JPH06139584A - Focus controller for optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To remarkably shorten a time required for focus search by focus searching without serveying one by one the maximum value and the minimum value of a focus error signal. CONSTITUTION:By a focus controller 30, a fixed value being a value calculated based on the maximum amplitude value and the minimum amplitude value of the focus error signal obtained from plural kinds of disks is stored in a ROM 23 previously. By a CPU 13, whether a focus servo is actuated or not is discriminated by using digital data Sa, Sb as the fixed value, and a focus servo loop is actuated when it arrives at within the range of drawing focus, and the servo is drawn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording capable of recording or reproducing information by setting it in a normal state even when there are variations in the reflectance of a pickup optical system or a disc. The present invention relates to a focus control device for a playback device.

[0002]

2. Description of the Related Art In recent years, the progress of information related industries such as computers has been remarkable, and the amount of information handled is dramatically expanding.

Therefore, instead of a conventional magnetic head, an optical information recording / reproducing method can be used to optically record information on a disk-shaped recording medium at a high density using a laser beam or to reproduce the information at a high speed. The device is in the spotlight.

By the way, when recording or reproducing on the disc-shaped recording medium (hereinafter referred to as a disk), it is necessary to set an optical pickup including an objective lens system to a focus state and maintain the focus state. Therefore, generally, by using the error signal of the photodetector whose output changes according to the distance from the disc, the optical system of the optical pickup is set within the focus servo area where focus can be maintained, and then the focus servo is set. A method of holding the focus state by operating it is adopted.

Further, when there are variations in the optical system portion of the optical pickup, the photodetector, etc., or the reflectance or transmittance of the disc varies from product to product, the output level of the error signal or The output waveform may change. Even in the above condition, drive the optical pickup before operating the auto focus so that the auto focus can be set normally.
The error signal output from the photodetector in each state is captured. Then, a method of closing the focus servo loop is adopted based on the output level of the taken-in error signal.

As a conventional example of this type of apparatus, there is, for example, one described in Japanese Patent Laid-Open No. 61-198431.

In the apparatus described in the above publication, first, the objective lens is moved before the actual focus search.
Find the maximum and minimum values of the focus error signal.

FIG. 2 shows the error signal output of the photodetector with respect to the distance from the disc. In FIG. 2, the maximum value and the minimum value are represented by SMAX and SMIN. When the maximum value and the minimum value of the focus error signal are obtained, the discrimination reference level S is then calculated from the maximum value and the minimum value by arithmetic operation.
b and Sa are required. For example, Sb = (SMIN + SMA
X) / 2, Sa = (Sb + SMIM) / 2.

In an actual focus search, the objective lens is driven in a direction away from the closest point on the disc,
The above-mentioned discrimination reference level Sa and the focus error signal are compared. The focus error signal is the discrimination reference level S
After detecting that it is smaller than a, the reference level Sb for determination and the focus error signal are compared while further moving the objective lens. When it is detected that the focus error signal is higher than the determination reference level Sb, the focus servo mechanism is activated immediately.

By the above operation, the focus servo can be reliably pulled in without being influenced by the dispersion of the optical system and the reflectance of the disk.

[0011]

In the conventional example, since the operation of sequentially measuring the maximum value and the minimum value of the focus error signal is performed before the actual focus search is performed, the time required for the focus search is very long. However, there is room for improvement.

The present invention has been made in view of the above circumstances. By performing a focus search without sequentially measuring the maximum value and the minimum value of the focus error signal, the optical time required for the focus search can be greatly reduced. An object of the present invention is to provide a focus control device for a dynamic information recording / reproducing device.

[0013]

A focus control device for an optical information recording / reproducing apparatus according to the present invention uses a focusing optical system as an optical recording medium to collect light from a light source in a spot shape to thereby form a recording medium. An optical pickup for irradiating the recording medium for recording or reproduction, and for operating the drive system to move the optical system by setting the optical system from the defocused state to the focused state with respect to the recording medium. A search means, a focus error signal detection means corresponding to a deviation from a focus state when the focus search is performed, and a focus servo means for operating a focus servo loop when the focus error signal reaches the focus pull-in range. have.

Further, the focus control device of the present invention is
The judgment level of whether to activate the focus servo is
It has a storage means that is stored as a fixed value that is a value calculated based on the maximum amplitude value and the minimum amplitude value of the focus error signal obtained from a plurality of types of recording media.

[0015]

[Operation] According to the present invention, a fixed value, which is a value calculated based on the maximum amplitude value and the minimum amplitude value of the focus error signal obtained from a plurality of types of recording media, is stored in advance in the storage means.

Further, according to the present invention, by using the fixed value, it is determined whether or not the focus servo is operated, and when the focus is within the focus pull-in range, the focus servo loop is activated to pull in the servo. There is.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 relate to an embodiment of the present invention, and FIG. 1 is a configuration diagram of an apparatus including a main part of the embodiment, and FIG.
Is a waveform diagram of the focus error signal with respect to the distance between the focusing optical system and the disc, FIG. 3 is an explanatory diagram showing an example of arithmetic operation of the reference level for determination, FIG. 4 is a flowchart for performing focus search, FIG. 5 and FIG. 6 is a waveform diagram of the focus error signal when the disc type is changed.

An optical information recording / reproducing apparatus 1 having a focus control device 30 according to an embodiment of the present invention is shown in FIG.

In the device 1, the disk 3 as an optical recording medium is driven to rotate. The laser light (not shown) is focused on the disk 3 by the objective lens 2 which constitutes an optical pickup and can be irradiated in a spot shape.

The laser beam is set to a high energy density state during recording, and is set to a weak energy density during reproduction.

The objective lens 2 is arranged so that the distance from the disk 3 changes depending on the drive signal level applied to the focus coil 5 via the focus driver 4. In the normal use state, the laser light is focused on the disk 3 in a spot shape (just), which is in a focused state.

The light reflected by the disk 3 is collimated by the objective lens 2. After that, the parallel light flux is incident on a four-division photodetector 6 used for focus setting, whose optical path is changed by the action of a λ / 4 plate, a polarization beam splitter, and the like (not shown) that constitute the optical pickup.

The outputs of the photodiodes D1, D2, D3 and D4 in the four-division photodetector 6 are added by adders 7 and 8, respectively. The outputs of the adders 7 and 8 are further converted into a direct current addition signal SDC and a focus error signal SFER by an adder 9 and a subtractor (differential amplifier) 10, respectively, and input to an A / D converter 12 of the CPU 13. I am doing it.

The focus error signal SFER obtained by the critical angle method has the following features. That is, as the objective lens 2 moves away from the distance from the disk 3, as the objective lens 2 moves closer to the focus position (JUST FOCUS) LJ as shown in FIG. In the focus pull-in range W including LJ in the approximate center, the focus rises sharply. Further, the signal SFER has an output waveform in which after reaching the maximum point of rising, the signal SFER suddenly falls again, passes through a valley portion, and slowly increases.

Focus control device 30 according to the present embodiment
Sets the objective lens 2 in advance to a distance close to the disc 3, and then drives the objective lens 2 so as to move away. The control device 30 controls the focus error signal S
The level Sa which is in the middle of falling into the first valley of FER is detected. Further, after detecting the level Sa, the control device 30 activates the focus servo when detecting the level Sb set at a position sufficiently close to the focus position LJ within the focus pull-in range W, for example. As a result, the (just) focus state can be set in a short time.

By the way, the focus error signal of the critical angle method is measured, for example, by changing the kind of the disk and the like, as shown in FIG.
The waveforms shown in (a) to (c) and FIGS. 6D and 6E are obtained. The type of the disc includes a recording system such as a write-once type and a rewritable type and a difference depending on the manufacturer, or even a disc of the same system and the same maker varies from one disc to another. this is,
For example, the difference in the reflectance (or the transmittance) of the disc causes a difference in the obtained focus error signal, and only one example is presented as the type, which is a factor that affects the error signal. Anything is acceptable as long as it is one.

Here, in FIG. 5, N is a reference voltage of the servo system circuit, and this reference voltage N is a substantially constant value if the servo system circuit is determined. In addition, in FIG.
A and B are amplitude values of the focus error signal with N as a reference, and are amplitude values when the amplitude is minimum and maximum, respectively. 5 (a) to 5 (c) and FIG.
In (d) and (e), the amplitude values A and B are shown by specific numerical values when the focus error signal has the minimum and maximum values.

The focus error signal is shown in the range defined by the following equation, for example. That is, the range is
In a servo system circuit that includes and is used with the optical system, it is necessary to set the range in such a manner that a focus error signal is obtained so that servo can be applied stably and surely depending on the medium used.

As an example, the focus error signal is the amplitude [A + B] = 2 ± 0.4 of the focus error signal.
[V] Symmetry of focus error signal [A / (A + B)] = 5
It is assumed that the allowable range is 0 ± 25 [%].

Here, the average, maximum and minimum values of the amplitude values A and B of the focus error signal will be calculated.

Average value of A and B: when amplitude = 2 [V] and symmetry = 50 [%], that is, when the waveform is as shown in FIG. 5A, A = 1 [V], B = 1 It becomes [V].

Maximum value of A: Amplitude = 2 + 0.4 = 2.4
When [V] and symmetry = 50 + 25 [%], that is, in the case of the waveform shown in FIG. 5B, A = 1.8 [V] and B = 0.6 [V].

Maximum value of B: Amplitude = 2 + 0.4 = 2.4
When [V] and symmetry = 50-25 [%], that is, in the case of the waveform shown in FIG. 5C, A = 0.6 [V] and B = 1.8 [V].

Minimum value of A: amplitude = 2-0.4 = 1.6
When [V] and symmetry = 50-25 [%], that is, in the case of the waveform shown in FIG. 6D, A = 0.4 [V] and B = 1.2 [V].

Minimum value of B: amplitude = 2-0.4 = 1.6
When [V] and symmetry = 50 + 25 [%], that is, in the case of the waveform shown in FIG. 6E, A = 1.2 [V] and B = 0.4 [V].

Here, the minimum value S of the focus error signal
Focusing on MIN-1 to SMIN-5, the minimum value SMIN-5 shown in FIG. 6 (e) is the largest. Therefore, the discrimination reference level S
a must be greater than SMIN-5 described above. Also, the maximum value of the focus error signal SMAX-1 to SMAX-5
6D, SMAX-4 is the smallest. Therefore, the discrimination reference level Sb must be smaller than the above-mentioned SMAX-5.

In the apparatus used, the focus error signal obtained by a plurality of types of discs to be mounted (or supposed to be mounted) has the waveforms shown in FIGS. 5 and 6, for example. That is, the focus error signal takes various values even if attention is paid to the maximum value SMAX and the minimum value SMIN. Of these, Figure 6
By setting the discriminating reference level Sa to be larger than the minimum maximum value SMAX-4 shown in (d), the obtained focus error signal will always have the level Sa regardless of which of the plurality of types of discs is used. It will cross (pass). Similarly, the maximum minimum value SMAX- shown in FIG.
By setting the discriminating reference level Sb to be smaller than 5, the obtained focus error signal always exceeds (passes) the level Sb regardless of which of a plurality of types of discs is used.

On the contrary, if the level Sa is too small or the level Sb is too large, the error signal may not pass the level depending on the type of the disc.

From the above, the maximum value and the minimum value of the focus error signal are limited to the above-mentioned SMAX-4,
Use SMIN-5 to find the reference level for discrimination. Also, the maximum and minimum digital data can be converted to DSFERMAX, DSFERM
Set to IN.

When the maximum value data DSFERMAX and the minimum value data DSFERMIN are determined in this way, the digital data of the discrimination reference levels Sb and Sa are calculated by arithmetic operation from the formula of FIG. 3 (a) or (b) or (c). DSb, D
Sa is required.

Using the formula shown in FIG. 3A, the level S
b is set to the average value of the maximum value SMAX and the minimum value SMIN,
The level Sa is set by the average value of the level Sb and the minimum value SMIN.

For example, if N = 2.5 [V], then Sb = (SMAX-4 + SMIN-5) / 2 = (2.9+) in the above example.
2.1) /2=2.5 [v], Sa = (Sb + SMIN-5)
/2=(2.5+2.1)/2=2.3 [V].

The levels Sb and Sa may be set using not only the equation shown in FIG. 3A but also the equations shown in FIGS. 3B and 3C. In addition, "128" in the same figure (c) means the maximum data of digital conversion data.

Digital data DSFE which is these set values
RMAX and DSFERMIN are already given as fixed values before the focus search is executed, and the CPU 13 shown in FIG.
The I / O port C22 (abbreviated as PORT C in the drawing) is stored in the ROM 23 as a storage means. And if necessary, CP
It is adapted to be read into the arithmetic logic unit (hereinafter abbreviated as ALU) 17 of U13.

The actual focus search is performed according to the flowchart shown in FIG. In step S1, the focus search is started. The objective lens 2 is driven in the direction away from the position close to the disc 3.
The focus error signal SFER obtained at this time is shown in FIGS.
One of the waveforms shown in (d) and (e) is obtained. The focus error signal SFER is converted into digital by the A / D converter 12 of the CPU 13. The converted digital data DSFER is monitored by the CPU 13.

The level of the signal SFER is the level Sa.
After passing through, the focus servo is turned on when the level becomes equal to or higher than the level Sb, a focus loop is formed, and the focus state is quickly set.

Explaining the above in accordance with the flowchart, the focus search is started in step S1, and the data content of the I / O port B14 is cleared in step S2. Then, after being cleared, in step S3, the output data of the I / O port B14 sequentially increases with an appropriate step width.

The output data of the I / O port B14 is D /
It is converted into an analog amount through the A converter 15 and applied to the focus coil 5 through the focus driver 4. At this time, the objective lens 2 is driven so as to gradually move away from the disc 3. Then, at the position where the objective lens 2 is moving, the focus error signal SFER output from the photodetector 6 becomes the digital data DSFER via the A / D converter 12, and becomes the AL of the CPU 13.
It is taken in by U17.

In the CPU 13, in step S4, the ALU 17 compares the digital data DSa corresponding to the level Sa with the digital data DSa. The acquisition of each A / D converted data is performed, for example, 10 times in each of steps S4 and S5. That is, as a result of the comparison, the data DSFER is (the digital data DSa of) the level Sa.
If so, the comparison will be repeated 10 times. Therefore, in step S5, if the number of comparisons does not reach 10, the A / D conversion data is subsequently captured.

When it reaches 10 times in step S5, the output data of the I / O port 14 is increased by one step width, and subsequently the A / D converted data DSFER and the digital data DSa of the level Sa are combined. The comparison is repeated.

By this process, the objective lens 2 moves away from the disk 3 in a stepwise manner or continuously, so that the focus error signal SFER becomes smaller than the level Sa. When the data DSFER becomes smaller than the level Sa in step S4, the output data of the I / O port B14 is increased by one step.

This time, in step S7, the digital data DSFER of the focus error signal SFER fetched is
A comparison is made as to whether or not the digital data DSb of level Sb has become larger. Similarly to the above, in the loop of steps S7 and S8, for example, A / D conversion is performed 10 times, and 10 times of A / D conversion data is compared with the digital data DSb of the level Sb for each step. Repeated.

When the comparison is performed 10 times in each step, if the level Sb is not exceeded, the I /
The output of the O port B14 is increased by one step.

By the above focus search, the objective lens 2 is gradually moved away from the disc 3, and soon the level S is reached.
b (that is, substantially the focus position LJ in the expression of FIG. 3A) is crossed. At this position, the digital data DSFER of the signal SFER becomes larger than the level Sb.
That is, in the case of No in step S7, the process proceeds to step S9.

Then, in step S9, the I / O port A
Servo for turning on the focus servo from 18 (Ser
The vo) signal is output to the analog switch 21 and the switch 21 is turned on. The output of the focus error signal SFER does not pass through the CPU 13, and the low pass filter (LPF) 19 and the phase compensation network (PCN) 20 are output.
And is supplied to the focus driver 4 via the switch 21.

By this focus error signal SFER, the objective lens 2 is almost held at the focus position LJ with respect to the disc 3.

In the coil 5, when the focus error signal SFER moves away from the focus position LJ,
While the polarity of the signal output acts in the direction of returning to the focus position LJ, if it gets too close, its action changes in the direction of returning the polarity to the focus position LJ. In any case, the error signal SFER acts to hold the objective lens 2 at the focus position.

Further, this focus error signal SFER
Is held at a position slightly deviated from the focus position LJ when there is an influence of temperature drift of the differential amplifier 10 or the like. At this time, the direct current addition signal SDC is taken into the ALU 17 of the CPU 13 at appropriate intervals via the A / D converter 12, is compared with the preceding data, and a correction signal for moving the objective lens 2 in a direction in which the value becomes large is output. Output. Since this correction is added to the focus drive output and then output, the focus state is always maintained without being affected by the temperature drift and the like.

In the above structure, the digital data D
For Sb and DSa, normally, those obtained from the formula shown in FIG. 3A are used, while when the servo pull-in is unsuccessful,
DSb, D obtained by the equation of FIG. 3 (b) or (c)
Instead of Sa, the servo may be pulled in again. That is, the plurality of data DSb and DSa are R
The configuration is stored in the OM 23 in advance.

In this embodiment, a fixed value is used as described above when performing focus search using the maximum and minimum limit values of the focus error signal measured in advance. That is, in the present embodiment, the minimum maximum value of the focus error signal obtained from a plurality of types of discs, and two determination reference levels obtained by arithmetic operation from the maximum minimum value are used. As a result, in the present embodiment, if the device is a disc including the disc originally supposed to be mounted and the error signal to be obtained passes the levels Sa and Sb, the servo pull-in is performed. Can be performed stably and reliably.

Further, in the present embodiment, the operation for obtaining the maximum value and the minimum value of the focus error signal is unnecessary, and the time required for the focus search operation can be greatly shortened.

The setting equations for the levels Sa, Sb, etc. are not limited to those described above.

The present invention is not limited to information recording / reproducing devices such as optical discs, but can be widely applied to information recording / reproducing devices such as magneto-optical discs. Alternatively, the recording medium may be a card-shaped medium.

[0064]

As described above, according to the present invention, it is not necessary to successively measure the maximum value and the minimum value of the focus error signal, and the focus search operation can be significantly shortened. is there.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus including a main part of an embodiment.

FIG. 2 is a waveform diagram of a focus error signal with respect to a distance between a focusing optical system and a disc.

FIG. 3 is an explanatory diagram showing an example of arithmetic operation of a judgment reference level.

FIG. 4 is a flowchart when a focus search is performed.

FIG. 5 is a waveform diagram of a focus error signal when the type of disc is changed.

FIG. 6 is a waveform diagram of a focus error signal when the type of disc is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical information recording / reproducing apparatus 2 ... Objective lens 3 ... Disk 4 ... Focus driver 5 ... Focus coil 6 ... 4 division | segmentation photodetector 7,8,9 ... Adder 10 ... Subtractor 12 ... A / D converter 13 ... CPU 14, 18, 22 ... I / O port 15 ... D / A converter 17 ... ALU (arithmetic arithmetic logic unit) 19 ... Low-pass filter 20 ... Phase compensation network 21 ... Switch 23 ... ROM 30 ... Focus control device

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 25, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

Here, the minimum value S of the focus error signal
Focusing on MIN-1 to SMIN-5, the minimum value SMIN-5 shown in FIG. 6 (e) is the largest. Therefore, the discrimination reference level S
a must be greater than SMIN-5 described above. Also, the maximum value of the focus error signal SMAX-1 to SMAX-5
6D, SMAX-4 is the smallest. Therefore, the discrimination reference level Sb must be smaller than SMAX-4 .

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

In the apparatus used, the focus error signal obtained by a plurality of types of discs to be mounted (or supposed to be mounted) has the waveforms shown in FIGS. 5 and 6, for example. That is, the focus error signal takes various values even if attention is paid to the maximum value SMAX and the minimum value SMIN. Of these, Figure 6
Than the minimum of the maximum value SMAX-4 to (d), the discrimination criterion les
By setting the bell Sb small , the obtained focus error signal always exceeds (passes) the level Sb regardless of which of the plurality of types of discs is used. Similarly, the maximum minimum value SMIN- shown in FIG.
5. By setting the discrimination reference level Sa to be larger than 5 , the obtained focus error signal always exceeds (passes) the level Sa even when any of a plurality of types of discs is used.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

The actual focus search is performed according to the flowchart shown in FIG. In step S1, the focus search is started. The objective lens 2 is driven in the direction away from the position close to the disc 3.
The focus error signal SFER obtained at this time is shown in FIGS.
The waveforms are within the ranges shown in (d) and (e). The focus error signal SFER is sent to the A / D converter 1 of the CPU 13.
Converted to digital by 2. The converted digital data DSFER is monitored by the CPU 13.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction content]

The above will be described with reference to the flow chart shown in FIG. 4. The focus search is started in step S1, and the I / O port B1 is started in step S2.
The data contents of 4 are cleared. Then, after being cleared, in step S3, the output data of the I / O port B14 sequentially increases with an appropriate step width.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction content]

By this process, the objective lens 2 moves away from the disk 3 in a stepwise manner or continuously, so that the focus error signal SFER becomes smaller than the level Sa. When the data DSFER becomes smaller than the level Sa in step S4, the route of steps S3 to S5 is
And the step S6 is executed.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0055

[Correction method] Change

[Correction content]

When the comparison is performed 10 times in each of the steps, if the level Sb is not exceeded, the step is continued.
At step S6, the output of the I / O port B14 is increased by one step.

Claims (1)

[Claims] 1. An optical recording medium is provided with an optical pickup for condensing light from a light source in a spot shape using a focusing optical system and irradiating the recording medium for recording or reproduction.
Focus search means for moving the optical system by operating a driving device to set the optical system from the defocus state to the focus state with respect to the recording medium, and a deviation from the focus state when the focus search is performed. Means for detecting a focus error signal corresponding to
In a focus control device of an optical information recording / reproducing apparatus having a focus servo means for activating a focus servo loop when the focus error signal reaches within the focus pull-in range, It is characterized in that it has a storage means in which a determination level as to whether or not to activate the focus servo is stored as a fixed value which is a value calculated based on the maximum amplitude value and the minimum amplitude value. Focus control device for optical information recording / reproducing apparatus.