Liveness-Enforcing Supervisors for Flexible Manufacturing Systems with Multiple Resource Acquisitions

This paper develops an approach for the deadlock prevention problems in flexible manufacturing systems (FMS) based on siphons of Petri nets. The analysis of S4PR, a subclass of Petri nets, leads us to characterize deadlock situations in terms of insufficiently marked siphons. A method is proposed to make elementary siphons max-controlled by the additional control places. When the liveness of the augmented S⁴PR net is not guaranteed, we modify the initial markings of the control places. Thus, the controlled net system (supervisor) can be enforced to be live by exploiting its structure analysis. Finally, an FMS example is used to illustrate the proposed techniques.