JPH10105979A - Optical disk medium, optical disk device and tracking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk medium, optical disk device and tracking method which are capable of normal tracking servo with a track pitch reduced, and which are provided with a track mark in a shape easy to cut in manufactur ing. SOLUTION: A pair of track marks Pb, Pc physically formed preliminarily is arranged in the servo area intermittently provided in each track, with intervals in the track direction made small to such an extent as mutual reproducing signals interfere. A phase of the peak position is detected for a reproducing RF signal of a pair of track marks Pb, Pc with a read-out means, the direction and the size of a tracking error are discriminated based on the detected phase, and the read-out position is controlled so as to make the tracking error zero. To be concrete, a peak pulse is formed that rises at the zero crossing position of a differential waveform of the reproducing RF signal, with the peak pulse compared with the separately formed servo clock and, on the basis of the polarity and the size of that phase difference, the direction and the size of the tracking error are discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk medium for storing, for example, computer data, an optical disk apparatus for recording / reproducing data on / from an optical disk, and a tracking method therefor.

[0002]

2. Description of the Related Art An optical disk is used as an external storage device of a computer, taking advantage of the ability to store a large amount of digital data. As a tracking servo system for an optical disk, a continuous groove system and a sample servo system are known. In the continuous groove method, grooves are provided on both sides of a track so that when a main beam for data recording / reproduction scans the track, two sub-beams positioned before and after the main beam in the track direction respectively scan the groove. The read position of the main beam is controlled so that the read signals of the two main beams are equal and the read signals of the main beam are equal.

In the sample servo method, servo areas including three marks provided in advance by embossing or the like are provided at regular intervals on each track. One mark is provided at a position coinciding with the center of each track, and two marks provided before and after in the track direction are:
The track center is provided at a constant distance in the radial direction of the disk and at a position separated in the opposite direction. These marks are also called wobbling pits. The reading position is controlled such that the levels of the reading signals generated when the recording / reproducing laser beam scans the two marks are equal to each other. Further, a reproduction clock can be stably generated using a read signal of a mark formed on the track center.

In the case where a servo area is provided in each of the minimum units (referred to as segments) of physical data units obtained by dividing a track, an example shown in FIG. 4 has been previously proposed. FIG.
In the example, the servo area has a length of 24 SCK (SCK means a servo clock generated based on a read signal of the servo area). The distances defined by the servo clocks are first, second, third,.
In the case where the segment mark is represented by the twenty-fourth position, a segment mark is formed using the third position to the seventh position,
The mark 1 is formed at the position 2 and the mark 2 is formed at the 16th and 17th positions. These marks 1 and 2 are called track marks.

The mark 1 is １ ／ · Tp in one direction (for example, inward) in the disk radial direction with respect to the track center.
The mark 2 is formed by embossing at a position shifted by (Tp: track pitch), and the mark 2 is １ ／ · T in the other direction (for example, outside) in the disk radial direction with respect to the track center.
It is formed by embossing at a position shifted by p (Tp: track pitch). By controlling the reading position of the laser beam so that the level of the reproduced RF signal when the laser beam crosses these marks becomes equal, the reading position can be made coincident with the track center.

One frame is composed of a plurality of segments, for example, 14 segments, one of the 14 segments is a segment in which address data is recorded in advance, and the other 13 segments are data recordable. Data segment. One sector has a predetermined size, for example, a size of 2 Kbytes.
One sector is composed of a plurality of address segments and data segments. The segment mark is provided for identifying the type of the segment, and when the data segment is at the head of the sector, when the data segment is at the end of the sector, and when it is not. That is, as shown in FIG.
The segment mark having the length of CK is provided at a position shifted by 1 SCK from the third position to the seventh position.

In the servo area shown in FIG. 4, no clock mark is provided at a position corresponding to the track center. Thereby, the length of the servo area can be reduced. The clock can be recovered by a differential detection method. That is, as shown in FIG. 5, the amplitudes of both shoulder portions of the reproduced RF signals of the mark 1 and the mark 2 are changed to the sampling position t based on the servo clock.
Sampling is performed by each of b1, tb2, tc1, and tc2, and the phase of the servo clock is controlled so that the levels b1 and b2 of the sampling output are equal to each other and the levels c1 and c2 are equal to each other. The levels b0 and c0 obtained at the sampling positions tb0 and tc0 are used for tracking servo. That is, tracking servo is applied so that these levels b0 and c0 become equal.

Further, the above-described differential detection method is used to detect the position of a segment mark. In this way, address segments are intermittently arranged,
By providing a segment mark in each segment, it is possible to eliminate the need to record a sector number and a tracking address in sector units.

[0009]

As described above, the track mark is provided on each track. One way to increase the recording capacity of the optical disk is to reduce the radial distance (track pitch Tp) of the track center between adjacent tracks, thereby increasing the track density. However, in the method of providing a track mark on each track, as the track pitch Tp decreases, the distance between the track marks in the radial direction of the disk decreases accordingly, making it difficult to detect a tracking error based on the reproduced RF signal of the track mark. Become.

FIG. 6 shows the spatial frequency (horizontal axis) in the radial direction versus M
The relation of TF (Modulation Transfer Function) (vertical axis) is shown. This graph shows that the wavelength of the laser beam is 680 [n
m] shows a change when an optical pickup with an aperture ratio NA of the objective lens of 0.55 is used. FIG. 6 shows that the track pitch Tp is (Tp = 1.6 μm, Tp = 1.2 μm)
(m, Tp = 0.8 μm) are shown. For example, when the track pitch of 1.2 μm is reduced to 0.8 μm, as can be seen from FIG. 6, the MTF is reduced to about ８. Since the MTF indicates the transfer characteristic of the amplitude, when the MTF is small, the level of a signal generated when a track mark is read becomes small, and normal tracking servo becomes difficult.

As a solution to the above problem, FIG.
As shown in FIG. 8, an oval track mark Pt is arranged on a track so as to cross the track diagonally (see Japanese Patent Application Laid-Open No. 5-73927). In this method, the reproduced RF signal shown in FIG. 7B is obtained according to the on-track and off-track states shown in FIG. 7A. FIGS. 7C and 8B show servo clocks generated so as to synchronize with the reproduced RF signal. Then, the reproduction RF signal of the track mark Pt shown in FIG. 8C is differentiated, and the time when the differentiated output shown in FIG. 8D becomes zero (T
3) and the phase difference ΔT between the rising edge of the servo clock (T2) is detected as a tracking error. In this method, the tracking error is not detected by the magnitude of the reproduction RF signal of the track mark itself. Therefore, the reduction of the MTF accompanying the reduction of the track pitch Tp does not become a problem, and the track pitch Tp is reduced. Can also detect a tracking error. However, this method has a problem in manufacturing optical disc media that cutting is difficult because it is necessary to form elliptical track marks. That is, it is necessary to move the head for embossing at a predetermined speed in the disk radial direction at the time of processing the optical disk medium, and high-precision control is required.

Accordingly, an object of the present invention is to provide a track mark having such a shape that a normal tracking servo can be performed even when the track pitch Tp is reduced in order to increase the track density and that the disk can be easily cut at the time of manufacturing the disc. An object of the present invention is to provide an optical disk medium, an optical disk device, and a tracking method.

[0013]

According to a first aspect of the present invention, a servo area is provided at a position intermittently in a track direction and aligned in a disk radial direction on each of concentric or spiral tracks. An optical disc medium characterized in that a pair of track marks formed physically in advance are arranged in a servo area with a space in the track direction small enough to cause mutual reproduction signals to interfere with each other.

According to a second aspect of the present invention, there is provided an optical disk apparatus for recording digital information on or reading digital information from a track formed concentrically or spirally on an optical disk medium.
Each of the tracks is provided with a servo area intermittently in the track direction and at a position aligned in the disk radial direction. The servo area has a small physical space in the track direction such that mutual reproduction signals interfere with each other. An optical pickup that generates a read signal by detecting a reflected light of a laser beam irradiated on an optical disk medium, and a reading position by the optical pickup. Tracking means for displacing in the direction, detecting the phase of the peak position of the reproduction RF signal of the pair of track marks, determining the direction and magnitude of the tracking error based on the detected phase, and setting the tracking error to zero. And the tracking control means for controlling the reading position. An optical disk apparatus according to symptoms.

According to a third aspect of the present invention, there is provided a tracking method for an optical disk apparatus, wherein digital information is recorded on or read from a track formed concentrically or spirally on an optical disk medium. In the optical disk medium, a servo area is provided intermittently in the track direction and at a position aligned in the disk radial direction, and a space in the track direction is reduced in the servo area to such an extent that mutual reproduction signals interfere with each other. Generating a read signal by detecting reflected light of a laser beam irradiated on the optical disk medium, and a peak of a reproduction RF signal of the pair of track marks. Detects the phase of the position and performs tracking based on the detected phase Determine the direction and magnitude of the error, so that the tracking error to zero, a tracking method for an optical disk apparatus characterized by comprising the step of controlling the reading position.

If the above-described optical disk medium, optical disk apparatus and tracking method are used, the reduction of the MTF due to the reduction of the track pitch Tp does not pose a problem, and normal tracking servo can be performed even if the track pitch Tp is reduced. is there. Moreover, there is an advantage that there is less problem in manufacturing the optical disc medium as compared with the above-mentioned proposed example in which an elliptical track mark is formed so as to obliquely cross a track.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a magneto-optical disk drive to which the present invention is applied. A sample servo type magneto-optical disk 1 as an information recording medium is rotated by a spindle motor 2. The magnetic head 3 includes a magnetic field control unit 18.
Disk 1 based on the signal supplied by
, A magnetic field having a polarity corresponding to the recording signal is applied. The optical pickup 4 irradiates the magneto-optical disk 1 with a laser beam and detects reflected light from the magneto-optical disk 1 to generate a reproduction signal. Although not shown, a slide motor is provided.
And the optical pickup 4 are moved in the radial direction of the magneto-optical disk 1. The signal read by the optical pickup 4 is supplied to the IV conversion and matrix unit 5.
The IV conversion and matrix unit 5 outputs a sum signal, a difference signal,
A focus error signal FE is generated. Laser controller 6
Controls, for example, a semiconductor laser incorporated in the optical pickup 4 and controls the intensity of laser light output therefrom.

Of the above three types of signals generated by the IV conversion and matrix unit 5, the sum signal is the A / D converter 7
After being subjected to A / D conversion, it is supplied to the PLL unit 8 and the differentiation circuit 9. The PLL unit 8 generates a servo clock SCK and a data clock DCK having a predetermined frequency and phase in response to the input of the A / D converted sum signal. The data clock DCK is supplied to the A / D converter 10 and the timing generator 12, respectively. The timing generator 12 generates a data synchronizing signal DSY and a clock and timing signal required for recording in accordance with the data clock DCK formed by the PLL unit 8,
The data synchronization signal DSY is supplied to the data detection circuit 11,
A clock and a timing signal necessary for recording are supplied to the data encoder 17. The operation of the data detection circuit 11 is as follows.
The data is synchronized with the data synchronization signal DSY, and the operation of the data encoder 17 follows a clock and timing signal required for recording.

On the other hand, the servo clock SCK formed by the PLL unit 8 is supplied to an A / D converter 7, a timing generator 12, and a phase comparison circuit 14. The timing generator 12 generates a mask signal corresponding to the servo clock SCK formed by the PLL unit 8, and supplies the mask signal to the peak detection circuit 13.

The differentiating circuit 9 supplied with the output of the A / D converter 7 (A / D converted sum signal) differentiates this signal, and the output of the differentiating circuit 9 is supplied to the peak detecting circuit 13. . The peak detection circuit 13 generates a peak pulse based on the output of the differentiation circuit 9 and the mask signal supplied from the timing generator 12, and supplies the generated peak pulse to the phase comparison circuit 14. The phase comparison circuit 14 detects the phase difference between the output of the PLL 8 (servo clock SCK) and the output of the peak detection circuit 13 (peak pulse). This phase difference is output to the servo control unit 19 as the tracking error signal TE. The servo control section 19 performs servo control based on the tracking error signal TE and the focus error signal FE from the IV conversion and matrix section 5.

On the other hand, the difference signal among the signals from the IV conversion and matrix section 5 is A / D converted by the A / D converter 10 and then output to the data detection circuit 11. The data detection circuit 11 detects data from the A / D-converted difference signal and outputs it to the controller 15 as reproduction data. The controller 15 supplies the reproduced data to the host computer 16. By this process, the host computer 16 makes the magneto-optical disk 1
Can be read out.

On the other hand, when writing data from the host computer 16 to the magneto-optical disk 1, recording data is supplied from the host computer 16 to the data encoder 17 via the controller 15. The data encoder 17 encodes the recording data and converts it into a recording signal for modulating a magnetic field. The output of the data encoder 17 is supplied to the magnetic field control unit 18. The magnetic field control unit 18
Based on the supplied recording signal, the signal supplied to the magnetic head 3 is controlled as described above, and the recording data is written on the magneto-optical disk 1.

Next, the operation of one embodiment of the present invention will be described. When, for example, a recording command is issued from the host computer 16 to the controller 15, the magneto-optical disk 1 is rotated at a predetermined speed by the spindle motor 2. Also, the host computer 16
Is supplied to the data encoder 17 via the controller 15. Data encoder 1
Reference numeral 7 encodes the supplied recording data at the timing of the data write clock, converts the encoded data into a recording signal, and supplies the recording signal to the magnetic field control unit 18. The magnetic field control unit 18 controls a signal supplied to the magnetic head 3 based on the recording signal supplied from the data encoder 17, and applies a magnetic field modulated by the recording signal to the magneto-optical disk 1. In this embodiment, the optical pickup 4 irradiates the magneto-optical disk 1 with pulsed laser light synchronized with the magnetic field modulated by the recording signal, so that the data supplied by the host computer 16 to the magneto-optical disk 1 Written. However, even during the operation according to the recording command, when the optical pickup 4 passes through the servo area of the optical disk medium, the same operation as the reproduction operation described below is performed. As a result of such an operation, the tracking servo is intermittently performed even during the operation according to the recording command.

On the other hand, when the reproduction mode is instructed, the laser control section 6 makes the intensity of the laser beam emitted from the optical pickup 4 to the magneto-optical disk 1 weaker than in recording. Then, information recorded on the magneto-optical disk 1 is read, and a read signal is supplied to the IV conversion and matrix unit 5. I-V corresponding to the read signal
Of the three types of signals generated by the conversion and matrix unit 5, the difference signal is supplied to the A / D converter 10. A
The / D converter 10 A / D converts the difference signal using the data clock DCK as a sampling clock, and supplies the difference signal to the data detection circuit 11. The data detection circuit 11 detects desired data from various data and outputs the data to the controller 15 as reproduced data.

An operation for eliminating a tracking error and a focus error will be described. The timing generator 12 generates a mask signal corresponding to the servo clock SCK formed by the PLL unit 8, and outputs the mask signal to the peak detection circuit 13. Peak detection circuit 1
3 extracts a differential waveform within a time limited by the mask signal, generates a peak pulse rising at a zero cross position where the differential waveform passes through zero (that is, a peak position of the reproduced RF signal (sum signal)), and generates the peak pulse. Is output to the phase comparison circuit 14. The phase comparison circuit 14 detects the phase difference between the servo clock SCK and the peak pulse from the peak detection circuit 13, and outputs this phase difference to the servo control unit 19 as a tracking error signal TE.

The servo control unit 19 includes a tracking error signal TE, an IV conversion and a matrix unit 5.
In response to the focus error signal FE output from the optical pickup 4, a tracking means such as a tracking mirror (not shown) of the optical pickup 4 and an actuator (not shown) for changing the distance between the objective lens and the magneto-optical disk 1 are controlled. .

FIG. 2 shows a mark pattern of a magneto-optical disk according to an embodiment of the present invention. The mark pattern is
Instead of a pair of track marks as in the conventional example, a pair of track marks P having a reduced space in the track direction
b and Pc are arranged on both sides of the track 20, and a clock mark Pa is provided at the track center.
These Pa, Pb and Pc are all provided in advance by embossing or the like.

In the example of FIG. 2, these three marks on the magneto-optical disk have a servo area of 24 SCK (SCK).
Means a servo clock generated based on the reproduced RF signal of the servo area). The distances defined by the servo clocks are first, second, third,
.., When represented by the 24th position,
The clock mark Pa is formed using the 2SCK over the position 2 and the 2SC clock is formed at the 14th and 16th positions.
A track mark Pb having a length of 2SCK is formed at the 16th and 18th positions.
Is formed. The space between Pa and Pb (2SCK in this example) has a sufficient length to prevent interference between reproduced RF signals. On the contrary, the space between the track marks Pb and Pc in the track direction is made small enough to cause the interference between the reproduced RF signals in order to easily form the above-mentioned peak pulse.

Each track of the sample servo type magneto-optical disk 1 to which the present invention is applied has a track mark P
The above-described mark patterns composed of b and Pc and the clock mark Pa are arranged radially from the inner circumference to the outer circumference and at predetermined intervals in the track direction. In FIG.
The track mark Pb on such a magneto-optical disk 1
When the spot of the laser beam from the optical pickup 4 hits (or Pc), the reflected light is converted into an electric signal by the optical pickup 4, and a tracking error is generated from the reproduced RF signals of the track marks Pb and Pc as described below. A signal TE is generated.

An embodiment of the tracking error detecting method according to the present invention will be described with reference to the timing chart of FIG. The PLL unit 8 outputs a servo clock SCK as shown in FIG. 3B in synchronization with the reproduction RF signal of the magneto-optical disk 1. The timing generator 12
A mask signal shown in FIG. 3F is generated based on the servo clock SCK and supplied to the peak detection circuit 13. The mask signal is output corresponding to a position within a predetermined range of the track mark (± 2 SCK around the boundary between Pa and Pb). During this mask signal period, the peak detection circuit 13 generates a peak pulse.

When the mark pattern arranged as shown in FIG. 3A is used, although not shown, the reproduced RF signal of the on-track locus is described above by the differentiating circuit 9 and the peak detecting circuit 13. The rising time of the peak pulse resulting from the above processing is shown in FIG.
B rise time t ₂ of the servo clock SCK generated in synchronization with the reproduced RF signal of the clock mark Pa shown in FIG.
Matches.

On the other hand, FIG.
Considering Xa of A, in this case, a reproduced RF signal as shown in FIG. 3C is mainly obtained by the track mark Pb. The above-described processing is performed by the differentiating circuit 9 and the peak detecting circuit 13 for the reproduced RF signal for the off-track locus Xa in exactly the same manner as the reproduced RF signal for the on-track.

That is, a reproduced RF signal as shown in FIG. 3C is supplied to the differentiating circuit 9. The differentiating circuit 9 differentiates the reproduced RF signal and supplies an output as shown in FIG. The peak detection circuit 13 extracts a differential waveform within a time limited by the mask signal, and generates a peak pulse as shown in FIG. 3E which rises at a zero cross position where the differential waveform passes through zero (that is, a peak position of the reproduced RF signal). The peak pulse is generated and output to the phase comparison circuit 14. As shown in FIG. 3E, the rising point of the peak pulse has a phase difference Δt (= t _{2) as} shown in FIG. 3E.
−t ₃ ) It is shifted. The phase comparison circuit 14 detects the phase difference Δt. The same applies to the off-track opposite to Xa, but the polarity of the phase difference Δt is opposite.

The phase comparison circuit 14 detects the detected phase difference Δt
(= T ₂ −t ₃ ) is output as a tracking error signal TE, and the servo control unit 19 controls a tracking means such as a tracking mirror (not shown) based on the tracking error signal TE, and the tracking error becomes zero. And apply the tracking servo.

The present invention relates to a rewritable disk such as a phase change disk PD other than a magneto-optical disk (MO),
The present invention can be applied to an optical disc device such as a write-once disc such as a DR or a read-only disc such as a CD-ROM. Further, the present invention is not limited to this embodiment, and various applications and modifications can be considered without departing from the gist of the present invention.

[0036]

As described above, the present invention relates to an optical disk medium comprising a pair of clock marks provided at the track center and a space in the track direction on both sides of the track reduced to such an extent that mutual reproduction signals interfere with each other. A track mark is arranged, and a tracking error is detected as a phase shift between the servo clock SCK generated in synchronization with the reproduction RF signal of the clock mark and the reproduction RF signal of the track mark. Therefore, according to the present invention, since it is not necessary to separate and reproduce the two track marks, a normal tracking servo can be performed even if the MTF is reduced as the track pitch Tp is reduced.
This makes it easier to reduce the track pitch Tp as compared with the related art, and can increase the recording capacity. Further, in the present invention, there is little problem that cutting is difficult at the time of manufacturing an optical disc medium in the above-mentioned proposed example having the same effect.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a magneto-optical disk drive to which the present invention is applied.

FIG. 2 is a schematic diagram showing a mark pattern on a sample servo type magneto-optical disk used in the present invention.

FIG. 3 is a schematic diagram of a tracking error detection method in a sample servo type magneto-optical disk according to the present invention.

FIG. 4 is a schematic diagram of a mark pattern of a conventional sample servo method.

FIG. 5 is a schematic diagram of a differential method used in a conventional example.

FIG. 6 is a schematic diagram for explaining a problem in a conventional sample servo type magneto-optical disk.

FIG. 7 is a schematic diagram for explaining a previously proposed oblong track mark obliquely crossing a track and a tracking error detection method using the track mark.

FIG. 8 is a timing chart for explaining the tracking error detection method of FIG. 7;

[Explanation of symbols]

1 ... Magneto-optical disk, 4 ... Optical pickup, 8
... PLL section, 9 ... differentiation circuit, 12 ... timing generator, 13 ... peak detection circuit, 14.
..Phase comparison circuits, 19 ... servo control units
Pa: clock mark, Pb, Pc: pair of track marks

Claims (3)

[Claims] A concentric or spiral track is provided with a servo area intermittently in the track direction and at a position aligned in the disk radial direction, and the reproduced signals interfere with each other in the servo area. An optical disk medium characterized in that a space in the track direction is reduced to such an extent that a pair of physically formed track marks are arranged. 2. An optical disk apparatus in which digital information is recorded on a track formed concentrically or spirally on an optical disk medium, or digital information is read from the track, wherein each of the tracks is provided in a track direction. Servo areas are provided intermittently and at positions aligned in the disk radial direction. The servo areas have a space in the track direction that is small enough to cause mutual reproduction signals to interfere with each other. An optical pickup for generating a read signal by detecting reflected light of a laser beam irradiated on the optical disk medium, and displacing a read position by the optical pickup in a disk radial direction; Tracking means; A phase of a peak position of a reproduced RF signal of the recording, a direction and a magnitude of a tracking error are determined based on the detected phase, and the reading position is controlled so that the tracking error is zero. An optical disk device comprising control means. 3. A tracking method for an optical disk apparatus, wherein digital information is recorded on a track formed concentrically or spirally on an optical disk medium, or digital information is read from the track. The servo area is provided intermittently in the track direction and at a position aligned in the disk radial direction, and the space in the track direction is reduced in the servo area to such an extent that mutual reproduction signals interfere with each other, and physically A step of generating a read signal by arranging the formed pair of track marks and detecting reflected light of the laser beam irradiated onto the optical disc medium; and generating a read RF signal of the pair of track marks. Detects the phase at the peak position, and based on the detected phase, Determining the direction and magnitude of the locking error and controlling the reading position so as to reduce the tracking error to zero.