A Web-Based VirtualLaboratory for TeachingAutomatic Control

ERNESTO GRANADO, WILLIAM COLMENARES, MIGUEL STREFEZZA, ALFONSO ALONSO

Universidad Simon Bolıvar, Dpto. Procesos y Sistemas, Caracas 1080, Venezuela

Received 27 August 2005; accepted 2 August 2006

ABSTRACT: This paper describes a web-based virtual laboratory that improves the

automatic control teaching of undergraduate courses. This is achieved by optimizing the time

the students spend in the real laboratory. The virtual world or three-dimensional scenes of real

laboratory plants gives the students the opportunity to ‘‘learning by doing’’ through web-based

systems at the location they want, and at the time they like. This virtual laboratory gives the

students the tools to be more prepared and therefore, use the time more efficiently and

effectively when working in the real laboratory plant. The student does not require the

installation of special software on his remote computer; only need a common VRML

enabled browser. An example of a developed virtual laboratory of interconnected tanks is

presented. � 2007 Wiley Periodicals, Inc. Comput Appl Eng Educ 15: 192�197, 2007; Published online in

Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20111

Keywords: control systems; education; improving classroom teaching; undergraduate

education; virtual reality; web-based laboratories

INTRODUCTION

Laboratory experiences, which imitate the complexity

of real life practices, are essential elements in engine-

ering education. In practical sessions, students learn,

not only by listening, like in theoretical courses, but

also through ‘‘learning-by-doing.’’ When students

interact with the laboratory plants they have the

opportunity to verify what happens when they modify

and manipulate the experiment. Several studies have

shown that laboratory practices have achieved positive

influence on learning skills, on well-prepared pro-

fessionals, especially in scientific and technological

fields. Rickel [1] illustrated that students retain 25%

of what they hear, 45% of what they hear and see and

70% if they use the ‘‘learning-by-doing’’ methodology.

The construction of fully furnished scientific

laboratories is very expensive because specialized and

sophisticated equipment is needed. Sometimes, this

cost is prohibited for many institutions. The few exis-

ting laboratory equipment has to be shared among

researchers and students enrolled in different programs

with adjusted schedule and different knowledge levels.

Instructional staff spends much time of every lab session

describing the equipment lab, demonstrating the correct

operation of laboratory equipment before doing theCorrespondence to E. Granado (granado@usb.ve).

� 2007 Wiley Periodicals Inc.

192

actual experiment, and review the experiment proce-

dures. As a result, the students do not have enough time

to finish their experiments efficiently and effectively.

It is important to optimize the time that the students

spend in the laboratory, so that they should begin the

experiments immediately after they start the lab session.

One solution addressing these needs is by deve-

loping web-based virtual laboratories. This gives the

students the opportunity to prepare for lab, including

the ‘‘handling’’ of the expensive equipment. Through

web-based systems, students are provided the oppor-

tunity to study at any location they want, on their own

schedule, instead of in a specialized laboratory on the

staff’s schedule.

The advances in computer graphics and multi-

media technology allow construction of virtual phy-

sical environments that are representative, detailed

and realistic. Virtual reality modeling language

(VRML), provides the technology that enables the

creation of a virtual world, including the ability to

animate objects. This enables users to navigate around

the virtual environment, move in three dimensions,

interact with objects, look behind or under them and

examine the world from different viewpoints, as if

they were in the physical world. They can familiarize

with the experimental setup, explore alternative choices

by varying plants parameters and obtain a visual

feedback result of their experimentation.

VRML files are text based and usually given

world (wrl) extension. These files can be viewed

through a VRML enabled browser [2]. Virtual reality

(VR) provides interaction and active participation

rather than passivity; it provides motivation for the

student to prepare the lab. VR con also be used jointly

with Remote Laboratory applications [3,4]. Although,

it is important to remark that, it should not be used as a

substitute for laboratory session in the physical labo-

ratory with real plants.

VR is a powerful technology that is currently

used in many areas such as: medical/health care [5],

training [6], architecture and construction [7], museum

education [8], virtual meeting [9], computer graphics,

CAD, CAM, CIM, robotics, military, multimedia,

games and so on [10]. Recently, there have been

attempts to integrate VR in education and research

[11,12]. This work features a virtual laboratory deve-

loped for Teaching Automatic Control, using Matlab,

Simulink and the VR toolbox.

ARCHITECTURE OF THE SYSTEM

The commercial MATLAB/Simulink environment

[13], which is the most popular simulation software

for research and teaching automatic control, is used

to design the system. There are several toolboxes

available in MATLAB for control application, such as

system identification, robust control, fuzzy logic,

and more. Additionally, Simulink provides a graphic

interface that simplifies the build of complex dynamic

systems as intuitive block diagrams by simple

drag and drop operations. It supports linear and

nonlinear systems, modeled in continuous and/or

sampled time.

The VR toolbox connects MATLAB and Simu-

link with a VRML-enabled browser to display a

simulated system trough Internet. This toolbox pro-

vides blocks to directly connect Simulink signals

with virtual worlds. The VR toolbox automatically

scans a virtual world for available VRML nodes

that Simulink can drive. This connection makes it

possible to visualize the model as a three-dimensional

animation. Thus, the user observes a dynamic

system simulation over time in a visually realistic

3D model and allows interacts with it. The changes

made to a virtual world are reflected in MATLAB and

Simulink. The blaxxun Contact plug-in [14] is a

VRML plug-in supported and distributed by the VR

toolbox.

This tool enables educators to focus their atten-

tion on the design of interesting virtual laboratory

sessions, rather than on time-consuming low level

programming (the code required for the simulation,

the virtual world interface and so on).

The development of virtual laboratory requires a

small numbers of steps:

* Create a virtual world of the laboratory plants

using a VRML editor.* Derive a mathematical model of the real plant.* Create a Simulink diagram for the dynamic of

the laboratory plant and add the VR blocks.* Select a virtual world and connect Simulink

signals to the virtual world.* Run a Simulink models on the host computer to

start the VR toolbox Server.

Components of the System

The system consists of two parts:

(1) The client computer runs a web browser only,

which opens a web page loaded from the

server. Hence, the remote user does not need

the MATLAB/Simulink or any other speci-

alized software installed on their machine. The

client computer communicates with the host

computer over TCP/IP, and it displays the

MATLAB-BASED VIRTUAL LABORATORY 193

virtual world using a VR client (VRML-

enabled Web browser). At any Internet enabled

computer students views the virtual represen-

tation of the experiment in the VRML browser

and gives the opportunity to explore experi-

ment and learn. With this interface, the students

can conduct their experiment before laboratory

session.

(2) The server computer is a desktop computer

where MATLAB, Simulink, and VR Toolbox

are installed. The VR Toolbox contains the

core files that interconnect MATLAB and

Simulink to VRML. It uses an internal HTTP

Server for communication between a Web

browser and the MATLAB/Simulink environ-

ment. The VR Toolbox server starts when a

Simulink block diagram with a VR block is

loaded into MATLAB. It is used as a web-front

for MATLAB and it makes possible the inter-

face with Simulink models.

Figure 1 shows the architecture of the virtual

laboratory system. The students can run a VR experi-

ment on a common VRML-enabled Web browser

using TCP/IP. The server runs, host and allows the

interface with the real plant Simulink models.

IMPLEMENTING THE SYSTEM

This section shows an example of a developed virtual

plant. The coupled water tanks are standard nonlinear

process in many control laboratories. Although the

setup is simple, it can illustrate several interesting

control phenomena and schemas able to make the

process ideal to use in control education. Conse-

quently, the students can study the effect of the

linearization, the control at different operating points

and a variety of controller algorithms.

Description of the Plant

The process consists of a coupled water tanks and one

pump. A schematic diagram of the system is shown

in Figure 2. It consists of two uniform cross-sections

tanks mounted on the front plate above a reservoir

which stores water. The flow from the first (upper)

tank flows into the second (lower) tank. Outflow from

the second tank returning to the water reservoir. Each

of the two tank has an outflow orifice at the bottom

through the liquid is withdrawn. The outlet pressure is

atmospheric. In order to introduce a disturbance flow,

Figure 1 Virtual laboratory system architectural overview.

Figure 2 The coupled tank process schematic diagram.

194 GRANADO ET AL.

the first tank has a drain tap so that, when opened, flow

can be released into the reservoir tank. The water level

in the tanks is measured using a pressure-sensitive

sensor located at the bottom of the tank. The system

input is the pump voltages and the water levels in the

two tanks are the outputs. It can be configured into

three main types of experiments [15]. Each of which

can be configured with diverse parameters values

(e.g., outlet diameters).

Physical Model

To derive a mathematical model for the coupled tanks

process the mass balance principle and Bernoulli’s

law for tanks is used. The following nonlinear first-

order differential equations are obtained:

A1

dh1

dt¼ KPVP|ffl{zffl}

Qin

� aout;1ffiffiffiffiffiffiffiffiffiffi2gh1

p|fflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflffl}

Qout;1

ð1Þ

A2

dh2

dt¼ gKPVP|fflfflffl{zfflfflffl}

Qin

þ aout;1ffiffiffiffiffiffiffiffiffiffi2gh1

p|fflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflffl}

Qout;1

� aout;2ffiffiffiffiffiffiffiffiffiffi2gh2

p|fflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflffl}

Qout;2

ð2Þ

where h1, h2 are the height of fluid in the tanks

(outputs), A1, A2 are the cross-sectional areas of the

tanks,Qin is the pump flow rate into thanks, andQout,1,

Qout,2 are flow rate of fluid out of the tanks, aout,1,

aout,2 are cross-section of the outlet holes, VP is the

pump voltage, KP is the pump flow constant, g is the

gravitational constant, and g2 (0, 1) is determinate by

the configured type of experiments.

Simulink Block Diagram

The mathematics equations (1) and (2) described the

nonlinear behavior of the physical systems which can

be easily implemented by standard Simulink blocks.

This model defines de behaviors of the three-dimen-

sional objects in virtual world.

Several types of controllers such as: generalized

state-space control, model predictive control, optimal

control, fuzzy based control and others can be imple-

mented as Simulink blocks. In this example, it is

wanted to control the level in the lower tank with a

PID controller by manipulating input voltages to the

pumps. The students can tune and compare different

controllers.

After the creation of a virtual world and a

Simulink plants model, it is necessary to add a VR

toolbox block to the model to define the associations

between the model signals and the virtual world.

Figure 3 shows the Simulink block diagram of the

overall system, which includes the coupled tank, the

PID controller and the VR blocks.

Figure 3 The physical plant Simulink diagram block.

MATLAB-BASED VIRTUAL LABORATORY 195

Web Interface

The user interface (VRML-enabled Web browser)

displays the VRML model of the coupled tanks

and some controls that change the systems parame-

ters. It allows the student to interact with the virtual

plant, and visualize the effects of the changes they

have done. Figure 4 shows the virtual laboratory

user interface (VR coupled tanks) and the physical

plant.

CONCLUSION

The advances in computer technologies, specially, the

multimedia web-based system, provide the necessary

tools to maximize the learning experience. A virtual

laboratory for undergraduate automatic control teach-

ing courses was developed and described in this

paper. The Matlab/Simulink environment enabled the

modeling and simulation of the laboratory plants, and

VR toolbox allowed the construction of three-dimen-

sional scenes driven by signals from the Simulink.

This virtual world is representative, detailed and

realistic. It has the ability to animate objects, and

gives users higher level of interaction with the virtual

plants and view from any angle.

This scenario was intended to serve as pre-

laboratory. Permit the students to familiarize them-

selves with the experimental setup. VR provides a

new approach to learning because it increases the

student’s motivation and interest, and provides an

alternative way for the control education process.

Students can conduct their experiment 24 h a day in

an easy way, from any computer connected to Inter-

net, and without any restriction due to laboratory

opening time. In this way, the students are well

prepared for the laboratory experiences and give the

opportunity to optimize the spent time in the time-

multiplexing laboratory schedules. Also, virtual labo-

ratory offers an excellent and suitable platform for

researchers to test and implement their new algo-

rithms as well.

Although VR technology can complement a stu-

dent’s laboratory experience, it is important to stress

that it should not be used as a substitute for ‘‘hands-

on’’ traditional experience in the physical laboratory

with real plants.

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Figure 4 Virtual laboratory interface and physical plant.

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BIOGRAPHIES

Ernesto Granado received his MSc degree

in system engineering from Universidad

Simon Bolıvar, Venezuela, in 1996, and the

doctoral degree (automatique et informatique

industrielle) from Institut National des Sci-

ences Appliquees, Toulouse, France, in 2004.

He is currently an associate professor with

the Department of Processes and Systems at

Universidad Simon Bolıvar. His current

research interests include predictive control and the use of new

technologies to improve and facilitate the learning process.

William Colmenares received his degree in

electrical engineering from Universidad

Simon Bolıvar, Venezuela, in 1977 and a

PhD (automatique) from Universite Paul

Sabatier, France, in 1996. He is currently a

full professor at Universidad Simon Bolıvar.

His research interests include robust and

predictive control, high performance con-

trol, e-learning, and new information tech-

nologies applied to education.

Miguel Strefezza received his BSc degree in

electronic engineering from Universidad

Simon Bolıvar, Venezuela, in 1984 and

the MSc and PhD degrees from Muroran

Institute of Technology, Japan, in 1991 and

1994, respectively. He worked in the indus-

try before joining the Department of Proc-

esses and Systems, Universidad Simon

Bolıvar, in September 1997. His research

interests include applications of fuzzy logic and neural networks to

system control.

Alfonso Alonso received his BSc degree in

mathematics and the MSc degree in systems

engineering (operations research), both from

Universidad Simon Bolıvar, Venezuela, in

1991 and 1995, respectively. He received the

DEA and the PhD degrees in control, both

from the Universite Paul Sabatier (Toulouse

III), France, in 1996 and 2000, respectively.

He is currently an associate professor in the

Department of Processes and Systems, Universidad Simon Bolıvar.

His research interests include modeling, simulation, optimization,

and operations management.

MATLAB-BASED VIRTUAL LABORATORY 197