2Actually, the term virtual prototypinga is also used in otherareas such as VLSI chip design.
*Corresponding author. Tel.: #49-89-39-23-46-37.E-mail address: firstname.lastname@example.org (A. Gomes
de SaH )1After all, this seems only natural, since they have been also
among the "rst who applied computer graphics.
Computers & Graphics 23 (1999) 389}403
Virtual reality as a tool for veri"cation of assembly andmaintenance processes
Antonino Gomes de SaH !,*, Gabriel Zachmann"
!BMW AG, Geometrical Integration, CAD/CAM, 80788 Munich, Germany"Fraunhofer Institute for Computer Graphics, Rundeturmstra}e 6, 64283 Darmstadt, Germany
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.
Keywords: Virtual environments; Virtual prototyping; Digital mock-ups; Assembly and maintenance process; Useracceptance; Direct manipulation
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.
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, revealed that the assembly process often drives themajority of the cost of a product  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.
1.1. Dexnitions of virtual prototyping
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
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
the former as virtual prototyping, and the latter asdigital mock-up (which is often confused with virtualprototyping).
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 . 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.
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 . This includesall kinds of geometrical, ergonomic, and functional simu-lations, whether or not involving humans.
So, immersive VP is one of many techniques for imple-menting DMU.
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?
2. Related work
A lot of development for utilizing VR for VP is beingrealized by automotive and aerospace companies. Manye!orts, however, are still feasability studies.
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 . At Daimler Benz the body of a car can bereviewed in an immersive virtual environment by the aidof zebra lighting .
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.
Researchers at Caterpillar Inc. use VR to improve thedesign process for heavy equipment. Their system 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.
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 .
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 .
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 . A lot of visionary prototypes have been pre-sented also by .
A prototype virtual assembly system is described in. 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.
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 . Although nodirect manipulation with objects is possible, problemscan be identi"ed earlier than through the aid of chartsand graphs produced by conventional simulations.
3. Assembly processes in the automotive business process
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.
Therefore, many PMUs are built during the develop-ment process to achieve a 100% veri"cation of the
390 A. Gomes de Sa& , G. Zachmann / Computers & Graphics 23 (1999) 389}403