Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-01-23
2003-05-13
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044250, C369S044290, C369S044320
Reexamination Certificate
active
06563772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of tracking control for an optical disc recorder and reproducer which discriminates a track deviation of an optical head and controls the track deviation in accordance with a result of discrimination when tracking an optical disc having a land/groove track structure.
2. Description of the Related Art
Recently, the demand for a large storage capacity has been increased in an optical write/read field or an optomagnetic write/read field. Accordingly, in an optical recording medium such as a digital versatile disc-random access memory (DVD-RAM), there has been proposed a so-called land/groove (L/G) write system for writing information both on a land track and a groove track of the DVD-RAM.
FIG. 1
is a block diagram of a conventional tracking control apparatus for a land/groove write type optical disc recorder and reproducer.
Referring to
FIG. 1
, the conventional tracking control apparatus includes an optical detector
11
for detecting a quantity of light of a laser signal reflected from an optical disc, a radio frequency (RF) amplifier
12
for amplifying a signal detected from the optical detector
11
as an RF signal, a first adder
13
for producing a tracking error signal TE by adding an offset value &dgr; to an output signal of the RF amplifier
12
, a digital signal processing section
14
for switching a polarity of the tracking error signal TE and outputting a control signal in accordance with a switched signal during switchover of a land/groove of the tracking error signal TE, an actuator
15
for finely moving an optical pickup in accordance with the control signal outputted from the digital signal processing section
14
, and a second adder
16
for adding an output of the actuator
15
and a disc eccentricity value &egr;, and feeding a position value x of an object lens of the optical pickup head back to a subtracter
17
to follow a desired track Xr.
The operation of the conventional tracking control apparatus for an optical disc recorder and reproducer as constructed above will be explained with reference to the accompanying drawings.
First, the eccentricity value &egr; of the optical disc and the output of the actuator
12
are added by the second adder
16
, and then feedback to the subtracter
17
. This feedback signal x is compared with a desired tracking target value Xr. At this time, the light reflected from the optical disc is detected as an electric signal by the optical detector
11
, and the detected electric signal is amplified as RF signal by the RF amplifier
12
. This amplified RF signal is added to the offset value &dgr; to produce the tracking error TE signal.
Here, the offset &dgr; of the optical disc is produced due to the quantity of light among signals A, B, C, and D formed on the optical detector
11
of the optical pickup, an offset that may be produced from an IC (i.e., master or sleeve) being used, and a degraded track following of a sled servo for moving the optical pickup from an internal periphery to an external periphery of the optical disc. The tracking error signal TE is offset from a track center Tc as much as the offset value &dgr;.
FIGS. 2
a
and
2
b
are waveform diagrams of the tracking error signal in the land/groove , tracks with respect to the offset &dgr;. In case of &dgr;=0 as shown in
FIG. 2
a,
the tracking error signal TE follows the track center Tc with TEG(x) and TEL(x). In case of &dgr;≠0, As shown in
FIG. 2
b,
the tracking error signal TE follows the track center Tc with TEG(x)+&dgr; and TEL(x)+&dgr;, being apart from the track center Tc as much as the offset value &dgr;.
The digital signal processing section
14
, which receives the tracking error signal TE as described above, switches the sign (i.e., “+” or “−”) of the tracking error signal TE in accordance with the land/groove (L/G) signal of the track that the optical head
1
follows, and outputs the control signal u to the actuator
15
in accordance with a switched track error em.
Here, the digital processing section
14
is composed of a sign switching section
14
a
and a tracking controller
14
b.
The sign switching section
14
a
outputs the track error em by switching the sign of the tracking error signal TE by the L/G signal inputted according as the track that the optical head
1
follows is the land or the groove. The tracking controller
14
b
judges the deviation and the tilt of the optical disc by the switched track error em, and outputs the control signal u to the actuator
15
.
The actuator
15
moves in a direction that the offset is removed according to the control signal u. At this time, the sled servo extracts a DC offset component of the tracking servo as a driving voltage of the actuator
15
, and drives a sled motor to move the pickup. The second adder
16
feeds the position value x of the object lens of the optical head
1
back to the subtracter
17
to follow the desired track Xr by adding the output of the actuator
15
and the disc eccentric signal &egr;.
Meanwhile, as shown in
FIGS. 2
a
and
2
b,
since the physical movement of the optical head in a radial direction r and the sign of the tracking error signal TE detected in a track direction t have a phase difference of 180°, respectively, in the land/groove, the sign switching section
14
a
switches the sign of the tracking error signal based on either of the land and groove according as the land/groove track is accessed. Also, the sign of the DC offset &dgr; is changed oppositely simultaneously with the switchover of the tracking error signal TE, and thus the tracking error signals having the different tracking deviation are inputted to the tracking controller
14
b.
Specifically, in the system, if the offset value added to the tracking error signal TE is &dgr; offset=0, the track error em in the radial direction r of the optical head
1
satisfies the following equation.
TE
G
=−TE
L
[Equation 1]
Here, TE
G
is the tracking error signal on the groove track, and TE
L
is the tracking error signal on the land track.
Also, in the system, if the offset value is not 0 (i.e., &dgr; offset≠0), the track error em on the groove with respect to the movement of the optical head
1
in the radial direction satisfies the following equation.
em=TE=TE
G
+&dgr; offset [Equation 2]
Meanwhile, in case of following the land of the track, the track error em is obtained by the following equation.
em=−TE=−
(
TE
GL
+&dgr; offset)=
TE
G
−&dgr; offset [Equation 3]
The tracking controller
14
b
receives the track errors obtained from the equations 2 and 3, and drives the actuator
15
. At this time, since the offset &dgr; exists though the tracking controller
14
b
is ideally designed and the condition that a standby state error is zero (“0” ), the object lens is actually offset from and follows the track center in the standby state.
The land/groove switching state in a system where the offset is not 0 will be explained with reference to
FIGS. 3
a,
3
b,
and
3
c.
FIG. 3
a
is a view illustrating the variation of the tracking error signal TE when the object lens crosses in the radial direction during the land/groove switching operation,
FIG. 3
b
is a view illustrating the time t and the movement of the object lens on the track, and
FIG. 3
c
is a view illustrating the track error level for the time t.
In case that the offset (&dgr;, {circle around (
1
)}) exists as shown in
FIGS. 3
a
and
3
b,
the object lens in the standby state is actually offset ({circle around (
6
)}) from and follows the track center. If the offset value is not completely removed, the track error em having twice the offset (2&dgr;, {circle around (
2
)}) is inputted to the tracking controller
14
b
during the switchover at the next land/groove switching time point.
Then, the tracking controller
14
b
outputs the control signal u to the actua
Hong Seong Pyo
Kim Kyung Soo
Edun Muhammad
Lee & Hong
LG Electronics Inc.
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