Concurrent Engineering http://cer.sagepub.com
Internet-Based Design Visualization for Layered Manufacturing Haeseong J. Jee and R. Ian Campbell Concurrent Engineering 2003; 11; 151 DOI: 10.1177/1063293X03035389 The online version of this article can be found at: http://cer.sagepub.com/cgi/content/abstract/11/2/151
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CONCURRENT ENGINEERING: Research and Applications Internet-based Design Visualization for Layered Manufacturing Haeseong J. Jee1,* and R. Ian Campbell2 1
Department of Mechanical Engineering, Hong-Ik University, 72-1 Sang-Su-Dong, Mapo-Ku, Seoul 121-791, Korea 2
Department of Design and Technology, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK
Abstract: When considering the use of layered manufacturing (LM), there are many issues a designer has to address for handling a stereolithography tessellation language (STL) model, the de facto standard for LM. In this paper, we propose an Internet-based design visualization tool for decision support when optimizing the LM process in support of a highly interactive and collaborative virtual environment between CAD designers and LM processes over networks. It directly provides designers with an advanced preprocessor functionality, design visualization/optimization, as well as model display, repair, and slicing over the network. This can help smooth data transfer from CAD to the LM process with minimum inconsistency in CAD data. Key Words: CAD, LM, internet, design visualization, STL.
1. Introduction Layered manufacturing (LM) technologies have an ability of creating a physical part directly from its computer model by adding materials on a layer by layer basis. Major application areas have been early verification of product designs and quick production of prototypes for testing. Once a computer model is generated for a physical object, it needs to be communicated to another computer system or LM machines for further processing. CAD model data is now frequently transmitted to various LM processes using STL. Sometimes, however, CAD systems generate STL files with geometric flaws. In fact, STL has drawbacks such as redundancy, inaccuracy, and lack of integrity. Most software efforts in the emerging LM community have thus focused on geometrical verification of STL CAD models prior to part fabrication [1–3], and there are now several very good software products available that will find and fix flaws in STL files [4]. Over the years, however, as more and more companies have switched to solid-modeling CAD software systems that almost always produce good STL files, STL fixing has become less of a concern for most designers. Nowadays, service bureaus that offer users the opportunity to try out new technologies and test their products are beginning to appear in large numbers,
*Author to whom correspondence should be addressed. E-mail:
[email protected]
and people want to do a lot more with STL files and LM than simply make three-dimensional prints of their CAD files. For example, designers themselves want to use visualization [5] and optimization [6,7] as well as repair of the STL file in order to avoid as much physical prototyping as possible since it is expensive to go through a full manufacturing and assembly prototyping cycle. Emerging LM industry has thus created a need for preprocessor software that enables designers to conduct design-oriented works such as visualization/optimization as well as do repair/conversion of an STL file into data recognized by the actual LM machine [8]. However, there are still many issues a designer has to address for handling an STL model and, moreover, most recent LM processes possess quite different capabilities, and most are not even isotropic. In the mean time, rapid advances in computing and communication technologies are creating a new approach for product design and manufacturing. Recently researchers and developers have moved toward creating manufacturing environments for automated LM capability on the network [9,10] and a number of companies have been working to establish the LM marketplace on the Internet in order to save a purchaser time by enabling him/her to submit requests for quotation to multiple service providers simultaneously. There is no doubt that the Internet will change the way LM services are delivered. Today designers can just skip all those irritating issues by visiting a webbased service bureau and leaving all to companies that readily supply LM services rather than set up and operate their own equipment. Orders are now taken for
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1063-293X/03/02 0151–8 $10.00/0 DOI: 10.1177/106329303035389 ß 2003 Sage Publications
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LM parts through service providers’ web pages; what designers are supposed to do is to upload their STL files to the company server in electronic form through the Internet either by direct upload, ftp file transfer, or as an e-mail attachment although many CAD models are still transferred through hand-carried tapes. Nevertheless, this does not fundamentally change the buying process itself, and it still requires a lot of back and forth communication between the service purchaser and the provider. Therefore, in many cases, designers still need to be playing an important part in the preprocess works even being together with web-based service providers, which, after all, requires highly interactive preprocess tools in support of the designer exchanging design decisions directly with service providers over the network. In this paper, we propose an Internet-based design visualization tool for decision support when optimizing the LM process in support of a highly interactive and collaborative virtual environment between CAD designers and LM processes over the network. Figure 1 shows two different process configurations for making interface between CAD designers and LM processes;
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the upper one is for the traditional configuration and the lower one for the new configuration. Compared to the traditional configuration that relies upon quotations through network connection only, the new configuration is additionally supported by an Internet based preprocessor that can be realized by developing a client/ server model on the network. The Internet based preprocessor allows the client to fully access and utilize preprocessor functionality such as model display, slicing, and visual simulation of the design in cooperation with the service providers over the network. Hence the new process environment is expected to fill the gap between CAD designers and various LM processes and, moreover, to help smooth data transfer from CAD to LM process over the network.
2. System Configuration and Functionality The configuration of the proposed system consists of three main parts; server, client, and the Internet in between as shown in Figure 2. In this client/server model the server end mainly manages the network connection with clients and continually listens on one end of the channel. On the contrary the client program periodically connects with the server to exchange data. The server has a database of STL files to be utilized by any client for file testing and processing. In other words the server manages a database for handling STL files and a client can access the server in order to search appropriate STL files. The client can also directly upload and register his own STL files to the server for preprocessing work. 2.1 Interactive Functionality Based on the Internet
Figure 2 shows a step-by-step server/client network connection and multithreading in server site for the system configuration. The server end first creates a listening socket to prepare network connection and awaits network access by clients. Whenever a client accesses the network the server creates a client socket to complete the connection. The server can create as many client sockets as the number of clients who wish to access the network, and all process data can be transferred to an appropriate client through the socket. The resulting image processed in the server can also be sent to the corresponding client for display. The client end, on the other hand, mainly serves as a convenient tool for interfacing to the server. It uploads/ registers an STL file to the server and restores the same file from the server sometime later for further processing. Though the client mainly displays the received Figure 1. Two different configurations for CAD–LM interface: image data processed and sent by the server it can also (a) Typical quotation-based CAD–LM interface; (b) Internet-based preprocessor for CAD–LM interface. send an order for setting a process parameter such as Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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server for iterative image display. Since a layer data may consist of more than one loop, e.g., a list of edges forming a closed circuit, a data structure using a doubly linked list is devised in order to describe the layer ! loop ! vertex_point relation. 2.2 Intelligent Preprocessor Based on Design Visualization When being fabricated by an LM apparatus, the object is built by laying down material layers in a gradual, controlled way, which results in the staircase (or laddering) effect on what should actually be smooth surfaces. Traditional geometry-based modelers which display a smooth, shaded object of the physical model hence provide the designer with no information on the actual surface finish of the object. Since, depending on the application area, the staircase effect can have a significant effect on part functionality software efforts for reducing/removing the staircase effect have been made for better surface finish of the physical LM part [11,12]. On the other hand, careful examination of the visually simulated model prior to actual fabrication can also help minimize unwanted design iterations due to the surface finish problem. In many cases, visualization in the LM community has been mainly for verifying surface roughness. Chandru et al. [13] have once suggested a voxel-based modeling for visualizing the geometrical effect on the surface of a physical LM part, which is very expensive due to its intensive memory usage but is also valuable when manufacturing parameters must be incorporated to properly describe the geometry of the visually simulated model; Jee and Sachs [14] have implemented a voxel-based visual simulation technique for facilitating surface macrotexture, which takes into account necessary geometric attributes and Figure 2. System configuration for the client/server model on the physical phenomena of the 3D Printing process. A network. cheaper and easier way of creating visually simulated models is thus shown in Figure 3. This layer stack model layer thickness for slicing an STL file to the server. Once can simply be made by first creating the geometry of an STL file is selected for the preprocess, the server sliced layer stacks that belong to one part. Each layer is provides the client with necessary functionality of then bonded together, one at a time consecutively, which cleaning/repairing ill-defined CAD files and editing/ eventually constructs the whole part (virtual model). In converting the STL file into a data form recognized by essence, a virtual model can be built purely based on the an actual LM machine. LM build file. The layer stack model, however, does not The client can also order a request for visual give any quantitative indication of the surface roughsimulation functionality on the server before the real ness. On the other hand, there is a different visualization fabrication of the STL file takes place using one or more algorithm of surface roughness based on the slanted LM machines. The server will first read and translate the angle of STL facets [15]. In this method the normal imported STL file into an analytic model for visualizavector for each facet in the STL file is analyzed with tion. It then creates a virtual LM model and the respect to the horizontal (xy) plane. The angle between resulting image data will be sent to the client so that it the vector and the plane is used to determine the local can be displayed on the client terminal. The resulting surface roughness value. The quantitative surface data of the file processing such as 3-D STL model, 2-D roughness values are then displayed as color shading sliced layers, and color information for visually simulaton the computer image. This gives the designer a visual ing the physical LM part can be also recorded inside the image of the overall surface roughness and any problem Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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Figure 3. Three different types of image display of a CAD model; original CAD model (left), accumulated sliced layers wire framed (center), and visually simulated layer stack model with a single color-shading (right).
Figure 4. A computer image displaying a surface roughness with differently shaded colors based on the slanted angle of STL facets.
i, j where i, j is the jth cusp size along the ith radial line areas in the model as shown in Figure 4. This type of visualization is of great benefit to the designer who can Ri from the bottom of a part. The second step is to decide the maximum/average cusp size out of every re-orient the part and check for any improvement in the group of cusp values estimated in between two adjacent color distribution across the part surface, which, layer boundaries. For example, both the jth maximum however, displays only a smooth, shaded object and cusp size Mj and the jth average cusp size Aj can be still provides the designer with no information on the chosen/calculated from the group of cusp values i, j actual surface finish of the object. estimated in between two adjacent layer boundaries, We hence combine the color-based quantitative Bjþ1 and Bj . Occasionally, multiple values for one i, j visualization tool with the layer stack model that can be found during the procedure due to the part visually simulates the physical LM part, and, as a geometry, which will be readily settled by keeping the conclusion, an improved visualization technique has maximum value only. A full set of maximum cusp values been devised. The procedure involves estimating first the M and a full set of average cusp values A through the maximum/average staircase cusp size between two part layers can then be obtained as adjacent layers and then adding a shaded color on each layer according to the estimated value. Figure 5 illustrates an example of estimating the maximum/ M ¼ 9 Mj jMj ¼ Max i, j ji ¼ 1, 2, 3, . . . , m , average staircase cusp size. Although estimating the Mj 2 R3 , j ¼ 1, 2, 3, . . . , n 1g cusp size in a single direction as shown in Figure 5(a) can be readily accomplished, generalization of the A ¼ 9 Aj jAj ¼ Avg i, j ji ¼ 1, 2, 3, . . . , m , overall cusp size along the boundary of the whole Aj 2 R3 , j ¼ 1, 2, 3, . . . , n 1g layer is not as straightforward. In this procedure, a number of regularly spaced radial where m is the number of radial lines and n is the lines from the moment center through the part layers, is number of part layers. Each layer stack can then be drawn first as shown in Figure 5(b). A more detailed colored differently according to the choice of a designer, illustration for the procedure is also given in Figure 5(c) Mj or Aj , during the visual simulation process. As an where a radial line Ri , for example, is drawn through the example, the variation of staircase cusp sizes in an LM layer boundaries Bjþ2 , Bjþ1 , and Bj . Line ‘jþ1 is then part is now visually displayed as a particular color drawn parallel to the boundary edge Bjþ2 and, similarly, shading together with the visually simulated layered line ‘j is drawn parallel to the boundary edge Bjþ1 in stacks on the computer image as shown in Figure 6(a) and order to estimate each correspondingDownloaded cusp size i, jþ1 from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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Figure 5. An illustration of estimating staircase cusp size between two adjacent layers.
(based on the average staircase cusp size on each layer stack). Since, however, surface quality is considered as a local property, we expect that the color coding based on the maximum staircase cusp size on each layer stack will be preferred by most designers, rather than the one based on the average size (another color coding example based on the maximum staircase cusp size will be shown later as a case study example). Though this method still does not provide a direct indicator of surface roughness it can be used as a quick test to see whether the designer should adjust the part orientation, then recreate the visualized model that has better surface quality for the LM part, or not over the Internet. An automated decision-making procedure for determining a proper part orientation can be alternatively conducted using a simple optimization algorithm with iterative slicing as shown in Figure 6(b). This would be particularly valuable if variable thickness layers were available. The color-coding could be used to decide which layers require to be sliced with a thinner value.
connection for system development. Users see the familiar browser interface at their client computers, and server computers can either supply simple Web-like pages or do complex data processing in response to the user input as shown in Figure 7. In constructing the proposed LM preprocessor on the network, we have introduced Window socket (Winsock) programming for server/client networking and Visual Cþþ & OpenGL on Windows operating system environment for 3-D geometric modeling. Assuming that client and server computers were connected to the Internet, it is possible to run exactly the same client and server software on a local intranet; An intranet is often implemented on a company’s local area network (LAN) and is used for distributed applications. The system using JAVA Web browser, on the other hand, might have some advantages – it will be more intuitive to the users and no complex network construction process is required. The loading speed of JAVA applet, however, is still not fast enough for the current network applications. In addition, JAVA3D library based on OpenGL has a difficulty 3. System implementation and a Case Study in providing images with good graphic quality and quick execution time. The network provides all necessary logic for supportFigure 8, as a case study example, shows computer ing the server–client interface and controls the network images displaying different design visualizations for Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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decision support; a computer image displaying smooth, shaded object of an STL file, spider (a), two different computer images displaying a visually simulated layer stack model of the LM part in different scales on the Internet (b and c), and a computer image displaying the
Figure 6. Two different visualizations for the decision support: (a) Various staircase cusp sizes with differently shaded colors on the layer stack model; (b) An automated decision-making procedure for determining a proper part orientation.
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various staircase cusp sizes with differently shaded colors on the same layer stack model (d – based on the maximum staircase cusp size on each layer stack). If the resulting image looks acceptable, the user can assign a working order for LM fabrication to the server. The server can then search an appropriate LM service bureau for the assigned order and pass the order information to the relevant bureau in order to execute the fabrication. Working orders, when using remote search and evaluation (RSE) tool, could be assigned directly to a specific service bureau depending on users’ choices. Using the RSE functionality on the Internet, users’ attention can quickly be switched to a specific LM service bureau in which they might be interested. In this paradigm of future client/server model, however, it is supposed that all LM service bureaus under consideration are bound by an agreement to have an Applet for publication of the manufacturing capabilities of their own processing LM machines on the Internet. Once the information concerning all of the LM processes are acquired, RSE can formulate a set of rules to evaluate the processes and select the most appropriate one based on the submitted requirements.
Figure 7. The server manager controlling the network connection with clients.
Figure 8. The client windows displaying different design visualizations; a smoothly shaded object of an STL file (a) – yellow, two build visualizations of the layer stack model (b),(c) – green, various staircase cusp sizes with shaded colors on the layer stack (d) – color coded. Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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Figure 8. Continued.
4. CONCLUSIONS
Internet without ironclad protection of their designs against all hazards, and they may still need venders’ own developing preprocessor software in order to execute some design-intensive works such as generation of complex internal build patterns/support structures and determination of optimum layer thickness of the LM part. It is expected that the method can construct a tentative collaborative environment on the Internet for automated LM capability and help smooth CAD data transfer with minimum inconsistency from CAD to LM process, which enables designers to be able to generate physical prototypes through a cheaper and betteramortized process.
The paper proposes an interactive and collaborative virtual environment between CAD designers and LM processes by directly providing designers with a new design visualization tool for LM parts together with traditional preprocessor functionality over the Internet. A client/server model on the network is introduced in order to realize the tool framework and an Internet-based design visualization tool for decision support when optimizing the LM process is devised and implemented on the framework. Traditional preprocessor functionality includes display, repair, and slicing of an STL model for satisfying the minimum requirement of LM preprocessor functionality over the Internet. The paper differs from previous approaches in two Acknowledgments respects; it provides a unique method visualizing the variation and distribution of cusp sizes on the surface of This work is supported by the Korea IMS research an LM part when oriented in a specific direction and it program managed by KITECH. also implements the methodology as an Internet-based decision support tool for optimizing the LM process. Though this method still does not provide a direct References indicator of surface roughness it can be used as a quick test to see whether the designer should adjust the 1. Bohn, J.H. and Wozny, M.J. (1992). Automatic CADmodel Repair: Shellclosure, In: Proceedings of the SFF part orientation, then re-create the visualized model Symposium, Department of Mechanical Engineering, that has better surface quality for the LM part, or not University of Texas at Austin, pp. 86–94. over the Internet. Implementation of direct tele2. Morvan, S.M. and Fadel, G.M., IVECS. (1996). manufacturing and tele-control of LM machine in Interactively correcting .STL Files in a Virtual Environcombination of the proposed method will be also ment, In: Proceedings of the SFF Symposium, Department desired for extending and invigorating the collaborative of Mechanical Engineering, University of Texas at Austin, pp. 491–498. virtual environment between CAD designers and LM 3. Krause, F.-L., Stiel, C. and Luddemann, J. (1997). processes. In addition, as it becomes more complex to Processing of CAD-Data – Conversion, Verification and work with LM, providing tooling design using the Repair, In: Proceedings of 4th ACM Symposium on Solid Internet is also becoming even more important and Modeling, pp. 248–254 Atlanta, GA. indispensable for the soft and hard tooling industry. The 4. Wozny, M.J. (March 1997). CAD and Interfaces, JTEC/ biggest potential barrier in realizing this method, WTEC Panel Report on Rapid Prototyping in Europe and however, will be the security of design data: Designers Japan, Vol. 1, Rapid Prototyping Association of the Society of Manufacturing Engineers, pp. 69–90. often tend to be reluctant to upload their files onto the Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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5. Jee, H. and Sachs, E. (2000). A Visual Simulation Technique for 3D Printing, Advances in Engineering Software, 31(2): 97–106. 6. Lan, P.T., Chou, S.Y., Chen, L.L. and Gemmill, D. (1997). Determining Fabrication Orientation for Rapid Prototyping with Stereolithography Apparatus, Computer-Aided Design, 29(1): 53–62. 7. Alexander, P., Allen, S. and Dutta, D. (1998). Part Orientation and Build Cost Determination in Layered Manufacturing, Computer-Aided Design, 30(5): 343–356. 8. Barequet, G. and Kaplan, Y. (1998). A Data Front-End for Layered Manufacturing, Computer-Aided Design, 30(4): 231–243. 9. Bailey, J.M. (1995). Tele-Manufacturing: Rapid Prototyping on the Internet, IEEE Computer Graphics & Applications, 15(6): 20–26. 10. Luo, C.R. et. al. (1999). Tele-Control of Rapid Prototyping Machine Via Internet for Automated TeleManufacturing, IEEE International Conference on Robotics and Automation, 3: 2203–2208. 11. Dolenc, A. and Ma¨kela¨, I. (1994). Slicing Procedure for Layered Manufacturing Techniques, Computer-Aided Design, 26(2): 119–126. 12. Kulkarni, P. and Dutta, D. (1996). An Accurate Slicing Procedure for Layered Manufacturing, Computer-Aided Design, 28(9): 683–697. 13. Chandru, V., Manohar, S. and Edmond Prakash, C. (November, 1995). Voxel-Based Modeling for Layered Manufacturing. IEEE Computer Graphics and Applications, 42–47. 14. Jee, H. and Sachs, E. (2000). Surface Macro-Texture Design for 3D Printing, Rapid Prototyping Journal, 6(1): 50–59. 15. Campbell, R.I., Jee, H. and Lee, H. (2000). Visualization Tools for Design Support in SFF, In: Proceedings of the SFF Symposium, Department of Mechanical Engineering, University of Texas at Austin, pp. 437–44.
R. I. CAMPBELL
R. Ian Campbell R. Ian Campbell worked as a design engineer at Ford Motor Company and Rover Cars before moving to academia in 1989. He is currently a Senior Lecturer at Loughborough University in the Department of Design and Technology where he is leader of the Design Research Group. He has had many papers published in international conferences and journals in the areas of engineering design and rapid prototyping. His latest research efforts have been in the area of user-centred design and advanced CAD interfaces. Dr Campbell is editor of the Rapid Prototyping Journal and serves on the programme committees of several international conferences.
Haeseong J. Jee Haeseong J. Jee is an Associate Professor in the Department of Mechanical Engineering, Hong-Ik University, Seoul, Korea. His prior association was with the National Institute of Standards and Technology (NIST), USA from 1996–1997 as a guest researcher. He holds a B.S. and an M.S. from Seoul National University, Korea, and a Ph.D. from the Massachusetts Institute of Technology, Cambridge, MA, USA. He has published papers in journals in the areas of engineering software and rapid prototyping. His current research interests include digital manufacturing, engineering graphics for optimal design/geometric modeling, and rapid prototyping/tooling. Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 10, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
