A review of design and control of automated guided vehicle systems <s> Multi-load capacity vehicles <s> Abstract An alternative to increasing automated guided vehicle (AGV) fleet size to improve vehicle availability for material transport requests is to introduce vehicles with multiple load-carrying capacities. Aside from alleviating communication and congestion problems, the use of multiple-load carriers can potentially reduce the deadhead or unproductive time of vehicles. This paper discusses several key issues related to multiple-load AGV systems and demonstrates the potential benefits of using them. Alternative vehicle dispatching strategies for multiple-load AGVs are discussed, stressing that different considerations are involved in dispatching empty and partially loaded vehicles. The effectiveness of single-load and two-load AGV systems is compared using simulation. The results show that, with multiple-load vehicles, the sensitivity of AGV system performance to guidepath layout is decreased, and the job input rate, which the AGV system can effectively handle without becoming a bottleneck for the overall system, is significantly increased. The relative effectiveness of selected control strategies is also investigated. <s> BIB001 </s> A review of design and control of automated guided vehicle systems <s> Multi-load capacity vehicles <s> In previous papers, we used a simulation model to look at how different dispatching rules can be classified, and at the effects on the performance of internal transport if the release time of loads can be forecasted using a virtual release time. We concluded that centralized rules outperform decentralized rules and that the performance of internal transport can be improved using virtual release times. <s> BIB002
The use of multi-load capacity vehicles can reduce the number of vehicles needed or increase the throughput of the system. A multi-load vehicle can pick up additional loads while transporting a previously assigned task. The use of multi-load vehicles can therefore reduce the amount of vehicles' empty trip time and also the total distance traveled is likely to reduce. BIB001 demonstrate the effectiveness of using multi-load vehicles compared to unit-load vehicles. After experimenting using simulation, they conclude that using multi-load AGVs increases the system throughput, especially in case of high transport demand. Using simulation, BIB002 also show that multi-load vehicles help to increase the system performance, especially, in the case where multiple loads can be picked up at one location. A disadvantage is that a more complex scheduling system is required. Using estimation models mentioned above, the estimated number of vehicles may considerably differ from the real vehicle requirements due to some impractical assumptions in the analytical models. Moreover, the number of vehicles is strongly affected by the dispatching rules used  , traffic management, congestion and other factors. Therefore, the estimated number should be re-evaluated using a simulation model for specific operational conditions.