GEOMETRIC REASONING FOR EXTRACTION OF MANUFACTURING FEATURES IN ISO-ORIENTED POLYHEDRA

This paper investigates the extraction of machining features from boun dary descriptions of iso-oriented (having no inclined faces) polyhedro ns. We prove that manufacturing the features proposed by our feature e xtractor results exactly in the desired part-in this respect, the appr oach is both sound and complete. Our method uses the adjacency informa tion between faces to derive the features. This keeps the determinatio n of isolated features in a part straightforward. However, interaction of features creates difficulties since the adjacency information betw een some faces is lost. We derive this lost information by considering faces that when extended intersect other faces to form concave edges. The derived face adjacencies are termed virtual links. Augmenting the virtual links to the cavity graph of the object leads to its feature graph, and subgraph matching of primitive graphs in this graph results in feature hypotheses. A feature hypothesis is considered valid if th e volume corresponding to it is not shared with the part in question; therefore, we verify the feature hypotheses by checking the regularize d intersection of the feature volume and the part. Thus, feature verif ication employs a Constructive Solid Geometry (CSG) approach. We have implemented a prototype of the system in the Smalltalk-80 environment. Simulation results verify our approach.