Optical head for focussing a light beam on an information record

Details Optical head for focussing a light beam on an information record Optical head for focussing a light beam on an information record

1984-05-22

1987-03-31

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

G11B 700, G11B 2110

Patent

active

046545158

ABSTRACT:
In a system provided with an optical head, a laser beam produced from a laser unit 30 is converged by an objective lens 42 and reflected from a light reflecting layer 14 of an optical disk 2. The reflected laser beam is converged by a projection lens 62 and is projected to photosensitive regions of a photodetector 48. The photosensitive regions have an area smaller than a portion of a beam spot which is formed outside the regions when the objective lens 42 reaches a predetermined defocusing state. Photo signals generated from the photodetector 48 are added and processed by a focusing signal generator 68. A focus signal generated from the focusing signal generator 68 is supplied to a voice coil driver 72 so that the objective lens 42 is moved to a position which is in a just-focusing state by a voice coil 44 which is driven by the voice coil driver 72. When the objective lens 42 reaches the predetermined defocusing state and the level of the added photo signal falls within a predetermined level, a CPU 74 generates a off-signal to open a switching circuit 70 so that a connection between the focusing signal generator 68 and the voice coil driver 72 is disconnected.

REFERENCES:
patent: 4517666 (1985-05-01), Ando 369 45

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