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We study the deadlock handling performance of a single-blade cluster tool and present a comparison of average flowtimes under deadlock detection and resolution versus prevention. Two detection and resolution policies are tested: either resolve permanent deadlocks or resolve both permanent and transient deadlocks. A permanent deadlock requires external intervention to resolve the deadlock, whereas a transient deadlock has a positive probability that the deadlock will resolve itself over time. Prevention averts deadlock by providing sufficient in-process buffer spaces. Our experiments indicate interplay of process and robot transfer times dictate the choice of deadlock strategy. Under low robot transfer times relative to process times, providing sufficient in-process buffer to prevent deadlock or resolving both permanent and transient deadlocks can be equally effective. We conclude with some practical guidelines for operating and designing cluster tools under deadlock conditions. Index Terms-Cluster tool design, deadlock detection and resolution, deadlock handling, deadlock prevention, flexible manufacturing systems, real-time control of cluster tools.

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In this article we develop an automatic deadlock detection scheme for general purpose simulation systems and offer deadlock-resolution algorithms for grouped resources and overlapping resources. Our intent is to provide capabilities that can be incorporated in professional simulation systems to facilitate modeling situations where deadlocking is a problem. Two general modeling situations are analyzed. In grouped-resources models, a set of resources is required to complete a task, whereas in overlapping-resources models, movement to the next process requires first gaining control of the next resource. Deadlocks occurring in these two different situations require different resolution algorithms. We develop a graph-theoretic description of the simulation over time and define deadlocks in terms of strongly connected components of this graph. We make a distinction between transient deadlocks and permanent deadlocks. A prototype implementation of the detection and resolution algorithms was incorporated in a simulation system to provide information concerning the computational requirements and performance of these algorithms. We demonstrate that resolving a possible transient deadlock before it becomes permanent is worthwhile in conjunction with overlapping resources, and that the computational performance of the approach is reasonable except for situations with frequent occurrences of overlapping-resources deadlocks.