Abstract: As a special subclass of Petri nets, S4R can model resource allocation systems with multiple processed that are more complex than S3PR. This paper proposed a deadlock prevention policy for S4R. First, checked the liveness of a flexible manufacturing system modeled by S4R by using MIP. Then designed a supervisor for the system if it is not live,which is based on a new concept of siphon control. Again, checked the livcness of the controlled system by using MIP.If the controlled system is not live, it will be further controlled. This policy can avoid some constraints that are not necessary. Usually a livencss-enforcing supervisor with more permissive can he obtained by the proposed policy.

Key words: Petri net, Flexible manufacturing system, S4R, Deadlock prevention