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Increased Concurrency between Industrial and Engineering Design Using CAT Technology Combined with Virtual Reality Casper Wickman and Rikard Söderberg Concurrent Engineering 2003; 11; 7 DOI: 10.1177/1063293X03011001001 The online version of this article can be found at: http://cer.sagepub.com/cgi/content/abstract/11/1/7

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CONCURRENT ENGINEERING: Research and Applications Increased Concurrency Between Industrial and Engineering Design using CAT Technology Combined with Virtual Reality Casper Wickman1,2,* and Rikard So¨derberg2 1

Volvo Cars, Body and Trim Engineering, Department 93980 PVS, SE-405 31 Go¨teborg, Sweden

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Chalmers University of Technology, Product and Production Development, SE-412 96 Go¨teborg, Sweden

Abstract: These days, when an industrial design concept is evaluated in an aesthetic manner, all models used are nominal. If the design is evaluated with nominal models, variation aspects and design solutions that would greatly influence the overall quality appearance might not be discovered until the first test series are made. By using nonnominal models during the design process, important geometric aspects can be issued, and the need for physical test series can be reduced. In the automotive industry, especially in body design, the relationships between doors, hoods, fenders and other panels are critical for quality appearance. This article suggests how combining traditional Computer Aided Tolerance (CAT) tools with modern Virtual Reality (VR) tools has the potential to enhance concurrency between industrial and engineering design and provide support for the geometry process in early phases. Traditional nonnominal verification can then already be conducted in the concept phase using digital models instead of physical. A VR–CAT tool supported geometry design process is proposed from a holistic point of view. Results and indications from a case study, where prescribed VR–CAT tool has been tried out in an on going project at Volvo Cars is presented. Key Words: concurrent engineering, virtual geometric verification, industrial design, nonnominal evaluation.

1. Introduction In the automotive industry today, some of the most critical issues are to reduce cost, increase quality and decrease lead-time. Concurrent Engineering (CE) has been described as a method that can satisfy these demands [1]. Engineering tasks are performed more simultaneously between different disciplines in CE, to shorten design time and to allow designs to be verified early in the developing process. One part of the design process, which is still carried out in a serial manner, is the interaction between Industrial Design (ID) and Engineering Design (ED) to solve geometry variation aspects. The geometry design process involves many activities that affect the final Quality Appearance (QA), cost and lead time. QA refers to aspects that give the customer an impression of quality, just by observing the product. QA aspects can be relationships between doors, hoods, fenders and other panels on the vehicle. The extent to which these relationships vary is not only affected by component and assembly variation but also by the robustness of the design. In the next section, geometrical robustness is *Author to whom correspondence should be addressed. E-mail: [email protected]

defined and discussed. Accurate information and tools for communication between ID and ED will have a significant impact on the extent to which a high final QA can be achieved. During the design process today, all ID concepts are evaluated using nominal models. Nominal means that the geometry is ideal in the sense of dimensions and shape. If a nominal dimension is set to a certain value it will always have that defined value irrespective of how many units are manufactured, which of course is not the case in real production. Consequently, nonnominal means that the variation that always affects all final products has been taken into consideration and the geometry is represented with positioning and component errors. Accordingly, the ID concept is evaluated under ideal conditions, which consequently means that information about how the ID concept will be interpreted is limited and can have the consequence that it is interpreted in an unexpected and undesirable way. Today, physical test series are made to verify the nonnominal geometry. Geometrical evaluation with physical test series is mostly done quite late in the design process, resulting in postconceptual changes. If problems identified by the virtual test series can be highlighted earlier in the process, economic benefits can be gained. Virtual evaluation might not replace physical

Volume 11 Number 1 March 2003 1063-293X/03/01 0007–9 $10.00/0 DOI: 10.1177/106329303032821 Downloaded from http://cer.sagepub.com by Roberto Hernandez Sampieri on October 21, 2008 ß 2003 Sage Publications

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test series in the immediate future, but some of the errors that test series reveal might be discovered in the concept phase. It has been stated that human evaluators will require more accurate support and assistance to maintain their objectivity in the evaluation process [2]. By supplying computer-supported tools and methods for early geometrical visualization, the potential for maintaining an efficient and reliable basis for early decisions is highly increased.

reduce the robustness. Output variation is controlled by two parameters, the position of the support and the input variation. These relationships can be described in matrix form as in Figure 2. Since the position of the locator controls two important product characteristics, this issue should be considered first. The tolerance for the input variation may then be determined on the basis of final requirements for the output variation and known sensitivity (relationship between input and output).

1.1 Geometrical Robustness and Variation 1.2 Previous Work Geometrical variation is introduced into the product as component variation and assembly variation, please refer to Figure 1. In most companies, the suppliers control component variation, whereas assembly variation is controlled in house. Design sensitivity is also an important contributor to final variation. In a sensitive design, the component and assembly variation is amplified, whereas in a robust design, variation is suppressed. Since the shape of the components and the positions of the locators govern the robustness of the product, it is very important to achieve the greatest possible geometrical robustness early on in the concept phase, when the freedom of design is less restricted. This may be achieved by the use of Computer Aided Tolerance (CAT) tools, see [3], and by early robustness analysis, see [4]. The relation between robustness and variation can be illustrated with a simple beam support example as in Figure 2. The robustness of the design is defined by the relationship between input and output variation, which is totally controlled by the position of the support in this case. Moving the support to the left will increase the robustness, whereas moving it to the right will

Evaluation of quality appearance with nonnominal virtual design models, early in the design process, is a quite immature and unreported discipline so far. In [5–7], a comprehensive outline of a computer system for visualization of cosmetic quality is presented. The system is based on a number of commercial tools combined with a visualization model, using Open GL 3D graphics. The papers report the progress achieved during the first years of a project where the system is still in a prototype stage. In [8], a tool system that visualizes statistical worst-case scenarios from CAT simulation is presented. Two commercial tools, a CAT tool and a Virtual Reality (VR) tool, are combined in order to create a virtual environment for nonnominal geometry verification. In [9], a method for assignment of quality appearance index weightings, used for early evaluation of styling models is presented. 1.3 Objectives This article describes how concurrent engineering between ED and ID can be enhanced and supported by

Component Variation Machine Precision

Assembly Variation

Process Variation

Assembly Precision

Manufacturing Process

Process Variation

Assembly Process Variation in Critical Product Dimensions Robustness

Design Concept

Figure 1. Variation sources in assembled products.

Figure 2. Relation between robustness and variation. Downloaded from http://cer.sagepub.com by Roberto Hernandez Sampieri on October 21, 2008

Increased Concurrency between Industrial and Engineering Design

CAT and VR techniques. A generic geometry design process, supported by nonnominal models in virtual environments, is described. By utilizing the tool described in [8], nonnominal models can be visualized in a realistic environment and manipulated in real time. The design process is illustrated with a case study that has been carried out in an ongoing project at Volvo Cars. The project is in an early stage of the design process and the new approach of nonnominal visualization has been tested on ED and ID. 1.4 Methods This article is part of a project that focuses on methods and computer tool support for the geometry design process. Design research is a multidisciplinary area, which involves many aspects such as decision-making, organization, human aspects, computer tools and methods. All disciplines have their own methods and research methodologies, which mean that many different methods can be used to address the various issues involved in design research. This project follows a generic design research methodology [10] that has been developed with the purpose of merging several different disciplines into a research methodology that links the research questions together and addresses them in a systematic way. This article constitutes one part of the prescriptive phase described in the research methodology. In the case study presented in the article, all the participants are involved in the project from where the case has been selected. They represent different disciplines within the company and they work on issues that concern both ED and ID. Some of the participants in the group represent management functions. In the case study, observations and structured interviews [11] have been held with the participants, for data collection.

2. Nonnominal Virtual Evaluation The demonstrator that is presented in [8] utilizes VR and CAT technology to create an environment for geometry evaluation. VR is a progressing technology aimed at creating an illusion of reality using a computer environment. VR tools allow the user to interact with the virtual environment and objects submitted to the environment. In virtual reality the user is ‘‘immersed in the experience’’ in what appears to be real-time. The main advantages of VR are that very large models can be visualized with high quality, in real-time; that advanced input and output devices can be used and that it is possible to define simulations and animations. Advanced input devices include, for example, data gloves and head tracker systems.

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Virtual Reality technique uses polygonal representation of the geometry. Tessellation algorithms convert the surface geometry into a mesh of triangular polygons. The number of polygons, i.e. the degree of tessellation, governs the accuracy of the surface and also affects the rendering speed. Real-time rendering, generating at least 20–30 frames per second, allows advanced models to be visualized with high quality, which enables users to inspect and interact with the model. Kamble and Arora [12] have presented a review of commercial VR technologies and their applications. VR systems that allow multiple participants to be immersed in the virtual environment will play a key role when geometrical aspects that concern both ID and ED are evaluated. CAT software allows analysis of the geometric variation and predicts the total variation in assembled products. A number of commercial CAT systems are available in the market today, mainly based on Monte Carlo simulation or direct linearization. A review of commercial CAT systems has been presented by Salomonsen et al. [13]. In the automotive industry, VR tools have so far been frequently used to simulate the manufacturing process [14]. Within this area, a significant effort has been concentrated on developing computer-aided systems to support concurrency within engineering work, please refer to [15]. VR has been used as a tool for both ED and ID, but it has not been used as a tool that integrates the two disciplines in order to create a higher level of concurrency. One problem in the geometry design process is the heterogeneous personnel that carry out geometry related tasks and the fact that ED and ID departments can be geographically distributed. This creates barriers to communication, which affects the design process. Simulation results from CAT tools presented as tables, distributions or matrices, please refer to Figure 3, are not always a suitable representation of the simulation result. The distribution, in Figure 3, shows how the geometrical variation is distributed for a critical dimension over a number of manufactured units. Nonnominal VR models enable a step towards faster design loops, qualitative evaluation

Figure 3. Distribution from CAT simulation.

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of results and a platform for increased communication and understanding between ED and ID. 2.1 Visualization Example In order to illustrate the use of nonnominal geometry, an example of the rear end of a Volvo S60 is presented. The focus is the split line between rear lamp, rear bumper and the outer rear body side, please refer to Figure 4. This example illustrates a visualization that is performed in the detailed phase since the tolerance model is built up of final reference points and tolerances. Two corresponding models are created, a CAT model and a VR model. To create the CAT model, the geometry has been imported into RD&T, a CAT package [16] from CATIA, a CAD tool [17]. Positions for locators are automatically transferred with the geometry. In RD&T the locating systems for all parts are defined. Here, the 3-2-1 or similar locating systems, used in the automotive industry, are available. When locking points have been defined and tolerances have been allocated for all components and fixtures, variation analysis may be carried out for defined critical

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dimensions. In RD&T, variation analysis is based on Monte Carlo simulation. The values of all critical dimensions are stored during each iteration, and the output distributions are calculated. A critical dimension for an automotive body could be a flush or gap relation between two components, for example. The result of the variation analysis can be presented in RD&T as distributions showing the variation for all the defined measures, please refer to Figure 5. The result can also be presented as color coding where different colors represent the amount of variation, see [18]. The results from the simulation are exported from RD&T to be viewed in Opus Studio [19]. Position data for different ‘‘worst case’’ scenarios, defined as the worst case situations for a number of defined critical dimensions in RD&T, are imported to Opus Studio. As for the CAT model, the rear end components have been imported from Alias Studio Tools [20] into Opus Studio in this case. Positioning and scalar information is transferred from RD&T to Opus Studio via the local network and predefined virtual ports. Figure 6 shows a scenario where the statistical worst case nonparallelism and flush between the bumper lid and body is visualized. A clear nonparallelism in the gap direction can be noticed for the split lines between rear lamp and bumper and rear lamp and body side. This example clearly demonstrates that the statistical tolerance analysis results can be displayed in a totally different manner, in order to reach a wider range of participants and to analyze the result in a qualitative manner. In the virtual environment, engineers and industrial designers can evaluate the effect of variations in real time, to offer concurrency in the geometry process.

3. Proposed Geometry Design Process Figure 4. Evaluated area of virtual model.

A conventional product development process that is carried out sequentially suffers from the problem of the design paradox [21]. At the beginning of the design process, the preferred stage to perform changes to the

Figure 5. Distribution from variation analysis in RD&T.

Figure 6. Non-nominal representation of evaluated area.

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product, information about the product is limited. This effect also limits the use of digital models. At the beginning of the design process, digital styling models of different design proposals are generated. The degree of details limits the use of the models at the beginning of the process. The digital models only consist of a shell or one surface, which implies that it is not possible to make the model nonnominal with respect to variations in different components and features. In this section, a holistic model of a geometry design process is presented, which increases quality appearance and extends CE. The use of numerical nonnominal models and CAT–VR techniques supports the process at all stages of the design. The process is described with reference to the four general design stages, clarification, conceptual, embodiment and detailed design proposed by Pahl and Beitz [22]. Since the idea is to support concurrency within the area of geometric variation, the process is described from a standpoint where the focus is on robust design and tolerance allocation. So¨derberg and Carlsson [23] have described a process for geometric robustness, derived from a general design process. This model is extended here to include the styling process as well, please refer to Figure 7. The dotted lines represent information that gives feedback to previous activities, due to integrated VR–CAT technologies. The solid lines represent information that gives feedback to previous activities, generated from CAT simulations.

Clarification

Market analysis

Concept Design

Input

Preliminary Sensitivity Analysis

Embodiment Design Re-define

Part Locating Scheme Definition & Fixture Design

Input

Robustness

Assembly Stability Analysis

Visual Sensitivity

Detail Design Re-define

Tolerance allocation

Clarification Phase VR–CAT integrated tools do not bring any benefits during the clarification phase. Concept Design Several styling concepts are generated during this phase. Traditionally, the selection of the final model is based on evaluation of nominal physical and virtual models. All models are divided into different components or surfaces by preliminary split lines, in order to stress aspects related to geometrical variation, when the final ID concept is selected. By creating preliminary radii along all split lines on the different surfaces and cover-up behind split lines as well, a more realistic model is created. By applying a unit disturbance in an arbitrary direction, i.e. not necessarily in the locking direction of locators, a preliminary sensitivity analysis can be performed. This analysis can give valuable information about sensitive areas and give input for the assignment of a locating scheme. Figure 8 illustrates the use of styling models. Before split lines have been defined is evaluation performed with nominal models. When the styling model has been divided by split lines it can be utilized as a base for CAD, geometry models and nonnominal VR models. The shaded boxes, in Figure 8, indicate that the same procedure is practiced as information gets available. Styling requirements are set for all concepts during this phase. When styling requirements are allocated, it is intricate to

Re-define

Geometry and Concept Design Styling Requirements

6-sigma

Assembly Variation Analysis

“Worst case “ Scenarios

Figure 7. Generic design process for visual robustness.

CAD Models

Styling Models

Nominal VR Models

Styling Models with Split lines

Nominal VR Models

Geometry Models

NonNominal VR Models

Figure 8. Schematic use of styling models.

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Gap Under-flush

Figure 9. Under-flush vs. gap appearance.

estimate and predict effects that may occur due to the geometry. For example, the gap requirement, illustrated in Figure 9, can be set less tight if a small-under flush is used, without detracting from the quality appearance. This kind of subjective decision can be supported very early in the process if nonnominal VR models with realistic appearance are used. Requirements such as flush and gap vary, depending on the geometry and the area of the vehicle. In a prominent or critical area, the requirements should be set higher and the opposite in a less prominent area. Allocation of the optimal distribution of styling requirements can be supported by the use of VR techniques. Embodiment Design After master locating points for each component have been defined, stability analysis can be performed. The stability analysis evaluates the geometrical robustness of the concept by applying a unit tolerance (disturbance) in the locating direction of all locators on all components, in order to visualize the geometrical sensitivity of the design. The most robust area is not necessarily the area that has the highest QA since the area can be visually sensitive. Consequently, by visualizing the result of the stability analysis, a locating scheme that takes the most visually sensitive areas into account can be defined. The stability analysis also gives the first indication of how other parameters such as reflections are affected by variation. If the geometry of the design concept still has critical visual sensitivity areas, the geometry and requirements can be redefined. Requirements are redefined during the process in order to finally meet the functional and aesthetic requirements. It is a commonly stated observation that requirements change when products mature [24]. Detail Design When tolerances have been allocated, variation analysis with respect to specified tolerances can be performed. Statistical worst-cases scenarios for a particular area can now be created and the final design can be qualitatively evaluated and verified. Scenarios that contain combinations of flush, gap and seam derivatives, contribute to giving a final quality appearance. Involved engineers and industrial designers study the result during review meetings. If the result is not satisfactory, tighter tolerances can be allocated to sensitive areas or component locating schemes and fixtures can be redefined.

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When companies reduce the use of physical prototypes and test series in favor of virtual environments, it is difficult to sustain the special attention that the first physical test series attracts. The first test series is a milestone in the developing process and it automatically attracts great attention. Engineers and other involved parties gather round the test series and discuss important issues. If variation related aspects are in serious need of adjustment, a physical prototype provides the necessary input or information injection to stress the issue. Accordingly, a nonnominal VR model is an important tool for stressing geometrical issues when traditional physical test series are reduced and postponed in the development process.

4. Case Study at Volvo Cars The geometry process presented in this article has been tried out in a progressing project at Volvo Cars. Since information about future car models cannot be revealed, there are restrictions on describing the object used. It is not possible to show any real figures or illustrations of the current model. The evaluated car model is referred to as X in this article. The approach is to stress problems related to critical or sensitive areas of a model that still is in the concept phase, by using nonnominal geometry models for evaluation. The critical areas were presented to a group consisting of both engineers and industrial designers, in order to address and emphasize the problem to the two groups. During the discussion that followed, data was collected by observation and interviews. 4.1 Objectives of the Case Study The main objectives of the case study were to find any indications among industrial designers and engineering designers about how geometrical effects, which can occur due to variations, should be an aspect that should be taken into consideration when the final ID of the product is chosen, i.e., to find opinions about where engineering conflicts with ID. Another aspect was also to discover their opinions about how nonnominal models could be used in general. 4.2 Critical Areas and Models Engineers had identified the area evaluated, which has been the focus in the case study, as a potential problem. The reason for stating this as a sensitive area so early in the process was that a similar design solution had been used in a previous project. In Figure 10, the previous area is shown on a Volvo S80.

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The split line is defined across a compound curvature surface, which has the result that any variation in one direction will affect the relationship along the split line in three directions. This is considered as a very sensitive design solution that does not, meet the quality appearance requirements, even in a nominal position. Depending on the viewing angle, the gap relation appears to vary along the split line. If a small amount of variation is added to the model, this effect becomes clearer. A similar solution, on another area of the new model, with a curved split line over a compound curvature surface is proposed. The X model is still in the concept phase, according to the proposed process, which means that the ID still is under development and the final geometry has not been selected. The styling or industrial design model only consists of a shell with preliminary split lines. To increase the realism of the model, radii along the split lines in question have been added. Moreover, surfaces underneath the split lines have been added to cover up between the parts. A model of the earlier known problem with the S80, please refer to Figure 10, was placed next to the identified critical area on the X model. A schematic CAT model of X was made in RD&T with an assumed locating scheme, based on previously locating schemes for trunks. Equal unit disturbances were assigned in the locating direction for all locators. Worst cases of gap, flush and nonparallelism were visualized in the virtual environment. The positioning errors were not only visualized in the X model. The same simulation result was transferred to the S80 model as well. Industrial designers and engineers can now view the two models that have been affected by the same variation, next to each other, in the same environment. The models were displayed on a back projection power wall. One part of the screen displayed the virtual environment with the two models and the other side of the screen displayed the CAT model. During the examination the participants could ask for changes to be performed on the CAT model and the result could

instantly be viewed in the virtual model. After the two groups had examined and evaluated the models, a general discussion about the possibilities and benefits of similar representations of variations followed and questionnaires were distributed to the participants to comment on.

Figure 10. Sensitive design solution for Volvo S80.

Figure 11. Identified visually sensitive areas of X.

4.3 Indications from the Case Study General conclusions cannot be drawn from the case study since the data source is not statistically sufficient. However, the objective was really to discover any indications of oppositions between ED and ID and also to establish a first broad view of how users regard such support. The following indications and opinions were noted: . Both engineering and industrial designers believed that it is of essential importance to bring more realism into virtual representations. Not only better graphical facilities but also by adjusting and adopting objects to take manufacturing aspects into consideration. . Some industrial designers thought that the tools presented could restrict the freedom for the industrial designers, although they are positive to similar tools. . Interfering with aspects other than purely industrial design aspects could result in rejection of a winning industrial design concept on the wrong basis. . Some industrial designers thought that it is of great importance to consider variation aspects, but this should not interfere with the process of selecting the final ID under any circumstances. This is a contradictory statement that illustrates the problem of this issue. At the same time as geometric variation is considered as an important issue, there is no understanding for collision with ED. . One area, shown by a circle by the D-pillar in Figure 11, at X had been identified as sensitive or critical. During evaluation another area, shown by the circle by the rear lamp in Figure 11, was stated as being potentially sensitive. This means that the trunk is confined between two sensitive and unforgiving

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areas, which are subject to variation. It was stated that if the solution by the D-pillar were used, another more forgiving solution for the rear lamp should be used. In [5], a case study among engineering designers recognizes that a system, similar to the one described in this article would greatly assist the setting of quality targets. This conclusion seems to be a general opinion among engineering designers in this case study as well. However, it seems that recognizing the benefits of an approach is not the major problem. Adopting the new approach seems to be far more troublesome.

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5. Conclusions In this article, we have proposed a geometry design process with a focus on visual quality, supported by a tool that combines CAT simulation and VR. We have shown how the tool extends the concurrent engineering and communication ability between ID and ED. Benefits from visualization of nonnominal models are presented. With the proposed tool, aspects that are evaluated with physical test series today can be evaluated earlier in the design process, using nonnominal models in virtual environments. Moreover, we have illustrated the use of CAT/VR technique with an example of a rear end of a Volvo S60. A case study at Volvo Cars indicates that many aspects are highlighted that might not have been discovered with a nominal model.

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Acknowledgments The authors would like to acknowledge the personnel concerned at Volvo Cars for their support and for participating in the case study. The authors would also like to acknowledge the Swedish foundation for Strategic Research through the ENDREA Research Program (The Swedish Engineering Design and Research Education Agenda) and the VINOVA (Verket fo¨r Innovationssysyem) for their financial support.

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Increased Concurrency between Industrial and Engineering Design 18. So¨derberg, R. and Lindkvist, L. (2001). Automated Seam Variation and Stability Analysis for Automotive Body Design, In: Proceedings of the 7th CIRP International Seminar on Computer Aided Tolerancing, 24–25 April, ENS de Cachan, France. 19. Opticore, A.B. (1999). Opus Studio Software Manual, Go¨teborg, Sweden. 20. Alias | Wavefront (2000). Studio Tools 9.5 Software Manual, Toronto, Canada. 21. Ullman, D.G. (1997). The Mechanical Design Process, McGraw-Hill International Edition, New York. 22. Pahl, G. and Beitz, W. (1996). Engineering Design – A Systematic Approach, Springer, cop, London. 23. So¨derberg, R. and Carlson, J. (1999). Locating Scheme Analysis for Robust Assembly and Fixture Design, In: Proceedings of the ASME Design Automation Conference, 12–15 September, Las Vegas, Nevada, USA. 24. Prasad, B. (1996). Concurrent Engineering Fundamentals, Volume I: Integrated Product and Process Organization, and Volume 2: Integrated Product Development, Upper Saddle River, Prentice Hall PTR, New Jersey.

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Rikard So¨derberg Dr. Rikard So¨derberg is currently Professor in Mechanical Engineering at the department of Product and Production Development at Chalmers University of Technology in Gothenburg, Sweden. Dr. So¨derberg is also Director of the Wingquist Laboratory and Project Manager of the research group 3D Tolerance Management. He received his M. Eng. (1989) and his PhD (1995) from Chalmers. Before returning to Chalmers in 1997, he worked at Prosolvia for 2 years as Product Manager. His research interests are within the area of robust design and variation simulation. His research is of high industrial relevance. A commercial tolerance analysis tool (RD&T) has been developed within the group.

Lic. Eng. Casper Wickman is a Research Student at the department of Product and Production Development at Chalmers University of Technology in Gothenburg, Sweden. He received his B. Eng. from University of Karlstad in 1998, his M. Eng. from Chalmers in 2000 and his Lic. Eng. in 2002 from Chalmers. He is employed by Volvo Cars, as an industrial PhD student, with the aim to accomplish research within the area of visualization of geometrical variation.

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