Deadlock Avoidance Policies in Production Systems by a Digraph Approach

Automated manufacturing systems (AMSs) consist of many workstations (machines) performing a set of generic operations and of a material handling system routing the parts (jobs) among the workstations. Machines and transport units are under the sophisticated control of computers. As a result of their capacity of simultaneously processing medium-sized volumes of various part types, AMSs combine efficiency in using and sharing available resources and rapidity in responding to change in the marketplace. However, since various jobs compete for a fixed number of resources, the management and the operation of AMSs bear some control problems such as blocking, conflicts and deadlocks. Specifically, deadlocks cause heavy damages because they establish a permanent blocking of processes and prevent parts from flowing. Namely, when a deadlock occurs, transferring some jobs from one resource to another is impossible because each of such jobs is waiting for a resource that is held by parts in the same set.