JP2626550B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk such as an optical video disk, a compact disk, and a recording / reproducing optical disk, and uses an optical disk capable of improving information signal characteristics when performing recording / reproduction or reproduction on the optical disk. An apparatus is provided.

[0002]

2. Description of the Related Art With the development of optical disks, optical disks capable of recording and reproduction have recently been commercialized. This recordable / reproducible optical disk imposes a greater load on the disk than a conventional read-only optical disk. That is, in a read-only optical disk, the eccentricity of the disk is ± 80-100 μm
While the disk surface deflection is allowed up to about ± 1 mm, the recording / reproducing disk allows only about half the allowable value.

On the other hand, a semiconductor laser having a wavelength of 780 to 830 nm is used for an optical head for recording / reproducing an optical disk, and an N.V. A. (Numerical A
Percent) of 0.45 to 0.55 is usually used.

Actually, if there is an error in the protective film thickness of the optical disk, spherical aberration occurs, and from the allowable value of the aberration, the allowable value of the thickness error of the optical disk is determined to be about 30 to 50 μm.
About.

If the angle θ between the objective lens of the optical head and the disk, the NA of the objective lens, the wavelength λ, and the thickness of the protective film of the optical disk are t, the wavefront aberration W caused by the inclination is:
When the aberration is very small

[0006]

(Equation 1)

## EQU1 ## n is the refractive index of the protective film. Most of the wavefront aberration appearing at this time is a coma aberration, and the allowable values of the wavefront aberration W ≦ 0.2λ and t = 1.2 m
m, n = 1.5, N.I. A. = 0.5, the allowable value θ of the angle between the optical head and the disk is obtained, and it is understood that the value is about 4 to 5 mrad.

That is, in order to keep the tilt of the objective lens of the optical disk within 4 to 5 mrad, the surface runout of the disk is about 250 μm or less for a 20 cm disk and 38 mm for a 30 cm disk, assuming that the surface runout component is a quadratic function.
It must be 0 μm or less. This value is extremely difficult when considering the manufacture of a disk, leading to a decrease in yield and an increase in manufacturing cost.

In a conventional reproduction-only machine, a special surface vibration detecting device is provided to correct the surface vibration, the surface vibration of the disk is detected, and the tilt correcting drive device attached to the head is operated to perform the correction. Had gone.

The operation of the conventional system will be described with reference to FIG. If the disc 5 has a tilt θ, the LED
The light beam emitted from 13 is reflected by the disk and enters detectors A14 and B15. At this time, the light beam incident on the detector B is stronger than the light beam incident on the detector A due to the inclination of the disk. Therefore, by obtaining the differential output of the detector A and the detector B, an output signal corresponding to the tilt of the disk can be obtained.
An actuator (not shown) including an optical head or an objective lens for amplifying the obtained output signal to obtain an information signal from the disk may be driven so that a light beam is incident perpendicularly to the disk. I can do it.

[0011]

Although such a conventional method has no problem with respect to a disk having a uniform reflection surface, the reflectance differs between a recorded portion and an unrecorded portion, such as a recording / reproducing disk. When applied to a disk or the like, a malfunction may occur in a boundary region between a recorded portion and an unrecorded portion. In the conventional method, signal detection is performed.
Configuration that detects a location different from the disc part
Therefore, an error signal slightly different from the actual one will be detected.
You. Therefore, a servo loop is formed based on this error signal.
And the correction device is driven, the correction that should actually be performed is
Different corrections are made. That is, the correct disk tilt is detected.
To form a servo loop.

The present invention solves such a conventional problem,
It is an object of the present invention to provide an optical disk device using an optical disk capable of performing stable tilt correction without fear of malfunction.

[0013]

According to the present invention, in order to solve the above-mentioned problem, a predetermined pattern for identifying a track is previously recorded on a disk in the form of a sample on a disk track, and the adjacent track is recorded. The tilt of the disk is derived by detecting the level of the crosstalk signal from the optical disk, and the tilt correction can be performed by driving an actuator including an optical head or an objective lens.

[0014]

According to the present invention, it is possible to eliminate the problem of erroneous operation occurring in the boundary area even when applied to a disk or the like having a different reflectance, which has been a problem in the conventional method. That is,
Servo operation based on the error signal
Operating the tilt correction device guarantees the quality of the playback signal
Is done. Therefore, when used for an optical disc for recording and reproduction with very high accuracy such as recording and reproduction, the effect of remarkably improving the characteristics of a reproduced signal appears.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 2 shows an embodiment of the present invention, in which a sampling section of a disk structure according to the present invention is enlarged and shown. On the tracks B2 and C3 adjacent to the track A1, patterns having different periods are recorded. The recording pattern is one formed <br/> pre Pi Tsu preparative shape during disc molding or can be a pin <br/> Tsu bets recorded on the disc.

FIG. 1 is a schematic view of an embodiment of the tilt servo mechanism. On the disk 5, there is a track ABC including an intermittent pattern 4 for tilt detection. A light beam emitted from a light source such as a semiconductor laser is focused on a track A on a disk by an objective lens (the optical system on the outward path is not shown). The light beam reflected on the disk enters the detector 7. The detector 7 reproduces a signal based on crosstalk from the tracks B and C in addition to a signal based on the pattern on the track A. The signal due to the crosstalk from the tracks B and C is amplified by the amplifier 8 and converted into an output corresponding to the signal level reproduced from each track by the frequency discrimination processor 9. The output signal is amplified by the drive circuit, and the entire optical head housing 12 or the actuator including the objective lens is rotated by the tilt motor. As a result of the rotation, the servo operation is performed such that the crosstalk amount from the track B and the crosstalk amount from the track A become equal.

Two embodiments are conceivable as embodiments of the present invention. In other words, in the case where the reflectivity of the disc changes when recording / reproducing is performed, in the case where the information signal is overwritten on this sample tilt pattern portion, it is considered that the reflected light from one of the adjacent tracks becomes strong. Can be At this time, it is possible to detect that a signal is recorded in the adjacent track in advance, and to correct by switching the detection gain when performing frequency discrimination. It is impossible with the conventional method to accurately detect the tilt amount only by changing one of the detection gains.

When recording / reproducing a signal such as code data, it is possible not to perform recording / reproduction on this sample tilt pattern portion. As described above, there are two methods in which the reflectivity changes due to recording and reproduction.

When the reflectance does not change as in magneto-optical recording, reflectance correction is not required at all, but the effect of maintaining high signal quality as compared with the conventional method is slightly reduced as described above. Not something.

[0020]

As described above, according to the present invention, a dedicated pattern equivalent to an information signal is read out and reproduced without providing a special inclination detecting mechanism for applying a servo by measuring the signal quality, that is, the crosstalk level. It is possible to keep the quality of the information signal high.

[Brief description of the drawings]

FIG. 1 is a block diagram of a tilt servo mechanism using an optical disk of the present invention.

FIG. 2 is a perspective view of an optical disc according to an embodiment of the present invention.

FIG. 3 is a block diagram of a conventional tilt signal detection mechanism.

[Explanation of symbols]

1, 2 and 3 each have different periodic patterns
Click 4 tilt detection pattern 7 detector 9 frequency discrimination processor 10 driving circuit 11 the tilt motor 12 optical head housing

Claims (4)

(57) [Claims] 1. An optical head having concentric or spiral tracks, and intermittently arranged on the tracks and having adjacent fixed patterns on both sides of the tracks, each of which is provided with a pattern having a fixed period different from each other. Track following means for causing a light spot to follow the track, tilt driving means for changing the tilt between the optical head and the information carrier, a photodetector receiving reflected light from the information carrier, and the photodetector Frequency discriminating means for discriminating the signal of the fixed period pattern from the outputs of the two, and comparing the fixed period pattern components of the tracks adjacent on both sides, and the inclination driving unit by a signal based on the output of the frequency discriminating unit. The tilt between the optical head and the information carrier is corrected by controlling the drive so as to make the signals of the fixed period pattern components of the tracks adjacent on both sides substantially equal. An optical disc device characterized by the following: 2. The optical disk device according to claim 1, wherein the tilt drive means is a drive means for tilting the objective lens of the optical head. 3. The optical disk device according to claim 1, wherein the tilt drive means is a drive means for tilting a housing of the optical head. 4. have a recording detection means for information signals from the output of the optical detector detects that the recorded tracks, when the one adjacent track information signal is recorded, the information signal recorded 2. The optical disk device according to claim 1, wherein the comparison gain of the frequency discriminating means is switched.