Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-06-09
2002-05-14
Hudspeth, David (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044370, C369S053230, C369S044410
Reexamination Certificate
active
06388963
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a recording and reproducing apparatus for recording and reproducing data using a laser disk, a compact disk, or other optical disk.
More specifically, the present invention relates to a signal generation method used in an optical disk reproducing apparatus for reproducing data recorded on an optical disk by using a beam of light (spot) to scan along a land and guide groove provided on the optical disk, which detects a tracking error signal representing the position of the spot of the beam of light with respect to a guide groove provided in the optical disk and a cross track signal of a phase advanced by 90° relative to the tracking error signal, and to an apparatus of the same.
Also, the present invention relates to an optical pick-up using this signal generation method.
Further, the present invention relates to an optical disk recording and reproduction method using the tracking signal and the cross track signal obtained by the above method to control the tracking servo from an off state to a tracking-on state, that is, so-called tracking servo pull-in control, and to an apparatus using the same.
FIG. 1
is a schematic view of the configuration of an optical disk reproducing apparatus of a differential push-pull system. The optical disk reproducing apparatus of the differential push-pull system illustrated in
FIG. 1
comprises an optical disk
2
on which the data is recorded, a spindle motor
4
for rotating the optical disk
2
, an optical pick-up
6
, a control processor unit
8
, and a drive amplifier unit
10
.
FIG. 2
is a view of the configuration of the optical system of the optical pick-up
6
illustrated in FIG.
1
.
In FIG.
1
and
FIG. 2
, the optical pick-up
6
has mounted on it a laser
61
, a collimator lens
62
, a diffraction lattice
63
, a beam splitter
64
, an objective lens
65
, a focus lens
66
, a photodetector and processor unit
67
, a tracking coil
68
, and a focus coil
69
.
The laser
61
, collimator lens
62
, diffraction lattice
63
, beam splitter
64
, objective lens
65
, and focus lens
66
constitute an optical system which directs a spot to the optical disk
2
and guides the reflected light of the spot from the optical disk
2
to the photodetector and processor unit
67
.
This optical pick-up
6
is an optical pick-up of a two-axis drive system. In this optical pick-up, large movement in the track direction of the optical disk
2
is carried out by using a carriage (not shown) on which the optical pick-up
6
is mounted. After the optical pick-up
6
mounted on the carriage moves to the vicinity of the target position of the optical disk
2
, a tracking coil
68
is used for positioning to the precise track position.
FIG. 3
is a view illustrating a method of detecting the position of a beam (spot) of light irradiated on the lands and grooves of the optical disk
2
and the reflected light of the beam of light at the photodetector and processor unit
67
mounted on the optical pick-up
6
illustrated in FIG.
2
and generating a tracking error signal and a cross track signal from the detection signal when the width of the lands and the width of the guide grooves (hereinafter referred to as the “grooves”) in the optical disk
2
are different.
The photodetector and processor unit
67
has a first side photodetector (or second photodetector)
671
, a center photodetector (main photodetector or first photodetector)
672
, and a second side photodetector (or third photodetector)
673
. The photodetector and processor unit
67
further has a signal processor unit
675
.
The first side photodetector
671
and the second side photodetector
673
are each comprised of split photodetectors having two sections in the track direction of the optical disk
2
. The center photodetector
672
is comprised of a split photodetector having four sections in the track direction (radial direction) and tangential direction (circumferential direction) of the optical disk
2
.
In this way, FIG.
2
and
FIG. 3
illustrate an example of optical disk
6
of the three-point optical detection system using three types of beams of light (three spots of light) and three types of photodetectors
671
to
673
.
The signal processor unit
675
has a signal input unit
675
A for receiving as its inputs detection signals from the photodetectors
671
to
673
, a focus error signal processor unit
675
B for calculating a focus error signal FE from the input signals, a tracking error signal processor unit
675
C for calculating a tracking error signal TE, a cross track signal processor unit
675
D for calculating a cross track signal CTS, and a sum signal processor unit
675
E for calculating a sum signal PI.
It is also possible to perform the signal processing of the signal processor unit
675
at the control processor unit
8
, but a case where it is performed in the photodetector and processor unit
67
will be explained below.
The control processor unit
8
has three analog/digital (A/D) converters
81
to
83
, two normalization circuits
84
and
85
, two phase compensation digital filters
86
and
87
, and two digital/analog (D/A) converters
88
and
89
.
The processing inside the control processor unit
8
is carried out in a digital manner by using for example a digital signal processor (DSP), therefore the A/D converters
81
to
83
convert the analog signals from the photodetector
67
to digital signals and convert the processing results of the DSP to analog signals suited for the drive amplifier unit
10
at the D/A converters
88
and
89
.
The drive amplifier unit
10
has two drive amplifiers
101
and
102
.
The first drive amplifier
101
is used for controlling the drive of the focus coil
69
in the optical pick-up
6
, while the second drive amplifier
102
is used for controlling the drive of the tracking coil
68
in the optical pick-up
6
.
The configuration of the first side photodetector
671
, the center photodetector
672
, and the second side photodetector
673
in the photodetector unit
67
illustrated in
FIG. 3
is also applied to embodiments of the present invention. However, as is apparent from the description given later, the conditions of the land width and the groove width in the optical disk
2
and the positional relationship of the spots differ between the related art and the present invention.
The general operation of the optical disk reproducing apparatus of the differential push-pull system illustrated in FIG.
1
and
FIG. 2
will be explained referring to
FIG. 3
as well.
In the optical system illustrated in
FIG. 2
, one beam of laser light emitted from the laser
61
is converged at the collimator lens
62
and made to strike the diffraction lattice
63
. The diffraction lattice
63
diffracts the beam of light from the collimator lens
62
to generate three beams of light and makes them strike the beam splitter
64
. The three diffracted beams striking the beam splitter
64
pass through the beam splitter
64
to strike the objective lens
65
. In the objective lens
65
, they are then converged to the lands and the grooves of the optical disk
2
as spots (indicated by the circles in FIG.
3
).
The spots of the beam of light irradiated to the lands or grooves of the optical disk
2
are reflected from the lands or grooves to return to the objective lens
65
, then enter from the objective lens
65
into the beam splitter
64
. At the beam splitter
64
, they are directed toward the focus lens
66
and are received at photodetectors
671
,
672
, and
673
of the photodetector unit
67
.
The spots on the optical disk
2
have different phases according to the lands or grooves. The amounts of light striking the photodetectors
671
to
673
are therefore different.
The photodetectors
671
and
672
detect the amounts of incident light. The focus error signal processor unit
675
B, tracking error signal processor unit
675
C, cross track signal processor unit
675
D, and sum signal processor unit
675
E perform the following processing
Chu Kim-Kwok
Crosby, Heafey Roach & May
Hudspeth David
Sony Corporation
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