| dc.description.abstract | Reverse engineering is a technique of using the scanning machine to obtain the digitized points and reconstructing the CAD model for an existing object or prototypes. The applications of inspection include acquiring the digitized points, getting the dimensions needed for constructing the CAD model and comparing the deviations between the points and the CAD model. Therefore, a complete CAD reconstructing process of products requires the combination of reverse engineering and inspection. In this study, the best fitting algorithm means finding the optimum relation between two different geometric data, which could be points, curves and surfaces. Thus, the best fitting algorithm can extensively be applied in reverse engineering and inspection.
The surface fitting is an important technique in reverse engineering. It calculates the control points of a surface by using some algorithms to minimize the errors between the points and the surface. At present, the digitization of an object is generally via optical scanning machines, which yields random point data. Hence, there are four algorithms developed in this study for different applications. They are surface wrapping, extended surface fitting, trimmed surface fitting and constrained boundary surface fitting. Several examples are presented to illustrate the feasibility of each algorithm. An air bag is finally used to demonstrate the integrated application.
The application of the best fitting algorithm in inspection focuses on minimizing the deviations between the measurement points and the CAD model. The measurement points come from a contact or non-contact scanning machine. The contact scanning machine usually means the CMM. The part coordinate in the inspection should ideally be the same as that of the CAD model. However, if there are not enough features such as planes, cylinders and spheres, it can not use 3-2-1 method to build the part coordinate. For the non-contact scanning machine, it doesn’t need the setting of the part coordinate before the digitization is performed. Therefore, the coordinates of the digitized points and the CAD model are usually mis-matched. When we want to inspect the deviations of some defined sections, we must translate the coordinate of the points to that of the CAD model, and minimize the errors between them. Thus, two localization algorithms are developed in this study for contact and non-contact scanning machines. It can calculate the optimal coordinate transformation matrix to minimize the deviations between the points and the CAD model. Several examples are presented also to demonstrate the feasibility of the proposed localization algorithms. | en_US |