Parametric Design Based on Topological and Geometrical Constraints

Recently, Parametric design is realized in the commercial CAD systems. However, there remain some problems in the feature modeling. Since parametric design is realized by history-based functions, that is re-execution of operation commands, the designerfs intent is not explicitly represented in the feature model, although the systems need much computational time. They cannot identify geometrical entities which are deleted, divided or combined, and they cannot maintain the validity of features when a feature is modified.

We realize a feature modeling method which executes parametric design according to the designerfs intent. The designerfs intent is represented as topological and geometrical constraints, which the designer specifies explicitly or implicitly with the shape properties, positions and sizes of a feature. Those constraints are consistently represented by Face-based Representation. When a designer attaches a feature, the system creates topological constraints by coincident faces and describes face equations with dimensions from datum faces symbolically. When he/she wants to modify the product according to the change of the dimensional value, the system checks the interference of the influence region with the product shape and the change of convex/concave properties of edges. When there exists interference and he/she wants this modification, it generates a swept volume and executes interference calculation between the influence region and the product, and detects deleted, divided, combined and newly generated faces. Then it determines new feature types for modified features, and maintains the geometrical constraints for the faces which are over- or under-constrained.

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