Servo controller

A servo controller, comprising:

• a reference model unit which inputs a reference to generate a model output and a model input;
• a feedback control unit which inputs a control output, which is output from a plant, and the model output to generate a feedback input so that the control output follows the model output;
• and
• an adder which adds the model input and the feedback input to generate a control input to be input to the plant,
• wherein the reference model unit comprises:
• a mathematical model which simulates characteristics of the plant, and generates the model output and a state variable from the model input;
• a model input memory which inputs the model input and which outputs, as a past model input, a stored signal of the model input of past;
• a model controller which inputs the reference, the state variable, and the past model input to generate the model input;
• and
• a model controller determining unit which determines the model controller based on the reference, the state variable, and the past model input.