Simplification of a Petri Net controller in industrial systems

Abstract

This paper deals with the problem of forbidden states in discrete event systems modeled by Petri Net. To avoid the forbidden states, some constraints which are called Generalized Mutual Exclusion Constraints can be assigned to them. Enforcing these constraints on the system can be performed using control places. However, when the number of these constraints is large, a large number of control places must be connected to the system which complicates the model of controller. In this paper, the objective is to propose a general method for reducing the number of the mentioned constraints and consequently the number of control places. This method is based on mixing some constraints for obtaining a constraint verifying all of them which is performed using the optimization algorithms. The obtained controller after reducing the number of the control places is maximally permissive.

Keywords

• Discrete Event System (DES)
• Supervisory Control Theory
• Petri Net (PN)
• Generalized Mutual Exclusion constraint (GMEC)
• Flexible Manufacturing System (FMS)