System and method for transporting inventory items

1. An apparatus, comprising:

a housing;

a drive module operable to selectively propel the apparatus in at least a first direction;

a docking head operable to at least one of couple to and support an inventory holder;

an elevating shaft connected to the docking head and operable to raise the docking head when the housing is rotated relative to the elevating shaft; and

a rotation module operable to induce rotation in the housing relative to the elevating shaft, the rotation module comprising:

a first actuator operable to rotate the housing; and

a second actuator operable to apply a torque to the elevating shaft so that an orientation of the docking head remains substantially constant while the first actuator rotates the housing.

2. The apparatus of claim 1 , wherein the drive module is operable to position the apparatus under an inventory holder, and wherein the apparatus is operable to dock with the inventory holder, at least in part, by raising the docking head towards the inventory holder.

3. The apparatus of claim 1 , further comprising a braking element operable to prevent the docking head from rotating when activated, and wherein the apparatus is operable to:

activate the braking element; and

rotate the housing while the braking element is activated.

4. The apparatus of claim 3 , wherein the braking element comprises one or more feet that, when deployed, press against a surface on which the apparatus is resting, and wherein the one or more feet are operable to prevent the docking head from rotating when deployed.

5. The apparatus of claim 1 , wherein the rotation module comprises all or a portion of the drive module.

6. The apparatus of claim 5 , wherein:

the drive module comprises a first wheel and a second wheel and is further operable to propel the apparatus in the forward direction by rotating the first wheel and the second wheel in a first direction and to propel the apparatus in the backward direction by rotating the first wheel and the second wheel in a second direction; and

the rotation module comprises the first wheel and the second wheel and wherein the rotation module is further operable to induce rotation in the housing by rotating the first wheel and the second wheel in opposite directions.

7. The apparatus of claim 1 , further comprising a processing module operable to selectively instruct the rotation module to perform one of a first rotation movement and a second rotation movement, wherein:

the first rotation movement comprises rotating the housing without substantially changing an orientation of the docking head; and

the second rotation movement comprises rotating the docking head while rotating the housing.

8. The apparatus of claim 1 , wherein the elevating shaft comprises a threaded shaft.

9. The apparatus of claim 1 , wherein the elevating shaft is operable to raise the docking head when the housing is rotated in a first direction relative to the elevating shaft; and wherein the elevating shaft is further operable to lower the docking head when the housing is rotated in a second direction relative to the elevating shaft.

10. A method for transporting inventory items, comprising:

positioning a mobile drive unit beneath an inventory holder at a first location, wherein the mobile drive unit comprises:

a housing;

a docking head; and

an elevating shaft, wherein the docking head is connected to the elevating shaft and wherein the elevating shaft is operable to raise the docking head when the housing is rotated relative to the elevating shaft;

raising the docking head with the elevating shaft by rotating the housing relative to the elevating shaft, wherein rotating the housing relative to the elevating shaft comprises:

applying a first torque to the housing a first actuator; and

applying a second torque to the shaft using a second actuator so that an orientation of the docking head remains substantially constant while the first actuator applies the first torque to the housing;

docking the mobile drive unit with the inventory holder so that the docking head at least one of couples to and supports the inventory holder; and

moving the mobile drive unit and the inventory holder to a second location.

11. The method of claim 10 , wherein the mobile drive unit further comprises a braking element operable to prevent the docking head from rotating when activated, and rotating the housing relative to the elevating shaft comprises:

activating the braking element; and

applying a torque to the housing while the braking element is activated.

12. The method of claim 11 , wherein the braking element comprises one or more feet operable, when deployed, to press against a surface on which the apparatus is resting, and wherein activating the braking element comprises deploying the one or more feet.

13. The method of claim 10 , wherein moving the first unit to the second location comprises:

moving the mobile drive unit in a first direction to the second location;

rotating the mobile drive unit without changing an orientation of the docking head while rotating the mobile drive unit; and

moving the mobile drive unit in a second direction to a third location.

14. The method of claim 13 , further comprising rotating the mobile drive unit and the docking head at the third location to present a particular face of the inventory holder to an operator.

15. The method of claim 10 , wherein raising the docking head with the elevating shaft comprises raising the docking head with the elevating shaft by rotating the housing in a first direction relative to the elevating shaft, and further comprising lowering the docking head by rotating the housing in a second direction relative to the elevating shaft.

16. A system for transporting inventory items, comprising:

a plurality of inventory holders, each operable to store inventory items; and

a mobile drive unit, comprising:

a housing;

a drive module operable to selectively propel the apparatus in a forward direction and a backward direction, wherein the drive module is further operable to position the mobile drive unit under a selected one of the inventory holders;

a docking head operable to at least one of couple to or support the selected inventory holder when the mobile drive unit is docked with the selected inventory holder;

an elevating shaft connected to the docking head and operable to raise the docking head when the housing is rotated relative to the elevating shaft; and

a rotation module operable to induce rotation in the housing relative to the elevating shaft, the rotation module comprising:

a first actuator operable to rotate the housing; and

a second actuator operable to apply a torque to the elevating shaft so that an orientation of the docking head remains substantially constant while the first actuator rotates the housing.

17. The system of claim 16 , wherein the mobile drive unit further comprises a load control module operable to maintain an orientation of the selected inventory holder when the housing rotates relative to the elevating shaft.

18. An apparatus for transporting inventory items, comprising:

means for positioning a mobile drive unit beneath an inventory holder at a first location, wherein the mobile drive unit comprises:

a housing;

a docking head; and

an elevating shaft, wherein the docking head is connected to the elevating shaft and wherein the elevating shaft is operable to raise the docking head when the housing is rotated relative to the elevating shaft

means for raising the docking head with the elevating shaft by rotating the housing relative to the elevating shaft, wherein the means for raising the docking head comprises:

means for applying a first torque to the housing; and

means for applying a second torque to the shaft so that an orientation of the docking head remains substantially constant while the first torque is applied to the housing;

means for docking the mobile drive unit with the inventory holder so that the docking head one of couples to and supports the inventory holder; and

means for moving the mobile drive unit and the inventory holder to a second location.