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The advanced application of IGES project
The advanced application of IGES project PHILIP SMITH
Abstract: This paper describes the methodology evolved during a project which brought together six pairs of trading partners who have a commercial need to make CADCAM data exchange work. The resultant methodology has been used by the companies and has moved the process of CADCAM data exchange forward by identifying and raising the issues involved in a formal way. This has led to improved software and procedures for CADCAM data exchange. Keywords: CADCAM data, data exchange.
T
he advanced application of initial graphics
exchange specification (IGES) project consisted of six pairs of companies who had a commercial need to exchange computer-aided design and computeraided manufacturing (CADCAM) data describing real products. The companies concerned were from the aerospace, automotive and railway industries and covered both vehicle manufacturers and suppliers to those manufacturers.
What is C A D C A M data exchange? There are now around 300 different CADCAM systems in the marketplace, some catering for special needs such as a particular industry sector or technology and some more general purpose systems. They each have their own methods of creating and storing the data that is being used to describe industrial products. This data varies in complexity and presentation, from simple twodimensional sketches through to three-dimensional solid models. The information may be used for a variety of reasons ranging from generation of detailed engineering drawings through to geometry which acts as input to other processes such as finite element modelling (FEM) for stresses or other factors and generation of numerical CADCAM Data Exchange Technical Centre, 171 Woodhouse Lane, Leeds LS 3AR, UK Paper received: 3 May 1989
22,t
control (NC) toolpaths which allow the component to be machined. Having stated that each system has its own mechanisms and structures for using and storing the data, it can be seen that data from one system cannot be readily used by a different system. There are two main approaches which are used to solve this problem: direction translation and neutral formats. Direct translators
A direct translator is a piece of software which will read a specific CADCAM database format and convert it to a different specific CADCAM database format. Direct translators have the advantage of being potentially quick and specific and have only to deal with the entities (e.g. lines, arcs, dimensions) that the systems have in common. The disadvantages include: • For each other system with which exchange is desired, two programs are required. This is no problem if it is desired to exchange with only a few systems but if a larger number are involved then the amount of software needed rises rapidly. For n systems n ( n - 1 ) programs are required. • There is the problem that new versions of either system probably require changes in the programs. • Database formats for each system are usually proprietary and descriptions of them may not be widely available. • Direct translation software tends to be expensive, mainly for the reasons described above. The problems with numbers of systems can be put into context with the fact that Volkswagen, the German automotive manufacturer, carried out a survey and found that with both inhouse and external suppliers, they had a requirement for data exchange between 46 different CADCAM systems. Neutral formats
Neutral formats may be described in a loose way as a kind of CADCAM international language. They consist of standards, formats and specifications to which all
0951-5240/89/040224-04503.00 ~t3 1989 Butterworth & Co. (Publishers) Ltd
Computer-Integrated Manufacturing Systems
suppliers of CADCAM systems have access. Each CADCAM system supplier then has to create the ability to read from (the postprocessor) and write to (the preprocessor) the neutral format in question. This reduces the amount of software since the translation process is then a 'hub and spoke' type of arrangement with the neutral format acting as the hub. n systems now require 2n translators which is a more manageable task to cover many different systems. A further advantage is that both pre- and postprocessors are likely to be written and supported by the CADCAM system supplier. The processes involved are shown in Figure 1. The most commonly used formats currently are IGES, SET and VDA-FS. Initial graphics exchange specification (IGES) is capable of transferring a variety of geometry, annotation and structure entities. It covers both two- and three-dimensional geometry from simple lines and arcs to complex curves and surfaces as well as solid models. It also has all the functionality necessary to transfer complete engineering drawings. It is run by the IGES organization based in the USA and the specification is released by the US National Institute of Standards and Technology (formerly the National Bureau of Stay:,' ~rds (NBS)). Most of the major CADCAM systems have some IGES capability. Standard d'exchange et de transfert (SET) has similar capabilities to IGES and came from the French aerospace industry. It is now a French national standard AFNOR z68300 and is widely used in the aerospace industry, for example, by the various Airbus collaborative projects. It is also used in the French automotive industry by PSA and Renault, for example. Verband des Automobilindustrie F1f.chenSchnittstelle (VDA-FS) is a standard developed by the German car manufacturers association (VDA) which covers points, parametric polynomial curves and surfaces. It has been designed to keep the interface simple and covers only a small number of entities necessary to transfer free-form curve and surface information. It is a German national standard DIN 66301 and most CADCAM system suppliers working in the automotive sector have processors available.
Preprocessor~/ ~essor-~ IGESfile ]
s or
Figure 1. Neutral format transfer processes
Background to the project These investigations with CADCAM data exchange using IGES have discovered the following issues. First, data exchange using IGES is not straightforward. Second, each different CADCAM system supplier supports a different set of IGES entities. Third, quality control of some system suppliers' processors is not of a sufficiently high standard. Finally, most of the trials have not been carried out in a formal manner and results and conclusions have not been tested. All of the above led a number of companies to discover that data exchange with a number of trading partners required different rules and procedures for each partner in order to be partially successful. The process also required a large amount of technical input and was expensive. This led to the project being conceived such that a number of trading partners with real commercial relationships, using different CADCAM systems, would investigate the data transfer processing using IGES in a formal manner, using a predefined methodology.
Partners in the project Reasons to use CADCAM data exchange There are many benefits to be obtained from CADCAM data transfer. These include: • reduced leadtimes--no need to transcribe data, • improved quality--no transcription or interpretation errors, • improved productivity, • reduced costs, • improved company image, • may be required to stay in business. For these and other reasons many companies have been investigating CADCAM data exchange, sometimes with threats to suppliers but more often as joint investigations between trading partners. Vol 2 No 4 November 1989
The project ran for a year and finished on 31 January 1989. The following companies were involved in the project. Ford Motor Company, Dunton, Essex, UK exchanged braking system details with Lucas Car Braking Systems, Pontypool, Gwent, UK using Computersion CADDS4X and IBM CADAM. Ford defined the envelope into which the braking master cylinder must fit and Girling transferred 2D design details for Ford to check, fit, and use in its quality assurance reviews. British Rail Engineering Limited, Derby, UK exchanged railway braking system details with Lucas Rail Products, Bromborough, UK using Intergraph and IBM CADAM. Ford New Holland, Basildon, Essex, UK exchanged fuel injection system details with Lucas Diesel Systems, Gillingham, UK using the GE Calma and Computervision
225
CADDS4X. Lucas transferred 3-dimensional component models for incorporation into Ford New Holland's engine design. Austin Rover, Coventry, UK exchanged steering gear details with TRW Cam Gears, Clevedon, Avon, UK using Computervision CADDS4X and IBM CADAM. TRW Cam Gears transferred 2D and 3D design details and models for inclusion in Austin Rover's model database and to record supplier liability. Austin Rover, Coventry, UK exchanged drive shaft details with Hardy Spicer, Birmingham, UK using Computervision CADDS4X and McDonnell Douglas Unigraphics II. Hardy Spicer similarly transferred 2D and 3D drawings and models for inclusion in Austin Rover's model database and to record supplier responsibility. Rolls-Royce plc, Derby, UK exchanged feasibility study 2D design data with Westland Helicopters plc, Yeovil, UK using IBM CADAM and Computervision CADDS4X. The project was devised and managed by the Society of Motor Manufacturers and Traders (SMMT) through its Organisation for Data Exchange through Teletransmission in Europe (ODETTE) UK Engineering Group. ODETTE is an eight country project working on electronic communication between vehicle manufacturers and their suppliers. The project was administered by the Motor Industry Research Association (MIRA) which undertook the user survey 'Corporate requirements and expectations for CADCAM data exchange' which was also published by the SMMT. The project was funded
Yes
Request'or I
IGES change
by the participating companies and the UK Department of Trade and Industry through a 'Support for innovation' grant. Technical support was provided by the CADCAM Data Exchange Technical Centre (CADDETC).
CADCAM systems involved The following systems were involved in the project: CADAM, supplied by IBM; CADDS4X, supplied by Computervision; DDM, supplied by Calma; IGDS, supplied by Intergraph and Unigraphics, supplied by McDonnell Douglas Information Systems. The project was supported by all the CADCAM systems' vendors.
The project methodology The methodology designed for the project is shown pictorially in Figure 2. A brief description of the various parts is given below.
Pre-transfer investigation The likely outcome of the transfer between the particular pair of CADCAM systems involved was investigated using CADDETC's Leeds University database for determining interCAD system transfer effectiveness (LUDDITE) software. This works by comparing the mapping from each system into and out of IGES and thus forecasting those entities which will transfer
No
No
I Mo i'yi part I
l CADpart "
Yes
=7 RecommendedI practice
J • • • • Database listing/plot
I t
[ Preprocess I • • • • Logfile
I IGESfile I
I
[ Checkfile
Yes
I Yes
I Fixb"gs I I
I
l CADpart
] • • • •
I
I
I
Database listing/plot
No
Figure 2. Advanced application of IGES project methodology 226
Computer-Integrated Manufacturing Systems
correctly, those which will be degraded and those which will not transfer.
The loop This consists of the following seven steps. First, analysis of the CAD part in the sending system. This involves interrogating the database of the system and generating plots and any other relevant information. Second, preprocessing of part to 1GES. This generates the IGES file and should also provide a 'log file' which details any problems encountered or entities which are not supported by the preprocessor. Third, checking the IGES file. This uses CADDETC's software tools for IGES file diagnosis. This stage identifies any non-compliances of the file with the IGES specification. Fourth, if any errors are found they are reported f~r correction to the sending system's supplier. Fifth, when the file is correct then postprocess the IGES file into the receiving system. Again a 'log file' should be produced by the postprocessor which details any errors or unsupported entities. Sixth, the CAD part in the receiving system can now be analysed using database interrogation, plots and other necessary techniques. If there are differences between the sent and received part then it may be due to: • Problems with the postprocessor. These are reported to the receiving system's supplier for correction. • Differences in interpretation of the IGES specification between the pre- and postprocessor. These are resolved by generating a recommended or best practice which both parties agree to.
Vol 2 No 4 November 1989
• Deficiencies in the IGES specification. These are raised as 'requests for change' to the IGES organization. • Lack of entity support at either pre- or postprocessor level. These are raised as enhancement requests with the relevant CADCAM system supplier. Seventh, if necessary the original part is altered on the basis of the findings, commercial pressures and CADCAM systems suppliers' bug-fixes and enhancements timescales and the part is retested.
Conclusions The project methodology worked well in 'proving the route' for CADCAM data exchange. The six pairs of companies were able to identify and raise about 70 issues with the system's suppliers. These issues are being resolved and the final changes should have filtered through to all users by the end of 1989. One of the concerns has been the length of time that bug-fixes have taken, particularly with software suppliers based in the USA. The methodology is intended for use at the prototype and testing phase of data transfer and not at the production phase. The issues to be resolved are highlighted and CADDETC can help with providing solutions to these problems subject to timescale and budgetary constraints. Overall, the project has proved the usefulness of the methodology and all the partners would recommend this approach to making CADCAM data exchange work. []
227
Abstract: This paper describes the methodology evolved during a project which brought together six pairs of trading partners who have a commercial need to make CADCAM data exchange work. The resultant methodology has been used by the companies and has moved the process of CADCAM data exchange forward by identifying and raising the issues involved in a formal way. This has led to improved software and procedures for CADCAM data exchange. Keywords: CADCAM data, data exchange.
T
he advanced application of initial graphics
exchange specification (IGES) project consisted of six pairs of companies who had a commercial need to exchange computer-aided design and computeraided manufacturing (CADCAM) data describing real products. The companies concerned were from the aerospace, automotive and railway industries and covered both vehicle manufacturers and suppliers to those manufacturers.
What is C A D C A M data exchange? There are now around 300 different CADCAM systems in the marketplace, some catering for special needs such as a particular industry sector or technology and some more general purpose systems. They each have their own methods of creating and storing the data that is being used to describe industrial products. This data varies in complexity and presentation, from simple twodimensional sketches through to three-dimensional solid models. The information may be used for a variety of reasons ranging from generation of detailed engineering drawings through to geometry which acts as input to other processes such as finite element modelling (FEM) for stresses or other factors and generation of numerical CADCAM Data Exchange Technical Centre, 171 Woodhouse Lane, Leeds LS 3AR, UK Paper received: 3 May 1989
22,t
control (NC) toolpaths which allow the component to be machined. Having stated that each system has its own mechanisms and structures for using and storing the data, it can be seen that data from one system cannot be readily used by a different system. There are two main approaches which are used to solve this problem: direction translation and neutral formats. Direct translators
A direct translator is a piece of software which will read a specific CADCAM database format and convert it to a different specific CADCAM database format. Direct translators have the advantage of being potentially quick and specific and have only to deal with the entities (e.g. lines, arcs, dimensions) that the systems have in common. The disadvantages include: • For each other system with which exchange is desired, two programs are required. This is no problem if it is desired to exchange with only a few systems but if a larger number are involved then the amount of software needed rises rapidly. For n systems n ( n - 1 ) programs are required. • There is the problem that new versions of either system probably require changes in the programs. • Database formats for each system are usually proprietary and descriptions of them may not be widely available. • Direct translation software tends to be expensive, mainly for the reasons described above. The problems with numbers of systems can be put into context with the fact that Volkswagen, the German automotive manufacturer, carried out a survey and found that with both inhouse and external suppliers, they had a requirement for data exchange between 46 different CADCAM systems. Neutral formats
Neutral formats may be described in a loose way as a kind of CADCAM international language. They consist of standards, formats and specifications to which all
0951-5240/89/040224-04503.00 ~t3 1989 Butterworth & Co. (Publishers) Ltd
Computer-Integrated Manufacturing Systems
suppliers of CADCAM systems have access. Each CADCAM system supplier then has to create the ability to read from (the postprocessor) and write to (the preprocessor) the neutral format in question. This reduces the amount of software since the translation process is then a 'hub and spoke' type of arrangement with the neutral format acting as the hub. n systems now require 2n translators which is a more manageable task to cover many different systems. A further advantage is that both pre- and postprocessors are likely to be written and supported by the CADCAM system supplier. The processes involved are shown in Figure 1. The most commonly used formats currently are IGES, SET and VDA-FS. Initial graphics exchange specification (IGES) is capable of transferring a variety of geometry, annotation and structure entities. It covers both two- and three-dimensional geometry from simple lines and arcs to complex curves and surfaces as well as solid models. It also has all the functionality necessary to transfer complete engineering drawings. It is run by the IGES organization based in the USA and the specification is released by the US National Institute of Standards and Technology (formerly the National Bureau of Stay:,' ~rds (NBS)). Most of the major CADCAM systems have some IGES capability. Standard d'exchange et de transfert (SET) has similar capabilities to IGES and came from the French aerospace industry. It is now a French national standard AFNOR z68300 and is widely used in the aerospace industry, for example, by the various Airbus collaborative projects. It is also used in the French automotive industry by PSA and Renault, for example. Verband des Automobilindustrie F1f.chenSchnittstelle (VDA-FS) is a standard developed by the German car manufacturers association (VDA) which covers points, parametric polynomial curves and surfaces. It has been designed to keep the interface simple and covers only a small number of entities necessary to transfer free-form curve and surface information. It is a German national standard DIN 66301 and most CADCAM system suppliers working in the automotive sector have processors available.
Preprocessor~/ ~essor-~ IGESfile ]
s or
Figure 1. Neutral format transfer processes
Background to the project These investigations with CADCAM data exchange using IGES have discovered the following issues. First, data exchange using IGES is not straightforward. Second, each different CADCAM system supplier supports a different set of IGES entities. Third, quality control of some system suppliers' processors is not of a sufficiently high standard. Finally, most of the trials have not been carried out in a formal manner and results and conclusions have not been tested. All of the above led a number of companies to discover that data exchange with a number of trading partners required different rules and procedures for each partner in order to be partially successful. The process also required a large amount of technical input and was expensive. This led to the project being conceived such that a number of trading partners with real commercial relationships, using different CADCAM systems, would investigate the data transfer processing using IGES in a formal manner, using a predefined methodology.
Partners in the project Reasons to use CADCAM data exchange There are many benefits to be obtained from CADCAM data transfer. These include: • reduced leadtimes--no need to transcribe data, • improved quality--no transcription or interpretation errors, • improved productivity, • reduced costs, • improved company image, • may be required to stay in business. For these and other reasons many companies have been investigating CADCAM data exchange, sometimes with threats to suppliers but more often as joint investigations between trading partners. Vol 2 No 4 November 1989
The project ran for a year and finished on 31 January 1989. The following companies were involved in the project. Ford Motor Company, Dunton, Essex, UK exchanged braking system details with Lucas Car Braking Systems, Pontypool, Gwent, UK using Computersion CADDS4X and IBM CADAM. Ford defined the envelope into which the braking master cylinder must fit and Girling transferred 2D design details for Ford to check, fit, and use in its quality assurance reviews. British Rail Engineering Limited, Derby, UK exchanged railway braking system details with Lucas Rail Products, Bromborough, UK using Intergraph and IBM CADAM. Ford New Holland, Basildon, Essex, UK exchanged fuel injection system details with Lucas Diesel Systems, Gillingham, UK using the GE Calma and Computervision
225
CADDS4X. Lucas transferred 3-dimensional component models for incorporation into Ford New Holland's engine design. Austin Rover, Coventry, UK exchanged steering gear details with TRW Cam Gears, Clevedon, Avon, UK using Computervision CADDS4X and IBM CADAM. TRW Cam Gears transferred 2D and 3D design details and models for inclusion in Austin Rover's model database and to record supplier liability. Austin Rover, Coventry, UK exchanged drive shaft details with Hardy Spicer, Birmingham, UK using Computervision CADDS4X and McDonnell Douglas Unigraphics II. Hardy Spicer similarly transferred 2D and 3D drawings and models for inclusion in Austin Rover's model database and to record supplier responsibility. Rolls-Royce plc, Derby, UK exchanged feasibility study 2D design data with Westland Helicopters plc, Yeovil, UK using IBM CADAM and Computervision CADDS4X. The project was devised and managed by the Society of Motor Manufacturers and Traders (SMMT) through its Organisation for Data Exchange through Teletransmission in Europe (ODETTE) UK Engineering Group. ODETTE is an eight country project working on electronic communication between vehicle manufacturers and their suppliers. The project was administered by the Motor Industry Research Association (MIRA) which undertook the user survey 'Corporate requirements and expectations for CADCAM data exchange' which was also published by the SMMT. The project was funded
Yes
Request'or I
IGES change
by the participating companies and the UK Department of Trade and Industry through a 'Support for innovation' grant. Technical support was provided by the CADCAM Data Exchange Technical Centre (CADDETC).
CADCAM systems involved The following systems were involved in the project: CADAM, supplied by IBM; CADDS4X, supplied by Computervision; DDM, supplied by Calma; IGDS, supplied by Intergraph and Unigraphics, supplied by McDonnell Douglas Information Systems. The project was supported by all the CADCAM systems' vendors.
The project methodology The methodology designed for the project is shown pictorially in Figure 2. A brief description of the various parts is given below.
Pre-transfer investigation The likely outcome of the transfer between the particular pair of CADCAM systems involved was investigated using CADDETC's Leeds University database for determining interCAD system transfer effectiveness (LUDDITE) software. This works by comparing the mapping from each system into and out of IGES and thus forecasting those entities which will transfer
No
No
I Mo i'yi part I
l CADpart "
Yes
=7 RecommendedI practice
J • • • • Database listing/plot
I t
[ Preprocess I • • • • Logfile
I IGESfile I
I
[ Checkfile
Yes
I Yes
I Fixb"gs I I
I
l CADpart
] • • • •
I
I
I
Database listing/plot
No
Figure 2. Advanced application of IGES project methodology 226
Computer-Integrated Manufacturing Systems
correctly, those which will be degraded and those which will not transfer.
The loop This consists of the following seven steps. First, analysis of the CAD part in the sending system. This involves interrogating the database of the system and generating plots and any other relevant information. Second, preprocessing of part to 1GES. This generates the IGES file and should also provide a 'log file' which details any problems encountered or entities which are not supported by the preprocessor. Third, checking the IGES file. This uses CADDETC's software tools for IGES file diagnosis. This stage identifies any non-compliances of the file with the IGES specification. Fourth, if any errors are found they are reported f~r correction to the sending system's supplier. Fifth, when the file is correct then postprocess the IGES file into the receiving system. Again a 'log file' should be produced by the postprocessor which details any errors or unsupported entities. Sixth, the CAD part in the receiving system can now be analysed using database interrogation, plots and other necessary techniques. If there are differences between the sent and received part then it may be due to: • Problems with the postprocessor. These are reported to the receiving system's supplier for correction. • Differences in interpretation of the IGES specification between the pre- and postprocessor. These are resolved by generating a recommended or best practice which both parties agree to.
Vol 2 No 4 November 1989
• Deficiencies in the IGES specification. These are raised as 'requests for change' to the IGES organization. • Lack of entity support at either pre- or postprocessor level. These are raised as enhancement requests with the relevant CADCAM system supplier. Seventh, if necessary the original part is altered on the basis of the findings, commercial pressures and CADCAM systems suppliers' bug-fixes and enhancements timescales and the part is retested.
Conclusions The project methodology worked well in 'proving the route' for CADCAM data exchange. The six pairs of companies were able to identify and raise about 70 issues with the system's suppliers. These issues are being resolved and the final changes should have filtered through to all users by the end of 1989. One of the concerns has been the length of time that bug-fixes have taken, particularly with software suppliers based in the USA. The methodology is intended for use at the prototype and testing phase of data transfer and not at the production phase. The issues to be resolved are highlighted and CADDETC can help with providing solutions to these problems subject to timescale and budgetary constraints. Overall, the project has proved the usefulness of the methodology and all the partners would recommend this approach to making CADCAM data exchange work. []
227