In order to efficiently use an automated shelf system the stacker cranes must perform all storage and retrieval operations ``as good as possible''. possible objectives are, e.g., minimizing the total distance of empty moves or the weighted sum of all waiting times. Due to non-predictable response times with respect to incoming orders, order completion or cancellation a real-time control system is needed, which is able to produce good solutions (i.e., an assignment of a transportation task to the stacker crane) in short time (sometimes less than a second).
In cooperation with Siemens-Nixdorf AG, mathematical models for the optimal routing of stacker cranes (asymmetric travelling salesman problems with additional side-contraints like precedences, time windows) have been developed. These are planned to be applied in the distribution center of our other industrial partner Herlitz PBS AG.
The real-time compliance of Various control methods will be evaluated in a simulation environment. Our goal is to develop a library of optimization procedures, suitable for various types of automated shelf systems.
