Controller and control method for machine tool capable of changing motion depending on motor temperature

A controller of a machine tool having a spindle motor for driving a spindle and a feed shaft motor for driving a feed shaft, the controller comprising:

• a numerical controlling part which transmits an operation command to the spindle motor and the feed shaft motor;
• an acceleration/deceleration judging part which judges as to whether the spindle motor is in an acceleration/deceleration state;
• a current detecting part which detects a current value flowing in the spindle motor;
• a first temperature estimating part which estimates a first amount of change in temperature of the spindle motor due to the current flowing in the spindle motor when the spindle motor is in the acceleration/deceleration state of operation;
• a second temperature estimating part which estimates a second amount of change in temperature of the spindle motor due to the current flowing in the spindle motor when the spindle motor is in a steady state of operation;
• a motor temperature obtaining part which obtains a total amount of change in temperature of the spindle motor, based on the first amount of change in temperature and the second amount of change in temperature;
• and
• a comparing part which compares the first and second amounts of change in temperature;
• wherein when the total amount of change in temperature exceeds a predetermined threshold, the numerical controlling part is configured to:
• 1) change the operation command of the spindle motor, when the comparison of the first and second amounts of change in temperature indicates that the first amount of change in temperature exceeds the second amount of change in temperature multiplied by a coefficient,
• 2) change the operation command of the feed shaft motor, when the comparison of the first and second amounts of change in temperature indicates that the second amount of change in temperature exceeds the first amount of change in temperature multiplied by the coefficient, and
• 3) change the operation command of the spindle motor and the feed shaft motor, when the comparison of the first and second amounts of change in temperature indicates that the first amount of change in temperature does not exceed the second amount of change in temperature multiplied by the coefficient and the second amount of change in temperature does not exceed the first amount of change in temperature multiplied by the coefficient.