Analysis of Accuracy and Measuring Range of Dual Absolute Encoder System

Abstract

As small-sized absolute encoders are currently being installed in small and high-power motors, a dual absolute encoder (DAE) system comprising two absolute encoders can now be constructed. The two absolute encoders in the DAE system are installed on a motor shaft and an output shaft; further, the two shafts are connected by a reduction mechanism. The DAE system will replace an ordinary dual encoder system in the future, because of its high accuracy and extended measurement range. In this paper, an analysis of the accuracy and measuring range of DAE system is presented. Index numbers that are calculated from readings of absolute encoders have a one-to-one correspondence with the number of rotations of the two shafts. Their positions are calculated based on the index number and extended greatest common factor ( EGCF ) of 1 and the inverse of reduction ratio. The error in the index number is investigated and maximum error tolerance of an absolute encoder that guarantees correct position estimation is proposed. Experiments are conducted separately in narrow and wide measurement ranges. Each range exhibits different types of errors, small random and large periodic errors. The large periodic errors are compensated using harmonic function model. The small random errors are utilized to calculate the maximum error tolerance and minimum resolution of the absolute encoder at the output shaft. The experimental results demonstrate that the final error decreases and the measurement range is extended to 1/ EGCF in the DAE system compared with the ordinary dual encoder system.