JPS63155425A - Focus pull-in method for optical disk device - Google Patents

Abstract

PURPOSE:To eliminate such a malfunction as a focus is pulled in on the surface of a protective layer by locking a focus once on the surface of a disk protective layer, and subsequently, closing a focus-servo by setting a longer time than the time required for locking on the surface of the protective layer, at the time of succeedingly executing a pull-in operation. CONSTITUTION:After having detected a light beam reflecting signal from the surface of a disk protective layer, which is generated at the time of pulling in a focus, a focus servo is closed, and locked to the surface of the protective layer once. Thereafter, the focus servo is opened, and subsequently, a focus pull-in operation is repeated. At the time of this repeated operation, the timing for closing the focus servo is set longer than the time required for locking to the surface of the protective layer. In such a way, after a reflecting signal from the surface of the protective layer is detected completely, the focus servo is closed, therefore, the focus servo is not pulled in on the surface of the disk protective layer, but can be exactly pulled in the recording film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a write-once or record-erasable optical disc device, and particularly to a focus servo pull-in method.

[Conventional technology]

There are various types of optical disk devices, but for example, a disc-shaped recording medium (hereinafter referred to as a disk) is rotated by a motor, and the amount of light beam irradiated onto the disk from a light source is changed during recording. During playback, the light beam irradiated onto the disc is set to a weak constant light intensity.
An example of this is a device that detects reflected light or transmitted light from a disk using a photodetector and reproduces a recorded signal.

Various types of disks have been proposed for use in such devices, including one in which a recording material film is provided on a substrate such as acrylic, and two disks are laminated with the recording material side facing inside. A base material such as acrylic is used as a protective layer to remove the influence of dust etc. on the reproduced signal.As a recording material, materials such as bismuth (BA) that evaporate due to the heat of the light beam, Known materials include amorphous semiconductors whose state changes due to the heat of the light beam, and manganese bismuthide (MnBL) which is easily magnetized by applying an external field due to the heat of the light beam.

Such a disk has warpage, unevenness, etc., and causes surface runout when the disk is rotated. This surface runout is large, about 1 meter, and may sag or warp due to humidity, temperature changes, gravity, etc. K, which records and reproduces signals at high density, requires the diameter of the light beam on the disk to be narrowed down to 1 μm or less, and the light beam on the disk, which has a wide variety of surface wobbles, must be focused so that it converges to a substantially constant state. It is necessary to take care of Chibo.

Description will be given below using a conventional technique.

FIG. 2 is a block diagram showing a conventional focus nervo, particularly a focus pull-in circuit. Note that Figure 3 is the same as Figure 2.
It is a waveform diagram of each part of the prior art shown in the figure.

In FIG. 2, a light beam 2 generated from a light source 1 such as a semiconductor laser is made into parallel light by a coupling lens 5, and is converged onto a disk 10 via a semitransparent mirror 4, a reflecting mirror 5, and a converging lens 6. The reflected light 7 reflected by the disk 10 is irradiated onto the photodetector 11.12 via the converging lens 6, the reflecting mirror 5, and the semi-transparent EA mirror 4. These optical systems are driven by a feed motor (not shown) connected to the transfer table 8. The disk 10 is rotated by the motor 9, and the focus chipo detects the difference between the outputs of the two-split photodetectors 11 and 12 using the differential amplifier circuit 13 so that the light beam follows the disk surface runout. Then, this error signal is sent to the phase compensation circuit 14 and the loop switch 15 (control terminal is 1H).
The amount of change in the actuator 17 is controlled via the drive circuit 16.

On the other hand, the outputs of the photodetectors 11 and 12 are input to the differential amplifier circuit 13 and also to the summing amplifier circuit 20, and are further led to the first comparator circuit 18 and the second comparator circuit 21, respectively. ing. However, once the input signal reaches the threshold voltage E1, the first comparator circuit 18 lowers the threshold voltage E1, and the output remains at 1.
It can be maintained at H level.

Note that details of the peripheral circuits 22 of the first and second comparator circuits 18 and 21 are shown in FIG. The first comparator circuit 18 uses a voltage generating circuit and an integrating circuit (both not shown) to bring the converging lens 6 close to the disk 10 surface to generate an error signal (third In Figure A), only the error signal from the disk recording film surface is compared with a preset threshold voltage E1, and is output as an input signal jH1'' level that is higher than the threshold voltage 81 (
(dashed line portion from T2 to Ti in FIG. 3B). however,
Since the focus is locked from T2, the jHa level signal is shown from T2. Similarly, in the second comparator circuit 21, only the addition signal from the disk recording film surface is predetermined among the addition signals (FIG. 3C) of the output of the addition amplifier circuit 20 that are generated during focus pull-in. By comparing it with the threshold voltage E2, the input signal having the threshold voltage 82 or higher is output as a 1H level signal (FIG. 3D). Generally, the light and -reflection signals on the surface of the protective layer are smaller than those on the surface of the recording film, but the relative level difference is determined by the combination of each material. Conventionally, the first and second comparator circuits 1 were designed so that each comparator circuit could detect only the signal reflected from the recording film surface due to the combination of the first layer material and the recording film material.
8.21 threshold voltage g1. I had set B2.

Next, in the AND circuit 19, the first comparator circuit 18
Both the output and the output of the second comparator circuit 21 output a period of 1H level (Fig. 3E), and the loop switch f-1
5 is controlled to close.

Note that related devices of this type include, for example,
Published Patent Publication Sho 57-115450. 1977-150
147 etc. are mentioned.

[Problem that the invention seeks to solve]

In the above conventional technology, the reflected signal from the surface of the protective layer may reach the threshold value due to variations in reflectance on the surface of the disk protective layer, and the focus is locked on the surface of the protective layer by closing the loop switch. There was a problem with that.

This K will be explained in detail using FIGS. 2 and 5. Figure 5 shows the error signal of the differential amplifier circuit 13 that occurs when the focus is pulled in, but the reflected signal from the protective layer surface is larger than the reflected signal from the recording film surface (indicated by the broken line). Since the threshold voltage E1 of the first comparator circuit 18 has been reached, an 'H' level signal is generated at the output of the first comparator circuit 18 (the broken line part from T2 to Ts in FIG. 4B). However, since the focus is locked from T2, the 1H'' level is shown from T2.

On the other hand, as shown in FIG. 5C, the output of the summing amplifier circuit 20 also shows that the signal reflected from the surface of the protective layer is larger than the signal reflected from the surface of the recording film (indicated by a broken line). 2
The threshold voltage E! of the comparator circuit 21 of has reached. Therefore, the output of the second comparator circuit 21 (FIG. 5D) also generates a 1H'' level signal.

Therefore, in response to these outputs, the AND circuit 19 outputs the #H'' level period of both human power (FIG. 5B), closes the loop switch 15, and outputs the signal on the surface of the protective layer (timing T2 in FIG. 5). The focus is locked.

Furthermore, due to the combination K of the protective layer material and the recording film material, the relative level difference between the reflected signals from both film surfaces may become extremely small, and therefore only the reflected signals from the recording film surface are detected. It is difficult to precisely set the threshold voltage of the comparator circuit so as to achieve this. Furthermore, as mentioned above, variations in the reflectance of the surface of the disk protective layer and variations in the threshold voltage settings of the comparator circuits make it even more difficult to detect only the reflected signal from the recording film surface.

In addition, it is generally known that in order to improve the C/N of the reproduced signal, the reflectance of the recording film surface of the disc is lowered, but in this case, the focus is more likely to be locked on the surface of the protective layer of the disc. .

An object of the present invention is to provide a focus pull-in method for an optical disc device that solves the above-mentioned problems.

[Means for solving problems]

The above objective can be achieved as follows. That is, after detecting a light beam reflection signal from the surface of the disk protective layer that occurs during focus pull-in, the focus servo is closed and the protective layer surface is once locked, and then the focus pull-in operation is repeated again. During this repeated retracting operation, the timing at which the focus servo is closed is set to be longer than the time required to lock onto the surface of the protective layer.

[Effect]

The operation of the present invention will be explained below.

After detecting the light beam reflection signal from the surface of the disk protective layer that occurs when the focus is pulled in, the focus servo is closed and the protective layer surface is once locked. After that, the focus servo is opened and the focus pull-in operation is repeated again. During this repeated operation, the timing at which the focus servo is closed is set to be longer than the time required to lock onto the surface of the protective layer. If you do K like this,
Since the focus servo is closed after the reflected signal from the surface of the protective layer has been completely detected, the focus servo does not pull in on the disk protective layer surface, and can be reliably pulled into the recording film.

Note that when performing the focus pull-in operation again, the timing for closing the focus servo may be set using, for example, a micro combinator. That is, when the focus is locked to the surface of the protective layer, the time Ts required for locking the focus is counted in advance, and when the retracting operation is performed again, a time longer than the Ts is set,
Close the focus servo.

〔Example〕

The present invention will be explained using the embodiment shown in FIG. 1 and the waveform diagram of each part shown in FIG. Further, in FIG. 1, parts having the same functions as those of the prior art shown in FIG. 2 are designated by the same numbers, and their explanations will be omitted.

In FIG. 1, 23 is a CPU (C47LλhaL p
4tb4jjLtLtU90). CPU 2
In many cases, 5 uses a single-chip microcontroller that houses ROM, RAM, and an I10 board in a 1f block.
ROM.

It may also be a multi-chip microcomputer that has external AM, I10 extended latches, buffers, etc. and an address decoder. In either case, the CPU 23 has a plurality of input ports and output ports, and controls these input and output ports according to a program recorded in advance in the ROM. This CPU 23 controls each f-point including the focus of the optical disc device.

In FIG. 1, an optical system from a light source 1 through a disk 10 to a photodetector 11, 12, a focus servo group from a differential amplifier circuit 13 to an actuator 17, and a first,
The operation of the focus pull-in circuit consisting of the second comparator circuit, ANDOo path 19, etc. is the same as that of the prior art shown in FIG.
The focus pull-in operation according to No. 1 will be mainly explained. Reference numeral 100 is a LASW signal, which stops light emission from the light source 1 such as a semiconductor laser when it is at the 'H' level, and starts emitting light from all the light sources 10 when it is at the jLI' level. 101 is the FOK signal, which releases the focus servo when it is at gLm level.
Or, it indicates that the focus servo is locked at the #)l ml level, and is input to the CPU 23. 102 is F! , AG flaw signal, and the AND circuit 19 to control the opening and closing of the loop switch 15.

In FIG. 6, the LASW signal 100 (FIG. 6A) is at 1H level and the light source 1 stops emitting light until timing T1. Next, at timing T1, LASW signal 1
00 to 1L'' level to cause the light source 1 to emit light, and set the FLAG signal 102 (Fig. 6E) to the g Hml level. When the converging lens 6 approaches the disk 10, the surface of the protective layer of the disk 10 An error signal is generated as shown in FIG. 6B due to the reflected signal from the E+. , E2, the AND circuit 19 output becomes #Hml level,
The loop switch 15 is closed and the focus is pulled in on the surface of the protective layer. The CPU 23 uses a timer to calculate the time Ts from the timing T1 when the light source 1 emits light to the timing T2 when the focus is pulled in on the surface of the protective layer.
The value is stored in RAMK. After that, timing T
Press I to stop light source 1 from emitting light and temporarily turn off the focus servo. Subsequently, at timing T4, the light source 1 is caused to emit light, and at the same time, the converging lens 6 is brought close to the disk 10 again. At this time, the reflected signal from the surface of the protective layer appears again at timing Ts, but the FLAG signal 102 (FIG. 6E) remains gL for at least Ts from timing T4.
Since it is the m level, the first. The input signals of the second comparator circuit 18.21 correspond to the respective threshold voltages E1. Even if H2 is exceeded, the output of the AND circuit 19 (D in FIG. 6) maintains the gLm level. Therefore, since the loop switch f-15 remains open, the focus is not drawn on the surface of the protective layer. Next, the FLAG signal 102 is set to 1 at timing T4 when the time Tr from 1 timing T4 becomes longer than the above-mentioned Ts.
After that, the reflected signal from the recording film exceeds the threshold voltage B1.E2 of each of the first and second comparator circuits 18 and 21, and the output of the AND circuit 19 becomes 1H level. Loop switch 1 at the timing of T7
5 closes, focus retracts.

Note that whether the focus is locked on the surface of the protective layer at timing T2 is determined by the tracking error signal (circuit and operation waveforms not shown), although detailed explanation is omitted.
The judgment can be made by detecting the presence or absence of the . Conversely, if the reflected signal level from the surface of one protective layer is extremely reduced due to dust, scratches, etc., there is a possibility that the signal may not be pulled in once on the surface of the protective layer, but suddenly pulled in at the recording film. In this case as well, the determination can be made by detecting the presence or absence of a tracking error signal as described above.

Further, the general algorithm of the CPU 23 will be explained using the flowchart of FIG.

(1) Timing memo to set the FLAG signal to 1H'' level at the start!l (hereinafter referred to as FLAGON)
(referred to as timing memory).

(2) Activate the timer function.

(3) As the light source emits light, the converging lens is raised.

t41 FIJAG O? '(Check whether the time indicated by the timing memory has elapsed (at the time of initial reset, the FLAGON timing memory is zero, so the process immediately passes).

+51 Set the FLAG signal to 1H'' level and wait for the focus to lock.

(61) After the focus is locked, it is checked whether or not it is locked on the surface of the protective layer (the checking method is performed based on the presence or absence of a tracking error signal as described above).

(7) Initially it locks on the surface of the protective layer, so FLAG
A time obtained by adding a preset predetermined time to the time from light emission of the light source to focus lock is stored in the ON timing memory.

(8) Stop the light source and guide the converging lens to the lowest point.

(9) Turn on the light source again and raise the converging lens.

Wait the time indicated in the QfI FLAGON timing memory and set the FLAG signal to 1H'' level.

However, if the focus is locked, check whether it is locked with the recording film. If it locks on the surface of the protective layer, it will reactivate again within the time indicated in the FLAG ON timing memory (in this case, the time required to lock on the surface of the protective layer at the initial reset is added to the predetermined time). The time added to the predetermined time is stored again, and the retracting operation is repeated.

With the above operation, it is possible to prevent the focus from being locked on the surface of the protective layer of the disc using the CP/U 23.

Note that after the focus is locked on the surface of the protective layer, F L
The timing for setting the AG signal to 1H'' level is set to the time required for locking on the surface of the protective layer plus a predetermined time, but the length of this predetermined time is determined as follows. In other words, the time interval between the reflection signal from the recording film surface and the reflection signal from the recording film that occurs when the converging lens 6 is raised is measured in advance, and variations in the raising speed of the converging lens 6 are taken into consideration. After that, an appropriate value (for example, the time when the dot is at the center) can be set.

The feature of this embodiment is that since it is controlled using a CPU, it can be realized with a small number of parts.

〔Effect of the invention〕

According to the present invention, when the focus is once locked on the surface of the disk protective layer and then the retraction operation is performed again, the focus servo is closed by setting a time longer than the time required to lock the focus on the surface of the protective layer. Therefore, there is no malfunction where the focus is pulled in on the surface of the protective layer.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram of the prior art, Fig. 3 is a waveform diagram of each part in the block diagram of the prior art to explain the operation, and Fig. 4 is a comparator peripheral circuit. Details #1 and FIG. 5 are waveform diagrams of various parts to explain malfunctions in the block diagram of the prior art, FIG. 6 is a waveform diagram of various parts to explain the operation in another embodiment of the present invention, and FIG. 7 is a flowchart of the CPU in another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Light source, 10... Disk, 13... Differential increase @ circuit, 15... Loop switch, 18... First comparator circuit. 19.-A N D circuit, 21.. second comparator circuit, 23.-CPU. W550 4th mouth jth ≦ prisoner

Claims (1)

[Claims] 1. The first reflected light from the information recording medium that occurs during focus servo pull-in and the second reflected light that occurs subsequent to the first reflected light are detected by a photodetector, respectively, as first reflected signals;
After detecting the second reflected signal, the focus servo is configured to be closed after detecting the first reflected signal, and the focus servo is once locked, and then the focus pull-in operation is repeated again, and this focus pull-in 1. A focus pull-in method for an optical disc device, comprising: means for setting a timing for closing a focus servo to be longer than the time required for the first focus lock when repeating the operation.