Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-12-09
2001-06-26
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06252836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a tracking controlling method and apparatus employing push-pull signals, a recording/reproducing apparatus, and an optical disc.
2. Description of the Related Art
Nowadays, research and development of an optical disc recording/reproducing apparatus, configured for reproducing data recorded on the optical disc or recording data on the optical disc, are proceeding briskly. With such recording/reproducing apparatus, tracking servo is applied using a one-beam push-pull method or a three-beam method. In view of the increasing capacity and recording density of the optical disc, LD laser power or adjustment capability of the optical system, it is desirable to apply tracking servo by the push-pull method.
In the optical disc recording/reproducing apparatus, employing the push-pull method, an output light difference of two photodetectors arranged symmetrically with respect to the track center, that is the output difference between light beams reflected and diffracted by a groove in the optical disc, is detected as a push-pull signal. Tracking servo is applied to, for example, a biaxial actuator, with this push-pull signal as a tracking error.
However, since the optical disc is rotated with a sizeable offset, the light beam spot is moved on the photodetector adapted for detecting the push-pull signal, so that an offset is produced in the push-pull signal, that is the tracking error signal, and hence high tracking accuracy cannot be achieved.
If assumed that the rotating optical disc is not subjected to offset, the reflected laser light is illuminated on the center of a photodetector
50
, as shown in FIG.
1
A. However, if the rotating optical disc is subjected to offset, the reflected laser light is illuminated at a position offset from the center of the optical disc in dependence upon the disc offset, as shown in
FIGS. 1B
,
1
C and
1
D. This produces the dc offset in the push-pull signal. The push-pull signal obtained by the reflected light from the groove is offset relative to an ideal push-pull signal indicated by a broken line in FIG.
2
A.
In an optical disc designed to record data on both the land and the groove, offset in the push-pull signal occurs at both the land and the groove, in which case the push-pull signals obtained by the reflected light from the land is subjected to offset from the ideal push-pull signal indicated by a broken line shown in FIG.
2
B.
If an offset is produced in the push-pull signal in this manner, correct tracking cannot be realized. Since the interstice between the land and the groove is continually being narrowed to keep up with the increased capacity and recording density of the optical disc, it is desired to achieve more accurate tracking.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a tracking controlling method and apparatus employing push-pull signals, a recording/reproducing apparatus and an optical disc whereby an offset produced in the push-pull signals is removed to achieve accurate tracking.
In one aspect, the present invention provides a tracking control apparatus includes push-pull signal generating means for generating push-pull signals from a detection output obtained by an optical head from an optical disc, formed in terms of a sector made up of an address area and a user area, as a unit, with the user area having a meandering groove and a correspondingly meandering land, formed therein, a pit-shaped groove being formed in the address area on a line of extension of the land, the pit-shaped groove being adjacent to another pit-shaped groove formed on a line of extension of another land, with the optical head being adapted to illuminate a light beam on the groove or land to detect its reflected light, pulse generating means for generating a first sample-holding pulse when the light beam is illuminated on the pit-shaped groove or the land surrounded by two such pit-shaped grooves, first sample-holding means for sample-holding push-pull signals generated by the push-pull signal generating means, in synchronism with the first sample-holding pulses, and for holding the push-pull signals for one sector period, difference detection means for detecting the difference between the push-pull signals outputted by the sample-holding means and the push-pull signals generated by the push-pull signal generating means, and tracking control means for controlling the tracking of the optical head based on the push-pull signals obtained by the difference detection means.
In the above tracking controlling apparatus, the first sample-holding pulses are generated when the light beam is illuminated on the pit-shaped groove or on the land surrounded by two such neighboring pit-shaped grooves. The push-pull signals are sample-held in synchronism with the first sample-holding pulses to hold the push-pull signals for one sector period. The difference between the sample-held push-pull signals and the original push-pull signals is detected. The optical pickup is tracking-controlled on the basis of the detected difference output.
In another aspect, the present invention provides a tracking control method including generating push-pull signals from a detection output obtained by an optical head from an optical disc, the optical disc being formed in terms of a sector, made up of an address area and a user area, as a unit, the user area having a meandering groove and a correspondingly meandering land, formed therein, a pit-shaped groove being formed in the address area on a line of extension of the land, with the pit-shaped groove being adjacent to another pit-shaped groove formed on a line of extension of another land, the optical head being adapted to illuminate a light beam on the groove or land to detect its reflected light, generating a first sample-holding pulse when the light beam is illuminated on the pit-shaped groove or the land surrounded by two such pit-shaped grooves, sample-holding push-pull signals in synchronism with the first sample-holding pulses, holding the push-pull signals for one sector period, detecting the difference between the held push-pull signals and the generated push-pull signals, and controlling the tracking of the optical head based on the push-pull signals detected as to difference.
In the above tracking controlling method, the first sample-holding pulses are generated when the light beam is illuminated on the pit-shaped groove or on the land surrounded by two such neighboring pit-shaped grooves. The push-pull signals are sample-held in synchronism with the first sample-holding pulses to hold the push-pull signals for one sector period. The difference between the sample-held push-pull signals and the original push-pull signals is detected. The optical pickup is tracking-controlled on the basis of the detected difference output.
In still another aspect, the present invention provides a recording/reproducing apparatus including push-pull signal generating means for generating push-pull signals from a detection output obtained by an optical head from an optical disc, the optical disc being formed in terms of a sector, made up of an address area and a user area, as a unit, the user area having a meandering groove and a correspondingly meandering land, formed therein, a pit-shaped groove being formed in the address area on a line of extension of the land, the pit-shaped groove being adjacent to another pit-shaped groove formed on a line of extension of another land, the optical head being adapted to illuminate a light beam on the groove or land to detect its reflected light, pulse generating means for generating a first sample-holding pulse when the light beam is illuminated on the pit-shaped groove or the land surrounded by two such pit-shaped grooves, first sample-holding means for sample-holding push-pull signals generated by the push-pull signal generating means in synchronism with the first sample-holding pulses and for holding the push-pull signals for one sector period, difference detection means for detectin
Frommer William S.
Frommer Lawrence & Haug LLP.
Huber Paul W.
Simon Darren M.
Sony Corporation
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