Feature-based Cad Research

In this paper,from the viewpoint of information integration,therepresentation of feature has been researched.The method with themix data structure of CSG model, B-rep model and feature massagetable are proposed to represent feature. utilizing the correspondingrelationship between them, the precision information can be inputwhile geometry shapes are built, and also be interactively modifiedthrough the B-rep model. This method can not only joint the shapefeature and precision feature effectively, but realize the productparametric design easily.3D and 2D base-feature parametric design has been researchedin depth. In 3D design, the concept of located face has beenproposed which convert the location constraints in 3D model into2D constraints on the located face,and simplify the calculation ofconstraints relationship, and as a result, complement the 3Dparametric design rapidly and effectively In 2D parametric design,with the description of constraint rules, the automatic recognitionand calculation of graph constraint relationship is achieved. Andthrough the driven-mechanism of size and constraints, the aim ofparametric design has been reached.At last, on the basis of constructing 2D bool operation, throughautomatic search of contour, for any part drawing, the inner andexternal contour can be found without the manual guidance, thenthe overlap-region has been obtained. In these regions, the lines inthe overlapped part drawing have been trimmed and deleted by the.inner and external contours. In this way,assembly drawing can begenerated.This paper has made some theoretic research on feature, anddeveloped size-driven and 2D drawing assemble programs on theAutoCAD platform. The test proved that they are practical and canmeet the request of small enterprises well.