JP2001307351A - Tracking servo method for optical pickup device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable high-precision tracking servo at the time of recording and to increase the recording density. SOLUTION: One main beam M is formed by diffraction means 3.
At least two pairs of side beams (at least four primary lights SB, SB) are formed around B, and each side beam is shifted by 1.5 track pitches around the main beam. So that
A side push-pull signal is generated by combining one of the four side beams located in front of and behind the main beam in the rotation direction of the optical disk 6, and the side beams in these sets are separated into different side photo detectors. The light is received by 8b and 8b and used as a signal for tracking error detection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel tracking servo method for an optical pickup device. More specifically, the present invention relates to an optical pickup device used also for a disk drive device of a recordable optical disk, and particularly to a technology that enables highly accurate tracking servo at the time of recording.

[0002]

2. Description of the Related Art An optical recording medium such as a CD (Compac
As a tracking servo system in a disk drive device such as a disc drive (D Disc), a differential push pulse (DPP) is used.
l) The method is known.

In the DPP method, a tracking error signal is generated by calculating an output signal of each light receiving element obtained from a main beam MB and two side beams SB, SB.

[0004] Specifically, in the DPP method, a diffraction means (grating) is arranged on the outward path of a beam emitted from a laser light source, and a zero-order diffracted light (main beam) and two first-order diffracted lights are placed on an optical disk. Each spot is formed by three (side beam) light beams, and these return lights are received by respective photodetectors a, b, and b, and a main spot MS by the main beam is used for writing or reading a signal. This is a system in which side spots SS by side beams are used for tracking error detection.

As shown in FIGS. 7, 9 and 11, a main photodetector a for receiving a main spot MS is provided.
Is divided into four in the vertical and horizontal directions, and the side photo detectors b, b for receiving the side spots SS, SS are divided into two on the left and right. Note that the output signal of each divided element is A,
Shown by B, C, D, E, F, G, H. Then, a tracking error signal is generated from a calculation output between the output signals from the photodetectors a, b, and b.

That is, a main push-pull (MPP) signal is generated from the output signal of the main photo detector a,
Side push-pull (SPP1, SPP2) signals are generated from the output signals of the side photo detectors b, b, and the differential push-pull (DP) is calculated by the following equation.
P) signal is obtained.

MPP = (B + C)-(A + D) SPP1 = EF FP SPP2 = GH DPP = MPP-K. (SPP1 + SPP2) DPP = ((B + C)-(A + D))-K. ((E-
F) + (GH)) K: Coefficient.

FIG. 7 shows photodetectors a, b, b and each spot M when there is no variation in optical parts and the like.
FIG. 8 schematically shows the relationship among S, SS, and SS. FIG. 8 shows the SPP1, SPP2, MPP, and DP signals in FIG.
4 shows a waveform of a P signal.

As can be seen from FIG. 8, the SPP1 signal and the SP
The P2 signal is in phase, the MPP signal is the SPP1 signal and the SP
The D signal is output in the same phase as the MPP signal, and the DPP signal is output in the opposite phase to the P signal 2.

FIG. 9 shows photodetectors a, b, and b when the intervals between the spots MS, SS, and SS are shifted due to variations in optical components and the like (in the drawing, the intervals between the spots are widened). And each spot MS, SS, S
FIG. 10 schematically shows the positional relationship with S, and FIG. 10 shows the waveforms of the SPP1, SPP2, MPP, and DPP signals in FIG. In this figure, solid lines indicate PP (push-pull) signals during signal reading (reading), and broken lines indicate SPP signals and DPP signals during signal recording (writing) described later. is there.

When reading a signal, the SPP1 signal, SPP
Although two DC offsets occur in both signals,
Since the absolute values of the offset amounts are the same, these DC offset amounts are canceled by the above arithmetic expression, and D
Since the PP signal is output without a DC offset, the on-track state can be maintained (FIG. 10).
See solid line).

FIG. 11 shows a photodetector in the case where each spot MS, SS, SS is shifted to one side (right in the drawing) on each photodetector a, b, b due to a positional shift of an objective lens, a photodetector, and the like. a, b, b
FIG. 12 schematically shows the positional relationship between the spots MS, SS, and SS. FIG. 12 shows the SPP1 signal, SPP2
3 shows waveforms of a signal, an MPP signal, and a DPP signal. In the figure, the solid line indicates each PP (push-pull) signal during signal reading (read), and the broken line indicates each PP (push-pull) during signal recording (write) described later. Signal.

In the case of signal reading, the SPP1 signal, SPP
The DC offset is generated in both the 2 signal and the MPP signal. However, these DC offset amounts are canceled by the above equation, and the DPP signal is output without the DC offset, so that the on-track state can be maintained. it can.

As described above, in the DPP method, when the intervals between the spots MS, SS, SS are shifted (see FIG. 9) due to the variation of the optical components, etc. , SS, S
In any case where S is deviated to one of the photodetectors a, b, and b (see FIG. 11), the DC offset amount of the tracking error signal (DPP signal) can be canceled by an arithmetic expression. The tracking servo system is very effective in an optical pickup of a signal reading system.

[0015]

However, when the distance between the spots MS, SS, SS is shifted due to variations in optical parts (see FIG. 9), or when the spots MS, SS, SS are displaced due to the positional shift of the objective lens, the photodetector and the like. , SS, S
When S is shifted to one of the photodetectors a, b, and b (see FIG. 11), the offset amount generated can be canceled only when the signal of the optical disk is read as described above. is there.

That is, an optical recording medium such as a CD-R
(Compact Disc-Recordable), CD-RW (Compact D
In an optical disc drive such as isc-ReWritable), each spot MS, S
At the time of signal recording when the interval between S and SS is shifted and an offset is generated, as shown by a broken line in the waveform diagram of FIG.
The DC offset amount 2 of the signal is different. Specifically, the offset amount 2 of the SPP2 signal has an absolute value smaller than the offset amount 1 of the SPP1 signal, and the DC offset amount 3 that cannot be canceled by the above equation occurs in the DPP signal that is the final output signal. .

In a drive for an optical disk such as a CD-R or a CD-RW, each spot MS, SS, SS may be displaced due to a positional shift of an objective lens, a photodetector or the like.
FIG. 12 shows the signal recording when the offset amount is shifted to one of the photodetectors a, b, and b.
As shown by the broken line in the waveform diagram of FIG.
The C offset amount 1 'differs from the DC offset amount 2' of the SPP2 signal. Specifically, the offset amount 2 'of the SPP2 signal is smaller than the offset amount 1' of the SPP1 signal, and the DC level is lowered. 'Occurs.

As described above, when the tracking servo is applied at the time of recording, a deviation occurs by an amount corresponding to the DC offset of the DPP signal, a detrack state (off-track state) occurs, and the recording characteristics are deteriorated. is there.

The problem is that when recording a signal on the optical disk c, one of the side beams (side beam preceding the main beam MB) SB1 has no pits d, d,. The other side beam (side beam following the main beam MB) SB2 is reflected on the surface of the disk between the recording state track T where the pits d, d,. This is because the light is reflected (see FIG. 11).

In order to make the offset amount within the allowable range in the optical pickup device, the accuracy of the optical parts itself, the accuracy of the objective lens and the photodetector itself, and the accuracy of their installation positions must be increased. ,
This leads to high equipment costs. In order to increase the recording density, the allowable range of the DC offset amount must be further narrowed. In the optical pickup device, it is difficult to increase the recording density. There is a problem that there is.

Accordingly, it is an object of the present invention to enable high-precision tracking servo particularly at the time of recording and to increase the recording density.

[0022]

According to the tracking servo method of the optical pickup apparatus of the present invention, at least two pairs of side beams (at least four pairs of side beams) centering on one main beam by a diffraction means are provided in order to solve the above-mentioned problems.
(Next light), and each side beam is n + 0.5 (n is 0) around the main beam.
Integers except for the track pitch are formed so as to be shifted by a track pitch. Of the at least four side beams, one positioned at the front of the main beam in the rotation direction of the optical disk and the one positioned at the rear thereof, Side push-pull signals are generated by combining side beams located on the inner circumference side and / or the outer circumference side, and the side beams in these groups are received by different side photo detectors as signals for tracking error detection. It was used.

Therefore, according to the tracking servo method of the optical pickup device of the present invention, the signal is recorded as a side push-pull signal in each photodetector by the side beam of the optical disk which is shifted to the same side in the radial direction of the optical disk. Even at the time, the pit formation state (presence / absence of pits) of the side beam for generating the side push-pull signal on the optical disk is the same, so that the DC offset amount generated in these side push-pull signals is the same, and The tracking error signal (DPP signal) generated based on the side push-pull signal from the side beam and the main push-pull signal from the main beam does not have a DC offset amount, and enables highly accurate tracking servo. ,
Further, it is possible to realize a higher recording density.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tracking servo method for an optical pickup device according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating the configuration of optical components of an optical pickup device 1 according to the present invention.

The optical pickup device 1 comprises a laser light source 2 for generating a light beam B, a diffracting means 3 for diffracting the light beam B emitted from the laser light source 2, and a light beam B transmitted or reflected in a predetermined direction. A beam splitter 4,
A collimator lens 5 for forming a parallel light beam and an objective lens 7 for condensing the light beam B on the signal surface of the optical disk 6;
A photodetector 8 for receiving return light from the optical disk 6.

The diffraction means 3 converts the beam B into one main beam MB and two pairs of side beams (four primary lights) SB1-
f, SB1-b, SB2-f, and SB2-b. Here, the main beam MB is the zero-order light, and the side beam SB is the ± first-order light. Thus, two sets of diffracted light (0-order light and ± first-order light are regarded as one set) are generated. In
For example, a hologram in which two diffraction gratings are bonded at a predetermined angle or a hologram can be used, and the 0th-order light is formed by two sets of ± 1st-order lights that are commonly and diffracted in different directions different from each other. Can be.

FIG. 2 is a schematic view of the surface of the optical disk 6 for schematically explaining the relationship between each beam and pits during recording.

Then, as shown in FIG. 2, one set of diffracted light has two side beams SB1-f and SB1-b.
Is shifted by 1.5 track pitches from the outer side to the inner side around the main beam MB, and the side beam SB1-f shifted to the outer side is slightly forward of the main beam MB in the rotation direction of the optical disk 6. Further, the side beam SB1-b shifted to the inner peripheral side is focused slightly behind the main beam MB in the rotation direction of the optical disk 6.

Similarly, in another set of diffracted light beams, two side beams SB2-f and SB2-b shift from the inner side to the outer side by 1.5 track pitches around the main beam MB. And the side beam SB2 shifted to the inner peripheral side
−f is focused slightly forward of the main beam MB in the rotation direction of the optical disc 6, and the side beam SB2-b shifted to the outer peripheral side is slightly focused back of the main beam MB in the rotation direction of the optical disc 6. The main beam MB of each set is common.

As described above, the side beam SB1-f and the side beam SB2-
are reflected on the unrecorded disk surface on which no pits 9, 9,... are formed, and the side beam SB2-f and the side beam SB1-b are formed on the inner peripheral side of the main beam MB. Are reflected on the disk surface between the tracks T in the recording state where the tracks 9, 9,... Are formed (see FIG. 2).

The photodetector 8 comprises a main photodetector 8a and two side photodetectors 8b and 8b, as described in the above-mentioned "Prior Art". The main photodetector 8a is divided vertically and horizontally into four main One side photo detector 8b receives the spot MS, and the front side spot S formed on the front and rear sides of the two sets of diffracted light is formed in the front and rear, respectively.
S1-f and SS2-f are received, and the other side photodetector 8b is a rear side spot SS1- formed in front and rear of the two sets of diffracted light, respectively.
b, SS2-b. The output signals of the divided elements are A, B, C, D, E, F,
G and H (see FIG. 3). Then, a tracking error signal is generated from a calculation output between the output signals from the photodetectors 8a, 8b, 8b.

Here, as described in the above-mentioned “Problems to be Solved by the Invention”, when the intervals between the spots MS, SS, SS on the photodetector are shifted (see FIG. 4), or when the spots MS, SS, In the case where SS and SS are shifted to one side on the photodetector 8 (see FIG. 5), during signal recording, the side spots SS1-SS are applied to the side photodetectors 8b and 8b as follows.
f, SS2-f, SS1-b and SS2-b are condensed, so that each side push-pull signal (SPP1 signal and SP
The DC offset amount generated in the P2 signal becomes the same.

That is, the side spots SS1-f and SS2
Since -b is the return light reflected by the unrecorded portion of the optical disk 6, if these are different push-pull signals, the DC offset amounts generated in the respective push-pull signals are the same, and , Side spot SS2-
f and SS1-b are return lights reflected by the recording portion of the optical disk 6 (the portion sandwiched between the tracks T on which the pits 9, 9,... are formed). When a push-pull signal is used, the DC offset amount (different from that due to the unrecorded portion) generated in each of the push-pull signals is the same.

The light received by one of the side photo detectors 8b is the side spot SS1-f of the unrecorded portion and the side spot SS2-f of the recorded portion.
f and the other side photo detector 8b
Is received by the side spot S due to the unrecorded portion.
S1-b and a side spot SS2-b by a recording portion.

Therefore, each side photo detector 8
Two different types of DC offset components of the side spot SS are added to b and 8b, respectively. The sum of the added offset amounts becomes the same, and the SPP1 signal and S
The DC offset generated in the PP2 signal becomes the same.

Thus, as described in the above-mentioned prior art, the SPP1 signal and the SPP2 signal having the same DC offset amount are used.
By calculating the DPP signal based on the signal, the DC offset amount can be canceled by the above equation, and the signal is recorded in a state where no DC offset amount occurs in the final output DPP signal and no detrack occurs. Can be.

By applying tracking servo with the DDP signal generated in this way, it is possible to record a signal on the optical disk 6 without detracking.

FIG. 6 shows a modification of the tracking servo method of the optical pickup device according to the present invention. This modification is different from the above-described embodiment in that each side photodetector 8b has one side spot SS. It is one.

The photodetector 10 used in this modification includes side photodetectors 10b and 10b.
b is disposed so as to be deviated more inward or outward than the main photodetector 10a, and of the four side spots SS, SS,. The side photodetectors 10b and 10b receive the two side spots SS and SS that are shifted toward the side or the outer periphery.

Specifically, among the side spots SS, SS,... In FIG. 2, the side spots SB2-f and SB1-b located on the inner peripheral side of the main spot MS are detected by the side photo detectors 10b and 10b. Receive light.

In such a case, both the side spots SB2-f and SB1-b are reflected by the recording portion of the optical disk 6 (the portion sandwiched between the tracks T on which the pits 9, 9,... Are formed). Since these are return lights, the DC offset amount generated in each of these push-pull signals is the same when these are made into separate push-pull signals.

Accordingly, since the DC offset amount can be canceled by the above equation, the side push-pull signals (SPP1 signal, SPP2 signal) of these side spots SB2-f and SB1-b and the main push from the main beam are used. The tracking error signal (DPP signal) generated based on the pull signal (MPP signal) has the DC offset cancelled, and the signal can be recorded without detracking.

In this modification, the side spot S
Of the S, SS,..., Those located on the inner peripheral side of the main spot MS were selected, but the present invention is not limited to this.
Those located on the outer peripheral side may be selected.

In the above-described embodiment and modified examples, the shift amount of the side beam with respect to the main beam is set to 1.
Although the 5-track pitch is used, the present invention is not limited to this, and a 2.5-track pitch and a 3.5-track pitch are also possible.

It should be noted that the shapes and structures of the respective parts shown in the above-described embodiments and modified examples are merely examples of the embodiments of the present invention, and the present invention is not limited thereto. The technical scope should not be interpreted in a limited manner.

[0047]

As is apparent from the above description, the tracking servo method of the optical pickup device of the present invention divides a light beam emitted from a laser light source into one main beam and a side beam by a diffraction means. When the return light of the optical disk is received by the photodetector, the main beam is received by the main photodetector to read or record a signal and detect a servo error. In the tracking servo method of the optical pickup device, wherein the side beams are respectively received by different side photodetectors and used for tracking error detection, the diffraction means includes at least two pairs of side beams (at least 4 One primary light) to form Idobimu each n + 0.5 about the main beam (n is an integer except 0) are formed such that the track pitch shift occurs, 4 with small
Of the two side beams, one positioned in front of the main beam in the rotation direction of the optical disc and the other positioned rearward, and combined with the side beams positioned on the inner circumferential side and / or the outer circumferential side with respect to the main beam. A push-pull signal is generated, and side beams in these groups are received by respective side photo detectors and used as signals for tracking error detection.

Therefore, according to the tracking servo method of the optical pickup device of the present invention, the signal is recorded as the side push-pull signal in each photodetector by the side beam of the optical disk which is shifted to the same side in the radial direction of the optical disk. Even at the time, the pit formation state (presence / absence of pits) of the side beam for generating the side push-pull signal on the optical disk is the same, so that the DC offset amount generated in these side push-pull signals is the same, and The tracking error signal (DPP signal) generated based on the side push-pull signal from the side beam and the main push-pull signal from the main beam does not have a DC offset amount, and enables highly accurate tracking servo. ,
Further, it is possible to realize a higher recording density.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the optical pickup device of the present invention together with FIG. 2 to FIG. 5, and FIG. 1 is a side view schematically showing the entire configuration.

FIG. 2 is a diagram schematically showing an arrangement of spots on an optical disk during recording.

FIG. 3 is a diagram schematically illustrating a relationship between a photodetector and a spot in a state where there is no variation in optical components and no positional displacement of an objective lens, a photodetector, and the like.

FIG. 4 is a diagram schematically illustrating a relationship between a photodetector and a spot in a state where optical components and the like have variations.

FIG. 5 is a diagram schematically showing a relationship between a photodetector and a spot in a state where the objective lens, the photodetector, and the like have a displacement.

FIG. 6 is a view showing a modification of the present invention and is a view schematically showing a relationship between a photodetector and a spot in a state where there is no variation in optical components and no displacement of an objective lens, a photodetector, and the like.

FIG. 7 is a diagram schematically illustrating a relationship between a photodetector and a spot in a state where there is no displacement of an objective lens, a photodetector, and the like.

8 is a waveform diagram of each push-pull signal in FIG.

FIG. 9 is a diagram schematically showing a relationship between a photodetector and a spot in a state where optical components and the like have variations.

FIG. 10 is a waveform diagram of each push-pull signal in FIG.

FIG. 11 is a diagram schematically illustrating a relationship between a photodetector and a spot in a state where the objective lens, the photodetector, and the like have misalignment.

12 is a waveform diagram of each push-pull signal in FIG.

FIG. 13 is a schematic diagram of a disk surface for schematically explaining a relationship between each beam and a pit during recording.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical pickup apparatus, B ... Beam light, MB ... Main beam, SB ... Side beam, 2 ... Laser light source, 3 ...
Diffraction means, 5: collimator lens, 6: optical disk,
7 Objective lens, 8a Main photodetector, 8
b: Side photo detector, MS: Main spot, SS: Side spot, 10a: Main photo detector, 10b: Side photo detector

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Tsutomu Maruyama F-term (reference) 5D118 AA13 BA01 BB01 CD03 CF05 CG05 CG17 CG24 CG36 CG44 DA35 5D119 AA29 6-35 Kita Shinagawa, Shinagawa-ku, Tokyo BA01 BB01 EA02 JA22 KA08 KA19

Claims (1)

[Claims] 1. A light beam emitted from a laser light source is divided into one main beam and a side beam by a diffractive means and condensed on an optical disk via an objective lens, and return light of the optical disk is detected by a photodetector. When light is received by the main photodetector, the main beam is received by the main photodetector for signal reading or recording and for servo error detection, and the side beam is received by each of the other side photodetectors for use in tracking error detection. In the tracking servo method for an optical pickup device, the diffraction means forms at least two pairs of side beams (at least four primary lights) around a main beam, and each side beam is n + around a main beam.
0.5 (n is an integer other than 0) is formed so as to shift by a track pitch. Of at least four side beams, one positioned in front of the main beam in the rotation direction of the optical disk and the other positioned in the rear. Generating side push-pull signals by combining side beams located on the inner and / or outer sides with respect to the main beam, and receiving the side beams in these sets by respective side photo detectors. A tracking servo method for an optical pickup device, wherein the tracking servo method is used as a signal for tracking error detection.