Data reading and/or writing apparatus for use with an optical card
US4918415A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 18, 1987 |
| Grant date | Apr 17, 1990 |
| Priority date | — |
| Expiry date | May 18, 2007 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/0908
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An apparatus for reading and writing a data signal from and on an optical card including an optical head having a semiconductor laser for emitting a writing light beam, a light emitting diode for emitting a reading light beam, a first object lens for projecting the reading light spots onto the optical card, a second objective lens for projecting the reading light beam reflected by the optical beam onto a photodetector and a half mirror arranged in an optical axis of the second objecive lens, the first and second objective lens having inclined optical axes with respect to a surface of the optical card, a driving mechanism for feeding the optical card in its lengthwise direction, and a focusing control mechanism for moving the optical head in a direction normal to the surface of the optical card. The photodetector includes first and second detectors which are arranged to receive equally an image of a part of the optical card illuminated by the reading light beam only in a focused condition. By deriving a difference between the first and second detectors there is produced a focusing error in response to which the focusing control mechanism is driven to correct the focusing error.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.