x p 0
x # 0
Figure 9.3 The AGV automaton
ARRIVED : the AGV has arrived at the next loading
UNLOADED : a piece has been unloaded from a machine output buffer to
LOADED : a piece has been loaded from the AGV buffer to the assembler
The inventory finite state automaton
The automated inventory system supplies raw pieces to the work cell at
random instants of time. The arrival frequency might correspond, for
example, to the production rate of an upstream work cell of the same
shopfloor that supplies raw pieces. Similarly, finished pieces leave the
work cell at random instants of time according to the production rate of a
downstream work cell that consumes them.
Figure 9.4 depicts two automata that model the behaviour of the auto-
mated inventory system. They each comprise two states. The automaton at
the left-hand side of the picture models the piece feeding into the drill or
cutter input buffers. The other automaton models the extraction of finished
pieces from the assembler output buffer. The state variable x represents the
number of raw pieces in the drill and cutter input buffers, while y represents
the number of finished pieces in the assembler output buffer.
W : the automated inventory system is working, i.e. it is loading raw pieces
into the drill and cutter input buffer or unloading finished pieces from the
assembler output buffer.
Figure 9.4 The automated inventory system automaton