Defocus detection device, defocus detection method and...

Details Defocus detection device, defocus detection method and... Defocus detection device, defocus detection method and...

2005-07-15

2009-06-02

Feild, Joseph H (Department: 2627)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044290, C369S053280

Reexamination Certificate

active

07542387

ABSTRACT:
Defocus detection device and method capable of detecting a defocus accurately during recording of information to an optical disk having a plurality of recording layers and an optical disk unit using the device and method are provided. A temporal restriction is imposed on defocus detection and besides, in comparison with a level for detection of a first change of a focus error signal developing during a defocus, a level for detection of a successively occurring second change of a polarity inverse to that of the first change is made to be smaller. When the first level is exceeded and thereafter the second level is exceeded within a restricted time, a defocus is detected.

REFERENCES:
patent: 6775208 (2004-08-01), Liu et al.
patent: 2002/0145952 (2002-10-01), Kono
patent: 2004/0207944 (2004-10-01), Ichimura
patent: 2007/0274167 (2007-11-01), Ishikawa
patent: 08-030990 (1996-02-01), None
patent: 8185637 (1996-07-01), None
patent: 2001-067686 (2001-03-01), None
patent: 2004-039125 (2004-02-01), None

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