JPH02192028A - Automatic focus lead-in control system - Google Patents

Abstract

PURPOSE:To promptly and stably attain an automatic focus lead-in operation by braking a convergent lens immediately before the lead-in of the focus. CONSTITUTION:After the high-speed scanning of a convergent optical system 4 is started, approach near the focus is detected by the fact that an automatic focus error signal 20 exceeds a certain level, and based on the detection, the scanning is stopped, and simultaneously a convergent optical system 4 is braked. Consequently the convergent lens slowly crosses a focal point. Further the crossing is detected, an automatic focal point servo circuit is closed, and tracing is started. Thus the convergent lens can be shifted to an initial stage at high speed, and by braking the lens, the relative speed between the convergent lens at the time of closing the servo circuit and the disk can be sufficiently reduced, and the stable lead-in operation is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic focus pull-in control method for optical recording media such as optical disks and magneto-optical disks, and in particular, the present invention relates to an automatic focus pull-in control system for optical recording media such as optical disks and magneto-optical disks. (This article relates to an automatic focus pull-in control method suitable for carrying out the following.

[Conventional technology]

Conventionally, as an automatic focus pull-in control system for this type of optical disk recording medium, there is one described in Japanese Patent Laid-Open No. 58-85940. In this method, when starting autofocus servo, the objective lens (diaphragm lens) is initially driven by the output of a lamp generator, etc. so that it gradually attaches to the recording medium from a distance, and the amount of laser light reflected from the optical disk surface is adjusted. Based on this, a focus error signal (focal shift detection signal) with figure-8 characteristics is obtained, a point in time when the focus error signal enters the linear region, and a switch provided in the servo circuit is closed at this point, the automatic focus servo is activated. was configured to start. At this time, the initial driving speed of the objective lens is set to such a speed that the objective lens can reliably follow the disk recording surface when autofocus servo is started.

[Problem to be solved by the invention]

In the optical disk device according to the above-mentioned conventional technology, after loading an optical disk as a recording medium, a diaphragm lens is scanned toward the disk from a distance, and when the defocus detection signal enters a linear range, the autofocus servo system is started and the focus is pulled in. However, as mentioned above, the initial speed of the objective lens cannot be made too large in order to ensure retraction and make the objective lens follow the disk surface stably. For this reason, with the prior art, it is difficult to speed up the pull-in and stabilize the autofocus servo system in a short time. In the above-mentioned conventional technology, no consideration was given to such problems of speeding up and stabilizing the pull-in.

On the other hand, 5-inch optical discs have recently been standardized, and the disc type, attributes, read conditions, etc. are recorded in advance on predetermined tracks on the disc, and consistency with recording and playback equipment is improved. I decided to take it. This determined track is called a control track, and the control track is divided into two types: PEP and SFP. Here, since the SFP is not related to the present invention, its explanation will be omitted. PEP is PhaseEn
Abbreviation for coded part, which means a part recorded in the modulation format P and E. It is usually provided on the inner circumference of the disk over about 300 tracks, and is recorded in P'
The EP records basic attributes of the disc, such as the reproduction laser power of the disc and whether it is write-once type or rewritable type.

Therefore, in an optical disc device, when a disc is loaded into the optical disc device, it is first necessary to read the contents recorded on the PEP before recording and reproducing.

To read PEP, autofocus servo must be applied. Note that PEP is recorded at a frequency that is sufficiently low compared to the frequency of normal data so that it can be read without applying a tracking servo (for example, in the case of recording using pits, the length of one pit is Record it so that it is longer. Therefore, in order to read PEP, automatic focus control may be applied. On the other hand, in order to facilitate reading of the PEP without tracking control as described above, the recording frequency is low. For this reason, PEP
As the data frequency approaches the autofocus control band, the data signal has a large influence on the autofocus error signal. As for the autofocus error signal, the PEP data signal is equivalent to noise, and there is a possibility that the timing for starting autofocus control will be detected incorrectly. On the other hand, if the signal is passed through a low-pass filter to remove this noise, since the frequency of the noise and the band of the autofocus error signal are close, a phase lag will occur and the timing of the pull-in will be shifted. Furthermore, since data is recorded on the PEP, the average amount of reflected light also decreases. In other words, in conventional discs where PEP data is not recorded on the inner circumference, the entire track reflects light, so the amount of reflected light is large, but where PEP data is recorded (for example, recording by pits) ) As described above, relatively long pits corresponding to relatively low frequencies are formed, so the average amount of reflected light decreases due to the influence of these long pits. For this reason, if the distance from the disk is too great when the objective lens is used to move it away, the difference between the amount of light reflected from the surface of the disk and the amount of light from the recording/playback surface will become small, causing variations in equipment. Considering disc variations, etc., what is done to start automatic focus control,
In the operation of detecting that the autofocus signal has become larger, there has also been a problem of erroneous detection. In other words, the timing to start autofocus control is determined based on the eight-character characteristic of the autofocus signal as described above, but if the difference between the amount of light reflected from the disk surface and the amount of light reflected from the recording/playback surface is small, This is because the pseudo 8-shaped characteristic is mistakenly detected as the true S-shaped characteristic due to reflection from the recording/reproducing surface.

The prior art disclosed in Japanese Patent Application Laid-Open No. 58-85940 did not target a standardized disk (having PEP). No consideration was given to the fact that the data signal would appear as noise, and that the amount of reflected light would effectively decrease and the signal would become smaller.As a result, when automatic focus was pulled in with PEP, the automatic focus control loop There was a problem in which the closing timing was incorrectly detected and the retraction failed. A similar problem also occurs in disks whose recording/reproducing surfaces have relatively low reflectance.

Accordingly, a first object of the present invention is to solve the problems of the prior art described above, shorten the focus pull-in time, and provide a high-speed and stable automatic focus pull-in control system.

A second object of the present invention is to
In addition to eliminating the influence of the P data signal and accurately detecting the timing to close the automatic focus control loop, it also eliminates the effects of spurious light reflections on the disk surface even when using a disk with a low reflectance on the recording/playback surface. It is an object of the present invention to provide an automatic focus pull-in control system that can prevent the above-mentioned erroneous timing detection and perform stable focus pull-in.

[Means to solve the problem]

In order to achieve the above first object, the automatic focus pull-in control method of the present invention starts high-speed scanning toward the recording medium from a far distance of the aperture optical system, and changes the amount of reflected light from the recording medium when approaching the focal point. Based on this detection (for example, when the autofocus error signal exceeds a predetermined level), the scanning of the aperture optical system is stopped and the brake is simultaneously applied for a predetermined period from the time of this detection, and the elapse of the predetermined period is The configuration is such that the rear autofocus servo system is closed and follow-up control is started using it.

In addition, in order to achieve the above second object, the automatic focus pull-in control method of the present invention starts scanning the irradiation direction of the light beam with respect to the recording medium of the focusing optical system, and detects an automatic focus error signal indicating a focus shift. and after the first comparison means detects that the autofocus error signal exceeds the first reference voltage, the second comparison means detects that the autofocus error signal exceeds the second reference voltage. detect the first and second
A system in which the autofocus servo system is closed when a detection output is obtained from the comparison means is characterized in that a peak hold or bottom hold means is provided for peak holding or bottom holding the autofocus error signal; The configuration is such that the peak-held or bottom-held output is supplied to the first comparing means.

Furthermore, in order to achieve the second object, if the -degree pull-in fails, the slice level (reference voltage applied to the comparison means) is changed and retry (rescanning) is performed.

Furthermore, in order to achieve the second purpose above, the head is made of PEP.
The head is moved to a different position (a position where no data is recorded), automatic focus pull-in is performed at that position, the head is then moved and positioned at the PEP, and the contents of the PEP are read.

Alternatively, to achieve the second objective above, before performing automatic focus pull-in, move the objective lens (diaphragm optical system), record the value when the automatic focus error signal becomes the largest, and adjust the slice level accordingly. (Reference voltage)
When determining and performing a pull-in operation, it may be configured to detect an increase in the autofocus error signal based on the slice level.

[Effect]

The operation based on the above configuration will be explained.

According to one invention, after the aperture optical system (objective lens) starts high-speed scanning, approaching the vicinity of the focus is detected when the autofocus error signal exceeds a certain level, and this detection causes the above-mentioned At the same time as stopping scanning, a brake is applied to the aperture optical system. This results in
The aperture lens slowly crosses the focal point. Detects further crossing and closes the autofocus servo circuit,
Start following. This allows the aperture lens to initially move at high speed, and by applying the brake, the relative speed between the aperture lens and the disc when the servo circuit is closed can be made sufficiently small, allowing stable retraction and preventing malfunctions. There is no.

According to another invention, the autofocus error signal is peak held by a peak hold means (or bottom hold means) before being supplied to the first comparison circuit, and this peak held voltage is applied to the first comparison circuit. The voltage is supplied to a comparator circuit where it is compared with a first reference voltage. The peak-held autofocus error signal has the effect of pits due to PEP removed and has the same voltage level as that obtained with a full-reflection track without bits. As a result, P
The EP data will not be mixed into the autofocus error signal as noise (and the difference between the peak level of the pseudo figure-8 characteristic due to surface reflection of the recording medium and the peak level of the true figure-8 characteristic will be sufficiently large). This prevents erroneous detection of pseudo-character 8 characteristics and eliminates the possibility of erroneous timing of closing the automatic focus control system.

In addition, if automatic focus acquisition fails once, you can change the slice level and retry, or find the peak value of the automatic focus error signal in advance before performing automatic focus acquisition, and set the slice level that matches that peak value. By making these settings, it is possible to accurately detect the timing to close the automatic focus control even when various types of disks are loaded.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, an embodiment of the first invention of the present application will be described with reference to FIGS. 1 and 2.

The automatic focus control system and positioning control system of an optical disk device for recording or reproducing information can be configured as shown in FIG. An optical disk 1, which is a medium, has an information recording film surface 2, and is controlled to rotate by a spindle motor 3 at a constant or variable speed. Recording of information on an optical disk and reproduction of information from the optical disk are performed as follows. 6 is an optical head, and the light beam emitted from the semiconductor laser 8 on the optical head 6 is transmitted to a galvano mirror.
After passing through the optical system including 7, the aperture lens 4
The beam becomes a light spot 5 and is focused on the recording surface 2. Information is recorded by the physical deformation or physical change of the recording surface caused by the light spot, and the reflected light from this recording surface is detected by a photodetector 9. By detecting the information, the recorded information is reproduced. The light spot of the laser beam irradiated onto the recording surface is required to have a minute dimension of 1 μm or less in diameter.
Automatic focus control is required to ensure that a light spot within a certain range is always obtained even when the recording surface is vertically moved or otherwise fluctuated. This automatic focus control is performed as follows. That is, the reflected light from the recording surface 2 is separated from the emitted light beam by an optical system, and the light spot detector 9 detects the distance between the recording/reproducing surface and the focal point of the narrowed-down light spot position. Then, in order to minimize this deviation (distance), the preamplifier circuit (autofocus error signal generation circuit) 12, changeover switch 13, control compensation circuit 14, addition circuit 15, and drive circuit 16
A desired current is passed through the actuator (voice coil motor) 10 through the focusing optical system (objective lens) 4.
By driving the optical system 4, the optical system 4 is controlled to follow the movement of the recording surface 2. On the other hand, in the light spot positioning system (tracking control system), in order to make the light spot follow the track on the disk, the light spot detector 9 detects a track deviation amount detection signal, and the control circuit 11 is activated by this detection signal. This is a control system that controls the mirror 7 through the mirror 7. A light source for recording/reproducing and the control system is obtained by light emission from a semiconductor laser 8, and the light emission is controlled by a laser control drive circuit 19.

Further, the output of the preamplifier 12 is input to a low level detection circuit 22 and a high level detection circuit 23 that detect the level of the detection signal, and furthermore, the output of these low level detection circuit 24 and high level detection circuit 25 is decoded. and is connected to a control logic circuit 21 including registers and the like. Control logic circuit 2
1 outputs 28 and 27 are input to the changeover switch 13, the brake pulse generation circuit 17, and the ramp function generation circuit 18. The output 28' of the brake pulse generation circuit 17 is input to the ramp function generation circuit 18, and the output 26 of the ramp function generation circuit 18 is input to the addition circuit 15.

In the automatic focus control method, factors that determine the servo pull-in speed at the start of control include the operating speed of the diaphragm lens 4 and the vertical vibration speed of the disk.

FIG. 2 shows a timing diagram for explaining the operation.

When the control logic activates the focusing optical system for automatic focus control and the ramp function generating circuit 18 gradually brings the light spot closer to the recording film, the automatic focus detection output signal (automatic focus detection output signal) amplified by the preamplifier 12 is activated. The focus error signal) 20 changes as shown in FIG. 2(a). FIG. 2(d) shows the command 27 to raise the diaphragm lens 4, and as a result, the output of the ramp function generating circuit 18 is as shown in FIG. 2(f).
A signal 26 is generated that causes the aperture lens 4 to approach the disk at a constant speed. As a result, the automatic focus detection output signal 20 first shows a positive peak P1, then as the camera approaches the camera further, it shows a negative peak P2, and then becomes zero at the in-focus position and then reaches a positive peak. P3, indicating a negative peak P4.

High level detection level v2 for the second peak P2
By providing a low level v1 that detects the level before reaching the third peak P3, it is possible to recognize the position of the output zero between the peak P2 and P3, which is the true focal position. When retracting the focus, a brake pulse 28' is generated immediately or after a certain period of time after the pulse of the output 25 of the high level detection circuit 23 falls, and is input to the ramp function generation circuit 18, and is determined with a certain pulse width. The vertical movement of the aperture lens is forcibly braked for the specified period of time. Next, the autofocus control signal 20 detects a low level, and when the low level detection circuit output 24 rises, the autofocus control activation signal 29 is turned on.

This makes it possible to operate the diaphragm lens at a higher speed than in the past, and to lower the relative speed to the vertical movement of the disk, thus making it possible to perform a stable retracting operation. The timing to generate the brake pulse and the pulse width depend on the operating speed of the aperture lens, the vertical vibration of the disc,
It is determined to be the optimum value, taking into consideration the relative pull-in speed that is allowable for pulling in the focal point, etc.

Next, an embodiment of the second invention of the present application will be described with reference to FIGS. 3 to 6.

FIG. 3 is a block diagram of this embodiment, in which the same parts as in FIG. 1 are given the same reference numerals and their explanations will be omitted.

As a feature of this embodiment, the automatic focus control signal (error signal)
Generation circuit (amplification circuit) 20 and comparator 23 (first
A peak hold circuit 53 is provided between the comparison means (comparison means).

The operation of this embodiment will be explained below. As described in FIG. 2(a), the autofocus error signal has an approximately figure-eight curve, and if the objective lens 4 and the disk 1 are too far apart, the autofocus error signal 20 will be approximately 0. Therefore, automatic focus control cannot be started at this position. In order to perform automatic focus pull-in, an objective lens vertical movement signal 26 is generated through a ramp function generation circuit 18 according to instructions from a logic control circuit 18, and a voice coil motor 10 is driven by a power amplifier 16 through an addition circuit 15. to move the objective lens. First, move the objective lens away and gradually bring it closer. When the autofocus error signal 20 exceeds a certain level (first reference voltage) ■2 (just before P2),
It is detected by the comparator 23 and its output 25 is transmitted to the logic control circuit 21. Further, as the object approaches the object, the autofocus error signal 20 suddenly decreases (zero crossing point), and as the object approaches the object further, it becomes larger with the opposite polarity. The level that suddenly decreased and started increasing with the opposite polarity (immediately after the zero cross)
is detected by comparing it with a threshold voltage (second reference voltage) V+ by a comparator (second comparison means) 22, and an output 24 is transmitted to the logic control circuit 21. The logic control circuit 21 detects that the output of the comparator 22 is output after the output of the comparator 23 is output, and generates a switch-on signal 2.
Switch 1 to output 9 and close the automatic focus control system
Close 3. The autofocus error signal 20 is transmitted through the switch 13,
The voice coil motor 10 is driven through the stabilizing circuit 14, the adding circuit 15, and the power amplifier 16, and the objective lens 4
control is started so that the recording film 2 is always in focus.

By the way, as mentioned above, due to the standardization of discs, the disc 1 has a PEP5 on its inner circumference as shown in FIG.
2, a control track is provided. PEP
52 is pre-formatted with data recorded using modulation methods P and E, and the minimum repetition period is, for example, 41.52 when the rotation speed is 180 rpm. It is crsec. This effect is plotted on top of the autofocus error signal (
and as shown in Figure 5. Here, in Figure 5, disk 1
Simultaneously, pseudo-autofocus error signals 51a to 51b due to light reflected from the surface 50 of FIG. Under the influence of the PEP 52, the autofocus error signal 20 becomes smaller on average, as shown by the broken line 20m in FIG. 4, than the original signal shown by the solid line 20h. Note that the dotted line 20β indicates the output corresponding to the low reflection level due to the bit portion, and the solid line 20h indicates the output corresponding to the high reflection level due to the portion without pits. It is an envelope waveform that vibrates (actually, it is an averaged waveform of 20 m). Therefore, 2 shown in FIG. 2 must be set smaller than in the case without the PEP 52. On the other hand, the distance between the optical head 6 and the disk 1 always varies depending on the mechanical dimensional accuracy in addition to the vertical movement of the disk 1. Therefore, as mentioned above, when performing automatic focus retraction, the objective lens 4 is always brought to the farthest position from the disk first, but it may be moved further away to a position where it focuses on the surface of the glass. .

At this time, the autofocus error signal includes 51a to 51 in FIG.
A pseudo signal shown in b appears, but if it exceeds v2 like 51P, automatic focus control will start at this point. In order to eliminate this possibility, it is necessary to choose ■2 to be thicker than the pseudo signal reflected from the surface (and smaller than the peak value 20P of the original signal (true autofocus error signal)). , the average light intensity decreases due to the influence of PEP, and the peak value drops to 20P', which means that the peak value of the true error signal, 20P', is suspicious (close to the peak value of the signal 51P).
Therefore, when considering variations in the output from the photodetector 9 of the optical head 20, it becomes difficult to select v2.

In order to solve the above-mentioned problems, this embodiment has been developed as shown in Fig. 6 (a).
) is provided with a peak hold (bottom hold) circuit 53 as shown in FIG. As a result, the autofocus error signal 54 input to the comparator 23 in the region of PEP 52 is as shown in FIG.
b)

As shown in FIG. 6(b), by passing through the peak hold circuit 53, the autofocus error signal 54 becomes 54a up to the zero cross point and 54b after the zero cross point. The portion 54a changes at approximately the same level as 20h in FIG. 5, and the portion 54b changes at approximately the same level as the portion 20j2 in FIG. This is because the peak hold circuit 53 has polarity (directivity), and for the purpose, it is necessary for the peak hold to work before the zero cross point to increase the output level. After the zero cross point, there is no problem even if the hold function does not work (the point is that it is sufficient to detect low health ■1).

Note that a peak hold circuit may also be inserted before the comparator 22, or the circuit 53 may be made common to the comparators 22 and 23), and both 22 and 23 may be used as hold inputs. In this way, by passing through the peak hold circuit, the peak value of the true autofocus error signal does not decrease even in the PEP signal region, and the difference from the pseudo autofocus error signal is large, so the reference voltage level 2 can be easily set, and a false autofocus error signal will not be detected erroneously. Note that FIG. 6(a) shows a general configuration of a peak hold circuit, and the configuration is not limited to this.

Below, an embodiment that is a modification of the second invention will be briefly described.

In one embodiment, prior to performing automatic focus pull-in, the optical head is first moved to a location other than the PEP, and automatic focus pull-in is performed at that location. It is preferable that no data is recorded in the moved location. This eliminates the influence of the PEP signal and similarly prevents false detection of pseudo signals.

In another embodiment, when automatic focus pull-in is performed at PEP or other locations, if -degree pull-in fails, the pull-in operation is normalized by decreasing or increasing the slice level v2 and performing the pull-in again. have it done.

In this case, whether to increase or decrease the slice level (2) is determined depending on whether the autofocus error signal exceeds (2) when the pull-in fails. That is, the case where ■2 is exceeded means that the test fails because ■2 is set below the peak of the pseudo signal, so in this case, the value of V2 is increased. Furthermore, the case where V2 is not exceeded is the case where there is a failure because v2 was set higher than the peak value of the true signal, so in this case, the value of v2 is reduced. It should be noted that this embodiment is also more effective if the peak hold circuit described above is also used.

In another embodiment, before performing automatic focus retraction,
First, start from the position farthest from the disc and gradually move closer to the disc. At this time, make sure that the peak value of the autofocus error signal can be detected (however, switch 13 remains open). Move the objective lens away from the disk again, and then Determine the corresponding optimal slice level ■2. Again, gradually bring the lens closer to the disc and perform automatic focus retraction.

In this way, the focus can be reliably pulled in even if there are variations in characteristics from disk to disk, without erroneously detecting the timing of the pull-in on the disk surface, although it takes a second time. In this case as well, PEP peak hold is effective.

Another embodiment is to start the automatic focus pull-in operation with the objective lens closest to the disk. That is, in FIG. 2(a) or FIG. 5, scanning is performed from right to left. Then, after detecting the first peak, that is, the peak P3 in FIG. 2, when the zero cross is passed, the pull-in is started. In this way, there is no possibility of erroneous timing detection on the disk surface, and the retraction can be performed reliably.

〔Effect of the invention〕

As described in detail above, according to the automatic focus retraction control method of the present invention, the means (braking means) for braking the aperture optical system (aperture lens) immediately before retracting the focus
By providing this, the scanning of the optical system is forcibly stopped, and then the focus is drawn into the autofocus servo system, which enables high-speed and stable autofocus servo system. This has excellent effects such as being able to shorten the startup time of the disk device.

In addition, even if autofocus is pulled in by the PEP section, level detection is performed after applying peak hold to the autofocus error signal, so the autofocus error signal level is not affected by noise due to PEP. There is no risk of erroneously detecting a false signal due to surface reflection due to a decrease in the amount of light, and there is an effect that automatic focusing can be reliably performed.

In addition, by changing the detection level and retrying when pull-in fails once, or by performing a trial scan in advance to find the optimal slice level, it is possible to accurately detect the timing to close automatic focus control for various types of discs. It produces the effect that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
3 is a block diagram of another embodiment of the present invention, FIG. 4 is a configuration diagram of a disk with PEP, and FIG. 5 is an explanation of the operation of a disk with PEP. Timing chart for
a) is a detailed circuit diagram of the peak hold circuit in Figure 1;
FIG. 3(b) is a timing chart for explaining the operation of FIG. 3. １・・・・・・・・・Optical disc, ２・・・・・・・・・
・Recording film surface, 3... Spindle motor,
4...Fitting lens (objective lens, focusing optical system), 5...Light beam, 6...
......Optical head, 7...Galvano mirror, 8...Semiconductor laser, 9...
・・・・・・Photodetector, 10・・・・・・・・・VC
M, 11...Tracking control circuit, 1
2...Auto focus error signal generation circuit, 13
・・・・・・・・・Selector switch, 14・・・・・・・
...Control compensation circuit, 15... Addition circuit,
16......Power amplifier (drive circuit), 1
7... Brake pulse generation circuit, 18.
...... Ramp function generation circuit, 19...
. . . Laser drive circuit, 20 . . . Automatic focus error signal, 21 . . . Logic control circuit,
22...Low level detection circuit (second comparison means), 23...High level detection circuit (first comparison means), 53... ...Peak hold circuit. v2

Claims (1)

[Claims] 1. A focusing optical system for focusing the light beam generated from the light source on the recording medium, and focusing the light beam on the recording surface by following the vertical movement of the recording medium. means for controlling the aperture optical system so as to control the aperture, the optical recording and reproducing apparatus comprising: means for scanning the aperture optical system at high speed toward the recording medium from a position away from the aperture when automatic focusing is started; means for detecting that the optical system is near the focal point based on the amount of light reflected from the recording medium; braking means for braking the narrowing optical system for a predetermined period from when the detection is made; and elapse of the predetermined period. 1. An automatic focus pull-in control method, comprising means for starting rear automatic focus control. 2. The automatic focus pull-in according to claim 1, wherein the means for detecting based on the amount of reflected light from the recording medium is configured by means for detecting that the automatic focus error signal has exceeded a predetermined level. control method. 3. A focusing optical system for focusing the light beam generated from the light source on the recording medium, means for starting scanning of the light beam irradiation direction of the recording medium by the focusing optical system, and a focusing device that accompanies the scanning. means for detecting an autofocus error signal indicative of a misalignment; first comparing means for detecting that the autofocus error signal exceeds a first reference voltage; automatic focus pull-in, comprising: a second comparison means for detecting the exceedance; and means for closing the automatic focus servo system when a detection is made by the second comparison means after the detection by the first comparison means is made; An automatic focus pull-in control method, characterized in that the automatic focus error signal is supplied to the first comparison means via a peak hold or a bottom hold means. 4. A focusing optical system for focusing the light beam generated from the light source on the recording medium, a means for starting scanning of the light beam irradiation direction of the recording medium by the focusing optical system, and a focus accompanying the scanning. means for detecting an autofocus error signal indicative of a misalignment; first comparing means for detecting that the autofocus error signal exceeds a first reference voltage; In an automatic focus pull-in control method, the automatic focus servo system is configured to include a second comparison means for detecting that the focus has been exceeded;
1. An automatic focus pull-in control method, characterized in that, when automatic focus pull-in fails, the first reference voltage is changed and scanning for focus pull is performed again. 5. Before performing automatic focus pull-in, test scan the aperture optical system once to detect the peak value of the automatic focus error signal, set the first reference voltage to match the detected value, and then 4. The automatic focus pull-in control system according to claim 3, wherein the automatic focus pull-in control system is configured to perform automatic focus pull-in.