| 摘要 |
PROBLEM TO BE SOLVED: To surely make change over from rough control to fine control when executing the fine control of number of revolutions by using an ATIP signal after the rough control of the number of revolutions is executed by using the signals generated by operation of a spindle motor. SOLUTION: The rough control of the number of revolutions is executed by calculating the difference between the results of counting obtained by counting FG pulses bases on the rotational driving motion of the spindle motor 3 and the target count value based on the target number of revolutions and forming the rough control signal at a rough rotation control section 19. When the control is shifted to the dine control using the ATIP signals from the rough control, the result of the calculation of the difference obtained by a fine rotation control section 18 and the result of the computation obtained by bit computation of the target count value are compared and the ratio of the result of the differential calculation to the result of the target counting is decided and a changeover timing signal is formed. A changeover control signal is outputted from a CPU 21 to a rotation control changeover section 20 in such a manner that the rough control in the fine rotation control section 18 is changed over to the fine control in a rough rotation control section 19.
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