JP4254038B2 - Objective lens, and optical pickup device and optical disc device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an objective lens that focuses a light beam on a signal recording surface of an optical disk such as a magneto-optical disk (MO), a compact disk (CD), or a CD-ROM, and an optical pickup device and an optical disk device using the objective lens.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an optical disc apparatus is known as a device for recording information on an optical disc or reproducing information recorded on an optical disc. In general, the optical disc apparatus focuses an optical disc on an optical disc via an optical disc driving device that rotates the optical disc, and an objective lens that is controlled and driven in a biaxial direction of a focusing direction and a tracking direction. And an optical pickup device that receives return light from the optical disc.
[0003]
FIG. 4 shows an example of the optical pickup device. In this example, the optical pickup device 1 is located below the objective lens 3 inserted below the optical disk 2 and inclined by 45 ° with respect to the optical axis. A beam splitter 4, a photodetector 5 disposed below the beam splitter 4, a grating element 7 disposed sequentially on the side of the reflecting surface 6 of the beam splitter 4, and a semiconductor laser. And 8.
[0004]
5 and 6 show an example of a drive unit that drives the objective lens in the biaxial direction. In this example, the objective lens drive unit 11 includes a suspension 12 made of an elastic body that extends horizontally. An objective lens holder 13, a focusing coil 14 and a tracking coil 15 respectively supported by the suspension 12, the objective lens 3 held horizontally by the objective lens holder 13, a yoke 17 made of a magnetic material, A counter balance 19 is provided at a position opposite to the objective lens 3 with a magnetic neutral (operation center) point M in between.
[0005]
As shown in FIG. 7, the objective lens 3 includes an optical surface 20 curved downward on the light source side, another optical surface 21 curved upward on the optical disk side, and another optical surface 20 different from the optical surface 20. A flange-shaped edge portion 22 formed between the optical surfaces 21, and the center of gravity G of the objective lens 3 is located above the boundary surface 23 between the optical surface 20 and the edge portion 22.
[0006]
In such a configuration, the optical disk 2 is rotated by the optical disk driving device (not shown), and the objective lens 3 is inserted into the optical path below the disk 2 by the objective lens driving unit 11. Then, the light beam 24 emitted in a horizontal direction from the semiconductor laser 8, the split by the grating element 7 to the main beam and sub-beams are reflected upward by the reflecting surface 6 of the beam splitter 4. The reflected light beam 24 is refracted by the objective lens 3, converged on the signal recording surface 25 of the optical disc 2, reflected downward, and becomes a return light beam 24. The return light beam 24 is refracted by the objective lens 3 again, passes through the beam splitter 4, and then enters the photodetector 5.
[0007]
Thereafter, photoelectric conversion is performed by the photodetector 5, and information recorded on the signal recording surface 25 of the optical disc 2 is reproduced based on the output detection signal. At that time, a focusing error signal and a tracking error signal are detected, and the drive currents of the focusing coil 14 and the tracking coil 15 are servo-controlled based on the respective signals. Then, the current flowing through the focusing coil 14 and the tracking coil 15 interacts with the magnetic field formed by the yoke 17 and the magnet 18, respectively, so that the objective lens 3 is driven and controlled in the focusing direction and the tracking direction.
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional objective lens, optical pickup device, and optical disk device, the center of gravity G of the objective lens 3 is located at a position considerably higher than the magnetic neutral (operation center) point M of the objective lens driving unit 11, so that the tip side is It becomes unstable and a large moment is generated in the focusing direction around the magnetic center point M. Therefore, the weight of the counterbalance 19 is increased in order to suppress the moment (see FIG. 5), or the counterbalance 19 is controlled in the magnetic field in order to suppress the moment while limiting the weight of the counterbalance. It is necessary to dispose it at a position far from the neutral (operation center) point M (see FIG. 6). When the weight of the counter balance 19 is large, the operation sensitivity such as displacement and acceleration when a constant voltage is applied to the objective lens driving unit 11 is deteriorated, and the counter balance 19 is moved to a far position. When arranged, since the arrangement of the objective lens 3 and the counter balance 19 is dispersed, the rigidity becomes weak, the secondary resonance frequency is lowered, and it is difficult to secure the servo band. There was a problem of rolling. Furthermore, the height and length dimensions of the objective lens driving unit 11 are increased, and it is difficult to reduce the size of the apparatus.
[0009]
In addition, when the above-described conventional objective lens, optical pickup device, and optical disc device are used in an environment where the temperature change is intense such as in a car, the lens shape changes due to the temperature change, and it is avoided that the aberrations deteriorate. It is effective to use a glass having a high refractive index when using a glass having a small coefficient of linear expansion and in applications where the numerical aperture is high. However, since glass is heavier than plastic and the like, the problems described above have become more serious in those cases.
[0010]
Therefore, in view of the above points, the present invention is an objective lens that is easy to balance, has improved stability, can be reduced in size and weight, has excellent sensitivity during operation, and is suitable for use in a vehicle or at a high numerical aperture. In addition, an optical pickup device and an optical disc device are provided.
[0011]
[Means for Solving the Problems]
The present invention is an objective lens comprising a single lens that focuses a light beam emitted from a light source on an optical disk and supported by a lens holder, and has a convex curved optical surface on the light source side and an optical surface on the light source side And an optical surface different from the optical surface on the light source side on the optical disc side from the edge portion, and the optical surface on the light source side is an optical surface on the optical disc side. A radius of curvature smaller than that, supported at the boundary surface between the optical surface on the light source side and the edge portion by the lens holder from the light source side, and from the boundary surface between the optical surface on the light source side and the edge portion. The center of gravity is formed so as to be located on the optical surface side of the light source side, the center of gravity is formed so as to be located within the thickness of the lens support portion of the lens holder, and the tip of the optical surface on the light source side is , The above It protrudes from's support.
[0012]
Preferably, the optical surface is an aspheric surface, has an aspheric optical surface on the optical disc side, and has a numerical aperture of 0.8 or more.
[0013]
Further, the present invention provides a light source that emits a light beam, an objective lens that is a single lens that focuses the light beam emitted from the light source on an optical disc, a photodetector that receives a return light beam from the optical disc, A lens holder that supports an objective lens, the objective lens including a convex-curved optical surface on the light source side, an edge portion formed on the optical disc side from the optical surface on the light source side, and an edge portion The optical surface includes an optical surface different from the optical surface on the light source side, the optical surface on the light source side is formed with a smaller radius of curvature than the optical surface on the optical disk side, and the objective lens includes the light source The center of light is supported by the lens holder from the light source side at the boundary surface between the optical surface on the side and the edge portion, and the center of gravity is located on the optical surface side on the light source side from the boundary surface between the optical surface on the light source side and the edge portion. Is formed so as to location, the optical position of the center of gravity, the formed so as to be located within the thickness of the lens support portion of the lens holder, the tip of the optical surface of the light source side, which projects from the lens support portion It is a pickup device.
[0014]
Further, the present invention focuses an optical disk driving device for rotating an optical disk and a light beam emitted from a light source on an optical disk through a single lens controlled and driven at least in a focusing direction and returns from the optical disk. An optical pickup device that receives light, and the objective lens includes a convex-curved optical surface on the light source side, an edge portion formed on the optical disk side from the optical surface on the light source side, and the edge portion from the edge portion. An optical surface different from the optical surface on the light source side on the optical disc side, the optical surface on the light source side is formed with a smaller radius of curvature than the optical surface on the optical disc side, and the objective lens is on the light source side Is supported from the light source side by a lens holder of the optical pickup device at a boundary surface between the optical surface and the edge portion. Formed on the optical surface of the light source side than the boundary surface between the surface and the edge portion so as the center of gravity is located, the position of the center of gravity, is formed so as to be located within the thickness of the lens support portion of the lens holder The optical disk device has a tip of the optical surface on the light source side protruding from the lens support portion .
[0015]
In such a configuration, the light beam emitted from the light source is incident on the objective lens, refracted by the optical surface, and then converges on the optical disk and reflects downward. The reflected light beam is incident on the objective lens again, refracted by the optical surface, and then incident on the photodetector. Thereafter, the information recorded on the signal recording surface of the optical disc is reproduced based on the signal output by the photodetector, and the objective lens is driven and controlled at least in the focusing direction.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 3, the same components as those in FIGS. 5 to 7 are denoted by the same reference numerals, and detailed description of their configurations and operations is omitted.
[0017]
Figure 1 shows the objective lens 31 according to the embodiment of the present invention, said objective lens 31 is, for example, made of glass, a convex curved optical surface 32 which is curved downwardly is a light source side, A flange-like edge portion 34 formed above the optical surface 32 on the optical disk side is provided, and another optical surface 35 is formed on the upper surface side of the edge portion 34. The distance from the lowest point of the optical surface 32 to the boundary surface 36 of the optical surface 32 and the edge portion 34, that is, the sag amount S of the optical surface 32 is sufficiently larger than the thickness D of the edge portion 34, The center of gravity G of the objective lens 31 is located below the boundary surface 36. Accordingly, since the optical surface 32 has a small radius of curvature and a large refractive power, the other optical surface 35 has a small refractive power or a negative refractive power. Preferably, the optical surface 32 and the another optical surface 35 are aspherical. The objective lens 31 is held by the objective lens holder 13 in the same manner as the objective lens driving unit of the conventional optical pickup device shown in FIGS. Specifically, as shown in FIGS. 2 and 3, the lens support portion 16 of the objective lens holder 13 supports a boundary surface 36 between the optical surface 32 and the edge portion 34 on the light source side of the objective lens 31. Further, the tip of the optical surface 32 of the objective lens 31 protrudes from the lens support portion 16 as shown in FIGS.
[0018]
FIG. 2 shows an objective lens driving unit 37 provided with the objective lens 31, and a counter balance 38 on the opposite side of the objective lens 31 across the magnetic neutral (operation center) point M. Is provided to balance the entire apparatus. In this case, the position of the center of gravity G of the objective lens 31 is closer to the optical surface 32 than the boundary surface 36, the vertical distance between the center of gravity G and the magnetic neutral point M is shortened, and the magnetic neutral point M is the center. Since the moment in the focusing direction is reduced, the counterbalance 38 can be reduced in weight.
[0019]
The operation of the objective lens 31 and the optical pickup device and optical disk device using the objective lens 31 will be described below with reference to FIGS.
[0020]
The objective lens drive unit 37 inserts the objective lens 31 into the optical path below the rotating optical disk 2. The light beam 24 emitted from the semiconductor laser 8 passes through the grating element 7, is reflected upward by the beam splitter 4, and enters the objective lens 31. The light beam 24 incident on the objective lens 31 is refracted by the optical surface 32, further refracted by the other optical surface 35, and then converged on the signal recording surface 25 of the optical disc 2 and reflected downward. The reflected light beam 24 becomes a return light beam 24, is incident on the objective lens 31 again, is sequentially refracted by the optical surfaces 35, 32, passes through the beam splitter 4, and is incident on the photodetector 5. .
[0021]
Thereafter, the information recorded on the signal recording surface 25 of the optical disc 2 is reproduced based on the detection signal output by the photodetector 5, and the focusing coil 14 is based on the focusing error signal and the tracking error signal. And the drive current of the tracking coil 15 is servo controlled. Then, the current flowing through the focusing coil 14 and the tracking coil 15 interacts with the magnetic field formed by the yoke 17 and the magnet 18, respectively, whereby the objective lens 31 is driven and controlled in the focusing direction and the tracking direction. As described above, since the counter balance 38 is reduced in weight, the sensitivity of the driving operation of the objective lens 31 at this time is improved.
[0022]
As shown in FIG. 3, the counter balance 39 can also be provided at a low position. In this case, the magnetic neutral point M and the counter balance 39 are vertically separated from each other as compared with the above embodiment. Therefore, the counter balance 39 can be further reduced in weight.
[0023]
In the above embodiment, each of the optical surfaces 32 and 35 has an aspherical shape, but may have a spherical shape. Further, the material of the objective lens 31 is not limited to the glass described above, but a material obtained by polishing or molding and bonding two or more materials such as plastic or a replica lens in which plastic and glass are combined, or an insert. What was shape | molded etc. may be sufficient.
[0024]
Further, in the above-described embodiment, the case where the optical disk 2 is disposed above the objective lens 31 and the light source 8 is disposed below the objective lens 31 has been described. However, the present invention is arranged in other arrangements, for example, the objective lens 31. This is also possible when the optical disk 2 is disposed below the light source 8 and the light source 8 is disposed above the light disk 8. In this case, it goes without saying that the posture of the objective lens 31 is also upside down.
[0025]
Furthermore, it goes without saying that the objective lens 31 according to the present invention can be used not only in the objective lens drive unit 37 but also in other drive devices such as a shaft slide type.
[0026]
【The invention's effect】
As described above, according to the present invention, the center of gravity of the objective lens is closer to the optical surface than the boundary surface, and the vertical distance between the center of gravity of the objective lens and the magnetic neutral point is shortened. Therefore, it is possible to suppress variation in weight, to reduce the counterbalance, and to reduce the size of the counterbalance, thereby improving the operation sensitivity of the apparatus. Further, the rigidity of the entire objective lens driving unit can be improved, the secondary resonance frequency can be increased, and the servo band can be easily secured. Furthermore, the rolling of the objective lens can be suppressed, and the stable operation of the apparatus can be ensured.
[0027]
In addition, since the refractive power of the objective lens can be increased, various excellent effects such as use in applications where the numerical aperture is high can be exhibited.
[Brief description of the drawings]
FIG. 1 is a side view of an objective lens according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram illustrating an objective lens driving unit including an objective lens according to an embodiment of the present invention.
FIG. 3 is a schematic configuration diagram illustrating another example of an objective lens driving unit including an objective lens according to an embodiment of the present invention.
FIG. 4 is a schematic configuration diagram showing an optical pickup device.
FIG. 5 is a schematic configuration diagram illustrating a conventional objective lens driving unit.
FIG. 6 is a schematic configuration diagram showing another example of a conventional objective lens driving unit.
FIG. 7 is a side view showing a conventional objective lens.
[Explanation of symbols]
31 Objective Lens 32 Optical Surface 34 Edge 35 Another Optical Surface 36 Boundary Surface 37 Objective Lens Drive Unit

Claims (8)

An objective lens composed of a single lens for focusing a light beam emitted from a light source on an optical disk and supported by a lens holder,
An optical surface having a convex curved surface on the light source side;
An edge portion formed on the optical disc side from the optical surface on the light source side;
An optical surface different from the optical surface on the light source side on the optical disc side from the edge portion,
The optical surface on the light source side is formed with a smaller radius of curvature than the optical surface on the optical disc side,
At the boundary surface between the optical surface on the light source side and the edge portion, supported by the lens holder from the light source side, and centroid from the boundary surface between the optical surface on the light source side and the edge portion to the optical surface side on the light source side Is formed to be located ,
The position of the center of gravity is formed so as to be located within the thickness of the lens support portion of the lens holder,
An objective lens in which a tip of the optical surface on the light source side protrudes from the lens support portion . The objective lens according to claim 1 , wherein the optical surface on the light source side is an aspherical surface.   The objective lens according to claim 1, wherein the optical surface on the optical disc side is an aspherical surface. The objective lens according to any one of claims 1 to 3 , wherein the numerical aperture is 0.8 or more. A light source that emits a light beam;
An objective lens composed of a single lens for focusing the light beam emitted from the light source on an optical disc;
A photodetector for receiving a return light beam from the optical disc;
A lens holder for supporting the objective lens,
The objective lens is
An optical surface having a convex curved surface on the light source side;
An edge portion formed on the optical disc side from the optical surface on the light source side;
An optical surface different from the optical surface on the light source side on the optical disc side from the edge portion,
The optical surface on the light source side is formed with a smaller radius of curvature than the optical surface on the optical disc side,
The objective lens is supported from the light source side by the lens holder at the boundary surface between the optical surface on the light source side and the edge portion, and is closer to the light source side than the boundary surface between the optical surface on the light source side and the edge portion. Is formed such that the center of gravity is positioned on the optical surface side of the lens holder, the position of the center of gravity is formed within the thickness of the lens support portion of the lens holder, and the tip of the optical surface on the light source side is the lens. An optical pickup device protruding from the support portion . Furthermore, an objective lens driving unit that controls and drives the objective lens at least in the focusing direction,
The optical pickup device according to claim 5 , wherein the objective lens is provided on one side across the magnetic neutral point of the objective lens driving unit, and a counterbalance is provided on the opposite side of the objective lens. An optical disk drive for rotating the optical disk;
An optical pickup device for focusing a light beam emitted from a light source on an optical disc through an objective lens composed of a single lens controlled and driven in at least a focusing direction and receiving return light from the optical disc,
The objective lens is
An optical surface having a convex curved surface on the light source side;
An edge portion formed on the optical disc side from the optical surface on the light source side;
An optical surface different from the optical surface on the light source side on the optical disc side from the edge portion,
The optical surface on the light source side is formed with a smaller radius of curvature than the optical surface on the optical disc side,
The objective lens is supported from the light source side by a lens holder of the optical pickup device at a boundary surface between the optical surface on the light source side and the edge portion, and is a boundary surface between the optical surface on the light source side and the edge portion. is formed so as the center of gravity is located more on the optical surface of the light source side, position of the center of gravity, the formed so as to be located within the thickness of the lens support portion of the lens holder, the optical surface of the light source side An optical disc apparatus having a tip protruding from the lens support portion . The optical pickup device further includes an objective lens driving unit that controls and drives the objective lens at least in a focusing direction.
8. The optical disc apparatus according to claim 7 , wherein the objective lens is provided on one side of a magnetic neutral point of the objective lens driving unit, and a counterbalance is provided on the opposite side of the objective lens.

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