Investigation of the measurement errors formation in optical linear encoders

Abstract

The thesis investigates the displacement measurement errors of the linear encoder and the causing factors. To achieve the thesis objectives, the theoretical and experimental research of the linear encoder behavior was performed under different operating conditions, including thermal effects, mechanical vibration, and different scanning speeds. Analyzed and systematized results were used to develop methods for error compensation and offer possible technical solutions to improve the performance of linear encoders. The dissertation consists of an introduction, analytical literature review, discussion of the research methodology, investigation results and conclusions, and four appended scientific articles. The literature review systemized information about the optical linear encoders and their performance. The section on research methodology presents theoretical and experimental methods used to study the impact of different environmental effects on the measurement error formation in linear encoders. The third chapter briefly discusses the results obtained in each of the appended articles with the intention of relating them to the overall objectives and general conclusions of the thesis. Based on analytical calculations, digital finite element analysis, and experimental research, Article 1 determines the mathematical models of thermal errors that are used for real-time compensation. Article 2 presents an experimental realization of the real-time thermal and geometric error compensation approach for an optical encoder achieved by using a field-programmable gate array (FPGA) computing platform. Article 3 presents the developed methodology for the estimation of linear encoder sub-divisional errors and the results of the experimental investigation based on the harmonic analysis of estimated errors. Article 4 reveals the linear encoder behavior under mechanical vibration, determining the most dangerous resonant frequencies and performing the modal analysis by using the finite element method. The appended scientific articles were published in four peer-reviewed scientific journals listed in the Clarivate Analytics Web of Science database with an impact factor. The other four related articles are printed in scientific journals listed in the Clarivate Analytics Web of Science database without the impact factor and other international databases. The results of the research were presented at three international conferences.