Simulation modelling of a narrow aisle automated storage and retrieval system (AS/RS) serviced by rail-guided vehicles

Abstract A computer simulation model of an Automatic Storage and Retrieval System (AS/RS) consisting of 5 storage conveyors, 5 retrieval conveyors, 2 bi-directional conveyors, 2 order-picking stations, 7 narrow-aisle cranes and 9,310 storage locations, was created in ARENA TM version 1.1. Rail-guided vehicles move material to and from the storage racks. The computer simulation model of the AS/RS was used to examine the operational logic of the entire system in order to determine the operational deployment strategy that yields the optimal number of rail-guided vehicles (RGVs), the utilisation of the narrow-aisle crane and also the maximum throughput of the system. This paper reports on the results of running the simulation model. For example, increasing the capacity of the storage and retrieval conveyor from 1 to 2 effectively reduces the number of RGV deadlocks by about 94%. A change of the topology of the RGVs' from 1-zone to 2-zone yielded a slightly better part retrieval time and also a reduction in the optimal number of RGVs from 5 to 4. Under these conditions, the number of storages/retrievals is about 430. The maximum throughput of AS/RS is estimated to be about 33 items per hour. The best retrieval time per part is almost 1205 seconds. As it stands, the system could do with less retrieval stations and narrow-aisle cranes which are under-utilised.