Optical reproducing device having focus servo system

Abstract

An optical reproducing device for reproducing information from a rotating record medium includes a focus control system for displacing a focusing lens perpendicular to the plane of the record medium. A light beam is conducted through the focusing lens on to the record medium. A capture range search system is provided to move the focusing lens at a substantially constant speed from a rest position until it is positioned within the capture range of the focusing control system. The capture range search system includes a bridge circuit for sensing the moving speed of the focusing lens. The bridge circuit includes a moving coil of a drive motor for said focusing lens and a variable impedance element. The bridge circuit is balanced by controlling the variable impedance element when the lens is at the rest position.