JPH09320070A - Focus control device of optical disk apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus control device of optical disk apparatus which assures stable focus control operation even during the seek operation while controlling the focus control by a sampling control method. SOLUTION: In the optical disk apparatus for controlling the focusing condition of a laser beam by feeding back a focus error signal indicating defocusing amount of laser beam for an optical disk, the focus control device which comprises an error signal detecting circuit 8 which samples the focus error signal for every sampling period (T) in the feedback loop and a notch fileter 22 having the minimal point of the gain at the frequency 1/(2T) to attenuate the crosstalk element superimposed to the focus error signal even if resolution of the drive signal is insufficient is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for irradiating an information track on an optical disk with laser light to record or reproduce information, and more particularly to a focus control device for controlling the focus state of laser light.

[0002]

2. Description of the Related Art Generally, in an optical disk device using a magneto-optical disk or the like as a recording medium, various controls are performed in order to record / reproduce information with a laser beam. For example, focus control for controlling the laser light so as to focus on the optical disk, tracking control for controlling the laser light so as to follow the information track on the disk, and information track for controlling the laser light to access a distant information track. The control such as the seek control for controlling the driving so as to traverse each of the lines is performed.

Of these, focus control is performed by detecting the state of defocus as a focus error signal by some method and driving the objective lens in the traveling direction of the laser beam based on the focus error signal. At this time, the focus actuator that drives the objective lens is passed through not the focus error signal itself but the phase advance compensation for stabilizing the focus control operation and the phase delay compensation for improving the followability of the focus control. A signal is applied. Of course, the focus control needs to be normally operated normally regardless of whether the tracking control or the seek control is performed.

By the way, it is known that when the laser light crosses the information track during the seek operation, an AC component (crosstalk) synchronized with the track crossing is superimposed on the focus error signal.

When a crosstalk component is superimposed on the focus error signal, the drive signal (phase compensation output) of the focus actuator oscillates at the crosstalk frequency, as pointed out in JP-A-7-169070. However, there is a problem that it becomes saturated (clip) and normal focus control cannot be performed.

In recent years, sampling control (digital control) by a DSP (Digital Signal Processor) is widely used in order to reduce the cost of the apparatus and improve the reliability. However, with this sampling control, the focus control cannot be normally performed more significantly.

That is, when the drive signal vibrates and is saturated, the focus position is in a state of being controlled by the duty ratio of the drive signal, but in the case of sampling control, the resolution of the duty ratio depends on the sampling cycle. Will be decided. Therefore, at the frequency, which is the most disadvantageous in terms of resolution, at which the drive signal oscillates positively and negatively in each sampling cycle, that is, the frequency at which the crosstalk frequency is half the sampling frequency, the error of the drive signal itself becomes large, and the large focus Misalignment is likely to occur.

During the seek operation, the number of crossing tracks and the moving speed are detected by the tracking error signal. However, when a focus deviation occurs, the amplitude of the tracking error signal decreases, and therefore these operations can be performed. The seek operation may be lost and the seek operation may fail.

Further, in Japanese Unexamined Patent Publication No. 5-135381, a bias voltage is applied to the focus error signal in order to prevent the focus shift due to the above-mentioned crosstalk component, and the focus control point is slightly moved from the true focus point to cross. Techniques for reducing the amount of talk are disclosed. This is effective in preventing malfunction of focus control because the amount of crosstalk changes depending on the focus state.

Further, in Japanese Unexamined Patent Publication No. 7-169070, a tracking error signal indicating a tracking error and a sum signal indicating the intensity of reflected light are multiplied by appropriate gains and added to generate a crosstalk correction signal and a focus error. A technique of canceling a crosstalk component by adding it to a signal is disclosed.

[0011]

However, in the technique described in Japanese Patent Laid-Open No. 5-135381 mentioned above, focus deviation occurs due to the bias applied to the focus error signal, which reduces crosstalk. However, since the amplitude of the tracking error signal is also reduced, it is difficult to prevent malfunctions in track counting and speed detection.

Further, according to the technique disclosed in Japanese Patent Laid-Open No. 7-169070, it is difficult to accurately generate the crosstalk correction signal, and a complicated circuit is required for generating the correction signal. There's a problem.

Further, in any of the above-mentioned techniques,
When sampling control is performed, no particular consideration is given to the phenomenon that the crosstalk frequency becomes particularly unstable in the vicinity of half the sampling frequency, and due to the crosstalk component that could not be removed by correction, focus Control may become unstable.

Therefore, the present invention provides a focus control device for an optical disk device, which is capable of performing stable focus control during seek operation without being affected by crosstalk while controlling focus control by sampling control. To aim.

[0015]

In order to achieve the above object, the present invention irradiates an information track on an optical disk with a laser beam to record and / or reproduce information, and to focus the laser beam on the optical disk. A focus control device for an optical disk device, which detects a focus error signal indicating a shift amount, forms a loop for feeding back the focus error signal to a focus actuator that drives the focus position of the laser light, and controls the focus state of the laser light. In the above loop, a focus control apparatus for an optical disk device, comprising: a sampling means for sampling the focus error signal in each sampling cycle (T) and a notch filter means having a minimum gain point at a frequency 1 / (2T) in the loop. I will provide a.

With the above configuration, the frequency of the crosstalk component becomes half the sampling frequency, and even if the resolution of the drive signal is insufficient, the frequency 1 / (2T) (the sampling frequency The crosstalk component superimposed on the focus error signal is effectively attenuated by the function of the filter having the minimum gain point at (1/2), and stable focus control operation can be performed without being affected by the crosstalk.

[0017]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an optical disc device including a focus control device according to a first embodiment of the present invention. Here, FIG. 1 characteristically shows only the configuration which is the gist of the present invention.

This optical disk device records an information on the optical disk 1 for recording information, a spindle motor 2 for mounting the optical disk 1 and rotating the optical disk 1 at a predetermined rotation speed, and irradiating the recording surface of the optical disk 1 with the information. And a laser beam 3 for reproduction, and an objective lens 4 for condensing the laser beam 3.
And a focus actuator 5 for driving the objective lens 4 in the optical axis direction (X-axis direction) to move the focus position of the laser light 3 with respect to the optical disk 1, a reflection mirror 6, and a semiconductor laser or optical disk serving as a light source. An optical system 7 including a photodetector for detecting reflected light from the optical disc 1, an error signal detection circuit 8 for detecting a servo error signal (focus error signal, tracking error signal, etc.), and a focus servo system. A focus control circuit 9 for performing phase compensation and the like, a driver 10 for driving the focus actuator 5 with a current,
A seek control circuit 11, which will be described later, and a carriage 12 on which the focus actuator 5 and the reflection mirror 6 are mounted and which can move in a direction crossing an information track (Y-axis direction). In the present embodiment, the focus control circuit 9 is realized by a DSP (Digital Signal Processor).

FIG. 2 shows a detailed structure of the focus control circuit 9 shown in FIG. The focus control circuit 9 includes an A / D converter 21 for A / D converting the focus error signal (FES) detected by the error signal detection circuit 8 at a cycle T (sampling frequency 1 / T), and sampling. A filter (notch filter) 22 having a minimum gain point at a frequency of 1/2 of the frequency (1 / T), and a selector for selecting and outputting either the output of the A / D converter 21 or the output of the filter 22. 23, a phase compensation filter 24 for stabilizing the focus servo system, and a D / A converter 25 for D / A converting the output of the phase compensation circuit filter 24.

The phase compensation filter 24 includes a phase delay compensation filter 26, a phase lead compensation filter 27, and
It is composed of an adder 28. Here, all the A / D / D / A converters and filters inside the focus control circuit 9 operate in synchronization with the sampling clock.
In the present embodiment, the sampling frequency is set to 30 kHz (sampling cycle 33.3 μs) for description.

FIG. 3 shows the seek control circuit 1 shown in FIG.
1 shows a detailed configuration of 1. However, this seek control circuit
It may be configured as an electric circuit, or a part or the whole thereof may be realized by processing by a DSP.

The seek control circuit 11 is a binarization circuit 31 which binarizes the tracking error signal (TES).
And a track count circuit 32 for detecting the number of moving tracks at the seek time by counting the binarized signal.
A target speed calculation circuit 33 that obtains a seek target speed at that time in correspondence with the track count value, a determination circuit 34 that determines the value of the control signal FLTON based on the value of the target speed, and a cycle of the binarized signal. It is composed of a speed detection circuit 35 for obtaining the current moving speed, and a speed control circuit 36 for obtaining a drive signal for a tracking (Tr) actuator (not shown) from the target speed and the current moving speed.

In the optical disc device having such a structure, the laser light 3 emitted from the laser diode included in the optical system 7 shown in FIG. 1 is reflected by the reflection mirror 6 and the surface of the optical disc 1 is reflected by the objective lens 3. Is focused on. The laser light reflected by the optical disc 1 is again
After passing through the objective lens 3, the light is reflected by the reflection mirror 6, returns to the optical system 7, and the amount of the reflected light is detected by the photodetector included in the optical system 7.

At this time, the focus state of the laser light 3 on the optical disc 1 is detected by the focus error detection optical system in the optical system 7 as a change in the light amount, and the focus error signal is calculated by the error signal detection circuit 8. (F
ES) is detected. Here, there are various methods for detecting the focus error, but a general method may be used.
Here, the description is omitted.

In the error signal detection circuit 8, a tracking error signal (a signal indicating how much the position irradiated by the laser beam 3 deviates from the center of the information track)
TES is also detected.

Then, the focus control circuit 9 negatively feeds back the focus error signal to the focus actuator so that the detected focus error signal becomes zero, that is, the disk surface is focused. At this time,
Generally, phase lead compensation is performed to stabilize the negative feedback operation, and phase delay compensation is also performed to improve the followability of the operation. Normally, during tracking or the like, the selector 23 selects the output of the A / D converter 21 and outputs it to the phase compensation filter 24.

On the other hand, during the seek operation, the selector 23 receives the control signal FLTON from the seek control circuit 11,
The output of the filter 22 is selected. Here, the frequency characteristic of the filter 22 is 30 k, which is the sampling frequency.
It has a minimum gain point at 15 kHz, which is half the frequency of Hz.

In the case of an analog circuit, such a characteristic is generated by a twin T filter, but in the case of a digital filter, even a simple high-frequency cutoff filter (LPF) characteristic filter is digitized. By (bilinear transformation), a minimum point of the gain appears at a frequency of 1/2 of the sampling frequency, and similar characteristics are obtained. For example, an LPF having a cutoff frequency of 15 kHz represented by G (s) = 1 / (1.06 × 10 ⁻⁵ · s + 1) (1)
Has a frequency characteristic as shown in FIG. 4, but if this is subjected to bilinear conversion at a sampling frequency of 30 kHz, the transfer function becomes: G (z) = 0.611 (z + 1) / (z + 0.222) (2) Thus, the frequency characteristic has a minimum gain point at 15 kHz as shown in FIG. Filter 22 of this embodiment
Is a digital filter having this frequency characteristic.

When the laser beam 3 moves in the direction traversing the information track on the optical disk as in the seek operation, a crosstalk component synchronized with the track cross is superimposed on the focus error signal. A / with selector 23
When the seek is performed while the output of the D converter is selected (corresponding to the conventional method), as shown in FIG. 6, the crosstalk frequency is close to a half of the sampling frequency,
The focus servo becomes unstable and defocus occurs (up to about 0.8 μm).

This is because, as described in the section of the prior art, the crosstalk frequency approaches 1/2 of the sampling frequency, the resolution in the time axis direction is insufficient, and the resolution of the drive signal fed back to the focus actuator is reduced. The cause is to do.

Therefore, in the present invention, the target speed calculation circuit 3
With respect to the seek target speed output at that time from No. 3, the judgment circuit 34 judges whether or not it is within a predetermined speed range, and F
The LTON signal is output, and the selector 22 filters the filter 22.
Output is selected and the signal input to the phase compensation filter 24 is switched to the output of the filter 22 (0.05 m / s
Hereinafter, it is assumed that the output of the filter 22 is switched to).

Then, as shown in FIG. 7, since the crosstalk component is attenuated in the vicinity of the frequency where the focus servo is most easily shaken, the focus servo is less susceptible to the crosstalk and the focus shake is extremely reduced. Becomes smaller (about 0.4 μm at maximum). Further, the drive signal FODRV also has less vibration, and power consumption can be reduced.

The timing at which the selector 23 is switched to the output of the filter 22 may be centered on the speed at which the crosstalk component becomes 1/2 of the sampling frequency. For example, when the track pitch is 1.4 μm and the sampling frequency is 30 kHz, the moving speed at which the crosstalk component is ½ of the sampling frequency, that is, 15 kHz is 15 (kHz) × 1.4 (μm) = 0.021 ( m
/ S).

Normally, when a filter having a characteristic like the filter 22 is inserted in the servo loop, the servo often becomes unstable due to the phase delay. For this reason, it is desirable that the time for selecting the output of the filter 22 by the selector 23 is short, but as can be seen from FIG. 6, focus shake due to crosstalk begins earlier than when crosstalk reaches 15 kHz, so the frequency around 15 kHz is the center. It is preferable to set the speed range with some allowance.

Next, FIG. 8 shows a detailed configuration example of the focus control circuit of the second embodiment, which will be described. Here, in this focus control circuit, the same components as those shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In the above-described first embodiment, a first-order digital filter having the characteristic expressed by the equation (2) in the velocity region susceptible to the influence of crosstalk is constructed, and the output thereof is used as the filter 22 and the phase compensation filter 24 is used. However, the filter 22 does not necessarily have to be such a digital filter.

The focus control circuit 9a shown in FIG.
The filter 22 is replaced with a delay element (memory) 81 and an average value calculation circuit 82, and the same effect is obtained without using the digital filter. These delay elements 81
The average value calculation circuit 82 and the average value calculation circuit 82 can be constructed as an electric circuit, but it is desirable to realize the software by a DSP together with a phase compensation filter.

The configuration of the focus control circuit 9a is nothing but obtaining the average value of the latest A / D conversion result of the focus error signal and the previous (one sample before) A / D conversion result. When the transmission characteristic from the error signal to the output of the average value calculation circuit 82 is expressed by an equation, G (z) = (1 + Z ⁻¹ ) / 2 (3), and the frequency characteristic is as shown in FIG. The gain has a minimum point at 15 kHz, which is half the sampling frequency. Therefore, if the focus control circuit 9a shown in FIG. 8 is used instead of the focus control circuit 9 shown in FIG. 2, a digital filter becomes unnecessary and the same effect can be obtained by a very simple arithmetic process in the DSP. You can

In this embodiment, the input signal to the phase compensation filter 24 is switched to the filter 22 or the average value calculation circuit 82 only during seek and at a predetermined speed (0.05 m / s or less). It may remain switched during a seek.

However, as shown in FIG. 5 and FIG. 9, a phase delay occurs due to the filtering and averaging processing, and the phase margin is reduced. Therefore, switching is performed only in the velocity range vulnerable to crosstalk. Is desirable.

In this embodiment, both the phase lead compensation and the phase lag compensation are used as the phase compensation filter.
This may be just phase advance compensation, or
Performing phase lag compensation processing separately, only for phase lead compensation,
A signal that has passed through a filter having a minimum gain point at half the sampling frequency may be input.

Further, the frequency at which the gain becomes a minimum and the dip frequency may be variable. When constructing a notch filter having a dip at 1/2 of the sampling frequency by obtaining the average value with the previous value, it is difficult to change the dip frequency because it is necessary to change the sampling frequency. When configured as, it is possible to change the dip frequency to some extent.

Therefore, if the dip frequency is changed corresponding to the frequency of the crosstalk component superimposed on the focus error signal, the focus servo is stabilized in the crosstalk in a wider frequency range, that is, in the wider seek speed range. It becomes possible to do it. In this case, as shown in FIG.
The dip frequency may be calculated with respect to the target speed value by 01, and the dip frequency of the filter 22a may be switched. Here, the dip frequency f is a velocity target value v and a track pitch p of information tracks on the optical disc.
On the other hand, if f = v / p, the influence of crosstalk can be effectively excluded without directly obtaining the frequency component of crosstalk. The track pitch in this case is the distance from the center of the land on the disk to the center of the adjacent land or between the centers of the grooves, and corresponds to one cycle of crosstalk.

Of course, the dip frequency may be switched according to the speed detection value instead of the speed target value. Further, also in the first and second embodiments, the selector may be switched based on the speed detection value.

Although the above embodiments have been described, the present invention also includes the following inventions. (1) The information track on the optical disc is irradiated with laser light to record and / or reproduce information, and a focus error signal indicating the amount of defocus of the laser light with respect to the optical disc is detected, and the focus position of the laser light is detected. In a focus control device of an optical disc device for controlling a focus state of the laser light by forming a loop for returning the focus error signal to a focus actuator for driving the focus error signal, a sampling cycle (T) of the focus error signal is included in the loop. A focus control device for an optical disk device, characterized in that sampling means for sampling each time and notch filter means having a minimum gain point at frequency 1 / (2T) are provided.

As a result, since the notch filter having the minimum gain point is provided at the frequency 1 / (2T), the crosstalk component is effectively provided at the frequency most susceptible to the crosstalk when the focus servo is performed by the sampling control. Attenuation is possible and stable focus servo operation becomes possible.

(2) Selection means for selecting and outputting either the output of the sampling means or the output of the notch filter means, and the output of the selection means as input
The phase compensating means for performing phase compensation for stabilizing focus control, and the driver means for driving the focus actuator based on the output of the phase compensating means are included. (4) A focus control device for an optical disk device according to item (1).

As a result, since it is possible to select whether the notch filter is incorporated in the servo loop by the selecting means,
When the focus servo becomes unstable due to the phase delay of the notch filter, the notch filter can be cut off and the normal focus servo operation can be stably performed.

(3) The notch filter means obtains and outputs the average value of the latest sampling value of the focus error signal and the previous sampling value, and outputs the average value. A focus control device for an optical disk device according to the item 2).

As a result, the averaging is used to obtain the same frequency characteristic as the notch filter, so that it is possible to simplify the processing contents particularly when the processing is performed by the DSP. (4) The selecting means selects the output of the filter means during a seek operation in which the laser light moves across an information track provided on the optical disc, and outputs the output of the sampling means in other states. The focus control device for an optical disk device according to the item (2) or (3), wherein

As a result, since the notch filter is incorporated in the servo loop only during the seek operation, it is possible to prevent the focus servo operation from becoming unstable due to the phase delay of the notch filter during the tracking operation.

(5) The selecting means is in the seek operation,
The optical disk device according to the item (4), wherein the output of the filter means is selected when the seek speed is within a predetermined speed range, and the output of the sampling means is selected in other states. Focus control device.

As a result, the notch filter is incorporated in the servo loop only within a predetermined speed range during the seek operation, so that the focus servo operation can be performed due to the phase delay of the notch filter during the tracking operation and most of the seek operation. It becomes possible to prevent instability.

(6) The selecting means selects the output of the filter means at least at a speed at which the seek speed is p / (2T) with respect to the sampling period T and the track pitch p of the information track. The focus control device for an optical disk device according to the item (5), which is a device.

As a result, since the notch filter is incorporated in the servo loop at the crosstalk frequency / speed at which the focus servo is most likely to be swung, the focus servo can be efficiently stabilized.

(7) The information track on the optical disk is irradiated with laser light to record and / or reproduce information, and a focus error signal indicating the amount of defocus of the laser light with respect to the optical disk is detected to detect the laser light. In a focus control device of an optical disk device for controlling a focus state of the laser light by forming a loop for returning the focus error signal to a focus actuator that drives the focus position of the dip frequency, the gain becomes a minimum in the loop. Is provided with a variable dip frequency variable notch filter, and during the seek operation in which the laser light operates so as to cross the information track provided on the optical disc, the dip frequency is set to a frequency at which the laser light crosses the information track. Characterized by switching so as to be substantially equal Focus control system of the disk drive.

Thus, by changing the dip frequency of the notch filter, crosstalk in a wider frequency range can be dealt with, and the focus servo operation can be stabilized at all seek speeds.

[0058]

As described in detail above, according to the present invention, a filter having a minimum gain point at a frequency of 1 / (2T) with respect to the sampling period (T) is provided in the focus control loop. Even if the crosstalk frequency is ½ of the sampling frequency and the focus control by sampling control tends to be unstable, stable focus servo operation can be performed without being affected by the crosstalk component. It is possible to provide a focus control device for another optical disc device.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical disc device including a focus control device according to a first embodiment.

FIG. 2 is a diagram showing a detailed configuration of a focus control circuit shown in FIG.

3 is a diagram showing a detailed configuration of the seek control circuit shown in FIG.

FIG. 4 is a diagram showing frequency characteristics of an output of an LPF and a phase and a gain.

FIG. 5 is a diagram showing frequency characteristics of a phase and a gain, which are outputs of the digital filter of the first embodiment.

FIG. 6 is a diagram for explaining a focus shift according to a conventional technique.

FIG. 7 is a diagram for explaining a focus shift in the first embodiment.

FIG. 8 is a diagram illustrating a detailed configuration example of a focus control circuit according to a second embodiment.

FIG. 9 is a diagram showing frequency characteristics of an output and a phase and a gain in the second embodiment.

FIG. 10 is a diagram showing a modification of the second embodiment.

[Explanation of symbols]

 1 ... Optical disc 2 ... Spindle motor 3 ... Laser light 4 ... Objective lens 5 ... Focus actuator 6 ... Reflecting mirror 7 ... Optical system 8 ... Error signal detection circuit 9 ... Focus control circuit 10 ... Driver 11 ... Seek control circuit 12 ... Carriage 21 ... A / D converter 22 ... Filter (notch filter) 23 ... Selector 24 ... Phase compensation time filter 25 ... D / A converter 26 ... Phase delay compensation filter 27 ... Phase lead compensation filter 28 ... Adder

Claims (3)

[Claims] 1. When a laser beam is applied to an information track on an optical disc to record and / or reproduce information, a focus error signal indicating a defocus amount of the laser beam with respect to the optical disc is detected, and the laser beam is detected. In a focus control device of an optical disc device for controlling a focus state of the laser light by forming a loop for returning the focus error signal to a focus actuator that drives a focus position of light, in the loop, the focus error signal is previously set. A focus control device for an optical disk device, comprising: sampling means for sampling every set sampling period (T); and notch filter means having a minimum gain point at frequency 1 / (2T). 2. The focus control device of the optical disk device further has a selection means for selecting and outputting either the output of the sampling means or the output of the notch filter means, and the output of the selection means as inputs. 7. A phase compensating means for performing phase compensation for stabilizing focus control, and a driver means for driving the focus actuator based on an output of the phase compensating means. 1. A focus control device for an optical disc device according to 1. 3. An information track on an optical disc is irradiated with a laser beam to record and / or reproduce information, and a focus error signal indicating a defocus amount of the laser beam with respect to the optical disc is detected to detect the laser beam. In a focus control device of an optical disc device that controls a focus state of the laser light by forming a loop that returns the focus error signal to a focus actuator that drives a focus position, in the loop, a dip frequency at which the gain becomes a minimum is A variable dip frequency variable notch filter is provided, and during the seek operation in which the laser light operates so as to traverse the information track provided on the optical disc, the dip frequency is approximately the frequency at which the laser light traverses the information track. The optical device is characterized by switching so that they become equal. Focus control unit for disk device.