Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2000-08-09
2002-06-04
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044320
Reexamination Certificate
active
06400666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup device, and more particularly, to an optical device which can detect a relative inclination between an objective lens and a recording medium.
2. Description of the Related Art
In general, an optical pickup device records/reproduces information signals while it moves across a recording medium such as a disk which is mounted on a turntable and rotates. When the rotating disk is inclined due to unevenness of the weight distribution, the recorded/reproduced signals deteriorate.
In particular, in the case of an optical pickup device adopting a light source for emitting light having a relatively short wavelength and an objective lens having a greater numerical aperture, in order to increase recording density, coma aberration is generated much due to the inclination of a disk so that deterioration of recording/reproducing signals is more severe.
An apparatus for detecting and correcting a relative inclination between a disk and a corresponding lens, as shown in
FIG. 1
, has been suggested to prevent the deterioration of the recording/reproducing signals.
Referring to
FIG. 1
, a holder
10
for supporting an objective lens
3
is movably installed at a main body
20
. A first tilt sensor is installed on the outer surface of a top side portion
22
of the main body
20
, facing a disk
1
, while a second tilt sensor is installed on the inner surface of the top side portion
22
. A reflection plate
17
is installed on the upper surface of the holder
10
, facing the second tilt sensor. Here, coil members (not shown) are installed around the objective lens
3
fixedly installed at the holder
10
so that the objective lens
3
can be actuated by interaction with a permanent magnet
21
installed at one side wall of the main body
20
. Although it appears in the drawing that the top side portion
22
is integrated with the main body
20
, a cover member (not shown) is generally provided instead of the top side portion
22
.
The first tilt sensor includes a light emitting diode
11
, and a pair of photodiodes
12
and
13
disposed at either side of the light emitting diode
11
, aligned in the radial direction. Light emitted from the light emitting diode
11
is reflected by the surface of the disk
1
and then received by the photodiodes
12
and
13
. The amounts of light detected by the photodiodes
12
and
13
are the same when the disk
1
is not inclined with respect to the main body
20
. When the disk
1
is inclined, the amounts of light detected by the photodiodes
12
and
13
are different from each other.
Likewise, the second tilt sensor includes a light emitting diode
14
, and a pair of photodiodes
15
and
16
disposed at either side of the light emitting diode
14
, aligned in the radial direction. Light emitted from the light emitting diode
14
is reflected by the reflection plate
17
installed on the upper surface of the holder
10
and then received by the photodiodes
15
and
16
. The amounts of light detected by the photodiodes
15
and
16
are the same when the holder
10
is not inclined with respect to the main body
20
. When the holder
10
is inclined, the amounts of light detected by the photodiodes
15
and
16
are different from each other.
In the above first and second tilt sensors, detection signals from the photodiodes
13
and
15
and the photodiodes
12
and
16
are input to (+) and (−) input terminals of a differential amplifier
18
where the signals are operated.
Thus, as shown in
FIG. 2A
, when the disk
1
and the objective lens
3
are not inclined, since the detection signals of the photodiodes
12
and
13
are the same and the detection signals of the photodiodes
15
and
16
are the same, an output signal value of the differential amplifier
18
is zero, which means that there is no relative inclination between the disk
1
and the objective lens
10
.
As shown in
FIG. 2B
, when the disk
1
is inclined to the main body
20
and the holder
10
is not inclined to the main body
20
, the amount of light detected by the photodiode
12
increases while the amount of light detected by the photodiode
13
decreases. Here, the amounts of light detected by the photodiodes
15
and
16
are the same. In this case, the differential signal of the differential amplifier
18
is a positive value according to the difference of the detection signals of the two photodiodes
12
and
13
.
To correct the inclination of the disk
1
, the holder
10
is made to be inclined to the same degree and in the same direction as that of the disk
1
, as shown in FIG.
2
C. Then, the amounts of light by the photodiodes
12
and
13
of the first tilt sensor are different from each other and simultaneously the amounts of light by the photodiodes
15
and
16
of the second tilt sensor are different from each other. However, the differential signal of the differential amplifier
18
is zero, which signifies that the inclination of the disk
1
is corrected and there is no relative inclination between the disk
1
and the objective lens
3
.
As described above, in the conventional disk inclination detecting apparatus, the inclinations of the disk
1
and the holder
10
are detected and the objective lens
3
mounted on the holder
10
is made to be inclined with respect to the main body
20
to the same degree as the inclination of the disk
1
so that a relative inclination of the disk
1
to the objective lens
3
can be corrected.
However, in the above disk inclination detecting apparatus, since two or more additional tilt sensors are needed, the number of parts are many and the manufacturing cost is high. Also, since the reflection plate
17
is installed at the holder
10
, a load on the actuating mechanism increases so that the actuating performance of an optical pickup device is lowered.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an optical pickup device which can detect a relative inclination between an objective lens and a recording medium without an additional tilt sensor.
Accordingly, to achieve the above objective, there is provided an optical pickup device which comprises a light source for generating and emitting light, optical path changing means for changing a proceeding path of incident light, an objective lens for focusing incident light on a recording medium which has a recording surface where information is recorded and a protection layer, at the side where light is input, for protecting the recording surface, a main photodetector for detecting the information signal and/or an error signal by receiving the light reflected by the recording surface of the recording medium and passing through the objective lens and the optical path changing means, and an inclination detecting unit for detecting inclination of the recording medium by receiving the light emitted from the light source and reflected by the surface of the protection layer or the recording surface of the recording medium.
It is preferred in the present invention that the inclination detecting unit comprises a holographic lens, disposed on the optical path between the light source and the optical path changing means, for diffracting and transmitting light input from the light source, and an inclination photodetector, disposed at one side of the main photodetector to receive incident light reflected by the surface of the protection layer and passing through the objective lens and the optical path changing means, and formed of a plurality of split plates, each performing photoelectric-conversion independently, the split plates being arranged in a track tangential direction and/or a radial direction of the recording medium.
Also, it is preferred in the present invention that the holographic lens comprises a first transmitting portion for transmitting light a portion of the light emitted from the light source within a near-axis area used for recording and reproducing information signals, and a second transm
Cho Kun-ho
Jung Seung-tae
Kim Seok-jung
Lee Chul-woo
Lee Yong-hoon
Burns Doane Swecker & Mathis L.L.P.
Edun Muhammad
Samsung Electronics Co,. Ltd.
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