Method and system for transporting inventory items

1. A method for transporting inventory items, comprising:

moving to a starting location associated with an inventory holder;

docking with the inventory holder;

moving towards a destination location;

while moving towards the destination location, determining a location of the inventory holder;

calculating a difference between the determined location of the inventory holder and an anticipated location of the inventory holder;

determining whether the difference is greater than a predetermined tolerance; and

in response to determining that the difference is greater than the predetermined tolerance:

undocking from the inventory holder;

determining a correction value based on the difference, wherein the correction value indicates at least one of a direction and a distance;

moving based on the correction value;

docking with the inventory holder; and

moving towards the destination location.

2. The method of claim 1 , further comprising:

in response to determining that the difference is not greater than the predetermined tolerance:

continuing moving towards the destination location;

determining that the destination location is reached; and

undocking with the inventory holder.

3. The method of claim 1 , further comprising:

detecting a fixed object associated with the starting location; and

in response to detecting the fixed object, stopping at the starting location.

4. The method of claim 1 , wherein determining the location of the inventory holder comprises determining a location of a mobile drive unit associated with the inventory holder and determining a position of at least part of the inventory holder relative to the location of the mobile drive unit.

5. The method of claim 4 , wherein determining the location of the mobile drive unit comprises:

detecting a fixed object; and

determining the location of the mobile drive unit based on the fixed object.

6. The method of claim 1 , wherein determining the location of the inventory holder comprises:

detecting a holder identifier associated with the inventory holder; and

determining the location of the inventory holder based on a position of the holder identifier relative to a location of a mobile drive unit.

7. An apparatus comprising:

a drive module operable to propel the apparatus towards a destination;

a docking actuator operable to facilitate docking with an inventory holder;

a control module operable to:

cause the apparatus to move to a starting location associated with an inventory holder;

cause the apparatus to dock with the inventory holder;

cause the apparatus to move towards a destination location;

while moving towards the destination location, determine a location of the inventory holder;

calculate a difference between the determined location of the inventory holder and an anticipated location of the inventory holder;

determine whether the difference is greater than a predetermined tolerance; and

in response to determining that the difference is greater than the predetermined tolerance:

cause the apparatus to undock from the inventory holder;

determine a correction value based on the difference, wherein the correction value indicates at least one of a direction and a distance;

cause the apparatus to move based on the correction value;

cause the apparatus to dock with the inventory holder; and

cause the apparatus to move towards the destination location.

8. The apparatus of claim 7 , the control module further operable to:

in response to determining that the difference is not greater than the predetermined tolerance:

cause the apparatus to continue moving towards the destination location;

determine that the destination location is reached; and

cause the apparatus to undock with the inventory holder.

9. The apparatus of claim 7 , the control module further operable to:

detect a fixed object associated with the starting location; and

in response to detecting the fixed object, cause the apparatus to stop at the starting location.

10. The apparatus of claim 7 , wherein the control module is operable to determine the location of the inventory holder by:

determining a location of the apparatus; and

determining a position of at least part of the inventory holder relative to the location of the apparatus.

11. The apparatus of claim 10 , wherein the control module is operable to determine the location of the apparatus by:

detecting a fixed object; and

determining the location of the apparatus based on the fixed object.

12. The apparatus of claim 7 , wherein the control module is operable to determine the location of the inventory holder by:

detecting a holder identifier associated with the inventory holder; and

determining the location of the inventory holder based on a position of the holder identifier relative to a location of the apparatus.

13. The apparatus of claim 7 , further comprising means for determining a location of the apparatus.

14. A system for storing inventory items, comprising:

an inventory holder operable to store inventory items; and

a mobile drive unit operable to:

move to a starting location associated with an inventory holder;

dock with the inventory holder;

move towards a destination location;

while moving towards the destination location, determine a location of the inventory holder;

calculate a difference between the determined location of the inventory holder and an anticipated location of the inventory holder;

determine whether the difference is greater than a predetermined tolerance; and

in response to determining that the difference is greater than the predetermined tolerance:

undock from the inventory holder;

determine a correction value based on the difference, wherein the correction value indicates at least one of a direction and a distance;

move based on the correction value;

dock with the inventory holder; and

move towards the destination location.

15. The system of claim 14 , the mobile drive unit further operable to:

in response to determining that the difference is not greater than the predetermined tolerance:

continue moving towards the destination location;

determine that the destination location is reached; and

undock with the inventory holder.

16. The system of claim 14 , the mobile drive unit further operable to:

detect a fixed object associated with the starting location; and

in response to detecting the fixed object, stop at the starting location.

17. The system of claim 14 , wherein the mobile drive unit is operable to determine the location of the inventory holder by:

determining a location of the mobile drive unit; and

determining a position of at least part of the inventory holder relative to the location of the mobile drive unit.

18. The system of claim 17 , wherein the mobile drive unit is operable to determine the location of the mobile drive unit by:

detecting a fixed object; and

determining the location of the mobile drive unit based on the fixed object.

19. The system of claim 14 , wherein the mobile drive unit is operable to determine the location of the inventory holder by:

detecting a holder identifier associated with the inventory holder; and

determining the location of the inventory holder based on a position of the holder identifier relative to a location of the mobile drive unit.

20. The system of claim 14 , further comprising means for determining a location of the mobile drive unit.