Automatic focus control unit

Abstract

Abstract PURPOSE: To secure the accurate automatic control for the focus regardless of the shift of the reflected laser beam by distributing the optical detector, comprising three light reception parts which receive the reflected laser beam spot with three divisions in the same direction, in such way that the dividing direction of the spot may be vertical to the reproduction information track direction. CONSTITUTION: The laser beams given from laser beam source 61 are condensed onto information recording disk through object lens 62 and then condensed only in one direction via cylindrical lens 65 and through beam splitter 64 to be converted into the astigmatic luminous flux. And optical detector 71 is provided on the optical path to give the three divisions to the laser beam spot in the same direction for reception 71a, 71b and 71c each, which are then distributed so as to be vertical to the reproduction information track direction. The output is added 72 between reception parts 71a and 71c, and then the difference is obtained between the both output through differential amplifier 73 along with the output of reception part 71b. The difference of these output is then supplied to lens driving circuit 74 to move lens 62 close to or away from disk 63 in accordance with the output of amplifier 73, performing the focusing. COPYRIGHT: (C)1980,JPO&Japio

Inventors

• 👤 Takahisa Aikawa
• 👤 Shigeo Tsuji

Bibliographic Details