Graphics Programs Reference
In-Depth Information
Table 8.2: Working schedules
Required
Machining times (min)
Class
Production
Process
Mix
Number M
1
M
2
M
3
AGV LU
15
−
2
a
20%
1
10
4
10
−
10
2
2
4
1
−
20
−
2
b
80%
4
2
−−
30
2
4
policy: the probabilities associated with transitions part
a
and part
b
depend
on the desired production mix (the proportion of produced parts of each
type).
A system with AGV transportation — We now consider a different
FMS with the following new features: (1) the transportation system con-
sists of a single AGV; (2) there are various alternative working schedules
(i.e., machine processing sequences) for each part type, that are summa-
rized in Table
8.2;
(3) parts of each type have to be loaded onto pallets of
corresponding type and there is a limited number of pallets of each type; the
available number of pallets thus constrains the number of parts of the various
types flowing through the system, and consequently affects the production
mix.
The AGV used to transport the parts among the machines is a resource
shared by all the parts in the system. Type a parts have two possible
working schedules that involve the following movements:
- from LU to M
1
;
- from M
1
to either M
2
or M
3
;
- from M
2
/M
3
to LU.
Type b parts have two possible working schedules involving the following
movements:
- from LU to either M
2
or M
3
;
- from M
2
/M
3
to LU.
The transportation system in this case is modelled as shown in Fig.
8.11.
The machines are modelled as in the previous example, except for the
presence of unlimited input/output buffers. The complete model is depicted
in Fig.
8.12.
Since the parts have alternative working schedules (both types
of parts can choose between M2 and M3), a policy is needed to select the
machine to be used. The policy we have modelled is very simple: if both
machines are free, the part chooses the fastest one, while if two types of
parts are waiting for the same machine, the part with shortest machining
Search WWH ::
Custom Search