Feature-based inspection and comparison of parts with free-form surfaces
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AbstractIn this research, a feature-based automatic localization and comparison method for free-form surface inspection is proposed. This method firstly defines and extracts necessary surface features from the measurement surface and the design model, and then localizes these two surfaces through two steps: the general and fine localizations. The general localization is a feature-based process that establishes the correspondence between measurement surface and design model based on the corresponding features of these two surfaces, and transforms the measurement surface to the design coordinate system. To establish the correspondence efficiently, a method called best-three-points is proposed, which selects only three pairs of the most similar features and uses them to decide the general corresponding relationship. In many inspections, it is very often that only portion of the surface requires inspections. For this case, a solution has been proposed to determine the correspondence by evaluating the geometric and topological information of the measurement data and design model. The fine localization focuses on the point to point correspondence and localizes the surfaces in such a way that the comparison can be made. The identification of the corresponding point in fine localization is carried out by searching a limited range of the neighbouring area of the result from general localization. This makes this process faster and more stable. Some techniques such as Subdivide-Grid and local range searching have been proposed to improve the robustness and stability of this process. For many engineering applications, the free-form surface is assigned profile tolerance with reference to design datums due to the consideration of assembly, functionality and other manufacturing requirements. The DDF (datum direction frame) approach has been proposed to solve this problem. The free-form surfaces studied m this research can have arbitrary positions and orientations in 3D space. The measurement data can be obtained by using either contact measuring facilities such as coordinate measuring machines (CMM) or through noncontact measurements such as laser scanners. Implementations and experiments have been carried out for verifying the overall methodologies.
Bibliography: p. 185-204
CitationLi, Y. (2004). Feature-based inspection and comparison of parts with free-form surfaces (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/12594
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