APPROXIMATE QUEUEING NETWORK MODELS FOR CLOSED FABRICATION/ASSEMBLY SYSTEMS. PART I: SINGLE LEVEL SYSTEMS

We address the issue of performance analysis of fabrication/assembly (F/A) systems, which are systems that first fabricate components and then join the components and subassemblies into a product. Here we consider an F/A system consisting of a single assembly station with input from K fabrication stations. We assume that the system uses a Kanban control mechanism with a fixed number of kanbans circulating between each input station and the assembly station. Even with Markovian assumptions, computing an exact solution for the performance evaluation of such systems becomes intractable due to an explosion in the state-space. We develop computationally efficient algorithms to approximate the throughput and mean queue lengths. The accuracy of the approximations is studied by comparison to exact results (K = 2) and to simulations (K > 2). Part II of this paper demonstrates how these models can be used as building blocks to evaluate more complex F/A systems with multiple levels of assembly stations.     

ON THE RELATIVE PERFORMANCE OF FUNCTIONAL AND CELLULAR LAYOUTS- AN ANALYSIS OF THE MODEL-BASED COMPARATIVE STUDIES LITERATURE

Paralleling the increased interest in cellular manufacturing in recent years, a large number of studies have emerged that focus on the relative performance of cell systems and the functionally organized systems they replace. This paper is an analysis of studies that use model-based, controlled experimentation to seek answers to the questions of if, when, and why cellular layouts outperform their functional counterparts. Twenty-four model-based studies are analyzed with respect to their definitions of cellular versus functional layouts, the experimental factors that have been investigated, the results concerning relative performance, and the findings' relevance to layout choice. We conclude that although the comparative studies have been very valuable in their efforts at identifying the factors that embody the essence of cells and shape performance improvements, most of the basic findings are known from past research. Furthermore, the studies' findings cannot assist practitioners in making specific choices between existing layouts and alternative cell systems. However, the totality of the findings reinforce our knowledge of how work systems in general can be designed and organized to reduce throughput time, and can also be used to identify environments and conditions for which conversions to cells may have more or less potential.     

MEASUREMENT OF MULTIPLE SITES IN SERVICE FIRMS WITH DATA ENVELOPMENT ANALYSIS

Data envelopment analysis (dea) has become an increasingly popular method to measure performance for service firms with multiple sites. DEA is superior to many traditional methods for firms that have multiple goals. The promise of DEA is that the complex, multi-objective problem of performance measurement can be reduced to a single number. Unfortunately, the practice of DEA often belies the promise. Misconceptions concerning the purpose and implementation of DEA can cause DEA applications to be less than successful. Here, the technique is explained, and a guide to the implementation of DEA is proposed, utilizing DEA studies of retail bank branches.