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Automated guided vehicle (AGV) systems complement the operation of flexible manufacturing systems (FMS) by providing integrated automated material handling that capitalizes on the system's flexibility. Previous research considering AGV systems for use in FMS installations has focused on complex control strategies to reduce the congestion problem often encountered in these systems. Recently, attention has been given to tandem system configurations that reduce congestion and simplify system control. The present study uses the simulation methodology to compare the performance of three AGV configurations under a variety of experimental conditions. The results indicate that system size, load/unload time, and machine failure rate factors have significant impacts on the operation of the systems considered. In general, with respect to due date performance, it is recommended to use the traditional configuration in small systems while using the tandem/loop configuration in larger systems. Furthermore, it is shown that the addition of the loop to the tandem configuration mitigates the sensitivity of the tandem configuration to the load/unload time factor as well as significantly improving its performance under high load/unload times. Thus, if tandem configuration is desired to reduce congestion and simplify system control, investments must be made to directly reduce the load/unload times or to construct a loop to avoid the load/unload time penalty. [ABSTRACT FROM AUTHOR]

With increases in maintenance, equipment, and labour costs, the need for an effective maintenance program is increasing. Previous research has shown that the use of preventive maintenance procedures may allow for a simpler and less expensive way of maintaining and operating equipment. Many studies have dealt with various characteristics of cellular manufacturing. However, almost all of these studies have assumed machines do not break down. The objective of this study is to compare the performance of three maintenance policies in conjunction with four two-stage group scheduling heuristics, under eight experimental conditions. Approaches which induce shop efficiency by performing preventive maintenance and machine setups simultaneously are also considered. The results of this study extend the findings of previous research by demonstrating that utilizing preventive maintenance procedures generally results in better average flowtime and percent tardy performance while deteriorating the average tardiness performance in some cases. Furthermore, it was shown that conducting preventive maintenance and machine setups simultaneously improves the average tardiness performance while maintaining the same average flowtime performance compared to the case where these activities are performed separately. Finally, it was demonstrated that if the primary concern is average flowtime or other efficiency oriented measures, the choice of group scheduling heuristic is critical. However, if the primary concern is due date attainment, the choice of maintenance policy becomes more critical. [ABSTRACT FROM AUTHOR]