| 摘要 |
PROBLEM TO BE SOLVED: To correctly measure linear velocity by reading positional information on the position where a disk is rotated by the prescribed number of revolution after reading positional information on a prescribed position of the disk in which signals are recorded at a constant linear velocity and obtaining the linear velocity of the disk from the time during the period and the length of a signal track during the period. SOLUTION: Positional information which is recorded in a disk 1 is read, and whether an optical type pickup 4 exists in a prescribed position or not is judged. When the pickup 4 does not exist in a prescribed position, the pickup 4 is moved to a prescribed position by a pickup feeding mechanism. When the pickup exists in the prescribed position, signal reading is started, a spindle motor 3 is rotated by the control operation of a spindle motor control circuit 11, the number of revolution is controlled at a constant. When signal reading is executed, positional information recorded in the position of the disk 1 is read when the number of revolution of the disk becomes the prescribed number based on the signals outputted by a revolution number detecting circuit 12.
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