Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1999-12-09
2002-04-30
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053140, C369S005000
Reexamination Certificate
active
06381205
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of and device for adjusting the optical axis of an optical pick-up of an optical disk device to be normal to the recording/playback surface of the optical disk.
FIG. 22
to
FIG. 25
shows a conventional optical disk device, and a device for adjusting the optical axis angle of the optical disk device. Referring to
FIG. 22
to
FIG. 25
, reference numeral
10
denotes an optical disk having spiral or concentric tracks. Reference numeral
1
denotes a main base,
2
a
and
2
b
denote a pair of guide shafts fixed to the main base
1
and disposed at a distance from and in parallel with each other,
3
denotes an optical pick-up guided by the guide shafts
2
a
and
2
b
in the radial direction of the optical disk
10
, and supported by the guide shafts
2
a
and
2
b
in such a manner that it can move in direction of the axes of the guide shafts. The signals recorded on the optical disk
10
are read by means of a reflected light resulting from a laser light via an objective lens
3
a
of the optical pick-up
3
. Reference numeral
4
denotes a tangential-direction adjusting screw threaded through a protrusion
3
b
of the optical pick-up
3
, and having an end abutting with one of the guide shafts,
2
b
. As shown in
FIG. 24
, when the screw
4
is turned, the optical pick-up
3
is rotated about the other the guide shaft
2
a
as shown by arrow A, and the optical axis angle of the optical pick-up
3
with respect to the optical disk
10
in the tangential direction is adjusted. Here, the “tangential-direction optical axis angle” means an angle of the optical axis of the optical pick-up
3
as seen in the direction of the guide shafts
2
a
,
2
b
(direction in which the guide shafts extend). When the optical axis angle is varied in this direction, the light spot formed by the optical pick-up
3
on the disk
10
is moved in the direction of a tangent on a track at a point confronting the optical pick-up
3
.
Reference numeral
5
denotes a motor mounting member fixed to the base
1
by means of fixing screws
6
a
and
6
b
, and resiliently fixed by means of a radial-direction adjusting screw
7
extending through a hole in a part
5
a
of the mounting member
5
distant from the screws
6
a
and
6
b
, and threaded through the base
1
. As shown in
FIG. 25
, when the radial-direction adjusting screw
7
is turned, the motor mounting member
5
is rotated about a line interconnecting the fixing screws
6
a
and
6
b
as shown by arrow B, for adjusting the radial-direction optical axis angle of the optical pick-up
3
with respect to the optical disk. Here, the radial-direction optical axis angle means an angle of the optical axis of the optical pick-up
3
as seen in direction normal to the axis of rotation of the turn table
9
, and to the guide shafts
2
a
and
2
b
. When the optical angle is varied in this direction, the light spot formed by the optical pick-up
3
on the disk
10
is moved in the radial direction of the track, i.e., in the direction parallel with the guide shafts.
Reference numeral
8
denotes a disk motor fixed to the motor mounting member
5
by means of screws, not shown. Reference numeral
9
denotes a turn table fixed, by pressure insertion, to the disk motor
8
.
The optical disk
10
is placed on the turn table
9
, and information recorded thereon can be reproduced by means of the optical pick-up
3
. Reference numeral
11
denotes a clamper for clamping the optical disk
10
in cooperation with the turn table
9
. It is turned together with the turn table
9
and the optical disk
10
by means of the disk motor
8
. Reference numeral
13
denotes an incident angle indicator connected to receive the output of the optical pick-up
3
, via a playback amplifier (not shown) and indicating the incident angle (or a value corresponding thereto) of the optical axis of the optical pick-up
3
relative to the surface of the optical disk
10
, which corresponds to the optical axis angle of the optical pick-up
3
with respect to the optical disk
10
. Because the variation in the incident angle results in a time-axis variation, a jitter meter is used, of which the indication (indicated value) is the minimum when the incident angle of the optical pick-up
3
with respect to the optical disk
10
is zero.
The operations of the above arrangement at the time when signals are reproduced by means of the optical pick-up
3
, and when the optical axis angle of the optical pick-up
3
with respect to the optical disk
10
is adjusted will next be described. The optical disk
10
which is clamped by the turn table
9
and the damper
11
is turned in a predetermined direction by means of the disk motor
8
. The optical pick-up
3
is moved along the guide shafts
2
a
and
2
b
by a drive means (not shown), for continuous or intermittent reproduction from the region where the information is recorded on the optical disk
10
. It is desirable that the optical axis of the laser light from the objective lens
3
a
of the optical pick-up
3
be normal to the optical disk
10
, and the time-axis variation (hereinafter referred to as “Jitter”) of the signal from the optical pick-up
3
is the minimum. If the optical axis angle is increased, and the jitter exceeds a certain value, skipping of sound, when sound is recorded on the optical disk, or noise in the image, when image is recorded on the optical disk, occurs. To prevent the skipping and noise, the optical pick-up
3
is rotated about the guide shaft
2
a
, for adjusting the tangential-direction optical axis angle of the optical pick-up
3
with respect to the optical disk
10
so that the indication at the incident angle indicator
13
is the minimum, and also, the motor mounting member
5
and the optical disk
10
mounted thereon are rotated about an axis (a line connecting the screws
6
a
and
6
b
) which is normal to the axis of rotation of the turn table
9
and the guide shafts
2
a
and
2
b
, by means of the radial-direction adjusting screw
7
, for adjusting the radial-direction optical axis angle of the optical pick-up
3
with respect to the optical disk
10
so that the indication at the incident angle indicator
13
is the minimum.
The permissible range of the optical axis angle of the optical disk device differs from one system to another. In a system in which the recording density is low, combining parts of high mechanical precision may be sufficient, and there may be no need for the adjustment. In a system in which the recording density is high, however, the permissible range of the optical axis angle may be narrow, and optical axis angle adjustment is often required in either one or both of the radial and tangential directions, and an optical axis angle adjusting device with a high accuracy is desired.
The optical axis angle adjusting device for the optical disk device in the prior art makes adjustment of the optical axis angle of the optical pick-up
3
with respect to the optical disk
10
such that the jitter is the minimum. The dependency of jitter on the incident angle in the radial and tangential directions is such that it is substantially flat in the region near the optimum position, as shown in FIG.
26
. Therefore, even if the incident angle of the image pick-up happen to be &thgr; i before the adjustment, the difference in the jitter compared with that in the optimum position is as small as J
1
, making it impossible to achieve accurate optical axis angle adjustment. As a result, during reproduction from the optical disk
10
with a surface undulation, jitter may be periodically increased with periodic variation in the incident angle due to the effect of the surface undulation, and sound skipping or image noise may be generated.
SUMMARY OF THE INVENTION
The invention has been made to solve the problems described above, and its object is to provide an optical axis angle adjusting method and device which enable high-precision adjustment of the optical axis angle of the optical pick-up
3
with respect to the optical disk
Fukasawa Akihiro
Yamashita Norio
LandOfFree
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