University of Windsor University of Windsor
Scholarship at UWindsor
Scholarship at UWindsor
Electronic Theses and Dissertations Theses, Dissertations, and Major Papers
1-1-1987
A microcomputer-based simulation model of a flexible
A microcomputer-based simulation model of a flexible
manufacturing system with application to scheduling rules.
manufacturing system with application to scheduling rules.
Thiruvengadam Ravi University of Windsor
Follow this and additional works at: https://scholar.uwindsor.ca/etd
Recommended Citation Recommended Citation
Ravi, Thiruvengadam, "A microcomputer-based simulation model of a flexible manufacturing system with application to scheduling rules." (1987). Electronic Theses and Dissertations. 6828.
https://scholar.uwindsor.ca/etd/6828
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A M I C R O C O M P U T E R - B A S E D S I M U L A T I O N M O D E L O F A
F L E X I B L E M A N U F A C T U R I N G S Y S T E M W I T H
A P P L I C A T I O N T O S C H E D U L I N G R U L E S
b y
T h i r u v e n g a d a m Ravi
A T h e s i s s u b m i t t e d t o t h e
F a c u l t y of G r a d u a t e S t u d i e s a n d R e s e a r c h t h r o u g h t h e D e p a r t m e n t of
I n dustrial E n g i n e e r i n g in P a r t i a l F u l f i l l m e n t of t h e r e q u i r e m e n t s f or t h e D e g r e e
of M a s t e r of A p p l i e d S c i e n c e at t h e U n i v e r s i t y of W i n d s o r
W i n d s o r , O n t a r i o , C a n a d a
1987
UMI Number: E C 54818
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All R i g h t s R e s e r v e d
I h e r e b y d e c l a r e t h a t I a m t h e s o l e a u t h o r of t h i s thesis.
I a u t h o r i z e t h e U n i v e r s i t y of W i n d s o r t o lend t h i s t h e s i s
t o o t h e r i n s t i t u t i o n s or i n d i v i d u a l s for t h e p u r p o s e of
s c h o l a r l y re s e a r c h .
T h i r u v e n g a d a m Ravi
I f u r t h e r a u t h o r i z e t h e U n i v e r s i t y of W i n d s o r t o r e p r o d u c e
t h i s t h e s i s b y p h o t o c o p y i n g or b y o t h e r means, in total or
in part, at t h e r e q u e s t of o t h e r i n s t i t u t i o n s or
i n d i v i d u a l s f o r t h e p u r p o s e of s c h o l a r l y r e s e a r c h .
T h e U n i v e r s i t y of W i n d s o r r e q u i r e s t h e s i g n a t u r e of all
p e r s o n s u s i n g or p h o t o c o p y i n g t h i s thesis. P l e a s e sign
below, a nd g i v e a d d r e s s an d data.
A B S T R A C T
T h i s r e s e a r c h d e a l s w i t h t h e d e v e l o p m e n t of a
m i c r o c o m p u t e r — b a s e d s i m u l a t i o n model of a F l e x i b l e
M a n u f a c t u r i n g S y s t e m (FMS) u s i n g t h e g e n e r a l p u r p o s e
s i m u l a t i o n l a n g u a g e S L A M ( S i m u l a t i o n L a n g u a g e for
A l t e r n a t i v e M o d e l i n g ) . T h e F M S u n d e r c o n s i d e r a t i o n is
c o m p o s e d of g e n e r a l p u r p o s e m a c h i n i n g c e n t e r s laid out in
s e p a r a t e lanes, a l o a d i n g a nd an u n l o a d i n g stat i o n , a
c e n t r a l p a r t s s t o r a g e t o s t o r e t h e r a w m a t e r i a l s and
w o r k — i n — p r o c e s s parts, a n d a u t o m a t e d m a t e r i a l h a n d l i n g
syst e m s .
T h e s i m u l a t i o n model w h i c h is a d a p t i v e to
v a r i a t i o n s in t h e layout, s e r v e s a s a d e c i s i o n tool to
s e l e c t a s c h e d u l i n g r u l e f r o m a m o n g s t t h e f i v e rules,
na m e l y . R a n d o m s e l e c t i o n ( R A N D O M ) , F e w e s t O p e r a t i o n s
R e m a i n i n g ( F O P R ) , M o s t O p e r a t i o n s R e m a i n i n g (MOPR) ,
S h o r t e s t P r o c e s s i n g T i m e (SPT) a nd L o n g e s t P r o c e s s i n g T i m e
(LPT). T h e model i n c l u d e s r e a l i s t i c a s p e c t s s u c h as,
a l t e r n a t e r o u t i n g f o r c e r t a i n o p e r a t i o n s , t r e a t m e n t of
f i x t u r e s a s r e s o u r c e s , a n d p a r t t y p e s w i t h p r i o r i t i e s .
T h e s i m u l a t i o n model is user— i n t e r a c t i v e and d o e s not
r e q u i r e a p r i o r w o r k i n g k n o w l e d g e of SLAM.
S t a n d a r d s t a t i s t i c a l t e c h n i q u e s a r e u s e d t o
s e l e c t a s c h e d u l i n g r u l e f r o m t h e f i v e r u l e s u n d e r
— vi —
c o n s i d e r a t i o n . An e x p e r i m e n t a l d e s i g n s e t u p is u s e d t o
a i d t h e s t u d y of t h e e f f e c t s of t h e d i f f e r e n t r e s o u r c e s on
t h e s y s t e m p e r f o r m a n c e . T h e s e p r o c e d u r e s a r e i l l u s t r a t e d
t h r o u g h e x a m p l e s .
ACKNOWLEDGEMENTS
I w o u l d l i k e t o t a k e t h i s o p p o r t u n i t y t o e x p r e s s m y
g r a t i t u d e t o Dr. R. S. L a s h k a r i a nd Dr. S. P. D u t t a f o r
t h e i r g u i d a n c e a nd s u p p o r t d u r i n g t h e e n t i r e c o u r s e of
t h i s r e s e a r c h . I w o u l d a l s o l i k e t o t h a n k Dr. R. J. C a r o n
a nd Dr. P. Brill fo r r e v i e w i n g m y t h e s i s a n d p r o v i d i n g
u s e f u l s u g g e s t i o n s . A s pecial n o t e of t h a n k s g o e s t o
J a c q u i e M u m m e r y a n d T o m W i l l i a m s f o r t h e i r i n v a l u a b l e h e l p
f r o m t i m e t o time.
I w i s h t o t h a n k m y f r i e n d s , all t h e g r a d u a t e s t u d e n t s
in t h e D e p a r t m e n t of I n d ustrial E n g i n e e r i n g , w h o h a v e
p r o v i d e d i n v a l u a b l e h e l p t h r o u g h usef u l d i s c u s s i o n s .
Fina l l y , I a m v e r y g r a t e f u l t o m y pare n t s .
D r . T h i r u v e n g a d a m a nd Dr. S u l o c h a n a , f o r a l w a y s b e i n g
t h e r e w h e n I n e e d e d them, in s p i t e of t h e d i s t a n c e .
— V I 1 1 —
L I S T O F F I G U R E S
F i g u r e P a g e
I- C o m p a r i s o n of v a r i o u s m a n u f a c t u r i n g
s y s t e m s ... - ... 2
2. L a y o u t of t h e F M S with L l a n e s ( L > 1 ) ... 10
3. S a m p l e p r i s m a t i c p a r t ... 2 7
4. F l o w c h a r t of p a r t - m a c h i n e s e l e c t i o n
a l g o r i t h m ... 31
5. F l o w c h a r t of p a r t f l o w in t h e s y s t e m ... 3 7
6. O r g a n i s a t i o n of t h e c o m p u t e r p r o g r a m ... 4 2
7. B l o c k d i a g r a m of t h e S L A M n e t w o r k model .... 51
8. S e g m e n t 1 a nd s e g m e n t 5 of t h e S L A M
n e t w o r k model ... 52
9- S e g m e n t 2 of t h e S L A M n e t w o r k model ... 5 3
10. S e g m e n t 3 of t h e S L A M n e t w o r k model.. . 54
II- S e g m e n t 4 of t h e S L A M n e t w o r k model . 55
12. L a y o u t of t h e F M S — P r o b l e m 1 . . . 6 6
13. L a y o u t of t h e F M S — P r o b l e m 3 ... 9 0
LIST OF TABLES
T a b l e P a g e
1- S u m m a r y of p a r t t y p e d a t a — P r o b l e m 1 ... 67
2. S u m m a r y of s y s t e m layout d a t a — P r o b l e m 1 ... 6 8
3. S u m m a r y of r e s o u r c e d a t a — P r o b l e m 1 ... 69
4. S u m m a r y of s p e e d and t i m e d e t a i l s of t h e
mate r i a l h a n d l i n g s y s t e m s — P r o b l e m 1 ... 69
5- W e i g h t e d s a m p l e m e a n s of m a k e s p a n — P r o b l e m 1 .. 71
6. R e s o u r c e q u a n t i t i e s and u t i l i z a t i o n —
F O P R r u l e ... 7 4
7. T r e a t m e n t c o m b i n a t i o n s for t h e t h r e e
r e s o u r c e s ... 76
8. 2 ^ f a c t o r i a l d e s i g n m a trix — F O P R r u l e ... 77
9. E f f e c t of f a c t o r s on s y s t e m r e s p o n s e —
F O P R r u l e ... 78
10. A v e r a g e m a c h i n e u t i l i z a t i o n s — P r o b l e m 1 ... 82
11. A v e r a g e r e s o u r c e u t i l i z a t i o n s — P r o b l e m 1 ... 84
12. A v e r a g e f i x t u r e u t i l i z a t i o n s — P r o b l e m 1 ... 8 6
13. W e i g h t e d s a m p l e m e a n s of m a k e s p a n —
P r o b l e m 2 ... 8 8
14. S u m m a r y of p a r t t y p e d a t a — P r o b l e m 3 ... 91
15. S u m m a r y of s y s t e m l a yout d a t a — P r o b l e m 3 ... 9 2
— X —
16. S u m m a r y of r e s o u r c e d a t a — P r o b l e m 3 . . . 9 3
17. S u m m a r y of s p e e d a n d t i m e d e t a i l s of t h e
m a t e r i a l h a n d l i n g s y s t e m s ... 9 3
18. W e i g h t e d s a m p l e m e a n s of m a k e s p a n — P r o b l e m 3 .. 9 4
TABLE OF C O N T E N T S
A B S T R A C T ... vi
A C K N O W L E D G E M E N T S vi i i L I S T O F F I G U R E S ... ix
L I S T O F T A B L E S ... x
C h a p t e r P a g e I- I N T R O D U C T I O N ... 1
II. F L E X I B L E M A N U F A C T U R I N G S Y S T E M S ... 5
2 . 1 D e f i n i t i o n a n d t y p e s of F M S ... . 5
2 . 2 C o m p o n e n t s of a n F M S . . . 6
2 . 3 C o n f i g u r a t i o n of t h e p r o p o s e d F M S .... 9
III. L I T E R A T U R E R E V I E W ... 14
3 . 1 F M S p r o b l e m s . . . 14
3 . 2 F M S m o d e l s ... 16
3 . 3 O b j e c t i v e s of t h e r e s e a r c h ... 2 3
IV. S I M U L A T I O N M O D E L O F T H E F M S ... 2 5
4 . 1 M o d e of o p e r a t i o n of t h e F M S ... 2 5
4 . 1 . 1 P a r t - m a c h i n e s e l e c t i o n
a l g o r i t h m ... 2 8
4 . 1 . 2 P a r t f l o w in t h e s y s t e m ... 3 0
4 . 2 D e v e l o p m e n t of t h e s i m u l a t i o n m o d e l .. 3 6
4 . 2 . 1 P r o g r a m 1 - I n p u t d a t a c r e a t i o n . 4 3
4 . 2 . 2 P r o g r a m 2 — S L A M s i m u l a t i o n
p r o g r a m .... 4 4
4 . 2 . 2 . 1 S L A M d i s c r e t e e v e n t
p r o g r a m .... 4 4
4 . 2 . 2 . 2 S L A M n e t w o r k p r o g r a m ... 4 6
4 . 3 M o d e l v e r i f i c a t i o n a n d v a l i d a t i o n .... 5 0
V. M O D E L A P P L I C A T I O N ... 5 8
5 . 1 S e l e c t i o n of t h e p o l i c y ... 5 8
5 . 1 . 1 N o t a t i o n s u s e d ... 6 0
5 . 2 P r o b l e m d a t a ... 6 4
5 . 2 . 1 P r o b l e m 1 ... 6 5
5 . 2 . 1 . 1 S e l e c t i o n of t h e
s c h e d u l i n g r u l e ... 6 5
— X I 1 —
5 . 2 . 1 . 2 E x p e r i m e n t a l d e s i g n
s e t u p .... 7 2
5 . 2 . 1 . 3 D i s c u s s i o n ... 7 9
5 . 2 . 2 P r o b l e m 2 ... 8 5
5 . 2 . 3 P r o b l e m 3 ... 8 7
VI. S U M M A R Y ... 9 6
r e f e r e n c e s 9 8
a p p e n d i c e s
A. C O M P U T E R P R O G R A M L I S T I N G - P R O G R A M 1 ... lOl
B. C O M P U T E R P R O G R A M L I S T I N G O F S L A M D I S C R E T E
E V E N T P R O G R A M ... 119
C. S A M P L E S C R E E N D I S P L A Y S O F T H E S I M U L A T I O N
M O D E L ... 157
D. C O M P U T E R P R O G R A M L I S T I N G O F S L A M
N E T W O R K P R O G R A M ... 160
E. S A M P L E T R A C E O F T H E S I M U L A T I O N ... 170
F- P A R T S K E T C H E S A N D P R O C E S S S H E E T S ... 172
G. F I X T U R E T Y P E A N D C U T T I N G T O O L S
I N F O R M A T I O N ... 179
V I T A A U C T O R I S ... 182
C H A P T E R I
I N T R O D U C T I O N
T h e f a c t t h a t a p p r o x i m a t e l y 7 5 % of t h e d o l l a r
v o l u m e of all m e t a l - w o r k e d p r o d u c t s a r e m a n u f a c t u r e d in
l ot s i z e s of l e s s t h a n f i f t y p i e c e s e a c h (Cook, 1975),
s p u r r e d i n t e n s i v e r e s e a r c h t o d e v e l o p a m a n u f a c t u r i n g
s y s t e m c a p a b l e of p r o d u c i n g m i d - s i z e d b a t c h e s of
a
w i d ev a r i e t y of p a r t s e f f i c i e n t l y . O n e i m p o r t a n t o u t c o m e of
t h i s r e s e a r c h w a s t h e d e v e l o p m e n t of F l e x i b l e
M a n u f a c t u r i n g S y s t e m s (FMS) - s y s t e m s c a p a b l e of
m a n u f a c t u r i n g m i d - s i z e d b a t c h e s of a w i d e v a r i e t y of p a r t s
w i t h t h e e f f i c i e n c y of a u t o m a t e d m a s s p r o d u c t i o n s y s t e m s
a n d t h e f l e x i b i l i t y of j o b s h o p s y s t e m s . R e f e r r i n g t o
F i g . l , it c a n b e s e e n t h a t f l e x i b l e m a n u f a c t u r i n g s y s t e m s
f it in b e t w e e n t h e s e t w o c a t e g o r i e s of m a n u f a c t u r i n g
systems.
R a p i d t e c h n o l o g i c a l a d v a n c e s in t h e a r e a s of
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 t o o l s ( N O , a u t o m a t e d
m a t e r i a l h a n d l i n g s y s t e m s (MHS) a n d c o m p u t e r
- 1
2
-Hi gh
V
o
L
U
M
E
M a s s p r o d u c t ion s y s t e m s
Job shop s y s t e m s
L o w Hi gh
V A R I E T Y
F i g . l C o m p a r i s o n of v a r i o u s man u - f a c t u r i n o s y s t e m s
3
-c o m m u n i -c a t i o n s h a v e m a d e f l e x i b l e m a n u f a -c t u r i n g s y s t e m s
p o s s i b l e . T h e h i g h e f f i c i e n c y a n d p r o d u c t i v i t y d e s i r e d
f r o m s u c h s y s t e m s c a n n o t b e a c h i e v e d , solely, b y
i n s t a l l i n g t h e s e h i g h l y s o p h i s t i c a t e d a n d e x p e n s i v e
h a r d w a r e . D u e c o n s i d e r a t i o n s s h o u l d b e g i v e n t o t h e
o p e r a t i o n a l aspects, i.e., t h e s o f t w a r e a s p e c t s , of t h e s e
syst e m s . T h i s is e s s e n t i a l l y a c o m p l e x m a n a g e r i a l
d e c i s i o n p r o b l e m a n d a t p r e s e n t is a m a j o r a r e a of f o c u s
of r e s e a r c h e r s in t h e f i e l d of a p p l i e d O p e r a t i o n s
Re s e a r c h .
T h i s r e s e a r c h d e a l s w i t h t h e d e v e l o p m e n t of a
m i c r o c o m p u t e r - b a s e d s i m u l a t i o n model of an F M S w h i c h c a n
b e u s e d t o a d d r e s s t h e o p e r a t i n g p r o b l e m s . A b r i e f
i n t r o d u c t i o n t o t h e t y p e s of f l e x i b l e m a n u f a c t u r i n g
s y s t e m s a n d t h e c o m p o n e n t s t h a t c o n s t i t u t e a n F M S is g i v e n
in C h a p t e r 2. T h e c o n f i g u r a t i o n of t h e F M S t h a t h a s b e e n
c o n s i d e r e d for t h e d e v e l o p m e n t of t h e s i m u l a t i o n model i s
a l s o d e s c r i b e d in C h a p t e r 2. In C h a p t e r 3. t h e v a r i o u s
p r o b l e m s p o s e d b y t h e s e s y s t e m s a n d t h e m o d e l i n g
t e c h n i q u e s t h a t h a v e b e e n u s e d in t h e p a s t t o a d d r e s s
t h e s e p r o b l e m s a r e d i s c u s s e d . T h e o b j e c t i v e s of t h i s
r e s e a r c h a r e a l s o p r e s e n t e d in t h i s chap t e r . T h e m o d e of
o p e r a t i o n of t h e F M S a n d t h e d e v e l o p m e n t of t h e s i m u l a t i o n
model on a m i c r o c o m p u t e r u s i n g S L A M ( S i m u l a t i o n L a n g u a g e
for A l t e r n a t i v e M o d e l i n g ) a r e d i s c u s s e d in C h a p t e r 4. In
C h a p t e r 5, t h e a p p l i c a t i o n of t h e model t o a n a l y s e
4
-p r o b l e m s i s i l l u s t r a t e d t h r o u g h t h e u s e of t h r e e e x a m -p l e s .
T h e s t a t i s t i c a l t e c h n i q u e f o r s e l e c t i n g a s c h e d u l i n g r u l e
(policy) a n d t h e e x p e r i m e n t a l d e s i g n s e t u p u s e d t o ai d t h e
s t u d y of t h e e f f e c t s of i m p o r t a n t r e s o u r c e s o n t h e s y s t e m
p e r f o r m a n c e a r e p r e s e n t e d in t h e s a m e c h a p t e r . C h a p t e r 6
s u m m a r i s e s t h e w o r k d o n e a n d p r o v i d e s s o m e d i r e c t i o n s f o r
f u r t h e r w o r k t h a t c o u l d b e d o n e t o e n h a n c e t h e f e a t u r e s of
C H A P T E R II
F L E X I B L E M A N U F A C T U R I N G S Y S T E M S
- -Jk D e f i n i t i o n a n d t y p e # of F M S
A f l e x i b l e m a n u f a c t u r i n g s y s t e m i s d e s c r i b e d a s
'an a u t o m a t e d b a t c h m a n u f a c t u r i n g s y s t e m t h a t c o n s i s t s of
a s e t of 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 t o o l s w h i c h a r e
c o n n e c t e d b y a u t o m a t e d m a t e r i a l h a n d l i n g s y s t e m s , all
u n d e r t h e c o n t r o l of a c e n t r a l c o m p u t e r " ( G r o o v e r &
Z i m m e r s , 1984).
F l e x i b l e m a n u f a c t u r i n g s y s t e m s a r e b r o a d l y
o s s i f i e d i n t o t w o t y p e s ( B r o w n e & R a t h m i 11, 1983),
n a m e l y :
(i) D e d i c a t e d s y s t e m s t h a t a r e c a p a b l e of p r o c e s s i n g a
l i m i t e d v a r i e t y of p a r t s in m e d i u m — s i z e d b a t c h e s ;
(ii) R a n d o m s y s t e m s t h a t a r e c a p a b l e of p r o c e s s i n g a
l a r g e r v a r i e t y of p a r t s in s m a l l — s i z e d b a t c h e s .
5
— 6 —
2 . 2 C o m p o n e n t * of a n FM9.
A n F M S c o n s i s t * of s e v e r a l c o m p o n e n t s t h a t
i n t e r a c t w i t h o n e a n o t h e r t o a c h i e v e t h e g o a l of p r o d u c i n g
m e d i u m - s i z e d or s m a l l - s i z e d b a t c h e s of a l i m i t e d o r l a rger
v a r i e t y of parts. T h e m a j o r c o m p o n e n t s t h a t c o n s t i t u t e an
F M S are:
(i) 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 s
(ii) A u t o m a t e d m a t e r i a l h a n d l i n g s y s t e m s
(iii) F i x t u r e s a n d p a l l e t s
(iv) C o n t r o l c o m p u t e r ( s ) .
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 s f o r m t h e n u c l e u s a r o u n d
W h i c h t h e w h o l e s y s t e m i s built. T h e s e m a c h i n e s a r e
c a p a b l e of m a c h i n i n g b o t h r o t a t i o n a l a n d n o n - r o t a t i o n a l
(prismatic) p a rts. M o r e t h a n 707. of t h e e x i s t i n g s y s t e m s
m a c h i n e p r i s m a t i c parts, w h i l e a p p r o x i m a t e l y 2 7 % m a c h i n e
r o t a t i o n a l p a r t s a n d a f e w of t h e m m a c h i n e b o t h t y p e s of
p a r t s (Bil a l i s & Mana l i s , 1985). T h e s e m a c h i n e s a r e
e q u i p p e d w i t h s e r v o m o t o r s t h a t c o n t r o l t h e m o v e m e n t of t h e
m a c h i n e s p i n d l e a n d w o r k table. M a nual o r p r o g r a m m e d
m e t h o d s a r e u s e d t o g e n e r a t e e l e c t r i c a l p u l s e s f r o m
e l e c t r o n i c c o n t r o l l e r s a n d t h e s e p u l s e s in t u r n a c t u a t e
t h e s e r v o m o t o r s . Tool m a g a z i n e s t h a t a r e c a p a b l e of
h o l d i n g 1 00 t o 1 50 c u t t i n g tool s , e.g., d rills, b o r i n g
tools, r e a m e r s , m i l l i n g cutters, taps, etc., a r e p r o v i d e d
_ 7
-i n t e r f a c e s t h e m a c h -i n e s p -i n d l e a nd t h e tool m a g a z -i n e .
T h i s d e v i c e c a n i n t e r c h a n g e t w o c u t t i n g t o o l s w i t h i n a f « .
seconds. Hence, a s l o n g a s t h e r e q u i r e d tool i s in t h e
tool m a g a z i n e , t h e s e t u p t i m e r e q u i r e d f o r i n t e r c h a n g i n g
t h e t o o l s in b e t w e e n s u c c e s s i v e , b u t d i f f e r e n t p r o c e s s e s
i s n e g l i g i b l e . T h e i n t r o d u c t i o n of a n e w p a r t t o b e
m a c h i n e d c a l l s f o r a d i f f e r e n t s et of c u t t i n g t o o l , w h i c h
c a n b e s e t u p q u i c k l y , t h e r e b y r e s u l t i n g in r e d u c e d s e t u p
time s . T h i s i s n o t t h e c a s e in 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
systems.
A u t o m a t e d m a t e r i a l h a n d l i n g s y s t e m s a r e b r o a d l y
c l a s s i f i e d a s p r i m a r y systems, e.g., t o w carts, a u t o m a t i c
g u i d e d v e h i c l e s ( A G V s ) a n d c o n v e y o r s , a n d s e c o n d a r y
syst e m s , e.g., s h u t t l e s . T h e p r i m a r y s y s t e m s t r a n s p o r t
t h e p a r t s b e t w e e n t h e v a r i o u s s t a t i o n s , a n d t h e s e c o n d a r y
s y s t e m s t r a n s p o r t t h e p a r t s b e t w e e n t h e p r i m a r y s y s t e m s
a n d t h e st a t i o n s . T h e s e c o n d a r y s y s t e m s a l s o s e r v e a s
s t o r a g e a r e a s f o r t h e p a r t s a t t h e m a c h i n e s , b e f o r e a n d
a f t e r m a c h i n i n g , a n d a r e k n o w n a s t h e i n p u t b u f f e r a n d t h e
o u t p u t bu f f e r , r e s p e c t i v e l y . T h e p u r p o s e of t h e i n p u t
b u f f e r i s t o k e e p t h e m a c h i n e busy, s o t h a t a . s o o n a s a
p a r t h a s b e e n p r o c e s s e d , t h e n e x t p a r t t o b e p r o c e s s e d o n
t h e m a c h i n e w o u l d b e w a i t i n g in t h e i n p u t bu f f e r . T h e
p a r t t h a t h a s c o m p l e t e d an o p e r a t i o n o n t h e m a c h i n e is
t r a n s f e r r e d t o t h e o u t p u t b u f f e r w h e r e it w a i t s f or t h e
u n l o a d i n g ABV. T h i s e s s e n t i a l l y p r e v e n t s t h e m a c h i n e d
8
-p a r t f r o m w a i t i n g o n t h e m a c h i n , t a b l e , w h i c h w o u l d
o t h e r w i s e r e s u l t in t h e m a c h i n e r e m a i n i n g idle.
F i x t u r e s a r e u s e d t o h o l d p a r t s i n a p a r t i c u l a r
o r i e n t a t i o n t o a l l o w p r o p e r m a c h i n i n g . A p a r t i c u l a r p a r t
t y p e m a y r e q u i r e o n e o r m o r e f i x t u r e t y p e s . F u r t h e r m o r e ,
a p a r t m a y b e r e o r i e n t e d i n t h e s a m e f i x t u r e t y p e f o r a
d i f f e r e n t o p e r a t i o n t o b e p e r f o r m e d . In g e n e r a l , t h e p a r t
i s c l a m p e d o n t o a f i x t u r e w h i c h i s t h e n b o l t e d t o a
p a l l e t . T h e w h o l e u n i t i s t h e n m o u n t e d o n a l o a d i n g A G V
w h i c h t r a n s p o r t s it t o t h e a p p r o p r i a t e m a c h i n e . All t h e
p a l l e t s u s e d in a p a r t i c u l a r s y s t e m a r e i d e n t i c a l
(Hartley. 19841. T h u s , i r r e s p e c t i v e of t h e p a r t t y p e o r
t h e f i x t u r e type, a n y p a l l e t o a n b e l o a d e d o n t o a n y A G V
o r m a c h i n e table.
T h e c o o r d i n a t i o n of all t h e a c t i v i t i e s of a n F M S
i s u n d e r t h e c o n t r o l of a c e n t r a l c o m p u t e r o r a g r o u p of
c o m p u t e r s . In s i t u a t i o n s w h e r e a g r o u p of c o m p u t e r s a r e
u t i l i z e d , t h e c o m p u t e r s a r e s e g r e g a t e d i n t o a h i e r a r c h y
w i t h p r o p e r c o m m u n i c a t i o n l i n k s e s t a b l i s h e d b e t w e e n t h e
d i f f e r e n t l e v e l s in t h e h i e r a r c h y . S o m e of t h e i m p o r t a n t
f u n c t i o n s p e r f o r m e d b y t h e c o m p u t e r s i n c l u d e :
— p r o d u c t i o n c o n t r o l
— t r a f f i c c o n t r o l
— l o a d i n g p a r t p r o g r a m s
— tool c o n t r o l
9
-Most syst e m s er e provided with a central p art,
storage a r e a to s t o r e raw material and work-in-process
parts.
T h e c a p a c i t y of this storage p l a c e is q uite large
and vertical space is m a d e u s . of t o c o m p e n s a t e for
r e s t r i c t i o n s in t h e floor space.
Cutting t o o l s are stored
in a tool crib (central tool storage) and ar e sent t o the
ap p r o p r i a t e m a c h i n e s as and when required.
L o a d g
stations, w h e r e t h e p a r t s are clamped on to t h e fixtures
and pallets, and u n loading stations, w h e r e t h e p a r t s are
d i smantled from t h e f i x tures and pallets, f o r m an integral
part of any FMS.
2 . 3 C o n f i g u r a t ion of t h e p r o pqsg4 a s
F r o m th e basic description of an F M S given in
Section 2.2, it is p o s s i b l e to h a v e several manufacturing
facilities r e f erred to as 'FMS'.
Therefore, it is
important to d e f i n e t h e configuration of t h e F M S assumed
for the d evelopment of t h e simulation mod e
R e ferring to Fig.2, it can b e seen that t h e F M S
c o n s i s t s of 'L' lanes (k=l,2,...,L), each lane
containing a certain number of machines. Thus, there are
Ni m a c h i n e s in L a n e 1, N g m a c h i n e s in L ane 2,
m a c hines in L a n e k, and so on.
T h e total number of
machines, M, in t h e e n t i r e sy s t e m is given by,
M - + N g ... + N | < + ...
10
-C E N T R A L P A R T S STORAGc.
I
L O A D I N G S T A T I O NI
U N L O A D I N G S T A T I O NL O A D I N G T R A C K "
I N P U T B U F F E R
C
L O A D I N G A G V
O U T P U T B U F F E R
□ N
L a n e k
L a n e 1
L a n e L U N L O A D I N G A G V
U N L O A D I N G T R A C K
T O O L C R I B
Il
-Thés. M machin.» ar. g.n.r.l purpo». Horizontal
Machining C.nt«-. <HMC) or Vm-tic.l Machining C.nt«-.
<VMC).
in .pit. of th.ir v«-.atility. it i» not always
posaibl. for th.». machin.» to p«-form .11 th. op.ration».
partly du. to th. t.chnologic.1 con.traint», for .xampl..
th. » z. of th. machin, tabl.. th. accuracy of th.
machin., . t e . and partly du. to th. typ. of op«-ation
it».lf. for .xampl». a vartical machining c n t m r i. mor.
suitable for drilling or reaming o p w a t i o n » than th.
horizontal machining center.
A central part, storage that .tores raw material,
as well as th. work-in-proc.ss parts forms a part of th.
system.
To compensate for restriction, in floor space a
vertical storage racking system is assumed.
Such a
centralised storage system is r.f.rr«i to a. an Automatic
Storage and Retrieval System <AS/RS> and provides
gr.at»-flexibility in terms of scheduling the part, into the
systma based on the different rules <Ranky. 19861.
Each machine in the system is provid«l with an
input buffer and an output buffer, each having the
capacity to hold on. pallet.
The parts that are selected
to be processed are transported from the central parts
storage to the loading station by means of a suitable
material handling system, usually a crane or a fork-lift
truck.
At the loading station they ar. clamped on to the
appropriate fixture and then bolted to the pallet.
Reproduced with permission of the copyright owner. Further reproduction prohibited wi
12
-w h o l e u n i t i s t h e n m o u n t e d o n a l o a d i n g A G V a n d
t r a n s p o r t e d t o t h e r e s p e c t i v e m a c h i n e . T h e p a r t s t h a t
h a v e c o m p l e t e d a n o p e r a t i o n e n t e r t h e u n l o a d i n g s t a t i o n
w h e r e t h e e n t i r e u n i t c o n s i s t i n g of t h e p a r t , f i x t u r e ,
p a l l e t a n d t h e u n l o a d i n g A G V i s d i s m a n t l e d . A c r a n e or a
f o r k - l i f t t r u c k t r a n s p o r t s t h e p a r t f r o m t h e u n l o a d i n g
s t a t i o n t o t h e c e n t r a l p a r t s s t o r a g e . T h e l o a d i n g a n d
U n l o a d i n g s t a t i o n s a r e m a n n e d . H e n c e , t h e a s s e m b l i n g a n d
d i s m a n t l i n g o p e r a t i o n s a r e d o n e b y h u m a n o p e r a t o r s .
T r a n s p o r t a t i o n of t h e p a r t s f r o m t h e l o a d i n g
s t a t i o n t o t h e m a c h i n e s i s d o n e b y o n e o r m o r e l o a d i n g
A G V s , w h i l e t r a n s p o r t a t i o n of t h e p a r t s f r o m t h e m a c h i n e s
t h e u n l o a d i n g s t a t i o n i s d o n e b y o n e o r m o r e u n l o a d i n g
s. E a c h l a n e i s p r o v i d e d w i t h a l o a d i n g a n d u n l o a d i n g
t r a c k o n w h i c h t h e A G V s t r a v e l . T h e m o v e m e n t of t h e
A G V 's i s c o n t r o l l e d b y t h e c o m p u t e r o n a real t i m e b a s i s .
T h e l o a d i n g a n d t h e u n l o a d i n g t r a c k a r e l a i d o u t
i n d e p e n d e n t l y (F i g . 2) a n d o n l y o n e l o a d i n g o r u n l o a d i n g
A G V i s a l l o w e d t o m o v e o n t h e i r r e s p e c t i v e t r a c k s . T h i s
^s d o n e t o p r e v e n t c o l l i s i o n s a n d t r a f f i c c o n g e s t i o n s . A
t e r m i n a l a t t h e l o a d i n g s t a t i o n a n d a n o t h e r o n e a t t h e
U n l o a d i n g s t a t i o n p r o v i d e i n f o r m a t i o n r e g a r d i n g t h e s t a t u s
t h e l o a d i n g o r t h e u n l o a d i n g t r a c k s . T h e l o a d i n g a n d
t h e u n l o a d i n g A G V s a r e n o t d i s p a t c h e d u n t i l t h e t r a c k on
*^hich t h e y a r e t o t r a v e l i s c l e a r .
13
-s u i t a b l e m a t e r i a l h a n d l i n g -s y -s t e m , -s u c h a -s a n o v e r h e a d
tool c o n v e y o r t h a t d o e s n o t i n t e r f e r e w i t h t h e A G V s
(movements, t r a n s p o r t s t h e t o o l s f r o m t h e tool c r i b t o t h e
m a c h i n e s w h e n e v e r a r e q u e s t f o r c u t t i n g t o o l s i s mad e . It
is a s s u m e d t h a t t h e r e q u e s t e d c u t t i n g t o o l s a r e a l w a y s
A v a i l a b l e a t t h e t o o l cr i b .
T h e a l g o r i t h m u s e d t o s e l e c t t h e p a r t s f r o m t h e
c e n t r a l p a r t s s t o r a g e a n d t h e a l g o r i t h m t h a t d e s c r i b e s t h e
•flow of a p a r t in t h e s y s t e m a r e d i s c u s s e d r e s p e c t i v e l y ,
in S e c t i o n 4 . 1 . 1 a n d S e c t i o n 4 . 2 . 2 . T h e m i c r o c o m p u t e r —
b a s e d s i m u l a t i o n m o d e l w a s d e v e l o p e d f o r t h e m u l t i — l a n e
t y p e of F M S (F i g . 2).
CHAPTER III
L I TERATURE REVIEW
FMS problems
F l e x i b l e m a n u f a c t u r i n g s y s t e m s a r e h i g h l y c o m p l e x
A n d d y n a m i c in n a t u r e a n d h e n c e p o s e a n u m b e r of p r o b l e m s
•"elated t o t h e i r d e s i g n a n d o p e r a t i o n . S t e c k e ( 1984) h a s
i d e n t i f i e d p r o b l e m s w h i c h a r e f r e q u e n t l y e n c o u n t e r e d o n c e
A d e c i s i o n t o i n s t a l l a n F M S h a s b e e n t a k e n . T h e s e
Pi^oblems a r e c l a s s i f i e d i n t o f o u r c a t e g o r i e s , n a m e l y :
(i) F M S d e s i g n p r o b l e m s
<ii) F M S p l a n n i n g p r o b l e m s
<iii) F M S s c h e d u l i n g p r o b l e m s
V) F M S c o n t r o l p r o b l e m s
T h e f i r s t , s e c o n d a n d f o u r t h t y p e of p r o b l e m s a r e o f t e n
•"Aferred t o a s 'static' p r o b l e m s - t h e w o r d s t a t i c m e a n i n g
o u e t i m e a l l o c a t i o n of t h e v a r i o u s r e s o u r c e s ; w h i l e t h e
t h i r d t y p e of p r o b l e m i s r e f e r r e d t o a s a 'dynamic'
problem.
— 15 —
_(i) FM S d e s i g n p r o b l e m s
T h e F M S d e s i g n p r o b l e m s a r e m a i n l y c o n c e r n e d w i t h
t h e s e l e c t i o n of t h e p r o p e r h a r d w a r e . T h e y i n c l u d e :
— s e l e c t i o n of m a c h i n e s a n d e q u i p m e n t ;
— d e t e r m i n a t i o n of t h e v a r i o u s p a r t t y p e s t o b e
m a n u f a c t u r e d ;
—determination of the layout of the machines,
equipment, etc.
Jii) F M S p l a n n i n g p r o b l e m s
T h e s e i n v o l v e c e r t a i n d e c i s o n s t h a t a r e t a k e n
b e f o r e t h e p a r t s a r e l o a d e d i n t o t h e F M S f o r p r o c e s s i n g .
T h e y i n c l u d e :
- s e l e c t i o n of a s e t of p a r t t y p e s f o r i m m e d i a t e
p r o c e s s i n g ;
— t h e p r o p o r t i o n a t w h i c h t h e s e l e c t e d p a r t t y p e s
• ^ u l d b e s i m u l t a n e o u s l y p r o c e s s e d in t h e F M S (part m ix
d A t e r m i n a t i o n ) ;
— t h e a l l o c a t i o n o f s p e c i f i c o p e r a t i o n s a n d t o o l s
s p e c i f i c m a c h i n e s .
•li^i) F M S s c h e d u l i n g p r o b l e m s
Scheduling is the allocation of jobs to be
processed on specfic machines and is classified as:
(a)
Off-line scheduling — Using this approach a
Scheduling algorithm is applied at the beginning of the
Scheduling period, to result in a complete schedule for
that period.
— 16 —
(b) O n - l i n e s c h e d u l i n g ( d y n a m i c s c h e d u l i n g ) —
U s i n g t h i s a p p r o a c h t h e d e c i s i o n c o n c e r n i n g t h e p a r t t o b e
p r o c e s s e d n e x t o n a p a r t i c u l a r m a c h i n e i s m a d e in real
t i m e a t t h e t e r m i n a t i o n of t h e o p e r a t i o n c u r r e n t l y b e i n g
p e r f o r m e d o n t h a t m a c h i n e .
T h e F M S o n - l i n e s c h e d u l i n g p r o b l e m s a r e e n c o u n t e r e d w h e n
t h e s y s t e m i s o p e r a t i n g a n d t h e y i n c l u d e :
— d e t e r m i n a t i o n o f t h e n e x t p a r t t o b e p r o c e s s e d
a m a c h i n e ;
— d e t e r m i n a t i o n of a l t e r n a t e r o u t i n g f o r a part.
F M S c o n t r o l p r o b l e m s
T h e s e a r e p r o b l e m s t h a t a r i s e w i t h r e s p e c t t o
k e e p i n g a c o n s t a n t c h e c k o n t h e p e r f o r m a n c e a n d q u a l i t y
s t a n d a r d s o f t h e m a c h i n e s . T h e y i n c l u d e :
—d e s i g n of p r e v e n t i v e m a i n t e n a n c e s c h e d u l e s f o r
^ h e m a c h i n e s a n d e q u i p m e n t ;
— d e v e l o p m e n t of a u t o m a t i c i n s p e c t i o n s y s t e m s f o r
P*i"ts a n d t o o l s .
— FM S models
A c o m p r e h e n s i v e r e v i e w of t h e v a r i o u s t e c h n i q u e s
U s e d t o m o d e l f l e x i b l e m a n u f a c t u r i n g s y s t e m s h a v e b e e n
p r o v i d e d b y W i l h e l m a n d S a r i n (1983). T h e s e t e c h n i q u e s
are:
17
-<ii) M a t h e m a t i c a l p r o g r a m m i n g
<iii> S i m u l a t i o n .
Q u e u e i n g n e t w o r k m o d e l s h a v e b e e n b a s e d o n t h e
r e s e a r c h i n i t i a t e d b y J a c k s o n (1957), in w h i c h n e t w o r k
e o d e l s w e r e d e c o m p o s e d a n d a n a l y s e d a s a s e t of
i n d e p e n d e n t s e r v i c e s t a t i o n s . B a s e d o n t h e q u e u e i n g
n e t w o r k m o d e l s of B a s k e t t , e t al. (1975) a n d t h e c o m p u t e r
A l g o r i t h m s of B u z e n (1973), S o l b e r g (1977) d e v e l o p e d a
C o m p u t e r p r o g r a m (CAN— Q) t o m o d e l a n FMS. B u z a c o t t a n d
S h a n t i k u m a r (1980) e x t e n d e d t h i s m e t h o d o l o g y t o s t u d y t h e
p a r t s e l e c t i o n p r o b l e m a n d e v a l u a t e a l t e r n a t i v e p l a n s f o r
w o r k — i n — p r o c e s s i n v e n t o r y . T h e s e n e t w o r k m o d e l s , w h i c h
p r o v i d e t h e r e s e a r c h e r s w i t h a v e r a g e p e r f o r m a n c e m e a s u r e s
O'f t h e s y s t e m , h a v e b e e n a p p l i e d m a i n l y t o s o l v e t h e
p l a n n i n g p r o b l e m s of a n FMS. R e a l i s t i c m o d e l i n g of a n F M S
U s i n g t h i s a p p r o a c h i s s e v e r e l y r e s t r i c t e d b e c a u s e t h e
e x i s t i n g m o d e l s f a i l t o i n c o r p o r a t e t h e v a r i o u s r e a l i s t i c
f e a t u r e s of a n F M S s u c h as, l i m i t e d b u f f e r c a p a c i t i e s at
^ h e w o r k s t a t i o n s , c o m p l e x s e r v e r d i s c i p l i n e s , etc.
Mathematical programming techniques, e.g..
I n t e g e r p r o g r a m m i n g , h a v e b e e n a p p l i e d in c e r t a i n s t a t i c
d e c i s i o n m o d e l s . A s e t of 0 — 1 i n t e g e r p r o g r a m m i n g
f o r m u l a t i o n s w e r e d e v e l o p e d t o e v a l u a t e t h e l o a d i n g
• e p e c t s of a n F M S (Stecke, 1981). K u s i a k (1983) p r o p o s e d
a f e w i n t e g e r p r o g r a m m i n g f o r m u l a t i o n s of t h e l o a d i n g
p r o b l e m s . A n o p t i m i z a t i o n a p p r o a c h t o d e t e r m i n e t h e
— 10 —
o p t i m a l p a r t r o u t i n g p o l i c y f o r a n F M S h a s b e e n p r o p o s e d
b y K i m e m i a & G e r s h w i n (1985). S h a n k e r a n d T z e n (1985)
d e v e l o p e d a m a t h e m a t i c a l m o d e l t o s t u d y t h e l o a d i n g a n d
d i s p a t c h i n g p r o b l e m s of a r a n d o m l y g e n e r a t e d FMS.
Solutions from this mathematical model were used as inputs
to a simulation model.
T h o u g h m a t h e m a t i c a l p r o g r a m m i n g t e c h n i q u e s a r e
a t t r a c t i v e i n t e r m s of t h e i r a p p l i c a t i o n t o s o l v e s t a t i c
p r o b l e m s of s m a l l a n d m e d i u m s i z e , t h e i r a p p l i c a t i o n t o
^ ^ r g e s i z e d p r o b l e m s i s r e s t r i c t e d . T h i s i s d u e t o t h e
^ * r g e f o r m u l a t i o n s t h a t a r e d i f f i c u l t t o s o l v e w i t h t h e
* ^ i * t i n g IP a l g o r i t h m s a n d p a c k a g e s . M o r e o v e r , c e r t a i n
C o n s t r a i n t s t h a t a r e c h a r a c t e r i s t i c of a n F M S (for
e x a m p l e , t o o l i n g c o n s t r a i n t s ) a r e d i f f i c u l t t o c o n s i d e r
d u e t o t h e c o m p l e x i t y i n v o l v e d i n t h e f o r m u l a t i o n s .
S i m u l a t i o n m o d e l s h a v e h a d t h e w i d e s t s c o p e of
A p p l i c a t i o n , p a r t l y d u e t o t h e p a u c i t y of o t h e r t y p e s of
* o d e l s , a n d p a r t l y d u e t o t h e i r a b i l i t y t o i n c o r p o r a t e
t h e r e a l i s t i c f e a t u r e s of a n FMS. S i m u l a t i o n i s m o r e
® u i t e d f o r i n v e s t i g a t i n g t h e o p e r a t i o n a l a s p e c t s of t h e s e
*-0(»»plex m a n u f a c t u r i n g s y s t e m s (Law, 1986). S t e c k e a n d
S o l b e r g (1981) e x p l o r e d a l t e r n a t i v e l o a d i n g a n d s c h e d u l i n g
* ^ ^ * t e g i e s f o r t h e s y s t e m i n s t a l l e d a t t h e C a t e r p i l l a r
A c t o r C o m p a n y . D u e t o t h e c o m p l e x i t y of t h e v a r i o u s
A y s t e m a s p e c t s , a n a l y t i c a l t r e a t m e n t w a s n o t v i a b l e a n d
19
-t h a -t w e r e i n v e s -t i g a -t e d , -t h e w e i g h -t e d s h o r -t e s -t p r o c e s s i n g
t i m e w a s f o u n d t o p r o d u c e t h e b e s t r e s u l t s f o r t h i s s y s t e m
in t e r m s of t h e n u m b e r of c o m p l e t e d p a r t s . T h o u g h t h e
r e s u l t s f r o m t h i s s t u d y c a n n o t b e e x t r a p o l a t e d t o o t h e r
s y s t e m s t h a t h a v e d i f f e r e n t c o n f i g u r a t i o n s a n d p r o c e s s
d i f f e r e n t p a r t t y p e s , it d e m o n s t r a t e d t h e u s e f u l n e s s of
s i m u l a t i o n in e v a l u a t i n g d i f f e r e n t s c h e d u l i n g s t r a t e g i e s .
E l M a r a g h y (1982) d e v e l o p e d a s p e c i a l s i m u l a t o r c a l l e d
F M S S X M ( F l e x i b l e lia n u f a c t u r i n g S i m u l a t o r ) t o a n a l y s e
f l e x i b l e m a n u f a c t u r i n g s y s t e m s d u r i n g t h e i r d e s i g n p h a s e .
T h e s i m u l a t i o n m o d e l w a s m a d e f l e x i b l e e n o u g h t o p e r m i t
v a r i a t i o n s in t h e q u a n t i t i e s of t h e v a r i o u s r e s o u r c e s u s e d
b y t h e s y s t e m . T h e m o d e l s e r v e d a s a d e c i s i o n t o o l in
d e c i d i n g t h e q u a n t i t i e s of t h e d i f f e r e n t r e s o u r c e s f o r
'^aricxis s y s t e m s p r o c e s s i n g d i f f e r e n t p a r t t y p e s .
P a r a l l e l t o t h e m a t h e m a t i c a l m o d e l i n g of t h e F M S
l e s t a i l e d a t t h e S C A M P S y s t e m s Ltd, R a t h m i 11, e t al.
(1983) d e v e l o p e d a s i m u l a t i o n m o d e l t o p r o v i d e a d e t a i l e d
I n v e s t i g a t i o n of t h e m a t e r i a l h a n d l i n g , c o n v e y i n g a n d
o v e r a l l w o r k f l o w a s p e c t s of t h e s y s t e m . A c r e e (1983)
A t u d i e d v a r i o u s p a r t , t o o l , a n d c a r t s c h e d u l i n g r u l e s f o r
A A y s t e m t h a t w a s i n s t a l l e d b y t h e m i l i t a r y . O n e of t h e
i m p o r t a n t f i n d i n g s of t h i s s t u d y w a s t h e s u p e r i o r i t y of
I n d i v i d u a l t o o l a l l o c a t i o n t o t h e m a c h i n e s a s a n d w h e n
^ b e y a r e n e e d e d , a s o p p o s e d t o t o t a l t o o l a l l o c a t i o n .
T h i s s t u d y w a s s y s t e m s p e c i f i c a n d s i n c e it w a s d o n e f o r
— 20 —
t h e m i l i t a r y , v e r y l i t t l e i n f o r m a t i o n h a s b e e n m a d e
A v a i l a b l e t o t h e p u b l i c .
C a r r i e , e t al. (1984) u s e d a s i m u l a t i o n m o d e l t o
a n a l y s e t h e s e n s i t i v i t y o f s y s t e m p e r f o r m a n c e t o
^ A r i a t i o n s in p a r t mix, o p e r a t i o n t i m e s a n d f a c i l i t y
A b i l i t y f o r t h e s y s t e m i n s t a l l e d a t A n d e r s o n
S t r a t h c l y d e , S c o t l a n d . W o r t m a n a n d M i n e r (1984) d e v e l o p e d
M A P /1, a s i m u l a t o r s p e c i f i c a l l y d e s i g n e d f o r m o d e l i n g
d i s c r e t e m a n u f a c t u r i n g s y s t e m s . U s i n g t h i s s i m u l a t o r t h e y
E v a l u a t e d a n F M S d e s i g n in w h i c h t h e v a r i a b l e s a n a l y s e d
t h e n u m b e r o f d e d i c a t e d a n d f l e x i b l e m a c h i n e s a n d t h e
n u m b e r o f f i x t u r e s a n d c a r t s . A n o t h e r a p p l i c a t i o n of t h e
s i m u l a t o r w a s in d e c i d i n g t h e n u m b e r of f i x t u r e s f o r
A m a c h i n e t o o l m a n u f a c t u r e r . C h a n g , e t al. (1986) u s e d
t h e g e n e r a l p u r p o s e s i m u l a t i o n l a n g u a g e , S L A M ( P r i t s k e r ,
1984), t o d e s i g n t h e m a t e r i a l h a n d l i n g s y s t e m of an FMS.
T h i s s t u d y d e m o n s t r a t e d t h e f l e x i b i l i t y of S L A M a s
c o m p a r e d t o t h a t o f Q - G E R T ( P r i t s k e r , 1977) o r G P S S
( S c h r i b e r , 1974), in t e r m s o f t h e m o d e l i n g a n d o u t p u t
A n a l y s i s .
S i n c e a n F M S c o n s i s t s m a c h i n e s w h i c h a r e f l e x i b l e
® n o u g h t o p e r f o r m a w i d e v a r i e t y of o p e r a t i o n s , c e r t a i n
o p e r a t i o n s o n c e r t a i n p a r t t y p e s c o u l d b e p r o c e s s e d b y
d i f f e r e n t m a c h i n e s . T h i s g i v e s r i s e t o t h e c o n c e p t of
A l t e r n a t e r o u t i n g s . H o w e v e r , t h i s i n h e r e n t f e a t u r e of a n
21
-A p p e a r i n g in t h e l i t e r a t u r e .
T h e e f f i c i e n t o p e r a t i o n of a n F M S i s d e p e n d e n t ,
A c e r t a i n e x t e n t , o n t h e a v a i l a b i l i t y of t h e v a r i o u s
•"©sources l i k e p a l l e t s , c a r t s , h u m a n o p e r a t o r s , etc.
T h o u g h a m a j o r p o r t i o n of t h e w o r k c a r r i e d o u t s o f a r h a s
**®Alt w i t h t h e i s s u e of d e c i d i n g t h e n u m b e r of p a l l e t s o r
a n d t h e a l l o c a t i o n o f t h e s e r e s o u r c e s t o d i f f e r e n t
part s , t h e r e h a s b e e n n o r e p o r t of a n y w o r k t h a t h a s
(Considered t h e f i x t u r e s a s a c o n s t r a i n i n g r e s o u r c e . W i t h a
C o n s i d e r a b l e i n c r e a s e in t h e n u m b e r of r a n d o m s y s t e m s ,
w h i c h m a c h i n e a l a r g e r v a r i e t y o f p a r t s a s c o m p a r e d t o
d e d i c a t e d s y s t e m s , t h e u s e of s t a n d a r d i s e d p a l l e t s t o h o l d
t h e p a r t s i n p r o p e r o r i e n t a t i o n f o r t h e m a c h i n i n g t o b e
P e r f o r m e d i s e x t r e m e l y d i f f i c u l t . T h i s h a s l e d t o t h e
d e v e l o p m e n t of f i x t u r e s t o i n t e r f a c e t h e p a r t a n d t h e
Pa l l e t . T h e s e f i x t u r e s a r e e x p e n s i v e d u e t o t h e prexiision
A e c h i n i n g i n v o l v e d a n d a r e a v a i l a b l e in l i m i t e d
P(*antities. E v e n w i t h a c o n s i d e r a b l e i n c r e a s e in t h e u s e
cT m o d u l a r f i x t u r e s , w h i c h a r e a s s e m b l e d f r o m s t a n d a r d
C o m p o n e n t s (Drake, 1984 ) , t h e a v a i l a b i l i t y of t h e s e
A t a n d a r d c o m p o n e n t s r e s u l t in a l i m i t e d q u a n t i t y of t h e
f i x t u r e s . M o r e o v e r , a p a r t t h a t h a s b e e n s e l e c t e d t o
^•^ter t h e s y s t e m w o u l d b e p r e v e n t e d f r o m d o i n g s o u n l e s s
b e r e q u i r e d f i x t u r e t y p e i s a v a i l a b l e , in s p i t e o f t h e
A b i l i t y of t h e o t h e r s h a r e d r e s o u r c e s l i k e p a l l e t s
A nd t h e A G V ' s . H e n c e , f i x t u r e s a r e i m p o r t a n t r e s o u r c e s
22
-a n d s h o u l d b e c o n s i d e r e d d u r i n g t h e d e v e l o p m e n t of t h e
m o d e l .
In d e d i c a t e d f l e x i b l e m a n u f a c t u r i n g s y s t e m s t h e
^ A r i e t y of p a r t s b e i n g p r o c e s s e d i s s m a l l a n d t h e b a t c h
of t h e v a r i o u s p a r t t y p e s a r e l a r g e e n o u g h t o
m a i n t a i n a c o n s t a n t n u m b e r of p a r t s of e a c h t y p e a s l o n g
A S t h e s e t of p a r t t y p e s r e m a i n u n c h a n g e d . M u c h r e s e a r c h
h a s b e e n d o n e in t h e p a s t t o f o r m u l a t e m o d e l s t h a t
d e t e r m i n e t h e p r o p e r p a r t m i x — t h e p r o p o r t i o n of t h e
V a r i o u s p a r t t y p e s in t h e s y s t e m — t o b e m a i n t a i n e d in t h e
s y s t e m a t all t i m e s . T h e p a r t m ix d e t e r m i n a t i o n p r o b l e m
C o n t r o l s t h e s c h e d u l i n g of p a r t s i n t o t h e s y s t e m , s i n c e a
p a r t t h a t l e a v e s t h e s y s t e m i s a l w a y s r e p l a c e d b y a n o t h e r
o n e of t h e s a m e t y p e , t o m a i n t a i n t h e s a m e p r o p o r t i o n .
H o w e v e r , a s m e n t i o n e d e a r l i e r , w i t h a c o n s i d e r a b l e
i n c r e a s e in t h e n u m b e r of r a n d o m s y s t e m s t h a t a r e c a p a b l e
p r o c e s s i n g a l a r g e r v a r i e t y of p a r t s in s m a l l e r b a t c h
(say, 5 o r l e s s ) , t h e d e t e r m i n a t i o n of a s u i t a b l e
P A r t m ix i s h i g h l y i n a p p r o p r i a t e . S u c h s y s t e m s a r e
S i m i l a r t o t h e t y p i c a l j o b s h o p s y s t e m s in w h i c h b a t c h
S i z e s of o n e a r e n o t u n c o m m o n a n d t h e s c h e d u l i n g of p a r t s
i n t o t h e s y s t e m h a s t o b e b a s e d o n s o m e c r i t e r i o n . T h e
C o m p l e x n a t u r e of t h e s e s y s t e m s r u l e o u t t h e p o s s i b i l i t y
t h e d e v e l o p m e n t of o f f - l i n e s c h e d u l i n g a l g o r i t h m s t o
inp u t p a r t s i n t o t h e s y s t e m . M o r e o v e r , i n c l u s i o n of t h e
2 3
-c o m p l i -c a t e t h e s e o f f - l i n e a l g o r i t h m s . O n - l i n e s c h e d u l i n g ,
c*" d y n a m i c s c h e d u l i n g , w h i c h e s s e n t i a l l y d e p e n d s o n t h e
A ^ A t e of t h e s y s t e m , i s m o r e s u i t e d t o s u c h s y s t e m s . T h e
c o m p l e x i t i e s i n v o l v e d in t h e d e v e l o p m e n t of t h e q u e u e i n g
n e t w o r k a n d m a t h e m a t i c a l m o d e l s t o a d d r e s s t h e p r o b l e m of
o n - l i n e s c h e d u l i n g a l o n g w i t h t h e c o n s i d e r a t i o n of t h e
r e a l i s t i c f e a t u r e s s u c h as, a l t e r n a t e r o u t i n g a n d t h e
^ ^ A A t m e n t of f i x t u r e s a s r e s o u r c e s , j u s t i f y t h e u s e of a
s i m u l a t i o n a p p r o a c h .
— O b j e c t i v e s of
the research
T h i s r e s e a r c h d e a l s w i t h t h e d e v e l o p m e n t of a
s i m u l a t i o n m o d e l of t h e F M S d e s c r i b e d in S e c 2 . 3 w h i c h c a n
b e u s e d a s a d e c i s i o n t o o l t o s e l e c t a s c h e d u l i n g r u l e
f r o m t h e f i v e r u l e s u n d e r c o n s i d e r a t i o n .
F i v e s i m p l e p r i o r i t y s c h e d u l i n g r u l e s c o n s i d e r e d
^n t h i s t h e s i s , b a s e d o n t h e p a r t c h a r a c t e r i s t i c s , are:
(i) Random selection rule
(RANDOM)(ii) F e w e s t o p e r a t i o n s r e m a i n i n g (FOPR) r u l e
(iii) M o s t o p e r a t i o n s r e m a i n i n g (MOPR) r u l e
(iv) S h o r t e s t p r o c e s s i n g t i m e (SPT) r u l e
L o n g e s t p r o c e s s i n g t i m e (LPT) r u l e
T b e s i m u l a t i o n m o d e l w h i c h w o u l d i n c o r p o r a t e f e a t u r e s s u c h
As, a l t e r n a t e r o u t i n g s , t r e a t m e n t of f i x t u r e s a s r e s o u r c e s
p a r t t y p e s w i t h p r i o r i t i e s , i s t o b e d e v e l o p e d o n t h e
24
-mi c r o c o m p liter u s i n g t h e g e n e r a l p u r p o s e s i m u l a t i o n
l a n g u a g e , SLA M . T h e s i m u l a t i o n m o d e l i s t o b e
user— i n t e r a c t i v e s o t h a t i t d o e s n o t r e q u i r e a p r i o r
w o r k i n g k n o w l e d g e of S L A M . T h i s f r o n t - e n d i n t e r f a c e
b e t w e e n t h e u s e r a n d t h e c o m p u t e r i s t o p r o v i d e
CHAPTER IV
S I MULATION MODEL OF T H E FMS
T h e d e v e l o p m e n t of t h e s i m u l a t i o n m o d e l of t h e
F M S u n d e r c o n s i d e r a t i o n i s d i s c u s s e d i n t h i s c h a p t e r . T h e
o p e r a t i o n of t h e FMS, n a m e l y , t h e p a r t — m a c h i n e s e l e c t i o n
a l g o r i t h m a n d t h e f l o w of t h e p a r t in t h e s y s t e m is
® x p i a i n e d in S e c t i o n 4 . 1 . 1 a n d S e c t i o n 4 . 1 . 2 ,
•"®spectively. T h e d e v e l o p m e n t of t h e d i f f e r e n t c o m p u t e r
p r o g r a m s w h i c h t o g e t h e r f o r m t h e s i m u l a t i o n m o d e l of t h e
^ M S is e x p l a i n e d in S e c t i o n 4.2. In S e c t i o n 4 . 3 t h e
t ® c h n i q u e s t h a t w e r e u s e d t o v e r i f y t h e m o d e l a r e
o u t l i n e d .
Mode
of
operation of the
FMS
T h e c o n v e r s i o n of a p a r t t y p e f r o m t h e r a w
"•aterial s t a t e ( g e n e r a l l y , c a s t i n g s o r f o r g i n g s ) t o a
u l l y m a c h i n e d p r o d u c t i n v o l v e s a s e r i e s of p r o c e s s i n g
These processing steps are generally combined into
2 5
