Objective lens focus initialization system
US4700056A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 13, 1985 |
| Grant date | Oct 13, 1987 |
| Priority date | — |
| Expiry date | Nov 13, 2005 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/0945
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A focus initialization system adapted for use with an optical data recording system. Focus initialization is performed while a tracking servo loop is in an open loop mode, and an objective lens is fixedly positioned along a tracking axis. With a focus servo system in an open loop mode, the objective lens is cyclically driven along a focus axis about a neutral position and between offset positions. Displacement of the offset positions from the neutral position is increased with each successive cycle. After the objective lens has been positioned at each peak offset position, the focus servo loop is closed and track crossings resultant from eccentricity of the servo tracks on the record carrier are counted. Focus capture is recognized when at least a predetermined number of track crossings are counted during a predetermined time period. If less than the predetermined number of track crossings are counted during the predetermined time period, the focus servo loop is opened and the objective lens is driven to a successive offset position.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.