JP2897090B2 - 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 for adjusting an optical axis of an optical disk device for optically writing or reading information on a disk-shaped recording medium.

[0002]

2. Description of the Related Art An optical disk apparatus is designed to move an objective lens in a direction perpendicular to the surface of a recording medium in order to correct a focus deviation or a tracking deviation due to a vertical movement of a warp of a disk-shaped recording medium such as a compact disk or an optical disk. Optical axis direction (hereinafter, referred to as a focus direction F) and a radial direction parallel to the recording medium surface (hereinafter, referred to as a tracking direction T) to perform optical recording or reproduction. In recent years, portable and personalized data file devices using compact disk players and optical disks have been developed, and optical pickups used in these devices have been required to be further reduced in size and thickness. Hereinafter, an example of a conventional objective lens driving device for an optical pickup will be described with reference to the drawings. FIG. 14 is an exploded perspective view showing the structure of a conventional objective lens driving device, and FIG. 15 is a front view showing the structure of the entire optical pickup. 14 and 15, 1 is an objective lens, 2
Holds the objective lens 1 with a lens holder. 7a and 7b are magnets fixed to the lens boulder 2, and 6a to 6d support the lens holder 2 with metal wires. 3 is a magnetic yoke and a magnet 7
a and 7b form a magnetic circuit. Reference numeral 5 denotes a tracking coil, and reference numeral 4 denotes a focus coil which is wound around the magnetic yoke 3. Reference numeral 8 denotes a base to which one ends of metal wires 6a to 6d are attached. Reference numeral 9 denotes a printed circuit board, which is attached to the base 8 for soldering and fixing the metal wires 6a to 6d. 10 is an optical unit, a semiconductor laser 30 as a light source,
In addition, a half mirror 32 for guiding light emitted from the semiconductor laser 30 to the objective lens 1, a rising mirror 13, and a photodetector 31 for detecting information are attached.

[0003] The operation of the objective lens driving device configured as described above will be described below. An operation of driving the objective lens in two axes of the focus direction F and the tracking direction T in order to correct a focus shift due to a vertical movement of the warpage of the disk or a tracking shift due to eccentricity or the like will be described. In the driving in the focus direction F, the lens holder 2 with the objective lens 1
Is translated through metal wires 6a to 6d by an electrokinetic transducer composed of magnets 7a and 7b attached to the optical unit 10 and a magnetic yoke 3 wound around the focus coil 4 and attached to the optical unit 10. can get. In the tracking direction T, the lens holder 2 on which the objective lens 1 is mounted is moved by the magnets 7a,
7b and a magnetic yoke 3 wound around the tracking coil 5 and attached to the optical unit 10, and is obtained by performing a translational movement through metal wires 6a to 6d. In addition, the entire objective lens driving device is access-driven by a motor in an access direction on the recording medium (the same direction as the tracking direction T). here,
In order to increase the rigidity of the movable part and reduce the heat generation of the movable part during driving, when achieving the miniaturization and thinning of the entire device,
MM (Movin) that attaches magnets 7a and 7b to lens holder 2
g Magnet) type drive system.

[0004]

In the objective lens driving device constructed as described above, the displacement frequency characteristic changes due to the unbalance of the driving force generated by the two magnets 7a and 7b, and at the same time, the lens holder 2 is supported. The load acting on the metal wires 6a to 6d changes. Hereinafter, problems of the conventional objective lens driving device will be described with reference to the drawings. FIGS. 4 and 7 are plan views showing the positional relationship between the movable part including the objective lens 1, the lens holder 2 and the magnets 7a and 7b and the magnetic yoke 3, and the state of the generated attraction force.
5 and 6 show an objective lens 1, a lens holder 2, and a magnet 7.
FIG. 4 is a plan view of a main part showing a positional relationship between a movable part composed of a and 7b and a magnetic yoke 3 and a state of generated driving force.
FIG. 8 is a Bode diagram showing the gain of the displacement frequency characteristic of the objective lens driving device in an ideal state, and FIG. 9 is a Bode diagram showing the phase of the displacement frequency characteristic of the objective lens driving device in an ideal state. FIG. 10 is a Bode diagram showing the gain of the displacement frequency characteristic of the objective lens driving device in the state of FIG. 6, and FIG.
FIG. 7 is a Bode diagram showing a phase of a displacement frequency characteristic of the objective lens driving device in the state of FIG. 12 is a Bode diagram showing the gain of the displacement frequency characteristic of the objective lens driving device in the state of FIG. 5, and FIG. 13 is a Bode diagram showing the phase of the displacement frequency characteristic of the objective lens driving device in the state of FIG. is there. As shown in FIG. 5, when the magnetic flux density between the magnet 7a and the magnetic yoke 3 is higher than the magnetic flux density between the magnet 7b and the magnetic yoke 3, the driving force F1 generated by the focus coil 4 , F2 are driving forces F1 generated by the magnet 7a.
Is larger than F2, and the displacement frequency characteristics of the objective lens 1 are as shown in FIGS.
A phase lead occurs near 00 Hz. On the contrary, as shown in FIG. 6, the magnetic flux density between the magnet 7a and the magnetic yoke 3
When the magnetic flux density is lower than the magnetic flux density between the magnet 7b and the magnetic yoke 3, the driving force F generated by the focus coil 4
1 and F2, the driving force F2 generated by the magnet 7b is larger than F1, and the displacement frequency characteristics of the objective lens 1 are as shown in FIGS.
A phase lag occurs in the vicinity. Here, when a phase delay as shown in FIG. 11 occurs, the entire servo system becomes unstable. Therefore, considering the stability of the servo system, as shown in FIG. 5, the magnetic flux density between the magnet 7a and the magnetic yoke 3 is higher than the magnetic flux density between the magnet 7b and the magnetic yoke 3. It is desirable to do. However, in this case, the attractive force Fa between the magnet 7a and the magnetic yoke 3 shown in FIG. 4 is larger than the attractive force Fb between the magnet 7b and the magnetic yoke 3, so that the metal wires 6a to 6d
(6a and 6c are not shown), a buckling load is applied, and there is a problem that the probability of collision between the magnet 7a and the focus coil 4 increases when disturbance vibration is applied. In view of the above problems, an object of the present invention is to provide an MM-driven objective lens driving device that realizes stable displacement frequency characteristics and has a very low probability of collision between a movable portion and a driving coil. Things.

[0005]

In order to solve the above-mentioned problems, an objective lens driving device according to the present invention has an objective lens fixed to a lens holder on a side close to a base with respect to a magnetic yoke and sandwiching the magnetic yoke. Of the two magnets arranged, the magnetic flux density between the magnet near the objective lens and the magnetic yoke is higher than the magnetic flux density between the magnet far from the objective lens and the magnetic yoke. .

[0006]

According to the present invention, the attractive force between the magnet and the magnetic yoke closer to the objective lens is greater than the attractive force between the magnet and the magnetic yoke farther from the objective lens. Since a tensile load acts on the supporting metal wire, the probability that the magnet and the drive coil collide with each other when disturbance vibration is applied becomes extremely low. In addition, the driving force generated by the magnet closer to the objective lens is larger than the driving force generated by the magnet farther from the objective lens, and the displacement frequency characteristics of the objective lens are stable because the phase delay does not occur. It is possible to realize an objective lens driving device that realizes characteristics and has a very low probability of collision between the movable portion and the driving coil.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An objective lens driving device according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a front view of an objective lens driving device according to one embodiment of the present invention, and FIG.
FIG. 3 is an exploded perspective view showing the configuration. 1, 2, 3, 1 denotes an objective lens, 2 is a lens holder, for holding the objective lens 1. 7a, 7b in the permanent <br/> magnet is attached to the lens holder 2. 6a ~
6d is a metal wire, support the lens holder 2. A magnetic yoke 3 forms a magnetic circuit with the permanent magnets 7a and 7b. Reference numeral 5 denotes a tracking coil, and reference numeral 4 denotes a focus coil , each of which is wound around the magnetic yoke 3. Reference numeral 8 denotes a base to which one ends of the metal wires 6a to 6b are attached. 9
In the printed circuit board is mounted on the base 8 to soldered metal wires 6 a to 6 d. Reference numeral 10 denotes an optical unit to which a rising mirror 13 for guiding light emitted from a semiconductor laser as a light source to the objective lens 1 is attached.

[0008] The operation of the objective lens driving device configured as described above will be described below. An operation of driving the objective lens 1 in two axes, the focus direction F and the tracking direction T, will be described. In the driving in the focus direction F, the lens holder 2 to which the objective lens 1 is attached is attached to the permanent magnets 7a and 7b attached to the lens holder 2 and the optical unit 10 and the magnetic yoke 3 around which the focus coil 4 is wound. the electrodynamic transducer ing from, obtained by translation through the metal wire 6 a to 6 d. In the driving in the tracking direction T, the lens holder 2 to which the objective lens 1 is attached is attached to the permanent magnets 7a and 7b attached to the lens holder 2 and the optical unit 10, and the tracking coil 5 is wound. the electrodynamic transducer ing from the yoke 3, obtained by translation through the metal wire 6 a to 6 d. Moreover, the entire objective lens driving device, the access direction of the recording medium (the tracking direction T is the same direction) Ru accessed driven by motor. The objective lens of the present invention
The permanent magnet 7a and the permanent magnet 7b of the drive unit are opposed with the same polarity.
The magnetic flux density between the magnetic yoke 3 and the permanent magnet 7a
Alternatively, the magnetic flux density between the magnetic yoke 3 and the permanent magnet 7b
When either of them is increased, the fork wound around the magnetic yoke 3
Current flowing through the focusing coil 4 and the tracking coil 5
To increase the sensitivity of the objective lens drive,
Simple winding of the focus coil 4 and tracking coil 5
You can do it. Incidentally, in the objective lens driving device of the present invention, as shown in FIG. 2, the gap between the side of the permanent magnet 7a and the magnetic yoke 3 close to the objective lens 1 includes a permanent magnet 7a on the side not far to the objective lens 1 It is arranged to be smaller than the cap with the magnetic yoke 3. Therefore, the attractive force between the permanent magnet 7a closer to the objective lens 1 and the magnetic yoke 3 is increased by the attractive force between the permanent magnet 7b closer to the objective lens 1 and the magnetic yoke 3. to become larger than the metal to metal wire 6a~6d supporting the movable portion
Since a load is applied in the direction along the line, the probability that the permanent magnet 7b collides with the focus coil 4 when disturbance vibration is applied becomes extremely low. This permanent magnet 7a and magnetism
Attraction force between the yoke 3 and the permanent magnet 7b and the magnetic yoke 3
As means for strengthening the suction force between
In addition to adjusting the gap, for example, the permanent magnet 7a and permanent
The magnetic material applied to the magnet 7b may be changed,
Even if the magnetization of the stone 7a and the permanent magnet 7b are made different, etc.
Can be achieved. Further, the permanent magnet 7 on the side close to the objective lens 1
a, the driving force generated by the
Larger than the driving force by the permanent magnet 7b thus produced, as the displacement frequency characteristic of the objective lens 1 for a phase delay no objective lens driving device having stable displacement frequency characteristics can be realized.

[0009]

As described above, according to the present invention, the objective lens is fixed to the lens holder on the side close to the base with respect to the magnetic yoke, and of the two magnets arranged with the magnetic yoke therebetween,
The configuration in which the magnetic flux density between the magnet near the objective lens and the magnetic yoke is higher than the magnetic flux density between the magnet far from the objective lens and the magnetic yoke allows the magnet near the objective lens and the magnetic yoke to be higher. Since the attractive force between the yokes is larger than the attractive force between the magnet and the magnetic yoke far from the objective lens, a tensile load acts on the metal wire supporting the movable part, and disturbance vibration is applied. In such a case, there is an effect that the probability that the magnet and the drive coil collide is extremely low. In addition, the driving force generated by the magnet closer to the objective lens is larger than the driving force generated by the magnet farther from the objective lens, and the displacement frequency characteristics of the objective lens are stable because the phase delay does not occur. It is possible to realize an objective lens driving device that realizes characteristics and has a very low probability of collision between the movable portion and the driving coil.

[Brief description of the drawings]

FIG. 1 is a front view of an objective lens driving device according to an embodiment of the present invention.

FIG. 2 is a plan view of a main part of an objective lens driving device according to an embodiment of the present invention.

FIG. 3 is an exploded perspective view illustrating a configuration of an objective lens driving device according to an embodiment of the present invention.

FIG. 4 is a plan view of a main part showing a positional relationship between a movable part and a magnetic yoke of a conventional objective lens driving device and a state of a generated attraction force.

FIG. 5 is a plan view of a main part showing a positional relationship between a movable portion and a magnetic yoke of a conventional objective lens driving device and a state of generated driving force.

FIG. 6 is a plan view of a main part showing a positional relationship between a movable part and a magnetic yoke of a conventional objective lens driving device and a state of generated driving force.

FIG. 7 is a plan view of a main part showing a positional relationship between a movable portion and a magnetic yoke of a conventional objective lens driving device and a state of a generated attraction force.

FIG. 8 is a Bode diagram showing a gain of a displacement frequency characteristic in an ideal state of a conventional objective lens driving device.

FIG. 9 is a Bode diagram showing a phase of a displacement frequency characteristic in an ideal state of a conventional objective lens driving device.

FIG. 10 is a Bode diagram showing a gain of displacement frequency characteristics of the conventional objective lens driving device in the state of FIG.

FIG. 11 is a Bode diagram showing a phase of a displacement frequency characteristic of the conventional objective lens driving device in the state of FIG. 6;

12 is a Bode diagram showing the gain of the displacement frequency characteristic of the conventional objective lens driving device in the state of FIG.

FIG. 13 is a Bode diagram showing the phase of the displacement frequency characteristic of the conventional objective lens driving device in the state of FIG. 5;

FIG. 14 is an exploded perspective view showing a configuration of a conventional objective lens driving device.

FIG. 15 is a front view of a conventional objective lens driving device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Objective lens, 2 ... Lens holder, 3 ... Magnetic yoke, 4 ... Focus coil, 5 ... Tracking coil, 6a-6d ... Metal wire, 7a, 7b ... Magnet, 8 ... Base, 9 ... Printed circuit board, 10 ... Optical Unit, 13…
Start-up mirror, 30… Semiconductor laser, 31… Photodetector,
32: half mirror, F: focus direction, T: tracking direction.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mamoru Mori 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/09 -7/095

Claims (2)

(57) [Claims] An objective lens for optically writing information on an information layer provided on a disc-shaped recording medium or condensing a light beam for optically reading information from the information layer is provided on the information layer of the disc-shaped recording medium. An objective lens driving device that drives in a radial direction parallel to a layer and an optical axis direction of the objective lens perpendicular to the information layer of the disc-shaped recording medium, wherein the objective lens and the optical axis direction A lens holder for holding the objective lens in the first opening formed in the optical disk, and respective central axes parallel to the optical axis of the objective lens are substantially aligned with the optical axis and the tangential direction of the disc-shaped recording medium. As the first
A movable part comprising two permanent magnets disposed so as to face two openings, and one end of the movable part being substantially perpendicular to the optical axis direction and the radial direction and substantially parallel to each other. Fixed to
A plurality of elastic members having the other end fixed to the base, and a drive coil for driving the movable portion are attached,
The second permanent magnet is sandwiched between the two permanent magnets .
A magnetic yoke disposed in an opening of the magnetic head, wherein the objective lens is disposed between the magnetic yoke and the base, and the objective lens of the two permanent magnets is provided. Wherein the magnetic flux density between the permanent magnet and the magnetic yoke closer to the objective lens is higher than the magnetic flux density between the permanent magnet and the magnetic yoke farther from the objective lens. Drive. 2. A gap between the permanent magnet and the magnetic yoke closer to the objective lens is smaller than a gap between the permanent magnet and the magnetic yoke farther from the objective lens. 2. The objective lens driving device according to claim 1, wherein the objective lens driving device is disposed.