| 摘要 |
PROBLEM TO BE SOLVED: To detect accurately linear velocity of a disk by simple constitution. SOLUTION: An optical pickup is moved to an arbitrary measurement position (S2), rotation speed of a spindle motor 4 is held constant (S3), in a state in which a tracking servo is turned of (S4), a pulse signal reversing with timing at which a frequency of a tracking error signal is minimized by that a tracking error signal is frequency/voltage-converted by a detecting circuit is obtained, a period T of this pulse signal is outputted by a system controller as a rotation period (t) (=T) of MD (S6), the outputted rotation period (t) is compared respectively with each reference rotation period t1, t2, t3 stored in its incorporated memory (S9), and it is judged that actual linear velocity V of MD is approximate to which of reference linear velocity V1, V2, V3.
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