Vehicles routing and scheduling algorithm for an automated storage and retrieval system of a warehouse

An automated storage and retrieval system is a new storage concept derived from a pallet-shuttle high-density-storage system. This new system (former system) has higher space utilization than the original one (latter system), and can store or retrieve palletized units automatically using automated storage & retrieval vehicles. In order to organize multiple vehicles moving orderly in the system, offline vehicle routing and online vehicle scheduling are performed, based on a path-net graph modeled from the racks and pallet lifters of the system. In offline vehicle routing, path payload and navigation factor are introduced to calculate the path cost, which can make the vehicles not only have short paths but also employ trunk rails and pallet lifters evenly. In online vehicle scheduling, to avoid vehicle collisions at path nodes, buffers are attached to path nodes in the path-net graph model for vehicle parking, and each vehicle can only pass through the path nodes after having acquired the authorization of the system. With the algorithm illuminated in this paper, the system can route and schedule vehicles efficiently, and the utilization rate of vehicles can achieve more than 98% and congestion rate of system less than 2%, with an appropriate number of vehicle.