[机械模具数控自动化专业毕业设计外文文献及翻译]【期刊】一种可进行产品数据转换并且基于PMD的制造规划系统-外文文献

65A STEP enabled and PDM-based manufacturing planning systemJ. X. Gao and R. SharmaSchool of Industrial and Manufacturing Science, Cranfield University,Cranfield, Bedford, MK43 0AL, UKEmail: james.gaocranfield.ac.ukABSTRACTThis paper reports results of a research projectaiming at the development of a new generationComputer Aided Manufacturing Planning System(SMPS) which has the following capabilities: fullycompatible with ISO 10303 Standard for Exchange ofProduct Data (STEP); manufacturing analysis in theearly product development stage; advancedmanufacturing knowledge capture and management;integration through Product Data Management (PDM);and a new generation feature model editor. This paperemphasises the implementation of STEP ApplicationProtocol 224 (AP224), which is a product definitionstandard for process planning using machining features.Although AP224 has been accepted as an internationalstandard, there is a surprising lack of compatiblesoftware packages in the market today. Therefore, thisproject has tried to produce a commercial strengthmanufacturing planning system as the final deliverable.The prototype STEP-enabled Manufacturing PlanningSystem (SMPS) offers domain flexibility and cangenerate manufacturing plans and associateddocuments from AP224 files automatically, withoutany user interaction.1 INTRODUCTIONProduct development is defined as the series of stepsthat take levels of product functional requirements, andusing the tools and methods available, translate theminto technically sound products that meet theserequirements . The ability to rapidly conceive andproduce new products that meet customer needs hasdramatic ramifications in terms of market opportunity,customer satisfaction, technology growth and costbenefits. Enabling technologies such as Computer-Aided Engineering (CAE), Computer-Aided Designand Manufacturing (CAD/CAM) and Computer-AidedProcess Planning (CAPP) are regarded bymanufacturing enterprises as crucial to their business.A key to the successful implementation of the abovesystems is the integration and exchange of informationbetween them. CAPP is the activity that links designwith manufacturing . In this project, the scope of CAPPhas been extended to include all associatedmanufacturing planning decisions and generation of allmanufacturing documents and NC codes. This enlargedscope is covered under the term Computer-AidedManufacturing Planning (CAMP). A major challengein providing quality-manufactured products on demandis the rapid creation of manufacturing plans, shop floordocuments, routing slips and NC codes. Computerisedplanning systems can help reduce planning time, andincrease consistency and efficiency. The main problemof transferring CAD data to a downstream CAMPsystem is the lack of neutral formats as well as contentto convey the CAD information.Features can be viewed upon as information sets thatrefer to aspects of form or other attributes of a part, insuch a way that these sets can be used in reasoningabout design, performance and manufacture of the partor the assemblies they constitute. Feature-basedcharacterisation of design is important for integrationwith downstream planning applications. Preparation ofproduct (feature) data for computer-aidedmanufacturing planning is a difficult task. If a CAMPsystem deals with a CAD database directly, the dataextraction system developed is not usable for anothersystem. In order to develop a procedure for consistent,unambiguous data abstraction from a generic datastructure, the foundation or the standard on which theprocedure is based is very crucial. ISO 10303 is theresult of International Standards effort to develop sucha neutral mechanism capable of completelyrepresenting the product data throughout the life cycleof a product. This project developed a new generationComputer Aided Manufacturing Planning System fullycompatible with ISO 10303 Standard for Exchange ofProduct Data (STEP) AP 224.2 STEP AND ITS APPLICATIONSTEP, standing for STandard for the Exchange ofProduct Model Data, is officially titled ISO 10303 1.The International organisation for Standardisation hasbeen working on this project since 1984 which is alsoone of its largest development efforts ever. The aim ofSTEP is to provide a representation of productinformation along with the necessary mechanisms anddefinitions to enable product data to be exchanged. Theexchange of data is intended between differentcomputer systems and environments associated withthe complete product lifecycle including design,manufacture, utilisation, maintenance, and disposal.STEP represents an open standard to meet product datarequirements over the entire life cycle of a product,including geometry, topology, tolerances, relationships,66attributes, assemblies and configuration.STEP uses application protocols (APs) to specify therepresentation of product information for one or moreapplications. The APs define the scope, the informationto be exchanged, the means of testing and a user guidefor implementing the application. The nature of thisdescription makes it suitable not only for neutral fileexchange, but also forms a basis for implementing andsharing product databases and archiving. The ultimategoal is an integrated product information database thatis accessible and useful for all the resources necessaryto support a product. Fowler 2 and Pratt 3 provide agood introductory text on this subject. The interest ofthis project is Application Protocol 224 4, whichcovers the following scope: product data to definesingle piece-machined parts that are to bemanufactured and machining by milling or turning.AP224 contains all the information needed tomanufacture the required part including the materials,part geometry, dimensions and tolerances. The productdefinition in AP224 contains the shape representationas well as definition of the machining features. Thedefinition also contains the initial shape of the materialbefore machining. This is very important forproduction of valid process plans.This project mainly implements and tests AP224 formachining applications. Within AP224, the machiningfeatures are divided into 16 categories, such as boss,pocket, hole, slot and knurl. The standard alsodescribes three different types of feature transitionsnamely, fillet, edge_round and chamfer. There is also amechanism for describing a pattern of features. Eachfeature is explicitly described using parameters. Unionof one or more feature yields a compound feature.Features are constructed using a combination ofprofiles and paths. Profiles are 2D shapes and Paths are3D. Features are created by defining a profile over theentire length of a path. For example, a completecircular profile along a linear path defines a round hole.Several standard profiles, both open and closed aredefined in the AP. Several standard paths are alsodefined. A combination of these paths and profiles canbe used to represent all the features. Tolerances arevery important for manufacturing. AP224 caters fordimensional tolerances, size tolerances, locationtolerances and geometric tolerances. The modeldescription also contains various other miscellaneousmanufacturing information like material, alternatematerial, material properties, notes and specifications.Administrative information about manufacturing of thepart is also included in the model.The commercial world is just beginning to embraceSTEP as the standard for data exchange. ParametricTechnology Corporations Pro/ENGINEER CADsystem 5 is one of the first CAD systems to generateSTEP AP203 data. This AP203 file contains aBoundary Representation (B-rep) solid model of thePro/ENGINEER part model, as well as configurationmanagement data. Other CAD systems likeUnigraphics and I-DEAS are also beginning to providefacility to export/ import AP 203 files. The GenerativeProcess Planning Environment (GPPE) system is aprocess planning system from South Caroline ResearchAuthority (SCRA) which provides feature-drivengenerative process planning capability for mechanicalparts. As its preferred mode of input, GPPE takesSTEP form feature data, which provides anunambiguous representation of the product to bemanufactured. GPPE accepts pure STEP AP203-formatdata, STEP AP224 or AP213-format data. SCRAdeveloped a technique called Rapid Acquisition ofManufactured Part (RAMP) for the US Department ofDefense 6, which demonstrated the feasibility ofcommercial implementation of STEP-based technologyin industry. The UK Navy RAMP project was a pilotproject supported by Naval Support Command . Theidea was to enable the navy to move away from thejust-in-time inventory by the use of innovative just-in-time-manufacturing techniques based oninternational standards. RAMP is unique within thistechnology in that it makes use of the InternationalStandard STEP to define the parts to be manufactured.In the context of RAMP, this information includes themanufacturing characteristics of the components, suchas holes, slots, pockets, grooves etc as well as material,surface and testing specifications.3 THE DEVELOPED SMPS SYSTEMThe final deliverable of this project is a STEP-enabled Manufacturing Planning System (SMPS) basedon the AP224 protocol. It has been developed as suiteof applications, which are linked to each other throughintermediate files/ databases. This has been done for anumber of reasons. Breakdown of the system intoindividual functional applications allows for bettercode development and maintenance. Anotheradvantage is that the individual applications can beupgraded as long as the intermediate file structurecompatibility is maintained. The system can be run ondifferent physical machines if the intermediate filedrive is shared. For example, the AP224 viewer couldbe on the CAD workstations and the database editorscould be installed on the PC of the process planner.Also the execution of the system could be done in abatch mode, i.e., the bulk files could be processed toget the intermediate and the post-processed filestogether. Each function of the system will be furtherexplained in this section.Each application needs to make a distinct boundarybetween the application itself and the data it uses.Although data may seem static at the time ofdevelopment, keeping it in an external database isalways a good practice. The pros and cons of adoptingone database schema over the other have been longdebated. Using a proprietary format database may befast to implement, but would pose a big problem if thesoftware were to be upgraded or ported to anotherplatform. One of the best ways to represent data toensure backward compatibility with future versions is67to use a three-tier database structure 7. In 3-tierimplementation the data access code is implemented ina separate layer. The main system makes standardStructured Query Language (SQL) calls to the dataaccess layer.3.1 The AP224 viewer/readerThe AP224 viewer/reader (see Fig.1) is anapplication for reading and viewing AP224 files. Theapplication is capable of reading the AP224 file anddisplaying the solid model as well as displaying thefeature tree of the component including all theattributes of the features. As shown in Fig.1, the AP224reader application window is divided into two panes.The left side of the pane displays the feature tree of thecomponent whereas the right side displays the solidmodel. Clicking on a particular feature in the featuretree highlights the feature in the solid model. Thefeature can also be selected from the drop-down list inthe toolbar.The STEP files, as discussed earlier are plain ASCIItext files. These files are read into the viewer anddisplayed using ST-Developer from Steptools, Inc 8.ST-Developer from StepTools Inc., is a set ofComputer-Aided Software Engineering (CASE) toolsthat reduce the effort required in implementing STEPapplications. ST-Developer is a set of software toolsand programming libraries for working with EXPRESSinformation models and EXPRESS-defined data sets.ST-Developer tools can be used for informationmodeling, application development, and conformancechecking for STEP files. ST-Developer containsprogramming environments that can be used to buildsoftware that works with STEP data in object-orienteddatabases, relational databases, and traditional files. Animportant component of ST-Developer is the ROSEC+ library. This library makes it possible forapplication programs to read, write, create, andmanipulate STEP digital product information. Thislibrary has been used to develop the AP224functionality of the system.3.2 The logic designer and databaseIn the SMPS system, the analytical logic, or morespecifically the domain and empirical knowledge iskept in an external database. This logic can be editedand viewed graphically as a flowchart using the LogicDesigner as shown in Fig.2. The user also has theoptions of having multiple nested logic flowcharts. Thepoint of entry into the logic, or the starting flowchartcan be selected/ configured by the user. This is veryconvenient in case the same system is to be used fordifferent domains. For example, the user could developthe logic for process planning of prismatic mechanicalparts and sheet metal parts as two separate flowchartsand use them as appropriate. Further flexibility isoffered by allowing nesting of flowcharts. Thisapproach to storing the logic has proved immenselysuccessful not only in making the application flexibleand updateable, but also helping in breaking down thedomain specific barriers and making the applicationmore generic. The application itself is only a shell torun the logic. Simple development of new analyticallogic allows the application to be used in a completelynew domain.The logic is captured using a set of standardcommands. The typical syntax of a command is:COMMAND=Arg1,Arg2,.Arg7where COMMAND is the name of the command beingcalled and Arg1.7 are the parameters passed to it.Some sample commands available are: COPY (Copythe value of a variable to another variable), DISP(Display a Line of Text), DLB (Display Scrollable PickList), DWN (Remove a Picture Display), FLOW(Branch into another Flowchart), FRL (Display FreeText Input Form), HELP (Display a Line of Help Text),Fig. 1 AP224 Viewer68LIST (Display a Text File), QS (Ask a Question) andPIC (Display a Picture). Component object (COM orCOM+) technology is used to enable the user to addmore commands. A component is described as areusable piece of software in binary form that can beplugged into other components or software withrelatively little effort. Using component softwareprovides a much more productive way to design, buildand reuse software .The manufacturing database editor allows the user toedit and maintain the resources data and other tables inthe database. The manufacturing database editor can beaccessed as a standalone application or accessed fromwithin the Logic Designer for easier navigation. Thismanufacturing database represents the empiricalknowledge of the assembly-planning expert.3.3 The logic engineThe logic engine is the heart of the system. It isresponsible for actually running the logic stored in thelogic database. During a planning session, the LogicEngine runs the stored logic, retrieves the required datafrom the database and generates an intermediate file.The intermediate file contains macro calls and not theplanning details. For example if the requirement was tomanufacture a hole feature using a drilling operation,the intermediate file would only have a call to themacro which contains the detailed operations formanufacturing the hole feature. These macro calls aretranslated into comprehensive detailed output by thepost-processor. The logic engine also uses thefunctionality of the AP224 viewer/reader to openAP224 file and generate a feature tree of thecomponent in the memory. This feature tree is loadedinto an internal memory data structure and can beinterrogated by using the appropriate flowchartcommands. For example, the developer could write alogic to load a AP 224 feature tree in the memory andthen write a recursive loop to interrogate the featuresone-by-one and process them depending on theirattributes.3.4 The postprocessorThe output of the Logic Engine is a physical filecontaining a series of Macro calls. Each macro is acollection of one or more planning commands forgenerating output. The post processor reads in thecommands from the intermediate file, retrieves themacro from the resource database and passes it theappropriate variables. After resolving the variables, themacro is then processed to generate the output database.The processing of the intermediate file and the processof generating the output is explained in detail in thecase study in the next section. The NC code is alsogenerated in a similar way. In fact the NC code issimilar to any other planning document but is writtenout directly by the post-processor instead of beingderived from an output database like the planningdocuments.3.5 Generating and directing the outputThe output of the macro postprocessor is an outputplan database. This database is a relational databasearranged is hierarchy. Each output plan has a headersection and a series of operations. Each operation has aseries of detail lines for that operation. Each detail linehas 10 Boolean flags corresponding to the 10 userdefined documents. The Boolean flags are used forfiltering the detail lines for generating the documents.Fig. 2 Logic Debsigner69The system is capable of generating the 10 user definedoutput documents either in Rich Text Format (RTF)files or as Extensible Mark-up Language (XML) . Theformat and layout of RTF documents is decided by theCrystal Report templates. The XML data is formattedfor viewing using Extensible Stylesheet Language(XSL). Each XSL stylesheet describes rules forpresenting an XML document source. XSLtransformations can turn XML into a grammar andstructure suitable for display in a browser and therebymake the output viewable on any hardware platform.T