| 摘要 |
An automatic optical focusing system suitable for apparatus for reading optically an information track on a record with the aid of a read beam (typically a video disc player) serves to keep the read spot automatically focused at the plane in which the information lies during playing of a record. The system comprises an optical focusing device, an oscillating optical element which cooperates with the radiation beam and which can effect high-frequency oscillations so as to cause high frequency oscillations of small amplitude about the coarse position of the focusing plane, an electromagnetic drive system for the high frequency drive of the oscillating optical element, a radiation-sensitive detector which responds to the radiation beam after it 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, and said mirror performs 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 performs high frequency bending oscillations between a convex and a concave shape. |
