Order fulfillment system

A system for transporting items within an order fulfillment center including a horizontal deck and one or more vertical storage racks, a vertical storage rack of the one or more storage racks including a plurality of horizontal rails, spaced apart from each other on respective levels of the vertical storage rack, and a pair of tracks, spaced apart from each other and extending between the plurality of levels of the vertical storage rack, the system comprising:

• support means for supporting the items during transport;
• horizontal drive means for driving the support means along a pair of horizontal rails on a level of the vertical storage rack;
• first retraction means for moving the horizontal drive means between an extended position where the horizontal drive means engages within the rails to enable horizontal movement of the support means, and a retracted position where the horizontal drive means does not engage with the rails;
• vertical drive means for driving the support means along the pair of tracks with the support means supported at a single end of the support means;
• second retraction means for moving the vertical drive means between an extended position where the vertical drive means engages within the pair of tracks to enable vertical movement of the support means, and a retracted position where the vertical drive means does not obstruct travel of the support means along the pair of horizontal rails past the pair of tracks;
• wherein the horizontal drive means is coaxial with the vertical drive means, and the horizontal drive means is extendible and retractable independently of the vertical drive means.

A mobile robot for travelling within an order fulfillment center including one or more vertical storage racks, a vertical storage rack of the one or more storage racks including a plurality of horizontal rails, spaced apart from each other on respective levels of the vertical storage rack, and a pair of tracks, spaced apart from each other and extending between the plurality of levels of the vertical storage rack, the mobile robot comprising:

• a plurality of horizontal traction drives configured to be driven to rotate to advance the mobile robot along a pair of spaced apart horizontal rails on a level of the vertical storage rack, the plurality of horizontal traction drives comprising:
• a pair of drive wheels comprising a first drive wheel, on a first side of the mobile robot, configured to engage a first rail of the pair of spaced apart rails, and a second drive wheel, on a second side of the mobile robot opposed to the first side, configured to engage a second rail of the pair of spaced apart rails, the pair of drive wheels having a common axis with each other;
• and
• a pair of vertical traction drives configured to be driven to rotate to advance the mobile robot along the pair of tracks, the pair of vertical traction drives comprising:
• a pair of drive gears comprising a first drive gear, on the first side of the mobile robot, configured to engage a first track of the pair of tracks, and a second drive gear, on the second side of the mobile robot opposed to the first side, configured to engage a second track of the pair of tracks, the pair of drive gears having a common axis with each other;
• wherein the pair of drive gears are further configured to move between extended positions where the pair of drive gears engage with the pair of tracks to enable vertical movement of the mobile robot while the mobile robot is cantilevered off the pair of tracks, and retracted positions where the pair of drive gears do not obstruct travel of the mobile robot along the pair of horizontal rails past the pair of tracks;
• and
• wherein the pair of drive wheels are coaxial with the pair of drive gears;
• and
• wherein the pair of drive wheels are extendible and retractable independently of the pair of drive gears.