Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-02-13
2001-11-13
Young, W. R. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053290
Reexamination Certificate
active
06317393
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to optical systems and, in particular, to seeking by an optical head in an optical system.
DESCRIPTION OF THE BACKGROUND ART
Certain types of storage media have constant reflectivity levels in the data storage areas. Data differentiation may be accomplished by phase comparison or other suitable methods. Other areas on the storage media, such as headers, may have differing reflectivity levels.
In seeking from one track to another, a track crossing number is determined. The track crossing number indicates the number of tracks to be crossed in seeking from an initial track to a target track. When the seek is performed, an actual track crossing count is kept, indicating the number of tracks crossed so far. When the actual track crossing count equals the track crossing number, the seek is finished and the target track has been reached.
In prior art systems, the actual track crossing count could be derived from the tracking error signal. However, if the path of a seek crossed the areas having differing reflectivity levels, the tracking error signal would erroneously indicate that a track had been crossed. Therefore, if the actual track crossing count relied on the tracking error signal, it would equal the track crossing number before the target track had been reached, causing undershoot of the seek and requiring either another seek or a seek correction.
SUMMARY OF THE INVENTION
A method is disclosed for moving an optical head from an initial track to a target track on a storage medium. The total number of tracks to be crossed is determined, and the optical head is moved toward the target track. A reflectivity level of light from the storage medium is measured, and a tracking error signal is derived from the reflectivity level. The tracking error signal has both true and false indicators of track crossings. A data indicator signal is derived from the reflectivity level, having indicator points corresponding to the false indicators of track crossings. A track count number is incremented for each true indicator of a track crossing, and the optical head is stopped when the track count number equals the total number of tracks to be crossed. In yet another method, an optical head is moved from an initial track to a target track on a storage medium. The total number of tracks to be crossed is determined, and the optical head is moved toward the target track. A reflectivity level of light from the storage medium is measured, and a tracking error signal is derived from the reflectivity level. The tracking error signal has both true and false indicators of track crossings. A track count number is incremented for each indicators of track crossings. A data indicator signal is derived from the reflectivity level, having indicator points corresponding to the false indicators of track crossings. The track count number is decremented for each indicator points, and the optical head is stopped when the track count number equals the total number of tracks to be crossed. Another method is disclosed whereby a track count signal is generated from the tracking error signal and the data indicator signal. The track count signal indicates track crossings corresponding to the true track crossing indicators in the tracking error signal. An apparatus is disclosed comprising a sensor for measuring the reflectivity level from a storage medium, a tracking error signal generator for generating a tracking error signal, a preamplifier for generating a data signal, a track crossing signal generator responsive to the tracking error signal, and a track/hold selector responsive to the data signal to direct the track crossing signal generator to generate a track crossing signal without the false track crossing indicators from the tracking error signal. A second apparatus is disclosed comprising a sensor for measuring the reflectivity level from a storage medium, a preamplifier for generating a data signal, a tracking error signal generator responsive to the reflectivity level for deriving a tracking error signal, a track/hold selector to direct the tracking error signal generator to generate a signal of constant amplitude for a predetermined period of time based on the data signal, and a track crossing signal generator responsive to the tracking error signal for deriving a track crossing signal indicating the crossing of an information track by the optical head.
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Discovision Associates
Do Caroline T.
Masaki Keiji
Wong Steve A.
Young W. R.
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