Reverse engineering of free-form surfaces: A methodology for threshold definition in selective sampling

Abstract

Reverse engineering is a technique used during the project phase of a new product, which makes it possible to trace, in terms of mathematical expressions, the geometrical features of a given physical model. Scientific literature presents many different approaches to reverse engineering. Great part of those are based on the analysis of point clouds acquired through coordinate measuring devices, such as, for example, Coordinate Measuring Machines (CMMs), Optical Scanners or Interferometric Systems. Referring to this kind of approach, a common problem is to individuate the surface zones, which present sensible variations of curvature. Many algorithms, commonly implemented on commercial software through semi-automatic procedures, are already based on this method. In these cases the local curvature variation of the measured surfaces is analyzed by defining a threshold over which it is necessary to perform a deeper scansion of the surface zones. However, most of the problems are related to the definition of an appropriate value for the threshold level. In the present paper a methodology for the definition of the threshold value based on the measurement system uncertainty is described. In the current description the method is applied to an elementary algorithm for curvature definition, but it could be extended to any other kind of more complicated approach. Furthermore, it will be demonstrated that this new methodology is simple to apply and can be easily automated in commercial software for points selective sampling in industrial reverse engineering applications. In the end a practical example is described in order to give an experimental validation of the method.