Web-Based Virtual Operating of CNC Machine Tools

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Web-based virtual operating of CNC milling machine tools

He Hanwu *, Wu Yueming

Faculty of Electromechanical Engineering, Guangdong University of Technology, Guangzhou 510090, China

1. Introduction

The international market place is becoming more dynamic and

fast changing, whilst the trends in manufacturing have been

shifting from mass-scale production to single (customized) or

small-scale production runs. These challenges call for the

manufacturing companies that want to succeed in the interna-

tional market, to respond to market agilely and shorten the lead-

time [1]. Virtual reality (VR) technology has many advantages such

as excellent interaction, high verisimilitude for 3D display and

offers opportunities for manufacturing firms to meet the above

challenges [2,3]. VR technology had been widely used in

manufacture simulation, especially, the web-based virtual

machining simulation system that has become the popular due

to its cooperation facility, good platform independence [46].

The Virtual Reality Modeling Language (VRML) is a file format

for describing interactive 3D objects, having the character of being

simple to use, open, interactive and web-based which make it a

powerful tool for setting up the web-based CNC machine

simulation systems [6,7]. The virtual operating of NC machineincludes various manual operations similar to practical manipula-

tion. To realize all these virtual manipulations, it is crucial to solve

information generated by mouse, keyboard and files between the

operator and the visualized virtual machine. Although VRML has

strong ability for graphics display and good web running, it lacks

the functions forfile reading and writing, as well as its inferior two-

dimensional word display effect. This means that make VRML

cannot meet the special demand of virtual operation of a CNC

machine. For these reasons, we propose combination of VRML,

JavaApplet and JavaScript to solve this problem.

This paper describes a VRML and web-based NC machine tool

operation and attempts to propose a virtual operating system that

can be applied to operation training of the manufacturing facility

and manufacturing process simulation. The rest of paper is

organized as follows. In Section 2, related research to virtual

machining simulation is discussed. Then, virtual operating defini-

tion is given in Section 3. This is followed by the realization of

interaction between operator and virtual machine in Section 4.

Development of CNC machine tools virtual operating system and its

implementations is described in Section 5. Finally, we drew some

conclusions in Section 6.

2. Recently related research

2.1. Virtual reality

The term VR was coined by Jaron Lanier in the early 1980s.

Initially, VR referred to an immersive system that allowed the user

to use natural head and hand movements to interact with the

computer-generated environment [8]. With the development of

VR technology, the meaning of VR has been broadened. Nowadays,

the semi-immersive systems like large screen projections, and

even the non-immersive system like monitor-based viewing of

three-dimensional objects are also called VR systems [9].

2.2. Web-based virtual reality

In the era of the Internet, great changes have taken place in the

research of virtual reality. The web, which is one of the most

Computers in Industry 60 (2009) 686697

A R T I C L E I N F O

Article history:

Received 15 July 2007

Received in revised form 21 March 2009

Accepted 18 May 2009

Available online 9 July 2009

Keywords:

CNC machine tools

Virtual operating

VRML

Training

Machining simulation

A B S T R A C T

This paper attempts to propose a virtual operating system applied to operation training of

manufacturing facility and manufacturing process simulation. The system is based on VRML and

browser/server structure, so user only needs to install a free plug-in, and run the package normally via

Microsoft Internet Explorer. Initially this paper studies the system framework, structure models andconceptmodels. Then, a communicationapproach based on VRML, Java andHTML, which is keyto realize

the virtual operating of CNC machines, has been presented. The algorithm of material removed

simulation based on VRML Z-map is also presented in this paper. It has the advantages such as a lower

memory requirement, and a faster computation speed. Finally, in order to validate the feasibility of the

proposed approach, the CNC millingmachine has beentaken as an illustrative example for the prototype

development.

2009 Elsevier B.V. All rights reserved.

* Corresponding author.

E-mail address: [email protected] (H. Hanwu).

Contents lists available at ScienceDirect

Computers in Industry

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p i n d

0166-3615/$ see front matter 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.compind.2009.05.009
mailto:[email protected]://www.sciencedirect.com/science/journal/01663615http://dx.doi.org/10.1016/j.compind.2009.05.009http://dx.doi.org/10.1016/j.compind.2009.05.009http://www.sciencedirect.com/science/journal/01663615mailto:[email protected]


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popularly used Internettools, aims to provide a light-weight, easily

deployed and system-independent platform for users to search,

browse, retrieve, disseminate and share the information remotely

[10,11]. Based on the web, cooperative design, remote teaching,

remote training and remote meeting can be easily achieved. For

these reasons, more and more web-based virtual reality applica-

tions have been developed and they play a more and more

important role in every walk of life.

In the design and manufacturing area, there has been a lot of

research and development and a numbers of software tools have

been developed in this area. Li [12] developed an Internet-based

integrated system which enabled designers to design products

collaboratively, supported product preview and evaluation of

design parts using web-based virtual reality technology. Kan et al.

[13] developed an Internet-based virtual reality collaborative

environment (VRCE) using VNet, Java, andVRML. As it is a platform

independent, VRCE can be run using inexpensive computer

hardware and software and is composed of a set of comprehensive

functionality with customizability which makes VRCE more

attractive than many existing VCS systems. Choi and Chan [14]

presented a virtual prototype system (VP) for rapid product

development. This VP system incorporates the dexel-based and the

layer-based fabrication approaches to simulate the powder-based

and laminated sheet-based RP process, respectively. The virtualprototypes of this system can be transmitted, via the Internet to

customers to facilitate global manufacturing.

In the teaching and training area, enormous interest has been

provoked by VR. Brodlie et al. [15] studied a cost-effective web-

basedvirtual reality system for surgery trainingusing VRML. Wang

et al. [16] proposed a methodology that enabled people with

acquired brain injury (ABI) to receive rehabilitation training at

home and in their own time to relearn activities of daily living

(ADL) at a low cost with the help of the Internet and desktop VR

applications. Waller and Foster [17] developed a web-basedvirtual

trainingapplication in chemistry. Students can learn to operate the

virtual instrument using this application.

There also has been considerable interest in the medical area

employing Internet technology and VR technology. Liang andOGrady [18] proposed a methodology using VR technology to

realize the medical collaboration via the Internet. A virtual surgical

telesimulation application for micrographic dermatologic surgery

(MOHS) has been presented by Velez et al. [19]. This application

can provide educational telesimulation in the dermatologic

surgery technique known as Mohs micrographic surgery.

In the Internet commerce, increasingly more e-commercial

applications are using virtual reality technology [20]. Lee and

Chung [21] developed an intelligent Internet shopping mall by

integrating virtual reality and avatar. This application can offer the

customer a far more interesting way to shop effectively.

2.3. Virtual machining simulation

Virtual machining simulation is receiving a lot of attention in

the field of virtual manufacture [1,22]. Suh and Lee [23] studied an

algorithm which was used to evaluate the NC controller error and

developed a software program for extracting the error patterns of

NC controller. Suh et al. [4] presented methods to represent the

motion paths andoperation of CNC machine tools on the Web. Ong

etal. [5] developed an Internet-based virtual CNC Milling system to

evaluate and optimize the machining process on the Internet. The

MTS company in German developed a virtual CNC machining

simulation system which can provide realistic 2D and 3D

machining simulation result [24]. Yeung et al. [25] presented a

comprehensive virtual simulation model of realistic and modular

CNC system which can be used to predict realistic CNC system

performance. These research papers focused on CNC program

verification, machining process simulation and machining error

evaluation, but ignored the virtual operating of CNC machine tools.

Since virtual operation of CNC machine tools can mimic the

realistic operation of CNC machine, it is very helpful for the

operational training of the companys staff. Ong and Mannan [26]

presented a web-based teaching package that provided a dynamic

and interactive environment for a module on automatic machine

tools, but it still cannot provide a realistic virtual environment for

the student to practice how to operate a CNC machine tool.

3. Virtual operation definition

3.1. Virtual machine model

A key factor for developing a virtual operating of CNC machine

tools system is how to represent the CNC machine tools precisely

and effectively in the virtual environment. In this paper, we only

focused on the key motion components of CNC machine tools and

ignore the physical status, such as the driving system of CNC

machine. The main components of CNC machine are as shown in

Fig. 1.

Based on the design method described in Ref. [4], those

components are defined as the follows (Node, SFVec3f, SFRotation,

MFFloat are the types of data defined in VRML):(1) Bed Definition

Object Bed

Importing data types Node, SFVec3f

Attributes

(A1) Shape: Node

(A2) Position: SFVec3f

(A3) Color: SFVec3f

End

Fig. 1. Main components of the CNC machine.

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(2) Workbench Definition

Object Workbench

Importing data types Node, SFVec3f, boolean

Methods

add-children(Node), set-position(SFVec3f)

Attributes

(A1) Shape: Node


(A3) Color: SFVec3f

(A4) Children: Node

(A5) children-added? : boolean

Valuation B: Node, P: Position

(V1) [add-children(B)]children-added? = true;

(V2) [add-children(B)]Children = B;

(V3) [set-position(P)]Position = P

Safety B: Node

(S1) Per(add-children(B))! children-added? = true

End

(3) Saddle Definition

Object Saddle


Methods

set-position (SFVec3f)

Attributes

(A1) Shape: Node


(A3) Color: SFVec3f

Valuation P: SFVec3f

(V1) [set-position(P)] Position = P

End

(4) Lifting Table Definition

Object Lifting Table


Methods

set-position(SFVec3f)

Attributes

(A1) Shape: Node


(A3) Color: SFVec3f

Valuation P: SFVec3f


End

(5) Spindle Definition

Object Spindle

Importing data types

Node, SFVec3f, Boolean, SFRotation

Methods

(M1) Add-children(Node)

(M2) Set-rotation(SFRotation)

(M3) Set-position(SFVec3f)

(M4) Remove-children(Node)

Attributes

(A1) Shape: Node

(A2) Color: SFVec3f


(A4) Rotation: SFRotation

(A5) Children: Node

(A6) children-added? : Boolean

Valuation B: Node, R: SFRotation, P: SFVec3f

(V1) [add-children(B)] children-added? = true;

(V2) [add-children(B)] Children = B;

(V3) [set-rotation(R)] Rotation = R;


(V5) [remove-children(B)]Children = NULL

(V6) [remove-children(B)]children-added? = false

Safety B: Node

(S1) Per(add-children(B))! children-added? = false

(S2) Per(remove-children(B)) ! children-added? = true

End

(6) Fixture Definition

Object Fixture


Node, SFVec3f

Methods

(M1) add-children(Node)

Attributes

(A1) Shape: Node


(A3) Color: SFVec3f

Valuation B: Node

(V1) [add-children(B)] children-added? = true

Safety B: Node

(S1) Per(add-children(B))! children-added? = false

End

The Objective model of CNC machine tools can be represented

as Fig. 2.

3.2. Operation command description

Although for the different CNC systems, its control panel,

operation methods are different, the final goal of a certain

operation among different CNC system is the same. Therefore,

classification and definition of each operating of the CNC machine

is advantageous to realize the rapid configurability of virtual

operating system and meet the requests for compatibility with

different CNC system.

In general, these operating of CNC machine tools can be

classified as follows:

(1) Manual Movement Control

The manual mode of a CNC control causes the machine tool

to react identically to a standard machine tool. It includes

continuous moving control, pointing control and hand-wheel

moving control.

(2) Spindle Control

It includes spindle rotation control and stop control.

H. Hanwu, W. Yueming/ Computers in Industry 60 (2009) 686697688


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(3) CNC Programming

CNC Programming includes CNC code entering, modifica-

tion, exporting and management.

(4) CNC Program Performance

It includes program selection, program performance,

program pause, program reset, and parameter settings.

(5) Reference Point Return and Machine Zero Point Return

3.3. Virtual control panel model

CNC control panel is an independent unit with control and

display elements. According to the operationcommand mentioned

above, a standard CNC control panel should combine with seven

elements as Fig. 3 shown.

In these seven elements, theLCD Screens is thedisplay elementof

the CNC control panel, whilst the others are control elements. Thus,

the virtual control panel model mimicks the counterpart in the real

world. Since a command translator is used to extract the valid

information from the operation command that the user inputs via

virtual control panel andsendsthe informationto thecentral control

moduleof thewholesystem to createthe virtual operation,it should

be populated in the virtual control panel mode either.

The architecture of the virtual control panel model is shown in

Fig. 4, it includes the following three main components:

(1) Virtual LCD Screen

The LCD screen in the virtual control panel model is created

by using HTML and JavaScript code. Each display format is

defined in a layer because of different display format of each

screen. In default status, the visibility attributions of layers are

all set to hiding. When a particular screen needs to be

displayed, the visibility attribution of that layer is set to show

andthe contents of that layer arerefreshed. The principle of the

virtual LCD screen is shown in Fig. 5.

(2) Control Elements

The control elements in the virtual control panel model are

achieved by using VRML. A TouchSensor node is situated in

each control element, and it will send the information to the

operation command translator when the user clicks the control

element. Fig. 6 indicates the principle of control elements.

Fig. 2. Objective model of the numerical control machine.

Fig. 3. Virtual CNC control panel.

Fig. 4. Architecture of control panel model.

Fig. 5. Virtual LCD.



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(3) Operation Command Translator

In the CNC control panel, a particular operation is accom-

plished by one or more buttons with a certain logical relations

and mutually restrains instead of only one isolative button. The

operation command translator model cannot guarantee versa-

tility if these relations are defined in its methods or its attributes

when themodelis being defined. Therefore,in order tocreatethe

versatility of the operation command translator model, a rule

library (called jRuleLib_IDj) is defined to store these restraint

relations. Different CNC systems have a different rule library.

The concept model of the command translator in the virtual

control panel is described as follows:

Object CommandTranslator


boolean, jRuleLib_IDj, int, cmddata

Constant

//the button clicked by user

(C1) jButtonKeyj: bk

Methods

(M1) Get-buttonkey;

//Search the rule in jRuleLib_IDj

(M2) Check-lib(buttonkey, jRuleLib_IDj);(M3) SendCommand;

Attributes

(A1) Buttonkey: int;

(A2) Rule-checked?: Boolean

(A3) Command: cmddata

Valuation

(V1) [get-buttonkey] buttonkey = bk

(V2) [check-lib(buttonkey,jRuleLib_IDj)]

rule-checked? =true or =false

Safety

(S1) Per(SendCommand)! rule-checked? = true

End

4. Interaction between operator and virtual machine

Virtual operations witha CNC machine includes various manual

operations similar to practical manipulation, such as selecting

work piece or tools, tool sitting, rectifying tools, input NC code and

setting the parameters of NC machine from virtual control panel.

So the virtual operating system should also has the ability to

display the text and other non-graphic status (such as feed speed,

rotation speed of the main shaft), and the ability of file reading and

writing by which the operator can import/export the work piece

model or NC code into/from the system. VRML is weak in the 2D

text display area, although it is strongin the3D graphic display. On

the other hand, JavaApplet is strong in the calculation and 2D text

display, but it does not have the capability of reading or writing

local files due to the security problem. To achieve the reading or

writing ability, it must draw support from the JavaScript that isembedded in the Hyper Text Mark-up Language (HTML) file.

The prototype system in this paper is an integrated system

which embeds JavaScript, Java applets and VRML plug-ins by using

HTML. In this system, VRML is used to create the virtual NC

machining environment, JavaScript and Java applets are used to

provide simulations and handle all the information inputted from

the operator. To create the prototype system, the following issues

have to be solved:

(1) Information transfer among JavaScript, JavaApplet and VRML;

(2) Information transfer among multi-VRML windows;

(3) Information transfer among JavaApplet in different pages.

4.1. Information transfer between JavaScript, JavaApplet and VRML

JavaScript and JavaApplet can communicate by using their

internal interface and JavaApplet can communicate with VRML by

using the External Authoring Interface (EAI). JavaScript cannot

make a communication with VRML directly. It has to communicate

with VRML through JavaApplet which plays the role of commu-

nication bridge. The principle is as shown in Fig. 7.

(1) Communication between JavaScript and JavaApplet

(a) Method of JavaScript accessing the function of JavaApplet

JavaScript can access the public function which is defined

in JavaApplet by the following code:

window. document. .

Here the name of the applet is the name given to it in

the applet tag in HTML code as the follows:

(b) Method of JavaApplet accessing the function of JavaScript

JavaApplet can access the function of JavaScript via the

imported class named netscape.javascript.JSObject.

The methods of JSObject class shown in Table 1.

The following steps indicate how to let JavaApplet

access the function of JavaScript:

Step 1: Add a new attribute called MAYSCRIPT into

applet tag in HTML code;

Fig. 6. Users operating information reception in manual operation area.

Fig. 7. Communication of HTML (JavaScript)JavaAppletVRML.



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Step 2: Create the instance object of JSObject class;

Step 3: Use JSObject method named call to evoke the

function of JavaScript.

(2) Communication between JavaApplet and VRML

The communication between JavaApplet and VRML is created

by external authoring interface of VRML plug-in. JavaApplet

can access the following three control types via EAI:

(a) Access any node in VRML environment;

(b) Send data to any node in VRML environment by EventIn

interface;

(c) Get data from any node in VRML environment by

EventOut interface.

To realize the Communication between JavaApplet and VRML

should be done as the following steps:

Step1: Get the environment information by creating the

instance of Browser Class.

Code: Browser [Instance name of Browser]

For example:

Browser browser = Browser.getBrowser(this);

Step2: Get a certain node by creating the instance of Nodeclass.

Code: Node [Instance name of Node]

For example:

Node theBall = browser.getNode(Ball);

Step3: Make the Communication between JavaApplet and

the EventIn or EventOut interface of Node.

(1) Make the Communication between JavaApplet and

EventIn interface of node:

[Variable Name] = (EventIn[Variable Type])[Instance

Name of Node].getEventIn([EventIn interface name])

For example:

Scalesize = (EventInSFVec3f)theBall.getEventIn(set_scale);

(2) Make the Communication between JavaApplet and

EventOut or exposedField interface of node:

[Variable Name] = (EventOut[Variable Type])[Instance

Name of Node].getEventIn([EventIn interface name])

For example:

Scalesize = (EventOutSFVec3f)theBall.getEventOut

(set_scale);

Step4: Send data to EventIn interface or get data from

EventOut or exposedField interface.

(a) Send data to EventIn interface by setValue method;

For example: scalesize.setValue(val);

(b) Get data from EventOut interface by getValue method.

For example: thescale[i] = Scalesize.getValue()[i];

4.2. Communication among multi-VRML windows

Virtual machine tools and control panels model are placed in

the two independence VRML windows, respectively. In order to

transfer the information between the control panel and the virtual

machine tools, the communication among the two or more VRML

windows should be setup.

As there is no interface to allow a VRMLwindow to communicate

with other VRML windows, we have to make a communication link

between multi-VRML windows by using JavaApplet as a commu-

nication bridge.

Fig. 8 shows the principle of communication between two

VRML windows. These two VRML windows, one is virtual machine

tool, the other is virtual control panel. A JavaApplet monitors the

EventOut interface of all buttons in the virtual control panel. Once

it gets the EventOut information from the virtual buttons, it will

activate the callback() function to handle the EventOut informa-

tion and send the information to the virtual machine tool in

another VRML window.

4.3. Information transfer among JavaApplet in different pages

In prototype system,different humancomputerinterfaces (such

as virtual the control panel, Tool installation interface, import/

outputworkpiecemodelinterface, etc.) areplaced in differentHTMLpages. As Fig.9 shows,the virtual operation in this prototype system

is achieved by coordinating the work between different function

pages.

As the functional screens are mutually independent, the

communication between them is achieved by JavaApplets in the

different functional screens. Therefore, a reliable information

transmission method between JavaApplets must be found.

Traditionally, the mutual communication between JavaApplets

is achieved by using the AppletContext getApplet method or the

AppletContext getApplets method. Both methods must run with

the following security restrictions [27]:

(1) The applets originate from the same directory on the server

(the same code base);(2) The applets are running on the same page, in the same browser

window.

Clearly, Fig. 9 indicates that the screens of the prototype system

are in different pages. Thus, the methods mentioned will not work

in this form. To achieve this, we must letthe applets share thesame

operational environment and the same static domain [28,29]. As

long as we canestablish a common sharedstatic JavaApplet as data

sharing pool for other applets in other pages to share the

information, communication among JavaApplets in different pages

can be achieved. In this prototype system, the static data sharing

pool is created by a JavaApplet (called main JavaApplet)at first, and

then, this main JavaApplet evokes all other JavaApplets in different

pages (called sub JavaApplet). After the above steps, all sub

JavaApplets can communicate with each others by the static datasharing pool. The principle of communication among JavaApplets

in different pages is shown in Fig. 10.

5. Implementation

The specification for the CNC machine tools virtual operating

prototype systems hardware and software environment is

described in the following sections.

5.1. Environment

5.1.1. Hardware environment

The hardware runs the supporting system and creates the

computerhuman interaction and determines the performance

Table 1

JSObject Methods.

Method Description

call(String functionName,

JSObject args[])

Call function of Javascript

eval( St ring expr ess ion) Call a J avaScript cod e

get Slot ( int ind ex ) G et a ind ex object fr om a cert ain cont ainer

getWindow(Applet applet) Get a JavaApplet window



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of the virtual CNC machine (i.e. the precision degree of the3D model, the calculation capacity of the computer and the

realities of the computerhuman interactive interface). The

hardware programming environment for the prototype system

is as follows:

Personal computer: CPU, P4 2.0G; Memory, 512 M.

Graphic card: GeForce FX5200 128 M DDR Memory.

Output device: 1700 CRT.Input device: keyboard and mouse.

5.1.2. Software environment

The prototype system is required to be network-oriented,

operating system independent with a high 3D render quality.

According to these requirements and the development

languages used, the software environment we chose is as

follows:

(1) Support platform: Windows, IE5.0 or above, and Cortona VRML

Client 4.0;

(2) VRML edit tools: VRMLPad;

(3) Java Development Platform: Visual J++ 6;

(4) Web page design Tools: Dreamweaver MX.

5.1.3. Performance test

As our prototype application only needs to communicate with

the server host to download key files, it requires only a low-

bandwidth network connection to the server. The VRML model

files have been optimized and zipped, the download time is 1 or

2 min even with 56Kbandwidth speed.The amount of RAM is more

important when the prototype application runs on client

computer. Table 2 shows the detail information in terms of

memory requirement, frame rate per second (FPS) and CPU usages

at client. As shown in Table 2, the key factor which affects the

performance is the size of work piece which needs more memory

and slows the frame rate.

Fig. 9. Coordinated working between function pages.

Fig. 8. Information interfaces between VRML windows.

Fig. 10. Communication among JavaApplets in different pages.



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5.2. Operation interface

Operation interface of this prototype system includes the

following screen mainly:

(1) Main operation interface (Fig. 11);

(2) Work piece set up or removal screen (Fig. 12);

(3) Cutting tool addition or removal screen (Fig. 13);

(4) Reference tools addition or removal screen (Fig. 14);

(5) CNC machining process (Fig. 15);

(6) The machining simulation result (Fig. 16);

(7) G-Code Editor Interface.

As shown in Fig. 17, user can enter the G-Code via the virtual

keyboard and can change the position of the cursor by using the

arrow buttons. User can also use the special button called Input

to import theG-Code from thetext fileand usethe Output button

to export the G-Code to text file.

5.3. Algorithm for the material removal simulation

This system adopts the Z-Map structure model algorithm

theory to achieve the cutting simulation [30]. This method has the

following advantages:

Table 2

Performance test.

Condition RAM

requirement

(MB)

Frame

rate per

second (FPS)

CPU

usage

No work piece amounted 85 42 48%

200 100 10 (length width

height) work piece mounted

113 23.81 1835%

200 100 30 work piece mounted 114 23.68 1836%



Fig. 11. Main operation interface of NC machine.

Fig. 12. Main interface of work piece set up or removal.Fig. 13. Main interface of cutting tool addition or removal.



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(1) The algorithm is very easy for program creation;

(2) The system memory will be released, raising the calculation

efficiency because the three dimension points are reduced to

one dimension (only the Z direction is used);

(3) There is ElevationGrid node in the VRML which can be used

directly, so it is not necessary to design other prototype nodes.

5.3.1. Work piece definition by the ElevationGrid node

Work piece can be described by the ElevationGrid node in the

VRML because the ElevationGrid node is very similar to the Z-map

structure model. The steps are:

Fig. 14. Main interface of reference tools addition or removal.

Fig. 15. NC Machining process.

Fig. 16. Machining simulation result.



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Step 1: Determine how many points on the X, Y direction are

needed to describethe work piece whichcan calculate by Eq. (1)

XDim L

D

YDim W

D

9>>=>>;

(1)

XDim is the required number of points on the Xdirection, YDim is

the required number of points on the Ydirection, L is the length of

the work piece, Wis the width,D is the distance between the two

vertices.

From Eq. (1), the smaller the D is, the more accurate the workpiece is and consequently more system memory is required.

Step 2: Set the height of the dispersed points of the work piece

As shown in Fig. 18, set the height of the edge points (the points

in the dotted line frame) to 0, the other is the height of work piece,

finishing the separation of the work piece.

5.3.2. The algorithm for material removed

The system judges whether the tool intersects the work piece

by the relative distance between them. The relative distance

between the tool and the work piece is defined as Fig. 19.

The meaning of the parameters in Fig. 19 is as the follows:

(1) HZ0 is the Zvalue of the chuck jaw, changing when the tool ismove through the Z direction;

(2) HZ1 is the Z axis value of the top plane of worktable in VRML

coordinates;

(3) Hj is the height of the fixture;

(4) TL is the length of the tool;

(5) Hw is the height of work piece;

(6) H= HZ0 HZ1;

(7) clearance = H ToolLength Hw Hj, the space between cut-

ting tool and work piece. The tool intersects the work piece

when the value of space is a negative number.

Set the current coordinates of cutting tool to be (x, y, z), the

relative zero point coordinates on the XY plane to be (x0, y0), thelength of work piece to be L, the width of work piece to be W,

discrete accuracyof work piece to beD, the lengthof cutting tool to

be LT, the radius of cutting tool to be R. XDim and YDim can be

calculated using formula (1).

Fig. 17. G-code Editor Interface.

Fig. 18. Work piece entity. Fig. 19. Relative position between tool and work piece.



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The detailed steps of the algorithm for material removal are as

the follows:

Step 1: Sequence operation of the center point coordinates of

cutting tool on the XY plane by Eq. (2).

TX jx x0j

D

TY jy y0j

D

9>>=

>>;(2)

Step 2: Find out the projection point on the work pieces XY

plane of the tool.

Set all the points of the work piece to be one-dimensional array,

and the subscript of each point to be number. Set all the points of

cutting tool on the XYplane to be two-dimensional array, and the

subscript of X is i, the subscript of Y is j.

First traverse through all the values of i and j. The range of i is

from TX to TX, the range of j is from TY to TY. If

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffii TX

2 j TY2

q (HZ0 LT), the height of the target point is considered

larger than the height of the tool, using Eq. (4) to refresh.

WHeighti HZ0 LT (4)

The workflow of the algorithm for material removed as shown

in Fig. 20.

6. Conclusion

This paper studied the web-basedCNC machine tool operations.

The versatile CNC machine tool model and CNC control panel

model had been discussed in this paper. Then, a communicationapproach based on VRML, JavaApplet and HTML, which is the key

to create the prototype system, had been described. Comparing

with the traditional EAI communication between VRML and

JavaApplet, this approach has two advantages:

(1) The designof thesystems control panel becomes more flexible.

(2) The reading/writing ability can be achieved by the JavaScript

imbedded in the HTML, overcoming the weakness that

JavaApplet needs to be complied with digital signature and

configure the complex system environment to allow it read/

write the local files.

Finally, in order to validate the feasibility of the proposed

approach, the CNC milling machine was taken as an illustrativeexample for the prototype development. In comparison with the

traditional stand alone CNC machine simulation system, our

prototype application is platform independent and no special

program needs to be installed on the client computer.

Acknowledgements

This work is supported by National Natural Science Foundation

of China (No. 50775047); Scientific and Technological Project in

Guangdong province, China (No. 2007A010100013). We would like

to express our gratitude to Robert Kelly who helped in correcting

the paper.

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He Hanwu is a Professor of the Faculty of Electro-

mechanical Engineering at Guangdong University of

Technology (GDUT) at Guangzhou,China.He is currently

head of the virtual reality research group at GDUT. He

receivedhis Ph.D. degree in ElectromechanicalEngineer-

ingin 2001, Master degree in Manufacturing Automation

Engineering in 1992 and Bachelor degree in Mechanical

Engineering in 1988, all from Huazhong University of

Science and Technology at Wuhan, China. His main

research interests are in the domain of virtual reality,

networked manufacturing, virtual reality applications in

driving simulation, product design, manufacturing sys-

tem and medical treatment. His research projects have

been sponsored by a number of organizations including the Natural Science

Foundation of China, HI-Tech Research and Development Program of China, the

Natural Science Foundation of Guangdong Province and Department of Science andTechnology of Guangdong Province. He received the third prize for the National

Science and Technology Progress from China in 1995.

Wu Yueming born in 1979, is currently a doctoral

candidate in Faculty of Electromechanical Engineering,

Guangdong University of Technology, China. He received

his master degree in Electromechanical Engineering in

2005 from Guangdong University of Technology. His

researchfocuses on virtualrealityand augmented reality

applications in manufacturing system.

http://www-vrl.umich.edu/beier/Papers/compit2000/WebBasedVR.htmhttp://www-vrl.umich.edu/beier/Papers/compit2000/WebBasedVR.htmhttp://www.mts-cnc.com/http://www.java.sun.com/docs/books/tutorial/deployment/applet/iac.htmlhttp://www.java.sun.com/docs/books/tutorial/deployment/applet/iac.htmlhttp://www.javaworld.com/javaworld/javatips/jw-javatip101.htmlhttp://www.javaworld.com/javaworld/javatips/jw-javatip101.htmlhttp://www.javaworld.com/javaworld/javatips/jw-javatip101.htmlhttp://www.javaworld.com/javaworld/javatips/jw-javatip101.htmlhttp://www.javaworld.com/javaworld/javatips/jw-javatip101.htmlhttp://www.java.sun.com/docs/books/tutorial/deployment/applet/iac.htmlhttp://www.java.sun.com/docs/books/tutorial/deployment/applet/iac.htmlhttp://www.mts-cnc.com/http://www-vrl.umich.edu/beier/Papers/compit2000/WebBasedVR.htmhttp://www-vrl.umich.edu/beier/Papers/compit2000/WebBasedVR.htm

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