Super-accurate angular encoder system with multi-detecting heads using VEDA method

An angular encoder that can detect angular motion with ultrahigh accuracy is needed to enhance the precision for the angular motion axis of computer numerical control (CNC) machine tools. Although a self-calibration method based on mounting multiple detecting heads has been proposed, it is impractical because the number of detecting heads needed to calibrate higher-order terms of the error components corresponds to the order. This paper presents a new self-calibration method for an angular encoder that uses fewer detecting heads. The method was compared with existing methods via simulation to confirm its feasibility. A prototype angle encoder was produced with six detecting heads to calibrate error component terms up to the 30th order. The error curves of the six sensor heads of the prototype encoder system were used to achieve a motion detection accuracy of ±0.07 s.