DETERMINATION OF OPTIMAL AGV FLEET SIZE FOR AN FMS

The required number of AGVs necessary to perform a given level of mate rial handling task in an FMS environment is determined using analytica l and simulation modelling. The analytical method involves considerati on of load handling time, empty travel time, and waiting and blocking time. Load handling lime is computed from given system parameters. Det ermination of empty vehicle travel is difficult due to the inherent ra ndomness of an FMS. Several research studies for this purpose are disc ussed and a new model is proposed. It entails formulation of a mixed i nteger programme with an objective of minimizing empty trips. The cons traints are in the form of upper and lower bounds placed on the total number of empty trips starting from or ending at a load transfer stati on. The phenomena of vehicle waiting and blocking are also discussed. The cumulative impact of these three time estimates are then translate d into an initial estimate of AGV fleet size as predicted by individua l models. The method is applied to an illustrative example. Finally, s imulation methodology is used to validate the initial estimates of fle et size. The results indicate that the different models either under-e stimate or over-estimate the actual number of vehicles required in the system. The proposed model, though under-estimates the minimum AGV re quirement, yet provides results which are close to the simulation resu lts. Hence, it can be used as an analytical tool prior to the simulati on phase of AGVS design.