Computers ind. En~n~ vol. 13, Nos 1-4, pp.I07-111, 1987 0360-8352/87 $3.00+0.00 Printed in Great Britain. All rights reserved Copyright c 1987 Pergamon Journals Lid

INTEGRATING MANUFACTURING RESOURCES PLANNING (NRP II) WITH FLEXIBLE MANUFACTURING SYSTEMS (FMS)

Dr. Howard W. Oden, P.E. Worcester Polytechnic Institute

Worcester, MA, 01609

ABSTRACT

This paper wall describe the gap that exists between the Manufacturing Resources Planning (MRP II) system end the Flexible Manufacturing System (FMS) end discuss severe1 epproachel for closing the gap. Consldereble effort has gone Ante developing end integrating the various modules in the MRP II system. The sodules ~or business planning, production planning, Beater production scheduling, materiel requirement planning, capacity requirements planning, end shop ~loor control have been integrated into s comprehensive coaputer package for planning and controlling manufacturing0 At the same time, e similar effort bee been underway to develop end integrate the several subsysteae of a FMS. In particular, s nuaber of coaputer control systems h a v e b e e n d e v e l o p e d to auto- aetically plan and control the operations of NC machines with automated tool changers, automated materiel handling, and automated teat e n d i n s p e c t i o n equipment. Unfortunately these two ef~orta have proceeded relatively inde- pendently with IAttle interaction between the two groups. If computer integrated aenu~ecturlng (CIM) is to become e reality, the resulting gap must be closed, a n d closed rapidly.

INTRODUCTION

Over the lest d e c a d e the varloua "islands'" o£ eutosatlon have been Ante- grated Ante three '*continents" of eutoaetion through seas very extensive integration efforts. These continents of sutoaatlon (MRP II, CAD/CAM, and FMS) have not completely integrated ell the islands of eutomstlon within them, but they have gone a long way towards establishing standards, computer architec- tures, end communications networks. However, there exiats huge gaps between these continents o£ autometlon, which As the subject of this paper.

In this paper we wall primarily be concerned with the gap that exiltl between the MRP II end FMS contlnente. This is not to say that the CAD/CAM

integration effort As not Important, or that all gaps between it end the other continents have been solved, but aerely to say that CAD/CAM Is not the focus of this paper.

An understanding o£ the nature and causes of the gap between MRP II end FMS can be obtained by tracing the evolution of these two continents o£ automation, which we will do in the following paragraphs.

THE EVOLUTION OF MANUFACTURING RESOURCE S PLANNING (MRP II)

The Manufacturing Resources Planning (MRP II) integration effort of the 1980"8 evolved from the Closed Loop Material Requirement Planning (MRP I) efforts o£ the 1970"m. The Closed Loop MHP I process ia shown in Figure 1 below:

Production Planning ......... < .... .

V I Master Production ......... • .... '

Planning ............. < .... . V J

...... • ......... Material Requirements ...... • .....

I Planning ............. < ........

I V

I ...... > .... Capacity Requirements Planning---<---.

V I

I N O V I • . . . . . . < . . . . . . . . . . . . . R e a l i s t i c ? ? ? I

YES V i V J

Executing Capacity Plans ..... • ..... V

Executing Material Plans ..... • .........

F I G U R E 1 . C L O S E D - L O O P M A T E R I A L R E @ U I R E M E N T S P L A N N I N G ( H R P I )

107

108 Proceedings of the 9th Annual Conference on Computers & Industrial Engineering

M a n u ~ a c t u r i n g R e s o u r c e P l a n n i n g (MRP I I ) h a s b e e n d e f i n e d ( W i g h t , 1 9 8 1 ) an e v o l v i n g f r o m t h e MRP I p r e c i s e and h a v i n g t h e f o l l o w i n g c h e r e c t e r £ e t i c a :

1 . T h e o p e r a t i n g and f i n a n c i a l s y s t e m a r e o n e and t h e e a s e . sese tranea~tiona, they uee the sale numbers. The financial a i r i l y e x t e n s i o n s o f t h e o p e r a t i n g n u m b e r s .

T h e y u s e t h e f i g u r e s a r e

2 . I t ham a " w h a t I f " c a p a b i l i t y . S i n c e a g o o d s y e t e s i a b a e i c a l l y a alsulatlon of reality, It can be ueed to simulate whet would happen I~

v a r i o u s p o l i c y d e c i s i o n s w e r e i m p l e m e n t e d .

3 . I t t a a w h o l e c o m p a n y a y e t e m n o w , A n v o l v A n g e v e r y f a c e t o£ t h e b u s i n e s s because the things the MRP II I s concerned with - sales, production,

inventories, achedulee, caeh flow, etc. - are the very ~undasental o f plannlng and controlllng a manufacturing or dietribution bueineaa.

Results OK?

!

I

I I

i

w

ACCOUNTING & HIS I

FINANCIAL PLANNING

Profit O b 3 e c t i v e a .......................

MARKETING

Sales Ob3ectives .......................

IMAHUFACTURING PLANNING

I Production Ob3ectIvea • .......... ^ ............ •

I

I

• ..... V ...... o

P l a n n i n g OK? . . . . . . . • . . . . . . o

Control I< ........ >! INTEGRATED I< ........ •

PURCHASING I I DATABASE I S u p p l i e r s I " . . . . . . . . . . . . .

SHOP FLOOR CONTROL I E x e c u t i o n I

I R e s o u r c e s OK? • ............... < .......................... • ............. •

!

I V I I

I

MASTER SCHEDULING

Products

MATERIAL PLANNING Parts

CAPACITY PLANNING Hours

I

FIGURE 2. CLOSED LOOP MANUFACTURING RESOURCES PLANNING (MRPII)

The c l o s e d l o o p p l a n n i n g and c o n t o l p r o o e e s shown a b o v e l a made p o a a £ b l a b y the integrated MRP II database which includee not only the manufacturing data (bill of materlale, inventorlea, routlngs, ehop ordere, etc.) but also market-

ing d a t a (order entry, £orecaeta, etc.) and financ£al date (accountm racily-

able, accountm payable, general ledger, cost accounting, etc.). Wlth the financial and marketing data combined with the manufacturing data, a truly closed loop bualneaa plan can be developed and executed. (Schultz, 1983)

THE SCHEDULING APPROACH OF MRP II

A review o£ the MRP I and MRP II proceaeee shown In Figures 1 and 2 shows a flow o~ Information from strateglc, long rmnge planning to intermediate sched-

uling and finally to execution end control. We are primarily concerned with t h e m i d d l e p h a s e o£ i n t e r m e d i a t e s c h e d u l i n g w h i c h i n c o m p o s e d o f m a s t e r p r o d u c - t i o n scheduling, rough-cut capacity plannlng, material requirements planning, cmpmcity requirements planning, and ehop floor control in current MRP II

myatamm.

Scheduling l a concerned wlth meeting the demand for the flrm'e products by ellocatlng permmnent and consumable resources. The driving function in echad- ullng am the demand which we attempt to forecaet.

I n MRP I I t h e e c h e d u l l n g p r o c e s s e t a r t a w i t h t h e m a s t e r s c h e d u l e a e ehown i n f i g u r e s 1 and 2 . T h i s I s c r e a t e d f r o m c u s t o m e r o r d e r s , p r o m i s e d t o s u i t a r o u g h c u t t e a t o f c a p a c i t y , and f o r e c a s t s o f f u t u r e o r d e r e , a l s o t e s t e d r o u g h l y agmlnat capacity. The capacity teat is ueualIy performed agalnat k n o w n bottle-

neck resources using broad time zones of weeke or months. It often use& product/resource profiles which are atatelente o f the reaourcee required to build a atandmrd quantity of a product. (IBM, 1975)

T h e m o r e d e t a i l e d s c h e d u l e s a r e d e r i v e d f r o m t h e m a s t e r p r o d u c t i o n s c h e d u l e b y e s s e n t i a l l y m e c h a n i c a l p r o c e d u r e s . I n t h e p r e c i s e c a l l e d m a t e r i a l r e q u i r e - s a n t a p l a n n i n g , t h e B e a t e r p r o d u c t i o n s c h e d u l e i a " e x p l o d e d " t h r o u g h t h e b i l l s

Oden: Integrating manufacturing resources planning 109

o f m a t e r i a l , t h e i n v e n t o r y n e t t e d , and d e t a i l e d make end b u y o : d e r s f o r p a r t s s c h e d u l e d u s i n g f i x e d p a r a m e t e r s f o r l o t s i z e s , l e a d t l m e a , and s a f e t y s t o c k . The a s s u m p t i o n i s made t h a t d e t a i l e d s c h e d u l e s can be c r e a t e d w i t h o u t c o n s i d e ~ - l n g t h e c e p a c l t y o£ p r o d u c t i o n r e s o u r c e s s i n c e t h e m a s t e r s c h e d u l e £m r o u g h l y w i t h i n c a p a c i t y .

U i t h t h e d e t a i l e d s c h e d u l e s d e v e l o p e d f o r p a r t s , t h e p r o c e s s o£ c a p a c i t y r e q u i r e m e n t s p l a n n l n g t h e n t e s t s w h e t h e r o u r a s s u m p t i o n i s c o r r e c t o r n o t . I n moat c a s e s I t l a n o t . P r o d u c t i o n s c h e d u l e s c r e a t e d I n t h e a b o v e manner o f t e n c r e a t e p e e k s end v a l l e y s o f demand on t h e p r o d u c t i o n r e s o u r c e s . The i n f i n i t e c a p a c i t y t e c h n i q u e e m p l o y e d b y c a p a c i t y r e q u i r e m e n t s p l a n n i n g , o n l y t a i l s ua 1£ we h a v e • p r o b l e m . Z t deem n o t h i n g t o s o l v e t h e p r o b l e m . T h a t mus t be done m a n u a l l y . Even t h e p r o b l e m d e f i n i t i o n Am n o t t o o c l e a r s i n c e CRP u s e s f i x e d l o a d tieoa and l o t m a z e s t o d e t e r m i n e t h e l o a d .

The s e 3 o r o u t p u t o f t h e NRP/CRP m o d u l e s a r e 3ob o r d e r s f o r beecham o f p a r t s t o be made i n t ame t o s u p p o r t t h e s e a t e r p r o d u c t i o n s c h e d u l e . From theme 3oh o r d e r s , t h e s h o p £ 1 o o ~ c o n t r o l s y s t e m p r e p a r e s d i s p a t c h l a s t s f o r each w o r k c e n t e r , w h i c h 1 1 s t a t h e 3abe t h e e e r e t o be p r o c e s s e d t h r o u g h t h e w o r k c e n t e r An t h e n e a r f u t u r e . A d d i t i o n a l l y , t h e d i s p a t c h l a s t p r o v i d e s t h e s u p e r v i s o r w i t h i n f o r m a t i o n ( p r i o r i t y , b a t c h s i z e , e t c . ) t h a t w i l l m e a i s t ham An a c h e d - u l i n g 3 e t a t h r o u g h t h e w o r k c e n t e r . H o w e v e r , a l l a c h e d u l ! n g Aa n o r m a l l y p e r f o r m e d m a n u a l l y by t h e w o r k c e n t e r l u p e r v i a o r end n o t a u t o m a t i c a l l y b y t h e shop f l o o r c o n t r o l mya tem. The s h o p f l o o r c o n t r o l s y s t e m m e r e l y p r o v i d e s t h e w o r k c e n t e r s u p e r v i s o r w i t h i n f o r m a t i o n t o a s s i s t h im i n m c h e d u l l n g ; A t d o e s no s c h e d u l i n g I t s e l f .

The g e n e r a l d e s i g n c o n c e p t o f t h e s h o p f l o o r c o n t r o l m o d u l e An mos t HRP I I pmckmges Am t h a t t h e f a c t o r y Am i m m e n s e l y t o o c o m p l e x and u n p r e d i c t a b l e t o a t t e m p t t o c o m p l e t e l y s c h e d u l e it b y c o m p u t e r . Thus t h e p u r p o s e o£ t h e s h o p f l o o r m o d u l e i a t o p r o v i d e t h e w o r k c e n t e r s u p e r v i s o r w i t h i n f o r m a t i o n t h a t w o u l d e n a b l e ham t o b e t t e r s c h e d u l e and menage p r o d u c t i o n m a n u a l l y .

S e v e r a l e a r l y a t t e m p t s t o a u t o m a t i c a l l y s c h e d u l e 3oba on t h e s h o p f l o o r w e r e d i s a s t e r s , m i n c e t h e shop f l o o r c o n t r o l s y s t e m d i d n o t h a v e s u f f i c i e n t l y a c c u r a t e end t i m e l y i n f o r m a t i o n t o p e r f o r m t h e s c h e d u l i n g t a s k e f f e c t i v e l y . They w e r e moon abandoned An f a v o r o~ p r o v i d i n g i n f o r m a t i o n t o t h e s h o p f l o o r s u p e r v i s o r s , so t h e y c o u l d do m b e t t e r 3oh o£ manua l s c h e d u l i n g .

THS CONCEPT AND EVOLUTZON OF FLEXIBLE NANUFACTURIHG SYSTENS (FHS)

A f l e x i b l e m a n u f a c t u r i n g s y s t e m c o n s l e t s o f a g r o u p o f p r o c e s s i n g s t a t i o n 8 ( u s u a l l y NC m a c h i n e s ) c o n n e c t e d t o g e t h e r b y a n a u t o m a t e d w o r k p a r t h a n d l i n g l y e t e m . Z t o p e r a t m a as an i n t e g r a t e d s y s t e m u n d e r c o m p u t e r c o n t r o l . The FHS Am c a p a b l e o f p r o c e s s i n g a v a r i e t y o f d i f f e r e n t p a r t t y p e s s i m u l t a n e o u s l y u n d e r NC c o n t r o l a t t h e v a r i o u s w o r k s t a t i o n s . ( G r o o v e r , 1980 )

; n g e n e r a l , i t hem been t h e m a c h i n e t o o l s u p p l i e r t h e e ham s e r v e d as t h e I n t e g r a t i n g f o r c e An t h e d e v e l o p m e n t o f FNS c e l l s . (Kochmn, 1 9 8 4 ) Zn e n d e a v - o r i n g t o a m t l a f y t h e c u s t o m e r ' s m a c h i n i n g n e e d s , t h e m a c h i n e t o o l s u p p l i e r ham a c t e d am t h e p r o 3 e c t manage r s e l e c t i n g m a t e r i a l h a n d l i n g c o m p o n e n t s and c o m p u t - e r c o n t r o l c o m p o n e n t s t o p r o v i d e an i n t e g r a t e d m a c h i n i n g c e l l . Zn t h e U n i t e d S t a t e s t h e mm3or d e v e l o p e r s o f FNS h a v e been t h e m a j o r m a c h i n e t o o l s u p p l i e r s much me: Hemrney and T r a c k e r , C i n c i n n a t i H i l a c r o n , G t d d i n g s & L e w i s , end W h i t e S u n d a t r a n d .

Zn moa t c a s e s , t h e m a c h i n e t o o l v e n d o r has n o t had t h e n e c e s s a r y e x p e r t i s e A n - h o u s e t o d e v e l o p t h e c o m p u t e r c o n t r o l s y s t e m , end hem r e l i e d on o b t a i n i n g t h e s e r v i c e s o f a n o t h e r v e n d o r t o d e v e l o p i t . Thus t h e d e v e l o p e r o f t h e c o m p u t e r c o n t r o l s y s t e m s l o o k s t o t h e m a c h i n e t o o l v e n d o r f o r f u n d i n g and g u i d a n c e , end l e n o t p a r t i c u l a r l y i n t e r e s t e d i n , n o r c a p a b l e o f , i n t e g r a t i n g h i e c o m p u t e r s y s t e m w i t h a n o t h e r c o m p u t e r s y s t e m such as NRP ZZ.

TH~ ~CHEDULZNG APPROACH REQUZRED BY FNS

The m c h e d u l l n g a p p r o a c h r e q u i r e d by a f l e x i b l e m a n u f a c t u r i n g s y s t e m I s s i m i l a r t o t h a t r e q u i r e d by a d y n a m i c 3oh s h o p . A v a r i e t y o f p a r t s e r e s £ m u l - t a n e o u a l y p r o G e a s e d t h r o u g h t h e s e = h l n e a o The o p e r a t i o n s on a p e r t can be a c c o a p l £ a h e d b y r o u t i n g t h e p e r t t h r o u g h a l t e r n m t e m a c h i n e s e q u e n c e s . S e v e r a l o p e r a t i o n s can be p e r f o r m e d on a m a c h i n e w i t h n e g l i g i b l e c h a n g e - o v e r t i m e . The d e c i s i o n t o s c h e d u l e t h e n e x t o p e r a t i o n on m p e r t d e p e n d s upon t h e m e a t u s o£ t h e m a c h i n e s end t h e max o£ p a r t s a v a i l a b l e f o r p r o c e s s i n g a t t h a t t i m e . The o b 3 o c t i v o i s g e n e r a l l y t o f i n i s h p e r t h An a a t n i n u m a m o u n t o£ t i m e , end t o m l n i m £ z e p a r t t a r d i n e s s o r m a x i m i z e m a c h i n e u t i l i z a t i o n . AS t h e m a c h i n e s i n v o l v e d I n a FNS e r e v e r y e x p e n s i v e , m a x i m i z i n g mmchlne u t £ 1 1 z a t l o n l a one o£

110 Proceedings of the 9th Annual Conference on Computers & Industrial Engineering

the more important objectlvea. utilization while minimizing 1 9 8 4 )

In practice, the dual ob3actlve of maxlmi:in 9 3ob tardiness ia very common. (Sarln & Day-el.

A nuabar of complex declalona must be made in e very short time, if the dual objectlvea of maximizing utilization and minimizing Job lateness ere to be achieved. Among theme are: (i) d i v i d i n g overall production targets into batches of parts, (2) within each batch, aaalgnlng production raaourcem in a harmer that mexkmlxea resource utili=atlon, (3) raapondlng to changes in upper level production plans or material availability, (4) work order scheduling end dlapetchlng (which part to intreduoe next into the FMS, end when), (5) movement of workplecea and material handling system (which machine to sand this work- piece to next, which cart to transport it, etc.), (6) tool management (aalectlng tools for job, keeping track of tools end tool ware, raactln 9 to tools breakage, etc.), (7) flxturea management (aalactlng fixtures for 3oh, keeping track o f flxturea, etc.), (8) NC program management (selecting NC programs for proceaalng and Inapectlon, downloadlng and uploadln@ at appro- priate tlaea, etc.), (g) reacting to dlaruptlona (failures of mechlnaa, tools, and material handling system, or mudden changes in production requirements), and (i0) system monitoring and dlagnoatica. (Surl & Whitney, 1984)

All o f theme declalona must be made correctly and made on time if the FMS le to operate effectively and efficiently. Due to their complexity, these decisions could not be made manually, even if there were people to m a k e them, which there la not in the normal FMS.

THE GAP BETWEEN THE MRP II AND FMS SCHEDULING APPROACHES

A review o £ the NaP I and NRP II processes shown in Figures 1 and 2 shows s very 1oglcal f l o w Of information free atrateglc, long range planning to inter- m e d i a t e s c h e d u l i n g , a n d f i n a l l y t o e x e c u t i o n e n d c o n t r o l . H o w e v e r , t h e d e t a i l s Of the scheduling are not so logical. The aaaumptlon that detailed schedules that ere within capacity can be derived from a master production schedule which la roughly in cepaclty la patently false. Experience has proven that this does not happen. Even if the master schedule was perfectly in balance with capacity, it la possible that the detailed schedules could be unbalanced, b e c a u s e O f t h e l u m p i n e s s O f d i a a g g r e g a t i o n .

The NRP/CRP a p p r o a c h f i r s t d e v e l o p s a s c h e d u l e w h i c h m a t l a f i a a d e m a n d , and then looks mt the resource lapllcatlona, rather that developing m schedule that aatleflea both the demand and the resource contralnta almultaneoualy. Thle separate modular mppromch is an anachronlem from the early d a y s , when computer systems did not have sufficient proceaelng power and main storage capability to s o l v e t h e c o m b i n e d p r o b l e m .

The MRP II achedullng approach la dealgned to plan and control the usa of only one of the consumable resources used in manufacturing materlala. It schedules none of the other consumable resources (tools, energy, etc.) and does not plan and control the usa of any permanent (non-consumable) resources of p e o p l e , m a t e r i a l p r o c e e d i n g a a c h i n e a , m a t e r i a l h a n d l i n g e q u i p m e n t , a s s e m b l y equipment, fixtures, and Informetlon. A FHS represents a large investment in permanent resources. The achedullng system should be dealgned to schedule and effectively utilize all the permanent and consumable resources.

The philoaphy currently espoused by HaP If, that the factory floor la Immensely too complex to be scheduled autometlcally by the computer, and the beat the computer can do la provide In£ormatlon to the human aupervlaora on the shop floor to aaelat in manually achedullng the factory, must change. Wlth the advent o~ flexible manu£acturlng systems, the factory floor la immensely too c o m p l e x a n d f e a t m o v i n g t o e v e r be s c h e d u l e d m a n u a l l y , e n d t h u s i t mumt be scheduled autoeatlcally with computers. However, the current MRP II systems do not have the capability to autommtlcally schedule a FHS. Consequently, any achedullng that la done must be done either manually or by the computer control s y s t e m O f t h e FHS.

SOLUTION APPROACH

T h e s h o r t r a n g e a p p r o a c h t o s o l v i n g t h e g a p b e t w e e n MRP I I a n d FMS w i l l i n v o l v e t h e i n t e r n a l d e v e l o p m e n t a n d i m p l e m e n t a t i o n o f a s o f t w a r e i n t e r f a c e t h a t w i l l b e u n i q u e t o e a c h c o m p a n y i n s t a l l i n g e FNS. A n u m b e r o f t h e m e e f f o r t a w i l l i n v o l v e t h e u t i l i z a t i o n o£ e c o m m e r c i a l l y ava£1eble f i n i t e s c h e d u l i n g p a c k a g e , s u c h a a OPT ( S a v a g e & H l k u r a k , 1 9 8 6 ) , t o a s s i s t i n b r i d g i n g t h e g a p . O t h e r s w i l l u t i l i z e a s c h e d u l i n g p a c k a g e a n d i n t e r f a c e t h a t l a d e v e l o p e d c o m p l e t e l y i n - h o u s e . ( W e b s t e r , 1 9 8 4 ) R e g a r d l e s s o f how t h e n e a r - t e r m i n t e r f a c e l a d e v e l o p e d , t h e d e v e l o p m e n t w i l l be l o n g e n d e x p e n s i v e e n d w i l l

Oden: In tegra t ing manufacturing resources planning 111

probably provide leas then satisfactory results.

The long range solution to this problem will involve a co~pleta rethinking of the logic end scheduling approach used in MaP II. It is quite obyloua that the MaP II systems of today cannot be used to schedule the FMS factorlaa of the future. However, developln 9 a schedulln 9 package that will automatlcally schedule the automated factorlos of the future ia no smell undertaking. It will requlra the cooperative efforts of a greet many people, end will probably require 9overnaent alelstanceo However, If America is to fully utilize the the capability of flexlbla manufacturing systems in world compatltlon thla effort must be undertaken.

SUMMARY AND CONCLUSIONS

If Aaerlcan manufacturers are to remain compotltlve in the world market, they must obtain the full benefit of flexible manufacturing syetemm. To do this, the gap between the aanufacturlng resources planning system and the flexible manufacturln 9 system Rust be closed, end closed rapidly. WLth today's vast Increase in the capability of computers end the draatlc roductlcn in thalr costa, the scheduling approach currently used by most MaP II eystaaa no longer sakes sense. Although it may not be easy to automatically schedule a flexible manufacturing ayatom, it la necossary end poaalble, end we auat get on with it.

REFERENCES

G r o o v e r , M l k a l l P. ( 1 9 8 0 ) , Au toma~;on~ P r o d u c t i o n S y a t e a s l and C o m p u t e r - A i d e d M a n u f a c t u r l n q , P r e n t i c e - M a l l , p . 564

International Bualnesa Machines (1975), Master Production Schedule P;an~lnq Gulde, International Buslneas Machinea, White Plalna, NY, p. 34

Howard, 3. end E. Sommerlad (1984), "The Future Direction of Packaged Manufacturing Software", Readings in Comnuters end Software, American Production and Inventory Control Society, pp. 48-52

Kochan, Anne (1984), "FMS: An Internatlonal Overview of Applicatlons", The FMS M a a a z l n e , Ju l y 1984

Satin, S.C. and E.M. Dar-el (1984), "'Approaches to the Scheduling Problem in FMS," ~84 Fq~l Induatrla~ Enqlnoerinq Conferanqe ProceedlnQa, Institute of Industrial Engineers, pp 225-235

Savage, E. and M. Mikurak (1986), "'Finite Scheduling: Staging a Comeback?", C~M Technoloay, Spring 1986, Society of Manufacturing Engineers, pp. 26-31

Schultz, T.R. (1983), "Top Manageaant Plannln 9 for Closed Loop Systems", 26th Annual Conference Proceedlnqa, Amerlcan Production end Inventory Control Society, 1983, pp. 338-340

Suri, R. and C.K. Whitney (1984), "Docision Support Roquirementa in Flexible Manufacturing," Journal of Manufacturlnq Syataaa, Vol. 3, No. I, Society of Manufacturing Englneera

Webster, W. Bruce (1984), "Production and Order Planning in the FMS Envlronaent," 1984 Fell Induatrlal Enqlnearinq Conference proceedlnqa, Institute of Induatrlal Engineers, pp. 173-181

Wight, O.W. (1981), MaP II: Unlockln q Aaerlca'a Productivity Potentlal, CBI Publlehlng Co., Inc. pp. 5?-58