Global J. of Engng. Educ., Vol.I, No.2
Printed in Australia

 

Copyright 1997 UICEE


 

Multimedia: A Help in Teaching
Electrical Machines and Drives

B.Renier
P.V Roy
K.Hammeyer
R.Belmans

Katholieke Universiteit Leuven, Electrical Engineering Department
DIV.ESAT/ELEN Kardinaal Mercierlaan 94, B-3001 Leuven-Heverlee, Belgium
   

 
 
The skills that should be taught to engineering students are very complex and manifold. Learning is one of the hardest tasks to fulfil and it is thus the duty of the university institutes to awaken enthusiasm in the student by choosing the right tools for teaching and knowledge transfer. This paper provides ideas and practical experiences using multimedia in the field of electrical machines and variable speed drives. By using multimedia developments, it is possible to confront undergraduate students with the subject of electrical machines and drives in a more attractive and efficient way. A multimedia computer is defined, and different authoring systems are compared. Practical examples for the visualisation of physical phenomena and the construction of ac and dc machines are presented. Also demonstrated is how the multimedia approach can contribute to laboratory experimental work.
 

 
 

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TABLE OF CONTENTS


Introduction

Society has changed to a world of images rather than the written or spoken word in recent years. The television and computer are extremely popular today. Powerful PCs can now be found in nearly every student household due to the constantly decreasing prices of standard computer hard- and software. To ensure equal opportunities, the Katholieke Universiteit Leuven, Belgium, is leasing hard- and software to students at a subsidised rate. For this purpose, the university is planning to buy 3000 new PCs in the Autumn of 1997. This means that the university teaching staff are able to use recent education tools, such as multimedia applications, to support the individual learning capabilities of the students.

The advantages of using multimedia at the university are numerous, not only as an aid to follow basic courses and to study physical principles, but also for self-study programs for advanced topics such as numerical field computation methods. Software packages and other equipment can use multimedia for getting started information, configuration, tips and on-line help. This can save a lot of time for the user, who need no longer struggle through the manuals. With multimedia it is possible to set up a self-test program that can be used by students to prepare themselves for examinations. The use of multimedia tools makes a presentation exciting and informative for the audience. One can conclude that the term multimedia indicates a mass of applications, large investments in money and time, and the raising of expectations.

This paper gives information concerning the term multimedia. The paper provides ideas and practical experiences of the use of multimedia in the Electrical Engineering Department of the Katholieke Universiteit Leuven in the field of electrical machines and variable speed drives. It should be stressed that the group targeted is quite large: all electrical, electronic and mechanical engineering students taking the basic course on electrical machines and variable speed drives in the third year of their curriculum, ie approximately 200 students every year. This group imposes special requirements on the teaching personnel, who spend a lot of time tutoring. The developed multimedia applications are distributed via the Internet and can be downloaded at any time.

The questions asked before starting this educational project were:

· What is multimedia?

· Can multimedia be used to confront students in a more attractive and efficient way with several topics of the course of electrical machines and drives?

These two questions are dealt with in the following sections.

Multimedia - The Technology

What is multimedia?

Multimedia is a topic of high interest in the academic world. A straightforward definition is not always available and the meaning of the term strongly depends on the accepted definition. Two generally accepted definitions can be found however, and both agree that multimedia is a technology and not a product.

To satisfy the first definition of a multimedia application, the application should be interactive with the user. This is a very broad definition and categorises a lot of modern programs into the multimedia range. It puts in perspective the fact that working with multimedia is different from working with television and movies however, as the users themselves determine what kind of pictures and sound are offered.

The second accepted definition is completely different: Multimedia is every combination of text, pictures, sound, animation and video. This definition can be specified to incorporate the interactive aspect as follows: First of all, one speaks of interactive multimedia if the user himself controls which information he wants to address and how detailed it has to be. That is why the user possesses a number of buttons on the screen which he can click on.

The second definition is the most accepted one.

Sometimes the term hypermedia is used instead of multimedia. In a hypermedia application a structure is provided where it is possible to link the different media in a certain way and the user can navigate or surf freely between them.

Multimedia-computer

The term multimedia-computer (MPC) does not refer to an electronic device, but refers to a standard with some minimum requirements. MPC is a trade mark of the Multimedia PC Marketing Council and refers to IBM-compatible personal computers. This council publishes and maintains MPC specifications. The MPC specifications are the result of a worldwide discussion with all parties concerned, manufacturers and consumers. This consensus stimulates the use of standardised multimedia computers and is the base for the development of multimedia software. Because MPC is a standard and not a computer, it is possible to compose a configuration with components from different suppliers conforming with the standard, eg the numerous available multimedia upgrade kits. The MPC-standard refers to the computer as well as to peripheral equipment. At the moment, three MPC levels have been published. The higher levels do not replace the lower ones, but they lead to an enhanced multimedia functionality. Table 1 provides an overview of the minimum specifications to satisfy MPC level 2.

Multimedia application

The aim of a multimedia application is to transfer a definite message or knowledge by means of certain media. The most important media are picture, video, sound and animation.

Video is one of the most recent developments in multimedia. The full-motion video is the highest level of computer animation with synchronous sound. This video technique combines, within one window on the PC, television images with sound. With a video player connected to the computer, videomovies can be shown in real time, but the real goal is the reproduction of moving video images stored on the hard disk. The video signal therefore needs to be digitised. A lot of compression techniques are developed to deal with the memory requirements of digital video, such as JPEG, MPEG, DVI and AVI.

A sound card and loud speakers were usually not present in standard PCs. As the use of sound requires hardware modifications, sound is probably the most recently added and perhaps still the least frequently used medium in multimedia applications. Other media, such as pictures, animation, etc, do not need hardware modifications and can be handled by standard packages that are present in almost every PC.

Sound means the use of a microphone, synthesiser, live radio etc. The sound signal is stored in digital form. The conversion between the analogue signal for reproduction and the digital form is the main task of the sound card. Important formats are the WAVE and the MIDI format.

Animation is the illusion of motion created by showing a sequence of static frames that vary only a little. It is recommended to show a minimum of ten frames per second to achieve a good effect. The main goal of animation is to give informative motion to an application.

A multimedia project

The realisation of a project comprises four steps: formation of an idea, planning, realisation and testing.

It is necessary, before starting, to have a well-defined idea of what exactly is desired. Under consideration, at this stage, are the required media, the employed data sources and whether the approach to the user will be interactive or not.

The scheduling of the project is done in the planning phase. The required means and the estimated time for the realisation are determined for each part of the project. The realisation is just a logical succession of the first two steps. In this phase, the real program is built up. After testing the software, eventual corrections and improvements are carried out before the program is ready to be used.

The whole project is realised with a specific tool, the authoring system.

Multimedia authoring systems

Authoring systems are indispensable to the development of a multimedia application. Depending on the specific purpose, a well considered choice of the system has to be made.

A multimedia authoring system supplies a frame for the project. To this frame are linked the different elements such as audio, video, text, images or animations. The authoring system supplies communication links and thus the co-operation of all the media in the particular application. The possibility to program the interactions between computer and user is also available.

Authoring systems deliver the environment to connect the contents and the functions of a multimedia project. They usually contain the program parts with the specific ability to manipulate the media (create, record, reproduce, data input etc).

Every medium has to be framed in order to be consistent with the other media. The authoring system should have as many editing tools as possible to handle each used medium. This frees the user from needing to buy extra specialised software and thus omits possible communication problems between the authoring system and extra specialised software when integrating that software.

Authoring systems make it possible to keep an overview of the program structure while elaborating contributions to simple subtasks. There are two different programming techniques: visual programming with keywords and icons, using a program language specific for the authoring system; and classical programming, which includes the use of other programmes (word processors, spreadsheets, motion pictures etc). The first technique is the most direct one, and it is possible to stress the content rather than the way of programming. If the classical method is used (programming language), the knowledge of the language is required, but a more concise formulation may be realised.

Two positive characteristics of an authoring system can be seen in the possibility to program interactions and the possibility of interim tests.

The authoring systems can be divided into three groups on the basis of the organisation method:

· Page-based.

· Time-based.

· Icon-based authoring systems.

The elements of a multimedia application are organised as pages of a book in a page-based authoring system. Designers gather all the elements of the same size and place them in logical sequences. This is done for all media. A page may contain a small script where commands are placed. They are executed when the corresponding page is selected. A special file co-ordinates the special tasks in an object oriented way. The pages contain objects, such as text, buttons, images, backgrounds etc, together with instructions for the further course.

A time-based authoring system organises the events and elements of a presentation on a time axis with a resolution down to 1/30th of a second. These systems are useful when a sequence of images has to be shown from beginning to end. The speed of the sequence can be adjusted by the designer as well as by the later user. Powerful time-based packages permit interaction. A time axis is visible on the monitor during programming.

In icon-based authoring systems, the general structure of the multimedia application can be realised the way the designer sees it. This type of approach is called visual programming. The designer builds up the program structure and afterwards a content is given to the building bricks, the icons. These icons may contain text, graphics, animation or sound. The designer keeps an overview of the program structure during the development of the application.

An icon-based authoring system, called IconAuthor, was chosen for the multimedia application developed at the Electrical Engineering Department of the Katholieke Universiteit Leuven. It was used for the development of an interactive multimedia application, combining text, images, animation, video and audio media. It is well equipped for computer supported education and interactive presentations. There are several reasons for this choice. First of all, IconAuthor works in a Windows™ environment, which means that pre-existing PC platforms can be used for the implementation. This avoids problems especially if the trainees are students working on their own computer platform, away from the laboratory. Secondly, IconAuthor was chosen, after a thorough market survey, because of its very easy programming technique. An additional reason for choosing IconAuthor was the modular approach to multimedia by this authoring system. IconAuthor contains several modules and each of them is specifically suited to the implementation and manipulation of a certain medium.

IconAuthor consists of nine different components:

· The Authoring system provides the direction of the media. Programming passes according to a fixed pattern. Once the structure of the multimedia application is fixed, it can be built up with icons selected from the icon library. Each icon represents a particular function.

· The Graphics Editor is used to create static coloured images which can also be used in an animation.

· The SmartObject Editor provides the layout of the program and the implementation of text and graphics drawn within the Graphics Editor.

· IAScope is a help utility to debug the structure during interim simulations.

· IconAnimate is the animation module in which the shooting script of the animation is generated.

· The VideoEditor handles video fragments.

· RezSolution is a graphical help providing the ability to adjust the resolution of bitmap pictures to the hardware configuration used when showing the application.

· The Resource Manager performs the book keeping during programming. This help program keeps track of all the fonts and all the files used in an application with a view to the distribution of the application.

· The Presentation System permits the reproduction of a designed multimedia application on any computer without installing the full IconAuthor program package.

Multimedia - A practical example

The basic course on general electricity, electrical machines and variable speed drives consists of lectures, theoretical exercises and laboratory sessions. Students often study their textbooks on the subject of general electricity, electrical machines and drives very deeply. They may still however have difficulties visualising important phenomena and ideas, and are not always able to see the links between the different parts of the matter. Laboratory sessions can clarify a lot, but they also have shortcomings.

First of all, laboratory sessions are normally done just once per student group. Secondly, the sessions take place in groups of three or four students per experimental test setup. Therefore it is not always enlightening for each student individually. Another point is that the sessions in the laboratory do not have the aim to recapitulate the theory of the textbook; they have to transfer practical expertise. Here it will be demonstrated how multimedia techniques can assist to overcome these problems.

An example at the Katholieke Universiteit Leuven

It is possible to confront students in an alternative way, with some difficult and basic topics of the course of electrical machines and drives, through use of a multimedia environment. The structure of the subject is more accentuated in a multimedia application. The student starts with a global overview. By clicking on the different parts, more detailed information is given. Using programmed links, more and more insight on specific topics is given. The use of video or animation is extremely suited for the visualisation of time dependent phenomena as, for example, the rotating field in ac machines or the commutation in dc machines.

It was initially intended to concentrate merely on the induction motor and, more specifically, on the behaviour of the rotating field when changing some machine design parameters. Because of the positive response and evaluation by the students, the program was extended and the developed application now consists of two main modules and several submodules:

· Induction motors:

- visualisation of the rotating field;

- mechanical construction of the induction machine;

- laboratory session.

· Dc-machines:

- basic knowledge;

- mechanical construction of the dc machine;

- laboratory sessions.

Induction motors: visualisation of the rotating field

It is possible to see the behaviour of the rotating field in the ideal case, that is, where the current distribution is continuous along the stator, in the part concerning the visualisation of the rotating field. Figure 1 shows an instantaneous view of the animation of the rotating field in a circular way, and Figure 2 is a linear representation.

The realistic case, where the current flows through conductors embedded in the stator slots, is examined as well. Figure 3 shows an instantaneous view of the linear animation of the rotating field.

Students can interact with the program by choosing all the important machine parameters, such as the number of pole pairs p and the number of slots per pole and per phase q. Each choice of parameter generates a different view. The animations are generated using MATLABä.

Other user interactions are the responses of the program to multiple choice questions where the answers have to be correct before the user can proceed with the session. Finally, a piece of digitised videotape is implemented to make the rotating field even more comprehensible. This part of a video gives an alternative presentation of the rotational field. A travelling wave is shown. The analogy between the physical principle of the rotating field and the visualisation with up and down going bars is demonstrated.

The same approach could be used to study the influence of the time harmonics in the voltage and current supplied by a frequency inverter.

DC machines: basic knowledge

Starting from a simple didactical model, the working principles of the dc machine are given in this part of the program. Different types, such as permanent magnets, independent excitation, shunt, series and compound machines and their characteristics, are explained. This module contains several animations. An instantaneous image of the animation illustrating the commutation principle is shown in Figure 4. This model is then refined to a real armature with all the windings and collector lamination.

Important effects, such as armature reaction, are discussed. By superimposing different pictures step by step, the student achieves a good insight into the phenomena. Figure 5 shows the resulting field, including the armature reaction.

Mechanical construction

The student is given an overall view of the considered motor in the mechanical construction module of the induction machine and the dc machine. Clicking on different parts of the machine, the student obtains the name and functionality of the machine part. The student can even get a more detailed picture. It is also possible to have a list of machine parts and to click on one of the names. The student, in this way, learns more about the functionality and location of the specific machine part inside the motor. Figure 6 shows an example of a detailed view of the rotor of the squirrel cage induction machine.

Most of the images shown in this part of the self study session are photos stored on a photo-CD and imported into the multimedia program.

Laboratory sessions

The third part of the two modules discusses topics of the practical laboratory sessions. By working with this program part, students can prepare themselves for the practical laboratories. All of the experiments and calculations that the student has to perform during the practice sessions are explained, and all the required measuring equipment and their connections are shown in detail. The software is used when elaborating the laboratory report. Furthermore, it can be used for the preparation of the final examination because it is impossible to repeat the laboratory experiments prior to the examination.

Experiences and feedback

The above mentioned application of a multimedia laboratory session at the Katholieke Universiteit Leuven is prepared for undergraduates in the third year of their engineering studies. This technique has been successfully used for education for almost two and a half year. It can be stated that multimedia, in combination with classical lectures, gets the undergraduates more interested in the subject and improves the transfer of knowledge and the understanding of the phenomena to a large extent.

Students have been asked to evaluate this project. In general, the reactions were very positive. The students judged the application as very user-friendly. The animations concerning the rotating field and commutation are found extremely enlightening. The multimedia application is available on the computers in the laboratory and can therefore be used at any time. This fact is seen as an improvement in teaching. Furthermore, many students possess their own PC so that the executables, downloaded from the Internet, can be used after working hours and during their preparation for their examinations. The software can be downloaded from http://www.esat.kuleuven.ac.be/elen.

Future projects

In the near future, multimedia programs on transformers and on power electronics will be developed along the same lines as the existing programs on induction and dc machines. It is also the intention to develop a multimedia program with a large amount of multiple choice questions to allow students to test themselves. Among the wrong answers, typical mistakes and misunderstandings will be highlighted.

Conclusions

An alternative and more efficient way to confront students with topics from the field of general electricity, electrical machines and variable speed drives is described in this paper. To get the undergraduates more interested, a multimedia session has been developed to visualise phenomena in squirrel cage induction machines and dc machines. The complex mechanical construction of this type of machine is introduced to the students during the multimedia sessions. Attention is paid to the preparation of the laboratory sessions and their practical implementation. Additional multimedia applications in other topics of the electrical engineering education are strongly recommended by the undergraduates.

Acknowledgment

The authors are grateful to the Belgian Fonds voor Wetenschappelijk Onderzoek Vlaanderen for its financial support of this work, and to the Belgian Ministry of Scientific Research for granting the IUAP No. P4/20 on Coupled Problems in Electromagnetic Systems. The research Council of the K.U.Leuven supports the basic numerical research.

References

1. Vaughan, T., Multimedia: making it work. Berkeley: Osborne McGraw-Hill (1993).

2. Jennings, R., Werken met Windows 3.1 Multimedia. Schoonhoven: Academies Service (1992).

3. The Math works Inc., The Students Edition of MATLAB. Englewood Cliffs: Prentice Hall (1992).

4. IconAuthor User Manual for Windows. Nashua: Aimtech Corporation (November 1992).

5. IconAuthor Reference Manual for Windows. Nashua: Aimtech Corporation (1992).

6. Matthijs, K., Gebruik van multimedia ter ondersteuning van de cursus inductiemachines. Masters Thesis at the Katholieke Universiteit of Leuven (1994).

7. Henning, E., Multimedia - animating your PC with sound and vision. PC Magazine, 303-308 (October 1992).

8. Malfait, A., Matthijs, K., Reekmans, R., Hameyer, K. and Belmans R., Using multimedia in the field of electrical machines. Using Hypermedia for education in electricity utilisation, UIE & CBEE Leuven, België (1995).

9. Olivié, H., Multimedia: meer dan een trend; een inleiding tot de studiedag Van Cauterenleerstoel, Leuven, België (1994).

10. Multimedia PC Computing, What you need to know - Frequently Asked Questions. Software Publishers Association, http:/www.spa.org/mpc/mpcaq.htm (1995).

11. Multimedia PC Computing, Multimedia PC Level 3 Specification. Software Publishers Association, http:/www.spa.org/mpc/mpc3spec.htm (1996).

Biographies

B.Renier
P.V Roy
K.Hammeyer
R.Belmans


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