JP2564494B2 - Optical disk drive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical disc apparatus that obtains a tracking error signal from pits formed in advance on an optical disc, and in particular, it is possible to eliminate an erroneous tracking error signal. The present invention relates to an optical disk device.

[Conventional technology]

As a tracking method for an optical disk, there is known a method in which pits are formed in advance around a track at regular intervals and a tracking error signal is obtained based on a reproduction signal obtained from the pits. That is, as such a tracking method, for example, as described in Japanese Patent Publication No. 58-21336, a plurality of pits are formed to meander with respect to the virtual track center, and a light beam is irradiated. A tracking error signal can be obtained because the amplitude of the reproduction signal obtained from the pit changes due to the difference in relative distance between the position and the position of the pit formed by meandering.

In addition, a tracking method similar to this is used in SP I, Proceedings, Volume 695, Optical Mass Data Storage II (1986), No. 11
Pages 2 to 115 and 239 to 242 (SPIE, Proce
eding, vol.695 Optical Mass Data Strage II (198
6), P112-P115, P239-P242).

This is a method that uses sampling marks consisting of three pre-pits (that is, pits 1, 2, and 3) as shown in FIG. 5, and 1376 sampling marks are arranged at equal intervals on one track. Has been done. Where the pit
Numerals 1 and 2 are pits for detecting a tracking error signal, and their positions are off-track by 1/4 track pitch in opposite directions to the virtual track center 4. The pit 3 is a pit for clock reproduction and is located above the virtual track center 4.

The tracking error signal is obtained as an amplitude difference between the reproduction signal obtained from pit 1 and the reproduction signal obtained from pit 2, and becomes a sinusoidal signal as shown in FIG. Here, points a, b and c shown in FIG. 6 are track center points as shown in FIG. 5, and points e, f and g are intermediate points between tracks.

Note that, in reality, both the reproduction signal obtained from the pit 1 and the reproduction signal obtained from the pit 2 are signals obtained intermittently in a certain cycle, so that the tracking error signal itself also has a certain cycle in the same manner. It will be obtained intermittently.
Therefore, although the signal waveform is continuously drawn in FIG. 6, it is actually obtained as a discrete value.

[Problems to be solved by the invention]

The above-mentioned conventional technique is characterized in that the tracking error signal is detected from the difference in the amplitude of the reproduced signal, and the tracking error signal is detected by using the diffracted light like the tracking method using the well-known group. Since it is not detected, there is an advantage that offset due to the inclination of the optical system and the disc does not occur.

However, since the optical disk is generally made of glass or plastic, minute defects and scratches are likely to occur, and in the above-mentioned conventional technique, the pit diameter of the formed pit and the beam diameter of the light beam are 1 to 2 μm. In this way, the defects and scratches are as small as the minute defects and scratches described above, and therefore the defects and scratches are easily detected. Therefore, in the above-mentioned prior art, there is a problem that an erroneous tracking error signal is unavoidable and stable tracking servo control cannot be performed.

That is, for example, if either or both of the pit pairs (pits 1 and 2) for obtaining the tracking error signal are damaged by defects or scratches, the correct tracking error signal cannot be obtained and the next pit pair is correct. Until the tracking error signal is obtained, the tracking servo control must be performed with the wrong tracking error signal. Therefore, when the optical disc has many defects or scratches, in the worst case, the tracking may be missed.

It is an object of the present invention to provide an optical disc device which solves the above-mentioned problems of the conventional technique and can eliminate an erroneous tracking error signal due to a defect or a flaw.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention uses an optical disc in which tracking pits are provided in advance in any desired cycle, detects the tracking error signal by sampling the signal level of the pitch, and detects the tracking error. In an optical disc device in which tracking servo control is performed using a signal, the detected tracking error signal and 1
First difference detecting means for obtaining a difference from a tracking error signal obtained a sampling period before as a first difference, the detected tracking error signal and a tracking error signal obtained a few sample periods earlier than that. Second difference detecting means for obtaining a difference between and as a second difference; first comparing means for comparing the obtained first difference with a predetermined reference value; A second comparison unit that compares the second difference with a certain reference value that is set in advance is provided, and the first difference obtained as a result of the comparison by the first comparison unit is set in advance. When the second reference value exceeds a predetermined reference value, and when the second difference obtained as a result of the comparison by the second comparing means exceeds a predetermined reference value, the detected tracking error signal is Decided to eliminate .

[Action]

Generally, when an optical pickup is made to follow a track on an optical disk, the external force applied to the optical pickup is 0 in terms of gravitational acceleration in the presence of track distortion.
It is about 5 to 1.0G. On the other hand, assuming that the disk rotation speed is 1800 rpm, the sampling cycle of the tracking error signal (as described above, the tracking error signal is a signal obtained in a certain cycle. Is about 25 μse.
becomes c. When the optical pickup that follows the track is moved from the center of the track by applying an external force (that is, off-track), the external force α (gravitational acceleration conversion) and the off-track amount x are related to each other. If time is t, Becomes

From the above, in one sampling period (that is, about 25 μsec), the off-track amount x
Is about 0.03 μm, and therefore, the level value of the tracking error signal cannot change abruptly during one sampling period.

Therefore, the absolute value of the amount of change in the level value of the tracking error signal is calculated, and when the calculated value is very large, it can be determined that an erroneous tracking error signal due to a defect or a flaw has been obtained. it can.

Therefore, if a certain reference value is set in advance in consideration of the track distortion of the optical disc, external vibration specifications, etc., and if the calculated absolute value of the change amount of the level value is larger than the reference value, the obtained tracking value is obtained. Instead of the level value of the error signal, the tracking servo control is performed by using the level value of the tracking error signal obtained before that, thereby eliminating the false tracking error signal and stabilizing the tracking. Servo control can be performed.

〔Example〕

The embodiments of the present invention will be described below. Before that, an optical disk device useful for understanding the embodiments of the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, 5 is a sample hold circuit, and 6 is analog / digital conversion (hereinafter referred to as A / D conversion).
, 7,8,10,12 are registers, 9 and 13 are subtractors, 11 is a digital / analog converter (hereinafter referred to as D / A converter), 14 and 15 are comparators, and 16 is a comparator. AND (A
ND) gate, IN is input signal, OUT is output signal, C1, C2, C3,
C4 is the clock, respectively.

FIG. 2 is a waveform diagram showing the signal waveforms of the main parts of FIG.

In FIG. 1, first, as an input signal IN, a signal reproduced from an optical disc (not shown) as shown in FIG. 2 (a signal indicating the intensity of the reflected light reflected by the optical disc and obtained from diffracted light). Signal that is not input) is input from the input terminal. Incidentally, in the input signal IN shown in FIG.
A and B are amplitude values (level values) corresponding to the pits 1 and 2 shown in FIG. 5, respectively. The A / D converter 6 converts the input reproduced signal of analog amount into digital amount by the clock C1. At this time, the sample hold circuit 5
The clock is used so that the A / D converter 6 can perform normal A / D conversion.
The reproduced signal is sampled and held by C1.

Next, the registers 7 and 8 respectively correspond to the amplitude values (levels) corresponding to the pits 1 and 2 of the reproduced signal converted into the digital amount at the rising timings of the clocks C2 and C3 as shown in FIG. Value) A and B are memorized. Subtractor 9
Calculates the difference between the amplitude value A corresponding to the pit 1 stored in the register 7 and the amplitude value B corresponding to the pit 2 stored in the register 8 and outputs the difference A-B. That is, this is the amplitude value (level value) of the tracking error signal before being protected.

On the other hand, at this time, the register 12 stores the output from the subtractor 9 one sample period before, that is, the amplitude value A′-B ′ of the tracking error signal one sample period before (this value is stored). Is stored in the register 12 at the rising timing of the clock C4 approximately one sample period before). Therefore, the subtractor 13 calculates the difference between the latest value AB of the amplitude value of the tracking error signal and the value A'-B 'of the previous sampling period, that is, the amount of change in the amplitude value of the tracking error signal. Will be done. Then, the comparator 14 compares the output of the subtractor 13 with the predetermined value -C, and the comparator 15 compares the output of the subtracter 13 with the predetermined value C.

That is, the following equation −C <(AB) − (A′−B ′) <C is calculated by the subtractor 13 and the comparators 14 and 15, and the amplitude of the tracking error signal is larger than the predetermined value C. When the absolute value of the change amount of the value is large, the output of the comparator 14 or 15 becomes zero.

The AND gate 16 outputs the outputs of the comparators 14 and 15 and the clock C4.
The logical product of and and is input to the register 10. Therefore,
When one of the comparators 14 and 15 is 0, the clock C4 input to the register 10 is masked.

The register 10 stores the amplitude value of the tracking error signal calculated by the subtractor 9 at the rising timing of the input clock C4. Therefore, when the clock C4 is masked, that is, when the absolute value of the amount of change in the amplitude value of the tracking error signal is larger than the predetermined value C, the value stored in the register 10 is not updated. The amplitude value A'-B 'of the tracking error signal before the sampling period remains held.

Finally, the D / A converter 11 converts the output of the register 10 into an analog amount and outputs it as an output signal OUT from the output terminal. The output tracking error signal is used for tracking servo control in the optical disc device.

In this apparatus, since the legitimacy of the tracking error signal is always evaluated by the difference with the amplitude value of the tracking error signal obtained one sampling period before, an abnormal value is obtained as the amplitude value of the tracking error signal. Then, not only the abnormal value is masked, but even if the next normal value is obtained, the normal value is masked.

FIG. 3 is a block diagram showing another optical disk device useful for understanding the embodiment of the present invention.

In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals.

This device operates basically the same as the device shown in FIG. 1, except that the register 10 performs the operation of the register 12 instead.

That is, in the present apparatus, the validity of the tracking error signal is not evaluated by the difference between the tracking error signal and the amplitude value of the tracking error signal obtained one sampling cycle before, as in the apparatus shown in FIG. The correctness of the tracking error signal is evaluated based on the difference from the amplitude value of the tracking error signal output from the output terminal. Therefore, even if an abnormal value is obtained as the amplitude value of the tracking error signal one sample period before, the legitimacy of the tracking error signal is not evaluated by the difference from the abnormal value, but
It will be evaluated by the difference from the value held in the register 10.

In this device, when an abnormal value is obtained as the amplitude value of the tracking error signal, only the abnormal value is masked, but it happens that the value held in the register 10 and the obtained abnormal value are The absolute value of the difference is a predetermined value C
If it does not exceed the limit, the abnormal value is then held in register 10, and after that, the correctness of the tracking error signal is evaluated by the difference from the abnormal value. The value obtained as the amplitude value of the error signal may be continuously masked.

 FIG. 4 is a block diagram showing an embodiment of the present invention.

4, the same parts as those in FIG. 1 are designated by the same reference numerals.

The configuration of this embodiment is the same as the configuration of FIG. 1 except that the register 17, the subtractor 18, the comparators 19 and 20, the AND gate 21, and the OR (O
R) Gates 22 have been added respectively.

That is, in the present embodiment, not only the difference with the amplitude value of the tracking error signal obtained one sampling period before as in the apparatus of FIG. 1 but also the amplitude value of the tracking error signal obtained two sampling periods before The correctness of the tracking error signal is also evaluated by the difference between and. That is,
If it is determined to be normal by either the difference with the amplitude value of the tracking error signal obtained one sampling period before or the difference with the amplitude value of the tracking error signal obtained two sampling periods before The amplitude value of the newly obtained tracking error signal is output from the output terminal.

In the present embodiment, when an abnormal value is obtained as the amplitude value of the tracking error signal, the abnormal value is masked, and when the next normal value is obtained, it is compared with the value obtained two sampling periods before. As a result of the comparison, it is determined that the value is normal, and the normal value is output correctly.

〔The invention's effect〕

As described above, according to the present invention, an erroneous tracking error signal due to a defect or scratch on the optical disc is detected and eliminated, so that stable tracking servo control that is not affected by the defect or scratch can be performed. It can be carried out.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical disk device useful for understanding an embodiment of the present invention, FIG. 2 is a waveform diagram showing a signal waveform of a main part of FIG. 1, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a block diagram showing another optical disk device useful for achieving the above, FIG. 4 is a block diagram showing one embodiment of the present invention, FIG. 5 is an explanatory view showing pit arrangement on the optical disk used in the present invention, and FIG. FIG. 6 is a waveform diagram showing a waveform of a tracking error signal obtained from pits 1 and 2 shown in FIG. Explanation of code 5 …… Sample hold circuit, 6 …… A / D converter, 7,8,1
0,12 …… Register, 9,13 …… Subtractor, 11 …… D / A converter, 14,15 …… Comparator, 16 …… And gate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Takeuchi 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Inside the Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Junichi Iida 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Yokohama Plant (56) References JP-A-56-37 (JP, A) JP-B-60-30016 (JP, B2)

Claims (1)

(57) [Claims] 1. A tracking error signal is detected by sampling a signal level of the pitch using an optical disk in which tracking pits are provided in advance in an arbitrary desired cycle, and tracking servo control is performed using the tracking error signal. In an optical disc device that performs the above, first difference detecting means for obtaining a difference between the detected tracking error signal and a tracking error signal obtained one sampling period before that as a first difference, and detected. Second difference detecting means for obtaining a difference between the tracking error signal and a tracking error signal obtained a few sample periods earlier than the tracking error signal as a second difference, and the obtained first difference is predetermined. First comparing means for comparing a certain reference value, the obtained second difference and a certain reference value set in advance And a second comparison means for comparing the first comparison means, the second comparison means compares the first difference obtained as a result of comparison by the first comparison means with a predetermined reference value, and the second comparison means. As a result of the comparison by the comparison means, when the obtained second difference exceeds a predetermined reference value,
An optical disk device, wherein the detected tracking error signal is excluded.