Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-11-30
2004-08-31
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053140, C369S053120
Reexamination Certificate
active
06785205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photo-record player, and more particularly, to an apparatus for controlling eccentricity in a photo-record player and a control method thereof which are applicable to normal servo or seek by measuring an eccentricity ratio and an eccentricity phase of a photo-record media.
2. Background of the Related Art
Generally, a photo-record medium, i.e. a photo-disc record player recording and regenerating a photo-disc, plays data recorded in a photo-disc using the photo-disc as a record medium such as CD (compact disc), DVD (digital versatile disc), and the like pr records data in the disc.
In order to find a demanded destination on the photo-disc, a laser beam generated from a pickup is moved to a target track precisely so as to be tracked on the target track, which is called ‘seek’or ‘search’.
Such a seek operation is carried out in a manner that an entire photo-pickup is moved near a demanded track by driving a sled motor when a count of tracks to be jumped is hundreds to thousand in accordance with the calculation of the count of the tracks to a target track and that the demanded track is found using a tracking actuator if a count of remaining tracks is below several hundreds. In this case, ‘jumping tracks by moving the sled motor’is called ‘rough seek’, while ‘jumping tracks by moving the actuator’is called ‘fine seek’.
FIG. 1
illustrates a block diagram of a general photo-disc recorder/player.
Referring to
FIG. 1
, a photo-pickup
102
makes a light beam, which is focused on a substance lens by a control of a servo control unit
104
, placed on a signal track of a photo-disc
101
, focuses an incident light reflected on a signal record surface, on the substance lens again, and then makes the light incident to a photo-detector to detect a focus error signal and a tracking error signal.
The photo-detector includes a plurality of photo-detecting devices and outputs electric signals proportional to the light intensity attained by the respective photo-detecting devices to an RF/servo error generating unit
103
.
The RF/servo error generating unit
103
detects an RF signal for data regeneration, a focus error signal FE for servo control, and a tracking error signal TE from the electric signals detected from the respective photo-detecting devices.
The detected RF signal is outputted to a data decoder (not shown in the drawing) for play, and servo error signals such as FE and TE are outputted to a servo control unit
104
.
The servo control unit
104
carries out a signal processing on the focus error signal FE so as to output a driving signal for a focusing control to a focus servo driving unit
105
, and carries out a signal processing on the tracking error signal TE so as to output a driving signal for a tracking control to a tracking servo driving unit
106
.
In this case, the focus servo driving unit
105
drives a focus actuator in the photo-pickup
102
in accordance with the focus driving signal to move the photo-pickup
102
up and down so that the photo-disc
101
rotates to follow the up and down movement correspondingly.
The tracking servo driving unit
106
drives a tracking actuator in the photo-pickup
102
in accordance with the focus driving signal so as to amend a location of a beam by moving the substance lens of the photo-pickup in a radial direction, thereby tracking a predetermined track. In this case, on a normal record/play operation or fine seek, the substance lens of the photo-pickup
102
is moved in the radial direction by driving the tracking actuator.
Meanwhile, in ‘rough seek’that the photo-pickup is moved entirely, the sled servo driving unit
107
receives a sled control signal from the servo control from the servo control unit
104
so as to transport a body of the photo-pickup
102
directly in a demanded direction by driving the sled motor
108
.
Moreover, the servo control unit
104
detects revolution speed information of a disc from the RF signal so as to output the information to a spindle servo
109
. The spindle servo
109
then carries out a phase locked loop (PLL) control on a spindle motor
110
in accordance with the revolution speed information so as to revolve the disc
101
. Namely, the spindle motor
110
gives a spindle (not shown in the drawing) a turning force for the revolution of the disc
101
, and then the spindle transfers the turning force given by the spindle motor
110
to the disc
101
, thereby enabling to revolve the disc
101
at a demanded speed.
In this case, the photo-disc
101
may be distorted during projecting and hardening steps of a resin in a manufacturing process. And, the distortion may causes eccentricity despite piercing a hole in a center of the disc. Moreover, tracks of the disc, even if recorded precisely with a spiral figure with pitches of a determined standard, may bring about eccentricity due to deviation of the center hole. As the disc revolves with the eccentricity, a central axis of a motor barely coincides with a center of each of the tracks. Namely, the original disc center fails to coincide with the track center.
Particularly, there are disc eccentricity occurring in manufacturing a disc, eccentricity occurring in mounting the disc, and eccentricity due to ‘run-out’of a revolving axis. Besides, the quantity by ‘run-out’of a photo-axis is relatively much smaller than a quantity of the eccentricity caused by each of the foregoing two factors.
Thus, it is difficult to precisely read a signal of a demanded track only. Hence, the eccentricity should be controlled. Specifically, if it fails to control the eccentricity, a seek location becomes inaccurate. Inevitably, a destined location is found by carrying out a number of track jumps to ‘fine seek. Therefore, a seek time is taken longer.
In a method of controlling eccentricity according to a related art, a quantity of eccentricity is measured when a track control loop is configured and then a control degree (i.e. servo gain) of a track loop is adjusted in accordance with the measured quantity of the eccentricity.
FIG. 2
including (a), (b), and (c) illustrates graphs of waveforms of a TE signal, a track zero crossing (TZC) signal at this time, and an FG signal which are measured on pre-running status.
The TZC signal in FIG.
2
(
b
) is a signal turned on/off at a track crossing time point, and is attained by slicing the TE signal in FIG.
2
(
a
) into internal reference levels. And, the FG signal in FIG.
2
(
c
) is a frequency generating (FG) signal, in which the frequency is generated from spindle revolution. In this case, a count of FG signals generated from one revolution of the spindle may vary in accordance with designer's choice. In the drawing, it is assumed that a count of the FG signals during one spindle revolution, i.e. one revolution of a photo-disc, as shown in FIG.
2
(
c
), is six.
In this case, when the photo-disc is inserted, a quantity of eccentricity is measured by the following Formula 1 at a pre-running state that a tracking servo and a focus servo are turned off and on, respectively.
[Formula 1]
a quantity of eccentricity=(TZC count per revolution of photo-disc)×
T
p
×½,
where T
p
is a track pitch. And, T
p
of DVD is 0.74 mm.
FIG. 3
illustrates a diagram for explaining a track jump in a general photo-disc structure such as DVD and finding a quantity of eccentricity at this time.
Namely, an absolute measurement of eccentricity is attained by counting TZC (track zero crossing) signals generated by one spindle revolution during pre-running. The one spindle revolution is known by counting the number of FG signals as shown in FIG.
2
(
c
).
Such a measured quantity of eccentricity is always constant while the disc is loaded.
The above-mentioned method enables a follow-up for a general track control but fails to be applicable to a ‘seek’with no track control. Hence, an error of a seek location becomes excessive when eccentricity is large, thereby affecting greatly an access time delay. And, eccentricit
Kim Eung Soo
Park Sang On
Park Yong Cheol
Edun Muhammad
LG Electronics Inc.
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