JP2004355708A - Optical disk device and tilt control method using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device capable of detecting a tilting amount not affected by lens shifting even without using any external tilt sensor, and to provide a tilt control method using the same. <P>SOLUTION: This device comprises a spindle motor 809 for rotating a disk, a laser 106 for irradiating the information recording surface of the rotated disk with a laser beam through an objective lens 102, a photodetector 107 for detecting a reflected light which is the result of reflecting the laser beam applied from the laser 106 on the information recording surface, a tilting amount calculating part 108 for detecting a tilting amount by dividing the detected reflected light, a lens shift sensor 403 for detecting the shifting of an objective lens position from an optical center, and a control unit 406 for detecting the location of the objective lens position in the optical center based on a signal detected by the lend shift sensor 403, and detecting the tilting amount detected by the tilting amount calculating part 108 when the objective lens is in the optical center. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk device that records data on an optical disk and reproduces data recorded on the optical disk, and a tilt control method using the optical disk device.
[0002]
[Prior art]
In the case of optical disks such as CDs (Compact Disks) and DVDs (Digital Versatile Disks), generally, irradiation light emitted from an optical head is obliquely incident on the optical disk due to warpage or surface deflection of the disk, displacement of an optical system, or the like. is there. As a result, coma aberration occurs and the beam spot diameter of the irradiation light is distorted, so that the quality of a reproduced signal is deteriorated due to deterioration of crosstalk and jitter from an adjacent track. In particular, next-generation optical discs currently under development require a shorter wavelength in order to realize a higher density, and there is a problem that even a slight tilt increases coma aberration.
[0003]
In order to solve such a problem, it has been proposed to provide a tilt servo mechanism that detects the amount of tilt between the optical disk and the head by using some means and corrects the optical axis of the irradiation light of the optical disk and the optical head so as to maintain the optical axis vertically. . The electrical component of the tilt amount is largely divided into a DC tilt amount due to the warpage of the disk, a clamp state, a displacement of the optical system, and the like, and a periodic tilt amount due to the disk shake and the like. Can be
[0004]
As a method for detecting the tilt amount between the optical disk and the optical head, a method of detecting the tilt amount between the optical disk and the head using a sensor called a tilt sensor separately from the optical head is well known in the related art. As a method not using the tilt sensor, a method using a difference signal between left and right signals of a photodetector divided into right and left of a track (for example, see Patent Document 1), a four-divided photodetector (For example, see Patent Document 2). The above method does not require a tilt sensor as a separate component, and is a low-cost and simple tilt detection method.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 8-036773 [Patent Document 2]
JP 2001-266381 A
[Problems to be solved by the invention]
However, in the above-described method of detecting the amount of tilt using the photodetector divided into right and left or divided into four parts, there is a problem that the influence of the lens shift is mixed with the detected amount of tilt.
[0007]
On the other hand, in recent years, a lens shift sensor for detecting a lens shift amount is mounted on an optical head compatible with a rewritable optical disk, and a low-cost sensor has been realized.
[0008]
Therefore, the present invention has been made to solve the above problem, and is included in the detected tilt amount in a method of detecting the tilt amount using a photodetector divided into right and left of the track or divided into four. It is an object of the present invention to provide an optical disk device capable of reducing the influence of a lens shift using information from a lens shift sensor, and a tilt control method using the device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a rotating means for rotating a disc, an irradiating means for irradiating a laser beam through an objective lens to an information recording surface of the disc rotated by the rotating means, The laser beam emitted by the irradiating means is reflected by the information recording surface, and a photodetector for detecting the reflected light is detected. The reflected light detected by the photodetector is subjected to a calculation process to detect a tilt amount. Tilt amount detecting means, a lens shift sensor for detecting a deviation of the objective lens position from the optical center, and detecting that the objective lens position is at the optical center by a signal detected by the lens shift sensor, Control means for detecting a tilt amount detected by the tilt amount detecting means when the objective lens is at the optical center.
[0010]
According to the above configuration, when the lens shift amount is 0 can be determined by detecting that the position of the objective lens is at the optical center by the lens shift sensor, the tilt amount at that time is measured. By doing so, a tilt amount that is not affected by the lens shift can be obtained without using an external tilt sensor.
[0011]
In order to achieve the above object, the present invention provides a rotating means for rotating a disc, an irradiating means for irradiating a laser beam through an objective lens to an information recording surface of the disc rotated by the rotating means, The laser beam emitted by the irradiating means is reflected by the information recording surface, and a photodetector for detecting the reflected light is detected. The reflected light detected by the photodetector is subjected to a calculation process to detect a tilt amount. Tilt amount detection means, a tracking actuator for moving the objective lens in a radial direction of the disk, and the tracking actuator based on a tracking error signal obtained from the reflected light detected by the photodetector. Tracking control means for outputting a drive signal to be driven, and output by the tracking control means. The lens shift amount is measured using the DC component of the drive signal, and the lens shift amount included in the tilt amount detected by the tilt amount detection unit is calculated using a conversion table prepared in advance from the measured lens shift amount. And a control means for controlling the tilt correction based on the tilt amount corrected by the tilt amount correcting means.
[0012]
According to the above configuration, by using the DC component of the tracking actuator drive signal instead of the lens shift sensor, the tilt amount can be corrected without providing a separate lens shift sensor.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the principle by which the amount of tilt detected by the photodetector divided into right and left or quadrant of a track is affected by lens shift will be described.
FIG. 1 is a block diagram of a tilt detection device using a signal from an optical head. The tilt detection device 420 irradiates the beam emitted from the semiconductor laser 106 after passing through the collimator lens 105 to be converted into parallel light, condensed by the objective lens 102, and focused on the information recording surface of the optical disc 101. Is done. The reflected light from the optical disk 101 passes through a beam splitter 104 and a lens 103 and is incident on a general photodetector 107 having a four-divided light receiving element divided into four parts corresponding to the left, right, up, and down of an information track of the optical disk 101. The tilt amount is detected by performing a calculation on the outputs A, B, C, and D of the four-divided light receiving elements of the photodetector 107 by the tilt amount calculation unit 108.
[0014]
FIG. 2A shows a positional relationship between a beam spot and an information pit when the beam spot irradiates the center of the track. If there is no tilt, no coma aberration occurs in the beam spot 201a, so the relationship between the information pits 202 of the information track and the spot shape is symmetric with respect to the radial direction of the optical disk. When the tilt exists, coma aberration occurs as shown in FIG. 2B, and the beam spot 201b has an asymmetric shape in the tilt direction. When the beam spot becomes asymmetric, the tilt is detected using the fact that the average | (A + C) − (B + D) |
[0015]
Paying attention to the beam intensity in FIG. 2A, the beam intensity is symmetrical with respect to the center of the track. It is known that the beam pattern of a general semiconductor laser has a Gaussian distribution, which is shown. In a general optical head, the influence of surface shake and eccentricity due to the rotation of the optical disk 101 is adjusted by moving only the objective lens to focus on the information recording surface and irradiate the beam spot to the center of the track. . Therefore, the objective lens 102 may come to a position shifted from the optical center as shown in FIG. 3 following the eccentricity of the disk. In such a case, since the beam spot 201c of FIG. 2C is formed on the optical center position of the objective lens 102, the beam spot 201c is formed on the optical center position of the entire optical head 402 having the highest beam intensity. 201c is not formed, and the beam intensity has a distribution in which the position of the highest beam intensity shown in the example of FIG. Then, since no tilt occurs, the spot shape is symmetric, but the beam intensity distribution of the beam spot 201c imaged on the photodetector 107 is not symmetric, so that the average | (A + C) − (B + D) | Becomes larger. That is, it is not possible to determine whether the change of (A + C)-(B + D) is due to the tilt or the lens shift only by detecting the amount of tilt from the magnitude of (A + C)-(B + D).
[0016]
Next, the cause of the lens shift will be described.
Generally, an optical disk has an eccentricity. Therefore, when the optical disk is rotated by a spindle motor to read the information track, the position of the information track changes. Therefore, the outputs A and B of a general photodetector having a four-division light receiving element divided into four parts corresponding to the left, right, upper and lower sides of the information track of the optical disk so that the objective lens always focuses on the information track of the optical disk. , C, and D into a tracking error signal generator to generate a track error signal proportional to the deviation between the focal point and the center of the information track, and calculate a radial control amount of the objective lens based on this signal to obtain the objective lens. Move. Also, the optical disc has information tracks spirally arranged on an information recording surface, and when trying to read and write information by focusing on the center of the information track, the objective lens must gradually move in the inner or outer peripheral direction. . Therefore, the tracking servo for keeping the focus on the center of the information track requires the above-described lens tracking system and the feed system described below. The feed system causes a motor for moving the optical head to calculate a control amount of the optical head from the obtained tracking error signal and move the optical head. The feed system tracks slow information track radial position variations caused by following the information track along the helix.
[0017]
As an ideal operation of the feed system, the average track center position excluding the influence of eccentricity always has a lens shift of 0, that is, the average operation amount of the objective lens in the radial direction performed by the lens tracking system is 0. It is to become. However, in practice, the feed system operates in a state where the objective lens is slightly shifted in the radial direction of the traveling direction. This is a major cause of lens shift.
[0018]
Therefore, the present invention describes an optical disk apparatus and a tilt control method for reducing the influence of a lens shift included in the tilt amount detected by the photodetector using information from a lens shift sensor, with reference to FIG.
[0019]
As shown in FIG. 4, the beam emitted from the semiconductor laser 106 passes through a collimator lens 105, is converted into parallel light, is then condensed by an objective lens 102, and is focused on the information recording surface of the optical disc 101. Irradiated. The reflected light from the optical disk 101 passes through a beam splitter 104 and a lens 103 and is incident on a general photodetector 107 having a four-divided light receiving element divided into four parts corresponding to the left, right, up, and down of an information track of the optical disk 101. This series of optical systems is called an optical head 402. The tilt amount is detected by performing a calculation on the outputs A, B, C, and D of the four-divided light receiving elements of the photodetector 107 by the tilt amount calculation unit 108. Further, a spindle motor 809, a lens shift sensor 403, a lens position determination unit 404, a tilt amount holding unit 405, and a tilt correction mechanism 401 are added to the tilt detection device 420 shown in FIG. The spindle motor 809 drives the optical disc 101 to rotate. The lens shift sensor 403 measures the amount of deviation of the objective lens 102 from the optical center position, and the lens position determination unit 404 monitors and outputs the amount of tilt when the objective lens 102 comes to the optical center position. The tilt amount holding unit 405 captures and holds the tilt amount. Further, the tilt correction mechanism 401 performs tilt correction by, for example, tilting a base (not shown) supporting the spindle motor 809 or tilting a head base on which an optical head is mounted.
[0020]
Next, the operation of the optical disk device shown in FIG. 4 will be described with reference to FIG.
When tilt correction is started during insertion of a disc or during disc playback, the lens position determination unit 404 monitors the amount of deviation from the optical center position of the objective lens 102 measured by the lens shift sensor 403 (ST51). . That is, when the objective lens 102 reaches the optical center position, the lens position determination unit 404 instructs the tilt amount holding unit 405 to capture and hold the tilt amount (Y in ST51). When the objective lens 102 does not come to the optical center position, monitoring is repeated until it comes to the center position (N in ST51). The tilt amount holding unit 405 holds the signal from the lens position determination unit 404 and the timing at which the lens position determination unit 404 captures the tilt amount (the signal including the lens shift amount) calculated by the tilt amount calculation unit 108. (When the objective lens 102 comes to the optical center position) (ST53). Usually, the optical disc 101 has eccentricity, and the objective lens 102 comes to the optical center position at least twice during one rotation of the optical disc 101. Therefore, the tilt amount holding unit 405 measures the output from the spindle motor 809. It is determined whether the disk has made one rotation since the start of the operation. If it is determined that the disk has made one rotation (Y in ST55), an average of two or more measurements is taken (ST57). If it is determined that one rotation has not been made (N in ST55), the flow returns to step ST51.
[0021]
The controller 406 calculates based on the average of two or more measurement values measured by the tilt amount holding unit 405 for the DC tilt correction and the tilt amount calculated by the tilt amount calculation unit 108, A required drive amount is instructed to the tilt correction mechanism 401 (ST59). The tilt correction mechanism 401 performs tilt correction based on the commanded drive amount (ST61).
[0022]
According to such a configuration, since only the tilt amount detection result when the objective lens 102 comes to the optical center position is used, the tilt correction is performed by obtaining the tilt amount detection result excluding the influence of the lens shift. Can be. Therefore, a tilt sensor that does not require a tilt sensor as a separate component and detects the amount of tilt by using a photodetector divided into right and left or a quadrant is used. Corrections can be made. Further, according to this method, even if the absolute value of the lens shift amount is unknown, only the value when the objective lens 102 comes to the optical center position need be known, so that the lens shift sensor 403 has high accuracy. Nothing is required, and a low-cost lens shift sensor can be used.
[0023]
Next, a second embodiment will be described with reference to FIG.
FIG. 6 is a diagram showing an optical disk device for detecting a tilt amount when the optical disk device is placed vertically. The same parts as those in FIG. 4 are denoted by the same reference numerals.
FIG. 6 shows the optical disc apparatus shown in FIG. 4 in which the tilt amount correction unit 501, tracking error signal generation unit 802, tracking control unit 805, low-pass filter 807, feed control unit 806, motor 803, feed mechanism 808, tracking actuator are used. 801 is newly provided.
[0024]
The beam emitted from the semiconductor laser 106 passes through the collimator lens 105, is converted into parallel light, is then condensed by the objective lens 102, and is emitted while being focused on the information recording surface of the optical disk 101. The reflected light from the optical disk 101 passes through a beam splitter 104 and a lens 103 and is incident on a general photodetector 107 having a four-divided light receiving element divided into four parts corresponding to the left, right, up, and down of an information track of the optical disk 101. This series of optical systems is called an optical head 402. The tilt amount is detected by performing a calculation on the outputs A, B, C, and D of the four-divided light receiving elements of the photodetector 107 by the tilt amount calculation unit 108. The lens shift amount obtained from the detected tilt amount and the DC component of the output of the tracking control unit 805 is input to the tilt amount correction unit 501. This lens shift amount is obtained by inputting the output of the tracking control unit 805 to the low-pass filter 807 and extracting the DC component of the input to the tracking actuator 801. Note that, since the tracking actuator 801 changes the position of the lens proportional to the DC input, if the input to the tracking actuator 801 is 0, if the objective lens 102 is on the optical center position of the objective lens 102, The DC component of the input to the tracking actuator 801 becomes the lens shift amount.
[0025]
The tilt amount correction unit 501 has a built-in approximation function or table for correcting the tilt detection amount affected by the above-described lens shift to a tilt detection amount excluding the effect of the lens shift. The excluded tilt detection amount is output to the controller 406. The controller 406 calculates and instructs the tilt correction mechanism 401 to calculate the required drive amount based on the average of the measured values of the optical disc 101 during one rotation for DC tilt correction.
[0026]
However, when the direction in which the tracking actuator 801 operates and the direction of gravity are the same, that is, when the optical disk device is placed vertically, the tracking actuator 801 is pulled in the radial direction of the disk by its own weight. Therefore, when the operation amount of the objective lens 102 is 0, the objective lens 102 does not always come on the optical center position.
[0027]
To cope with this, it is necessary to measure a command value for setting the lens shift amount to 0 when the power is turned on (before performing the tilt correction operation). The operation will be described below with reference to FIG. That is, after the power is turned on, the output of the lens shift sensor 403 is input to the lens position determination unit 404, and the lens position determination unit 404 determines whether the objective lens 102 is at the optical center position (ST71). If it is determined that the objective lens 102 is not at the optical center position (N in ST71), the lens position determination unit 404 outputs information to that effect to the tilt amount correction unit 501 (ST73). The tilt amount correction unit 501 issues a drive command to the tracking control unit 805 to move the objective lens 102. The tracking control unit 805 gives a sine-wave or triangular-wave drive command to the tracking actuator 801 to move the objective lens 102 (ST75). Then, the processing is repeated until the objective lens 102 comes to the optical center position.
[0028]
When it is determined that the objective lens 102 is at the optical center position (Y in ST71), the lens determination unit 404 outputs a command value to the tracking actuator 801 to the tilt amount correction unit 501, and corrects the tilt amount. Unit 501 stores this command value (ST77). Then, when the reproduction operation is actually started (Y in ST79), the tilt amount correction unit 501 receives the output from the low-pass filter 807 that has received the output from the tracking control unit 805. Then, the command value stored in ST77 is removed from the output from the low-pass filter 807 (ST81). By performing this operation, the relationship between the lens shift amount obtained from the DC component of the output of the tracking control unit 805 and the optical center position of the objective lens 102 can be corrected. Using the obtained lens shift amount, the lens shift amount excluding the offset due to gravity can be known. If the reproduction operation is not started in ST79, the operation is repeated until the reproduction is started.
[0029]
Further, when the tilt amount correction unit 501 receives the tilt amount obtained by calculating the reception signal from the photodetector 107 in the tilt amount calculation unit 108, the tilt amount correction unit 501 performs an arithmetic process using the approximate function held from the tilt amount and the value removed in ST81. And outputs it to the controller 406 (ST83). The controller 406 outputs a drive command to the tilt correction mechanism 401 based on the result of the arithmetic processing, and the tilt correction mechanism 401 performs tilt correction based on the drive command (ST85).
[0030]
According to such a configuration, tilt correction can be performed by obtaining a tilt amount detection result excluding the influence of the lens shift. Therefore, no tilt sensor is required as a separate component, and the influence of lens shift is eliminated even if a low-cost and simple tilt detection method that detects the amount of tilt using a photodetector divided into right and left of the track or divided into four is used. Tilt correction can be performed. Further, even when the objective lens 102 is not provided with a command value to the tracking actuator due to the influence of gravity or the like and the objective lens 102 is not located on the optical center position, the tilt correction that does not require the accurate lens shift sensor 401 can be performed. It is.
[0031]
The present invention is not limited to the above-described embodiment, and can be variously modified in an implementation stage without departing from the gist of the invention.
[0032]
【The invention's effect】
As described above, when the optical disk device is placed horizontally, the time when the lens shift amount is 0 can be determined by detecting that the objective lens position is at the optical center by the lens shift sensor. By measuring the tilt amount at that time, a tilt amount that is not affected by the lens shift can be obtained without using an external tilt sensor.
[0033]
Further, when the optical disk device is vertically set, the tilt amount can be corrected without using a separate lens shift sensor by using the DC component of the tracking actuator drive signal instead of the lens shift sensor. In this case, the processing can be performed even in the case of horizontal installation.
[Brief description of the drawings]
FIG. 1 is a block diagram of a tilt detection device that performs tilt detection using a signal from an optical head according to an embodiment of the present invention.
FIG. 2 is a diagram showing a shape relationship between an information pit and a beam spot.
FIG. 3 is a diagram illustrating a lens shift.
FIG. 4 is a block diagram illustrating an optical disc device that reduces the influence of a lens shift included in a tilt amount by using information from a lens shift sensor.
FIG. 5 is a flowchart showing the operation of FIG.
FIG. 6 is a block diagram illustrating an optical disk device that detects a tilt amount that is not affected by a lens shift when the optical disk device is placed vertically.
FIG. 7 is a flowchart showing the operation of FIG. 6;
[Explanation of symbols]
101 Optical Disk 107 Photo Detector 108 Tilt Amount Calculator 401 Tilt Correction Mechanism 403 Lens Shift Sensor 404 Lens Position Judgment Unit 406 Controller 501 Tilt Correction Unit 801 Tracking Actuator 802 Tracking Error Signal Generation Unit 805 Tracking Control Unit 807 Low Pass Filter

Claims (8)

Rotating means for rotating the disk,
Irradiating means for irradiating the information recording surface of the disc rotated by the rotating means with laser light via an objective lens,
The laser beam irradiated by the irradiation unit is reflected on the information recording surface, and a photodetector that detects the reflected light,
Tilt amount detection means for detecting the amount of tilt by performing a calculation process on the reflected light detected by the photodetector;
A lens shift sensor for detecting a deviation of the position of the objective lens from the optical center,
The signal detected by the lens shift sensor detects that the position of the objective lens is at the optical center, and detects the amount of tilt detected by the tilt amount detecting means when the objective lens is at the optical center. An optical disc device comprising a control unit. Rotating means for rotating the disk,
Irradiating means for irradiating the information recording surface of the disc rotated by the rotating means with laser light via an objective lens,
The laser beam irradiated by the irradiation unit is reflected on the information recording surface, and a photodetector that detects the reflected light,
Tilt amount detection means for detecting the amount of tilt by performing a calculation process on the reflected light detected by the photodetector;
A tracking actuator for moving the objective lens in a radial direction of the disk,
Tracking control means for outputting a drive signal for driving the tracking actuator based on a tracking error signal obtained from the reflected light detected by the photodetector,
The lens shift amount is measured using the DC component of the drive signal output by the tracking control unit, and the lens shift amount is detected by the tilt amount detection unit using a conversion table prepared in advance from the measured lens shift amount. Tilt amount correction means for correcting the lens shift amount included in the tilt amount,
An optical disk device comprising: a control unit that controls tilt correction based on the tilt amount corrected by the tilt amount correction unit. The control means determines the optical center position of the objective lens based on an average of measured values of the number of times the objective lens has reached the optical center position during one rotation of the disk. 3. The optical disk device according to claim 1, wherein: 3. The optical disk device according to claim 1, further comprising a tilt correction mechanism that corrects a tilt between the disk and the irradiation unit based on the tilt amount detected by the control unit. Rotating the disc;
Irradiating a laser beam onto the information recording surface of the rotated disk via an objective lens;
The laser beam emitted by the irradiating means is reflected by the information recording surface, and detecting the reflected light;
A step of detecting the amount of tilt by performing a calculation process on the detected reflected light;
Detecting a deviation of the position of the objective lens from the optical center with a lens shift sensor,
Detecting that the position of the objective lens is at the optical center based on a signal detected by the lens shift sensor, and detecting the detected tilt amount when the objective lens is at the optical center. A tilt control method. Rotating the disc;
Irradiating a laser beam onto the information recording surface of the rotated disk via an objective lens;
The laser beam emitted by the irradiating means is reflected by the information recording surface, and detecting the reflected light;
A step of detecting the amount of tilt by performing a calculation process on the detected reflected light;
Outputting a drive signal to a tracking actuator for moving the disk in a radial direction based on a tracking error signal obtained from the detected reflected light;
The lens shift amount is measured using the DC component of the output drive signal, and the lens shift amount included in the detected tilt amount is calculated using a conversion table prepared in advance from the measured lens shift amount. Correcting,
Controlling the tilt correction based on the corrected amount of tilt. The optical center position of the objective lens is determined based on an average of measured values of the number of times the objective lens comes to the optical center position during one rotation of the disk. 7. The optical disc device according to any one of claims 1 to 6. 7. The tilt control method according to claim 5, wherein the tilt between the disk and the objective lens is corrected based on the corrected tilt amount.

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