MODELLING FLEXIBLE MANUFACTURING SYSTEMS - Modelling with Generalised Stochastic Petri Nets - page 182

idleM i

busyM i OutM i

(a)

EnterM i Process ExitM i

EnterM i ExitM i Process a

BusyM i OutM i

idleM i

(b)

BusyM i OutM i

EnterM i ExitM i Process b

Figure 8.7: GSPN models of machines

respect to a failure in the middle cell.

8.3 Push Production Systems

The second system we are going to model is a push production system.
It comprises a Load/Unload (LU) station, used to mount raw parts on
“pallets” and unload finished parts from them, and three machines (M 1 ,
M 2 and M 3 ) that are used to process two different kinds of parts. We
consider two alternative transportation systems: the first one is a continuous
transportation system (i.e., a conveyor) while the second is an Automated
Guided Vehicle (AGV). Machines that process only one type of part are
modelled as shown in Fig. 8.7( a) while machines that process two different
types of parts are modelled as shown in Fig. 8.7( b). The reason for including
in the model place OutM i and immediate transition ExitM i depends on
the fact that an already processed part may have to stay in the machine
because there is no space in the output buffer. If this is not the case,
transition ExitM i can be merged with transition Process and place OutM i
disappears.