Track follower system employing an optical scanner with automatic

Abstract

A radially acting track follower system is provided with an optical scanner pickup for an audio or video record playback apparatus. The system generates three light spots disposed on a line with a movable phase grating (diffraction grating) and the three spots can be adjusted relative to the tangent at the track pickup scanning location. The middle or main light spot serves to provide scanning of the track signal information. The two outer or auxiliary light spots serve to provide readjustment. They are displaced radially oppositely to each other by equal amounts and are disposed at equal distances from the middle spot. The light intensity of the outer spots is picked up by detectors and processed into control signals. These are used as a drive for the phase grating, which can be controlled around its center point and the rotation axis of the phase grating coincides with the light beam, which can be provided by a semiconductor laser. The drive can operate electrodynamically or can be provided by a piezoelectrical torsion converter. The control signal can have for example 10 kilohertz and is superposed to the control signal for the drive and it improves the sensing and following properties of the system without the disadvantage of the superposition of the scanned information signal with the control signal.