Eccentricity error correction method for angle detector and robot system

An eccentricity error correction method for an angle detector in a robot system that includes a motor, an arm that is connected to an output shaft side of the motor via a reducer, an input shaft angle detector that detects a rotation angle of the motor as an input shaft angle, and an output shaft angle detector that detects a rotation angle of the arm as an output shaft angle, the eccentricity error correction method correcting eccentricity error that occurs due to eccentricity in the output shaft angle detector, the eccentricity error correction method comprising:

• detecting the output shaft angle in at least three measurement positions at which an effect of an own weight of the arm on a rotation direction is suppressed;
• determining a difference between an arm angle value at each measurement position and the output shaft angle detected at each measurement position as an eccentricity error;
• determining an error curve as a function of the arm angle value by approximating the eccentricity error at each measurement position with a sine wave of which a single cycle is a single rotation of the arm, the error curve indicating a relationship between the arm angle value and the eccentricity error;
• determining a correction formula that associates the output shaft angle and the arm angle value using the error curve;
• and
• determining a correction value corresponding to the detected output shaft angle based on the correction formula and correcting the eccentricity error when the arm is rotated.