Materials Science Forum Vols. 505-507 (2006) pp 631-636 online at http://www.scientific.net © (2006) Trans Tech Publications, Switzerland Online available since 2006/Jan/15
Development of a Virtual Controller Integrating Virtual and Physical CNC Y. C. Kao1,a, H. Y. Cheng2,b, Y. C. Chen1,c 2
1
Department of Mechanical Engineering, Department of Mold and Die Engineering National Kaohsiung University of Applied Sciences 415 Chien Kung Road, Kaohsiung 807, Taiwan, R.O.C
a
b
c
[email protected],
[email protected],
[email protected]
Keywords: virtual controller, virtual CNC, distributed, learning assistance, CORBA
Abstract. This paper describes the development of a virtual CNC controller. Controller is the major driver for a CNC machine. Similarly, virtual controller is the key driving component for a virtual CNC, which is a three-dimensional digitized physical CNC. A virtual CNC can exist in every PC serving as the complementary safer counterpart in lecturing and learning the hand on operation of expensive machinery such as five-axis milling machine, high speed CNC and mill-turn because the virtual CNC will not break. Virtual reality environment provided by EON studio software has been adopted in establishing the interactivity of a virtual CNC based on the geometry model constructed in off-the-shelf CAD software. Visual Basic was used in implementing the graphical user interface to operate the virtual CNC through the developed virtual controller. The virtual controller is in charge of (1) parsing user’s NC codes, (2) simulating the tool path of the parsed NC codes, and (3)driving the virtual CNC according to the tool path. The developed virtual CNC controller has been successfully applied in implementing virtual CNCs based on two physical three-axis CNC machines and has also been demonstrated in an international exposition successfully. The virtual controller can enable the virtual CNC in facilitating lecturing, tutoring, self-learning, and reducing the chances of accidental breakdown of precious CNC equipment. Introduction Numerical control technology has been greatly enhanced since early 1950s owing to the advances of electronic and electrical industries. Traditional machines such as lathe, milling machine, drilling machine, grinding machine, punching machine, boring machine, machining center, and metal forming machines have been gradually computerized and/or automated through the integration of a machine control unit (MCU) to enhance control, increase accuracy, repeatability and reduce the dependence of operators etc. based on the powerful numerical computation capabilities. Therefore, computer numerical controlled machines, as shown in Figure 1, have been the norm of contemporary automation machinery. The functionalities of computer numerical controlled (CNC) machines have also been the key enabler towards the rapid development of precision industry. However, Lin [1] stated that limitations of CNC include (1) high initial investment and (2) high maintenance. That is to say, CNC machines are normally expensive and it is not feasible to provide every student with one CNC machine in learning the practice of CNC operation in classroom. This is because more and more of the education institute just could no longer be able to afford the expenditure in purchasing new CNCs for each student. The price of maintaining existed CNCs is also costly and becoming heavier burden in conducting CNC classes. Advances in the computer and communication technology have offered a lot of convenience to human beings. For example, the rapid development of networking technology has shortened the distances among one another; electronic document exchange, commercial businesses, and abundant multimedia (text, image, audio, and video) information have demonstrated the great influential power of the Internet in the 21st century. The development of virtual reality technology has been one of the hottest research focus of information technology (IT) resulted from the performance enhancement of video adapter (graphics accelerator card). Three-dimensional mimic display that traditionally could All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 130.203.133.34-17/04/08,08:50:33)
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only be displayed on high-level workstation computer can now be displayed in common personal computers with effective performance. Similarly, technology of virtual reality has been demonstrated in earlier military drill and computer games showing very reasonable results and attractive impressions. Virtual technology has also impacted lecturing methods, for example, web-based asynchronous servers has been gradually adopted to replace traditional blackboard teaching methods; students can attend the virtual classroom at any time he or she preferred. Web-based programming has therefore attracted more and more engineers’ interests. Virtual reality technology can now be integrated with World Wide Web technology and has very high percentage of opportunity to revolutionize traditional way of learning through immersive, interactive and imaginary interface.
Machine structure: Servo motor, Machine drive system, Machine tool table, Feedback system
Machine Control Unit (MCU), i.e. Controller
Fig.1. basic elements of a typical computer numerical controlled (CNC) machine Literature review of VR on CNC. The application of virtual reality technology has been extended to more and more domains such as medical, architectural, aeronautical, and engineering etc. owing to the great advancement of 3D computer graphics. Education and training of CNC technology has also been paid great attention in these years. For example, Hsu [2] studied the kinematic movements for multi-axis machine tool by virtual reality technology. Cheng and Lee [3] applied virtual reality in the education and training of Lathe operation. Kao and Cheng et al [4] have also developed a web-based interactive virtual CNC system in learning assistance. Ong and Mannan [5] adopted virtual reality in the simulation and animation of a web-based interactive manufacturing engineering module; 2D and 3D user interface were developed individually, 3D panoramic view was accomplished via VRML (Virtual Reality Modeling Language) and JAVA programming environment. Ong, Jiang and Nee [6] also developed an Internet-based virtual CNC milling system by using VRML as the 3D model and controlled via JAVA through External Application Interface (EAI) where G code could be simulated to emulate simple virtual cutting operation; collision detection, and cutting parameters; tool life estimation could be calculated. VRML and JAVA EAI have also been applied by Suh et al in developing a Web-based Virtual Machine Tools (WVMT) [7]; NC tool path could be displayed in WVMT but cutting parameters were not integrated. Lin et al have also applied virtual reality in developing a virtual environments VRTSs (Virtual Reality-based Training Systems) [8] under UNIX for industrial training by considering task-planning knowledge based on Petri net theory and SGI Reality Engine II. This system is difficult to be applied for learning assistance because of its special hardware and software requirements. Wang et al developed a remote real-time CNC machining system for web-based manufacturing [9]; JAVA 3D was adopted to create the virtual scene and sensors were installed on the remote physical CNC machine to synchronize virtual CNC and remote physical CNC. Although only minor movement data were transmitted and therefore network bandwidth consumption was far less than that of remote network video transmission, real-time synchronization between virtual CNC and physical CNC could not be guaranteed based on the publicly shared characteristics of the Internet. Similarly, real-time simulation of machine tool dynamics through the virtual machine tool concept has also been proposed by Jınsson, Wall and Broman [10].Furthermore, five-axis virtual CNC has been studied [11][12][13] and distributed three-axis virtual CNC has also been studied by the authors [14][15][16]. From the above review, the
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possibility of applying 3D graphics and VR technology to emulate CNC is very feasible in PC environment. Objectives. Although VR technology has been greatly applied in constructing VR CNC, the key component “Virtual CNC controller” of a virtual CNC has not been explored. Therefore, the objectives of this paper were focused on studying a vertical VR CNC based on the viewpoint of functionality in integrating the virtual CNC and the real CNC. By so doing, the virtual CNC can be used in CNC subject lecturing, tutoring and training. Traditional way of teaching CNC course can be more fruitful and safer by incorporating three-dimensional VR CNC as a new graphical user interface. The most difficult part on coordinates system setting and transformation such as G92, G54-G59 can then be enhanced with movable 3D VR CNC machine. System architecture of a VR CNC The VR CNC developed in this paper consists of two modules: (1) VR CNC structure, and (2)VR CNC controller. These modules will be described as follows. These modules are described as follows: VR CNC structure. The VR CNC structure includes machine table, servomotor, driving system and feedback system. The virtual CNC machine table, as shown in Figure 2, of a general PC-based vertical three-axis CNC can be represented by one solid block that can be moved in both X and Y directions while Z-axis movement is controlled through the up and down translation of the spindle head (the cutter).
Z-axis movement Machine Table: X, Y movement
Fig. 2 Virtual CNC in virtual scene The dimension of the real CNC was measured before the virtual CNC structure was constructed in EON studio software. Components of the virtual CNC structure was divided into two categories: (1) movable – spindle, machine table, and door, (2) fixed – other components. Movable components must be constructed one by one so that the movement can be controlled independently, while the fixed component can be constructed in one or more solid pieces. Both movable and fixed components can be built in CAD software that can output either STL (stereo lithographic) or VRML (Virtual Reality Modeling Language) format in which the adopted VR software EON studio is able to import. The CNC components will then be organized into nodes in EON studio such as model mesh, material, motion, light source, etc. These nodes will be displayed in “Component-Nodes” window and the behavioral relationship among the components can be assigned in the “Route” window. The sequence in constructing the VR CNC is shown in Figure 3. Motion control of a real CNC was fulfilled through control of the servomotor, driving system and feedback system. Similarly, the virtual CNC machine table could be actuated according to the NC codes such as G00 and G01 for linear motion, G02 and G03 for circular motion. Virtual CNC controller. The VR CNC controller is composed of Human Machine Interface (HMI), NC codes parser, and interpolation algorithm. Visual Basic 6.0 was used in developing the VR CNC controller. The VR controller HMI interface, as shown in Figure 4, was developed underlying Microsoft Visual Basic 6.0 environment based on a Mitsubishi V30 PC-based three-axis vertical machining center in the Remote Virtual Rapid Laboratory, Department of Mechanical Engineering,
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National Kaohsiung University of Applied Sciences, Taiwan, as shown in Figure 1. For the purpose of demonstrating VR controller in assisting education and training, the HMI of the VR controller has been simplified from the full functional Mitsubishi V30 controller. The VR controller can emulate Cycle Start, Cycle Stop, Spindle, Feed rate, Home, Tool exchange, Emergency Stop, and MDI mode such as Jog, Handle, Rapid, Memory, Tape, etc. Machine coordinates and Workpiece coordinates can also be shown dynamically. NC codes can also be displayed and edited.
(a) build up CAD geometry
(b) import geometry into (c) setting levels in EON studio “simulation tree” Fig. 3 sequence of constructing VR CNC
(d) setting behaviors in “Route: simulation” window
NC codes parser. Operation of a CNC machine is based on the user entered commands and these commands are mostly the numerical control (NC) codes or programs. Currently, most of the complex NC codes are generated by off-the-shelf computer aided manufacturing (CAM) software and the purpose of NC codes parser is to realize the meaning of the user’s intention in operating the CNC through NC codes. The NC codes parser developed in this paper can restructure the entered NC program and categorize the machining data into Line, Arc, Canned Cycle, Fig.4 Virtual controller HMI interface and Zero Return structures, as shown in Figure 5. The coordinate system code G92, G54~G59 for work piece origin settings can also be interpreted and transformed. Line Line No.
Movement Type
Line No.
Start
Coordinates
Arc Coordinate System
Offset Type
Line No.
Movement Type
Coordinates
Coordinate System
Offset Type
Line No
Start.
Coordinates
Canned Cycle Coordinates
Coordinate System
Offset Type
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Zero Return
Fig.5 NC codes restructured by the developed NC codes parser Interpolation. Interpolation algorithm dedicated for the VR CNC needs to be implemented in the VR controller to ensure the correct motion. For example, total tool path length must be obtained for the linear motion before X-, Y-, and Z-axis components were calculated. Every axial component needs to be subdivided to smoothing the movement, as shown in Figure 6(a). Circular motion was represented via radius and angles, as shown in Figure 6(b), and arc length was subdivided and converted back to circular angles for the angular movement. The unit linear motion in this paper was set to 1 mm and 0.1 radian for angular movement. Integration of virtual CNC controller and virtual CNC machine. The embedded EONX component provided by the EON studio was adopted in the VB environment to bridge the interfacing parameters so that the components movement of the VR CNC can be controlled from the developed virtual CNC controller by VBScript connection in the developed VB program through EONX 3.0 Type Library. These parameters can be used to transfer the structured data, as shown in Figure 5.
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(b) Circular motion through radians (a) Linear motion through X-, Y-, and Z-components Fig. 6 Movement for Linear and Circular motion Implementation and case study Two VR CNCs have been constructed. One is the Davinci three-axis milling machine developed by the Precision Machinery Corporation, as shown in Figure 7, and the V30 milling machine, as shown in Figure 2. The operation of the developed VR CNC was started from edge tracing of X coordinate, as shown in Figure 8(a); the edge tracing of Y coordinate is similar to X edge. The Z workpiece origin is obtained as shown in Figure 8(b). Both Figure 8(a) and Figure 8(b) were operated in MDI mode of the VR CNC. Once the workpiece edge (X,Y,Z) is obtained from the VR MDI Figure 7 VR Davinci milling mode, either G92 or G54~G59 can be used to set the workpiece machine origin before the NC tool path can be started. Coordinates settings in through the MDI mode is the easiest way to teach a novice to be familiar with the meaning of machining coordinate systems. However, it is always very dangerous in hand on practice for configuring the work piece zero origin. With the assistance of the developed VR CNC and accompanied VR CNC controller, hand on operation through VR CNC will not break anymore. The tool exchange can be operated, as shown in Figure 8(c), and the tool path simulation can also be started as well, as shown in Figure 8(d).
(a) tracing origin in X direction
(b) tracing origin in Z direction
(c) tool exchange (d) tool path simulation Figure 8 Tracing workpiece origin, tool exchange and tool path simulation Conclusions and future work This paper has successfully developed a VR CNC milling machine through the integration of virtual reality software and Microsoft Visual Basic programming environment. The key enabler of the VR CNC – VR controller was created to parse NC codes and to provide 3D graphic user interface to ease
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the operation of the VR CNC. The NC codes parser can restructure the user entered NC codes file and the tool path can be simulated afterwards. The file size of he established VR CNC were very small compared with that of CAD file size, for example, Davinci VR CNC was about 20MB (approximately 120 MB in original CAD geometry) and V30 VR CNC was about 7MB (approximately 80 MB in original CAD geometry), which is one of the major advantages of VR CNC. The developed VR CNC has been tested in a CAD/CAM class conducted by the author showing very reasonable performance. The CNC courses is expected to be changed through the application of VR CNC. Although the function of real time material removal was not supported directly by the VR software, some work around might be possible to tackle this issues; for example, collision node and shape deformation might be possible. Further development can also be focused on integrating electronic message gloves or Head Mounted Display (HMD) with the VR CNC so as to emulate the operation of VR CNC by hands. VR CNC structures can also be gradually constructed and installed in the machine data base so that the VR CNC user can change VR machines as will and so is the VR controller. Acknowledgments The authors would like to express their appreciation for the support from the National Science Council (NSC) in Taiwan through Grand NSC-93-2212-E-151-019. References [1] S.C. Lin, “Computer Numerical Control – From programming to Networking”, Delmar Publisher, 1994, pp. 6-22 [2]Peng-Sheng Hsu, “Study on Kinematic Movements for Multi-axis Machine Tool by Virtual Reality”, Master Thesis, Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan, R.O.C., 2001 [3]Hui-Chin Cheng, Chou-Chen Lee, “The Technique of Virtual Reality Applies and Studies in the Training of Lathe Machine Operation”, Proceedings of the 21stNational Conference on Mechanical Engineering, the Chinese Society of Mechanical Engineers, Kaohsiung, pp.6131-6136, 2004 [4]Y. C. Kao, H. Y. Cheng, M. S. Chen, Y. C. Chen, ” Development of a Web-based Interactive Virtual CNC Learning System”, SME Taipei Chapter 2004 Annual Meeting and the 4th Conference on Precision Mechanical Manufacturing, B04-003, Taipei, 2004 [5]S.K. Ong and M.A. Mannan, “Virtual reality simulations and animations in a web-based interactive manufacturing engineering module”, Computers & Education, Vol.43, pp. 361–382, 2004 [6]S. K. Ong, L. Jiang and A. Y. C. Nee, “An Internet-based Virtual CNC Milling System”, The International Journal of Advanced Manufacturing Technology 20:20-30, 2002. [7]Suk-Hwan Suh, Yoonho Seo, So-Min Lee, Tae-Hoon Choi, Gwang-Sik Jeong, Dae-Young Kim “ Modelling and Implementation of Internet-Based Virtual Machine Tools ”The International Journal of Advanced Manufacturing Technology 21:516-522, 2003 [8]Fuhua Lin, Lan Ye, Vincent G. Duffy, Chuan-Jun Su “Developing Virtual Environments for Industrial Training” Information Sciences140, pp.153-170, 2002 [9]Lihui Wang, Peter Orban, Andrew Chunningham, Sherman Lang ”Remote Real-time CNC Machining for Web-based Manufacturing” Robotics and Computer Integrated Manufacturing 20, pp563-571, 2004 [10]Anders Jınsson, Johan Wall, Gıran Broman*, ”A virtual machine concept for real-time simulation of machine tool dynamics”, International Journal of Machine Tools & Manufacture 45, pp795–801, 2005 [11]Wei-Cheng Hsu, ” Study on Cutting Motion of Multi-axis Machine Tool by Virtual Reality”, Master Thesis, Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan, R.O.C., 2002 [12]Ta-Lung Liu, ” Study on Simulation of Cutting Motion in Multi-axis Machine Tool by Interpolation Algorithm”, Master Thesis, Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan, R.O.C., 2003 [13]Rong-Shean Lee, Yan-Hong Lin, ”Study on Universal Construction of Five-axis Virtual Machine Tool”The 13th Automation Technology Conference, Taipei, pp.52-59, 2004 [14]Y. C. Kao, H. Y. Cheng, M. S. Chen, Y. C. Chen, “The Development of a CORBA-Based Virtual CNC Milling System”, The 13th Automation Technology Conference, Taipei, pp.51-56, 2004 [15]Y. C. Kao, H. Y. Cheng, M. S. Chen, Y. C. Chen, “Research on the Integrated Human-Machine Interface of Virtual CNC and Remote Networked Machining”, Proceedings of the 21stNational Conference on Mechanical Engineering, the Chinese Society of Mechanical Engineers, Kaohsiung, pp.6179-6185, 2004 [16] Y.C. Chen, Cheng-An Fang, Mau-Sheng Chen, H. Y. Cheng, Yung-Chou Kao, “Study on the Integration of a Virtual and Physical CNC Milling System”, Proceedings of Automation 2005, The Eighth International Conference on Automation Technology Conference, Taichung, Taiwan, 2005
