(US5173893-A)      The disc player includes a casing having a disc inserting opening and a turntable driven by a spindle motor. A clamper arm operating mechanism is provided for a clamper arm in cooperation with the turntable, a centering mechanism guiding a disc from the disc inserting opening onto the turntable. The centering mechanism includes a pair of centering arms (13,14), each having at distal end portions contact portions which are to be brought into contact with a circumferentially movable at a predetermined distance in the disc inserting opening. A lever (42) detects a condition that the disc is laid on the turntable, a disc double insertion preventing lock linkage (43,57) preventing another disc from being inserted into the casing through the disc inserting opening when the first-mentioned disc is already located on the turntable. The double insertion preventing lock linkage cooperates with the centering mechanism.    USE -   To prevent double disk insertion at the reading head of a CD (compact disc) player.    (GB2230639-B)      A disc player comprising: a casing having a disc insertion opening; a turntable driven by a spindle motor; a clamper arm operating means for operating a clamper arm in cooperation with the turntable; a centering means for guiding a disc from the disc insertion opening onto the turntable and including a pair of centering arms each having, at distal end portions thereof, contact portions which, in use, are brought into contact with a circumferential edge of the disc, the centering arms being pivotally movable at a predetermined distance in the disc insertion opening; detecting means for detecting location of the disc at a predetermined position within the casing; and double insertion preventing lock means for preventing another disc from being inserted into the casing through the disc insertion opening when the first mentioned disc is already located at the predetermined position within the casing, the double insertion preventing lock means being in cooperation with the centering means.    (DE4006584-C2)      A record player for records of different dias. has a sensor to detect a record on the turntable. The sensor (41) is mechanically connected to a locking mechanism (58) which stops centering arms (13,14) from spreading outwards when the sensor detects a record on the turntable.    Pref. a centering lever (15) coupled to the centering arms prevents the arms from spreading outwards when the edge of a recorded (106) touches only one of the contact elements (18,19) on the arms. Pref. a lever assembly has one lever (42) coupled to the sensor and a second lever (43) carrying the locking mechanism (58).    ADVANTAGE -   Total security against inserting second record when one is already in machine.