Development of a Virtual Controller Integrating Virtual and Physical CNC

Y. C. Kao1,a, H. Y. Cheng2,b, Y. C. Chen1,c 1Department of Mechanical Engineering,

2Department of Mold and Die Engineering

National Kaohsiung University of Applied Sciences

415 Chien Kung Road, Kaohsiung 807, Taiwan, R.O.C

ayckao@cc.kuas.edu.tw,

bhycheng@cc.kuas.edu.tw,

ca092313106@cc.kuas.edu.tw

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

Materials Science Forum Vols. 505-507 (2006) pp 631-636Online available since 2006/Jan/15 at www.scientific.net© (2006) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/MSF.505-507.631

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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.

�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

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).

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,

Machine

Table: X, Y

movement

Z-axis

movement

Materials Science Forum Vols. 505-507 633

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

EON studio

(c) setting levels in

“simulation tree”

(d) setting behaviors in

“Route: simulation” window

Fig. 3 sequence of constructing VR CNC

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,

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 Arc

Line

No.

Movement

Type

Coordinates Coordinate

System

Offset

Type

Line

No.

Movement

Type

Coordinates Coordinate

System

Offset

Type

Canned Cycle Zero Return

Line

No.

Start Coordinates Coordinate

System

Offset

Type

Line

No

Start. Coordinates - -

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.

Fig.�4 Virtual controller HMI interface

634 Progress on Advanced Manufacture for Micro/Nano Technology 2005

(a) Linear motion through X-, Y-, and Z-components (b) Circular motion through radians

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

mode, either G92 or G54~G59 can be used to set the workpiece

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

Figure 7 VR Davinci milling

machine

Materials Science Forum Vols. 505-507 635

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.

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