Study of variable part model based constraint and 3-D feature

To improve the integration and intelligence degree of the CAD/CAM system, this paper presents a part definition model based on constraints and feature technology. In this model a series of new methods are introduced to define, classify and represent features. According to characteristics of 3D constraints, they are classified as constraints inside feature and constraints between features through high level abstraction. The former classification is represented as shape constraint, and the latter one is represented as dependent constraint, location constraint and shape dependence. On this basis, a directed feature multibranch tree has been built to maintain the part constraint model. Moreover, three kind algorithms are also developed to build part model and edit part model, and erase feature.