ANALYSIS OF GEOMETRIC DEVIATIONS OF FREE-FORM SURFACES DETERMINED IN COORDINATE MEASUREMENTS

摘要

In coordinate measurements, local geometric deviations of free-form surfaces are determined as normal distances of these points from the nominal surface (the CAD model). Different sources of errors in the manufacturing process result in deviations of different characters, deterministic and random. The different nature of geometric deviations may be the basis for separating the random and deterministic components in order to compute deterministic geometric deviations and further to introduce corrections to the processing program. The paper suggests applying the methods of analyzing spatial data to research on geometric deviations of free-form surfaces in order to test the existence of spatial autocorrelation. Identifying spatial correlation of measurement data proves the existence of a systematic, repetitive processing error. In such a case, the spatial modelling methods may be applied to fitting a surface regression model representing the deterministic deviations. The first step in model diagnosing is to examine the model residuals for the probability distribution and then the existence of spatial autocorrelation.