The estimation of measurement uncertainty of small circular features measured by coordinate measuring machines

Abstract

This paper examines the measurement uncertainty of small circular features as a function of the sampling strategy; i.e., the number and distribution of measurement points. Specifically, we examine measuring a circular feature using a three-point sampling strategy in which the angular distance between the points varies from widely spaced, 120°, to closely grouped, a few degrees. Both theoretical and experimental results show that the measurement uncertainty is a strong function of the sampling strategy. The uncertainty is shown to vary by four orders of magnitude as a function of the angular distribution of the measurement points. A conceptual framework for theoretically estimating the measuring uncertainty is described, and good agreement with experiments is obtained when the measurements are consistent with the assumptions of the theoretical model. This paper is an expansion of a previous internal report 1 with additional material on analog probes and probe lobing models.