Java Reference
In-Depth Information
Piece machining
(nut drilling and screw cutting) operations consist of the
following sequence of actions:
■
The machine picks up a piece from the input buffer. If the input buffer is
empty, it waits for a piece.
■
The machine manufactures the piece and produces a nut (screw). The
operation duration is known.
■
The machine drops the nut (screw) in the output buffer, if it is not full;
otherwise it waits for a position available in the output buffer.
■
The machine performs the above steps sequentially and repeats the
sequence until the program halts.
Bolt assembling
operations consist of the following sequence of actions:
■
The assembler picks up either a nut or a screw from the input buffer. If the
input buffer is empty, it waits for a piece.
■
The assembler picks up a second piece (nut or screw), which must be
different from the first one. If the piece is not available, the assembler
waits for that piece.
■
The assembler assembles a nut and a screw and produces a bolt. The
operation duration is known.
■
The assembler drops the bolt in the output buffer, if it is not full;
otherwise it waits for a position available in the output buffer.
■
The assembler repeats the above sequence of steps until the control
program halts.
Piece moving
operations consist of the following sequence of actions:
■
The AGV elaborates the next operation, if any. Otherwise, it waits for the
next operation.
■
The AGV moves to the unloading station.
■
The AGV unloads a piece from a machine output buffer.
■
The AGV moves to the loading station.
■
The AGV unloads the piece in the assembler input buffer.
■
The AGV repeats the above sequence of steps until the control program
halts.
The automated inventory system feeds the drill and cutter input buffers
with new raw pieces at random instants of time. Similarly, it extracts
finished pieces from the assembler output buffer at random instants of time.
We are now able to formally specify the behaviour of each component of the
work cell. This is an important step towards the definition of the simulation
model. The complexity of this modelling activity lies in the difficulty of
enumerating all the admissible combinations of the basic ingredients: states,
events and transitions.
9.2.2
The drill and cutter finite state automata
The drill and cutter machine are made up of an input buffer, a production
unit and an output buffer (see Figure 9.1). The input and output buffers have
