Research On Feature Recognition And Model Establishment Based On Part File

With the rapid development of informatization in industrial domain, NC technology is used extensively. As a new standard interface in NC systems, STEP-NC is an extension of STEP in machining. It has the same format in description of geometry information and solves limitations of ISO 6983. Aiming at exchange file, this dissertation focuses on feature recognition and model establishment from part information.The down-top pattern (L-H pattern) for product information acquisition is proposed to deal with problems such as vast quantity and complexity of information in modeling, and is used in the extraction process of STEP-NC files. With this pattern, product data models have been established with reducing information redundancy and much storage space has been saved. Furthermore, relative elements lists have been conveniently realized and reasonable product information could be acquired and managed conformably from the use of this pattern, so that expedient model maintenance is supported.In order to fulfill the boundary information in exchange file, a feature extracting method, which based on bounding information of geometry elements, is proposed and is used in STEP-NC file for product visualization, through the analysis of expression of product model in exchange file. With the traversing of relative elements lists, product features are extracted by the extracting method, which takes advantage of bounding information in product model. With this method, calculation about the concavity and convexity of curves is not needed and the construct process of product feature model can be simplified.It is an important component in realizing management of part information to accomplish information flow among different part modules effectively and quickly. The definition of feature block is proposed on feature and its relative elements. And the object of feature block is used in information exchange among different product models. Take features as principal units, related information in product models is assorted, arranged and stored in data structure of feature block. With the feature block as link, a platform for information flow among product models is established and the feature-based amendment and refresh of product model can be achieved.Through the analysis of critical technologies such as presentation method in exchange file and mapping method of element definition, the definition and implication method of the product geometry information model, the product feature model, the product visualization model and the product tolerance model are discussed. A prototype system for product features and a product information management system are achieved. With a flange and other files as examples, the feasibility of every product models and the information flow among those models is validated.