JPH103675A - Objective lens driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep excellently a slide of a lens bobbin for a support shaft and to apply it to an optical recording medium with high density recording by diameter size reducing parts in the vicinity of opening parts in the bearing hole of the lens bobbin and contact sliding it on the outer peripheral surface of the support shaft. SOLUTION: This device is provided with the lens bobbin 1 attaching an objective lens 2 and a columnar support shaft 7 movably supporting the bobbin 1, and the bobbin 1 is provided with the bearing hole 9 penetrated with the support shaft 7, and the lens 2 whose optical axis is made parallel to the support shaft 7 and is attached to the bobbin 1 on a position parted from the hole 9. The hole 9 is diameter size reduced in sliding parts 14 of the parts in the vicinity of both side opening parts then the size expansion part of the central part. The bobbin 1 is slid only on inner wall parts 17 of respective sliding parts 14 for the support shaft 7. Further, the hole 9 is made so that the contact area for the support shaft 7 becomes small, and the slide for the support shaft 7 is performed in the state with less friction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field of an objective lens driving device for moving an objective lens in an optical pickup device to follow an optical recording medium.

[0002]

2. Description of the Related Art Hitherto, optical recording media such as optical disks and magneto-optical disks have been proposed, and optical pickup devices for writing and reading information signals to and from such optical recording media have been proposed.

When the optical recording medium is configured as a disk-shaped recording medium, it has a disk-shaped transparent substrate and a signal recording layer formed on the transparent substrate. On this signal recording layer, a recording track formed in a substantially concentric spiral shape is formed. In this signal recording layer, information signals are recorded along the recording tracks. The optical pickup device includes a light source, and an objective lens that condenses a light beam emitted from the light source on a signal recording layer of the optical recording medium.
And a photodetector for detecting the light beam reflected by the signal recording layer.

[0004] The disk-shaped recording medium is rotated while its central portion is held. In the optical pickup device, the objective lens is opposed to the main surface of the disk-shaped recording medium to be rotated, and the optical pickup device is moved and operated over the inner and outer peripheries of the disk-shaped recording medium. Then, the optical pickup device sequentially collects and irradiates the light beam along the recording track over the entire surface of the signal recording layer of the disc-shaped recording medium, thereby covering the entire surface of the signal recording layer. Thus, writing and reading of an information signal can be performed.

[0005] The transparent substrate of the disk-shaped recording medium is formed in a flat plate shape, but may have a slight distortion. Therefore, when the central portion is rotated and operated, so-called surface run-out occurs. . That is, the signal recording layer of the disc-shaped recording medium periodically moves in a direction of coming and going with respect to the objective lens of the optical pickup device when the disc-shaped recording medium is rotated while the center portion is held. I do. The recording track of the disc-shaped recording medium is formed so that the center of curvature coincides with the center of the transparent substrate, but may have a slight eccentricity, so that the transparent substrate holds the central portion. When it is rotated and operated, it periodically moves in a direction perpendicular to the optical axis of the objective lens of the optical pickup device.

[0006] In order to make the objective lens follow such surface wobble and eccentricity, the optical pickup device is provided with an objective lens driving device (actuator). The objective lens driving device includes a lens bobbin on which the objective lens is mounted, and a cylindrical support shaft that movably supports the lens bobbin. That is,
The lens bobbin has a bearing hole through which the support shaft is inserted. By inserting the support shaft through the bearing hole, the lens bobbin moves in the axial direction of the support shaft and in the direction around the support shaft. It has been made possible. The objective lens is attached to the lens bobbin with an optical axis parallel to the axis of the support shaft.

A focusing drive coil and a tracking drive coil are mounted on the lens bobbin. The objective lens driving device has a magnetic circuit that positions each of the driving coils in a magnetic field.

In the objective lens driving device, when a driving current is supplied to the focus driving coil, the lens bobbin is acted on by a magnetic field formed by the magnetic circuit, and acts in the axial direction of the support shaft, ie, in the axial direction of the support shaft. The moving operation is performed in the focus direction (the optical axis direction of the objective lens). Further, in the objective lens driving device, when a driving current is supplied to the tracking drive coil, the lens bobbin is rotated by the magnetic field formed by the magnetic circuit around the support shaft. In the tracking direction of the objective lens (direction orthogonal to the optical axis of the objective lens)
Move to.

In the objective lens driving device, the focus drive coil is based on a focus error signal indicating a shift amount in the focus direction between a focal point of the light beam by the objective lens and a surface portion of the signal recording layer. The supply of the focus drive current always positions the focal point on the surface of the signal recording layer. Further, the objective lens driving device supplies a tracking drive current to the tracking drive coil based on a tracking error signal indicating a shift amount in the tracking direction between the focal point of the light beam by the objective lens and the recording track. As a result, the focal point is always positioned on the recording track.

[0010]

On the other hand, in an optical recording medium such as an optical disk as described above, an information signal recording medium is used as an auxiliary storage device for a computer or as a recording medium for audio and image signals. Higher densities are being promoted.

In order to write and read information signals on an optical recording medium having a high recording density, the objective lens must have a larger numerical aperture (NA) and the light source must have a higher numerical aperture. It is necessary to shorten the light emission wavelength of the optical recording medium and reduce the beam spot formed by condensing the light beam on the optical recording medium.

However, when the numerical aperture of the objective lens increases, the inclination of the optical recording medium, the thickness unevenness of the transparent substrate of the optical recording medium, and the defocus (defocus) of the light beam on the optical recording medium. , And writing and reading of information signals to and from this optical recording medium becomes difficult.

For example, when an inclination (skew) of the optical axis of the objective lens with respect to the optical recording medium occurs, a wavefront aberration occurs in a light beam condensed on the signal recording surface,
The electric signal (RF output) output from the photodetector is affected.

The wavefront aberration is dominated by tertiary coma which occurs in proportion to the cube of the numerical aperture of the objective lens and about the square of the tilt angle (skew angle) of the optical recording medium. Therefore, the permissible value for the tilt of the optical recording medium is inversely proportional to the cube of the numerical aperture of the objective lens, that is, it decreases as the numerical aperture increases.

In the objective lens driving device, the inclination of the support shaft with respect to the optical recording medium can maintain necessary accuracy by adjusting and adjusting the mechanical accuracy at the time of mounting. Therefore, in an objective lens driving device used for an optical pickup device for performing writing and reading of an information signal on an optical recording medium in which the recording density of an information signal is increased, the lens bobbin with respect to the support shaft It is necessary to regulate the inclination strictly.

In order to restrict the inclination of the lens bobbin with respect to the support shaft strictly, it is preferable to make the gap between the outer peripheral surface of the support shaft and the inner peripheral surface of the bearing hole as narrow as possible. However, if the gap between the outer peripheral surface of the support shaft and the inner peripheral surface of the bearing hole is excessively narrowed, the bearing hole may not be able to slide on the support shaft.

Accordingly, the present invention has been proposed in view of the above-described circumstances, and it has been proposed that a lens bobbin on which an objective lens is mounted is satisfactorily slid with respect to a spindle supporting the lens bobbin. An objective lens suitable for application to an optical pickup device for writing and reading information signals on an optical recording medium in which the inclination of the lens bobbin with respect to the support shaft is strictly controlled and the recording density of information signals is increased. An object of the present invention is to solve the problem of providing a driving device.

[0018]

In order to solve the above-mentioned problems, an objective lens driving device according to the present invention comprises a columnar support shaft, a bearing to which an objective lens and a drive coil are mounted and through which the support shaft is inserted. A lens bobbin having a hole and supported by the support shaft so as to be movable in the axial direction of the support shaft and in the direction around the support shaft when the support shaft is inserted through the bearing hole;
A magnetic circuit for positioning the drive coil in a magnetic field,
In the bearing hole of the lens bobbin, the portions near the openings on both sides are smaller in diameter than the central portion, and the portions near these openings are to be in sliding contact with the outer peripheral surface of the support shaft. .

According to the present invention, in the objective lens driving device, at least a portion around the bearing hole of the lens bobbin is formed by integral molding means.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

The objective lens driving device according to the present invention is used in the configuration of an optical pickup device for writing and reading information signals on a disk-shaped optical recording medium such as a so-called optical disk or magneto-optical disk.

As shown in FIG. 1, the disc-shaped optical recording medium has a disk-shaped transparent substrate and a signal recording layer formed on the transparent substrate. On this signal recording layer, a recording track formed in a substantially concentric spiral shape is formed. In this signal recording layer, information signals are recorded along the recording tracks.

The optical pickup device includes a semiconductor laser 12 serving as a light source and a light beam emitted from the semiconductor laser
And a photodetector 13 for detecting a light beam reflected by the signal recording layer on the signal recording layer. In this optical pickup device, the semiconductor laser 12 and the photodetector 13 are provided on the same semiconductor substrate to form a so-called laser coupler 11.

The disk-shaped optical recording medium 101 has a central portion held by a disk table (not shown).
It is rotated by a spindle motor. In the optical pickup device, the objective lens 2 is opposed to the main surface of the disk-shaped optical recording medium 101 that is rotated, and the optical pickup apparatus is moved over the inner and outer circumferences of the disk-shaped optical recording medium 101. The optical pickup device sequentially collects and irradiates the light flux along the recording track over the entire surface of the signal recording layer of the disk-shaped optical recording medium 101, thereby obtaining the entire surface of the signal recording layer. Over and over, information signals can be written and read.

When the transparent substrate of the disk-shaped optical recording medium 101 is rotated while its central portion is held, so-called surface run-out occurs. In other words, the signal recording layer of the disc-shaped optical recording medium 101 has a direction in which the disc-shaped optical recording medium 101 comes into contact with and separates from the objective lens 2 of the optical pickup device when the disc-shaped optical recording medium 101 is rotated while its central portion is held. Move periodically. The recording track of the disc-shaped optical recording medium 101 moves periodically in a direction perpendicular to the optical axis of the objective lens 2 of the optical pickup device when the transparent substrate is rotated while the central portion is held. I do.

The objective lens driving device according to the present invention causes the objective lens 2 to follow the surface deflection or eccentricity of the disk-shaped optical recording medium 101. As shown in FIGS. 1 to 3, the objective lens driving device has a lens bobbin 1 on which the objective lens 2 is mounted, and a cylindrical support shaft 7 that movably supports the lens bobbin 1. It is configured. The support shaft 7 stands substantially perpendicularly to the base plate 6 of the objective lens driving device.

The lens bobbin 1 has a bearing hole 9 through which the support shaft 7 is inserted. By inserting the support shaft 7 into the bearing hole 9, the axial direction of the support shaft It is movable in the direction around the support shaft.
The objective lens 2 is attached to the lens bobbin 1 at a position separated from the bearing hole 9 with an optical axis parallel to the axis of the support shaft 7. Therefore, when the lens bobbin 1 is moved with respect to the support shaft 7, the objective lens 2 moves in the optical axis direction of the objective lens 2 indicated by an arrow F in FIG. The moving operation is performed in a direction perpendicular to the optical axis of the objective lens 2 indicated by an arrow T in FIG.

The lens bobbin 1 is provided with focus drive coils 3 and 3 and tracking drive coils 4 and 4 which are drive coils, respectively. A pair of the focus drive coils 3 and 3 are attached to both side portions of the lens bobbin 1 with the winding axis direction being parallel to the optical axis of the objective lens. The tracking drive coils 4 and 4 are mounted on both side surfaces of the lens bobbin 1 with the direction of the winding axis perpendicular to the optical axis of the objective lens.

Further, the objective lens driving device has a magnetic circuit for positioning each of the driving coils in a magnetic field. The magnetic circuit includes a pair of U-shaped yokes 10, 10 erected on the base plate 6 and the U-shaped yokes 1.
A pair of magnets 5 attached corresponding to 0, 10
And 5. Each of the above U-shaped yokes 10, 1
0 has a pair of contact pieces which are formed in parallel with each other and are formed by bending a plate-shaped magnetic material into a U-shape, and have a base end connected thereto. It is arranged upright on the base plate 6. Each of the U-shaped yokes 10, 10 has one contact piece inserted into each of the focus drive coils 3, 3 so as to correspond thereto. Also,
The magnets 5 and 5 are opposed to the tracking drive coils 4 and 4, respectively.

In this objective lens driving device, when a driving current is supplied to the focus driving coils 3, 3,
The lens bobbin 1 receives an action from a magnetic field formed by the magnetic circuit, and as shown by an arrow F in FIG. 1, the axial direction of the support shaft 7, that is, the focus direction (the optical axis direction of the objective lens 2). ). In the objective lens driving device, when a driving current is supplied to the tracking driving coils 4 and 4, the lens bobbin 1
Is rotated about the axis of the support shaft 7 under the action of the magnetic field formed by the magnetic circuit, and moves the objective lens 2 in the tracking direction (the direction orthogonal to the optical axis of the objective lens 2).
Move to.

In this objective lens driving device, the focus drive coils 3 and 3 are provided with a focus indicating the amount of shift in the focus direction between the focal point of the light beam by the objective lens 2 and the surface of the signal recording layer. The focus point is always located on the surface of the signal recording layer by supplying the focus driving current based on the error signal. Also,
This objective lens driving device supplies the tracking drive coils 4 and 4 with a tracking drive current based on a tracking error signal indicating a shift amount in the tracking direction between the focal point of the light beam by the objective lens 2 and the recording track. Is supplied, the focus point is always positioned on the recording track.

In the objective lens driving device, the inclination of the support shaft 7 with respect to the disk-shaped optical recording medium 101 is required depending on the mechanical accuracy and adjustment when the support shaft 7 is mounted on the base plate 6. Accuracy can be maintained. In this objective lens driving device, as shown in FIG. 4, the bearing holes 9 are such that the sliding portions 14, 14 near the openings on both sides are larger than the diameter-enlarging portion 15, which is the central portion. The diameter is slightly reduced. The difference between the inner diameters of the sliding portions 14, 14 and the enlarged diameter portion 15 is about several μm. Therefore, between the sliding parts 14 and 14 and the enlarged diameter part 15, step parts 16 and 16 having a height of several μm are formed. Therefore, the lens bobbin 1 is
As shown in FIG.
Since only the inner wall portions 17 of the shafts 4 and 14 slide and are supported by the base end and the front end of the support shaft 7, the inclination with respect to the support shaft 7 is strictly restricted. That is, in this objective lens driving device, the inclination of the lens bobbin 1 with respect to the disk-shaped optical recording medium 101 is severely restricted.

The bearing hole 9 has a small contact area with the support shaft 7 so that sliding with the support shaft 7 can be performed well with little friction. That is, in this objective lens driving device, the state in which the bearing hole 9 can slide well on the support shaft 7 is maintained, and the inclination of the lens bobbin 1 with respect to the support shaft 7 is strictly restricted.
Therefore, the objective lens driving device can be used for an optical pickup device for writing and reading information signals on a disk-shaped optical recording medium in which the recording density of information signals is increased.

In the lens bobbin 1, at least the cylindrical portion 8 around the bearing hole 9 is formed by integral molding means. The lens bobbin 1 is formed by injection molding using a composite material such as a synthetic resin material mixed with glass fibers. In the bearing hole 9, the portion of the enlarged diameter portion 15 is formed by die-cutting, which is so-called “forced punching”. That is, in the mold for forming the lens bobbin 1, the cylindrical portion forming the bearing hole 9 has a halfway enlarged diameter of several μm in the middle, and the bearing hole 9 is formed. Later, it does not come out of the bearing hole 9 as it is. At this time, the lens bobbin 1 is slightly elastically deformed by applying a certain force or more in a direction in which the formed lens bobbin 1 is separated from the mold, and the lens bobbin 1 is separated from the mold. You.

As shown in FIG. 8, the bearing holes 9 have tapered portions 18 and 1 as shown in FIG. 8 in order to facilitate "forcible removal" from the mold.
8 may be formed. These taper portions 18,
Reference numeral 18 is formed such that the inner diameter is gradually increased from the sliding portions 14 to the enlarged diameter portion 15.

In the bearing hole 9, as shown in FIG. 7, the enlarged diameter portion 15 and one sliding portion 14 are formed integrally with the cylindrical portion 8 of the lens bobbin 1, and the other is formed. The sliding portion 14 may be formed by pressing a bearing (thrust bearing) 19 into the bearing hole 9. The bearing 19 is formed in a ring shape with a material such as a so-called oil-impregnated metal (“oil-less metal”), and has an inner diameter equal to the inner diameter of the sliding portion 14.

Further, in the bearing hole 9 shown in FIG.
As shown in the figure, the enlarged diameter portion 15 is formed integrally with the cylindrical portion 8 of the lens bobbin 1, and the sliding portions 14 are formed by press-fitting the bearings 19, 19 into the bearing holes 9, respectively. You may do it.

[0038]

As described above, in the objective lens driving device according to the present invention, the portions of the bearing holes of the lens bobbin on which the objective lens is mounted are reduced in diameter near the opening on both sides than in the center. The portions near the openings are in sliding contact with the outer peripheral surface of the spindle inserted into the bearing holes.

However, since the lens bobbin is supported by the proximal end and the distal end of the support shaft, the inclination with respect to the support shaft is strictly controlled. Further, since the bearing hole has a small contact area with the support shaft, sliding with respect to the support shaft can be performed satisfactorily with little friction.

That is, according to the present invention, the inclination of the lens bobbin with respect to the support shaft is strictly controlled while maintaining good sliding of the lens bobbin on which the objective lens is mounted on the support shaft supporting the lens bobbin, It is possible to provide an objective lens driving device suitable for being applied to an optical pickup device that writes and reads information signals to and from an optical recording medium in which the recording density of information signals is increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an objective lens driving device according to the present invention.

FIG. 2 is a longitudinal sectional view showing a configuration of the objective lens driving device.

FIG. 3 is a plan view showing a configuration of the objective lens driving device.

FIG. 4 is a longitudinal sectional view of a main part showing a configuration (first example) of a main part of the objective lens driving device.

FIG. 5 is a vertical sectional view of a main part showing a configuration of a main part (second example) of the objective lens driving device.

FIG. 6 is a vertical sectional view of a main part showing a configuration of a main part (third example) of the objective lens driving device.

FIG. 7 is a longitudinal sectional view of a main part showing a configuration (a fourth example) of a main part of the objective lens driving device.

FIG. 8 is a vertical cross-sectional view of a main part showing a configuration (a fifth example) of a main part of the objective lens driving device.

[Explanation of symbols]

Reference Signs List 1 lens bobbin, 2 objective lens, 3 focus drive coil, 4 tracking drive coil, 5 magnet, 7 support shaft, 9 bearing hole, 10 yoke, 14 sliding section, 15 enlarged diameter section

Claims (2)

[Claims] An object lens and a drive coil are attached to the support shaft, and a bearing hole through which the support shaft is inserted is provided. The support shaft is inserted through the bearing hole. A lens bobbin supported by the support shaft so as to be movable in the axial direction of the support shaft and a direction around the support shaft; and a magnetic circuit for positioning the drive coil in a magnetic field. The objective lens driving device, wherein the portion near the opening is smaller in diameter than the central portion, and the portion near the opening comes into sliding contact with the outer peripheral surface of the support shaft. 2. The lens bobbin according to claim 1, wherein at least a portion around the bearing hole is formed by integral molding means.
An objective lens driving device according to claim 1.