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 the d e s i g n a t e d layout for a s p e c i f i c p r o d u c t i o n s i t ua t io n .
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 d i s t a n c e tr a v e l l e d by ma t e r i a l s p r a c ti c e d in l
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