JP2010277659A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably suppress influence of a tracking error signal leaking into the focus error signal in a focus servo system. <P>SOLUTION: An optical disk device includes: an actuator for driving an objective lens that irradiates an optical disk with a beam from a laser in a focus direction and a tracking direction and moves the beam to irradiate the optical disk, a focus servo control part for inputting the focus error signal and driving the actuator to control a focal position of the beam, and a tracking servo control part for inputting the tracking error signal to control a tracking position of the beam. The tracking servo control part adds a signal having a second frequency exceeding a first frequency to a tracking driving signal calculated from the tracking error signal, and the focus servo control part attenuates the second frequency of the input focus error signal to correct the focus error signal and calculates a focus driving signal by using the corrected focus error signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus, and more particularly to improvement of a servo system using a tracking error signal and a focus error signal.

  In an optical disc apparatus that records information on an optical disc such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a BD (Blu-ray Disc), the information recording surface of the optical disc is irradiated with laser light while rotating the optical disc at high speed. Information is reproduced or recorded by detecting the reflected light of the laser beam.

  In an optical disc apparatus, an optical pickup equipped with a photodetector for irradiating a laser beam and detecting reflected light is arranged in a direction facing the surface of the optical disc (focus direction) and a radial direction of the optical disc (tracking direction (or slide direction)). The servo control is performed so that the laser beam is focused on the information recording surface of the optical disk. It is well known that the servo control in the focus direction and the servo control in the tracking direction use a focus error signal and a tracking error signal from the laser light detected by the photodetector.

  In such servo control, a problem that a tracking error (hereinafter referred to as TE) signal leaks into a focus error (hereinafter referred to as FE) signal is widely known when the optical pickup is moved in the tracking direction. Due to this leakage, there is a problem that an unnecessary current is supplied to the actuator that drives the optical pickup, or the focus servo of the optical pickup is saturated and the focus is lost while moving in the track direction.

  The following techniques are known as techniques for suppressing a decrease in leakage of the TE signal to the FE signal.

  Patent Document 1 is known as a technique for suppressing the influence of a TE signal leaked into an FE signal in a focus servo system. In this Patent Document 1, a compensator of a focus servo control unit is provided with a limiter between the former-stage emphasis and the latter-stage de-emphasis, and a focus servo drive signal is output from the latter-stage emphasis. And in this patent document 1, the gain of a specific frequency band is increased by the emphasis of the front stage, the output of this emphasis is attenuated by the limiter, and the gain of the specific frequency band is reduced by the de-emphasis of the rear stage. The purpose is to suppress a specific frequency band in which a signal leaks.

  Further, Patent Document 2 is known as a technique for providing a crosstalk level detecting means for an FE signal and suppressing defocusing by reducing a focus gain when the crosstalk is equal to or greater than a threshold value.

  Further, the influence of the laser beam traversing the groove of the optical disk is measured by the amount of leakage of the TE signal into the FE signal by means of the groove crossing amount detection means. If the leakage amount is large, the gain of the focus servo system Patent Document 3 is known as a technique for adjusting the disk rotation speed.

  Patent Documents 4 and 5 are known as techniques for canceling FE signal crosstalk of an FE signal using a compensation signal extracted from a TE signal.

Japanese Patent Laid-Open No. 4-98625 JP 2006-216132 A JP 2001-84605 A Japanese Patent No. 3480377 Japanese Patent No. 3813826

  In recent years, in order to increase the amount of information that can be stored in a single optical disc, techniques for multilayering the information recording surface of the optical disc have been studied, and a technique using a laser hologram or a method that uses a voltage applied to the information recording surface can be selected. A technique of reading and writing with laser light is known. An optical disc having a multi-layered information recording surface (hereinafter referred to as a multi-layer optical disc) is configured by laminating a large number of information recording surfaces such as 3 to 100 layers.

  In a multi-layer optical disk, the amount of eccentricity of each information recording surface is different, and the information currently in focus is caused by errors in the position of each information recording surface (distance from the disk surface to each information recording surface). The laser beam reflected from the information recording surface of a layer different from the recording surface leaks into the focus error signal, which causes the focus servo system to become unstable as in the conventional example. That is, the track eccentricity of each layer is different, and a track cross occurs due to the eccentricity in a track in a layer different from the track in the currently focused layer. For this reason, track cross signals from other layers leak into the focus error signal, and noise is generated. As the number of layers on the information recording surface increases, there is a problem that the noise that the laser light reflected from the plurality of layers leaks into the focus error signal increases.

  In the above conventional example, the tracking error signal leaking into the focus error signal is mainly suppressed on a single information recording surface, and the tracking error signal from other layers leaking into the focus error signal in the multilayer optical disk is effective. Cannot be suppressed. In particular, the conventional example cannot be applied as it is to noise leaking into a focus error signal from many layers.

  Accordingly, the present invention has been made in view of the above problems, and in a focus servo system of an optical disc apparatus that reproduces or records a multilayer optical disc, the influence when a tracking error signal from another layer leaks into the focus error signal. The purpose of this is to realize a stable focus servo.

  The present invention includes an objective lens that irradiates a beam from a laser onto an optical disk, an actuator that drives the objective lens to move the focal point of the beam irradiated onto the optical disk in a focus direction and a tracking direction, and the reflected light from the optical disk An optical sensor that detects a beam and outputs it as a detection signal; and drives the actuator to output a focus error of the beam from the detection signal of the optical sensor as a focus error signal, and from the detection signal of the optical sensor, the beam A signal generation unit that outputs a deviation from the track as a tracking error signal; a focus servo control unit that inputs a focus error signal from the signal generation unit and drives the actuator to control the in-focus position of the beam; Tracking error from the signal generator And a tracking servo control unit that drives the actuator to control the tracking position of the beam. The tracking servo control unit tracks the actuator based on the tracking error signal. A tracking drive signal for driving in the direction is calculated, a signal having a second frequency exceeding the first frequency is added to the tracking drive signal, and the focus servo control unit outputs the focus error signal out of the input focus error signals. A focus error signal is corrected by attenuating the second frequency, and a focus drive signal for driving in the focus direction for driving the actuator is output based on the corrected focus error signal.

  Therefore, according to the present invention, a stable focus servo system can be realized.

1 is a block diagram illustrating an optical disc apparatus according to an embodiment of the present invention. It is a block diagram which shows embodiment of this invention and shows the function of a servo system. The graph which shows embodiment of this invention and shows the influence of the tracking error signal of the other layer leaked into the focus error signal, and shows the relationship between the frequency and the gain of the focus servo system. The graph which shows embodiment of this invention and shows the focus error signal input into a notch filter, and shows the relationship between a signal level and time. A graph showing a focus error signal input to a notch filter when a SIN wave is added to a tracking driver signal according to an embodiment of the present invention, and shows a relationship between signal level and time. The graph which shows embodiment of this invention and shows the focus error signal output from a notch filter, and shows the relationship between a signal level and time. 1 is a schematic view showing an information recording surface of a multilayer optical disc according to an embodiment of the present invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to an embodiment of the present invention.

  The optical disk apparatus includes a spindle motor 2 that rotates a multilayer optical disk 3 on a base 1, a pickup 4 that performs irradiation of laser light and detection of reflected light, and a pickup 4 in the radial direction (tracking direction or thread direction) of the multilayer optical disk 3. An actuator that drives the focus direction (direction in contact with and away from the recording surface of the multilayer optical disc 3) is arranged, and the control unit 10 that controls the actuator based on a signal detected from the pickup 4 is mainly configured. The multi-layer optical disk 3 is an optical disk in which a large number of information recording surfaces are stacked as described in the above problem, but may be an optical disk having one or two information recording surfaces.

  A spindle motor 2 is mounted on the base 1. A turntable 21 attached to the tip of the rotating shaft of the spindle motor 2 is mounted with a multilayer optical disk 3 that is an optical information recording medium that enables recording or reproduction of information, and the control unit 10 controls the spindle motor 2 in a predetermined manner. Drives at a speed of

  On the base 1, adjacent to the spindle motor 2, a semiconductor laser 41 that is a light source inside, a half mirror 42 that reflects / transmits a laser beam and guides it in a predetermined direction, and condenses the laser beam. The objective lens 43 that irradiates the information recording surface (the lower surface in the figure) of the multilayer optical disc 3 and a voice coil that finely controls the position of the objective lens 43 with respect to the information recording surface of the multilayer optical disc 3 using electromagnetic force. A so-called pickup 4 provided with an actuator 44 and a light detection element 45 for detecting reflected light from the information recording surface via an objective lens 43 is arranged in the radial direction of the optical disk by, for example, a rack and pinion 5 or the like. It is attached to be freely movable. Note that a motor 6 for driving the rack and driving the pickup 4 in the sled (movement between tracks in the radial direction) direction is coupled to the pinion of the rack and pinion 5.

  The actuator 44 includes a focus drive unit that displaces the objective lens 43 in the focus direction, and a tracking drive unit that displaces the objective lens 43 in the radial direction of the multilayer optical disc 3. About the structure of the said actuator 44 and the pick-up 4, what is necessary is just to use a well-known or well-known technique, Therefore It is not detailed in detail.

  The relative position of the objective lens 43 driven by the actuator 44 within the pickup 4 with respect to the information recording surface, the rotational speed (disk rotational speed) of the multilayer optical disk 3 driven by the spindle motor 2, the rack and pinion 5 and the motor. 6, the position of the track of the pickup 4 in the radial direction of the multilayer optical disk 3 is controlled by the control unit 10. The control unit 10 includes an analog front end (AFE) unit 40 that processes an analog signal, and a digital signal processor (DSP) unit 100 that processes a digital signal mainly by a system controller 101 including a processor.

  In the pickup 4, a signal detected by a light detection element 45 that detects reflected light from the information recording surface of the multilayer optical disk 3 is input to an analog front end (AFE) unit 40 of the control unit 10. The AFE unit 40 includes an arithmetic unit that performs various analog operations. The AFE unit 40 performs various processes on the signal from the light detection element 45 input to the analog front end (AFE) unit 40 to obtain a tracking error signal. (TE signal) and a focus error signal (FE signal) are generated. The tracking error signal and the focus error signal generated by the AFE unit 40 are converted into digital signals via an A / D converter (not shown), and then input to the DSP unit 100 described below to perform predetermined processing. Is called.

  The DSP unit 100 includes a system controller 101 including a CPU (or processor) that is an arithmetic element, and various elements such as a RAM 102 and a ROM 103 that store data and programs, and a driver that amplifies a drive signal. 1, the DSP unit 100 is shown as a functional block diagram by functional elements. The control program for the optical disk device executed by the system controller 101 is stored in the ROM 103 as a storage medium, loaded into the RAM 102 every time the optical disk device is started, and executed by the CPU of the system controller 101.

  First, the tracking error signal from the AFE unit 40 is input to the DSP unit 100, and the tracking driver (TRD) signal tracking servo system is configured with the track compensator 120 as the center. The focus error signal from the AFE unit 10 is input. Thus, the focus servo system that outputs the focus drive (FOD) signal is configured with the focus compensator 110 as the center, and the rotational frequency (FG) signal of the spindle motor 2 is input to achieve the rotational speed commanded by the system controller 101. A rotation servo system that outputs a rotation speed (SPD) signal for driving the multi-layer optical disk 3 is configured around the rotation control unit 160.

  The track compensator 120 of the tracking servo system corrects the tracking driver signal TRD so as to hold the track commanded by the system controller 101 based on the tracking error signal input from the AFE unit 40. Although not shown, the DSP unit 100 includes a thread signal generation unit that instructs the motor 6 to provide a thread signal for driving the pickup 4 in the thread direction (movement between tracks) based on the tracking error signal. Since the thread signal generation unit and the track compensator 120 may apply a known or well-known technique, they will not be described in detail in this embodiment.

  The tracking driver signal TRD output from the track compensator 120 is input to the driver circuit 152 via the adder 140. The driver circuit 152 amplifies the tracking driver signal TRD, drives the tracking unit of the actuator 44, displaces the position of the objective lens 43 in the radial direction of the multilayer optical disc 3, and starts from the track on the information recording surface of the multilayer optical disc 3. Correct the deviation.

  The adder 140 adds the SIN wave from the SIN wave generating unit 130 to the tracking driver signal from the track compensator 120 and outputs the tracking driver signal TRD after the addition to the driver circuit 152.

  The SIN wave generation unit 130 generates a sine wave having a predetermined frequency F2 and adds it to the focus error signal by the adder 140. The frequency F2 of the SIN wave from the SIN wave generator 130 is a preset value that satisfies F2> F1, for example, when the frequency of the servo band used by the focus compensator 110 is 0 to F1 [Hz].

  A switch 180 controlled by the system controller 101 is connected between the SIN wave generator 130 and the adder 140. When the system controller 101 sets the switch 180 to OFF, the SIN wave is cut off, and the adder 140 is Only the tracking driver signal TRD is output.

  In the rotation servo system, the rotation control unit 160 inputs the rotation frequency from the spindle motor 2 and corrects the rotation speed signal SPD so that the rotation speed commanded by the system controller 101 is obtained. The rotation speed signal SPD output from the rotation control unit 160 is input to the rotation driver circuit 161 that drives the spindle motor 2. The rotary servo system is not described in detail in this embodiment because a known or known technique may be applied.

  Next, the focus servo system includes a notch filter (BEF in the figure) 170 that attenuates a specific frequency and a focus compensator 110. The focus error signal input from the AFE unit 40 is input to the notch filter 170 to attenuate the predetermined frequency F2. The frequency at which the notch filter 170 attenuates is the SIN wave frequency F2 generated by the SIN wave generator 130.

  The focus compensator 110 drives the objective lens 43 in the focus direction based on the focus error signal input from the notch filter 170 so that the laser beam is focused on the information recording surface of the multilayer optical disc 3. The drive signal FOD is corrected.

  The focus compensator 110 outputs a focus drive signal FOD to the driver circuit 151. The driver circuit 151 drives the focus drive unit of the actuator 44 and responds to the focus drive signal FOD in which the frequency F2 of the SIN wave is attenuated by the notch filter 170. The position of the objective lens 43 is displaced.

  Note that the notch filter 170 may be a low-pass filter, and in this case, the notch filter 170 is configured with a frequency characteristic that attenuates a frequency higher than a frequency band (for example, 0 to F1 [Hz]) used by the focus servo system.

  Note that the switch 180 for blocking the SIN wave is turned OFF, for example, when the pickup 4 is moved between tracks, to prevent the SIN wave from being added to the tracking driver signal TRD, and to suppress the noise of the tracking servo system.

  FIG. 2 is a functional block diagram showing an outline of the servo system of the present invention.

  The laser light emitted from the pickup 4 to the information recording surface of the multilayer optical disc 3 is reflected by the information recording surface selected from the many layers of the multilayer optical disc 3 and enters the light detection element (optical sensor) 45. The AFE unit 40 extracts a focus error signal from the laser light detected by the light detection element 45 by a known or known technique such as an astigmatism method or a spot size method. In the extracted focus error signal, a leakage component of the tracking error signal is added as a noise component.

  When the switch 180 is ON, a SIN wave having the frequency F2 is added to the tracking driver signal TRD, and a SIN wave having the frequency F2 is also added to the tracking error signal leaking into the focus error signal.

  A tracking error (FEin) signal in which a focus error signal including a SIN wave leaks is first input to the notch filter 170 to attenuate a predetermined frequency F2. The notch filter 170 outputs a focus error signal (FEout) obtained by attenuating a predetermined frequency F2 to the focus compensator 110.

  Since the tracking error signal leaked into the focus error signal includes the SIN wave added from the SIN wave generating unit 130 of the tracking servo system, when the notch filter 170 attenuates the predetermined frequency F2, a noise component is included together with the SIN wave. The tracking error signal is removed.

  In the focus compensator 110, the focus error signal from which the tracking error signal has been removed by the notch filter 170 is input, and the focus direction of the objective lens 43 is determined in accordance with the in-focus position shift amount included in the focus error signal from which the noise component has been removed. The focus drive signal FOD for correcting the position of is calculated and output.

  As a result, the objective lens 43 is driven in the focus direction without being affected by noise due to leakage of the tracking error signal, and the influence of the reflected light from the other layers of the multilayer optical disk 3 is reduced as in the conventional example. Without receiving, it is possible to hold a predetermined in-focus position (distance from the objective lens 43 to the information recording surface) according to the height of the information recording surface of the selected layer of the multilayer optical disc 3.

  3 to 7 show details of removing only the tracking error signal (noise component) leaked into the focus error signal. FIG. 3 shows the relationship between the frequency characteristics of the notch filter 170 and the tracking error signal included as a noise component in the focus error signal.

  In FIG. 3, when the switch 180 for applying a SIN wave to the tracking driver signal TRD is OFF, a noise component appears in the frequency band of TE leakage noise in the figure below F1, which is the control frequency of the focus servo system.

  On the other hand, when the switch 180 is turned on and a SIN wave is added to the tracking driver signal TRD, the tracking error signal included in the focus error signal is distributed in a frequency band centered on the frequency F2 of the SIN wave. The tracking error signal leaked into the focus error signal can be suppressed by attenuating the frequency F2 of the SIN wave by the notch filter 170.

  FIG. 4 shows a focus error signal when no SIN wave is applied to the tracking driver signal TRD, and shows an input (FEin) of the notch filter 170. In a state where no SIN wave is applied, the tracking error signal leaks into the focus error signal and becomes a noise component tail.

  FIG. 5 shows a focus error signal when a SIN wave is added to the tracking driver signal TRD, and shows an input (FEin) of the notch filter 170. When the SIN wave is added, the frequency band of the tracking error signal included in the focus error signal moves to the frequency band of the SIN wave frequency F2.

  FIG. 6 shows the output FEout of the notch filter 170 when the SIN wave of FIG. 5 is applied. Since the notch filter 170 attenuates and removes the frequency F2 of the SIN wave, the leakage component of the focus error signal that is a noise component moved to the frequency F2 of the SIN wave is attenuated.

  Accordingly, since the focus compensator 110 can calculate the focus drive signal FOD with the focus error signal from which the noise component is removed or suppressed, it follows the selected information recording surface of the multilayer optical disc 3 without removing the focus position of the laser beam. And a stable focus servo system can be realized.

  FIG. 7 shows how the tracking error signal leaks from the other layers into the focus error signal in the multilayer optical disk 3 having four layers. In the figure, Layers 0 to 3 indicate stacked information recording surfaces. For example, even when the laser beam is focused on the Layer 0 layer in the drawing, the reflected light from the Layers 1 to 3 that do not follow returns to the pickup 4 and noise occurs in the focus error signal. As shown in FIG. 4, even if the laser beam follows the track at Layer 0, this noise is transmitted through Layer 0 because the tracks of each Layer are shifted from each other due to eccentricity as described in the above problem. Since the laser beam has crossed the track due to the eccentricity of another layer, a tracking error signal is generated and leaks into the focus error signal.

  In the present invention, a SIN wave having a frequency F2 higher than the control frequency (F1 or less) of the focus servo system is added to the tracking driver signal TRD in advance to the tracking driver signal TRD, and a notch filter 170 provided before the focus compensator 110 is provided. Thus, when the SIN wave is removed, the noise component included in the focus error signal can be suppressed by simultaneously suppressing the tracking error signal that is a noise component.

  In the above embodiment, an example in which the notch filter 170 is provided in front of the focus compensator 110 has been described. However, as described above, a low-pass filter is used to cut a frequency higher than the control frequency of the focus servo system. May be.

  In the above embodiment, an example in which the sine wave generator 130 adds a sine wave to the tracking driver signal TRD as a noise removal signal has been described. However, any waveform can be used as long as it can be removed by the notch filter 170 or the low-pass filter. Can be used as a signal for noise removal.

  In the above embodiment, the example in which the present invention is applied to the multilayer optical disk 3 has been described. However, the present invention can also be applied to an optical disk having a single information recording surface.

  As described above, according to the present invention, when a second frequency signal higher than the control frequency of the focus servo system is added to the tracking drive signal in advance, and the first frequency is attenuated by the focus servo control unit. At the same time, by suppressing the tracking error signal that is a noise component, the noise component included in the focus error signal can be suppressed, and a stable focus servo system can be realized.

  Further, as described above, the present invention can be applied to an optical disc apparatus that performs tracking servo with a tracking error signal and performs focus servo with a focus error signal.

3 Optical disk 40 AFE unit 43 Objective lens 44 Actuator 10 Control unit 100 DSP unit 101 System controller 110 Focus compensator 120 Track compensator 130 SIN wave generating unit 140 Adder 170 Notch filter

Claims (2)

An objective lens for irradiating the optical disc with a beam from a laser;
An actuator that drives the objective lens to move the focal point of the beam applied to the optical disc in a focus direction and a tracking direction;
An optical sensor that detects the beam reflected from the optical disc and outputs a detection signal;
Signal generation that drives the actuator to output the focus shift of the beam from the detection signal of the optical sensor as a focus error signal, and outputs the shift from the track of the beam as a tracking error signal from the detection signal of the optical sensor And
A focus servo control unit that inputs a focus error signal from the signal generation unit, drives the actuator, and controls the focusing position of the beam;
A tracking servo control unit that inputs a tracking error signal from the signal generation unit and drives the actuator to control the tracking position of the beam.
The tracking servo control unit
A tracking drive signal for driving the actuator in a tracking direction based on the tracking error signal is calculated, and a signal having a second frequency exceeding the first frequency is added to the tracking drive signal and output.
The focus servo control unit
Attenuating the second frequency of the input focus error signal to correct the focus error signal, and outputting a focus drive signal for driving in the focus direction for driving the actuator based on the corrected focus error signal. An optical disc apparatus characterized by the above. The optical disc apparatus according to claim 1,
The tracking servo control unit
A track compensator for calculating a tracking drive signal for driving the actuator in a tracking direction based on the tracking error signal;
A signal addition unit that adds a signal having a second frequency exceeding the first frequency to the tracking drive signal output from the track compensation unit;
The focus servo control unit
A filter that inputs the focus error signal and attenuates the second frequency;
A focus compensation unit that calculates a focus drive signal for driving the actuator in a focus direction based on a focus error signal attenuated by the filter;
The optical disc apparatus, wherein the predetermined frequency is a frequency used by the focus compensation unit for control.