Data face detector for optical data storage disc - indicating failure to focus laser beam on data track using flip=flop arid RC delay when wrong face is exposed

摘要

The compact disc (10) is in the form of a metallic plate (11) with data (12) on one face which is protected by a transparent plastic film (13). It is examined by a laser beam (15) focussed by a movable lens (16). The lens is repositioned in response to signals from an electronic control circuit (17) coupled to a flip-flop (18) with an RC delay circuit in its connection to a switch (19), operated by insertion of the disc. If the disc is inserted upside down and no data can be read by the laser beam, the flip-flop (18) produces a control signal (S) indicating that no satisfactory focus has been achieved during the delay interval of e.g. 5 sec. The delay circuit may be replaced by a counter of unsuccessful attempts at focussing.