Servo controller

A servo controller used in a machine tool having a feed axis driven by a servo motor, comprising:

• a speed command creation unit that creates a speed command value of the servo motor;
• a torque command creation unit that creates a torque command value of the servo motor;
• a speed detection unit that detects a speed of the servo motor;
• a speed control loop formed by the speed command creation unit, the torque command creation unit, and the speed detection unit;
• a speed control gain which is a control gain of the speed control loop;
• a sinusoidal disturbance input unit that performs sinusoidal sweeping on the speed control loop;
• an actual frequency characteristics calculation unit for estimating a gain and a phase of an input/output signal of the speed control loop from an output of the speed control loop when a sinusoidal wave was input to the speed control loop;
• a reference characteristics changing unit that changes a characteristic formula that characterizes reference frequency characteristics of the speed control loop;
• a reference frequency characteristics calculation unit that calculates reference frequency characteristics for characteristics designated by the reference characteristics changing unit;
• and
• a control gain adjustment unit that adjusts a speed control gain on the basis of an actual frequency response calculated by the actual frequency characteristics calculation unit and the reference frequency characteristics calculated by the reference frequency characteristics calculation unit, wherein
• the sinusoidal disturbance input unit changes a frequency sequentially, the reference frequency characteristics calculation unit calculates the reference frequency characteristics for the characteristics designated by the reference characteristics changing unit sequentially for respective frequencies, and the actual frequency characteristics calculation unit calculates actual frequency characteristics of a control system sequentially for respective frequencies, and
• the reference frequency characteristics calculation unit stores the characteristic formula of the reference characteristics changing unit when the reference frequency characteristics and the actual frequency characteristics match most closely.