JP2005182968A - Optical disc apparatus and eccentricity correction method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eccentricity correction device and an eccentricity correction method capable of accurately operating eccentricity correction even when the rotational frequency is suddenly and greatly different.
A laser beam is focused on the recording / reproducing surface of an optical disc 11 by an objective lens of an optical pickup 12 to form a light spot, and an optical pickup for detecting reflected light and the objective lens are arranged in a radial direction of the optical disc by a tracking actuator 15. The optical disk apparatus that moves to the memory reads out the displacement signal stored in the memory 21 in synchronization with a signal from a frequency generator (FG) 17 that outputs a frequency signal proportional to the rotation speed of the spindle motor that rotates the optical disk, An actuator drive signal is generated by the eccentricity correction control means 18 that performs feedback control via the controller 22 so that the difference from the displacement signal from the lens position sensor becomes small.
[Selection] Figure 1

Description

  The present invention relates to an apparatus for recording or reproducing information on an optical disk, such as an optical disk drive, and more particularly to an optical disk apparatus having a tracking servo system and an eccentricity correction method therefor.

  In an optical disk apparatus that irradiates an information storage medium called a disk-shaped optical disk with a light beam and records or reproduces information, the rotation axis of the spindle that rotates the optical disk often does not coincide with the center of the track of the optical disk. A phenomenon called eccentricity occurs. Such eccentricity acts as a main periodic disturbance in the optical disk drive apparatus, and is therefore a major factor that degrades the track following performance of the apparatus. The adverse effect due to such eccentricity becomes greater as the rotational frequency (speed) of the optical disc increases.

  By the way, in recent years, in addition to various types of optical disks, it is possible to record or reproduce information from such optical disks at high speeds, especially with the use of optical disks capable of high-density recording to record a large amount of information including video information. Optical disk apparatus, that is, high speed is remarkable.

  With such a high speed increase, even when the optical disk is rotated at such a high speed, in order to accurately follow the track, it is necessary to realize compensation that effectively cancels the adverse effect of the eccentricity. . Until now, various eccentricity compensation techniques have been implemented in order to compensate for such eccentricity.

  For example, as an eccentricity compensation technique that is a conventional technique, for example, according to Patent Document 1 below, an eccentricity compensation device using the frequency characteristics of an actuator is proposed. That is, in this eccentricity correction method, the eccentric component measured by the phase of the spindle is stored in the memory, and the tracking control system is synchronized with the rotational frequency of the spindle, and the actuator drive signal The above-mentioned eccentricity correction is performed by adding up to. Here, the eccentricity has a characteristic that when the rotational frequency of the disk changes, its magnitude is constant, but its frequency component changes in synchronization with the rotational frequency.

  Here, since the displacement amount of the actuator varies depending on the frequency of the input signal due to the frequency characteristics of the actuator, the displacement amount of the actuator varies depending on the rotation frequency of the optical disc, and therefore the effect of the eccentricity correction varies. It turns out that. Therefore, in the conventional technique, when the rotational frequency of the optical disk changes, the actuator drive control value predicted for eccentricity correction under a specific rotational frequency is calculated from the actuator frequency characteristics and eccentricity characteristics. By compensating in consideration of the frequency characteristics, the eccentricity correction is performed even if the rotational frequency of the optical disk changes, using the control value once predicted as it is.

JP 2002-208240 A

  However, in general, an actuator is composed of a plurality of mechanical members. Therefore, there is a so-called variation in the frequency characteristics of the actuator due to the mounting accuracy of each member. Moreover, in order to suppress the amplitude in the main resonance in a general actuator, it is comprised so that a damping effect may be given, for example with rubber | gum etc. By the way, the frequency characteristic of the actuator also changes in the rubber or the like depending on the temperature characteristic or the change with time. In particular, in the vicinity of the main resonance, the phase changes abruptly. Therefore, even if the main resonance frequency changes a little, the phase deviates greatly, which makes it difficult to compensate for eccentricity.

  On the other hand, the characteristic of the tracking servo loop gain is designed so that the gain becomes higher in the lower frequency band for the purpose of increasing the DC gain. Therefore, when it is necessary to change the rotation speed of the optical disc, when the eccentricity data is first acquired and added to the tracking servo signal output, the gain differs depending on the rotation frequency. End up. For this reason, for example, when the rotational frequency changes drastically and greatly, such as when moving greatly in the radial direction by a seek operation, it is difficult to simply operate the eccentricity correction with the feedforward control system. was there.

  Therefore, in the present invention, in view of the above-described problems in the prior art, and based on the above recognition, it is possible to accurately operate the eccentricity correction even when the rotation frequency is drastically different. An object of the present invention is to provide an eccentricity correction apparatus and an optical disk apparatus and an eccentricity correction method thereof that are more excellent in tracking performance by including such an apparatus.

  In order to solve the above problems, in the present invention, a frequency generator that outputs a signal having a frequency proportional to the rotation speed of the spindle, an objective lens for irradiating an optical disc with laser light for recording and reproduction, and Generates an actuator that operates to follow the track of the optical disc, a lens position sensor that measures the position of the objective lens operated by the actuator, a memory that stores the measured information, and a signal that controls the actuator It consists of a feedback control system consisting of a controller. The controller is designed as a control compensator in which the frequency characteristic of the feedback control system is such that the gain is always constant within the range of the rotation frequency of the spindle. A control system with a small deviation is desirable.

  In the present invention, in order to achieve the above object, first, a spindle motor that rotates the optical disk; and a light spot formed by condensing the laser beam by the objective lens on the recording / reproducing surface of the rotating optical disk. A photodetector that detects reflected light; a tracking actuator that moves the objective lens in a radial direction of the optical disc in an optical pickup; a lens position sensor that measures the position of the objective lens; and a spindle that rotates the optical disc An optical disc apparatus comprising: a frequency generator that outputs a signal having a frequency proportional to the number of rotations of the motor; and an eccentricity correction control unit that generates a signal for driving the actuator. The correction control means records the displacement signal output from the lens position sensor. And a displacement signal output from the lens position sensor and stored in the storage means within a range of the rotation speed of the spindle motor is synchronized with a signal output from the frequency generator. Thus, there is provided an optical disc apparatus including a controller that reads out and generates a signal for driving the actuator based on a displacement signal from the lens position sensor.

  Further, in the present invention, in the optical disc apparatus described above, the eccentricity correction control means uses a signal read out and output from the storage means in synchronization with the output signal of the frequency generator as a reference signal, and The feedback control system is constructed by taking the displacement signal from the lens position sensor, and the eccentricity correction control means is in a state where the tracking servo of the tracking actuator is stably following the optical disc. , The displacement signal output from the lens position sensor is synchronized with the signal output from the frequency generator, the one rotation of the spindle motor is stored in the storage means, and the feedback control system includes: The signal read out from the storage means in synchronization with the output signal of the frequency generator is output as a reference signal. When the difference between the displacement signal outputted in real time from the lens position sensor is constructed as smaller.

  According to the present invention, in the optical disc apparatus, the controller constituting the eccentricity correction control means is such that the gain of the frequency characteristic of the feedback control system is substantially constant at least in the rotational frequency range of the spindle motor. Is designed to create a signal for driving the actuator, or the feedback control system is in parallel with the tracking servo control system, or the feedback control system is It has an exclusive relationship with the tracking servo control system.

  Furthermore, according to the present invention, in order to achieve the above-mentioned object, a laser beam is condensed by an objective lens on the recording / reproducing surface of an optical disk rotated by a spindle motor to form a light spot, and the reflected light is reflected by light. A method of performing eccentricity correction in an optical disc apparatus that detects by a detector and moves the objective lens in a radial direction of the optical disc by a tracking actuator, and measures the position of the objective lens and synchronizes with the rotation of the spindle motor, A signal for driving the actuator is generated based on the measured position of the objective lens, the position signal of the measured objective lens is taken into the drive signal, and the difference between the drive signal and the position signal of the objective lens Provides an eccentricity correction method of an optical disc apparatus that performs feedback control so that the frequency becomes small It is.

  According to the above-described optical disc apparatus and the eccentricity correction method thereof according to the present invention, the eccentricity correction apparatus capable of always operating the eccentricity correction accurately even when the rotational frequency is suddenly and greatly different, and therefore. It is possible to provide an eccentricity correction method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, FIG. 2 attached herewith is a block diagram showing a schematic configuration of an optical disc apparatus according to the present invention, particularly a schematic configuration of its tracking control system. In this figure, as is generally known, an optical pickup 12 condenses a laser beam on an information recording surface of an optical disc 11 through an objective lens (not shown) to form a light spot and irradiates the reflected light. Sense light. That is, by this, the optical pickup 12 described above has an error (hereinafter referred to as “position error”) between the track formed on the optical disc 11 and the light beam spot-irradiated on the recording surface of the optical disc. ) And a so-called tracking error signal is created by the error signal generation means 13.

  Subsequently, in response to the tracking error signal generated as described above, the tracking control unit 14 changes the actual position of the objective lens by, for example, signals generated by passing through various filters, Actuator 15 is actuated to compensate for the position error. Accordingly, the feedback control system designed so that the detected position error is within a predetermined range is a tracking servo system in the optical disc apparatus.

  On the other hand, in the above optical disc apparatus, the position information of the objective lens mounted on the optical pickup 12 is used, that is, the objective lens position signal generated by the displacement signal generating means 16 and the frequency generator (FG) 17. Using the output FG signal as an input, the eccentricity correction control means 18 creates an eccentricity correction signal. The control system designed to operate the actuator 14 by this eccentricity correction signal and thereby apparently reduce the eccentricity amount in the tracking error signal is the feedback control system for eccentricity correction according to the present invention. . Next, the feedback control system for correcting the eccentricity will be specifically described.

  FIG. 1 shows, in particular, a feedback control system of an eccentricity correction apparatus in an optical disc apparatus according to the present invention. That is, the portion surrounded by a dotted line in FIG. 1 shows the eccentricity correction control means 18 shown in FIG. Incidentally, when the optical disk apparatus is recording or reproducing information on the optical disk 11, the tracking servo is normally stable, and the objective lens of the optical pickup 12 follows the eccentric operation. From this, the signal output by the displacement signal generating means 16 is a signal corresponding to the eccentricity of the optical disk 11, and specifically, the same output waveform is repeated every time the optical disk 11 makes one round. Will be output.

  At this time, according to the present invention, the output signal from the displacement signal generating means 16 is recorded in the memory 21 for one rotation of the spindle. Thereafter, the signal from the displacement signal generating means 16 recorded in the memory 21 is output in synchronization with the FG 17 (that is, addressed by the FG signal), and this signal is used as a reference signal r (t). Then, the difference between the reference signal r (t) and the signal y (t) output from the displacement signal generating means 16 in real time is taken (r (t) −y (t)). Then, the difference signal (r (t) −y (t)) is input to the controller 22, and an actuator drive signal is output therefrom. Thus, by driving the actuator 15 with the differential signal and operating the objective lens in synchronization with the eccentric operation of the optical disk 11, the apparent eccentric component can be suppressed.

  Next, FIG. 3 is a waveform diagram showing the transient response of the signal in the feedback control system of the optical disc apparatus having the above configuration, particularly the eccentricity correction apparatus shown in FIG. In other words, time (t) is shown on the horizontal axis in the figure, and the signal r (t) shown in the upper part of the figure shows that the tracking servo is stable with respect to the optical pickup 12 during recording or reproduction of the optical disk 11. The reference signal is a reference signal output from the displacement signal generator 16 when the signal is output to the memory 21 and the information is output in synchronization with the FG 17. The signal y (t) shown in the middle of FIG. A difference signal (r (t) −y (t)), which is a signal output from the displacement signal generation means 16 in real time and is a difference between them, is shown in the lower part of the figure. As shown in FIG. 1, according to the present invention, the difference signal (r (t) −y (t) between the reference signal r (t) and the displacement signal y (t) in real time. The above-described controller 22 is designed so that a so-called feedback control system is configured so that)) becomes small.

  Subsequently, FIG. 4 attached is a block diagram showing the tracking control system and the control system for eccentricity correction. Here, first, the tracking control system will be considered. In this block diagram, Gt represents the characteristics of the controller (see reference numeral 22 in FIG. 1) of the tracking servo control system, and Ga represents the characteristics of the actuator (see reference numeral 15 in FIG. 1). Gb indicates the characteristics of the tracking error signal generating means (see reference numeral 13 in FIG. 2). In this block diagram, Xr is the displacement of the track of the optical disk 11 and X is the displacement of the objective lens 12. From the block diagram shown in FIG. 4, the following expression is obtained.

  Here, Gt, Ga, and Gb indicate the open loop gain of the tracking control. When this open loop gain is sufficiently large as in the following expression,

The displacement X of the objective lens and the displacement Xr of the track of the optical disk are expressed by the following equations.

That is, the track change and the displacement of the objective lens are substantially the same, which means that the tracking control system operates so that the light spot follows the track.

  Similarly, when considering the control system for correcting eccentricity, Gs indicates the characteristics of the controller (see reference numeral 22 in FIG. 1), and Gc is the displacement signal generating means (see reference numeral 16 in FIG. 1). ) Characteristics. R represents the reference signal, and Y represents the signal y (t) output from the displacement signal generating means 16 in the real time. These are represented by the following equations from the block diagram shown in FIG.

  At least in the range of the rotational frequency of the disk, when Gs, Ga, and Gc are in the relationship of the following formulas,

Similar to the tracking control described above, the following equation is obtained.

Here, at least in the range of the rotational frequency of the disk, when there is a secondary component in the eccentric vibration, the above-mentioned even at a frequency several times the rotational frequency of the disk. It is to say that it is necessary to satisfy the formula.

  As described above, the reference signal R is based on the information obtained by fetching the output of the lens displacement signal generating means 16 into the memory in the state where the light beam follows the track of the optical disk by the tracking control. Has been generated. The fact that the output Y of the displacement signal generating means 16 is substantially equal to the reference signal R means that the objective lens is displaced in the same manner as when tracking the track by tracking control. That is, it shows that the eccentricity correction is realized by the eccentricity correction control.

  As described above, according to the eccentricity correction control means 18, the actuator 15 is driven so that the gain of the frequency characteristic of the feedback control system is substantially constant at least in the range of the rotational speed of the spindle motor. For this purpose, the controller 22 is designed so that the feedback control system is stable in the control system design theory.

  According to the present invention, the tracking control system and the control system for eccentricity correction are provided in parallel, and both of these two control systems satisfy the above equation. Are mutually exclusive. In other words, the control system for eccentricity correction is effective when the tracking control system does not operate (that is, the tracking servo control system is not connected). It means to do.

  As described above, according to the present invention, even when the optical pickup moves in the radial direction due to the movement between tracks on the optical disk, the eccentricity is corrected even when the rotational frequency of the disk changes rapidly. Can be performed.

It is a block diagram which shows the feedback control system of the eccentricity correction apparatus in the optical disk device which becomes this invention. It is a block diagram which shows the whole schematic structure of the optical disk apparatus which becomes the said invention. It is a wave form diagram which shows the transient response of the signal in the eccentricity correction feedback control system in the optical disk device of the said invention. It is a block diagram which shows the said tracking control system and the control system for eccentricity correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical disk 12 Optical pick-up 13 Error signal generation means 14 Tracking control means 15 Actuator 16 Displacement signal generation means 17 Frequency generator (FG)
18 Control means for eccentricity correction 21 Memory 22 Controller

Claims (7)

A spindle motor that rotates the optical disc;
A photodetector for detecting reflected light from a light spot formed by condensing a laser beam with an objective lens on the recording / reproducing surface of the rotating optical disc;
A tracking actuator for moving the objective lens in a radial direction of the optical disc;
A lens position sensor for measuring the position of the objective lens;
A frequency generator for outputting a signal having a frequency proportional to the rotational speed of a spindle motor for rotating the optical disc; and
And an eccentricity correction control means for creating a signal for driving the actuator, wherein the eccentricity correction control means records the displacement signal output from the lens position sensor. And a displacement signal output from the lens position sensor and stored in the storage means within a range of the rotational speed of the spindle motor is synchronized with a signal output from the frequency generator. And a controller that generates a signal for reading and driving the actuator based on a displacement signal from the lens position sensor.   2. The optical disk apparatus according to claim 1, wherein the eccentricity correction control means uses a signal read out from the storage means in synchronization with an output signal of the frequency generator as a reference signal, and the lens. An optical disk apparatus characterized in that a feedback control system is constructed by taking in a displacement signal from a position sensor.   3. The optical disc apparatus according to claim 2, wherein the eccentricity correction control means outputs a displacement signal output from the lens position sensor in a state where tracking servo of the tracking actuator is stably following the optical disc. In synchronization with the signal output from the frequency generator, one revolution of the spindle motor is stored in the storage means, and the feedback control system outputs the output signal from the storage means to the frequency generator. An optical disc apparatus constructed so that a difference between a reference signal and a displacement signal output in real time from the lens position sensor is reduced as a signal read out and output synchronously.   4. The optical disk apparatus according to claim 3, wherein the controller constituting the eccentricity correction control means is configured such that a gain of a frequency characteristic of the feedback control system is substantially constant at least in a range of a rotation frequency of the spindle motor. In addition, the optical disc apparatus is designed to generate a signal for driving the actuator.   4. The optical disc apparatus according to claim 3, wherein the feedback control system is in parallel with the tracking servo control system.   4. The optical disc apparatus according to claim 3, wherein the feedback control system is in an exclusive relationship with the tracking servo control system. A laser beam is condensed by an objective lens on the recording / reproducing surface of the optical disk rotated by a spindle motor to form a light spot, and the reflected light is detected by a photodetector, and the objective lens is detected in the radial direction of the optical disk by a tracking actuator. A method of correcting eccentricity in a moving optical disk device, wherein the position of the objective lens is measured, and a signal for driving the actuator based on the measured position of the objective lens is measured in synchronization with the rotation of the spindle motor. An optical disc apparatus characterized by generating and capturing the measured position signal of the objective lens in the drive signal, and performing feedback control so that a difference between the drive signal and the position signal of the objective lens is reduced Eccentricity correction method.

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