JPH0262727A - Optical disk and optical disk device - Google Patents

Abstract

PURPOSE:To eliminate the need for an additional data and to attain quick and highly accurate access by deviating a servo area arranged periodically on each track in th direction of track length between adjacent tracks. CONSTITUTION:A servo area As is provided at a prescribed period T on tracks 3a - 3d, and two servo pits 1a, 1b with a deviation of DELTA in the track longitudinal direction are provided on each servo area As. The servo area As is deviated by DELTA in the track longitudinal direction between adjacent tracks. In the case of detecting a recording data from the optical disk, a signal regenerated from the optical disk by a photodetector 5 is fed to a sample-hold circuit 6 and a binarization circuit 8, in which the regenerative signal is binarized and a pulse signal representing each pit on the optical disk is waveform-shaped, fed to a control circuit 12 and the data pattern is decided. Thus, the high speed access is implemented quickly with high accuracy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical disc in which servo areas in which servo pits including at least clock synchronization information are recorded are arranged periodically for each track, and an optical disc for the optical disc. The present invention relates to an optical disc and an optical disc device that perform high-speed access by detecting the number of tracks traversed.

[Conventional technology]

Conventionally, various high-speed access methods have been proposed for optical disc devices such as CD players and optical video disc devices, one of which is known as a method using an external scale. In this method, the position of the optical head is detected using an external scale, and based on the detection result, the movement of the light spot from the optical head is controlled to a target track. However, this method has problems such as the need for a highly accurate external scale, the need for correction for eccentricity of the optical disk, and the coarse scale pitch of the external scale, which causes rounding errors.
Since track-by-track access is not possible, this method is used for coarse access and requires a separate means for fine access.

Therefore, there was also a problem that the access time became long.

In contrast, the number of tracks crossed by the light spot is detected,
A method is also known in which the position and moving speed of the light spot are determined from this detection result, and the light spot is moved to a target track while controlling the moving speed of the light spot.

One method for detecting the number of tracks crossed by a light spot is to use a guide groove (pre-group) provided in advance on the optical disc to control tracking of the light spot when reproducing data from the optical disc (for example, Paper ``High-speed access method for optical disk memory'' at the ``Optical Memory Symposium '86'' held on December 18, 1986).

A guide groove is formed in advance in a spiral or circular shape on the optical disk. A tracking control signal is obtained from this guide groove, and tracking control is performed using this so that the light spot follows this guide groove, and this light spot records and plays data.

This guide groove is formed continuously, and there is a guide groove for each track.

Therefore, when the light spot crosses this guide groove, the track also crosses it, and for this reason, it is necessary to detect and count the amplitude fluctuation caused by the light spot of the signal obtained from the photodetector crossing the guide groove. This allows us to know the number of tracks crossed by the light spot.

On the other hand, as another example of the tracking control method, a so-called sample servo method is also known, in which areas for detecting tracking control signals are provided discontinuously on an optical disc.

In an optical disc adopting this method, as shown in FIG. 9, each track 3a+3b of the optical disc.

A servo area A3 is provided at a constant period (interval) for every 3c, 3d,... Two servo pits la and lb are recorded which are offset from each other in the longitudinal direction of the track. Assuming that the optical disk rotates in the direction of arrow X and the light spot 4 is on the track 3a, the light spot 4 first detects the servo pit 1a and then the servo pit 1b in the servo area A. do. Therefore, a tracking control signal is obtained by comparing the amplitude of the detection signal from the servo pit la and the amplitude of the detection signal from the servo pit 1-1b.

Note that a synchronization pit is also recorded in the servo area A, and the clocks are synchronized by this synchronization pit, but this synchronization pit will be omitted in the following explanation.

Such optical discs do not require guide grooves whose width and depth must be uniform with high precision, and therefore interference between information reproduced from the guide grooves and data to be reproduced is not a problem. However, during high-speed access, the fact that the light spot 4 has crossed the track is detected by the light spot 4 crossing the servo area A3 on the track, but the servo area A is discontinuous. Therefore, the light spot 4 often crosses tracks between the servo areas As, and the number of tracks crossed by the light spot 4 cannot be detected as it is.

One way to make this possible is, for example, with 5PTE
Vol 695 0ptical MassDa
ta Storagell (1986) pp.
160-164. This is to record a gray code or the like representing a track address for each track. During high-speed access, when the light spot is moving rapidly in the radial direction of the optical disc, the light spot may cross parts of the track where the code is not recorded, but the light spot may cross the part where the code is recorded. When this code is detected across the track, the position of the light spot can be determined from this and the code of the start track of the fast access.

[Problem to be solved by the invention]

By the way, in the above-mentioned high-speed access using an optical disk in which guide grooves are formed in advance, if no data is recorded on the tracks, each track traversed by the light spot can be determined one by one.

However, if data is recorded on the track and the light spot crosses this part, if data is recorded in the guide groove, this guide groove is deformed by the data bit, and the light spot crosses the guide groove. The waveform of the detection signal due to the crossing may be distorted, and a signal detection error may occur, resulting in an error in the number of detected tracks. There is also a method that focuses on the frequency difference between the data bit detection output and the guide groove detection output, and separates the guide groove detection output from the reproduced signal using a filter or the like. However, when the moving speed of the optical spot is low, this method is possible because the frequency of the detection output of the guide groove is sufficiently low compared to the frequency of the detection output of the data bit, but the moving speed of the optical spot is high. Then, the frequency difference between the two becomes small, making it impossible to separate them. For this reason, the moving speed of the optical spot is also limited, and there is a problem in that the access time cannot be shortened.

On the other hand, in the case of an optical disk using the sample servo method, the above code is detected, so the movement speed of the optical spot can be increased and the access time can be shortened, but the above code is not required. Therefore, there is a problem that the data recording area is reduced, and the recording capacity of this spectroscopic disk is therefore reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disk and an optical disk device that eliminate such problems and enable quick and highly accurate access without requiring additional data.

[Means to solve the problem]

In order to achieve the above object, an optical disc according to the present invention employs a sample servo method, in which servo areas periodically arranged for each track are shifted in the track longitudinal direction between adjacent tracks. .

Further, an optical disk device according to the present invention uses the optical disk according to the present invention, and includes means for detecting a servo signal from a servo pit from a detection signal of a photodetector, means for generating a clock synchronized with the servo signal, and a means for generating a clock synchronized with the servo signal. means for counting and outputting the count value at the timing of the servo signal, and means for generating a light spot speed control signal from the outputted count value.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial plan view showing an embodiment of the optical disc according to the present invention, in which la and lb are servo pits, 2 is a data bit, 3a, 3b, 3c, and 3d are tracks, 4 is a light spot, and A3 is a The servo area and Ao are data areas.

In the figure, each track 3a to 3d is provided with a servo area A with a constant cycle T.

In each servo area A, there are two servo pits la and l that are offset by an equal distance in the opposite direction from the center of the track indicated by the broken line, and are also offset by Δ in the longitudinal direction of the track.
b is provided. Furthermore, between adjacent tracks, the servo areas As are shifted by Δ in the track longitudinal direction.

Moreover, the directions of deviation of the servo areas A are opposite to each other between adjacent tracks on both sides.

Here, if the arrow
For example, regarding the track 3b, the servo area A in the adjacent track 3a on the outer circumference side on the negative side is advanced by Δ, and the servo area A on the other adjacent track 3C on the inner circumference side is delayed by Δ.

Between these servo areas A is a data area AI where data bits are recorded.

When detecting (reproducing) recorded data from such an optical disc, servo pits la and lb of servo area A are used for tracking control. When moving the optical head, and therefore the optical spot 4, at high speed in the radial direction of the optical disk to perform high-speed access, these servo pits l
a and lb are used to detect the number of tracks crossed by the light spot 4.

Next, an embodiment of the disk device according to the present invention which performs the above operation will be described with reference to FIG. However, in the same figure, 5 is a photodetector (optical head), 6 is an S/H (sample hold) circuit, 7 is a phase compensation circuit, 8 is a binarization circuit, and 9
is a gate circuit, 10 is a counter, 11 is a PLL (phase locked loop) circuit, 12 is a control circuit, 13
14 is a switch, 15 is a power amplifier, and 16 is a tracking actuator.

First, when reproducing data from an optical disc, the switch 14 is closed to the A side.

The optical disc (FIG. 1) is rotating at a constant angular velocity (CAV), and a signal reproduced from the optical disc by a photodetector 5 is supplied to an S/H circuit 6 and a binarization circuit 8. 2
The digitization circuit 8 differentiates this reproduced signal, slices it at an appropriate slice level, and converts it into a binary value, thereby forming a waveform of a pulse signal representing each bit on the optical disc. This pulsed reproduction signal is supplied to the control circuit 12, and the data pattern is determined.

On the other hand, the reproduced signal output from the binarization circuit 8 is supplied to the gate circuit 9. This reproduction signal includes a data signal based on data bit 2 reproduced from data area AI of the optical disc shown in FIG. 1, and a servo pit la reproduced from servo area A.

1b and a servo signal, and in the gate circuit 9,
A gate signal output from the PLL circuit 11 separates the servo signal from the reproduced signal.

The PLL circuit 11 generates a periodic clock.

In FIG. 1, the deviation amount Δ of the servo area A between tracks and the deviation amount Δ of the servo pick l-12, lb are set to m (where m is a natural number) times the period t of this clock. The servo signal separated by the gate circuit 9 is a PLL
The phase of the clock supplied to the circuit 11 and generated here is synchronized with this servo signal, and the above-mentioned gate signal is generated from this clock. PLL circuit 11
is initialized as described later, whereby the gate circuit 9 generates a gate signal that can separate the servo signal, and also synchronizes the clock with this separated servo signal.

On the other hand, from the PLL circuit 11 to the S/H circuit 6, servo pits la and lb are provided for each servo area A in FIG.
A sampling pulse is supplied in accordance with the reproduction timing of . In the S/H circuit 6, for each servo area A,
The signal amplitudes from the servo pits 1a and 1b are sampled and held, and the held values are compared to generate a tracking error signal. This tracking error signal is subjected to phase lead compensation or phase lead/delay compensation in order to stabilize the tracking servo loop in the phase compensation circuit 7, and then to the switch 14 and the power amplifier 15.
is supplied to the tracking actuator 16 as a tracking control signal. As a result, tracking control is performed so that the signal amplitudes from the servo pits la and lb are equal, that is, so that the optical sbot 4 scans each track without deviation.

For high-speed access, the switch 14 is switched to the B side.

The optical head is a track (hereinafter referred to as
The optical head is moved at high speed in the radial direction of the optical disk to a target track (hereinafter referred to as a target track), and the control circuit 12 sets a target moving speed (hereinafter referred to as target moving speed) vl of the optical head. If this target movement speed V" is made proportional to the square root of the number of remaining tracks to the target track, it will be highest at the start of high-speed access and decrease as it approaches the target track, and the seek (movement of the optical head) time will be In FIG. 3, an example of this target moving speed v1 is shown by a solid line.

However, in the figure, the horizontal axis represents the number of remaining tracks to the target track, and Xo is the total number of tracks traversed from the track at the start of high-speed access (hereinafter referred to as the "start track") to the target track. is set in the control circuit 12 when

In addition, in the optical disc shown in FIG. 1, the period T of the servo area A is
The deviation amount Δ of s is multiplied by n (where n is a natural number).

Therefore, if the period of the clock is t, then Δ=nt according to the above, so T=nΔ= m n t
...-・" (1), and this period T is also an integral multiple of the clock period t. Tracks on an optical disk may be formed concentrically or spirally. Concentrically In the case of the track, the periods t and T of the clock and servo area A3 may be set to an integer fraction of the rotation period of the optical disk, and the position of the servo area A may be shifted by Δ in the order in which the tracks are arranged. On the other hand, in the case of a spiral track, there are two methods:

(1) Period t of clock and servo area A.

Let T be an integer fraction of the rotation period of the optical disk, and the period T of the servo area A is increased or decreased by Δ every rotation of the optical disk.

(2) The rotation period of the optical disk is set to be an integral multiple of the clock period t and larger or smaller than the integral multiple of the period of the servo area A by Δ.

Regarding (1) above, a synchronization shift occurs in the part where the period T of servo area A3 is shifted, which is undesirable as a servo pit detection timing shift occurs.As for (2) above, recording and playback are performed continuously over several tracks. Servo area A.

Since the period T is always constant, the S/H circuit 6 and the gate circuit 9 operate stably. In addition, in the case of (2) above, k
When is a natural number, the rotation period TI of the optical disc is T, = kT±Δ=(kn±1)Δ −・−・・−・(2
”). Generally, n-10, m-1, k ~ 3000
That's about it.

In FIG. 2, when the target track is set, the control circuit 12 also controls the number of tracks X0 to cross to reach the target track.
(Fig. 3) is set, first the number of tracks X is set.

A control signal corresponding to the D/A is output from the control circuit 12, and the D/A
After being converted into an analog signal by converter 13, switch 1
4. The signal is supplied to the tracking actuator 16 as a speed control signal via the power amplifier 15. As a result, the optical spot 4 (FIG. 1) begins to access the optical disk at high speed in the radial direction.

Therefore, as in the case of data reproduction above, the photodetector 5
The reproduced signal is binarized by a binarization circuit 8, and is supplied to a gate circuit 9, where the servo signals are separated. Assuming that the PLL circuit 11 is initialized as described below,
Since the optical disk is rotated at a constant angular velocity and the rotation period of this optical disk is an integral multiple of the clock, the PLL circuit 11 is drawn in by the servo signal from the gate circuit 9 even during high-speed access.

When the light spot 4 crosses the servo area As (FIG. 1), the photodetector 5 outputs a servo signal. Therefore, by supplying a gate pulse from the PLL circuit 11 to the gate circuit 9 at this timing, the gate circuit 9 can separate the servo signals.

Here, in the case of data reproduction, the scanning locus of the optical spot 4 coincides with the track, but in the case of high-speed access, the scanning locus of the optical spot 4 is inclined with respect to the track, and the optical spot 4 moves at high speed. The greater the angle of inclination, the greater the angle of inclination. Also, since the servo areas A between adjacent tracks are shifted by Δ in the track longitudinal direction (Fig. 1), the period of the servo signal detected during data reproduction is T (Fig. 1). On the other hand, during high-speed access, this period T' becomes T'=T±lΔ (3). However, l is a natural number, and the larger the moving speed of the light spot (and the larger the inclination angle of the scanning locus of the light spot with respect to the track), the larger the inclination angle of the light spot with respect to the track.In addition, the sign of 2 in equation (3) is the servo area A.

The direction of the adjacent track in which the phase of is delayed (in Figure 1,
When accessing at high speed in the direction of arrow B), the number 1 is taken, and when accessing at high speed in the direction of the adjacent track, which is the advance, the number - is taken.

In the gate circuit 9, the period T' expressed by this equation (3)
is predicted, and a gate is applied to the reproduced signal to separate the servo signal. This will be explained with reference to FIGS. 4 and 5.

Now, in FIG. 4, it is assumed that the optical spot 4 obliquely traverses the tracks 3a, 3b, . Here, oblique band-like areas with respect to the tracks including servo areas shifted by Δ between each track are respectively servo areas As+, Asz+ Ash...
..., when the light spot 4 almost crosses the track 3C, it reaches the servo area A8. and then the next servo area A when crossing track 3e. Cross the track, then move to the next servo area A between 3f and 3g.
It crosses 33.

Therefore, as shown in FIG. 5(a), the reproduced signal from the photodetector 5 is transmitted to the servo area (1a) on the track 3d when the light spot 4 crosses the servo area (A3l).
, 1b appear, and light spot 4 is in servo area A. Similarly, two waveforms are generated when traversing . However, light spot 4 is in servo area A.
When crossing 53, servo pit 1 of track 3f
Since the servo spot 1a of the track 3g and the servo spot 1a of the track 3g are simultaneously scanned, only one waveform is generated.

When this reproduced signal is binarized by the binarization circuit 8 (FIG. 2), as shown in FIG. 5(b), when the light spot 4 crosses the servo area A□, the time difference becomes Δ. A servo signal consisting of two pulses is obtained, and the light spot 4 is in the servo area A! When crossing z, a similar servo signal consisting of two pulses is obtained. When the light spot 4 crosses the servo area A13, a servo signal consisting of one pulse is obtained.

The gate circuit 9 predicts the timing of the next servo area from the servo signals from each servo area shown in FIG. 5(b), and generates a gate signal for separating the servo signals of the next servo area. That is, although FIG. 5(c) shows this gate signal, the gate signal of the servo signal from the servo area AH shown in FIG. 5(b) is formed from the servo signal detected from the servo area immediately before it, The gate signal of the servo signal from servo area Agz is formed from the servo signal from servo area A31.

Even if the light spot moves at high speed, if this speed is constant, the period T of the servo signal shown in equation (3) is constant, so this period T' is detected and the period of the gate signal is set to this period. If it is adjusted to T', each servo signal can definitely be separated. Further, when accelerating or decelerating the movement of the light spot 4, l in equation (3) changes and the period T' of the servo signal changes, but this change is not so sudden. For this reason, there is no large difference between the number of tracks that the light spot 4 crosses between one servo area and the number of tracks that the light spot 4 crosses between the next servo areas.

Therefore, the generation timing of the gate signal is set in anticipation of this difference in the number of tracks. For example, in the case of high-speed access as shown in FIG. 4, the sign of 10 is taken in the above equation (3), and the period T' of the servo signal is longer than the period T.
Using the detected servo signal as a reference, a gate signal is generated with a delay of .DELTA. from the period T' of the servo signal detected so far. Now, servo area A8. Assume that the servo signal of is separated by the gate circuit 9, and the period between this and the servo signal of the subarea separated before that is T'.
If this period T' is increased from the previous period, the gate signal for the servo signal of the next servo area AH is generated with a delay of period T' + Δ from the servo signal of servo area A31. let

Furthermore, when the light spot 4 is decelerated, the cycle T' of the servo signal decreases, so contrary to the above, the generation timing of the gate signal is determined from the detected servo signal by T'-Δ
shall be.

When starting high-speed access, the phase and period of the gate signal are set so as to separate the servo signal at the start track by initialization described later. In this state, high-speed access is started, and the timing of the gate signal is set for each servo area as described above. The time width of the gate signal is set to 3Δ or less, and the servo pit 1b running in each servo area before and after the servo pit laO
By providing a blank space with a period Δ after each servo area, at least a pulse due to the servo pit la is extracted by the gate signal in each servo area.

In FIG. 2, the servo signal separated by the gate circuit 9 as described above is supplied to the counter 10. Also,
In the PLL circuit 11, a clock with a period of "m" is divided by m,
A pulse with a period Δ is generated and supplied to the counter 10. The counter 10 counts pulses of this period Δ.

Further, in the counter 10, a count value is sent to the control circuit 12 at the timing of a pulse generated by the servo pit la of the servo signal from the gate circuit 9. The number of tracks crossed by the light spot 4 is calculated from this count value, and the actual moving speed (hereinafter referred to as "actual moving speed") (2) of the light spot 4 is calculated. This point will be described in detail below.

The counter 10 is reset every revolution of the optical disc by means not shown. Further, since the period T (FIG. 1) of the servo area on the optical disk is nΔ as shown in the above equation (1), the counter 10 is arranged to carry up at least every n counts.

Therefore, if the counter 10 is reset at the start track when the servo signal is first supplied from the gate circuit 9, then the counter 10 will be reset for each revolution of the optical disc based on this reset time. In the case of data reproduction, the count value of the counter 10 at the time when the servo signal is output from the gate circuit 9 for each rotation of the optical disc is n+ 2 n* 3 n+ ・
. . . However, the value n0 of the least significant digit is 0.

On the other hand, in the case of high-speed access, the period T' of the servo area differs from that in the case of data reproduction, as shown in the above equation (3), depending on the moving speed of the optical spot 4. Assuming that one track is crossed before crossing the area, the value n0 of the least significant digit of the count value of the counter 10 at the time when the servo signal from the servo pit 1a of this servo area is output from the gate circuit 9 is When spot 4 moves in the direction of the adjacent track where the servo area advances (in the direction of arrow A in Figure 1), (n-
1), and when moving in the opposite direction (direction of arrow B in FIG. 1 or direction of arrow in FIG. 4), it becomes +l. Therefore, in the former case, by subtracting the value n by the value n0 of the least significant digit of the counter lO, and in the latter case, directly from the value n0 of the least significant digit, the track that the light spot 4 crosses between the servo areas I can understand the numbers. The number of tracks that the light spot 4 crosses while moving between servo areas can be obtained by subtracting the number of tracks obtained when the light spot 4 crosses the previous servo area from the number of tracks thus obtained.

Further, the number of remaining tracks up to the target track is calculated from the number of tracks obtained from this counter 10, and the target moving speed V'' at this time is obtained from this.

Now, if the track pitch is P and the number of tracks crossed by the light spot 4 between servo areas is l, the travel time of the light spot 4 during this time is expressed by the above equation (3), so these servo When moving in the direction of arrow A in FIG. 1, the actual moving speed V of the light spot 4 between
Δ n-1 ...... (4) When moving in the direction of arrow B in Fig. 1, l P
P! ! ■ Ya = T+1Δ Δ. +l ・・・・・・・・・(5) It becomes. This actual movement speed V- or ■. is compared with the target movement speed v1 obtained as described above, and the deviation thereof is outputted from the control circuit 12 and converted into an analog signal by the D/A converter 13, which is then sent to the switch 14 and the power amplifier as a speed control signal. 15 to the tracking actuator 16. As a result, the light spot 4 becomes
Movement is controlled so that the actual movement speed V- or V becomes the target movement speed V'' as shown by the broken line in FIG.

Here, n=10, and in FIG. 4, track 3c
Detection of the count value of the counter 10 when high-speed access is performed from track 3C as the starting track as shown by the arrow will be described.

FIG. 6(a) shows a pulse with a period Δ from the PLL II supplied to the counter 10 in FIG. 2, and the value n of the least significant digit of the count value of the counter 10 that counts the pulse. and

When the optical spot 4 is on the track 3C and data is being reproduced, as shown in FIG. 6(b),
Based on the timing shown in FIG. 6(a), each subarea A! It Asz, Servo pit la with Asi+,
When detecting lb, the value n0 of the least significant digit of the count value of the counter 10 is 0.1.

Next, as shown in FIG. 4, if high-speed access is started with the light spot 4 in the vicinity of the servo area A5H of the truck 3C, the light spot 4 crosses the servo area As□ and the servo pit 1a When is detected, as shown in FIG. 6(c), the count value of the counter 10 counts by 12, and the value n of the least significant digit
0 becomes 2. In this case, since the light spot 4 moves in the direction of arrow B in Fig. 1, this degree value 2 changes while the light spot 4 moves between the servo areas ASI+ASW.
In other words, it is the number of tracks traversed after high-speed access is started.

Next, when the light spot 4 crosses the next servo area As and the servo pit 1a is detected, as shown in FIG. 6(c), the lowest digit value n0 of the count value of the counter 10 is detected. is 4. Therefore, the number of tracks that the optical spot 4 has crossed since the start of high-speed access is four.

In this way, when the counter 10 is initialized as described above (FIG. 6(b)) at the start track, the servo pit la
The value n0 of the least significant digit of the count value of the counter 10 obtained every time the light spot 4 is detected represents the number of tracks crossed by the optical spot 4 during high-speed access.

In this way, each time a servo signal is detected, the number of tracks crossed by the light spot 4 is obtained, and thereby, the target moving speed v0 and the actual moving speed V can be obtained as described above.

In the case of the above example, the value n0 of the least significant digit of the count value of the counter 10 becomes smaller again every time the light spot 4 crosses 10 or more tracks. By adding , the number of tracks crossed by the light spot 4 can be obtained.

As mentioned above, the light spot 4, as shown in FIG.
Movement is controlled so that the actual movement speed V follows the target movement speed V°. Here, in the above, this target movement speed V"
is made proportional to the square root of the number of remaining tracks to the target track, but is not particularly limited to this. For example, even if the target moving speed v1 is set as described above, the deceleration may be made gentle near the target track.

However, in any case, information such as a function that defines the target moving speed V'' is stored in the internal memory of the control circuit 12.

Further, the actual moving speed of the light spot 4 is also expressed by the above equation (4).

It may be obtained by a method other than the method (5).

For example, since the sequential positions of the light spot 4 can be detected from the count value of the counter lO as described above, the reference time is set in the control circuit 12, and the position signal obtained from the change in the position of the light spot 4 is detected during this reference time. It may also be obtained by differentiating based on . Furthermore, S/H is added to this position signal.
By adding the tracking error signal obtained from the circuit 6 (first time), tracking control of the optical spot 4 is also effected, especially when moving at low speed near the target track, so low speed seek is stabilized. The light spot 4 is smoothly drawn into the target track in a tracking state.

Here, the actual moving speed v- shown in equations (4) and (5)
,v. From this, it is possible to determine the limit actual moving speed of the light spot 4 at which the number of tracks crossed can be detected.

First, as shown by arrow A in FIG. 1, when the light spot 4 moves to the adjacent track side where the servo area advances,
The light spot 4 must move across the next servo area.

Therefore, in FIG. 7, when considering the movement of the light spot with n=10, when track 3a is the reference,
From this, the servo area of the IO main track 3m is the same as that of the reference track 3a.

Therefore, if the light spot moves in the direction of arrow (B) and crosses the next servo area Asz with a track of 3 m, the count value of the counter 10 (FIG. 2) at this time indicates that the light spot crosses the servo area A S +. Reference track 3
The count value when crossing at a is dark, for this reason,
Regardless of whether the light spot actually crosses a track, the count value of the counter 10 is the same as when the light spot moves along the same track, and the number of tracks cannot be detected. However, the servo areas of tracks 3a, 3m, etc., which have the same servo areas, are arranged in the radial direction of the optical disc, and the light spot is placed on the rotating optical disc in this way. It is impossible to move. Moreover, arrow (A)
It is not possible to move the light spot in any direction.

Therefore, the limit direction of movement of the light spot relative to the optical disc in which the light spot can move and the number of tracks crossed can be detected is the direction shown by arrow (C), that is, the next servo area AH reaches the reference track. Track 3 is shifted by Δ from servo area All on 3a
This is the direction of the first servo area As2. In other words, as mentioned above, if the period T of the servo area is nΔ and the number of tracks crossed between servo areas is n, then n-1≧1
......When (6), the number of tracks crossed can be detected. Therefore, the formula (4
), and substituting it into equation (6), the limit of the moving speed V- of the light spot is V-≦(n-1>...
(7) Δ. Here, P=1.6μm, Δ=0.6μsec
, n=20, then -≦50 m/sec, which is a practically sufficient value.

Next, as shown by arrow B in FIG. 1, a case will be described in which the light spot moves to the side of the adjacent track where the servo area lags.

In FIG. 8, as in FIG. 7, n=10, and if track 3a is used as a reference, the tenth track 3 from this reference track has a servo area in phase with this reference track 3a. For this reason, as in the case of FIG. 7, the detection limit moving speed of the light spot is, as shown by the solid arrow, if the light spot crosses the servo area All on the reference track 3a, then the next servo area Asz In this case, the value is such that it crosses the ninth track 3j from the reference track 3a. Therefore, in general, in order to be able to detect the number of tracks, n+! Since ≦2n-1 (8), when l is obtained from the above equation (5) and substituted into this equation (8), the following is obtained. Here, under the above conditions, P=1.6 μm.

If Δ=0.6 μm and n=20, then v, ≦1.3 m
/ sec, which is sufficient for practical use.

Next, a description will be given of the initial setting of the PLL circuit 11 to pull in the servo signal and the gate circuit 9 to adjust the phase of the gate signal to the servo signal.

When reproducing data or performing high-speed access, first, rotation of the optical disk is started and then tracking control is performed, but before performing this tracking control, initial settings are performed.

Before initialization, the PLL circuit 11 generates a clock with an arbitrary phase, and also generates a gate signal with a period T from this clock. With this gate signal, the gate circuit 9 separates a part of the output signal of the binarization circuit 8, but the PLL circuit 11
determines whether this separated signal is a servo signal or not. If this separated signal is not a servo signal, the phase of the gate signal is sequentially changed. When the servo signals are separated in the gate circuit 9 in this way, the PLL
In circuit 11, a clock is synchronized to this servo signal. This completes the initial settings and allows the S/H circuit 6 to correctly sample and hold the servo signal.
Tracking control is performed.

Here, in order to enable the PLL circuit 11 to determine the servo signal, there are the following methods.

(1) The servo pits are arranged in a pattern different from that of the data bits in the servo area (for example, the bit interval is made different from that of the data bits), and the discrimination is made by pattern matching.

This method has the advantage that the servo area is thicker (which increases redundancy), but it is less affected by defects.

(2) Record special pattern data in the data area.

Although this method does not directly judge the servo signal,
The gate signal is first phase-adjusted so that the special pattern data is separated by the gate circuit 9, and when this is determined by pattern matching or the like, the phase of the gate signal is adjusted to match the servo signal. The bits of this special pattern data can be provided discretely in several data areas, resulting in excellent data efficiency.
When all these bits are separated to obtain special pattern data, the phase of the gate signal is adjusted to match the servo signal.

〔Effect of the invention〕

As explained above, according to the present invention, in order to perform high-speed access to an optical disk that performs sample servo tracking control, the number of tracks crossed by a light spot can be reduced per track without adding information to the servo area. It is possible to detect the optical spot with high resolution and improve the position detection accuracy of the optical spot. Moreover, even when seeking the optical spot at high speed, this position detection accuracy can be kept high, allowing high-speed access to be performed accurately and quickly. You can get excellent results by doing this.

[Brief explanation of the drawing]

FIG. 1 is a partial plan view showing an embodiment of an optical disk according to the present invention, FIG. 2 is a block diagram showing an embodiment of an optical disk device according to the present invention, and FIG. 3 is a diagram showing the moving speed of a light spot during high-speed access. FIG. 4 is a diagram showing an example of movement of the spot on the optical disk shown in FIG. 1 during high-speed access. FIG. 5 is a diagram showing an example of movement of the optical spot on the optical disk shown in FIG. Figure 6 shows the operation of the counter in Figure 2, and Figures 7 and 8 show the detection limit moving speed of the light spot. FIG. 9 is a partial plan view showing a conventional sample servo type optical disk. la, lb... Servo pit, 2...
...Data bit, 3μm3m...
...Track, 4...Light spot, 5.
・・・・・・・・・Photodetector, 6・・・・・・・Sample hold circuit, 7・・・・・・・Phase compensation circuit, 8・・・・・・・・・Binarization circuit, 9...
...Gate circuit, 10...Counter, 1
1... PLL circuit, 12...
...Control circuit, 13...Digital/analog conversion circuit 14...Switch, 15.
1 Old...Power Ann 16...Tracking actuator 1, A31. Ash Ass・
...... Servo area, ...... Data area. Fig. 4 Fig.
-te- 1-0--Q-,,,3d

Claims (5)

[Claims] (1) In an optical disc in which servo areas in which servo pits containing at least clock synchronization information are recorded are arranged periodically in each track, the servo areas are arranged offset in the longitudinal direction of the tracks between adjacent tracks. Characteristic optical disc. (2) The optical disk according to claim 1, wherein the amount of deviation of the servo area between adjacent tracks is an integral multiple of the period of the clock generated based on the clock information. (3) The optical disc according to claim (1) or (2), wherein the servo area includes wobble pits for tracking control. (4) In claim (1), (2) or (3), a synchronization pull-in area in which a clock synchronization auxiliary signal is recorded is provided in a part of the data area where data between the servo areas is to be recorded. An optical disc characterized by: (5) An optical disk in which servo areas in which servo pits containing at least clock synchronization information are recorded are arranged periodically in each track, and the servo areas are arranged shifted in the longitudinal direction of the tracks between adjacent tracks at a constant angular velocity. In an optical disk device, the optical disk device includes a rotation drive means for rotating the optical disk, and an optical head moving means for moving an optical head for detecting a signal from the optical disk in the radial direction of the optical disk. A first means for detecting a servo signal from the servo pit from a detection signal of the optical head, a second means for generating a clock synchronized with the detected servo signal, and a third means for counting the clock. and fourth means for generating a speed control signal based on the count value of the third means at the detection timing of the servo signal by the first means, and the speed control signal generates a speed control signal in the radial direction of the optical disk. An optical disc device characterized in that the optical disc device is configured to control a moving speed of the optical head.