Virtual reality as a tool for verification of assembly and maintenance processes

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<ul><li><p>2Actually, the term virtual prototypinga is also used in otherareas such as VLSI chip design.</p><p>*Corresponding author. Tel.: #49-89-39-23-46-37.E-mail address: (A. Gomes</p><p>de SaH )1After all, this seems only natural, since they have been also</p><p>among the "rst who applied computer graphics.</p><p>Computers &amp; Graphics 23 (1999) 389}403</p><p>Technical Section</p><p>Virtual reality as a tool for veri"cation of assembly andmaintenance processes</p><p>Antonino Gomes de SaH !,*, Gabriel Zachmann"</p><p>!BMW AG, Geometrical Integration, CAD/CAM, 80788 Munich, Germany"Fraunhofer Institute for Computer Graphics, Rundeturmstra}e 6, 64283 Darmstadt, Germany</p><p>Abstract</p><p>Business process re-engineering is becoming a main focus in todays e!orts to overcome problems and de"cits in theautomotive and aerospace industries (e.g., integration in international markets, product complexity, increasing numberof product variants, reduction in product development time and cost). In this paper, we investigate the steps needed toapply virtual reality (VR) for virtual prototyping (VP) to verify assembly and maintenance processes. After a review oftodays business process in vehicle prototyping, we discuss CAD-VR data integration and identify new requirements fordesign quality. We present several new interaction paradigms so that engineers and designers can experiment naturallywith the prototype. Finally, a user survey evaluates some of the paradigms and the acceptance and feasability of virtualprototyping for our key process. The results show that VR will play an important role for VP in the near future. ( 1999Elsevier Science Ltd. All rights reserved.</p><p>Keywords: Virtual environments; Virtual prototyping; Digital mock-ups; Assembly and maintenance process; Useracceptance; Direct manipulation</p><p>1. Introduction</p><p>In order to stay competitive on international markets,companies must deliver new products with higher qualityin a shorter time with a broader variety of versions atminimum costs. Virtual prototyping is quickly becomingan interesting strategy for product development. Auto-motive industries seem to be among the leaders in ap-plying virtual reality (VR) for real-world, non-trivialproblems.1 Although there are already several commer-cial 3D engineering tools for digital mock-up (and thenumber continues to grow), all of them lack one thing:intuitive direct manipulation of the digital mock-up bythe human. Therefore, they are inherently inferior to VRfor certain applications.</p><p>While some automotive companies have already be-gun to routinely use VR as a tool in styling and designreviews in the concept phase, it has not been clear thatVR can be an e$cient tool in assembly/disassemblysimulations and maintenance veri"cations. Assemblysimulations are much more di$cult in that they involvea lot of interaction and real-time simulation. However,[1] revealed that the assembly process often drives themajority of the cost of a product [2] point out that up to70% of the total life cycle costs of a product are commit-ted by decisions made in the early stages of design.</p><p>1.1. Dexnitions of virtual prototyping</p><p>There seem to be two di!erent understandings of whatexactly virtual prototyping is: the computer graphicsaand the manufacturinga point of view.2 We will de"ne</p><p>0097-8493/99/$ - see front matter ( 1999 Elsevier Science Ltd. All rights reserved.PII: S 0 0 9 7 - 8 4 9 3 ( 9 9 ) 0 0 0 4 7 - 3</p></li><li><p>the former as virtual prototyping, and the latter asdigital mock-up (which is often confused with virtualprototyping).</p><p>By virtual prototyping (VP) we understand the applica-tion of virtual reality for prototyping physical mock-ups(PMUs) using product and process data. The VR systemsimulates and renders all characteristics relevant to theparticular context as precisely and realistically as pos-sible in an immersive environment [3]. Some examplesare: veri"cation of assembly and disassembly procedures,assessment of product characteristics (e.g., ergonomics),and visualization of simulation data. The idea is to re-place, at least partly, physical mock-ups (PMUs) by soft-ware prototypes.</p><p>Digital mock-up (DMU) is a realistic computer simula-tion of a product with the capability of all requiredfunctionalities from design/engineering, manufacturing,product service environment, maintenance, and productrecycling; DMUs are used as a platform for product andprocess development, for communication, and makingdecisions from a "rst conceptual layout [4]. This includesall kinds of geometrical, ergonomic, and functional simu-lations, whether or not involving humans.</p><p>So, immersive VP is one of many techniques for imple-menting DMU.</p><p>Assembly/disassembly veri"cation has several goals.The "nal goal, of course, is the assertion that a part orcomponent can be assembled by a human worker, andthat it can be disassembled later on for service andmaintenance. However, other questions need to be ad-dressed, too: is it di$culta or easya to assemble/disas-semble a part? How long does it take? How stressful is itin terms of ergonomics? Is there enough room for tools?</p><p>2. Related work</p><p>A lot of development for utilizing VR for VP is beingrealized by automotive and aerospace companies. Manye!orts, however, are still feasability studies.</p><p>Practically all automotive companies investigate theuse of VR for styling reviews and other mere walk-through applications. Some of them already employ it fordaily work. Usually, the model is rendered on a large-screen stereo projection or in a cave. Variations can becompared on the #y with realistic colors and illuminatione!ects [5]. At Daimler Benz the body of a car can bereviewed in an immersive virtual environment by the aidof zebra lighting [6].</p><p>Since VR provides an intuitive and immersivehuman}computer interface, it is perfectly suited to doergonomics studies. Consequently, many projectscapitalize on this advantage of VR. Ford employsvirtual prototypes with several proposed dashboardcon"gurations to verify visibility and reachability ofinstrument.</p><p>Researchers at Caterpillar Inc. use VR to improve thedesign process for heavy equipment. Their system [7]allows them to quickly prototype wheel loader and back-hoe loader designs to perform visibility assessments ofthe new design in a collaborate virtual environment.Further the engineers can simulate the operation of theequipment and evaluate visual obstructions.</p><p>Volkswagen has incorporated some useful applica-tions in the vehicle development process. They havecoupled a commercial human inverse kinematic packagewith VR to investigate di!erent ergonomic features. Theyalso visualize the results of FEA crash computations inVR interactively. The virtual product clinic avoids faultydevelopments and helps assess customers wishes [8].</p><p>Chrysler launched a project to study the process of VP,to investigate the steps required for the creation of a vir-tual representation from CAD models, and for the sub-sequent use of the prototype in immersive VR [5].</p><p>A vision of VP was developed within the ESPRITproject AIT (Advanced Information Technologies in De-sign and manufacturing). Project partners were manyEuropean automotive, aerospace, IT suppliers, and aca-demia [4]. A lot of visionary prototypes have been pre-sented also by [9].</p><p>A prototype virtual assembly system is described in[10]. Our approach integrates many more interactionparadigms, and we present the results of a user surveyevaluating some of them. Although they do not describethe process of authoring a virtual environment, it seemsto us that they pursue the toolbox approach, i.e., thesystem is a monolithic program on top of a set of libra-ries, while our approach is the scripting approach.</p><p>Systems for designing in VR are presented by [11,12].Our approach is to use VR only for investigation andsimulation. No geometry can be designed by our system,because we do not feel that this would take advantage ofthe strengths of VR. A factory simulation for immersiveinvestigation has been presented by [13]. Although nodirect manipulation with objects is possible, problemscan be identi"ed earlier than through the aid of chartsand graphs produced by conventional simulations.</p><p>3. Assembly processes in the automotive business process</p><p>Todays computer-aided tools (CAx) for automotiveand other industries can simulate a lot of the functionsand operating conditions of a new product. In somecases, software simulations are as good or even betterthan PMUs. However, they still do not meet all require-ments to avoid PMUs completely. Certain functions ofa new product cannot be simulated at all by current CAxtools, while others do not provide the results in anacceptable time.</p><p>Therefore, many PMUs are built during the develop-ment process to achieve a 100% veri"cation of the</p><p>390 A. Gomes de Sa&amp; , G. Zachmann / Computers &amp; Graphics 23 (1999) 389}403</p></li><li><p>Fig. 1. Process chain for the vehicle prototype activities.</p><p>geometry, the functions, and the processes of a new carproject. Additionally, todays CAx tools do not providea natural and intuitive man}machine interface thatallows the user to feel and to get the spatial presence ofthe virtual product.</p><p>In order to "lla these gaps, many automotive andother companies have established projects to investigatethe use of VR technologies for veri"cation of designs andprocesses [14].</p><p>3.1. Todays approach</p><p>The automotive business process chain comprises vari-ous key processes from the early concept phase through"nal service, maintenance and recycling. Those that willbe highlighted in this paper are the assembly and mainten-ance processes. The veri"cation process can be brokendown into three sub-processes which are described in thefollowing (see Fig. 1):</p><p>f Fast CA loops. CAx tools are used to quickly verifydi!erent design concepts and assembly/disassembly ofthe design concepts. These veri"cations take placein-between the design and the CA prototype process(see Fig. 1). At the beginning of the business processchain the freedom to change concepts and the numberof variations of a component is higher. Due to this fact</p><p>the number of CA veri"cations during the develop-ment process will decrease.</p><p>f PMU loops. For detail veri"cation of design conceptsand assembly processes in some sections of a product,various PMUs are built. This sub-process can be iden-ti"ed in Fig. 1 between the design and the PMUprocess (see dashed line).</p><p>f PMU verixcation. Some complete PMUs of the "nalproduct (e.g., a car) are built to verify if all the designedcomponents ful"l all the requirements related to ergo-nomics, functions and processes. Before these full proto-types are built, a freeze of the styling and designprocesses occurs. In Fig. 1 these phases are marked bythe deadlines SF and DF.</p><p>In the traditional process chain several problems arisedue to the fact that veri"cations of the processes aremade using PMUs and CAx tools:</p><p>f Parallel verixcation processes. Veri"cations are madewith CAx tools and with PMUs (in this case they areobtained by e.g., the use of rapid prototype techniquesand/or hand-built prototypes) concurrently. The cor-relation between these two veri"cation processes isvery hard to obtain.</p><p>f Not enough co-ordination. The handling, synchroniza-tion, correlation, and management of these processes is</p><p>A. Gomes de Sa&amp; , G. Zachmann / Computers &amp; Graphics 23 (1999) 389}403 391</p></li><li><p>Fig. 2. Transition from physical-to-digital mock-up [6].</p><p>very di$cult and in some cases impossible. In order tobuild a PMU, a design stage needs to be freezed. Atthis time, the building of the PMU starts and can take6}12 weeks. Due to concurrent engineering, furtherchanges of CAD parts (sometimes even signi"cantones) can be made during the build-time. Therefore, bythe time results are obtained by the PMU veri"cationthey no more have a direct correlation to the currentdesign. Even if there have not been changes in thedesign, the transfera of the results of the PMU veri"-cation to the DMU is, in some cases, very di$cult.</p><p>3.2. Vision</p><p>Most companies already de"ne their products digitally(e.g., CA methods) and manage the data by product datamanagement systems (PDM). However, the digital dataare not used as the basis for the core business process.Instead, they are maintained in parallel to a more tradi-tional process based on PMUs, more as an auxiliary orsupporta of the PMU process or the building of PMUs.</p><p>The goal of DMU is to replace the traditional businessprocess, based on PMUs, by one which fully maximizesDMU technologies available today and in the future. Thevisionary goal is a process with only a single PMU for</p><p>a "nal veri"cation, certi"cation, and release to volumemanufacturing (see Fig. 2).</p><p>The goal is to perform veri"cations as early as possible,i.e., front-loading of engineering, manufacturing, service,manufacturing, and recycling tasks to the concept phase[6]. We believe that by utilizing VR, DMUs can beevaluated in the concept phase.</p><p>3.3. Objectives of the verixcation of assembly processes</p><p>Objectives can be classi"ed by two categories: strategicand operative.</p><p>Strategic objectives are global and involve the com-plete business process. The most important ones are:reduction of development costs, development time, andtime-to-market; increase of product innovation, productquality, #exibility, and maturity at series start.</p><p>Operative objectives are more local, related to onlyone or a few key processes. The most important objec-tives which need to be ful"lled for assembly and mainten-ance are [15]:</p><p>f Service, inspection, and repair locations should beeasily accessible;</p><p>f visibility should be ensured;</p><p>392 A. Gomes de Sa&amp; , G. Zachmann / Computers &amp; Graphics 23 (1999) 389}403</p></li><li><p>Fig. 3. Data #ow between CAD and VR system.</p><p>f exchange of components should be easy;f use few and standard service and inspection tools.f accessibility of service tools, and hand and arm of the</p><p>worker;f calculation and investigation of minimal distances to</p><p>avoid collisions, e.g., during operating conditions;f calculation of assembly/disassembly paths for o!-line</p><p>robot programming;f calculation of sweeping envelop of movable compon-</p><p>ent for packaging investigations, e.g., for reservation ofspace in engine bay.</p><p>Additionally, these objectives must be veri"ed with1}20 mm precision, related to the business process phase.They must be documented in digital form. These elec-tronic reports should be managed by the PDM systemtogether with the geometry and further administrativeand technological data. As soon as a new version ofa electronic report is created, the PDM system shouldinform involved users that a new report is available forassembly processes.</p><p>The electronic report contains information relatedto simulation and investigation results, proposals forchanges of CAD components, assembly/disassembly</p><p>paths, collision areas, sweeping envelopes, and the statusof all veri"cation processes.</p><p>4. From CAD to VR</p><p>The complete data pipeline form the CAD system tothe VR system has various modules. CAD systems arethe source of most of the data. This data is stored ina PDM system, which also ma...</p></li></ul>


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