Control device for machine tool

A control device for a machine tool, comprising:

• a fluctuation command calculation unit configured to calculate a fluctuation command based on a speed command for a main spindle motor of the machine tool and a fluctuation condition for causing a rotation speed of the main spindle motor to periodically fluctuate;
• and
• a speed control unit configured to control the rotation speed of the main spindle motor based on the speed command and the fluctuation command,
• wherein the fluctuation command calculation unit being configured to calculate, when the fluctuation condition is changed, the fluctuation command in which an amplitude of the rotation speed that periodically fluctuates and/or a frequency of the rotation speed that periodically fluctuates gradually changes, and
• wherein the fluctuation command calculation unit is configured to compare, when the fluctuation condition is changed, values of the amplitude of the rotation speed that periodically fluctuates and/or the frequency of the rotation speed that periodically fluctuates before and after the change, and to calculate, when the value after the change is greater than the value before the change, the fluctuation command in which the amplitude of the rotation speed that periodically fluctuates and/or the frequency of the rotation speed that periodically fluctuates gradually increases, and to calculate, when the value after the change is smaller than the value before the change, the fluctuation command in which the amplitude of the rotation speed that periodically fluctuates and/or the frequency of the rotation speed that periodically fluctuates attenuates.