Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1996-01-25
2001-02-06
Davis, David D. (Department: 2754)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S044280
Reexamination Certificate
active
06185181
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optional data recording medium, and more particularly to an optical disk for a sampled servo system.
2. Prior Art
An optical data recording medium (hereinafter referred to as “an optical disk”, when applicable) is an optical memory device for recording or reproducing data with a laser beam focused on its recording surface, and therefore the data recording and reproducing operation with the optical disk needs a focusing operation for focusing a laser beam on the recording surface and a tracking operation for causing the focused laser beam to scan the recording surface along tracks.
The focusing operation has been substantially established using means well known in the art. On the other hand, the tracking operation is provided with a so-called “continuous servo system” in which grooves for guiding the focused light beam are employed. Data are recorded in the grooves or in the spaces between the grooves (hereinafter referred to as “on land”, when applicable) or reproduced therefrom. A so-called “sampled servo system” in which, clock signals formed with clock pits arranged at predetermined intervals, the signals of servo pits wobbly with respect to the direction of a track, are sampled to perform the tracking operation.
As is apparent from the above-description, the specific feature of the sampled servo system resides in that a tracking operation can be performed without provision of guide grooves in a recording surface.
FIG. 2
is an explanatory diagram showing the arrangement of a conventional optical disk for the sampled servo system. As shown in
FIG. 2
, tracks
203
are generated on a recording surface as indicated by the broken lines, and clock pits
201
are formed on the tracks
203
of the recording surface at predetermined interval, and in addition servo pits
202
are formed in the recording surface in such a manner that they are wobbly with respect to the direction of a track. The clock pits are arranged so that clock pit signals are generated with a constant time interval at the time of a reproducing operation. As a result, the clock pits are arranged in alignment with a radial direction of a disk with a predetermined angle. Recording pits representing data are not shown in FIG.
2
.
In the sampled servo system, the signals of the servo pits
202
are sampled and outputted as tracking error signals.
FIG. 3
is a block diagram showing a tracking servo circuit according to the conventional sampled servo system.
FIG. 4
is a time chart showing various signals in FIG.
3
.
A photodetector (not shown) converts the intensity of light reflected from pits of the optical disk into an electrical signal, which is applied, as a reproducing signal (a) to, the tracking servo circuit shown in FIG.
3
. In the tracking servo circuit, a peak detecting circuit
10
detects the peak of the reproducing signal, and converts it into a digital pit signal (b), which is applied to a clock pit signal extracting circuit
11
. The pit signal (b) includes the signals of servo pit
202
, clock pit
201
and recording pit (not shown). The clock pit signal extracting circuit
11
extracts only the clock pit signal (c) from the pit signal (b). The clock pit signal (c) thus extracted is applied to a PLL (phase locked loop) circuit
12
, which outputs a clock signal (d), whose frequency is an integer times that of the clock pit signal (c), in synchronization with the latter (c). The clock signal (d) is applied to a sampling timing signal generating circuit
13
, which in turn produces sampling timing signals
1
and
2
for sampling changes which are caused in the reproducing signal (a) by the servo pits
202
. The sampling timing signals
1
and
2
are applied to a sample and hold circuit I
14
and a sample hold circuit II
15
, respectively. In the sample and hold circuits I and II, the signals of two servo pits are sampled with the sampling timing signals
1
and
2
, so that sampled reproducing signals (servo pit signals)
1
and
2
are outputted. The sampled reproducing signals
1
and
2
are applied to a differential amplifier
16
, which outputs a tracking error signal (e).
The tracking error signal (e) thus provided by the tracking servo circuit is applied to a circuit which, in response to it, operates to displace a laser beam lens actuator to decrease the tracking error, so that a tracking servo is effected to accomplish the tracking operation.
In the conventional optical disk according to the sampled servo system, the clock pits are located only on the tracks as shown in FIG.
2
. Therefore, in the case where the tracking operation has been accomplished and the focused light beam is scanning the tracks, the signals of the clock pits can be detected. However, before the tracking operation is accomplished, the focused light beam may scan the inter-tracks. In this case, the signals of the clock pits are decreased, as a result of which the clock signals may not be generated sufficiently. If the clock signals are not generated satisfactorily, then the jitter of the clock signals is increased, and the sampling of the signals of the servo pits is not correctly carried out. As a result, the time required for accomplishment of the tracking operation is increased. In addition, in the case where the tracking operation is not achieved yet, the focused light beam may jump over the tracks at the time of start or access. Therefore, at the time of start, it may be necessary to repeatedly perform the starting operation; and at the time of access, the access time may be increased.
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional optical disc of sampled servo system.
More specifically, an object of the invention is to provide an optical disk of a sampled servo system reduced clock signal jitter, which can be started with high stability and positively accessed at high speed.
The foregoing object and other objects of the invention have been achieved by providing an optical data recording medium which, according to one aspect of the invention, comprises: clock pits formed on tracks at predetermined intervals; servo pits arranged wobbly with respect to the tracks; and auxiliary clock pits arranged in such a manner that at least one auxiliary clock pit is located between two clock pits which are adjacent to each other radially of the optical data recording medium.
In the optical data recording medium, according to another aspect of the invention, the clock pits adjacent to one another radially of the optical data recording medium are formed in such a manner as to overlap one another, thus providing an auxiliary clock groove extended in a direction perpendicular to the tracks.
In the optical data recording medium thus constructed, the clock pit signals are less variable or substantially not variable in peak, and clock pulses signals are outputted with high accuracy.
REFERENCES:
patent: 4094013 (1978-06-01), Hill et al.
patent: 4313191 (1982-01-01), Winslow et al.
patent: 4736352 (1988-04-01), Satoh et al.
patent: 4831609 (1989-05-01), Suzuki
patent: 4858221 (1989-08-01), Romeas
patent: 4980882 (1990-12-01), Baer et al.
patent: 5063546 (1991-11-01), Ito et al.
patent: 5511063 (1996-04-01), Kawase
patent: 63-44322 (1988-02-01), None
patent: 63-42035 (1988-02-01), None
patent: 1-201847 (1989-08-01), None
Davis David D.
Pillsbury Madison & Sutro LLP
Seiko Epson Corporation
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