European Journal of Operational Research 63 (1992) 173-191 173 North-Holland Tandem AGV systems: A partitioning algorithm and performance comparison with conventional AGV systems * Yavuz A. Bozer and Mandyam M. Srinivasan Department of Industrial and Operations Engineering, The University of Michigan, Ann Arbor, MI 48109, USA Received October 1990; revised February 1992 Abstract: In an earlier paper, Bozer and Srinivasan introduced the tandem concept for automated guided vehicle (AGV) systems and presented an analytical model to evaluate the throughput performance of a basic component of the system; namely, a single vehicle serving a set of workstations under the First-Encountered-First-Served rule. In this study, using the above analytical model and certain column generation techniques, we present a heuristic partitioning scheme to configure tandem AGV systems. The partitioning scheme is based on a variation of the well-known set partitioning problem. It is aimed at evenly distributing the workload among all the AGVs in the system. We demonstrate the procedure with two numerical examples. Using simulation, the performance of the tandem configuration obtained for each example is compared to that of the corresponding conventional AGV system. Keywords: Automated guided vehicle systems; optimization; set partitioning; heuristics; facilities 1. Introduction The tandem concept for AGV systems was introduced in an earlier paper by Bozer and Srinivasan (see [2] or [3]). As shown in Figure l(a), in a conventional AGV system all the vehi- cles are allowed to serve any workstation in the system. In contrast, a tandem AGV system (shown in Figure l(b)) is obtained by partitioning all the workstations into single-vehicle, non-overlapping zones. Additional pick-up/deposit (P/D) points are provided between adjacent zones to serve as 'transfer points'. * Both authors have been supported by a research grant (DRDA 90-908) from General Motors. The first author is also supported by a Presidential Young Investigator Award under NSF Grant DMC 8858562. Correspondence to: Y.A. Bozer, Department of Industrial and Operations Engineering, The University of Michigan, Ann Arbor, MI 48109, USA. The tandem concept offers three principal ad- vantages. First, it dramatically simplifies the con- trol system since only one vehicle must be con- trolled in each zone and the vehicles never inter- fere with one another. Second, it eliminates the delays caused by congestion and blocking in con- ventional AGV systems; and third, it offers more flexibility since zones (and workstations) can be added, removed, or modified without affecting other zones, and different types of vehicles (in- cluding bidirectional and/or self-guided vehicles) can be used in different zones. The principal limitations of the tandem concept are as follows: first, a load may have to be handled by several vehicles before it reaches its destination; this will not only require additional pick up and deposit operations but it will also induce additional de- lays at the transfer points. Second, additional floor space and capital investment is required to provide the transfer points. 0377-2217/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved