Development of a Virtual Controller Integrating Virtual and Physical CNC

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 21 st 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 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 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) 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. 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 Machine Control Unit (MCU), i.e. Controller Machine structure: Servo motor, Machine drive system, Machine tool table, Feedback system 632 Progress on Advanced Manufacture for Micro/Nano Technology 2005