JP2000011389A - Focus control method and record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus control method rapidly performing focusing. SOLUTION: A control circuit 41 moves an optical part 32 to a first arrival point set based on the maximum value of an error signal FE obtained by moving the optical part 32 and the level of the error signal on a focal point position, and obtains the maximum value of the levels of the now and then error signals FE while moving the optical part 32 and updates the level of a second arrival point set based on the maximum value and the level of the error signal on the focal point position. Then, when the present position of the optical part 32 becomes lower than the level, it is defined that the optical part 32 arrives at the second arrival point, and focus servo control is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CD-ROM,
The present invention relates to a focus control method in a data reading device for reading data from a recording medium such as a VD (Digital Video Disk).

[0002] In recent years, the amount of data has been steadily increasing with the adoption of multimedia. Large-capacity optical discs are attracting attention as recording media for storing an increasing amount of data.
D, CD-ROM, MD, PD and the like have been developed. At present, DVDs and DVD-ROMs having the same size as a CD-ROM and capable of realizing about 7.5 times the capacity have been used.

[0003] As for the data reading device which handles such a large-capacity recording medium, it is desired to improve the performance such as increasing the reading speed. Therefore, even in focus search control in which a pickup device for reading data is moved to a focal point, an increase in processing speed is required.

[0004]

2. Description of the Related Art Conventionally, in an optical disk apparatus for reading data from an optical disk such as a CD-ROM or a DVD,
The disk is rotated by a spindle motor, and stored data stored as digital signals on the recording surface of the disk is optically read by a pickup device.

The stored data read by the pickup device is output from the pickup device as an analog signal, the analog signal is amplified to a predetermined amplitude by an amplifier, and then the voltage level of the output signal of the amplifier is set to a predetermined threshold. The data is binarized based on the value, converted into a digital pulse signal, and a predetermined demodulation process is performed on the digital pulse signal to generate read data.

By the way, in order to read data as described above, it is necessary that the beam irradiated from the LD (Laser Diode) of the pickup device onto the optical disk is focused on the recording surface. The drive device controls the position of the pickup device and performs focus control for focusing the beam on the recording surface.

That is, the drive device moves the pickup device up and down to change the distance between the optical disk and the pickup device. At this time, an output signal of the pickup device is input to the drive device as a focus error signal. The drive device, based on the focus error signal,
A focus search is performed to search for a focused position where the beam is focused on the recording surface. When the pickup device reaches the in-focus position by the focus search, the drive device switches from the focus search to a servo control that causes the position of the pickup device to follow the position change of the recording surface due to the undulation (surface deviation) of the optical disk.

[0008]

In the above-described optical disk apparatus, the speed of reading data is increased by rotating the optical disk at a linear velocity higher than a predetermined linear velocity, for example, at a linear velocity of 2 ×, 4 × or more. It is planned. However, the fluctuation width of the relative position of the recording surface with respect to the pickup device increases accordingly. Further, the frequency at which the recording surface fluctuates increases. Thus, the optical disc device needs to increase the speed of focus control.

However, if the speed of the focus control is increased, the pickup device will exceed the focal point at the start of the servo control. Then, it takes time for the drive control device to move the pickup device to the in-focus position by the servo control. This hinders an increase in the reading speed.

If the pickup device goes far beyond the in-focus position, the pickup device cannot be returned to the in-focus position. This requires re-execution of the focus search, which hinders an increase in the reading speed.

To solve the above problem, a method of reducing the rotation speed of the optical disk only at the time of focus search can be considered. However, in this method, it takes time for the focus control, which hinders an increase in the reading speed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a focus control method capable of performing focusing at high speed and a recording medium recording the method. .

[0013]

In order to achieve the above object, the invention according to claim 1 comprises a recording surface of an optical disc,
From focus search control to focus servo control, the optical unit is moved to a focal point based on an error signal whose level changes in accordance with the distance from the optical unit that irradiates the recording surface with light for reading data on the recording surface. In the focus control method, the arrival point is set before the in-focus position with respect to the search direction in the focus search control based on the level of the error signal, and the current position of the optical unit exceeds the arrival point. Switch to the focus servo control at the time of

According to a second aspect of the present invention, in the focus control method according to the first aspect, after switching the arrival point to the focus servo control, the focus unit controls the optical unit to focus on the error signal. Is set at a position where it is possible to converge to the in-focus position beyond.

[0015] The third aspect of the present invention is the first or second aspect.
In the focus control method according to the above, the reaching point,
Based on the peak level of the error signal and the level of the error signal at the focal point, the error signal is set at a point where the first level set based on the peak level matches the error signal.

The invention described in claim 4 is the first to third aspects of the present invention.
In the focus control method described in any one of the above, the servo calculation in the focus servo control is started during the focus search control.

[0017] The invention according to claim 5 is the invention according to claims 1 to 3.
In the focus control method according to any one of the above, a preset value is set as an initial value of the servo control during the focus search control.

The invention described in claim 6 is the invention according to claim 4 or 5
In the focus control method described in the above, when the error signal exceeds a point where the second level set based on the in-focus position based on the peak level of the error signal and the level of the error signal at the in-focus position exceeds the point Start of servo calculation or setting of initial value.

The invention according to claim 7 is the invention according to claims 1 to 6
In the focus control method according to any one of the above, a gain for a drive signal for driving the focus actuator is changed according to a position of an optical unit.

According to an eighth aspect of the present invention, in the focus control method according to the seventh aspect, the gain is increased to near a peak immediately before the focal point, and is decreased when the peak is exceeded.

According to a ninth aspect of the present invention, an error signal whose level changes in accordance with a distance between a recording surface of an optical disk and an optical unit that irradiates light for reading data on the recording surface onto the recording surface is provided. A focus control method for switching from focus search control to focus servo control, in which the optical unit is moved to a focal point based on the step of acquiring the maximum value of an error signal by moving the optical unit; and Setting a first point of arrival based on the level of the error signal in step, moving the optical section to the first point of arrival, moving the optical section, and setting the maximum value of the error signal level at each time And updating a second arrival point to be set based on the maximum value and the level of the error signal at the in-focus position. It is determined whether reaches the second arrival point, and initiating a focus servo control upon reaching a second arrival point based on the determination result.

According to a tenth aspect of the present invention, there is provided a recording medium storing a program for executing the focus control method according to any one of the first to ninth aspects. (Operation) Therefore, according to the first aspect of the present invention, the focus servo is performed when, based on the level of the error signal, an arrival point set before the in-focus position with respect to the search direction in the focus search control is exceeded. Since the control is switched to the control, even when the moving speed of the optical unit is increased, it is difficult for the optical unit to exceed the focal point.

According to the second aspect of the present invention, after the arrival point is switched to the focus servo control, the focus servo control allows the optical section to converge to the in-focus position beyond the peak of the error signal. Since the position is set, the focus servo calculation is started earlier and the initial value is stabilized.

According to the third aspect of the present invention, the error point coincides with the first level whose arrival point is set on the basis of the peak level of the error signal and the level of the error signal at the in-focus position with reference to the peak level. Therefore, even if the moving speed of the optical unit is increased, it is difficult for the optical unit to move beyond the focal point.

According to the fourth aspect of the present invention, since the servo calculation in the focus servo control is started during the focus search control, the initial value at the start of the focus servo control becomes stable.

According to the fifth aspect of the present invention, the preset value is set as the initial value of the servo control during the focus search control, so that the initial value at the start of the focus servo control becomes stable. .

According to the sixth aspect of the present invention, since the second level is set based on the focus position based on the peak level of the error signal and the level of the error signal at the focus position, the servo operation can be started or initialized. The timing of setting the value can be easily set.

According to the present invention, the gain for the drive signal for driving the focus actuator is changed according to the position of the optical unit. According to the eighth aspect of the present invention, the gain is increased near the peak immediately before the focal point, and is decreased when the gain exceeds the peak, so that the optical unit approaches the peak earlier.

According to the ninth aspect of the present invention, after the optical unit is moved to the first arrival point set based on the maximum value of the error signal obtained by moving the optical unit and the level of the error signal at the focal position. While moving the optical unit, the maximum value of the error signal level at each time is obtained, the second arrival point set based on the maximum value and the error signal level at the focal point is updated, and the current position of the optical unit is updated. Since the focus servo control is started when reaches the second reaching point, it is difficult for the optical unit to exceed the focal point even if the moving speed of the optical unit is increased.

According to the tenth aspect, a program for executing the focus control method according to any one of the first to ninth aspects can be easily supplied on a recording medium. .

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic block diagram of an optical disk device.

The optical disk device 11 is connected to a host computer 12. The optical disk device 11 reads the stored data recorded on the optical disk 21 as a recording medium in response to a read request from the host computer 12 and outputs the data to the host computer 12.

An optical disk 21 made of a DVD is driven to rotate at a predetermined angular speed by a spindle motor 22. The optical disk 21 is a CD-ROM or a CD-ROM.
R, CD-RW, DVD-ROM, MD, PD, etc. may be used.

The pickup device 23 includes an optical section 24, a slider motor 25, a focus actuator 26, and a tracking actuator 27. The slider motor 25 moves the pickup device 23 in the radial direction of the optical disc 21.

The optical section 24 includes a laser diode (LD) 28 as a light emitting element, a beam splitter (BS) 2
9, including a cylindrical lens 30, an objective lens 31, and a photodetector (PD) 32 as a light receiving element.

The light emitted from the LD 28 is transmitted to the BS 29,
The light is irradiated onto the recording surface of the optical disc 21 via the cylindrical lens 30 and the objective lens 31. The BS 29 reflects light reflected by the recording surface to the PD 32. The PD 32 includes a plurality of light receiving elements 32a to 32c. First light receiving element 3
Reference numeral 2a denotes a four-divided photodetector, and each of the four detectors outputs a signal of a voltage corresponding to the amount of received light. This signal is used for focus control and reproduction of recorded data. Each of the second and third light receiving elements 32b and 32c outputs a signal of a voltage corresponding to the amount of received light. These signals are used for tracking.

A focus error signal generating circuit (hereinafter referred to as a first
The generation circuit 33 generates an error signal FE for focus control based on the output signal of the first light receiving element 32a. Assuming that the output signals of the detectors of the first light receiving element 32a are signals A, B, C, and D, the first generating circuit 33
An error signal FE that satisfies FE = (A + C)-(B + D) is generated. The first generation circuit 33 outputs the error signal FE to the drive control device 36. Note that the error signal FE is called a focus error. The error signal FE may be called an S-shaped curve due to its shape.

The RF signal generation circuit (hereinafter, referred to as a second generation circuit) 34 generates an RF signal (= A + B + C + D) obtained by adding the output signal of the first light receiving element 32a. The second generation circuit 34 outputs the generated RF signal to the FOK signal generation circuit 37 and the signal processing device 38.

The track error signal generation circuit (hereinafter, referred to as a third generation circuit) 35 includes second and third light receiving elements 32b, 3
An error signal TE for tracking is generated based on the output signal of 2c. Each of the second and third light receiving elements 32b, 32
Assuming that the output signals of c are signals E and F, respectively, the first generation circuit 33 outputs the error signal T based on the signals E and F.
Generate E (= EF). The third generation circuit 35 outputs the error signal TE to the drive control device 36.

The drive control device 36 comprises a DSP. The drive control device 36 includes a control circuit 41, a pulse width counter (PWC) 42, analog-digital conversion circuits (ADC) 43 and 44, an input port 45, pulse width modulation circuits (PWM) 46 and 47, and a digital-analog conversion circuit. (DAC) 48, 49.

The pulse signal TG output from the encoder 50 provided in the spindle motor 22 is input to the drive control device 36. The encoder 50 outputs a pulse signal T having a pulse width corresponding to the rotation of the spindle motor 22.
G is output to the drive control device 36.

The output signal TG of the encoder 50 is input to the PWC 42. The PWC measures the pulse width of the signal TG and outputs the measured data to the control circuit 41. The control circuit 41 calculates control data of the spindle motor based on the measurement data, and outputs the control data to the first PWM 46. The first PWM 46 outputs a signal pulse-modulated based on the input data to the spindle motor driver 51, and the driver 51 outputs a drive signal based on the input signal to the spindle motor 22. The spindle motor 22 rotates the output shaft, that is, the optical disk 21, based on the drive signal. Thus, the drive control device 36 controls the spindle motor based on the output signal TG of the encoder 50 to rotate the optical disk 21.

The control circuit 41 calculates servo control data of the spindle motor 22 based on the measurement data, and outputs the servo control data to the first PWM 46. In this way, the control circuit 41 servo-controls the spindle motor 22 to rotate the optical disk 21 at a desired angular velocity.

The first ADC 43 includes the third generation circuit 3
5, a track error signal TE is input.
The first ADC 43 converts the error signal TE into a digital signal, and outputs the digital signal to the control circuit 41. The control circuit 41 calculates control data of the slider motor 25 based on the output signal of the first ADC 43, that is, the error signal TE, and outputs the control data to the second PWM 47. The second PWM 47 outputs a pulse-modulated signal based on the control data to the slider motor driver 52, and the driver 52 outputs a drive signal based on the input signal to the slider motor 25. The slider motor 25 moves the pickup device 23 in the radial direction of the optical disc 21 based on the drive signal.

The control circuit 41 calculates servo control data of the slider motor based on the error signal TE,
The servo control data is output to the second PWM 47. Thus, the control circuit 41 servo-controls the slider motor 25. Thus, the drive control device 36
Performs coarse movement control for moving the pickup device 23 to a desired track.

The control circuit 41 calculates servo control data of the tracking actuator 27 based on the error signal TE, and converts the servo control data into the first DA signal.
Output to C48. The first DAC 48 outputs an analog signal corresponding to the servo control data to the tracking actuator driver 53. The driver 53 outputs a driving signal based on the analog signal to the tracking actuator 2.
7, the actuator finely moves the optical section 24 in the radial direction of the optical disk 21 based on the drive signal.
Thus, the control circuit 41 performs tracking control for finely controlling the optical unit 24.

The second ADC 44 includes the first generation circuit 3
The focus error signal FE output from 3 is input. The second ADC 44 converts the error signal FE into a digital signal, and outputs the digital signal to the control circuit 41. The control circuit 41 has a FOK
A signal FOK output from a signal generation circuit (hereinafter, referred to as a fourth generation circuit) 37 is input.

The fourth generation circuit 37 receives the RF signal output from the second generation circuit 34. The fourth generation circuit 37 converts the RF signal into a pulse signal at a predetermined threshold level, and outputs the pulse signal FOK.

The control circuit 41 generates a signal based on the pulse signal FOK and the output signal of the second ADC 44, that is, the error signal FE.
The control data of the focus actuator 26 is calculated, and the control data is output to the second DAC 49. Second
The DAC 49 outputs an analog signal based on the control data to the focus actuator driver 54. The driver 54 outputs a drive signal based on the analog signal to the focus actuator 26,
Moves the optical unit 24 in a direction perpendicular to the recording surface of the optical disk 21 (hereinafter, referred to as a focus direction) based on a drive signal. Thus, the control circuit 41 controls the optical unit 24
Is finely controlled in the focus direction to perform a focus search.

The control circuit 41 moves the optical section 24 so that the focus of the readout light irradiated on the optical disk 21 by the focus search coincides with the recording surface, and starts the focus servo control. That is, the control circuit 41 calculates servo control data of the focus actuator 26 based on the focus error signal FE, and outputs the servo control data to the second DAC 49. In this way, the control circuit 41 causes the focal point of the light applied to the optical disc 21 to follow the fluctuation of the recording surface. And the control circuit 4
When the focus servo control is started, 1 outputs a focus-on signal to the signal processing device 38.

The signal processor 38 converts the RF signal input from the second generator 34 into a digital signal in response to the focus-on signal, and performs a predetermined digital decoding process on the digital signal. The signal processing device 38 outputs the processed signal to the controller 56.

The controller 56 analyzes commands for write / read processing and the like input from the host computer 12 and outputs signals for control to the drive control device 36 and the signal processing device 38. Controller 5
6 converts the data input from the signal processing device 38 into a DRA
It is stored in M57. The controller 56 includes the DRAM 5
7 is output to the host computer 12. Thus, the DRAM 57 functions as a read buffer.

FIGS. 13A to 13E show the shapes of the reflected light with respect to the distance between the recording surface 61 and the lens 62. FIG. Lens 6
2 is a cylindrical lens 30 and an objective lens 3 of FIG.
Including 1.

The cross-sectional shape of the reflected light incident on the first light receiving element 32a in FIG. 1 is a perfect circle when the optical section 24 is at the in-focus position (see FIG. 13C). When the optical unit 24 is located before and after the focal point, the cross-sectional shape of the reflected light is such that the major axis and minor axis directions of the ellipse are reversed (see FIGS. 13B and 13D). When the lens 62 is too far or too close from the recording surface 61, the reflected light is applied to the entire surface of the first light receiving element 32a (see FIGS. 13A and 13E).

Therefore, as shown in FIG. 5, the focus error signal FE has an S-shape whose level changes in accordance with the distance between the recording surface 61 and the lens 62. The size of the S-shaped peak (peak level) corresponds to the intensity of the reflected light.

FIG. 5 shows a waveform diagram of the error signal FE in a two-layer single-sided disk or a two-layer double-sided disk. These disks have two recording surfaces accessed from one side. The first recording surface (LAYER0) from the side closer to the surface,
This is the second recording surface (LAYER1).

The S-shape appears in the waveform of the error signal FE depending on the location where the laser light is reflected. Therefore, as shown in FIG. 5, an S-shape appears in the error signal FE also on the surface of the optical disk 21. Since the intensity of the reflected light on the surface is smaller than that on the recording surface, the S-shaped peak level is also small.

The control circuit 41 performs focus control based on the level of the error signal FE. The focus control includes focus search control and focus servo control. Therefore, the control circuit 41 performs focus search control for moving the optical unit 24 to the focal point based on the error signal FE. Further, the control circuit 41 performs focus servo control for holding the optical unit 24 at the focal point based on the error signal FE.

Next, the focus control of the control circuit 41 is performed as follows.
This will be described in detail with reference to FIGS. First, the principle of the focus search control will be described in detail with reference to FIG. The lens of FIG. 1,
That is, when the optical unit 24 is lowered, the distance of the lens from the optical disk 21 increases. Accordingly, the value of the focus error signal FE increases from left to right in FIG.
(Positive → 0 → negative → 0).

In the control circuit 41, the value of the error signal FE at the in-focus position where the optical section is servo-controlled is set as a servo level FE0. The control circuit 41 performs servo control so that the error signal FE becomes the servo level FE0.

The control circuit 41 calculates the maximum value F of the error signal FE.
The first levels FAEND and FBEND are set based on MAX, the minimum value FMIN, and the servo level FE0. The control circuit 41 outputs the error signal FE to the first level FAEND, FEND.
When the optical unit 32 is moved to a position where the position becomes BEND, the focus search control ends and the focus servo control starts. The control circuit 41 controls the first level FAEND, F
BEND is set as the search end level.

That is, the control circuit 41 controls the servo level FE
0, that is, the focus servo control is started before the in-focus position in the search direction. This reduces the amount (distance from the focal point) of the high-speed moving optical unit 32 (lens) beyond the focal point position. Setting the position (level of the error signal FE) at which the focus servo control is started so that the distance is close to zero improves controllability.

The end level of focus search control (start level of focus servo control) will be described in detail.
The control circuit 41 sets the level lower than the positive peak by a predetermined value (or the level higher than the negative peak by a predetermined value) to the search end level FAEND (FBEND).
And The control circuit 41 uses a positive peak or a negative peak based on the search direction.

When the optical section 32 is moved away from the optical disk 21 (the optical section 32 is lowered), the error signal FE rises to a positive peak value and then drops to the servo level FE0. Conversely, when bringing the optical unit 32 closer to the optical disk 21 (elevating the optical unit 32), the error signal FE decreases to a negative peak and then increases to the servo level FE0.

Therefore, when lowering the optical section 32, the control circuit 41 starts servo control at the search end level FAEND between the positive peak and the servo level FE0. When raising the optical unit 32, the control circuit 41 starts the servo control at the search end level FBEND between the negative peak and the servo level FE0.
The level of the positive peak is the maximum value FMAX, and the level of the negative peak is the minimum value FMIN. When lowering the optical unit 32, the control circuit 41 sets the search end level FAEND
On the basis of the maximum value FMAX and the servo level FE0,
A level lower than the maximum value FMAX by 1/4 of the difference between the maximum value FMAX and the servo level FE0, that is, FAEN
D = FMAX- (FMAX-FE0) / 4.

When raising the optical section 32, the control circuit 41 sets the search end level FBEND to the minimum value FMIN.
And the servo level FE0, from the minimum value FMIN to 1/4 of the difference between the minimum value FMIN and the servo level FE0.
Higher level, ie, FBEND = FMIN + (F
E0-FMIN) / 4.

The search end level FAEND (FBE
ND) is lower (higher) than the maximum value FMAX (minimum value FMIN) by half (or 1/3, 1/5, 1/6) of the difference between the maximum value FMAX (minimum value FMIN) and the servo level FE0. May be set.

By the way, as shown in FIG.
E indicates that the optical unit 32 has the maximum value FM at the positions P1 and P2.
It matches the search end level FAEND lower than AX by a predetermined level. The control circuit 41 sets the position P1 or the position P2 as the servo start position according to the moving speed of the optical unit 32.

That is, when the servo control is started at the position P1 closer to the focal point than the peak, the position of the optical section 32 converges to the focal point position by the servo control. However, if the moving speed of the optical unit 32 is too high, the position of the optical unit 32 may exceed the focal point position and take time to converge.

When the servo control is started before the position P2, the servo control abnormally accelerates the moving speed of the optical unit 32. As a result, the optical unit 32 exceeds the minimum value peak. As a result, the optical unit 32 moves out of the area near the focal point, and does not converge at the focal point.

On the other hand, if the servo control is started at the position P2 before the peak when the moving speed of the optical unit 32 is slow, the control amount of the servo control acts on the moving speed of the optical unit 32 in the opposite direction to the moving direction. To move the optical unit 32 away from the focal point. As a result, the optical section 32 cannot exceed the peak and does not converge to the focal point.

As described above, the control circuit 41 controls the optical unit 32
The start point at which the servo control is started is set to the position P1 or the position P2 based on the moving speed of. Note that the same applies to the positions P3 and P4 where the error signal FE is at the search end level FBEND that is higher than the minimum value FMIN by a predetermined level, and a description thereof will be omitted.

The control circuit 41 determines the maximum value F of the error signal FE.
The second levels FEA and FEB are set based on MAX, the minimum value FMIN and the servo level FE0. Control circuit 41
Are used to determine whether the second levels FEA and FEB have approached or exceeded the in-focus position.

That is, when the optical unit 32 is away from the focal point, the error signal FE is at the servo level FE0 (zero or a value close to zero). When the optical section 32 approaches the focal point, that is, the peak, the value of the error signal FE becomes higher or lower.

Therefore, the control circuit 41 sets the servo level F
A level higher (or lower) by a preset value from E0 is set as a second level FEA (FEB). And
When the error signal FE rises (or falls) to the second level FEA (or FEB), the control circuit 41 determines that the focus position has been approached. The control circuit 41 changes the control state based on this determination result.

The control circuit 41 lowers the gain of the drive signal for driving the focus actuator 26 that moves the optical unit 32 when the optical unit 32 approaches the focal point based on the determination result. Thereby, the moving speed of the optical unit 32 becomes slower as it approaches the focal point position.

That is, the control circuit 41 increases the moving speed when the optical section 32 is away from the focal point. This shortens the time required for the optical unit 32 to approach the focal point. Then, when the optical unit 32 approaches the in-focus position, the control circuit 41 reduces the moving speed of the optical unit 32. Thereby, the optical unit 32 slowly approaches the focal point position, so that the controllability of the focus servo control is improved.

The control circuit 41 starts servo calculation in the focus servo control when the optical section 32 approaches the in-focus position, based on the result of the determination. The start position of this servo operation is determined by the search end level FA.
The position is closer to the END position P1 (P2). That is, the control circuit 41 starts the servo calculation before ending the focus search control.

The focus servo control includes a servo calculation process for calculating control data of the focus actuator 26 based on the error signal FE, and a data output process for outputting a calculation result. Servo operation processing is performed by the error signal FE
And a filtering process for the digital signal obtained by AD-converting. Since the initial value of this filtering process is undefined at the start, the control circuit 41 may calculate erroneous control data in some cases. As a result, the operation of the optical unit 32 becomes unstable, so that the time required for the position of the optical unit 32 to converge to the focal point position increases.

On the other hand, only servo calculation processing is started before the end of the focus search control. This means
The initial value of the filtering process at the end of the focus search control is stabilized. Thereby, the control circuit 41
In order to calculate correct control data, the optical unit 32 operates stably at the start of the focus servo control. As a result, the time required for the position of the optical unit 32 to converge to the in-focus position is shortened, and the speed of focus control can be increased.

The control circuit 41 controls the second level FEA, FE
Based on B, it is determined whether the position of the optical unit 32 has exceeded the focal point position. This is used when the optical disk 21 is a single-sided double-layer disk or a double-sided double-layer disk (hereinafter, simply referred to as a double-layer disk). That is, as shown in FIG.
In a layer disc, there are two focal positions.

When reading the data of the second layer, the control circuit 41 needs to exceed the focal position of the first layer in the focus search control. Therefore, the control circuit 41
It is determined based on the second levels FEA and FEB whether or not the focal point of the first layer has been exceeded. Then, when the control circuit 41 determines that the in-focus position of the first layer has been exceeded, the control circuit 41 operates to search for the in-focus position of the second layer. The same applies to the case where the search is performed in the order of the second layer and the first layer.

The setting of the second levels FEA and FEB will be described in detail. The control circuit 41 outputs the second level FEA on the positive side.
On the basis of the maximum value FMAX and the servo level FE0,
A level higher than the servo level FE0 by 1/4 of the difference between the maximum value FMAX and the servo level FE0, that is, FEA =
Set to FE0 + (FMAX-FE0) / 4.

The control circuit 41 outputs the second level FEB on the negative side.
On the basis of the minimum value FMIN and the servo level FE0,
A level lower than the servo level FE0 by 1/4 of the difference between the minimum value FMIN and the servo level FE0, that is, FE
Set B = FE0- (FE0-FMIN) / 4.

Incidentally, the second level FEA (FEB) is set to 1/2 (or 1/3, 1/3) of the difference between the servo level FE0 and the maximum value FMAX (minimum value FMIN) and the servo level FE0.
(5, 1/6) higher (lower) level.

As shown in FIG. 6, the error signal FE is
The optical unit 32 matches the second level FEA on the positive side at positions P5 and P6, and matches the second level FEB on the negative side at positions P7 and P8. The control circuit 41 outputs the error signal FE
The position P5 or the position P6 (the position P7 or the position P8) is used based on the amount of change in.

That is, when the optical unit 32 is moved away from the optical disk 21 (the optical unit 32 is lowered), the control circuit 41 determines that the focus position is approached by the position P5 within the range where the error signal FE increases. And the control circuit 41
Determines that the error signal FE has exceeded the focal point at the position P7 where the error signal FE has a negative value. When the optical unit 32 is moved closer to the optical disk 21 (the optical unit 32 is raised), the same applies to the above description, and a description thereof will be omitted.

Next, the focus control of the control circuit 41 will be described with reference to the flowcharts of FIGS. 2 and 3 show a flowchart of the focus search control, and FIG. 4 shows a flowchart of the focus servo control. The program data for these controls is stored in a predetermined recording medium (ROM, FD, CD-RO).
M and the like, and are provided and stored in the control circuit 41.

The control circuit 41 starts focus search control based on a control signal input from the controller 56. Now, a two-layer disc is set as the optical disc 21 of FIG. The first layer of the optical disc 21 (FIG. 7)
Of the set value LAY so as to focus on
1 (= 1) is set. The optical unit 32 is at a neutral position (the center position of the moving range of the optical unit 32). The set value UP (= 0) is set so that the focus search direction is performed by lowering the optical unit 32.

First, step S1 is an initial setting process, and the control circuit 41 initializes variables related to focus search control. Next, step S2 is an initial position moving process, and the control circuit 41 moves the optical unit 32 to the initial position (time t1 in FIG. 7). This initial position is set in advance below the neutral position. The recording surface of the optical disk 21 exists above the initial position. The control circuit 41
The optical unit 32 is moved to the initial position (time t2 in FIG. 7).
And a timer function for a predetermined period (from time t2 to time t3).
After waiting until the period elapses, the process moves from step S2 to step S3.

Step S3 is a maximum value / minimum value fetching process, and the control circuit 41 raises the optical section 32 (time t3 in FIG. 7). The control circuit 41 takes in the maximum value FMAX and the minimum value FMIN of the error signal FE. At this time,
When the H-level pulse signal FOK is input (at time t4 in FIG. 7), the control circuit 41 responds to the pulse signal FOK to set the upper limit position MAXY of the focus search based on a preset search range value SOF. Set (see FIG. 6).

The search range value SOF is set based on the interval between the recording layers so that the two recording layers formed on the optical disc 21 exist within the range. When moving the optical unit 32 to the upper limit position MAXY (time t5 in FIG. 7), the control circuit 41 stops the optical unit 32. Then, the control circuit 41 proceeds from step S3 in FIG. 2 to step S4.

Step S4 is a search direction determination process, and the control circuit 41 performs a branch process based on the set value UP. The control circuit 41 proceeds from step S4 to step S5 based on the set value UP (= 0).

Step S5 is a first arrival point setting process, and the control circuit 41 sets a first arrival point for detecting that the peak has been approached. That is, the control circuit 41
The second level FEA corresponding to the first reaching point is set based on the maximum value FMAX of the error signal FE and the servo level FE0. When the setting is completed, the control circuit 41 proceeds from step S5 to step S6.

In step S6, the control circuit 41
The optical unit 32 is lowered by a predetermined distance (step), and the process proceeds from step S6 to step S7. More specifically, the control circuit 41 controls the level of the error signal FE at the current position of the optical unit 32 (hereinafter, referred to as the current position) FCSI
A preset step value is added to N, and the calculation result is set as a new current position FCSIN. The new current position FCSIN is converted to an analog signal by the second DAC 49 in FIG. The focus actuator 26 moves the optical unit 32 to a position according to the analog signal.

At step S7, the control circuit 41
Compare the second level FEA with the current position FCSIN,
It is determined whether or not the arrival point has been exceeded. If not, the control circuit 41 proceeds from step S7 to step S6. That is, the control circuit 41 repeatedly executes the loop of steps S6 and S7 until the control point 41 exceeds the first arrival point. When the control circuit 41 exceeds the first arrival point (time t6 in FIG. 7), the control circuit 41 proceeds from step S7 to step S8.

At step S8, the control circuit 41
Initialize the maximum value FMA. In this initialization, the control circuit 41 clears the maximum value FMA (stores 0).
This is the first level FAEND for the mountain at that time
Is performed in order to detect accurately. That is, the control circuit 41
The maximum value FMA is cleared once, and the next steps S9 to S1
In one loop, the maximum value FMA is updated based on the level of the error signal FE. Thereby, the control circuit 41
Accurately determines the value of the peak. And the control circuit 41
Can accurately detect the first level FAEND based on the value of the peak. Note that the control circuit 41 may store the level FE0 of the in-focus position in the maximum value FMA.

The loop of steps S9 to S11 will be described. First, in step S9, the control circuit 41 lowers the optical unit 32 by a predetermined distance (step) as in step S6. Move to S10.

Step S10 is a second arrival point setting process. The control circuit 41 compares the error signal FE with the maximum value FMA, and the error signal FE is larger than the maximum value FMA (F
E> FMA), the error signal FE is set to the maximum value FMA (FMA
MA ← FE). The control circuit 41 sets the first level FAEND (= FMA- (FMA-FE0) / 4) of the second destination based on the maximum value FMA and the servo level FE0. When the setting is completed, the control circuit 41 proceeds from step S10 to step S11.

In step S11, the control circuit 41
Determines whether or not the second reaching point has been reached. Control circuit 4
1 is the first level FAEND of the second arrival point and the current position F
Compare CSIN. If the current position FCSIN is larger than the first level FAEND based on the comparison result, the control circuit 41 determines that the control circuit 41 has not reached the second destination. In this case, the control circuit 41 proceeds from step S11 to step S9.

That is, the control circuit 41 repeatedly executes the loop of steps S9 to S11 until the second arrival point is reached. In step S10 in this loop, the control circuit 41 compares the error signal FE with the maximum value FMA, and updates the maximum value FMA based on the comparison result. Thus, the control circuit 41 detects an S-shaped peak in the waveform of the error signal FE.

Control circuit 41 updates first level FAEND based on maximum value FMA to be updated. Maximum value FM
A becomes constant by detecting the peak. As a result, the control circuit 41 outputs the first level F after the S-shaped peak is exceeded.
Determine AEND. Then, the control circuit 41 determines whether or not the second reaching point has been reached by comparing the determined first level FAEND with the current position FCSIN.
When the control circuit 41 determines that the second point has been reached, the process proceeds from step S11 to step S12.

Step S12 is a layer determination process.
The control circuit 41 determines the second value based on the set value LAY1.
It is determined whether the recording surface at the arrival point is the target recording surface. The control circuit 41 proceeds from step S12 to step S13 based on the set value LAY1 (= 0).

Step S13 is a third reaching point setting process. The control circuit 41 sets the third reaching point P7 (see FIG. 6) by the second level FEB in order to determine that the in-focus position has been exceeded. I do. When the setting is completed, the control circuit 41 proceeds from step S13 to step S14.

In step S14, the control circuit 41
Moves down the optical unit 32 as in step S6, and proceeds from step S14 to step S15. Step S15
In, the control circuit 41 determines whether or not the vehicle has reached the third reaching point P7 by comparing the second level FEB with the current position FCSIN. If not reached, the control circuit 41 repeatedly executes the loop of steps S14 and S15. When reaching the third reaching point, the control circuit 41 proceeds from step S15 to step S16.

In steps S16 to S18, the control circuit 41 operates in the same manner as in steps S9 to S11. That is, the control circuit 41 lowers the optical unit 32 in step S16 as in step S8. Control circuit 4
1 sets the maximum value FMA in step S17 as in step S10, and sets the first level FAEND of the second reaching point P1 (see FIG. 6) based on the maximum value FMA and the servo level FE0. Control circuit 41
In step S18, the first level FAEND is compared with the current position FCSIN, and it is determined whether or not the vehicle has reached the second reaching point P1 based on the comparison result.

When the control circuit 41 determines that the second point P1 has been reached (time t7 in FIG. 7), the process proceeds from step S18 to step S19. In step S19, the control circuit 41 starts focus servo control. Then, the control circuit 41 ends the focus search control.

As another example, now, the second
The set value LAY1 (= 1) is set so as to focus on the layer (LAYER1 in FIG. 8). In this case, the control circuit 41 executes steps S1 to S11 in FIG. 2 in the same manner as described above. Then, in step S12 (time t6 in FIG. 8), the control circuit 41 sets the set value LAY1.
Then, the process moves from step S12 to step S19. In step S19, the control circuit 41 starts focus servo control. And the control circuit 41
Ends the focus search control.

The case where the focus search control is performed in the descending direction of the optical unit 32 has been described above. Next, a case where focus search control is performed in the upward direction of the optical unit 32 will be described with reference to FIG.

Now, the focus search direction is determined by the optical unit 32.
The set value UP (= 1) is set so as to increase the value. The control circuit 41 proceeds from step S4 to step S21 in FIG. 3 based on the set value UP (= 1) in step S4 in FIG. In step S21, the control circuit 41 sets the optical unit 32 to the search range value SOF.
Is moved to the lower limit position MINY set based on.

That is, the control circuit 41 lowers the optical section 32. At this time, when the H-level pulse signal FOK is input (time t6 in FIG. 9), the control circuit 41 responds to the pulse signal FOK, and sets the search range value S set in advance.
The lower limit position MINY of the focus search is set based on the OF. The control circuit 41 moves the optical unit 32 to the lower limit position MINY. The movement ends (time t7 in FIG. 9).
And the control circuit 41 proceeds from step S21 to step S22.
Move to

Step S22 is a first reaching point setting process. The control circuit 41 determines the first reaching point P8 (FIG. 6) based on the minimum value FMIN of the error signal FE and the servo level FE0.
2) is set as the second level FEB. When the setting is completed, the control circuit 41 proceeds from step S22 to step S23.

At the step S23, the control circuit 41
Raises the optical unit 32 by a preset step. In step S24, the control circuit 41 compares the second level FEB with the current position FCSIN to determine whether or not the first level P8 has been exceeded. When exceeding the first arrival point (time t8 in FIG. 9), the control circuit 41 proceeds from step 24 to step S25.

In step S25, the control circuit 41
Raises the optical unit 32 by the set step. In step S26, the control circuit 41 outputs the error signal FE
Is compared with the minimum value FMB, and the minimum value FMB is updated based on the comparison result. The control circuit 41 calculates the minimum value FMB
And the servo level FE0, the first level FBEND of the second reaching point P3 (see FIG. 6) is set. When the setting is completed, the control circuit 41 proceeds from step S26 to step S27.

In step S27, the control circuit compares the first level FEB with the current position FCSIN, and determines whether or not the second point P3 has been reached based on the comparison result. When the second reaching point is reached (time t9 in FIG. 9), the control circuit 41 proceeds from step S27 to step S28.

Step S28 is a layer determining means.
The control circuit 41 determines the second value based on the set value LAY1.
It is determined whether the recording surface at the arrival point P2 is the target recording surface. In the case of the target recording surface, the control circuit 41 shifts from step S28 to step S19, and in that step S19
Starts servo control.

As another example, the second
The set value LAY1 (= 1) is set so as to focus on the layer (LAYER1 in FIG. 10). In this case, the control circuit 41 performs steps S1 to S4 and S21 in FIGS.
Steps S27 to S27 are executed in the same manner as described above. And the control circuit 4
In step S28, the process proceeds from step S28 to step S29 based on the set value LAY1.

Step S29 is a third reaching point setting process. The control circuit 41 sets the third reaching point P7 (see FIG. 6) by the second level FEB in order to determine that the in-focus position has been exceeded. I do. When the setting is completed, the control circuit 41 proceeds from step S29 to step S30.

In step S30, control circuit 41
Moves the optical unit 32 down as in step S23, and proceeds from step S30 to step S31. Step S3
In 1, the control circuit 41 compares the second level FEA with the current position FCSIN to obtain the third arrival point P7.
Is determined. When the third reaching point is reached, the control circuit 41 proceeds from step S31 to step S32.

In steps S32 to S34, the control circuit 41 operates in the same manner as in steps S25 to S27. That is, the control circuit 41 lowers the optical unit 32 in step S32 as in step S25. The control circuit 41 sets the minimum value FMB in step S33 as in step S26, and sets the first level FBEND of the second reaching point P3 (see FIG. 6) based on the minimum value FMB and the servo level FE0. . Control circuit 41
In step S34, the first level FBEND is compared with the current position FCSIN, and it is determined based on the comparison result whether the second level P3 has been reached.

When the control circuit 41 determines that the second arrival point P3 has been reached (time t9 in FIG. 10), the process proceeds to step S34.
Then, the process goes to step S19. In step S19,
The control circuit 41 starts focus servo control. Then, the control circuit 41 ends the focus search control.

FIG. 11 and FIG.
FIG. 4 shows a waveform diagram of focus search control when a layer disc and a CD-ROM are set. In this case, the control circuit 4
1 operates similarly to the above. And the control circuit 41
Reaches the second reaching point P1 (or P3) in FIG. 6 (FIG. 1).
1 (time t6, time t8 in FIG. 12) and the focus servo control is started.

FIG. 4 shows a flowchart of the focus servo control. The control circuit 41 has an interrupt function using a timer.
s) Execute focus servo control every time. Note that the control circuit 41 may appropriately change the interval at which the focus servo control is executed.

In step S41, the control circuit 41
Determines whether the operation switch is on (= 1). When the operation switch is ON, the control circuit 41 executes a servo operation process of the next step S42, and calculates servo control data based on the input signal.

Next, in step S43, the control circuit 41 determines whether or not the control switch is on (= 1). When the control switch is on, the control circuit 41 executes a data output process in the next step S44, and outputs servo control data to the second DAC 49 in FIG.

The operation switches and control switches are based on the state of the register 41a included in the control device 41 of FIG. That is, the control device 41 controls the operation switch and the control switch to be on or off by storing predetermined data in the operation flag and the control flag of the register 41a.

In the focus search control shown in FIGS. 2 and 3, the control circuit 41 performs on / off control of an arithmetic switch and a control switch in accordance with an arrival point. That is, the control circuit 41
Controls the arithmetic switch to be turned on when exceeding the first arrival point P6 (P8) in FIG. 6 (steps S7, S15 (S2
4, S31)). That is, the control circuit 41 starts servo calculation before reaching the second destination in the focus search control. Then, when reaching the second arrival point P1 (P3) in FIG. 6, the control circuit 41 controls the control switch to be turned on (step S19). Thereby, the control circuit 41
Prevents the operation from becoming unstable due to indefinite initial values at the start of focus servo control.

As described above, the present embodiment has the following advantages. (1) The control circuit 41 moves the optical unit 32 to the first reaching point P6 set based on the maximum value FMAX of the error signal FE acquired and the level of the error signal at the focal point position, and then moves the optical unit 32 While moving the unit 32, the maximum value FMA of the level of the error signal FE at each time is obtained, and the maximum value FMA and the level FE of the error signal at the focal point are obtained.
0, and the current position FCSIN of the optical unit 32 is changed to the level FAEND.
When it becomes lower than END, the second servo point is reached and focus servo control is started. As a result, the moving speed of the optical unit 32 can be increased because the optical unit 32 does not easily move beyond the focal point. This allows
The time required for focus control can be reduced, that is, focusing can be performed at high speed.

(2) The control circuit 41 starts the servo calculation of the focus servo control when the first reaching point is reached. As a result, the control circuit 41 can prevent the operation from becoming unstable due to the indefinite initial value at the start of the focus servo control.

(3) The control circuit 41 lowers the gain of the drive signal for driving the focus actuator 26 that moves the optical unit 32 when the optical unit 32 approaches the focal point. As a result, the control circuit 41 controls the optical unit 3
When 2 is away from the focal point, the moving speed can be increased to shorten the time required to approach the focal point. Further, the control circuit 41 slows down the moving speed when the optical section 32 approaches the focal point position, and slowly moves the optical section 32 to the focal point position, so that the controllability of the focus servo control can be improved.

The present invention may be embodied in the following modes in addition to the above embodiment. In the above embodiment, the control circuit 41 determines that the level FSCIN of the error signal FE at the current position is the second level FSC.
When it becomes larger than EA or becomes smaller than the second level FEB, the arithmetic switch is controlled to be turned on to start the servo arithmetic processing before the end of the focus search processing. It may be set as a value. Thereby, the control circuit 41
Can stabilize the operation of the optical unit 32 at the start of the servo processing.

The movement amount is increased up to the peak. As the method, a method in which the control circuit 41 changes the gain of the error signal FE, a method in which the gain of the driver is changed, or the like is used. Also in these cases, the gain for the drive signal can be easily changed according to the position of the optical unit 32 as in the above embodiment.

[0133]

As described in detail above, according to the first to ninth aspects of the present invention, it is possible to provide a focus control method capable of performing focusing at high speed.

According to the present invention, the initial value at the start of the focus servo control can be stabilized to prevent the operation from becoming unstable. According to the invention as set forth in claim 7 or 8, the time required for approaching the focal point can be shortened, and the controllability of the focus servo control can be improved.

According to the tenth aspect, it is possible to provide a recording medium on which a focus control method capable of performing focusing at high speed is recorded.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical disk device.

FIG. 2 is a flowchart of a focus search control process.

FIG. 3 is a flowchart of a focus search control process.

FIG. 4 is a flowchart of a focus servo calculation process.

FIG. 5 is a waveform diagram of a focus error signal.

FIG. 6 is a waveform chart for explaining a reaching point and a set level.

FIG. 7 is a waveform chart showing an operation of focus search control.

FIG. 8 is a waveform chart showing an operation of focus search control.

FIG. 9 is a waveform chart showing an operation of focus search control.

FIG. 10 is a waveform chart showing an operation of focus search control.

FIG. 11 is a waveform chart showing an operation of focus search control.

FIG. 12 is a waveform chart showing an operation of focus search control.

FIG. 13 is an explanatory diagram illustrating a state of reflected light with respect to a distance between a recording surface and an optical unit.

[Explanation of symbols]

 32 Optical unit 41 Control circuit FE Error signal FMAX Maximum value FCSIN Current position P6 First arrival point P1 Second arrival point FE0 level (focusing position) FEA level (First arrival point) FAEND level (Second arrival point)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D117 AA02 CC01 DD03 DD06 DD10 FF03 FF06 5D118 AA13 BA01 BF02 CA08 CA11 CB03 CC12 CD02 CF05

Claims (10)

[Claims] An optical section is focused on an optical section based on an error signal whose level changes in accordance with a distance between a recording surface of an optical disk and an optical section for irradiating the recording surface with light for reading data on the recording surface. In a focus control method of switching from focus search control to move to a position to focus servo control, based on a level of the error signal, an arrival point is set before the in-focus position with respect to a search direction in the focus search control. A focus control method wherein switching to the focus servo control is performed when the current position of the optical unit has exceeded an arrival point. 2. The focus control method according to claim 1, wherein after switching the reaching point to the focus servo control, the focus servo control causes the optical unit to move beyond the peak of the error signal and the focus position. Focus control method set to a position where it can be converged to 3. The focus control method according to claim 1, wherein the arrival point is set based on a peak level based on a peak level of the error signal and a level of the error signal at a focal position. Focus control method set at the point where the level and the error signal match. 4. The focus control method according to claim 1, wherein a servo operation in the focus servo control is started during the focus search control. 5. The focus control method according to claim 1, wherein a preset value is set as an initial value of the servo control during the focus search control. . 6. The focus control method according to claim 4, wherein the second level set based on the focus position based on a peak level of the error signal and a level of the error signal at the focus position. A focus control method for starting servo calculation or setting an initial value when an error signal exceeds a point where the error signal coincides. 7. The focus control method according to claim 1, wherein a gain for a drive signal for driving the focus actuator is changed according to a position of an optical unit. Control method. 8. The focus control method according to claim 7, wherein the gain is increased to near a peak immediately before the focal point, and is decreased when the peak is exceeded. 9. The optical unit is focused on the basis of an error signal whose level changes in accordance with the distance between the recording surface of the optical disc and an optical unit for irradiating the recording surface with light for reading data on the recording surface. In a focus control method for switching from focus search control to move to a position to focus servo control, a step of moving the optical unit to obtain a maximum value of an error signal, and based on the maximum value and a level of the error signal at a focal position. Setting the first reaching point, moving the optical section to the first reaching point, moving the optical section, obtaining the maximum value of the error signal level at each time, Updating a second arrival point set based on the level of the error signal at the in-focus position; and the current position of the optical unit has reached the second arrival point Determines whether the focus control method comprising the steps of starting the focus servo control upon reaching a second arrival point based on the determination result. 10. A recording medium on which a program for executing the focus control method according to claim 1 is recorded.