length is substantially equal to the tracking direction movement amount Δy. Here, if the fine movement of the movable part is in a low frequency range, the center of moment can be set as the support center 33, but in the high frequency range, the moment center becomes the center of gravity of the movable part.

However, the objective lens driving device is generally designed so that the center of gravity substantially coincides with the center of support 33.
Regardless of the frequency band, the principle of tilting the objective lens 15 does not change.

FIG. 5 shows a magnetic circuit of the objective lens driving device according to the present invention. The magnetic fluxes 34a and 34b by the magnets 21a and 21b flow as shown in the figure. Here, currents 35a, 3a are applied to the focus coils 17a, 17b.
5b flows as shown in the figure, the focus coil driving forces 36a, 36b, 37a, 3 according to Fleming's law.
7b occurs. Similarly, the tracking coils 18a,
When currents 38a and 38b are applied to the 18b as shown in the figure, the tracking coil driving forces 39a, 39b and 40
a and 40b occur. This force causes the objective lens 15
Is movable in the focus direction and the tracking direction.

FIGS. 6A and 6B show the relationship between the focus coils 17a and 17b of the present invention and the magnets 21a and 21b. Air-core coil-shaped focus coil 1
7a and 17b are arranged as shown in the drawing in parallel with the Z-axis direction around the objective lens 15, and the movable portion is movable in the focus direction Δzmax and the tracking direction Δymax. In FIG. 6, the movable range is shown by hatching. Assuming that the focus coil width is Lcafw, the magnet width Lmafw is L
Assuming that mafw> Lcafw + 2Δymax is satisfied and the focus coil height is Lcafh, the magnet height Lmaf
h satisfies Lmafh> Lcafh + 2Δzmax, in other words, the size of the magnet is greater than the movable wave of the coil.

By taking the size of the magnet, the magnetic flux density applied to the focus coils 17a and 17b is almost constant irrespective of the position of the focus coils 17a and 17b. The drive center, support center, and center of gravity can be matched,
The objective lens 1 in which the moment force 30 described above does not occur.
It is possible to realize an objective lens driving device that suppresses the inclination of 5 to almost zero.

Similarly, although not shown, assuming that the magnet size and the tracking width are Lctrw for the tracking coils 18a and 18b, the magnet width Lmtrw is Lmtr.
Assuming that trw> Lctrw + 2Δymax is satisfied and the focus coil height is Lctrh, if the magnet height Lmtrh is the size of a magnet satisfying Lmtrh> Lctrh + 2Δzmax, the tracking coils 18a and 18b
Unnecessary moment due to is not generated.

Further, the magnets 21a, 21 satisfying the above conditions
Considering the minimum volume of the shape 1b, it takes a cross shape. At this time, the magnet 21 is used to effectively use the space.
a, 21b in the tracking direction
4a and the gap between the suspension 24b in the Z-axis direction and the optical axis direction, and the suspensions 24c and 24d in the Z-axis and optical axis direction gap, respectively, so that the objective lens driving device can be downsized.

FIG. 7 shows a magnetic circuit of the objective lens driving device in which the cross-shaped magnets 21a and 21b are arranged. In order to save space, the protrusions in the tracking direction of the magnets 21a and 21b are connected to the suspensions 24a and 24c.
And the suspensions 24b and 24d are arranged in gaps in the Z-axis and optical axis directions, respectively.

[0028]

According to the present invention, the tilt of the objective lens can be suppressed to almost zero without generating a moment force due to the driving force of the focus coil when the objective lens is moved in the tracking direction.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic structure of an embodiment of an optical disk device according to the present invention.

FIG. 2 is a perspective view showing a schematic structure of an embodiment of a mechanical unit according to the present invention.

FIG. 3 is a perspective view showing an appearance of an embodiment of an objective lens driving device according to the present invention.

FIG. 4 is a diagram illustrating a principle that an objective lens is moved by Δy in a tracking direction, a moment force is generated by a focus coil driving force, and the objective lens is tilted.

FIG. 5 is a perspective view illustrating a magnetic circuit configuration of the objective lens driving device.

6 (a) and 6 (b) are a plan view and a front view of FIG. 6 (b) for explaining a dimensional relationship between a coil and a magnet according to the present invention.

FIG. 7 is a perspective view showing an appearance of a cross-shaped magnet according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Disc, 2 ... Turntable, 3 ... Disc tray, 4 ... Clamper, 5 ... Clamper holder, 6 ... Unit mechanical chassis, 7 ... Mechanical base, 8a-8d ... Vibration-proof legs, 9
... optical head, 10 ... objective lens driving device, 11 ... bottom cover, 12 ... top cover, 13 ... spindle motor, 15 ... objective lens, 16 ... lens holding member, 17
a, 17b, 26: Focus coil, 18a, 18b
... Tracking coils, 19a, 19b ... outer yokes, 20a, 20d ... inner yokes, 21a, 21b, ...
28: magnet, 22: damping holder, 23: suspension mounting board, 24a to 24d: suspension, 25a, 25b: side yoke, 27: yoke, 2
9, 36a, 36b, 37a, 37d: Focus coil driving force, 30: Moment force, 31, 35a, 35
b, 38a, 38b current, 32 drive center, 33 support center, 34a, 34b magnetic flux, 39a, 39b, 40
a, 40b: Tracking coil driving force.

Continued on the front page (72) Inventor Seiichi Kato 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. (72) Inventor Katsuhiko Kimura 502-Kindachi-cho, Tsuchiura-city, Ibaraki Pref. In-house (72) Inventor Michio Miura 1 Kitano, Makino, Mizusawa-shi, Iwate Prefecture Inside Hitachi Media Electronics Co., Ltd. (72) Inventor Akio Yabe 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi Image Information System ( 72) Inventor Shinya Fujimori 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Multimedia System Development Division, Hitachi, Ltd. (72) Inventor Nobuyuki Maeda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Multi Corporation Hitachi, Ltd. F-term in the Media System Development Division (reference) 5D118 DC03 EA02 ED08

Claims (1)

[Claims] 1. An objective lens driving device mounted on an optical head for coarsely moving a disk in a radial direction and comprising a movable portion including an objective lens and a support member for supporting the movable portion, comprising: an objective lens; And a magnetic circuit formed by a magnet, a focus coil disposed in the magnetic circuit to finely move the objective lens in a focusing direction, and a tracking coil disposed in the magnetic circuit to finely move the objective lens in the tracking direction. In the lens driving device, the size of the magnet is set to the focus coil or
An objective lens driving device, wherein the objective lens driving device is set to be larger than a movable range of a tracking coil.