JPH05298730A - Tracking control apparatus and method of optical disk - Google Patents

Abstract

PURPOSE:To realize the tracking control apparatus and method of an optical disk, in which the generation of offset can be suppressed by a simple constitution so that a stable tracking servo control can be realized. CONSTITUTION:A main spot and advance side spot preceding the main spot are applied to an optical disk 1 in the form of a detected quantity of light varying with an information storage and the reflected light of the main spot and preceding side spot in the optical disk is detected by an optical pickup 4a. A tracking error signal TE is obtained from the difference between the preceding side spot signal FPP and main spot signal MPP detected in a tracking error signal generation circuit 5a and the tracking control of the optical pickup 4a is performed on the basis of the tracking error signal TE.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for controlling tracking of an optical pickup in an optical disk device.

[0002]

2. Description of the Related Art In an optical disc, an eccentricity of about 200 μm occurs with respect to a light beam emitted from an optical pickup due to eccentricity of its center hole, eccentricity of a track, axial runout of a rotary shaft of a mounted turntable and the like. .. Therefore,
In order to accurately read and write information on the track, it is necessary for the light beam from the optical pickup to accurately track the track, that is, to perform tracking. Therefore, a tracking servo method has been conventionally used as a means for compensating for the eccentricity and realizing accurate tracking.

The push-pull method and the three-spot method are known as typical ones of the tracking servo methods for optical disks. In the push-pull method, the light reflected and diffracted on the optical disc is received by two light receiving portions of a two-division-photodetector symmetrically arranged with respect to the center of the track.
This is a method of detecting a tracking error by extracting the difference between two output signals.

The three-spot method uses three light beams, a main spot for reading a signal, and a leading side spot and a trailing side spot that are arranged in front of and behind the main spot, and are shifted by a half track pitch on both sides thereof. This is a method in which the amount of reflected light from the optical disk of the spot and the trailing side spot is detected by a photodetector, and the direction and amount of deviation of the main spot are obtained from the output difference between the two.

However, in the push-pull method, an offset occurs in the tracking error signal due to the tilt of the optical disc, the shift of the objective lens, or the like. When an offset occurs in the tracking error signal, even if the tracking error signal indicates "0", the light beam is not located at the center of the track, so that accurate reading and writing of information cannot be performed. As a result, an optical disk device that employs the push-pull method requires a circuit for removing the offset, which complicates the device.

On the other hand, in the three-spot method, although no offset occurs due to the inclination of the disc, information can be recorded on a rewritable so-called write-once type optical disc.
When reproducing, an offset occurs due to the difference in the amount of reflected light between the leading side spot and the trailing side spot.

In recent years, a differential push-pull method has been proposed to compensate for these drawbacks. FIG. 3 is a block diagram of an optical disk recording apparatus adopting the differential push-pull method. In the figure, 1 is an optical disk, 2 is a signal input section, 3 is a laser diode (LD) drive circuit, 4 is an optical pickup,
Reference numeral 5 is a tracking error signal generation circuit, 6 is a phase compensation circuit, and 7 is an objective lens drive circuit.

This optical disk recording apparatus operates as follows. That is, the laser drive circuit 3 drives the LD 41 of the optical pickup 4 by the laser drive circuit control signal CTL input to the signal input unit 2. This allows
Laser light is emitted from the LD 41, and the laser light emitted from the LD 41 is converted into a parallel light flux by the collimator lens 42 and then incident on the grating 43. The laser light that has passed through the grating 43 is diffracted and separated into a main light flux and a side light flux. The main light flux and the side light flux emitted from the grating 43 pass through the beam splitter 44 and then enter the objective lens 45, where they are condensed and are focused on the main spot MS and the preceding side of the desired track of the optical disc 1. The spot FS and the trailing side spot BS are irradiated. At this time, the objective lens 45 is servo-controlled by the objective lens drive coil 46 by the drive signal DR supplied from the objective lens drive circuit 7.

Each spot light applied to the optical disc 1 is reflected on the optical disc 1. These reflected return lights are reflected by the beam splitter 44 through the objective lens 45, are condensed by the condenser lens 47, and the reflected return lights of the main spot MS are separated by the main-spot 2-split-push-pull photodetector 48a. , The return light of the preceding side spot FS is divided into two for the side spot-push-pull photodetector 4
At 8b, the return light of the trailing side spot BS is received by the side spot 2-split-push-pull photodetector 48c.

The reflected / reflected light of the main spot MS received by the two-split push-pull photodetector 48a for the main spot is converted into an electric signal of a level corresponding to the amount of light, and the main spot light output signal MSO is obtained. Is output to the differential amplifier 51 for. The reflected return light of the preceding side spot FS received by the two-sided push-pull photodetector 48b for the preceding side spot is converted into an electric signal of a level corresponding to the light quantity, and the side spot is output as the preceding side spot light output signal FSO. Difference amplifier 5
2 is output. Similarly, the reflected return light of the trailing side spot BS received by the two-sided push-pull photodetector 48c for trailing side spots is converted into an electric signal of a level corresponding to the amount of light, and the trailing side spot light. The output signal BSO is output to the side spot difference amplifier 53.

The main-spot difference amplifier 51 produces a main-push-pull signal MPP, the preceding side-spot difference amplifier 52 produces a preceding side-push-pull signal FPP, and similarly the trailing-side-spot difference amplifier. At 53, the trailing side-push-pull signal BPP is generated. Difference amplifier 51 for main spot
The main-push-pull signal MPP generated by
It is input to the non-inverting input (+) of the push-pull signal synthesizing difference amplifier 55. On the other hand, the preceding side-push-pull signal FPP generated by the main-spot difference amplifier 52 and the succeeding side-push-pull signal BPP generated by the main-spot difference amplifier 52 are added by an adder 54.
And the added push-pull signal is added to the inverting input (-) of the differential amplifier 55 for synthesizing the push-pull signal.
Entered in. Difference amplifier 55 for push-pull signal synthesis
Then, the difference between both input push-pull signals is obtained, and the tracking error signal TE that is the servo control signal is obtained.
Is generated. Difference amplifier 55 for push-pull signal synthesis
The tracking error signal TE generated in 1 is phase-compensated in the phase compensation circuit 6 and is supplied to the objective lens drive circuit 7 as a servo control signal. The objective lens drive circuit 7 outputs a drive signal DR to the objective lens drive coil 46 based on this servo control signal. As a result, the objective lens 45 is moved to an appropriate position. That is, servo control is performed.

In the optical disk recording apparatus adopting the above-mentioned differential push-pull method, it is possible to remove the offset caused by the tilt of the optical disk 1 in the radial direction and the shift of the objective lens, which are the drawbacks of the push-pull method.

The principle of this offset removal is shown in FIG.
Will be described in detail below. In addition, in FIG.
Is a main spot, FS is a leading side spot, BS is a trailing side spot, LND is a land portion, and GRV is a groove portion.

Now, assuming that the push-pull signal is a sine wave,
Main-spot 2-split-push-pull photodetector 48a
The amplitude of the push-pull signal thus obtained is A1, and the offset is B1. Similarly, the amplitude of the push-pull signal obtained from the two-sided push-pull photodetector 48b for the preceding side spot is A2, the offset is B2, and the push-pull obtained from the two-sided push-pull photodetector 48c for the following side spot. Signal amplitude is A3, offset is B3
And At this time, assuming that the push-pull signals of the main spot MS, the leading side spot FS and the trailing side spot BS are TE1, TE2 and TE3, these push-pull signals TE1, TE2 and TE3 are expressed as follows. TE1 = A1 · sin (2πX / P) + B1 (1) TE2 = A2 · sin (2π (X−Q) / P) + B2 (2) TE3 = A3 · sin (2π (X + Q) / P) + B3 (3) Since the three spots are imaged through the same objective lens 45, the offset caused by the tilt of the optical disc 1 in the radial direction (X direction) and the shift of the objective lens 45 occur at the same rate. That is, the following relationships are satisfied. B1 / A1 = B2 / A2 = B3 / A3 (4) Here, the difference between the main and side push-pull signals is calculated. When the intensities of the spots are different, it is necessary to make the gains the same, so the calculation is as follows. TE = TE1-G1 · (TE2 + G2 · TE3) (5) Here, if the gains G1 and G2 are G1 = A1 / 2A2 (5) G2 = A2 / A3 (6), the tracking error signal TE is , TE = A1 (1-cos (2πQ / P) sin (2πX / P) (7), and the offsets B1, B2 and B3 are canceled.

[0015]

However, even if the above-mentioned differential push-pull method is adopted, it is difficult to completely remove these offsets in the write-once optical disc. That is, as shown in FIG. 5, the trailing side spot is always formed with the pit PT during the recording operation.
Since a trace is made between the pit PT and the pit PT, the push-pull signal varies depending on the presence or absence of the pit PT. For example, comparing the case of FIG. 5A with the case of FIG. 5B, the pit P formed at the main spot MS is
Due to the influence of T, the beam image on the photodetector 48c obtained from the trailing side spot BS and this photodetector 48c
It can be seen that the push-pull signal obtained is different.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical disk tracking control device and method capable of suppressing the occurrence of offset with a simple structure and realizing stable tracking servo control. To provide.

[0017]

In order to achieve the above object, in a tracking control device of the present invention, in a tracking control device for an optical disk of a type in which a detected light amount changes depending on whether information is stored or not, a leading side spot signal and a main spot are detected. A circuit for calculating a tracking error signal from the difference between the signal and the signal is provided, and the optical pickup is controlled based on the tracking error signal.

Further, in the tracking control device of the present invention, a mechanism for forming two or more spots on the optical disc, a photodetector for observing the amount of light reflected back by the optical disc at each spot, and an output from the photodetector. And a tracking error signal generation circuit for generating a tracking error signal from the difference signal of each push-pull signal from the two spots.

According to the tracking control method of the present invention, the main spot and the preceding side spot preceding this main spot are irradiated to the optical disc of the type in which the detected light amount changes depending on the presence or absence of information storage, and the main spot and the preceding side spot are irradiated. The amount of reflected light on the optical disc is detected, a tracking error signal is obtained from the detected difference between the leading side spot signal and the main spot signal, and tracking control of the optical pickup is performed based on this tracking error signal.

Further, in the tracking control method of the present invention, two or more spots, one as a main spot, the other as a sub-spot, and at least one of the sub-spots precedes the main spot, are recorded on the optical disc. The amount of light reflected back from the optical disk of each spot is detected by forming an image on the upper side, and a tracking error signal is generated from the difference signal of the push-pull signals from the two spots obtained by the detection.

[0021]

According to the tracking control device of the present invention, the main spot and the side spot are simultaneously irradiated onto the optical disc, and the light amount of the return light reflected by the optical disc of these spot lights is detected. Next, in the tracking error signal generation circuit, among the detected signals,
A tracking error signal is calculated from the difference between the preceding side spot signal and the main spot signal, and the optical pickup is controlled based on this tracking error signal.

Further, in the tracking control device of the present invention, two or more spots are imaged on the optical disk by the spot image forming mechanism. The amount of light reflected back by the optical disc for each spot imaged on the optical disc is observed and detected by the photodetector. A push-pull signal is output from this photodetector, and a tracking error signal is generated from the difference signal between the push-pull signals from the two spots.

Further, according to the tracking control method of the present invention, the main spot and the preceding side spot are irradiated onto the optical disc at the same time, and the amount of reflected return light of the spot light from the optical disc is detected. Next, a tracking error signal is obtained from the difference between the preceding side spot signal and the main spot signal, and tracking control of the optical pickup is performed based on this tracking error signal.

Further, in the tracking control method of the present invention, two or more spots, one as a main spot, the other as a sub-spot, and at least one of them as a main spot precedes the main spot. Imaged above. The amount of reflected return light from the optical disc of each spot imaged on the optical disc is detected, and a tracking error signal is generated from the difference signal of the push-pull signals from the two spots obtained by the detection.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of an optical disk recording apparatus according to the present invention, and FIG. It is a figure for demonstrating the relationship with a push pull photodetector, Comprising: The same component as FIG. That is,
1 is an optical disc, 2 is a signal input unit, 3 is a laser diode (LD) drive circuit, 4a is an optical pickup, 5a is a tracking error signal generation circuit, 6 is a phase compensation circuit, and 7
Indicate the objective lens drive circuits, respectively.

The optical pickup includes an LD 41 that emits laser light under the drive control of the LD drive circuit 3, a collimator lens 42 that converts the emitted light of the LD 41 into parallel light, and a main light that diffracts the emitted light of the collimator lens 42. Luminous flux (0
A grating (diffraction grating) 43 that separates into a side diffracted light) and a side light beam (first-order diffracted light);
Beam splitter 44 that transmits the diffracted light of and transmits the reflected light of the optical disk 1 in a direction orthogonal to the incident direction of the diffracted light.
An objective lens 45 that collects the transmission of the beam splitter 44 and irradiates the recording surface of the optical disc 1 as the main spot MS and the side spots FS and BS, and an objective lens drive coil 46 for driving the objective lens 45.
And a condensing lens 47 for condensing the reflected light of the beam splitter 44, the light condensed by the condensing lens 47, and a composite light for outputting a main spot signal MSO and a leading side spot signal FSO which are electric signals. It is composed of a detector 49. As shown in FIG. 2, the composite photodetector 49 includes a main-spot 2-split-push-pull photodetector 4.
9a and a side spot 2-split-push-pull photodetector 49b. The main spot signal MSO is output by the main spot 2-split-push-pull photodetector 49a, and the preceding side spot signal FPP is a side spot. The 2-split-push-pull photodetector 49b outputs.

The tracking error signal generation circuit 5a is
Output signal M of 2-split-push-pull photodetector 49a for main spot of composite photodetector 49 of optical pickup 4a
A differential amplifier 56 for main spot which receives SO and generates a main-push pull signal MPP, and a composite photodetector 4
9-side split for 2-sided push-pull photodetector 4
Side-spot differential amplifier 5 which receives the output signal FSO of 9b and generates the preceding side-push-pull signal FPP.
7, main-push-pull signal MPP and leading side-
It comprises a push-pull signal synthesizing difference amplifier 58 which receives the push-pull signal FPP and generates a tracking error signal TE from the difference between the two.

Next, the spots MS, FS, and BS irradiated on the optical disk 1 and the two-split for the main spot-the push-pull photodetector 49a and the two-split for the side spot-
The relationship with the push-pull photodetector 49b will be described with reference to FIG. In FIG. 2, MS is a main spot, FS is a leading side spot, BS is a trailing side spot, LND is a land portion, and GRV is a groove portion.

In this example, the leading side spot FS is irradiated on the optical disc 1 with a shift of half the track pitch (P) (Q) in the radial direction with respect to the main spot MS. Then, as described above, for the spots MS and FS on the main side and the leading side, the push-pull signal is divided into main spot 2-split-push-pull photodetector 49a and side spot 2-split-push-pull photodetector 49b.
The tracking error signal TE is obtained by detecting the difference and detecting the difference.

As in the case of FIG. 4, assuming that the push-pull signal is a sine wave, the amplitude of the push-pull signal obtained from the main-spot 2-split-push-pull photodetector 49a is Aa, and the offset is Ba. To do. Similarly, the amplitude of the push-pull signal obtained from the side spot 2-split push-pull photodetector 49b is Ab, and the offset is B.
b. At this time, assuming that the push-pull signals TEa and TEb of the main spot MS and the preceding side spot FS are, the push-pull signals TEa and TEb are expressed as follows. TEa = Aa · sin (2πX / P) + Ba (8) TEb = Ab · sin (2π (X−Q) / P) + Bb (9) Since the two spots are imaged through the same objective lens 45, The offset caused by the inclination of the optical disc 1 in the radial direction (X direction) and the shift of the objective lens 45 occur at the same rate. The relationship shown below is satisfied. Ba / Aa = Bb / Ab (10) Here, the difference between the main and side push-pull signals is calculated. When the intensities of the spots are different, it is necessary to make the gains the same, so the calculation is as follows. TE = TEa−G1 · TEb (11) Here, if the gain G1 is G1 = Aa / Ab (12), the tracking error signal TE is TE = Aa · sin (2πX / P) −Aa · sin. (2π (X−Q) / P) (13), and the offsets Ba and Bb are canceled. Here, when Q / P = π, that is, when the interval between the main spot MS and the preceding side spot FS is set to half the track pitch (P), TE = 2 · Aa · sin (2πX / P) (14) ..

Next, the operation of the above configuration will be described. Laser drive circuit control signal CTL input to signal input unit 2
As a result, the laser drive circuit 3 causes the LD of the optical pickup 4a to
41 is driven. As a result, laser light is emitted from the LD 41. The laser light emitted from the LD 41 is converted into a parallel light flux by the collimator lens 42 and then incident on the grating 43. The laser light that has passed through the grating 43 is diffracted and separated into a main light flux and a side light flux. The main light flux and the side light flux emitted from the grating 43 are reflected by the beam splitter 4
After passing through 4, the light enters the objective lens 45, is condensed here, and is irradiated as a main spot MS, a leading side spot FS, and a trailing side spot BS on a desired track of the optical disc 1. At this time, the objective lens 45 is servo-controlled by the objective lens drive coil 46 by the drive signal DR supplied from the objective lens drive circuit 7.

Each spot light applied to the optical disc 1 is reflected on the optical disc 1. These reflected return lights are reflected by the beam splitter 44 through the objective lens 45, are condensed by the condenser lens 47, and the reflected return lights of the main spot MS are the two-split-push-pull photodetector 49a for the main spot. Then, the return light of the preceding side spot FS is divided into two for the side spot-the push-pull photodetector 4
The light is received by 9b and a beam image is formed there.

The reflected / reflected light of the main spot MS received by the two-split-push-pull photodetector 49a for the main spot is converted into an electric signal of a level corresponding to the amount of light, and the main spot light output signal MSO is obtained. It is output to the differential amplifier 56 for. Similarly, the reflected return light of the preceding side spot FS received by the side spot two-split-push-pull photodetector 49b is converted into an electric signal of a level corresponding to the amount of light, and as a preceding side spot light output signal FSO. It is output to the side spot difference amplifier 57.

The main-spot difference amplifier 56 produces a main-push-pull signal MPP, and the side-spot difference amplifier 57 produces a preceding side-push-pull signal FPP. Main-push pull signal MPP generated by main spot difference amplifier 56
Is input to the non-inverting input (+) of the push-pull signal synthesizing difference amplifier 58, and the preceding side-push pull signal FPP generated by the side-spot difference amplifier 57 is the inverting input of the push-pull signal synthesizing difference amplifier 58 ( -) Is input. In the push-pull signal synthesizing difference amplifier 58, the difference between the input push-pull signals MPP and FPP is obtained, and a tracking error signal TE which is a servo control signal is generated. The tracking error signal TE generated by the push-pull signal synthesizing difference amplifier 58 is phase-compensated by the phase compensation circuit 6 and supplied to the objective lens drive circuit 7 as a servo control signal. The objective lens drive circuit 7 outputs a drive signal DR to the objective lens drive coil 46 based on this servo control signal. As a result, the objective lens 45 is moved to an appropriate position. That is, servo control is performed. When the main-push-pull signal MPP is input to the push-pull signal synthesizing difference amplifier 58 and, at the same time, it is necessary to detect absolute time information (ATIP) or the like, this is set to A
It is output to an external circuit such as a TIP demodulation circuit.

As described above, according to this embodiment,
Since only the preceding side spot FS as the side spot is detected and only the detection signal is used for detecting the tracking error signal, the side spot always traces the unrecorded portion during the recording operation. Therefore, there is no influence of the already recorded portion of the optical disc 1 which is physically altered by the irradiation light, and as a result, stable servo control can always be performed.

[0036]

As described above, according to the present invention,
Since the side spot of the optical disc used for detecting the tracking error signal always traces the unrecorded portion during the recording operation, it is not affected by the recorded portion of the optical disc which is physically altered by its own light. Therefore, stable servo control can always be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical disc recording apparatus according to the present invention.

FIG. 2 is a diagram for explaining the relationship between each spot on the optical disc of the apparatus of FIG. 1 and a two-split-push-pull photodetector for main spots and a two-split-push-pull photodetector for side spots.

FIG. 3 is a block diagram showing an example of an optical disc recording apparatus adopting a differential push-pull method.

FIG. 4 is a diagram for explaining the relationship between each spot on the optical disc of the apparatus of FIG. 3 and a two-split-push-pull photodetector for main spots and a two-split-push-pull photodetector for side spots.

FIG. 5 is a diagram showing each mode of detection spots in the operation push-pull method to which the three-spot method is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical disk 2 ... Signal input part 3 ... Laser diode (LD) drive circuit 4a ... Optical pickup 41 ... Laser diode (LD) 42 ... Collimating lens 43 ... Grating 44 ... Beam splitter 45 ... Objective lens 46 ... Objective lens drive coil 47 … Condenser lens 49… Composite photodetector 49a… Main spot 2-split-push-pull photodetector 49b… Side spot 2-split-push-pull photodetector 5a… Tracking error signal generation circuit 56… Main spot difference amplifier 57 ... Side-spot differential amplifier 58 ... Push-pull signal composition differential amplifier 6 ... Phase compensation circuit 7 ... Objective lens drive circuit TE ... Tracking error signal MS ... Main spot FS ... Leading side spot BS ... Trailing side spot

Claims (4)

[Claims] 1. A tracking control device for an optical disc of a type in which a detected light amount changes depending on whether information is stored or not, and a tracking error signal is calculated from a difference between a leading side spot signal and a main spot signal. A tracking control device for an optical disk, which controls an optical pickup based on a ringing error signal. 2. A mechanism for imaging two or more spots on an optical disk, a photodetector for observing the amount of reflected light reflected by the optical disk of each spot, and each of the two spots output from the photodetector. The tracking control device for an optical disk according to claim 1, further comprising a tracking error signal generation circuit that generates a tracking error signal from a differential signal of the push-pull signal. 3. A main spot and a preceding side spot preceding the main spot are irradiated onto an optical disc of a type in which the detected light amount changes depending on whether information is stored or not, and the reflected light amount of the main spot and the preceding side spot on the optical disc is determined. A tracking control method for an optical disc, comprising: detecting, obtaining a tracking error signal from the detected difference between the leading side spot signal and the main spot signal, and performing tracking control of the optical pickup based on the tracking error signal. 4. Two or more spots, one as a main spot, the other as a sub-spot, and at least one of the sub-spots is imaged on the optical disk in advance of the main spot, and each spot is formed. 4. The tracking control method for an optical disk according to claim 3, wherein the amount of reflected light reflected by the optical disk is detected, and a tracking error signal is generated from the difference signal between the push-pull signals from the two spots obtained by the detection.