Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-08-05
2001-06-26
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044350
Reexamination Certificate
active
06252835
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to an automatic focus offset adjustment in a disc player, and more particularly to an automatic focus offset adjusting apparatus and method of a disc player for performing a reliable automatic controlling operation with respect to an abnormal condition of a disc such as a scratch or dust.
B. Description of the Prior Art
FIG. 1
is a functional block diagram showing a generally conventional compact disc player. Referring to
FIG. 1
, a pickup assembly
2
reads out data from a disc
1
to provide an electric signal. A RF signal generator
3
receives the electric signal supplied from pickup assembly
2
to produce a RF signal. The RF signal from RF signal generator
3
is amplified by a predetermined level in a RF amplifier
4
, and is waveform-shaped in an analog waveform shaping part
5
. Thereafter, the signal from analog waveform shaping part
5
is supplied to a digital signal processor
6
to be subjected to demodulating and decoding processing, thereby reproducing information recorded on disc
1
.
Meanwhile, the output signal from pickup assembly
2
is provided to a focus error detector
7
and a track error detector
8
. Focus error detector
7
detects a focus error signal FE from the signal supplied from pickup assembly
2
to provide the detected focus error signal to a servo controller
9
. Track error detector
8
detects a track error signal TE from the signal supplied from pickup assembly
2
to provide the detected track error signal to servo controller
9
.
Then, servo controller
9
receives focus error signal FE and track error signal TE respectively from focus error detector
7
and track error detector
8
to provide a focus control signal FC and a track control signal TC. A motor drive
10
receives focus control signal FC and track control signal TC to drive a slide motor
11
, thereby transferring pickup assembly
2
up and down and side to side. Also, servo controller
9
controls a spindle motor
12
via motor driver
10
to rotate disc
1
at a predetermined speed.
FIG. 2
is a view showing a construction of the pickup assembly
2
of FIG.
1
. As shown in
FIG. 2
, pickup assembly
2
has a laser diode
21
for radiating laser beam, and a collimator lens
22
for converting the diverging beam into parallel rays. In addition, a beam splitter
23
separates incident light and reflected light, and a quarter-wave plate
24
changes a polarized plane of the reflected light by 90 degrees. An objective lens
25
focuses the light, and a photodetector
26
converts the light from beam splitter
23
into an electric signal. Further, a focusing coil and a tracking coil (not shown) are disposed around objective lens
25
.
Current flowing through the focusing coil applies a force in conformity with the Fleming's left hand law, and objective lens
25
attached to the coil is moved up and down to perform the focusing. Also, by current flowing through the track coil, objective lens
25
is moved side to side to perform the tracking.
To begin with, the laser beam produced from laser diode
21
is transformed into the parallel rays from the diverging beam by passing through collimator lens
22
. At this time, a beam-splitting diffraction grating (not shown) is interposed between laser diode
21
and collimator lens
22
. When the laser beam generated from laser diode
21
passes through the diffraction grating, three beams consisting of one main spot and two side spots are produced.
After this, the parallel rays from collimator lens
22
are focused onto objective lens
25
via beam splitter
23
and quarter-wave plate
24
. Successively, objective lens
25
generates the beam spot to emit it to disc
1
. The beam spot emitted from objective lens
25
is reflected from disc
1
to return to objective lens
25
, and the reflected beam is to changed into parallel rays via objective lens
25
. The parallel rays pass though quarter-wave plate
24
to advance toward beam splitter
23
. Then, beam splitter
23
shifts the advancing direction of the parallel rays by as much as 90 degrees to permit the parallel rays to proceed toward photodetector
26
.
FIG. 3
is a block diagram for illustrating a general principle of generating the RF signal, focus error signal FE and track error signal TE. Photodetector
26
includes four light-receiving devices A, B, C and D for receiving the main spot and two light-receiving devices E and F for receiving the side spots. Four light-receiving devices A, B, C and D convert the received light into electric signals and supply them to RF signal generator
3
and focus error detector
7
. RF signal generator
3
sums the signals from light-receiving devices A, B, C and D to provide a sum signal A+B+C+D. The sum signal is used as the RF signal. The signals from light-receiving devices A, B, C and D are also provided as a difference signal (A+C)-(B+D) via focus error detector
7
. The difference signal is used as focus error signal FE.
Light-receiving devices E and F receive the side spots to convert them into the electric signals. The signals from light-receiving devices E and F produce a difference signal E-F via track error detector
8
. The difference signal E-F is used as track error signal TE. Thereafter, servo controller
9
receives focus error signal FE and track error signal TE to produce focus control signal FC and track control signal TC.
FIG. 4
is a block diagram for illustrating a conventional focus offset adjusting method. As is illustrated, servo controller
9
receives focus error signal FE to generate focus control signal FC. At this time, in order to provide accurate focus control signal FC, a variable resistor VR is manually regulated by a user to adjust a focus offset to generate focus control signal FC.
Furthermore, since the specific disc is adjusted only once in its fabricating line, the conventional method has the disadvantage of being incapable of obtaining the accurate focus offset value associated with the kind or state of the disc.
SUMMARY OF THE INVENTION
The present invention is devised to solve the foregoing disadvantages of the prior art. Therefore, it is an object of the present invention to provide an automatic adjusting apparatus of a focus offset for performing a more reliable automatic controlling operation with respect to abnormal conditions of a disc, such as a scratch and dust.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the above object of the present invention, according to one aspect of the present invention, an automatic focus offset adjusting apparatus, as broadly defined and embodied herein, includes pickup means for reading recorded data from the disc, means for detecting a focus error signal from an output signal read by the pickup means, means for converting an output signal read by said pickup means into a RF signal, means for separating a specific component from said RF signal, means for comparing the separated specific component from said separating means with a signal having a predetermined frequency to provide a phase difference value, and means for controlling a focus operation of an objective lens by varying a focus offset value within a predetermined range of the phase difference value, setting an optimal focus offset value within the predetermined range, adding the optimal focus offset value to the focus error signal, and providing the added signal as a focus control signal to drive the objective lens.
According to another aspect of the present invention, an automatic focus controlling method of a disc player, as broadly defined and embodied herein, includes initializing the focusing operation based on an initial focus offset data stored
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
L G Electronics Inc
Tran Thang V.
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