Probe Radius Compensation and Fitting Errors in Cad-based Measurements of Free-form Surface: a Case Study

− the present paper will present problems connected with accuracy inspection of free-form surfaces, performed with coordinate measuring machines equipped with touch measurement probes. The most important among them are, apart from the number and distribution of measurement points on a surface, errors caused by the probe radius compensation and determining the coordinate system. A theoretical analysis as well as the results of tests on the influence of compensations errors and errors in fitting the data to a CAD model on the results of computation of the points on the milled free-form surface will be presented. Considering any of these factors separately makes it impossible to obtain the complete picture of their mutual dependence. It turns out that applying compensation, leading to errors in determining measurement points, influences the uncertainty of the position and orientation of the coordinate system determined by fitting the compensated data to the CAD model.