A Petri net approach of deadlock prevention in batch processes in case of failure

This paper deals with a method of using a Petri net to prevent the deadlock which can occur in industrial plants where batch processes are used, such as food, pharmaceutical and cement industries. Individual pieces of equipment in these plants are controlled by independent programmable logical controllers (PLC), which are later interconnected into the local area network (LAN). PLCs communicate with each other and synchronize their work. However, when such plants produce various products using different recipes simultaneously, and when one part abruptly gets out of the system, a system deadlock can occur and cause great damage. Designers of these control systems for batch processes have to think of failure possibility, and they have to insure that the process continues in that case. This paper shows how it is possible to synthesize the supervisor that will prevent deadlock occurrences in a batch process by the use of Petri nets in the case of equipment failure. The synthesis of the supervisor that insures the deadlock-free operation is illustrated by one example of a batch process.