Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-11-20
2001-06-05
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S044350
Reexamination Certificate
active
06243335
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 62132/1997, filed Nov. 22, 1997, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk drive, and in particular, to a tracking servo control method and device for preventing a tremble of an object lens during a fast search mode.
2. Description of the Related Art
Compact disks (CD), a kind of an optical disk, are typically used for recording audio data such as music. Recently, however, the CDs are widely used as an auxiliary storage for text and computer data because of its high storage capacity.
In general, the CDs have a large number of tracks arranged at fine intervals of 1.6 &mgr;m, wherein the number of the tracks is about twenty thousand for recording music of one hour. Therefore, in a microscopic view, the CDs may rotate acentrically. From the standpoint of an optical pickup, each track with a width of about 0.5 &mgr;m rotates (or proceeds) sinusoidally. A tracking servo allows the optical pickup to accurately search (or seek) the tracks and radiate a laser beam to them. A fundamental structure of the tracking servo is illustrated in FIG.
1
.
In
FIG. 1
, reference numeral
2
denotes an optical disk (i.e., CD), reference numeral
4
denotes a disk motor, and reference numeral
6
denotes a pickup. As illustrated, the pickup
6
includes an object lens
30
, a tracking coil
32
, a magnet
34
, a ¼-wavelength plate
36
, a beam splitter
38
, an optical detector
40
and a laser diode
42
. Further, reference numeral
8
denotes a feeding motor for feeding the pickup
6
, reference numeral
10
denotes a tracking error detector
10
, reference numeral
12
denotes a phase compensator, reference numeral
14
denotes a system controller, and reference numerals
16
and
22
denote adders. Moreover, reference numerals
18
and
24
denote drivers, and reference numeral
20
denotes a lowpass filter (LPF).
In operation, the tracking error detector
10
generates a tracking error signal according to a beam trace status, and the phase compensator
12
generates a phase compensation signal according to the tracking error signal. The tracking servo corrects the position of a laser beam spot by moving the object lens
30
and the pickup body
6
in any direction according to the phase compensation signal. After tracking, the pickup
6
follows a specific track. For moving the pickup
6
, the adder
22
adds a search control signal output from the system controller
14
to an output signal of the lowpass filter
20
which lowpass-filters the phase compensation signal output from the phase compensator
12
. The driver
24
then drives the feeding motor
8
according to an output signal of the adder
22
, to move the pickup
6
in any direction. Further, for moving the object lens
30
, the adder
16
adds the search control signal output from the system controller
14
to the phase compensation signal output from the phase compensator
12
, and the driver
18
drives an actuator (comprising the tracking coil
32
and the magnet
34
) according to an output signal of the adder
16
, to move the object lens
30
.
FIG. 2
illustrates a schematic block diagram of a conventional tracking servo control device for preventing a tremble of the object lens during a fast search (or course seek) mode. Referring to
FIG. 2
, a switch
54
has a common node connected to the input of the adder
16
, a contact node A connected to an output of the phase compensator
12
and a contact node B connected to an output of an amplifier
52
. In the conventional tracking servo control device, the pickup
6
outputs a central-point servo signal for positioning the object lens
30
at a stable central point, to prevent a tremble of the object lens
30
during the fast search. The central-point servo signal is amplified in the amplifier
52
and then applied to the contact node B of the switch
54
. The phase compensator
12
outputs the phase compensation signal according to the tracking error signal from the tracking error detector
10
and provides the phase compensation signal to the contact node A of the switch
54
.
FIG. 3
illustrates a diagram for explaining the tracking error signal and the central-point servo signal, in a heterodyne tracking servo. In
FIG. 3
, reference numeral
60
denotes a photodiode divided into A, B, C and D areas, and reference numeral
62
denotes an optical spot. The tracking error signal output from the tracking error detector
10
has a value of (A+C)−(B+D), and the central-point servo signal output from the pickup
6
has a value of (A+D)−(B+C). As can be appreciated, the central-point servo signal and the tracking error signal have opposite phases relative to each other.
FIG. 4A
illustrates a frequency and a servo-on time of the tracking error signal in the state where the object lens
30
does not tremble during slow search (or fine seek), and
FIG. 4B
illustrates a frequency and a servo-on time of the tracking error signal in the state where the object lens
30
trembles during the fast search (or course seek). As illustrated, the servo-on time during the fast search of
FIG. 4B
is delayed by a time t as compared with the servo-on time during the slow search of FIG.
4
A. Accordingly, track searching is delayed by the time t.
To prevent the delay in searching the tracks, the system controller
14
switches the common node of the switch
54
to the contact node B slightly before the servo-on time. The adder
16
then adds the search control signal to the central-point servo signal output from the amplifier
52
instead of the phase compensation signal output from the phase compensator
12
. As a result, the driver
18
provides the tracking coil
32
with a driving current corresponding to the central-point servo signal. The central-point servo signal having the phase opposite to the phase of the tracking error signal, stabilizes the object lens
30
which was trembling by a driving current corresponding to a tracking signal.
However, the conventional tracking servo control device is disadvantageous in that it cannot use a pickup which does not output the central-point servo signal. Further, although the pickup outputs the central-point servo signal, the central-point servo signal, the central-point servo signal itself may have a deviation, which makes it difficult to accurately stabilize the trembling object lens.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a tracking servo control method and device for preventing a tremble of an object lens during a fast search mode without regard to a type of a pickup used to read information from a compact disk.
It is another object of the present invention to provide a tracking servo control method and device for preventing a tremble of an object lens during a fast search mode without using a central-point servo signal.
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.
To achieve the above and other objects of the present invention, there is provided a tracking servo control method of preventing a tremble of an object lens installed in a pickup in an optical disk drive. In the method, it is determined whether a distance between a target track and a current track where the pickup is presently placed is longer than a first distance. When the distance between the target track and the current track is longer than the first distance, both ends of a tracking coil through which a driving current for moving the object lens flows, are shorted. In the meantime, when the distance between the target track and the current track is shorter than a second distance as the pickup moves to the target track, both ends of the tracking coil are opened. Here, the first dista
Edun Muhammad
Samsung Electronics Co,. Ltd
Staas & Halsey , LLP
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