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Synthesis of the digital mock-up system for heterogeneous CAD assembly In-Ho Song a , Sung-Chong Chung b, * a Mechanical Engineering Department, Hanyang University, Seoul 133-791, Republic of Korea b School of Mechanical Engineering, Hanyang University, Seoul 133-791, Republic of Korea 1. Introduction Many collaborators are involved in design processes of cars, ships, aircrafts, machine tools, etc. Instead of a single CAD source, several CAD systems are used to design such complex products in the distributed design environment. Lots of mismatches and interferences due to designers’ faults as well as several kinds of CAD systems are occurred. To remove and compensate for such difficulties in the design process, real mock-ups and CAD systems have been used so far. Digital mock-up (DMU) system, a tool to build a virtual mock-up in the design stage, is used widely to prevent the interferences and mismatches during precision design and assembly processes without physical mock-ups. In 2003, Rezayat [1] translated topological CAD information into XML data by using KBPD (Knowledge-Based Product Devel- opment), and proposed a DTD type schema called CADML (CAD Markup Language). He applied the XML to exchange of CAD data. To realize the collaborative design work in the distributed environment, Shyamsundar and Gadh [2] proposed simplified assembly model, AREP (Assembly REPresentation). In 2004, Chen et al. [3] studied e-Assembly to develop a real-time web-based collaborative design for assembly through the ACIS kernel and the CAR (Collaborative Assembly Representation) model. Yang et al. proposed a macro data representation method of XML data for CAD model exchange [4]. Based on XML and standard modeling language, they constructed part databases of various CAD systems, but it was limited to part design. XML-based e-Assembly for design and manufacturing has not been studied yet. In 2003, Mervyn et al. [5] utilized JAVA and XML to develop an Internet-enabled IFD system enabling design work by placing its modeler at the server. It delivers fixture shape facet information to XML, and visualizes the information. Therefore, it is good to design of simple assembly shapes such as fixtures, but is inefficient for the modeling of complex assembly shapes as well as not applicable to the integration of commercial CAD systems. In 2005, Pan et al. [6] developed a converter extracting STEP data directly in a JAVA- based program, and built a system interpreting whether there is any interference among parts. Interference-free matrices were derived from the interference test function of the system. In this work, Standard Data Access Interface for STEP linked to JAVA (JSDAI) was used for the interference examination. However, as the file size of the STEP files was big, it was not applicable on the Internet environment. It was also difficult to apply for the assembly DMU of heterogeneous commercial CAD systems. In 2003, Jezernik and Hren developed a low cost VR (virtual reality) system by using XML and VRML [7]. JT of UGS [8] and HSF of HOOPS [9] visualize Computers in Industry 60 (2009) 285–295 ARTICLE INFO Article history: Received 18 November 2006 Received in revised form 10 April 2008 Accepted 4 September 2008 Available online 2 November 2008 Keywords: Assembly DMU (digital mock-up) Heterogeneous CAD STEP PDM schema XML ABSTRACT Many collaborators are involved in design processes of cars, ships, aircrafts, machine tools, etc. Instead of a single CAD source, several CAD systems are used to design such complex products in the distributed design environment. There are many mismatches and interferences due to designers’ faults as well as several kinds of CAD systems. Digital mock-up (DMU) system, a tool to build a virtual mock-up in the design stage, has been used to prevent the interferences and mismatches during precision design processes. In this paper, a heterogeneous CAD assembly method to construct the DMU system is proposed through an XML and the lightweight CAD file. The XML data contain hierarchy of heterogeneous CAD assemblies. STEP PDM schema is applied to construct the XML data. The lightweight CAD file produced from a CAD file through ACIS kernel and InterOp includes not only mesh and B-Rep data, but also topological data. They are used to visualize CAD data and to verify dimensions of the parts. Developed system is executable on a desktop computer. It does not require commercial CAD systems to visualize 3D assembly data. Assembly of heterogeneous CAD models has been conducted to verify the effectiveness of the developed DMU system on the Internet. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +82 2 2220 0444; fax: +82 2 2298 4634. E-mail address: [email protected] (S.-C. Chung). Contents lists available at ScienceDirect Computers in Industry journal homepage: www.elsevier.com/locate/compind 0166-3615/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.compind.2008.09.004

Synthesis of the digital mock-up system for heterogeneous CAD assembly

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Synthesis of the digital mock-up system for heterogeneous CAD assembly

In-Ho Song a, Sung-Chong Chung b,*a Mechanical Engineering Department, Hanyang University, Seoul 133-791, Republic of Koreab School of Mechanical Engineering, Hanyang University, Seoul 133-791, Republic of Korea

Computers in Industry 60 (2009) 285–295

A R T I C L E I N F O

Article history:

Received 18 November 2006

Received in revised form 10 April 2008

Accepted 4 September 2008

Available online 2 November 2008

Keywords:

Assembly

DMU (digital mock-up)

Heterogeneous CAD

STEP PDM schema

XML

A B S T R A C T

Many collaborators are involved in design processes of cars, ships, aircrafts, machine tools, etc. Instead of

a single CAD source, several CAD systems are used to design such complex products in the distributed

design environment. There are many mismatches and interferences due to designers’ faults as well as

several kinds of CAD systems. Digital mock-up (DMU) system, a tool to build a virtual mock-up in the

design stage, has been used to prevent the interferences and mismatches during precision design

processes. In this paper, a heterogeneous CAD assembly method to construct the DMU system is proposed

through an XML and the lightweight CAD file. The XML data contain hierarchy of heterogeneous CAD

assemblies. STEP PDM schema is applied to construct the XML data. The lightweight CAD file produced

from a CAD file through ACIS kernel and InterOp includes not only mesh and B-Rep data, but also

topological data. They are used to visualize CAD data and to verify dimensions of the parts. Developed

system is executable on a desktop computer. It does not require commercial CAD systems to visualize 3D

assembly data. Assembly of heterogeneous CAD models has been conducted to verify the effectiveness of

the developed DMU system on the Internet.

� 2008 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Computers in Industry

journal homepage: www.e lsev ier .com/ locate /compind

1. Introduction

Many collaborators are involved in design processes of cars,ships, aircrafts, machine tools, etc. Instead of a single CAD source,several CAD systems are used to design such complex products inthe distributed design environment. Lots of mismatches andinterferences due to designers’ faults as well as several kinds ofCAD systems are occurred. To remove and compensate for suchdifficulties in the design process, real mock-ups and CAD systemshave been used so far. Digital mock-up (DMU) system, a tool tobuild a virtual mock-up in the design stage, is used widely toprevent the interferences and mismatches during precision designand assembly processes without physical mock-ups.

In 2003, Rezayat [1] translated topological CAD informationinto XML data by using KBPD (Knowledge-Based Product Devel-opment), and proposed a DTD type schema called CADML (CADMarkup Language). He applied the XML to exchange of CAD data.To realize the collaborative design work in the distributedenvironment, Shyamsundar and Gadh [2] proposed simplifiedassembly model, AREP (Assembly REPresentation). In 2004, Chenet al. [3] studied e-Assembly to develop a real-time web-based

* Corresponding author. Tel.: +82 2 2220 0444; fax: +82 2 2298 4634.

E-mail address: [email protected] (S.-C. Chung).

0166-3615/$ – see front matter � 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.compind.2008.09.004

collaborative design for assembly through the ACIS kernel and theCAR (Collaborative Assembly Representation) model. Yang et al.proposed a macro data representation method of XML data for CADmodel exchange [4]. Based on XML and standard modelinglanguage, they constructed part databases of various CAD systems,but it was limited to part design. XML-based e-Assembly for designand manufacturing has not been studied yet. In 2003, Mervyn et al.[5] utilized JAVA and XML to develop an Internet-enabled IFDsystem enabling design work by placing its modeler at the server. Itdelivers fixture shape facet information to XML, and visualizes theinformation. Therefore, it is good to design of simple assemblyshapes such as fixtures, but is inefficient for the modeling ofcomplex assembly shapes as well as not applicable to theintegration of commercial CAD systems. In 2005, Pan et al. [6]developed a converter extracting STEP data directly in a JAVA-based program, and built a system interpreting whether there isany interference among parts. Interference-free matrices werederived from the interference test function of the system. In thiswork, Standard Data Access Interface for STEP linked to JAVA(JSDAI) was used for the interference examination. However, as thefile size of the STEP files was big, it was not applicable on theInternet environment. It was also difficult to apply for the assemblyDMU of heterogeneous commercial CAD systems. In 2003, Jezernikand Hren developed a low cost VR (virtual reality) system by usingXML and VRML [7]. JT of UGS [8] and HSF of HOOPS [9] visualize

I.-H. Song, S.-C. Chung / Computers in Industry 60 (2009) 285–295286

assembled parts composed of heterogeneous CAD data. However,since they are not interfaced with XML or STEP/PDM schema, theyare not applicable to various PDM (product data management)systems.

In this paper, the visualization of an XML-based DMU systemfor assembled parts composed of heterogeneous CAD data isproposed through the visualization of the lightweight CAD file[10]. The developed system does not require expensivecommercial CAD systems. Cost of ownership is cheaper thanthat of other systems. In addition, the system has functions ofreal-time interference check, dimensional inspection, and designverification of heterogeneous CAD assembled parts on theInternet environment. The lightweight CAD data [10] are usedfor sharing and assembly. XML is used for displaying andinterfacing of BOMs (bill of materials) of assembled parts. Bydesigning a schema based on the international standard of ISO/STEP PDM, the developed system is interfaced with mostcommercial PDM systems. In order to interface with othersystems, modified positional information generated in theassembly process is stored as the XML format and is registeredin the PDM system database.

2. Related researches

2.1. XML

XML was introduced at W3C (World Wide Web Consortium)in 1998. It is a standard to exchange structured documentsand data in the Internet environment. XML makes users definetags arbitrarily. It stores the structure and meaning of datawithout any changes. It is applied to exchange data withother systems. XML displays various characters through theunicode and is independent upon languages. Therefore, XML

Fig. 1. Multi-level assembly DMU insta

exchanges information in heterogeneous platforms and systems[11].

In this paper, to develop a digital mock-up system, an XMLassembly is to be designed based on the standard information, ISO10303-28 XML rule and STEP PDM schema. It guarantees the dataexchange between PDM systems.

2.2. VRML

VRML (Virtual Reality Modeling Language) was appeared byreleasing rule 1.0 in 1994, and has been spread through theInternet. The VRML now adopted as the international standardof ISO/IEC 14772-1 [12]. VRML defines the interaction betweenmulti-medias as a programmable object by using Java script. Thedefinition of object is called Node. The Nodes are arranged in thehierarchical structure called scene graphs. They might bedistinguished from other nodes or might affect to the others.However, the VRML translator in CAD system supports only textbased VRML. The text based VRML has similar data sizecomparing with original CAD data. It takes longer time to readthe data.

2.3. X3D

After VRML was adopted as an ISO standard, XML based X3D,developed in the Web3D consortium, was released in 1999 [13].X3D means extensible 3D and extended functions of VRML. Itrepresents the integration of them with XML. Contrary to VRML,X3D follows standard type of XML grammar. It has goodcompatibility and is extensible by the code modulization. X3Dsupports NURBS (Non-Uniform Rational B-Spline) as well. How-ever, CAD systems do not support it directly conversion. Thus, it isdifficult to use X3D for CAD data verification.

nce diagram in the PDM schema.

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2.4. ISO/STEP PDM schema

The PDM schema (ISO/TC184/SC4), the standard of ISO/STEP,provides integrated modeling technique of product information[14]. This is the core standard of a product information manager. Asthe PDM schema has general product information applicable tovarious AP (Application Protocol), it is extensible and flexible as astandard.

The STEP PDM schema supports a clear hierarchy representingthe product structure and its elements. Especially, PDM schemadistinguishes not only the relationship between closed child andparent assemblies, but also the advanced relationship of elementsin the assembly. Fig. 1 displays several steps of assembly DMUinstance. By using this, the PDM schema distinguishes every singlecomponent in the multi-assembly structure. A number of different

Fig. 2. XML schema stru

views under the each part version are defined. In addition, positionand topological information, and component’s characteristics arespecified and recognized. Using the ‘specified_higher_usage_oc-currence’ entity, higher and lower relationships of an assembly aresearched [14].

The PDM schema is imported and used to design XML schemastructure to manage and verify the assembly information designedon various CAD, PDM and DMU systems. The contents, interfacedfrom XML, are stored at the data storage to register in the PDMsystem by mapping the XML schema database.

3. Visualization of assembly

The visualization of assembly is designed by the PDM schemaof the STEP standard. Fig. 2 shows an XML schema structure of

cture for assembly.

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an assembly and parts. The XML schema structure consistsof assemblies called subassemblies, and its parts calledcomponents. The subassemblies may adopt other assembliesor parts.

The parts and subassemblies have matrix data to representpositional information. The matrix data containing thepositional information are constructed with transformationmatrices (V1–V9) and position vectors (T1–T3) at ‘Position’of the parts or subassemblies, respectively. ‘Name’ in Fig. 2means the name of the part or sub-assembly on BOM. ‘Id’ is anumber to distinguish assemblies or parts. ‘Type’ means thetype of link data. According to the ‘Type’, users are able toselect an appropriate translator for visualization. ‘Version’describes the version of drawings. ‘Higher_info’ is an entityrepresenting higher-level information, and it supports asearching function of a hierarchy in the multi-level assembly.‘Link’ in an assembly supports the connection between sub-assemblies or parts. ‘Link’ in a part is connected to physicalvisualization data. The XML schema expresses up to n levelassemblies and accesses CAD BOM. As the XML data is designedaccording to DMU of the multi-level assembly, higher and/orlower stage searches are conducted conveniently. If theassembly data structure is designed as one-directional referencetype, the child parts do not have information of the parents.Thus, when a sub-child part is modified, all parts of the childrenin the parent level should be searched in order to understandwhich parents have modified the sub-child. However, as

Fig. 3. Overall framework

the developed XML schema allows quick searching whethera parent or a child is modified, CAD data registered in variousPDM systems are easily interfaced to the developed XML schema[15].

4. System architecture

Fig. 3 shows overall structure of the proposed system. It consistsof following modules: the CAD API (Application ProgrammingInterface), PDM server and data base, Web server and servletengine for Web interface, data translator for visualization, andPDM-viewer client.

The operating procedure of the system is conducted asfollows: various CAD data are registered to PDM by selecting the‘Check in’ menu of the PDM system. The menus are constructedby CAD APIs (CATIA’s CAA, Pro/Engineer’s Pro-toolkit, Unigra-phics’s UG Open). Fig. 4 describes the check-in process of theassembly CAD data to find positional information of a partthrough the flowchart. The check-in button is selected from thePDM menu embedded in the CAD system to start the assemblycheck-in process. Parts registered in the CAD system aresearched through the CAD API. When the parts are retrieved,the position matrix of the parts is extracted using the CAD API.Once extraction of the position matrix is completed, the Part IDand position matrix are saved on the XML file according to theXML schema shown in Fig. 2, and the algorithm continues to findother parts. When there are no more parts to be found,

of the DMU system.

Fig. 4. Check-in process of an assembly data on the CAD system.

Fig. 5. Comparisons of translation processes.

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construction of the XML file is ended. Then the XML andassembly CAD data are saved on the PDM system and thealgorithm terminates. When the CAD data are registered into thePDM, the system extracts position and assembly information ofthe CAD data by using the CAD API as shown in Fig. 3(a). The CADdata, registered in the PDM system, are translated to the visualdata as a lightweight CAD file [10] by the CAD Translator [16–19]shown in Fig. 3(b), and PDM database is constructed by the PDMsystem as shown in Fig. 3(c). CAD translation is conductedaccording to the three steps procedure. First, CAD data is loadedto the InterOp translator as shown in Fig. 3(b.1). Secondly, theloaded CAD data is translated to the ACIS format through theInterOp translator as shown in Fig. 3(b.2). Finally, ACIS format istranslated to visual data by the ACIS API as shown in Fig. 3(b.3)[10]. Details of the visual data structure are described in Section5. When users check out an assembly need to be verified, thenthe DMU Web viewer is plugging into the Web browser. Theassembly XML and the lightweight CAD file as visual data ofcomponents are visualized on the web viewer as shown inFig. 3(d). After verification by the assembly DMU, the systemchecks in the assembly on the viewer, and then delivers thechanged assembly position by XML as shown in Fig. 3(e). Theverified file, checked by the DMU web viewer, is to be verifiedagain on CAD systems. To be verified on the CAD system, thefile should be searched through the PDM system, and then‘Check-out’ to the CAD system (Fig. 3(f)). By using theseprocedures, users are able to check whether the CAD data haveinterferences. If there are interferences, clients can modify themand register modified data through ‘Check-in’ procedure of thePDM system.

5. Generation of visual data

Most PDM systems convert CAD data into visual datafor efficiency and security. In this paper, visual data aregenerated separately as the component file and the assemblyinformation. Lightweight CAD file structure [10,19] is appliedto construct the visual data as follows: ‘‘Group’’ is the top entityfor managing the assembled structure of several solids. ‘‘Solid’’is applicable to represent the solid of the CAD entity. In addition,a solid consists of faces. ‘‘Face’’ is located under the ‘‘Solid’’.‘‘Face’’ consists of tessellated triangle data for visualizationof the CAD model and edge information for the dimensionalverification. ‘‘Edge’’ is saved with a separator to be classifiedinto ‘‘Line’’, ‘‘Conic’’ and ‘‘Curve’’. They are composed oflinear lines, conic curves and spline curves, respectively. Theseparator identifies edges and enables dimensional verification[10,19].

CAD data corresponding to the part generate visual datathrough the translator shown in Fig. 3(b), but the other CAD datacorresponding to the assembly consist of the connecting andposition informations as matrices including the visual data.These assembly data corresponding to sub-parts of the PDMsystem data are obtained through the check-in process as shownin Fig. 4. Using both informations, clients are able to search thedata on the PDM. An XML-writer generates an XML filesaccording to the XML schema structure shown in Fig. 2 for theassembly visualization. The XML-writer was developed by usingXerces XML Parser [20].

Table 1Comparisons of visual data size.

Data name Original CAD

file size (MB)

Previous [21]

visual data size (MB)

Proposed visual

data size (MB)

A0 70 7 –

A1 20 2 –

P1 10 1 1

P2 10 1 1

P3 10 1 1

P4 10 1 1

P5 10 1 1

P6 10 1 1

P7 10 1 1

Total 160 16 7

Fig. 6. PDM database structure for an assembly model.

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In general, the generation process of visual data converts allCAD data (size 70) of an assembly at once in the translationserver as shown in Fig. 5(a). In addition to the conversion of thepart data, the conversion (size 70) of the assembly itself isrequired as well. Since the two conversions are required at once,a high performance translation server is mandatory. However,using the proposed method of this paper, only the conversion ofvisual data of parts is required. Minimum requirement of thetranslation server is limited to the size 20 of the maximumpart as shown in Fig. 5(b). If an assembly is composed ofduplicated parts, the visual data might be reduced remarkably. Ifthere is frequent design modification, the translation servershould have big capacity for data storage. However, as only thevisual data of the modified parts are required in this paper,clients are able to save memories and reduce the server sizeremarkably.

Table 1 shows the translated data size of the original CAD datashown in Fig. 6. It consists of A0–P7 parts. The third column showsthe data size of the previous visual data [21]. The fourth column isthe data size of the proposed visual data generated from thedeveloped system.

6. Assembly data management in the PDM

The management method of assembly data is as follows: First,extract part feature and positional information from the assembly.Define the extracted positional information according to therelative position in the assembly structure. ‘Id’ in Fig. 6 means theidentity information of each part and assembly. The assembly tabledenotes interrelation between the assembly and subordinatedparts. System stores the parent ‘Id’ value to the ‘Higher info’element, and then stores the child ‘Id’ value to ‘Link’. Part’s relativepositional data corresponding to the higher assembly is stored in‘Position’.

Fig. 6(a) shows an assembly with three levels. The linkedstructure of the higher-level and lower-level assemblies, which arethe assembly XML structure shown in Fig. 2, should be expressed.The linked structure between the lower-level assembly and theparts should be identical in the database. To keep it and to save theassembly data in the database as shown in Fig. 6(b), designcontents of it is constructed as follows: Identity numbers of eachassembly and part are A0, A1, P1, P2 and P3, etc. Connectivity of A1is defined at the third and fourth rows of Fig. 6(b). A ‘NULL’ value isstored at both ‘Higher info’ and ‘Position’ columns because themain assembly A0 does not have any parent parts. The ‘NULL’ valuemeans that there is no argument. Since the parent of A1 is A0, A0 isstored in ‘Higher info’. On the other hand, A1’s children are P2 andP3, both P2 and P3 are stored at ‘Link.’ Parts P1, P2, and P3 save

their parent information at ‘Higher info’. The parents meanassemblies.

Visualization data V1, V2, and V3 are stored at ‘Link’. Positionalinformation is found by multiplying the position matrices on thepath. For example, position P2 is calculated by multiplying M3,1 ofP2, M2,2 of A1, and A0. However, A0 does not have the matrix, andthe position matrix of part P2, Mpart2 is calculated by multiplyingM3,1 and M2,2 in the order from the lower level to the higher level asgiven by the following equation:

Mpart2 ¼ M3;1 �M2;2 (1)

As an example of the DMU method for heterogeneous CADdata, parts P2 and P3 constructed on different CAD systems areproposed for an assembly A1. When the design of parts iscompleted, they are registered from the CAD system to the PDMsystem. Then, visualization data of P2 and P3 are generated on

Fig. 7. CAD assembly using an XML file.

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Fig. 8. Kart assembly for multi-level DMU.

Fig. 9. Check-in of the assembly data on a CAD system.

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Fig. 10. The assembly structure on the PDM system.

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the PDM system, respectively. As they have been designed underdifferent CAD systems, the location information of each part inassembly A1 is not generated on the CAD system. To generatethe assembly A1, parts P2 and P3 are searched on the PDMsystem and are visualized on the DMU viewer. This process isconducted through the DMU of the assembly A1 and theselection of optimal locations of each part. After the completionof DMU, the selected locations of P2 and P3 are registered on thePDM system. The information on assembly A1 is accessible onthe PDM system. This means that CAD data of each part isreturned to initially designed CAD system to modify the originalCAD data.

7. Case study

7.1. Application of the XML schema

To implement the developed assembly verification systemusing XML, previously developed lightweight CAD translator[10,17,19] and the XML file composer developed in this paperare applied to the system. Oracle is used as a database of thePDM system. Fig. 6 shows an example of an XML file and thelightweight CAD data generated when the visualization data isrequired in the PDM system. Fig. 7(a) saves relative positiondata of each part to ‘Position’. Fig. 7(b) saves link information ofthe real visualization data to ‘FilePath’. The visualization datalink of (b) is connected to Fig. 7(c) to visualize data. When theseparts are connected to the CAD system, they are replaced withCAD data. Finally, DMU verification is conducted on the CADsystem.

7.2. Application of multi-level assembly

A kart assembly shown in Fig. 8(b) is used as a case study. It isa three-level assembly as shown in Fig. 8(a). CAD data designedby CAD systems are registered in the PDM system through the‘Check in’ process as shown in Fig. 9. Using this function, all partfiles and conversion matrices at each level of the assembly isregistered on the PDM system at once. The registered assemblyfile is verified step by step through the various searchingfunctions of the PDM system as shown in Fig. 10. The previouslydeveloped viewer [19] enables visualization and DMU of theassembly at each level.

Using the ‘‘Group’’ entity, the multi-level assembly on thepreviously developed viewer [19] is expressed as the parent andchild level assemblies. The ‘‘Link’’ of the parent level assemblyexpresses the child level assembly, which is expressed by the‘‘Group’’. The ‘‘Link’’ of the lower level assembly is linked to ‘‘Solid’’.For example, the three-level assembly shown in Fig. 8 is visualizedwith the Group–Group-Solid structure. In addition, this systemrepresents BOM structure of an assembly as shown in Fig. 8(a). Itconfirms the case study is a three-level assembly.

Fig. 11 shows a mold base assembly composed of injection andejection sides, and plates. Cooling channels, ejection components,cores and cavities, sliding units, and screws are assembled to makea final mold base assembly. Interference of injection moldsgenerates fatal problems, such as impossible assembly, damageof injection molds, etc. Using the developed system, it is possible todesign and fabricate interference free molds rapidly.

These assembly jobs conclude that the developed system isapplicable to visualization and DMU of any level of assembly.

Fig. 11. Mold base assembly for multi-level DMU.

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8. Conclusions

By designing an XML based digital mock-up system for hetero-geneous CAD assembly, following conclusions have been obtained:

(1) Position information of parts in an assembly is extractedthrough the CAD API when the CAD data is registered to thePDM system. Selection of optimal locations of the partsgenerated on the heterogeneous CAD data is conducted onthe developed DMU viewer. These data are converted to XMLand registered to the PDM system.

(2) Since the feature information is constructed through thelightweight CAD data and the assembly data are designed byXML, multi-level assembly and visualization of the feature dataare performed efficiently.

(3) Visualization data of an assembly are constructed to parts andsubassemblies. As the parts include feature data and the sub-assemblies include only the positional data of each part, allvisualization data are generated and managed very efficiently.

(4) As the system is applicable to visualization of the assemblydata through the conversion of visual data of parts, theperformance of the developed system is maximized when it isused to design an assembly requiring frequent designmodification.

(5) The effectiveness of the multi-level assembly of heterogeneousCAD files linked with the PDM and DMU viewer systems isconfirmed through case studies.

Performance of the developed system is maximized when thevisual data conversion procedure is required frequently in the

DMU process connected to PDM. In this study, DMU of hetero-geneous CAD assemblies is limited to CATIA, UG and Pro/E, etc.Application to the mid-range CAD systems is to be conductedthrough the analysis of the CAD APIs.

Acknowledgement

This work was supported by the research fund of HanyangUniversity (HY-2007-I).

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[20] Xerces C++ XML Parser. <http://xml.apache.org/xerces-c>, 2005.[21] K.S. Lee, S.H. Lee, Development of a DMU system operated on a PDM system,

Transactions of the Society of CAD/CAM Engineers 8 (3) (2003) 157–166.

In-Ho Song received the B.S. and M.S. degrees in

mechanical engineering from Kunsan National Uni-

versity, and Ph.D. degree in mechanical engineering

from Hanyang University, Seoul, Korea in 2007. From

2002 to 2007, he served as a team manager to develop

CAD and PLM systems in CIES in Korea. As a senior

engineer of eZ-Robotics he has developed a lightweight

Digital Manufacturing System for the auto industry in

Korea. He is currently a post-doc researcher of

mechanical engineering department in Hanyang Uni-

versity. As he had developed a lightweight CAD viewing

kernel for CAD/CAM systems, he received a New

Technology Certificate from Korean Government (MOCIE) in 2005. He also received

several prizes from the Korean Society of CAD/CAM Engineers in 2003 and 2004. He

is specialized in geometric modeling, CAD kernels, product design and digital

manufacturing systems. He is currently participated in development of next

generation reverse engineering and medical CAD systems.

Sung-Chong Chung received the B.S. degree with

honors in mechanical engineering from Hanyang

University, Seoul, Korea, and the M.S. degree in

production engineering and the Ph. D. degree in

mechanical engineering from Korea Advanced Institute

and Science of Technology, Seoul, Korea in 1979, 1981

and 1987, respectively. Since 1983, he has been a

professor in the School of Mechanical Engineering,

Hanyang University, Seoul, Korea. In 2000, he received

the outstanding paper award from the North American

Manufacturing Research Institution of the Society of

Manufacturing Engineers. He received the academic

research award and the software development award from the Korean Society of

Mechanical Engineers and the Korean Society of CAD/CAM Engineers in 2003 and

2004, respectively. His research interests include CAD/CAM, control, mechatronics,

manufacturing and precision engineering. He is a member of the Society of

Manufacturing Engineers, American Society for Precision Engineering, and Korean

Society of Mechanical Engineers.