Stylus tip envelop method: corrected measured point determination in high definition coordinate metrology

Scanning technology is now widely used in coordinate metrology and is increasingly used for the measurement of small features. The high density scans now possible results in a new context which can be called high definition coordinate metrology. The availability of such high point density allows the proposition of a new approach to the old problem of probe ball tip radius correction based on the successive positions of the probe tip envelop. The resulting outer boundary is made of a succession of arcs, each of which potentially defining a likely contact point with the measured surface. The method aims at selecting the most likely contact point for each successive arc by applying geometrical criteria and a fuzzy logic estimator. The method is particularly, but not exclusively, suitable for the metrology of features with small radii as well as metrological discontinuities. It does not require obtaining the normal vector traditionally used for probe tip correction. The algorithm performance was verified experimentally on a Mitutoyo Legex 910 CMM equipped with a MPP-300 scanning probe.