Determining feedback gain

A feedback control method comprising:

• a first step of provisionally determining a predetermined value of a feedback gain;
• a second step of executing feedback control by using the provisionally determined feedback gain;
• a third step of detecting an error between a designated value and an actual value of the subject of control during the execution of said second step;
• a fourth step of calculating a first evaluation value, a second evaluation value and a third evaluation value, said first evaluation value relating to stability of control, the second evaluation value relating to off-set error of control and the third evaluation value relating to a response control according to the error detected in said third step;
• a fifth step of executing said second to fourth steps repeatedly a plurality of times after provisionally determining a new feedback gain value different from the previous value;
• a sixth step of calculating a first feedback gain value for the proportional gain from the first evaluation value, calculating a second feedback gain value for the integral gain from the second evaluation value, and calculating a third feedback gain value for the differential gain from the third evaluation value which provides for a suitable evaluation value according to the relation between the feedback gain value and the evaluation value obtained through the execution of said fifth step;
• and
• a seventh step of executing a feedback control on the subject to be controlled by using the first, second and third feedback gain values obtained in the sixth step.