Automatic dithering optical focusing system using an oscillating mirror in the path of the radiation beam

Abstract

An automatic optical focusing system suitable for an apparatus for reading an information track on a record carrier with the aid of a read spot which is focused in an imaginary focusing plane and which is formed by a radiation beam which is produced by a radiation source, more in particular suitable for a video disc player which employs optical reading, and serving for automatically keeping the read spot focused at the plane in which the information is disposed (information plane) during playing of a record carrier, comprising an optical focusing device, an oscillating optical element which cooperates with the radiation beam and which can effect high-frequency oscillations so that a high frequency oscillation of small amplitude about the coarse position of the focusing plane is obtained, an electromagnetic drive system for the high-frequency drive of the oscillating optical element, a radiation-sensitive detector which responds to the radiation beam which has been modulated by the information track, and a control circuit for producing a control signal which depends on the output signal of the detector, which control signal is applied to the control coil of the optical focusing device. The oscillating optical element is constituted by an oscillating mirror which reflects the radiation beam which mirror effects high-frequency bending oscillations of which at least a component has the direction of the reflected part of the radiation beam. Preferably, the oscillating mirror is round and effects high frequency bending oscillations between a convex and a concave shape.

Dependencies are inferred from the claim text.