Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Patent
1981-10-20
1984-05-22
Richardson, Robert L.
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
250204, G11B 700
Patent
active
044505477
ABSTRACT:
A focal position detecting optical apparatus wherein a light beam focused by a first optical system is irradiated on an object to be illuminated, focal point images are formed at two foci spaced apart from each other by a cylindrical lens disposed in a path of light beam reflected from the object, and a shielding element having a tip edge making an angle of approximately 45.degree. with an operating axis of the cylindrical lens is inserted at a site between the two foci and at which the light beam has a circular cross section to extract a portion of the light beam travelling between the two foci. The extracted portion is detected by two photodetectors disposed symmetrically with an axis lying in substantially the same direction as the tip edge, and the difference between outputs of the two photodetectors is produced for detection of an actual focal position of the first optical system.
REFERENCES:
patent: 4123652 (1978-10-01), Bouwhuis
patent: 4273998 (1981-06-01), Kanamaru
patent: 4290132 (1981-09-01), Kotaka
patent: 4293944 (1981-10-01), Izumita et al.
Kaku Toshimitsu
Kaneda Tokuya
Maeda Takeshi
Nakamura Shigeru
Takasugi Wasao
Hitachi , Ltd.
Richardson Robert L.
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