Computer recognition and extraction of form features: A CAD/CAM link

The future success of CAD and CAM depends on the ability of these two processes to communicate with each other and with the intermediate manufacturing database. CAD-generated objects can be defined and stored as complete geometric and topologic solids. The elements of CAM, however, cannot make full use of the CAD part description because it exists in terms of low-level faces, edges and vertices or primitive volumes usually unrelated to manufacturing processes. Consequently, manufacturing planning continues to depend upon human interpretation of the part definition according to manufacturing needs. The automatic linking of CAD and CAM involves a computer interpretation of the part database to extract manufacturing-specific semantic knowledg about the part. This knowledge can enable process planning and other CAM operations to proceed automatically without human guidance or intervention. A method has been developed to automatically extract manufacturing information in the form of part features. The procedure consists of searching the part description, recognizing cavity features, extracting those features as solid volumes of material to be removed and arranging them in a feature graph, a high level data structure appropriate for manufacturing process planning. The feature recognition step uses logic programming implemented in PROLOG. Using rules of logic, definitions have been formulated to describe some common features of a part, such as holes and slots. The part is represented as a set of facts in a boundary representation format and these facts are searched to satisfy the feature rules. Multiple feature cavities can be separated into their component feature parts. This work has relevance in the areas of CAD/CAm linking, automated process planning, expert systems and, in fact, the interpretation of any 3-D data.