Measurement and compensation of errors in absolute encoder using dual absolute encoder system
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TECHNICAL PAPER
Measurement and compensation of errors in absolute encoder using dual absolute encoder system Kyung-min Lee1
•
Taehyeong Gu2 • Young-bong Bang3
Received: 30 October 2019 / Accepted: 9 June 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The dual absolute encoder (DAE) system is a measurement system for a motion control system that comprises two absolute encoders and one reduction mechanism. In terms of accuracy and measuring range, DAE is superior to ordinary dual encoder systems, which comprise one incremental encoder, one absolute encoder, and a reduction mechanism. In this study, we focus on the error measurement and compensation using DAE system. There have been many studies to measure and compensate for the errors in measuring systems. However, this typically demands high precision equipment to measure the errors, and attaching and detaching the equipment affects the errors. We measured the errors in the absolute encoder by using the DAE systems solely. The measured errors are modeled using harmonic functions and compensated for by using the modeled errors. The experimental results reveal that the maximum errors and mean absolute errors decrease by oneseventh and one-twelfth, respectively, after error compensation. As a result, we can compensate the errors in the encoders with the encoder system, itself. Additionally, the modeled errors in a DAE system are observed to remain constant even when changing the reduction ratios between two absolute encoders. Once the errors are measured and modeled in the DAE system, the modeled errors can be applied to a DAE system with a different reduction ratio for error compensation.
1 Introduction An encoder is a device that measures the angular position of the shaft. The main performance indicator of the encoder is its resolution, which defines the minimum angular displacement that the encoder can detect. The resolution is expressed in bits, and N bit indicates that the minimum detectable angle is 360 °. The encoders are classified into 2N two types according to their disk patterns (Danapar 2003). One is an incremental encoder and the other is an absolute encoder. The incremental encoder has a simple structure, high resolution, and low price compared to the absolute encoder. Thus, many systems adopt incremental encoders to measure the position of the shaft. However, an incremental encoder only detects the change of angle and cannot & Young-bong Bang [email protected] 1
School of Mechanical Engineering, Chungnam National University, Daejeon, Korea
2
Department of Neurosurgery, University of Texas Health Science Center at Houston, Houston, USA
3
Advanced Institute of Convergence Technology, Seoul National University, Suwon-si, Korea
measure the absolute position. If a z-phase output exists on the incremental encoder, the absolute position can be measured using the z-phase output, but this is only possible when the incremental encoder rotates until a point at which the z-phase is
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