JP2731403B2 - Optical disk drive - Google Patents

Description

The present invention relates to an optical disk drive.

[Prior Art] JP-A-63-90035 describes an optical disk drive device having a so-called sample servo type optical disk and tracking signal detection means.

This sample servo type optical disk has concentric or spiral tracks as shown in FIG. 4, and a servo area is provided on this track separately from the data area. Of the center servo data pit B and the track pitch from the center of the track to both sides (in the radial direction)
It has at least a first shifted servo data pit A and a second shifted servo data pit C shifted by 1/4.
The dotted line in the figure indicates the center of the track. These servo data pits A, B, C are provided, for example, at 1,376 locations per track.

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

FIG. 6 shows the state of the reproduced signal obtained when the light spot passes over the servo data pits A, B, and C. As shown in the figure, when the light spot passes along the track at the center of the track, the servo data pit
The levels of the reproduced signals a and c generated by A and C are equal, but when the light spot passes along the track in a state where it is off the center of the track as shown in FIG. Are not equal.

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

Although not particularly described in the above-mentioned Japanese Patent Application Laid-Open No. 63-90035, it is generally determined whether or not this track following operation is normally performed when an optical spot is made to follow a track during information reproduction or recording. Has been performed. This is necessary in order to prevent erroneous reproduction and erroneous recording of information due to deviation of the track of the light spot.

 FIG. 7 shows an example of a conventional track deviation detecting circuit.

In this example, a window comparator composed of two comparators 6 and 7 and an OR circuit 8 detects that the tracking signal (ac) has exceeded the threshold values Vref1 and Vref2 of the power supplies 9 and 10, thereby detecting the light spot. Track deviation is detected. FIG. 8 shows the operation of the track deviation detecting circuit. The off-track detection signal from the OR circuit 8 is such that the tracking signal (ac) has a positive threshold value.
This signal is output when the voltage becomes larger than Vref1 on the positive side or when the voltage becomes larger on the negative side than the negative threshold value Vref2. In the vicinity of the track center, the tracking signal (ac) is output.
Is not output because the value is between the threshold values Vref1 and Vref2.

[Problems to be solved by the invention]

In an optical disk drive device using the above-described track deviation detection circuit, the amplitude of the tracking signal changes due to fluctuations in the reflectivity of the optical disk or the like. Will change. For this reason, even if the deviation of the light spot from the track center while following the track does not matter, a track deviation detection signal is output even if it is slight, or conversely, a track deviation detection signal is not output even if a light spot track deviation occurs. There was a large variation in operation such as slipping. When the operation greatly varies in this manner, there arises a serious problem that recording and reproduction of information become impossible at all, or information on another track is destroyed due to erroneous recording of information.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical disk drive signal which can solve the above-mentioned drawbacks and can reliably detect a track deviation even if a tracking signal varies due to a change in the reflectivity or the like of the optical disk.

[Means for solving the problem]

In order to achieve the above object, the present invention has a concentric or spiral track, in which a servo area is provided separately from a data area, and the track is centered in the servo area. At least one central servo data pit and approximately 1/4 of the track pitch from the center of the track to both sides.
An optical disc drive apparatus using an optical disc having at least a first shifted servo data pit and a second shifted servo data pit shifted by only the central servo data pit and the first shifted servo data pit; A servo signal generating means for responding to the second shift servo data pit;
Detection signal a for the first shift servo data pit
Tracking signal detecting means for obtaining a tracking signal by subtracting the detection signal c for the second deviation servo data pit, the detection signal b for the central servo data pit, and the detection signal for the first deviation servo data pit a, comparing the detection signal b for the central servo data pit with the detection signal c for the second shift servo data pit, and outputting a signal when b> a. And a second comparing means for outputting a signal when b> c, and when b> a and b> c by the output signals of the first comparing means and the second comparing means. And outputs an off-track detection signal.

(Operation)

The tracking signal detecting means obtains a tracking signal by subtracting a detection signal a for the first shifted servo data pit and a detection signal c for the second shifted servo data pit, and the first comparing means obtains a tracking signal for the central servo data pit. The detection signal b is compared with the detection signal a for the first shift servo data pit, and a signal is output when b> a. The second comparing means compares the detection signal b for the central servo data pit with the detection signal c for the second shift servo data pit and outputs a signal when b> c, and the servo signal generation means outputs the first signal. The output signals of the comparison means and the second comparison means output a track deviation detection signal when b> a and when b> c.

〔Example〕

 FIG. 1 shows an embodiment of the present invention.

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

The light beam emitted by the laser diode 13 in the optical pickup 12 is transmitted through a predetermined optical system to the objective lens 14.
And is irradiated on the optical disk 11 to form a light spot. The optical disk 11 is driven to rotate by a motor, and the reflected light from the optical disk 11 is converted into an electric signal by a photodetector 15 via an objective lens 14 and a predetermined optical system to become a reproduction signal. This reproduced signal is input to a servo signal generator 16 as a servo signal generating means,
The servo signal reproducer 16 generates a tracking signal and a track deviation detection signal. The tracking actuator control circuit 17 drives the tracking actuator 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, and moves the objective lens 14 to the track diameter. Then, it is checked whether or not the track following is normally performed by the track deviation detection signal from the servo signal generator 16. Further, information is recorded or reproduced on the optical disk 11 by the optical pickup 12 as in the conventional case.

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

The sample-and-hold circuit 18 samples and holds the signal a generated by the first shift servo data pit A in the reproduced signal from the photodetector 15 by using the sampling timing signal Ta.
Reference numeral 19 denotes a signal b generated by the central servo data pit B in the reproduction signal from the photodetector 15, which is sampled and held by the sampling timing signal Tb. The sample and hold circuit 20 generates the second shift servo data pit in the reproduction signal from the photodetector 15. The signal c generated by C is converted to a sampling timing signal Tc.
And hold it. sampling
The timing signals Ta, Tb, and Tc are signals generated by a timing circuit (not shown), and are generated at each timing when the light spot passes through each of the servo data pits A, B, and C.

A subtraction circuit 21 as a tracking signal detecting means obtains a tracking signal (ac) by subtracting the output signal c of the sample and hold circuit 20 from the output signal a of the sample and hold circuit 18, and obtains the tracking signal (a-c).
c) is a signal whose output level becomes 0 at the center of the track.

The comparator 22 as a comparing means compares the levels of the output signals a and b of the sample and hold circuits 18 and 19, and b> a
A high level signal is output when. A comparator 23 as a comparing means compares the levels of the output signals b and c of the sample and hold circuits 19 and 20, and outputs a high level signal when b> c. The output signals of these comparators 22 and 23 are ORed by an OR circuit 24 to become an off-track detection signal.

FIG. 3 shows the state of the signal in each part of the servo signal generator 16. As can be seen from this figure, comparator 2
The output signals 2 and 23 are shifted in the radial direction of the optical disk 11 by 135 ° and 45 ° with respect to the tracking signal (ac), respectively. Therefore, these comparators 22, 23
The off-track detection signal obtained by taking the OR of the output signal is ± 1/8 of the light spot from the track center.
This signal is output when a track having a track pitch or more deviates. The value of ± 1/8 track pitch is ± 1.5 at the track pitch of 1.5 μm which is actually widely used.
0.1875 μm. Generally, the deviation of the track during the tracking of the light spot is about ± 0.1 μm,
A detection point of 875 μm is quite reasonable.

In this embodiment, consider the case where the reflectance of the optical disk 11 changes. When the reflectance of the optical disk 11 changes, the sample and hold circuits 18 and 19 shown in FIG.
The levels of the 20 output signals a, b, and c change substantially in proportion to the change in reflectance. Therefore, the amplitude of the tracking signal also changes, but the phase shift relationship between the tracking signal and the output signals of the comparators 22 and 23 does not change. This is because the levels of the output signals a, b, and c of the sample and hold circuits 18, 19, and 20 all change only at the same rate.

This is the same even when the output light amount of the laser diode 13 changes. Therefore, the detection point of the track deviation detection signal does not deviate from the ± 1/8 track pitch, and extremely stable track deviation detection can be performed.

Thus, according to the present embodiment, the servo data pits A, B,
Track deviation detection is performed from the output signals of the comparator 22 for comparing the levels of b and a using the reproduced signals a, b and c generated by C, and the comparator 23 for comparing the levels of b and c. Even if a change in the reflectivity of the optical disk 11 or a change in the output light amount of the laser diode 13 occurs, there is no change in the detection point of the track deviation detection. For this reason, the deviation of the light spot from the center of the track while following the track does not cause a problem, and the detection signal of the deviation of the track is output even if it is slight, or the detection signal of the deviation of the track is not output even if the deviation of the track occurs. Therefore, there is no problem that information recording and reproduction cannot be performed at all, or information on another track is destroyed due to erroneous recording of information.

〔The invention's effect〕

As described above, according to the present invention, at least a concentric or spiral track is provided, a servo area is provided on the track separately from the data area, and the track is centered in the servo area. One central servo data pit, at least a first shifted servo data pit and a second shifted servo data pit shifted from the center of the track toward both sides by approximately 1/4 of the pitch of the track;
An optical disk drive apparatus using an optical disk having the following deviation servo data pits: a servo signal generating means responsive to the central servo data pit, the first deviation servo data pit, and the second deviation servo data pit. The servo signal generating means has the first
Tracking signal detection means for obtaining a tracking signal by subtracting a detection signal a for the deviation servo data pit of the second and a detection signal c for the second deviation servo data pit; a detection signal b for the central servo data pit; First comparing means for comparing a detection signal a for one shift servo data pit and outputting a signal when b> a, a detection signal b for the center servo data pit and the second shift servo A second comparing means for comparing the detection signal c with the data pit and outputting a signal when b> c, wherein b> c is determined by the output signals of the first comparing means and the second comparing means. a and b>
Since the track deviation detection signal is output at the time of c, the detection signal a for the first shifted servo data pit and the detection signal b for the central servo data pit even if the tracking signal varies due to a change in the reflectivity of the optical disk or the like. Since the level of the detection signal c for the second shift servo data pit changes substantially in proportion to the reflectivity of the optical disk, there is no change in the detection point of the track deviation detection, and the track deviation detection can be reliably performed. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of a servo signal generator in the embodiment, and FIG. 3 is a diagram showing signals and servo data of various parts in the servo signal generator. FIG. 4 is a diagram showing an example of servo data pits on an optical disk, FIG. 5 is a block diagram showing an example of a conventional tracking signal detection system, and FIG. FIG. 7 is a diagram showing a state of a reproduced signal obtained when a light spot passes over a servo data pit. FIG. 7 is a block diagram showing an example of a conventional track deviation detecting circuit. FIG. 8 is an operation of the track deviation detecting circuit. FIG. 16 Servo signal generator, 18, 19, 20 Sample hold circuit, 21 Subtraction circuit, 22, 23 Comparator, 24
… Or circuit.

Claims (1)

(57) [Claims] At least one central servo data having a concentric or spiral track, a servo area provided separately from a data area in the track, and a center of the track in the servo area. An optical disc using an optical disc having pits and at least a first shifted servo data pit and a second shifted servo data pit shifted from the center of the track toward both sides by approximately 1/4 of the pitch of the track. A drive device, comprising: servo signal generating means responsive to the central servo data pit, the first shift servo data pit, and the second shift servo data pit;
The servo signal generating means includes: a tracking signal detecting means for obtaining a tracking signal by subtracting a detection signal a for the first deviation servo data pit and a detection signal c for the second deviation servo data pit; First comparing means for comparing a detection signal b for the servo data pit with a detection signal a for the first shift servo data pit and outputting a signal when b> a, and detecting the central servo data pit The signal b and the second
And a second comparing means for comparing the detection signal c with the deviation servo data pit and outputting a signal when b> c, the output of the first comparing means and the output of the second comparing means. An optical disc drive device which outputs a track deviation detection signal when b> a and when b> c by a signal.