Scheduling automated triple cross-over stacking cranes in a container yard

We describe an approach for scheduling triple cross-over stacking cranes in an automated container storage block with asynchronous hand over at the transfer areas at both block front ends. The problem is characterised by frequent long crane moves that make job assignment and crane routing particularly challenging, as an intricate synchronisation between the cranes is required. The main objective is to maximise the productivity of the crane system under peak load while preventing delays in the transport of import and export containers from and to the transfer areas. Our method solves an online optimisation problem by constructing a new crane schedule for a certain planning horizon whenever a new job arrives or a job is completed. We report on extensive simulation studies for evaluating the scheduling strategy. The results show that the method performs significantly better than commonly used heuristics, leading to a productivity gain of more than 20%.