clock is centralized and shared among all the subsystems of the production
line. When an event is notified, the affected subsystems trigger state tran-
sitions and update their current states. A new event might be activated.
Then the simulation clock is advanced to the time of the next event to be
notified. This procedure is repeated until the end of the simulation.
We are now able to summarize all the main features that have emerged from
the problem analysis.
Event-driven architecture . The simulator enforces a strict separation of
concerns between the components (discrete processes) that model finite
state automata and the components that execute them.
Work cell simulation . The finite state automata that model the behaviour
of each work cell subsystem: the drill, the cutter, the assembler, the AGV
and the Inventory. The behaviour of the whole system will emerge from
the interactions between the subsystems.
Graphical user interface . The step-by-step evolution of the simulation is
under the control of the user who fires the next scheduled event with a
simple mouse click. The graphical representation of the work cell physical
structure depicts the components and displays the last event that has
been fired and depicts the current state of the work cell system (the
position of the AGV, which machines are working, etc.).
In order to verify the correct behaviour of the simulator, we need to test the
behaviour of each single automaton and the interactions among them, and
The conservative behaviour of the system: the number of pieces in the
system should always be equal to the difference between the number of
pieces that entered and exited the system.
The correct order of the scheduled events.
Architecture and planning
The architecture of the discrete event simulator is structured according to
the simulation model described in the previous section. The basic compo-
nents are the event clock, the subsystems of the production line (inventory
system, machines, transport and assembler), and the graphical user inter-
face (see Figure 9.6).
The development process of the work cell simulator is organized into
three phases that produce three prototypes. The first phase focuses on the