some communication problems of kb-controlled

8/8/2019 Some Communication Problems of KB-Controlled

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P e r g a m o nPII :S0952-1976(97)00005 5

E n g n g A p p l i c . A r t i f . I n t e ll .Vol. 10, No. 2 , pp. 225-23 0, 1997 1997 Elsevier Science Ltd

Pr inted in Great B r i ta in . Al l r ightsreserved0952 -1976197 $17 .00+ 0 .00

Contributed Pa per

Som e C omm unica t i on P rob lems o f KB -con t ro ll edManufac tu r ing Sys t ems

G E O R G E L . K O VA C SComputer and Automation Research Institute of H AS, B udapest, Hungary

J /k N O S N A C S AComputer and Automation Research Institute of H AS, Budapest, Hungary

(Received September 1996)

Know ledge-based or in te l l igen t cont ro l o f f lex ib le m anufac tur ing sys tems (F MS) involves the cont inuous orf requent observa t ion and eva lua t ion o f the s ta tus and condi t ion o f the sys tem performance , dec is ion-makingbase d both on the evaluation results and on pre-defined knowledge, a nd then system operat ion a ccording tothese decisions. In the case o f normal, s cheduled operat ion, there is no need fo r ei ther intel l igence orinteract ions to mod ify the operat ion. T he procedure given above may, however, help if any kind o f disturban ceor irregulari ty happens, a s is rather commo n in the case of highly sophist icated, comp lex systems. This pap erdea ls wi th cont ro l and comm unica t ion problems in f lex ib le manufac tur ing sys tems us ing programs based on areal- t ime expert-system environment, taking into considerat ion the requirement fo r open ness in up-to-datesystems. Two robot applicat ions wil l be discussed as demonstrat ions.

1997 Elsevier Science Ltd. All r ights reserved

Keywords: Flexible manufactur ing systems, open systems, exper t sys tems, arc welding, robot control ,industr ia l n etworking.

I . I N T R O D U C T I O N

Recent d iscre te manufactur ing and/or assembly systems(FMS/FMA) are more and more of ten control led us ingMAP /MMS (Manufac tu r ing Automat ion Pro toco l, Manu-factur ing Message S pecif icat ion) (Bri ll and G ramm, 1991)because th is technology is widely avai lable f rom manyvendors and gives real ly safe and open solutions accordingto the demands of OS[ (Open System Interconnect ion) .

Many users are not aware that they have such inter-connect ions; they jus t enjo y the useful features of MAP. I tmust a lso be admit ted that MAP or MAP-rela ted solut ionsare sti l l rather expensive.

On the other h and, so-cal led " inte l l igent control" i sincreas ingly in gen eral deman d. There is l ively discuss ionin the l i tera ture and in pr ivate communicat ions amongcontrol engineers about the exis tence of , and need for,in te l ligent control (Frankl in and Meyste l , 1994 ) . Someexper ts c la im that there is n o such thing, that could real ly be

Correspondence should bes e n t t o : Dr G. L. Kowics, CIM ResearchLaboratory, Co mpute r and Automation Research Insti tute of HAS, POB63, 15 18 Budapest, Hun gary.

designated as " inte l l igent" control . Most of them arespeaking only about process control , and not about d iscre temanufactur ing or robot control ; however the control tasksand problems of manufactur ing systems are basical lys imilar to those o f batch-l ike process control . Without go inginto fur ther d iscuss ion of th is i ssue how ever, the authors o fthis paper accept the necess i ty for in te l l igent control , whichis of ten provided by using exper t sys tems. Some commer-cia l exper t sys tems a l ready provide goodproblem-descript ion and sof tware-developm ent tools ,where the programming is c loser to the problem to besolved and to the user, and limited real-t ime facili t ies aresupported as well (Laffeyet al., 1988).

The next sect ion br ief ly in t roduces the basic sys tem, f romwhich the developments described later, started. Section 3discusses the comm unicat ion problems of exper t sys tems inFMS appl icat ions , and gives a problem decomposi t ion.Later on, there is a br ief descr ipt ion of the features of theMA P-based Vir tual Manufactur ing Device mo del , used inintell igent control. Finally, there is a presentation of thedeta i led basic def ini t ions in the context of an " inte l l igent

robot cel l control ler wi th open com munica t ion" .225


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226 GEORGE L. KOVACS and JANOS NACSA: KB-CONTROLLED SYSTEMS

2. A K N O W L E D G E - B A S E D H Y B R I DS I M U L AT I O N - S C H E D U L E R SY S T E M

T h e f i r s t p ro to type t o be deve loped i n t h i s wor k w as ak no wledge -based s imu la t i on - schedu l e r sy s t e m ca l l e d S im-S ch e d -Q (Kovz i c se t a l . , 1993 ) . I n t he S imSche d -Q sy s t em(Fig . 1) the s imula t ion was implemented in a " t rad i t iona l"

s i m u l at i o n /a n i m a t io n s y s t e m c a l le d S I M A N / C i n e m a t h a tco u l d , howeve r, be u sed t h roughou t t he wor l d . T h i s w assu r r ou nded by exp e r t - sy s t em mod u le s ( p r epa ra t io n , on - l i neq u a l i ty and s ched u l e r adv i so r, and eva lua t io n ) , imp l em e n te din the same G2 Vet . 3 .0 objec t -or ien ted rea l - t ime in te l l igente nv i r onmen t . The s t udy i n t h i s pape r r e f e r s s p ec i f i c a l l y t othe S i mSched -Q sys t em, a s t he r e su l t i ng s che du l i n g d a t aprovide the bas ic input for ( in te l l igent ) FMS cont ro l .S imi l a r e f fo r t s a r e , howeve r, a l so be ing m ade e l s ewhe re(e .g . Somlo and Buzid i , 1996) .

T h e re a r e f ou r expe r t sy s t ems i nvo lved : t w o o f t he s e a r esh a l l o wly coup l ed w i th t he s imu la t i on (P re pa r a t i o n andEv a l ua t i on ) , wh i l e t he o the r two a r e deep ly coup l ed ( t h e

Q u a l i t y and Schedu l e r adv i so r s ) . The s t r u c tu r e and fu n c -t i o n a l it y o f t he sy s t em were de s igned and de v e lope d i n ou cha w ay t ha t t he s imu la t i on migh t l a t e r be r ep l a ce d by a r e a lF M S e n v i r o n m e n t , a n d t h e E S w o u l d b e c o m e t h e r e a l- t im econt ro l le r.

T h e p ro to type app l i c a t i on was deve loped u s i n g r e a l d a t a( l a yo u t , c apac i t i e s, p roce s s p l ans , mac h ine p a r ame te r s , e t c . )f r o m s ome ex i s t i ng FMS, fo r examp le t he P i l o t FM S a t t heTe c h n i ca l Un ive r s i t y o f Budapes t . Th i s s y s t e m c on t a in s f o u r" h o lo n - l i ke " c e l ls ( s t o r age w i th AGV , measu r emen t , a s s em -b ly a n d me ta l - cu t t i ng cons i s t ing o f a CNC l a t h e and a CN Cm a c h i n ing cen t e r s e rved by robo t s ) on a ne tw o rk .

To address rea l - t ime cont ro l in th i s sense , a l l thesc h ed u l i ng da t a i s needed - - such a s t h e s t a r t i n g andf i n is h i ng da t e s o f a l l ope r a t i ons o f a l l equ i p m en t (m ac h ine -

tools , robots , t ransfer uni t s such as A G Vs , e tc . ), toge th erw i t h t h e p o s s ib i l i t i e s f o r d own l o ad in g C N C con t ro l p ro -g r ams t o a l l e qu ip m en t . I t i s a l so ne ce s s a r y t o a ccep t ande va l u a t e d i f f e r en t s i gna l s f r o m the e qu i pme n t , e t c . Thet imes o f l oad i ng / un l o ad i n g s h ou ld be ca l c u l a t ed t oo .

3 . C O M M U N I C AT I O N W I T H E X P E R T SY S T E M S

T h e p r a c t ic a l p r o b l e m s o f t h e c o m m u n i c a t i o n o f e x p e r ts y s t e m s i n C IM (Compu t e r I n t e g ra t ed M anufac tu r i ng )a pp l i c a t i ons c an be d iv i d ed i n t o two pa r t s . One i s t heh a rd w are - so f twa r e conn e c t i on ( phys i ca l ) a n d t he o the r i st he l og i c a l conne c t i on be twe en t h e c o n t ro l l e r ( s ) and t hec on t r o l l ed de v i c e s . T h i s d eco m p o s i t i on w as found t o bev e ry u s e f u l , i n b o th t h e de s ign a nd imp l e m e n ta t i on phase sd u r in g r ece n t p ro j ec t s i n t h e au t h o r s ' C I M L abo ra to ry. I ft h i s d eco m p os i t i on i s no t s o sh a rp , man y p rob l ems mayo ccu r d u r i n g t he de v e l o p m en t , and e s pe c i a l l y i n ma in -tenance la te r on .

T h e r e a r e r e l a t i v e l y e a sy p rog r amming i n t e r f ace s (C /C+ + , e t c .) i n m o s t a v a i l ab l e ES she l ls . T he se i n t e r f ace sp rov i de cap a b i l i t i e s f o r da t a t r a n s f e r a n d co mmun ica t i onwi th ex terna l tasks , s ta t ions , e tc . They suppor t c lear ande asy p r o g ra m min g t o r e ach ob j ec ts , t o c a ll p r ocedu re s , t o s e ta nd ge t v a r i ab l e s , e t c . Th e i n t e r f ace s a r e ded i ca t ed t os p ec i f i c so f twa re t oo l s o f t he ES , and t h e y a r e gene ra l l ya ime d t o w a rds t he ex t e r n a l wor l d w i thou t b e i n g ab l e t o t akea cc o un t o f t he sp e c i f i c r equ i r e m e n t s o f t h e g iven app l i c a -t i on . S o a l m o s t a l l C IM i m p leme n ta t i o ns r equ i r e t hed eve l opme n t o f s p ec i a l s o f t w a re t o c o ve r t h i s gap be tweent h e ex t e rn a l w o r l d an d t he E S .

C le a r l y, t he c o m m u n ic a t i o n f unc t i ons d epend on t hec apa b i l i t i e s o f t h e ex p e r t s y s t e m . The m e t ho ds o f l e a rn inga nd kn o w l edge han d l i ng de t e r m ine t he l o g i ca l l eve l s o f the

PreparationExpert System

cell configu ration, orders,quality measuremen tsetups

OnlineScheduling

Expert System

Online Qua lity !Expert System

Expert System !

schedulir

ge s

asurements / Jof qua lity

/

/"~ch ed ule, statistics

~ S i m u l a t i o n

j S t M A N IV. !C i n e m a

Fig. 1. SimS ched-Q system: rad itional simulation surrounded with expert system swithin one shell.


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GE ORG E L. KOV,A,CS and J,/~NOS NAC SA: KB-CONTR OLLED SYSTEM S 227

c om m un ica t i on . Th ree d i f f e r en t t ypes o f wo rk i n g m ode , a n dd i f f e re n t l eve l s o f t he com mun ica t i on o f an i n t e l li g en t c e l l-co n t r o l l e r i n a C IM env i ronmen t , have been d e f i n ed ( Nac s aand Kovf i c s , 1994 ) . These l eve l s a r e i m p leme n te d - - o fco u r s e - -w i th in t he s ame p ro toco l . The l owe s t l ev e l (Da t aA cq u i s i t i on and Con t ro l Leve l ) ha s t he ba s i c con t ro l a n dda t a - acqu i s i t i on t ype messages . The o t he r t wo l e v e l s( K n o w l e d g e A c q u i s i t i o n a n d K n o w l e d g e C o m m u n i c a t i o nL ev e l s ) have mes sages i f and o n ly i f the " i n t e l l igen ce o f thece l l c on t ro l l e r is no t h idden" . "H idden" i n t e ll i ge n ce m ean sin t h i s con t ex t t ha t t he knowledge -based t e chno l ogy i sappl ied only ins ide the ce l l cont ro l le r, and i t has no spec i f ica c t i o n s v i a t he commun ica t i on channe l . A t yp i c a l e xamp l eo f the h idden ca se occu r s i f a KB sys t em i s bu i l t u p on thetop of a t rad i t iona l cont ro l sys tem, us ing i t s or ig ina lc ommun ica t i on . On t he h ighes t l og i ca l l eve l t he knowl edgeac qu i s i t i on and t he so - ca l l ed "knowledge commun i ca t i on s "h av e been s epa ra t ed . The fo rm er con t a in s spe c i f i c da t a f o rm o d i fy ing o r ve r i f y ing t he knowledge o f t he g iv en c on -

t r o l l e r. When a KB sys t em sha re s i t s knowl edge ( n ew o rm o d i f i ed ) , i t b e longs t o t he knowled ge com mun i ca t i o n l eve l(Bu t a and Sp r inge r, 1992 ). The co mm un ica t i on m e s sag e s o fm o s t r e a l and p i l o t KB a pp l i c a t i ons fo r FMS con t ro l be l ongto the lowes t , o r poss ib ly to the middle , log ica l leve l .

4 . M M S - - A N O B J E C T- O R I E N T E DC O M M U N I C AT IO N T O O L

G o i ng back t o t he so - ca l l ed "phys i ca l " c o nne c t i o n , t h e r ea r e many pos s ib i l i t i e s t o f o l l ow. Mos t c o n t r o l l e r a n dc o n t r o l l ed -dev i ce vendo r s o f f e r good (p rop r i e ta r y ) s o lu ti o n sto be u sed t o commun ica t e ; vendo r- i ndepen d en t s t anda rdsa r e a l so ava i l ab l e .

A l s o i n t he CIM a rea , the r e a r e o the r a cc ep t ed mo d e l s o rm o d e l i ng t oo l s t o de sc r i be t he ob j ec ts o f an F M S. F rom t h ec o m m un ica t i on po in t o f v i ew, the mos t p romi s ing one i s th eo b j e c t -o r i en t ed v i ew o f the so - ca l l ed MM S (Ma n ufa c tu r i ngMe s s age Spec i f i c a t i on ) , wh ich was o r i g ina l l y an ap p l i c a -t i on - l aye r p ro toco l i n t he MAP OSI ne tw o rks . I t wa s l a t e rrea l ized tha t th i s spec i f ica t ion i s a l so good on the h igherleve l of the FMS (Nagy and Haidegger, 1994) , to g ive ac ommun ica t i on -o r i en t ed v i ew o f t he ne twor k e l e m en t s a n dthe i r resources .

MMS g ive s a so - ca l l ed VMD (Vi r t ua l Ma n ufa c tu r i ngD e v i c e ) v i ew o f e ach r e sou rce o f t he FMS. A l l t h e ob j ec t so f th e M MS (e .g . VMD , dom a ins , d i ff e r e n t t yp es o fv a r i ab l e s , p rog ram invoca t i ons ) a r e ob j ec t - o r i e n t e d , w i t hspec ia l se t s of a t t r ibu tes and ac t ions (ca l led "serv ices" inMM S ) be long ing t o a g iven ob j ec t t ype . F i gu re 2 s hows as i m p le , bu t r a the r gene ra l , t ype o f VMD : an a r c -w e l d ingro b o t VMD. In a VMD i t i s pos s ib l e t o c r ea t e , r e ad an dw r i t e d i f f e r en t t ypes o f va r i ab l e s , t o up - a n d dow n loa dd oma i ns (wh ich can be p rog rams o r mach ine d a t a ) , t o s t a r ta nd s t op d i f f e r en t t a sk s (w i th p rog ram invo ca t i ons ) and t oh an d l e even t s . The ob j ec t -o r i en t ed v i ew o f M M S a l l ows theVM D mod e l o f a c e r ta i n dev i ce t o be de s i g ned , a nd i t i sim m e d ia t e ly pos s ib l e t o u se t h i s mo de l a s a s p ec i f i c a ti on o f

t h e commun ica t i on , whe re t he s e rv i ce s (wha t on e c an d o

A r c w e ld i ng R o b o t V M D( K U K A - E S S )

Ve n d o r , M o d e l , R e v i s i o nP h y s i c a l & L o g i c a l S t a t u s

Fig. 2. Virtual Manufacturing Dev ice mo del of a ro bot (an exam ple).

w i th a g ive n o b j e c t o f t he V M D) a r e de f i ned and a r ew o rk i n g i n t h e MMS ne t work s .

5 . A N E X P E R I M E N TA L R O B O T C O N T R O LS Y S T E M

As th e g oa l o f t h i s wor k w as t o p ro v i de r ea l - t ime ,i n t e l l i g en t con t ro l o f FMS s y s t e m s , t he n e x t s t ep was t oa pp l y a l l t h e de v e lo p m en t r e su l t s , a nd t o i n t eg r a t e t hei n d e p en d e n t ly w o r k i n g a n d t e s te d s o f t w a r e - h a r d w a r e m o d -ules.

As a f i r s t exper imenta l se t -up (F ig . 3) a s imple conf igura-t i on was c h ose n . F rom ea r l i e r p r o j e c t s a M i t sub i sh i r obo twa s ava i l a b l e , w i th a s e r i a l D N C c onne c t i on t o a PC tha th a d a M A P i n te r fa c e . T h e t ri v ia l T I C - TA C - TO E g a m e w a sse rve d by t h e rob o t i n t h e f o l l owi n g man ne r : a u se r cou ldp l ay ag a in s t t h e G 2 s y s t e m . O f c o u r s e , t h i s i s no t a p rob l emf o r wh ic h s uch a n i n t e ll i ge n t s y s t e m i s n ee de d , bu t t h i s we l l -k n o wn gam e i s a b le t o demo n s t r a t e c l e a r l y th e " i n t e l l i gen t "fea tures of the cont ro l . On the o ther hand , the fu l l cap abi l i tyo f M M S n e t w o r k in g w a s u s ed .

Th e s t r uc tu r e o f t he s e t u p s hows t h a t a sp e c i a l ga t ew aywa s de v e lo p ed b e twe en t h e G2 b a se d c o n t r o l l e r and t her o bo t . T h i s c oup l e s t h e G 2 sy s t em i n t e r f a c e ( ca l led G SI ) t ot h e MM S s t and a rd com m u n i ca t i on (M M S - E A SE, 1994 ). I nt h i s ca se , t hi s was t h e "g ap -b r idg i ng so f tw a r e" m en t ioned i nSec t i o n 3 . Th i s s p ec i a l ga t ew ay o f t h e G 2 a l l ows anyd i s c r e t e ma nu f a c t u r i n g app l i c a t i ons t o be d eve loped i n G2us i n g t he MM S s t and a rd i n t e r f ac e , and w i t hou t hav ing t omod i fy t h e i n t e r f ace . I n t h e de m o ns t r a t i on ve r s i on , t heg a t e w a y s u p p o r t s t h e c o n t e x t m a n a g e m e n t a n d s o m ep r o g r a m i n v o c a ti o n s e r v i c es o f M M S .

For t h i s so l ut i on a sp ec i a l o b j e c t h i e r a r ch y ca l l ed M LG O( MMS- l ike G2 o b j e c t s ) a n d a p r o ce d u re s e t we re neededwi t h in t he G2 t o m ake up t he k nowl ed g e ba s e t o hand l e t heMMS i n t e r f a ce . Th r ee so l u t i on s we r e e x a mined be fo r ed e v e l o p i n g t h e M L G O :

T h e f i rs t s t u d y c ons i d e r ed ho w the com p l e t e MM S o b j ec ts t ruc ture could be bui l t up wi th in the G2. This took a lo t

o f e f fo r t a n d gav e a r e l a t i ve ly c o m p l i ca t e d and no t ve ry


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228 GE ORG E L. KOV.A,CS and JANOS NACSA: KB-CONTROLLED SYSTEMS

I N T E L L I G E N T [GSIC O N T R O L L E R ,,/o bj. &

(G 2 " p r o c e -E N V I R O N M E N T ) dures

MM S like G2 objects I

G S [

C

inter-face

C O N T R O LR E S P O N S E

G A T E W A Y

ik

MM client ]

CONTROLREQUEST

M M S s e r v e r o f r o b o t ( P N I U )

/ /3 IB ' I l l /

Fig . 3 . Knowledg e-based con t ro l o f a robo t wi th OSI ne twork .

usefu l s t ruc ture . Because of the d i ffe rent se rv ices andt h e i r pa r ame te r s , many ex t e rna l p roce du r e ca l l s a r ed e f i n e d b y b i g p a r a m e t e r s e t s . A l l i m p l e m e n t e d M M Ss e r v i ce s have t he i r own GSI p rocedu re s , an d a l l MMSo b j ec t t ypes have t he i r i n t e rna l G2 ob j e c t de s c r i p t i o n s .T he complex i t y o f t he i nne r s t r uc tu r e i s t he s ame a s t ha to f t he MM S i t se l f. I t d i d no t g ive a c l e a r and ea sy - to - u set o o l f o r t he G2 u se r.

I t w ou ld a l so have been pos s ib l e t o de f i ne i n d epe nde n tp r o cedu re s f o r a l l c a se s when MMS se rv i ce s sho u ld b eu s e d . In t h is c a se , t he who le M M S func t iona l i t y wou l d beimp l emen ted w i th in t he ga t eway. Th i s i s t he s o lu t i onw i t h o u t a n y M L G O s u p p o rt .

T h e t h i rd so lu t i on r educed t he num be r o f nec e s sa ryo b j e c t s and p rocedu re s t o some g ene ra l t e rms . I t a l s o u s e s

a l im i t ed numbe r o f e x t e r na l GSI p roce d u re ca l l s , bu tg ives a ra ther genera l in te r face (wi th few l imi ta t ions) toM M S .

A s i m p le e xamp l e o f t h e me t h od ca n be s een i n F ig . 4 .W hen t h e u s e r wa n t s t o t ake a box t o a g i ve n p l ace , he o rs he shou l d c l i ck t he mo u s e abo v e t hep l a c e . A G2 "use r-def ined-ac t ion" be longs to the p lace , and s ta r t s then e x t - m o v e p r o ce d u re . I t w i l l p i c k u p t h e p a r a me te r s o f as t a r t - p r o g r a m - i n v o c a t i o n M M S s e rv i ce f ro m t h e M L G Oand ca l l t he GS Im m s - s e r ve x t e r na l p r o ce d u re t h a t s ends t her eq u es t t o t h e r obo t a c ro s s t he ga t eway. Th i s me thod i sr a t h e r g ene ra l , a n d o t h e r M M S A p p l i ca t i o n Enab l e r p ro -g r a m s on t h e ma rke t a r e u s i ng s im i l a r s o l u t i ons ( e . g .EasyMAP, 1993) .

s t a r t n e x t - m o v e( u s e r , P L A C E 3 )

c a l l m m s - s e r v ( o p e r a t i o n ,r e m o t e - a p p 1 , o b j e c t , d o m a i n ,t y p e , p a r a m ) a c r o s s m y g s i - 1

I V

O p e r a t i o n " S t a r t P l "

P a r a m I 3

Last va lue -1R e m o t e a p p l " p c . m m s "M m s objec t type ) r o g - i n v

M m s o b j e c t n a m e " R - G E T "D o m a i n ....N a m e d t y p e ....

Fig . 4. Rea l i za t ion o f MM S w i th in the G2 sy s tem.


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GEORGE L. KOVACS and JANOS NACSA: KB-CONTROLLED SYSTEMS 229

PRO AR C system

AutoCADR13 ~ 1 ~ ,~ f i r~on calls

A u t o C ~ ~ " Modelling and v, ldingplmning rr,tx~ule

STEP ile ~, RCM3 ie

[ Progr~ n generationmodule ~Z

MlVlS netw ork

G 2environnm t

Weldingfeatures

- -

. . W o r e l

~ Knov,ed ~ basediv- con lrol ystem

~ th MMS interface

Cormaunacationmodule

i iFig. 5. Structureof the dua l system: PROARC and G2-based KB environment.

6 . K N O W L E D G E - B A S E D C O N T R O L O F A N A R C -W E L D I N G R O B O T

In t he l a s t two yea r s a CAD/CAM in t eg ra t ed robo tp rog ramm ing sys t em (PROA RC) has been deve loped , i nco-opera t ion wi th German and Hungar ian par t ic ipants ,w i th in t he f r amew ork o f an EC Eas t -Wes t p ro j ec t (Weeketal., 1995) . The goal of the sys tem is to ass is t a rc-weldingwith robots in SME s, mo st ly for smal l and med ium lo t s izes ,wi th a PC-based, in terac t ive , off - l ine robot programmingsystem. Most commercia l ly avai lable sys tems are e i ther too

expens ive , o r canno t p rov ide enough f ea tu re s fo r a r c -we ld ing . CAD /CAM in t eg ra t ion means tha t a ft e r add ing theneces sa ry t echno log ica l i n fo rma t ion to t he Au toCA D-basedgeometr ic des ign, the appropr ia te programs provide auto-ma t i c p rog ram gene ra t ion and r emote con t ro l fo r t he app l iedrobot to execute the welding tasks.

The PROARC sys t em can be d iv ided in to d i f f e r en tmodu le s : Mode l l i ng , Weld ing P lann ing , P rog ram Gene ra -t ion and C omm unica t ion . In t h isf u n c t i o n a l divis ion of thesys tem the d i fferen t phases of an off l ine session are mapped .However, the under ly ing s t ruc ture i s not tha t separable ,especia l ly not for the f i rs t two modules . In the Model l ingModule , bas ica l ly, the welding ce l l and i t s components areinput in to the sys tem. The Welding Planning Moduleprovides the capabi l i t ies to associa te seams to the mod el ledworkpieces , and to genera te a l l movements dur ing thewe ld ing se s s ion . The P rog ram Gene ra t ion gene ra t e s t herobot-speci f ic code , inc luding some sys tem- and environ-ment-speci f ic fea tures as wel l . The Communicat ion Moduleprovide s the conne ct ion to the robot cont ro l ler.

F igu re 5 shows the connec t ions o f the K B-based con t ro land the PROARC sys t em, where t he o r ig ina l communica -t ion modu le o f PRO AR C has been r ep l aced wi th the KBcontrol module . This modif ica t ion wi l l lead to the in tegra-t ion of more par ts in to the KB , and then the rea l fea tures and

pow er of the in tegra ted KB tool wi l l appear.

There are severa l poss ib i l i t ies to increase the " in te l l i -gence" o f the r ecen t PRO ARC sys tem:

The s imi lar i ties be tween the workp iece famil ies could bemanaged and ana lyzed in a mo re soph i s t ica t ed way, evenif th is fea ture i s a specia l one in PR OA RC . T he in te l l igentcompar ison of workpieces in the des ign phase can ass is tin re-us ing welding se t t ings , or even pieces of robotprogram par ts .

The present sys tem al ready suppor ts the unski l led user by

offer ing defaul t va lues of the d i fferent welding var iables ,bu t a knowledge -based too l cou ld expand the capac i ty o fthis feature.

Current ly, the sys tem uses on ly a s imple tac t i le senso r toprovide safe welding. The in te l l igent evaluat ion o f sensorin fo rma t ion cou ld he lp in mak ing the sys t em morere l iable , by means of analys is and forecas t ing proce-dures.

The area o f the f i rst exper im ents ass is ts in performin g thecontro l tasks of the sys tem. This means tha t theComm unica t ion Modu le o f t he PROAR C sys t em iscomple t e ly r ep l aced by the G2-based con t ro l w i th MM Sinterface.

As the PROAR C i s comple t e ly PC-based and therecent G2 vers ion i s running on a SUN, some addi t ionalin ter fac ing problems have to be solved, which are notshown in Fig . 5 . The b ig ar rows show the data f lowthrough the sys tem in the f i rs t vers ion; the l i t t le ones arethe potent ia l or a l te rnat ive conn ect ions .

7 . C O N C L U S I O N S

The p aper deals wi th in te l ligent rea l -t ime contro l of FMS .As examples , the s imula t ion of a rea l FMS, then a robot icscel l (where the robot i s def ined as a v i r tua l manufactur ingdevice (VMD)) and f ina l ly an arc-welding robot cont ro l led

by a rea l - t ime computer sys tem, are presented . The contro l


6/6

2 30 G E O R G E L . K O V, ~ C S a n d J A N O S N A C S A : K B - C O N T R O L L E D S Y S T E M S

s o f t w a r e h a s b e e n i m p l e m e n t e d u s i n g a r e a l - t i m e i n t e l l i g e n te n v i r o n m e n t ( G 2 ).

A n i n t e r f a ci n g p r o b l e m w a s s o l v e d w h e n t h e G 2 s y s t e ma n d t h e M A P / M M S n e t w o r k w e r e c o n n e c t e d to a c h i e v er e a l - t i m e i n t e l l ig e n t c o n t r o l .

T h e s e r e s u l t s w i l l b e v e r y u s e f u l a n d i n t e r e s t in g i n t h ef u t ur e , w h e n t h e y w i l l b e a p p l i e d t o m o r e c o m p l e x a n d

s o p h i s t i c a te d l a r g e - s c a l e m a n u f a c t u r i n g a n d a s s e m b l y s y s -t e m s w h i c h a r e h a r d t o d e s i g n a n d c o n t r o l w i t h o u t u s i n gs i m u l a t i o n a n d e x p e r t s y s t e m s .

Acknowledgements--ThePROARC project (Ref. No. 7831) was partlysupported by the EC, in the framework o f Copernicus '93. The authors aregrateful to the partners, the WZL of RWTH Aachen and the University ofVeszpr6m, for their contributions. This work was partly supported by theHungarian Research Fund (OTKA), projects T 4122 and T 14549.

R E F E R E N C E S

Brill, M. and Gramm, U. (1991) MMS: MAP application services for themanufacturing industry.Compute r Ne tworks and ISDN Sys tems ,21 ,357-380.

Buta, P. and Springer, S. (19 92) Comm unicating the knowledge inknowledge-based systems.Expert Systems with Applicat ions,5,389-394.

E a s y M A P(1993) User Guide. CRI, Denmark.Franklin, G., Meystel, A.,et al. (1994 ) Private discussion by E-mail in

Architectures for Intelligent Control Systems Discussion List ([email protected] > B UFFALO.EDU).

Kov~cs, G. L.,et al. (1993) Integrated application of real-time expertsystems for FMS evaluation and control.Applicat ions of Art i f ic ialIntelligence in Engin eering VIII,

ed. Rzevski, Pastor, Adey, Vol. 2, pp.835-847. Elsevier, Amsterdam.Laffrey, T. J.et al. (19 88 ) Real-time knowledge based systems.A I

Magazine, 9(1 ), 27- 45.M M S - E A S E(1994) User Guide. SISCO Inc., MI.Nacsa, J. and Kov~ics, G. L. (1994) Communication problems o f expert

systems in manufacturing environment. InAIRTC '94 ,Valencia, Spain,ed. Crespo. Preprints of the Symposium on Artificial Intelligence inReal-time Control, IFAC, pp. 377-38 I.

Nagy, G. and Haidegger, G. (1994) Object oriented approach for analyzing,designing and controlling manufacturing cells. InProceed ings o fAUTOFACT '94 ,Detroit, ed. Moody. SME, pp. 12/1-10.

Somlo, J. and El Buzidi, A. (1996) Reverse scheduling, a new approach tothe solution of FMS scheduling problems.RAA D '96, Proceedings of the5th International Workshop on Robotics,Alpe-Adria-Danube Region,Budapest, Hungary, pp. 417-425.

Weck, M.,et al. (1995) A PC-based offline programming system to assist

robotized welding.ICRA M '95, Proceedings of the Internat ionalConference On Recent Advances in Mechatronics ,Istanbul, Turkey, pp.533-538.

some communication problems of kb-controlled

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