Abstract
Petri net with external inputs and outputs is proposed in this paper to represent the control of event-driven systems. Several fundamental problems arise for the design and analysis of the control system, when a Petri net is subject to the external inputs and outputs. Among these, the free-firing, the observability and the controllability are of crucial importance.
Major results of the analysis of free-firing are:
-a Petri net is firee-firing for any initial state, any external input place set and any control input seqence if and only if it is conflict-free.
-any Petri net can be made free-firing for any initial state by choosing properly the external input place set and the input control sequence.
Analysis of the controllability of the conflict-free Petri net in this study gives the necessary and sufficient condition for the reachability of the net. The condition leads to the method to determine the external input place set and the control input which bring the net from the initial state to the target state.
