Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-12-22
2002-08-13
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S059190, C369S124150
Reexamination Certificate
active
06434093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for controlling tracking for an optical recording medium, and more particularly to an apparatus and method for controlling tracking detecting an exact track center value from an optical recording/reproducing apparatus.
2. Description of the Related Art
Generally, an optical recording medium system, i.e., an optical recording/reproducing apparatus reproduces data recorded in an optical disc or records data in the optical disc using the optical disc, such as compact disc (CD) and digital versatile disc (DVD), as a recording medium.
At this time, a rewritable optical disc, particularly, DVD-RAM includes a signal track of a land and groove structure, and respectively records an information signal in tracks of the land and the groove to increase recording density.
FIG. 1
is a block diagram illustrating the construction of a typical apparatus for recording and reproducing data on the optical recording medium. Referring to
FIG. 1
, an optical disc
101
includes a signal track of a land and groove structure. Data can be recorded or reproduced in a track of the land or the groove, or both tracks thereof. An optical pickup
102
places an optical beam condensed on an object lens on a signal track of the optical disc
101
under the control of a servo control unit
106
, and makes the optical beam reflected from a signal recording surface of the track condensed on the object lens and incident upon an optical detector (not shown) to detect a focus error signal and a tracking error (TE) signal. The optical detector is composed of several optical detecting elements, and electric signals in proportion to quantities of light obtained by the respective optical detecting elements are output to a radio frequency (RF) and servo error generating unit
104
.
The RF and servo error generating unit
104
generates an RF signal required for data reproduction from the electrical signals output from the optical detector, a focus error (FE) signal and a (TE) signal for servo control. At this time, the RF signal is output to a decoder
105
for data reproduction, the servo error signal such as FE and TE to a servo control unit
106
, and the control signal for data recording to an encoder
103
.
The encoder
103
encodes the data to be recorded to recording pulses of a format required by the optical disc
101
, and records the encoded pulses on the optical disc
101
through the optical pickup
102
. The decoder
105
restores the data of the original form from the RF signal.
Meanwhile, a host such as a personal computer (PC) may be connected to the optical disc recording/reproducing apparatus. This host transmits a recording/reproducing command to a microcomputer
111
through an interface
110
, transmits the data to be recorded to the encoder
103
, and receives reproduced data from the decoder
105
. The microcomputer
111
controls the encoder
103
, the decoder
105
, and the servo control unit
106
in accordance with the recording/reproducing command from the host.
At this time, an advanced technology attached packet interface (ATAPI) is typically used as the interface
110
. Specifically, the ATAPI is the interface standard between the host and the optical recording/reproducing apparatus such as a CD or DVD driver proposed to transmit the data decoded by the optical recording/reproducing apparatus to the host, and serves to convert the decoded data into a protocol of a data packet that can be processed in the host and transmit the data packet.
Meanwhile, the servo control unit
106
processes the focus error signal (FE), and outputs a driving signal for focusing control to a focus servo driving unit
107
. The servo control unit
106
also processes the tracking error (TE) signal, and outputs a driving signal for tracking control to a tracking servo driving unit
108
. Also, the servo control unit
106
generates a track zero crossing (TZC) signal switched on/off at a zero cross point of the tracking error (TE) signal. The TZC signal is used as various reference signals, and as an example, the TZC signal may be used as a reference signal which determines a kick pulse, a brake pulse, and brake-on time during seeking operation.
The focus servo driving unit
107
moves the optical pickup
102
up and down by driving a focus actuator in the optical pickup
102
, so that the optical pickup
107
traces the movement of the rotating optical disc
101
.
The tracking servo driving unit
108
moves the object lens of the optical pickup
102
in a radial direction by driving a tracking actuator in the optical pickup
102
, so that the object lens adjusts the position of the optical beam, and traces a predetermined track.
At this time, the optical beam should trace the center of the track. If the optical beam deviates from the track center, the tracking actuator fails to trace the track center. In this case, the tracking servo fails to trace a corresponding track, thereby resulting in that the tracking servo may be inactivated. This makes the recording/reproduction of the data difficult.
It is essentially necessary to estimate DC level of the tracking error for exact tracking control. This is because that DC components of the tracking error directly cause deviation of the track.
Accordingly, in the typical optical recording/reproducing apparatus, the track center is first traced when the tracking servo starts. There may be various methods for tracing the track center. As one example, there is a method for estimating a traverse center value as a track center value when the tracking servo starts. That is, a DC-offset of the tracking error becomes an error value of the estimated traverse center. As another example, there is a method for estimating a peak-to-peak center of the TE signal as shown in FIG.
2
. That is, as shown in
FIG. 2
, the peak-to-peak center of the TE signal (TEVpp), i.e., potential level of V
1
=V
2
is set as the track center, and the tracking control is performed based on the set track center.
However, signals of the optical detector may vary due to characteristic difference of the optical detector for detecting reflecting light from the optical disc or in case that the optical detector is wrongly designed. If the TE signal is detected by such an optical detector, the TE signal may be generated asymmetrically as shown in FIG.
2
.
At this time, the traverse center or the potential level of V
1
=V
2
is not an actual track center. Other point acts as a track center.
In case that the tracking servo starts using the estimated track center value as above, a risk may arise in that tracking control starts at a point where an optical head is deviated from the track excessively. In this case, it is not possible to obtain initial stable tracking performance due to excessive response characteristic caused by the excessive tracking error.
Accordingly, to set a proper tracking servo starting point, the exact track center value is required. Particularly, if the tracking is activated in a portion not the track center, recording is performed in a wrong position. For this reason, the RF signal becomes smaller and jitter characteristic is degraded. Particularly, recording characteristic is degraded.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an apparatus and method for controlling tracking for an optical recording/reproducing apparatus that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus and method for controlling tracking for an optical recording/reproducing apparatus, in which a track center value is estimated from a TE signal generated during free-running or traverse to control tracking.
Another object of the present invention is to provide an apparatus and method for controlling tracking for an optical recording medium, in which a track center value is estimated from a TZC signal generated after adjusting asymmetry of a TE s
Birch & Stewart Kolasch & Birch, LLP
Edun Muhammad
LG Electronics Inc.
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