JPH01263947A - Tracking servo control system for optical disk device - Google Patents

Abstract

PURPOSE:To prevent the excessive detection of a servo error at the time of writing by gating a servo error signal with a gate signal to mask the rear of the ID part of an optical disk. CONSTITUTION:In a tracking servo control part 3 to tracking-servo-control an optical head 2 based on a tracking error signal, an off-track detecting circuit 34b to compare the tracking error signal at a prescribed slice level and to generate the servo error signal, and a gate circuit 38 to gate the servo error signal at the rear of the ID part of an optical disk 1 by the gate signal are provided. Thus, the servo error detection can be masked at the rear of the ID part for a suitable time, and the excessive detection of the tracking servo error can be prevented.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Prior Art (Figs. 5 and 6) Problems to be Solved by the Invention (Fig. 7) Means for Solving the Problems (Fig. 1) Figure) Working Example (a) Explanation of the configuration of one embodiment (Figures 2 and 3) (b) Explanation of the operation of one embodiment (Figure 4) (C) Explanation of another embodiment of the invention Effect [Summary] Regarding the track servo control method that detects the position of the optical head of an optical disk device with respect to the track and controls the optical beam to follow the track, a servo error during writing occurs when the ID is not formed at the center. In order to prevent over-detection of the optical disc, the optical head irradiates the optical disc with a light beam, receives the light from the optical disc, and obtains a received light signal. In the optical disk device, the optical disk device includes a track servo control unit that performs track servo control of the optical head based on the track servo control unit, in which the track servo control unit includes an off-track detection unit that compares the track error signal at a predetermined slice level and generates a servo error signal. and a gate circuit that gates the servo error signal with a gate signal that masks the rear of the ID section of the optical disc.

[Industrial application field]

The present invention relates to a track servo control method for detecting the position of a light beam of an optical head of an optical disk device with respect to a trunk and controlling the tracking of the light beam to a track.

Optical disk devices are attracting attention as large-capacity storage devices because they can read/write using light beams, allowing the trunk spacing to be several microns.

In this optical disk device, track servo control is used to control the tracking of a light beam to the relevant track.

In track servo control, a track error signal is obtained using diffraction of a guide groove (pre-group) of an optical disk medium, and a servo is applied to cause a spot light to follow a track (guide groove).

In such track servo control, there is a need for a technique for controlling to avoid servo errors during writing.

[Conventional technology]

FIG. 5 is an explanatory diagram of the track servo.

As shown in FIG. 5(A), the optical disc device has a motor 1a.
For the optical disc 1 rotating around the rotation axis,
The optical head 2 is moved and positioned in the radial direction of the optical disc 1 by a motor (not shown), and the optical head 2 reads (reproduces)/writes (records) onto the optical disc 1.

On the other hand, the optical head 2 guides the light emitted from the semiconductor laser 24, which is a light source, to the objective lens 20 via the lens 25 and the polarizing beam splitter 23. The light reflected from the optical disc l is configured to enter a four-split light receiver 26 from a polarizing beam splinter 23 via an objective lens 20.

In such an optical disc device, a large number of tracks or bits are formed at intervals of several microns in the radial direction of the optical disc 1, and even slight eccentricity causes large track positional deviations, and undulations of the optical disc 1 cause the beam spot to change. Focus position shifts occur, and it is necessary to make the beam spot of 1 micron or less follow these position shifts.

For this purpose, a focus actuator (focus coil) 22 that 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 that moves the objective lens 20 in the horizontal direction in the figure to change the irradiation position in the track direction. A track actuator (track coil) 21 is provided to change the position.

Correspondingly, the focus servo control section 4 generates a focus error signal FES from the light reception signal of the light receiver 26, drives the focus actuator 22, and generates a track error signal TES from the light reception signal of the light receiver 26. , a truck servo control section 3 that drives the trunk actuator 21 is provided.

The principle of track servo control is to utilize the diffraction phenomenon of the beam spot BS by a spiral guide groove (track) 10 provided in advance on the optical disc 1, as shown in FIG. 5(B).

That is, depending on the position of the beam spot BS with respect to the track 10, the reflected light amount distribution on the light receiver 26 is
The position error of the beam spot with respect to the track 10 is obtained by utilizing changes caused by the diffraction of light by O.

For example, the light receiver 26 has 26a, 26b, 26c, 26d.
When using the push-pull method using a 4-split receiver, the distribution of the amount of reflected light on the receiver 26 is as shown in FIG. Figure (D), when the beam spot is at P with respect to track 10 (in the case of on-trunk), Figure 5 (E), and when the beam spot is at P2 with respect to truck 10, Figure 5 (F). Become.

Therefore, the track servo control unit 3 controls the light receivers 26a to 2.
When ((a+b) - (c+d)) is obtained from the outputs a-d of the outputs 6d, the track error signal TBS shown in FIG. By driving in the direction, the beam spot can be controlled to follow the track 10 of the optical disc 1 regardless of the eccentricity of the optical disc 1.

FIG. 6 is an explanatory diagram of the prior art.

In the servo-on state, the track error signal TBS is normally below the slice level, and the light beam follows the track.

On the other hand, in order to detect that the light beam has deviated from the track, an off-track detection circuit is provided, and the off-track detection circuit compares the track error signal TBS with a predetermined slice level SL,
When the amplitude of S exceeds the slice level SL, the servo becomes off-track, which cannot be followed, and a servo error signal is generated.

If a servo error occurs while the servo is on, the track servo is immediately interrupted and the write or read operation is stopped.

[Problem to be solved by the invention]

FIG. 7 is a diagram illustrating problems in the prior art.

Incidentally, writing on the optical disc 1 is performed in units of one sector, and an ID (mark) is provided at the beginning of the sector.

The ID is formed by a preformatted pit PT at the center of the land 10 of the disk medium 1, as shown in FIGS. 7(A) and 7(B).

If this pit PT, like PT', is not located exactly at the center of the land 10, a track error signal TBS is generated as shown in FIG. 7(C) by the ID of the pit PT', and a light beam is generated.

This swung return is shown by the dotted line, and is below the slice level SL at the time of reading, so it does not pose a problem.

However, this shaken location (i.e., ID pit PT'
If you start writing from a location (where 0 is not in the center), the sensitivity of the TES increases during writing, so the track error signal TBS will rise to the slice level S, as shown by the solid line in Figure 7(C).
It may exceed L.

This means that even if the actual amount of off-track is small and well within the margin, the sensitivity of the TES increases during writing, so the track error signal may exceed the slice level.
This causes a servo error, resulting in a problem of over-detection of the error.

The reason why the sensitivity increases during writing is that the writing starts at the return portion swung by the 10 pits, and the light changes greatly in the amount of reflected light, so the sensitivity increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a track servo control method for an optical disk device that can prevent over-detection of servo errors during writing that occur when the ID is not formed at the center.

(Means for solving problems) 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 received light signal, and obtains a track error signal from the received light signal. In an optical disk device having a trunk servo control section 3 that controls the trunk servo of the optical head 2 based on a track error signal, the track servo control section 3 compares the track error signal at a predetermined slice level and performs servo control. An off-track detection circuit 34b that generates an error signal and a gate circuit 38 that gates the servo error signal with a gate signal that masks the rear of the ID section of the optical disc 1 are provided.

[Effect]

Since a servo error is detected when writing after the ID section, the present invention creates a gate signal that masks servo error detection for an appropriate time after the ID section, and masks the servo error signal. This prevents excessive detection of servo errors.

For example, a masking time of about 1/10 of one sector is sufficiently effective. Also, even if a real error occurs within this time, it can be sufficiently detected after masking because the light beam does not move very quickly.

〔Example〕

(a) Description of the configuration of one embodiment FIG. 2 is an overall 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 servo control operation of the track servo control section 3 and the servo control operation of the focus servo control section 4 (see FIG. 5).

60 is an RF generation circuit, and the output a of the 4-division light receiver 26
61 is an amplifier circuit that creates an RF signal (read signal) RFS from w d, which amplifies the output aw d of the 4-split light receiver 26 and outputs a servo output of 5 Va-sva.

62 is a sector detection circuit, which generates a sector detection signal from the rotation of the optical disc 1; 63 is an ID read gate generation circuit, which generates an ID read gate from the sector detection signal.
64 is a pulse generation circuit that generates the D IJ-dog gate signal DG, pulses the RF signal RFS, reproduces it into read data, and outputs ID data and normal data by distinguishing them according to the ID read gate signal DC. things, 6
5 is an ID read circuit, which assembles ID data and notifies the control unit (MPU) 5.

66 is a write pulse generation circuit, which converts upper write data into a write pulse having a width according to the inner/outer signal of the MPU 5; 67 is a write circuit, which drives the semiconductor laser 24 with the light pulse; This is what allows the light to operate.

30 is a TBS creation circuit, which includes an amplifier 61 (61a~
61d) creates the track error signal TES from the servo outputs 5Va-SVd, and 31 is a total signal creation circuit which adds the servo outputs SVa-ySVd to create the total signal DSC which is the total reflection level. , 32
A G C (Automatic Ga1nCont
rol) circuit, which divides the track error signal TES by the total signal (total reflection level) D, C3, performs AGC using the total reflection level as a reference value, and compensates for fluctuations in irradiation beam intensity and reflectance. It is something.

33 is a phase compensation circuit, which outputs the track error signal TBS.
and add it to the proportional bone of the track error signal TBS,
This advances the phase of the high range.

34a is a zero-crossing detector which detects the zero-crossing point of the track error signal TES and outputs the track zero-crossing signal TZC to the MPU 5; 34b is the aforementioned off-track detection circuit which detects the zero-crossing point of the track error signal TBS;
is a constant value in the positive direction■. (SL) or more and a constant value in the negative direction -■. (-3L) or less, that is, an off-track state is detected, and an off-track (servo error) signal TO3 is output to the MPU 5.

35 is a servo switch, which closes when the servo-on signal SvS of the MPU 5 is turned on, closes the servo loop, opens when it is turned off, and opens the servo loop; 36 is an inverting amplifier, which inverts the output of the servo switch 35; 37; is a power amplifier, which amplifies the output of the inverting amplifier 36 and provides the track drive current TDV to the track actuator 21.

38a is a play (delay) circuit, which delays the ID read gate signal DG to create the gate signal GT; 38 is the aforementioned gate circuit, which is composed of an AND gate, and which outputs the gate signal GT and the off-track signal; This is for calculating the AND of TO3 and notifying the MPU 5 of a servo error.

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

The TES creation circuit 30 includes an addition amplifier 300 that adds the servo outputs SVa and Svb through input resistors rlsr2.
And servo output SVc,! :SVd for each input resistance r3,
Adding amplifier 301 that adds via r4 and adding amplifier 3
Adding amplifier 301 from the output of 00 - (SVc + 3yd)
Addition amplifier 30 that subtracts the output of -(SVs+5vb)
track error signal TBS(-(SVa+5Vb)-(SVc+5Vd)) from the addition amplifier 302.
Output.

The entire signal generation circuit 31 has each servo output SVa to SVd.
summing amplifier 310 that adds the values through input resistors r, ~r8.
total reflection level signal DC3 (=SVa+SVb+
SVc+5Vd).

The AGC circuit 32 includes an operational amplifier 320 to which the trunk error signal TBS is input, and a first FET (field effect transistor) 321 that controls the voltage division of the input side of the first operational amplifier 320 according to the output of the operational amplifier 320. A second operational amplifier 322 receives the total reflection level signal DO3 and controls the FET 321;
A total reflection level signal DC which is the output of the operational amplifier 322.
5 controls the first FET 321, and the operational amplifier 3
The gain of the second FET 323 is controlled to obtain the AGC track error signal TBS of (TES/DO3) from the output of the operational amplifier 320.
This is provided to compensate for the non-linear characteristics of the FET 321 and provide it with linear characteristics.

The zero-cross detector 34a includes a comparator 340 that compares the trunk error signal TBS from the AGC circuit 32 with a zero-cross potential, and outputs a zero-cross signal TZC from the comparator 340.

The off-track detection circuit 34b compares the track error signal TBS from the AGC circuit 32 with a constant value V0, and
The first comparator 341 outputs a "low" output when BS>V2O, and the track error signal TBS and a constant value (-
V. ), TBS<-V. The second comparator 342 outputs a "low" output when
3 and an inverting circuit 343 that outputs 3.

The play circuit 38a is composed of a shift register, and has an ID
For reading, the gate signal DC is delayed for a predetermined time to create a gate signal GT with a constant time width (1/10 of one sector or less).

The gate circuit 38 performs an AND operation between the off-track signal TO3 of the inversion circuit 343 and the gate signal GT of the play circuit 38a.

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

When the MPU 5 receives a seek command from the host, it controls a moving motor (not shown) to position the optical head 2 near the target track, turns on the servo-on signal SvS, pulls in the track servo, and controls the track servo.

The optical disc 1 is a write-once type, and a preformatted ID bit is formed at the beginning of a sector.

The sector detection circuit 62 generates a sector detection signal in accordance with the beginning of the sector, and the ID read gate generation circuit 63 generates an ID read gate signal.
The ID read gate DG is generated in synchronization with the ID read gate DG.

If this ID pit is not at the center of the land 10, a track error signal TBS will be generated at the ID section, as shown in FIG.

The return of this swing is small because it is not recorded when reading.
The slice level V0, -Vo also applies to the ID and return.
not exceed.

However, in writing, since the semiconductor laser 24 writes immediately after rD, it is synchronized with the return of the deflection, and the amount of reflected light changes greatly during writing, resulting in high sensitivity (and actually off-track). Even though there is no servo error, the slice level v0 is exceeded, and the comparator 341 of the off-track detection circuit 34b is low.
The i-th TOS is generated and inverted by the inverting circuit 343, and an off-track signal (error signal) TO3 is output to the gate circuit 38 as shown in FIG.

On the other hand, the gate circuit 38 has an ID read gate signal DG.
A mask signal (gate signal) GT shown in FIG. 4 which is delayed is inputted, and this signal is at a low level for a certain period of time after the ID section.

Therefore, since the gate circuit 38 masks the error signal TO3 for a certain period of time after ID using the mask signal GT, M
It is not output to the PU5 as shown in FIG.

Of course, during other periods, since the mask signal GT is "high", the error signal TO3 of the off-track detection circuit 34b is directly notified from the gate circuit 38 to the MPU 5.

In this way, the servo error signal is masked for a certain period of time after ID, so the high sensitivity during writing allows TBS
Even if it exceeds the slice level and a servo error is detected, it will not be output to the MPU 5.

That is, since over-detection of servo errors during writing is prevented, it is possible to prevent the servo from being turned off due to such over-detection and the write operation from being stopped.

(c) Description of other embodiments In the embodiments described above, the servo error signal is masked for a certain period of time after ID during both read and write operations, but it may be masked only during write operations.

Furthermore, although the mask signal GT is created from the ID read gate signal, it may be created from other signals as long as the mask signal is created to mask the ID section for a certain period of time.

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, the optical disc ID
This has the effect of preventing over-detection of servo errors during writing that would occur if the land is not formed at the center of the land, preventing the write operation from being stopped due to over-detection, and making the write operation smoother. Further, it is possible to increase the margin of an optical disc preformatted with such an ID, and it becomes possible to use an optical disc in which an ID portion is not formed in the center of the land.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is an overall configuration diagram of an embodiment of the invention, Fig. 3 is a diagram of the main part of an embodiment of the invention, and Fig. 4 is an operation of an embodiment of the invention. FIG. 5 is an explanatory diagram of the track servo, FIG. 6 is an explanatory diagram of the prior art, and FIG. 7 is an explanatory diagram of the problems of the prior art. In the figure, 1-optical disk, 2-optical head, 3--track servo control section, 30--TBS creation circuit, 34b--off-track detection circuit, 38--gate circuit.

Claims (1)

[Claims] (1) An optical head (2) that irradiates an optical disk (1) with a light beam and receives light from the optical disk (1) to obtain a received light signal; and an optical head (2) that obtains a track error signal from the received light signal; In an optical disk device having a track servo control unit (3) that performs track servo control of the optical head (2) based on , an off-track detection circuit that generates a servo error signal (
34b), and a gate circuit (38) that gates the servo error signal with a gate signal that masks the rear of the ID section of the optical disc (1).
) A track servo control method for an optical disc device, characterized in that it is provided with: