JP2516659B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION [Table of Contents] Outline Industrial field of application Conventional technology (FIGS. 5 and 6) Problem to be solved by the invention (FIG. 7) Means for solving the problem (first Fig.) Action Embodiment (a) Description of configuration of one embodiment (Figs. 2 and 3) (b) Description of operation of one embodiment (Fig. 4) (c) Description of another embodiment Effect [Overview] Regarding an optical disk device that detects the position of the optical beam of the optical head of the optical disk device with respect to the track and controls the tracking of the optical beam to the track, there is a servo error error during writing that occurs when the ID is not formed in the center. For the purpose of preventing detection, an optical head that irradiates an optical disc with a light beam, receives light from the optical disc to obtain a light reception signal, and obtains a track error signal from the light reception signal, and based on the track error signal The optics In an optical disc device having a track servo control unit for performing track servo control of a head, an off-track detection circuit that compares the track error signal at a predetermined slice level to the track servo control unit and generates a servo error signal, A gate circuit that gates the servo error signal with a gate signal that masks after the ID portion of the optical disk is provided.

[Industrial applications]

The present invention relates to an optical disc device that detects the position of a light beam of an optical head of the optical disc device with respect to a track and controls the light beam to follow the track.

Since the optical disk device can read / write by a light beam, the track interval can be set to several microns, and it is attracting attention as a mass storage device.

In this optical disk device, track servo control is used to control the light beam to follow the track.

The track servo control obtains a track error signal by using the diffraction of the guide groove (pre-group) of the optical disc medium, applies servo, and tracks the spot light to the track (guide groove).
Is to follow.

In such track servo control, there is a demand for a technique for controlling so as not to cause a servo error during writing.

[Conventional technology]

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

The optical disk device has a motor 1a as shown in FIG.
The optical disc 1 that rotates around the rotation axis by
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 performs reading (reproduction) / writing (recording) on 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 polarization beam splitter 23, narrows the beam spot (spot light) BS with the objective lens 20, and irradiates the optical disc 1 with the beam spot. Then, the reflected light from the optical disk 1 is configured to enter the four-division light receiver 26 from the polarization beam splitter 23 via the objective lens 20.

In such an optical disk device, the optical disk 1
Since a large number of tracks or pits are formed at intervals of several microns in the radial direction, the track position shift is large due to slight eccentricity, and the waviness of the optical disk 1 causes a beam spot focus position shift. It is necessary to follow a beam spot of 1 micron or less.

Therefore, the objective lens 20 of the optical head 2 is moved in the vertical direction in the figure to change the focus position, and the focus actuator (focus coil) 22 is moved in the horizontal direction in the figure to move the irradiation position in the track direction. A track actuator (track coil) 21 to be changed to is provided.

Corresponding to this, the focus error signal FES is generated from the light reception signal of the light receiver 26, and the focus servo control unit 4 for driving the focus actuator 22 and the light receiver 26.
A track servo control unit 3 for generating a track error signal TES from the received light signal and driving the track actuator 21 is provided.

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

That is, the fact that the distribution of the amount of reflected light in the light receiver 26 changes due to the diffraction of light by the track 10 depending on the position of the beam spot BS with respect to the track 10
The beam spot position error for 10 is obtained.

For example, when the push-pull method using the four-divided photodetectors 26a, 26b, 26c, and 26d is used for the photodetector 26, the reflected light amount distribution in the photodetector 26 is as shown in FIG. 5 (D) when there is a positional relationship such as P ₁ , and when the beam spot is on P for track 10 (on-track), FIG. When the spot is at P ₂ , it is as shown in FIG. 5 (F).

Therefore, in the track servo control unit 3, the light receivers 26a to 26d
When {(a + b)-(c + d)} is obtained from the outputs a to d, the track error signal TES of FIG. 5C is obtained,
Thus, if the track actuator 21 is driven and the objective lens 20 is driven in the left-right 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 a conventional technique.

The track error signal TES is usually below the slice level in the servo-on state, 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 TES with a predetermined slice level SL to detect the track error signal TES. When the amplitude exceeds the slice level SL, the servo is not able to follow off track and the servo error signal is generated.

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

[Problems to be Solved by the Invention]

 FIG. 7 is a diagram for explaining the problems of the prior art.

By the way, recording (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 pre-formatted pit PT at the center of the land 10 of the disk medium 1, as shown in FIGS.

If this pit PT is not exactly present in the center of the land 10 like PT ', the track error signal TES is swung by the ID by the pit PT' as shown in FIG. 7C, and the light beam is swung.

This shaken return is as shown by the dotted line, and is equal to or lower than the slice level SL at the time of reading, which is not a problem.

However, if the writing is started from this shaken place (that is, the place where the ID pit PT 'is not in the center), the TES sensitivity will be higher during writing, so as shown by the solid line in Fig. 7 (C), The track error signal TES may exceed the slice level SL.

This means that even if the actual off-track amount is small and is within the margin, the TES sensitivity is high during writing, so the track error signal exceeds the slice level,
There is a problem that a servo error occurs and an over-detection of the error occurs.

The reason why the sensitivity is increased during writing is that the writing starts at the return portion shaken by the ID pits and the light changes greatly in the amount of reflected light, so the sensitivity becomes higher.

It is an object of the present invention to provide an optical disc device capable of preventing excessive detection of a servo error at the time of writing which occurs when an ID is not formed in the center.

[Means for solving the problem]

 FIG. 1 is a principle diagram of the present invention.

As shown in FIG. 1, the present invention illuminates an optical disc 1 with a light beam and receives the light from the optical disc 1 to obtain a light reception signal, and a track for producing a track error signal from the light reception signal. The error signal generator 30 and
A track servo control unit 3 for performing track servo control of the optical head 2 based on the track error signal is compared with the track error signal at a predetermined slice level, and a servo error signal is generated when the slice level is exceeded Off A track detection unit 34b, and a servo error signal correction unit 38 which receives the servo error signal and outputs a corrected servo error signal masking the servo error signal for a predetermined period after the ID section of the optical disc, It is characterized by

[Action]

According to the present invention, when a write operation is performed after the ID section, a servo error is detected. Therefore, by creating a gate signal for masking the servo error detection for an appropriate time after the ID section and masking the servo error signal, This is to prevent excessive detection of servo errors.

This mask time is sufficiently effective, for example, about 1/10 of one sector. Further, even if a true error occurs within this time, the light beam does not move so fast, so that it can be sufficiently detected after the mask.

〔Example〕

 (A) Description of Configuration of One Embodiment FIG. 2 is an overall configuration diagram of one embodiment of the present invention.

In the figure, the same components as those shown in FIGS. 1 and 4 are denoted by the same symbols.

5 is a control unit, which is composed of a microprocessor,
The servo control operation of the track servo control unit 3 is controlled, and the servo control operation of the focus servo control unit 4 (see FIG. 5) is controlled.

Reference numeral 60 denotes an RF generation circuit, which outputs a to d of the four-division photodetector 26.
From which an RF signal (read signal) RFS is created, 61 is an amplifier circuit, which amplifies the outputs a to d of the four-division light receiver 26,
The servo outputs SVa to SVd are output.

62 is a sector detection circuit, which generates a sector detection signal from the rotation of the optical disk 1, 63 is an ID read gate creation circuit, which generates an ID read gate signal DG for ID from the sector detection signal, 64 Is a pulsing circuit, which pulsates the RF signal RFS, reproduces the read data, and
D read gate signal DG distinguishes and outputs ID data and normal data, and 65 is an ID read circuit, which assembles ID data and notifies the control unit (MPU) 5.

Reference numeral 66 is a write pulse creation circuit, which converts write data from the higher order 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 write pulse. This is what makes the write operation.

Reference numeral 30 is a TES creating circuit, which creates the track error signal TES from the servo outputs SVa to SVd of the amplifier 61 (61a to 61d), 31 is an all-signal creating circuit, and servo output SVa to SVa
32 is an AGC (Automatic Gain Control) circuit that creates the total signal DSC that is the total reflection level by adding Vd. The track error signal TES is the total signal (total reflection level) D
AGC is performed by dividing by CS and using the total reflection level as a reference value, and is used to correct fluctuations in irradiation beam intensity and reflectance.

A phase compensation circuit 33 differentiates the track error signal TES, adds it to the proportional portion of the track error signal TES, and advances the phase of the high frequency band.

34a is a zero-cross detector, which is a track error signal T
The one that detects the zero-cross point of ES and outputs the track zero-cross signal TZC to MPU5. 34b is the above-mentioned off-track detection circuit, and the track error signal TES has exceeded a certain value V ₀ (SL) in the positive direction. Also, off-track (servo error) is detected by detecting that it is below a certain value -V ₀ (-SL) in the negative direction, that is, off-track state.
The signal TOS is output to the MPU5.

Reference numeral 35 is a servo switch, which is the MPU5 servo-on signal SV.
The one that closes when S is on, the one that closes the servo loop and the one that opens when it is off, opens the servo loop, 36 is an inverting amplifier, which inverts the output of servo switch 35, 37 is a power amplifier, the output of inverting amplifier 36 Amplifies the track drive current
The TDV is applied to the track actuator 21.

38a is a delay (delay) circuit that delays the ID read gate signal DG to create a gate signal GT. 38 is the aforementioned gate circuit, which is composed of an AND gate, and includes the gate signal GT and the off-track signal TOS. AND of MPU5
To notify the servo error.

 FIG. 3 is a block diagram of the essential parts of one embodiment of the present invention.

The TES creating circuit 30 includes a summing amplifier 300 for adding the servo outputs SVa and SVb via the input resistors r ₁ and r ₂ , respectively, and the servo output SVa.
Summing amplifier 3 that adds Vc and SVd via input resistors r ₃ and r _4.
01 and the output of addition amplifier 300- (SVc + SVd) minus the output of addition amplifier 301- (SVs + SVb)
And the track error signal TES from the summing amplifier 302.
The output is {= (SVa + SVb)-(SVc + SVd)}.

All signal generating circuit 31 includes a summing amplifier 310 which adds through an input resistor r ₅ ~r ₈ each servo output SVa～SVd, outputs a total reflection level signal DCS (= SVa + SVb + SVc + SVd).

The AGC circuit 32 includes an operational amplifier 320 to which the track error signal TES is input, a first FET (field effect transistor) 321 that controls the input side of the first operational amplifier 320 in accordance with the output of the operational amplifier 320, A second operational amplifier 322, which receives the total reflection level signal DCS and controls the FET 321, and a second operational amplifier 322
Second FET 323 for controlling the voltage division of the input side of the operational amplifier 322 of
The first FET 321 is controlled by the total reflection level signal DCS, which is the output of the operational amplifier 322, and the gain of the operational amplifier 320 is controlled, from the output of the operational amplifier 320 (TES / DC
The second FET 323 is provided for compensating the non-linear characteristic of the first FET 321 and giving a linear characteristic.

The zero-cross detector 34a is a comparator 3 that compares the track error signal TES from the AGC circuit 32 with the zero-cross potential.
Comprised of 40, ZEROSL signal TZC from comparator 340
Is output.

The off-track detection circuit 34b compares the track error signal TES from the AGC circuit 32 with a constant value V _0, and outputs a “low” output when TES> V ₀ , and the track error signal TES. And a constant value (-V ₀ ) are compared, and TES
Second comparator that outputs "low" when <-V ₀
342 and an inverting circuit 343 that inverts the sum of both comparators 341 and 342 and outputs an off-track signal TOS.

The delay circuit 38a is composed of a shift register, delays the gate signal DG for a predetermined time for reading the ID, and creates a gate signal GT having a constant time width (1 sector 1/10 or less).

The gate circuit 38 uses the off-track signal TOS of the inverting circuit 343.
And the gate signal GT of the delay circuit 38a are ANDed.

(B) Description of Operation of One Embodiment FIG. 4 is an operation explanatory diagram of one embodiment of the present invention.

When receiving a seek command from the host, the MPU 5 controls a moving motor (not shown) to position the optical head 2 near the target track, turn on the servo-on signal SVS, pull in the track servo, and perform track servo control.

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

The sector detection circuit 62 generates a sector detection signal at the beginning of the sector, and the ID read gate creation circuit 63 generates an ID read gate DG synchronized with the ID section.

If the ID pit is not in the center of the land 10, the track error signal TES is swung in the ID section as shown in FIG.

The return of this shake is small at the time of reading because it is unrecorded, and both the ID and the shake of return do not exceed the slice levels V ₀ and −V ₀ .

However, in writing, since the semiconductor laser 24 writes immediately after the ID, it synchronizes with the return of the shake, and since the change in the reflected light amount during writing is large, the sensitivity is high and the off-track (servo) Error), the slice level V ₀ is exceeded, the comparator 341 of the off-track detection circuit 34b generates a low error signal TOS, and the inversion circuit 343 inverts the signal to turn it off-track as shown in FIG. The signal (error signal) TOS is output to the gate circuit 38.

On the other hand, the gate circuit 38 is supplied with the mask signal (gate signal) GT of FIG. 4 obtained by delaying the ID read gate signal DG, and this signal is a low level signal for a certain period after ID.

Therefore, since the gate circuit 38 masks the error signal TOS by the mask signal GT for a certain period after ID, it is not output to the MPU 5 as shown in FIG.

Of course, in the other periods, the mask signal GT is "high", so that the error signal TOS 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 after ID, so even if TES exceeds the slice level and a servo error is detected due to the high sensitivity during writing,
It is not output to MPU5.

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

(C) Description of Other Embodiments In the above-described embodiments, the servo error signal is masked for a certain period after the ID during read / write, but it may be masked only during write.

Further, the mask signal GT is generated from the ID read gate signal, but in short, if the mask signal is generated so as to mask for a certain period after the ID portion, it may be generated from another signal.

Although the present invention has been described with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention, and these modifications are not excluded from the present invention.

〔The invention's effect〕

As described above, according to the present invention, the ID of the optical disc
It is possible to prevent the servo error from being excessively detected at the time of writing that occurs when the portion is not formed in the center of the land, to prevent the write operation from being stopped due to the excessive detection, and to make the write operation smooth. Further, there is an effect that the margin of the optical disc in which the ID is pre-formatted can be increased, and it is possible to use the optical disc in which the ID portion is not formed in the center of the land.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is an overall configuration diagram of an embodiment of the present invention, FIG. 3 is a configuration diagram of essential parts of an embodiment of the present invention, and FIG. 4 is an operation of an embodiment of the present invention. Explanatory drawing, FIG. 5 is a track servo explanatory drawing, FIG. 6 is a prior art explanatory drawing, and FIG. 7 is a subject explanatory drawing of a prior art. In the figure, 1 ... Optical disc, 2 ... Optical head, 3 ... Track servo control unit, 30 ... TES creation circuit, 34b ... Off-track detection circuit, 38 ... Gate circuit.

Claims (1)

(57) [Claims] 1. An optical head (2) for irradiating an optical disk (1) with a light beam to receive light from the optical disk (1) to obtain a light reception signal, and a track for producing a track error signal from the light reception signal. An error signal generating section (30) and the optical head (2) based on the track error signal
And a track servo control section (3) for performing track servo control of the track error control unit, and compares the track error signal with a predetermined slice level, and when the slice level is exceeded, a servo error signal for interrupting the track servo control is generated. An off-track detection section (34b), the servo error signal is input, and the ID of the optical disc
And a servo error signal correction section (38) for outputting a corrected servo error signal masking the servo error signal for a predetermined period after the section.