dynamit - learning system dynamics using multimedia

European Control Conference 1999

31. 08 - 3. 09 1999 Karlsruhe, Germany

DYNAMIT LEARNING SYSTEM DYNAMICS USING MULTIMEDIA T. Löhl*, S. Pegel*, K.-U. Klatt*, S. Engell*, Chr. Schmid# and A. Ali# * Process Control Laboratory Department of Chemical Engineering University of Dortmund, D-44227 Dortmund, Germany fax: +49 231 755 5129 e-mail: [email protected] # Control Engineering Laboratory Department of Electrical Engineering and Information Technology Ruhr-University Bochum, D-44780 Bochum, Germany fax: +49 234 709 4101 e-mail: [email protected] Keywords: Education, Control, Internet, CBT, MATLAB

Abstract A CBT system for system dynamics and control engineering is presented and an introduction into the related educational aspects, the elements and their realisation is given. The system is based on multimedia web components, which integrate the MATLAB/MAPLE V system for calculations in the background. CACSD operation is completely hidden from the learner, which can concentrate on the tutorial, exercises and experiments. The latter are realised in an integrated virtual laboratory, which uses virtual reality techniques to animate and interact with virtual laboratory plants.

well-known user interface, i.e. a web browser, the time to become familiar with such an environment is generally very short. The communication between MATLAB/MAPLE and the web browser requires some basic extensions to the standard web browser facilities taken from the VCLab environment [Sch98]. To avoid heavy network traffic, the client/server architecture of Fig. 1 is used. Model Library Standardised form for symbolic and numeric calculations

A disadvantage of the use of CACSD tools for learning control engineering may be the necessity of learning the ‘language’ of the design tool. In some cases, this requires a large amount of time, which is lost for the actual educational aim. In DYNAMIT, only the knowledge of handling a standard web browser and a limited mathematical formalism is needed to accomplish the exercises. Commonly used browsers provide facilities to handle different media types such as graphics, videos, sound and hypertext. Because of the integration of standard mathematical computing environments such as MATLAB or MAPLE V and the use of a

Exercises Web Server

W eb Server

Virtual Laboratory Plants VRML models

W eb Server

Internet

1 Introduction Traditional lectures, exercises and laboratory courses show some common shortcomings. These classical teaching/learning situations with one teacher at the blackboard and a group of students are dependent on time and location. It is obvious that this restriction limits the possibility to expose interconnections of different topics or treat problems in more detail. A computer-aided teaching and learning environment aims at improving the learning situation by setting up an additional learning environment similar to a tutorial or private teacher. Advantages of the use of Computer Aided Control System Design (CACSD) to elaborate merits and demerits of different methods to solve a problem can hardly be overemphasised.

CBT Lessons

Client Netscape Web Browser

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HTML page MATLAB Plugin

Graphics Plugin

JavaScript

Java Applets

VRML Plugin

MATLAB MAPLE V calculation and simulation engine DynaMit Toolbox

ToolbookII CBT Plugin

Fig. 1: Client/server structure to broadcast courseware, client configuration and interconnection between MATLAB/MAPLE and web elements.

2 Control engineering educational aspects The purpose of the DYNAMIT project is to establish a multimedia-based Internet course on systems and control engineering that enables students to learn independent of time and location. The students can access DYNAMIT either from their own computers or from university computer pools. Reflecting the classical learning situation DynaMit is divided into three parts, tutorials, exercises and laboratory experiments, each of which has different goals. The control education tutorial acts as a summary of basic concepts, methods and approaches. In the exercise section problems are proposed. The major aim is to model and to analyse a system in the time or the frequency domain and to propose an appropriate solution to the problem. The virtual control laboratory simulates a laboratory environment, so that small, real world experiments can be performed. The virtual control laboratory uses virtual worlds to visualise the laboratory plant to be analysed or controlled.

frequency domain formulation. Secondly, a glossary is available from everywhere within the learning environment. This glossary is a collection of keywords. Each keyword is linked to a page, which describes the selected keyword briefly. This approach becomes important, if the student had already learned a topic but forgot some of its important aspects. For a better understanding, each lesson is structured in a uniform way as illustrated below: 1.

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A detailed description of the three parts of the software is given below. The interconnection between the exercise section, the virtual control laboratory and the more theoretical control tutorial is established via hyperlinks. The use of the HTML language makes cross-references of topics and notions very easy.

2.1 Tutorial The tutorial, the ‘lecture’ part of the DYNAMIT, may be used either independently to learn the basics of systems and control theory, or as an interactive facility for solving the exercises. The tutorial is not intended to be a substitution of the conventional lectures of the curriculum held by the tutors, but to be an extension of them. Both ways of using the tutorial are supported by the proposed structure. Therefore, the tutorial section is divided into independent lessons. The tutorial can be used in two different ways according to the prior knowledge of the student and his learning preferences. For a less knowledgeable student, the subchapters of the tutorial can be worked out successively in order to learn the fundamentals of systems and control theory. For a skilled student, who already has a fundamental knowledge of the basic theory, only special lessons are of interest. These special issues can be found either in the table of contents or by the help mechanism implemented in the exercise section to accomplish a given subtask. There are at least two ways to look up special topics of the tutorial section. Firstly, the complete section can be accessed by an hyperlink, which links the appropriate chapter of the tutorial to the current exercise. This becomes necessary if the student has never heard of the method, which should be used. For example, the student is unable to remember the transformation of a time-domain state-space model into the

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Fundamentals of the lesson: In this part, references to the required knowledge from mathematics, systems analysis, process engineering and electrical engineering are given. Here, the students will find links to those parts of the tutorial, which they have to comprehend in order to understand the contents of the lesson. Description of different possibilities: Since several alternative methods for solving a problem are presented, interconnections of different approaches can be made transparent. This part acts also as a motivation for the lesson. With the help of a technical example the necessity of describing the problem in a mathematical way is explained. Thus the methodlearning approach is replaced by a more sophisticated context sensitive one. At this step a decision has to be made, which way of solution should be taken, what are the advantages of solving a problem this way and what are the disadvantages of another solution. Therefore the formulation of the goal of this lesson is straightforward. Details of the solution: After analysing the problem, a presentation of the way of solution follows. This part of the lesson is the most important one. At this point the application of abstract methods to the real problem is elaborated. Review of the method : In this step the reliability of the solution should be discussed. To understand the theoretical solution of a technical problem, it is important to analyse the solution from the point of view of the real task. With the help of multimedia, short video-clips, animations, and simulations the behaviour of the real plant can be illustrated. Feedback of the student: An evaluation part follows each lesson. Students are provided with the option to put any question or suggestion relevant to a specific subject or about DYNAMIT in general. The learning system is thus not a replacement but only a supplement to the conventional education. Tutor-learner communication is still needed.

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2.2 Exercise section As the level of student’s knowledge is not previously known, an Internet-based hypermedia learning environment has to be designed very skilfully. A key issue for the success of an exercise is testing the knowledge. A trivial method is to check keywords, which leads in the extreme to drill-and-practice exercises. This type of knowledge evaluation is not appropriate for education, because the student is requested to try different answers until the correct one is found. The benefit with respect to a comprehensive view of a topic of this approach is regarded to be very small [Sch97]. To motivate both skilful and unskilled learners, a compromise between a guided exercise, where each subtask is well defined and an unguided exercise, where only the main goal is formulated has to be worked out. An unguided or unstructured exercise may result in confusion in the case of unskilled learners, whereas a guided exercise may bore skilful learners. Thus, we propose a help mechanism, which is available for the student at any time. This on-line help assists the student in solving the particular task and furthermore provides links to the appropriate tutorial lessons if desired.

In order to take different preferences of the learner into account, he/she is given the opportunity to choose an exercise out of a pool of exercises. The exercises in control engineering mainly consist of the task to model and analyse a given physical system with respect to a given evaluation criterion. For example, capacitance and resistance of different elements in an RC circuit are to be adjusted so that the step response of the circuit exhibits a desired behaviour. This approach combines systematic learning and explorative learning. Since there is no need to validate intermediate results, different routes can be adopted to solve a given problem. Thus the explorative character of the exercises is emphasised. To elucidate the advantages of a mathematical formalism to analyse the properties of a dynamical system without placing too much emphasis on the mathematical formalism, the use of symbolic computation techniques is helpful [Beq97]. Properly designed graphical user interfaces provide an easy handling of symbolic computation software packages such as MAPLE embedded in MATLAB, Fig. 2. Finally, numerical computations, e.g. simulation experiments enable the learner to investigate system dynamics at their own pace and therefore act as a motiva-

Fig. 2: Screenshot of the use of symbolic computation techniques as part of an exercise

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2.3 Virtual Control Laboratory An important part of control engineering education is the combination of theoretical knowledge with practical experience. The first is taught in the tutorial and exercise sections. The practical experience is conventionally obtained during separate laboratory courses. Learning based on design and visual feedback is an important aspect of control engineering instruction. For this reason, students have to be in a laboratory to gain laboratory experience. A supplementary virtual laboratory during a conventional laboratory course and within the DYNAMIT tutorial or exercise section fully engages the students in the learning process through the interactive, dynamic environment. This combination of a widespread CACSD and simulation tool with hypertext classroom material leads to the concept of an integrated virtual laboratory. During a virtual control laboratory experiment the major aim is to explore the dynamical behaviour of a plant by simulation studies under varying conditions. By means of virtual reality modelling and simulation techniques it is possible to bring visual and acoustic plant behaviour together with manual plant interaction directly on the desk.

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Technical realisation

3.1 Interface design A proper graphical user interface is very important for a computer-based learning system. It influences the student's concentration and interest in the lesson. A simple, pleasant and user-friendly environment attracts the students and can enhance the efficacy of the programme. The DYNAMIT user interface is designed very carefully. A uniform graphical layout, which demonstrates the following features, is used to develop all the tutorials and exercises: 1. Description of the consequences of user actions: The learning environment describes what consequences may arise if the user chooses different options. 2. Immediate response to user actions: In case of complex and time-consuming background computations the system does not let the user be confused due to response time lags. 3. Current status display: The system always indicates the current status for user orientation. This is important to prevent the user from getting 'lost-in-hyperspace' 4. Easy navigation: It is obvious that the navigation should be easy and intuitive.

Main frame contains the actual learning contents where as the Navigation makes the navigation through the environment easy. The contents of this frame are configured dynamically as desired by the main pages. Shared scripts are located in a JavaScript library. Furthermore, it is sometimes desirable to disable subsequent pages until a specific condition is met. This 'guidJavaScriptLibrary

Main

Browserwindow

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tion to engage in the analysis of complex dynamical systems as well as in the verification of the symbolically predicted system properties.

Parent

Fig. 3: Frame layout of the DynaMit Web pages ance' for the user either avoids inconsistencies of the underlying model data or forces, for example, some didactic aims to be met before the next topic is presented. This requirement is achieved with a navigation bar, which is configured dynamically according to the desired navigation scenario.

3.2 Implementation aspects A model is the basic object, on which all manipulations are performed. Since systems and control theory is mainly based on mathematical formalisms, DYNAMIT's internal model representation is based on symbolic equations. Furthermore, it is much desirable to develop a library of model objects, and to combine components from this library to build the model of a system. Besides, the complete model should not be easily accessible to avoid accidental change of model properties by the learner. To accomplish this task, the basic symbolic objects of MAPLE had to be extended. An external model library provides the ability to partially reuse model components. This external model definition is independent of the number and the physical nature of inputs and outputs. As a consequence, the model structure is very flexible. The structure of objects, which are implemented in MATLAB as the DYNAMIT Toolbox is outlined in Fig. 4.

To achieve an environment, with the above features, the frame layout as shown in Fig. 3 has been developed. The

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SystemObject ModelObject

SimulationObject

and analyse the given system. The student will get assistance if needed. But numerical/symbolical operations are completely hidden from the learner. The basic structure of this event driven approach is outlined in Fig. 5.

MathModelObject User action

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symbol definitions Logon

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Fig. 4: Client-side object diagram [Boo94] of the implemented class structure in MATLAB. The basic object is the SystemObject, which describes the complete system. The system may consist of one or more model objects (ModelObject). The model objects contain information about the underlying mathematical equations (MathModelObject), the connections between different models (Ports) and the definition of the symbols, as well as an associated visual and graphical representation and a textual description of the complete model. The visual/graphical model entries contain links to related files. The visual representation is modelled in the Virtual Reality Modelling Language (VRML) and is used for animation purposes. The graphical representation may contain block diagrams or real world pictures of the plant. An important issue of this object design is the distinction between models and experiments. Models describe the basic behaviour of a system in terms of mathematical equations. Experiments reflect the behaviour of a specific instance of a model, that is to say all symbols used are either inputs, outputs, states or constant parameters and all dependencies are known. This is realised by the use of simulation objects, which refer to one basic system model (SimulationObject). Both basic model descriptions and experiments can be analysed by the learner. Since all transformations and calculations are based on the basic formulation of the model, it is very easy for the administrator to add new models, which can be used within new exercises. If the learner wants to perform an exercise session, the related model definition files are downloaded and defined in the MATLAB workspace. The model definition files contain: 1. The properties of the complete system and references to sub-models. 2. A set of model object files containing systems of differential and/or algebraic equations, which define the sub-models. 3. Declaration and explanation of the symbols used in the sub-models. After the client has loaded this information, the problem to be solved by the student is presented in a hypertext document. The student on the client machine performs all the numerical and symbolical operations required to model

Start MATLAB and initialize Model

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Problem presentation

Basic symbolic transformations (e.g. linearization)

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Help required ?

Input partial solution so far

Calculate solution for subtask Display/edit partial solutions if required

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Calculate final solution

Fig. 5: Communication event diagram of a guided exercise example.

4 Evaluation An evaluation procedure is being performed to judge the quality of the developed system. This evaluation will be based on the feedback received from students participating in the Systems Analysis course at the Department of Chemical Engineering, University of Dortmund and other learners. DYNAMIT is accessible to everyone via the Web [Dyn99]. All DYNAMIT users are requested to fill a questionnaire and return it to the authors. The evaluation questionnaire consists of 22 questions concerning different aspects of the system and the student. Some features of the questionnaire are listed below: 1.

General information about the student/learner including his personal skills and motivation for DYNAMIT.

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The Learner’s opinion about general layout and overall structure of DYNAMIT.

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Style, navigation, and usefulness of the learning system.

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Questions about tutorials inquiring the learner’s opinion about the level of difficulty and the quality of the contents and the style of the presentation.

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Questions inquiring the learner’s opinion about the level of difficulty and the style of the exercises and their relevance to the lessons and deficiencies.

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General remarks and/or proposals for improvements.

We hope that the results of this evaluation will be presented in the conference.

tion techniques will be improved. In response to the evaluation results the style of presentation will be improved to make DYNAMIT even more interesting, explorative and attractive for the students and to make them inquisitive about the knowledge.

References [Sch97]

5 Conclusions This contribution presents a learning framework, which addresses students and learners in the area of control engineering. Basic methods of system analysis and controller design are taught via the World Wide Web allowing easy access round the clock. The use of standard web browsers as well as commonly used mathematical tools such as MATLAB and MAPLE makes the handling of the learning environment easy and flexible enough to tackle tasks with different degrees of complexity. The use of symbolic computation techniques offers the possibility to relate the abstract mathematical formalism to the actual problem to be solved. In the future we intend to implement some advanced and more complex topics from control engineering and theory of dynamical systems. Visualisation and anima-

Schulmeister, R., Grundlagen hypermedialer Lernsysteme: Theorie - Didaktik - Design Addison-Wesley, (1997)

[Beq97] Bequette, B. W.: "An Undergraduate Course in Process Dynamics", Comp. chem. Engng., Vol. 21, 261-266, (1997) [Boo94] Booch, G.: Objektorientierte Analyse und Design, Addison Wesley, (1994) [Dyn99] The DYNAMIT Homepage (Online March 1999) http://astwww.chemietechnik.uni-dortmund.de/~mume

[Sch98]

Schmid, Chr., "The Virtual Control Lab VCLab for Education on the Web". In Proceedings of the 17th American Control Conference ACC’98 (Philadelphia, USA, June24-26), IEEE, Piscataway, N.J., 1314-1318, (1998)

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