Manufacturing as a System-Determined Science

W O R K I N G P A P E R

I n t e r n a t i o n a l I n s t i t u t e tor -lid Systems Analysis

NOT FOR QUOTATION

WITHOUT THE PERMISSION OF THE AUTHOR

WWUFACTURING AS A

Fl[STEK-DErExMrNED SCIENCE

J o h n L.Casti

October

1986 WP-86-43

Working Papers are interim r e p o r t s on work of t h e International Institute f o r Applied Systems Analysis and have r e c e i v e d only limited review. Views o r opinions e x p r e s s e d h e r e i n do not n e c e s s a r i l y r e p r e s e n t t h o s e of t h e Institute o r of i t s hiational Member Organizations.

INTERNATIONAL INSTITUTE FOR APPLIED SYSTEMS ANALYSIS 2361 Lzxenburg, Austriz

FORWARD

During t h e p a s t y e a r , as p a r t of i t s p r o g r a m , t h e Theory of Manufacturing Feasibility Study investigated t h e d e g r e e to which modern manufacturing problems are "systems-determined", i.e., dominated by m a t t e r s of functions r a t h e r t h a n s t r u c t u r e ; software as opposec? to h a r d w a r e . This r e p o r t by John Casti a d d r e s s e s t h i s issue, as well as s e v e r a l o t h e r m a t t e r s of system t h e o r e t i c c o n c e r n r e l e v a n t to c u r r e n t manufacturing.

Thomas H. Lee D i r e c t o r , IIASA

MANUFACTURING

AS

A

2 z ' s r E x - D - m

SCIENCE

J o h n L . C a s t i

1. Manufacturing in Transition

To t h e a v e r a g e man on t h e s t r e e t , mention of t h e word "manufacturing", likely c o n j u r e s up visions of red-hot blast f u r n a c e s , clanking assembly lines, unfathom- a b l e machinery and h o s t s of blue-shirted w o r k e r s scurrying t o and f r o conveying components from one p a r t of a d a r k , dingy, d i r t y f a c t o r y t o a n o t h e r . This image, f o s t e r e d by t h e automobile manufacturing p r o c e s s in t h e e a r l y 1900s, i s finally un- dergoing a long overdue r e f u r b i s h i n g as a r e s u l t of t h e introduction of widespread, c h e a p information processing and communication c a p a c i t y into t h e in- dustrial workplace. While i t i s t r u e t h a t manufacturing s t i l l consists of t h e e t e r n a l triangle: Design. Production and Marketing, welded t o g e t h e r by Planning and Management, t h e manner in which t h e manufacturing t a s k s a r e being c a r r i e d out i s undergoing a r a d i c a l transformation, a transformation comparable in scope, p e r h a p s , only t o t h a t e x p e r i e n c e d by a g r i c u l t u r e a few decades ago. In s h o r t , t h e introduction of modern information processing facilities into virtually e v e r y nook and cranny of t h e manufacturing e n t e r p r i s e i s resulting in a vision of t h e

"factory-of-the-future" as d i f f e r e n t from t h e "Model-T" image d e s c r i b e d above as a Model-T i s from a new F e r r a r i . We a r e moving into a n e r a in which a v e r y s m a l l f r a c t i o n of t h e l a b o r f o r c e will b e involved in producing all t h e material goods t h a t society can consume, t h e same situation w e a l r e a d y have in a g r i c u l t u r e . This pa- p e r i s devoted to a n exploration of t h e "system-determined" c h a r a c t e r i s t i c s of t h e s e f u t u r e manufacturing e n t e r p r i s e s and t o pointing o u t t h e system problems t h a t c u r r e n t l y stand in t h e way of a realization of t h i s vision.

How, then, h a s t h e introduction of advanced d a t a processing capability changed t h e o v e r a l l manufacturing p r o c e s s and what are t h e likely consequences f o r t h e s h a p e of industrial production in t h e f u t u r e ? First, let us t a k e a look at some of t h e new o r enhanced capabilities of tomorrow's factory:

f l e z i b i l i t y

-

t h e possibility f o r producing products from a n almost limitless variety of designs and materials: "economies of scope" r e p l a c e economies of scale;

a d a p t a b i l i t y

-

ability t o r e s p o n d quickly to changing market demands and unexpected environmental fluctuations;

r e l i a b i l i t y

-

t h e capacity to more effectively schedule maintenance. in- c r e a s e d use of automation (robots), and numerically-controlled equipment all contribute to h i g h e r levels of reliability in finished goods;

e m c i e n c y

-

b e t t e r use of machines, reduced inventories, and fewer stoppages f o r missing materials and p a r t s a r e all r e s u l t s of t h e improved management capabilities emerging out of advanced software;

c o n t r o l l a b i l i t y

-

enhanced s e n s o r technology, coupled with improved informa- tion processing, gives h e r e t o f o r e unprecedented management information and c o n t r o l o v e r all o p e r a t i o n s .

In s h o r t , t h e f a c t o r y of t h e f u t u r e will b e flexible and efficient, t o g e t h e r with g r e a t e r complexity of both p r o d u c t and p r o c e s s . Finally, such a f a c t o r y will con- sistently p r o d u c e high-quality products. Only t h e computer-integrated manufac- t u r i n g system, with i t s vastly improved information and decision capabilities, o f f e r s a means t o t r a n s f o r m t h e f a c t o r y of y e s t e r d a y into t h i s t y p e of f a c t o r y of tomorrow. But, t h e shift in emphasis from p r o d u c t t o p r o c e s s b r i n g s with i t a s h i f t from h a r d w a r e t o software, t h e ultimate consequence being a n emergence of t h e c r u c i a l r o l e of systems thinking in building t h e f a c t o r y of tomorrow. In t h e final analysis, t h i s means t h a t manufacturing must become more of a s c i e n c e and less governed by "rules of thumb" and intuitive judgement. After all t h e smoke c l e a r s away, what remains i s t h e need t o develop a systems-based "theory of manufactur- ing". In what follows. w e s h a l l a t t e m p t t o provide a n "alphabet" from which such a t h e o r y may b e composed.

2. FACTORIES OF TOMORROW

-

A

SKELETAL

OUTLINE

P r i o r t o e n t e r i n g i n t o a detailed consideration of manufacturing and manufac- t u r i n g problems. i t i s useful t o gain a bit of p e r s p e c t i v e by taking a look at what a typical manufacturing o p e r a t i o n might look like 10 t o 15 y e a r s from now. A s we s h a l l see in t h e next section. t h e o v e r a l l i s s u e of Manufacturing encompasses s e v e r a l levels ranging from r a w materials considerations t o social values. b u t t h e l e v e l of g r e a t e s t c o n c e r n and t h e l e v e l most of u s intuitively feel r e p r e s e n t s "real"

manufacturing i s t h e level of t h e individual manufacturing unit. i.e. a plant o r a firm. The s k e l e t a l outline p r e s e n t e d h e r e of how t h e plant of tomorrow will func- tion t o u c h e s only t h e mountain-tops and gives a compact overview of t h e principal f e a t u r e s distinguishing such a p l a n t from i t s contemporary c o u n t e r p a r t . F o r a de- tailed t r e a t m e n t along t h e same lines f o r a prototypical metal-working plant, w e highly recommend t h e v e r y extensive and p e r c e p t i v e r e p o r t [I]. The manufactur- ing l i t e r a t u r e contains a v a r i e t y of speculations and prognostications of similar n a t u r e ; some of t h e b e s t are found in [Z-41.

The most distinguishing a s p e c t of t h e manufacturing plant of t h e f u t u r e i s i t s h e t e r a r c h i c s t r u c t u r e . The ability t o t r a n s f e r information almost instantaneously from o n e p a r t of t h e p r o c e s s t o a n o t h e r means t h a t t h e traditional h i e r a r c h i c a l . t r e e - s t r u c t u r e , sequential manufacturing system w i l l b e transformed into a h e t e r a r c h i c a l , distributed, parallel-processing system capable of a high level of flexibility in producing a myriad of p r o d u c t s with high quality and efficiency. The e f f e c t i v e coordination of s u c h a d i s t r i b u t e d p r o c e s s would b e unthinkable, of c o u r s e . without t h e information processing r e s o u r c e s t h a t have only r e c e n t l y be- come available. I t i s probably not a n e x a g g e r a t i o n t o say t h a t t h e ultimate aim of any d e c e n t t h e o r e t i c a l study of such manufacturing p r o c e s s e s i s t o devise a frame- work t h a t e n a b l e s us

to

understand how t o configure t h e various components of t h e manufacturing p r o c e s s (design. production. distribution. management) t o most effi- ciently and effectively employ t h e computing r e s o u r c e s available. We s h a l l have considerably more

to

s a y a b o u t t h i s point later on, b u t f o r t h e moment let u s con- s i d e r a typical s c e n a r i o f o r such a plant.

The p r o c e s s of designing a p r o d u c t will begin with a n i t e r a t i v e dialogue between t h e designer a n d t h e computer (CAD). The d e s i g n e r will supply t h e pr*

d u c t , concepts, and specifications, while t h e computer c a r r i e s o u t design calcula- tions and p r o v i d e s s t a n d a r d i z e d information. During t h i s p r o c e s s , t h e computer c a n b e continually taking into account information on t h e manufacturing c o s t s a n d capabilities needed t o actually p r o d u c e t h e p r o d u c t u n d e r design. The computer will then employ t h i s information t o g e n e r a t e a design t h a t not only meets t h e pr*

d u c t specifications, but a l s o c a n b e manufactured in some "optimal" way. I t is im- p o r t a n t t o note t h a t t h i s design p h a s e of t h e p r o c e s s may b e physically f a r re- moved from t h e a c t u a l p l a n t facilities involved in t h e production of t h e product.

Nevertheless, c u r r e n t information technology will e n a b l e t h e design computer t o b e in continual c o n t a c t with t h e s t a t u s of t h e plant a n d t o employ t h i s information as p a r t of t h e design p r o c e s s .

A t almost t h e same time t h e design p r o c e s s i s going on, t h e production plan- ning p a r t of t h e system will u s e t h e design information to set up a n optimized pr*

duction plan to p r o d u c e t h e p r o d u c t . This plan will involve selecting t h e p r o p e r equipment and p r o c e s s e s , configuring t h e sequence of o p e r a t i o n s , choosing t h e o p e r a t i n g conditions, etc. A l l of t h e design and production information will t h e n b e used t o c o n t r o l t h e automatic machines t h a t will actually p e r f o r m t h e physical operations. Each of t h e s e machines continually f e e d s information a b o u t i t s s t a t u s back t o t h e production c o n t r o l system, which t h e n p e r f o r m s dynamic adjustments to t h e production plan as needed.

While t h e production p r o c e s s is u n d e r way, t h e v a r i o u s machines will b e c a r - rying on self-diagnosis of t h e i r condition and if a f a i l u r e i s impending, t h e y will perform automatic c o r r e c t i v e actions. In addition, t h e machines will also c a r r y o u t automatic quality c o n t r o l inspections at each s t a g e of t h e p r o d u c t ' s manufac- t u r e , s o t h a t t h e final finished p r o d u c t will b e fully inspected a n d conform to t h e original design requirements.

During t h e c o u r s e of production, t h e distribution planning component of t h e system will be in communication with t h e production p a r t , g a t h e r i n g information as t o how to b e s t a l l o c a t e t h e finished p r o d u c t among v a r i o u s distribution c e n t e r s . The distribution program must optimally balance c u r r e n t demands and o r d e r back- logs with available t r a n s p o r t a t i o n facilities and c o s t s

to

decide t h e optimal m e a n s f o r distributing t h e finished p r o d u c t among various distributors/consurners and in- ventory warehouses.

This brief s k e l e t a l outline of t h e o p e r a t i o n of t h e f a c t o r y of t h e f u t u r e is not- a b l e f o r i t s r e l i a n c e upon a high d e g r e e of communication, both within e a c h major component and, more importantly. between components. Each s t a g e must b e plan- ning i t s action upon information as t o what's happening in t h e preceding s t a g e s with t h e loop being closed by management s t r a t e g y reading t h e results of t h e dis- tribution network (sales, p r o f i t s , and t h e marketplace) a n d feeding this informa- tion back

to

t h e design s t a g e .

Even in as s k e t c h y an outline of tomorrow's f a c t o r y as t h a t given h e r e , s e v e r a l dominant themes a l r e a d y e m e r g e c h a r a c t e r i z i n g major d e p a r t u r e s of fu- ture f a c t o r i e s ' ways of doing business from t h e f a c t o r i e s of today. Among t h e most significant f e a t u r e s , w e find t h e following:

a e e d

-

in today's f a c t o r y , t h e typical throughput time from o r d e r placement

to

fulfillment i s measured in weeks a n d months; in t h e f u t u r e t h i s time will b e measured in h o u r s a n d days. I t i s important to n o t e h e r e t h a t t h e push f o r speed is only p a r t l y motivated by a d e s i r e t o give b e t t e r customer s e r v i c e . An equally important motivation i s t h e need f o r b e t t e r c o n t r o l and c o s t reduc- tion (Just-in-time inventory c o n t r o l , f o r example). The downside in t h i s push

f o r s p e e d will b e t h e e m e r g e n c e of s e r i o u s bottlenecks in t h e p r o c e s s as o p e r a t i o n s t h a t are now r o b u s t d u e to long leadtimes lose t h e i r s t a b l e . c h a r a c - ter a n d become p o t e n t i a l problems.

FZezibiLity

-

many v a r i a t i o n s in p r o d u c t specifications t h a t w e now r e g a r d as e x c e p t i o n a l will become normal in t h e f u t u r e . A s a r e s u l t , equipment will b e v e r s a t i l e enough t h a t i t s c o s t c a n b e amortized o v e r many d i f f e r e n t p r o d u c t s . In addition, t o make small b a t c h sizes economical, i t will b e n e c e s s a r y t o r e d u c e set-up c o s t s t o t h e point where t h e y are no longer a f a c t o r in t h e pro- d u c t c o s t calculations.

ArtificiaL (Machine) InteLLigence

-

t h e f a c t o r y o p e r a t i o n d e s c r i b e d a b o v e re- l i e s heavily upon t h e ability to manage enormous quantities of d a t a , and t h e c a p a c i t y to t r a n s f o r m t h a t d a t a into information and t h e n i n t o knowledge.

Such a f a c t o r y must ultimately r e d u c e i t s dependence upon human judgment and i n t e r p r e t a t i o n . r e p l a c i n g i t with a r a t i o n a l foundation f o r design, produc- tion, and distribution b a s e d upon p r o c e s s models and physical laws. To c a r r y o u t t h i s transformation from today to tomorrow will r e q u i r e a genuine s c i e n c e of manufacturing, not just a l a r g e body of e x p e r i e n c e .

I n t e g r a t i o n of TechnoLogies

-

i t i s a comrrionplace today t h a t f a c t o r i e s are o f t e n unable t o benefit from known technologies because t h e s e technologies do not comfortably f i t t o g e t h e r . Advances in highly specialized areas of r e s e a r c h a r e wasted b e c a u s e bottlenecks at t h e i n t e r f a c e impede e f f e c t i v e utilization of t h e new technology. In t h e f u t u r e f a c t o r y , c o c s i d e r a b l e a t t e n - tion will b e given t o i n t e g r a t i o n of individual technologies into a harmonious whole. This will b e a "rebuild-from-common-fou~dations" kind of i n t e r p r e t a - tion, r a t h e r t h a n a "paste t o g e t h e r " s o r t [I].

With t h e foregoing image of tomorrow's manufacturing e n t e r p r i s e in mind, let uS now t u r n t o a more detailed c o n s i d e r a t i o n of t h e t y p e s of systems problems s u c h a n organization will g e n e r a t e .

3. A TAXONOlKY FOR MANUFACTURING PROBLEMS

When w e use t h e t e r m "systems problem" t o d e s c r i b e a manufacturing situation what d o w e r e a l l y mean? Are t h e r e some identifying "fingerprints" t h a t e n a b l e u s t o c h a r a c t e r i z e c e r t a i n a s p e c t s of manufacturing as "systems" a s p e c t s , while deny- ing t h i s l a b e l t o o t h e r problems? Basically, i s t h e r e such a thing es a "system"

t h e o r y of manufacturing distinguishable from any o t h e r garden-variety t h e o r y of manufacturing? O u r contention i s t h a t t h e answer t o all t h e s e q u e r i e s i s yes. but i t i s an answer t h a t comes in s e v e r a l p a r t s .

Before embarking upon a justification of o u r claim. let u s clear t h e a i r a b i t r e g a r d i n g what w e think of as a "systems" problem. Basically, w e c o n s i d e r a sys- t e m s problem t o b e o n e in which t h e emphasis is placed u p o n f u n c t i o n r a t h e r t h a n form; p r o c e s s r a t h e r t h a n s t r u c t u r e ; soflurare r a t h e r t h a n h a r d w a r e . Of c o u r s e , t h i s is a c r u d e , vague s o r t of classification. but i s evocative of t h e f e a t u r e s c h a r a c t e r i z i n g a system-dominated problem. W e shall e l a b o r a t e a n d embroider upon t h e s e basic ideas within t h e c o n t e x t of manufacturing as w e p r o c e e d , e a c h level of e l a b o r a t i o n f u r t h e r r e f i n i n g t h e systems n a t u r e of manufacturing o p e r a - tions.

A t t h e o u t s e t , w e must recognize t h a t t h e v e r y c o n c e p t of a m a n u f a c t u r i n g s y s t e m i s a multi-faceted o n e and t h a t t h e identification of systems problems i s v e r y much dependent upon o u r p e r s p e c t i v e of t h e o v e r a l l p r o c e s s of manufactur- ing. W e h a v e found i t useful t o consider manufacturing as a n activity t o b e s t r a t i - fied into t h e l a y e r s depicted in Figure 1.

(macro) M

-

Values

-

s o c i o - c u l t u r a l

i m p a c t s VIII

-

Wmld I n d u s t r y

-

global economy VlI

-

Manufactured foods

-

national economy VI

-

I n d u s t r y

-

n a t i o n a l I n d u s t r y V

-

Local I n d u s t r y

-

r e g i o n a l I n d u s t r y (meso)

(

^IV

-

F f n i s h e d Product

-

^{f l m}

(micro)

I

^I

^-

^Materials

-

a s s e m b l y l i n e

-

s h o p f l o o r

-

r a w r n a t e r i a l s

( s o c i a l s c i e n c e , t r a n s d i s c i p l i n a r y )

( s o f t w a r e , natural s c i e n c e , m u l t i d l s c l p l i n a r y , p r o c e s s , l n f ormation)

T

(hardware,

disc!pUnary-or1 e n t e d , s t r u c t u r a l )

Figure 1. Manufacturing System S t r a t i f i c a t i o n

H e r e w e h a v e indicated t h a t t h e systems-determined a s p e c t s of manufacturing tend to emerge at t h e middle levels of t h e diagram, while t h e u p p e r and lower levels are dominat.ed by problems in which t h e systems a s p e c t i s of lesser importance. Notice t h a t w e s a y "of l e s s e r importance" and not "unimportant". What determines a sys- tems problem in manufacturing i s t h e r e l a t i v e emphasis upon issues of p r o c e s s and function, grounded in c o n s t r a i n t s from t h e natux-a1 s c i e n c e s , r e q u i r i n g a knowledge of s e v e r a l disciplines f o r t h e i r t r e a t m e n t . The dominant problems at t h e lower lev- els a r e primarily disciplinary (e.g., physics, chemistry, materials s c i e n c e ) in orientation. focusing upon physical p r o p e r t i e s and s t r u c t u r e s ; u p p e r level prob- lems, f o r t h e most part, emphasize t h e social s c i e n c e s a n d humanities (e-g., philo- sophy, economics, theology) a n d are r e a l l y transdisciplinary in n a t u r e . s t r e s s i n g n e i t h e r p r o c e s s n o r s t r u c t u r e . Thus, just as in c h e s s where t h e action i s in t h e middle game, so i t i s in manufacturing: t h e systems problems r e s i d e in t h e mid- r a n g e of o u r h i e r a r c h y , roughly speaking levels I1

-

V, a n d especially in t h e p a t h s l i n k i n g t h e s e levels. A s indicated in t h e diagram, t h e r e are f e e d b a c k s a n d feed-

.forwards from a l l levels, which no decent o v e r a l l t h e o r y of manufacturing c a n af- f o r d t o neglect. Nevertheless, w e feel t h a t t h e r e a l power of system thinking can most effectively b e employed in t h e problems arising a t t h e mid-levels, and we shall focus most of o u r remaining r e m a r k s t h e r e .

To f u r t h e r s h a r p e n a n d r e f i n e o u r thinking a b o u t t h e systems n a t u r e of things in manufacturing, i t i s helpful t o recognize t h a t e a c h l a y e r of t h e s t r a t i f i c a t i o n of Figure 1 c a n ' b e sub-divided into t h r e e components which w e c a n a b s t r a c t l y label

"Design" (D), l'Production" (P) and "Marketingu/ "Distribution" (M). A t t h e level of t h e firm itself (level IV), t h e s e labels have t h e i r e v e r y d a y i n t e r p r e t a t i o n ; at o t h e r levels w e shall have t o i n t e r p r e t them in a fashion c o c s i s t e n t with t h a t level. For example, at t h e national economy level (level VII), we h a v e

"Design"

-

planned s t r u c t u r e and o p e r a t i o n s of t h e economy as envisioned by government policymakers

"Production"

-

a c t u a l operation of t h e economy, i.e. a c t u a l mechanisms employed in t h e production of goods and s e r v i c e s

"Yarketing "

-

distribution of goods and s e r v i c e s t o consumers, t o g e t h e r with t h e feedback from consumers t o decisionmakers and p r o d u c e r s .

A s a n o t h e r example c o n s i d e r r a w materials (level I). H e r e w e h a v e

-

specifications a n d / o r determination of p r o p e r t i e s of a given material

l ' P ~ o d u c t i o n "

-

means f o r a c t u a l c o n s t r u c t i o n o r e x t r a c t i o n of t h e material

"Marketing"

c'=3

means of conveying materials t o u s e r s (manufacturers)

W e leave i t

ta

t h e r e a d e r t o fill-in a p p r o p r i a t e D-P-M i n t e r p r e t a t i o n s f o r o t h e r levels in o u r s t r a t i f i c a t i o n . The important point is t h a t s u c h i n t e r p r e t a t i o n s c a n b e given and t h e y enable u s

to

see more c l e a r l y t h e systems a s p e c t s of problems at a given level.

Neither t h e '1-IX" n o r t h e "3-?-Y" subdivision of manufacturing pro:;.'-:r-s makes any distinction between those problems which we would term "systems- determined" a n d t h o s e t h a t are not. To g e t at t h e systems a s p e c t of things, w e in- t r o d u c e a t h i r d subdivision aimed at isolating t h o s e conceptual f e a t u r e s of manufacturing problems t h a t give t h e problems a distinctly systems flavor. I t is possible t o identify at l e a s t eight conceptual issues whose emphasis in a given manufacturing problem stamps i t as primarily a "systems-determined" problem.

These concepts a r e

Efficiency/Optimality

( E E )

Flexibility/Adaptability (FLX)

Complexity (COM)

Vulnerability/Resilience (VUL) Reliability (REL)

Uncertainty/Fuzziness (UNC)

Self-Organization/Replication (SLF) P e r f o r m a n c e (PRF)

L e t us examine t h e ucderlying c o n t e n t of e a c h of t h e s e themes in t h e c o n t e x t of manufacturing.

A. E m c i e n c y / O p t i m a L i t y

-

traditionally when one thought of a systems prob- lem in t h e manufacturing a r e a s , t h e idea t h a t s p r u n g t o mind was t h e e f f e c t i v e util- ization of some r e s o u r c e : manpower, money, time a n d / o r materials. Problems of t h i s kind include optimal scheduling of machines in a job-shop, optimal levels of in- ventory, maximal use of raw materials in a stock-cutting operation, minimal t r a n - s p o r t a t i o n c o s t s in warehousing finished goods and s o f o r t h . In a l l c a s e s , t h e p r o b -

!em emphasis i s upon optimizing a given quantity subject t o r e s o u r c e , m a t e r i a l , s p a c e and time c o n s t r a i n t s of various s o r t s . The traditional tools of o p e r a t i o n s r e s e a r c h such as l i n e a r programming, network flow analysis. PERT. and dynamic programming were originally developed to handle systems problems focused upon t h e c o n c e p t of e m c i e n c y .

B.

FZezibiLity/AdaptabiLity

-

probably t h e most overworked word in t h e manufacturing lexicon today i s "flexibility", used t o convey a whole host of ideas centering upon t h e theme of a n i n t e g r a t e d , computer-controlled complex of au- tomated material handling devices a n d machine tools t h a t can simultaneously p r o - duce medium-sized volumes of a v a r i e t y of p a r t s types. In t h e manufacturing en- vironment, w e c a n identify at l e z s t eight t y p e s of flexibility [5]:

(i) m a c h i n e flexibility c h a r a c t e r i z i n g t h e ease of making changes r e q u i r e d to p r o d u c e a g i v e n set of p a r t s types;

(ii) p r o c e s s flexibility involving t h e ability t o p r o d u c e a given set of p a r t s types, e a c h possibly using d i f f e r e n t materials, in s e v e r a l ways;

(iii) p r o d u c t flexibility measuring t h e ability t o changeover t o a new set of p r o - d u c t s v e r y economically and quickly;

(iv) r o u t i n g flexibility dealing with t h e ability to handle breakdowns and t o still p r o d u c e a given s e t of p a r t s types;

(v) volume flexibility indicating t h e c a p a c i t y to profitably o p e r a t e a manufac- turing systems at d i f f e r e n t production volumes;

(vi) e z p a n s i o n flexibility e x p r e s s i n g t h e capability of building a system a n d ex- panding i t , as needed, easily and modularly;

(vii) o p e r a t i o n flexibility associated with t h e ability to interchange t h e o r d e r i n g of s e v e r a l o p e r a t i o n s f o r e a c h p a r t type;

( v i i i ) p r o d u c t i o n flexibility, a measure of t h e universe of p a r t s t y p e s t h a t t h e manufacturing system c a n produce.

Of c o u r s e , not all of t h e s e notions of flexibility are independent. Figure 2 displays t h e r e l a t i o n s h i p s among t h e various t y p e s of flexibility, where t h e a r r o w s denote

"is n e c e s s a r y for".

(ii ) (i)

+

^{i i -J-,}

(vii)

(viii)

Figure 2. Dependencies Among Notions of Flexibility

Systems problems emphasizing flexibility focus upon means t o e n h a n c e one o r more of t h e above flexibility c a p a c i t i e s , while at t h e s a m e time not degrading any of t h e o t h e r s . For example, keeping routing options open and not p r e d e t e r m i n i n g e i t h e r t h e "next" o p e r a t i o n o r t h e "next" machine i c c r e a s e s o p e r a t i o n flexibility a n d , as a r e s u l t , improves o v e r a l l p r d u c t i o n flexibility, too. One of t h e major dif- ficulties with flexibility-dominant problems i s t h e lack of a consistent measure of flexibility t h a t would e n a b l e o n e t o t r a n s f e r back and f o r t h between t h e various t y p e s , i.e. a "common c u r r e n c y " of flexibility, s o t o speak.

C. C o m p l e z i t y

-

complexity i s a t e r m a l n o s t as overworked as flexibility, c h a r a c t e r i z i n g some measure of t h e difficulty in understanding t h e p r o d u c t s and p r o c e s s e s of manufacturing operations. I t h a s been a r g u e d elsewhere [9] t h a t . in g e n e r a l , complexity i s a contingent p r o p e r t y of a system, emerging from t h a t system's i n t e r a c t i o n with a n o t h e r . In t h e predominantly engineering environments of manufacturing o p e r a t i o n s , t h i s contingent p r o p e r t y i s mostly hidden and i t makes s e n s e t o think of complexity as an i n t r i n s i c system p r o p e r t y c h a r a c t e r i z e d by some combination of t h e number of system components, t h e n a t u r e of t h e i r in- terconnection. t h e dynamical flow of information between t h e p a r t s a n d t h e in- t e r a c t i o n between t h e v a r i o u s h i e r a r c h i c a l levels comprising t h e system.

In t h e manufacturing setting, complexity emerges because t h e traditional p r o c e s s e s involving simple o p e r a t i o n s such as machining, forming, joining and t h e l i k e h a v e been augmented o r r e p l a c e d by o t h e r novel techniques such as lasers f o r cutting, plasma etching techniques a n d ion beam p a t t e r n processing. In addition, new m a t e r i a l s like plastics, ceramics a n d c a r b o n f i b e r s i n t e r a c t with t h e manufac- t u r i n g p r o c e s s in many unexpected ways contributing to t h e o v e r a l l complexity of t h e manufacturing.

Generally speaking. complexity-dominated manufacturing problems emphasize questions pertaining t o e i t h e r t h e r e d u c t i o n in production and/or p r o c e s s com- plexity by, f o r example, introduction of automated p r o c e s s e s , combinations of pro- cessing o p e r a t i o n s , a l t e r n a t e scheduling p r o c e d u r e s and t h e like o r t o t h e e f f e c t on system complexity of c h a n g e s d i r e c t e d to o t h e r p r o p e r t i e s like flexibility, resi- lience, a n d / o r optimality. A s a n illustration, i t seems t o be a folk-theorem t h a t system complexity and system stability are d i r e c t l y r e l a t e d , i.e., i n c r e a s e d com- plexity g e n e r a t e s i n c r e a s e d stability. The intuitive argument given to s u p p o r t t h i s contention i s t h a t greater complexity g e n e r a t e s a d e n s e r network of connections between system components, and t h i s h i g h e r level of connectivity r e s u l t s in t h e system being more c a p a b l e of absorbing potentially destabilizing disturbances.

Unfortunately, without a c l e a r e r concept of t h e notion of complexity, i t s relation- ship t o t h e interconnection of t h e system components, and t h e impact of t h e con- nective s t r u c t u r e upon t h e t y p e of stability being considered, i t i s impossible t o ei- t h e r confirm o r deny t h e claimed complexity/stability relationship. An account of t h i s problem in t h e c o n t e x t of ecological networks and food webs is given in [6], b u t t h e corresponding c o n c e p t s and r e s u l t s f o r manufacturing systems have y e t t o b e developed.

D. TAlnerabilit.y/Resilience

-

what is t h e d e g r e e t o which a system c a n sus- tain d i s t u r b a n c e s and disruptions in i t s normal operating environment and continue t o perform i t s designated function? This i s t h e essence of what w e mean by a system's vulnerability, while t h e capacity of t h e system t o a b s o r b p e r t u r b a t i o n s and continue functioning i s a meascre of i t s resilience. Both of t h e s e notions a r e , of c o u r s e , p a r t i c u l a r c a s e s of t h e g e n e r a l problem of system stability, i.e. if w e change something a b o u t t h e system, when does i t m a t t e r ?

In t h e manufacturing context, issues of vulnerability are among t h e most fre- quent and important t h a t t h e system manager faces. Equipment breakdowns, delays in supplies, unexpected design changes, market fluctuations, variations in r a w ma- t e r i a l quality, and a thousand o t h e r minor and major shocks are continually im- pacting t h e system, and it is of t h e utmost importance t h a t t h e o v e r a l l manufactur- ing o p e r a t i o n b e s t r u c t u r e d in a manner t h a t makes i t relatively cheap and easy t o accommodate such disturbances. The h e a r t of t h e vulnerability question in manufacturing l i e s in t h e determination of good ways t o configure t h e system t o provide i t with a sufficiently l a r g e safety margin t o enable i t t o "roll with t h e punches" continually impacting i t from a n uncooperative e x t e r n a l environment.

From what h a s been said e a r l i e r , i t should b e c l e a r t h a t t h e notion of system vulnerability i s closely intertwined with ideas of flexibility. adaptability and com- plexity; in f a c t , i t seems difficult t o imagine how t o a t t a c k one of t h e s e problem areas without consideration of t h e o t h e r s . But, as with flexibility and complexity, s o i t i s with vulnerability and resilience and w e have, as yet, no c o h e r e n t measures of a manufacturing system's vulnerability, n o r any c o n c r e t e idea of t h e n a t u r e of t h e relationships linking t h e s e system concepts.

E. Reliability

-

in manufacturing, reliability r e f e r s t o t h e system's ability t o maintain uniform quality and consistent delivery schedules in t h e f a c e of changing demands a n d / o r operating circumstances. In t h e past, t h e assembly line and nurnerically-controlled machine tools generated major advances in quality because of product standardization; t h e f u t u r e challenge will b e to achieve even higher levels of reliability in quality without standardization o r long learning c u r v e s , while working to f i n e r t o l e r a n c e s and scales. One major innovation in this direc- tion i s t h e widespread introduction of r o b o t s into t h e manufacturing process;

a n o t h e r i s t h e introduction of new analytical design tools t h a t will automatically p r e v e n t t h e designer from making inadvertent e r r o r s . o r from specifying toler- a n c e s t h a t are e i t h e r t o o loose o r t o o tight.

Again, i t i s c l e a r t h a t reliability i s closely r e l a t e d to o t h e r system concepts.

especially vulnerability and resilience. But t h e flavor h e r e is somewhat different, as reliability focuses upon consistency in t h e product and i t s production process.

while t h e e a r l i e r concepts emphasized t h e viability of t h e o v e r a l l manufacturing operation. But i t i s r e a l l y more a question of d e g r e e r a t h e r t h a n kind, and w e can readily e x p e c t advances in understanding system reliability to provide insight into vulnerability, and conversely.

F.

Uncertainty

-

many of t h e t y p e s of d i s t u r b a n c e s w e h a v e r e f e r r e d t o in connection with t h e concepts of vulnerability, r e s i l i e n c e and reliability h a v e t h e i r origin in s t o c h a s t i c phenomena affecting t h e manufacturing system. Random machinery f a i l u r e s , unpredictable market demands, fluctuating s u p p l i e r s c h e d u l e s and t h e l i k e are well-known phenomena in manufacturing c i r c l e s , and many of t h e classical OR tools h a v e been developed t o a d d r e s s them. But t h e r e i s a n o t h e r kind of u n c e r t a i n t y c o n c e p t not having i t s s o u r c e in any s t o c h a s t i c f e a t u r e s , but r a t h e r in a c e r t a i n linguistic "fuzziness" in t h e v e r y problem description itself. In such si- tuations, t h e v a r i a b l e s describing t h e problem are themselves only vaguely de- fined, and t h e task i s t o c r e a t e a t y p e of calculus f o r combining and o p e r a t i n g with such "fuzzy" v a r i a b l e s .

A s a n illustration, consider t h e concept of a "tall" man. I t ' s c l e a r t h a t e v e r y man h a s a well-defined, definite height measured on some scale, s a y s o many cen- timeters. What i s not c l e a r is t h e notion "tall". Is i t a l l men o v e r 190 cm, o v e r 188 cm, and l e s s t h a n 200 cm, o r what? I t ' s impossible t o say, and a l l we c a n d o i s as- sign a degree-of-membership function t o t h e set consisting of tall men. This i s t h e essential idea underlying t h e theory offuzzy sets, as developed in r e c e n t y e a r s by Zadeh, Negoita a n d o t h e r s .

Many problems in manufacturing h a v e t h i s second kind of u n c e r t a i n t y as a n essential p a r t of t h e i r specification. W e want t o "rapidly" produce p r o d u c t s of

"good" quality in "small" b a t c h e s at a "low" cost. This is a typical d e s c r i p t i o n of a manufacturing o p e r a t i o n given t o t h e media by a CEO and, a s c a n b e c l e a r l y s e e n , i s riddled with vaguely-defined linguistic variables. Many of t h e o b s t a c l e s standing in t h e way of a t r u l y flexible automated f a c t o r y hinge upon t h e development of good software c a p a b l e of dealing with this t y p e of uncertainty. The fuzzy set con- c e p t s are o n e d i r e c t i o n , t h e "possibility" t h e o r y of Klir is a n o t h e r , and t h e r e may b e many more. What i s needed f o r t h e specific p r o b l e m of manufacturing remains.

at t h i s d a t e , a n open question.

G. Self-Organization/Replication

-

two of t h e c h a r a c t e r i z i n g f e a t u r e s of living organisms are t h e i r abilities t o r e p a i r s t r u c t u r a l damages and t o r e p r o d u c e them- selves. When one r e a d s d e s c r i p t i o n s of envisioned f u t u r e f a c t o r i e s , [8,9], a s t r i k - ing a s p e c t of t h e s e p r o j e c t i v e speculations is how similar t h e y sound t o a d e s c r i p - tion of a living organism. While t h e m a t t e r of "self-reproducing f a c t o r i e s " sounds somewhat fanciful, t h e r e is ample r e a s o n t o t a k e seriously t h e idea of f a c t o r i e s t h a t engage in automated sensing of t h e i r o p e r a t i n g environment and a c t s of self- r e p a i r a n d self-reconfiguration (organization) according t o t h e ambient conditions and circumstances.

An essential a s p e c t of t h e concept of self-organization i s t h a t a t some level of systems complexity (however i t is measured), new forms of organization and func- tions emerge, forms whose v e r y e x i s t e n c e i s determined by t h e inability of t h e system's components t o adequately a d a p t at a lower level of organization. With t h e added complexity i n h e r e n t in t h e advanced information processing, communication, and automation available, issues of self- organization and i t s a t t e n d a n t c o n c e p t s of bifurcation, adaptation. and s e l f - r e p a i r w i l l play a n increasingly important r o l e in f u t u r e manufacturing system studies.

H.

Performance

-

one of t h e t h o r n i e s t a s p e c t s of many system problems, especially those involving social and behavioral phenomena, i s t h e determination of a y a r d s t i c k by which to measure t h e "goodness" o r "badness" of t h e system's behavior; t h i s i s no l e s s t r u e in manufacturing. How t o evaluate p r o s p e c t i v e changes such as introduction of r o b o t s , flexible machinery equipment. new p r o c e s s techniques, e x o t i c materials,

JIT

inventory procedures. and s o on i s likely t h e most

difficult task facing t h e manager of a manufacturing operation. I t ' s p r o b a b l y t r u e t h a t t h e f u r t h e r down t h e h i e r a r c h y of Figure 1 you go, t h e e a s i e r i t i s to identify a p r e c i s e evaluation c r i t e r i o n . such as number of items produced p e r unit time, unit p r o f i t s , production efficiency, e t c . , b u t even a t t h e lowest l e v e l s t h e problem i s by no means totally s t r a i g h t f o r w a r d . And a t h i g h e r levels w h e r e one must bal- a n c e t h e manufacturing system's needs with t h e r o l e t h e system plays in t h e global o p e r a t i n g environment, i t i s far from c l e a r what measure adequately r e f l e c t s t h e system's o v e r a l l "performance". What i s c l e a r i s t h a t much more t h a n just quality, productivity and profitability a r e involved.

S o , t h e final jewel in o u r crown of system concepts in manufacturing, a n d t h e concept t o which a l l o t h e r s a r e s u b s e r v i e n t , i s t h e notion of a c r i t e r i o n ( o r c r i - t e r i a ) of performance. The development of s c c h c r i t e r i a i s t h e uninvited guest at t h e banquet t a b l e in t h e analysis of any problem involving t h e c o n c e p t s and levels introduced above.

4. SYSTEM PROBLEMS

IN

HA.NUFACTURING: A GENERATrVE MECHANISM The t h r e e levels discussed in Section 3 comprise a taxonomy f o r manufactur- ing problems and provide u s with a n algorithmic, o r g e n e r a t i v e , p r o c e d u r e f o r f o r - mulating a n almost infinite v a r i e t y of systems-determined manufacturing issues. W e f i r s t summarize t h e levels of taxonomy by t h e c h a r t in Figure 3.

Hierachical Functional Conceptual

Level Level Level

(1x1 Values

(VIII) World Industry Efficiency (EFF)

(VII) Manufactured Goods Design (D) Flexibility (E'LX)

(VI) Industry Production (P) Conplexity (COM)

( v ) Local Industry Vulnerability (VUL)

(Iv) Finished P r o d u c t Marketing (M) Reliability (REL)

(111) Components

(11) P a r t s

(1 Materials

Uncertainty (UNC) Self-organization (SLF) P e r f o r m a n c e (PRF)

F i g u r e 3. Manufacturing System Taxonomy

Our almost automatic mechanism f o r generating manufacturing problems with a sys- t e m s f l a i r follows a p r o c e d u r e t h a t i s t h e essence of simplicity: p i c k o n e i t e m f r o m e a c h of t h e c o l u m n s of f i g u r e 3 a n d combine t h e m t o f o r m u l a t e t h e problem. The p r o c e d u r e c a n b e x s e d in two directions: as just indicated, t o g e n e r a t e new system problems in manufacturing o r , in t h e opposite direction, t o classi'py o r c a t e g o r i z e a n existing problem.

A s illustration of both u s e s of t h e "taxonomy principle", c o n s i d e r t h e follow- ing.

G e n e r a t i v e M o d e

1. @VD/COM)

-

t h i s would b e a problem involving s o c i e t a l values (level IX), t h e i r determination ("Design"), and t h e complexity (COM) in t h e context of manufacturing systems. A typical problem of t h i s s o r t would involve t h e way in which manufacturing systems impact t h e o v e r a l l goals of society, how t o

(re-)design those goals t o t a k e into account t h e anticipated r o l e of manufacturing in t h e f u t u r e , and t h e complexity associated with t h e i n t e r a c t i o n between a techno- logical o b j e c t (the manufacturing system) and a social organism (society, at l a r g e ) . 2. (m/P/W

-

t h i s code r e p r e s e z t s a problem izvolving production (P) flexi- bility (E'LX) in a n individual firm (level IV). A prototypical problem of t h i s s o r t i s to determine t h e i n c r e a s e in o v e r a l l productive c a p a c i t y by introduction of au- tomated machining o p e r a t i o n s , emphasizing t h e enhanced flexibility of t h e plant.

3. (I/M/RE:L)

-

in t h i s c a s e , t h e code suggests a problem dealing with t h e relia- bility (RGL) of t h e distribution network (M) of r a w materials (level I) needed f o r manufacturing operations. This t y p e of problem i s of c e n t r a l importance, f o r in- s t a n c e , in consideration of implementing a JIT inventory c o n t r o l system.

Neglecting codes involving i n t e r f a c e s a n d / o r multiple column e n t r i e s , t h e above scheme admits 216 s e p a r a t e classification codes f o r systems problems in manufacturing, with e a c h of t h e s e c a s e s capable itself of s u p p o r t i n g a v a s t a r r a y of individual problems. However, as noted e a r l i e r , i t is a l s o possible t o r u n t h e foregoing coding scheme in r e v e r s e t o classify a given manufacturing problem. Let us consider a few examples.

C l a s s i f i c a t i o n M o d e

E z a m p l e 1. In discussion with t h e management of a l a r g e J a p a n e s e e l e c t r o n i c s f i m , t h e plant manager r e m a r k e d t h a t one of his biggest problems i s how t o in- c r e a s e engineering productivity. By t h i s h e meant t h e s p e e d and efficiency by which t h e e n g i n e e r s could modify c i r c u i t designs and production p r o c e d u r e s t o s u i t t h e specific needs of individual customers. Such a problem i s most suitably ad- d r e s s e d at t h e level of t h e individual plant (level IV), and involves both Design (D) and Production (P) a s p e c t s . Finally, t h e essential n a t u r e of t h e problem i s t h e Ef- ficiency (EFF) of t h e plant, although t h e problem a l s o touches upon issues of flexi- bility (E'LX) and o v e r a l l f a c t o r y performance (PRF). Consequently, i t would b e ap- p r o p r i a t e t o assign t h i s problem t o t h e c l a s s (IV/D-P/EFF-FLX-PRF), illustrating a l r e a d y t h e point noted e a r l i e r t h a n t h e most system-determined of system prob- lems a r e t h o s e involving t h e i n t e r f a c e s and/or combinations between t h e various levels and categories.

E z a m p l e 2. A problem of a q u i t e d i f f e r e n t c h a r a c t e r a r o s e during conversa- tions with t h e managing d i r e c t o r of a n o t h e r l a r g e Asian e l e c t r o n i c s company. I t w a s mentioned t h a t t h e f i r s t p r i o r i t y of t h e firm, at t h e moment, w a s t h e installa- tion of a computer information system t o monitor t h e various s t a g e s of design, pro- duction and distribution. Then came t h e surprisingly candid admission t h a t once t h e h a r d w a r e w a s in p l a c e , t h e firm would b e faced with t h e difficulty of what t o do with t h e d a t a a c q u i r e d . S o , t h e e s s e n c e of t h i s problem i s how t o transform ? a t a irto i ~ f o r m a t i o n . In t e r m s of o u r taxonomic scheme. this i s again a factory-!eve;

g r o k l e 3 (level IV), involving a l l t h r e e functional levels (D-P-M).

me

primary sys- tem concept at work h e r e i s t h e ideas of complexity (COM): t h e objective of t h e aanagement information system i s t o r e d u c e a collection of increasingly i n t e r - dependent p r o c e s s e s t o manageable (read: simple) levels. Thus, t h e p r o p e r code f o r t h i s problem i s (IV/D-P-M/COM).

E z a m p l e 3. A t a n American computer company in California, t h e manager of advanced manufacturing r e l a t e d t h e p r o c e d u r e s followed in t h e construction of t h e i r v e r y low-volume (500 units/year), high complexity machines. He s t r e s s e d t h e point t h a t "manufacturability"/"testability" w a s t h e c u r r e n t p r i o r i t y c o n c e r n f o r t h e i r group. This question essentially deals with t h e design of t h e computer com- ponents in such a way t h a t t h e physical s t r u c t u r e f a c i l i t a t e s e a s y construction and testing. Relating t h i s problem t o o u r taxonomic s t r u c t u r e , i t involves t h e comput- e r Components (level 111). and t h e choice of t h e i r Design (D) t o r e d u c e Complexity (COM) t o facilitate t h e i r Reliability (REL). Putting t h e s e o b s e r v a t i o n s t o g e t h e r , a suitable c a t e g o r y f o r t h i s problem i s (III/D/COM-REL).

Exampies of t h e a b o v e s o r t could b e multiplied severalfold, but t h e basic principles are a l r e a d y c l e a r . The qcestion t h a t remains i s what t o d o with o n e of t h e s e myriad system problems o n c e i t h a s been identified and classified. This is a question not of l a b e l s o r codes, b u t of tools, t h e final ingredient in o u r dissection of manufactwing from a systems p e r s p e c t i v e .

5. SYSTEM-THEORETIC TOOLS. TECHNIQUES. AND STRUCTURE IN MANUFACTURING

The preceding development h a s amply demonstrated t h e i n h e r e n t systems na- ture of many manufacturing problems; but, problems without solutions are like b r e a d without b u t t e r . Consequently, in t h i s section w e e x p l o r e t h e equation

problems

+

tools

+

a world view

=

insight,

emphasizing t h e s p e c t r u m of system-theoretic tools t h a t c a n b e b r o u g h t t o b e a r upon manufacturing problems of t h e s o r t considered above.

In t h e above equation, a n indispensable r o l e in determining t h e n a t u r e and de- g r e e of insight t h a t c a n b e gained a b o u t any problem i s played by one's scientific W e l t a n s c h a u u n g , o r "world view". When translating a problem statement into a formal mathematical s t r u c t u r e , t h e world view is r e p r e s e n t e d by t h e t y p e of formal mathematical system chosen to r e f l e c t t h e f e a t u r e s of t h e problem. In t u r n . this mathematical world view t h e n d i c t a t e s t h e kinds of question t h a t c a n b e a s k e d and t h e tools a n d techniques t h a t c a n b e used in seeking insights a n d answers.

Schematically, w e h a v e t h e situation depicted in Figure 4.

A c r u c i a l a s p e c t of t h e s u c c e s s o r f a i l u r e of any modeling v e n t u r e i s t h e c h o i c e of t h e "right" mathematical s t r u c t u r e t o employ on t h e r i g h t s i d e of t h i s diagram.

When faced with a new c l a s s of prcblems like those arising in manufacturing, where

E x p e r i m e n t a t i o n and

O b s e r v a t i o n s

Encoding

X Formal T n T o o l s d

Mathernatica

T e c h n i q u e s

Decoding

Figure 4. The Mathematical Modeling Relation f o r Manufacturing

a substantial body of p a s t work is unavailable t o draw upon, i t may b e n e c e s s a r y t o employ a n intermediate s t e p as shown in Figure 5.

Manufacturing S y s t e m

I

a l

S y s t e m X

Mathematical

Figure 5. S u r r o g a t e System Model

H e r e t h e i d e a i s t o s e l e c t a s u m o g a t e system X whose mathematical r e p r e s e n t a t i o n i s relatively well-understood ( t h e coding/decoding

6).

If w e c a n c o n s t r u c t t h e

"dictionary" a between X and o u r manufacturing system of i n t e r e s t , t h e n by com- position w e are a b l e to implicitly g e n e r a t e t h e map y of primary i n t e r e s t . A r e s e a r c h p r o g r a m based upon t h e exploitation of Figure 5 examining v a r i o u s choices f o r t h e system X (biological, computer, e l e c t r i c a l c i r c u i t , language) i s given in a n e a r l i e r r e p o r t [9]. The point t o b e emphasized i s t h a t t h e r e i s no s u c h thing as t h e " c o r r e c t " o r "right" way to t a c k l e a n y of t h e problems a r i s i n g in manufacturing; e a c h world view, or "paradigm", g e n e r a t e s i t s own slice of r e a l i t y and i t is t h e t a s k of t h e analyst to p i e c e t o g e t h e r enough such s l i c e s to c r e a t e a p i c t u r e of g r e a t enough detail f o r t h e t a s k at ^hand. Now let us t u r n to a n examina- tion of s o m e t y p e s of world views f o r manufacturing.

I t seems t o b e convenient

to

divide t h e set of mathematical paradigms f o r manufacturing i n t o f o u r principal components. For s a k e of nomenclature, w e t e r m t h e s e c l a s s e s Operations R e s e a r c h (OR), Computer S c i e n c e s (CS), Control Theory (CT) and System Theory (ST). W e briefly indicate t h e p r i n c i p l e t y p e s of problems

a n d s p e c i f i c t e c h n i q u e s c h a r a c t e r i z i n g t h e s e paradigms.

A. m e r a t i o n s R e s e a r c h

-

p r o b l e m s in t h i s c a t e g o r y basically r e v o l v e a r o u n d i s s u e s of planning a n d scheduling. Thus, w e h a v e i s s u e s of m a n u j i z c t u r i n g s y s t e m p l a n n i n g involving t h e s p e c i f i c a t i o n a n d o r g a n i z a t i o n of manufacturing r e s o u r c e s n e e d e d t o meet some long-term p r o d u c t i o n goals; p r o d u c t i o n p l a n n i n g which t a k e s f a c i l i t i e s design as given, a n d s e t s a g g r e g a t e production rates t o b e con- s i s t e n t with f a c i l i t i e s c a p a c i t y a n d demands; flow p l a n n i n g f o r d e t e r m i n a t i o n of a c t u a l p r o d u c t i o n b a t c h e s in a m a n n e r c o n s i s t e n t with both t h e production plan a n d t h e resource c o n s t r a i n t s ; finally. s c h e d u l i n g involving t h e implementation of t h e flow plan a n d t h e sequencing a n d c o o r d i n a t i o n of production a c t i v i t i e s .

Methodologically s p e a k i n g , t h e t e c h n i q u e s t h a t a r e employed in t h e OR-based p r o b l e m s are t h e t r a d i t i o n a l OR tools: r e s o u r c e allocation, scheduling t h e o r y , in- v e n t o r y c o n t r o l . queuing t h e o r y . mathematical programming. decision analysis a n d so f o r t h . In t h e c o n t e x t of modern manufacturing, t h e OR problems are e x a c t l y t h e same p r o b l e m s as t h o s e e n c o u n t e r e d in t h e t r a d i t i o n a l manufacturing environments of t h e 1950s. The a d v e n t of CAD/CAM a n d f l e x i b l e manufacturing systems h a s n o t c h a n g e d t h e n a t u r e of t h e s e p r o b l e m s o n e iota: a scheduling problem is still a s c h e d u l i n g problem a n d what was difficult in t h e 1950s i s s t i l l difficult today. In f a c t , t h e p r o b l e m s may b e e v e n m o r e difficult t o d a y because of t h e h i g h e r l e v e l s of information p r o c e s s i n g a n d automation found in modern manufacturing environ- ments.

As i l l u s t r a t i o n s of some of t h e p r o b l e m s on t h e OR r e s e a r c h a g e n d a today, we have:

i ) a g g r e g a t e p r o d u c t i o n s m o o t h i n g

-

development of means to dynamically smooth p r o d u c t i o n in a n u n c e r t a i n environment o v e r multiple p r o d u c t i o n s t a g e s ; development of means t o a g g r e g a t e p r o d u c t s f o r production planning t a k i n g i n t o a c c o u n t lot-size f a c t o r s .

ii) l o t - s i z i n g a n d r e o r d e r i n t e r v a l s

-

how t o link lot-sizing with a g g r e g a t e p r o d u c t i o n r a t e s ; determination of t h e r e l a t i o n s h i p between l o t s i z e s a n d machine sequencing.

iii) p l a n n e d l e a d t i m e s

-

^{how to set} planned l e a d times f o r flow planning; how to i n t e g r a t e l e a d times with lot-sizing, scheduling a n d production planning; how t o u s e l e a d times to set "promise d a t e s " f o r c u s t o m e r deliveries.

iv) p r o t e c t i o n stock

-

how t o d e a l with production d i s r u p t i o n s a n d delays; how to s p r e a d p r o t e c t i o n s t o c k a c r o s s many p r o d u c t i o n s t e p s ; how to i n t e g r a t e p r o t e c - t i o n s t o c k with production planning a n d scheduling; determination of t h e relation- s h i p between p r o t e c t i o n s t o c k a n d planned l e a d times.

v ) s c h e d u l i n g

-

how t o i n t e g r a t e scheduling activity with planning; how t o r e s c h e d u l e dynamically; how to create s t a b l e flow plans; how to s c h e d u l e r e w o r k . While t h e f o r e g o i n g OR p r o b l e m s c o n c e n t r a t e upon o p e r a t i o n a l c o n t r o l s design, t h e r e are a c o r r e s p o n d i n g set of i s s u e s f o r f a c i l i t i e s , p r o d u c t , a n d p r o c e s s design.

B . C o n t r o l t h e o r y

-

d u r i n g tine 1 9 6 0 s , c o n s i d e r a b l e a d v a n c e s w e r e made in t h e methods of optimal c o n t r o l , stimulated mainly b y problems in a e r o s p a c e and m e c h a n i c a l engineering. C u r r e n t l y t h e r e i s a movement underway to a c q u a i n t t h e c o n t r o l s community with manufacturing problems t h a t p o s s e s s t h e q u a l i t a t i v e con- c e p t s a s s o c i a t e d with t r a d i t i o n a l c o n t r o l problems: complexity, h i e r a r c h y , u n c e r - t a i n t y , f e e d b a c k . I t i s a l r e a d y c l e a r t h a t s t a n d a r d c o n t r o l t h e o r y t e c h n i q u e s usu- a l l y d o n o t a p p l y in a s t r a i g h t f o r w a r d m a n n e r to manufacturing problems; t h i s i s

not surprising since standard techniques have been developed f o r standard prob- lems outside manufacturing. Thus, new s t a n d a r d techniques will have to b e developed if c o n t r o l t h e o r y is t o contribute in a major way t o manufacturing.

Let us just briefly indicate some of t h e s o r t s of manufacturing questions of c u r r e n t i n t e r e s t t o control engineers.

i) m a c h i n e control

-

calculation and implementation of optimal r o b o t arm tra- jectories; control of cutting tools; control of furnaces and o t h e r s t e p s in semicon- ductor fabrications.

ii) plezible m a n u f a c t u r i n g control

-

sequencing p z r t s , fixture, and opera- tions in a FMS; determination of optimal r o u t e s f o r t r a n s p o r t s carts; feedback mon- itoring of component quality in a FMS.

iii) p r o d u c t i o n control

-

development of factory-level models t h a t integrate actual r e s o u r c e capacity with production requirements; determination of "just-in- time" material control in high uncertainty environments; decomposition of produc- tion lines into two-machine, one-buffer subsystems.

C. C o m p u t e r Science

-

t h e main manufacturing problems of this type c e n t e r upon t h e development of new computer languages and/or operating systems specifi- cally designed f o r manufacturing and t h e use of AI/expert system techniques f o r manufacturing. A s r e p r e s e n t a t i v e of t h e f i r s t type of problem, t h e U.S. Air Force is c u r r e n t l y supporting a p r o j e c t called ICAM devoted t o production of a language t h a t is specifically aimed a t making t h e integration of design and production e a s i e r . Similarly, due t o t h e increasing level of decentralization in n o d e r n manufacturing systems, t h e r e is heightened i n t e r e s t in work on new operating sys- tems t o s e r v e t h e h e t e r a r c h i c s t r u c t u r e of many c u r r e n t manufacturing opera- tions. Much of t h i s work is aimed at dealing with the inherent information ex- change problem emerging from a non-hierarchic decisionmaking environment.

Problems in t h e AI/expert system area involve t h e need t o develop s i t u a t i o n (not pattern) r e c o g n i t i o n programs, i.e. programs t h a t recognize situations t h a t t h r e a t e n t h e continued viability of t h e manufacturing system. Other AI-oriented manufacturing problems focus upon t h e need f o r failure detection and c o r r e c t i o n programs. H e r e t h e work is devoted t o means f o r automatic recognition of failures, as w e l l as determination of remedial action and operating regimes under a total o r p a r t i a l f a i l u r e mode.

D . S y s t e m T h e o r y

-

^{in at} l e a s t partial c o n t r a s t to t h e OR, Control Theory, and Computer Science-type manufacturing paradigms, a System Theory world view focuses more upon paradigm construction than upon techniques and algorithms as- sociated with a given framework. Roughly speaking, in OR/CT/CS a particular for- m a l s t r u c t u r e i s selected (linear program. set of differential equations, M / M / l queue o r whatever) and t h e basic problems revolve about how various manufactur- ing questions c a n b e addressed w i t h i n t h e given paradigm (or a minor variation thereof). In s h o r t , one starts with a framework, o r point of view, toward manufac- turing processes and e x p l o r e s how t h e important concepts and issues of manufac- turing fit into this framework.

The c e n t r a l issue in System Theory f o r manufacturing i s quite different in spirit: start with all t h e manufacturing concepts and problems t h a t matter and s e e k those paradigms within which t h e s e concepts c a n b e consistently accommodated.

The types of concepts t h a t one starts with include notions such as complexity, flex- ibility, self-repair. adaptability, self-regulation, reliability, resilience, and p e r - formance. The objective is to develop a set of paradigms f o r manufacturing sys- tems t h a t will give an objective, precise, consistent and useful meaning t o t h e s e

every-day t e r m s . Since w e are i n t e r e s t e d in making p r e d i c t i o n s a b o u t r e a l manufacturing systems, what i s sought &e formal mathematical structures within which t h e c o n c e p t s show up a s relations between t h e elements comprising t h e mathematical formalism. The problem, a t p r e s e n t , i s t h a t n o o n e h a s any r e a l l y good idea of what such a formal mathematical s t r u c t u r e would look like f o r a modern manufacturing system. So, t h e only way t o p r o c e e d i s to a r g u e by analogy with o t h e r t y p e s of n a t u r a l systems t h a t w e do h a v e such paradigms f o r . This i s t h e essential c o n t e n t of Figure 5 and r e p r e s e n t s what amounts t o a r e l a t i o n a l , r a t h e r t h a n structural, view of a system in t h e s e n s e t h a t w e d e a l with c l a s s e s of systems possessing some functional similarities and neglect all a s p e c t s of physio- chemical s t r u c t u r e . A detailed account of t h i s view i s e x p r e s s e d in [lo].

6- TAXONOMY

AND

TECHNIQUE: A SUMHAKY

The foregoing sections h a v e outlined a scheme f o r classification of systems- determined manufacturing problems, and have p r e s e n t e d a rough breakdown of t h e tools and techniques f o r t h e i r resolution. A t t h i s point i t i s useful to compactly summarize t h e i d e a s and arguments in t h e following diagram.

Hierarchical Manufacturing

Level Area

(D-P-M)

Formal Paradigm

S y s t e m Classfficatf o n

Concept

Tools and Techniques

(owcr/a)

World Hew

Figure 6. A Systems View of Manufacturing