Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-07-03
2004-08-24
To, Doris H. (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053190, C369S044370, C369S044410, C369S112050
Reexamination Certificate
active
06781930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diffraction grating, an optical pick-up for focusing a laser beam passing through the diffraction grating to an optical disc, and an error signal detection device and an error signal detection method for detecting for example a tracking error signal or other error signal.
2. Description of the Related Art
In an optical disc drive, when an optical disc is tilted, a signal quality of a recording signal and/or reproduced signal of the optical disc may be lowered. When correcting this tilt of the optical disc, it is necessary to detect the tilt of the optical disc and generate a signal (tilt error signal) in response to the detected tilt.
U.S. Pat. No. 5,936,923 discloses an optical pick-up having a laser beam source, an object lens, and a liquid crystal panel for correcting aberration, and changing a refractive index of the liquid crystal panel in response to the thickness or tilt angle of the optical disc.
U.S. Pat. No. 5,936,926 also discloses the detection of tilt angle by a tilt sensor and the drive of the liquid crystal panel by a liquid crystal panel control circuit based on the detected tilt angle for changing the refractive index thereof.
When accessing at a predetermined address region on a track of an optical disc by an optical pick-up, it is necessary to generate a track traverse, (cross track) signal. This cross track signal is a signal electrically shifted in phase from a tracking error signal by 90 degrees, and is spatially shifted by exactly ¼ of a pitch of the tracks or track guide grooves.
In order to move an optical spot from the optical pick-up to a predetermined target track, it is necessary to detect a speed of movement and a direction of movement of the optical spot. In an optical disc drive, in order to detect the direction of movement of the optical spot, generally the tracking error signal and the cross track signal are used.
The optical disc drive performs a tracking servo control based on the tracking error signal.
As the method of detection (or method of generation) of the tracking error signal, there are known a one spot push-pull method for generating the signal from an output signal of a photo detector by utilizing one optical spot, a differential pushpull (DPP) method for generating the signal from output signals of the photo detector utilizing three optical spots, and so on.
FIGS. 1A and 1B
are views illustrating an enlarged recording surface of an optical disc and a circuit for generating a tracking error signal and other signals. In the optical disc drive, for example, the optical pick-up focuses the laser beam on the recording surface of the optical disc to generate an optical spot M
0
and receives the laser beam reflected at the recording surface to generate various signals, such as a track error signal, a focus error signal and an RF signal.
FIG. 1A
is a view of the recording surface of an optical disc. Lands LA and grooves GR are formed on the recording surface. The pitch of the lands LA and the pitch of the grooves GR are equal to a track pitch Tp. The center of the optical spot M
0
is positioned at the center of the land LA of the recording surface. This optical spot M
0
moves in a radial direction R.
FIG. 1B
is a view illustrating a circuit for generating a tracking error signal or other signal based on the laser beam reflected at the recording surface (reflected laser beam).
The light receiving portion
15
S of a two-divided photo detector receives a laser beam reflected at the recording surface (or the optical spot M
0
on the recording surface) whereby an optical spot M
10
is formed. The optical spot M
10
moves in the direction R corresponding to the radial direction R when the optical spot M
0
on the recording surface moves in the radial direction R. The light receiving portion
15
S is equally divided into two along a direction corresponding to the track direction and has first and second light reception regions
15
A and
15
B.
The first light reception region
15
A generates a light reception signal S
15
A in accordance with the laser beam irradiated on the region
15
A.
The second light reception region
15
B generates a light reception signal S
15
B in accordance with the laser beam irradiated on the region
15
B.
A subtractor
101
generates a tracking error signal TE
10
(=S
15
A−S
15
B) as the push-pull signal by subtracting the light reception signal S
15
B from the light reception signal S
15
A.
An adder
102
generates a sum signal RF
10
(=S
15
A+S
15
B) by adding the light reception signals S
15
A and S
15
B. This sum signal (reproduced signal) RF
10
corresponds to the amount of reflected light of the laser beam.
A high pass filter (HPF)
103
generates a cross track signal CT
10
by extracting an alternating current component (or high frequency component) of the sum signal RF
10
.
FIG. 2
is a schematic waveform diagram illustrating the tracking error signal TE
10
and the sum signal RF
10
, generated in the circuit in FIG.
1
.
The sum signal RF
10
becomes the maximum value when the center of the optical spot M
0
is positioned at the center of the land LA and becomes the minimum value when the center of the optical spot M
0
is positioned at the center of the groove GR.
By eliminating a direct current component DCr from this sum signal RF
10
(for example eliminating the direct current component DCr by extracting the alternating current component by the HPF), the cross track signal CT
10
can be obtained.
The tracking error signal TE
10
becomes 0 in signal level when the center of the optical spot M
0
is positioned at the center of the land LA and when it is positioned at the center of the groove GR, while becomes the maximum value or minimum value when the center of the optical spot M
0
is positioned at a border between the land LA and the groove GR.
FIGS. 3A and 3B
are views illustrating the recording surface of the optical disc and the light receiving portion of the photo detector when generating the cross track signal. In the optical disc drive, for example, the optical pick-up generates a laser beam comprised of a 0-th order diffraction light and ±1st order diffraction light by a diffraction grating, focuses the laser beams via an object lens to the recording surface of the optical disc to form three optical spots M
1
, S
1
, and S
2
, and receives the laser beams reflected at the recording surface by the photo detector to generate various signals.
FIG. 3A
is a view of the recording surface of the optical disc. Lands LA and grooves GR are formed on the recording surface. The pitch of the lands LA and the pitch of the grooves GR are equal to the track pitch Tp. The center of the main optical spot M
1
is positioned at the center of the land LA, and the centers of the sub optical spots S
1
and S
2
are positioned at borders between lands LA and the groove GR. The main optical spot M
1
is positioned at the middle of the sub optical spots S
1
and S
2
. The optical spots M
1
, S
1
, and S
2
move in the radial direction R of the optical disc.
FIG. 3B
is a view illustrating light receiving portions of the photo detector receiving the laser beams reflected at the recording surface.
A main light receiving portion
16
S
0
and sub light receiving portions
16
S
1
and
16
S
2
of the photo detector are irradiated with the laser beams reflected at the recording surface, whereby main optical spot M
11
, first and second sub optical spots S
11
and S
12
are formed. The optical spots M
11
, S
11
, and S
12
move in the direction R corresponding to the radial direction R when the optical spots M
1
, S
1
, and S
2
on the recording surface move in the radial direction R of the optical disc.
The main light receiving portion
16
S
0
is irradiated with the laser beam reflected at the recording surface of the optical disc (or the main optical spot M
1
on the recording surface), whereby the main optical spot M
11
is formed. This main light receiving portion
16
S
0
is equally divide
Ortiz-Criado Jorge L
Sony Corporation
To Doris H.
LandOfFree
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