The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 10, 2005
Filed:
Aug. 22, 2000
Koichi Tada, Gifu, JP;
Koichi Tada, Gifu, JP;
Sanyo Electric Co., Ltd., Moriguchi, JP;
Abstract
A defect detecting circuit generates a defect detection signal when the level of a sum signal obtained from an optical sensor in an optical pickup is lower than a predetermined level, and a gate circuit responds to the defect detection signal to set the level of a fine clock mark signal to zero, that is a difference signal obtained from the optical sensor in the optical pickup. A fine clock mark is thus distinguished from any defect such as scratch and a correct fine clock mark signal is accordingly generated. Alternatively, the value of a sum signal, which indicates the total amount of reflected light output from the optical pickup, is compared with a predetermined threshold. When the period in which the value of the sum signal is smaller than the threshold lasts for a predetermined threshold time period, it is determined that focus of an objective lens deviates from an optical disk and accordingly focus servo control is stopped. The threshold is defined by gradually reducing a drive signal while detecting peak and bottom values of the sum signal which is generated as the objective lens is moved in the direction of its optical axis, and then setting the threshold between the detected peak and bottom values. In this way, defocus of the objective lens is surely detected.