Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-06-27
2004-09-07
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053190
Reexamination Certificate
active
06788627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus for optically recording or reproducing information on a medium, such as an optical disk, and also relates to a tilt correction method, a tilt correction program and a medium.
2. Related Art of the Invention
In the present information-oriented age, technological development of high-density, large-capacity memory devices is proceeding actively. Capabilities required for such memory devices are high density, large capacity, high reliability, a rewritable function and the like. An optical disk is available as a medium capable of satisfying these requirements. The present invention relates to an optical recording apparatus for recording and reproducing information on such an optical disk used as a medium. Conventionally, numerous reports have been made as to the commercialization of optical disks and optical disk apparatuses for recording and reproducing the optical disks, typified by CD, MD and DVD systems, as well as technologies for them.
A DVD system and its drive will be described below as a conventional example referring to the accompanying drawings. FIGS.
7
(
a
) to
7
(
c
) are views illustrating schematic configurations of a digital video disk (DVD) serving as an optical disk and an optical head in an optical disk apparatus for reproducing information on the disk. The configurations and operations of the disk and apparatus will be described below.
In FIG.
7
(
a
), numeral
6
a
designates a digital video disk (DVD) serving as a medium, i.e., an optical disk. Numeral
1
designates a spindle motor for rotating the DVD (
6
a
) loaded thereon. Numeral
2
designates an optical head having a light-emitting portion and a light-receiving portion. Numeral
3
designates an object lens, mounted on the optical head
2
, for condensing light emitted from the light-emitting portion into the information face of the DVD (
6
a
) and thereby forming a light spot. Numeral
4
designates an object lens drive for driving the object lens
3
in a focus direction F and a tracking direction T so that the light spot stably follows the wobbling and eccentricity of the DVD (
6
a
). Numeral
5
designates a drive shaft system for moving the optical head
2
in the radial direction of the DVD (
6
a
).
Since the DVD (
6
a
) is intended for reproduction only, flat land areas L and pit rows P are formed thereon, thereby forming tracks TR as an information face on which pit row information signals are recorded. FIG.
7
(
b
) is a sectional view of the DVD (
6
a
). The cross section shown herein is obtained by cutting the optical disk from its center to its outer circumference in a zigzag form so as to cross the pit rows without fail.
The reproduction operation of the DVD system will be described below. During reproduction on the DVD (
6
a
), the optical head
2
emits DC light having a relatively small power, and a minute light spot is formed on a pit row on the information face by the object lens
3
. To cope with wobbling and eccentricity owing to the rotation of the DVD (
6
a
) by the spindle motor
1
, the object lens
3
is driven in the focus direction F and the tracking direction T by the object lens drive
4
so as to follow the track and to form a stable light spot. With this configuration, the presence or absence of pits is detected depending on the intensity of the light reflected by pit rows, and information is reproduced as a pit information signal. In addition, by moving the optical head
2
in the radial direction of the DVD (
6
a
) using the drive shaft system
5
, it is possible to reproduce information signals in the whole area of the DVD (
6
a
).
If the DVD (
6
a
) has a large warp (tilt), the DVD system cannot stably detect the pit row signal. Generally, such a tilt occurs in the radial direction of the DVD (
6
a
). In this case, by subjecting the drive shaft system
5
to rotation operation A around the axis in the tangential direction (TG) of a predetermined track (TR), the relative angle between the DVD (
6
a
) and the optical head
2
, that is, the relative angle between the DVD (
6
a
) and the axis of the outgoing light from the object lens
3
is adjusted so that the pit row information signal can be reproduced with minimal errors. The predetermined track is a track wherein the light spot is formed. The graph of FIG.
7
(
c
) illustrates the reproduction characteristic of the pit row information signal, wherein the abscissa represents the angle of the above-mentioned rotation of the drive shaft system
5
, i.e., the amount of the tilt of the DVD (
6
a
), and the ordinate represents the amount of reproduction jitter. By carrying out the rotation operation A of the drive shaft system
5
, the relative angle between the DVD (
6
a
) and the axis of the outgoing light of the object lens
3
is adjusted to an angle wherein the amount of reproduction jitter becomes nearly minimal. This adjustment performs the so-called tilt correction. Although the drive shaft system
5
is subjected to the rotation operation A as described above, another system is available wherein the object lens drive
4
has a function of subjecting the object lens
3
to rotation operation B around the axis in the tangential direction (TG) of the above-mentioned predetermined track TR in order to carry out tilt correction. Furthermore, the amount of the tilt for the tilt correction carried out in this way may be an amount of correction fixed beforehand by a drive, or the amount of correction may be determined each time the DVD (
6
a
) is loaded. The configuration of the tilt correction thus differs depending on the drive.
Other components of the drive, that is, components not based on the purpose of the present invention, such as circuits and mechanisms, are not illustrated or explained herein.
The above-mentioned conventional configuration, however, has the following problems.
FIG.
7
(
a
) illustrates a case wherein the DVD (
6
a
) has a large warp (tilt), and the tilt occurs generally in the radial direction of the DVD (
6
a
). In this case, the above-mentioned rotation operation A of the drive shaft system
5
and the above-mentioned rotation operation B of the object lens
3
by the object lens drive
4
are detected depending on the characteristic of the amount of the reproduction jitter shown in FIG.
7
(
c
). Hence, it is necessary to detect the reproduction signal of the disk by carrying out the so-called focus servo-control, tracking servo-control and reproduction characteristic detection. In other words, the tilt correction operation for obtaining an optimum position by carrying out the above-mentioned rotation operations is substantially the same as a series of operations required for ordinary signal reproduction. Hence, the algorithm for the operations becomes complicated. Furthermore, this operation algorithm needs a constant time. For example, when the amount of correction in this tilt correction is fixed beforehand by the drive, a short time may be used at the completion time of drive operation. However, in the case when tilt correction is carried out each time the DVD (
6
a
) is loaded, or when tilt correction is carried out every moment depending on the radial position on the DVD (
6
a
), the proportion of the constant time becomes larger in comparison with the operation time for the function of reproducing an actual information signal. This is equivalent to reduction of the operation function of the drive in view of the usage feeling of a user.
Furthermore, in the conventional configuration, a pit row information signal is present as shown in FIG.
7
(
b
), since the DVD (
6
a
) is intended for reproduction only. However, in the case of a recording optical disk, no information signal is present. Hence, the characteristic of the amount of the reproduction jitter shown in FIG.
7
(
c
), required to be detected for tilt correction, cannot be obtained, thereby causing a problem. To solve this problem, for example, a DVD-RAM system has a format wherein pit rows fo
Aikoh Hideki
Nakamura Tohru
Huber Paul W.
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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