Research On Reuse And Suppression Of Freeform Features

With the development of modem industry, the traditional regular feature represented by plane and quadratic surface can not already respond to the request of the modern industrial product design on both function and appearance, consequently the freedom surface is introduced to CAD field and the freeform feature modeling emerges. Employing the freeform feature, the designer can design product freely with freeform surfaces. Freeform features have more complicated geometric elements and more freedom degrees, which make their modeling and processing much harder than regular features, e.g. the representation, parameterization, recognization and reuse, etc.This dissertation focuses on the reuse and suppression of the freeform features. And the main contributions are presented as follows:1,Reuse of freeform feature represented by NURBSAfter analyzing the differential properties of NURBS surface, a freeform feature reuse algorithm preserving its differential geometric properties is obtained. This algorithm can also guarantee good continuity between the feature and the target surface besides the differential properties of the feature. And the features can be reused on the target surface adaptively for good appearance.2,Suppression of freeform feature represented by NURBSBy analyzing the factors determining the differential properties of NURBS surface, a suppression algorithm for freeform feature with NURBS representation is proposed. Relevant geometric information around the feature is obtained to reconstruct a smooth surface whose geometry suits the surrounding geometric differential properties as well as possible. Compared with smooth algorithm, our method can get more fair appearance.3,Reuse of freeform feature represented by hierarchical B-splineBy analyzing the advantages of hierarchical B-Spline on product modeling, a freeform feature reuse algorithm based on hierarchical B-Spline is proposed. Only local modification need to be performed in our algorithm and the complexity of target surface after reuse is reduced remarkably. And the rotation operation of arbitrary angle during reusing is also well supported.4,Suppression of freeform feature represented by triangular meshAfter analyzing the geometric differential properties and the differential operators on mesh, a suppression algorithm for freeform feature with mesh representation is presented. The suppression is achieved by replacing the freeform feature with a new mesh patch constructed from the differential properties around it. This algorithm is robust, effective and accurate.