AUTOMATIC OPTICAL FOCUSING SYSTEM

摘要

An automatic optical focussing system suitable for a video disc player comprises an optical focussing device with an objective which is moved to and fro at high frequency in the direction of its optical axis by electrodynamic drive means. The resultant high frequency component thus superimposed on the signal which has been modulated by the information track of the video disc is employed for automatic control of the position of the objective. For the sake of low power consumption the objective is connected to an oscillation compensation element by means of at least one resilient element, for example a circular plate which compensation element is axially movable relative thereto and, together with the objective and the resilient element, constitutes a mechanical resonant system. On the resonant system a piezo-electric acceleration transducer may be mounted with the aid of which the mechanical resonant system can be included in a selfoscillating loop.