Performability of Automated Manufacturing Systems

Abstract Automated manufacturing systems (AMSs) can be regarded as flexible, degradable, fault-tolerant systems. To evaluate such systems, we need combined measures of performance and reliability, called performability measures. The most important performability measures in the AMS context are related to throughput and manufacturing lead time (MLT) since high productivity and low lead times are prime features determining the competitiveness of AMSs. Performability has a strong relation to the notion of flexibility in manufacturing systems. Performability modeling is an active research topic in the area of fault-tolerant computing systems. Performability studies are of great interest in the AMS context also, since performability enables to quantify flexibility and competitiveness of a manufacturing system. In this article, we use the conceptualization available in the area of fault-tolerant computing, to formulate performability notions for AMSs. We consider steady-state performability, interval performability, and distribution of performability with respect to throughput and MLT measures. Through several illustrative examples and numerical results, we bring out the importance of performability modeling and evaluation in AMS design. The AMS examples discussed are: (i) a versatile machine center with machine failures and repairs, and (ii) a generic flexible manufacturing system with centralized material handling, where the performance could be described by a closed central server model.