31-07-2012, 12:48 PM
A New Approach of Composite Surface Reconstruction based on Reverse Engineering
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Introduction
Reverse engineering is the method that reconstructs CAD models from physical models. The main process of reverse engineering consists of data acquisition, data pre-processing, surface fitting, and making a CAD model. In reverse engineering, we mainly handle point data of the surfaces of a model acquired by measuring devices such as CMMs or 3D laser scanners. Usually a complex freeform shape model cannot be represented by a single patch; therefore, it must be divided into several less complicated surfaces.
The benefit of CAD/CAM is that the existence of computer models provides opportunities for improving the quality and efficiency of a design and is convenient for manufacture. Reverse engineering starts with measuring an existing object using a laser scanner, and then the measuring data is used to construct a surface or solid model [1].
Although reverse engineering technically does not include the machining process as one of its stages, an evaluation of the part dimensional accuracy after machining was nonetheless performed. Machining provides a physical model which can be compared easily to the original part, since better visualization and measurement is possible. In addition, actual machining of the parts using CAM software establishes a foundation for the second phase of this project, i.e. reverse engineering and CAM system integration.
Methodology
Much work has been carried out on constructing a triangular mesh data from point data. Figure (1) shows the overall procedure of the proposed methodology. After obtaining triangular meshes, the normal vectors of the triangular patches are compared with each other to identify whether or not they are on the same plane. This process is continued until all the triangular patches are searched. Then, the planes and base geometry are expanded and intersected with each other to find the edges of the object. Finally, the planes are trimmed with the edges.
Conclusions
This paper presents a new approach to the reconstruction of a surface. The proposed methodology finds the basic parts of the surface and blends surfaces between them. Each basic geometric part is divided into triangular patches which are compared using normal vectors for face grouping. Each group is categorised into analytical surfaces such as a part of a cylinder, a sphere or a cone, and plane shapes to represent the basic geometric surface. Each basic geometric surface is then implemented to the infinitive surface. The infinitive surface’s intersections are trimmed by boundary representation model reconstruction. The proposed methodology has several advantages such as computational efficiency and automatic functional modelling in reverse engineering. Reverse engineering should be the 3D equipment of the photocopying process. Furthermore, the proposed algorithm is computationally efficient and can be used in an automatic functional modelling system. In further work, it will be necessary to reconstruct a composite free from surface.