JP2004164720A - Optical head and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head wherein a signal recorded in an optical disk and/or a signal reproduced therefrom has a good quality. <P>SOLUTION: This optical head is provided with a semiconductor laser, a diffraction grating, an objective lens, and an optical detector. A first sub-beam is converged along the scanning direction of the optical head with respect to an information medium on a position before a main beam. A second sub-beam is converged along the scanning direction of the optical head with respect to the information medium on a position after the main beam. The diffraction grating divides the optical beam into the main beam and the first and second sub-beams so as to converge the first sub-beam before the main beam on the outer peripheral side of the information medium more than the main beam, and the second sub-beam after the main beam on the inner peripheral side of the information medium more than the main beam. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head for reproducing information from a spirally formed information track on a rotating information medium and / or irradiating the information track with a light beam for recording information on the information track, and an optical head for the same. The present invention relates to an optical disk device including
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. H11-296875 (pages 7-8, FIG. 1) discloses a conventional optical head and optical disk apparatus. Even if the NA and the wavelength are shortened as much as possible to increase the density of the information recorded on the optical disk, the limit of reducing the spot diameter of the light beam that converges on an information track with a narrow track pitch is limited. There is. Therefore, information recorded on an information track is reproduced by a light beam converging at a spot diameter slightly larger than the width of the information track, and the influence of intersymbol interference and crosstalk is reduced by PRML and a non-linear equalizer. A method for increasing the density and capacity of an optical disk has been proposed. In an optical disc having such a narrow track pitch, the track deviation allowable error in the tracking control becomes very severe.
[0003]
FIG. 12 is a schematic diagram showing a relationship between a light beam emitted from a conventional optical head to an optical disc and information tracks formed on the optical disc. An information track 7 on which information is recorded is formed in a spiral shape on the optical disc 6. The information track 7 is constituted by a groove formed on the surface of the optical disc 6. On the information track 7 formed in a spiral shape on the optical disk 6, information is recorded from the inner peripheral side to the outer peripheral side of the optical disk 6. In the information track 7 formed in a spiral shape on the optical disc 6, a recording area R5 in which information has already been recorded is arranged on the inner circumferential side of the information track 7, and an unrecorded area R6 in which information has not yet been recorded is located. It is arranged on the outer peripheral side of the information track 7. The recording area R5 is shown with diagonal lines.
[0004]
An optical head provided in a conventional optical disk device is configured to reproduce a main beam divided by a diffraction grating from a light beam emitted by a light source in order to reproduce information from a spirally formed information track 7 on a rotating optical disk 6. M, the first sub-beam S1, and the second sub-beam S2 are converged on the information track 7 by the objective lens. The light source is constituted by, for example, a semiconductor laser.
[0005]
In the example shown in FIG. 12, the optical head irradiates the main beam M, the first sub-beam S1, and the second sub-beam S2 to the boundary between the recording area R5 and the unrecorded area R6 arranged on the information track 7. I have. The main beam M converges on the boundary between the recorded area R5 and the unrecorded area R6 in the information track 7. The first sub-beam S1 converges to a position preceding the main beam M1 along the scanning direction of the optical head with respect to the optical disk 6. The second sub-beam S2 is converged at a position following the main beam M in the scanning direction of the optical head with respect to the optical disk 6. The first sub-beam S <b> 1 that precedes the main beam M converges on the inner peripheral side of the optical disk 6 with respect to the main beam M. The second sub-beam S2 following the main beam M converges on the outer peripheral side of the optical disk 6 with respect to the main beam M.
[0006]
The photodetector provided in the optical head is configured to generate a main beam signal, a first sub beam signal, a second sub beam signal from the main beam M, the first sub beam S1, and the second sub beam S2 reflected by the information track. Are respectively detected. The optical disk device is configured to perform the differential push-pull method based on the main beam signal, the first sub-beam signal, and the second sub-beam signal detected by the photodetector, and to determine the center of the objective lens generated due to the eccentricity of the optical disk 6. A tracking error signal is generated so as to cancel a lens shift indicating a deviation from the center of the photodetector. The tracking of the optical head is controlled based on the tracking error signal so as to follow the information track 7 formed on the optical disc 6.
[0007]
Off-track due to lens shift can be reduced by such tracking control using the differential push-pull method.
[0008]
[Patent Document 1]
JP-A-11-296875 (pages 7-8, FIG. 1)
[0009]
[Problems to be solved by the invention]
However, in the above-described configuration of the related art, when the main beam M converges on the boundary between the recording area R5 and the unrecorded area R6 arranged on the information track 7 in order to record information on the information track 7, The first sub-beam S1 that precedes the main beam M overlaps the recording area R5 in the inner peripheral area R91, but overlaps the unrecorded area R6 in the outer peripheral area R92. Therefore, the light amount of the first sub-beam S1 reflected by the optical disk 6 and incident on the photodetector varies, so that the first sub-beam S1 fluctuates in light amount. Similarly, the second sub-beam S2 following the main beam M overlaps the recording area R5 in the inner peripheral area R93, and overlaps the unrecorded area R6 in the outer peripheral area R94. I have. For this reason, the light amount of the second sub-beam S2 reflected by the optical disk 6 and incident on the photodetector also varies, so that the light amount of the second sub-beam S2 fluctuates.
[0010]
Accordingly, an imbalance occurs between the first sub beam signal and the second sub beam signal detected from the first sub beam S1 and the second sub beam S2 by the photodetector, respectively. Therefore, an offset occurs in the tracking error signal generated based on the first sub beam signal and the second sub beam signal. As a result, there is a problem that the quality of the signal recorded on the optical disk and / or the quality of the signal reproduced from the optical disk may be degraded due to the occurrence of track deviation.
[0011]
If coma aberration occurs in the beam spot where the sub-beam is converged, the position where the push-pull signal based on the sub-beam signal crosses zero is shifted from the center of the groove forming the information track. Further, when the objective lens is displaced, the shift amount changes. Therefore, in the tracking control method using such a differential push-pull, a track shift occurs even if the tracking control is performed so that the differential push-pull becomes zero. As a result, there is a problem that the quality of a signal recorded on the optical disc and / or a signal reproduced from the optical disc may be degraded.
[0012]
The present invention has been made in order to solve such a problem, and an object of the present invention is to provide an optical head and an optical disk device having good quality of a signal recorded on an optical disk and / or a signal reproduced from the optical disk. is there.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an optical head according to the present invention is an optical head for irradiating a light beam onto an information track formed in a spiral shape on a rotating information medium so as to record information on the information track. A light source that emits the light beam, a diffraction grating that divides the light beam emitted from the light source into a main beam, a first sub-beam, and a second sub-beam, and a diffraction grating that is diffracted by the diffraction grating. An objective lens for converging the main beam, the first sub-beam, and the second sub-beam on the information track formed on the information medium, respectively, and reflecting the information beam on the information track formed on the information medium, respectively. Detecting a main beam signal, a first sub beam signal, and a second sub beam signal based on the main beam, the first sub beam, and the second sub beam, respectively. Wherein the first sub-beam converges to a position preceding the main beam along the scanning direction of the optical head with respect to the information medium, and the second sub-beam includes: The optical medium is configured to converge to a position following the main beam along the scanning direction of the optical head with respect to the information medium, and the diffraction grating is configured such that the first sub-beam preceding the main beam has the first sub-beam. The light beam is converged on the outer peripheral side of the information medium with respect to the main beam, and the light beam is converged on the inner peripheral side of the information medium with respect to the main beam. The main beam, the first sub-beam, and the second sub-beam are divided.
[0014]
An optical disc device according to the present invention includes an optical head according to the present invention, a motor for rotating the information medium, the main beam signal detected by the photodetector provided on the optical head, and the first A differential push-pull signal generator that generates a differential push-pull signal based on the sub-beam signal and the second sub-beam signal, and, according to the differential push-pull signal generated by the differential push-pull signal generator, The first sub-beam converges ahead of the main beam along the scanning direction of the optical head on the information medium, and the second sub-beam converges on the information medium along the scanning direction of the optical head on the information medium. A rotation direction setting device that sets the rotation direction of the motor so as to converge after the beam. Characterized by comprising.
[0015]
Another optical disk device according to the present invention is an optical head for irradiating a light beam to the information track for recording and / or reproducing information on the information track, wherein a light source for emitting the light beam; A diffraction grating that diffracts the light beam emitted from the light source so as to divide the light beam into a main beam, a first sub beam, and a second sub beam; and the main beam, the first sub beam, and the diffracted beam that are diffracted by the diffraction grating. An objective lens for focusing each of the second sub-beams on the information track formed on the information medium; and an main lens and the first sub-beam respectively reflected on the information track formed on the information medium. An optical head comprising: a photodetector for detecting a main beam signal, a first subbeam signal, and a second subbeam signal based on the second subbeam, respectively; A main beam push-pull signal is generated based on the main beam signal detected by the photodetector provided in the optical head, and the first and second sub-beam signals detected by the photodetector are generated. Differential push-pull signal generation for generating a corrected differential push-pull signal based on the main beam signal, the first and second sub-beam signals, and a predetermined correction coefficient β. At the timing when the main beam push-pull signal MPP generated by the differential push-pull signal generator becomes the center level of the amplitude of the main beam push-pull signal MPP, the level of the main beam push-pull signal and the To make the level of the sub beam push-pull signal equal, Correction coefficient changing means for changing the predetermined correction coefficient β for generating the corrected differential push-pull signal by the differential push-pull signal generator.
[0016]
Still another optical disc device according to the present invention is an optical head for irradiating a light beam to the information track to record and / or reproduce information on the information track, and a light source that emits the light beam; A diffraction grating for diffracting the light beam emitted from the light source so as to divide the light beam into a main beam, a first sub beam, and a second sub beam; and the main beam and the first sub beam diffracted by the diffraction grating. An objective lens for converging the second sub-beam on the information track formed on the information medium, the main beam and the first sub-beam respectively reflected on the information track formed on the information medium And a photodetector for detecting a main beam signal, a first subbeam signal, and a second subbeam signal based on the second subbeam and the second subbeam, respectively. And a main beam push-pull signal is generated based on the main beam signal detected by the photodetector provided on the optical head, and the first and second signals are detected by the photodetector. A differential push-pull signal that generates a sub-beam push-pull signal based on the sub-beam signal and generates a corrected differential push-pull signal based on the main beam signal, the first and second sub-beam signals, and a predetermined correction coefficient β A pull signal generator, provided for driving the objective lens provided on the optical head along a radial direction of the information medium on which the information track is formed, based on the corrected differential push-pull signal. Tracking drive circuit, and the main beam push-pull signal in a state where tracking control is operating. The corrected differential push-pull signal is generated by the differential push-pull signal generator so that the level of the differential push-pull signal substantially coincides with the level of the center of the amplitude of the main beam push-pull signal when tracking control is inactive. And a correction coefficient changing means for changing the predetermined correction coefficient β.
[0017]
Still another optical disc device according to the present invention is an optical head for irradiating a light beam to the information track to record and / or reproduce information on the information track, and a light source that emits the light beam; A diffraction grating for diffracting the light beam emitted from the light source so as to divide the light beam into a main beam, a first sub beam, and a second sub beam; and the main beam and the first sub beam diffracted by the diffraction grating. An objective lens for converging the second sub-beam on the information track formed on the information medium, the main beam and the first sub-beam respectively reflected on the information track formed on the information medium And a photodetector for detecting a main beam signal, a first subbeam signal, and a second subbeam signal based on the second subbeam and the second subbeam, respectively. And a main beam push-pull signal is generated based on the main beam signal detected by the photodetector provided on the optical head, and the first and second signals are detected by the photodetector. A differential push-pull that generates a sub-beam push-pull signal based on a sub-beam signal and generates an offset differential push-pull signal based on the main beam signal, the first and second sub-beam signals, and a predetermined offset amount A signal generator and a level of the main beam push-pull signal at a timing at which the main beam push-pull signal MPP generated by the differential push-pull signal generator becomes a center level of the amplitude of the main beam push-pull signal MPP. And the level of the sub-beam push-pull signal is equal Kunar so on, characterized by comprising an offset amount changing means for the change a predetermined offset amount for generating the offset differential push-pull signal by the differential push-pull signal generator.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
In the optical head according to the present embodiment, the first sub-beam converges to a position preceding the main beam in the scanning direction of the optical head with respect to the information medium, and the second sub-beam converges with the optical head with respect to the information medium. Is converged to a position following the main beam along the scanning direction, and the diffraction grating is configured such that the first sub-beam preceding the main beam converges on the outer peripheral side of the information medium with respect to the main beam. The light beam is split into a main beam, a first sub beam, and a second sub beam such that a second sub beam that follows the main beam converges on the inner peripheral side of the information medium with respect to the main beam.
[0019]
For this reason, the preceding first sub-beam is converged so as to straddle the unrecorded area of the information track and another unrecorded area of the information track arranged on the outer peripheral side of the unrecorded area of the information track. And a second sub-beam that follows so as to straddle the recording area of the information track and another recording area of the information track that is disposed adjacent to the recording area of the information track on the inner peripheral side. Can be converged. Therefore, the balance between the first sub-beam signal detected based on the first sub-beam and the second sub-beam signal detected based on the second sub-beam is improved. No offset occurs in the differential push-pull signal generated by the sub beam signal. As a result, the quality of the recording / reproducing signal can be improved.
[0020]
The diffraction grating is such that the first sub-beam converges to the outer peripheral side of the information medium beyond the information track by about １ ／ of a track pitch of the spirally formed information track, and the second sub-beam is The light beam is split into the main beam, the first sub-beam, and the second sub-beam so that the light beam converges to the inner peripheral side of the information medium from the information track by about の of the track pitch. Is preferred.
[0021]
The first sub-beam converges so as to straddle a first area of the information track and a second area of the information track disposed adjacent to the first area of the information track on the outer peripheral side, The second sub-beam converges so as to straddle a third area of the information track and a fourth area of the information track disposed adjacent to the third area of the information track on the inner peripheral side. Is preferred.
[0022]
It is preferable that the information track is a groove formed on a surface of the information medium.
[0023]
It is preferable that the information is recorded from the inner peripheral side to the outer peripheral side on the information track formed in a spiral shape on the information medium.
[0024]
In the information track formed in a spiral shape on the information medium, a recording area in which the information is already recorded is arranged on the inner peripheral side of the information track, and an unrecorded area in which the information is not yet recorded. Are preferably arranged on the outer peripheral side of the information track.
[0025]
The optical head starts recording the main beam, the first sub-beam, and the second sub-beam on the information track from a boundary between the recording area and the unrecorded area arranged on the information track. Is preferred.
[0026]
The main beam is a zero-order diffracted light of the light beam, the first sub-beam is one of a plus first-order diffracted light and a minus first-order diffracted light of the light beam, and the second sub-beam is the light Preferably, the beam is the other of the plus first order diffracted light and the minus first order diffracted light.
[0027]
A beam splitter provided between the diffraction element and the objective lens for guiding the main beam, the first sub beam, and the second sub beam reflected on the information track to the photodetector; Preferably, it is provided.
[0028]
In the optical disc device according to the present embodiment, the first sub beam precedes the main beam along the scanning direction of the optical head with respect to the information medium in accordance with the differential push-pull signal generated by the differential push-pull signal generator. Then, the rotation direction of the motor is set so that the second sub-beam converges after the main beam in the scanning direction of the optical head with respect to the information medium.
[0029]
For this reason, the preceding first sub-beam is converged so as to straddle the unrecorded area of the information track and another unrecorded area of the information track arranged on the outer peripheral side of the unrecorded area of the information track. And a second sub-beam that follows so as to straddle the recording area of the information track and another recording area of the information track that is disposed adjacent to the recording area of the information track on the inner peripheral side. Can be converged. Therefore, the balance between the first sub-beam signal detected based on the first sub-beam and the second sub-beam signal detected based on the second sub-beam is improved. No offset occurs in the differential push-pull signal generated by the sub beam signal. As a result, the quality of the recording / reproducing signal can be improved.
[0030]
Based on the differential push-pull signal generated by the differential push-pull signal generator, the light is emitted along a radial direction of the information medium so that the main beam emitted from the optical head follows the information track. It is preferable to further include a tracking drive circuit for driving the head.
[0031]
In another optical disk device according to the present embodiment, at the timing when the main beam push-pull signal MPP generated by the differential push-pull signal generator becomes the level of the center of the amplitude of the main beam push-pull signal MPP, The predetermined correction coefficient β for generating the corrected differential push-pull signal is changed by the differential push-pull signal generator so that the level of the main beam push-pull signal is equal to the level of the sub-beam push-pull signal.
[0032]
For this reason, it is possible to realize good tracking control in which no track deviation occurs.
[0033]
A main beam detection unit that detects the main beam signal based on the main beam, a first sub-beam detection unit that detects the first sub-beam signal based on the first sub-beam, It is preferable that the apparatus further includes a second sub beam detection unit that detects the second sub beam signal based on the second sub beam.
[0034]
The main beam detecting unit, the first sub-beam detecting unit, and the second sub-beam detecting unit are respectively provided in two regions along a direction corresponding to a circumferential direction of the spirally formed information track. Preferably, it is divided.
[0035]
Based on the corrected differential push-pull signal generated by the differential push-pull signal generator according to the correction coefficient β changed by the correction coefficient changing unit, a radial direction of the information medium on which the information track is formed is formed along the radial direction of the information medium. Preferably, the apparatus further comprises a transfer device provided for transferring the optical head.
[0036]
Based on the corrected differential push-pull signal generated by the differential push-pull signal generator according to the correction coefficient β changed by the correction coefficient changing unit, a radial direction of the information medium on which the information track is formed is formed along the radial direction of the information medium. Preferably, the optical head further includes a tracking drive circuit provided to drive the objective lens provided in the optical head.
[0037]
An objective lens displacement representing a displacement of the objective lens driven by the tracking drive circuit based on the main beam signal, the first sub beam signal, and the second sub beam signal detected by the photodetector; It is preferable to further include an objective lens displacement signal generation circuit that generates a signal.
[0038]
The objective lens generated by the objective lens displacement signal generation circuit while changing a set value set in the tracking drive circuit in a state in which the tracking control by the tracking drive circuit is deactivated, The level of the main beam push-pull signal and the level of the sub beam push-pull signal are equal to each other at the timing when the displacement signal and the main beam push-pull signal MPP become the center level of the amplitude of the main beam push-pull signal MPP. It is preferable that the predetermined correction coefficient β changed so as to be stored in a predetermined memory.
[0039]
In still another optical disk device according to the present embodiment, the tracking drive circuit moves in the outer peripheral direction so that the beam spot of the main beam emitted from the optical head to the information medium moves to the information track adjacent to the outer peripheral side. During the period in which the objective lens is driven, the differential push-pull signal generator corrects the differential push-pull signal so that the positive maximum amplitude BV of the main beam push-pull signal is substantially equal to the negative maximum amplitude SV. The predetermined correction coefficient β for generating is changed.
[0040]
Therefore, the main beam push-pull signal crosses zero at a timing corresponding to the midpoint between the information track and the adjacent information track. As a result, off-track in the main beam push-pull signal can be removed.
[0041]
The correction coefficient changing means is configured to determine, based on a level of the main beam push-pull signal during a period other than a jumping period in which the light beam moves in the radial direction, a maximum amplitude BV of the main beam push-pull signal on the positive side. And the maximum amplitude SV on the negative side, and it is preferable to change the predetermined correction coefficient β so that the maximum amplitude BV on the positive side and the maximum amplitude SV on the negative side are substantially equal.
[0042]
The correction coefficient changing unit is configured to control the tracking drive circuit so that a beam spot of the main beam emitted from the optical head to the information medium moves to an information track adjacent to one of an outer peripheral side and an inner peripheral side. During the period in which the objective lens is driven toward the one of the outer peripheral side and the inner peripheral side, the level of the main beam push-pull signal in a state where tracking control is operating is referred to. The maximum amplitude BV on the positive side and the maximum amplitude SV on the negative side of the main beam push-pull signal are measured in such a manner that the maximum amplitude BV on the positive side and the maximum amplitude SV on the negative side are substantially equal. It is preferable to change the predetermined correction coefficient β.
[0043]
It is preferable that the tracking drive circuit performs the tracking control by setting the correction coefficient β to substantially zero for a predetermined period after starting the tracking control.
[0044]
It is preferable that the correction coefficient changing means limits a range in which the correction coefficient β is changed.
[0045]
In still another optical disk device according to the present embodiment, the level of the main beam push-pull signal and the level of the sub-beam push-pull signal are set at the timing when the main beam push-pull signal MPP reaches the center level of the amplitude of the main beam push-pull signal MPP. The predetermined offset amount for generating the offset differential push-pull signal is changed by the differential push-pull signal generator so that the signal level becomes equal.
[0046]
For this reason, it is possible to realize good tracking control in which no track deviation occurs.
[0047]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0048]
FIG. 1 is a block diagram showing a configuration of the optical disc device 200 according to the first embodiment. The optical disk device 200 includes the optical head 100.
[0049]
FIG. 2 is a diagram showing a configuration of the optical head 100, and FIG. 3 is a schematic diagram showing a relationship between a light beam emitted from the optical head 200 to the optical disk 6 and an information track 7 formed on the optical disk 6. The optical head 100 irradiates the optical disk 6 with a light beam in order to record information on the information track 7 formed in a spiral shape on the optical disk 6 rotated by the spindle motor 9. The optical head 100 is provided with a light source. The light source is constituted by the semiconductor laser 4, for example. The semiconductor laser 4 emits a light beam to the diffraction grating 1. The diffraction grating 1 diffracts the light beam emitted from the semiconductor laser 4 so as to split the light beam into a main beam M, a first sub-beam S1, and a second sub-beam S2. The main beam M is a zero-order diffracted light of the light beam, the first sub-beam S1 is a plus first-order diffracted light of the light beam, and the second sub-beam is a minus first-order diffracted light of the light beam.
[0050]
The main beam M, the first sub-beam S1, and the second sub-beam S2 diffracted by the diffraction grating 1 pass through the beam splitter 5 and are condensed by the condenser lens 104, reflected by the reflection mirror 105, and reflected by the objective lens 2 Incident on. The objective lens 2 converges the incident main beam M, the first sub-beam S1, and the second sub-beam S2 on the information track 7 formed on the optical disc 6, respectively.
[0051]
Referring to FIG. 3, an information track 7 on which information is recorded is formed in a spiral shape on the optical disc 6. The information track 7 is constituted by a groove formed on the surface of the optical disc 6. The optical disc 6 is constituted by, for example, a CD-R / RW, a DVD-R / -RW, or the like. On the information track 7 formed in a spiral shape on the optical disk 6, information is recorded from the inner peripheral side to the outer peripheral side of the optical disk 6. On the information track 7 formed in a spiral shape on the optical disc 6, a recording area R5 on which information has already been recorded is arranged on the inner peripheral side of the information track 7, and an unrecorded area R6 on which information has not yet been recorded is located. It is arranged on the outer peripheral side of the information track 7. The recording area R5 is shown with diagonal lines. When additional information is recorded on such an optical disk, information recording is started from the boundary between the recording area R5 and the unrecorded area R6.
[0052]
In the example shown in FIG. 3, the optical head 100 irradiates the main beam M, the first sub-beam S1, and the second sub-beam S2 to the boundary between the recording area R5 and the unrecorded area R6 arranged on the information track 7. ing. The main beam M converges on the boundary between the recorded area R5 and the unrecorded area R6 in the information track 7. The first sub-beam S1 converges to a position preceding the main beam M along the scanning direction of the optical head with respect to the optical disk 6. The second sub-beam S2 is converged at a position following the main beam M in the scanning direction of the optical head with respect to the optical disk 6. The first sub-beam S1 that precedes the main beam M converges on the outer peripheral side of the optical disk 6 from the main beam M by about 約 of the track pitch of the information track 7. The second sub-beam S2 following the main beam M converges on the inner circumference side of the optical disk 6 with respect to the main beam M by about の of the track pitch of the information track 7.
[0053]
The first sub-beam S1 converges so as to straddle the first region R1 of the information track 7 and the second region R2 of the information track 7 arranged on the outer peripheral side of the first region R1 of the information track 7. The second sub-beam S2 includes a third region R3 of the information track 7 and a fourth region R4 of the information track 7 disposed adjacent to the third region R3 of the information track 7 on the inner peripheral side. Converge to straddle.
[0054]
As described above, the first sub-beam S1 preceding the main beam M overlaps the unrecorded area R6 on both the inner peripheral side and the outer peripheral side thereof, and the second sub-beam S1 following the main beam M S2 overlaps the recording area R6 on both the inner side and the outer side.
[0055]
The main beam M, the first sub-beam S1, and the second sub-beam S2 reflected by the optical disk 6 pass through the objective lens 2, are reflected by the reflection lens 105, pass through the condenser lens 104, and are passed by the beam splitter 5. The traveling direction is changed to a substantially right angle.
[0056]
The main beam M, the first sub beam S1, and the second sub beam S2 whose traveling directions have been changed by the beam splitter 5 pass through the hologram 109 and the cylindrical lens 110, and enter the photodetector 3, respectively.
[0057]
FIG. 4 is a front view illustrating the configuration of the photodetector 3. The light detection record 3 has a main beam detection unit 16. The main beam detection unit 16 is divided into two areas along a direction corresponding to the circumferential direction of the spirally formed information track 7 on the optical disc 6. The main beam detection unit 16 detects a main beam signal A and a main beam signal B corresponding to each of the divided areas based on the incident main beam, and outputs them to the preamplifier 201.
[0058]
On both sides of the main beam detection unit 16, a first sub-beam detection unit 17 and a second sub-beam detection unit 18 are arranged. The first sub-beam detection unit 17 and the second sub-beam detection unit 18 are divided into two regions along the direction corresponding to the circumferential direction of the information track 7, similarly to the main beam detection unit 16. . The first sub-beam detection unit 17 detects a first sub-beam signal C and a first sub-beam signal D respectively corresponding to the divided areas based on the incident first sub-beam S1, and sends them to the preamplifier 201, respectively. Output. The second sub-beam detection unit 18 detects a second sub-beam signal E and a second sub-beam signal F based on the incident second sub-beam S2, and outputs them to the preamplifier 201, respectively.
[0059]
The preamplifier 201 includes a main beam signal A and a main beam signal B detected by the main beam detection unit 16, a first sub beam signal C and a first sub beam signal D detected by the first sub beam detection unit 17, and a second The second sub-beam signal E and the second sub-beam signal F detected by the sub-beam detection unit 18 are respectively amplified and output to the differential push-pull signal generator 10.
[0060]
The differential push-pull signal generator 10 outputs the main beam signal A, the main beam signal B, the first sub beam signal C, the first sub beam signal D, the second sub beam signal E, and the second sub beam output from the preamplifier 201. Based on the signal F, a differential push-pull signal is generated according to the following (Equation 1) and output to the digital signal processor (DSP) 13.
[0061]
(AB) −α × ((CD) + (EF)) (α is a constant) (Equation 1)
The DSP 13 converts the differential push-pull signal output from the differential push-pull signal generator 10 into a digital signal, and performs digital filter operation processing for phase compensation and gain compensation by addition and multiplication by a core processor built in the DSP 13. Apply to signal. Then, the digital signal subjected to the digital filter operation processing is converted into an analog signal again by a DA converter built in the DSP 13 and output to the tracking drive circuit 12, the spindle drive circuit 205, and the rotation direction setting device 11. .
[0062]
The tracking drive circuit 12 current-amplifies the differential push-pull signal output from the DSP 13 and moves the optical head 100 along the radial direction of the optical disk 6 so that the main beam M emitted from the optical head 100 follows the information track 7. 100 is driven. Therefore, the main beam M can be controlled so that the main beam M follows the track deviation represented by the differential push-pull signal.
[0063]
According to the differential push-pull signal output from the DSP 13, the rotation direction setting device 11 causes the first sub-beam S1 to converge before the main beam M along the scanning direction of the optical head 100 with respect to the optical disk 6, and The rotation direction of the spindle motor 9 is set so that the second sub-beam S2 follows the main beam M and converges along the scanning direction of the optical head 100 with respect to 6.
[0064]
The spindle drive circuit 205 drives the spindle motor 9 based on the rotation direction of the spindle motor 9 set by the rotation direction setting unit 11 and the rotation speed command value output from the DSP 13.
[0065]
As described above, according to the first embodiment, the first sub-beam S1 converges to a position preceding the main beam M along the scanning direction of the optical head 100 with respect to the optical disk 6, and the second sub-beam S2 is The beam converges to a position following the main beam M along the scanning direction of the optical head 100 with respect to the optical disk 6, and the diffraction grating 1 outputs the first sub beam S1 preceding the main beam M to the main beam M. The light beam and the main beam M are converged so that the second sub-beam S2 converging on the outer peripheral side of the optical disk 6 with respect to the main beam M and converging on the inner peripheral side of the optical disk 6 with respect to the main beam M. The beam is split into a first sub beam S1 and a second sub beam S2.
[0066]
For this reason, the leading side is straddled so as to straddle the unrecorded area R6 of the information track 7 and another unrecorded area R6 of the information track 7 disposed adjacent to the outer peripheral side of the unrecorded area R6 of the information track 7. The first sub-beam S1 can be made to converge, and the recording area R5 of the information track 7 and another recording area R5 of the information track 7 disposed adjacent to the recording area R5 of the information track 7 on the inner peripheral side. The second sub-beam S2 that follows can be converged so as to straddle. Accordingly, the balance between the first sub-beam signal detected based on the first sub-beam S1 and the second sub-beam signal detected based on the second sub-beam S2 is improved. No offset occurs in the differential push-pull signal generated by the second sub-beam signal. As a result, the quality of the recording / reproducing signal can be improved.
[0067]
Conventionally, since the light amount distribution of the first sub-beam S1 and the light amount distribution of the second sub-beam S2 fluctuate at the boundary between the recording region R5 and the unrecorded region R6, the detection is performed based on the first sub-beam S1. An imbalance occurs between the detected first sub beam signal C and first sub beam signal D and the second sub beam signal E and second sub beam signal F detected based on the second sub beam S2. For this reason, an error occurs in the calculation result obtained by the above-described (Equation 1), and this error causes a track shift.
[0068]
In the first embodiment, the first sub-beam S1 overlaps the unrecorded area R6 on both the inner side and the outer side. Therefore, in the calculation of (C-D) in (Equation 1), the fluctuation of the reflected light amount at the boundary between the recording area R5 and the unrecorded area R6 is canceled. The second sub-beam S2 overlaps the recording area R5 on both the inner and outer peripheral sides. Therefore, in the calculation of (E−F) in (Equation 1), the fluctuation of the reflected light amount at the boundary between the recording area R5 and the unrecorded area R6 is canceled. Therefore, the offset of the tracking error signal generated at the boundary between the recording area R5 and the unrecorded area R6 can be removed.
[0069]
The first sub-beam S1 converges to the outer peripheral side of the optical disk 6 by about の of the track pitch of the information track 7, and the second sub-beam S2 forms the information track by about の of the track pitch. 7 are converged on the inner peripheral side of the optical disk 6. When the first sub-beam S1 and the second sub-beam S2 converge at a position shifted by about 1/2 of the track pitch of the information track 7, a coefficient α shown in the following (formula 2) is multiplied. The amplitude of the push-pull signal due to the sub-beam before the operation is maximized.
[0070]
The more the position where the first sub-beam S1 converges is shifted from the position on the outer periphery side of the information track 7 by about 1/2 of the track pitch, and the more the position where the first sub-beam S2 converges is the track pitch , The amplitude of the push-pull signal by the sub-beam before being multiplied by the coefficient α shown in the following (Equation 2) decreases as the position deviates from the position on the inner peripheral side of the information track 7 by about 1/2. I do.
[0071]
(CD) + (EF) (Equation 2)
When the amplitude of the push-pull signal due to the sub-beam before multiplying by the coefficient α is reduced in this manner, the optical disk 6 is susceptible to disturbance such as a scratch on the surface.
[0072]
In the first embodiment, an example is shown in which information is recorded from the inner peripheral side to the outer peripheral side on the spirally formed information track 7 on the optical disk 6, but the present invention is not limited to this. On the information track 7 formed in a spiral shape on the optical disc 6, information may be recorded from the outer peripheral side toward the inner peripheral side. In this case, the rotation direction of the spindle motor for rotating the optical disk 6 may be reversed.
[0073]
(Embodiment 2)
FIG. 5 is a block diagram illustrating a configuration of an optical disc device 200A according to the second embodiment. In Embodiment 1, the same components as those of the optical disk device 200 described above with reference to FIGS. 1 to 4 are denoted by the same reference numerals. Therefore, a detailed description of these components will be omitted. The difference from the optical disk device 200 described above is that the differential push-pull signal generator 10 is provided with a differential push-pull signal generator 10A, the DSP 13 is provided with a DSP 13A, and the tracking drive circuit 12 is replaced with a tracking drive circuit 12. The point is that a drive circuit 12A is provided, and the objective lens displacement amount generation circuit 15 and the transfer device 14 are further provided.
[0074]
The differential push-pull signal generator 10A is configured by an operational amplifier. Based on the main beam signal A and the main beam signal B amplified by the preamplifier 201, the main beam push-pull signal is generated according to (Equation 3) shown below. Generate an MPP.
[0075]
MPP = (AB) (Equation 3)
The differential push-pull signal generator 10A also performs the following based on the first sub beam signal C, the first sub beam signal D, the second sub beam signal E, and the second sub beam signal F amplified by the preamplifier 201. The sub beam push-pull signal SPP is generated according to (Equation 4).
[0076]
SPP = α × ((C + E) − (D + F)) (Equation 4)
Here, the coefficient α is a predetermined constant.
[0077]
The differential push-pull signal generator 10A further includes a main beam signal A, a main beam signal B, a first sub beam signal C, a first sub beam signal D, a second sub beam signal E, a second sub beam signal F, and a predetermined Based on the correction coefficient β, a corrected differential push-pull signal CDPP is generated according to (Equation 5) shown below.
[0078]
CDPP = (AB) −α × ((1 + β) × (C + E) − (1−β) × (D + F)) (Equation 5)
The corrected differential push-pull signal CDPP when the correction coefficient β is zero is set as the pre-correction differential push-pull signal. The differential push-pull signal before correction is the same as the differential push-pull signal generated by the differential push-pull signal generator 10 described in the first embodiment.
[0079]
The DSP 13A uses the differential push-pull signal generator 10A so that the timing at which the sub-beam push-pull signal SPP generated by the differential push-pull signal generator 10A crosses zero matches the timing at which the main beam push-pull signal MPP crosses zero. A predetermined correction coefficient β for generating the corrected differential push-pull signal CDPP is changed.
[0080]
The transfer device 14 has a transfer motor drive circuit 302. The transfer motor drive circuit 302 current-amplifies the corrected differential push-pull signal CDPP generated by the differential push-pull signal generator 10A according to the correction coefficient β changed by the DSP 13A, and the radius of the optical disc 6 on which the information track 7 is formed. A signal for moving the optical head 100 along the direction is output to the transfer motor 304. The transfer motor 304 transfers the optical head 100 along the radial direction of the optical disk 6 on which the information tracks 7 are formed, based on a signal output from the transfer motor drive circuit 302.
[0081]
The tracking drive circuit 12A is arranged along the radial direction of the optical disc 6 on which the information tracks 7 are formed, based on the corrected differential push-pull signal CDPP generated by the differential push-pull signal generator 10A according to the correction coefficient β changed by the DSP 10A. This is provided to drive the objective lens 2 provided in the optical head 100 by a tracking actuator (not shown).
[0082]
The DSP 13A converts the corrected differential push-pull signal into a digital value, and processes the digital value with a built-in core processor. The processing by the core processor built in the DSP 13A is processing for performing phase compensation and gain compensation for stabilizing the tracking control system, and is realized by a digital filter. The low-frequency component of the corrected differential push-pull signal CDPP processed by the core processor is converted into an analog signal again by a DA converter built in the DSP 13A, and supplied to the transfer motor drive circuit 302. Accordingly, the transfer stage 14 responds to the low frequency component of the corrected differential push-pull signal CDPP, and the objective lens 106 provided in the optical head 100 responds to the high frequency component of the corrected differential push-pull signal CDPP. In this way, the main beam M emitted from the optical head 100 is subjected to tracking control so as to follow the information track 7.
[0083]
The DSP 13A also has a function of disabling the tracking control. The DSP 13A also has a function of outputting a predetermined value to the tracking drive circuit 12A in a state where the tracking control is disabled, and displacing the objective lens 2 provided in the optical head 100.
[0084]
The objective lens displacement amount generation circuit 15 is driven by the tracking drive circuit 12A based on the main beam signals A and B, the first sub beam signals C and D, and the second sub beam signals E and F amplified by the preamplifier 201. An objective lens displacement signal indicating the amount of displacement of the objective lens 2 of the optical head 100 is output to the DSP 13A.
[0085]
FIG. 6 is a diagram showing a main beam push-pull signal MPP, a sub-beam push-pull signal SPP, and a differential push-pull signal before correction for explaining the operation of the optical disc device 200A according to the second embodiment. The horizontal axis indicates a position on the information track 7 along the radial direction of the optical disc 6.
[0086]
The cross section of the optical disk 6 in which the information tracks 7 are formed in a spiral shape so as to correspond to the respective waveforms of the main beam push-pull signal MPP, the sub-beam push-pull signal SPP, and the differential push-pull signal before correction is shown. The position Xa, the position Xb, and the position Xc indicate the position of the center of the information track 7 along the radial direction of the optical disk 6.
[0087]
Each waveform shows a waveform when the tracking control is not operating. Therefore, the displacement of the objective lens 2 from the neutral position of the objective lens 2 along the radial direction of the optical disk 6 is zero. When the objective lens 2 is at the neutral position, the optical axis of the objective lens 2 and the optical axis of the incident light beam coincide with each other.
[0088]
If the beam spot where the sub-beam converges has coma as described above, the zero-cross position of the sub-beam push-pull signal SPP is shifted from the center of the information track 7 and the zero cross position of the main beam push-pull signal MPP is shifted. The position is shifted from the center of the information track 7.
[0089]
However, since the deviation of the main beam push-pull signal MPP is substantially zero, it can be ignored in signal recording and reproduction. Therefore, in the description of the second embodiment, the description will be made assuming that the deviation amount of the main beam push-pull signal MPP is zero.
[0090]
The main beam push-pull signal MPP crosses zero at positions Xa, Xb, and Xc indicating the center of the information track 7 along the radial direction of the optical disc 6.
[0091]
If there is an error in the mounting of the photodetector 3 provided on the optical head 100, the position where the main beam push-pull signal MPP crosses zero is shifted from the center of the information track 7. In the following description, it is assumed that there is no error in mounting the photodetector 3.
[0092]
Similar to the main beam push-pull signal MPP, the sub-beam push-pull signal SPP indicated by a broken line crosses zero at positions Xa, Xb, and Xc indicating the center position of the information track 7.
[0093]
When coma aberration occurs in the beam spot where the sub-beam push-pull signal SPP converges, the sub-beam push-pull signal SPP is deviated from the center of the information track 7 by positions Xa3, Xb3, and Xc3 as indicated by the solid line. Zero crossing at.
[0094]
As described above, when coma aberration occurs in the beam spot, the sub-beam push-pull signal SPP does not become zero level even if the main beam M converges at the center of the information track 7, and the information track 7 Zero crossing occurs at positions Xa3, Xb3, and Xc3 deviated from the center.
[0095]
It should be noted that the main beam push-pull signal MPP and the sub beam push-pull signal SPP cross zero near the center of the information track 7 and also cross near the middle point between the information tracks 7. I have. Whether the zero crossing position is the center of the information track 7 or the midpoint position of the information track 7 or the information track 7 can be determined based on the level of the amount of light reflected from the surface of the optical disk 6 and the like.
[0096]
In the present specification, the “zero-crossing position” indicates a zero-crossing position near the center of the information track 7 unless otherwise specified.
[0097]
As described above, the main beam push-pull signal MPP crosses zero at the positions Xa, Xb, and Xc indicating the center of the information track 7, and the sub-beam push-pull signal SPP deviates from the center Xa3, position of the information track 7. Since zero crossing occurs at Xb3 and Xc3, the differential push-pull signal before correction includes a position Xa2 between positions Xa and Xa3, and a position Xb2 between positions Xb and Xb3, as shown in FIG. Zero crossing occurs at a position Xc2 between the position Xc and the position Xc3.
[0098]
Therefore, when tracking control of the optical head 100 is performed such that the uncorrected differential push-pull signal crosses zero at positions Xa, Xb, and Xc indicating the center position of the information track 7, the beam spot of the main beam M becomes Converge to a position deviated from the center of.
[0099]
FIG. 7 is a graph showing a relationship between an objective lens displacement amount and a phase shift in the optical disc device 200A according to the second embodiment. The horizontal axis indicates the amount of displacement of the objective lens, and the vertical axis indicates the phase shift. Referring to FIG. 7, when the objective lens displacement amount is zero, a predetermined phase shift P occurs.
[0100]
Hereinafter, an operation in which the DSP 13A corrects the shift amount between the position where the sub-beam push-pull signal SPP crosses zero and the center of the information track 7 by changing the correction coefficient β will be described.
[0101]
The DSP 13A measures a deviation between a timing at which the main beam push-pull signal MPP crosses zero and a timing at which the sub-beam push-pull signal SPP crosses zero at the center of the information track 7 with the tracking control disabled. The DSP 13A changes the above-described correction coefficient β so that the timing at which the sub-beam push-pull signal SPP crosses zero coincides with the timing at which the main beam push-pull signal MPP crosses zero. Next, the DSP 13A stores the changed value of the correction coefficient β in a predetermined memory. In this state, the value of the objective lens displacement output from the objective lens displacement generating circuit 15 is stored in a predetermined memory.
[0102]
The process of changing the correction coefficient β so that the timing at which the sub-beam push-pull signal SPP crosses zero matches the timing at which the main beam push-pull signal MPP crosses zero is performed by the main beam push-pull signal output from the differential push-pull signal generator 10A. It can be easily realized by the DSP 13A converting the MPP and the sub-beam push-pull signal SPP into digital values and processing them.
[0103]
FIG. 8 is a diagram showing a main beam push-pull signal MPP, a sub-beam push-pull signal SPP, and a corrected differential push-pull signal CDPP for explaining the operation of the optical disc device 200A according to the second embodiment. 6, the horizontal axis indicates the position on the information track 7 along the radial direction of the optical disk 6. The cross section of the optical disk 6 in which the information tracks 7 are spirally formed so as to correspond to the respective waveforms of the main beam push-pull signal MPP, the sub-beam push-pull signal SPP, and the corrected differential push-pull signal CDPP is shown. The positions Xa, Xb, and Xc indicate the positions of the centers of the information tracks 7 along the radial direction of the optical disk 6, respectively.
[0104]
The main beam push-pull signal MPP crosses zero at positions Xa, Xb, and Xc indicating the center of the information track 7 along the radial direction of the optical disc 6.
[0105]
The sub-beam push-pull signal SPP indicated by the broken line indicates the sub-beam push-pull signal when the correction coefficient β is zero. The sub-beam push-pull signal SPP indicated by a solid line indicates the sub-beam push-pull signal when the correction coefficient β is set to an optimum value. The sub-beam push-pull signal SPP indicated by a solid line crosses zero at positions Xa, Xb, and Xc indicating the center of the information track 7. As described above, the timing at which the sub-beam push-pull signal SPP crosses zero as indicated by the solid line with the correction coefficient β at the optimum value coincides with the timing at which the main beam push-pull signal MPP crosses zero. The corrected differential push-pull signal CDPP generated based on the optimum correction coefficient β crosses zero at positions Xa, Xb, and Xc indicating the center position of the information track 7.
[0106]
As described above, according to the second embodiment, the timing at which the sub-beam push-pull signal SPP generated by the differential push-pull signal generator 10A crosses zero matches the timing at which the main beam push-pull signal MPP crosses zero. A predetermined correction coefficient β for generating the corrected differential push-pull signal CDPP is changed by the differential push-pull signal generator 10A.
[0107]
Therefore, the timing at which the sub-beam push-pull signal SPP crosses zero can be matched with the timing at which the main beam push-pull signal MPP crosses zero. Accordingly, the timing at which the sub-beam push-pull signal SPP crosses zero coincides with the timing corresponding to the center of the information track 7. As a result, it is possible to realize good tracking control in which no track deviation occurs.
[0108]
As described above, when there is an error in mounting the photodetector 3, the position where the main beam push-pull signal MPP crosses zero is shifted from the center of the information track 7. Therefore, if there is an error in the mounting of the photodetector 3, the correction coefficient β is changed so that the timing at which the sub beam push-pull signal SPP crosses zero matches the timing at which the main beam push-pull signal MPP crosses zero. The spot position of the main beam is shifted from the center of the information track 7.
[0109]
However, even when there is an error in the mounting of the photodetector 3, the timing at which the main beam push-pull signal MPP becomes the level of the center of the amplitude of the main beam push-pull signal MPP corresponds to the center of the information track 7. Match the timing.
[0110]
Therefore, when there is an error in the attachment of the photodetector 3, the level of the main beam push-pull signal MPP and the level of the The correction coefficient β may be changed so that the level of the beam push-pull signal SPP becomes equal.
[0111]
Next, another operation of the optical disc device 200 according to the second embodiment will be described.
[0112]
When the tracking control is disabled, the DSP 13A outputs a predetermined value to the tracking drive circuit 12A to displace the objective lens 2 provided in the optical head 100. Thereafter, the DSP 13A measures a shift between the timing at which the main beam push-pull signal MPP crosses zero at the center of the information track 7 and the timing at which the sub-beam push-pull signal SPP crosses zero. The DSP 13A changes the above-described correction coefficient β so that the timing at which the sub-beam push-pull signal SPP crosses zero coincides with the timing at which the main beam push-pull signal MPP crosses zero.
[0113]
Next, the DSP 13A stores the changed value of the correction coefficient β in a predetermined memory. The value of the changed correction coefficient β is a value at which the correction coefficient β is optimized when a predetermined value is output to the tracking drive circuit 12A and the objective lens 2 is displaced, that is, the corrected differential push-pull signal CDPP is This is a value at which the zero crossing position coincides with the center of the information track 7.
[0114]
Next, the operation of the objective lens displacement amount generation circuit 15 will be described. The objective lens displacement amount generation circuit 15 is configured by an operational amplifier, and is based on the main beam signals A and B, the first sub beam signals C and D, and the second sub beam signals E and F amplified by the preamplifier 201. Then, an objective lens displacement signal LS representing the displacement of the objective lens 2 of the optical head 100 driven by the tracking drive circuit 12A is generated according to the following (Equation 6) and output to the DSP 13A.
[0115]
LS = (AB) + α × ((C + E) − (D + F)) (α is a constant) (Equation 6)
The DSP 13A also stores the objective lens displacement LS output from the objective lens displacement generation circuit 15 in a predetermined memory.
[0116]
Next, the DSP 13A sets the optimal value of the correction coefficient β in a state where the value set in the tracking drive circuit 12A is changed while changing the value set in the tracking drive circuit 12A, and sets the objective lens displacement amount generation circuit 15 Is measured, and the value of the optimum correction coefficient β and the output value from the objective lens displacement amount generation circuit 15 are stored in a predetermined memory. Therefore, the memory provided in the DSP 15 stores a table indicating the relationship between the output value from the objective lens displacement amount generation circuit 15 and the optimum correction coefficient β. The processing for obtaining the optimum correction coefficient β is the same as the above-described processing for obtaining the optimum correction coefficient β without displacing the objective lens 2.
[0117]
Next, the DSP 13A takes in the objective lens displacement amount output from the objective lens displacement amount generation circuit 15 in a state where the tracking control is operated. The DSP 13A reads the optimal correction coefficient β corresponding to the objective lens displacement amount output from the objective lens displacement amount generation circuit 15 from the previously prepared table, and based on the read correction coefficient β, the differential push-pull signal. The correction coefficient β of the generation circuit 10A is changed. Accordingly, the phase shift shown in FIG. 7 caused by the shift between the zero cross of the sub beam push-pull signal SPP and the center of the information track 7 is removed.
[0118]
When dust or the like having a reflectance of zero adheres to the surface of the optical disk 6, the level of the sub-beam push-pull signal SPP becomes zero because the correction coefficient β is changed. Therefore, tracking control does not become unstable due to dust or the like adhering to the surface of the optical disc 6.
[0119]
FIG. 9 is a waveform diagram for explaining still another operation of the optical disc device 200A according to the second embodiment. For the sake of simplicity, it is assumed that there is no deviation between the zero-cross position of the sub-beam push-pull signal SPP and the center of the information track 7.
[0120]
The main beam push-pull signal MPP indicated by the broken line represents the main beam push-pull signal when the objective lens 2 is at the neutral position, and the main beam push-pull signal MPP indicated by the solid line indicates that the objective lens 2 has a predetermined amount. 5 shows the main beam push-pull signal when the main beam is displaced.
[0121]
Similarly, the sub-beam push-pull signal SPP indicated by the broken line represents the sub-beam push-pull signal when the objective lens 2 is at the neutral position, and the sub-beam push-pull signal SPP indicated by the solid line is Represents a sub-beam push-pull signal when is displaced by a predetermined amount. The objective lens displacement signal LS indicated by the broken line represents the objective lens displacement signal when the objective lens 2 is at the neutral position, and the objective lens displacement signal LS indicated by the solid line indicates that the objective lens 2 is displaced by a predetermined amount. 5 shows the objective lens displacement signal when the camera is moving.
[0122]
As shown in FIG. 9, when the objective lens 2 is at the neutral position, the average value of the maximum value and the minimum value in the main beam push-pull signal MPP is at the zero level, and the maximum value in the sub beam push-pull signal SPP is The average of the value and the minimum value is at the zero level. When the objective lens 2 is at the neutral position, the phase of the AC component is shifted by 180 degrees, so that the objective lens displacement signal LS is zero.
[0123]
As shown in FIG. 9, when the objective lens 2 is displaced by a predetermined amount, the average value of the maximum value and the minimum value in the main beam push-pull signal MPP is not zero level, and The average value of the maximum value and the minimum value is no longer at the zero level. The main beam push-pull signal MPP and the sub-beam push-pull signal SPP are 180 degrees out of phase with each other in the AC component. Therefore, the objective lens displacement signal LS is a signal having only the DC component because the AC component is canceled. The average value of the maximum value and the minimum value of the main beam push-pull signal MPP and the average value of the maximum value and the minimum value of the sub beam push-pull signal SPP change according to the amount of displacement of the objective lens 2. Therefore, the objective lens displacement signal LS indicates the amount of displacement of the objective lens 2.
[0124]
If there is a deviation between the zero cross position of the sub-beam push-pull signal SPP and the center of the information track 7, the AC component is not completely canceled, but the AC component is ignored because it is extremely small compared to the change in the DC component. be able to.
[0125]
When the phase shift between the position where the sub-beam push-pull signal SPP crosses zero and the center of the information track 7 shows the characteristic represented by the broken line in FIG. Since the amount hardly changes, only the optimum correction coefficient β when there is no displacement of the objective lens 2 may be obtained, and the value of the correction coefficient β may be fixed to that value regardless of the displacement amount of the objective lens 2. This simplifies the processing of the DSP 10A.
[0126]
In the above description, an example in which the correction coefficient β is changed so that the timing at which the sub beam push-pull signal SPP crosses zero with the timing at which the sub beam push-pull signal SPP crosses zero with the main beam push-pull signal MPP has been described. However, the present invention is not limited to this. . Instead of changing the correction coefficient β, the target position of the tracking control may be changed. Specifically, tracking control may be performed based on a signal obtained by adding an offset to the differential push-pull signal before correction. In this case, the offset amount is changed instead of changing the correction coefficient β.
[0127]
Further, a similar result can be obtained by generating the corrected differential push-pull signal CDPP based on (Equation 7) shown below and changing the correction coefficient β ′.
[0128]
CDPP = (AB) −α × (β ′ × (C + E) − (1 / β ′) × (D + F)) (Equation 7)
In the above-described second embodiment, the DSP 13A measures the shift between the timing at which the main beam push-pull signal MPP crosses zero at the center of the groove and the timing at which the sub-beam push-pull signal SPP crosses zero, and calculates the sub-beam push. Although the example in which the correction coefficient β is changed so that the timing at which the pull signal SPP crosses zero and the timing at which the main beam push-pull signal MPP crosses zero has been described, the present invention is not limited to this. The optimum correction coefficient β can also be obtained by a method described later.
[0129]
The DSP 13A operates tracking control. Therefore, the main beam M is controlled to follow the center of the information track 7. Then, the DSP 13A moves the light beam to the inner groove every time the optical disk 6 makes one rotation. Hereinafter, a period during which the light beam moves is referred to as a jumping period. The information track 7 of the optical disk 6 is formed in a spiral shape. Therefore, when the light beam is controlled to follow the information track 7, the light beam moves by one groove toward the outer circumference every time the optical disk 6 makes one rotation. Therefore, when the light beam moves to the inner groove every time the optical disk 6 makes one rotation, the beam spot where the light beam converges is always located at a predetermined position on the information track 7. Further, the transfer table 14 is controlled such that the displacement amount of the objective lens 2 becomes zero.
[0130]
When the light beam is moved to the inner groove, the tracking control is stopped, the objective lens 2 is moved to the inner periphery by the tracking drive circuit 12A, and the tracking is performed again after the light beam moves to the inner information track. Activate control.
[0131]
The DSP 13A measures the positive-side amplitude and the negative-side amplitude of the main beam push-pull signal MPP during the jumping period with reference to the level of the main beam push-pull signal MPP during periods other than the jumping period. The positive amplitude is defined as a positive amplitude BV, and the negative amplitude is defined as a negative amplitude SV. The DSP 13A changes the coefficient β so that the positive amplitude BV becomes equal to the negative amplitude SV.
[0132]
FIG. 10 is a waveform diagram of a main beam push-pull signal MPP, a sub-beam push-pull signal SPP, and a differential push-pull signal before correction for explaining still another operation of the optical disc device 200A according to the second embodiment.
[0133]
The main beam push-pull signal MPP crosses zero at the midpoint position P10 of the information tracks 7 adjacent to each other. The sub-beam push-pull signal SPP has a zero cross at a position separated by a distance H from the position P10. Therefore, the differential push-pull signal before correction crosses zero at a position shifted from the midpoint position P10. The distance H corresponds to the displacement P shown in FIG.
[0134]
FIG. 11 is a waveform diagram of a main beam push-pull signal MPP, a sub-beam push-pull signal SPP, and a corrected differential push-pull signal CDPP for explaining still another operation of the optical disc device 200A according to the second embodiment.
[0135]
While changing the correction coefficient β, the DSP 13A obtains the value of the correction coefficient β at which the positive amplitude BV and the negative amplitude SV of the main beam push-pull signal MPP become equal, as shown in FIG. When the positive side amplitude BV and the negative side amplitude SV of the main beam push-pull signal MPP become equal, the main beam push-pull signal MPP crosses zero at the midpoint of the information tracks 7 adjacent to each other. If the main beam push-pull signal MPP crosses zero at the midpoint of the adjacent information tracks 7, the main beam push-pull signal MPP also crosses zero at the center of the information track 7. Therefore, off-track is eliminated.
[0136]
As shown in FIG. 11, the positive and negative amplitudes of the corrected differential push-pull signal CDPP are unbalanced. For this reason, during a predetermined period after the start of the tracking control, the transition to the tracking control becomes unstable due to overshoot. Therefore, during a predetermined period after the start of the tracking control, the tracking control is performed with the correction coefficient β set to zero. The predetermined period is a period until the tracking control system is settled, and is generally about several milliseconds.
[0137]
When the correction coefficient β becomes extremely large, the dynamic range on one side of the corrected differential push-pull signal becomes extremely narrow, so that disturbance such as vibration may cause unstable tracking control. Therefore, the range in which the correction coefficient β is changed is limited.
[0138]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an optical head and an optical disk device having good quality of a signal recorded on an optical disk and / or a signal reproduced from the optical disk.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disk device according to a first embodiment.
FIG. 2 is a diagram showing a configuration of an optical head provided in the optical disk device according to the first embodiment.
FIG. 3 is a schematic diagram showing a relationship between a light beam emitted from the optical head to the information medium and information tracks formed on the information medium according to the first embodiment;
FIG. 4 is a front view showing a configuration of a photodetector provided in the optical head according to the first embodiment.
FIG. 5 is a block diagram showing a configuration of an optical disc device according to a second embodiment.
FIG. 6 is a waveform chart for explaining the operation of the optical disc device according to the second embodiment.
FIG. 7 is a graph illustrating a relationship between an objective lens displacement amount and a phase shift in the optical disc device according to the second embodiment.
FIG. 8 is another waveform chart for explaining the operation of the optical disc device according to the second embodiment.
FIG. 9 is a waveform chart for explaining still another operation of the optical disc device according to the second embodiment.
FIG. 10 is a waveform chart for explaining still another operation of the optical disc device according to the second embodiment.
FIG. 11 is a waveform chart for explaining still another operation of the optical disc device according to the second embodiment.
FIG. 12 is a schematic view showing a relationship between a light beam emitted from a conventional optical head to an information medium and an information track formed on the information medium.
[Explanation of symbols]
1 diffraction grating
2 Objective lens
3 Photodetector
4 Semiconductor laser
5 Beam splitter
6 Information media
7 Information Track
8 Light beam
9 Spindle motor
10 Differential push-pull signal generator
11 Rotation direction setting device
12 Tracking drive circuit
13 Digital signal processor
14 Transfer device
15 Objective lens displacement generation circuit
16 Main beam detection unit
17, 18 Sub main beam detection unit
100 optical head
200 optical disk device
R1, R2, R3, R4 regions
R5 recording area
R6 unrecorded area

Claims (23)

An optical head for irradiating a light beam to the information track in order to record information on an information track formed in a spiral shape on a rotating information medium,
A light source for emitting the light beam;
A diffraction grating that diffracts the light beam emitted from the light source so as to split the light beam into a main beam, a first sub beam, and a second sub beam;
An objective lens for converging the main beam, the first sub-beam, and the second sub-beam diffracted by the diffraction grating to the information tracks formed on the information medium, respectively;
A main beam signal, a first sub beam signal, and a second sub beam signal based on the main beam, the first sub beam, and the second sub beam respectively reflected on the information track formed on the information medium; And a photodetector for respectively detecting
The first sub-beam converges to a position preceding the main beam along the scanning direction of the optical head with respect to the information medium, and the second sub-beam converges in the scanning direction of the optical head with respect to the information medium. Along and converges to a position following the main beam,
The diffraction grating is configured such that the first sub-beam preceding the main beam converges to the outer peripheral side of the information medium with respect to the main beam, and the second sub-beam following the main beam is connected to the main beam. An optical head, wherein the light beam is split into the main beam, the first sub-beam, and the second sub-beam so that the light beam converges to an inner peripheral side of the information medium. The diffraction grating is such that the first sub-beam converges to the outer peripheral side of the information medium beyond the information track by about １ ／ of a track pitch of the spirally formed information track, and the second sub-beam is The light beam is split into the main beam, the first sub-beam, and the second sub-beam so that the light beam converges to the inner peripheral side of the information medium from the information track by about の of the track pitch. The optical head according to claim 1. The first sub-beam converges so as to straddle a first area of the information track and a second area of the information track disposed adjacent to the first area of the information track on the outer peripheral side,
The second sub-beam converges so as to straddle a third area of the information track and a fourth area of the information track disposed adjacent to the third area of the information track on the inner peripheral side. The optical head according to claim 1. The optical head according to claim 1, wherein the information track is a groove formed on a surface of the information medium. 2. The optical head according to claim 1, wherein the information is recorded on the information track formed in a spiral shape on the information medium from an inner peripheral side toward an outer peripheral side. 3. In the information track formed in a spiral shape on the information medium, a recording area in which the information is already recorded is arranged on the inner peripheral side of the information track, and an unrecorded area in which the information is not yet recorded. 2. The optical head according to claim 1, wherein the optical head is disposed on an outer peripheral side of the information track. The optical head starts recording the main beam, the first sub-beam, and the second sub-beam on the information track from a boundary between the recording area and the unrecorded area arranged on the information track. The optical head according to claim 6. The main beam is a zero-order diffracted light of the light beam,
The first sub-beam is one of a positive first-order diffracted light and a minus first-order diffracted light of the light beam,
The optical head according to claim 1, wherein the second sub-beam is the other of the plus first-order diffracted light and the minus first-order diffracted light of the light beam. A beam splitter provided between the diffraction element and the objective lens for guiding the main beam, the first sub beam, and the second sub beam reflected on the information track to the photodetector; The optical head according to claim 1, comprising: An optical head according to claim 1,
A motor for rotating the information medium,
A differential push-pull signal generator for generating a differential push-pull signal based on the main beam signal, the first sub-beam signal, and the second sub-beam signal detected by the photodetector provided in the optical head; When,
In response to the differential push-pull signal generated by the differential push-pull signal generator, the first sub-beam converges ahead of the main beam along the scanning direction of the optical head with respect to the information medium, A rotation direction setting device that sets a rotation direction of the motor so that the second sub-beam converges behind the main beam along the scanning direction of the optical head with respect to the information medium. Characteristic optical disk device. Based on the differential push-pull signal generated by the differential push-pull signal generator, the light is emitted along the radial direction of the information medium so that the main beam emitted from the optical head follows the information track. 11. The optical disk device according to claim 10, further comprising a tracking drive circuit that drives the head. An optical head for irradiating an information track with a light beam for recording and / or reproducing information on an information track, comprising: a light source for emitting the light beam; and a main beam for emitting the light beam from the light source. A diffraction grating that diffracts the light into a first sub beam and a second sub beam so as to split the main beam, the first sub beam, and the second sub beam diffracted by the diffraction grating into the information medium. An objective lens that converges on the information track formed on the information medium, and a main lens, the first sub beam, and the second sub beam reflected on the information track formed on the information medium, respectively. An optical head including a light detector for detecting a beam signal, a first sub-beam signal, and a second sub-beam signal, respectively;
A main beam push-pull signal is generated based on the main beam signal detected by the photodetector provided in the optical head, and the first and second sub-beam signals detected by the photodetector are generated. Differential push-pull signal generation for generating a corrected differential push-pull signal based on the main beam signal, the first and second sub-beam signals, and a predetermined correction coefficient β. Vessels,
At the timing when the main beam push-pull signal MPP generated by the differential push-pull signal generator becomes the center level of the amplitude of the main beam push-pull signal MPP, the level of the main beam push-pull signal and the sub beam push Correction coefficient changing means for changing the predetermined correction coefficient β for generating the corrected differential push-pull signal by the differential push-pull signal generator so that the level of the pull signal becomes equal. Optical disk device. The light detector, a main beam detection unit that detects the main beam signal based on the main beam,
A first sub-beam detection unit that detects the first sub-beam signal based on the first sub-beam;
13. The optical disk device according to claim 12, further comprising a second sub-beam detection unit that detects the second sub-beam signal based on the second sub-beam. The main beam detecting unit, the first sub-beam detecting unit, and the second sub-beam detecting unit are respectively provided in two regions along a direction corresponding to a circumferential direction of the spirally formed information track. 14. The optical disk device according to claim 13, wherein the optical disk device is divided. Based on the corrected differential push-pull signal generated by the differential push-pull signal generator according to the correction coefficient β changed by the correction coefficient changing unit, the information track is formed along a radial direction of the information medium on which the information track is formed. 13. The optical disc device according to claim 12, further comprising a transfer device provided for transferring the optical head. Based on the corrected differential push-pull signal generated by the differential push-pull signal generator according to the correction coefficient β changed by the correction coefficient changing unit, the information track is formed along a radial direction of the information medium on which the information track is formed. 13. The optical disk device according to claim 12, further comprising a tracking drive circuit provided to drive the objective lens provided in the optical head. An objective lens displacement representing a displacement of the objective lens driven by the tracking drive circuit based on the main beam signal, the first sub beam signal, and the second sub beam signal detected by the photodetector; 17. The optical disk device according to claim 16, further comprising an objective lens displacement signal generation circuit that generates a signal. The objective lens generated by the objective lens displacement signal generation circuit while changing a set value set in the tracking drive circuit in a state in which the tracking control by the tracking drive circuit is deactivated, The level of the main beam push-pull signal is equal to the level of the sub-beam push-pull signal at the timing when the displacement signal and the main beam push-pull signal MPP become the level of the center of the amplitude of the main beam push-pull signal MPP. The optical disk device according to claim 17, wherein the predetermined correction coefficient β changed so as to be stored in a predetermined memory. An optical head for irradiating an information track with a light beam for recording and / or reproducing information on an information track, comprising: a light source for emitting the light beam; and a main beam for emitting the light beam from the light source. A diffraction grating that diffracts the light into a first sub beam and a second sub beam so as to split the main beam, the first sub beam, and the second sub beam diffracted by the diffraction grating into the information medium. An objective lens that converges on the information track formed on the information medium, and a main lens, the first sub beam, and the second sub beam reflected on the information track formed on the information medium, respectively. An optical head including a photodetector for detecting a beam signal, a first sub-beam signal, and a second sub-beam signal, respectively;
A main beam push-pull signal is generated based on the main beam signal detected by the photodetector provided in the optical head, and the first and second sub-beam signals detected by the photodetector are generated. Differential push-pull signal generation for generating a corrected differential push-pull signal based on the main beam signal, the first and second sub-beam signals, and a predetermined correction coefficient β. Vessels,
Based on the corrected differential push-pull signal, along a radial direction of the information medium on which the information track is formed, a tracking drive circuit provided for driving the objective lens provided on the optical head,
The level of the main beam push-pull signal in the state where tracking control is operating is substantially the same as the level of the center of the amplitude of the main beam push-pull signal in the state where tracking control is inactive, and An optical disc device comprising: a correction coefficient changing unit configured to change the predetermined correction coefficient β for generating the corrected differential push-pull signal by a differential push-pull signal generator. The correction coefficient changing unit is configured to control the tracking drive circuit so that a beam spot of the main beam emitted from the optical head to the information medium moves to an information track adjacent to one of an outer peripheral side and an inner peripheral side. During the period in which the objective lens is driven toward the one of the outer peripheral side and the inner peripheral side, the level of the main beam push-pull signal in a state where tracking control is operating is referred to. The maximum amplitude BV on the positive side and the maximum amplitude SV on the negative side of the main beam push-pull signal are measured in such a manner that the maximum amplitude BV on the positive side and the maximum amplitude SV on the negative side are substantially equal. 20. The optical disk device according to claim 19, wherein said predetermined correction coefficient β is changed. 20. The optical disk device according to claim 12, wherein the tracking drive circuit performs the tracking control by setting the correction coefficient β to substantially zero for a predetermined period after starting the tracking control. 20. The optical disk device according to claim 19, wherein the correction coefficient changing unit limits a range in which the correction coefficient β is changed. An optical head for irradiating an information track with a light beam for recording and / or reproducing information on an information track, comprising: a light source for emitting the light beam; and a main beam for emitting the light beam from the light source. A diffraction grating that diffracts the light into a first sub beam and a second sub beam so as to split the main beam, the first sub beam, and the second sub beam diffracted by the diffraction grating into the information medium. An objective lens that converges on the information track formed on the information medium, and a main lens, the first sub beam, and the second sub beam reflected on the information track formed on the information medium, respectively. An optical head including a light detector for detecting a beam signal, a first sub-beam signal, and a second sub-beam signal, respectively;
A main beam push-pull signal is generated based on the main beam signal detected by the photodetector provided in the optical head, and the first and second sub-beam signals detected by the photodetector are generated. Differential push-pull signal generator for generating an offset differential push-pull signal based on the main beam signal, the first and second sub-beam signals, and a predetermined offset amount. When,
At the timing when the main beam push-pull signal MPP generated by the differential push-pull signal generator becomes the center level of the amplitude of the main beam push-pull signal MPP, the level of the main beam push-pull signal and the sub beam push Offset level changing means for changing the predetermined offset amount for generating the offset differential push-pull signal by the differential push-pull signal generator so that the level of the pull signal becomes equal. Optical disk device.

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