JPH01260635A - Focus servo control system for optical disk device - Google Patents

Abstract

PURPOSE:To prevent the shift of a focus point due to the write (record) operation of an optical disk by providing a focus servo control part with a circuit to generate an offset signal from write data to an optical head, and correcting a focus error signal by the offset signal. CONSTITUTION:In an optical disk device provided with the focus servo control part 4 to control the focus position of the optical head 2 according to the focus error signal, the focus servo control part 4 is provided with the circuit 48 to generate the offset signal from the write data to the optical head 2, and the focus error signal is corrected by the offset signal. Namely, by canceling offset occurring at write time, the focus error signal FES free from the offset can be obtained even in the course of write. Thus, the variation of the focus position in the course of the write to the optical disk can be prevented, and the write operation can be performed as keeping the focus position at a just focus position.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Fig. 5) Problem to be solved by the invention (Fig. 6) Means for solving the problem (Fig. 1) Effect implementation Example (a) Explanation of the configuration of one embodiment (Figures 2 and 3) (b)
Explanation of the operation of one embodiment (Fig. 4) (C) Description of another embodiment Effects of the invention [Summary] A focus servo control unit device for plagiarizing the position of the optical beam of the optical beam of the optical head of an optical disk device. (Regarding this, an optical head that irradiates a light beam onto an optical disc and receives light from the optical disc to obtain a light reception signal for the purpose of preventing the focus point from moving due to a write operation on the optical disc; In an optical disk device including a focus servo control unit that determines a focus error signal from the light reception signal and controls a focal position of the optical head based on the focus error signal, the focus servo control unit is configured to transmit write data to the optical head. A circuit for creating an offset signal from the focus error signal is provided, and the focus error signal is corrected using the offset signal.

[Industrial Application Field] The present invention relates to a focus servo control method for controlling the focus position of irradiated light from an optical head of an optical disc device.

Optical disk devices are attracting attention as large-capacity storage devices because the track spacing can be several microns.

In such optical disk devices, optimal control of the focus position of the light beam is essential to maintain good read and write characteristics, and in particular, technology to control the focus position so that it does not change due to write operations is required. It has been demanded.

[Conventional technology]

FIG. 5 is an explanatory diagram of the prior art.

The optical disc device has a motor 1 as shown in FIG. 5(A).
The optical head 2 is moved and positioned in the radial direction of the optical disc 1 by a motor (not shown) with respect to the optical disc 1 rotating around the rotation axis by the optical head 2, and the optical head 2 reads (plays)/writes (records) the optical disc 1. will be held.

On the other hand, the optical hand 2 guides the emitted light from the semiconductor laser 24, which is a light source, to the objective lens 20 via the lens 25 and the polarizing beam splinter 23. The optical disk 1 is configured such that the reflected light from the optical disk 1 is incident on a four-division light receiver 26 via a polarizing beam splitter 23 via an objective lens 20.

In such an optical disk device, a large number of tracks or pits are formed at intervals of several microns in the radial direction of the optical disk 1, and even slight eccentricity causes a large displacement of the trunk, and undulations of the optical disk 1 cause the beam spot to change. Focus position shifts occur, and it is necessary to follow these position shifts with a beam bond of 1 micron or less.

For this purpose, a focus actuator (focus coil) 22 moves the objective lens 20 of the optical head 2 in the vertical direction in the figure to change the focal position, and a focus actuator (focus coil) 22 moves the objective lens 20 in the horizontal direction in the figure to change the irradiation position in the tracking direction. A track actuator (track coil) 21 for changing is provided.

Correspondingly, the focus servo control section 4 generates a focus error signal FES from the light reception signal of the light receiver 26 and drives the focus actuator 22, and generates a 1-rank error signal TES from the light reception signal of the light receiver 26. A track actuator 21 is generated and a track actuator 21 is driven by a track actuator 1 to a track actuator control unit 3.

The principle of focus servo control is as shown in Figure 5 (B).
A light beam 1. is placed on the recording surface of the optical disc 1. BS When the S is in focus, f is the case, and when the focus is shifted back and forth, it is f2.
, fl, as shown in FIG. 5(C), the light receiver 26
The focus position is detected by utilizing the difference in the distribution of the amount of reflected light on the four-divided light-receiving surfaces 26a to 26d.

That is, when the focal point position is far from 11, as shown in the received light amount distribution on the right side of FIG.
When the light is received at 6<1 and the focus position is f, all the light receiving surfaces 26a to 26d are
When the light is received and the focal position is close to f2, as shown in Fig.
As shown on the left side of the figure, the light is received by the two halves of the light receiving surfaces 26a and 26c.

Therefore, the focus error signal FES can be obtained from the outputs a to d of the light receiving surfaces 26a to 26d, and the S-shaped signal shown in FIG. 5(D) can be obtained.

That is, F E S = 0 is the focused point, and the level increases as you move away from the focused point.

Therefore, by driving the focus actuator 22 and driving the objective lens 20 up and down using the focus error signal FES, the focus of the irradiated light can be made to follow the recording surface of the optical disc 1 on the submicron order, regardless of the waviness of the optical disc 1. I can do it.

[Problem to be solved by the invention]

By the way, recording (writing) on an optical disk medium with a light beam changes the reflectance.
Proportional to the product of the intensity of the light beam.

When such writing is performed, a problem arises in that an offset occurs in the focus error signal FES during writing, and the focus position moves.

That is, as shown in FIG. 6(A), when the distribution of the amount of reflected light for one light pulse is shown, during writing by the light pulse, the level of the amount of reflected light changes, and the level of the amount of reflected light changes as shown in FIG. The distribution of the amount of reflected light on the light receiving surfaces 26a to 26d also changes.

As a result, although before writing, FES = 0 at the focused point, during writing, from equation (1), FES - α
-(2), and an offset occurs.

With this offset, as shown in FIG. 6(B),
The focus servo signal FSV is swung, driving the focus actuator 22 and moving the focus position by the offset α, making it impossible to change the focus state during writing, resulting in a large light beam and an insufficient light intensity. It became sufficient and a write failure occurred.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus servo control method for an optical disc device that can prevent a focus point from moving due to a write operation on an optical disc.

Means to solve problem C8] FIG. 1 is a diagram showing the principle of the present invention.

As shown in FIG. 1, the present invention includes an optical head 2 that irradiates a light beam onto an optical disc 1, receives light from the optical disc 1 to obtain a light reception signal, and calculates a focus error signal from the light reception signal. , a focus servo control unit 4 that controls the focal position of the optical head 2 based on a focus error signal, the focus servo control unit 4 receives an offset signal from write data to the optical head 2. A circuit 48 is provided to correct the focus error signal using the offset signal.

[Effect]

In the present invention, by canceling the offset α that occurs during writing, a focus error signal FES without offset is obtained even during writing, and the in-focus position is maintained.

By creating the write offset signal OFS that cancels this from the write data, it is possible to generate the write offset signal OFS only during writing, and also to generate an offset of a value proportional to the duty of the write data, thereby accurately determining the focus position. can be kept.

〔Example〕

(a) Description of the configuration of one embodiment FIG. 2 is a configuration diagram of an embodiment of the present invention.

In the figures, the same parts as those shown in FIGS. 1 and 4 are indicated by the same symbols.

Reference numeral 5 denotes a control section, which is composed of a microprocessor, and controls the optical head 2 by a servo control operation of the focus servo control section 4, a servo control operation of the track servo control section 3 (see FIG. 5(A)), and a movement motor (not shown). It controls the movement of.

6a is an RF generation circuit, which generates an RF signal (read signal) RI? 6b is an amplifier circuit that amplifies the output a%d of the 4-split optical receiver 26, and generates the servo output SVa -SV
It outputs d.

7a is a pulse width control circuit (Lie 1-pulse creation circuit), which controls the pulse width (inner) corresponding to the position of the head 2 (inner/outer =) from the MPU 5 in response to the write pulse (write data) from the upper level. 7b is a write circuit that creates the write data (narrow width, wide width on the outer side), and 7b is a write circuit that generates write data from the semiconductor laser 2 of the optical head 2.
4.

40 is an FES generation circuit, which generates a focus error signal F from the servo output S V a −S V d of the amplifier 6a.
ES is created, 41 is a total signal creation circuit, which adds the servo outputs S V a - S V d to create a total signal DSC which is a total reflection level, 42 is an AG
C(＾utoma'tic Ga1n Control
) circuit, which converts the focus error signal FES into the entire signal (
Total reflection level) is divided by DSC and AGC is performed using the total reflection level as a reference value, and is used to correct fluctuations in irradiation beam intensity and reflectance.

'13a is a zero-crossing detector that detects the zero-crossing point of the focus error signal FES and outputs the focus zero-crossing signal FZC to M1) U5; 43b;
is an off-focus detection circuit, which turns off when it detects that the focus error signal FES has exceeded a certain value VO in the positive direction and has become below a certain value -Vo in the negative direction, that is, it has entered an off-focus state. 44 is a phase compensation circuit that outputs the focus signal FO3 to the MPU 5, which differentiates the focus error signal FES given a gain, adds it to the proportional part of the focus error signal FES, and advances the phase of the high frequency range. It is.

45 is a servo switch, which closes when the servo-on signal SVS of the MPU 5 is turned on, closes the servo loop, and opens when it is turned off, opening the servo loop; 46 is an inverting amplifier, which inverts the output of the servo switch 45; , 47 is a power amplifier, which amplifies the output of the inverting amplifier 46,
A focus drive current F is applied to the focus actuator 22.
It outputs DV.

48 is the aforementioned write offset correction circuit, which creates a write offset from the write data rite Data and subtracts it from the focus error signal FES.

FIG. 3 is a diagram showing the main part of an embodiment of the present invention.

In the figure, the same components as those shown in FIG. 2 are shown with the same symbols, and the FES creation circuit 40
and SVc through input resistors r1 and r3, an adder amplifier 401 which adds servo outputs svb and SVd through input resistors r2 and r4, and an adder amplifier 400 that adds servo outputs svb and SVd through input resistors r2 and r4, respectively, and an adder amplifier 400 that adds servo outputs svb and SVd through input resistors r2 and r4, and an adder amplifier that uses the output (SVa+5Vc) of the adder amplifier 400. The adder amplifier 402 subtracts the output ('SVb + 5Vd) of the 401, and the focus error signal FES (-(SVa + 5Vc) - (SVb +
Outputs 5Vd)l.

The total signal generation circuit 41 includes an addition amplifier 410 that adds each servo output SVa to SVd via input resistors r5 to r8, and generates a total reflection level signal DC3 (-3Va+5Vb-1
-3Vc+5Vd).

The AGC circuit 42 includes a first operational amplifier 420 to which the focus error signal FES is input, and a first operational amplifier 4
20, the first I? ET (field effect transistor) 421 and total reflection level signal DC3 are input, and F
a second operational amplifier 422 that controls the ET421;
A second FE that divides and controls the input side of the operational amplifier 422 of
T423, the first FET 421 is controlled by the total reflection level signal DC3 which is the output of the operational amplifier 422, the gain of the operational amplifier 420 is controlled, and the focus error is AGCed from the output of the operational amplifier 420 (FES/DC3). The signal FES is obtained, and the second FES is obtained.
The ET 423 is provided to compensate for the non-linear characteristics of the first FET 421 and give it linear characteristics.

The write offset correction circuit 4 includes a write offset creation circuit 48a and an addition circuit 48b.

The write offset creation circuit 48a is a write offset generating circuit 48a.
An inverted Hanwha BF that inverts Wri b mouth aLa,
It has voltage adjustment resistors r1, r7, and r3, and integrates write data *Write Data to write off cell 1.
~Create the signal OFS.

The adder circuit 48b is connected to the AG input manually through the human resistor r5.
From the focus error signal FES after C, input resistance r4
It subtracts the offset signal OFS inputted through the offset signal OFS and outputs it to the phase compensation circuit 44.

Note that "6 is a gain adjustment resistor.

(b) Description of operation of one embodiment FIG. 4 is an explanatory diagram of the operation of one embodiment of the present invention.

In the servo-on state, the focus error signal FES of the focus error generation circuit 40 is AGC-controlled, phase-compensated by the phase compensation circuit 44, enters the inverting amplifier 46 via the servo switch 45, and is sent to the actuator 22 by the power amplifier 47 as a focus servo signal. Drive.

If it is not in RIE I~, then RIE 1~ data has not been input, so OFS is zero, and AGC
The subsequent focus error signal FES is input to the phase compensation circuit 44, and focus servo control is performed according to equation (1).

On the other hand, when writing is performed, the 4-split light receiver 2 at the time of writing
Letting the outputs of 6 be a (w) to d (w), the focus error signal FES is as follows.

α is offset 1- and is proportional to lie 1~data.

That is, the offset is large when data with a high duty is being written, and becomes small when data with a low duty is being written.

Therefore, the write data *Write Data is integrated, the write offset α is created in the write offset sensor l-creation circuit 48a, and the adder circuit 48b subtracts it from the focus error signal FES after AGC to set the offset of the focus error signal FES. erase.

As a result, the offset of the focus error signal -F that occurs during writing is canceled, and there is no focus servo shake, and writing can be performed while maintaining the in-focus point.

Therefore, the write operation can be performed satisfactorily without causing insufficient light intensity.

Also, since it is created from the write 1 data, a write offset proportional to the duty of the write data can be obtained.
It is possible to accurately cancel the offset on the focus error signal.

(C) Description of other embodiments In the above embodiments, the light offset correction circuit 48 was explained as having the configuration shown in FIG. The parts may also have other configurations.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent the fluctuation of the frame position that occurs during writing to an optical disc, and to perform the writing operation while maintaining the just focus position, thereby spreading the light beam. , the strength is insufficient,
There is no possibility of a light failure.

Further, it has the effect that it can be realized by relatively simple means, and the write characteristics can be improved easily and at low cost, which greatly contributes to improving the performance of the optical disk.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a block diagram of main parts of an embodiment of the present invention, Fig. 4 is an explanatory diagram of the prior art, and Fig. 5 is a diagram of the principle of the present invention. The figure is an explanatory diagram of problems in the prior art. In the figure, 1-optical disk, 2-optical head, 4-focus servo control section, 48-write offset correction circuit. Procedural amendment (method) Yoshi Yoshi, Commissioner of the Patent Office 1) Mr. Tsuyoshi Moon■, Indication of the case Patent Application No. 886134, 1986 2
, Title of the invention Focus servo control method 3 for optical disk devices, relationship to the case of the person making the correction Patent applicant address 1015 Kamiodanaka, Nakahara-ku, Yozaki City, Kanagawa Prefecture Name (522) Fujitsu Co., Ltd. Representative Taku Makoto Yamamoto 4. Address of the agent: 1-19-8 Kanda-Awaji-cho, Chiyoda-ku, Tokyo Date of delivery: June 28, 1988 6. Number of inventions increased by amendment None 7. Subject of amendment Brief description of drawings in the specification Explanation Column Correction Contents 1, Page 18 of the Specification, Lines 11 to 15 [FIG. 1 is an explanatory diagram. ' shall be corrected as follows. [Figure 1 is a diagram showing the principle of the present invention, Figure 2 is a diagram showing the configuration of an embodiment of the invention, Figure 3 is a diagram showing the configuration of essential parts of an embodiment of the invention, and Figure 4 is a diagram showing the operation of an embodiment of the invention. FIG. 5 is an explanatory diagram of the prior art, and FIG. 6 is an explanatory diagram of problems with the prior art. 1 or more

Claims (1)

[Claims] (1) An optical head (2) that irradiates a light beam onto an optical disc (1) and receives light from the optical disc (1) to obtain a light reception signal; and a focus error signal that is determined from the light reception signal and a focus error signal. In an optical disc device comprising a focus servo control section (4) that controls a focal position of the optical head (2) based on a signal, the focus servo control section (4)
) is provided with a circuit (48) for creating an offset signal from write data to the optical head (2), and the focus error signal is corrected by the offset signal.