Servo control system having function of measuring characteristic of learning controller

A servo control system for a machine tool having a feed shaft driven by a servomotor, comprising:

• a position command generator for generating a position command to drive the feed shaft in a specific repeated operation pattern;
• a position detector for detecting the position of the feed shaft;
• a positional deviation obtainer for obtaining a position command value generated by the position command generator and a position detection value detected by the position detector, and calculating a positional deviation that is the difference between the position command value and the position detection value;
• a position control loop including the position command generator, the position detector, and the positional deviation obtainer;
• a band limiting filter for attenuating a high frequency component of the positional deviation outputted from the positional deviation obtainer;
• a dynamic characteristic compensation element for advancing the phase of the positional deviation outputted from the band limiting filter;
• a learning controller including the band limiting filter and the dynamic characteristic compensation element;
• a sine wave sweep input unit for performing a sine wave sweep to the position control loop;
• and
• a frequency characteristic calculator for estimating the gain and phase of position control loop input and output signals from the output of the position control loop when sine waves are inputted to the position control loop, wherein
• the frequency characteristic calculator calculates an evaluation function that indicates the characteristic of a position control including the learning controller based on the measurement value of the frequency characteristic of the position control loop, the band limiting filter, and the dynamic characteristic compensation element.