Single Direction Traffic Rule for GRID System - An Innovative Automated Material Handling System

The Goods Retrieval and Inventory Distribution (GRID) system is a conceptual automated material handling system. The compact and complex structure makes the routing of the trolleys difficult, which limits the system performance and structural extendability. Motivated by city traffic which sets direction on certain roads to create traffic loops, we proposed a single direction traffic rule (SDTR) for the GRID system by creating loops over the network. Comparing with the free routing traffic rule (FRTR) developed in previous study, SDTR significantly reduce the vehicle conflicts. The numerical experiment further showed that FRTR outperforms SDTR when the number of trolleys is small since the trolleys may not travel on the shortest path in SDTR. However, SDTR is much better than FRTR when the number of trolleys are large due to the increasing number of conflicts in FRTR. SDTR has shown to be capable of further improving the throughput of the vertical expanded layout, however, due to the structure limit, the long waiting time near horizontal paths remains an issue in the horizontal expanded layout for further study.