JP3528229B2 - Spot position control method and device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot position control method and apparatus.

[0002]

2. Description of the Related Art In an optical disk device, it is necessary for a laser beam to accurately track (track) a track in order to perform accurate writing and reading on the track, and tracking servo control is used. A so-called push-pull method using a single spot is known as a method for detecting a so-called tracking error signal used for the tracking servo control.

Further, the optical disc apparatus is designed to control a track jump by using a tracking error signal (hereinafter referred to as push-pull signal) obtained by the push-pull method. Specifically, as shown in FIG. 8, the push-pull signal when the spot crosses the so-called groove G _i (i is an integer) is a so-called S-curve signal having a track pitch of one cycle.

By the way, in the push-pull method, for example, an offset occurs in the push-pull signal and the level fluctuates due to, for example, the tilt of the disk and the shift of the optical axis caused by the movement of the objective lens by the tracking servo control. Therefore, a so-called differential push-pull method is used to obtain a tracking error signal (hereinafter referred to as a differential push-pull signal) to prevent level fluctuations. Specifically, in the differential push-pull method, as shown in FIG. 9, one main spot MS and two side spots SS ₁ and SS ₂ are formed by a diffraction grating, and both side pots S
S ₁ and SS ₂ are arranged so as to be displaced by a 1/2 track pitch in the direction orthogonal to the track with respect to the main spot MS, and the differential push-pull signal DPP is calculated by the following formula 1.
Trying to get.

[0005]   DPP = (A−B) −K ((E−F) + (G−H)) ... Equation 1

Here, AB is a push-pull signal with respect to the amount of reflected light of the main spot MS detected by the two-divided photodetector D ₁ , and EF is a side spot SS detected by the two-divided photodetector D _2. It is a push-pull signal for the amount of reflected light of ₁ and GH is 2
It is a push-pull signal for the reflected light amount of the side spot SS ₃ detected by the split photodetector D ₃ .

The differential push-pull signal DPP has no level fluctuation due to the movement of the objective lens, and the so-called zero-cross timing corresponds to the timing when the main spot MS is located at the center of the land or groove.
It is possible to detect the position of the main spot MS at a 1/2 track pitch. Therefore, the conventional device also controls the track jump by using the differential push-pull signal DPP.

Recently, in order to increase the recording density, FIG.
As shown in FIG. 3, an optical disc in which the width W _R of the land is wider than the width W _G of the groove and a plurality of tracks are provided on the same land is considered. Specifically, for example, FIG.
As shown in, the width W _R of the land R _i is made wider than the width W _G of the groove G _i , the mutual distance in the direction orthogonal to the track is approximately half the groove pitch G _P , and tracking servo is applied. In the state (hereinafter, referred to as track lock state), two spots S ₁ and S ₂ having the same distance from the groove G _i are respectively land R _i−1 ,
While disposed on R _i, by arranging the two spots S _3, S ₄ on the groove G _i, two tracks Tr _1, provided Tr ₂ on the land R _i.

In this optical disk, the spots S ₁ and S _{2 are formed} by the push-pull method using a single spot.
Crossing the groove G _i , the push-pull signal obtained has a groove pitch G _P of 1 as shown in FIG.
This signal has a cycle and has a substantially constant level on the land R _i . The push-pull signal also undergoes the level fluctuation due to the movement of the objective lens described above, and therefore the differential push-pull method is used. That is, the tracking servo control is performed by obtaining the differential push-pull signal DPP by the following formula 2.

DPP = (A ₁ −B ₁ ) + (A ₂ −B ₂ ) −K ((E−F) + (G−H))

Where A₁-B₁Is a two-part photo
Tecta D₁Spot S detected at ₁The amount of reflected light
Push-pull signal₂-B₂Is a two-part fo
To detector D₂Spot S detected at₂Amount of reflected light
EF is a push-pull signal for
Photodetector D₃Spot S detected at₃Reflected light
It is a push-pull signal for the quantity, and GH is divided into two.
Photo detector D_FourSpot S detected at_FourReflection of
It is a push-pull signal for the light amount.

[0012]

As shown in FIG. 12, the differential push-pull signal DPP obtained by the above equation 2 has the groove pitch G _P as one cycle, and zero cross points are 4 in one cycle. When the spots S ₁ and S ₂ are located on the groove G _i or in the vicinity thereof, there is no level fluctuation due to the movement of the objective lens, but otherwise, it is due to the movement of the objective lens. There is a level variation, and therefore the tracking servo control can be performed using this differential push-pull signal DPP, but it cannot be used for spot position detection during a track jump. In other words, this differential push-pull signal DPP
Cannot be used to control track jumps.

Therefore, the spots S ₁ and S ₂ are in the groove G.
a light amount when located on _i, using the difference between the amount of light when located on the land R _i, it is conceivable to detect the position of the spot, the reflectance of the optical disc is different depending on the location, also In the write-once type optical disc, the position of the spot cannot be stably detected because the reflectance is different before and after writing.

The present invention has been made in view of the above circumstances, and stabilizes the position of the spot without being affected by the shift of the optical axis caused by the movement of the objective lens due to the tracking servo control. It is an object of the present invention to provide a spot position control method and device for a disk device which can detect and thereby control a track jump.

[0015]

In order to solve the above problems, a spot position control method according to the present invention has a groove and a land having a width wider than the width of the groove, and a plurality of tracks are provided on the land. The first spot and the second spot are formed on the formed disc at a position where the distance in the direction orthogonal to the track is approximately half the groove pitch, and the first spot and the second spot are formed. At a position where the distance from the
Laser for forming a fourth spot at a position where the distance from the first spot and the second spot in the direction orthogonal to the track is equal and at a position different from the third spot. Light is irradiated, push-pull signals corresponding to four spots are generated from the reflected light from the disc, and the first spot and the second spot are formed on a plurality of tracks based on the generated four push-pull signals. Along with the tracking, the spot is moved in a direction orthogonal to the plurality of tracks based on the number of times that the difference between the push-pull signal corresponding to the first spot and the push-pull signal corresponding to the second spot becomes zero.

Further, the spot position control device according to the present invention has a laser light irradiating means for irradiating the laser light, a groove for diffracting the laser light, and a land having a width wider than the width of the groove. The first spot and the second spot are formed at a position where the distance in the direction orthogonal to the tracks is approximately half of the groove pitch on the disc having a plurality of tracks formed on the first spot. The third spot is formed at a position where the distance from the second spot in the direction orthogonal to the track is equal, and further the first spot is formed.
Diffracting means for forming a fourth spot at a position having the same distance from the second spot and the second spot at a position perpendicular to the track and different from the third spot; Based on the detection means for detecting each push-pull signal corresponding to the spot and the four push-pull signals detected by the detection means, the first spot and the second spot are made to follow a plurality of tracks, and the first spot Spot position control means for moving the spot in the direction orthogonal to the plurality of tracks based on the number of times when the difference between the push-pull signal corresponding to the spot and the push-pull signal corresponding to the second spot becomes zero.

Further, this spot position control device is provided with a drive means for moving the laser light irradiation means and the diffraction means. The spot position control means makes the laser light irradiation means and the diffraction means orthogonal to the track based on the number of times when the difference between the push-pull signal corresponding to the first spot and the push-pull signal corresponding to the second spot becomes zero. The drive means is controlled so as to move in the direction.

The spot position control means controls the drive amount of the drive means based on the difference between the push-pull signal corresponding to the first spot and the push-pull signal corresponding to the second spot.

[0019]

[0020]

In the spot position control method and apparatus according to the present invention, the two spots (first and second spots) are formed so that the distance in the direction orthogonal to the track is approximately 1/2 of the track pitch. , Two spots (third and fourth spots) having different distances in the direction perpendicular to the track from these two spots are formed at fixed positions, and each push-pull signal corresponding to these four spots is formed. Based on approximately 1/2 of track pitch
The two spots formed at the positions can be tracking-controlled while suppressing the occurrence of offset, and the two spots can be controlled based on the difference between the push-pull signals corresponding to these two spots. It is possible to reliably detect the position at which is moving in the direction orthogonal to the track.

Further, in this spot position control device, the spot position control means is based on the number of times that the difference between the push-pull signal corresponding to the first spot and the push-pull signal corresponding to the second spot becomes zero. The drive means is controlled so as to move the laser light irradiation means and the diffraction means in the direction orthogonal to the track.

The spot position control means controls the drive amount of the drive means based on the difference between the push-pull signal corresponding to the first spot and the push-pull signal corresponding to the second spot.

[0023]

[0024]

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A spot position control method and apparatus according to the present invention will be described below with reference to the drawings. Figure 1
It is a figure which shows the structure of the optical head of the optical disk apparatus to which this invention is applied.

As shown in FIG. 1, this optical head diffracts the laser diode 11 and the light emitted from the laser diode 11 to form four spots S ₁ , S ₂ , S ₃ and S on the optical disc 1. Diffraction grating (hereinafter referred to as grating) 14 forming ₄ and the grating 14
The objective lens 16 that collects the emitted light diffracted by the optical disc 1 and irradiates the optical disc 1, the polarization beam splitter (hereinafter referred to as PBS) 15 that separates the reflected light from the optical disc 1, and the PBS 15 separates it. The detector 19 which detects the reflected light corresponding to each of the spots S _{1 to} S ₄ is provided.

In this optical head, the laser diode is arranged so that the distance between the _two spots S ₁ and S ₂ formed (disposed) on the optical disk 1 in the direction orthogonal to the track is approximately half the groove pitch. The light emitted from the optical disc 11 is applied to the optical disc 1, and the reflected lights corresponding to the _two spots S ₁ and S ₂ from the optical disc 1 are detected by the detector 19 to obtain two push-pull signals. The difference between the push-pull signals is obtained, and the positions of the spots S ₁ and S ₂ on the optical disc 1 in the direction orthogonal to the track are detected based on this difference. Further, the optical head drives an actuator (not shown) that moves the objective lens 17 in the direction orthogonal to the track based on the difference between the two push-pull signals to perform the track jump. .

Specifically, the collimator lens 12 collimates the emitted light from the laser diode 11, and the beam shaping element 13 makes the luminous flux of the collimated emitted light into a circular shape and makes it enter the grating 14.

In the optical disc 1, for example, as shown in FIG. 2, the width W _R of the land R _i (i is an integer) is made wider than the width W _G of the groove G _i , and a plurality of lands are formed on the same land R _i . For example, the optical disc is provided with _two tracks Tr ₁ and Tr ₂ to increase the recording density. And the grating 14
As shown in FIG. 2, the distance from each other is approximately half of the groove pitch G _p , and the distance from the groove G _i is equal when the tracking servo is applied (hereinafter referred to as the track lock state). One spot S ₁ ,
S ₂ is formed on the lands R _i-1 and R _i , respectively, and the emitted light incident from the beam shaping element 13 is formed so that two spots S ₃ and S ₄ are formed on the groove G _i. Diffract.

The outgoing light diffracted in this way is linearly polarized light, passes through the PBS 15, and is incident on the quarter-wave plate 16. The quarter-wave plate 16 converts the linearly polarized outgoing light into circularly polarized light, and the circularly polarized outgoing light is condensed by the objective lens 17 and applied to the optical disc 1. Thus, the four spots S _{1 to} S ₄ are formed (disposed) on the optical disc 1 as described above.

The reflected light reflected by the optical disk 1 is incident on the quarter-wave plate 16 through the objective lens 17 and
The / 4 wave plate 16 converts the circularly polarized reflected light into linearly polarized light having a polarization plane orthogonal to the polarization plane of the outgoing light, and the reflected light converted into the linearly polarized light is reflected by the PBS 15 and also the lens It is condensed by 18 and is incident on the detector 19.

As shown in FIG. 2, the detector 19 detects the light quantity of each reflected light corresponding to the spots S _{1 to} S _4, and each photo detector D ₁ , D ₂ , D _{3 is} divided into _two . , D ₄ and a plurality of differential amplifiers (not shown). And this detector 19
Similar to the conventional device, the differential push-pull signal DPP is obtained by the following equation 3 and the differential push-pull signal DPP is obtained.
Is supplied to the tracking servo circuit 21 as a tracking error signal.

DPP = (A ₁ −B ₁ ) + (A ₂ −B ₂ ) −K ((E−F) + (G−H))

Where A₁-B₁Is a two-part photo
Tecta D₁Spot S detected at ₁The amount of reflected light
Push-pull signal₂-B₂Is a two-part fo
To detector D₂Spot S detected at₂Amount of reflected light
EF is a push-pull signal for
Photodetector D₃Spot S detected at₃Reflected light
It is a push-pull signal for the quantity, and GH is divided into two.
Photo detector D_FourSpot S detected at_FourReflection of
It is a push-pull signal for the light amount.

Then, the tracking servo circuit 21
Differential push-pull signal D supplied from the detector 19
A drive signal is supplied to the actuator drive circuit 22 so that PP becomes 0, and the actuator drive circuit 22 drives the actuator that moves the objective lens 17 in the direction orthogonal to the track based on this drive signal. Thus, the tracking servo is applied and the spots S ₁ , S
₂ tracks tracks Tr ₁ , Tr ₂ . In this track-locked state, the data recorded on the optical disc 1 is reproduced based on a so-called sum signal detected by the two-division photo detectors D ₁ and D ₂ , and
For example, in a magneto-optical disk device that uses a magneto-optical disk as the optical disk 1, data is recorded on the optical disk 1.

Further, the detector 19 obtains the difference between the push-pull signals (A ₁ -B ₁ , A ₂ -B ₂ ) detected by the two-divided photodetectors D ₁ and D ₂ , that is, according to the following equation 4, The track jump signal TJ is obtained, and the track jump signal TJ is supplied to the track jump control circuit 23.

TJ = (A ₁ −B ₁ ) + (A ₂ −B ₂ ) ... Equation 4

Specifically, the track jump signal TJ
For example, as shown in FIG. 3, the groove pitch is one cycle, and for example, as shown in FIG. 4, the spots S ₁ and S ₂ are ¼ G from the track lock state to the inner or outer circumference side.
It is a signal whose level becomes 0 when it moves to a position displaced by _P. Then, the detector 19 supplies the track jump signal TJ to the track jump control circuit 23.

The track jump control circuit 23, for example, as shown in FIG. 5, detects the spots S ₁ and S ₂ based on the track jump signal TJ from the detector 19.
Comparator 31 for detecting the position in the direction orthogonal to the tracks Tr ₁ and Tr ₂ of the above, and a flip-flop (hereinafter referred to as FF) 45 for generating an acceleration pulse based on the position of the spot detected by the comparator 31. An FF 47 or the like that generates a deceleration pulse based on the position of the spot detected by the comparator 31.

The track jump control circuit 2
In FIG. 3, a system controller (not shown) for controlling each part of the optical disc apparatus is used to display, for example, FIGS.
As shown in FIG. 11, a clock, a jump instruction signal JUMPF / R for instructing the direction of the track jump, and a trigger signal JUMPTRIG for instructing the start of the track jump.
And the track jump signal TJ are supplied from the detector 19.

The comparator 31 receives the track jump signal TJ.
When comparing the zero voltage, when the spot S _1, S ₂ is moved in one direction of the inner circumferential side or outer circumferential side, for example, as shown in FIG. 6d, spots S _1, S ₂ from the track lock state 1 / 4G _P shifted high level when moved to a position (hereinafter, referred to as "1".) and then outputs a "0" when moved to the 3 / 4G _P shift position.

The FFs 32 and 33 sequentially delay the output of the comparator 31 based on a clock, as shown in FIGS. 6e and 6f, for example. The NAND circuit (hereinafter, referred to as NAND circuit) 34 obtains the NAND of the output of the FF 32 and the value obtained by inverting the output of the FF 33 (hereinafter, simply referred to as inverted output), as shown in FIG. 6g, for example. To FF3
The NAND circuit 35 outputs a negative pulse having a 1-clock width in synchronization with the rising edge of the output of the second output, and the NAND circuit 35 obtains the NAND of the inverted output of the FF32 and the output of the FF33.
For example, as shown in FIG. 6h, a negative pulse synchronized with the falling edge of the output of the FF 32 is output.

The monostable multivibrator 36 is activated at the fall of the output of the NAND circuit 35 and outputs a pulse having a predetermined time width, as shown in FIG. 6i, for example.

The FFs 37 and 38 sequentially delay the output of the monostable multivibrator 36 based on the clock, as shown in FIGS.
By obtaining the NAND of the inverted output of F37 and the output of FF38, a negative pulse synchronized with the trailing edge of the output of FF37 is output, for example, as shown in FIG. 6m.

NAND circuit 3 thus obtained
The outputs of 4, 35, 39 are output to the changeover switches 40, 41,
42, 43. These changeover switches 40-
43 is controlled based on the jump instruction signal JUMPF / R, and the changeover switches 40 and 42 are triggered by the trigger signal JUMF / R.
The output of PTRIG and the NAND circuit 35 is switched and selected, and is supplied to the FFs 45 and 47 as a set signal. Further, the changeover switches 41 and 43 are used for the NAND circuit 3
The output of 9 and the output of the NAND circuit 34 are switched and selected,
The selected output is supplied to the AND circuits 44 and 46, respectively.

More specifically, the change-over switch 40 is, for example, when the track is jumped to the forward side which is the outer peripheral side, that is, the jump instruction signal JUMPF / R is "1".
When the jump signal JUMPF / R is “0”, the output of the NAND circuit 35 is selected and the selected signal is supplied to the FF 45 as a set signal.

The change-over switch 42 has a jump instruction signal J.
When UMPF / R is "1", the output of the NAND circuit 35 is selected, and when it is "0", the trigger signal JUMPTRIG is selected.
Is selected and the selected signal is used as a set signal in the FF 47
Supply to.

The changeover switch 41 has a jump instruction signal J.
When UMPF / R is "1", the output of the NAND circuit 34 is selected, and when it is "0", the output of the NAND circuit 39 is selected and the selected output is supplied to the AND circuit 44.

The changeover switch 43 has a jump instruction signal J.
When UMPF / R is "1", the output of the NAND circuit 39 is selected, and when it is "0", the output of the NAND circuit 34 is selected, and the selected output is supplied to the AND circuit 46. Hereinafter, when the jump instruction signal JUMPF / R is “1”,
That is, the operation when the track jumps to the forward side will be described.

The FF 45 is, for example, as shown in FIG.
Trigger signal JUM supplied via changeover switch 40
The output of the NAND circuit 34 supplied via the AND circuit 44, that is, the negative pulse is latched by the clock when the output of the NAND circuit 34 is set by PTRIG and outputs "1". "0" is output in synchronization with the rising edge of the output. Thus, FF4
The output of No. 5 becomes "1" by the trigger signal JUMPTRIG, and the rising edge of the comparator 31, that is, the spot S ₁ ,
It becomes “0” when S ₂ moves to the position deviated from the track lock state by 1/4 _GP .

On the other hand, the FF 47 is set by the output of the NAND circuit 35 supplied through the changeover switch 42 to output "1" as shown in FIG. The output of the FF 39 supplied via the circuit 46, that is, the negative pulse is latched by the clock, and "0" is output in synchronization with the rising edge of the output of the FF 39. Thus, the output of FF47, the comparator 31 fall, ie spots S _1, S ₂ is "1" when moved to a position shifted 3 / 4G _P from the track lock state, the monostable multivibrator 36
After the lapse of a predetermined time determined by, the value becomes "0". Then, the outputs of the FFs 45 and 47 are supplied to the differential amplifier 48, and the differential amplifier 48 obtains the difference between the output of the FF 45 and the output of the FF 47 and amplifies the difference, for example, as shown in FIG. , An acceleration pulse and a deceleration pulse are generated, and these pulses are supplied to an actuator drive circuit 22 which moves the objective lens 17 in a direction orthogonal to the tracks Tr ₁ and Tr ₂ .

That is, this track jump control circuit
23 is a track lock state as shown in FIG. 7 described above.
At time t₁In tracking servo circuit 2
1 is turned off and the trigger signal JUMPTRIG is supplied.
Then, for example, in order to move the objective lens 17 to the outside,
Acceleration pulse is output and spot S₁, S₂Is 1 / 4G _P
Time t when the vehicle moved to the shifted position₂At the acceleration pulse
Stop output. And spot S₁, S₂Is 3/4
G_PTime t to move to a displaced position₃Until neutral (add
Do not add speed or deceleration).

Next, the track jump control circuit 23
A deceleration pulse is output from time t ₃ to time t ₄ after a lapse of a predetermined time so that the moving speeds of the spots S ₁ and S ₂ become substantially 0 in the vicinity of the next tracks Tr ₁ and Tr _2. . Then, at time t ₄ , the tracking servo circuit 21 is turned on. As a result, at time t ₅ , the track lock state is set for the next tracks Tr ₁ and Tr ₂ .

That is, in the optical disk device of this embodiment, the tracks Tr ₁ and Tr of the _two spots S ₁ and S ₂ are
_The optical disc 1 is irradiated with laser light so that the distance in the direction orthogonal to ₂ is approximately half the groove pitch, and two push-pulls based on the amount of reflected light corresponding to each spot S ₁ , S ₂ from the optical disc 1 are performed. Signal (A ₁ -B ₁ ,
A ₂ −B ₂ ), a track jump signal TJ which is the difference between these push-pull signals, and the positions of the spots S ₁ , S ₂ on the optical disc 1 are detected based on the track jump signal TJ. By doing
The positions of the spots S ₁ and S ₂ can be stably detected without being affected by the deviation of the optical axis caused by the movement of the objective lens 17 due to the tracking servo control.

In this optical disk device, the optical disk 1 is an optical disk in which the width W _R of the land R _i is wider than the width W _G of the groove G _i , and the track jump signal T
By detecting the position of the spot on the basis of the zero cross point of J, it is possible to accurately detect the position where the spots S ₁ and S ₂ deviate from the track lock state by 1/4 _GP or 3/4 _GP. .

Further, in this optical disk device, based on the track jump signal TJ obtained as described above,
By driving the actuator that moves the objective lens 17 in the direction orthogonal to the tracks Tr ₁ and Tr ₂ , the track jump can be performed without being affected by the deviation of the optical axis caused by the movement of the objective lens 17 by the tracking servo control. It can be performed.

[0057]

As is apparent from the above description, according to the present invention, the optical disc is irradiated with laser light so that the distance between the two spots in the direction orthogonal to the track becomes approximately half the groove pitch. The two push-pull signals based on the amount of reflected light corresponding to each spot are obtained, the difference between these push-pull signals is obtained, and the position of the spot on the optical disc is detected based on this difference, thereby tracking The spot position can be stably detected without being affected by the shift of the optical axis caused by the movement of the objective lens by the servo control.

Further, in the present invention, the optical disc is such that the width of the land is wider than the width of the groove, and by detecting the spot position based on the zero cross point of the difference, the spot can be tracked. 1 / from locked state
It is possible to accurately detect a position shifted by 4 groove pitch or 3/4 groove pitch.

Further, according to the present invention, the objective lens under the tracking servo control is driven by driving the actuator which moves the objective lens in the direction orthogonal to the track based on the difference between the two push-pull signals obtained as described above. The track jump can be performed without being affected by the deviation of the optical axis due to the movement of the.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical head of an optical disc device to which the present invention is applied.

FIG. 2 is a diagram showing a specific arrangement of spots on an optical disc having a land wider than a groove.

FIG. 3 is a waveform diagram of a track jump signal.

FIG. 4 is a diagram showing a state in which spots are deviated by ¼ groove pitch.

FIG. 5 is a diagram showing a specific circuit configuration of a track jump control circuit which constitutes the optical disc device.

FIG. 6 is a time chart for explaining the operation of the track jump control circuit.

FIG. 7 is a time chart for explaining the operation of the track jump control circuit.

FIG. 8 is a waveform diagram of a push-pull signal using a single spot.

FIG. 9 is a diagram showing the arrangement of spots for explaining the differential push-pull method.

FIG. 10 is a waveform diagram of a push-pull signal obtained from an optical disc having a land wider than a groove.

FIG. 11 is a diagram showing a specific arrangement of spots on the optical disc.

FIG. 12 is a waveform diagram of a differential push-pull signal obtained from the optical disc.

[Explanation of symbols]

1 optical disc 14 Grating 17 Objective lens 19 detector 22 Actuator drive circuit 23 Track jump control circuit 31 Comparator 45, 47 FF 48 differential amplifier

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 08-7/22

Claims (4)

(57) [Claims] 1. A disk having a groove and a land having a width wider than that of the groove, and a plurality of tracks formed on the land has a groove pitch as a distance in a direction orthogonal to the track. to approximately half a position and forming the first spot and the second spot, bets from the first spot and the second spot
The third spot is formed at a position where the distance in the direction orthogonal to the rack is equal, and further, the third spot is formed at a position where the distance from the first spot and the second spot in the direction orthogonal to the track is equal. Laser light is irradiated to form a fourth spot at a position different from the spot, push-pull signals corresponding to the four spots are generated from the reflected light from the disc, and the generated four push-pull signals are generated. Based on the first spot and the second spot based on the plurality of tracks based on the
Spot position control for moving the spot in a direction orthogonal to the plurality of tracks based on the number of times the difference between the push-pull signal corresponding to the first spot and the push-pull signal corresponding to the second spot becomes zero. Method. 2. A laser beam irradiating means for irradiating a laser beam, a groove for diffracting the laser beam, and a land having a width wider than the width of the groove, and a plurality of tracks are formed on the land. The first spot and the second spot are formed at a position where the distance in the direction orthogonal to the track is approximately half of the groove pitch, and the first spot and the second spot are formed on the disk. distance direction perpendicular to the track to form a third spot are equal positions, further the direction of the distance <br/> away perpendicular to the track from that of the first spot and the second spot equal from a diffraction means for forming a fourth spot at a position different from the and the third spot in position, each push-pull signal corresponding to the four spots from the reflected light from the disk Detecting means for detecting, and causing the first spot and the second spot to follow the plurality of tracks based on the four push-pull signals detected by the detecting means, and corresponding to the first spot. Position control means for moving the spot in the direction orthogonal to the plurality of tracks based on the number of times the difference between the push-pull signal and the push-pull signal corresponding to the second spot becomes zero. apparatus. 3. A drive means for moving the laser beam irradiation means and the diffraction means is provided, and the spot position control means corresponds to a push-pull signal corresponding to the first spot and the second spot. 3. The driving means is controlled so as to move the laser light irradiating means and the diffracting means in a direction orthogonal to a track based on the number of times when the difference from the push-pull signal becomes zero. Spot position control device. 4. The spot position control means includes the first
The drive amount of the drive means is controlled based on the difference between the push-pull signal corresponding to the spot and the push-pull signal corresponding to the second spot.
Item 3. The spot position control device according to item 3 .