The effect of input/output location in an automated storage/retrieval system with two cranes

This paper studies the scheduling of two cranes in automated storage and retrieval systems that have a single output/input location. The cranes are located on a common rail, which restricts their movement, and which also makes the scheduling interesting as the cranes have to dodge each other while operating. The purpose of the paper is to study the scheduling of the retrieval of cartons from the storage to the output location. In order to do that, the paper introduces different scheduling restrictions and constructs a local search heuristic for scheduling the cranes. The heuristic relies on simulation to calculate the length of a given schedule, i.e., the makespan. In the numerical experiments different scheduling restrictions are compared in three different types of automated storage and retrieval systems. The results show how the length of the schedule changes when the input/output location changes in the storage.