MODELLING FLEXIBLE MANUFACTURING SYSTEMS - Modelling with Generalised Stochastic Petri Nets - page 173

8
MODELLING FLEXIBLE
MANUFACTURING
SYST E MS
In this chapter we show that GSPNs represent a versatile tool for the mod-
ular construction of models that capture the most important features of the
behaviour of Flexible Manufacturing Systems (FMSs).
In the last thirty years FMSs have emerged as a new strategic technology
able to cope with the rapid changes in the market demand. In the design and
construction of FMSs, a performance evaluation of the system is required at
two different stages of development.
• At the beginning of the design of the system, when the machines, the
layout, and the transport system are chosen and dimensioned. At this
stage the performance estimates need not be particularly accurate;
usually only the order of magnitude of the parameters of the system
is known in this initial phase, and crudely approximated analytical
methods are used.
• During the tuning phase of the system, when most of the parame-
ters (the machines, the layout, etc.) have already been chosen, and
only minor changes in the system (e.g. the size of buffers, or produc-
tion mixes) can be introduced to optimize the overall throughput or
the machine utilizations. For this purpose, an accurate performance
evaluation of the system is required, usually obtained by developing
complex simulation models.
In this chapter we will primarily address the first type of problem.
In Section 8.1 we give a very brief introduction to FMSs; for further details
on automated manufacturing systems and related performance issues the
reader may refer to [ 72] . In Sections 8.2 and 8.3 two FMS systems are
modelled and analysed by means of GSPNs.
187