Real-time scheduling for twin RMGs (Rail Mounted Gantries) in an automated container yard

This paper proposes heuristic-based and local-search-based real-time scheduling methods for twin rail-mounted gantry (RMG) cranes working in a block at an automated container terminal. The methods reschedule the cranes in real time for a given fixed-length look-ahead horizon whenever an RMG finishes a job. One difficulty with this problem is that sometimes additional rehandling of containers needs to be carried out in order to complete a requested job, especially when other containers are stacked on top of the target container. These rehandlings are the main cause of the delay of the crane operations, leading to extended waiting of automated guided vehicles (AGVs) or external trucks that co-work with the cranes. By treating the rehandling operations as independent jobs in our solution methods, we can greatly facilitate the cooperation between the two RMGs. Through this cooperation, the workload of the two RMGs can be better balanced and interference can be more easily avoided, thereby maximizing crane utilization. Simulation experiments show that the waiting times of AGVs and external trucks are significantly reduced due to the increased utilization through cooperation.