An approach to control automated warehouse systems

The goal of this paper is the development of control algorithms for the management of an automated warehouse system. As usual, the implementation of a control algorithm requires three preliminary steps: development of a reliable model; design of control procedures according to some optimality criteria; validation of these control procedures. As for modelling, a new level in the control architecture, namely an optimizer system, is introduced which performs real-time optimization thus simplifying the low-level control and improving the overall performance. In this context, the role of a detailed model of the whole warehouse is discussed and such a model is built up by using the colored timed Petri nets framework. As for control, we propose two control algorithms, derived under the simplifying continuity assumption of the rack locations, to optimize the operations of the cranes (moving within the aisles of the warehouse) and the operations of the shuttle (moving on a straight line placed between the aisles and the picking/refilling area), respectively. To evaluate the performance of the proposed control algorithms we define three different cost indices. As for the validation, extensive simulations are performed on the model in order to prove the effectiveness of the proposed control algorithms. A further validation of the algorithms has been performed on a test bed in order to take into account communication delays and computation times. Finally, the proposed architecture and control algorithms have been applied to a real plant.