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ABSTRACT: Mechanical standard part library is an important means for sharing mechanical standard part resource, it based on ISO part library standard by which mechanical standard parts library information should be rational expressed and exchanged on the level of design methodology, its implementing technology included variant design, tabular layouts of article characteristics and parametric cad system, the method and key technology to construct parametric mechanical 3D standard parts library was introduced. Engineer could build mechanical standard part through this system automatically and improve the design efficiency. KEY WORDS: parts library standard, tabular layouts of article characteristics, CAD, part modeling 1 INTRODUCTION In the process of mechanical product design, large numbers of standard parts would be used. When designer constructed the model of standard part, they need refer to design manual in order to make certain the dimension and material and so on, it spend much hours with them. Now, complexity and precision of mechanical product design are increasing along with the development of technology, it put forward more advanced requirement for mechanical design. In order to improve design efficiency, reuse resource and shorten design cycle, standard parts library was brought forward. Two-dimensional standard parts library based on AutoCAD was applied widely at present, according as requirements of design, we design a three-dimensional standard parts library based on Solid Edge. Solid Edge is a three-dimensional design system found on Windows, it is the product of Unigraphics Solutions Corp and high efficiency and easy using are its characteristics. Solid Edge possesses powerful function at parts design, assembly design, sheet metal and engineering drawing etc and fulfills various mechanical design tasks. It has a fine user interface, and Smartribbon technology was used in it, so user could complete the design assignment step by step according to its hints. Solid Edge is a perfect CAD system, and involved technology for redeveloping is used by designer far and wide, we construct the three-dimensional standard parts library by redeveloping Solid Edge, thereby the parts would be designed automatically. 51991
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2 THE PRINCIPLE OF STANDARD PARTS LIBRARY For the sake of interchanging, integrating and sharing information of standard parts library, International Organization for Standardization defined the international standard iso13584, GB/T 17645 adopt the identical standard, the chief aim of the the standard provides a neutral mechanism which can transfer the data of parts library and unattached to application system which used parts library data system. The standard is not only suit to interchanging parts, but also become the database basis of implementing and sharing parts library data. Since defined the parts library standard, a great deal of students researching the contents and application of parts library standard, which involves many aspects and issues of design and applying method for parts library. Many researches done in the areas of the computer integrated manufacturing has considered the probability for applying parts library technology to share product information. Yangdong thought the standard provided a representation of parts library information together with the necessary mechanisms and definitions to enable parts library data to be exchanged, used and updated, but it did not standardize the uniform realization, so he introduce a kind of realization means of modeling mechanical part library using extended express language, and dealt with the architecture and detailed construction of a case based on the standard [13]. At the same time, he gave an overview of the architecture of the standard and the relationship between ISO13584 and STEP, gave the guideline for introducing this standard to domestic industry, discussed to build a part library information system based on the standard in detail [6]. Cao Yunfu and Li Feng presented formal method and standard format used to represent and model part family in PLIB, represented information of part family by physical file defined in ISO and taking the flange family as an example [5]. Wu Yizhong and WuBin proposed a XML-based parametric standard part library system in order to improve the adaptability to all kind of heterogeneous CAD system, analyzed current standard part library system, and pointed out the existing problems, presented system structure of the standard part library system based on XML, discussed the XML description of features in common use in 3D CAD parametric feature modeling systems and put forward established method of XML-based 3D standard part library, developed different CAD platform by means of appropriative API interface modules, realized the parametric standard part library prototype system under some CAD systems which include pro/e, UG et al [14]. Yu Junhe and Qi Guoning thought STEP described product model information for life cycle, it was the base of the product data change, but there was lack of advanced semantic express, parts library standard studied the rational express and exchange of computational parts library information based on design methodology, and shared the product resource among enterprises, PLIB expressed product model information by general mode;, functional model, functional view model and representation category, provided the capabilities to describe product information multi-domain and multi-level perspective, presented the geometry view model providing a method to build the product representation [7]. Wan Jiutuan and Huang Xiang [15] considered it is an important way to enhance efficiency of products dsign to establish standard parts library in CAD system, they focused on the development of clamp CAD system, with the adoption of parameterized technology and feature modeling technology, by way of distributed database oracle, as well as second development tool UG/Open API, standard parts was established, it may applied in the design of clamp CAD system, obtained satisfactory effects. Lu Yong and Liao Wenhe [16] focused on data description norm and techniques to build library in network, the key points included information representation and sharing technique of parts library in network based, feature-based part explicitly geometric model, network-data driving parametric design, visualization of web-based part feature model, gave the application schema to realize the sharing of parts library information in and among enterprises. These studies are most still located in the theory phase, but we could obtain helped to know status that applied parts library technology and correlative computer technology to manufacturing industry. The contents of parts library standard include summarize and rationale, concept description, logic model of expression, logic model of supplier library, information supplier identifier, implementing resource, description method, viewer interchange protocol (part 101) and viewer interchange protocol (part 102). The architecture of the standard consists of three layers [1，2], which are application layer, logic layer and physics, as shown in figure 1. concept model application layerlogic layerphysics layerlogic modelphys ic s applic at ionconcept modeldictionary methodgeneral resourcelogic resourceSETP documentexternal document Fig.1 Parts library standard architecture In application layer, framework of parts library and mechanism of its updating and interchanging are defined, in logic layer, information model of parts library and resource component were described, in physics layer, implement mode of information model of parts library is stated, including neutral document format and memory operation format etc. Parts library standard defines the reference model of parts library system [1], showed in figure2, which compose of dictionary, library content and library management system, it describes parts library as a part class hiberarchy, which is a tree construction. dictionarycontentfunction model class general model classlibrary management systemexpressiontransfer intefac eaccessing intefac edatabase Fig.2 Parts library reference model The description of parts model has tow layers, one is part’s attribute including name, identification data type and otherwise, another is component class including class identification, class attribute and class document etc, dictionary describes part class and its attribute and library defines case of every class, the information model of dictionary and library content are expressed as logic layer of parts library information model which was described by Express language. Library management system is a software system by which provided the function that user querying, choosing part in user library and integrating vendor library into user library [3, 4]. Outer interface of parts library includes expression transfer interface and accessing interface, expression transfer interface set up a set of application programming interface using in CAD system, accessing interface provided basal routine which query part in user library. In parts library, every part is regarded as object which attribute is its characteristic. The parts that has similar characteristic constitute class. Child class part inherit the whole attribute form parent class part, it also has its special attribute. Parent class part may possess one or multi-class, so parts library hiberarchy would be formed. Figure3 illustrate a standard parts class layer for manufacturing. 3 STANDARD PARTS LIBRARY SYSTEM IMPLEMENTING 3.1 System Implementing Rationale In order to establish the standard parts library, designer should analysis the correlative parts according to the principles of comparability and reusability, and make certain the representative character and geometry structure of this type of parts and possible variant design scheme and correlative parameter, thereby the main model of the part would be determined. We evaluate for attribute and parameter and make the model instantiation, a new part would be achieved. coupling part classrivet part class screw thread part classt pin class spline classbolt class screw class screw shank class nut class washer classhexagonal bolt T slot bolt foudation bolt U model bolt Fig.3 A standard parts class layer Part main model is a parameter variant model in which was expressed by geometry graph of CAD system. The part instant may derive form part main model. The part main model was constructed by certain CAD system. Here we adopt SolidEdge based on Windows, it is a strong parameter three dimensions design system, its variable table technology may set up parameter table for model and edit the relation among parameters [5]. Through its modeling ability, variable table, setting model parameter rational and ensuring restriction relation in parameter, we can implement automatic variant design based the model and build needful part. By the ActivexAutomation-based application program interface, developer may develop user module by which reading and writing model parameter and updating parameter value, so the roboticized design would be realized. Owing to restriction relation in part, the dimension value of new part might be different form old one, but its topology frame is similar to old one, their functions do not change. The parts are classified in term of function and structure and parameter model library would be established, the database of parameter and attribute would be established too, so a standard parts library system may be implemented by user module, the efficiency of design and management level would be improved. Here the main steps of system development included: first, analysizing various kinds parts according to before-mentioned principle, establishing main model in CAD system, sorting part by function and construct, composing parts model library [6]. Secendly, establishing parameter table of part main model and making certain relation in parameter based on engineering restrict condition. Thirdly, establishing datasheet in database in which storing parameter value and other attribute value [7]. Fourthly, establishing interactive standard parts library management module, implementing data communication between user module and database by interface program, so the new parameter value would be stored and model parameter would be updated. 3.2 System Architect and Key Supporting Technology System logic architect consists of user layer, interim logic layer and database layer. User layer is user interface in which data could be browsed, searched, read and wrote. Interim logic layer may integrate CAD system with database system, the interface of CAD is based upon ActiveXAutomation and database interface is ADO and ODBC etc. Database layer includes part database and part model library, database save the tabular layouts of article characteristics of each part in which describe the article characteristics parameter and relation among them, model library save the 3D parameter model of part, the variant table could be edited through CAD system [8]. Establishing mapping relation between variant table and tabular layouts of article characteristics, the tabular layouts of article characteristics may drive variant table by interface program and update part model, implementing design automatization. This system rely on SolidEdg in which model variant module allow designer set up relation among variant by equation and funcation, all variant has name and they are called by their name. Variant and dimension are all shown in variant table, designer may found new variant and formula for existent variant to establish relationship, when independent variable value change, the one that had set up relationship would update automatically. Variant table object contact each other by object hiberarchy, when accessing a variant object in application, we need access object tree form top to root until that object was found [9]. Figure 4 illustrates the variant table object layer in this system, user evaluates for parameter in customer program, they could drive model to finish the design task. ApplicationDocumentsDocumentVar iablesVar iable Fig.4 Variable object layers The other key technology is variant design technology based on tabular layouts of article characteristics. 51991