Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Utility Patent
1999-08-23
2001-01-02
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044260
Utility Patent
active
06169715
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc for storing information by irradiating laser light onto an optical disc medium, and an optical disc device for same.
2. Description of the Related Art
In recent years, great developments have been made in optical disc devices as means for storing and reproducing large volumes of data, and approaches for achieving high storage density have been adopted, one of these methods being a phase change-type optical disc device utilizing reversible crystal—non-crystal state changes.
In a phase change-type optical disc device, marks (amorphous sections) and spaces (crystalline sections) between these marks are formed on an optical disc medium, by irradiating semiconductor laser light onto the optical disc medium using two power settings: a peak power for rendering crystalline regions amorphous, and a bias power for crystallizing amorphous regions.
Land/groove recording technology exists for recording these marks and spaces in tracks in both the land region and the groove region of a guide groove on a disc.
In order to improve the reliability of optical discs, it is necessary to store and reproduce high-quality signals on the optical disc. If there is an inclination (tilt angle) of the recording surface of an optical disc with respect to the optical axis of the light beam, then an aberration occurs in the light spot and it becomes difficult to record and reproduce high-quality signals on the optical disc. Therefore, in order to record and reproduce signals to and from the optical disc, it is necessary to detect the aforementioned tilt angle accurately, and to correct this tilt angle.
A conventional method for correcting tilt by a tilt device is shown in FIG.
2
.
In
FIG. 2
,
201
is an optical disc,
202
is an optical head which focuses a light beam onto the optical disc,
203
is a tilt platform,
204
is a signal calculating circuit,
205
denotes focus control means for controlling the focal position of the light spot on the optical disc surface,
206
denotes tracking control means for controlling the position of the optical spot on the track,
207
is a tilt sensor for irradiating light for detecting the inclination of the optical disc signal with respect to the optical axis of the aforementioned optical beam, onto the optical disc, receiving light reflected by the optical disc, and detecting the inclination of the recording surface of the optical disc with respect to the optical axis of the aforementioned light beam, and
208
denotes tilt control means for controlling the inclination of the recording surface of the aforementioned optical disc with respect to the optical axis of the aforementioned light beam, by inclining the aforementioned tilt platform according to the value detected by the aforementioned tilt sensor.
FIG. 3
shows a graph of a case where the tilt position is corrected at both the inner circumference and outer circumference of the optical disc, in a conventional optical disc device.
SUMMARY OF THE INVENTION
However, in the conventional composition, since a tilt sensor and tilt controlling means as illustrated in
FIG. 2
are used to detect the tilt position of the optical disc, it has been necessary to provide a tilt sensor
207
for detecting tilt, separately from the optical head
202
, in order to correct the inclination of the recording surface of the optical disc with respect to the optical axis of the optical beam. The incorporation of two optical systems in the optical head and the tilt sensor makes the optical disc device more complex, increases the space occupied by the device, and leads to cost rises. Moreover, the optical axes of the two optical systems in the optical head and the tilt sensor must be adjusted, and therefore adjustment tasks become more complex, and errors are liable to occur between the tilt sensor and the inclination (tilt angle) of the recording surface of the optical disc with respect to the optical axis of the aforementioned optical beam, making it difficult to detect the tilt angle accurately.
The present invention overcomes all of the aforementioned problems, an object thereof being to improve the quality of the light spot and recording and reproduction characteristics by correcting the inclination of the optical disc with respect to the optical axis of the light beam at radial positions at the inner circumference, middle circumference and outer circumference of the optical disc, in such a manner that the value detected by the tilt detecting means is a suitable value.
In order to resolve the aforementioned problems, the present invention comprises the following aspects.
The first aspect of the invention corresponds to method (1) in the embodiments.
The first aspect is a tilt detection device for detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of the optical disc with respect to the optical axis of said light beam by a difference signal output representing the difference between the signals from said first and second photo detecting elements when reflected light from said continuous track is received by the two-split photo detector.
Thereby, it is possible to improve signal quality during recording and reproduction, by detecting the tilt angle by pits recorded previously in the optical disc, without needing to provide an optical system for detecting the tilt angle separately from the optical system for recording and reproducing signals. Consequently, this has the effect of reducing the installation size of the device and lowering costs.
The second aspect of the invention corresponds to method (4) in the embodiments.
The second aspect is a tilt detection device detecting inclination of the recording surface of an optical disc having tracks and first shifted pits and second shifted pits formed such that the first shifted pits and the second shifted pits are displaced respectively to a first side and a second side of a track from the center of the track, comprising:
an optical head for recording and reproducing signals by focusing a light spot onto said optical disc;
a two-split photo detector for receiving light reflected from said optical disc, said photo detector including a first photo detecting element and a second photo detecting element divided in a direction parallel to the track;
tracking control means for controlling the position of said light spot on a track; and
tilt detecting means for detecting inclination of the recording surface of the optical disc, by comparing a first summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said first shifted pits is received by the two-split photo detector, with a second summed signal representing the sum of the outputs from the first and second photo detecting elements when reflected light from said second shifted pits is received by the two-split photo detector.
The third aspect of the invention corresponds to method (4) in the embodiments, and in particular, to the lower signal level illustrated in
FIGS. 21A
,
21
B and
21
C.
The third aspect is the tilt detection device according to the second aspect of the invention, wherein said tilt detecting means compares the lower level of the absolute value of the envelope signal of the first summed signal with the lower level o
Ishida Takashi
Nakamura Atsushi
Shoji Mamoru
Hindi Nabil
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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