JPH0262731A - Optical disk and optical disk device - Google Patents

Abstract

PURPOSE:To adopt a sample servo system by forming a servo pit to be a V-shaped slot recorded on a servo area so as to detect the moving direction of an optical spot from the servo pit. CONSTITUTION:When an optical head including a photodetector 1 makes access to an optical disk of the sample servo system having servo pits made of V-shaped slots by moving the head at higher speed than that of recording and reproduction of a data, the intensity of the optical spot 2 is changed every passing on the pit on the optical disk and signals A, B subjected to intensity modulation by the pit are outputted from detection elements 1a, 1b. The output signals A, B are added by an adder 3 and a modulated detection signal C modulated by a pit on which the optical spot 2 passes is obtained. A detection signal C is sampled and held by using a clock coincident with a detection timing of the servo pit in the servo area of the optical disk. Thus, a signal E with a level representing the detection amplitude of the servo pit is outputted from a sample-hold circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides an optical disk in which servo areas in which servo pits are recorded are arranged periodically for each track, and the servo pits are detected to perform tracking control. The present invention relates to an optical disk and an optical disk device using a so-called sample servo system, and particularly to an optical disk and an optical disk device that perform access by counting the number of traversed trunks.

[Conventional technology]

Conventionally, in optical disk devices such as CD players and optical video disk devices, one method for accessing a target track is to detect the number of tracks that a light spot crosses, and from this detection result, the position of the light spot and the A method is known in which the moving speed of the light spot is determined 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, According to the paper "High-speed access method for optical disk memory" at the "Optical Memory Symposium '86" held on December 18, 1986, an optical disk has a guide groove formed in advance in a spiral or concentric shape. A tracking control signal is obtained from the groove, and this is used to perform tracking control so that the optical spot follows the guide groove, and data is recorded and reproduced using this optical spot.

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. The outline of the sample servo system will be explained below with reference to FIGS. 13 and 14.

FIG. 13 is an enlarged view of a part of an optical disk for the sample servo system.

In the figure, each track 12a on the optical disc.

Servo areas A1 are periodically provided in 12b, 12c, L2d, . Also, servo area A.

The period A is an integer fraction of the rotation period of the optical disk, and therefore the servo area A is arranged in the radial direction of the optical disk. Servo area A.

The data area AD in between is an area for recording data bits. In each servo area A, they are spaced equidistantly from each other in opposite directions with respect to the center of the track (indicated by the broken line).
In addition, two servo pits lla and Ilb are also recorded which are shifted from each other in the longitudinal direction of the track. This optical disk rotates in the direction of arrow X, and the light spot is on track 12.
If it is on servo area A, this light spot is on servo area A.
, first detects servo pit lla, and then detects servo pit llb. Therefore, the servo pit
A tracking control signal is obtained by comparing the detection signal amplitude caused by a and the detection signal amplitude caused by servo pip)llb.

In addition, a synchronization bit is also recorded in servo area A8,
Although the clocks are synchronized using this synchronization bit, this synchronization bit will be omitted in the following explanation.

FIG. 14 is a block diagram showing a circuit for generating a tracking error signal for such an optical disc.

In the figure, a photodetector 39 outputs a detection signal modulated by the bits on the track of the optical disk shown in FIG. This detection signal is processed by the sample and hold circuit (
The S/H circuit (hereinafter referred to as S/H circuit) 40 samples and holds the signal using the clock φ8, and the S/H circuit 41 samples and holds the signal using the clock φ2. Here, the clock φ1 matches the detection timing of the servo pit lla of each servo area A1 in FIG. 13, and the clock φ2
matches the servo pit llb. For this purpose, S/
In the H circuit 40, the signal amplitude due to the detection signal servo pit (lla) is sampled and held, and in the S/H circuit 41, the signal amplitude due to the servo pit (llb) is sampled and held. The output signals of these S/H circuits 40 and 41 are subtracted by a differential amplifier 42.

Therefore, if the optical spot has a tracking deviation toward the servo pit lla side in FIG. becomes large, and a positive signal is output from the differential amplifier 42. Also,
On the other hand, if the optical spot causes a tracking deviation toward the servo pit llb side, the amplitude of the output signal of the S/H circuit 41 becomes large, so that the differential amplifier 42 outputs a negative signal.

In this way, the differential amplifier 42 has different positive or negative polarity depending on the direction of tracking deviation of the optical spot.
In addition, a signal with an amplitude corresponding to the amount of deviation can be obtained. Therefore, this signal can be used as the tracking error signal str and used for tracking control of the optical spot.

[Problem to be solved by the invention]

By the way, when moving (seek) the optical spot during access, it is also necessary to be able to detect the moving direction of the optical spot. This is the number of tracks crossed by the direction of the target track if the seek speed becomes high and the optical spot is not drawn to the target track and the optical spot overruns or the optical disk is eccentric, and if the moving direction of the optical spot is not known. Even if the light spot can be detected from
Therefore, the light spot cannot reach the target track.

In the case of an optical disc having a continuous guide groove, the direction can be determined by using the variation in the light intensity when the light spot crosses the guide groove (Japanese Patent Laid-Open No. 58-91536).
Publication No.). However, if the optical disk rotates at a large tilt, or if the shape of the guide groove is inaccurate and the width or depth fluctuates, the tracking position will be offset and the accuracy will be compromised (access cannot be performed. Therefore, very high precision is required in the production of optical discs.

On the other hand, optical discs based on the sample servo method, in which servo areas are periodically arranged on each track, do not require guide grooves and do not have the above problem. The tracking error signal Str' is outputted from the differential amplifier 42 in FIG. 14 by accessing the spot by increasing the seek speed.
As shown in FIG. 15, the waveform shows a waveform in which the polarity changes periodically. Here, point P in the figure is assumed to be the point at which the light spot crosses the track. Therefore, when the light spot is moving in a certain direction, as shown in Fig. 15(a),
At point P, tracking error signal S2. , the polarity is reversed from negative to positive, and when the light spot is moving in the opposite direction, as shown in Fig. 15),
The polarity of the tracking error signal Sur is reversed from positive to negative at point P. Note that the point at which the polarity between points P is reversed is when the light spot is at the center between the tracks.

In this way, the polarity of the tracking error signal Str is reversed depending on the moving direction of the optical spot, with the timing of crossing the optical spot as a reference. Therefore, if the timing (point P) at which the light spot crosses the track can be detected from this tracking error signal Str at the time of access, then from FIGS. Although the moving direction of the light spot may be detected depending on the order, the timing at which the polarity of the obtained tracking error signal Str is reversed from positive to negative or from negative to positive is the timing at which the light spot crosses the track. It is not possible to determine whether

Therefore, in a sample servo type optical disc, unlike an optical disc having a guide groove, it is not possible to determine the moving direction of the optical spot from the tracking error signal.

Therefore, in sample servo type optical discs, by adding a bit indicating the track center to the servo area and detecting this pit, it is possible to determine which polarity reversal point in the tracking error signal is the timing at which the light spot crosses the track. It is also conceivable to determine the moving direction of the light spot as described above based on this determination. However, this method has the problem that the servo area is expanded by the additional pits, and the effective data area is reduced accordingly.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and to provide an optical disk and an optical disk device that can also detect the direction of movement of a light spot from a servo pit and that can be accessed using a sample servo method. .

[Means to solve the problem]

In order to achieve the above object, in the optical disc according to the present invention, the servo pits recorded in the servo area are 7-shaped grooves.

Further, the optical disc device according to the present invention is constructed of a plurality of detection elements arranged perpendicularly to the track as a photodetector, and processes the output signal of the detection element to obtain a tracking error signal. The output signal of the detection element is processed to obtain a track-crossing signal having a different phase relationship with the tracking error signal depending on the moving direction of the light spot. By detecting the phase relationship between the tracking error signal and the track crossing signal, the moving direction of the optical spot can be determined.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of an optical disc device according to the present invention, in which ■ is a photodetector, fatIb is a detection element, 2 is a light spot, 3 is an adder, 4 is a subtracter, 5-
8 is an S/H circuit, and 9.10 is a subtracter.

In the figure, the photodetector 1 has two detection elements fat1b
These detection elements 1a and lb are arranged perpendicularly to the longitudinal direction of the tracks on an optical disc (not shown). Further, a light beam from a light emitting element (not shown) is irradiated onto the optical disk and is reflected. When this light beam is reflected from a flat part of the surface of the optical disk, the light spot 2 receives the same amount of light and the detection element 1a, The arrangement relationship of these detection elements 1a and 1b is set so that light is received at lb.

Now, for the sample servo type optical disk shown in FIG. 13, the optical head including the photodetector 1 is used to record data.
When the light spot 2 is accessed by moving at a higher speed than during reproduction, the intensity changes each time the light spot 2 passes a pit on the optical disc, and the detection element 1a changes in intensity.

From 1b is a signal A whose intensity is modulated by pits.

B is output. In this case, the detection elements 1a and lb are shifted in the direction perpendicular to the track longitudinal direction, and the light receiving portions of the light spot 2 are different, so when the light spot 2 passes through a pit on the track, the detection elements 1a and 1b The amount of light received by lb differs, and also differs depending on the path of the light spot 2 at the pit.

The output signals A and B of the detection elements 1a and lb are added by an adder 3, and a detection signal C modulated by the pit through which the light spot 2 passes is obtained. This detection signal C is sampled and held in the S/H circuit 5 by a clock φ1 that coincides with the detection timing of the servo pit 1la (FIG. 13) in the servo area A of the optical disk.

Therefore, from the S/H circuit 5, the servo pit lla
A signal E having a level representing the detected amplitude of is output. Further, the detection signal C from the adder 3 is sent to the S/H circuit 7 to detect the servo pitch in the servo area A of the optical disk.
-11b (FIG. 13) is sampled and held by the clock φ2 that coincides with the detection timing. Therefore, the S/H circuit 7 outputs a signal F having a level representing the detected amplitude of the servo pips). Output signal E of S/H circuit 5.7.

F is subtracted by the subtracter 9 (here, the S/H circuit 5
(subtracting the output signal Ft- of the S/H circuit 7 from the output signal E of the S/H circuit 7), a tracking error signal Str representing the level difference between these is obtained.

This tracking error signal S is similar to the tracking error signal str obtained from the differential amplifier 42 in FIG. 14, and as shown in FIGS. 15(a) and (b), the track center and the center between tracks The polarity reverses each time it passes.

Furthermore, the output signals A and B of the detection elements 1a and 1b are subtracted by a subtracter 4 (here, the output signal B is subtracted from the output signal A). As will be described later, the difference signal output from the subtracter 4 indicates in which direction the path of the light spot 2 on the bit is shifted with respect to the center line of the pit along the longitudinal direction of the track. . This difference signal is sampled and held in the S/H circuit 6 using the clock φ1, and sampled and held in the S/H circuit 8 using the clock φ2. Therefore, the S/H circuit 6 outputs a signal G representing the deviation of the path of the light spot 2 at the servo pin (Fig. 13), and the S/H
Similarly, a signal H for the servo pit 11b (FIG. 13) is obtained from the circuit 8. These output signals G and H are subtracted by a subtracter 10 (here, the output signal H is subtracted from the output signal G), and a track crossing signal 5clI representing the difference between them is obtained.

Here, a tracking error signal Sur and a track crossing signal S according to the path of the light spot with respect to the servo pit are calculated.
The level with CI will be explained.

FIG. 2 shows different positions of the light spot in the direction perpendicular to the longitudinal direction of the track on the optical disc,
lla, lla', 11a' are the preceding servo pits of the servo area, llb, llb', ll
b' is the same (following servo pit, 12a "12
c is a track, 13 is a light spot, lla, l
lb is the servo pit of track 12b, lla +1
1b' is the servo pit lla, 1 of the track 12a.
1b' is a servo pit of the track 12c. The light spot 13 is shifted by 178 of the track pitch in the order of Fig. 2 (a), (b), ..., (h),
In Fig. 2(a), the light spot 13 is on the track 128°12.
2 (C1), the light spot 13 is shifted from the track 12b to the preceding servo pit lla side of the servo area by 174 of the track pitch,
If it is located almost through the center of the servo pit lla,
Figure 2 (el) indicates that when the optical spot 13 is on the track 12b, the optical spot 3 is shifted from the track 12b to the servo pit llb side that follows the servo area by 174 of the track pitch, and this servo pit llb
The cases where the position passes approximately through the center of are shown in each case.

Now, assuming that the diameter of the optical spot 13 is slightly smaller than the track pitch, the right half of this optical spot 13 is received by the detection element 1a of the photodetector 1 in FIG.
It is assumed that the left half of the light is received by the detection element 1b.

Therefore, first of all, in the state shown in FIG. 2(a), the light spot 13
After the right half passes through the servo pit 11b', the left half passes through the servo pit 11b'. Hereinafter, a point t is indicated by a dashed dot line when the light spot 13 passes through the preceding servo pit portion of the servo area.

Similarly, the passage of the optical spoiler 1-13 through the trailing servo pit portion is represented by a time point 1t shown by a dashed line. For this reason, the output signal A of the detection element 1a of the photodetector 1 (hereinafter referred to as detection signal A.Similarly, the output signal B of the detection element 1b is also referred to as detection signal B) is such that the light spot 13 detects the servo pit 11a. When the light spot 13 passes through the servo pit 11b', that is, at time t, the detection signal B has a negative polarity with a large amplitude.

Moreover, their amplitudes are equal, so adder 3
The output signal C of (FIG. 1) is at the time tInt! and negative polarity with equal amplitude. Therefore, the tracking error signal st obtained by subtracting these has a level of zero.

In addition, in order to be able to compare the polarity and amplitude of the tracking error signal Str and the track crossing signal SCI at each position of the optical spot 13 shown in FIGS. 2(a) to (h),
They are shown as pulses at time t2.

Furthermore, the output signal of the subtracter 4 (FIG. 1) in the case of FIG. 2(a) has a negative polarity with a large amplitude at time t1, and
At t, the polarity becomes positive with the same amplitude. Therefore, the track crossing signal 5clI has a large amplitude and negative polarity.

Next, the second exposure in which the light spot 13 is closer to the track 12b by 178 of the track pitch than in FIG. 2(a))
In this case, since the center of the light spot 13 slightly enters the servo pit lla, the point 1. In this case, the negative amplitude of the detection signal A becomes slightly smaller than that shown in FIG.
passes through a part of servo pit 11b' and a small part of servo pit llb. Therefore, at this point t2,
A slight negative amplitude due to the servo pit 11b' appears in the detection signal A, and the negative amplitude of the output signal B due to the servo pit 11b' is smaller than in the case of FIG. 2fa).

Therefore, the output signal C of the adder 3 has a smaller negative amplitude at time t than at time t1, and a negative tracking error signal SL representing the amplitude difference is obtained. Also, the output signal of the subtracter 4 is at time 1. ．． The amplitude of 1t is reduced compared to that in Fig. 2(a), and therefore,
The negative amplitude of the track crossing signal Sc is reduced compared to the case of FIG. 2(a).

In the state shown in FIG. 2 (C1), the optical spot 13 moves closer to the track 12b by 178 of the track pitch, so the amplitude of the detection signal A at time t1 is smaller than in the case of FIG. 2(b). In contrast, in the detection signal B, the amplitude at time t becomes large and the amplitude at time t! becomes small.However, the center of the light spot 13 is located at the servo pit lla. Since it passes through the center and the middle of the servo pits 11b' and 11b, the waveforms of the detection signals A and B are equal, and the amplitude at time t is larger than at time 1t.

Time 1. of the output signal C of the adder 3. ．． The amplitude difference at 1t is thicker than in the case of FIG. 2(b), and therefore the negative amplitude of the tracking error signal Str is larger than in the case of FIG. A, B
are equal, the amplitude of the output signal of the subtracter 4 becomes zero, and therefore the amplitude of the track crossing signal 5CII becomes zero.

When the state shown in FIG. 2(d) is reached, the detection signal A at time tI+
The amplitude of detection signal B at time t2 further decreases, and the amplitude of detection signal A at time tZ+detection signal B at time 1. The amplitude of will further increase. In this state, the light spot 13 is in a symmetrical position with respect to FIG. 2 (C1 and BL), and therefore,
The waveforms of detection signals A and B are shown in Fig. 2 (detection signal B of bl).
, the waveform is A. For this purpose, the output signal C of adder 3
is the same as in the case of FIG. 2(b), and therefore the tracking error signal Sur is also the same as in the case of FIG. 2(b), but the output signal of the subtractor 4 is With the opposite polarity, the track crossing signal 5ell is also shown in FIG. 2(b).
The polarity is opposite to the case of l.

In the state shown in FIG. 2(e), the light spot 13 is located on track 1.
2b, the detection signal A has a large negative amplitude at time t2, and the detection signal B has a large negative amplitude at time t, and these amplitudes are equal. Therefore, the output signal C of the adder 3 is the same as in the case of FIG.
The polarity is opposite to that in the case shown in FIG.

In the above state changes from Fig. 2 ia) to Fig. 2 (e), the amplitude of the tracking error signal Str gradually increases from zero with negative polarity, and reaches its maximum negative polarity in the state shown in Fig. 2 fc). After that, it gradually decreases to zero. Also, track crossing signal 5
The negative amplitude of CII decreases sequentially and becomes zero in the state shown in FIG. 2(C), and further increases sequentially with positive polarity.

Next, from the state of Fig. 2 (el) to Fig. 2 (f), (g)
, (h), in the detection signal A, the amplitude at time t1 gradually increases from zero to negative polarity, and the negative amplitude at time t2 gradually decreases. Moreover, in detection signal B,
Conversely, the negative amplitude at time t decreases sequentially, and the amplitude at time t2 increases sequentially from zero to negative polarity.

For this reason, the amplitude of the tracking error signal Str increases from zero in positive and negative polarities, reaches a maximum in the state tg+ in FIG. 2, and then gradually decreases. In addition, the track crossing signal Sl:
The amplitude of II gradually decreases with positive polarity, reaches zero in the state shown in FIG. 2(g), and further increases with negative polarity.

As shown above, the amplitudes of the tracking error signal SL and the track crossing signal SCI in each state of Figure 2 (a) and --------1 (h) are summarized as follows. Become.

Table 〉 Now, from this table, if we assume that the light spot 13 crosses the track from the state shown in Fig. 2 (a) to (in the same figure) → (e) → -・- → (h), then the light spot 13 crosses the track as shown in Fig. 3. As shown in FIG. 2, the tracking error signal SL□ and the track crossing signal S0 change periodically, but the track crossing signal Sc,l leads the tracking error signal Sur by 174 of its period.

However, the point P where the tracking error signal Str changes from negative to positive is the state where the optical spot 13 coincides with the track (second
Figure (e)).

On the other hand, contrary to the above, when the light spot 13 crosses the track from the state of FIG. As shown in Fig. 4, the track crossing signal 5ell lags behind the tracking error signal Sur by 1/4 of its period, however, the point P where the tracking error signal Str changes from positive to negative is when the optical spot 13 coincides with the track. It is a state of

In this way, if the optical spot is moved faster than when recording or reproducing data, and the tracking state of the optical spot in the servo area is changed as described above, a tracking error signal will be generated depending on the direction of movement of the optical spot. The phase relationship between Str and the track crossing signal 5Cjl is different, and by detecting this phase relationship, the moving direction of the optical spot can be determined. Furthermore, the number of tracks crossed by the light spot can be detected by counting the wave number of the tracking error signal SL+' and the number of inversions from positive to negative or from negative to positive.

However, for this purpose, the optical disk must be rotated at a constant angular velocity.
Moreover, as is clear from the difference in amplitude between the tracking error signal Str and the track crossing signal SCI in FIG. 174 or less. Therefore, the moving speed V of the light spot is as follows, where T is the cycle of the servo area and L is the track pitch.

As described above, the tracking error signal Sur and the track crossing signal SCR are obtained from the subtracter 9.10 of the embodiment shown in FIG. 1, respectively. The access control unit based on the error signal Str, ) rack crossing signal SCR will be described. In addition, in the same figure, 14 is a switch, 15 is a phase compensation circuit, 16 is an adder, 17 is a power amplifier, and 18
is the tracking actuator, 19.20 is the comparator,
21 is a mono multi-pipe lake, 22 is an inverter, 2
3.24 is an AND gate, 25 is a frequency/voltage converter (
26 is a counter, 27 is a D/A (digital/analog) converter, 28 is a subtracter, and 29 is a switch.

In the figure, when recording or reproducing data, switch 1
4 is closed and switch 29 is open.

This forms a tracking servo loop.

Tracking error signal SL from subtracter 9 (Fig. 1)
. The light is supplied to a tracking actuator 18 via a power amplifier 17, and tracking control of the light spot is performed.

In case of access, switch 14 opens and switch 2
9 closes.

The tracking error signal SLr is compared with a zero level by a comparator 19, and a pulse P that is at a high level (positive) during its positive polarity period is obtained. This pulse P1 is fed to a monomulti-bibreak 21 and triggered at its rising edge to obtain a high level pulse P2. That is, this pulse P2 represents the point in time when the tracking error signal SLr is inverted from negative to positive. Pulse P2 is supplied to AND gates 23 and 24. On the other hand, the track crossing signal SCR is compared with a zero level by a comparator 20, and a pulse P which is at a high level during its positive polarity period is obtained. This pulse P3 is supplied to the AND gate 24 as a gate pulse, and is also inverted by the inverter 22 to form the AND gate 23.
supplied to

As shown in FIG. 6, when the track crossing signal SCI+ lags the tracking error signal Str by 174 cycles, the pulse P2 passes through the AND gate 23 because it deviates from the high level pulse P. , pulse P
, is counted by the counter 26. Further, as shown in FIG. 7, the track crossing signal 5Cjl is the tracking error signal S1. , the pulse P2 is among the high-level pulses P, so it passes through the AND gate 24 and is counted by the counter 26 as the pulse P1. That is, the pulse P or P is output from the AND gate 23 or 24 depending on the difference in the phase relationship between the tracking error signal SL, , and the track crossing signal 5CII, and therefore the difference in the moving direction of the optical spot. . Also, Fig. 2.

As is clear from the explanation of FIGS. 3 and 4, in the case of FIG. 7, the pulse P1 represents that the light spot successively traverses the track, but in the case of FIG.
, represents that the light spot sequentially crossed the middle between the tracks. However, in the case of access, the count value of the pulse P1°P can be the number of tracks traversed by the light spot in any case.

Therefore, now, Fig. 2 (a) → (b) →...
→The direction in which the light spot moves so that the state changes as shown in (h) is the direction in which this light spot moves from the outer circumference side to the inner circumference side of the optical disc, and this is the negative movement direction of the light spot. . Further, on the contrary, the direction in which the light spot moves from the inner circumferential side to the outer circumferential side of the optical disk is defined as a positive moving direction. In the negative direction of movement, the tracking error signal S
The phase relationship between the track crossing signal Sc and the track crossing signal Sc and l is as shown in FIG. 3, and in the positive direction of movement, the phase relationship between them is as shown in FIG.

When performing access, the number of tracks that the light spot crosses before reaching the target track and the moving direction of the light spot are set. Along with this setting, in FIG. 5, when the moving direction of the light spot is a negative moving direction, the number of tracks that the light spot must cross before reaching the target track is set as a negative value, and when the moving direction of the light spot is positive, In the case of direction, the number of tracks to be crossed is set as a positive value. This setting value is set as No.

When this value N0 is set in the counter 26, it becomes D/
It is converted into a negative or positive analog signal by the A converter 27,
Subtractor 28. Switch 29. Subtractor 16. The signal is supplied to a tracking actuator 18 via a power amplifier 17. As a result, the light spot starts moving in a direction according to the polarity of the analog signal output from the D/A converter 27, and therefore the polarity of the set value N0 of the counter 26. As a result, the tracking error signal Str and the track crossing signal 5ell are detected, and the AND gate 23 or 24 outputs the pulse P5 or P.

The counter 26 is set to a negative value N0 and the light spot moves in the negative movement direction, and the AND gate 24 outputs a pulse P,
is supplied (FIG. 7), this pulse P is counted up from the set value N0.

Since the number of supplied pulses P is the number of tracks crossed by the light spot, the absolute value IN+ of the count value of the counter 26 is the number of tracks to the target track. Furthermore, when the counter 26 is set to a positive value N0 and the light spot moves in the positive movement direction, the AND gate 23 outputs a pulse Pb (FIG. 6); This pulse Pb is counted down. Therefore, the count of the counter 26 at this time (
N is also the number of tracks up to the target track.

Therefore, the analog signal obtained by converting this count value N by the D/A converter 27 is proportional to the number of remaining tracks up to the target track, and hereinafter, this is the target moving speed of the light spot, i.e. It represents the target movement speed v0. That is, in this embodiment, the counter 26
Accordingly, a target moving speed v1' is set for the light spot in proportion to the number of remaining tracks to the target track, and each time a pulse P or P is supplied, the light spot is moved from the D/A converter 27. Target movement speed v0 at the current position of
A signal representing . This target movement speed v0 is
As shown in FIG. 8, it is maximum at the start of access and becomes zero when the light spot reaches the target track.

On the other hand, the pulse P! output from the monomultipipe lake 21! is supplied to the /v converter 25. This pulse P
The frequency 2 is proportional to the actual moving speed V of the light spot (hereinafter referred to as the actual moving speed), and the f/V converter 25 outputs a signal V representing the actual moving speed. Subtractor 28
, the signal representing the actual movement speed V from the f/V converter 25 is subtracted from the signal representing the target movement speed v1 from the D/A converter 27, and these difference signals are sent to the switch 29.
The adder 16 is supplied via the power amplifier 17 to the tracking actuator 18 as a speed control signal.

As a result, as shown by the broken line in FIG. 8, the actual moving speed V of the light spot is the absolute value 1 of the target moving speed v'' of the light spot.
v“ changes to be equal to 1.

Note that the polarity of the output signal of the D/A converter 27 differs depending on the moving direction of the optical spot, whereas the output signal of the f/■ converter 25
The output signal of has a constant polarity regardless of the direction of movement of the light spot. Further, the subtracter 28 is connected to the D/A converter 27.
The absolute value of the output signal of the D/A converter 27 must be subtracted by the output signal of the f/V converter 25. For this, the subtracter 28
is, for example, the count value N output from the counter 26
Addition and subtraction operations are switched by the positive and negative sign bits.

For example, if the output signal of the f/V converter 25 is of positive polarity, the subtracter 28 performs a subtraction operation when the output signal of the D/A converter 27 has a positive polarity, but performs an addition operation when the output signal of the D/A converter 27 has a negative polarity. do. Of course, the polarity of the output signal of the f/V converter 25 may be switched depending on the sign bit of the count value N.

When the count value N of the counter 26 becomes zero, the switch 2
9 opens and switch 14 closes. Tracking control is thereby performed. When the light spot is in the positive moving direction, the count value N of the counter 26 becomes zero when the light spot crosses the target track, as shown in FIGS. 4 and 6, and the switch 14.29 is not switched as described above. Even if the light spot sometimes passes slightly past the target track, tracking control allows the light spot to track the target track. When the light spot is in the negative movement direction, the count value N of the counter 26 becomes zero when the light spot crosses the middle between the target track and the track immediately before it, as shown in FIGS. 3 and 7. When the switch 14.29 is switched as described above, the light spot is slightly offset to the example target track rather than halfway between these tracks, so that the light spot is tracked to the target track.

The tracking actuator 18 has a two-stage structure for coarse control and fine control, and coarse control is performed using the speed control signal from the subtracter 28, and the phase compensation circuit 15
Detailed control may be performed using a tracking error signal from. In the above example, the target moving speed v9 is set to be proportional to the number of remaining tracks up to the target track, but it may be set to show other changes, such as being proportional to the square root of the number of remaining tracks. Furthermore, instead of speed control as described above, only simple phase control may be used. Furthermore, speed control using an observer or the like may be used.

FIG. 9 is a block diagram of main parts showing another embodiment of the optical disc device according to the present invention.

In the figure, a photodetector 1 is a three-part detector in which detection elements 1a, 1c, and 1b are arranged perpendicularly to the longitudinal direction of the track. These detection elements 1a,
, 1c, 1b are added in an adder 53', and the detection signals A, B of the detection elements 1a, Ib at both ends are subtracted as push-pull signals in a subtracter 4'. The output signal C' of the adder 3' is equal to the output signal C' of the adder 3 in FIG. 1, and the output signal D' of the subtracter 4' is equal to the output signal of the subtracter 4 in FIG. According to this embodiment, the detection efficiency of the diffracted light by the pits is good, and the S/N of the difference signal of the push-pull signal is good.

FIG. 10 is a block diagram showing still another embodiment of the optical disc device according to the present invention, in which 30 to 33 are S/H circuits, 34 to 36 are subtracters, and 37 is an adder. Corresponding parts are given the same symbols.

In the figure, in this embodiment, the detection elements A and B in the signal detector 1 are set at the detection timing of the preceding servo pit and the following servo pit in the servo area, that is, clock φ2. After sampling and holding at φ2, the tracking error signal SL is generated by these subtraction and addition processes.
) A rack crossing signal SCM is obtained.

The detection signals A and B are sampled and held by the clock φ in the 378 circuits 30 and 31, respectively.
8 circuits 32 and 33 sample and hold the data using the clock φ2. The output signals of the S/H circuits 30 and 32 are subtracted by a subtracter 34, and the output signals of the S/H circuits 31 and 33 are subtracted by a subtracter 35. The output signals of the subtracters 34 and 35 are added by an adder 37 and subtracted by a subtracter 36. The adder 37 outputs the tracking error signal str, and the subtracter 36 outputs the track crossing signal S.
CR is obtained respectively.

This embodiment differs from the embodiment shown in FIG. 1 only in the arrangement of the S/H circuit, adders, and subtracters, and the same effect as the embodiment shown in FIG. 1 can be obtained. It will be done.

As shown in FIG. 13, the optical disc in the optical disc apparatus according to the present invention described above has a leading servo pit and a trailing servo pit for each track, but as shown in FIG. One servo pit is provided between each other, and the optical disc is periodically inserted so that the servo pits 11 between every other track and the servo pits 11αυ between every other track are shifted in the longitudinal direction of the tracks 12. A servo area may also be provided.

In such an optical disc, the track density can be increased, and as shown in FIG.
A phase difference occurs between the two, and these phase relationships differ as shown in FIGS. 3 and 4 depending on the moving direction of the light spot.

In the optical disc described above, when the light spot passes through the servo pit, a signal with sufficient amplitude must be detected. If the servo pit has a concave or convex portion with a flat bottom or top and a rectangular cross section, the depth or height of the servo pit is λ/4 (where λ is the wavelength of the light spot) or λ. /2
If it is in the vicinity, the amplitude of the push-pull signal of the signal detector is small (the S/N is poor and it is not suitable. Therefore, it is recommended to set this depth or height to about λ/8 to λ/6). Also, the cross-sectional shape of the servo pit is shown in Figure 13 (
aJ, as shown in (b), it may be made to have a 7-character shape.

〔Effect of the invention〕

As described above, according to the present invention, in the sample servo method, the moving direction of the optical spot can also be determined by detecting servo pits, and access can be executed with high accuracy without the need for additional bits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an optical disc device according to the present invention, and FIG. 2 shows the amplitude and polarity of the tracking error signal and track crossing signal in FIG. 1 according to the amount of deviation of the optical spot from the track. Figures 3 and 4
The figures show changes in the tracking error signal and track crossing signal in Fig. 1 with respect to the movement of the optical spot during access, respectively. Fig. 5 is a block showing the access control unit using the tracking error signal 2 in Fig. 1 and the track crossing signal. 6 and 7 are waveform diagrams showing the signals of each part in FIG. 5, FIG. 8 is a diagram showing an example of the target moving speed and actual moving speed of the light spot in FIG. 5, and FIG. 10 are block diagrams showing other embodiments of the optical disk device according to the present invention, FIG. 11 is a partial plan view showing one embodiment of the optical disk according to the present invention, and FIG. 12 is a tracking error obtained from this optical disk. FIG. 13 is a diagram showing an example of the cross-sectional shape of a servo pit, FIG. 14 is a partial plan view showing an optical disc using the conventional sample servo method, and FIG. 15 is a diagram showing the optical disc using this optical disc. FIG. 16 is a waveform diagram showing a tracking error signal obtained by the optical disk device shown in FIG. 15 when the optical spot is moved at high speed in the direction perpendicular to the track. 1... Photodetector, 1a+1b, lc... Detection element,
2... Light spot, 3, 3QI) -... Adder, 4,
401)...Subtractor, 5-8...Sample hold circuit, 9.10...Subtractor, 11.11' +1
1a+lla' +11a+llb, l
lb'11b#... Servo pit, 12.12a,
12b...Track, 13...Light spot, 30~
33...Sample hold circuit, 34-36...Subtractor, 37...Adder, SL? ... Fig. FIG. FIG. FIG. FIG. FIG. FIG. Figure, Fig. Fig. Figure (B) Fig. 16.

Claims (5)

[Claims] (1) In an optical disc in which a plurality of servo areas extending over the entire track are arranged at equal intervals in the longitudinal direction of the track, and servo pits for tracking control are recorded in the servo areas, servo areas in the direction perpendicular to the longitudinal direction of the track are An optical disc characterized in that the cross-sectional shape of the servo pit is V-shaped. (2) A plurality of servo areas spanning the entire track are arranged at equal intervals in the longitudinal direction of the track, and one servo pit is provided between each track in each servo area, and the servo pits between every other track and other An optical disc characterized in that servo pits between every other track are shifted in the longitudinal direction of the track. (3) The optical disc according to claim (2), wherein the servo pit has a V-shaped cross-section in a direction perpendicular to the longitudinal direction of the track. (4) Recording desired data between the servo areas on an optical disc in which a plurality of servo areas spanning the entire track are arranged at equal intervals in the longitudinal direction of the track, and servo pits for tracking control are recorded in the servo areas. In an optical disc device for reproducing signals, a photodetector for reproducing signals from the optical disc is composed of a plurality of detection elements arranged in a direction perpendicular to the track center line, and the output of the detection elements at the servo pit is An optical disc device characterized by comprising means for processing a signal to generate a tracking error signal and a track crossing signal having a phase different from that of the tracking error signal. (5) The optical disc device according to claim 4, wherein the track crossing signal has a phase relationship different from the tracking error signal depending on the moving direction of the optical spot on the optical disc.