The Accuracy Research of the Exposed Incremental Encoder Based on Image Formation Method for SEMS Applications

Problem statement Linear and angular optoelectronic encoders are among the most precise and high-speed displacement measurement devices for complex control systems. High accuracy and high performance, electromagnetic resistance, and ability to operate in a fast-changing environment determined usage of optical encoders in many SEMS applications. The increasing requirements on SEMS for precise and accurate displacement measurement modules is one of the most demanded topics of modern research. The need to solve problems of accuracy improvement determines the relevance of studying new data processing methods. Purpose of research The purpose of the research is theoretical and experimental study of the construction and error estimation of incremental optical encoder based on image formation method. The study examines the influence of design features and data processing algorithms on the measured position error of incremental optical encoder. Methods The article discusses the specifics of the incremental optical encoders design based on image formation method. Algorithms for output data processing are considered with respect to real-time applications of adaptive SEMS. Data processing algorithms such as parabola approximation and energy center calculation are presented. Error estimates were obtained for each of the listed algorithms. Results Computer modeling and physical evaluation were used for the experimental study. The computer model was implemented and evaluated in Zemax and MATLAB. Physical evaluation was performed on a prototype of linear displacement encoder. Prototype consists of a lens f′ = 3.6 mm, 5 × 5 mm beam-splitting cube, sensor OV5640 (pixel size: 1.4 μm × 1.4 μm, pixel amount: 2592 × 1944), FPGA-based computing module with Artix XC7A35T chip. Automated measuring stand based on the Thorlabs LTS300/M linear translator (displacement step from 4 μm, displacement range up to 300 mm) and the XD Laser XD6 LS interferometer (accuracy 0.5 μm/m) was built. For the energy center calculation algorithm 9.85 μm resulting error was obtained at a distance 10 mm. For the parabola approximation algorithm 4.28 μm resulting error was obtained at a distance 10 mm. Practical significance The considered algorithms, prototype and developed measuring stand can be used for development of SEMS modules for precise detection of robot joints position. The accuracy research of evaluated displacement measurement methods could be used as a reference for selection of electronic interpolation methods.