PERFORMANCE OF CAD MODEL RECOVERING METHOD BASED ON CMA MEASUREMENT AND NURBS MODELING APPLIED TO SMALL FREE FORM SURFACES

Abstract

This paper presents the description and the performance evaluation of an alternative approach to reconstruct the Computer-aided Design (CAD) model of small free form surfaces. This approach required the measurement of a small size sample using a Coordinate Measuring Arm (CMA) with contact probe and Non-Uniform Rational B-Splines (NURBS) fitting techniques. A measurement strategy was developed on a tooth prosthesis sample and the measurement was carried out with a needle type stylus along predefined paths over the tooth surface. The obtained data points were used to reconstruct the tooth surface using NURBS curves and surfaces modeling techniques. The analysis of the CAD model errors was implemented by the difference between data points and the respective CAD model point and it was observed that the total amount of determined points resulted in a suitable CAD model of the small free form surface. The use of reduced cost equipment in relation to the digitization ones as laser scanning proved suitable to perform the reverse engineering of small parts having free form surfaces. Keywords: reverse engineering, free form surfaces, coordinate measurement, NURBS modelling