Automatic focus offset correction system

Details Automatic focus offset correction system Automatic focus offset correction system

1984-02-09

1986-08-19

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 45, G01J 120

Patent

active

046071571

ABSTRACT:
A small amplitude, low frequency, signal is added to the focus servo signal controlling the position of the objective lens of an optical disc storage system after focus acquisition has been achieved, so as to produce a slight defocusing effect of the light spot on the disc. The resulting variations in the read back signal is utilized by a synchronous detection circuit scheme to extract magnitude and polarity information of the focus offset present. That information is fed back to the focus servo signal to null out the focus offset, thereby assuring continual accurate focusing of the laser beam even under conditions of changes in the mechanical alignment of the optics of the storage system and/or the d.c. stability of the electronics of the storage system.

REFERENCES:
patent: 3596064 (1971-07-01), Markevitch
patent: 3673412 (1972-06-01), Olson
patent: 4032776 (1977-06-01), van Rosmalen
patent: 4097730 (1978-06-01), Korpel

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