ABSTRACT
Because non contact instruments are best suitable for freeform measurements, a freeform calibrated artefact should be adopted for performance evaluation. Results of this artefact measurement are compared to the known geometry of the artefact, and performance are evaluated. However, with respect to standard reference artefacts, freeform reference artefacts pose a series of problems. Several standard procedures are available for uncertainty evaluation when dealing with “standard” geometrical features, like the length of a gauge block or the diameter of a gauge ring, but the definition of the real geometry of a freeform artefact, together with its uncertainty, is not straightforward. Therefore, common practice to evaluate system performance is to perform a software registration between the measured surface and the calibrated or, sometime, nominal surface, and then evaluate differences. Registration is required to express measured and calibrated/nominal surface
1 INTRODUCTION
Differing from other coordinate measuring systems, non contact measuring systems based on laser stripe, structured light and similar technologies usually are not part of a fixed frame (e.g. a cartesian robot), i.e. sometime they are not part of a Coordinate Measuring Machine (CMM). This kind of measuring systems usually consist of a fixed scanner which, in a single step, digitizes the whole measuring volume, often generating an very dense cloud of points in a short time. Not requiring any framework, their flexibility is greatly enhanced, and therefore they may be adopted for on-line process control, biomedics, forensics, reverse modeling, and in general situations where system portability is important and freeform are found.
