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COMPUTER-AIDED DESIGN Computer-Aided Design 34 (2002) 741±754

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Hybrid rapid prototyping system using machining and deposition Junghoon Hur a, Kunwoo Lee b,*, Zhu-hu b, Jongwon Kim b a

b

Research and Development Center, INUS Technology, Inc., 601-20 Yuksamdong Kangnamgu, Seoul 135 080, South Korea School of Mechanical and Aerospace Engineering, Seoul National University, San56-1 Shilimdong Kwanakgu, Seoul 151-742, South Korea Received 9 May 2001; revised 31 August 2001; accepted 11 September 2001

Abstract Many rapid prototyping (RP) systems are commercially available, and others are introduced daily. RP has proven to be an effective tool for dramatically reducing the time and expense involved in the realization of a new products and for overcoming the bottlenecks of existing manufacturing processes. However, its ®elds of application are currently saturated, and the emphasis has moved towards using RP for shortrun manufacture. The current need is for a technique that will produce ®nished parts of the required quality in the shortest possible time, and which meet this need, the focus now falls on improvements in production speed, accuracy, variety of materials, and cost. For these practical reasons, we concentrated on a new form of hybrid-RP system, which performs both deposition and machining in a single station. Our proposed system meets the requirements of material deposition (RP) and material removal (CNC) at the process planning and manufacturing level. We believe that this new production system, which incorporates a combined RP concept, offers an optimum manufacturing solution by adopting the advantages of the RP and CNC systems. In this paper, we describe the system architecture and the fabrication process in detail and present the framework of the process planning system and the concepts of the geometric algorithms involved in developing such an environment. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Rapid technologies; Hybrid rapid prototyping; Material deposition; Free-form surface machining; Deposition feature segment; Machining feature segment

1. Introduction The technology of rapid prototyping and manufacturing (RP&M), also referred to as layered manufacturing (LM), has drawn considerable interest owing to its ability to overcome many limitations of traditional manufacturing techniques. However, it also introduces new limitations, which result from its unique manufacturing methodology, and which are not encountered in the conventional CNC machining process. RP process draws its appeal from its ability to allow parts to be built directly from CAD descriptions, without any tooling, and this ability has eliminated the need for skilled machinists. In general, the RP process breaks down a part with complex geometry into a set of simpler shapes which are easier to manufacture. These are then fabricated layer by layer until the ®nal part is built. However, the layered approach produces a stair-step effect that limits the accuracy of parts, and exponentially increases the total build time for a large sized part. An additional problem stems from the * Corresponding author. Tel.: 182-2-880-7141; fax: 182-2-883-8061. E-mail addresses: [email protected] (J. Hur), [email protected] (K. Lee), [email protected] (Zhu-hu), [email protected] (J. Kim).

standard ®le format, STL, used to represent part geometry. This format limits the accuracy of the model representation since all the free-form geometric features are approximated by a set of triangular facets. Another limitation concerns the range of material usable in the RP process. RP was initially used to prototype a complex part for model visualization and assemblability check when the part cannot be fabricated by the conventional CNC process. None of these RP applications impose structural requirements on the part. There has been a continuous drive to improve the part properties to enable the use of the RP technique for structural applications, such as a secondary tooling or medical applications. From the viewpoint of process planning, the RP system is simple and ef®cient, and current personal computers can perform the task economically. However, `easy' planning can cause other critical problems such as the low productivity or nonfunctional parts. As the demand and need for a breakthrough in terms of the above-mentioned problems increase, the conventional CNC process is becoming a new substantial solution to the limitations of the RP processes. With the emergence of the RP process, continuous improvements in CNC machining technologies have been made. Modern CNC

0010-4485/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0010- 448 5( 01) 00203- 2

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J. Hur et al. / Computer-Aided Design 34 (2002) 741±754

Fig. 1. Positions of RP and CNC processes in terms of their characteristics.

technology offers high-precision, high-speed, high¯exibility, effective process planning technique, and fully dense metal part with the desired structural properties. Consequently, the effective combination of RP and CNC technologies could bring about a new hybrid manufacturing system that completely meets the requirements of the nextgeneration of production systems, especially for short-run production. Fig. 1 shows the characteristics and the evolution of RP and CNC technologies, and indicates the convergence between RP that is appropriate to meet the rapid manufacturing goals, and CNC that produces high-accuracy ®nal part. The implications of the new hybrid system that adopts the technologies of both RP and CNC will impinge on the development strategies of the new manufacturing methodology. In this paper, a new hybrid-RP system is proposed, which combines the advantages of the one-setup process of RP and high-accuracy of CNC. It uses structural material to produce functional parts by performing both deposition and machining in a single station. It incorporates both material deposition in the form of layers and material removal to produce the required surface ®nish. Consequently, the new hybrid-RP system can dramatically reduce the total build time and improve shape accuracy compared with conventional RP systems. In particular, it combines the concepts of RP and CNC at the process planning level and

at the manufacturing stage as it adopts a machining-featurebased process planning technique, usually used in CNC process planning. Since each machining feature is machined as a whole, the number of deposition feature segments is reduced remarkably. To ef®ciently take advantage of the hybrid system, more sophisticated process planning techniques are naturally needed. In Section 5, a newly developed RP process based on the hybrid technique, i.e. an additive and subtractive process, and its hardware framework are presented. In addition, a new process planning methodology based on geometry and feature information, and a software framework for the process planning are also proposed for the new hybrid-RP system. 2. Overview Research projects at the Toyota Technological Institute, LaserCAMM, the University of Utah, Queensland, Delft, Case Western Reserve, University of Hong Kong, and Stanford University have delivered systems, algorithms, and techniques based on the hybrid methods [1±9]. The common feature of these hybrid-RP systems is that they combine the advantages of conventional RP systems, i.e. rapid process planning and independence of geometry, with those of CNC machining, i.e. accuracy and precision

Fig. 2. Machining process applied in the existing hybrid-RP systems.


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Fig. 3. Advantages of proposed hybrid-RP system, ECLIPSE-RP.

with a good surface ®nish. Some of hybrid systems have ever been applied to the real manufacturing process such as mold making and ®xing, tooling, etc. [10]. However, such new hybrid-RP systems have their problems. The research issues in hybrid-RP systems are: how to build shapes with as few layers as possible, avoid the staircase effect, which is more severe than in conventional RP systems owing to thick layers, automatically decompose a model of complex geometry, handle a hidden geometry inside a thick layer, solve the shrinkage problem when a large amount of melting material is deposited, and ef®ciently combine deposition and machining in a station, etc. The unique approach proposed in this research can effectively solve the above-mentioned problems through ef®ciently combining the deposition process with the machining process in a part building cycle and by developing a sophisticated process planning technique. The key point for the successful development of the hybrid-RP system is how to combine two different processes. In the proposed approach, the machining process is considered early in the process planning phase to maximize the advantages provided by the CNC technique, while other existing hybrid-RP systems adopt the machining process as a tool for only the ®nishing operation to remove the staircase effect. Fig. 2 shows the different concept between the proposed system and other systems for effectively utilizing the machining process. As can be seen in the ®gure, the machining is used just for ®nishing the deposited material in the other hybrid-RP systems, while the whole machining feature is machined after the deposition is done without considering the machining feature if it can be realized by a simple machining process. In the proposed hybrid-RP system, when the shape information of the piece to be manufactured is given, all the machining features that can be ef®ciently machined by a CNC machining center are extracted before the shape decomposition is carried out in the same way as the process planning technique used for the conventional CNC process.

After all the machining features are identi®ed, the process planning system checks the tool interference and tool access for the other faces and decomposes the part such that all the part surfaces can be accessed without interference. Consequently, the process planning job starts with a feature-based machining concept and solves the limitation of the conventional CNC machining process by part decomposition methodology, which is presented by the RP process planning technique. To verify the new approach for the hybrid-RP system, a test bench system was developed, which is called `ECLIPSE-RP' [11]. The main features of the test bench system can be summarized by six core concepts. First, the ECLIPSE-RP system is also a hybrid-RP system performing both deposition and machining. Thus, it inherits the advantages of both the conventional RP process and the CNC machining process. Second, ECLIPSE-RP builds a model by stacking thick layers with full three-dimensional shapes. In contrast to the conventional RP systems that use thinner layers, 0.01±0.5 mm, ECLISPSE-RP uses 3±30 mm chemical wood sheets as a building material. Consequently, the total building time can be dramatically reduced and the process can be applied to build a full-scale model of large objects. Third, each sheet is inverted to allow two machining setups in a building cycle. Thus, all the hidden geometries that reside on the backside of a sheet can be machined. Fourth, a machining feature concept is adopted to maximize process ef®ciency. Four types of machining features are semi-automatically extracted from the CAD model in the process planning system before the initial shape decomposition is carried out. By handling the features separately from the deposition process, the total number of threedimensional manufacturable volumes to be glued together is remarkably reduced. In this paper, the machining feature is called the machining feature segment (MFS) and the three-dimensional manufacturable volume is called the deposition feature segment (DFS). Fifth, ECLIPSE-RP uses a specially developed machining center based on a 6-axis parallel mechanism as a cutting station. As its spindle

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axis can be tilted to 908 with respect to the centric vertical axis, 5-axis/5-side prismatic machining is possible in a single setup. Consequently, machining directions that the 6-axis machining center can cover form a hemispherical shape and all the geometries in the MFS and DFS can be rapidly machined using the sheet reverse process. Finally, ECLIPSE-RP imports the shape information through a physical ®le from STEP AP203, which carries the exact geometry instead of the STL ®le, which carries the facet (polygon) geometry. Thus, the shape error resulting from the approximation into a polygonal model does not occur and a high-accuracy model can be produced. Fig. 3 shows the advantages of proposed hybrid-RP system, ECLIPSERP which is beyond the common limits of conventional RP systems. 3. Hybrid-RP process The ECLIPSE-RP process consists of two cycles. One is the main process cycle, which repeats periodically until the whole building process is completed, and the other is the additional machining process, which can be carried out at any optimal instant to machine the MFSs. Fig. 4 shows the whole ECLIPSE-RP process. The upper part of the ®gure shows the main process cycle, which is composed of four steps, i.e. backside machining, sheet reverse, sheet deposition, and frontside machining, and the lower part does the additional machining process. Though stacking thick layers accompanies many hidden geometries that reside within a sheet material, ECLIPSE-RP effectively solves this problem by inverting and machining the backside of the sheet.

Fig. 4. Process of proposed hybrid-RP system, ECLIPSE-RP.

4. Process planning technique 4.1. Architecture of the process planning system In the proposed process planning system, CAD models (STEP AP203) are partitioned into three-dimensional manufacturable volumes called DFSs after machining features called MFSs are extracted from the initial CAD model. Once MFSs and DFSs are identi®ed, the process planning system arranges them into a chain of processes and automatically generates the machining information for each DFS and MFS [12]. Fig. 5 shows the framework of the process planning system. As shown in Fig. 5, it takes the three-dimensional geometric models (STEP AP203) as input and outputs the process description ®les that specify the contents and the sequence of operations that are necessary to produce the input parts. The contents contain the machineunderstandable codes for driving ECLIPSE-RP to perform the desired operations, whereas the sequences specify all possible orders of operations that are valid to manufacture the input parts.

Fig. 5. Architecture of process planning system: software.


Fig. 6. Overall procedure of process planning.

Fig. 7. Effect of MFSs in generating DFSs.

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Fig. 8. Four types of MFS; hole, slot, pocket, and misc. surface.

Fig. 9. Architecture of MFS extraction system.

The ®rst requirement of the process planning system is the ability to interface with the existing CAD systems. The supplied shape information ®le must support free-form surface geometry and contain topologic data to overcome the disadvantages resulting from the conventional standard ®le format, i.e. STL. Thus, the proposed process planning system uses STEP AP203 as an input and performs operations, such as the determination of the setup direction, extraction of MFS, three-dimensional decomposition of the model into a set of DFSs, generation of machining information for each MFS and DFS, construction of the process

sequence, generation of the working path for each process, and the ®nal evaluation of the generated process plans. Fig. 6 shows the overall the process planning procedure for an example part. The following sections explain the extraction of MFSs and the generation of DFSs because they are the unique concepts of ECLIPSE-RP. 4.2. Extraction of machining feature segment The ef®ciency of the proposed process is dramatically

Fig. 10. Faces associated with each setup: (a) algorithm for DFS generation; (b) subdivision and merging concept for DFS generation.


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Fig. 11. Procedure of DFS generation.

improved owing to the machining feature concept applied in the process planning phase. The machining feature to be extracted in the proposed process planning system, MFS, is de®ned as a machining feature that can be effectively manufactured by a 6-axis universal machining center in station-1 (see Fig. 16). Through the extraction of MFS before breaking-down the part into DFSs, many details in the original model can be ignored in derivation of the DFSs and resultantly the number of DFSs is dramatically reduced.

Fig. 7 shows the effect caused by adopting the concept of MFS. In addition, the shape accuracy of the machining features can be guaranteed by machining each MFS in a single machining operation and the strength of a part can be improved because the number of part segments is reduced. Besides, it is possible to effectively manage and evaluate the whole process based on a feature concept. In the proposed process planning system, MFSs are

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Fig. 12. Process chain de®ned by MFS and DFS.

Fig. 13. Setup reverse module: invert/deposit/press.

1 Miscellaneous surface (Misc. Surface) is de®ned as a group of connected small surfaces, which can be manufactured in a single milling operation with a 6-axis parallel machining center of station-1. The Misc. surface could be a set of small surface patches, which is ®nally to be selected by a user.

categorized into four types of the machining features, i.e. hole, slot, pocket, and miscellaneous surface 1 as shown in Fig. 8. As these machining features are commonly found, machining them in a single operation instead of using multiple depositions effectively improves the productivity of ECLIPSE-RP process. For MFS recognition, a hybrid


method combining interactive and automatic recognition was devised to develop the process planning system module. Thus, the MFS recognition system consists of a geometric reasoning engine, ef®cient user interface, and manufacturability evaluation module. The geometric reasoning engine is implemented based on a hint-based feature recognition approach which was designed to correctly handle the intersecting features [13]. Consequently, all the potential MFS are automatically extracted and the ®nal MFSs are selected by the user referring the result of the manufacturability evaluation engine. Fig. 9 shows the architecture of MFS extraction module in the process planning system. 4.3. Part decomposition into deposition feature segment The part should be sub-divided into DFSs such that every DFS is visible either from the top or the bottom, i.e. should be manufacturable in two setups at most. In other words, no interference should occur in the deposition or machining process of the main process cycle in the build-up direction. Fig. 10 shows the faces of a DFS to be machined in each setup. Note that 3-axis milling capability of the machining center is considered to determine the shape of DFSs for simplifying the criterion while the current process planning system is designed to allow 6-axis milling capability for machining MFSs. The algorithm that sub-divides a part into DFSs is as follows. The algorithm can be broken down into four substeps, i.e. face split, pseudo-DFS construction, subdivision and merge, and DFS construction. Once a build-up direction has been determined, some faces are split along silhouette curves and additional connection curves, which indicate transitions from downward faces to upward faces or vice versa. As a result of the face split, every face has the same sign of z coordinate value of its normal vector. A sequential grouping of [2]-z-sign-face-set and [1]-z-sign-face-set forms a set of pseudo-DFSs. Consequently, each pseudoDFS is a set of side faces with openings at the top and the bottom. If the height of a generated pseudo-DFS is bigger than the maximum sheet thickness, it is subdivided and merged with the other adjacent pseudo-DFSs. After every pseudo-MFSs are adequately generated, the top and bottom faces are added to convert each pseudo-DFS into a ®nal DFS, which is a solid. Fig. 11 shows the overall procedure described above. Once the DFSs are generated, a chain of processes based on the prede®ned MFS information is created as shown in Fig. 12, where nodes represent MFSs and DFSs, and edges represent the precedence between unit processes. Each DFS is associated with the main process cycle that includes both geometric and process information, i.e. machining parameters for each sub-operations and its process order as shown in Fig. 12. Additionally, a set of alternative process sequences can also be constructed as a result of the manufacturability test mentioned earlier.

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5. Implementation 5.1. Hardware architecture The hardware of ECLIPSE-RP consists of six submodules, i.e. station-1, station-2, station-3, conveyer module, setup reverse module, adhesive dispenser module as shown in Fig. 7. Station-1 is used for all the machining processes. It is based on a 6-axis parallel mechanism. As this enables 5-axis simultaneous machining, 5-sided prismatic machining, and vertical turning all in a single step, all the geometries in a model can be theoretically machined and the ef®ciency and ¯exibility of the resulting hybrid-RP process can be maximized [14]. Station-2 is a place where new DFSs are continuously deposited until the whole building process ®nishes. Station-3 is a place where a new sheet material is supplied and the main process cycle begins. Conveyer module automates the work piece ¯ow between the stations. There are two material ¯ows in the main process cycle: between station-3 and station-1 and between station-2 and station-1. Setup reverse module is for inverting the sheet material whose backside has been completely machined. Fig. 13 shows the setup reverse module implemented in ECLIPSE-RP. It is designed to grab, invert, transfer, and press the platform loaded with a sheet material. Finally, the adhesive dispenser module ejects the cyanoacrylate on the top of the already-deposited DFSs along the prede®ned bonding paths. It consists of an adhesive dispenser controlled by a PC and a SCARA robot for holding and moving the dispenser as shown in Fig. 14.

Fig. 14. Adhesive dispenser module.

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Fig. 15. Process work¯ow in ECLIPSE-RP system.

5.2. Work¯ow in ECLIPSE-RP system The workpiece ¯ows in the proposed hybrid-RP system are shown in Fig. 15. In the ®gure, the gray arrow lines represent the paths of the platforms loaded with a sheet material or a set of deposited DFSs, and the circle numbers represent the steps of the whole building process. In step 1, a sheet material is supplied to platform-A 2 in 2 There are two platforms, i.e. platform-A and platform-B, in ECLIPSERP. New sheet material is supplied to platform-A in station-3 and a sheet material whose backside has been machined is deposited to platform-B in station-2.

station-3 and the main process cycle begins. In step 2, the platform-A is transferred to station-1 by the conveyer module of an air cylinder mechanism and the backside of the new sheet is machined. Backside roughing and ®nishing, and the machining of the MFSs which reside on the backside are carried out in this step. The sheet material whose backside has been completely machined is transferred to station-3 for the next process by the conveyer module in step 3. In step 4, the setup reverse module lifts and inverts the platform-A. In step 5, the adhesive (cyanoacrylate) is dispensed on the top of the already-deposited DFSs in station-2 where the glued DFSs are waiting on platformB. The sheet material whose setup direction has been


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Fig. 16. Implemented process planning system (GUI).

inverted in step 4 is deposited on the top of the glued DFSs in step 6. In the deposition process, the setup reverse module moves downward to press the sheet material for a few minutes to ensure strong bonding between the DFSs. In step 7, the conveyer module transfers the platform-B to station-1 and the front side geometries are machined, i.e. roughing and ®nishing are performed. Then the unmachined outer rim is removed. In the meantime, the setup reverse module carries the platform-A back to station-3 for the next main process cycle. Finally, in step 8, the platform-B is transferred back to station-2 together with a set of completed DFSs after the front side machining has been completed. The repetition of the above-mentioned main process cycles and the additional machining processes produce a ®nal part. Note that some additional machining processes are performed before all the DFSs are deposited while others are performed after all of them are deposited. The instant when each MFS is handled is determined by the process planner after considering overall ef®ciency. 6. Case study The current process planning system being developed at the CAD laboratory in Seoul National University is based on

a Parasolid modeling kernel from Unigraphics Solutions, Inc., ST-Developer V7.0 from STEP Tools, Inc., and Visual C11 V6.0 from Microsoft. MFSs and DFSs are generated automatically from a STEP AP203 model, and the complete process and machining information are derived by the process planning system. Fig. 16 shows a graphical user interface (GUI) of the implemented process planning system. Fig. 17 shows a test part, a tailstock, and a fan considered in our case studies. The test part consists of four holes and is made up of four DFSs. Also, the tailstock and fan model can be broken down into four and three DFSs, respectively. Note that these parts cannot be manufactured with a single setup operation of a conventional CNC machining process because there are so many undercut regions and unreachable features in the parts with respect to the setup direction. It was built with the proposed hybrid process with a material of chemical wood as a deposition sheet. Fig. 18 shows as an example, a cylinder block of a real engine. It consists of 49 holes, 15 slots, 6 pockets, 3 miscellaneous surfaces, and is composed of 5 DFSs. In order to verify the effectiveness of the proposed hybrid prototyping system, a number of manufacturing experiments have been done using various parts. The engine block shown in Fig. 18, whose dimension is 100 £ 90 £ 70,

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Fig. 17. Experimental examples fabricated with proposed hybrid process: (a) test part (four DFSs); (b) tailstock model (four DFSs); (c) fan model (three DFSs).

has been manufactured using the proposed hybrid prototyping system. The total run time for ®nishing the part from the STEP ®le is 8 h with the material cost of $204, and the accuracy of the ®nished part is 0.05 mm. But using SLA, the run time is estimated to be 39 h with material cost of $1200, and the accuracy of the SLA is only 0.1 mm. 7. Conclusion A new methodology for the development of a hybrid-RP system is proposed. This method combines the advantages

of a one-setup process from RP and the high-accuracy offered by CNC. It uses structural materials to produce functional parts by performing both deposition and machining in a single station. In particular, it completely combines the concepts of RP and CNC at the process planning level as well as during manufacture by adopting a machiningfeature-based process planning technique usually used in CNC process planning. Since each machining feature is machined as a whole, the number of DFSs is remarkably reduced. In addition, a test bench system, called ECLIPSE-RP, has been developed to verify the proposed approach. As the


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Fig. 18. Example of cylinder block.

hybrid-RP system performs both deposition and machining with a facility for inverting the setup direction, it is expected to become a new cost-effective manufacturing technique that will produce completely ®nished quality parts of arbitrary shape in a very short time. The developed process planning system maintains the same degree of process automation as current processes like SLA and FDM. It provides a feasible process plan to build a part from its CAD model (STEP AP203). The main tasks are to partition a model into three-dimensional manufacturable volumes after machining

features are extracted from the initial geometric model. Once the DFSs and the MFSs are identi®ed, the process planner arranges them into a chain of processes and automatically generates machining information for each MFS and DFS. Acknowledgements This research is a part of the national project of Critical

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Technology 21 Program in Korea. Also, it was partially supported by National Research Laboratory Program of the Ministry of Science and Technology, and Brain-Korea 21 (BK21) Program of the Ministry of Education and Human Resource Development in Korea. References [1] Killander LA. Future direct manufacturing of metal parts with freeform fabrication. Ann CIRP 1995;44(1). [2] HorvaÂth I, KovaÂcs Zs, Vergeest JSM, Broek JJ, de Smit B. Free-form cutting of plastic foams: a new functionality for thick-layered fabrication of prototypes. Proceedings of the Time Compression Technologies Conference, London, October 13±15, 1998. [3] CAM-LEM, Inc. Computer aided manufacturing of laminated engineering materials, CAM-LEM. http://dora.eeap.cwru.eud/ camlem/camlem.html. [4] LaserCAMM, Inc. LaserCAMM. http://www.lasercamm.com. [5] Bohlander T. The Sixth International Dayton Conference on Rapid Prototyping: New Technologies. Rapid Prototyping Report, CAD/ CAM Publishing, June 1995. p. 3±5. [6] Hope RL, Jacobs PA, Roth RN. Rapid prototyping with sloping surfaces. Rapid Prototyping J 1997;3(1):12±9. [7] Chen YH, Song Y. The development of a layer based machining system. Computer-Aided Des 2001;33(4):331±42. [8] Rapid prototyping builds karma for the next millennium. Rapid Prototyping Report, Vol. 9, No. 3. March 1999. [9] Kai CC, Fai LK. Rapid prototyping in Singapore: 1988±1997. Rapid Prototyping J 1997;3(3):116±9. [10] Jeng JY, Lin MC. Mold fabrication and modi®cation using hybrid processes of selective laser cladding and milling. J Mater Process Technol 2001;110(1):98±103. [11] Hur JH et al. Development of hybrid rapid prototyping systemÐ hardware and software. Proceedings of the Third World Congress on Intelligent Manufacturing Process and Systems. Cambridge, Massachusetts, USA, June 28±30, 2000. [12] Hur JH. Development of hybrid rapid prototyping systemÐhardware and software. PhD dissertation, Seoul National University, Seoul, Korea. [13] Han J, Regli WC, Brooks S. Technical note 4-hint-based reasoning for feature recognition: status report. Computer-Aided Des 1998; 30(13):1003±7. [14] Kim JW et al. Performance analysis of parallel manipulator architectures for CNC machining. Proceedings of 1997 ASME IMECE Symposium on Machine Tools. Dallas, 1997.

Junghoon Hur is a chief researcher in the Research and Development Center, INUS Technology, Inc. He holds a BS, an MS, and a PhD from Seoul National University. His current research interests include threedimensional optical scanning, reverse engineering, rapid prototyping/tooling, geometry modeling, computer graphics, and manufacturing.

Kunwoo Lee is a professor in the Department of Mechanical Design and Production Engineering at Seoul National University in Korea. He received his BS (1978) from Seoul National University, and MS (1981) and PhD (1984) in mechanical engineering from MIT. He was previously an assistant professor in the Department of Mechanical and Industrial Engineering, University of Illinois at UrbanaChampaign, and a visiting associate professor in the Department of Mechanical Engineering at MIT. Currently, he is on the editorial board of Computer-Aided Design, and Computer Integrated Manufacturing. He is also a program committee chair of Solid Modeling Symposium 2002. Zhu-hu is currently a PhD student in the Department of Mechanical Design and Production Engineering at Seoul National University in Korea. He received his MS from Seoul National University. His research interests include CAD/CAM, computer graphics, and rapid prototyping/tooling.

Jongwon Kim is currently a Professor at the School of Mechanical and Aerospace Engineering at the Seoul National University. He received his PhD from University of Wisconsin-Madison, MS from Korea Advanced Institute of Science and Technology, BS from Seoul National University. His primary research interests include a Parallel Mechanism System and a Hybrid Rapid Prototyping System based on Parallel Mechanism Technology.