Calibration of Angle Artifacts and Instruments using a High Precision Angle Generator

Various angle artifacts and instruments are used in precision engineering, and their calibrations are important to ensure high accuracy and reliability in angle metrology. In this paper, we present uncertainty analysis and calibrations of several angle artifact and instruments to evaluate the performance of the high precision angle generator which is newly developed as the primary angle standard of Korea Research Institute of Standards and Science (KRISS). The configuration of the angle generator is explained shortly, which uses multiple ultrasonic motors and a self-calibratable encoder adopting the equal-division-averaged (EDA) method. The expanded uncertainty (k = 2) of the angle generator, which are mainly contributed by nonlinearity and scale error of a divided circle, was evaluated less than 0.03″. The calibration result of a high precision angle encoder was compatible with that of manufacturer within the expanded uncertainty of calibration, 0.04″. Using the calibration result of an electronic autocollimator, the nonlinearity error of the angle generator was analyzed and a calibration method is proposed to reduce the nonlinearity error related to the signal period of the divided circle. In the calibration of a 36-face optical polygon, we applied the complete closure method to obtain the error of the angle generator separately, and its magnitude was less than 0.015″, which is less than half of the estimated uncertainty of the angle generator.