Design of supervisors to avoid deadlock in flexible assembly systems

Modern production systems exhibit a high degree of resource sharing that can lead to deadlock conditions. Deadlock arises when some parts remain indefinitely blocked because each of them requests access to a resource held by some other parts. One of the tasks of the control system lies in preventing such situations from occurring by proper resource management. This article addresses the deadlock problem for an important class of production facilities, that is, flexible assembly systems, that can perform both manufacturing or assembly operations. In particular, we develop an approach to deadlock avoidance based on a supervisory control that works by inhibiting or enabling the events involving resource allocation. The article proposes two supervisors characterized by easy implementation, efficiency, and flexibility in resource management. The analysis of some case studies, performed by discrete event simulation, confirms the effectiveness of the approach.