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第 1 頁譯文標(biāo)題 基于工程數(shù)據(jù)庫的起重機(jī)結(jié)構(gòu)計(jì)算機(jī)輔助設(shè)計(jì)原文標(biāo)題CAD/CAM OF CRANE’S STRUCTURE BASED ON ENGINEERING DATABASE作 者 Chonghua Wang 譯 名 王重華 國 籍 中國原文出處 Department of Mechanical Engineering Shanghai Maritime University P.R.China e-mail spmtc@shmtu.edu.cn第 2 頁原文：LathesCAD/CAM OF CRANE’S STRUCTURE BASED ON ENGINEERING DATABASEABSTRACT According to the specialties of CAD/CAM for largescale complex structures of machinery, a CAD/CAM system based on engineering database for crane’s structures is proposed in this paper. Based on the top-down hierarchical product structure, feature technology, assembly constraint relationship, bottom-up assembly process and down-to-top dimension constraint relationship, a CAD platform of 3D parametric model family is built to allow generation of feasible configurations of crane structures. With a sum up of background knowledge of GUI and APDL patterns of ANSYS, the finite element model of the crane is set up based on composite pattern. Synchronous updating and analysis of FEA model are realized. Two kinds of engineering databases are constructed in the system. One is a parameterized database and contains all kinds of parameterized parts and components common used in crane structures. Another is designed for every individual crane and contains all parts and components used in crane structure, where parameterized variables are replaced by definite values. The later can be used to create BOM, to build FEM model, to arrange parts in the steel sheet for numerical control cutting and to design technological apparatus for welding and manufacture. Microsoft SQL Server is selected to construct the databases and the CAD/CAM integration is achieved using MS VC++6.0 and Pro/TOOLKIT. KEYWORDS CAD/CAM, Structure, Crane, Engineering database, 3D design 1. INTRODUCTION The international trades which increase rapidly in the last few decades rely on the transportation chains of world logistics. The abilities of the deepwater ports to swiftly handle and distribute the large quantity of containers and goods which are surging in continuously play a key role in the logistics chains. Almost all ports in the world are busy expanding nowadays. The port cranes increase rapidly all over the world in the recent years. The port cranes are very large and complex machines and becoming larger, more automatic and with higher speeds to meet the huge ships and the great quantity of load and 第 3 頁unload. Comparing with normal machines, it has a unique component that is the huge and complicated structure. The characters of CAD/CAM for crane’s structure are: a) Crane’s structure has various types and a lot of design parameters to meet the different natural, environmental and operating conditions of every harbor. b) The structure is consisted of several components. Every component is formed by welding numerous parts. Although a lot of parts are rectangle plates, their thickness may vary continually along the component to reduce the weight while keeping enough strength. In addition, there are lots of construct details to let the component support external loads. So the components are very complicated. c) The design of the structure should conform to the requirements about strength, stability, bucking, cumulative damage and vibration frequency etc. of the Standards and Specifications. So it is necessary to do finite element analysis on the structure. As the structure is very large and complex, any FEA package of commercial CAD software is insufficient to handle the complex structures of crane. d) The techniques of CAM for crane structure are comparatively simple. Especially numerical control cutting and automatic welding are widely used in most factories. An integrated CAD/CAM for the crane’s structure is proposed in this paper. It is mainly based on the technologies of parametric 3D modeling, finite element analysis, engineering database technique, Pro/ENGINEER, ANSYS, MS Visual C++ and Microsoft SQL Server. The system includes building CAD platform of 3D parametric model family for crane, setting up FEA model, the second exploiting of 3D parametric model, the synchronous updating and analysis of FEA, construction and collection information of parametric and certain models of parts, components and cranes and supply a platform to develop the application of CAM. 2. CAD PLATFORM OF 3D PARAMETRIC MODEL FAMILY FOR CRANE In order to support the designing of crane family, CAD representations for product platform is developed to allow generation of feasible configurations of cranes, components and parts for each family member and then scaling them to the desired size. The framework of CAD model platform for port container crane has to provide support functions listed as follows: 2.1. Decompose crane into components and parts based on top-down hierarchical product structure To be able to facilitate design tasks to the members of a development team, a crane to be designed has to be structured in some way. The well-known hierarchical product structure is used for this. A crane consists of a number of components. Each component can either consist of a number of subcomponents or be a part. The first type of component is called a compound component (in following text, we only call it as component), the second type a single component (we call it as part below). The product structuring continues recursively in this way, until all components at the lowest level in the hierarchy are parts. So the product is structured in a top-down way, creating as many levels 第 4 頁as desired by the designers. Figure 1 shows a simplified hierarchical product structure of a container crane. 2.2. Construct 3D part model based on feature technology Feature technology provided by CAD software platform such as Pro/ENGINEER, Solidworks etc. includes: a)Draft features which are fundamental geometry characters produced by drawing cross sections and stretching, rotating or scanning them; b)Attachment features which are added to the fundamental characters include hole, round corner, collapse corner and so on. According to the feature technology describes above, the 3D models of the parts of the container crane are generated. 2.3. Specify spatial constraint relationships of components to create product variety The spatial relationships among the components and parts in the product family are represented using assembly constraint relationship. In the assembly module of CAD software such as Pro/ENGINEER, constraint relationships in assembling, for example, matching, aligning, inserting and tangential etc. are provided. Here, based on the hierarchical structure of crane, relationships among parts and components are built using the assembly constraints provide by Pro/ENGINEER. Figure 2 represents the assembly constraint relationships among the parts of portal frame. 2.4. Establishment of down to top size constraint relationship In order to regenerate the new 3D model of parts, components and crane when the values of design parameters are changed, a down to top size constraint relationships between size variables and design parameters in a part or component should be built. Design parameters are established by designers according to the structure of part or component. Size variables, which are generated automatically when 3D models of parts or components are built, control the real geometrical size and topological relationship of a part or a component. Therefore, in order to regenerated the accurate new model of a part, a component or crane when the values of design parameters are changed, the relationship between design parameters and size variables should be constructed accurately. Commercial CAD software such as Pro/ENGINEER has provided function to set up design parameters and build relationships between design parameters and size variables. It must be pointed out that every part would be used to compose a component. All the references which are not on the entity of the part would be invalidated then and must be setting up again. So it is important to setting all the references of parameters on the model of the part. 2.5. Generation of component or product assembly model based on constraint relationships in bottomup way Based on the hierarchical structure of the crane, a designer can start building 3D model of a part as soon as the task has been assigned to him. On the other hand, 3D modeling of a component by a designer to whom it was assigned can only start just after its subcomponents and parts have been created. So the actual modeling 第 5 頁activity is bottom-up process, starting at the leaves of the hierarchical product structure. According to the hierarchical product structure of the crane and assembly constraint relationships among components and parts, 3D models of a component desired are generated. The parameters on the model of a part should be evaluated and can be modified before it is assembled to a component. If it is necessary to amend the part after it has been assembled, the part should be deleted and a new model of the part is evaluated to the proper values and to be assembled. All design parameters must be setting on the models for parts or components. No design parameter is setting on the assembling model of the crane in the system to avoid failure in regenerating the model of whole crane after any parameter has changed. Figure 3 shows the 3D assembly model of the boom based on constraint relationships among subcomponents and parts. Figure 4 and 5 show 3D models of different portal frames based on assembly constraint relationships among subcomponents and parts.3. GENERATION OF FEA MODEL FOR THE CRANE In finite element analysis, the mathematical model shall simulate the real object, loads and constraints as accurately as possible to get the reliable results. The FEA should usually be carried out on the whole crane structure. As the structures are very large and complex, any FEA package of commercial CAD software is insufficient to fulfill the task. The ANSYS is selected because of its powerful structural analysis functions. As the same reason, the plate elements in ANSYS could not be adopted. The beam188 elements are used to build the FEA model of the crane. In ANSYS, two modeling patterns are provided to build the FEA model, i.e. the human-machine interactive pattern also called GUI pattern and the command stream flow input pattern also known as APDL pattern. Two patterns have also advantages and shortcomings which are described in reference literature. With a sum up of background knowledge of GUI and APDL patterns of ANSYS, the FEA model of the crane is built based on composite pattern. First, FEA model of the crane can be built through ANSYS GUI pattern. Second, CAE analyses of the crane are carried out and corresponding log file is also generated. The log file can be amended by using parametric design language APDL provide by ANSYS after some changes have been made on the parts, components or crane. The APDL of the crane including generation of model, imposing of load and constraint, finite unit solution and post treatment is built. Generation of model consists of parameter definition, node/unit/section establishment etc. A new FEA model of the crane is constructed by running the APDL file. Synchronous updating and analysis of FEA model are realized. See Figure 6 and 7 for the FEA model and stress analysis chart of a crane structure.4. DATABASE SYSTEM In order to manage all the information about design and 第 6 頁manufacture of crane, achieve the data to be shared by every module of CAD/CAM integration system, keep the programs independent from the data and guarantee the data integrality and security, the database system must be used. Among the popular database management systems for microcomputer such as FoxPro, Visual FoxPro, SQL Server and so on, Microsoft SQL Server 2000 is final selected. 4.1. GDB and SDB In order to speed up design, improve design quality and reduce repeat work, two kinds of databases are designed in the system. One is called general database (GDB). The others are special databases (SDB) for individual cranes. The GDB is a parameterized database and contains all kinds of parameterized parts and components common used in crane structures. The parts and components are stored in many branches and levels as a tree structure. Although there may be lots of rectangular plates in a component, for example, in the boom, in the girder,…. There is only one parameterized rectangular plate in every branch to reduce redundancy. The GDB can be visited by all designers of the company. As soon as a designer is assigned to design a component, he can first search the corresponding branch of GDB to make use of the existing parameterized parts and components to building 3D model of the component. At the same time, the information of the parts and components used are recorded in the SDB. He can modify the parts and components in GDB if they are slightly different from what are needed. Even he can create a new parameterized part and component and save them into GDB with the approval of an authority.The SDB is designed for every individual crane and contains all parts and components used in crane structure. They are also stored in a tree structure. Different from GDB, every part has its corresponding record in SDB. Parameterized variables are replaced by definite values. Along with these, the code, name, location of storage, coordinates of location, parameters of material, weight, center of weight, parameters of manufacture etc. are recorded. Some data, for example weight of the part, are calculated as soon as the part has been scaled. The SDB can be used to create BOM, to build FEM model, to arrange parts in the steel sheet for numerical control cutting and to design technological apparatus for welding and manufacture. 4.2. Database structure With the use of database, some general problems would be addressed: Data integrity: On a file system, the changes of the designer who saves the file first are then deleted by the designer who saves the same file afterward. But a CAD model can not be amended by two designers at the same time by using the transaction mechanism of database. Direct relations: With direct relations of data entities of models, technical dependencies among 3D models can be easily found. Direct relations give the designer a 第 7 頁hint to which models must also be changed after making the changes in a model. Center data management: The central data pool offers several advantages for backup and versioning. Data clustering: The data clustering speeds up the data access, since each designer can get the desired information on his local PC. This is quite important for distributed and collaborative design projects. We have used the Entity-Relationship (ER) model, which is a popular high-level conceptual data model, to design the database. This model and its variations are frequently used for the conceptual design of database applications, and many database design tools employ its concepts. The ER model describes data as entities, relationships and attributes. The basic object that the ER model represents is an entity, which is a thing in the real world with an independent existence. Each entity has attributes, namely, the particular properties that describe it. A particular entity will have a value for each of its attributes. The attribute values that describe each entity become a major part of the data stored in the database. A relationship type R among n entity types E1, E2… En defines set of associations or a relationship set among entities from these types. As entity types and entity sets, a relationship type and its corresponding relationship set are customarily referred to by the same name R. The database has entities according to the hierarchical product structure of the crane. Each part, component and the crane can be represented as an entity which has attributes described by its design parameters. Spatial relationships among the components and parts in the crane products are represented as relationship set R. The database is constructed using Microsoft SQL Server and Component Object Model (COM). 5. INTEGRATION OF CAD/CAM BASED ON VISUAL C++ As the SQL Server DBMS is selected to manage the engineering database and Pro/ENGINEER is used to build 3D models, Visual C++ is adopted to be the programming language to construct the integer system of CAD/CAM. The first reason is that Visual C++ is one of the languages which can visit SQL database. Second, when we are setting up GDB we must visit the database as well as to visit the 3D models by use of Pro/TOOLKIT, which is a second exploiting software kit provided by Pro/ENGINEER. When we are dealing with SDB, we need also to visit the database and the parameterized models simultaneously and do some modification. Visual C++ is powerful to compile the programmes which are able to visit Pro/ENGINEER and SQL Server 2000 simultaneously and to implement the data communication between them. Third, Visual C++ is a programme software of OOM which has a lot of advantages. 6. CONCLUSION The CAD/CAM integration system of container crane’s structure based on engineering database is introduced in this paper. Based on the top-down hierarchical product structure, feature technology, assembly constraint relationship, 第 8 頁bottom-up assembly process and downto-top dimension relationship provided by Pro/ENGINEER, a CAD platform of 3D parametric model family is built to allow generation of feasible configurations of cranes. With a sum up of background knowledge of GUI and APDL patterns of ANSYS software platform, the finite element model of the crane are built based on composite pattern. Synchronous updating and analysis of FEA model are realized. By using Microsoft SQL Server 2000, two kinds of databases are designed in the system to communicate with every module of CAD/CAM integration system. The data are shared by whole system. With the help of MS Visual C++, the integration development method of CAD/CAM is achieved. The system can improve greatly the design efficiency of port container crane’s structure and supply a platform to develop the application of CAM in largescale complex structures of machinery. ACKNOWLEDGMENTS This paper is supported by shanghai Leading Academic Discipline Project, Number: T0601.REFERENCES Chandrupatla, T., and Belegundu, A., (1991), "Introduction to Finite Elements in Engineering", Prentice Hall. Claesson, A., Johannesson, H., and Gedell, S., (2001), "Platform Product Development: Product Model a System Structure Composed of Configurable Components", Proc. 2001 ASME DETC/CIE Conference, Pittsburgh, ASME, New York, ASME Paper No. DETC2001/DTM-21714Conner, C. G., De Kroon, J. P., and Mistree, F., (1999), "A Product Variety Tradeoff Evaluation Method for a Family of Cordless Drill Transmissions", Proc. 1999 ASME DETC/CIE Conference, Las Vegas, ASME, New York, ASME Paper No. DETC99/DAC-8625. Martin, M. 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