JP2001189022A - Focus controller, focus control method and recording/ reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the focus control method capable of increasing reliability of the focus control by allowing each focus error signal to coincide with respect to lands and grooves. SOLUTION: In an optical pickup, a main beam and a sub-beam are produced by diffracting the laser beam, and a track of the optical disk constituted of the lands and grooves is irradiated with convergence of the main beam, and also the border part between the guide area of the track of optical disk and this track is irradiated with convergence of the sub-beam, then the beam reflected by the optical disk is supplied to a photodetector. By a producing circuit, a sum signal SUM0 corresponding to the light quantity of the main beam and the focus error signal FE of the sub-beam are produced from the output signal of the photodetector. By the focus controller, an objective lens is moved based on the sum signal SUM0 so that the value of the focus error signal FE of the sub-beam reaches the value in the linear area from the value at the outside of the linear area of the sigmoid curve, and next, the objective lens is moved based on the above focus error signal FE.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device and a focus control method for controlling the focus of a laser beam on an optical disk, and a recording and reproducing device for reproducing recorded information from the optical disk.

[0002]

2. Description of the Related Art FIG. 1 is a schematic diagram showing a conventional optical pickup. The optical pickup 1 includes a semiconductor laser 4, a collimator lens 5, a beam splitter 3, an objective lens 2, a condenser lens 6, and a cylindrical lens 7.
And a photodetector 8.

The semiconductor laser 4 outputs a linearly polarized laser beam and supplies it to a collimator lens 5. The collimator lens 5 converts the laser beam from the semiconductor laser 4 into parallel light and supplies the parallel light to the beam splitter 3. The beam splitter 3 passes the laser beam from the collimator lens 5 and supplies the laser beam to the objective lens 2. The objective lens 2
The laser beam from the beam splitter 3 is condensed and supplied to the track of the optical disk 82.

[0004] The objective lens 2 returns the laser beam reflected by the optical disk 82 to the beam splitter 3. The beam splitter 3 receives the laser beam from the objective lens 2, reflects the incident laser beam, and supplies the reflected laser beam to the condenser lens 6. The condenser lens 6 condenses the laser beam from the beam splitter 3 and supplies it to a cylindrical lens (cylindrical lens) 7. The cylindrical lens 7 passes the laser beam from the condenser lens 6 and supplies the laser beam to the photodetector 8. The photodetector 8 receives a laser beam from the cylindrical lens 7 at a light receiving section and generates an output signal.

FIG. 2 is an explanatory diagram showing the configuration of the light receiving section of the photodetector 8. The photodetector 8 is a quadrant photodetector in which the light receiving section 8S is divided into four equal parts by two division lines 8Sx and 8Sy. The light receiving section 8S has four divided areas 8A to 8D. A beam spot MS is formed on the light receiving section 8S of FIG. 2 by the laser beam from the cylindrical lens 7.
The photodetector 8 is arranged such that when the laser beam is focused on the track, the beam spot MS of the return light is projected in a circular shape at the center of the light receiving section 8S.

The direction of the generating line of the cylindrical lens 7 is
4S with respect to the direction of the dividing line 8Sx or 8Sy.
Make an angle of 5 degrees or about 135 degrees. Dividing line 8Sx,
The intersection of 8Sy is located at or substantially at the center of the laser beam that has passed through the cylindrical lens 7. The shape of the beam spot MS formed on the light receiving section 8S is
Changes in a diagonal direction according to the distance between the object and the objective lens 2,
The focus shift on the optical disk 82 can be detected by the astigmatism method. Focus error signal (focus error signal) fe
Are output signals SA to SD generated by the divided areas 8A to 8D.
And is expressed by the following equation.

[0007]

## EQU1 ## fe = SA + SC- (SB + SD) ...

FIG. 3 is a schematic enlarged view showing the optical disk 82. On the optical disk 82, lands 11L and grooves 11G having physical unevenness along the tracks are formed on the substrate 11. In the land-groove recording method, a recording mark 12M is recorded on the recording layer 12 at both positions of the land 11L and the groove 11G. Optical disk 82 using land-groove recording method
In general, the width of the land 11L and the width of the groove 11G are the same or substantially the same, and the depth of the groove 11G is about λ / 8 with respect to the laser beam wavelength (laser wavelength) λ.
~ Λ / 4.

[0009]

In an optical disk having a structure having a land and a groove, the focus error signal has a different value depending on whether the focus position is on the land or on the groove. This will be described with reference to FIG.

FIG. 4 is a characteristic diagram showing focus error signals fe for lands and grooves. The focus error signal fe when the track is a land is indicated by a dotted line LA, and the focus error signal fe when the track is a groove is indicated by a dotted line G.
Indicated by R. Characteristic curves LA and G of the focus error signal shown in FIG.
R is a value obtained by the above equation for convenience.
The value of the percentage (100 × fe / Σ) normalized (normalized) by the sum Σ of D (= SA + SB + SC + SD). Further, the relative distance from the focus position (focus position) where the laser beam from the objective lens is focused to the recording surface of the optical disk is defined as the defocus amount.

In an optical disk having a land-groove structure, the value of the focus error signal fe does not become 0 when the recording surface of the optical disk is at the in-focus position and is in focus (when the defocus amount is 0). This is because light diffraction due to lands and / or grooves occurs when the laser beam reflects off the track. The object of the present invention is
Provided are a focus control device, a focus control method, and a recording / reproducing device capable of causing the focus error signals for the lands and grooves to coincide or substantially coincide with each other when a focus of a laser beam is formed on a track of an optical disk having a land / groove structure. Is to do.

[0012]

A first focus control device according to the present invention comprises a diffraction grating for diffracting a laser beam to generate a main beam and a sub beam, and a track for an optical disk having a land-groove structure. An objective lens for converging and irradiating the main beam and converging and irradiating the sub-beam on a boundary between the track guide area and the track of the optical disc; and the main beam reflected on the optical disc. And a photodetector to which a sub-beam is supplied via the objective lens, and generating a sum signal corresponding to the light amount of the main beam and a focus error signal of the sub-beam based on an output signal of the photodetector. A circuit and an actuator for moving the objective lens in a focus direction perpendicular to the recording surface of the optical disc, wherein a focus error signal of the sub beam is provided. The objective lens is moved based on the sum signal so that the value reaches a value within the linear region from a value outside the linear region of the S-shaped curve, and then the objective lens is moved based on the focus error signal of the sub-beam. An actuator for moving the lens.

[0013] In the first focus control device according to the present invention, preferably, the actuator moves the objective lens based on the sum signal, and subsequently, the value of the focus error signal of the sub-beam is changed to S. The objective lens is moved based on the focus error signal of the sub-beam so as to be maintained at or substantially at the zero point within the linear region of the curve.

In the first focus control device according to the present invention, preferably, the diffraction grating diffracts the laser beam to generate the main beam and the first and second sub-beams. The distance between the centers of the first and second sub-beams on the recording surface in the disk radial direction is the same or substantially the same as an odd multiple of the track pitch, and the generation circuit includes the first and second sub-beams. Generating a focus error signal for each of the sub-beams, and further generating a combined focus error signal by synthesizing the two focus error signals, wherein the actuator moves the objective lens based on the focus error signal of the sub-beam. Then, the composite focus error signal is used as the focus error signal of the sub beam.

A second focus control device according to the present invention is a diffraction grating for diffracting a laser beam to generate a main beam and a sub beam, and condensing the main beam on a track of an optical disk having a land-groove structure. And irradiate
An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area of the track of the optical disc and the track, and the main beam and the sub-beam reflected by the optical disc are supplied via the objective lens A photodetector, a generation circuit that generates a focus error signal of the main beam and a focus error signal of the sub beam based on an output signal of the photodetector, and the objective lens is perpendicular to a recording surface of the optical disc. An actuator for moving the objective lens until the value of the focus error signal of the main beam reaches a zero point or a value near the zero point in the linear region from the value outside the linear region of the S-shaped curve. And an actuator for moving the objective lens based on a focus error signal of the sub-beam.

In the second focus control device according to the present invention, preferably, the actuator is configured so that the value of the focus error signal of the main beam is maintained at a zero point in the linear region or a value near the zero point. Moving the objective lens and subsequently moving the objective lens so that the value of the focus error signal of the sub-beam is maintained at or substantially zero at a zero within the linear region of the S-curve. Move based on signal.

In the second focus control apparatus according to the present invention, preferably, the diffraction grating diffracts the laser beam to generate the main beam and the first and second sub-beams. The distance between the centers of the first and second sub-beams on the recording surface in the disk radial direction is the same or substantially the same as an odd multiple of the track pitch, and the generation circuit includes the first and second sub-beams. Generating a focus error signal for each of the sub-beams, and further generating a combined focus error signal by synthesizing the two focus error signals, wherein the actuator moves the objective lens based on the focus error signal of the sub-beam. Then, the composite focus error signal is used as the focus error signal of the sub beam.

A first recording / reproducing apparatus according to the present invention comprises a laser for outputting a laser beam, a diffraction grating for diffracting a laser beam from the laser to generate a main beam and a sub-beam, and an optical disk having a land-groove structure. An objective lens for converging and irradiating the main beam to a track of the optical disk, and condensing and irradiating the sub-beam to a boundary portion between a track guide area of the optical disk and the track; A photodetector to which the main beam and the sub-beam reflected at are supplied through the objective lens, and a sum signal and a focus of the sub-beam corresponding to the light amount of the main beam based on an output signal of the photodetector. A generation circuit for generating an error signal; and an actuator for moving the objective lens in a focus direction perpendicular to a recording surface of the optical disc. Moving the objective lens based on the sum signal so that the value of the focus error signal of the sub-beam reaches a value within the linear region from the value outside the linear region of the S-shaped curve; An actuator for moving the objective lens based on a beam focus error signal; and a detection circuit for detecting information recorded on the optical disk based on the sum signal.

In the first recording / reproducing apparatus according to the present invention, preferably, the actuator moves the objective lens based on the sum signal, and subsequently, the value of the focus error signal of the sub-beam is changed to S. The objective lens is moved based on the focus error signal of the sub-beam so as to be maintained at or substantially at the zero point within the linear region of the curve.

In the first recording / reproducing apparatus according to the present invention, preferably, the diffraction grating diffracts the laser beam to generate the main beam and the first and second sub-beams. The distance between the centers of the first and second sub-beams on the recording surface in the disk radial direction is the same or substantially the same as an odd multiple of the track pitch, and the generation circuit includes the first and second sub-beams. Generating a focus error signal for each of the sub-beams, and further generating a combined focus error signal by synthesizing the two focus error signals, wherein the actuator moves the objective lens based on the focus error signal of the sub-beam. Then, the composite focus error signal is used as the focus error signal of the sub beam.

A second recording / reproducing apparatus according to the present invention comprises a laser for outputting a laser beam, a diffraction grating for diffracting the laser beam from the laser to generate a main beam and a sub-beam, and a land-groove structure. An objective lens for condensing and irradiating the main beam on a track of the optical disc and condensing and irradiating the sub-beam on a boundary between the guide area of the track of the optical disc and the track; A photodetector to which the main beam and the sub-beam reflected by the optical disc are supplied via the objective lens; and a reproduction signal, a focus error signal of the main beam, and a sub-beam based on an output signal of the photodetector. A generation circuit for generating a focus error signal of the optical disk; and an actuator for moving the objective lens in a focus direction perpendicular to a recording surface of the optical disk. Moving the objective lens until the value of the focus error signal of the main beam from a value outside the linear region of the S-shaped curve reaches a zero point or a value near the zero in the linear region; An actuator for moving the objective lens based on a beam focus error signal; and a detection circuit for detecting information recorded on the optical disk based on the reproduction signal.

In the second recording / reproducing apparatus according to the present invention, it is preferable that the actuator maintain the focus error signal value of the main beam at a zero point in the linear region or a value near the zero point. Moving the objective lens, and then moving the objective lens based on the sub-beam focus error signal such that the value of the sub-beam focus error signal is maintained at a zero within the linear region of the S-curve. .

In the second recording / reproducing apparatus according to the present invention, preferably, the diffraction grating diffracts the laser beam to generate the main beam and the first and second sub-beams. The distance between the centers of the first and second sub-beams on the recording surface in the disk radial direction is the same or substantially the same as an odd multiple of the track pitch, and the generation circuit includes the first and second sub-beams. Generating a focus error signal of the sub-beam, further combining the two focus error signals to generate a combined focus error signal, wherein the actuator moves the objective lens based on the focus error signal of the sub-beam. The composite focus error signal is used as the focus error signal of the sub beam.

In a first focus control method according to the present invention, a diffraction grating for diffracting a laser beam to generate a main beam and a sub-beam, and condensing the main beam on tracks of an optical disk having a land-groove structure. And irradiate
An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area of the track of the optical disc and the track, and the main beam and the sub-beam reflected by the optical disc are supplied via the objective lens And a generation circuit that generates a sum signal corresponding to the light amount of the main beam and a focus error signal of the sub-beam based on an output signal of the photodetector. A focus control method of a focus control device for moving a recording surface of an optical disc in a focus direction perpendicular to a recording surface of the optical disc, wherein a value of a focus error signal of the sub beam is changed from a value outside a linear region of the S-shaped curve to a value within the linear region. A first step of moving the objective lens based on the sum signal so as to reach a value, and a second step of moving the objective lens based on a focus error signal of the sub-beam. And a degree.

In the first focus control method according to the present invention, preferably, in the second step, the value of the focus error signal of the sub beam is set to a zero point or substantially in a linear region of the S-shaped curve. The objective lens is moved based on the focus error signal of the sub-beam so as to be maintained at the zero point.

In the first focus control method according to the present invention, preferably, the diffraction grating diffracts the laser beam to generate the main beam and the first and second sub-beams. The distance between the centers of the first and second sub-beams on the recording surface in the disk radial direction is the same or substantially the same as an odd multiple of the track pitch, and the generation circuit includes the first and second sub-beams. Generating a focus error signal for each of the sub-beams, and further combining the two focus error signals to generate a combined focus error signal. In the second step, the objective lens is controlled based on the focus error signal of the sub-beam. When moving, the combined focus error signal is used as the focus error signal of the sub beam.

In a second focus control method according to the present invention, a diffraction grating for diffracting a laser beam to generate a main beam and a sub-beam, and condensing the main beam on tracks of an optical disk having a land-groove structure. And irradiate
An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area of the track of the optical disc and the track, and the main beam and the sub-beam reflected by the optical disc are supplied via the objective lens And a generating circuit for generating a focus error signal of the main beam and the sub beam based on an output signal of the photodetector, wherein the objective lens is perpendicular to a recording surface of the optical disc. A focus control method of a focus control device for moving in a focus direction, wherein a value of a focus error signal of the main beam reaches from a value outside a linear region of the S-shaped curve to a zero point in the linear region or a value near the zero. A first step of moving the objective lens, and a second step of moving the objective lens based on the focus error signal of the sub-beam after the first step
And the step of

In the second focus control method according to the present invention, preferably, the value of the focus error signal of the main beam is maintained at a zero point in the linear region or a value near the zero point after the first step. The method further comprises a third step of moving the objective lens and proceeding to the second step, wherein the value of the focus error signal of the sub-beam is a zero point in a linear region of the S-shaped curve. Moving the objective lens such that the objective lens is maintained at or substantially zero.

In the second focus control method according to the present invention, preferably, the diffraction grating diffracts the laser beam to generate the main beam and the first and second sub-beams. The distance between the centers of the first and second sub-beams on the recording surface in the disk radial direction is the same or substantially the same as an odd multiple of the track pitch, and the generation circuit includes the first and second sub-beams. Generating a combined focus error signal by combining the two focus error signals, and moving the objective lens based on the focus error signal of the sub beam in the second step. In this case, the composite focus error signal is used as the focus error signal of the sub beam.

The objective lens focuses and irradiates a main beam on a track of an optical disc having a land-groove structure, and converges a sub-beam on a boundary between the guide area of the track of the optical disc and the track. By irradiating the main beam, the focus error signals of the sub-beams can be matched between the case where the track irradiated with the main beam is a land and the case where the track is a groove, and the focus is adjusted based on the coincident focus error signal. It is possible to control.

In the above-described first focus control device, since the main beam has a larger light amount than the sub-beam, the main lens is moved until the value of the focus error signal of the sub-beam reaches the linear region of the S-shaped curve. By moving and pulling in based on the sum signal of the beams, the reliability of focus control can be improved as compared with the case where the objective lens is moved based on the sum signal of the sub-beams.

In the above-mentioned second focus control device, since the main beam has a larger light quantity than the sub-beam, the focus error signal of the main beam is monitored and the value of the focus error signal of the main beam is changed to the S-shaped curve. By moving and retracting the objective lens until it reaches the zero point or a value near the zero point in the linear region, the focus error signal of the sub beam is monitored, and the value of the focus error signal of the sub beam is linear from outside the linear region of the S-shaped curve. The reliability of the focus control can be improved as compared with the case where the objective lens is moved and retracted until reaching the zero point in the region or a value near the zero point.

[0033]

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

First Embodiment FIG. 5 is a schematic block diagram showing an embodiment of a recording / reproducing apparatus according to the present invention. This recording / reproducing device 90
Has a motor 30, a motor drive circuit 35, an information detection circuit (detection circuit) 65, and a focus control device 95.
The focus control device 95 includes a phase compensation circuit 40 and an amplification circuit 4
2, an optical pickup 50, an amplification circuit (head amplifier) 52, a laser drive circuit 55, a generation circuit 60,
And a control circuit 70. The recording / reproducing device 90 reproduces the recorded information recorded on the optical disk 80.

The control circuit 70 is a controller that controls the entire recording / reproducing device 90, and has a microcomputer. The control circuit 70 performs various operations using a microcomputer, and performs various operations on the motor 30, the motor drive circuit 35, the laser drive circuit 55, the optical pickup 5
0, phase compensation circuit 40, generation circuit 60, information detection circuit 6
5 and so on.

The optical pickup 50 irradiates a laser beam LB to a reproduction position of the optical disk 80 during reproduction. The laser drive circuit 55 generates a drive signal SLZ under the control of the control circuit 70, drives the semiconductor laser in the optical pickup 50 by the drive signal SLZ, and outputs a laser beam LB from the semiconductor laser.

The motor 30 is constituted by, for example, a spindle motor, and rotates the optical disk 80 at a predetermined rotation speed. The motor 30 rotates the optical disk 80 so that the linear velocity becomes constant, for example.

The motor drive circuit 35 supplies drive power to the motor 30 to drive the motor 30. The motor drive circuit 35 may perform rotation control of the motor 30 by PWM (Pulse Width Modulation) control, and may perform PLL (Ph
Rotation control may be performed by ase Locked Loop) control.

The amplifying circuit 52 amplifies the output signals SA to SL of the light receiving section of the photodetector of the optical pickup 50 and supplies the amplified signals to the generating circuit 60.

The generation circuit 60 generates a reproduction signal RF, a focus error signal FE, a tracking error signal TE, and push-pull signals PP0 to PP0 based on the output signals SA to SL of the photodetector supplied from the amplification circuit 52. And PP2. The generation circuit 60 outputs, for example, a sum signal SUM0 (=) obtained by adding the output signals SA to SD from the amplification circuit 52.
SA + SB + SC + SD) to generate a reproduction signal RF. Further, the tracking error signal TE is, for example, T
It is generated by performing an operation of E = SA + SD- (SB + SC).

The phase compensation circuit 40 generates a compensation signal by compensating (phase compensation and / or frequency compensation) the focus error signal FE and the tracking error signal TE, and supplies this compensation signal to the amplifier circuit 42.

The amplification circuit 42 has a focus error signal FE.
Is supplied to the focusing actuator 2F in the optical pickup 50 (i.e., the drive signal Sfe obtained by amplifying the compensation signal of the optical pickup 50). The amplifier circuit 42 also converts the drive signal Ste (ie, the signal amplified by compensating the tracking error signal TE) obtained by amplifying the compensation signal of the tracking error signal TE,
It is supplied to the tracking actuator 2T in the optical pickup 50.

The information detection circuit 65 is supplied with the reproduction signal RF from the generation circuit 60, demodulates the reproduction signal RF, reproduces the recorded information on the optical disk 80, and outputs the reproduced recorded information as the output signal So.

FIG. 6 is a schematic structural view showing the optical pickup 50 of the recording / reproducing apparatus 90 of FIG. The optical pickup 50 includes a semiconductor laser 4, a collimator lens 5, a diffraction grating 9, a beam splitter 3, an objective lens 2, a condenser lens 6, a cylindrical lens 7, a photodetector 18, a lens holder, 2H, focusing actuator 2F, and tracking actuator 2
T.

The objective lens 2 is held by a lens holder 2H. The focusing actuator 2F is
Based on the drive signal Sfe, the lens holder 2H is moved in a focus direction perpendicular to the recording surface of the optical disc 80, and as a result, the objective lens 2 is moved in the focus direction.
The tracking actuator 2T moves the lens holder 2H in the radial direction of the optical disk 80 based on the drive signal Ste, and as a result, moves the objective lens 2 to the optical disk 80.
In the radial direction.

The semiconductor laser 4 outputs a linearly polarized laser beam based on the drive signal SLZ and supplies it to the collimator lens 5. The collimator lens 5 converts the laser beam from the semiconductor laser 4 into parallel light and supplies the parallel light to the diffraction grating 9. The diffraction grating 9 separates the laser beam from the collimator lens 5 into a main beam and first and second sub beams and supplies the split beam to the beam splitter 3. The beam splitter 3 passes the laser beam (main beam and first and second sub-beams) from the diffraction grating 9 and supplies it to the objective lens 2.

The objective lens 2 condenses the laser beam from the beam splitter 3 and condenses and supplies the main beam to the track of the optical disk 80 having a land-groove structure. The sub-beam is condensed and supplied to the boundary. For example, a first sub-beam is condensed and irradiated on one boundary between a guide area of a track and the track, and a second sub-beam is condensed and irradiated on the other boundary. . When the track is, for example, a land, a sub-beam is applied to the boundary between the groove on both sides (or both sides) of the land and the land. It is desirable that the center of the sub beam is located on the boundary between the land and the groove. Optical disk 8
0 is composed of, for example, a compact disk (CD), a digital video disk (DVD), a phase change optical disk (PD), or the like.

The objective lens 2 returns the laser beam reflected by the optical disk 80 to the beam splitter 3. The beam splitter 3 receives the laser beam from the objective lens 2, reflects the emitted laser beam, emits the reflected laser beam, and supplies the laser beam to the condenser lens 6. The condenser lens 6 condenses the laser beam from the beam splitter 3 and supplies it to a cylindrical lens (cylindrical lens) 7. Cylindrical lens 7
Supplies the laser beam from the condenser lens 6 to the photodetector 18 through the laser beam. The photodetector 18 receives a laser beam from the cylindrical lens 7 at a light receiving section and outputs output signals SA to S
Generate L.

FIG. 7 is an explanatory diagram showing the configuration of the light receiving section of the photodetector 18. The light receiving section of the photodetector 18 is the main light receiving section 1
8S0, a first sub-light receiving portion 18S1, and a second sub-light receiving portion 18S2. The main light receiving section 18S0 is
Are reflected by the optical disk 80 and supplied through the objective lens 2, the beam splitter 3, the condenser lens 6, and the cylindrical lens 7.
The main light receiving portion 18S0 includes two orthogonal dividing lines Sx0, Sx
It is divided into four equal parts or substantially four equal parts by y0, and has four divided areas 18A to 18D. The divided area 18A has an output signal SA corresponding to the received laser beam.
Generate The divided area 18B generates an output signal SB corresponding to the received laser beam. The divided area 18C is
An output signal SC corresponding to the received laser beam is generated. The divided area 18D generates an output signal SD according to the received laser beam. A beam spot MS is formed by the main beam from the cylindrical lens 7 in the main light receiving section 18S0 in FIG.

The direction of the generatrix of the cylindrical lens 7 is
An angle of about 45 degrees or about 135 degrees is formed with respect to the direction of the dividing line Sx0 or the dividing line Sy0 of 8S0. Division line S
The intersection of x0 and Sy0 is located at or substantially at the center of the main beam passing through the cylindrical lens 7. Main light receiving section 18
The shape of the beam spot MS formed in S changes diagonally according to the distance between the optical disk 80 and the objective lens 2.

The first sub-light receiving portion 18S1 receives the first sub-beam generated by the diffraction grating 9 and reflected by the optical disk 80 by the objective lens 2, the beam splitter 3, and the condensing lens. 6 and a cylindrical lens 7. The first sub light receiving portion 18S1 has two split lines S
It is divided into four equal parts or substantially four equal parts by x1 and Sy1, and has four divided areas 18E to 18H. The divided area 18E generates an output signal SE corresponding to the received laser beam. The divided area 18F generates an output signal SF according to the received laser beam. Division area 18
G generates an output signal SG corresponding to the received laser beam. The divided area 18H generates an output signal SH corresponding to the received laser beam. First sub-light receiving unit 1 in FIG.
At 8S1, a beam spot SS1 is formed by the first sub-beam from the cylindrical lens 7.

The direction of the generatrix of the cylindrical lens 7 forms an angle of about 45 degrees or about 135 degrees with the direction of the dividing line Sx1 or the dividing line Sy1 of the first sub-light receiving portion 18S1. The intersection of the division lines Sx1 and Sy1 is located at or substantially at the center of the first sub-beam that has passed through the cylindrical lens 7.
Beam spot S formed on first sub-light receiving portion 18S1
The shape of S1 changes diagonally according to the distance between the optical disk 80 and the objective lens 2.

The second sub-light-receiving portion 18S2 receives the second sub-beam generated by the diffraction grating 9 and reflected by the optical disk 80 by the objective lens 2, the beam splitter 3, and the condenser lens. 6 and a cylindrical lens 7. The second sub-light receiving portion 18S1 has two split lines S
It is divided into four equal parts or substantially four equal parts by x2 and Sy2, and has four divided areas 18I to 18K. The divided area 18I generates an output signal SI corresponding to the received laser beam. The divided area 18J generates an output signal SJ corresponding to the received laser beam. Division area 18
K generates an output signal SK corresponding to the received laser beam. The divided area 18L generates an output signal SL corresponding to the received laser beam. Second sub-light receiving unit 1 in FIG.
At 8S2, a beam spot SS2 is formed by the second sub-beam from the cylindrical lens 7.

The direction of the generatrix of the cylindrical lens 7 forms an angle of about 45 degrees or about 135 degrees with the direction of the dividing line Sx2 or the dividing line Sy2 of the second sub-light receiving portion 18S2. The intersection of the dividing lines Sx2 and Sy2 is located at or substantially at the center of the second sub-beam that has passed through the cylindrical lens 7.
Beam spot S formed on second sub-light receiving portion 18S2
The shape of S2 changes diagonally according to the distance between the optical disk 80 and the objective lens 2.

FIG. 8 is a schematic enlarged sectional view showing an optical disk. In the optical disc 80, a recording layer 22 and a protective film 23 are sequentially laminated on a transparent substrate 21. The optical disk 80 is irradiated with the laser beam LB from the optical pickup 50 from the surface 21 </ b> A facing the outside of the transparent substrate 21, and a signal is written to or read from the recording layer 22.

The transparent substrate 21 is formed of a hard material having a light-transmitting property with respect to the laser beam LB in a disk shape. The optical disc 80 is configured to write and / or read signals to and from the recording layer 22 along the lands 21L and the grooves 21G. The optical disk 80 has a land 21L and a groove 21G.
Are the same or substantially the same, and a track pitch Tp of substantially the same width is formed as shown in the figure.

The main beam and the first and second sub-beams generated by the diffraction grating 9 in the optical pickup 50 are transmitted through the beam splitter 3 and the objective lens 2 to the optical disk 80.
The recording layer 22 is focused on the surface or almost the surface of the recording layer 22.

In the optical disk 80, as shown in FIG.
The main beam and the first and second sub-beams are incident toward the recording layer 22, and the main beam spot B0, the first sub-beam spot B1, and the second sub-beam spot B2, which are the respective beam spots, are recorded. The layer 22 is irradiated. In FIG. 9, the transparent substrate 21 of the optical disk 80 is omitted.

In FIG. 9, the main beam spot B0 is applied to the land 21L, and the first sub-beam spot B1 and the second sub-beam spot B2 are applied to both edges of the irradiated land 21L. The sub beam spot B2 is irradiated. In FIG. 9, the first sub-beam spot B1 and the second sub-beam spot B2 are irradiated with the main beam spot B0 at the same or substantially the same interval as the track pitch. However, the distance between the centers of the first sub beam spot B1 and the second sub beam spot B2 in the disk radial direction is equal to the track pitch T.
It is assumed to be an odd multiple of p. The first sub beam spot B1
And the second sub beam spot B2 are the main beam spot B
It is desirable that 0 is applied to both edges of the track to be irradiated, whereby the followability of the main beam spot B0 to the track to be recorded / reproduced is improved.

The main beam and the first and second sub-beams are:
Each light is reflected by the recording layer 22 and becomes return light. This return light is supplied to the photodetector 18 via the objective lens 2, the beam splitter 3, the condenser lens 6, and the cylindrical lens 7. When the main beam is focused on the track, the light detector 18 detects the light spots B0 to B2 of the main beam and the first and second sub-beams on the light receiving portions 18S0 to 18S0 of the light detector 18.
It is arranged so that it is projected on the central part of 18S2. Each of the light receiving units 18S0 to 18S2 of the photodetector 18 generates output signals SA to SL according to the received beam and supplies the output signals SA to SL to the generation circuit 60 via the amplification circuit 52.

The generation circuit 60 generates a focus error signal based on the output signals SA to SL of the photodetector 18 supplied from the amplification circuit 52. Specifically, the focus error signal FE0 of the main beam and the focus error signal FE1 of the first sub beam
And the focus error signal FE2 of the second sub-beam are generated by performing the following equation.

[0062]

FE0 = SA + SC- (SB + SD) FE1 = SE + SG- (SF + SH) FE2 = SI + SK- (SJ + SL)

The focus error signal FE0 of the main beam fluctuates as shown in FIG. 4, for example, depending on whether the track irradiated by the main beam spot B0 is the land 21L or the groove 21G. On the other hand, the focus error signal FE1 of the first sub beam and the focus error signal FE2 of the second sub beam
Is, for example, as shown in FIG.
Does not depend on the track to be irradiated, and when the defocus amount is 0, the value becomes 0 or substantially 0, resulting in substantially the same characteristic curve. This is because the first and second sub-beam spots B0 are irrespective of whether the track irradiated by the main beam spot B0 is the land 21L or the groove 21G.
This is because 1 and B2 are applied to the boundary between the land 21L and the groove 21G.

The focus error signals FE1 and FE2 of the first sub-beam and the second sub-beam are used when the optical pickup 50 is moved in the radial direction of the disk to perform the seek, and the main beam and the first and second sub-beams are used. When the beam traverses the land 21L and the groove 21G, for example, as shown in FIG. 11, a sinusoidal variation having an extreme value at the center of the land 21L and the groove 21G is shown. Since the first and second sub-spots are separated by substantially the same interval as the track pitch, the focus error signals FE1 and FE2 have opposite phases of fluctuation. Therefore, a combined focus error signal F obtained by combining the focus error signals FE1 and FE2 as shown in the following equation
E3 can reduce the amount of signal by doubling the signal amount and canceling the fluctuation at the time of seeking of the optical pickup 50.

[0065]

FE3 = FE1 + FE2 = SE + SG- (SF + SH) + SI + SK- (SJ + SL)

When combining the focus error signals FE1 and FE2, the focus error signals FE1 and FE2 are expressed by the following equations.
2 is normalized (normalized) by the total light amount of the corresponding sub-light receiving units 18S1 and 18S2, and then added to produce a combined focus error signal FE.
It is desirable to generate Thereby, the difference between the irradiation states of the first sub beam spot B1 and the second sub beam spot B2 can be reduced.

[0067]

FE1 '= {SE + SG- (SF + SH)} / (SE + SF + SG + SH) FE2' = {SI + SK- (SJ + SL)} / (SI + SJ + SK + SL) FE = FE1 '+ FE2' ...

The control circuit 70 of the recording / reproducing apparatus 90 determines the defocus amount of the main spot B0 from the track based on the focus error signal FE generated by the generation circuit 60. Also, the actuator 2F of the optical pickup 50
Performs focus control by moving the objective lens 2 based on the focus error signal FE generated by the generation circuit 60.

In the recording / reproducing apparatus 90, the focus error signal FE has substantially the same value regardless of which track of the land 21L and the groove 21G is irradiated with the main beam. Record and / or
Or playback can be performed. Also, the focus error signal F
By performing focus control based on E, when recording and reproducing by irradiating the main beam to the tracks of the land 21L and the groove 21G, it becomes unnecessary to use separate signals and circuits, The circuit configuration can be simplified.

The generation circuit 60 performs the following operation, and based on the output signals SA to SL of the photodetector 18 from the amplification circuit 52, generates a push-pull signal PP0 of the main beam and a push-pull signal of the first sub-beam. A signal PP1 and a second sub-beam push-pull signal PP2 are generated and supplied to the control circuit 70 and the like.

[0071]

PP0 = SA + SB- (SC + SD) PP1 = SE + SF- (SG + SH) PP2 = SI + SJ- (SK + SL)

The push-pull signals PP0 to PP2 fluctuate when the optical pickup 50 performs a seek, similarly to the focus error signals FE1 and FE2 shown in FIG.
The control circuit 70 controls the push-pull signal PP0 of the main beam.
And push-pull signals PP of the first and second sub-beams
The phase change is compared with one of the first and PP2 to determine whether the phase change is advanced or delayed. From this determination result, it is possible to determine whether the position of the main beam spot B0 is the land 21L or the groove 21G.
The recording / reproducing apparatus 90 can reliably irradiate the land 21L with the main beam when performing recording / reproducing using the land-groove recording optical disk 80 based on the determination result, and Thus, the main beam can be reliably irradiated.

In the recording / reproducing apparatus 90, the focus error signal FE
Has shown that the defocus amount is determined based on
For example, the focus error signal FE0, the focus error signal FE1,
The defocus amount may be determined based on one of FE2. Accordingly, the focus error signal used for determining the defocus amount can be made substantially the same regardless of which track of the land 21L and the groove 21G is irradiated with the main beam.

FIG. 12 is an explanatory diagram showing the relationship between each light receiving portion of the photodetector and a beam spot formed by irradiating each light receiving portion. As the state shifts from FIG. 12A to FIG. 12E, the focus state is deviated, and the degree of deviation increases.
FIG. 12A shows a case where the focal point of the laser beam is located on the recording surface, that is, a so-called in-focus state.
In FIG. 12A, the main beam spot MS is the main light receiving unit 1
8S0 is formed in a circular shape, and the sub beam spot S
S1 and SS2 are formed in circular shapes in the sub-light receiving portions 18S1 and 18S2, respectively.

In FIG. 12B, the main beam spot MS
Is formed in the main light receiving portion 18S0 in an elliptical shape, and the sub beam spots SS1 and SS2 are
Each is formed in an elliptical shape in S2.

In FIG. 12C, the main beam spot MS
Has a considerably squashed elliptical shape and slightly protrudes from the main light receiving portion 18S0, and the sub beam spots SS1 and SS2 have a considerably squashed elliptical shape and has the sub light receiving portions 18S1 and 18S2.
Is slightly protruding.

In FIG. 12D, the main beam spot MS
Protrudes out of the main light receiving portion 18S0 and goes out of the sub light receiving portion 18S1,1.
8S2 slightly, and the sub beam spot SS1,
SS2 protrudes from the sub light receiving portions 18S1 and 18S2 and slightly extends to the main light receiving portion 18S0.

In FIG. 12E, the main beam spot MS
Protrudes out of the main light receiving portion 18S0 and goes out of the sub light receiving portion 18S1,1.
8S2, the sub beam spots SS1, SS
Numeral 2 protrudes from the sub-light receiving portions 18S1 and 18S2 and covers the main light receiving portion 18S0.

The main beam spot MS has a higher light intensity than the sub beam spots SS1 and SS2.
From (D) to FIG. 12 (E), the sub-light receiving units 18S1, 1
The output signal of 8S2 has a large influence of the main beam spot MS, while the output signal of the main light receiving section 18S0 has little or no effect of the sub-beam spots SS1 and SS2. For this reason, FIG.
In the state (E), it is desirable that the output signals of the sub-light receiving units 18S1 and 18S2 are blocked or attenuated and not used for focus control, and the output signals of the main light receiving unit 18S0 are used for focus control.

FIG. 13 is a waveform diagram showing various signal waveforms in the recording / reproducing apparatus 90. The generation circuit 60 in the recording / reproducing device 90 includes a sum signal SUM0 and a focus error signal FE0.
FE2, FE3, and FE are generated and supplied to the control circuit 70. The focus error signals FE0 to FE2, FE3, and FE have an S-shaped curve with respect to the recording surface of the optical disc 80. The focus error signals FE0 to FE are stored in the internal memory of the control circuit 70.
The value (threshold) Lth of the sum signal SUM0 is stored in advance so that the values of 2, FE3, and FE become values in the linear region of the S-shaped curve.

First Focus Control Method FIG. 14 is a schematic flowchart showing an example of a focus control method in the recording / reproducing apparatus 90. First, in step S11, the control circuit 70 outputs a pull-in instruction to the generation circuit 60 when the switching signal FOK is at a low level.

Next, in step S12, the control circuit 70
Generates a pull-in signal and supplies it to the actuator 2F via the compensation circuit 40 and the amplification circuit 42. In step S13, the objective lens 2 is set based on the pull-in signal.
To make the sum signal SUM0 equal to or larger than the threshold value Lth.

At step S 14, the control circuit 70 sets the switching signal FOK to high level and outputs it to the generation circuit 60. In step S15, the generation circuit 60 outputs the switching signal F
When OK is at the high level, the focus error signals FE1 and FE2 of the sub-beams or the combined focus error signal FE3 or the combined focus error signal FE are generated and supplied to the actuator 2F via the compensation circuit 40 and the amplification circuit 42.

In step S16, the actuator 2F
Moves the objective lens 2 based on the focus error signals FE1 and FE2 or the combined focus error signals FE3 and FE to bring the object lens 2 into a focused state. Specifically, the actuator 2F operates such that the value of the focus error signal FE1, FE2 or the combined focus error signal FE3 or FE is maintained at or substantially at a zero within the linear region of the S-curve.
The objective lens 2 is moved.

Second Focus Control Method FIGS. 15 and 16 are schematic flowcharts showing another example of the focus control method in the recording / reproducing apparatus 90. Steps S21 to S24 are the same as steps S11 to S14 in the flowchart of FIG.
The description is omitted.

In step S25, when the switching signal FOK is at a high level, the generation circuit 60 generates a focus error signal FE0 of the main beam, and supplies it to the actuator 2F via the compensation circuit 40 and the amplification circuit 42.

In step S26, the actuator 2F
Moves the objective lens 2 until the value of the focus error signal FE0 of the main beam reaches a zero point or a value near the zero point in the linear region of the S-shaped curve, and proceeds to step S27. In step S27, the control circuit 70 sets the zero-cross signal FZ
C is changed to a high level in a pulse form and output to the generation circuit 60.

In step S28, the generation circuit 60 detects that the zero-cross signal FZC has changed to a high level, and generates the focus error signals FE1 and FE2 of the sub beam or the combined focus error signal FE3 or FE.
0 and supplied to the actuator 2F via the amplifier circuit 42.

In step S29, the actuator 2F
Moves the objective lens 2 based on the focus error signals FE1 and FE2 or the combined focus error signals FE3 and FE to bring the object lens 2 into a focused state. Specifically, the actuator 2F operates such that the value of the focus error signal FE1, FE2 or the combined focus error signal FE3 or FE is maintained at or substantially at a zero within the linear region of the S-curve.
The objective lens 2 is moved.

In step S26, the actuator 2F moves the objective lens 2 so that the value of the focus error signal FE0 of the main beam is maintained at the zero point in the linear region or a value near the zero point, and then proceeds to step S27. It is good also as a structure which advances. The recording / reproducing apparatus 90 may perform the focus control using any one of the first focus control method and the second focus error signal.

The above embodiment is an exemplification of the present invention, and the present invention is not limited to the above embodiment. The focus control device and the focus control method according to the present invention may be used for a phase change type optical disk or a magneto-optical disk. When using a magneto-optical disk,
A magneto-optical signal corresponding to the rotation of the polarization plane of the reflected laser beam may be used as the reproduction signal.

[0092]

According to the present invention, the objective lens converges and irradiates the main beam onto the track of the optical disk having the land-groove structure, and also emits the main beam to the guide area of the track of the optical disk and the boundary between the track. By converging and irradiating the sub beam, the focus error signal of the sub beam can be matched between the case where the track irradiated with the main beam is a land and the case where the track is a groove. Focus control can be performed based on the error signal.

In the above-described first focus control device, first recording / reproducing device, and first focus control method, since the main beam has a larger light quantity than the sub beam, the value of the focus error signal of the sub beam is By moving and pulling the objective lens based on the sum signal of the main beam until the objective lens reaches the linear region of the S-shaped curve, the reliability of focus control can be reduced as compared with the case where the objective lens is moved based on the sum signal of the sub beam. Performance can be improved.

In the above-described second focus control device, second recording / reproducing device, and second focus control method, since the main beam has a larger light amount than the sub-beam, the focus error signal of the main beam is monitored. By moving the objective lens until the value of the focus error signal of the main beam reaches a zero point or a value near the zero point in the linear region of the S-shaped curve, the focus error signal of the sub beam is monitored, and the focus error signal of the sub beam is monitored. The reliability of the focus control can be improved as compared with the case where the objective lens is moved and retracted until the value of the focus error signal reaches the zero point or a value near the zero point in the linear region from outside the linear region of the S-shaped curve.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a conventional pickup.

FIG. 2 is an explanatory diagram showing a light receiving section of a photodetector included in the optical pickup of FIG.

FIG. 3 is a schematic enlarged perspective view showing a configuration of an optical disc.

FIG. 4 is a characteristic diagram illustrating characteristics of a focus error signal.

FIG. 5 is a schematic block diagram showing an embodiment of a recording / reproducing apparatus according to the present invention.

6 is a schematic configuration diagram illustrating an optical pickup 50 included in the recording / reproducing device 90 of FIG.

7 is a photodetector 1 included in the optical pickup 50 of FIG.
FIG. 8 is an explanatory diagram illustrating a configuration of a light receiving unit of No. 8;

FIG. 8 is a schematic enlarged sectional view showing an optical disc.

FIG. 9 shows a beam spot irradiated on an optical disc;
FIG. 3 is an explanatory diagram showing a light receiving unit of a photodetector corresponding to each beam spot.

FIG. 10 is a characteristic diagram illustrating a focus error signal of a sub beam.

FIG. 11 is a characteristic diagram showing a relationship between an irradiation position of a sub beam and a change in a focus error signal of the sub beam.

FIG. 12 is an explanatory diagram showing a relationship between each light receiving unit of the photodetector and a beam spot formed by irradiating each light receiving unit.

13 is a waveform chart showing various signal waveforms in the recording / reproducing device 90 of FIG.

FIG. 14 is a schematic flowchart showing an example of a focus control method in the recording / reproducing device 90 of FIG.

15 is a schematic flowchart showing another example of the focus control method in the recording / reproducing device 90 in FIG.

FIG. 16 is a schematic flowchart showing another example of the focus control method in the recording / reproducing device 90 of FIG. 5, following FIG. 15;

[Explanation of symbols]

1, 50 optical pickup, 2 objective lens, 2F focusing actuator (actuator), 2
H: lens holder, 2T: tracking actuator, 3: beam splitter, 4: semiconductor laser (laser
5) Collimator lens, 6: Condensing lens, 7: Cylindrical lens, 8, 18: Photodetector, 8A to 8D, 18A to
18L: divided area, 8S: light receiving section, 8Sx, 8Sy, S
x0 to Sx2, Sy0 to Sy2 ... dividing line, 9 ... diffraction grating, 11, 21 ... substrate (transparent substrate), 11G, 21G ...
Groove, 11L, 21L land, 12, 22 recording layer, 12M recording mark, 18S0 main light receiving section, 18S
DESCRIPTION OF SYMBOLS 1 ... 1st sub light receiving part, 18S2 ... 2nd sub light receiving part, 21
A: surface of substrate 21, 30: motor, 35: motor drive circuit, 40: phase compensation circuit, 42: amplifier circuit, 55: laser drive circuit, 60: generation circuit, 65: information detection circuit (detection circuit), 70 ... Control circuit, 80, 82 ... Optical disk, 90 ... Recording / reproducing device, 95 ... Focus control device, B0 ...
Main beam spot, B1... First sub beam spot, B
2 ... second sub beam spot, FE0 ... focus error signal of main beam, FE1 ... focus error signal of first sub beam, F
E2: Focus error signal of the first sub beam, FOK: Switching signal, FZC: Zero cross signal, LB: Laser beam, L
th: threshold value, MS: main beam spot, SS1, SS
2 ... sub beam spot, SUM0 ... sum signal, Tp ... track pitch.

Continuation of the front page (72) Inventor Atsushi Fukumoto 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) 5D117 CC01 CC04 DD08 FF04 FX06 GG02 HH02 5D118 AA13 BC03 BF02 BF03 CA11 CB03 CC06 CC12 CD02 CF05 CG24 DA02

Claims (18)

[Claims] A diffraction grating for diffracting a laser beam to generate a main beam and a sub-beam; converging and irradiating the main beam onto a track of an optical disc having a land-groove structure; An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area and the track; and a photodetector to which the main beam and the sub-beam reflected on the optical disc are supplied via the objective lens A generation circuit that generates a sum signal corresponding to the light amount of the main beam and a focus error signal of the sub beam based on an output signal of the photodetector; and the objective lens is perpendicular to a recording surface of the optical disc. An actuator for moving in a focus direction, wherein a value of a focus error signal of the sub-beam is determined from a value outside a linear region of the S-shaped curve in the linear region. An actuator that moves the objective lens based on the sum signal so as to reach a value within the range, and then moves the objective lens based on a focus error signal of the sub-beam. 2. The actuator moves the objective lens based on the sum signal, and then causes the value of the focus error signal of the sub-beam to be at or substantially at a zero within the linear region of the S-curve. 2. The focus control device according to claim 1, wherein the objective lens is moved based on a focus error signal of the sub-beam so that the objective lens is maintained. 3. The diffraction grating diffracts the laser beam to generate the main beam and first and second sub-beams, and the center of the first and second sub-beams on a recording surface of the optical disc. The distance in the radial direction of the disk is the same or substantially the same as an odd multiple of the track pitch. The generation circuit generates the respective focus error signals of the first and second sub-beams. The actuator further comprises: synthesizing a focus error signal to generate a synthetic focus error signal; wherein, when the objective lens is moved based on the focus error signal of the sub beam, the actuator sets the synthetic focus error signal as a focus error signal of the sub beam. 2. The focus control device according to claim 1, wherein a signal is used. 4. A diffraction grating for diffracting a laser beam to generate a main beam and a sub-beam; and converging and irradiating the main beam onto a track of an optical disc having a land-groove structure; An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area and the track; and a photodetector to which the main beam and the sub-beam reflected on the optical disc are supplied via the objective lens A generation circuit that generates a focus error signal of the main beam and a focus error signal of the sub beam based on an output signal of the photodetector; and moves the objective lens in a focus direction perpendicular to a recording surface of the optical disc. An actuator for causing the focus error signal value of the main beam to change from a value outside the linear region of the S-shaped curve to a zero point within the linear region. Or an actuator for moving the objective lens until reaching a value close to the value, and then moving the objective lens based on a focus error signal of the sub-beam. 5. The actuator moves the objective lens such that the value of the focus error signal of the main beam is maintained at or near a zero point in the linear region. 5. A focus control device according to claim 4, wherein the objective lens is moved based on the focus error signal of the sub-beam so that the value of the signal is maintained at or substantially at a zero within the linear region of the S-curve. . 6. The diffraction grating diffracts the laser beam to generate the main beam and first and second sub-beams, and the center of the first and second sub-beams on a recording surface of the optical disc. The distance in the radial direction of the disk is the same or substantially the same as an odd multiple of the track pitch. The generation circuit generates the respective focus error signals of the first and second sub-beams. The actuator further comprises: synthesizing a focus error signal to generate a synthetic focus error signal; wherein, when the objective lens is moved based on the focus error signal of the sub beam, the actuator sets the synthetic focus error signal as a focus error signal of the sub beam. 5. The focus control device according to claim 4, wherein a signal is used. 7. A laser for outputting a laser beam, a diffraction grating for diffracting a laser beam from the laser to generate a main beam and a sub-beam, and collecting the main beam on a track of an optical disk having a land-groove structure. An objective lens for irradiating and irradiating the light beam, and condensing and irradiating the sub-beam on the boundary between the track guide area and the track of the optical disc; A photodetector supplied through the objective lens; a generation circuit that generates a sum signal corresponding to the light amount of the main beam and a focus error signal of the sub beam based on an output signal of the photodetector; An actuator for moving an objective lens in a focus direction perpendicular to a recording surface of the optical disc, the focus error signal of the sub-beam being The objective lens is moved based on the sum signal so that the value of the S-shaped curve reaches a value within the linear region from a value outside the linear region, and then the objective lens is moved based on the focus error signal of the sub-beam. A recording / reproducing apparatus comprising: an actuator for moving an objective lens; and a detection circuit for detecting information recorded on the optical disk based on the sum signal. 8. The actuator moves the objective lens based on the sum signal, and then changes the value of the focus error signal of the sub-beam to a zero or substantially zero within a linear region of the S-shaped curve. 8. The recording / reproducing apparatus according to claim 7, wherein the objective lens is moved based on a focus error signal of the sub-beam so that the objective lens is maintained. 9. The diffraction grating diffracts the laser beam to generate the main beam and first and second sub-beams, and the center of the first and second sub-beams on a recording surface of the optical disc. The distance in the radial direction of the disk is the same or substantially the same as an odd multiple of the track pitch. The generation circuit generates the respective focus error signals of the first and second sub-beams. The actuator further comprises: synthesizing a focus error signal to generate a synthetic focus error signal; wherein, when the objective lens is moved based on the focus error signal of the sub beam, the actuator sets the synthetic focus error signal as a focus error signal of the sub beam. The recording / reproducing apparatus according to claim 7, wherein a signal is used. 10. A laser for outputting a laser beam, a diffraction grating for diffracting the laser beam from the laser to generate a main beam and a sub-beam, and applying the main beam to a track of an optical disk having a land-groove structure. An objective lens for converging and irradiating the light beam, and converging and irradiating the sub-beam on a boundary between the track guide area of the optical disc and the track; A photodetector supplied through the objective lens, and a generation circuit that generates a reproduction signal, a focus error signal of the main beam, and a focus error signal of the sub beam based on an output signal of the photodetector. An actuator for moving the objective lens in a focus direction perpendicular to a recording surface of the optical disc, The objective lens is moved until the value of the point error signal reaches a zero point or a value near the zero point in the linear region from a value outside the linear region of the S-shaped curve, and then, based on the focus error signal of the sub beam, A recording / reproducing apparatus comprising: an actuator for moving an objective lens; and a detection circuit for detecting information recorded on the optical disk based on the reproduction signal. 11. The actuator moves the objective lens such that the value of the focus error signal of the main beam is maintained at or near a zero point in the linear region. 11. The recording / reproducing apparatus according to claim 10, wherein the objective lens is moved based on a focus error signal of the sub beam so that a signal value is maintained at a zero point within a linear region of the S-shaped curve. 12. The diffraction grating diffracts the laser beam to generate the main beam and first and second sub-beams, and the center of the first and second sub-beams on a recording surface of the optical disc. The distance in the radial direction of the disk is the same or substantially the same as an odd multiple of the track pitch. The generation circuit generates the focus error signals of the first and second sub-beams, An error signal is synthesized to generate a combined focus error signal, wherein the actuator moves the objective lens based on the focus error signal of the sub-beam, and the combined focus error signal as a focus error signal of the sub-beam. The recording / reproducing apparatus according to claim 10, wherein: 13. A diffraction grating for diffracting a laser beam to generate a main beam and a sub-beam; and converging and irradiating the main beam to a track of an optical disc having a land-groove structure; An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area and the track; and a photodetector to which the main beam and the sub-beam reflected on the optical disc are supplied via the objective lens And a generation circuit that generates a sum signal corresponding to the light amount of the main beam and a focus error signal of the sub beam based on an output signal of the photodetector, wherein the objective lens is a recording surface of the optical disc. Is a focus control method of a focus control device for moving in a vertical focus direction, wherein a value of a focus error signal of the sub beam is a linear region of the S-shaped curve. A first step of moving the objective lens based on the sum signal so as to reach a value within the linear region from an outside value, and a second step of moving the objective lens based on a focus error signal of the sub-beam. And a focus control method. 14. In the second step, the objective lens is adjusted so that a value of a focus error signal of the sub-beam is maintained at or substantially at a zero within a linear region of the S-shaped curve. 14. The focus control method according to claim 13, wherein the movement is performed based on a focus error signal of the beam. 15. The diffraction grating diffracts the laser beam to generate the main beam and first and second sub-beams, and the center of the first and second sub-beams on a recording surface of the optical disc. The distance in the radial direction of the disk is the same or substantially the same as an odd multiple of the track pitch. The generation circuit generates the respective focus error signals of the first and second sub-beams. Generating a composite focus error signal by synthesizing the focus error signal; and in the second step, when moving the objective lens based on the focus error signal of the sub beam, the focus error signal of the sub beam is used as the focus error signal of the sub beam. 14. The focus control method according to claim 13, wherein a composite focus error signal is used. 16. A diffraction grating for diffracting a laser beam to generate a main beam and a sub-beam; and converging and irradiating the main beam onto a track of an optical disc having a land-groove structure; An objective lens for condensing and irradiating the sub-beam on a boundary between the guide area and the track; and a photodetector to which the main beam and the sub-beam reflected on the optical disc are supplied via the objective lens And a generation circuit that generates a focus error signal of the main beam and the sub beam based on an output signal of the photodetector, and moves the objective lens in a focus direction perpendicular to a recording surface of the optical disc. A focus control method for a focus control device, wherein a value of a focus error signal of the main beam is calculated from a value outside a linear region of the S-shaped curve in the linear region. A first step of moving the objective lens until the zero point or a value near the zero point is reached; and a second step of moving the objective lens based on a focus error signal of the sub-beam after the first step. Control method. 17. After the first step, the objective lens is moved such that the value of the focus error signal of the main beam is maintained at or near a zero point in the linear region, and the process proceeds to the second step. The method further comprises a third step, wherein the second step is such that the value of the focus error signal of the sub-beam is maintained at or substantially at a zero within a linear region of the S-shaped curve. 17. The focus control method according to claim 16, further comprising a step of moving a lens. 18. The diffraction grating diffracts the laser beam to generate the main beam and first and second sub-beams, and the center of the first and second sub-beams on a recording surface of the optical disc. The distance in the radial direction of the disk is the same or substantially the same as an odd multiple of the track pitch. The generation circuit generates the focus error signals of the first and second sub-beams, Combining the error signal to generate a combined focus error signal; and in the second step, when moving the objective lens based on the focus error signal of the sub beam, the combining is performed as a focus error signal of the sub beam. 17. The focus control method according to claim 16, wherein a focus error signal is used.