Methodical uncertainty in the two-point measurement of parts prismatic elements linear dimensions

摘要

The article is devoted to the topical problem of the reliability of measurements of geometrical specifications of technical products. The purpose of this article is to improve the quality control of the linear dimensions of the parts by the two-point measurement method. The goal of the article is the study of advanced methodical uncertainties of measurement of linear dimensions of plane-parallel prismatic elements. The method of research is geometric modeling of deviations of the element surfaces form and position in the rectangular coordinate system. The research was carried out for various executive elements with regard to their information content corresponding to the classes of kinematic pairs in the theory of mechanics and the number of constrained degrees of freedom in function of the basic elements. Prismatic elements with informative content 3, 2, 1 and θ (zero) were studied. Uncertainty assessment of two-point measurements were made by comparing the measurements results of linear dimensions and functional dimensions of the element maximum and minimum material constrained by the limits of maximum and minimum. As a result of studies of the two-point measurements accuracy, it is found that the methodical uncertainty is formed when measuring the average size of elements for all types of form deviations. The two-point measurement method cannot account for deviations of the location dimension of the element and therefore its use for items with less than the maximum informativeness creates unacceptably large methodical uncertainties of measurement the maximum, minimum and medium linear sizes. The same methodical uncertainties occur under the arbitration control of the parts linear dimensions by the limit two-point gauges.