Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1987-08-06
1989-03-28
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 45, G01J 120
Patent
active
048166650
ABSTRACT:
Method and apparatus for astigmatic focusing control which is independent of intensity distribution and is implemented with a combined data/focus error sensor array is described. An objective lens is utilized to focus a laser beam for use in reading and/or writing in an optical disk storage system. An astigmatic focus control system is utilized in which a cylindrical lens is disposed in the path of light reflected from the optical disk. The light from the cylindrical lens forms an astigmatic image on a sensor array. The image shifts between a circle at the focal point and one of two ellipses disposed orthoganally to each other depending on whether the focal point of the objective lens is above or below the plane of the optical disk. In the preferred embodiment, a circular bi-cell sensor is disposed so as to receive and encompass a reflected beam through the cylindrical lens when the objective lens is "in focus". An outer array of four sensors is disposed symetrically about the central bi-cell. The sensor is such that no light is disposed on the outer four sensors except when the object lens is out of focus. By utilizing only the four outer sensors, false focus error signals are avoided, since there is only one true "zero" condition, namely when the objective lens is properly focused. Data information may be derived from the sum of the two inner elements (bi-cell) when the system is properly focused. In an alternate embodiment, a single sensor is utilized in the central region in lieu of a bi-cell.
REFERENCES:
patent: 4458144 (1984-07-01), Reilly et al.
patent: 4654838 (1987-03-01), Sugiki
patent: 4695158 (1987-09-01), Kotaka et al.
Maxtor Corporation
Nelms David C.
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