THE ESTIMATION OF MEASUREMENT UNCERTAINTY OF SMALL CIRCULAR FEATURES MEASURED BY COORDINATE MEASURING MACHINES

This paper examines the measurement uncertainty of small circular feat ures as a function of the sampling strategy; i.e., the number and dist ribution of measurement points. Specifically, we examine measuring a c ircular feature using a three-point sampling strategy in which the ang ular distance between the points varies from widely spaced, 120 degree s, to closely grouped, a few degrees. Both theoretical and experimenta l results show that the measurement uncertainty is a strong function o f the sampling strategy. The uncertainty is shown to vary by four orde rs of magnitude as a function of the angular distribution of the measu rement points. A conceptual framework for theoretically estimating the measuring uncertainty is described, and good agreement with experimen ts is obtained when the measurements are consistent with the assumptio ns 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. Published by Elsevier Science Inc.