Self-calibratable rotary encoder

Abstract

In the National Metrology Institute of Japan (NMIJ)/AIST, a rotary encoder calibration system was developed as the national primary standard for an angle, and a highly precise standard calibration service has been supplied from 2003. The source of uncertainty that influences most greatly in calibration is the attachment error (eccentricity) of a rotary encoder. Even if users get the calibrated rotary encoder, the error when attaching in using apparatus cannot be estimated. In NMIJ, we developed the new rotary encoder that can be calibrated by rotary encoder itself. Its mechanism is very simple; some reading heads are arranged at the equal angle interval around a scale disk. The calibration curve that contains not only all graduation lines deviation but eccentricity can be obtained by analyzing in series the signals acquired from heads. In order to check the performance of this epoch-making rotary encoder, we set up this system on the national primary standard and compared this self-calibration data with the data by using the primary standard system. The accuracy for 0.5′′ or less could be acquired. Since this method is applicable also to a small rotary encoder, it is expected that the self-calibratable rotary encoder be used in many angle control instruments.