Development of a Virtual Training Workshop in Ultra-Precision Machining*
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Int. J. Engng Ed. Vol. 18, No. 5, pp. 584±596, 2002 0949-149X/91 $3.00+0.00 Printed in Great Britain. # 2002 TEMPUS Publications. Development of a Virtual Training Workshop in Ultra-precision Machining* W. B. LEE, J. G. LI and C. F. CHEUNG Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. E-mail: [email protected] This paper presents the development of a virtual training workshop (VTW) for supporting training of engineering personnel to acquire the theoretical know-how, practical skills and the problem troubleshooting techniques on the usage of ultra-precision machining and inspection facilities, which might not be affordable in conventional training workshop. The architecture, underlying theoretical basis and implementation aspects for the development of the VTW are described. Experimental work for realizing the capability of VTW together with the future development of a distributed virtual training environment (DVTE) are also discussed. INTRODUCTION simulators for conducting training for the pilots. However, relatively little research has been found in THE ACQUISITION of skill through education the development of VR as an enable training tool and training has long been acknowledged as one of for ultra-precision machining and nano-metrology. the principal forces driving economic growth. In order to provide a VR environment for Effective training programs can result in increased interactive user interface and for conducting train- productivity and quality [1]. Virtual Reality (VR) ing, a virtual training workshop (VTW) is purpo- technology has been used in various forms in sely built based on the theoretical background of a training systems for many years, especially for virtual machining and inspection system proposed military applications, flight training, equipment by the authors [3]. The VTW will provide an operating training, surgical techniques simulating, interactive 3D graphic interface for the operator etc. Ultra-precision machining based on single- to simulate the diamond turning and surface integ- point diamond turning is a machining process rity measuring processes. The use of VR techni- making use of a mono-crystal diamond cutting ques [4] allows individuals to become immersed in tool which possesses nanometric edge sharpness, a computer-simulated environment that mimics form reproducibility and wear resistance. The the real operation of the ultra-precision machine process is capable of producing components with and inspection equipment. The user or trainee can micrometer to sub-micrometer form accuracy and practice all necessary switching operations, proce- surface roughness in the nanometre range [2]. The dures and skills in a complete safety, while main- success of the technology does not only rely on the taining a high degree of realism. In addition, they sophisticated machine design and control but also can acquire the theoretical know-how of ultra- depends on its associated nano-metrology. precision machining and surface metrology as However, ultra-precision machining and nano- well as develop the problem troubleshooting tech- metrology are expensive processes. The skill and niques (Fig. 1). In this paper, the architecture, the techniques incurred in the operations of these underlying theoretical basis and implementation sophisticated facilities are complex. These issues for the development of the virtual training demand a well-trained and high skillful operator workshop are highlighted. The experimental work to operate the ultra-precision machining and nano- and applications of the VTW are also discussed. metrology facilities. Since any faults in the opera- tion of the ultra-precision machine and measuring equipment might lead to fatal damage and great THE VIRTUAL TRAINING WORKSHOP loss of the expensive facilities or even hazard to the (VTW) operators, it might not be affordable to conduct conventional workshop training on the use of the The architecture of the VTW ultra-precision facilities. As shown in Fig. 2, the VTW is basically Virtual reality (VR) has been recognized as an composed of five functional modules which are indispensable tool for developing interactive the control console, the information module, the training tools for skills and knowledge training. virtual environment simulator, the event process- Examples can be found in the use of flight ing module and the virtual objects, respectively. The control console provides the interactive * Accepted 18 February 2002. graphic interface for the users to input the control 584 Development of Virtual Training in Ultra-precision Machining 585 Fig. 1. Functions of the virtual training workshop. command, NC program, product and tooling to mimic the real-world scenarios in the training information. The user inputs are processed and workshop. the corresponding events are ordered sequentially by the event-processing module. The outputs of Control console the module are the control command for the The control console is the graphic user interface virtual environment simulator and the machine in which the user interacts with the virtual environ- models. Based on the control command issued by ment. Fig. 3 shows the snapshot of control panel of the event-processing module and the internal data- the virtual Nanoform 300 ultra-precision machine. base, the virtual objects simulate the machining It consists of `press buttons', `selecting knobs', and inspection operations. The virtual environ- `screen', etc. During the training process, the user ment simulator makes use of the control can adjust and control the activities of virtual commands from the event-processing module, machine tool via operations of these `press information module as well as the virtual objects buttons' and `selecting knobs' on control panel. Fig. 2. Framework of the VTW. 586 W. Lee et al. Fig. 3. Control panel of the virtual machine. The editing of NC program, the setting of cutting of the workpiece during machining, the status of the tools and work offsets can also be done via this control panel buttons, etc. The internal database, on control panel. The states of axis position of NC the other hand, composes of libraries of tool infor- machine tool and settings are fed back to the mation, machine characteristics, workpiece infor- control panel. mation,materials,setupparametersofthemachines, etc. The major difference between the data buffer Information module and the internal database is that data in the data The information module is composed of two buffer are updated automatically by the interaction sub-module which are the data buffer and internal between the users and the virtual environment database. The data buffer is a dynamic database, whereas the internal database contains the which consists of the run-time data for real-time nominal data used in the training system. updating the scenarios of the virtual machine motions. Examples include the real-time coordi- Event processing module nates of the position of the machine slides and As shown in Fig. 4, the event processing module spindle, the change of the geometry and attributes is used to process the user's operations on the Fig. 4. Schematic diagram of the event processing module. Development of Virtual Training in Ultra-precision Machining 587 control console. Every user's operation on the physical skills. The representation of 3D object control console can be processed as an event. geometry is an important step in the graphical When there is a user's operation on the control simulation of reality, since it describes the real console, it will be delivered to the event processing objects and provides the required data for the module. Then the event processing module realistic simulation of the original entities and processes the event and the related message, and their behaviors. The geometric modeling and its decides the sequence of the actions that would be related representation schemes are already well carried out. The virtual objects will be called after studied [11±13]: wire frame, surface, constructive the events are processed. Exceptional operations solid geometry (CSG), manifold and non-manifold are treated as error operations. The rest of opera- boundary representation (B_Rep). Each of these tions, such as tool offset setting, work offset representations has pros and cons that characterize setting, the editing of NC program, etc., are and enable them to be used in a specific applica- processed and the related information are stored tion context such as product modeling, virtual in the information module. environments, etc. Virtual objects Selection of virtual reality system (VRS) The VTW is basically made up of two major Virtual reality (VR) can be described as the virtual objects which are the virtual ultra-precision science of integrating human with information machine for performing single-point diamond [14]. It consists of three-dimensional, interactive turning process as well as the virtual inspection and computer generated environment. A VR machine for surface metrology. The virtual ultra- model differs from that produced by a CAD precision machine is designed based on the speci- system in two basic ways. Firstly, the objects, fications of a Nanoform 300 two-axis CNC ultra- some of which represent the users, can interact. precision machine from Taylor Hobson Pneumo Secondly, behaviors can be associated with objects. Co. In the virtual ultra-precision machine, the The model itself may represent a system in the real thermal model, kinematic