A Thesis Submitted for the Degree of PhD at the University of Warwick
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A Non-determ/n/stfc Approach to Dynamfc Layout P/ann/ng
ofFUeadbfeManufacturing Systems
A th esis su bm itted fo r th e d eg ree o f D o c to r o f Ph ilosoph y in th e D epartm ent o f E n g in eer^ U n iversity o f W arwick
By
S .P.H atam i K hosrow shahi B .S c., At.Sc.
The U n iversity o f W arwick
ACKNQWLEPQEMENTS
The author w i s h e s to thank D r .T .C .Go o d h e a d for his
c o n t i n u o u s supervision, gu i dance and e n c o u r a g e m e n t dur i n g
the c ou r s e of this r e se a r c h work.
The author w o u l d a l s o like to e x p r e s s his th a n k s to
D r . S . G r i n s t e d for her help in m o d i f i c a t i o n of the s o f t w a r e
use d in this research.
F i n a l l y the auth o r w i s h e s to thank his p a re n t s and family
for t heir patience and c o n st a n t e n c o u r a g e m e n t t h r o u g h o u t
ABSTRACT
A new a p p r o a c h to the d y n a m i c layout p l a n n i n g p r o b l e m is pr oposed which pro v i d e s solu t io n s t o hi g hl y v a r i a b l e material flow patt e r n s oc c u r r i n g o v e r a m u l t i - p e r i o d pl anning horizon and is e s p e c i a l l y s u i t a b l e for f l e x i b l e m a n u f a c t u r i n g systems. A n o n - d e t e r m i n i s t i c e n v i r o n m e n t is c o n s i d e r e d in which t here is assumed to be u n c e r t a i n t y in the future material f low data. The p e r f o r m a n c e of the met hod is assesse d by c o m p a r i ng the s ol u ti o n p r o d u c e d by this met h o d w it h a set of d a t a p r o vided in the li terature for which th e c l a im e d optimal s o l u t i o n is known. There is c lose a g r e e m e n t w i t h the s t a t e d s ol u ti o n a n d the result is o b t a i n e d wi t h a fraction of the c o m p u t a t i o n a l effort.
The computational e f f i c i e n c y is due to a new c o n s t r u c t i o n method to generate s ta t i c layout solu ti o n s . This m e t h o d uses an a l g o r i t h m in w h i c h the n u m b e r of s t a g e s is proportional to the n um b e r of f a c i l i t i e s rather t h a n an exponentional relat i o n s h i p as found in m o s t other m e t hods. The m e t h o d also uses an e l e m e n t of f o r w a r d p l a n n i n g to ensu re that early lo c ation a s s i g n m e n t s p r ov i de m i n i m u m r e s t riction to a s s i g n m e n t s made later in th e procedure.
Results of e x t e n s i v e t ests s how that the ne w st a t i c layout planning pr o c e d u r e p r o d u c e s solu t io n s g e n e r a l l y b e t t e r t h a n exi sting c o n s t r u c t i o n t e c h n i q u e s and c o m p a r a b l e w i t h im pro vement techn i q u e s such as CRAFT. T h e e x e c u t i o n s p e e d of the p r o c e d u r e m a k e s it p o ssible to s o l v e large s c a l e prob l e m s ( >30 )in very short time s ca l e s on M i c r o c o m puters .
C O N T E NT
C H AP TER O N E PAGE
1.1 P r o b l e m S t a t e m e n t 1
1.2 Flexibl e M a n u f a c t u r i n g Syst e ms 6 1.2.1 P r o d u c t i o n S y s t e m A r r a n g e m e n t s 7
1.3 Material H a n d l i n g S y s t e m s 9
1.4 Facil i t i e s L a y o u t T ec h n i q u e s 12 1.4.1 Stat i c and D y n a m i c Layout Pl a nning 13
C H APT ER TWO
STATIC LAY O U T PLAN N I N G
2.1 I n t r o d u c t i o n 20
2.1.1 D i s t a n c e M e a s u r e m e n t 24
2 . 1 . 2 Model V a l i d i t y 26
2 . 1 . 3 Steps of La y ou t De s i g n Process 26
2.2 Static Layout P l a n n i n g 29
2.2.1 Trad i tional A p p r o a c h e s to SLP 29
2 . 2 . 2 Analytical and C o m p u t e r i z e d
T e c h n i q u e s f or SLP 43
2.3 D y nami c Lay o u t P l a n n i n g 45
2.3.1 D y na m i c La yo u t P l an n i n g P r ob l e m 45 2 . 3 . 2 Exist i ng S o l u t i o n P r ocedures 48
C H A P T E R T H R E E
Q U A D R A T I C A S S I G N M E N T P R O B L E M
3.1 I n t r o d u c t i o n 54
3.2 F o r m u l a t i o n of F a c il i t i e s Layout
P l a n n i n g (F L P ) as Q A P 54
3.2.1 A s s i g n m e n t of n F a c i li t ie s to n
Lo c a t i o n s w i t h no A l l oc a t i o n Cost 56 3 .2.2 I n c o r p o r a t i o n of A l l o c a t i o n Cost
to the F o r m u l a t i o n 58
3.3 A p p l i c a b i l i t y of the QAP in Layout
P l a n n i n g A s p e c t of FMS 58
3.4 Existin g S o l u t i o n P r o c e d u r e s for QAP 63
3.4.1 C o m p l e x i t y of the Q A P 63
A C K N O W L E D G E M E N T S
The auth o r w i s h e s to t h a n k D r .T .C .G o o d h e a d f o r his
c o n t in u ou s supe r v i s i o n , g u i d a n c e and e n c o u r a g e m e n t during
the course of this r e s earch work.
The author w o u l d a l s o like to express his t h a n k s to
D r . S . G r i n s t e d for her help in m o d i f i c a t i o n of the s o ft w a r e
used in this research.
Finally the a u t h o r w i s h e s to t hank his p a r e n ts and family
for their p a t i e n c e and c o n s t a n t e n c o u r a g e m e n t t h r o u g h o u t
the du r a t io n of this work.
ABSTRACT
A new a p p r o a c h to the d y n a m i c layout p la n ni n g p r o b l e m is p rop osed w h i c h provides sol ut i on s to highly v a r i a b l e material f l o w patterns o c c u r r in g over a m u l t i - p e r i o d pl annin g ho r i z o n and is e s p e c i a l l y s ui t a b le for fl e x i b l e m a n u f a c t u r i n g systems. A n o n - d e t e r m i n i s t i c e n v i r o n m e n t is c o n s i d e r e d in which there is assumed to be un c e r t a i n t y in the fut u r e material flow data. The p e r f o r m an c e of the me t h o d is assessed by co m p ar i ng the s o lution pr o d u c e d
by this method with a set of data pr o vided in the
l it eratu re for which the c l a i m e d optimal s ol u t i on is known. There is c l o s e agreement w i t h the stated s o l ution and the result is obtained with a f ra c t i on of the c o mp utational effort.
The computational e f f i c i e n c y is due to a new c o n s t r u c t i o n m e t h o d t o generate stati c layout solutions. Thi s me t h o d uses an a l g o r i t h m in w h i c h the number of sta g es is
propo rti onal to the number of f a cilities rather tha n an
e x p o n e n t i o n a l relationship as found in m o s t other methods. The m et h o d also uses an e l e m e n t of forw a rd p l a n n i n g to e n s u r e t h a t early location as s i g n m e n t s provi d e m i n i m u m r es t r i c t i o n to assignments m a d e later in the procedure.
R esu lts of ex t e n s i v e tests s h o w that the new static layout p lan ning p r o c e d u r e produce s s o l ut i o n s ge nerally b e t t e r than ex is t i n g const r u c t i o n t e c hn i qu e s and c o m pa r a b l e with imp r o v e m e n t t e chniques such as CRAFT. The e x e c u t i o n speed of the p r o c e d u r e m akes it p os sible to s olve large scale pr ob l e m s ( >30 )1n very s h or t time scales on M i c r o co m p u t e r s .
I n c o r p o r a t i o n of the fast n e w con s tr u ct i o n m e t h o d into dy n a m i c layout planning al lo w s decision mak i n g c on c e r n i n g whe n and h o w to re-layout f a c i l it i es in response to changes in p r e d i c t e d material flow.
SQMTENT
C H A PT E R QNE p a g e
INTRO DUCTI ON
1.1 P r oblem S t a t e m e n t 1
1.2 Flexible M a n u f a c t u r i n g S y s t e m s 6 1.2.1 P r o d u c t i o n S y s t e m A r r a n g e m e n t s 7
1.3 Material H a n d l i n g Syste m s 9
1.4 F a c i l i t i e s Lay o u t T e c h n i q u e s 12 1.4.1 Static and D y n a m i c Layout P l a n n i n g 13
CH A P T E R TWO
S T A T I C LAYOUT PLANNING
2.1 I n t r o d u c t i o n 20
2.1.1 D i s t a n c e M e a s u r e m e n t 24
2.1.2 Model V a l i d i t y 26
2 . 1 . 3 Steps of La y ou t Design P r o c e s s 26
2.2 Static L a y o u t P la n ni n g 29
2.2.1 T r a d i tiona l A p p r o a c h e s to SLP 29 2 .2.2 A nalytical and C o m p u t e r i z e d
T e c h n i q u e s for SLP 43
2.3 Dynamic L a y o u t Pl a n n in g 45
2.3.1 D y namic La y o u t P l a n ni n g P r o b l e m 45 2 .3.2 Exis t i n g S o lu t i o n P r o c e d u r e s 48
C H A P T E R THREE
Q U A D R A T I C A S S I G N M E N T P R O B L E M
3.1 I n t r o d u c t i o n 54
3.2 F o r m u l a t i o n of F a c i l it i es Layout
Planning (F L P ) as Q A P 54
3.2.1 A s s i g n m e n t of n F a c i l i t i e s to n
Loc a t i o n s w ith no A l l o c a t i o n Cost 56 3.2.2 I n c o r p o r a t i o n of A l l o c a t i o n Cost
to the F o r m u l a t i o n 58
3.3 A p p l i c a b i l i t y of the Q A P in Layout
Planning A s p e c t of FMS 58
3.4 Existing S o l u t i o n P r oc e d u re s for Q AP 63
3.4.1 C o m p l e x i t y of the Q A P 63
3.4.3 H e u ristic A p pr o a c h e s to th e QAP 68
3.5 A l t e r n a t i v e A p p r o a c h e s to the Q A P for
For m u l a t i n g F L P 69
C H A P T E R FOUR
A N E W S O LUTION TO THE S T A T I C LAYOUT P L AN N I N G PROBLEM - THE I N IT IAL LA YOUT GEN E R A T O R
4.1 Introd u c t i o n 74
4.2 A New C o n s t r u c t i o n Te c h n i q u e for G e n e r a t i n g N e a r Optimal Solu t io n
-The Initial La y o u t G e nerator (ILG) 74
4.2.1 Formation o f the Link Table 80
4.2.2 The S e l e c t i o n P r ocedure 81
4 .2.3 The A l l o c a t i o n Procedure 84
4.3 D a t a M o d i f i c a t i o n of N o n - Sq u ar e
Facil i t i e s 86
4.4 Illust r a t i v e E x a m p l e s 89
4.4.1 A M a n u f a c t u r i n g System w i t h 20
eq u a l l y s i z e d fa cilities 90
4.4.2 A M a n u f a c t u r i n g System w i t h 8
f acilities o f dif f er e nt sizes 99
C H A P T E R FIVE
E V A L U A T I O N OF THE ILG P E R F O R M A N C E
5.1 I n t r o d u c t i o n 108
5.2 Des c r i p t i o n of MAT Procedure 110
5.3 T e s t s and R e s u l t s 112
5.3.1 T ests P e r f o r m e d on Problems
O r i g i n a t e d by Nugent et.al. 112
5.3.2 I n v e s t i g a t i o n into the R e l ation b e tween ILG and C ha r a c t e r i s t i c s
of the ma t erial flow m at r i c e s 124
C H A P T E R SIX
A- NSW N Q N - P E T E R M I N I S T I C A P P R O A C H TO DYNAMIC LAYOUT PL A NNING
6.1 Intro d u c t i o n 127
6.2 Exis t i n g DLP Proce d u r es and Their
S h o r t c o m i n g s 128
6.2.1 D y n a m i c P r o g r a m m i n g A p p r oa c h to
the Layout P r o b l e m 128
6.2.1.1 C o m p u t at i on a l Feasibility of
Dynamic P r o g r a m m i n g 134
Layout Plann i n g o f FMSs 140
6.3 A New App roach to D y n am i c La yo u t
Plan n i n g of F a c i l i t i e s for FMSs 143
6.3.1 F o r m u lation of DLP P r o b l e m 147
6.3.2 Esta b l i s h m e n t of T im e P e r i o d s 150
6.3.3 A Numerical Example 152
6.3.3.1 The R e p r e s e n t a t i v e P r o b l e m 152
6. 3 . 3 . 2 P r oblem Solution 156
C H A P T E R SEVEN D I S C U S S I O N
7.1 I n t r o d u c t i o n 169
7.2 E v a l u a t i o n of ILG in G en e r a ti n g S o l u t i o n s for the S t a t i c Layout
P r o b l e m 169
7.2.1 ILG Q u a l i t y 170
7.2.2 ILG Speed 175
7.2.3 ILG Appl i c a b i l i t y 176
7.3 D i f f e r e n c e s Ob s er v e d in the S ol u t i on
to the problems in t h e literature 180
7.4 D i s c u s s i o n of the P r o p o s e d DLP M e t h o d 181
7.4.1 Benefits of C o p i n g with
Non-d e t e r m i n i s t i c and U p -d a te d Data 181 7.4.2 C o n s i d e r a t i o n of "Time V a l ue of
M o n e y " i n Solution o f M ul t i - p e r i o d
Layout Probl e m 181
7.4.3 Sen s i t i v i t y of the P r o p o s e d D y n am i c Met h o d to the F o r e c a s t Flow Mat ri x
Data 182
CHAPTER EIGHT
C O N C L U S I O N 1S6
R E F E R E N C E S 190
A P P E N D I C E S
A - W i m m e r t ’s Method. A-1
B - Sw e e n e y and T a t h a m s ’s Theorem. B-1
C - Material Flow Data and Plant
Shapes for the N u g e n t ’s Problems. C-1
D - ILG Solution A s s i g n m e n t s to the
E Initial Sol u t io n s
P r o b l e m s . for N u g e n t ’s
E-F - U p - D a t a e d E-F r om - T o M a tr i c e s for
Example in C h a p te r Six.
F-G - C o m p a r i s o n of Material Flow C o s t s Re s u l t i n g fro m S o l u t i on s P r o d u c e d by CRAFT Sta rting w i t h R a n d o m and
ILG Ge n e r a t e d Initial Layouts.
G-H - Dif f e r e n c e s O b s e r v e d in R a n d o m Solu t i o n Co s ts to the N u g e n t ’s
Probl e m s R e p o r t e d in the
Liter a t u r e and O b t a i n e d by M i c r o -
H-CHAPTER ONE
INTRO D U C T I O N
1.1 P r o b l e m S t a t e m e n t
S h i f t i n g ma rket d e m a n d p at te r n and f r e quent f l u c t u a t i o n in
p r o d u c t i o n output level to ge t h e r with v a r i a t i o n in p r o d u c t
mix a n d design has c r e a t e d the requirement fo r responsive
f l e x i b l e m a n u f a c t u r i n g sy s t e m s (FMS).
F l e x i b i l i t y inherent in the e l e m en t s of FMSs, s u c h as
C o m p u t e r Numerical Control (CNC) machi n e s a n d Aut o m a t e d
G u i d e d Vehicles (AGV), may well cope w ith v a r i a t i o n s of
p ar ts produced (either in q u a n t i t y or in d e s ign), si m p l y by
r e p r o g r a m m i n g these elements. But r e p r o g r a m m i n g the
a u t o m a t e d elements of FMS doe s not n e c e s s a r i l y gu a rantee
the e f f i c i e n c y of p r o d u c t i o n of the total system. A part
from e f f e c t i v e u t i l i z a t i o n of f acilities 1n produ c t i o n
systems, the way 1n w h i c h f ac i l i ti e s are laid out and
lo c a t e d relative t o each other is a key factor in
a c h i e v i n g system e f f i c i e n c y and e co n o m i c production.
H a r m o n i o u s a l l o c a t i o n of f a c i l i t i e s 1n the layout and
e n s u r i n g the a d j a c e n c y or n e a rn e ss of f a c i l i t i e s (1n the
s y s t e m layout) with high v o l u m e of parts f l o w between
them, 1s the most c o m m o n l y e x e r c i s e d way, 1n industry, of
r e d u c i n g material h a n d l i n g r eq u irements. This in turn has
the b e n efi t of reduction in material h a nd l i n g costs.
T h e r e f o r e one of the f a ctor s i nf l u e n c i n g the total cost of
m a n u f a c t u r e is tha t of material h a n dl i n g c o s t and
thi s is f u n d a m e n t a l l y linked to the layout of facilities.
To m a i n t a i n their c o m p e t i t i v e n e s s , co m p a n i e s e m p l o y i n g
FMSs have to keep m a n u f a c t u r i n g c o s t to a minimum, w h i l e
b e i n g able to respond to the c h a n g e s m e n t i o n e d earlier.
Thi s implies that the layout of f a c i l i t i e s sh o u l d be
c o n t i n u o u s l y reviewed.
C o n t i n u o u s e v a l u a t i o n of layout, g e n e r al l y t er m e d as
D y n a m i c Layout P l a n n i n g (D L P ) in the literature,
[ M o o r e ( 19 7 4 ) , R o s e n b l a t t ( 1986), A f e n t a k i s ( 1990)], has been
s u g g e s t e d as a means of m a i n t a i n i n g e f f i c i e n c y in batch
p r o d u c t i o n systems w h e r e pa r t m i x / d e s i g n and p r o d u c t i o n
c h a n g e s are regularly introduced.
S i n c e the o c c u r r e n c e of f r e q u e n t c h a n g e is a feat u r e
of F M S ’s, 1t is clea r tha t c o n s i d e r a t i o n of the
c o n f i g u r a t i o n of m a c h i n e s is of g r e a t i mportance for FMSs
e v e r y time material flo w ch a n g e s are n e c e s s a r y t o satisfy
the m a r k e t demand.
DLP, has been de v e l o p e d f r o m Sta t ic L a y o u t P l a n n i n g (SLP)
plann ing periods within the total p l an n in g horizon.
This are a is h o wever relatively n e w and has raised o t h e r
qu e s t i o n s which hav e not yet b een fully investigated.
These q u e s t i o n s can be c a t e g o r i s e d as follows:
* What are t h e
the practical o p t i m u m
dynamic s i t u a t i o n ?
c r i t e r i a for p l a n n i n g
fa c i l it y layout in t h e
* If one o f the c r i t e r i a is
m i n i m i z a t i o n of m a te r ia l m o v e m e n t cost, w h a t
c o n s i d e r a t i o n s are g i v e n to thi s cost if there is
a need to change the initial layout in order to
cope with v a r iat io n in p r o d uc t mix and d e s i g n ?
* How sh o u ld the length of the t i m e
periods between w hi c h r e - l a y o u t s are c o n s i d e r e d
be determined?
* Is t h er e a n y way in w hich r e - l a y o u t
can be delayed?
* If r e - l a y o u t is d e c i d e d upon at th e
end of a time p e r i o d s ho u l d the n e w
p h a s e d manner? i.e. e x a c t l y w hen to
in s t i g a t e the layout.
In addition to the above q u e s t i o n s t h e r e also ex i s t s the
p r ob lem of u n c e r t a i n t y in the d ata r e g a rd i n g f ut u r e prod u c t
volume and the m i x of p r o d u c t d e s i g n to be produced. Many
c o m pan ies e m p l o y i n g FMSs do so b e c a us e of the v o l a t i l e
nature of the mar k e t in w h i c h t he y o p e r a t e and they may
com mon ly e x p e r i e n c e the c a n c e l l a t i o n of or d er s they have
p r e v i o u s l y received, or a l t e r n a t i v e l y receive or d e r s
unexp e c t e d l y w h i c h they c o u l d not have a n t i c ip a t e d
accur a t e l y in advance. T h e r e f o r e ignor i n g the e f f e c t s of
u n c ert ain f ut u r e data on the f a c i l i t i e s layout can lead
to u ndesi rab le a n d costly conseq u e n ce s .
The p rob lem of d y namic layout p l a n n i n g (DLP), in the FMS
context, can be stated b r i ef l y as i n v o l vi n g the f o l l o w i n g
ele m e n t s w hich are additional to t ho s e a d d r e s s e d in
’c o n v e n t i o n a l ’ DLP:,
(i) d e t e r m i n a t i o n of tim e p e r i o d s w i t h i n
the pl anning ho r i z o n in w h i c h re- l a y ou t will be
n e c es sary to m a i n t a i n s y s t e m effici en c y ,
(ii) c o n s i d e r a t i o n in a d v a n c e of f o re c a s t
da t a of u n known accuracy, and Its impact on the m u l t i
In all exis t i n g solu t i o n p r o c e d u r e s to the D L P prob l em none
takes a c c o u n t of both of the a b o v e aspects. In some of the
approaches, for example, c h a n g e s in ma t e r ia l flow data
are as s u m e d to occur at f i x e d time periods, w hile a
t o t all y d e t e r m i n i s t i c view of p r o d u c t design and
p r o d u c t i o n volume is c o n s i d e r e d w i t h i n these time
p eri ods ( R o s e n b l a t t ( 1986)). O t h e r a p p r o a c h e s in which
some limited var i a b i l i t y is t o l e r a t e d in the data, are only
a p p l i c a b l e to systems c o n t a i n i n g a small number of
f a c i 1 i t i e s .
A fu r t h e r sig n i f i c a n t p r o b l e m w i t h e x i s t i n g s ol utions is
the c o n s t r a i n t on p r o b l e m size. This a r i s e s due to an
exponent ial increase in s o l u t i o n tim e wit h th e increase in
the nu m b e r of facilities. Full s o l u t i o n s to probl e m s
c o n t a i n i n g no mo r e than nine f a c i l i t i e s h ave been reported
in the literature, [A f e n t a k i s ( 1990), Shore and
T o m p k i n s ( 1980)], b e cause of the e n o r m o u s amount of
co m p u t i n g time needed to p r o d u c e s o l u t i o n s by their
pr opose d methods.
The main o b j e c t i v e in this r e s e ar c h is t h e r e f o r e to develop
a d y n a m i c layout p l a n n i n g p r o c e d u r e w h i c h will determine:
(a) WHE N is the co s t e f f e c t i v e time to re-ar r a n ge the
(b) WHA T is the m o s t a p p r o p r i a t e layout for the
cu r r e n t period.
The p r o c e d u r e mus t take a c c o u n t of t h e f act that f o re c a s t
material flow data is u n l i k e l y to be a c c u r a t e and th a t the
rate at w h i c h the system n e e d s to resp on d to change m u s t be
m a t c h e d by the rate at w h i c h the p r o c e d u r e can p r o d u c e
solutions.
In the fo l l o w i n g sections o f this chapter, a reas rela t e d to
t his w ork will be briefly o u t l i n e d for the p u rp o s e of
identi fyi ng the background t o the work. T h e p r o b l e m of
d y n a m i c facil i t i e s r e - l a y o u t and a new so l u t i o n
p r o c e d u r e is detailed f o l l o w i n g an e x t e n s i v e review of
e x i s t i n g m e t h o d s and s o l u t i o n s to th e p r o b l e m of static
layout planning.
1.2 F l e x i b l e M a n u f a c t u r i n g Sy s t e m s (FMSs)
D efinition: An FMS is a hi g hl y a u t o m a t e d pr o d u c t i o n
s y s t e m c o n s i s t i n g of f l e x i b l e m a c h i n e s or w o r k s t a t i o n s
c o n n e c t e d by an automated m a t e r i a l h a n d l i n g system, all
under the control of one or m o r e c o m p u t e r s .[ H a r t l e y (1984),
S u l e ( 1988)]
A l t e r n a t i v e l y an FMS can be d e f i n e d as" an i ntegrated
c o m p u t e r c o n t r o l l e d c o m p l e x of a u t o m a t e d material
handli ng d e vices and n u m e r i c a l l y c o n t r o l l e d m a c h i n e
tools that can s i m u l t a n e o u s l y proc e s s m e d i u m - s i z e d volume
of a varie ty of part types" .[ B r o w n e ( 1984)]
1.2.1 P rod uction S y s t e m A r r a n g e m e n t s
Typical p rodu c t i o n s y stems are c l a s s i f i e d a c c o r di n g to the
layout of mach i n e s an d d e p a r t m e n t s w i t h i n the
m a n u f a c t u r i n g plant. A c c o r d i n g to H a r t l e y (1984), t h e s e are:
* Ran d o m Layout; m a c h i n e s are laid ou t r a nd o m l y
on the shopfloor.
* Functional (process) Layout; simi la r m a c h i n e s
are grouped t o g e t h e r wi t h i n th e plant to f o r m a
department. U s u a l l y used for jobb i ng & small
b atch type p r o d u c t i o n tha t p r o d u c e s many
d i f f e r e n t p r o d u c t s in r e la t i v e l y small volumes.
* M o dular (product) Layout; identical m o d u l e s
p e r f o r m s i milar p r o c e s s e s in parallel. S u i t a b l e
for batch p r o d u c t i o n in which nu m er o u s items are
pr oduced but not s o large a v a r i e t y as r eq u i r e d
in a job shop type of production.
* C e l l u l a r Layout; d es i g n e d s p e c i f i c a l l y for
ce ll u l a r and f l e x i b l e m a n u f a c t u r i n g (also
large number of com mo n p a r t s are grouped
t o g e t h e r and pr o d u c e d in a cell c o ns i s t i n g
of all the m a c h i n e s t h a t are ne ed e d to
p r o d u c e that group. This s y s t e m lends itself to
the introduction of FMS for d i f f e r e n t types of
workpieces.
The e m e r g e n c e of flex i b l e m a n u f a c t u r i n g syst em s in the
batch m a n u f a c t u r i n g environment, ha s p r e s e n t e d a
s i g n i f i c a n t d e p arture fro m c o n v e n t i o n a l m a n u f a c t u r i n g
approaches. Y e t little a t t e n t i o n has b e e n paid to the
importance of the study of d y n a m i c la y o u t pl a n n i n g of this
type of m a n u f a c t u r i n g system, in the s e n s e that re-l a y o u t
costs co uld be jus t i f i e d by savi n gs in material m o v e m e n t
costs. Some of the reasons for this a r e a not h a v i n g been
fully i n v estigated are sum ma r i s e d below:,
- a ssumptio n tha t an F M S makes h a n d l i n g
costs very in s en s i t iv e t o layout.
diffi c u l t y in e v a l u a t i o n of material
m o v e m e n t cost.
a ssumpti o n that d y n a m i c layout pl a nn i n g
is only r el evant to large p r o d u c t i o n
s y s t e m s .
assum p t i o n that d y n a m i c layout p la n n i n g
is only suit ab l e for p r o d u c t i o n s y s te m s in
which v a r i a t i o n s in material f l o w only occur
at fixed time intervals.
a s s u m p t i o n tha t DLP is o n l y r el evant to
systems o p e r a t i n g to or n ear full capacity.
It is probably the f i r s t of the a b o v e po i n ts t h a t leads to
th e belief that FMS layout does n o t contr i bu t e
s i g n i f i c a n t l y to o p e r a t i n g costs. Bu t the cos t of
p r o v i d i n g flex i b l e au t o m a t i c m a t e r i a l s h a n d l i n g in FMS,
t y p i c a l l y using a u t omated guided v e h i c l e s ( A G V ’s ) , is very
h i g h so small increases in the total ma t erial h a n dling
r e q u i r e m e n t may increase costs si gn i fi c a n tl y . Further m o r e
p o p u l a r trends to m i n i m i s e w o r k - i n - p r o g r e s s in o r d e r to
m o v e nearer to j u s t - i n - t i m e p r o d u c t i o n leads to a nee d to
m o v e smaller q u a n t i t i e s of pa r t s m ore f r e q u e n t l y thus
l e adi ng to a general growth in the m a terial handl i n g
requirement. H a n d l i n g costs are t h e r e f o r e significant.
1.3 Material H a n d l i n g S y s t e m s (M H S )
In d eveloping a new FMS or m o d i f i c a t i o n of an e x is t i n g
plant, a nalysis of the material h a n d l i n g s y s t e m is on e of
the mo s t important a s p e c t s . [ M o n t a l e n t i (1985)]
material ha ndling system. O n e of the m o s t c o m p r e h e n s i v e
d e f i n i t i o n s is provided by the Material H a n d l i n g
Inst itute (MHI), USA, which s t at e s : " Material h a n d l i n g
embra c e s all of the basic o p e r a t i o n s involved in t h e
m o v e m e n t of bulk, packaged, an d individual p r o ducts in a
s e m i - s o l i d or a solid state by m e a n s of m a c hi n e r y a n d
within the limits of place o f b u s i n e s s " .[ S u l e ( 1985)]
D.R .Su le e st i m a t e d that m a t e r i a l h a n d l i n g can a c c o u n t
for 3 0-70 percent of the total m a n u f a c t u r i n g cost a n d
e f f i c i e n t material hand l i n g ca n be p r i m a r i l y r e s p o n s i b l e
for red ucing a p l a n t ’s o p e r a t i n g c o s t by 15-30 percent. In
another c l a i m by T o m k i n s a n d W hi t e ( 1 9 8 4 ) it is
e s t i m a t e d that between 20 and 50 p e r c e n t of the total
m a n u f a c t u r i n g e x p e n d i t u r e can be a t t r i b u t e d to material
handli n g .
The main o b j e c t i v e s in s e l e c t i o n of a M HS for an FMS are:
* To increase the e f f i c i e n c y of material flow by
e nsur i n g the a v a i l a b i l i t y of r eq uired m a t e r i a l s
when and w here they ar e needed.
* To reduce material h a n d l i n g cost.
* To improve facil i t y u t i li z a t io n .
* To mini m i s e work in progress.
Recent d e v e l o p m e n t s in A u t o m a t e d Gui d e d V e h i c l e Systems
(A G V s ) have further inc r ea s e d t h ei r c a p a b i l i t y in
achieving the a b o v e o b j e c t i v e s as well as pro vi d i n g
flexibility in route layouts w h i c h is r e q u ir e d w i t h i n an
FMS.[Turpin( 1988), Grossman, (1988) and G o o d h e a d
e t . a l .(1988)]
In a large p r o p o r t i o n of re c ently i m p l e m e n te d flexible
manuf act uring systems AGVs h a v e bec o m e an essential
compo nent of t h e material h a nd l i n g system. [Vosniakos
e t . a l .(1989), H a m m o n d (1986) and G u n s s e r (1988)]
M ost current A G V systems are not howe ve r as q uick and easy
to change as may be required. F r e e ranging AGVs w h i c h are
now c o m me rcially available offer the d e g r e e of f l e x i b i l i t y
required. [E v a n s (1988)]
However, the s y s t e m flow patte r n d e t e r m i n e d by the process
requirements go v e r n s material flow paths and this
implies that a n y attempt at a s y s t e m o p t i m i s a t i o n process
should begin w i t h the layout d e s i g n . [ P u t r u s ( 1986)]
In other words a partic u l a r l y f l e x i b l e material h an dling
sys tem may be a b l e to a c c o m m o d a t e the e f f e c t of a layout
opera te as cost e f f e c t i v e l y as whe n the h a n d l i n g d is t a n c e
is minimised. The tim e to ch a n ge the l a y o u t o c c u r s when
the cost penalties ac c r u e d o ver a p e r i o d i nc u rr e d through
op e r a t i n g an i n a p p r o p r i a t e layout e x c e e d the c os t s of
cha ngi ng to a more e f f i c i e n t layout.
1.4 F a cil ities Layout T e c h n i q u e s
Faci l i t i e s layout techniques, o f te n c a l l e d p la n t layout,
[Foulds and R o b i n s o n ( 1976 ) ], is a m e t h o d w h i c h d e s c r i b e s
the process of desi g n a r r a n g e m e n t an d c o o r d i n a t i o n of
physical facilities. P l a n t layout t e c h n i q u e s can be used
in man y areas includi ng the d e s i g n of serv i c e
facilities, such as hospitals, l ibraries a n d etc.
Ho w e v e r the c o ncern In this thesis is o n l y w i t h the
a r r a n g e m e n t of m a n u f a c t u r i n g m a c h i n e s and w o r k c e n t r e s in an
FMS shopfloor, in a m u l t i - p e r i o d p l a n n i n g horizon.
Since the beg i n n i n g of o r g a n i z e d manufac t ur i n g ,
c o n s i d e r a b l e eff o r t has been e x p e n d e d t o m a k e the
f a c i l i t i e s layout as e f f i c i e n t as pos s ib l e. In t his goal
the importance of e f f e c t i v e p la n n i ng of f a c i l i t i e s has
been realised and the potential b e n e f i t s are well
d o c u m e n t e d . [ T o m k i n s and White(1984), S u l e ( 1 9 8 5 ) ] In
general there are four stag e s of hist or i c a l d e v e l o p m e n t 1n
the tec hn i q u e s treating the layout p l a n n i n g p r o b l e m :
I. Us e of graphical t e c h n i q u e s and templ a t e m a n i p u l a t i o n by
a layout engineer f o l l o w e d by d e v e l o p m e n t of the
layout and subjective e v a l u a t i o n of it.
II. S y ste matic layout planning, s u g ge s te d initially by
M u t h e r (1974). He has a t t e m p t e d to p r o v id e proc e d u r e s
with s u f f i c i e n t structure p e r m i t t i n g practical p r ob l e m s to
be sol v e d e c o nomically t h r o u g h a s ystematic approach.
III. Use of quantitative techniques, w hen facil i t i e s
rel a t i o n s h i p s are e x p ressed qu antitatively, for e x a m p l e by
material flow quantities in a From-To chart. The o b j e ct i v e
f u n c t i o n is then to m i n i m i z e the material h a n d l i n g cost,
that is, the product of t h e distance betw e en facilities,
the material flow, and u n i t - h a n d l i n g cost.
IV. Compu ter aided layout planning.
Wi t h the recent use of o p e r a t i on a l research t e c h n i q u e s and
c o m p u t e r technology more analytical p r oc e d u r e s can be
a p p l i e d to th e generation a n d c o mp a r i so n of layouts. A
d e t a i l e d a c c o u n t of these a r e pr o vided in c h a p t e r two.
1.4.1 Static and Dynamic L a y o u t Planning
The general approach, until recently, to the facility
I. Us e of graphical t e c h n i q u e s and t e m p l a t e m a n i p u l a t i o n by
a layout e n g i n e e r f o l l o w e d by d e v e l o p m e n t of the
layout and s u b j e c t i v e e v a l u a t i o n of it.
II. S y s t e m a t i c layout planning, s u g g e s t e d initially by
M u t h e r ( 1974). He has a t t emp t ed to p r o v i d e proce d u re s
with s u f f i c i e n t s t r u c t u r e p e r m i t t i n g p r actical p r ob l e m s to
be s o l v e d e c o n o m i c a l l y t hrough a s y s t e m a t i c approach.
III. Use of q u a n t i t a t i v e techniques, when f ac i li t i e s
r e l a t i o n s h i p s are e x p r e s s e d q u a n t i t a t i v e l y , for e x a m pl e by
material f l o w q u a n t i t i e s in a F r o m - T o chart. Th e o b j ec t iv e
f u n c t i o n is then to m i n i m i z e the m at e r i al h a n d l i n g cost,
that is, the pr o d u c t of the d i s t a n c e b e t w e e n facilities,
the material flow, and u n i t - h a n d l i n g cost.
IV. C o m p u t e r aided layout planning.
With the rec e n t use of operation a l r e s e a r c h t e c h n i q u e s and
c o m p u t e r t e c h n o l o g y mor e analytical p r o c e d u r e s can be
a p p l i e d to the g e n e r a t i o n and c o m p a r i s o n of layouts. A
d e t a i l e d a c c o u n t of these are p r o v i d e d 1n c h a p t e r two.
1.4.1 St at i c and D y n a m i c Layout P l a n n i n g
The general approach, until recently, to t h e fa c ility
P I a n n i n g ( S L P ) the a i m is to o pt i m i z e s o m e eval ua t i o n
c r i t e r i a eithe r q u a l i t a t i v e l y or q u a n t i t a t i v e l y w ith a
fixed (or static) set o f material flow d a t a a p p l i c a b l e to
a fixed period of time.
A com m o n pro c e d u r e e m p l o y e d wit h q u a l i t a t i v e c r i t e r i a is
to e s t a b l i s h a r e l a t i o n s h i p - c h a r t based on the clo s en e s s
d e s i r a b i l i t y of t h e facilities, [Sule(1988),
M u t h e r (1974), Francis a n d W h i t e ( 1974)].
The m o s t common q u a n t i t a t i v e criteria, however, use d in
e v a l u a t i o n of layout is based on F r o m - To c h a r t s ob t a i ne d
fr o m pr e d i c t e d in t e n s i t y of material flow between
f a c i 1ities.
In an international s u r v e y of p r o gr e ss in t h e s u b j ec t of
C o m p u t e r - A i d e d F a c i l i t i e s Layo ut (C A F L ), it has been
o b s e r v e d that material m o v e m e n t is the m o s t co mm o n layout
e v a l u a t i o n criteria, [Driscoll and S a n g i (1985 ) ].
In SLP, m i n i m i z a t i o n of t h e total material m o v e m e n t c o s t is
a s s o c i a t e d wi t h a s s i g n i n g d i f f e r e n t f a c i l i t i e s to
d i f f e r e n t locations a n d is f or m u l a t e d as a qua dr a t i c
a s s i g n m e n t problem, w h i c h is di s c u s s e d in det a il in chap t e r
3 of t his thesis.
A l t h o u g h SLP can be a useful p r o c e du r e 1n d e s i g n i n g a new
proc edure in FMS w h e r e f r e q u e n t r e - a r r a n g e m e n t of the
layout may be required in order t o respond to the var i at i on
in demand a n d p r o d u c t design [ M o o r e ( 1969), Nicol and
Hoi 1 i e r ( 1983 ) ].
Dyna mic e v a l u a t i o n of plant re-layout, inv o lv i n g the
c o n s i d e r a t i o n and m e t h o d o l o g y o f c h an g i n g f r o m an old to
a new layout has not received m u c h a t t en t io n until recently
[Driscoll a n d S a w y e r ( 1985)]. W i t h the p r o g r e s s made in
comp uter a i d e d layout planning, dynam i c layout p la nning
(D L P ) a p p r o a c h e s to the p r o b l e m have been suggested.
[Rosenblatt (1986) and A f e n t a k i s ( 1990)]
In t hese approaches, the layout des i g n st r a t e g y is studied
not just f o r a single time period, but for a m u l t i p e r i o d
pla nni ng horizon, duri n g w h i c h v a r i a t i o n s o c c u r in the
material f l o w that is antici p a t e d . The o b j e c t i v e is to
m i n i m i s e t h e sum of the costs a t t r i b u t a b l e to facil i ty
location o v e r the w h o l e p l a n n i n g horizon not s i mp l y for
individual d i s c r e t e periods.
In alm ost all of the s o l u t i o n s p r ov i d e d to date, a
d e t e r m i n i s t i c environment, in t e r m s of material fl o w data,
has been c o n s idered. A s i g n i f i c a n t c o n t r i b u t i o n made
by this r e s e a r c h is to extend t h e DLP c o n c e p t to deal
wit h u n c e r t a i n t y in the material f l o w that may be e xp e ct e d
to o c cur in b ot h the near future and in th e longer term.
The very nature of FMSs m eans t ha t p ro d u c ts and t h e product
mix can change and the inh e r en t f l e x i b i l i t y in the
pro c e s s e s and handling s y s t e m c an p er m i t a v a r i e t y of the
products to be made.
But the p r o d u c t i o n cost is not n e c e s s a r i l y m i n i m i z e d if the
layout an d han d l i n g m e t h o d s remain the s a m e as was
o r i g i n a l l y defin ed for a c o n s i d e r a b l y d i f f e r e n t set of
pro duc ts and flo w paths. In o r d e r to m i n i m i z e costs, the
sys t e m m u s t respond to c h a n g e s in dem a nd and the response
rate mus t be s u f f i c i e n t l y high t o deal wit h large and rapid
flu ctuations. Freq u e n t f l u c t u a t i o n s in material flo w are
so m e t i m e s not e c o n o m i c a l l y d e a l t w ith by r e - l a y o u t due to
the costs of m a c h i n e m o v e m e n t s bu t can be a d d r e s s e d by re
p r o g r a m m i n g the guide paths of f r e e - r a n g i n g A GVs. For
longer t e r m f l u c t u a t i o n s d y n a m i c r e - l a yo u t c a n be a
via b l e o p t i o n but the u n c e r t a i n t y and v a r i a b i l i t y of
the d ata used is c o n s i d e r e d to require t e c h n i q u e s w hi c h
c r e a t e s v a r i a b l e p l a n n i n g h o r i z o n s and a s s i gn s d i f f e r e n t
w e i g h t i n g f actors to dat a d e p e n d i n g on the level of
c e r t a i n t y that can be a t t r i b u t e d to it.
Thi s the s i s t h e re fore aims to p r o v i d e m e t h o d s t h a t will
all ow d e c i s i o n s to be ma d e w h i c h will en s u r e t h a t an FMS
can be a d ap ted to su i t the d y n a m i c and u n c e r t a i n
natu r e of demand. The c o n c e p t 1s to c o n t i n u o u s l y m o n i t o r
a mor e cost e f f e c t i v e c o n f i g u r a t i o n w h en e v e r it is
p r o f i t a b l e to do so. Econo m i c c o n s i d e r a t i o n s ar e to be
used to i ntroduce damping into the s y s t e m so tha t onl y
s i g n i f i c a n t or s u s t a i n e d c h a n g e s result in a d e c i s i o n to
c h a n g e the layout. The use of a r b i t r a r y f i x e d t ime peri od s
o v e r which to m e a s u r e dem a n d are c o n s i d e r e d to be total l y
ina p p r o p r i a t e in a dynamic situation, as is the not io n of
an ’optimal l a y o u t ’ w h i c h can only b e optimal for a
given set of d e m a n d data.
All exi st i n g te chn i q u e s assume de ma n d d a t a to be a c cu r a t e
and const a n t o v e r a time period s e l e c t e d for c o n v e n i e n c e
rather than for economic reasons. A me t h o d is
prop o s e d to intro duce an ant i c i p a t e d level of u n c e r t a i n t y
into the da t a t o g e t h e r w i t h a m e a n s of p r o c e s s i n g this into
u s e a b l e form. In this m e t h o d a r b i t r a r y f i xe d length tim e
p e r i o d s are not assumed, rather a time pe r i o d is
d e t e r m i n e d whe n f a c i l i t i e s r e - la y o ut is required.
As m e n t i o n e d earlier, in dy n a m i c layout p l a n n i n g c o n t i n u o u s
m o n i t o r i n g of c h a n g e s in material flow is needed. This in
turn n e c e s s i t a t e s d e v e l o p m e n t of a s t a t i c layout d es i g n
w h e n e v e r a ch a n g e occurs, so that a d y n a m i c layout po li c y
deci s i o n can be made based on the s t a t i c layouts at e a c h
time period. It was found that e x i s t i n g m e t h o d s of
g e n e r a t i n g s o l u t i o n s to the SLP p r o b l e m w e r e u n a c c e p t a b l y
slow f o r use in the p r o p o s e d m e t h o d o f solv i ng the DLP
problem. This is p r i m a r i l y b e c a u s e the m a jo r c r i t e r i o n for
such m e t h o d s is to g e n e r a t e an optimal s o l u t i o n or as near
as to t h e optimal s o l u t i o n as the m e t h o d was c a p ab l e of
produc ing. H o w e v e r in c i r c u m s t a n c e s w h e r e dat a is
c h a n g i n g a n d its accu r a c y is u nc e r t ai n , the j u s t i f i c a t i o n
for f i n d i n g the ver y b e s t s o l u t i o n based on
u n r e l i a b l e or u n r e p r e s e n t a t i v e data is c o n s i d e r e d to be
not va lid . It was instead c o n s i d e r e d to be far m ore
imp o r t a n t to use a met h o d tha t was Past e no u g h to e n a b l e
re a l - t i m e de c i s i o n s to be m a d e in r e s p o n s e to m a r k e t
ch a n g e s p r o v i d e d that the a c c u r a c y of r e su l ts pr o d u c e d were
c o n s i s t e n t with the a c c u r a c y o f the d a t a used.
A h e u r i s t i c p r o cedure for g e n e r a t i n g s o l u t i o n s to the SLP
p r o b l e m w a s there fore d e v e l o p e d purely to g e ne r a t e initial
s o l u t i o n s for DLP. This was s u b s e q u e n t l y f ou n d to p r od u ce
s o l u t i o n s at least as good as m a n y e s t a b l i s h e d m e t h o d s but
with far g r e a t e r c o m p u t ational e f f i c i e n c y than any of the m
since it p e r m itt ed large p r o b l e m s (30 facili ti e s) to be
solved m a n u a l l y even w i t h o u t the a i d of a computer.
A l t h o u g h it was not an orig i n a l o b j e c t i v e of the r es earch
it is n e v e r t h e l e s s c o n s i d e r e d to be an original and
s i g n i f i c a n t c o n t r i b u t i o n to w o r k in t h e a r e a of layout
p l a n n i n g and essential for t h e p r actical a p p l i c a t i o n of
The new static layout p r o c e d u r e na m e d Initial Layout
Ge n e r a t o r (ILG) is pr e s e n t e d in c h a p t e r f o u r of this thesis
f o l lo wing the survey of the e x i s t i n g S L P m e t h o d s and
Q u a d r a t i c A s s i g n m e n t P r o b l e m (QAP) in c h a p t e r s two and
three. In chapter five c a p a b i l i t y and p e r f o r m a n c e of the
new s t a t i c layout p l a n n i n g p r o c e d u r e (ILG) is ex a m i n e d
v i g o r o u s l y using the d a t a in th e l i t er a t u r e and o t h e r data
origina ted I by the author. C h a p t e r six contai ns the
propo sed m e t h odology for DLP of FMSs t o g e t h e r w ith an
e x a m p l e . In chapter seven the resu l ts obtai ned 1n
chap ter s five and six are d i s c u s s e d and fina l ly the
c o n c l u d i n g remarks are given in c h a p t e r eight.
CHAPTER TWO
STATIC LAY O U T PLA NNING
2.1 I n t rod uctio n
The p r o b l e m of f a c i l i t i e s l a y o u t has b e e n the s u b j e c t of
anal ysis for many years [ A p p l e ( 1973), F r a n c i s and
W h i t e ( 1974)]. Dif f e r e n t n a m e s have b e e n applied to this
p r o b l e m in the literature. M u t h e r ( 1 9 7 4 ) pref er s
"Layout Planning", K o o p m a n (1957) u s e s " L ocation of
Econ o m i c Activities", B u f f a e t . a l . ( 1 9 6 4 ) uses "Fa c il i t i es
A l l o cat ion", w hile H i l l i e r ( 1 9 6 3 ) and others, Apple(1976),
Lee and Mo ore(1967), R e e d ( 1 9 6 1 ) prefer "P la n t Layout".
On the import anc e of the prob l e m , M u t h e r ( 1974), on e of the
early p i o n e e r s of a s y s t e m a t i c s o l u t i o n a pp r o a c h to the
pr o b l e m s t a t e s ,"PIant layout is an industrial fundamental.
It d e t e r m i n e s the efficiency, and in s ome i n stances the
survival of an enterprise".
In one of the very early s u r v e y s , M u t h e r ( 1 9 5 7 ) c o n d u c t e d in
1947, It was indicated t h a t of all t h e Im p roved plans
"improve p l a n t layout" was s e c o n d only, in importance, to
"install new pro du c t i o n m a c h i n e r y an d equipm e n t " as a
c o s t - c u t t i n g technique.
was gener all y treated q u a l i t a t i v e l y and traditional
a p p r o a c h e s relied heavily on int u i t io n and e n g i n e e r i n g
j u d g e m e n t [Francis and W h i t e ( 1974)]. In solving the
f a c i l i t i e s layout problem, iconic and a n a l o g u e mod e l s were
used as scalar representation of objects. In these
a p p r o a c h e s a num b e r of a l t e r n a t i v e s o l u t i o n s wer e generated,
b a s ic ally de p e n d a n t on the s u b j e c t i v e c r i t e r i a of the
analyst, by m a n o e u v a r i n g t e m pla te s and s c a l e mo d e l s on a
floor pl a n and then these a l t e r n a t i v e s w e r e c om p a r e d on
the b a sis of q u a l i t a t i v e objectives. W i t h the recent
d e v e l o p m e n t of s ymbolic and mathem a ti c a l models, much of the
research work has been directed to w a r d s q u a n t i t a t i v e
t e c h n i q u e s for an al y s i s of the layout problem.
For mathema tic al models, two general t y p e s have been
developed, ( i)descriptive mod e l s w h i c h are used to d es c r i be
the beh avi our of the s y s t e m involved, and
( i i )pr esc ripti ve (or normative) w h i ch are u sed to s u gg e st
a c o u r s e of a ct i o n to be t aken in o r d e r to o b t a i n the best
solu t i o n procedure. D e c i d i n g w h i ch s o l u t i o n is the best
among a l t e r n a t i v e results, depe nd s on the s e l e c t i on of
a p p r o p r i a t e criteria.
As s t a t e d in the introduction chapter, m i n i m i z a t i o n of
p r o d u c t i o n cos t while m a x i m i z i n g m a n u f a c t u r i n g sys te m
e f f i c i e n c y has been the m a j o r c r i te r io n for se le c t i ng the
best f aci l i t i e s layout s o l u t i o n and thi s is also
a c c o r d a n c e with Majid(1980).
The di r e c t link b e tween material ha n d l i n g cost and
produ c t i o n cos t has been the p rim e reason for j u s t i f i c a t i o n
of e m p l o y i n g the c r i t e r i o n of m i n i m i z i n g some f u n c t i o n of
d i s t a n c e t r a ve lled by parts. P o p u l a r i t y o f m i n i m i z a t i o n of
material m o v e m e n t cost i l l u s t r a t e d by a s u r v e y by D r i scoll &
Sangi(1 985) indicates its impo r t a n c e and the d eg r e e of
e m p h a s i s g ive n to this criterion. H o w e v e r the a p p r o a c h e s by
which a sing le fact o r being s e l e c t e d as basis for
se l e c t i o n of a solution has been c r i t i c i s e d by V o l l m a n n &
Buffa (1966).
V o l l m a n n & B u f f a state tha t " th e layout p r o b l e m s h o u l d
be c o n s i d e r e d in the light of p r o b l e m uniqueness, the
c o n c o m i t a n t u n i q u e n e s s of s p e c i f i c p r o b l e m criteria, and
the need to reflect this u n i q u e n e s s in p r o b l e m a p p r o ac h es .
The f a c i l i t i e s layout p r o b l e m is i nh e r e n t l y m u l t i - v a l u e d and
is n o t p rop e r l y ha n d l e d by a si ng l e c r i t e r i o n mod e l.
Prob l e m s c a n n o t be forced Into models, m od e l s m us t be
a d a p t e d to problems."
This c r i t i c i s m is v alid in the s e n se t h a t the f a c i l i t i e s
layout p r o b l e m is a c o m p l e x p r o b l e m and all e l e m e n t s of t h e
produ c t i o n sys t e m c ould hav e some de g r ee of i n f luence on
However, the fo llowing points are c o n s i d e r e d to just i fy the
s e l e cti on of m i ni mum m a t e r i a l h a n d l i n g distance as the p r i m e
cri teri a :.
(i) In an FMS e n v i r o n m e n t reduction of work in
p r o g r e s s and storag e as an o b j e c t i v e re q uires
m i n i m i z a t i o n of d i s t a n c e tr a v e l l e d by p a r t s
in the s y s t e m w h i c h in turn ca n lead to
r e d u c t i o n in material m o v e m e n t / h a n d l in g cost.
(ii) R e d u c t i o n of total material h an d l i n g d i s t a n c e
in the s y s t e m will reduce total traf fi c
( d i stance * part v o l u m e ) c i r c u l a t i n g in t h e
system h ence eas i ng the t r a f f i c control
problem.
(iii) In t h e FMS layout, c r i t er i a other t han
material handling d i s t a n c e may not remain
valid d u r i n g the la y o u t p l a n n i n g horizon,
whereas ad j a c e n c y of facil i t i es with h ig h
volume o f flow betw ee n them is alw a ys d es i r e d
as one of the mo s t important, if not t he
only, cr i t e r i a .
(iv) P o p u l a r i t y of m i n i m i z a t i o n of material
m o v e m e n t cost by m e a n s such as redu c ti o n of
industry r e pres en t s the i mportance and
p r a c t i c a l i t y o f this criteria.
2.1.1 D i s t a n c e M e a s u r e m e n t
D i s t a n c e s travelled by p a r t s are m e a s u r e d with resp ec t
to the centre of locations of m a c h i n e s / w o r k c e n t r e s betw e en
which p a r t s travel, and are eith e r R e c t i l i n e a r (also k nown
as M a n h a t t a n ,[Tam and Li (1991)]) or Euc l i d ia n distance,
shown in Fig.2.1.
R e c.D ist ance |xi -
XjJ
+ | Y* - Yj|Eue.D ist a n c e [(Xi - X j ) 2 +(Yi - Y j ) 2 ]1'*
where ( X i , Y i ) and (Xj,Yj ) a r e the c o o r d i n a t e s of c en t r e
points o f locations i and j.
E u c l i d e a n di stanc e is g e n e r a l l y u s e d as a m e a s u r e of
d i s t a n c e between ce n t r o i d s of f a c i l it i es and R e c t i l i n e a r
d i s t a n c e trave lled by p a r t s 1n t h e s y s t e m a l on g a
Fi g . 2.1 Sc h e m a t i c d i a g r a m r e p r e s e n t i n g E u c l i d e a n and R e c t i l i n e a r d i s t a n c e me as u rement.
R e c t i l i n e a r di sta nce c o r r e s p o n d s mor e closely to t h e usual
mode of industrial t r a n s p o r t s i n c e it s i m ul a te s tra v e l a long
a se t of orthogonal aisles. H en c e the di s t a nc e m e a s u r e m e n t
in the pr opo sed ILG m e t h o d (in c h a p t e r four) is c o n s i d e r e d
to be rectilinear. A p o i n t w o r t h m e n t i o n i n g h e r e is t hat
if travel cost is not p r o p o r t i o n a l to travel d i s t a n c e , t hen
the pa r a m e t e r r e p r e s e n t i n g the d i s t a n c e in t h e layout
ob j e c t i v e fun ction (see e q u a t i o n s 4.1 and 4.4 ) can be
adju s t e d so that 1t b e c o m e s an a p p r o p r i a t e m e a s u r e of
2.1.2 Model V a l i d i t y
Based on the s e l e c t e d criteria, m o d e l s are d e v e l o p e d to
represent and aid the a n a l y s i s of p l a n t layout. T h e r e ar e
two m e tho ds of v a l i d a t i n g t hese models:.
a) Testing t o e s t a b l i s h w h e t h e r they are c a p a b l e o f
leading to r e a s o n a b l e p r e d i c t i o n s o f a known s y s t e m ’s
p e r f orman ce and p r o d u c i n g s u b s e q u e n t impr o v e me n ts in the
system.
b) C o m p a r i s o n of the s o l u t i o n s o b t a i n e d from the model
with answers o b t a i n e d for the same p r o b l e m from d i f f e r e n t
m o d e l s .
The latter method is used t h r o u g h o u t t h i s thesis to p r o mo t e
con s i s t e n c y and t o p e r m i t dir e c t c o m p a r i s o n w i t h o t h e r
techniques.
2.1.3 Steps of L a y o u t Des i g n Proce s s
After cri ter ion a n d model selection, the layout de si g n
proce ss is f o l l owed. A general a p p r o a c h for this is
sugges ted by K i r c k ( 1 9 6 5 ) which s p e c i f i e s the f o l l o w i n g
steps
