| 摘要 |
An acceleration command calculator 22 calculates an acceleration command "as" based on an output torque Tmb of the spindle motor applied when the rotational speed is less than or equal to a base rotational speed and an inertia Jm+Jl of the overall spindle. A switching speed calculator 23 calculates a control mode switching speed Vs based on the acceleration command "as". A control mode switching switch 5 switches from a speed control mode to a position control mode when the motor speed Vm becomes less than or equal to the control mode switching speed Vs, to stop the spindle at a desired rotational position. The control mode switching speed Vs may be a value calculated using the following equation: Vs=60×(amax×0.5)1/2, where a maximum acceleration that can be achieved at this time is represented by a max.
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