JPH02132644A - Optical disk driving device - Google Patents

Abstract

PURPOSE:To surely detect track slip-off even when tracking signal dispersion is generated by comparing detecting signals for central servo data pit and first and second deviating servo pits, and outputting a track slip-off detecting signal. CONSTITUTION:A central servo data pit B whose center is aligned with the track, and first and second deviating servo data pits A and C which deviate by approximately 1/4 pitch of the track from the track center toward both sides are provided in a servo area. A servo signal generator 16 obtains tracking signals (a-c) from signals (a) to (c) generated by the respective pits A to C in regenerative signals from a photodetector 15, and compares the levels of output signals (a) and (b) and output signals (b) and (c). Further, the output signals of comparators 22 and 23 are turned off by an OR circuit 24, and a track slip-off detecting signal is outputted. Thus, even when the dispersion of the tracking signals is generated, the track slip-off is surely detected.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical disc drive device.

[Conventional technology]

Japanese Unexamined Patent Publication No. 63-90035 describes an optical disk drive device having a so-called sample servo type optical disk and tracking signal detection means.

As shown in Figure 4, this sample servo type optical disk has concentric or spiral tracks, and a servo area is provided in this track, separate from the data area, and the center of the disc is aligned with the track in this servo area. The center servo data pinot B with
at least a first shifted servo data pit A and a second shifted servo data pit C shifted by /4.

The dotted line in the figure indicates the center of the track. For example, these servo data pits A, B, and C are provided once per lap of the track.
, installed in 376 locations.

In addition, in the tracking signal detection method described above, as shown in FIG. 5, the reflected light from the optical disk is detected by a four-part detector 1, and the output signals of each divided part of this detector 1 are added by an adder 2. By doing this, a reproduced signal can be obtained.

FIG. 6 shows the reproduction signal obtained when a light spot passes over the servo data pits A, B, and C. When the light spot passes through the center of the track along the track as shown in ■ in the same figure, the reproduction signals a and c generated by servo data pits A and C have the same level, but as shown in ■ and ■ in the same figure, If the light spot passes along the track while being deviated from the center of the track, the levels of the reproduced signals a and c will not be equal.

As shown in FIG. 5, the reproduced signal from the adder 2 is sampled by the sample and hold circuits 3 and 4 into the reproduced signals a and c from the servo data pits A and C, and the difference between the output signals of the sample and hold circuits 3 and 4 is A tracking signal (ac) is obtained by being taken by the subtraction circuit 5.

In addition, although it is not specifically described in the above-mentioned Japanese Patent Laid-Open No. 63-90035, it is generally important to check whether the track following operation is performed normally when the optical spot is made to follow the track during reproduction or recording of information. Detection is being carried out.

This is necessary to prevent erroneous reproduction and recording of information due to mistracking of the optical spot.

An example of a conventional track deviation detection circuit is shown in FIG.

In this example, a window comparator consisting of two comparators 6, 7 and an OR circuit 8 converts the tracking signal (a-c) to a threshold value Vref from power supplies 9, 10.
, Vref2 is detected, the track deviation of the optical spot is detected. FIG. 8 shows the operation of this track deviation detection circuit. The track deviation detection signal from the OR circuit 8 is a tracking signal (a-c
) becomes larger than the positive threshold value Vrefl, or becomes larger than the negative threshold value Vref2, the tracking signal (a-c ) is the threshold value Vrefl, V
It is not output because it is in the middle of ref2.

[Problem to be solved by the invention]

In an optical disk drive device using the above-mentioned track deviation detection circuit, the amplitude of the tracking signal changes due to changes in the reflectance of the optical disk, etc., so the amount of deviation of the optical spot from the track center when the track deviation detection signal is output is It will change. Therefore, an off-track detection signal is output even if the deviation from the track center is so small that it does not cause a problem while the optical spot is following the track, and conversely, even if the optical spot is off-track, the off-track detection signal is not output. There was a large variation in movement. If the operation varies greatly in this way, serious problems arise, such as it becomes impossible to record or reproduce information at all, or information on other tracks may be destroyed due to erroneous recording of information.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical disc drive device which can improve the above-mentioned drawbacks and reliably detect track deviation even if variations in tracking signals occur due to changes in the reflectance of the optical disc.

[Means to solve the problem]

In order to achieve the above object, the present invention has a concentric or spiral track, a servo area is provided on this track separated from a data area, and the servo area is centered with the track. at least 1
an optical disk having two central servo data pits, and at least a first shifted servo data pit and a second shifted servo data pit that are shifted from the center of the track toward both sides by approximately 1/4 of the pitch of the track. An optical disk drive device using a servo signal generator includes a servo signal generating means responsive to the central servo data pit, the first shift servo data pit, and the second shift servo data pit, and the servo signal generator means tracking signal detection means for obtaining a tracking signal by subtracting a detection signal for the first shifted servo data pit and a detection signal for the second shifted servo data pit; a first comparing means for comparing a detection signal for the shifted servo data pit; and a second comparing means for comparing the detection signal for the central servo data pit and the detection signal for the second shifted servo data pit. It is designed to have the following.

[For production]

A tracking signal is obtained by subtracting the detection signal for the first shifted servo data pit and the detection signal for the second shifted servo data pit by the tracking signal detection means, and the tracking signal is obtained by subtracting the detection signal for the central servo data pit and the first shifted servo data pit.
The detection signal for the shifted servo data pit is compared by the first comparison means. Then, the detection signal for the central servo data pit and the detection signal for the second deviation servo data pit are compared by the second comparing means, and the track deviation is detected based on the output signals of the first comparing means and the second comparing means. A signal is output.

〔Example〕

FIG. 1 shows an embodiment of the invention.

In this embodiment, the optical disk 1l is the sample servo type optical disk described above.

That is, the optical disk 11 has a concentric or spiral track, a servo area is provided on this track separated from a data area, and a central servo data pit B centered on the track is provided in this servo area.
and at least a first shifted servo data pit A and a second shifted servo data pit C, which are shifted from the center of the track toward both sides (in the radial direction) by approximately 1/4 of the pitch of the track. These servo data pits A
, B, and C are, for example, 1,376 per lap of the track.
provided at certain locations.

The light beam emitted by the laser diode 13 in the optical pickup 12 passes through a predetermined optical system, is focused by the objective lens l4, and is irradiated onto the optical disc 11 to form a light spot. The optical disc 11 is rotationally driven by a motor. The reflected light from the optical disk 1l is transmitted to the photodetector 1 via the objective lens 14 and a predetermined optical system.
5, it is converted into an electrical signal and becomes a reproduction signal. This reproduction signal is input to the servo signal generator 16, and the servo signal generator 16 generates a tracking signal and an out-of-track detection signal. Tracking actuator control circuit 1
7 drives the tracking actuator to move the objective lens 14 in the radial direction of the track using the tracking signal from the servo signal generator 16 in the track following state so that the light spot on the optical disk 11 follows the track center. Also, it is checked whether track following is being performed normally using a track deviation detection signal from the servo signal generator 16. Further, information is recorded on or reproduced from the optical disc 11 by the optical pickup 12 as in the conventional case.

FIG. 2 shows the configuration of the servo signal generator 16.

The sample hold circuit 18 converts the signal a generated by the first deviation servo data pit A in the reproduced signal from the photodetector 15 into a sampling timing signal Ta.
The sample and hold circuit 19 samples and holds the signal b generated by the center servo data pit B in the reproduced signal from the photodetector l5 using the sampling timing signal Tb, and the sample and hold circuit 20 samples and holds the signal b generated by the center servo data pit B in the reproduced signal from the photodetector l5. The signal C generated by the second shifted servo data pit C in the reproduced signal from 15 is sampled and held using the sampling timing signal Tc. The sampling timing signals Ta, 7b, and Tc are signals generated by a timing circuit (not shown), and are generated at each timing when the light spot passes through each servo data pit A, B, and C.

The subtraction circuit 21 receives the output signal a of the sample hold circuit 18.
Obtain the tracking signal (a − c) by subtracting the output signal C of the sample and hold circuit 20 from
This tracking signal (a-c) is a signal whose output level is 0 at the center of the track. Converter 22
compares the levels of the output signals a and b of the sample and hold circuits 18 and 19, and outputs a high level signal when b>a. Comparator 23 is sample hold circuit 1
9. Compare the levels of output signals b and C in 20, and
) Outputs a high level signal when c. The output signals of these comparators 22 and 23 are ORed by an OR circuit 24, thereby becoming an off-track detection signal.

FIG. 3 shows the state of signals in each part of this servo signal generator 16. As you can see from this diagram, comparator 2
The output signals of 2 and 23 are angled by 135° and 45°, respectively, from the tracking signal (.-c) to the optical disc 11.
The phase is shifted in the radial direction. Therefore, the track deviation detection signal obtained by ORing the output signals of these comparators 22 and 23 is output when the optical spot deviates from the track center by ±178 track pitches or more. This value of ±l/8 track pitch becomes ±0.1875 μm when the track pitch is 1.5 μm, which is actually often used. Generally, the track deviation during tracking of a light spot is about ±0.1 μm, and a detection point of ±0.1875 μm is extremely appropriate.

In this embodiment, consider a case where a change occurs in the reflectance of the optical disc 1l. When a change occurs in the reflectance of the optical disc l1, the sample hold circuit 18 shown in FIG.
, 19.20, the levels of the output signals a, b, and Q change approximately in proportion to the change in reflectance. For this reason,
Although the amplitude of the tracking signal will change similarly, the phase shift relationship between the tracking signal and the output signals of the comparators 22 and 23 will not change. This is because the levels of the output signals a, b, and Q of the sample and hold circuits 18, 19, and 20 all change only at the same rate.

This holds true even when the amount of output light from the laser diode l3 changes. Therefore, the detection point of the track deviation detection signal does not deviate from the ±178 track pitch, and extremely stable track deviation detection is possible.

In this way, according to this embodiment, the servo data pits A, B
, C is used to detect track deviation from each output signal of a comparator 22 that compares the levels of b and a, and a comparator 23 that compares the levels of b and C. Therefore, even if there is a change in the reflectance of the optical disk 11 or a change in the output light amount of the laser diode 13, there is no change in the detection point for out-of-track detection. For this reason, a track deviation detection signal may be output even if the deviation from the track center is so small that it is not a problem while the optical spot is following the track, or conversely, a track deviation detection signal may not be output even if a track deviation occurs. Therefore, problems such as recording and reproducing information becoming completely impossible, or information on other tracks being destroyed due to erroneous recording of information, are eliminated.

〔Effect of the invention〕

As described above, according to the present invention, a concentric or spiral track is provided, a servo area is provided on this track separated from a data area, and at least one servo area is provided in this servo area and centered on the track. an optical disk having two central servo data pits, and at least a first shifted servo data pit and a second shifted servo data pit that are shifted from the center of the track toward both sides by approximately 1/4 of the pitch of the track. An optical disk drive device using a servo signal generator includes a servo signal generating means responsive to the central servo data pit, the first shift servo data pit, and the second shift servo data pit, and the servo signal generator means tracking signal detection means for obtaining a tracking signal by subtracting a detection signal for the first shifted servo data pit and a detection signal for the second shifted servo data pit; a first comparing means for comparing a detection signal for the shifted servo data pit; and a second comparing means for comparing the detection signal for the central servo data pit and the detection signal for the second shifted servo data pit. Since the track deviation detection signal is output based on the output signals of the first comparison means and the second comparison means, the track deviation detection signal can be reliably detected even if variations in the tracking signal occur due to changes in the reflectance of the optical disc, etc. can be done.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing the configuration of a servo signal generator in the same embodiment, and Fig. 3 is a signal and servo data of each part in the servo signal generator. Fig. 4 is a diagram showing an example of servo data pits on an optical disc, Fig. 5 is a block diagram showing an example of a conventional tracking signal detection method, and Fig. 6 is a diagram showing an example of a conventional tracking signal detection method. A diagram showing the reproduced signal obtained when a light spot passes over a servo data pit, Figure 7 is a block diagram showing an example of a conventional track deviation detection circuit, and Figure 8 shows the operation of the same track deviation detection circuit. FIG. 16... Servo signal generator, 18, 19. 20・
...Sample hold circuit, 2l...Subtraction circuit, 22
．． 23... Comparator output, 24... OR circuit. D1ffi <Introduction Ob

Claims (1)

[Claims] a concentric or spiral track, the track having a servo area separate from the data area, in the servo area at least one central servo data pit centered with the track; In an optical disc drive device using an optical disc having at least a first shift servo data pit and a second shift servo data pit that are shifted by approximately 1/4 of the pitch of the track toward both sides from the center of the center, servo signal generation means responsive to the servo data pit, the first deviation servo data pit, and the second deviation servo data pit; the servo signal generation means generates a detection signal for the first deviation servo data pit; tracking signal detecting means for obtaining a tracking signal by subtracting the detection signal for the second shifted servo data pit, and the detection signal for the central servo data pit and the detection signal for the first shifted servo data pit. a first comparing means for comparing; and a second comparing means for comparing a detection signal for the central servo data pit and a detection signal for the second shifted servo data pit; and an optical disc drive apparatus, wherein a track deviation detection signal is output based on the output signal of the second comparing means.