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AN INTELLIGENT CAD SYSTEM

FOR De MACHINES

by

Zongfan Zhu (M.Eng. Zhejiang University, Hangzhou, P.R.China)

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements

for the degree of Master of Engineering

Department of Electrical Engineering McGiIl University

Montréal. Québec, Canada

July, 1991

© Zongfan Zhu

For my motller,

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ABSTRACT

This thesis presents the development of an intelligent CAD system (IC'ADS)

for OC machines, This system was implemented on a PC llsillg Commull I.I:-'p

provided by GoldWorks Il and connected with a SUIl Workstatioll workillg lIndel thl'

Unix system for file transfer,

Both frame-based and rule-hased knnwlcdge reprcsentatloll technIques have

heen used tn capture the knowledge ahout the deSIgn of electnc machine:-.. The

system has its own inference engme specially designed to handle both deci~.ioll Illaklllg

and numerical computation. Forward-chmn reél~oning and procedural attachlllellt

were llsed tn construct thb Inference engllle, The knowkdgc ha .. e m:llwgl'I11L'JlI

system provides a user intel face for knowledge acquiSItIon, knowledge rl'pre~enlatl{)n,

man-machine communication, design document preparation, etc, The de~lgl1 result~

are translated to a finite element analysis hie and !lent to MagNet2D, :t powcrlul

electromagnetic field analy~is package for deSIgn checking and rellllCl11ent.

The system provides different levels ot design automation tn ~uit the need!l of

the system liser. As examples the deSIgn results of a series of universal l11()tor~ and

a small DC motor are provlded in the thesio;,

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RÉSUMÉ

Un système intelligent (lCADS) de CAO pour les machines à courant continu

(DC) a été développé au lahoratoire de conception et d'analyse numérique de

l'univer~ité McGi11. Le système a été implanté sur un PC et tourne sous Common

Lisp de Goldworks Il est relié fi une station de travail Sun sous Unix pour le transfert

des fichier~.

Les deux technique~ de représentation de connaissances par règles et par

cadres ont été utilisées pour le modelage des connaissances requises en conception

de machines électnques. Ce ~ystème possède son propre méchamsme d'inférence

spécialement conçu pour pouvoir h la fois gérer les prises de déciSions et les calculs

numériques. Le méc"am~me d'inférence travaille en chaine d'avancée et est capahle

de gérer des attaches procédurales. Le système de ge~tion de la base de données

comprend une Interface utilisateur pour l'acquisition ~t la représentation des données,

ainSI que pour le dialogue homme-machine, la préparation des documents de

conception, etc. Les résultats de la conception sont alors traduits en un fichier de

données pour analyse d'éléments fims, et transtërés a MagNet2D, un puissant logiciel

d'analyse de champs électromagnétiques, pour vérifications et raffinement de la

conce pt ion.

Ce système comprend plusieurs niveaux de conception automatique,

sati~faisant ainSI différents utilisateurs. Plusieurs exemples portants sur une série de

moteurs ul1lverseb et un petit moteur DC sont fournis dans ce thèse, illustrant ainsi

le potentiel du système.

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ACKNOWLEDGEMENTS

First of ail 1 wOlild like to exprel>s my deep appreciation to Dr. D.A Lowthl'I,

my supervisor, for hi:, invalliable guidance and assistance. His help incllllk'd in ail

aspects and every stage toward the suhmi~sioll of this thesl~. 1 Il' intrOlluœd Illl' thl'

expert system field for engineering design and l>pent time ln the construction uf my

design system. He read through and made coml11ents of this thesls in his s:lhhatrcal

leave time, t'rom technical aspect to literate style.

1 also thank memhen in CADLah of McGi11 UI1lVer~lty, II1dudlllg proteSl>OI!-.

and graduate students. They are ail willing to dlscu!-.s problems wlth me and proville

help in my need. Special thélnks are to Derek Dyck élnd Fayad Gilles who tranl>lilted

my thesis ahl>tract twm English into French.

Last, but not Iea~t, 1 should mention here the patience and underl>tandll1g 01

my wife and son. These are detïnitely important for a man, with his fa 1111 Iy, wh() are

seeking an academic goal.

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TABLE OF CONTENTS

ABSTRACT ................................................... i

RÉSUMÉ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. III

TABLE OF CONTENTS ........................................ IV

CIIAPTER 1 INTRODUCTION .................................. 1

1.1 Review of CAO Systems for Electrical Machine Design ......... 1

1.2 Analysis of Design Process for Electrical Machines ....... , . . . .. 4

1.3 Motivation of the Research and Outline of the Thesis .......... 6

CIIAPTER 2 KNOWLEDGE REPRESENTATION .................... 8

2.1 Classification of Knowledge in Electric Machine Design ......... 8

2.2 Frame-hased Knowledge Representation. . . . . . . . . . . . . . . . . . .. 10

2.3 Rule-hased Knowledge Representation. . . . . . . . . . . . . . . . . . . .. 13

2.3.1 R ules for Design Synthesis . . . . . . . . . . . . . . . . . . . . . . .. 13

2.3.2 Rules for Design Analysis ........................ 14

2.3.3 Rules for Design Formulas ....................... 17

2.4 Knowledge Base of ICADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18

2.5 Sunlnlary ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19

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CHAPTER 3 INFERENCE ENGINE ............................. . 2()

3.1 Forward Chaining for Design Synthesis and Analysis .......... . 21

3.2 Pattern Matching for the Forward Chaining ................ . ..,..,

3.2.1 Matching of the Antecedents of éI Rule ............. . .,..,

3.2.2 Checking ot the Consequent of a Rule .............. . .." _.'

3.3 Procedural Attachment ................................ . 24

3.4 Considerations of Efficiency ............................ .

3.5 Summary .......................................... . 27

CHAPTER 4 THE MANAGEMENT SYSTEM OF THE KNOWI..EDGE

BASE ................................................ 2:-:

4.1 Role Dt the Management System of Knowledge Base .......... 2:-:

4.1.1 Knowledge Acquisition . . . . . . . . . . . . . . . . . . . . . . . . .. 21)

4.1.2 Design Analysis ............................... 30

4.1.3 Knowledge Maintenance. . . . . . . . . . . . . . . . . . . . . . . .. JO

4.2 Structure ot the Management System .................... " JO

4.2.1 Text Edltor .................................. 30

4.2.2 The Gold Hill Windows System ................... 31

4.3 Irr.plementation of the Management System. . . . . . . . . . . . . . . .. 32

4.3.1 Main Windows for Intertace .................... " 32

4.3.2 Data Input .................................. 34

4.3.3 Design Analysis ............................... 3~

4.3.4 Output of Design Results ..JO

4.4 Summary ................ . 44

CHAPTER 5 INTERFACE BETWEEN SUBSYSTEMS ................ 45

5.1 The Need for Integrating the Numerical Analy!-.is with the Dc!.ign

System .......................................... 45

5.2 Tools for the Finite Element Analysi!-. . . . . . . . . . . . . . . . . . . . . .. 4(,

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5.2.1 Advantages of PC-based ICADS ................... 46

5.2.2 MagNet2D Package for Finite Element Analysis ....... 47

5.2.3 Interface between ICADS and MagNet2D ..... . . . . . .. 48

5.3 Generation ('ff Fmite Element Analysis Files ... . .. .......... 48

5.4 Design ModificatIon l'rom Finite Element Analysis ............ 49

5.5 Sl1Jllmary .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52

CIIAPTER 6 EXAMPLES OF DESIGN ........................... 53

6.1 Univers.al Motors .... . . . . . . . . . . . . . . . . . . . .. ........... 53

6.2 Design Automation of a Small OC Motor . . . . . . . . . . . . . . . . . .. 59

CIIAPTER 7 CONCLUSIONS ................................... 62

AI)I)ENDIX A SOME OF THE DESIGN FORMULAE FOR UNIVERSAL

M01'ORS .............................................. 64

{ APPENDIX B DEFJNED FUNCfIONS USED IN THE THESIS ......... 70

API)ENDIX C COMMAND MENU ITEMS OF MS " . . . . . . . . . . . . . . . .. 71

REFERENCES ............................................... 72

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CHAPTER 1 INTRODUCTION

This thesis is ahout the design of direct current (OC) machines using computer!'>.

Computer design systems for electrical machines will l1t' ftrst reviewed in tlm

mtroductory chapter and the ohjectlves ot this thesis resean:h Will he L1antied

afterwards.

1.1 Review of CAD Systems for Electrical Machine Design

According to conventional classification, electricalmachines include transformer!'>

and rotating machines. They t'orm the large~t suhset of e1ectrom;lgnetic dcvlcc~. They

generate, transmIt electric power and convert electric energy IIltn other klJlds llt

energy, for example, mechal11cal energy. With the advance (lI' technology in elel'trlcal

engineering, many new kinds of electrical machine!'> are heing invellted ;lI1d

developed. The design ot these machines IS the important !'>tage bctore developing

them. Over the years engl11eers have accumulated expencnce 111 thl! de!'>lgn procc!'>!'>

of these machines. MlIch more expef'ence b ~tlll net::dt>d to IInprove the alrc;ldy

constructed ones and to develop new form~ of devlcc.

With the advent of compllter~ and their apphcatl(ln~ Hl englllecnng d~,.,ign, the

mBnllal design proces!'> for electrical machine!'> has hecn revolutlol1lzed. Computer­

aided design (CAO) packages have been widely lI~ed and will play a more Important

role in the near future. The development of CAO for electncal machme!'> l'an he

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dlvlded into three ~tages.

1) At the tir~t stage the mélnllal design eftorts were replaced by digital computers

123]. According to the expertise nt the machine design expert the program designer

translated Cl ~et Clt design formulae into computer codes. The user of the se design

progfams ran them on the computer and ohtamed the design results. If the user felt

that the re~ult~ were not ~ati~tactory, he could change some of the parameters or

c.llmensions of the ùe~ign ohJect and fun the program again. This fixed sequence

woulù he repcated lIntil satisfactory results were ohtained.

2) The application ot nllll1erical methods m electromagnetlc fields hegan the

:-.econù stage ot CAO. The approximate machine moùel with magnetic circuits was

replaced hy mllch more accurate tmlte ditfefence or tïnite element analysis. These

n1l111cncal methoùs helped the machme ùesigner greatly. He coulù examine a

particular part ot the 1l1'lchine and predict the pertormance \Vith the results ohtained

by nUlllerical methoùs. Mlich work has heen dcme m thls aspect of CAO [16].

NUl11erical meth()(h are usually invoked after the InItiaI design has heen generated.

There eXlst ùiftlellities m puttll1g numerieal analysis m the design iterative loop at this

moment, not only hecause numerical analysls needs m('re computer stc;''1ge and

cOll1puting tlme, but also due tn the faet that usually numerieal analysis packages

need detéllied mput and relatively eomplex postprocessing for the results of analysis.

3) Wlth the advent ot artlflcial intelligence (AI) techniques the design process

entered éI new stage. The intelligent computer aided design system (ICADS),

lltherwise known as knowledge based systems or expert systems, have heen developed

and ,Ire still developll1g. The deSign ~ystem II1corporated wlth human intelligence is

LJulte dilterent tWill the conventional one. The expert's experience can be captured

as l'ully as possIble hy thl~ kmù nt design system. These systems work in a manner

similm to that of a human de~igner. The advantages of these newly developed design

systems are easy tu understand. We can give some of them helow.

(a) They can store dlfferent kinùs of knowledge, sorne of which are hard to

translate into a tradltlOnal computer program.

(h) The knowledge base may be irnproved and enlarged easily when necessary.

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(c)

This can be done without changing the integration of the system.

The infercnce engine can be forward chaining or hackward chaining to suit

the particular problem tn be solved.

(d) It is possihle to develop a general purpose system to deSIgn dilfercnt

domain-speciflc obJects.

(e) The liser of these systems is guided and not restricted in the design p\l)CL'S~

and he has the freedom to select a satistactory deSign himself.

(f) They can handle the uncertain or incomplete information encoulltcred in

the real world.

ICADS for electrical machines can be lIsed tn deSIgn ail kinds of machines.

Garrett and Jain reported a system for deslgning 1ransformers and II1ductors uS1l1g an

object-oriented environment [6). Freeman and Muko\era descnbed a system u~ing

Prolog to design OC machines [4]. Kaplan and Landy presented a diagno~tic

approach for the design ot 3-phase induction motors [Il J. 1t is abo posslhle to set up a system tn design ail types of electrical l11:1chlllL''i,

because usually the inference engine and the user interface are Împlcmented

generally. EDS (Electromagnetic Design System) is a knowledge-based system aimed

at the design of electromagnetic devices [20]. EDS al1nws the expert designer to mil!

tt.e corresponding information to fulfJl the deSIgn task of a speClllc kll1d ul maclune.

ICADS can be bllIlt by expert sy~tel11 development lOols or L1~lI1g AI l:lngLlage~

directly. When built by tools the performance of the sy~tell1 i~ atlected by the tool

used. The selection of a tool to develop an expert system IS \1ot ca~tly made,

especiaI1y for large systems.

Lisp and Prolog are the two mam AI languages comll1only used m ICADS. Some

authors incline tn lise Prolog tn implement electric machine design systems. Prolog

is designed for loglc programming. Its backtracking teature tacÎIÎtate~ the

implementatlon of the hackward chaining mechanism used in a rule-ba~ed expert

system.

Lisp remains the most widely used language tor AI programming. It al..' provldl!~

good facilities for

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t (a) manipulating Iists.

(h) pattern matching, both ta identify data and to determine control. S( a

forward-chaining inference engine is easily encoded using Lisp.

Whatever tools or computer languages are used to implement an IeADS for

electrical machines, the in-depth understanding of the design process is essential. The

following sections investigate the design process and describe the research motivation

ot this the sis.

1.2 Analysis of Design Process for Electrical Machines

Design is an art, an empirical and scientific work. The rules, formulae and

II1formation used in the design process are not, in general, as precise as in numerical

computation. A given design problem may have more than one solution. The

specifications of electric machines lIsually coyer such items as output power, speed,

voltage, torque, efficiency, etc. The final results of the design process must satisfy

these rC<.juirements without exceeding the permissible limits of cost, heating,

commutation, mechanical strength, noise, etc.

The design of electrical machines is a complex process. The designer should take

many factors inta account as mentioned above, also the knowledge involved in the

design process is very extensÎ\.e. Therefore, in any decision to be made the designer

needs to consider many different aspects. These requirements for design must be

satistïed in ICADS which assists the designer ta generate a machine which is reliable,

efficient, small in volume, and easy to maintain.

Usually the design process hegms WIth the specifications and technical

requirements provided by the cllstomer. These specifications and requirements

include:

(a) Power rating: the output mechanical power for motors or the output

electric power for generators.

(b) Voltage rating.

(c) Number of phases of the power supply and the connection of these phases.

(d) Speed rating or synchronous speed.

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(e) Power factor.

Besides, sorne specifie requirements may be given for different kind of machines.

In the design of OC machines the suhtasks involved can he olltlined in the

following.

(a) Selection and calculation of the electromagnetic pantmeters in the

machine, such as the current density in the windings, the tlux density in the

magnetic circuit, etc.

(b) Winding (field winding, armature winding and interpole winding) design

which inc1udes the selection of the type of winding conncctinn and the \Vire

gauge, determination of turns and calculation 01 resistanccs 01 thl'~l'

windings.

(c) Commlltator and hrll~h design. Design the structure ot the co 111 111 ulil tor.

Calculate and check the induccd electromagnetlc lorces (emls) in the

commutating coils.

(d) Design of the mechanical components of the machine. We l11ust decide the

dimensions of stator, rotor, poles, interpoles, slots, tee th, shah, etc.

(e) Calculation of losses, heating and temperature rise and the deSIgn 01 the

cooling system of the machine.

Cf) Design of insulators used in the machine.

(g) Calculation of materials consumed and the cost for these matcrials.

These subtasks cannot be fulfilled separately. Usually we must procecd with

several subtasks simultaneously.

The above mentioned design subtasks can be c1assified into the eIectrol11agnetlC

design process and the mechanical design process (It is not mtended tu lIH.:luded the

mechanical analysis and thermal analysis in the mechanical design process in thi~

thesis because of their complexity). The former is more complicated than the latter

in that it is based on the electromagnetic theory. So the emphasis will he on the

electromagnetic design process.

Even incorporated with human intelligence, the design process is still an iterativc

process. To automate this process as fully as pOSSIble we can divide it into thc

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,\yllllze,\'L\' process and the aflalysL~ process. The synthesis process constructs design

alternatives from the given specifications while the analysis process evaluates the

proÙllcts of synthesis. The analysis process may use diagnosis rules and/or numerical

analy~is programs.

It is usually impossible to obtain a complete design by the synthe sis process only.

On the other hand, the pure diagnosis approach is not quite effective because of the

large design space. Only the combination of these two processes can provide a design

routine similar to that taken by an expert designer.

1.3 Motivation of the Research and OutHoe of the Thesis

Based on the discussion in section 1.1 and 1.2 wc may conclude that a CAO

system for electrical machine design should be intelligent, interactive and integrated.

The main components of such a system include:

1) An effective and efficient inference engine capable of decision making and

problem solving.

2) A knowledge base including ail information concerning machine design. This

knowledge should be structured and reasonably c1assified.

3) An interactive knowledge management system for knowledge acquisition, man­

machine communication, design document preparation and so on.

4) Integration of the intelligf!nt design system with other CAD software for

machine design.

The objective of this thesis research is to set up an ICADS for DC machines

(ICAOS stands for this system l'rom now on) with the above mentioned features.

Becallse this system is intended to be accepted by industry for machine manllfacturing

\\-hen neces~ary, it is implemented on a microcomputer for its prototype.

The thesis begins with the review of CAD in electrical machines and motivates

the need for research in this area from the analysis of the design pro~ess in the

present chapter.

Chapter 2 classifies the knowledge in machine design and represents it with the

framc-based and rllie-based structures. It is very natural using the hierarchical

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organization of frames ta represent the physical structures, dimensions anù

parameters of the machine. It is pointed out that rules are capable of perforl11ing

both design synthesis and design analysis and handling the design formulac

encountered in the design process.

Chapter 3 explores the construction of the inference engine of leADS. Thl'

pattern matching technique and forward chaining approach are employed here. It

is shawn that the response time of the system can be shortencd hy cflÎL'Il'nt

programming in the construction of the inference mechanisl11.

Chapter 4 describes the knowledge management system for the construction ot,

and access to, the knowledge hase for machine design. The window implclllentation

of this system provides a friendly user interface in knowledge acquisitIon, knowledge

maintenance, design analysis and output of design reslllts.

Chapter 5 is dedicated to the interface hetween thc dcslgn sy~tem and the

numerical analysis package. The interface with MagNet2D working on a Unix system

is considered here. The results of field analysis in universal motors are "Iso givcn in

this chapter.

Chapter 6 presents design examples using ICADS for OC machincs. These

examples include a senes of lIniversal motors and a small OC ll1otor.

The conclusions of the thesis research and the suggestions of the further work arc

presented in Chapter 7.

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CIIAPTER 2 KNOWLEDGE REPRESENTATION

Intelligent CAO Systems represent a new programming approach and

methodology that differ from conventional design programs in the structure of the

software. The separation between declarativ(~ and procedural knowledge is explicit

in the intelligent systems. The implementation of such a system needs the

classification and representation of the design knowledge and they become the key

Issue for an efficient design system.

2.1 Classification of Knowledge in Electric Machine Design

The design abjects, OC machines here , are very complicated. From the structural

point of view they are camposed of many components. Every component possesses

dimensions and different properties. For example, ta de scribe the stator winding of

a OC machine it is necessary tn specify the number of turns, the wire gauge used, its

resistance, etc. This hierarchical and interrelated property of the knowledge

representing the design abjects makes their representation become complex. Besides,

the knowledge representing design expertise which provides directional control for

the design process is even mure difficult to acquire and represent. We can classify

knowledge about design into three categories:

(a) Structural knowledge about the machine, e.g. the selection of the type of

excitation in stator winding and the number of stator poles of a De

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machine, etc.

(h) Knowledge relating the dimensions, machine parameters and performance.

It is often expressed by mathematical equations, e.g.

where

R2: Resistance of rotor winding.

N,: Total number of conductors in rotor winding.

12: Mean length of a rotor conductor.

S2: Cross-sectional area of the conductors.

(c) The designer's expertise that is used to provide directional control lor the

design process. This type of knowledge IS the most ahstract kmd 01

knowledge. For example, when the calculated efticiency IS not satislactory

we can change the wire gauge, provldlOg there is space aV<lllahle in the

slots and interpole area, or we could increase the Icngth of the iWIl core

if the space is too small to increase the wire gauge.

There are several approaches to represent knowledge. Each ditferent kll1d ni

knowledge can he represented by a different approach. In general the dec1arative

representation and the procedural representatlon are the twu arproache~ l11o~t widely

used in Al.

In declarative representation the knowledge is represented by a ~tatic collection

of data. These data tell us "what" an abject is by giving descriptions of its properties,

rather than "how" these abjects af!! interrelated by giving algorJthl11~ or

methodologies.

In procedural representation the knowledge is represented hy the

interrelationship of data using algorithms or methodologies. These algorithms or

methodologies tell us "how" an object intluences its environment, rather than "what"

that abject is by glving descriptions of its propertie~.

ICADS for electric machines requires the use of the two knowlcdge

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t representatlon approaches described above. The structural and dimensional

knowledge are represented hy frames. Production rules can be used ta represent the

de~igner's expertise tn control the design process.

2.2 Frame-based Knnwledge Representati1tO

A frame b a data structure used to represent a complex object or a c\ass of

()hJect~. The trame-hased representation is a technique for representing structured

knowledge; it uses slots to describe the different attributes an abject of that frame's

type may have.

Frames are suitahle for representing electrical machines. We can set up the

trames acconJing to the physical structure of the machine directly. The information

ahout an obJect obtained from different pomts of view can be kept in different slots

as slot values under the same frame. In this way frames contain information about

many aspects of the ohjects or situations that they describe.

From the structural point of view the machine is composed of many components,

such as the stator, the rotor, the windings, the commutator, etc., for a DC machine

(Figure 2.1). Each component can be descrihed hy its dimensions and properties

specific to it. The following are sa me frames relating ta the structure of a universal

1110tor.

dim-s/ator Dl (value): outer diameter of stator core.

dimas/a/or L (value): length of core.

dim-Sla/Or D12 (value): inner diameter of core.

dim-sla/Or Ile 1 (value): height of stator yoke.

dim-slator hps (value): width of pales.

dimas/a/or rf (value): pole enclosure.

elim-s/a/or IIp (valLle): height of pales.

dim-sta/Or /llO (value): pole pitch.

(.'i111-slalOr 1l100 (mille): pole arc.

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Machines

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Dimensions

Figure 2.1 structure of DC machines

dim-rolor D2 (value): outer diameter of rotor core.

dim-rolOr s (value): length of air gap.

dim-rolOr D22 (value): iJII;cr diameter of rotor core.

dim-rolor Z (value): number of tee th.

dim-rolor lze2 (value): height of rotor yoke.

dim-rolor kdlt (value): Carter coefficient.

wùzdùzg-stator Wl (value): turns per pole.

wùzdùzg-stator Sl (value): cross-section area of wire.

windùlg-slalOr ddl (value): dlameter of bare wlre.

wbzdùzg-stalor III (value): number of wires in parallel.

windùzg-stator W3 (value): number of turns per layer.

windùzg-stalOr Lm (value): length of coils.

windùzg-stator am (value): width of coils.

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wbldillg-stator hm (value): thickness of eoits.

willdblg-stator H3 (value): height of coils.

windÎllg-staior RI (value):

wÙldillg-rotor Nr (value):

willdillg-rolor Ns (value):

wùulùlg-rolor S2 (value):

wil/dillg-roJor R2 (value):

wbulillg-rotor W2 (value):

willdillg-roJor ys (value):

wbuiillg-roJor kp (value):

dim-commWator K (value):

resistance.

total number of conduetors.

number of eonduetors per slot.

cross-sectional area of wire.

resistance.

turns per coil of rotor winding.

coil pitch.

coefficient of coil pitch.

number of commutator bars.

dim-commWator De (value): diameter of commutator.

dim-commlllalOr hh (value): width of brushes.

dim-commU/alOr bll (value): degrees of brush shift angle.

dim-commWalOr le (value): piteh of commutator bars.

Each line above consists of the frame name and the slot name folJowed by the

slot value. In this way structural information concerning the machine is mapped

directly onto the frames.

ln additIOn, there are frames representing the electric and magnetic loads of the

machine, such as current density in the windings and flux density in magnetie

components; anù frames about the performance of the machine such as lasses of the

machine. The following is the trame describing the machine ratings.

ratil/g P (value):

ralblg V (vaille):

ral;'lg Il (l'allie):

rat;'lg f (value):

output power of the machine.

voltage.

speed.

frequency of the power supply.

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ratÎllg el (value):

roting pf (value):

ratillg Pin (value):

ratÎllg M (value):

rarillg 1 (value):

efficiency of the machine.

power factor.

input power.

output torque.

current rating.

2.3 Rule-based Knnwledge Representation

The knowledge structure represented hy production rules IS lIuite mmlul:1I and

stylized. Each rule consists ot antecedents and one or more conc\maons. Th~ tmm lit

a rule is simple. But how the knowledge pertaining to machine design is cncapslliated

is still worthwhile discussing.

2.3.1 Rules for Design Synthesis

Usually a design begins with the synthesis procedure. In this procedure the

designer takes a\l relevant aspects into account to prodllce él preliminary object tn hl'

designed. These aspect~ include machIne specitication~, machllle pertormalll'e

requested hy the customer, constraints that must he met concerning eIectnc machl\ll:

the ory, etc. AIl of these aspect~ must be considered carefully hy the designer

Inwrporating his experience In machine design.

Structural knowledge ahout the machine i~ the knowledgc olten cncollntercd III

design synthesls. Take a OC machIne as an example. The nU1l1her ot :-.tator pole:-. ilnd

the type of stator excItation must he decided at the start of the design prm:e~~.

Selection ot the numher ot poles:

As we know, there is no fixed relationship hetween the number of pole~ allu the

speed of the machme. When the tlux denslty in the élir gap and the diameter ot the

stator core remain constant, increasing the number of p()le~ rc~ults 111 the decrea~c

of the pole pitch and the tlux per pole, and hence the amount of materi:1I (mlll :tnd

copper) used because of the decrease in the cro~s sectIon area ot the stator y()ke and

the pole pitch. Meanwhile the alternating freguency in the rotor wIll lIlcrca~c é1~ wIll

the iron lasses. Usually the number of poles depends on the diameter ot the stator

13

t

l

core ~elected. When the diameter of the core is less than 12 cm, a two pole machine

I~ selected.

Selection of types of field windings:

(a) Shunt motors. Shunt-wound motors have the field connected in shunt with

the armature and have essentially constant-speed characteristics.

(h) Series motors. Series-wound motors have the field connected in series with

the armature and have the varying speed characteristics.

(c) Compound motor~. Compound-wound motors employ both a series and a

shunt field and have speed charactenstics intermedlate between those of

shunt and series Illotors depending upon the amount of the compoundirag.

(d) Permanent magnet motors. Permanent magnet motors have no field

windings. A permanent magnet mate rial is used in the field structure to set

up the required tlux. The speed-torque curve of this type of motor is

generally a straight line.

2.3.2 Rules for DeSIgn Analysis

There will he many specIfications and constraints to he met in the design process.

These specifications and constraints may be explicit or implicit [14]. It is impossible

that ail of them are satisfied in the first procedure of design synthe sis. The refore ,

once a preliminary design has been created, a design analysis procedure should he

tollowed to verify and evaluate ail aspects of the initial design. A set of checking rules

IS responslble for this task.

Typlcal checkmg rules for design analysis are:

1) To check If the computed voltage of the machine coincides with the voltage

rating or not, we can use the followmg rules.

(tlefrlliel (RIOI (?a ERRV lx) (> ?x I)

((V-too-high))) )

(tlefrlllel (RJ02 (?a ERRV ?x) « ?x-1)

( (V-too-low ))) )

14

I~ ,

1

Here clefrlliel is a function 10 store the rules in the data hase of rule sets. Wc

céln identify a rule by its name ( e.g. R101, RJO] in the abllve rules ) with its

antecedents and consequent l'ollowed. If ERRV, Ihe voltage V:IlIilIIOn \Vith

respect to the voltage rating, excced!> the limit ( herc 1 pl'r cent ), the

con!>equent V-Ioo-high and V-lOiI low whlch are alsn defmcd l'unctions will gl\'l'

actions during the tinng of these rule~.

2) To check if the error of etflciency ot the designed machine exceeds tllL'

tolerance, e.g. 1 per cent, the following rules are invoked.

(elefrulel (RI03 (?(I ERRer ?x) (> ?\ 1)

(?h ERRV0') « (ah.\'0') 1)

( ( ef-Ioo-h igh» ) )

(llefrulel (R104 (?a ERRer ?x) « ?x -1)

(?h ERRV :~}') « (ah.\' :y) 1)

( (ef-Ioo-/o..,»»

Becallse the conditions that the absolllte value of ERRV is less than 1 arc

included in the antecedent~, the voltage equatlon must be sllti~tïed bctore the :lb()ve

rules can be executed.

If a contllct hetween the de~lgn re~ult~ anù specll'ication~ or col1~tralnb I!>

detecled, a wmning can he issued by the ~ystem. The designer can change ~()mc

dimensions or parameters of the machine accordlllg 10 the ~lIggestl()ll~ glven by the

system to resoJve the contlict.

ICADS is alsa capable of handJmg the modification of the de~ign rC~lIll~

automatically. In the design process bOlh the voltaf:,é error and the elllciency l'rrm

are set to he Jess than 0.01 (i.e. 1%). If ally error IS grcater than 0.01, Itl'ratl()n~ will

take place.

When the calculated voltage V' exceeds the error limit:

(a) Ca\culate the step of change in potential E

v'-v 6.E=--3

15

{

(

(h) Set the new potential

E=E-ll.E

(c) Re-design.

This method is always effective. For example, if V' is greater than the rated value

V we redllcc E. The results of changing E can he shown as following:

where

f/>: Main tlllX in the machine.

AT: Tutal Ampere-tllrns needed.

HI,: TlIrns of the stator winding.

R,: Resistance of the stator winding.

IR,: Voltage drop in R,.

The rule to tulfi1 the above has the following form:

(defrllie (R25 (?a ERRv ?x) (?a V':y) (?b V?z)

(?c E ?x1) (> (abs ?x) 1)

((?c de/lE (setf deitE (1 (- !Y ?z) 3)))

(?c E (- ?xI deitE)))))

When the calculated efficiency 11' exceeds the limit there are severa] ways to settle

this problem.

(:1) If the space m mterpole area or slots is available, increase the cross-section

of the stator \VIre or rotor condllctors. Sa

where

Rz: Resistance of the rotor winding.

IZR,: Copper loss in R,.

FRz: Copper loss in Rl'

(b) lncrease the number of conductors N in the rotor.

( 16

1

1

" ~

Nt -cp l-flux-densities l -iron-losses 1-11' f

(c) Increase the length of the core 1.

1 f =1lux-densities l-iron -losses 1 =>T1' t

2.3.3 Rules for Design Formulae

There are many formulae and equations encountered in the design proœss. They

express the knowledge relating the dimenslOns, parameters and pertornlélllCé ot the

machine. They appear everywhere in the design pr()ces~ and 11111~t be calclliated or

solved immediately once they are encountered for the proper propagation of the

design process. Rules for these formulae and equatlOns are data-dnven.

In a design formula once the parameters III the right sidc of the tormula have

been determined the parameter in the left slde can he calculated. For the l'ollowing

formula to calculate the resistance of the rotor winding

the rule that can be invoked is like thls:

(defrule (R7 (?a Nr ?x) (?h 12 ?y) (?c S2 ?z)

((?a R2 (J (* 5.35 ?x ry 1.()e-5) ?z»»)

After the above rule is triggered, the value of the resi·,tance ot the rotor wimllllg I!'!

stored in slot R2.

For a specifie equation one variable is left to be determined hut It I!'! not

necessary to state which one it is.

The following equation relates the output power P with the output torquc M élml

the speed of the machine Il.

17

p= 2nMn ><9.8 60x1oo

These are the rules tn handle this equation:

(lle/rule (R1 (?1I P ?x) (?an :;y) ((?a M {/ (* 60 100 ?x) :;y 2 3.14 9.8»)))

(de/rule (R1a (?a M lx) (?a Il ?Y)

(('la P (1 (* 23.149.8 ?x :;y) 60100)))

When P and Il are given rule R1 will be triggered. If AI and Il are given ru le R1a will

he triggered.

2.4 Knowledge Base of JeADS

The knowledge base of the system holds aIl of the knawledge relating ta machine

design. ft is necessary to store the different kinds of knowledge in different parts of

the knowledge base. The separation of the knowledge base is essential for the

inkrence engine to access this knowledge efficiently. The reason will be c1arified in

more detail in the next chapter.

Facts relating the structure, dimensions, parameters and performance of the

mélchine are stored in the data base * Assertions*. Assertions are the fundamental way

that these facts are represented in ICADS. They are entered in the knowledge base

by defil1lng assertions and the firing of rules.

Rules for design synthesis are stored in the database *Rules* while those for

design analysis are stored in *Rulesl *.

Many curves and tables, such as B-H curves and wire tables are involved in

machine design. They must be entered into the knowledge base. Those curves which

ca n he expressed by equations should be treated in this way as far as possible. Those

curves which can't he treated with equatiJns must be converted into tables first. Then

we can define assertions to store tables.

B-H curves are stored in the databases *Bhcurvel *, *Bhcurve2*, etc. and the wire

table is stored in *Wire-table*. For a point in the B-H curve, a simple assertion, such

18

1 as ( bill 40001.06 ), is enough. Here the symbol hlll reprcsents the B-H curve 1; the

value of B at this point is 4000 (gauss) and the corresponding value of H is 1.06

(ampere/cm). Ta find the H value accurately for a given B value we prctà to define

assertions with pairs of points, e.g. ( Ml 4000 4100 l'()6 l'()8 ). For any 8 hetwecll

4000 (gauss) and 4100 (gauss) we can get the nearest H values, 1.06 (amperc/cm) and

1.08 (ampere/cm) through pattern matching in the firing of the rule, and calculatc the

exact H value carresponding the given B value through interpolation aftcrwards. The

same rule applies to the representation of wire tables.

2.5 Summary

To capture the knowledge about machine design needs diverse techniques of

representing knowledge. Frames and production rules as described in this chaptcr an,'

suitable. The construction and the need to partition the knowledge base in leADS

are also discussed here briefly. The integration of these knowledge representation

techniques with inference mechanism will be discussed in the next chapter (Chapter

3).

19

1

CIIAPTER 3 INFERENCE ENGINE

The inference mechanism is the core of the system with the responsibility for the

overall design strategy and updating of data. Its effectiveness and efficiency are vital

tn the who le design system. hs function incIudes

(a) Transfer of the knowledge represented by frames, slots and rules ta the

knowledge base.

(b) Forward chaining of rules ta update data in the process of design synthesis

through pattern matching.

(c) Inference using checking ru les in design analysis.

(d) Provision of the t\ser interface for the finding, editing and deletion of

assertions and rules through pattern matching.

Tu transfer data into the knowledge base we use the fol1owing define-functions:

Define-assertions: Faet (assertion) and Facts (assertions);

Define-rule: Defrule (rule) and De/rulel (rule).

Foel, Fact.'!, Defrule and Defrillel are macro procedures. Defru/el is used to define

checking rules for design analysis.

Fiml-fact and De/ete-faCI are procedures for finding and deleting an assertion from

the knowledge hase. Find-siot-vaille is used to find the slot value when the fraInt; and

sint are known.

20

-, 1

1

" '. .,

t-'i-

.. f. t r,

1

Before describing the mechanism of forward chaining the reason why it can he

used for bath design synthesis and design analysis will he given hcIow.

3.1 Forward Chaining for Design Synthesis and Analysis

Forward chaining is a problem-solving approach that uses rules 10 determine \Vhat

can be concluded from the given data. We can use forward chaining tn infer ail

possihle solutions from a givtn set of assertions in the data hase. Whcn olle mie fm:s

it creates assertions that are matched to the anlecedents nt olher lorward l'hallllllg

rules, the system can then fire these mies, creating more assertions and initiating

further forward chaining. The system forward chains until there are no more forward

rules whose antecedents match assertions in the assertion base.

Il is obvious that the forward chaining technique can l'le usd ln infer a deSIgn

alternative without difficulty. For example, in the design of smallunivcrsal \1101ors the

fol1owing rule may be employed:

IF Output power less thnn 1 kw

THEN Number of main poles equals 2

and

No commutating poles added.

Forward chaining is straightforward, but how far can it reach in the deSIgn spaœ?

The answer depends on the expression of the production rules used. 1 n the fol\owlIlg

rule the cause of an action and the result is in a normal direction:

IF The length of the core of the machine is II1creased

THEN The tlux densities in the core will decrease

Ta analyze a present design the above rule can he rewriuen as follows after the

flux densities are detected to be too high:

IF Flux densities in the core are too high

THEN Increase the length of the core

Usually the causes of a certain result are diverse, especially in machine de~ign.

For example, many ways are involved ta improve the efficiency of a machine. 1 n this

case the system may give an overall consideration or aralyze the cause one hy onc

21

c

(

and thcn give the right one to rectify the undesirable result.

3.2 Pattern Matching for the Fm'ward Chaining

Pattern matching is an important procedure for the forward chaining inference

mechanism. Il compares symbolic patterns and data element by element and keeps

variable hinding on an association list. Matching is easily implemented by a recursive

procedure using Lisp r25].

ln the frame-ha!'ed representation of knowledge, after a fuie is fired and a new

value qf a sint generated the old value is replaced immediately. If a slot is newly

instantiated it is added ta the data base. As soon as one of the ab ove situations

occurs the cngine checks the antecedents of the previous rules to see if any of them

will he fired or nnt. During the running of the program any change of a slot value will

callse those fuies whlch have the changed slot value in their antecedents ta fire again.

ln this way the program will proceed automatlcally until the desirable goals are met.

3.2.1 Matching of the Antecedents of a Rule

To see if the antecedents of a rule match the assertions in the data base we use

the malch procedure. Match returns a binding list of the variables in the antecedents

when the patterns of the antecedents are aIl successfuIly matched. Otherwise it

returns fai!.

Predicates, such as >, <, zerop, are relational functions in Lisp. They can be used

in the antecedents of a rule. The following is a checking rule using predicates in its

antecedents.

(cie/miel (RIOO (?a ERRV ?x) « (abs ?x) 1)

(?b ERRpf ?y) « (abs ry) 1)

(?c ERRe! ?z) « (abs ?z) 1)

( ( design-filli.\'''))))

The malch will return fai! for its antecedents if it is not designed to handle the

"Iess than" symhol "<", because these assertions with < are not stored in the data

I:'Illse. In this case the inference engine l'irst instantiates the variables in the predicate

22

-

expressions \Vith pattern bindings and then evaluates the predicates. If the results of

evaluation is 1 the match procedure is still successful.

3.2.2 Checking of the Consequent of a Rule

After a rule has been fired and the variables in the then-part of the mie

instantiated it should be decided how tn modity the data hase.

(a) If the consequent of the rule involves a new frame or a new slot of an nid

frame the consequent can be added to the data hase directly.

(b) If the consequent of the rule involves the change of the value ot an okl

slot we should change this value irnmediately.

(c) Nothing is do ne otherwise.

In cases (a) and (b), new facts come up or a slot value is changed. It they Ilwtch

any of the previous rules the forward chaining should repeat again. It can be flllfilled

using a recursive procedure.

The procedure to app)y ail rules in database *Rules'" using fllnction Il.\·e-rule is

like this:

( deflm forward-chain ()

(do ((mie-stream *mles* (stream-rest rule-stream)))

((stream-elldp mIe-stream)

(progll

(format l ,,- %Elld of the nt/es. ")))

(wlzen (use-rule (stream-first ntle-stream) rule-stream)

(forward-chainJ (stream-rest mie-stream)))))

When case (a) or (b) occurs functlOn use-rule retllrns 1 and the following tllnction

forward-chainl is called.

(deflm forward-chaillJ (nt les)

(do ((mie-stream *ntles* (stream-rest mie-stream)))

((eq ntle-slream ntles)

(formaI t Il - %lteratioll elld. "))

23

(

t

(wlzell (use-rule (stream-first mie-stream) mie-stream)

(foTWard-chainl (stream-rest rule-stream»)))

The difference betweenforward-chain andforward-chailll lies in that the former

applies ail of the rules in data base *Rules* during its running while the latter will

stop at the rule when use-rule in f()rward-chai" returns t. The recursive property of

tlll1ctionfiJrward-chaill1 assures that once a piece of data in the data base is changed

ail relevant data will be updated immediately.

Here is an example. After the Iinear current density A is selected, the total

1111mber of tllrns in the rotor winding, N" can be calculated by equation

21tD~ N,

1

where

Dl.: Diameter of the rotor core.

1: Current rating of the machine.

The tllrns per coil of rotor winding is

where

K: N umber of commutator bars.

(3.1)

(3.2)

Because W,l must be rounded ta an integer, Nr is re-computed using (3.2). Once

Nr is finally decided, the value of Iinear current density A should be changed

according to equation 3.1. This is done by the inference engine automatically.

3.3 Proccdural Attachment

In the design process bath the declarative and the proœdural knowledge are

involved at the same time. For examp]e, once the current density in the winding is

determined a formula ta ca1culate the cross-sectional area of the wire used follows.

24

1

l

Then the wire gauge is selected. A specially designed inference engine is needed 10

handle this kind of knowledge. In other words, the infcrence engine must he capahle

of the generation of the symhohc and quantitative values in the slots of framcs. A

technique calkd procedural attachment can he used herc.

Frames are the data structure used to represent the dcclarative knowlcdgc.

Frames have the problem that there is no conventional way to reason \Vith them as

there is with ru les. Procedural attachment is a techl11<.)ue which comhines proccdure~

with the data structure. The association of procedures \VIth trames elliarges the

application range of the rule-based systems. The inferencc cnginc must he capahle

of handling this association. The slot value of a frame can he a Lisp expression 01 a

procedure. The inference engine evaluates this expression or procedure and I1l1s the

slot with the result of evaluation.

The fillillg of the slot which has a procedure attached to it can he executcd

through the fmng of the rule. For example, the following ru le is involved in the

ca\culation of the cross-sectional area of the wlre for the rotor winding:

(defrule (R3 (?a 1 ?x) (?h .\'2 ?y)

((wÎ1zdillg-rotor S 2 (area ?x ?y)))))

Here area is a function ta calculate S2' the cross-sectional area of the wire, l'rom

the current 1 and the current density S2:

(defull area ( x y )

(/xy2))

This evaluate-and-fill mechanism of the inference engme also facilitates the design

analysis. The following checking rule has a procedure V-t(}(}-";g" as its consequent:

(defrulel (Rl01 (?a ERRV ?x) (> ?x 1)

( (V-lo(}-hig"))))

When the percentage difference between the rating and the actual value of the

machine voltage exceeds the Iimit ( e.g. 1 % ) the procedure V-too-";g" will he

executed and the methods of remedy will he given.

25

1

1

{

3.4 Considerations of Efficiency

The etficiency of an inference engine is important for an expert system running

on mlcrocomputers. Forward chaining is a data-driven approach; its mechanism is

simple and can he used to provide ail solutions to a given problem. The disadvantage

of the data-driven approach is that the hehaviour of the system can be inefficient. It

may proceed hlindly to execute the rules unrelated ta the current problem being

solved.

To avoid the aimless and time-consuming reasoning the following function match­

or-no/ is executed every time after the data base has been modified.

(de(wz match-or-not (patterns assertion)

(do ((patterns pallerns (rest pal/ems))

(matclz-switclz nit))

((elldp patterns) match-switclz)

(ull/ess (eq '[ail (match (first pallems) assertion))

(setf matclz-switclz t))))

This function will return t if and only if the match procedure between the patterns,

i.e. the if-part of the rule, and the newly added assertion is successfully executed. If

and unly if match-or-not returns t can the forward chaining start once more.

The match procedure can also be time-consuming. For a given pattern ail the

assertions in the data base must be tested. The separation of the different kinds of

knowledge in the data hase can be used to facilitate the match procedure, i.e. before

matching, search for the appropriate part of data base and then try to match the

assertions in this part of data hase. In the following patterns in Table 3.1 the first

element indicates the corresponding part of data base.

Table 3.1 Knowledge base of JeADS

Pattern Knowledge Base Knowledge Type

26

l

(BHI ?xl ?yI) *BHCURVEl* B-H Curve No. 1

(BH2 '!x2 ?y2) *BHCURVE2* B-H Curve No.2

(BH3 ?z ?x3 ?y3) *BHCURVE3* B-H Curve NO.3

(W ?xI ?x2 ?yl ?y2) *WIRE-TABLE* Tahle of wire gauge

Other * ASSERTIONS* Other

The separation of the rules for design synthe sis from the rules for design analysls

also serves the purpose of raising the eftïciency of the inferencc enginc. In the

process of design synthesis rules in data base *Rules* are involved while 111 de~ign

analysis rules in *Rulesl* are invoked.

3.5 Summary

The choice of an inference mechanism depends on several considerations. The

selected programming language, the structure of the knowledge, the specifie prohlem

to be solved and the efficiency that can be achieved are within these considerations.

As shawn in this chapter the forward chaining technique accord~ with the

selection of Lisp language and is capable of perforrning both design synthesis and

analysis for electric machines. The coupling of the declarative knowledge and the

procedural knowledge in the design process can be télckled with procedural

attachrnent.

The processing speed of the inference engine should he of concern for cxpert

systems implemented on microcomputers. Several techniques have heen prcsclltcd

in this chapter to raise the efficiency. Here are sorne of them:

The search strate,gy can save processing time in the matching ot data with

patterns.

The different kind of knowledge should be stored in a different part of the data

base to avoid aimless forward chaining.

27

(

(

(

CIIAPTER 4 mE MANAGEMENT SYSTEM OF THE

KNOWLEDGE BASE

The knowledge base of ICADS for machine design is a collection of aIl kinds of

kllowledge concerning machine design. It is evident that we need a tool to manage

this data base. This tool is known as " the management system (MS) of the

kllowledge base ". The MS is an important part in ICADS. It provides a tool for

kllowledge acquisition, knowledge representation, knowledge maintenance and man­

machine communication. In this chapter we '11 discuss the role and the structure of MS

tïrst and then de scribe the implementation of MS .

.... 1 Rote uf the Management System of Koowledge Base

Before we can understand the raIe of MS tet's examine the relationship of the

components in an expert system. The compone'1ts of an expert system inc1uding the

liser (here the designer of the electric machine) and the output of the system (design

documents) are Iisted in the following:

(a) Designer.

(b) System editor.

(c) Knowledge base.

(d) Inference engine.

Ce) Design documents.

28

J The relationship of these components CHn he iIIustrated in Figure 4.1.

1 1 - , ~1 \' ,t t' BI r II 1 t l' t

1 t

1 -- -- - -- L 1 } li II 'vi 1 l' li q t~ l ~ ,1 .-, t-'

l------------l i ,." .. ",". 1

- --1 "'It' rA l, 1. ~ l' t "Ii "1 1 1" Il rI,", Oc l g n 0:= l __ _ _ _ _

--l r 1 ct ID Cl " \ Il,1 1,1.1 1 ,-. <;

::'lot.s rlhClllt

II a. ch 1 n f' " l _____________ _

I---t----- --------- - Lt -- --IllLetenl co L:llqlnt->

---------~- - - -- -- - - - - -

Fiqure 4.1 Relationship between components of an expert system

Ali the information needed for machine design can be entered tn the knnwledgL'

base by MS and/or throllgh the editor provlded by the system. MS I~ abll re~plll1Slbk

for the maintenance of the knowledge ba~e, such as the hnding, additIon or ddetioll

of a fact using fllnctions provided hy the interence engme. The request 10 load, save

or output the design results must also be managed hy MS.

4.1.1 Knowledge Acquisition

In general the knowledge acquisition proce~s mvolves several steps.

(a) Interviewing the expert in machme design and extractmg of the uomalll

specifie knowledge.

(b) Representing the knowledge using the appropriate ïcprcscntation mcthod.

(c) Entering the knowledge into the data base.

For the problem of OC machine design frames, si ob élnd production rules arc ail

prepared using the methods de:;crihed in chapter 2. They are rcady to he entcreu IIlI!)

the knowledge base. An editor is usually provided in the Lisp environmcnt. III

29

{

G()ldWork~ it is the G MACS editor, an EMACS-like editor. A large portion of

knowleùge can he entereù into the knowledge base via edited files ta save time. This

portion of knowledge II1clude~ B-H curves, wire tables and even production rules, etc.

The machine ~peciticati()ns and other data specified hy the system user are

u .... llétlly entered hy the user. MS should provide a user friendly interface ta input

t Ile~e data. MS abo provldes guidance for the selection of these data, e.g. give a

range for the dil11en~lon of stator punehing, recommend the numher of slots in the

rotor, etc. ft the detalled reasons for this selection are given by the system it can

certainly play a role as a tutor of DC machine design. When the user does not give

tlle selection the system assigns a default value.

4.1.2 Design Analy~is

1 n de~ign analysi~ the inference engine analyses the preliminary design results.

The lIn~atlsfied constraints will he found. At this stage MS gives instructions ta the

liser on how to Improve the preliminary design.

.... 1.3 Knowledge Maintenance

The knowledge hase 01 ICADS is a huge collection of ail the information relevant

tu maclline design. MS IS responsible for finding, adding, altering or deleting any of

the information stored in the knowledge base. At the same time MS keeps the truck

of ail the added, altered m deleted information for the reference of the system user.

-4.2 Structure "f the Management Sys(em

Berme the aetllal implementation of MS the components required In its

construction should be introduced.

-+.2.1 Text Edltor

GllldWorks provides the GMACS text editor for the user to edit a Lisp file or a

data file. G MACS is a lull-teatured screen display editor modeled after EMACS. It

has many text editll1g and LISp editing features, su ch as:

30

1 * Transpose characters, words, lines, and regions.

* Exit to a Lisp hstener and re-enter GMACS without disturl1ing the currcllt

environment.

For example, tn enter the data of a B-H curve wc CHn simply edit the following:

(fact.\' (

(bILl 4000 (J. 7(0)

(blzl 4100 0.716)

(bill 4200 (J.732)

(bl! 1 1900055.30)))

Here facts is the function to store its pélrameters in the knowledge hase. After the

loading of this file the data about B-H curve 1 will he entered into the know\edgc

base automatically.

Similarly, the following file can be edited to store the data ot a wire table:

(facto\' (

(w 0.15 O.I6 0.180.20)

(w 0.16 (J.I7 0.20 (J.2I)

(w 0.95 1.04 1.00 1.11)))

4.2.2 The Gold Hill Windows System

The Gold Hill Windows System (GHW) provided by GoldWorks enables LI!'>p

programmers to develop window-based applications that can he ported easily t'rom

one host window system to another. It can provide ICADS a flexible and friendly

interface with the machine designer. The tollowing items in G HW are lIsed in the

construction of MS.

31

(

1[ ...

Make-windnw. This is a function to create a window and define its parameters

élnd attributcs. After a window is created text can be drawn on, or output to it (using

the formai primitive in Lisp). Command menus and hotspots attached ta this window

can also be defined.

Cnmmand Menus. Command menus are fixed menus that appear at the top Dt

a window. Each menu can be detined to have a number of menu items which are in

turn dctined tn invoke Cl particular action or operation when selected. Make­

commlilld-mellu and make-commmzd-mellu-item are functions to create a menu and

its items.

Hntspots. Hotspots are rectangular regions on the canvas of a window that are

:-.e nsitive to mouse input. When a mOllse button is clicked while the mouse is over a

hotspot, a particular method is called. Hotspots are used to create user interfaces that

rc Iy on l110use input, e.g. mouse-activated icons or menus. Once a hotspot is created

li method can be defmed to invoke the desired operation.

Methods. In GHW methods are used to perform operations on windows. For

cxample the metllOd 111011se-le{l-dOlvll can be defined to respond the mouse action

()ver a hotspot.

4.3 1 mplementatinn of the Management System

The user interface created by MS will be illustrated step by step in this section.

~,3, 1 Main Windows for Interface

After the loading ot the files of ICADS for DC machines three windows are

illtroduced 10 the system user: a parent window with title "Data Management System"

and two viewport-bound childl'en windows (Figure 4.2).

32

., Figure 4.2 Main windows created by MS

The parent window contains a command menu with seven menu items: Input,

Load, Facts, Design, Output, Save and Exit. Each of these menu items may contain

several sub-menu items. For example under the menu item Facts there are Find and

Add sub-menu items from which data can be found, added, edited or deleted.

During the process of knowledge maintenance a dialogue box appears é1sking the

liser to provide the information of the data to be processed. The resllits of processing

and options provided are given in the "Expia nation & Selection" window. The trace

of data added or deleted is kept in the "Data lnput & Deletion" window ,Figure 4.3).

The design results of a machine can be saved to a file using the Save option. The

Load option is used to re ,Id the design result of a machine from a file back to the

system. When one of these options is mvoked a window asking for the pathname 01

the file will appear (Figure 4.4).

33

(

.... il:"~" . ~) i', ....

~ i'. ..

Figure 4.3 Function of Facts option

The Design menu item provides

two options: design synthesis and design

analysis while the Exit menu item is

lIsed to exit from the Management

System.

4.3.2 Data Input

To design a machine from scratch

the user should input the machine

ratings, the performance required or any

constraints on the physical dimensions Figure 4.4 Enter the pathname of a file

of the machine. The Input menu item

l'an he clicked to input these data and the data type selected. Ta input the machine

ratings the form shawn in Figure 4.5 appears.

34

'.J

Figure 4.5 Window to input machine ratings

Most of slots on this form have àefault values given hy the system. The user may

accept or edit these values. When the user is not sure how to select a value on the

l'orm he/she can get help by typing "h" in that slot. The information concerning the

input power rating, voltage rating, frequency rating and speed rating is shown in

Figure 4.6, 4.7, 4.8 and 4.9 respectively.

35

.. -------------- -

.. >~N \"0

, •• ,._: "'-i.li '.11:#*: ".' ,.1.C.ttt'

," ....

, , , ......... .; ~. .. .. ':-....

Fiqure 4.6 Explanation of power rating

Fiqure 4.7 About voltage rating

36

1

Figure 4.8 About the frequency

Figure 4.9 Explanation of the speed rating

37

,(

After the user inputs the required information the design synthesis can be started

lIsing the Design:Synthesis option.

4.3.3 Design Analysis

After a preliminary design is generated the design analysis follows. Ali the

performance and constraints of the machine to be satisfied will he! checked in this

stage. For example, the errors of the calculated voltage and efficiency should not

exceed the specified limits, the windings of rotor and stator should fit in the slots and

interpole area properly, etc.

Once the Design:Analysis option is c1icked a window with title "Check Design

Results" b opened. If any unsatisfactory design result is detected by the inference it

is reported on this window and the methods of remedy will be given (Figure 4.10 and

4.11) by the MS. The design analysis will end with congratulations from the MS

(Pigure 4.12)!

Figure 4.10 Method to me et the voltage equation

38

1

Figure 4.11 Methods to raise the efficiency

" , " " , ... ..: .. : ... : .. ....

..... <.. .. ..

...... ..

Figure 4.12 End of design analysis

39

(

4.3.4 Output of Design Results

To output the design results use the Output option. These results should be weil

(/ocumented. Design documents can appear on the screen or be written to a file using

Output:Screen and Output:File options.

When printing to the screen a pop-up menu will appear (Figure 4.13). The system

liser can select the set of documents of interest. Figure 4.14 to 4.19 are captured from

screens related to a universal motor with 550W output power designed by IeADS.

Fiqure 4.13 print menu

40

Figure 4.14 Design output of a 550W universal motor (1)

Figure 4.15 Design output of a 550W universal motor (2)

41

Fiqure 4.16 Design output of a 550W universal motor (3)

(

Fiqure 4.17 Design output of a 550W universal motor (4)

42

'.'

Figure 4.18 Design output of a 550W universal motor (5)

Figure 4.19 Design output of a 550W universal motor (6)

43

(

(

4.4 Summary

An expert system consists of two major parts, the knowledge base and the

Illference engine. The Management System of the knowledge base is the bridge

connecting the two parts and the system user together. The efficiency and

cffectiveness of MS are tool-dependent. This chapter described the GoldWorks

window implementation of the MS. The results achieved show that the fun usage of

the utility provided by the tool is important for a flexible user interface.

44

CHAPTER 5 INTERFACE BE1WEEN SUBSYSTEMS

Normally engineering design systems use complex llul11erÏL:al and optillllZ:ltloll

procedures dunng the design process. There is no exception tor electl ic Illilchine

design. Usually these numencal analysis systems are implemented in dllTelent

compllting environments using ditferent computing languages. The issue of interfaces

between the intelligent design system and the numencal analysls system should be

considered before the tool to fulfil thls ktnd of analysis IS selected.

5.1 The Need for Integrating the Numerical Analysis with the Design System

The conventional representation of an electric machine is an e\ectric circuit mlllid

which consists of resistances, inductances, etc. It is an approximation to the rl'i11

machine. To approximate the real machme more exactly the analysi~. of the

electromagnetic fields inside the machine is necessary. The analy"is of these field"

involves complicated nUl11erical computation. Field analysis is encountered in the

tollowing situations:

In the machine design proce~s a magne tic circuit model is ot'len u~ed. It I!-.

necessary because machine de~ign is an Iterative process. The mélgnetÎC circuit model

simplifies the calculation of the tlux densities m different parts of the circuit, ami III

this way a preliminary design can be generated quickly. After that the magnetlc

circuit model shollid be checked by a more accu rate magnetic field mode!. llere 1 ield

45

Hl1élly~is I~ involvcd.

Once the design of the machine has been completed, the performance of the

Illélchine mll~t he predicted. Take a DC motor as an example, the speed-torque is of

importance 111 the operation of the motor. Ta predict the machine performance more

exactly the Illllllericai analysis of the electromagnetic fields is neeessary. For the

(Iccuwte calculation ot machine losses and the temperature ri se in the machine parts,

the eddy cllrrents in the iron core and windings are to be determined. Here field

anillysl~ is nlso II1volved.

5.2 'l'nuls fur the Finite Element Analysis

Most nUl11erical analysis systems of electromagnetic fields are based on the finite

clement Illethoù [22] [16]. They can be implemcnted in different languages and llsing

dillelent opaatlllg system!'> and hardware. Before considering the interface between

the design systelll anù the finite element analysis system the reason for the PC

implemelltatlon ot the design system should be cJarified first.

5.2.1 Advantages of PC·based ICADS

ICADS is to be targeted at the business of machine manufacturing in an

IIldllstnal ellvironment. USlIéllly it is installed in the design office in such an

cllvironlllcnt to ~erve design engmeers. The data base of ICADS also serves several

glOllp~ ot :-.tatt, slIch as ~ales engineers, test engineers, drawing personnel and

estimator:-. lor ditterellt purposes ot use. To suit for these requirements ICADS

shollld be easy to learn and operate. The cast of development, installation and

111l1intcnant:e of the ~ystem has ta be as low as possible.

The PC-hased ICADS provides the following advantages compared with its

main!Imne cOllnterparts:

(a) The low cost of software development (because of the low priee for an

expert system shell) and hardware requirement.

(11)

(r)

Availahility and transportability.

The system is easy to extend both in software and hardware.

46

1 The growing power of microcomputers makes it possihle 10 lise them for thL'

development of expert systems. From the software point of view, PC-hased e:..pt'II

system development tools are also becoming available, althollgh must of them are not

quite suitable for the engineering design. We can expect the advent 01 a dL'~ign tool

more suitable for electric machine design in the near futurc throllgh the et tOI ts (lI

both knowledge engineers and electric machine design experts.

5.2.2 MagNet2D Package lor Finite Element Analysis

MagNet2D is a two dimensional e1ectromagnetic field analysis package lkvdllpl'd

by Infolytica CorporatIOn [10]. Based on the finite clcment mcthOlI, MagNct2D

provides user fnendly preproce~sing ami postproœssing lor the field analysi~ prohlelll.

ft contains the following suhprograms:

(a) Draw2D. Draw2D i~ a genmetric preproce~sor ll~ed hl con~lrlict the

geometry of the prohlem 10 he solvcd. Il provldes graphieal input and

stores the information m an ASCII tilc.

(b) Mesh2D. Mesh2D IS a t'mite clement J11csh generator. The IIlput IIIl' 01

Mesh2D is the output flle of Draw2D. After graphical interaction with the

system user. Mesh2D generate~ the Imite clements autoJl1éltlcally.

(c) Curv2D. Curv2D is used tn input the mformation concernmg the propelty

of the materialll~ed. ft provides the alternatives ot graphH.:al input :1 III 1 1 ilL'

input.

(d) Prob2D. Proh2D i~ a slIbprogram 10 defme the problem 10 he ~olvcd lully.

It is used to edit the information ~lIch a~ the mate fiais lI~ed, the excitatioll

ot the problem model and so on.

(e) Snlv2D. Solv2D provides several ~uhprogram~ u~ed tn ~()Ive dilfen:nt killd~

of field prohlems.

(f) Post2D. P()~t2D i~ the postprocessing suhprogram of MagNet2D. ft

provides diverse outputs of the results ohtained from Solv2D.

Besides, there are several file management programs to handle the output and

47

input Illes ut the above slIbprograms.

5.2.3 Interface between ICADS and MagNet2D

The electromagnetic field analysis systems based on the finite element method

including MagNet2D are relatively complex packages which need sufficient computer

me mory and computing tune 10 run. MagNet2D has different versions. We selected

the ven,ion running on a Sun Workstation (Sun-4) lIsing the UnIX operating system.

The Unix :-.y:-.wlll p(}sse~se~ the power to interface between different kind~ of

computer hardware. This selection of computing environment for field analysis makes

it p()ssible tn interface the design ,rstem with the finite element analysis system.

The IInpkmentation of the i.,terface between subsystems is completed by file , tramler. We ~tore the neces~ar~ information ohtained in the design process in an

output lile fm the flfst ~tep. ThiS flle is transferred to the Sun Workstation and

retneved by MagNet2D afterwards. The information from field analysis is fed back

10 the de~lgll ~y~teil1 to make the deSign modifications. In this way the goal of design

fermement f~ reached (Figure 5.1).

5.3 Generatiun ()f ..... inite Element Analysis Files

Ali of the subprograms of MagNet2D accept input files before they execute. Most

ni thell1 accepl ASCIIlrle~, elther directly or via a file management program which

1:-' u!'>ed to c()nvert t he ASCII trie to the corresponding file type accepted by the

:-.uhploglam. The lile management programs allow the liser to interface MlIgNet2D

\VIth (lther programs through tile transfer.

The MagNct2D system uses three basic file types: mate rial CUlves, geometric

l110dels (includlllg mndeb hefore and after meshing) and problem files.

Data mput for Curv2D can be furnished from a ASCII file. This file is very

:-'lll1ilm to the !ile to be cntered inlo the knowledge hase of the de~ign system. A little

l11odl!ïcatloll I~ ~uttïciènt for the change hetween the two files.

The geomctrH: file created hy the Draw2D prograrn consists of simple geometric

elements, sud as lines, circles and arcs. This file can be generated by the design

48

r -- - - - - - ~ ~ -- --

--- 1

.:. Ir t'I '_l' .. - 1

1 r Il' 1 ~ r. ~ , ! " l III! " --- --r----' ~

L' c ': 1 -' t. .1_' i '=> tel!>

I~" o:~erl g~1 Ua se

t- l 1 UII' Il t

l Ill,

1 - - T

_________ J

1'.- 1 t JI UI 1 Il •

1'\ Il t l' ,1 ,

____ - - - - 1

Figure 5.1 Interface of subsystems

JI." '" l 1 Il 1

system. Ta generate a file for the use of Mesh2D, the menu item, OutIHlt:FEA File,

can be selected t'rom the main windnw of the knowledge management ~ystem. Artel

this option i~ invoked MS caIculates the necessary data to deserihe thc gcol11etly 101

t'Imte element analysi~ and st()re~ th~se data ln the tile named by the user. At tilt'

~ame time a graphie output of thb geometry I~ drawn on the sereen. Figure 5.2 shows

the cross-section of a univer~al motor wlth 550 watt output power.

The problem tile used tor running Solv2D (Ind Po~t2D contallls inlormatlon Oll

the meshes generated hy Mesh2D and mcludes S()lutl()n~ alter the rllllning ()I the

Solv2D program. It is uSllally generated by Proh2D after the meshing of the gcol11ctry

hy the rllnning ot Mesh2D. After that the problem tIle IS furnl~hed to thc Solv2D

program to provide ail the geometric élnd problem detlllition data, "long with the

names of materials given during the running of the Curv2D progwl11.

5.4 Design Modification frnm Finite Element Analysis

Atter the field prohlem is solved hy Solv2D design modification will lollow.

Post2D of MagNet2D is an important tool to evalllélte the design results created by

49

(

Figure 5.2 Geornetry of a universal motnr for finite element analysis

the design system. It can be used 10 display the field distribution graphically and

calculate the tlux density at any point in the area to be solved, the tlux, the

inductance of windings, etc.

ln the de~ign nt universal motors the average tlux densities in the magnetic

components 01 the machine are used. The field analysis using MagNet2D shows

ditferent values of the tlux density ln ditferent positions of the same compone nt. Ta

calculatt: the field excitation more accurately the following components of the field

excitation are consldered in the design system:

(a) Air gap.

(11) Stator yoke.

(c) Rotor yoke.

(d) Pole body.

(e) Rotor teeth.

50

"'.

(f) Compensation for armature reactinn.

(g) Compe nsa tion for hrllsh shift.

(h) Ampere-tllrns increased by commutation.

Formulae for the calclliation of the above can be found in Appendix A.

ln the field analysis the ettect of the armature reaction and the hrllsh shift 011 the

field distribution is taken Illtn accollnt. So components (a) to (g) are inrludcd in the

fIeld ca1clllatioll, but (h) IS not mcluded. Fortunate\y it only constltutcs il very !'.lIlilll

part in the total excitation. Table 5.1 show!'. the \l1~lin flux of a St'nes of 1I1l1Wls:1I

motors obtained by the design system and these data are compared with tlHlsl'

ohtained by finite element analysis. The agreement hetween the two shows that the

magnetic circuit model in the design sy!'.tcm is acceptable.

Table 5.1 COl11pan!'.on nt main tlux in llniver~:11

m()tor~ obtamed by dlfterent methm.ls

Output Power DeSign Result FlI1ite Element

(watt) (maxwell) (maxwell )

140 51215 520H3

204 6H35H 6H933

275 H9335 H9167

3R5 I0276 1 99516

550 143394 142346

770 !47H25 15014()

1250 202303 1 tJH 1 1 ()

Error

(% )

-1 J) 7

-O.K1

O. 1 tJ

3.2()

0.74

-1.55

2.11

Sometimes it IS probable that a disagreement between the de~lgn results and the

51

{

linite clement analysis occurs. In this case the relative part of the design system

shollid be reconsidered. The reason for the disagreement may arise from the fact that

éI œrtélJ/1 factor is overlooked or that the tormula used has certain inaccuracy. The

Il1spection 01 the tield dIstribution is also necessary. If the tlux density in same area

i~ cxceedingly high the B-H characteristics of the material need to be checked.

Otherwi.,c the dimensions of the geometry shollid he modified to improve the field

dbtnblltillll.

5.5 Summnry

Systems for machine design are hard to integrate not only beeause of the faet that

they are implemented in different environments but also because of the camplexity

01 nlll1leric~lI analysi~ sy~tems. This chapter has dealt with the interface of the design

~ystel11 and MagNet2D wlth the fullest utilization of the software and hardware

provlded. A~ an example the design results of universal motors were evaluated by

MagNet2D and It ha~ been shown how the purpose of design refinement can be

reached lrom thls evaluatlon.

52

CHAPTER 6 EXAMPLES OF DESIGN

An engineering design system is only as good as the design engineers lISll1g il.

The value of the system Will increase as it is run more often. The design of a sem'!'.

of universal motors and a small OC mot or has heen carried out lIsing ICADS lm De

machines.

6.1 U niversal Motors

The universal motor is a series commutator machine suitahle for lise on De or

single phase AC supply, wlth CI similarity to a OC motor in structure and operating

performance. It is usually a 2 pole machine hecause of its small size.

Design systems for DC machines may be easdy tn moditïeù to SUit the llc~lgll 01

universalmachmes. Umver~almotors whose ~peciflcati()ns are IIsteù III Table 6.1 have

heen de~lgned uSll1g ICADS.

Table 6.1 Specifications of universal motors ùesigned hy JCADS

Output watt 140 204 275 3S5 550 770 12S0

power

Speeù rpm 14000 14300 12100 13200 <)900 1320() 1 250()

53

(

Voltage volt 220 220 220 220 220 220 220

Frcquency Hz 50 50 50 50 50 50 50

Etflciency % 60.0 62.08 63.8 68.0 68.2 69.0 76.0

Power p.u. 0.965 0.952 0.934 0.955 0.917 0.936 0.940

factor

Torque kg! 0.974 1.39 2.215 2.842 5.413 5.684 9.874

cm

Current amp LlO 1.57 2.10 2.69 4.00 5.42 8,06

The electromagnetic design of universal motors is an iterative process. In the

machllle speciflcatlon~, ~everal factors simultaneously affect the voltage rating,

eftlciency and power factor. Two relationships are important; one is that between the

applled voltage and the voltage components, the other is the relationship between the

cfticiency and the power lmses.

The major design process can be outlined in the following steps.

S'ep 1

a) Selection of the main dimensions of the machine and the length of the air gap.

h) Selection of the numher of slots in the rotor and the design of the shape of

slots and tee th.

Sten 2

a) Calculation of the full load current t'rom output power, voltage rating, power

factor and efficiency.

b) Selection of the wire gauge and the number of rotor conductors.

c) Estllnate the back emf in the armature winding.

d) C'alculate the mam tlux and the tlux densities in the magnetic circuits.

54

j ;

f

'"';.

e) Calcula tian of the mmfs needed.

f) Selection of the wire gauge and turns of the stator winding.

g) Check the voltage equation and the power factor.

Step 3

a) Calculation of the power lasses.

b) Check the efficiency.

In the design process iterations of the ahove steps are carried out until the design

goals are met. Sorne of the formulae lIsed can he found in Appendix A.

The design results of a 550 watt machine are Iisted in the following.

*Machine Specifications*

Rating Design Results Errnr(%)

Output Power (watts) 550.0

Speed (rpm) 9900.

Voltage (volts) 220.0 220.2 O.OX

Frequency (Hz) 50.00

Efficiency (%) 68.20 68.85 0.95

Power factor (p.u.) 0.917 0.916 -0.1 1

Torque (Kg*cm) 5.413

Current (amperes) 4.00

*Electric and Magnetic Loads*

Linear current density (amp/cm) 126.3

55

{ Current density in stator winding (amp/mm2) 10.18

Current density in rotor winding (amp/mm2) 10.18

Machine back e.m.f. (volts) 164.7

Total flux per pole (maxwell) ]43394.

Flux density in stator yoke (gauss) 17394.

Flux density in pole body (gauss) 8200.

Flux density in rotor yoke (gauss) 17000.

Flux density in rotor teeth (gauss) ]7492.

Flux density in é1lr gap (gauss) 5264.

Excitation per pole

Stator yoke (A-t) 291.

Rotor yoke (A-t) 136.

,If'

~ Pole (A-t) 3.

"- Teeth (A-t) 66.

Air gap (A-t) 433.

Brush shift (A-t) 171.

Arma t u re react ion (A-t) 138.

Commutation (A-t) 95.

Total m.m.f. per pole (A-t) 1143.

*Winding Parameters*

Rotor wiD<ling

Total nllmher of condllctors 988.

56

1

" . . '

Numher per slot

Resistance (ohm)

Turns per coil

Coil pitch (slot)

Leakage permeance

Stator winding

Turns per pole

Diameter of bare copper wire (mm)

Number of wires in parallel

Resistance (ohm)

*Machine Main DimensÎnns*

Stator

Outer diameter

Inner diameter

Length of the core

Length of air gap

Number of poles

Pole enclosure

Pole width

Pole height

Rotor

Outer diameter

Inner diameter

(cm)

(cm)

(cm)

(cm)

(cm)

( CI11)

(cm)

(cm)

9.0

5.1

5.20

0.060

2

0.67

3.HO

1.00

4.98

1.60

57

52.

2.74

13.

9.

3.147

143.

0.50

2.

3.95

Numbcr ot slots 19.

*Shape uf Siots and Teeth*

Siols

Depth h2 (cm) 0.900

Radius of hottom r (cm) 0.160

hl (cm) 0.670

Siot opening bO (cm) 0.250

hl (cm) 0.540

Tccth

Width t (cm) 0.258

{ hO (cm) 0.070

ThlCkllcss of wedges h (cm) 0.100

*Losses*

Copper Joss in stator winding (watt) 63.1

Copper loss ln rotor wmding (watt) 43.8

Total iron loss (watt) 49.2

CommutatIOn Joss (watt) 15.5

RotationaJ Joss (watt) 70.0

Loss between hrushes and commutator (watt) 9.6

( 58

t

'';

Total losses

Output power

Input power

6.2 Design Automation nf fi Small De Motnr

(watt)

(watt)

(watt)

251.2

550.0

H06.5

ICAOS éllso provides different levels of design automation tn suit the need 01 the

system user. After the generation of a prelimmary design the system ran an:tlyze thl'

design results and take aetH,ms automatieally aecording to th~ analysis 10 gl'I il

complete design. To test this function of the design system a SI11é111 series De motol

i~ tn be designed with the following specltïcations:

Output power

Output torque

Full load speed

Applied voltage

Efficiency

Full load current

P = 80 watts.

M = 2.78 kg*cm.

n = 2800 rpm.

V = 24 volts.

fi = 0.5.

1 = 6.67 élmperes.

Because the motor is supplied by a battery the rated voltage must he low. The

full load speed of the motor is mllch lower them that in lIslial fractiona: horsepower

motors because this device is intended for a special pllrpose, for example, to dnve

a micro~pllmp. Becallsc Dt the low speed and the low voltage Il I~ dilficult to wise the

efficiency of the machine. Since the cupper loss of the windlllgs lorll1~ a large portion

of the total power IŒses, it is very important to ~elect turns and wire gauge l'<Irelully

tor the stator wmding and the rotor winding.

Main dimensions of the motor selected:

Oiameter of stator core

Oiameter of rotor core

Dl = 8 cm.

O2 = 4.01 cm.

59

Length of air gap

A .... ml Iength of the core

Pole enclosure

N lImber of slots

s = 0.0425 cm.

L = 3.25 cm.

u = 0.66.

Z = 12.

Table 6.2 contains the step~' taken by the design system. In step 1 the eftïciency

I~ not satisfactory. In step 2, to meet the design goals the system increases the

l1umber ot the rotor conductors and selects a larger wire for the stator winding in

~tep 3. The etficiency still remains unsatisfactory. In step 4 the system increases the

axial length of the machine by 0.05 cm (l'rom 3.25 cm to 3.30 cm). This causes the

resistance of the stator winding R j to decrease and the efficiency passed.

Table 6.2 Steps of design taken by ICADS

r- I Step 1 Step 2 Step 3

N 456 480 480

Hdohms) O.5~4 0.615 0.615

E(volt~) 14.2 14.3 14.5

wj(tllrns) 64 56 58

Rj(()hm~) 0.648 0.586 0.554

E. < 1% <1% <1%

E Il -7% - 3.3% - 1.6%

ln Tahle 6.2:

NUlllher of conductors in rotor winding.

ReSistance ot rotor wmding.

Machine back potential.

60

Step 4

480

0.619

14.6

56

0.535

< 1%

< 1%

l' Wl:

RI:

~.:

El):

Turns per stator winding.

Resistance of stator winding.

Error of cakulated voltage with respect to voltage rating.

Error of calculated efficiency with respect to etTicicncy rating.

61

CIIAP1'ER 7 CONCLUSIONS

The AI approach to the design of electrical machines can offer many benefits for

both sophbticated engmeers and novice designers of electrical machines. In this thesis

we have de~cnhed the applIcation of AI techniques in an intelligent CAO system for

De machmes and the implementation issues ot this system.

The PC Implementation of ICADS for DC machmes provides a system which can

~erve the l1eed~ ot an mdustrial envlronment. Usmg Lisp directly the system can

olfset. to some extent, the 11I11Itations of mlcrocomputers in teTlns of memory size and

plOcessing speed.

The leatures of ICADS for DC machines include:

(li) A hyhnd knowledge representation suitable for electrical machine design.

(b) A ~peCially deslgned inference engine capable of reasoning with rules and

Il li l11e~.

(c) A flexible and friendly user interface implemented with window systems.

(d) A practical and convenient interface with MagNet2D or simllar finite

clement package~.

ICADS lor OC machmes ha~ h~en tested on the design of a small OC motor and

a ~erie~ 01 1I111Vèrsai motors which are similar in theory and structure with DC

madll Iles.

Expert sy~tel11~ are hmued by the information stored in their knowledge base. To

62

1

.'

develop li more complete system for DC machine design the knowledgc basc lIf thl'

system needs to he élugmented with ail the types of knowledge norl11i1l1y lISl'd III !'IlIch

a process.

Other sUl..u,testiolls tor tllrther work are ~iven below: ~~ ~

First, a friendly u!'Ier Ifltertace which !'Ihow!'l clearly the relationsillps amung!'lt the

dimension!'l, parameters and pertormance of the machmc IS prdcrab\c bccausl' lill'y

are highly mterrelated in the de!'lign proce!'lS.

Second, diverse techmcal problems, !'Ilich as thermal, I11l'Challical and Stllll'tlil:d

prohlems, are involved in e\ectrical machine design. Tools 10 lacklc thc!'Ie probkl11!'1

need 10 he integrated with the design syste m. after the sliltable unes have hcl' Il ruund.

63

.,. ,~ -lo.

(

APPENIJ/X A SOME OF THE DESIGN FORMULAE FOR UNIVERSAL MOTORS

EQ.I Full load clirrent

I= p

Vll cos cp

P: OWpltf power. V: Voltage ralil/g. 1]: E{{iciellcy. cos f/J: Power JaclOl'.

EQ.2 Cross-sectional area of the rotor wire

I 8 2=--282

Sl: Currelll dellsity ;1/ Ihe rotor WÙldùzg.

EQ.3 Number of conductors in the armature winding

N= 2 TtD2A

I

Dl: allier diameler of Ihe rolor core. /J: Lil/ear cu,.ren/ density in the rotor.

EQ'" Nlimher ot conductors per slot

N N=-s Z

Z: Numher oJ slols ;11 Ilze rolor.

EQ.5 Resistance of the rotor winding

64

• 5.35N1 2 -5 R2= xIO .. 8 2

12: Meall lellgtll per armature cOllCiuctor.

EQ.6 Back emf in the armature winding

E= (l+k:J xP+ Pm

l

Pm: Mecluillicai los.\' of the machine. k2: coefficiellt.

EQ.7 Usdui tlux per pole

<1>= 60V2E xl0 B

kpnN

k,,: Pitell factor of Ihe wil/ding. n: Full lnad speed or the motor.

EQ.8 Flux density ln the stator yoke

B = 1.094> cl 2xO. 96hc1 L

Izel: Heiglzt oI tlze Slator yoke. 0.96: Iron stackùzg ./actor. L: Lengtlz of Ihe stator core.

EQ.9 Flux den!lity ln the rotor yoke

B = 4> c2 2xO. 96h

c2L

Ize]: Heiglzt of the l'O/Or yoke.

EQ.IO Flux denslty ln stator poles

B::: 1. 094> p O.96bp L

b,,: Widtll of stator poles.

,:oIft-

'~ 65

EQ.II

a: r:

EQ.12

1",:

1:

EQ.U

Flux density in the air gap

Pole-arc factor. Pole pite/l.

B =~-g <XtL

Flux density in rotor teeth

Toollz pite/l at armalure surface. Willlll of leelll.

Ampere-turns for the stator yake

ATcl=atclxlcl

(1/,,: Ampere-lll1llS per Ullit lellgllz of IIze stator yoke correspondillg to BeJ. 1,,: Meal! lel!glll o{ Ille slalor yoke.

EQ.14

EQ.IS

EQ.16

Ampere-turns for the rotor yake

ATc2=atc2xlc2

Ampere-wl'l/s pel' unit lellgllz al/Ize rotor yoke correspolldùlg to Bel'

Meal! lellglll of Ilze rotor yoke.

Ampere-turns for pales

ATp =2xatp ,t<hp

Ampere-tul'lls pel' UI/it lellgllz of the pole cOlTespOlldillg ta Bf" Heiglzt of IIze pole.

Ampere-turns for the air gap

ATg=1.13xBg XKg xg

Carier coefJïcielll. Lmgt" of the air gap.

66

EQ.17

al,: l,:

EQ.18

cl:

EQ.19

bh :

le: e\: e,,: JV2:

EQ.20

k:

EQ.21

EQ.22

Ampere-turns for the teeth

ATt;=atr;xlt;

Ampere-Iums pel' unit tellgtlz of Ilze /oollz correspol/clillg 10 Br Meall lellg//z of Iwo Ieellz.

Ampere-turns due to hrush shift

1td ATb =Kb xD2 x 180 xA

0.333 for 3 commuta/or segl1lellls pel' stol, 0.625 for 2 commuta/or segmellIs per stOl. Degrees (~f hru.\/z s/zifl.

Ampere-turns increased hy the wl11l11l1tating coils

bb ' ATc=O. 069x (--):<x (ex+ea ) xW-;xI tc

Wiel/h of hrllshes. Pitc/z of COl1!nlllla/or segmelll.\. Illduced emf in flle COHll1ll1/cuillg coils tille 10 Ille .\e1! il/cilIelclllce. /!uluced emf in Ihe C(;mmllllllillg coil.\ cilie lu Ihe arma/lire reac/i(}/I Ttmzs per coi! of Ille rolOr willclùzg.

Demagnetizmg Ampere-turns due to the armature current

k (ATg+3ATr;+O. 5a'tA) AT = xax'txA

a AT g

3.333 X ( 60.0 - al, ) X JO 4 + {)'{)89.

Total Ampere-tllrns consul11ed

AT= AT g + AT cl + AT c2 + AT p + AT c + AT b + AT a - A Tc

Turns per pole coil

67

EQ.23

EQ.24

EQ.25

f:

EQ.26

2..1:

EQ.27

EQ.28

EQ.29

w= AT 1 2I

Cross-sectional area of the stator wire

I 5 =--1 S

1

Currelll dellsity ill the stalOr wbzdbzg.

Resistance of the stator winding

4.28W111 4 R1 = xl0-

51

Mean lellgth per IUm of the stator wùzdùzg.

Induced emf in the stator winding due to the transformer reaction

Ed=8 . 88fW14>xl0- B

Fre(jueJU.y rtaillg.

Active compone nt of the voltage

Vr =IR1+IR2 +2.4+E

Voltage drop ùz the brushes alld the commtUator.

Calculated voltage

Calculated power factor

coscp

Copper loss in the stator winding

68

EQ.30

EQ.31

Pm: PFI.': Pk:

EQ.32

Copper loss in the rotor winding

Total power losses

LP=PCU1+PCU2+2 .4 l +Pm+PFe+l\

Meclumical loss. Iron losses. CommlllatÎoll loss.

Calculated efficiency

" '= VIcoSP-LP Vlcos<p

69

{

(

API'ENDIX B

(Irca:

tlefmle: tlefmle 1 : tlelete-filet: tle ... ';gll-jill;.\'h:

fllct: .fàct ... ·: .fiIll11act: . /illl/-.... lot·mllle: .fiJrH'artl·eha;Il : .fim.·artl-ellaill 1:

maleh: malch·or·llot:

.\Iream·jir.\'t:

.\!ream·re.\'I:

",'(I·rllle:

V·too·loH':

DEFINED FUNCTIONS USED IN THE THESIS

fWlction to calculate tlze cross-secliollal area of a wire j;nl1Z /Ize currelll alld tlze Clin'ent dellsity.

jimctùm to store design rules ill data hase *Rllles*. {wlctùm to store clleckblg rules in data base *Rulesl *. fWlctioll to delete ail assertion frOln tlze knowledge base. (tlllctùm to give congratulations wlzell a design is sllcces.~rlllly completed,

fWlction to give illstructions wlzen the calculated ef{iciell")' is 100

Iziglz. (wlctùm to giw ;'lstnICt;oflS wlzell tlze calculated efficiell")' is /00

IOH!.

jilllc/ùm 10 defille ail asser/ioll. fUllc/ùJIl /0 defille several assertions . fWlclion to filld ail assertion from the kllowledge base . fWlction to filld tlze slot value of a slot wlder a frame . f01ward-clwÎllillg ftmctioll ta apply al/tlze nt/es ill da/a base, fOl'Ward-clzaÎllillg ftmction wlziclz will stop al tlze succes~:{ttl mie ill ciMa base.

{tlllc/ùm to compare pal/ems alld data. /lmctùm 10 clzeck ~{ a Ilew asserlioll ma/clzes tlze pallem of a rule or 110/.

streams are sequellces of data abjects, /Izis fUllc/ion takes //ze firs/ objec/ of a s/ream. {tlllc/ioll 10 /ake Ilze re.\t of a slream .

{tlllc/ùm to apply a mie /0 Ilze data base.

ftlllc/ùm /0 give instructions wlzell Ilze calcula/ed voilage is /00

/zig". fWlctioll to give ÎllSlruc/iOlIS wlzen Ilze calcula/ed voltage is /00 IOH!,

70

r APPENDIXC

INPUT Ratings: E-Ioad: Main-dim: Windings: Sints-teeth: Cnmmutator: Lusses:

LOAD:

FACTS Find: Add:

DESIGN Synthesis: Analysis:

OUTPUT Sereen: File: FEA-file:

SAVE:

EXIT:

COMMAND MENU ITEMS OF MS

menu item to mput machine ratmgs. menu item to II1put e\ectric loads. menu item 10 input main dimensIons. menu item to input winding information. menu item to input shape of !>\ots and tl'eth. menu item to mput commutatm mlmnwtilln. menu Item to input mlormatiol1 about powcr 1()!l~L·~.

menu item to Joad the design re!lult!> ul a machinc 110111

él tile.

mt!nu item tn tind data lm clhting m delcting. menu Item 10 add data.

menu item for design synthcsls. menu item for design analysb.

menu Item to output the deSIgn rcsulb un the ~L'leell.

menu Item to output the de~lgn re~lllt:-. tn a tile. menu item to generate a flle lm tmite elemcnt anaIY:-'I!>.

menu item 10 save the deSign reslllt~ tu él Ille.

menu item 10 eXIt lrom the MS.

71

t

{ "

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74