JPS6157084A - Tracking servo method - Google Patents

Abstract

PURPOSE:To continue the tracking under the vibration of an optical disk or defects, etc., by executing a tracking control between sectors with the aid of the addition signal of a position signal of an optical head, decentering correction signal and a tracking error signal at the time of detecting a center mark. CONSTITUTION:A tracking error signal is inputted and added to an addition amplifier 41 together with an arm position holding adjustment signal corrected by a decentering correction table value, controls a rear motor 15 as a tracking control signal, shifts an optical head 14 in the radium direction of an optical disk and follows a data track with the aid of a light beam. The arm position holding adjustmen signal always detects whether or not a target track is the arm positio corresponding to a target track, and causes the target track to hold the position of the optical head. Since the tracking error signal shifts slightly the optical head in such a way that said head will not deviate from the track caught currently, the target track can follows the optical head. Thus the stable tracking becomes possible without fail.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a method for recording and reproducing information on an optical disc.
Regarding a tracking servo method that enables a light beam to follow a desired track, specifically, it is a tracking servo method for an optical disc that has a plurality of concentric tracks without a track guide structure, and each track has a sector mark. Regarding methods (“).

(Prior Art) In recent years, optical disks have been developed as a new recording medium and are rapidly becoming popular in the fields of video and digital audio. This optical disc is superior to conventional optical discs in that it has an extremely large recording capacity, can be used semi-permanently because the pickup is non-contact, is easy to random access, and is cheap per bit. It is extremely superior to TC recording media, and research is being conducted to use it as a recording medium in the computer field.

When the original disk is used for a computer, random access is performed extremely frequently, and in addition to the operation of detecting a desired track at high speed, the transition operation from this detection operation to tracking operation is extremely difficult. It must be done quickly and stably. In such optical discs, the amount of reflected light or transmitted light from the disc surface of the irradiated light beam is detected, and tracking is performed based on this detected value. the current,
Most optical discs are optical discs with tracking guide grooves, and tracking is achieved by focusing the reflected return light beam affected by the guide grooves on the disc surface onto the light receiving surface of a photodiode that is divided into multiple parts. A tracking error voltage is generated based on the output difference of each light receiving element, and the amount of movement of the optical head in the disk radial direction is controlled by this tracking error voltage.

When an optical disc has a tracking guide groove in this way, tracking is easily possible using the guide groove during both recording and reading (playback), but manufacturing of the recording medium, including the formation of the guide groove, is difficult. It is complicated and optical discs are expensive. Furthermore, since the structure is complicated and the defect rate of the recording medium itself is high, there is a drawback that the signal error rate is high when recording or reproducing signals on the recording medium. Furthermore, if the guide grooves have already been formed, there is a restriction that it is not possible to record and reproduce data using a free format on the optical disc. In particular, if various marks are previously provided in accordance with a specific format at the same time as the guide grooves, signals cannot be recorded on the optical disc in other formats.
1 (Object of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a tracking servo method that enables tracking with an optical disk that does not have a tracking guide structure (no groove). Another object of the present invention is to provide a tracking servo method that continues tracking a target track even if a grooveless optical disk vibrates or there is a defect on the optical disk.

(Structure of the Invention) The above-mentioned object of the present invention is to obtain a position signal of an optical head corresponding to a target track in the tracking of an optical disk having concentric tracks having only sector marks and no track guide structure. This is achieved by a tracking servo method that performs tracking control between sectors based on the total sum of the eccentricity correction signal and the tracking error signal at the time of sector mark detection. The tracking error of the optical head is detected, and tracking control is performed by retaining all of this tracking error signal until the next sector mark. At the same time, the eccentricity correction amount of the original disk is added to this tracking control, and furthermore, the eccentricity correction amount for the current track is The position of the optical head is always maintained and tracking control is performed. Therefore, in tracking control, □For one rotation of the optical disk, tracking error control is performed for the number of sectors.
Eccentricity correction is performed at least as many times as the number of sectors.

As a result, normal tracking is normally achieved, but since the position of the optical head is constantly checked and corrected with respect to the current track by a position sensor installed outside the original disk, the optical head may move to another track due to vibration etc. Even if it moves, it will not continue to follow that track.

Here, a sector mark is a plurality of pits provided in a part of a track, and the length and interval of a series of these pits are determined to be different from those of pits for data information. . These marks are arranged so as to be shifted in the rotational direction of the disk for each track, for example, so that the track address can be recognized by detecting the angle from the nine reference positions.

In addition, the position signal of the optical head corresponding to the target track is a signal that holds the value indicated by the position counter of the optical head when the optical head detects the sector mark of the target track, and is a signal that holds the value indicated by the position counter of the optical head. This is a hold adjustment signal. This signal is not obtained from the optical disk, but from a position sensor for the optical head provided in the optical disk drive device.

(Example) l! First, the optical disc used in the present invention will be explained.

FIG. 1 is a schematic diagram of an optical disc for explaining the format of the original disc. In the figure, an optical disk 1 has a disk shape with a circular hole 2 at the top and center, and has a recording layer made of a thin metal film or the like on a transparent or opaque support. This recording layer is deformed or otherwise changed by, for example, irradiation with focused laser light, forming optically detectable pits in the irradiated areas. Any material and structure of the recording layer for forming such a recording layer, as well as the structure of the optical disc, can be used as desired.

The range indicated by 3 in the figure is a data recording area, in which data tracks, which will be described later, are formed concentrically at regular intervals. The recording layer is provided outside the inner and outer peripheries of the data recording area. 4 is data recording area 3
A reference track provided on the outside or inside of a
It is a concentric track larger than a book. The reference track 4 is provided to detect eccentricity with the optical head of the device when the optical disk 1 is loaded into the device, and is recorded so as to be completely concentric with a data track, which will be described later.

Reference numeral 5 indicates an origin mark, which is placed one on the circumference, and reference numeral 6 indicates a reference point mark, which is provided in multiple numbers on the circumference.These marks are detected by a photoelectric conversion device, etc. each time the optical disc rotates, and thereby The rotational position of the original disk is detected. For example, 64 base point marks are provided along with the origin mark at equal angular intervals' (angle A in the figure). The origin mark 5 and the base point mark 6 are detected separately as signals, and the marks themselves may have any shape.

7 is a sector mark provided for each angle on each data track, and is a mark indicating the beginning V of each sector on the track. As shown in an enlarged view in FIG. 2, sector marks 7 are fixed marks provided at regular intervals on concentric tracks 8 (in the figure, the boundaries between tracks are indicated by broken lines for convenience). There is no guide such as a groove indicating a track between the sector -8, - mark and the sector mark on the same track. The sector marks between adjacent tracks are shifted by a certain angle in one direction when viewed from the center of the disk, and when the sector marks are sequentially shifted by a specific number n (six in the figure) of tracks, n, The same angle as the sector mark 2 of the inner or outer track is made, and sector marks are provided on all data tracks by repeating this process. The above-mentioned specific number of tracks is indicated by track group 9 in the figure. A track group is formed of, for example, 16 tracks.

FIG. 3 is an enlarged view of the sector mark 7. The sector mark 7 is a pit in which a plurality of pits 10 are arranged.
The length and bit interval of each pit are set to a size that is different from the pit length and pit interval of the data to be recorded, so that it can be distinguished and identified as a signal. For example, if the data hit length and pit spacing are approximately 1μ to 2μ, the sector mark 7
The length and spacing of the pits 10 used for this need only be about 4 μ, and the number of pits 10 should be about 12.

That is, the source disk used in the present invention does not have a track guide such as a group, but tracks are identified by pits, and at least one circular reference track is provided separated from the data track. 1 data track is provided concentrically with the reference track, and each data track
Sector marks that divide the circumference of a track are provided at equal angular intervals in each data track, but these sector marks are shifted by a certain angle in adjacent tracks! lln tracks are provided so as to be shifted by an angle of one sector. Therefore, n books! The sector marks for each track are arranged at the same angle. Sector marks are provided as pits with a different length from the pits of the recorded data, and are a common mark that only indicates the start of a sector, and does not indicate the track number or sector number. Furthermore, this optical disc is provided with at least one mark for detecting the rotational position of the original disc. Such marks are used as motor control signals for controlling the rotation of the optical disk or sector identification signals.

Next, the tracking servo method of the present invention will be explained using the drawings. FIG. 4 is a block diagram of an example for implementing the method of the present invention, mainly showing the flow of signals in the tracking servo system. In the figure, the optical disc 1 is loaded into the original disc recording/reading device, is engaged with the spindle 12 of the motor 11 through the circular hole 2, and is further fixed by the mounting member 13. The recording surface of the optical disc 1 faces the optical head 14, and the optical head 14
Signals are written to and read from the optical disc 1. The optical disc 1 is rotated by the motor 11 at 45
The optical head 14 rotates at a constant speed of about 0rrW, and is moved in the radial direction of the optical disk 10 by a linear motor 15, recording signals on the track with a light beam, and reading signals from the track with a light beam. A light beam 16 passing through the optical head 14 is outputted from a semiconductor laser 17, and the beam diameter is appropriately adjusted by a lens system, and then sent to a polarizing beam splitter 18, 174, a wavelength plate 19, and a mirror 20.
．． 21, the beam is irradiated onto the optical disk 1 by the objective lens 22 with a beam diameter of approximately 1 μm.

Further, the light reflected from the optical disk 1 passes through the objective lens 22, the mirror 21, and the 20.1/4 wavelength plate 19, and then is reflected by the polarizing beam splitter 18 and is sent to the photodetector 23.
The pits recorded on the optical disc 1 are read out as signals by the photodetector 23.

The photodetector 23 may be, for example, a well-known four-split photodetector, and its output is inputted via a processor 24 to a data signal reader 25, a tracking error detector 26, and a sector mark detector 27. Data signal reading section 2
The data signal from 5 is sent to the data signal processing section, and the tracking error signal output from the tracking error detection section 26 is input to the sample hold circuit 50 and the summing amplifier 41. Further, the sector mark detection signal output from the sector mark detection section 27 is input to each sample and hold circuit as a signal for sampling and holding the output from the rotation angle counter and a signal for sampling and holding the tracking error signal.

On the other hand, the reference position detector 28 detects the origin mark 5 and the reference point mark 6 provided on the outer periphery of the optical disc, and inputs a reference pulse to the synchronization pulse generator 29. For example, a total of 64 origin marks 5 and 64 origin marks 6 are provided, so each time the optical disc 1 rotates, 6 reference pulses are generated.
4 occur. The synchronizing pulse generating section 29 is composed of a PLL circuit, which inputs a reference lock, synchronizes the reference pulse with the PLL, and outputs its output to the motor control circuit 30 and rotation angle counter 31. The motor control circuit 30 controls the motor 11 to rotate at a constant speed based on the input pulses. Further, the rotation angle counter 31 counts the input pulses and outputs them to the sample/hold circuit 32.
Output to. The pulse generation circuit 33 generates, for example, 256 pulses as sample-and-hold signals for each revolution of the optical disk, and sends them to sample-and-hold circuits 40, 44, and 4.
Output to 9. Assuming that the aforementioned track group of the optical disc is formed of 16 tracks, if there are 64 sectors, there are 16×64=1024 sector mark positions (angles seen from the center of the optical disc).

First, track seek will be explained. Track seek moves the optical head 14 to a target data track.Rough seek moves the optical head 14 at high speed to near the target track position, and rough seek moves the optical head 14 to the target track position accurately. It can be divided into two modes: fine seek and movement to the track position.

First, when the target track value (bottom left in the figure) is set, this value is converted by the track value/position counter value converter 34 as a position counter value and inputted to the subtracter 35 . On the other hand, the current position of the optical head 14 is determined by a position counter 38 counting pulses generated from a position sensor 37 that moves together with the optical head 14 and detects the amount of movement of the arm 36 of the near motor. It is stored as a position counter value. The current position counter value of the optical head 14 is output from the position counter 38 to the above-mentioned subtracter 35.
The subtracter 35 calculates a position counter value corresponding to the difference between the target position and the current position and outputs it to the speed table 39.

The speed table 39 contains a signal for controlling the linear motor 15 to reduce the moving speed when the target track position approaches, in order to avoid an overshoot operation in which the optical head 14 passes the target track position when moving at high speed. occurs. A signal indicating the amount of movement corresponding to the difference between the current position and the target position output from the speed table 39 is input to the sample/hold circuit 40, where it is sampled by the pulses from the pulse generation circuit 33 mentioned above and becomes an arm drive signal. Adding amplifier 41 as (signal ■)
sent to. The addition amplifier 41 outputs its output to the linear motor 15 to move the arm 36 in a predetermined direction. The amount of movement of the arm 36 is read by a position counter 38 via a position sensor 37, and the value is also input to a subtracter 35. In this way, the current position of the optical head approaches the target position, and when the distance between the two positions is large, the arm 36 is moved at high speed via the speed table 39, and when the distance is small, the arm 36 is moved at low speed.

When it is determined that the optical head 14 has reached the target position according to the position counter value, the rough seek by the signal ■ is completed.

If a delay in arm tracking during arm drive becomes a problem, the error corresponding to the delay in arm movement is output as a counter error value (signal ■) from the position counter 38 and directly added to the amplification signal. If the signal is sent to the device 41, the accuracy of arm drive will be improved. This counter error value is a signal proportional to the moving speed of the arm (obtained by differentiating the count value in the position counter).

A linear encoder may be used as the position sensor 37, but its accuracy may be as long as it can detect about half the radial width of one track group. For example, if the track spacing is 2μ and the track group is formed by 16 tracks, then the accuracy of about 10μ is sufficient. Here, we will explain highly accurate position sensors and position counters.

The arm for moving the optical head is provided with a grating along the moving direction of the arm, that is, the radial direction of the optical disk. This grating may have a grating spacing of approximately 128 microns, for example. The position sensor is fixed to the apparatus side close to the grating portion of this arm, and has a grating having the same grating spacing as the grating and slightly shifted angle, a light irradiation means, and a light detection means. The two gratings form a moire pattern, and the moire spacing is selected depending on the accuracy of position detection. Further, the photodetecting means is formed of four photodetectors arranged in the direction in which the moire pattern moves depending on the interval between the moire patterns. That is, four photodetectors aI b
l C+d are arranged at equal intervals in the moving direction of the moiré so as to equally divide the l interval into four. The difference signal between photodetectors a and C generates a sine wave in response to the movement of the moire, that is, the movement of the arm holding the optical head. Similarly, the difference signal between the photodetector and the photodetector d also generates a sine wave. However, the phases of both signals are shifted by π/2, and the amplitude and phase are fully adjusted by drawing, for example, a Lissajous waveform so that both signals become a perfect sine wave. In this way, from the position sensor, the grid interval is 128 depending on the position of the optical head.
A sin whose amplitude and phase are periodically aligned every time it moves μ
X XCO5X is output to the position counter. On the other hand, in the position counter, when a target track value is set, the position at the position sensor corresponding to that track is converted,
According to the phase y, sin V XCO3V is output from the table. 5inxco in position counter
sy −cosxsin3' = sin (x −y
), each of the above signals is input to a circuit of 5in(X-
X is set so that y)=0. In this way, X is determined, but since X has the precision of dividing into 2π'i 4096, the grid size of the position sensor is 128μ'! :4.0
The accuracy of dividing into 96, that is, this position sensor is 0.03
It has an accuracy of 2μ.

In other words, the total track spacing of the optical disc is 2μ, and 16
When one track group is made up of tracks, if the grid spacing of the position sensor is 128μ, the grid spacing is 64 tracks (4 track groups), but as mentioned above, the position sensor has very high precision. , the optical head can be moved close to the target track even during rough seek.

Next, fine seek will be explained. Since the optical head 14 is moving to a track near the target track in the rough seek, the target track is detected from several tracks before and after the target track based on the angle of the sector mark in the fine seek. The input target track value is output by the track value position counter value converter 34 to the temporary target track value correction circuit 42 as a position counter value of the target track. The temporary target track value correction circuit 42 initially outputs the input value to the subtracter 43, and the subtracter 43 combines this value with the position counter value corresponding to the currently detected track obtained from the position counter 38. Subtraction is done. The output of the subtracter 43 is sampled by a sample/hold circuit 44 using pulses from the pulse generating circuit 33 (256 pulses per rotation of the optical disk) and outputted to the summing amplifier 41 as an arm movement amount adjustment signal (signal ■). . In this way, the addition amplifier 41 outputs, for example, an arm movement amount adjustment signal indicating a movement amount of several tracks to the linear motor 15, and the optical head moves in a direction closer to the target track.

On the other hand, the current track value is detected from the optical disc 14 as follows. The binary code signal from the rotation angle counter 31 is input to the sample and hold circuit 32, where it is sampled and held by the sector mark detection signal from the sector mark detection section 27. That is, the rotation angle counter value when sector mark 7 was detected is held, and the output from this sample/hold circuit 32 is a value corresponding to the angle from the base point of the original disk to the sector mark, so the track value The identification circuit 45 identifies the currently detected track value. Track value identification circuit 45
outputs a signal corresponding to the current track value to the above-mentioned temporary target track value correction circuit 42, and if there is an error between the signal corresponding to the target track value already set in the temporary target track value correction circuit 42; Then, the signal corresponding to the target track value is modified and outputted to the subtracter 43 as a position counter value so that the track value identified by the track value identification circuit 45 matches the target track value. The subtracter 43 outputs its output to the sample-and-hold circuit 44, and the sample-and-hold circuit 44 outputs it as an arm movement amount adjustment signal to the addition amplifier 41, and the addition amplifier 41 sends this signal to the linear motor. to move the optical head.

Repeat this signal for each sampling described above. Repeat nine times to make the optical head reach the target track.

Fine seek ends in this way.

Note that even after the optical head detects the target track, the track value identification is always repeated, and the signal (2) acts as an arm position holding adjustment signal so as not to deviate the optical head from the track.

The eccentricity correction during this fine seek will be explained.

When an optical disk is loaded, the reference track 4 is first followed by the optical head 14, and if there is no eccentricity, the reference track 4 is
The difference between the position counter value of the concentric circle that should be indicated and the position counter value of the reference track 4 obtained by actual tracking is sampled at 9256 points per rotation of the optical disc to obtain the eccentricity amount, and the value is stored in the eccentricity correction table 46. to be memorized. At this time, the signal obtained by the tracking error detection section 26 is used as it is as the tracking error signal (signal ■). The bias 6 correction value from the table 46 is outputted by the changeover switch 47, added to the position counter value, and inputted to the subtracter 43. In this way, even if the position counter value fluctuates during one revolution of the optical disk due to the optical disc tracking an eccentric track, the amount of fluctuation is offset and the eccentricity of the track is corrected as a constant position count value. It is input to the subtracter 43 and calculations are performed without the influence of eccentricity.

This changeover switch 47 is normally set so that this correction value is output.

Further, a feedforward eccentricity correction value is calculated based on the eccentricity value of this eccentricity correction table, and is stored in the feedforward eccentricity correction table 48. The feedforward eccentricity correction value is a correction value given to correct the eccentricity of the current rotational angular position at a position before the currently detected rotational angular position of the optical disc, and is This is a correction value given in advance in anticipation of a delay in the response of the lJ near motor 15. Note that this correction value is a value proportional to the actual amount of eccentricity, and is given at a sampling point several points in advance depending on the response of the linear motor.

The correction value outputted from the feedforward eccentricity correction table 48 is sampled by the sample-and-hold circuit 49 using the pulse from the pulse generation circuit 33, sent to the summing amplifier 41 (signal ■), and applied to the linear motor 15. This will explain the tracking servo method in detail for fine seek. Here, what is tracking servo? □Before. 4. Wow. 57. -1
Eye 7: After the target data track □ is detected by the optical head by seek, the optical head □ is accurately followed on the data track.
: (tracking'). The light beam emitted from the optical head is the data tiger.

If the bit deviates from the center of the track, the tracking leg error detection unit will track the deviation in the radial direction of the optical disc in the optical spatula 1 due to the distribution of reflected light from the optical disc, etc., and generate a tracking error signal. do. Means for generating such a tracking error signal are well known, and any means can be used. Tracking error signals are generated not only from the sector mark part in the data track but also from the data recording part between the sector marks, so in order to extract only the tracking error signal based on the sector mark, it is necessary to sample according to the sector mark detection signal. - Sampling is performed by the hold circuit 50, and the signal is held until the next sampling and sent to the summing amplifier 41 as a tracking error signal (signal ■). The linear motor 5 is controlled by this signal, and the optical head is held at a constant position from one sector mark to the next sector mark.

Note that this tracking error signal is used occasionally to follow and check the track during the fine seek described above, but is not used during the seek operation.

This tracking error signal (signal ■) is input to the addition amplifier 41 together with the arm position holding adjustment signal (signal ■) corrected by the eccentricity correction table value described above, and is added to the linear motor 15 as a tracking control signal.
is controlled, the optical head 14 is moved in the radial direction of the optical disk, and the original beam is caused to follow the data track. The above-mentioned arm position holding adjustment signal always detects whether or not the arm position corresponds to the target track and maintains the position of the optical head with respect to the target track, and the tracking error signal detects whether the arm position corresponds to the target track or not, and the tracking error signal is used to detect whether or not the arm position corresponds to the target track. Since the entire optical head is moved minutely so as not to deviate from the target track, the target track is always followed.

If you calculate it, you can get even more accurate tracking. By using this feedforward eccentricity correction, even if the optical head is heavy or the drive system such as a linear motor has a slow response, it can be used for a high-speed optical disk rotation system.

The above-mentioned signals are collectively shown in the table.

In the table, mark the mode in which each signal is used in the corresponding column.
It is indicated by a mark.

Table □' To set each operation mode as described above, each input terminal of the summing amplifier 41 is provided with a switch, and the mode setting sequencer is used to switch the switch 2 according to the mode as shown in the table above. Bye. A selected signal is output from the addition amplifier 41 to the near motor 15 for each mode.

Although the servo system circuit in this embodiment has been described above, the circuit that can implement the present invention is not limited to this, and various other circuits can be considered.

(Effects of the Invention) According to the tracking servo method of the present invention, the currently tracked track is not only followed by an optical head based on an optical signal, but also by a position sensor provided outside the optical disk.・Since the position of the optical head is maintained by using the optical head, stable tracking is possible at all times. According to the method of the present invention, even if the optical head deviates from the target track due to vibration or the like, the optical head returns to the target track immediately, so that stable tracking can be achieved. Furthermore, even if the optical disc has a defect, stable tracking is possible without losing sight of the target track.

According to the present invention, tracking is possible even on an original disk without a track guide structure.

Also, when using the optical disc used in the present invention, the track number and sector number can be changed to the optical disc! Track seeking is possible even if the optical disc is not recorded, and high-speed seeking is possible since there is no judgment means for detecting the number of tracks on the optical disc. Furthermore, when this optical disk is used, the seek functions are divided into rough seek and fine seek, so it is possible to use a device sensor with a precision coarser than the track spacing.゛

[Brief explanation of drawings]

i・□1. 〜□3゜. ,,,Good,□ゎExplanatory diagram of the format of the Aka disk, 1. Fig. 4 is a block diagram of an embodiment of the method of the present invention.
・1... Optical disc 3... Recording area 4... Reference track 5... Origin mark 6...
・Base point mark 7... Sector mark 8...
Data track 9...Track group 10...Bit 14...Optical head 1
6... Original beam 22... Objective lens 23...
Photodetector 26...Tracking error detection unit 27...Sector mark detection unit 31...Rotation angle counter 33...Pulse generation circuit 34...Track value-position counter value converter 37...
・Position sensor 38...Position counter...Additional amplifier 42...Temporary target track value correction circuit 45...Track value identification circuit 46...Eccentricity correction teni, pull 48...Feed forward type AQ-ω in the eccentricity correction table

Claims (1)

[Claims] In tracking an optical disk that has concentric tracks with only sector marks and no track guide structure, the position signal of the optical head corresponding to the target track, the eccentricity correction signal, and the tracking error signal when detecting the sector mark A tracking servo method characterized in that tracking control between sectors is performed based on a signal obtained by adding the signals.