A Learning Environment Coupld with a CACSD Pcakage

Copyright ~' IFAC Advances in Control Education. Tokyo. Japan. 1994

A LEARNING ENVIRONMENT COUPLED WITH A CACSD PACKAGE. C. BASSOT, N. MASSEUX, F. MICHAU and C. STIHARU-ALEXE

Laboraloire d'AlllomQliq/U! tU Gr~1lObl~, U.R.A. C.N.R,s. 228, Ecok Nali~k d'["genUlUs EkctricieAs tU Grenobk. BP 46, Sainl-Martin d'Heres Ceda. FrQIfC~.

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Abstrac:L CACSD-Tools (Computer-Aided Control System Design) are increasingly used in Control Engineering Education. This paper presents Atrro-DIDACT, a research project which purpose is to integrate Learning Aids with a CACSD package. The pedagogical objective is both to help the student to develop a concrete approach of systems dynamic behaviour utd to lead him to explore a wide variety of cause-effect relationships. Atrro-DIDACT contains an Exercise Base with short generic exercises utd real applications problems (for the moment limited to aeronautic domain) and two Knowledge-Based-Systems in order to guide the student through the exercises and to help him to inlerpl'et graphic results. Key Words. Educational aids; Computer-aided instruction; Computer-aided system design; Learning systems; Artificial intelligence; Knowledge-based system.

handling of relevant simulations through short exercises, -2- to improve his generic basic knowledge through problems using several concepts and modeling tools on real applications emphasizing physical interpretation , -3- to help him to solve graphic interpretation problems, on time and frequency responses, in a rigOlDOUS and consistent way. To fulfil those learning objectives AUTO-DIDACY' is built with several components (see Fig. 1).

1. INTRODUCI10N Control of continuous time systems presents specific learning difficulties; especially, the sbldents have to handle a great number of dynamic concepts with varied modeling tools. Students hardly grasp all the links between the handled entities, for example : links between time and frequency approaches, links between continuous and discrete time studies, effects of parameters modifications on performances. The present paper describes AUTO-DIDACT, a knowledge-based learning environment coupled with a CACSD package, suited to train the students in linking up know ledges and observing cause-effect relationships through simulations. This on-going research project is developed at the Laboratoire d'Automatique de Grenoble and a first prototype is now experimented by the students of the Electrical Engineering School of Grenoble. It is an interdisciplinary work which contributes to the growing research domain of "adding Intelligent Aid to CAD package" (Sens, 1991; Antao & ai, 1992).

AUTO-DIDACT

2. OBJECI1VES AND OU1LINE OF TIlE WHOLE ENVIRONMENT AUTO-DIDACT is a learning environment about Linear Systems Analysis, dedicated to basic conceptS illustration in Control Engineering. Its objectives are threefold: -1- to allow the user to explore Linear Systems Analysis through a personnal study path, by direct

Fig.1. The software architecture of AUTO-DlDACf

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dynamic behaviour of the studied system. For that, AUTO-DIDACT supplies the user with interactive graphic tools in order to fixe the parameters of the system's model and run dynamically the simulation. By this way. the student works by trial and error. experimenting several simulations. This learning straaegy is underlyied by the idea of a self learner's knowledge discovery through the interpretation of simulation results (Vivet, 1991). For the exercises based on a pedefmed system. AUI'O-DIDACT easily evaluates the validity of the user's answer. Othc'l'wise. for example exercises where students can choose transfer function parameters. tools deducing the answer from the numerical result of the simulation. are used. Finally. the user consults the list of connected study themes suggested by AUTODIDACT that are complement to those he has already studied. The initial learning situations and the complement ones are the set of problems describing the conceptual field of a given notion . For the student, solving this set of problems allows him to build the sense of his knowledge through the exploration of a conceptual field (Vergnaud. 1984). This assistance is founded on guidance rules. based on the knowledge network. For example. consider a study theme based on the link between two notions : "precision" and "stability" for a given context (continuous. third order. closed loop system) and using models with their parameters (Black diagram. step response. gain and phase margin. static error). The connected study themes suggested by AUTODIDACTare - the same "precision-stability" link studied for discrete-time system (change of context) - the same "precision-stability" link studied by using Bode diagram (change of modeliog tool) - the influence of the characteristic behaviour of the open-loop system (minimum phase. dominant time constant. origin pole order) on the "precisionstability" link in closed-loop.

The Exercise Base contains soon generic exm:ises and real applications problems (for the moment limited to aeronautic domain). The Knowledge Based System for user guidance contains a Systems Analysis knowledge-network and strategies to build dynamically sequences of exercises on larget subjects and to propose new explorative studies to the user. For each domain. generic or aeronautic. the Information Data Base contains definitions and examples structured as a tree-like hyper-documenL The whole environment is coupled with a commercialy available CACSD package named ACSYDE. a SIMULINK like. widespread french professionnal. package.

3. GENERIC BASES AND USER GUIDANCE A didactical study of Conuol led to modelise the knowledge as a network with a tree-like representation to structure the hierarchy of dynamic concepts and modeling tools (see Fig. 2) and involving also transverse links between the nodes. Systems (process" control) are studied

duough

4. AERONAUTICAL BASES Working with real systems is necessary to fully grasp the difficulties of control that the learner is likely to find later in his engineering activity. The aeronautical exm:ises objectives are both to interest the learner in the study of dynamic phenomena and to describe a coherent sequencing of several analysis stages in order to reestablish the relation between theory and practice. A further objective is to bring. besides the primary Generic Linear Systems Analysis Knowledge Base. a phenomenological and synthetic view of the aeronautical field. thus promoting intuitive understanding of analysis results. The knowledge that is to be communicated to the learner and all information that is needed to engage the learner in activities that might stimulate personal experience are stored in an Aeronautical Infonnation Data Base (AIDB) structured as a hyper-documenL The AIDB provides aeronautical information on flight dynamics (Etkin.1972; MC Lean. 1990). introducing physical state variables and controls as

Fig.2. An extract ot the knowledge network.

First the user explores a hyper-document built from the hierarchical model. He visualises the structure of the knowledge and defines his study theme (one notion or the link between two notions) and eventually a context (continuous. discrete •...). Then. AUTO-DIDACT supplies a sequence of exercises aimed at the current study theme and contexL This generation of exercises is founded on filtering and sorting rules deduced from the knowledge network. The solving of each exercise needs to simulate the

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well as movement modeling assumptions. The aeronautical exercises deal with linear models of aircraft motion adequate to design stabilisation loops. The learner may browse tIuough the models network. presented as a hyper-document. from the most general to the simplified ones. Each node of the Hypertext network gives access to appropriate applications in the execcise base .Aeronatical exercises present an interdisciplinary proflle. While primarily illustrating analysis stages on linear systems. they also teach coherent thought processes to gain an insight into physical phenomena. As presented in Fig. 3. relations between physical parameters. such as the air speed. the altitude or the aircraft aniwde. and flight qualities are explored in terms of generic abstract systems theory (Basile &. Marro. 1992; Kailath. 1990). G~_riI:

Awo...uical S:Jstntll

characterization of a notion on a curve concerns both elementary graphic and not graphic parameters (overshoot, ...). and complex concepts (stability. precision). The second kind is the comparison between values of a parameter on two curves. The last kind of study is prediction. It may be either a prediction of a transfer function from a curve. or a prediction of the closed-loop behaviour from the open-loop behaviour. The KBS-GI decomposes these problems into sub-tasks in order to solve them itself with cooperation with the user. The interpretation process has to be structured in order to be transposed to any problem. Several resolution strategy types have been worked OUL Rqormulalion and decomposition are two types of strategy. These strategies are based upon notions structures and links between these notions. For example. the notion step response behoviour has three independant components: the inilial-bdaviour. the transient-behoviour and the steady-state. This notion structure implies that the characterization of the step response behaviour must always be reformulated into three sub-tasks : the choracterization of the initial-behoviour. the characterization of the transient-behoviour. and the choracterization of the steady-state. These tasks structurations will enable the students to get the largest quantity of information from the step response. The links existing between the notions lead the decomposition of tasks into sub-tasks. The knowledge of these links detennines the set of subtasks stepping in an initial task decomposition. The Object-Oriented-Representation matches with implementing the ideas about knowledge and methods structuring. [Prevosto &al 91] show both concepts and tasks may be encapsulated with this

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involveH Physical JlIIII-'CICI I S

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Flight qualities

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Fig.3. Aeronautical exercise Iopic:s

The learner can apply at any moment of his tutorial for additional information. The learner may identify his lack of knowledge among several suggestions covering topics on both Generic Linear Systems Analysis Knowledge Base and Aeronautical Information Data Base.

representation. The advocated resolution process has to be explained by defining the concepts. exhibiting their components. displaying links between them and justifying these links. Two flDlCtioning modes are embedded : the user-mode and the system-mode. In the user-mode. the learner tries to solve the current problem. He may ask Why? when he does not understand the relevance of this problem either in Control domain, or in the decomposition where it intervenes. The learner may ask How? when he does not know how to solve the current problem and the system provides him a text that displays the resolution process. Then. either the learner gives an answer. or the KBS-GI successively submits to it all steps of the decomposition ; this process is executed again at each of these steps. So. the user chooses the detail level of the problem terms according to his knowledge level. In the system-mode. the KBS-GI solves the problem and presents its results to the learner who has chosen the decomposition level whose resolution he wants to see ; besides. he may ask the execution of an explicative procedure tied to the on hand problem.

5. A KNOWLEOOE-BASED SYSTEM FOR GRAPInC INTERPRETAnON AlITO-DIDAcr includes a Knowledge-Based System for Graphic Interpretation (KBS-GI) as the interpretation of graphic results is a very important part of the student work. A typical behaviour of students is to simulate many responses eventually needless. and to subsequently try to interpret them. Moreover. they have difficulties in getting relevant infonnations from the response of a complex system : for example in bringing out a main behaviour and a secondary one. Two aims lead the KBS-GI design: to solve sole an interpretation problem in order to demonstrate it to the user and to guide the learner along the steps of an interpretation and to verify at each step the results he gives. Besides. the KBS-GI supplies students with a geometric tool-box (for example tangent drawing) a well as a calculus library (for example slope calculus). and leads them onto further simulations (immediate drawing of another response with parameters variations). The KBS-GI deals with frequency reponses and time responses. Three kinds of graphic interpretation work have been listed. The qualitative or quantitative 97

6. INFORMATION ABOUT INPLEMENTATION

8. ACKNOWLEOOMENTS

AUTO-DIDACT runs on UNIX workstation with X Window environment An Object Oriented Modeling technique has been used to develop both knowledge bases and Exercise or Information data bases. This technique allows a suuclUred description of handled objects and permits to make explicit the sense of each object through approprialcd slots (see Fig. 4).

We thank the Rtgion Rh6ne-Alpes for its fmancial support to this project. 9. REFERENCES

Anl8O, B.A.A., Brodersen, AJ., Boume, 1.R. and Cantwell, 1.R.(1992) Building Intelligent Tutorial Systems for Teaching Simulation in Engineering Education. lEE Transactions 011 Educatioll, Vol. 35, No I, FtbnI4TJ 1992, p 50-

( curvel is-a step-response

56. Basile,G. and Marro, G. (1992) Controlled and Conditionated Invariants in Linear System Theory. Prt1llict Hall. Etkin, B. (1972). Dynamics of Aunospheric Flight John Wilty & Sons 11tC., Ntw York. Kailath, T. (1990) Linear System. Prtllliu Hall

= initial-behaviour ( Cl-ioit-behaviour is-a orderl-invene.no-delay-behaviour initial-slope = zcro.sJope relative-direction delay

=

inverse-relative-direction )

= no-deJay

ttansient-behaviour = ( Cl-uansient-behaviour is-a type2-transient-behaviour oscillation-period 3.3 fU'Sl-Overshoot = 0.5

11IIeT7lQ/U)nal. McLean, D. (1990). Automatic Flight Control System. Prtl'llict Hall11Jlen&alionai. PrevOSlO, M. and Rechenmann, F.(1991). SAID : A knowledge-based system for signal processing.

=

steady-swe-bdlaviour = { Cl-steady-state-behaviour is-a convergent-behaviour time-response = 1.5 static-gain 1.

=

...

European COlllrol ConftrtltCt.GrtllOblt. FraItCt. 1991, ppI21-125. Sens,U. (1993) Computei' Integrated Insb'UCtion for I with a CACSD-Tool. IFAC. Advallcts ill COlllrol EdMcatioll. BOstOll, USA. JUM 1991. P

)

245-249. Vergnaud, G. (1984). Interaction sujet-situations.

...

AClts de la tTowme ecole d'ele de didJJc~ des malhimtJlUiun, GrtllOble.

}

Vivel, M. (1991). Learning science &. engineering with open knowledge based systcms.ll'IltrMlionai COII!trtltCt 011 Compultr Aided Ltarllillg and

Fig. 4. An instance of step-response-object

IlISIructWlI ill ScitltCt and Ellgillttring. Lausannt.

Domain knowledge is made up of dynamic concepts, modeling tools, links and solving tasks. It is

Willamowski, 1., Chevenel, F. and lean-Marie F. (1993]. A developpment shell for cooperative solving environments. Third IlIltrllatiollal

represented through several tree-like classifications. For the KBS-GI, the knowledge complexity and the need of inference mechanism led to use a KBS development tool : SCARP (Willamowski, 1993). The communication between AUTO-DIDACT and ACSYDE, the CACSD package, uses UNIX standards and has been designed in order to need no modification of the CACSD package. A first prototype containing system analysis generic exercices and aeronautic exercices is used by the students fCX' experimenL

Con!trtllct 011 Numerical Compulillg, PurdMt (IN. USA), Mm 1993.

7. CONCLUSION Such an ambitious project as AUTO-DIDACT requires an interdisciplinary collaboration, a time consuming development and uses a high computing environment The increasing need of self-training tools in Engineering Education and the effICiency of simulation to support the study of dynamic phenomena in the field of Control, justify such an effort to build powerfulleaming environmenL

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