Automatic High Precision Calibration System for Rotary Encoder

This paper describes the automatic calibration system for rotary encoders which is installed at the NRLM (National Research Laboratory of Metrology). The system consists of two rotary encoders, the precise rotating mechanism, the division mechanism, the error measurement circuit and the computer. The detecting methods of the slight angular differences are the time-conversion method and the counter method. Their resolutions are 0.002" at 5 rpm and 0.072" respectively. The two encoders are calibrated by the self-checking method so called the Equal-Division-Averaged Method without any reference encoder. By the preliminary examination, the all graduations of the two encoders can be calibrated and it is verified that their accuracy is approximately ±0.5" and its repeatability is ±0.02".