Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-03-29
2003-04-08
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06545957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling track jumps of an optical pickup. More particularly, the invention relates to a method for controlling track jumps of an optical pickup incorporated in an optical disc apparatus by controlling the optical pickup in fine-tuned fashion such that the optical pickup is moved rapidly and accurately to a target track without suffering from any effects of disturbances such as scars on the disc the track jumps.
2. Description of the Related Art
The optical disc apparatus referred herein is a data reproducing apparatus that reproduces recorded data from an optical disc, or is an apparatus that records and reproduces data to and from an optical disc.
A typical optical disc apparatus is outlined below with reference to FIG.
6
.
FIG. 6
is a block diagram showing an overall structure of an optical disc apparatus.
As illustrated in
FIG. 6
, the optical disc apparatus
20
basically comprises: a spindle motor
2
for rotating an optical disc
1
; an optical pickup
3
for irradiating a laser beam to the optical disc
1
upon data recording or reproduction; a dual-axis mechanism
4
for getting an actuator to displace an objective lens
3
a
of the optical pickup
3
radially across the optical disc
1
and in a way approaching and leaving the disc
1
; a sled motor
5
for moving the optical pickup
3
radially across the optical disc
1
; and a magnetic head, not shown, for applying a modulated magnetic field to the optical disc
1
.
The optical disc apparatus
20
further includes a recording and reproducing circuit
6
. The recording and reproducing circuit
6
processes video and audio signals coming from the optical pickup
3
according to predetermined formats and sends the processed results to the outside. These data are also fed back to the optical pickup
3
.
In addition, the optical disc apparatus
20
comprises a servo processing circuit
7
, a first driving circuit
8
and a second driving circuit
9
as control systems.
The servo processing circuit
7
analyzes reflected light signals that are detected by the optical pickup
3
from the optical disc
1
. In so doing, the servo processing circuit
7
detects a focal point on the optical disc
1
of the laser beam irradiated by the optical pickup
3
, as well as a relative positional relation between the laser beam and the irradiated track.
Through the first driving circuit
8
, the servo processing circuit
7
then supplies a focusing control unit of the dual-axis actuator
4
in the optical pickup
3
with a control signal FOUT for controlling the focal point to within a predetermined range, and feeds a tracking control unit of the dual-axis actuator
4
in the optical pickup
3
with a control signal TOUT (tracking drive signal) for controlling to within a predetermined range the relative positional relation between the laser beam and the irradiated track.
Through the second driving circuit
9
, the servo processing circuit
7
also supplies a control signal SOUT (sled drive signal) for moving the optical pickup
3
in accordance with the amount of shift made by the objective lens of the dual-axis actuator
4
, to the sled motor
5
that moves the optical pickup
3
. The servo processing circuit
7
thus moves the optical pickup
3
as a whole in accordance with lens moved by the dual-axis actuator
4
, whereby so-called tracking control is effected for track follow-up.
Furthermore, the servo processing circuit
7
obtains through the second driving circuit
9
a detected speed value from a speed sensor
10
detecting a moving speed of the optical pickup
3
. With the speed value acquired, the servo processing circuit
7
supplies the second driving circuit
9
with a control signal SDCNT (sled feed voltage) for controlling the moving speed of the optical pickup
3
. This allows the optical pickup
3
to move (i.e., track jump) smoothly at the suitably controlled moving speed.
Described below with reference to
FIGS. 7A through 7D
is how track jumps of the conventional optical pickup
3
are typically controlled.
FIGS. 7A through 7D
show timing charts of signals involved in the control of track jumps of the optical pickup.
An initial motion sled kick pulse Kick D indicated by waveform in
FIG. 7C
is first fed to the second driving circuit
9
to start driving the sled motor
5
in a desired direction. The sled motor
5
is firstly driven so as to absorb elements of delay caused by inertia upon starting as well as by the initial motion sensitivity and static friction of the motor.
An initial motion tracking kick pulse Kick F indicated by waveform in
FIG. 7B
is then supplied to the first driving circuit
8
to drive the tracking control unit of the dual-axis actuator
4
in the optical pickup
3
, whereby driving the objective lens
3
a
of the optical pickup
3
in a desired direction.
A detected signal of reflected light output from the optical pickup
3
is analyzed to find illustratively the difference in reflectance between tracks and non-track portions on the recording surface of the optical disc. Such analyzing process yields a tracking error (TE) signal representing the relative positional relation between the laser beam and tracks as indicated by waveform in FIG.
7
A.
Counting zero-cross (TZC) points of the tracking error (TE) signal provides the number of tracks traversed by the optical pickup
3
in track jumps. Then, in accordance with the number of jumped tracks, a control signal SDCNT for controlling a target moving speed of the optical pickup
3
is adjusted as indicated by waveform in FIG.
7
D. In addition, a tracking kick voltage is applied to a tracking actuator so as to control the track jumps of the optical pickup
3
, thereby allowing the optical pickup
3
to reach a desired track.
As outlined above, the optical pickup is conventionally controlled in track jumps using control signals based on a number of factors: constant time intervals, a predetermined voltage level, or a variable voltage signal, all associated with polarity inversion between starts and stops. However, each of these control signals is determined on the basis of the result of the immediately preceding single track jump, so failure to measure that particular track jump triggers the output of erroneous kick pulses, leading to unstable control of the optical pickup.
The conventional method is thus limited in controlling capability and has had difficulty in providing high-speed access to the target track.
Furthermore, not only being poor in accuracy on jump performance, the conventional controlling method for the optical pickup exhibits tardy recovery from unstable jumps caused by scars or smears on the disc surface, leading to a jump error in some cases, thereby making it impossible to reach the target track.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and provides a method for controlling track jumps of an optical pickup in gaining high-speed access to a target track freeing from any effects of disturbances.
When devising the present inventive schemes, the inventors of this invention studied the conventional method and came to the conclusion that; the conventional speed control type method for the optical pickup exhibits its poor control capability ascribed to the process of determining the following control signal based on the result of the preceding single track jump, regardless of whether the control voltage or pulse width of the control signal was fixed or variable. The solution proposed by the inventors to the deficiency above is as follows:
Illustratively, time intervals of TZC (tracking zero cross) signals are continuously measured for comparison between a target time and a measured time. The difference therebetween is computed as an error, and a control signal with a voltage or a pulse width representing the magnitude of that error is output to the actuator of the optical pickup. For control of the driving speed of the actuator, the comparison between target and
Enomoto Tetsuo
Hiraga Hitoshi
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