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Deadlock-free resource allocation has been an active area of research in flexible manufacturing. Most researchers have assumed that allocated resources do not fail, and thus, little research has addressed the discrete-event supervision of manufacturing systems that are subject to resource failure. In our previous work, we developed supervisory controllers to ensure robust deadlock-free operation for systems with unreliable resources. These controllers guarantee that parts requiring failed resources do not block the production of parts that are not requiring failed resources. This previous work assumes that parts requiring failed resources can be advanced into failure-dependent (FD) buffer space (buffer space exclusively dedicated to parts requiring unreliable resources). Supervisors admit only states for which a sequence of such part advancements is feasible. The research presented in this paper relaxes this assumption because, in some systems, providing FD buffer space might be too expensive or it might be desirable to load the system more heavily with FD parts. In this paper, we concentrate on distributing parts requiring failed resources throughout the buffer space of shared resources so that these distributed parts do not block the production of part types that are not requiring failed resources. The approach presented here requires no state enumeration and is polynomial in stable measures of system size. We also present results from simulation experiments that compare system performance under these new policies with system performance under our previously published supervisors. These results show that our new policies allow better performance if the required part mixes favor FD part types. The systems of interest are single-unit resource allocation systems.
Systems, Man and Cybernetics, Part A: Systems and Humans, IEEE Transactions on (Volume:38 , Issue: 3 )
Date of Publication: May 2008