Models for the design and analysis of a large package sort facility

At the sort facility in a large overnight package delivery operation, palletized loads are moved in a container (called an inbound ULD) from a plane to a bin, unloaded from the bin, and moved by forklift one item at a time from a bin to a rack. At the rack, each palletized load is loaded into a container (called an outbound ULD) and this outbound ULD is delivered to a plane for delivery to its final delivery airport. The purpose of this study was to determine the optimal design of this sort facility that acts as a hub in a hub-and-spoke system. For a given topology of the sort facility (a topology being the specification of the locations of the bins and the racks), a design of this sort facility is the assignment of inbound ULDs to bins and outbound ULDs to racks and the determination of the number of forklifts needed to carry out the sort. In this paper, the Bin and Rack Assignment Model (BRAM) is developed to perform this analysis; the objective of the BRAM is to minimize the daily operating and amortized capital cost of performing the sort. Since the BRAM is computationally difficult to solve, the BAM and RAM algorithm is developed to derive heuristic solutions to the BRAM. Several examples of the BAM and RAM algorithm are presented. A modification to the BAM and RAM algorithm for solving practical-sized problems is then presented and future directions for this analysis are discussed.