Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-12-02
2002-10-15
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S112120
Reexamination Certificate
active
06466526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for recording and replaying information on optical information record medium and an apparatus for replaying information on optical information record medium, and more particularly to an optical information record/replay apparatus capable of recording information into and/or replaying recorded information from an optical information record medium using a focus error signal and a tracking error signal generated from reflected light beams from the optical information record medium.
2. Description of the Related Art
An optical information record/replay apparatus is generally provided with an optical head for recording information into a record medium. The optical bead includes an object lens for focusing a light beam radiated from a light source such as a laser. The object lens is configured movable along the optical axis and information track width direction.
The optical information record/replay apparatus detects the focus error signal and tracking error signal in order to actuate the object lens along the optical axis and the information track width direction in response to the signals. A method and apparatus for detecting the focus error and tracking error signals will be briefly explained below with reference to the drawings.
PRIOR ART 1
FIG. 8
is a diagram showing an optical information record/replay apparatus according to the prior art
1
. A light source or laser diode
1
radiates a laser light, which enters a deflection beam splitter
2
onto a deflection surface
2
a
as a P-wave straight polarized light with respect to the polarization surface of the deflection beam splitter
2
. Therefore, it mostly passes through the deflection surface
2
a
and enters a collimator lens
3
.
The collimator lens
3
converts an incident laser light into a parallel light. The parallel light becomes a circular polarized light when it passes through a &lgr;/4 plate
13
, and then enters an object lens
4
. The object lens
4
collects incident laser lights to form a small spot on an information-bearing surface of an optical disc
5
.
Referring also to
FIG. 9
, light
10
reflected at the information-bearing surface of the optical disc
5
enters the deflection beam splitter
2
through the object lens
4
, &lgr;/4 plate
13
and collimator lens
3
. The reflected light is converted into an S-wave straight polarized light at the &lgr;/4 plate
13
. Therefore, it almost reflects at the deflection surface
2
a
of the deflection beam splitter
2
and enters a complex prism
26
.
The complex prism
26
diffract the reflected light into two diffracted light beams as described later. Each diffracted light beam is radiated to a predetermined position of a photodiode substrate including photodiodes or photoreceptor elements (not depicted).
The photodiode receives the reflected light from the optical disc
5
and outputs an optical signal to an arithmetic circuit
14
. The arithmetic circuit
14
generates a focus error signal and a tracking error signal from the optical signal and outputs them to a controller circuit
16
. A drive circuit
17
supplies a drive current into a magnetic coil in a lens actuator
18
. The lens actuator
18
controls the object lens
4
to drive along the focus and tracking directions.
The complex prism
26
and photodiode substrate
8
, will be described next using FIGS.
9
and
10
A-
10
C.
FIG. 9
is a schematic diagram of the complex prism
26
and photodiode substrate
8
. The complex prism
26
and photodiode substrate
8
are positioned at predetermined positions and fixed with a UV setting adhesive and the like.
FIGS. 10A-10C
are diagrams obtained from monitoring the reflected light detected at photodiodes
8
a
and
8
b
. The six-part split photodiodes
8
a
and
8
b
consist of respective photodiodes A-F.
When the small spot on the optical disc
5
is located at the focus position on the information-bearing surface of the optical disc, the reflected light from the optical disc
5
enters a surface
26
a
of the complex prism
26
so as to converge upon a focus point FP in the diagram.
50% of the incident reflected light
10
, for example, enters the photodiode
8
a
without being reflected from the surface
26
b
of the complex prism
26
. The other 50% on the other hand reflects from the surface
26
b
of the complex prism
26
at about a right angle and then reflects at a surface
26
c
and enters the photodiode
8
b.
If a distance relation between the optical disc
5
and the object lens
4
is a desired value, light spots detected at the photodiodes
8
a
and
8
b
are monitored as spots having the same diameters as shown in FIG.
10
A.
If a distance between the optical disc
5
and the object lens
4
is shorter than the desired value, a spot diameter of the light spot detected at the photodiode
8
a
becomes larger and a spot diameter of the light spot detected at the photodiode
8
b
becomes smaller as shown in FIG.
10
B.
If a distance between the optical disc
5
and the object lens
4
is longer than the desired value, the spot diameter of the light spot detected at the photodiode
8
a
becomes smaller and the spot diameter of the light spot detected at the photodiode
8
b
becomes larger as shown in
FIG. 10
c.
When the track advancing direction of the optical disc
5
is as represented by an arrow in
FIG. 10
, the focus signal can be detected by a spot size method and the track signal can be detected by a push-pull method. Arithmetic equations for use in detection are shown below:
Focus signal=(
A+C+E
)−(
B+D+F
)
Track signal=(
A+F
)−(
C+D
)
PRIOR ART 2
The prior art
2
will be described next using
FIGS. 11-13C
.
FIG. 11
is a diagram showing an optical information record/replay apparatus according to the prior art
2
. This optical information record/replay apparatus comprises a grating hologram device
27
and a photodiode substrate
8
.
FIG. 12
is a diagram showing reflected light in a state of entering the grating hologram device
27
.
FIGS. 13A-13C
are monitor diagrams of the reflected light received at the photodiode
8
. Other parts of the optical information record/replay apparatus shown in
FIG. 11
are similar to those in the prior art
1
.
A hologram grating surface
27
a
is formed on a surface of the hologram device
27
. The hologram grating surface
27
a
has a grating pattern provided with the following lens power characteristic.
The reflected light
10
from the optical disc
5
is diffracted at the hologram grating surface
27
a
into three diffracted light beams having a predetermined angle of diffraction. A diffracted light beam of plus first order is characteristically converged upon a near location (close to the hologram surface) relative to a convergence position
12
a
of a diffracted light beam of zero order that passes through the hologram. A diffracted light beam of minus first order is characteristically converged upon a distant location (apart from the. hologram surface) relative to the convergence position
12
a.
When the reflected light
10
enters the hologram grating surface
27
a
, it is diffracted at the hologram grating surface
27
a
into three diffracted light beams including a diffracted light beam of plus first order, a diffracted light beam of zero order and a diffracted light beam minus first order. The diffracted light beams are converged upon the positions
12
c
,
12
a
and
12
b
, respectively In this case, a photodiodes
121
,
122
,
123
are arranged so as to meet its photoreceptor surface with the position
12
a.
The photodiode substrate comprises a seven-part split photodiode. The seven-part split photodiode includes a three-part split diode
123
consisting of photodiodes A-C, three-part split diode
122
consisting of photodiodes D-F, and photodiode
121
consisting of a photodiode M.
A diameter of the light spot varies in accordance with a distance relation between the optical disc
5
and the object lens
4
. If a distance
Hayes & Soloway P.C.
NEC Corporation
Tran Thang V.
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