US Patent 9389609 Container holder utilization and selection

An inventory system includes inventory holders, container holders, containers carried by the container holders, mobile drive units, stations, and a management module. The management module instructs the mobile drive units to move the inventory holders and container holders to stations. Container holders are loaded with containers of inbound inventory items at a first station. Inbound inventory items are transferred from containers to inventory holders at a second station. Outbound inventory items are transferred from inventory holders to containers at a third station. Containers of outbound inventory items are removed from container holders at a fourth station.