An Applicative Method to Evaluate the Geometric Correspondence of a Manufactured Sweep Object to its CAD Model by Means of Point Cloud Manipulation

This paper presents an applicative method for evaluating the global axis deformation of a sweep object caused by the manufacturing process with respect to its ideal CAD model. Object and CAD shapes are given in form of point clouds, the former derived from a laser-scanning measurement, the latter from sampling the original surface by a dense and uniform point grid. After an initial rigid registration, approximated centroidal axes of both shapes are extracted, compared and processed in order to evaluate macroscopical translation errors occurring in any scanned object's section.This method has been applied and tested to the analysis of a helical Darrieus blade prototype, parametrically designed and modelled with McNeel Rhinoceros and Grasshopper software, manufactured with a three-axes CNC machine and reinforced by a carbon fibre composite laminate. The point cloud obtained from the subsequent laser scanning has been processed and compared to the original NURBS model in order to build the global contour map of the mutual difference. The application of this procedure is able to check the conformity of the manufactured airfoil to the theoretical one and, therefore, to establish the efficiency of the final prototype of the blade turbine.