Servo motor controller having self-measuring function and self-monitoring function of mechanical stiffness

A controller that controls a servo motor for driving a machine tool, comprising:

• a speed command generating unit configured to generate a speed command value of the servo motor;
• a speed detecting unit configured to detect a speed of the servo motor;
• a torque command generating unit configured to generate a torque command value of the servo motor on a basis of the speed command value and the detected speed;
• a sine wave generating unit configured to generate a sinusoidal disturbance value;
• a frequency response calculating unit configured to add the sinusoidal disturbance value generated by the sine wave generating unit to the speed command value, thereby calculating a frequency response on a basis of output from a speed control loop when the sinusoidal disturbance value has been input to the speed control loop including the torque command generating unit and the speed detecting unit;
• a resonance frequency detecting unit configured to detect a resonance frequency which is a frequency at which a gain of the calculated frequency response is maximized;
• a resonance frequency storing unit configured to store the resonance frequency detected by the resonance frequency detecting unit;
• at least one filter that attenuates a specific frequency band component included in the torque command value;
• and
• a resonance frequency comparing unit configured to measure stiffness of a machine tool on a basis of the resonance frequency stored in the resonance frequency storing unit, and adjusts the filter with respect to the resonance frequency.