Automated storage system

A method of retrieving a storage container from a storage system comprising a storage grid structure and multiple container handling vehicles (200,300), the storage grid structure comprises vertical column profiles defining multiple storage columns, in which storage containers can be stored one on top of another in vertical stacks, and at least one transfer column (119,120), the column profiles are interconnected at their upper ends by top rails (110,111) forming a horizontal top rail grid upon which the container handling vehicles (200,300) may move in two perpendicular directions, the container handling vehicles are able to retrieve storage containers from, and store storage containers in, the storage columns, and transport the storage containers on the storage grid structure,

• wherein the storage grid structure comprises at least one horizontal transfer section;
• and
• the storage system comprises multiple container transfer vehicles and a transfer floor upon which the container transfer vehicles may move horizontally, and
• the transfer section is arranged at a level below the top rail grid and extends from an external side of the storage grid structure to a position below the at least one transfer column and comprises at least a section of the transfer floor;
• and
• each of the container transfer vehicles comprises a container carrier for carrying a storage container and a wheel arrangement for moving the container transfer vehicle in at least two perpendicular directions on the transfer floor;
• and
• wherein the at least one transfer column extends from the top rail grid to the transfer section, such that a storage container may be transferred between the top rail grid and the container carrier of one of the container transfer vehicles;
• wherein the method comprises the steps of:
• retrieving a storage container from one of the storage columns by one of the container handling vehicles;
• moving the container handling vehicle and the storage container to the at least one transfer column;
• lowering the storage container to a container transfer vehicle arranged in the transfer section at a position below the transfer column;
• and
• moving the container transfer vehicle and the storage container to a position external to the storage grid structure.