Servo system for reading from a disc-shaped record carrier containing signals coded in optical form

Claim 1

Apparatus for reading a disc-shaped record carrier of the type wherein video and/or audio signals are recorded in tangential tracks, the apparatus being of the type wherein an optical system directs a light beam from a light source to the record carrier, and images the information from the record carrier on a radiation detector means for converting the optical image into an electrical system, wherein position detector means for measuring the radial position of the optical system relative to a desired track provides position signals to a coarse position feedback loop for moving the optical system radially with respect to the record carrier and further provides position signals to a fine position feedback loop, wherein the fine position feedback loop controls a beam deflection means pivotally mounted in the path of the light beam of the optical system for selectively angularly redirecting said beam with respect to said radiation detector means in response to said position signals from said fine position feedback loop, the improvement wherein switching means are provided in said fine position feedback loop for selectively opening said fine position feedback loop and for providing a preselected auxiliary control signal to said beam deflection means thereby angularly deflecting said beam by a predetermined amount and for subsequently reconnecting said fine position feedback loop.