Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-12-17
2002-04-23
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044280, C369S053230
Reexamination Certificate
active
06377522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc apparatus capable of recording information onto lands and grooves, which are formed on an optical disc, respectively, or capable of reproducing recorded information, respectively, and relates to a land/groove detecting circuit. Particularly, the present invention relates to an optical disc apparatus, which appropriately detects the lands and grooves, making it possible to stably perform track pull-in operations with respect to the lands and grooves, respectively, and relates to a land/groove detecting circuit.
2. Description of the Related Art
In generally, the optical disc comprises groove portions, which are referred to as grooves, and land portions, which are referred to as lands, such that they are helically or concentrically provided in a row arrangement alternately. The conventional optical disc apparatus records or reproduces information using either the lands or the grooves.
In recent years, to improve recording density of the optical disc, there has been known an optical disc apparatus, which employs a land/groove recording and reproducing system in which information can be recorded in the lands and the grooves and reproduced.
FIG. 16
is a block diagram showing one example of the conventional optical disc apparatus using the land/groove recording and reproducing system.
As shown in
FIG. 16
, the optical disc apparatus comprises an optical head
101
, a thread motor
121
, a focus control system
300
, and a track control system
310
.
The optical head
101
comprises a laser
102
, an objective lens
120
, a beam splitter
103
, an optical sensor
104
, a focus actuator
105
, and a track actuator
106
, and records information onto the lands and grooves of the optical disc
100
, which is driven at a given number of revolutions by a spindle motor (not shown), and reproduces information stored therein, respectively.
The laser
102
generates optical beams (laser beams), and irradiates the optical disc
100
through the objective lens
120
. The objective lens
120
converges the optical beams onto a track surface of the optical disc
100
(where the lands and grooves are formed) to be irradiated therewith. Also, the object lens
120
sends the reflected light of optical beams to the optical sensor
104
, and forms an image on the optical sensor
104
through the beam splitter
103
. The beam splitter
103
changes an optical path of the reflected light from the optical disc
100
, and supplies the reflected light to the optical sensor
104
. The optical sensor
104
has four light-receiving sections, generates a servo signal in accordance with the amount of light received by the respective light-receiving sections, and supplies the generated servo signal to the focus control system
300
and the track control system
310
.
The focus actuator
105
, which is controlled by the focus control system
300
, moves the objective lens
120
along an optical axis (focus direction). The track actuator
106
, which is controlled by the track control system
310
, moves the objective lens
120
in the direction of the radius of the optical disc
100
(tracking direction). In other words, the track actuator
106
controls the objective lens
120
such that the optical beams with which the optical disc
100
is irradiated are rendered to follow the target lands or grooves.
The thread motor
121
moves the entirety of the optical head
101
in the radial direction of the optical disc
100
.
The focus control system
300
comprises a focus error signal generating circuit
107
, a phase compensation filter
109
, a switch circuit
125
, a driver amplifier
122
, and a CPU
124
, and controls the focus actuator
105
.
The focus error signal generating circuit
107
generates a focus error signal
108
, which shows the shift of the optical beams, with which the optical disc
100
has been irradiated, from the focal point of the disc surface, in accordance with the servo signal. The phase compensation filter
109
supplies the focus error signal
108
to the driver amplifier
122
through the switch circuit
125
as compensating for its phase. The switch circuit
125
, which is controlled by CPU
124
, turns on or off the entire operation of the focus control system
300
. The driver amplifier
122
drives the focus actuator
105
such that the value of the supplied focus error signal
108
becomes “0”.
The track control system
310
comprises a track error signal generating circuit
110
, a phase compensation filter
112
, a switch circuit
126
, a driver amplifier
123
, and a CPU
124
, and controls the track actuator
106
.
The track error generating circuit
110
generates a track error signal
111
, which shows the shift of the optical beams, with which the optical disc
100
has been irradiated, from the track (the center of the lands or grooves), in accordance with the servo signal. The phase compensation filter
112
supplies the track error signal
111
to the driver amplifier
123
through the switch circuit
126
as compensating for its phase. The switch circuit
126
, which is controlled by CPU
124
, turns on or off the entire operation of the track control system
310
. The driver amplifier
123
drives the focus actuator
106
such that the value of the supplied track error signal
111
becomes “0”.
The CPU
124
performs on/off control of the entire operation of each of the focus control system
300
and the track control system
310
by controlling the switching circuits
125
and
126
.
The following will specifically explain the track error signal
111
, which is generated when the optical beams irradiated from the optical head
101
move on the optical disc
100
, with reference to FIG.
17
.
If the optical beams irradiated from the optical head
101
move on the rotating optical disc
100
in the radial direction, the actual track is shown by an arrow LB of FIG.
17
A. In other words, the optical beams pass through the lands and grooves as crossing them sequentially along the arrow LB and they pass through the headers on the way. Since the reflection state of optical beams changes at the time of these passages, the amount of received light of each light receiving sections of the optical sensor
104
, which receives the reflected light, also changes. The signal level of the track error signal
111
generated by the track error signal generating circuit
107
changes with the above change.
More specifically, as shown
FIG. 17B
, if the optical beams move on the optical disc
100
, the signal level of the track error signal
111
becomes “0” when the optical beams are present at the centers P
1
, P
3
, P
5
of the lands and grooves. Then, if the optical beams deviate from these centers, the signal level changes to a positive side or a negative side.
For this reason, the track control system
310
provides feedback control to the track actuator
106
such that the signal level of the track error signal
111
becomes “0”, rendering the optical beams irradiated from the optical head
101
to follow the centers of the target lands or those of the grooves.
The polarity of the track error signal
111
differs between a case in which the optical beams move from the land to the groove and a case in which the optical beams move from the groove to the land. For this reason, in a track pull-in operation in which the optical beams are rendered to follow the target track (lands or grooves), in some cases, the optical disc apparatus has difficulty in performing the track pull-in operation stably. In other words, if the track actuator
106
is controlled with the polarity opposite to the actual case, the track control system
310
is subjected to a positive feedback (the signal level is not changed to “0”).
Therefore, when the track control system
310
controls the track actuator
106
, the polarity of the track error signal
111
must be inverted in a case in which the optical beams are rendered to follow the lands and a case in which the optical beams are rendered to follow t
McGinn & Gibb PLLC
Tran Thang V.
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