Fleet sizing of laser guided vehicles and pallet shuttles in automated warehouses

The paper deals with emerging automation technologies for pallet handling in warehouses characterized by multiple-depth rack storage systems. In particular, this study addresses the adoption of Pallet Shuttles (PSs) for material handling within the rack structure, i.e., for put-away and retrieval operations from the rack face to the specific pallet location and vice versa. PSs are used in combination with Laser Guided Vehicles (LGVs) so as to obtain a fully automated warehousing system. The study develops an analytical model for the joint LGV-PS fleet sizing problem, also taking into consideration stochastic phenomena and queueing implications. This enables the analyst to compute the utilization of LGVs and PSs as a function of sizes of the two fleets. Then, a queueing model can be applied to estimate the cycle time of the orders in the warehousing system. An example to clarify the application of the method is also provided.