Analysis of the dynamic method of line scale detection parameters

Abstract

The main sources of measurement uncertainty in long-stroke line scales are line detection errors and external factors, especially temperature effects. The number of calibration errors of this type increases with the lengthening of the calibration time. Therefore, dynamic methods of line scale detection for modern long-stroke line scale comparators are used [1, 2, 3, 7]. The article describes the dynamic method of line scale detection by means of an optical microscope equipped with a photosensitive cell matrix and a line scale detection algorithm. A measurement uncertainty estimate of the dynamic method for calibration of long-stroke line scales has been created [4, 5, 7]. The method’s error correlations with the detection rate, number of rated lines, measuring rate, and exposure delay are described. Optimal values of these parameters are estimated. When applying the dynamic method to calibration of long grating scales under the existing industrial conditions, evenness of illumination becomes an important factor of accuracy of the detection of line position, which has been one of the main sources of inaccuracy in conventional measurements. Analytical and experiential distributions of illumination were tested as a function of exposure time and pattern influence to the calibration error. The method of reducing this error was analyzed, implemented and tested on the longstroke line scale comparator, which has been developed and realized at JSC Precizika Metrology in cooperation with the Kaunas University of Technology and the Vilnius Gediminas Technical University.