Optimization Aspects of Experimental FMS at the Technical University of Budapest (TUB)

Copyright © I FAC Decisional Structures in Auto ma ted Manu facturing. Geno\'a. Ita ly. 19H9

OPTIMIZATION ASPECTS OF EXPERIMENTAL FMS AT THE TECHNICAL UNIVERSITY OF BUDAPEST (TUB) J.

Som16, M. Girot and A. Szende

Budapesti Miisza ki Egyetem, Gepgyartastechnologia Tanszek, Egry Budapest, H unga ry'

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Abstract. The Department of Production Engineering, the Institute for Mechani cal Techno l ogy and the Information Laboratory of the Technica l University of Budapest are develop i ng an experimental Flexible Manufacturing System (FMS). In the present paper the structure , devices, the rea I - time con t r 0 I are 0 uti i ne d . A mo red eta i led des cri p t ion 0 f the prod u c t ion s ch e dui i n g s y stem and some 0 pt i m i z a t ion i de a s are pr e s e n t e d. As one of the way toward the total system performance optimization , the sec 0 n d a r y 0 pt i m i z a t ion i s pro p 0 sed. The b as i cid e as 0 f t his me t hod are given. ~~~Q~~~ CAD , CAM, Computer control , Flexible manufacturing, Manufacturing processes optimization , Product ion control.

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The system strurcture is shown in f i g 1.

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A deta il ed description of the cel l s i s not given, however , bas i c data about each device is I i sted below.

The Depar t ment of Production Engineering , the I ns tit u t e for Me c h ani c a I Te c h n 0 log y and the Information Laboratory of Technical University of Budapest are developing an experimental Flexible Manufacturing System (FMS) . The aim of such a system i s to develop highly automat i zed manufactur i ng hardware and software modules based, where possible , on Hunga r ian made elements and to use it for experimental production and fo r education. MA P -TOP approaches are to be rea I i sed w it h the use of devices best suitable and availab l e in Hungary. The production planning solutions are restr i cted to the schedul i ng l evel . The f i x t u rea n din s t r ume n tat ion f low s a r e not au t omat i zed. A number of problems such as a d apt i ve con t r 0 I , mo nit 0 r i n g, d i a g nos t i c s , s i mu I a t i on me t hod san d the use 0 f ex per t systems form the research projects connect ed w i th the FMS development. One of these prob I ems is the opt imi zat i on of sys tem pe r formance which is described in deta il in this paper. The max imum goal of the system integrati on would be the production of a gearbox type unit wich welded housing, designed by a p r oper CAD program , where almost a I I c omme r cia I I y a v a i I a b I e par t s are ma n u f act u red , q u a l i t y con t r 0 I led and assembled in the system. The bas i c aspect of the construction of the FMS is the use of " turn key " modules whe r e possible. The main supp l iers are Hungarian firms including FLEXYS fo r real- ti me control and ROBOPLAN / REKARD for t ransportation and storage system.

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- Turning CNC machine EEN 400 (SZIM Hungary) (for shaft type parts 0 max 100 mm ; Imax = 300 mm; for disc type parts 0 max = 250 mm ; Imax = 50 mm). - Horizontal CNC machining center TC3 (SZIM - Hungary) (400 x 400 x 350 mm) - Portal robot - located on the top of the turning machine - MR 10 (REKARD Hungary) - Cyl indrical robot FANUC M3 . ~.!.Q.!:.~£~~!2~_I.!:.~!2~QQ.!:..!.~.!.iQ!2~~.!..!.

The layout at the transportat ion routes are given in Fig . 2. - Three level storage system w i th CNC feeding and 30 storage un its - Robocar (ROBOPLAN/REKARD - Hungary) wit h i n d u c t ion a I n a v i gat ion s y stem. \y~.!.~i!2£_'£~.!..!.

- L IMAT 280 (REKARD - Hungary ; I GM Austria l i cence) 6 degree freedom heavy arc-weld i ng r o b ot RP 60 1 /60 (USSR made, wi th TUNGSRAM Hungary - cont ro I) spot we l ding r obot - Other complementary equipment.

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Th e FMS cons i sts o f five main modules: cutting ce l l - storage and t r ansportation ce l l - we l ding cell - measu ri ng cel - ass emb I y c e I I

UMC-850 CNC 40 measuring mach i ne (OP TONFRG) ODS 803 quality control unit (OPTON FRG) MITUTOYO hand held measuring u nits(J apan)

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The r ea I - t i",e ce I I con t ro I h ardware and soi t war e u r , its ca I led F LEXCELL are be i ng developed by the Inst i tute of Computer S c i en c e and Aut orra t i 0 Cl 0 f the Hu n g a r i an Acade~y

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Sciences a n d are being imple i n d us t r i a I t y p e I BM PC - s. The

me n tee 0 Cl FLEXCE L L sys tem a llo ws the control of up to 8 ind i vidual technological units using the L SV -2 (S IE MENS) protocol . The ope r aI i 0 Cl a I CO:l t r ei r r 0 g ra m i s w r i t ten i n I an gU'lge ,..: (8erto -< , Zsuffa , Szilagyi 1988) .

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On the upper level a ,V !CROVAX- II o r a VT32 (VIDE C T O ~ - Hunga r y) computer synchro:lises the act ions o f the d i fferent cel Is . T his c o'-'-,p u I e r i s c C' n nee tee t o t h e E THE RN E T network 01 the Mechan ica l Engineering F aculty o f TUB . T he basic CAD cap aci t ies are pro '/ i de d wit h the F' A 1; / 580 c omp u t e r 0 f t he Inforrr,at i c,", Labo ra tory . Powerful CAD stations are installed on the upper level of the Producti o n Engineeri:lg Facu l ties w o rk shop , ", her e the F,'1,S is to be installed .

4 . ~.c.9.Q~£ll9.'2_ 2£~£.Q~ll'2£ T h e pr oduc ti on task for the experimental FMS comes fr ,:Jm a simulated production planning system . The lo t si z es and due da tes are cbtained fr om the medium level p I an (Ye ama n S a '1 dot he r s 1985 j De s i g n r ul e s for a C I M syst em) . T he manu facturing

77

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sequences for the parts are determined by the process planning systems interfaced wi th the product ion schedul ing s y stem. The t ask 0 f the s ch e dui i n g i s t 0 determine the operation schedule of ma ch i net 00 I s for the g i v e n (s h 0 r t ) period of time and of other processing dev i ces of the system in such a way that the given requirements to the system perf ormance could be met . The schedu ling is based on the cont i nuous mo nit 0 r i n g 0 f the c e I I con d i t ion s . The input s for schedu ling sys tem are the id entification tags, the lot sizes, due dates and process plan sequences includi n g the fix t u re , ins t r ume n tan d NC program i n for ma t ion. The s c h e dui i n g s y stem produces a short time schedule based on the production orders which take into account the condition of the production s y stem (i e. ma chi ne f a i I u re s , ins t r ume n t conditions, etc.) as well as future expec ta t ions. The schedu ling is so I ved in severa I I evels. The first level is called the " re c omme n d e d " s c h e dui e w h i chi sus e d for per i ods of up to one week. I t allows the system to meet demands whi le opt imizing ma ch i ne uti I i z a t ion. Pr i 0 r i t y r u I e s are used in this type of scheduling. The SLACK ru I e is used in many cases but it can be substituted with others such as SPT , EDD , SOT/TOT, QTP, SWPT , SNQ , OPN , MF , MW or MTM . Heuristic ru l es may be used for the ref I ec t i on of spec i a I requirements. T he second level wh i ch is ca I I ed the " actua I " schedu I e deta i I s one day or one shift. Teh " actual " schedule uses

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up d ate d con d i t ion san d me t hod s s i m i I a r t 0 those used to set the " recommended " schedule . Frequently it is necessary to activate the scheduling system when interruptions such as breakdowns, defec t i ve par t s , lack of too I, fixture or urgent new orders

occur. I n these cases a th i rd I eve I, " dynami c " scheduling , i s used. At this stage , r ather s i mp l e procedures are applied which frequently neglect the priority cons id erations to facilitate speedy executio n.

5. QQli~~~liQ~_~~2~El~ The 0 pt i m i z a t ion 0 f the C I M per for ma n c e i san ex t r eme I y d i f f i cui t t ask . I t i s frequently difficult to determine what i s understood by opt imizat ion. In fact when evaluat ing elM performance, a number of points should be kept in mind. Product ion planning and control, process planning, storage, transportation , man i pu I at ion, ins t r ume n tat ion , se r v ice and other problems should be solved using different constraints. It is clear t hat exper t sys tem approaches and mu It i cr i terion optimization wi II play more and more important role in solving these problems. ( S om I 0 , 1 986 ) In this paragraph only some of the aspects of opt imizat ion wi I I be out li ned. Let us first consider the simp le st case of the so l ut ion of job-shop type scheduling when the following conditions are assumed: - N job , M machine tool problem is considered (Somlo , Horvath 1981 ; Watanabe ,

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78

Soml6, M. Girnt and A. Szende

Sak amo t o 1984 , 1985) . No ove r l a pping p r od u ct i on is allowed on di ffer ent machine too l s for the parts be l onging t o one batch. - On ly a s i ng le technologica l sequence f or one batc h is supposed (no technologica l va r iants a r e al l owed) . - T he t ec h no l ogical p r ocess par ame t ers ma y v ar y depend i ng on the schedu l ing s it u ati ons. Most o f th e systems use t h e prio r ity ru l es based heuristic methods for the so l ut i on o f j ob-shop type schedu l ing pro bl ems. Expert system approaches (see e.g. Kim , 1988) are coming i nto practice but t h ese are a l so us i ng priority conside r at i ons. Du e to performance improvements o f contemporary comuter environment , the eff e ct of using differenct priority ideas may well be estimated. The prioriy ru l es may be changed in a dynamic way so as to obtain the " best " schedu l er. T he au t hors of this paper (sim il arly to Wa t anabe , Saka t omo 1984) have found the SLACK p ri o ri ty rule su i tab l e i n many r ea l s i tu a tions. L et us now suppose that the " best " solut i on for the schedu ling has been dete r mined using the proper prior i ty ru l e . It is st il l poss i ble that the " best " solut ion ma y res u I t i n i die ma chi net i me san d bottle-neck situations. One way to improve the FMS performance is to change the cutting paramete r s in order to i mprove the tota I performance index of the system . Watanabe and Fuji i (1988) analysed the improvement of total system pe r fo r mance by process parameter changes us i n g a s c h e dui i n g s i mu I a tor a p pro a ch. Som l o and Nagy (1976) proposed the so cal l ed secondary optim i zat i on method wh i ch uti li zes a mathematical approach to change the process parameter va l ues a c co r d i n g t 0 ma nag eme n t (s c h e du i i n g ) requi r ements. Le t us short l y outline the basic i dea of secondary opt i mization. A we l l known mathematical model for cutting parameter opt i mization for a sir.lgle pass consists of t hree par t s (Goransk i i , 1963). As an example the turning type ope r at i ons are assumed: 7 A. .. = i V ," , = !\re x , i J.

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Opti m ization Aspects of Experimental FMS The o pt im izat i on o f i n depe n d e nt proc e ss sequen ces i s o nl y su ita b le whe n the c ut t ing p r o c ess i s s ep a r a t ed f rom th e producti o n s i t u ati o n a s i t i s in th e c a se o f cl a ss i c al ma nu fa ctu r ing .

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Let us examine the Gantt chart in Fig. 4. The fi r st number is the number of the pa r t , the sec 0 n d i s the numb er 0 f the operational seque nc e and the third i s the mach i ne numbe r. The due date i s not achieved for part 1 on the 4 - th machine due t o a bott l e-neck situat i on . It can be e I i m i n a t e d by de c rea sin g pro C e s sin g time of the f ollowing sequences: 1 , 5 , 4 ; 4 , 2 , 4 ; 5 , 2 , 4 and 2 , 1 , 4. It , i n tu rn , ma y ne C e s s i t ate a de c rea S e i n p r ocess i ng t ime for sequences 1 , 4 , 5 ; 5 , 3 , 5 ; 1 , 3 , 2 and others . It is ;nteresti ng to note tha t fo r part No 1 , independen t of the bot t le-neck situation , i n seq uences 1 , 1 , 1 and 1 , 2 , 3 the increase of p r o C e ss i n g t ime i s po ss i b l e . It is not ve r y difficult to develop the a l go r ithms fo r the determinat i on of poss i b l e time inte r vals for p r ocess paramete r cha n ges us i ng the simulated scheduli ng r esul ts .

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I t i s possib l e to determine the optimum process parameter values by determini ng t he sequences for wh i ch time increase or dec r ease is necessary as we I I as the time i nte r vals . The same method used for a sing l e pass opt i mization may be used wi t h a new extremal to o l life value: T ex t r ·I

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with Aa 0 to decrease and wi t h Ao < 0 to increase processing time . In a s imi I ar way tool I i f e synchronizat ion problems may be solved .

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The process planning tasks in the experimenta l CIM are solved by a number of 1 compu ~ er aid d sys~ems i nc uding TUSY , 1 1 FAMUS , FA~N , NC T , NC~-1 , VUL~ANUS l G TIPR OG -T~ , GTIPR9G-FM , jPE APT , SS F , SSF-SOL ID , EUCL ID , ANVIL and MEDUSA 3 . To in t e r connect p r oduct i on plann i ng a nd proc e ss plann i ng an optim i zat i on mod u le should be co n nected with the process pl a nni ng sys t em. Many o f t hem do not h a v e thi s cap a bil i ty . A speci al system was de v el o ped f o r t he so l ut i on o f sch e du li ng p r o bl e ms ment ; on e d above.

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human contro l is appl ied . The formal ization of approaches is ve r y d i fficult , so heuristic methods are commonly used. Here agai n the expert systems wi I I result a b r eak-through . Process planni ng variants may be generated using computer aided des i gn systems. A new method for the optimization of discrete technology processes ( Toth , Detzky , Eszes 1988) has oppor tun it i es fo r use in connect ion wi th research and development works out li ned in the present paper. ~Q~~l~~iQ~~

The experimental CAD/CAM system at TUB gives excellent opportunity for solv i ng application , research and educationa l problems . The opt imizat i on aspects formulated are principal in the effective utili z ation o f FMS . The solution o f this problem deep l y connects the process planning , schedul ing and process control subsystems into an integrated environment . References

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1./ P.BertOk - Zs.Zsuffa - Zs . Sz i lagyi : An easy to opera te window based man machine interface for manufacturing dells. IFAC Man Machin e Conf. , Oulu Finland , 1988 . 2 . / R . W. Yeoman s - A. Choundry - P.J.W. Ten Hagen : Design rules for CIM systems . North - Holland , 1985 . 3./ J . SomIO : Some problems of opt i m i z ati on in c omputer integrated manufacturing systems. IFAC Symp . Large Scale Systems , Zu ri ch , 1986. 4 . / J . SomIO - M.Horvath : On the hierar chi c a I s y stem s , 0 p t i m i z a t i on and a d apt i ve con t r 0 I 0 f ma chi net 00 Is. IFAC 8-th World Congress , Kyo t o , 1981 . 5 . / T . Watanabe - M. Sakamoto : On -I ine schedul i ng for adapt ive cont r ol mach i ne tools i n FMS . IFAC 9 - th World Congress Budap e st , 1984 . Developed a t the Pr oduc t ion Eng i nee ri ng Departrrent of TUB 2 Ot he r systems developed in Hungar y 3 Depending on the ava i la b i I i t y in Hungar y

so

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Somlo, M. Girnt and A. Szende

6./

J.Kim - E.F.Fichter - K.H.F unk : Building an expert system for FMS schedu l ing. USA- Japan Symp. on F l exib l e Automation Minneapo l i s , 1988 .

7. /

T. Watanabe - R.Fujii : Determining th e job operational spee d and schedule for mach in e tools in FMS by forecasting using a simulator and a system performance index. USA-Japan Symp. on F l exible Autom ati on M i nneapo li s , 1988.

8./

J . Somlo - J . Nagy : On a new approach to cutt ing data opt imizati on prob l em. PROLAMA T ' 76 Symp . Sti rling, See also : North Holland, 1977.

9. /

T . Toth - I .Detzky - L.Eszes: Optim izati on of discrete technology processes using a method traced back to cons trai ned travel I ing sa l esman problem . MATADOR Con f. Manchester , 1988.

10./G . K.Goranski i: Computer aided determination of cutting parameters. ( i n Russian) Gos izdat , Minsk , 1963.