JP2003115127A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the accurate control of the position of a movable lenses group included in a group of spherical aberration correcting lenses which is provided in the device for movably being operated in the direction of optical axis, and also to allow the moving operation of the movable lenses group at a high speed without generating the tilt or the optical axis deviation. SOLUTION: This device is furnished with objective lenses 8, 9 for converging a luminous flux generated from a light source 1 on a signal recording surface of an optical recording medium 201 and the spherical aberration correcting lens groups 6, 7 including the movable lenses group 7 which is disposed on an optical path between the light source 1 and the objective lenses 8, 9 and supported so as movably operative in the direction of optical axis. The movable lenses group 7 is radially aligned keeping equal angle spaces with respect to the optical axis and supported with at least two leaf spring shaped arm parts formed to the spiral shape in the same direction, then the generation of decentration accompanied by the moving operation in the direction of optical axis is prevented.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for writing or reading an information signal on or from an optical recording medium such as an optical disk. 2. Description of the Related Art Conventionally, optical recording media such as optical disks have been widely used as recording media and distribution media for various data such as music, video, and computer software. In addition, the so-called “DVD (registered trademark)” has been replaced by the so-called “DVD (registered trademark)”.
(Registered trademark) ”has an increased data capacity per disc and an improved recording density. Further, in such an optical recording medium, further higher density is desired in the future. In order to increase the recording density of an optical recording medium, it is effective to shorten the wavelength of light and increase the numerical aperture of an objective lens. In recent years, optical discs and optical pickup devices with such high densities have been proposed. An optical pickup device having a spherical aberration correcting lens group has been proposed. This spherical aberration correction lens group is used for a plurality of types of optical recording media having different thicknesses of the transparent substrate, and a spherical aberration generated according to the thickness of the transparent substrate or a variation in the thickness or the refractive index of the transparent substrate. Is to be corrected. The spherical aberration correcting lens group is disposed on the optical path between the light source and the objective lens, and is composed of two lens groups, one of which is a fixed lens group and the other of which is a fixed lens group. The group is a movable lens group that can be moved in the optical axis direction. The spherical aberration correcting lens group corrects spherical aberration by adjusting the position of the movable lens group in the optical axis direction according to the thickness of the transparent substrate of the optical recording medium. Conventionally, as a mechanism for movably supporting a movable lens group of a spherical aberration correcting lens, FIGS.
As shown in FIG. 1, a worm wheel 102 is mounted on a movable lens group 101, and the worm wheel 102 is rotated by a DC motor 104 via a worm gear 103. A worm wheel 102 pin 102a is attached. This pin 1
02a is engaged with a groove provided in the lens holder 101a. The lens holder 101a is a holder for holding the movable lens group 101. When the worm wheel 102 is rotated, the lens holder 101a rotates the V-groove 1 in the main body of the optical pickup device.
The moving operation is performed in the optical axis direction with 01b as a guide. As a mechanism for movably supporting the movable lens group of the spherical aberration correction lens group, as shown in FIGS. 9 and 10, the movable lens group 101 is supported by a plurality of parallel leaf springs 105. A device driven by a voice coil motor (VCM) 106 has been proposed. In this case, the movable lens group 101 held by the lens pobin 101a is movable in the optical axis direction via two parallelly arranged leaf springs 105, 105, and is elastically movable with respect to the fixed block 105a. Have been supported. The fixed block 105a is fixed to the main body of the optical pickup device. Two coils 106a, 106a constituting the voice coil motor 106 are attached to the lens bobbin 101a. When current is supplied to the coils 106a and 106a, the lens bobbin 101a receives the magnetic field of the magnetic circuit formed by the magnet 106b and the ake 106c that constitute the voice coil motor 106, and moves in the optical axis direction. Is done. The performance required of the mechanism for moving and operating the movable lens group in this manner is that the residual deviation from the target position when the position of the movable lens group is controlled is small, and that the mechanism moves in a direction other than the movable axis. Does not move. Further, considering the case of handling an optical disk having two recording layers, it is necessary to correct the difference in the thickness of the light transmitting layer caused by switching of the recording layers. In this case, a speed for quickly switching to a different recording layer is required, and a large acceleration is required when moving the movable lens group. In the above-described optical pickup device, the supporting mechanism shown in FIGS. 7 and 8 has a large residual deviation due to backlash or the like generated between the gears. That is, there is a problem that the positioning accuracy cannot be increased and the movable lens group cannot be driven at a high speed. Further, the support mechanism shown in FIGS. 9 and 10 has a small residual deviation and is suitable for high-speed operation, but has a problem that the optical axis is easily shifted due to the inclination of the movable lens group. If such an optical axis shift occurs, astigmatism will occur. Further, when the numerical aperture of the objective lens is increased, such an optical axis shift of the movable lens group affects the aberration of the light spot formed on the signal recording surface of the optical recording medium. The occurrence of such aberrations becomes sensitive to various types of accuracy, such as lens shape accuracy, lens assembly accuracy, and optical recording medium thickness accuracy, and requires extremely high component accuracy and assembly accuracy. Would. Accordingly, the present invention has been proposed in view of the above situation, and has a spherical aberration correction lens group including a movable lens group that is moved and operated in the optical axis direction. It is an object of the present invention to provide an optical pickup device capable of accurately controlling the position and moving the movable lens group at high speed without causing tilt or optical axis deviation. In order to solve the above problems, an optical pickup device according to the present invention collects a light source and a light beam emitted from the light source on a signal recording surface of an optical recording medium. An objective lens that emits light, a spherical aberration correction lens group including a movable lens group that is provided on an optical path between the light source and the objective lens and that is movable and supported in the optical axis direction, and a spherical aberration correction lens An actuator that supports the movable lens group of the group and moves the movable lens group in the optical axis direction. In this actuator, the movable lens groups are radially arranged at equal angular intervals with respect to the optical axis and form a spiral shape in the same direction. And is supported by at least two leaf spring-shaped arm portions to prevent eccentricity caused by a movement operation in the optical axis direction. Embodiments of the present invention will be described below with reference to the drawings. In the optical pickup device according to the present invention, as shown in FIG. 1, a diffused light beam emitted from a semiconductor laser (LD) 1 passes through a grating 2, a polarizing beam splitter (PBS) 3, and a collimator lens. 4
To form a parallel light beam. The light beam is split in the grating 2, and a sub-beam for detecting a tracking error signal by the differential push-pull method is formed. These light beams enter the quarter-wave plate 5. The luminous flux emitted as linearly polarized light from the semiconductor laser 1 is converted into circularly polarized light by the quarter-wave plate 5 while keeping the parallel luminous flux. Next, this light beam is slightly spread by the first correction lens 6 into a diffused light beam, passes through the second correction lens 7 serving as a movable lens group, and becomes a parallel light beam again. The second correction lens 7 is supported by a correction lens actuator 11 and can be moved in the direction of the optical axis to change the distance from the first correction lens 6. As described above, by changing the distance of the second correction lens 7 from the first correction lens 6, the light beam emitted from the second correction lens 7 is expanded into a diffuse light beam, or It is narrowed down to a convergent beam. As described above, the first and second correction lenses 6 and 7 whose distances can be changed constitute a spherical aberration correction lens group having a function of correcting spherical aberration. The light beam emitted from the second correction lens 7 is condensed by the objective lenses 8 and 9 on the signal recording surface of an optical disk 201 as an optical recording medium. The objective lenses 8 and 9 have a two-group configuration including a first objective lens 8 and a second objective lens 9, and are high NA lenses having a numerical aperture (NA) exceeding 0.8. The objective lenses 8 and 9 are supported by a biaxial actuator 10 and are perpendicular to the main surface of the optical disk 201 and parallel to the main surface of the optical disk 201 and orthogonal to recording tracks of the optical disk 201. Is operated in two directions. By the operation of the biaxial actuator 10, a focus servo operation and a tracking servo operation are performed. The light beam reflected by the signal recording surface of the optical disk 201 is returned as the second objective lens 9, the first objective lens 8, the second correction lens 7,
In the order of the correction lens 6. This return light, in turn,
By passing through the quarter-wave plate 5, the light is converted from circularly polarized light to linearly polarized light again. At this time, the direction of the linearly polarized light is orthogonal to the polarization direction of the light beam going to the optical disk 201. This return light is incident on the polarizing beam splitter 3 again while being collected by the collimator lens 4. Since this return light is linearly polarized light in a direction orthogonal to the polarization direction of the incoming light flux, it is S-polarized light with respect to the inclined reflection surface of the polarization beam splitter 3 and reflected by this reflection surface. Is done. Polarizing beam splitter 3
Is reflected from the optical path returning to the semiconductor laser 1 and is condensed on the photodiode IC 13 via the multi-lens 12. The multi lens 12
A lens having a concave surface on one side and a cylindrical surface on the other side, which produces astigmatism in the return light and enables detection of a focus error signal by the astigmatism method. In the photodiode IC13, the return light is
Converted to electrical signals. In the optical pickup device, the electric signal converted from the return light in the photodiode IC 13 is sent to a modulation / demodulation circuit 16 of a recording / reproducing device configured using the optical pickup device. The modulation / demodulation circuit 16 demodulates the transmitted electric signal and outputs it as an information signal to the outside. With this operation, the information signal recorded on the optical disc 201 is reproduced. When recording an information signal on the optical disc 201, the modulation / demodulation circuit 16 modulates the information signal sent from the outside and sends it to the control circuit 15 of the recording / reproducing apparatus. This control circuit 15 is a circuit for controlling each part of the recording / reproducing apparatus, and controls the optical output of the semiconductor laser 1, the operation of the biaxial actuator 10, the operation of the correction lens actuator 11, and The rotation speed of the spindle motor 14, which is supported and rotated, is controlled. The control circuit 15 controls the modulation / demodulation circuit 1
The information signal is recorded on the optical disk 201 by controlling the optical output of the semiconductor laser 1 in accordance with the signal modulated by 6. By the way, in the optical system of the optical pickup device, the thickness unevenness of the light transmitting portion of the optical disk 201, the error in the thickness of the first objective lens 8 and the second objective lens 9, the first objective lens 8 Spherical aberration occurs in the light beam condensed on the signal recording surface of the optical disk 201 due to an error in the distance between the optical disk 201 and the second objective lens 9. And
In this optical system, the spherical aberration is corrected by moving the second correction lens 7 in the optical axis direction. In the correction lens actuator 11 for moving the second correction lens 7 in the optical axis direction, as shown in FIGS. 2 and 3, the second correction lens 7 is mounted on a cylindrical lens holder 17. The main body 21 of the optical pickup device is supported via two leaf springs 22a and 22b arranged in parallel. Each of the leaf springs 22a and 22b is radially arranged at equal angular intervals around the optical axis from the portion where the leaf springs 22a and 22b are fixed.
2c. These bent arms 22
“c” is a so-called “spiral spring”, which spirals around the optical axis from the center side toward the outer peripheral side so as to wrap in the same direction (clockwise direction in FIG. 3). Each of the leaf springs 22a and 22b is connected to the side where the leaf springs 22a and 22b are fixed to the optical pickup device body 21. The two leaf springs 22a and 22b have the same shape as each other, and when viewed from the optical axis direction, the three arm portions 22c of the two leaf springs 22a and 22b have the same direction. It is attached in a spiral. Second
The correction lens 7 is elastically supported by these two leaf springs 22a and 22b so as to be movable in the optical axis direction. A coil 18 wound in a cylindrical shape is fixed to the lens holder 17. The coil 18 is moved in the optical axis direction together with the lens holder 17 by receiving an electric current and receiving a magnetic field of a magnetic circuit formed by the magnet 19 and the yoke 20 attached to the main body 21 side. These leaf springs 22a and 22b keep the second correction lens 7 in the second position even when the second correction lens 7 is moved in the optical axis direction.
When the correction lens 7 rotates around the optical axis, the distortion of each arm 22c is absorbed, so that the lens center of the second correction lens 7 does not move from the optical axis center. Therefore, in this optical pickup device, astigmatism does not occur on the signal recording surface of the optical disk 201 even when the second correction lens 7 is moved in the optical axis direction. In an optical system such as this optical pickup device, when the second correction lens 7 is decentered with respect to the optical axis, as shown in FIG.
The wavefront aberration occurs according to the amount of eccentricity. The aberration allowed to occur due to the optical axis eccentricity of the second correction lens 7 is 0.0
It is 1λrms or less. Therefore, the second correction lens 7
Is 20 μm. In the optical system of the optical pickup device described above, the required movable range of the second correction lens 7 in the optical axis direction is about ± 0.5 mm to ± 1 mm. In the moving operation mechanism in the conventional optical pickup device shown in FIGS. 9 and 10, the distance from the fixed block 105a to the movable lens group 101 is 15 m.
m, the movable lens group 101 is moved by ± 0.7 in the optical axis direction.
When the movable lens group 101 is moved by mm, the eccentricity of the movable lens group 101 is about 16 μm from the optical axis center. This eccentricity is
This corresponds to the amount of eccentricity that causes aberration of 0.008 λrms. That is, in the optical pickup device according to the present invention, the eccentricity associated with the operation of moving the second correction lens 7 in the optical axis direction does not theoretically occur. The aberration generated by 008 λrms is small. Here, "accuracy of disk thickness" is considered as an example of a factor that causes aberration. If the disk thickness is 1
If the numerical aperture of the objective lens is 0.9 at 00 μm, the above-mentioned aberration amount (0.008λrms) corresponds to a disc thickness error of 8 μm. When the moving operation mechanism in the conventional optical pickup device shown in FIGS. 9 and 10 is used, the required disc thickness accuracy is 100 μm.
It is about ± 2 μm. On the other hand, in the optical pickup device according to the present invention, the disc thickness accuracy is 100
It may be about μm ± 10 μm. Disc thickness 1
In order to maintain the accuracy of 00 μm ± 2 μm, it is difficult to produce an optical disk only by a method of attaching a 100 μm film sheet, and mass production of the optical disk becomes difficult. On the other hand, when the disk thickness is 100 μm ±
If the accuracy is maintained at 10 μm, the so-called “sbin coat method” can be used, and mass production of optical disks becomes easy. In this optical pickup device, the leaf springs 22a, 22
Since b is used, there is no load due to backlash or friction, and highly accurate position control of the second correction lens 7 is possible. Further, in this optical pickup device, since the inertia of the movable portion including the second correction lens 7 is small, the second correction lens 7 can be moved at a high speed with high acceleration. The number of the spirally bent arms 22c in the leaf springs 22a and 22b is 3 as described above.
The number is not limited to a book, but may be two as shown in FIG. 5, or four as shown in FIG. 6, or may be a large number of five or more. As described above, the optical pickup device according to the present invention comprises an objective lens for condensing a light beam emitted from a light source on a signal recording surface of an optical recording medium, and a light source and an objective lens. And a lens group for correcting spherical aberration including a movable lens group which is disposed on an optical path between them and is movably operated in the optical axis direction and supported. The movable lens group is supported by at least two leaf spring-like arms that are arranged radially at equal angular intervals with respect to the optical axis and have a spiral shape in the same direction, and are moved in the optical axis direction. As a result, the occurrence of eccentricity is prevented. That is, even when the movable lens group is moved in the direction of the optical axis, the distortion is absorbed by the rotation of the movable lens group around the optical axis. The lens center of the group is not moved from the optical axis center. In this optical pickup device, since a leaf spring arm is used to support the movable lens group, there is no load due to backlash or friction.
Highly accurate position control of the movable lens group is possible. Further, in this optical pickup device, since the inertia of the movable section including the movable lens group is small, the acceleration can be easily generated and the movable lens group can be moved at high speed. That is, the present invention has a spherical aberration correction lens group including a movable lens group that is moved and operated in the optical axis direction, and the position of the movable lens group can be controlled accurately, and the movable lens An object of the present invention is to provide an optical pickup device capable of moving a group at high speed and without causing a tilt or an optical axis shift.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view and a block diagram showing a configuration of an optical pickup device according to the present invention and a recording / reproducing device configured using the optical pickup device. FIG. 2 is a longitudinal sectional view showing a configuration of a correction lens actuator in the optical pickup device. FIG. 3 is a plan view showing a configuration of the correction lens actuator. FIG. 4 is a graph showing the relationship between the amount of eccentricity of a movable lens group and the amount of generated wavefront aberration in an optical pickup device. FIG. 5 is a plan view showing another example of the configuration of the correction lens actuator in the optical pickup device according to the present invention. FIG. 6 is a plan view showing still another example of the configuration of the correction lens actuator in the optical pickup device according to the present invention. FIG. 7 is a side view showing a configuration of a mechanism for moving a movable lens group in a conventional optical pickup device. FIG. 8 is a plan view showing a configuration of a mechanism for moving a movable lens group in a conventional optical pickup device. FIG. 9 is a side view showing another example of the configuration of the mechanism for moving the movable lens group in the conventional optical pickup device. FIG. 10 is a plan view showing another example of the configuration of the mechanism for moving the movable lens group in the conventional optical pickup device. [Description of Signs] 1 semiconductor laser, 3 polarization beam splitter, 4 collimator lens, 6 first correction lens, 7 second correction lens, 8 first objective lens, 9 second objective lens, 10-axis actuator , 11 Correction lens actuator

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Claims (1)

Claims: 1. A light source, an objective lens for condensing a light beam emitted from the light source on a signal recording surface of an optical recording medium, and an optical path between the light source and the objective lens Arranged in
A spherical aberration correction lens group including a movable lens group that is movable and supported in the optical axis direction, and an actuator that supports the movable lens group of the spherical aberration correction lens group and moves and operates in the optical axis direction, In the above actuator, the movable lens group is supported by at least two leaf spring-like arms that are radially arranged at equal angular intervals with respect to the optical axis and form a spiral shape in the same direction. An optical pickup device wherein occurrence of eccentricity due to a moving operation is prevented.