AS/RS lift having vertically-aligned dual carriages

1. A material handling system comprising:

a storage rack having more than one vertically-spaced level, wherein each vertically spaced level has a plurality of storage locations accessible from an adjacent aisle;

a shuttle vehicle that services a vertically-spaced level of the storage rack;

a vertical lift having a vertical support structure positioned proximate to the storage rack and having a vertically aligned first carriage and second carriage independently positionable along a respective first vertical portion and a second vertical portion of the vertical support structure, wherein at least a portion of each of the first vertical portion and the second vertical portion of the vertical support structure overlap;

a first vertical drive system coupled to the first carriage to position the first carriage to pick up and to deposit articles at selected levels within the first vertical portion of the vertical support structure;

a second vertical drive system coupled to the second carriage to position the second carriage to pick up and to deposit articles at selected levels within the second vertical portion of the vertical support structure; and

a processor subsystem in communication with the first vertical drive system and the second vertical drive system to:

selectively position the first carriage and the second carriage at respective selective levels along the vertical support structure to avoid collision between the first carriage and the second carriage; and

activate the first carriage to pick up and to deposit articles at a selected level and concurrently position the second carriage out of a path of the first carriage to avoid collision between the first carriage and the second carriage.

2. The material handling system of claim 1 , wherein:

the first vertical portion comprises an overlapping zone and a first exclusive zone above the overlapping zone; and

the second vertical portion comprises the overlapping zone and a second exclusive zone below the overlapping zone.

3. The material handling system of claim 2 , further comprising at least one in-feed conveyor and at least one out-feed conveyor that are adjacent to a level of the overlapping zone and that are serviced by a selected one of the first carriage and the second carriage.

4. The material handling system of claim 2 , further comprising:

at least one in-feed conveyor and at least one out-feed conveyor that are adjacent to a level of the first exclusive zone and that are serviced by the first carriage; and

at least one in-feed conveyor and at least one out-feed conveyor that are adjacent to a level of the second exclusive zone and that are serviced by the second carriage.

5. The material handling system of claim 1 , wherein:

the first vertical portion is coextensive with a first exclusive zone and spaced apart from the second vertical portion that is coextensive with a second exclusive zone; and

the processor subsystem selectively positions the first carriage within the first exclusive zone and selectively positions the second carriage within the second exclusive zone to prevent colliding.

6. A vertical lift comprising:

a vertical support structure positionable proximate to a storage rack;

vertically aligned first carriage and second carriage received for vertical movement along the vertical support structure, each one of the first carriage and the second carriage independently positionable on the vertical support structure respectively in a first vertical portion and a second vertical portion of the vertical support structure, wherein at least a portion of the first vertical portion and the second vertical portion of the vertical support structure overlap;

a first vertical drive system coupled to the first carriage to position the first carriage to pick up and to deposit articles at selected levels within the first vertical portion of the vertical support structure that correspond to levels of a storage rack, the levels having a plurality of storage locations accessible from an adjacent aisle that are serviced by one or more shuttle vehicles;

a second vertical drive system coupled to the second carriage to position the second carriage to pick up and to deposit articles at selected levels within the second vertical portion of the vertical support structure that correspond to levels of the storage rack, the levels having a plurality of storage locations accessible from an adjacent aisle that are serviced by one or more shuttle vehicles; and

a processor subsystem in communication with the first vertical drive system and the second vertical drive system to:

selectively position the first carriage and the second carriage at respective selective levels along the vertical support structure to avoid collision between the first carriage and the second carriage; and

activate the first carriage to pick up and to deposit articles at a selected level and concurrently position the second carriage out of a path of the first carriage to avoid collision between the first carriage and the second carriage.

7. The vertical lift of claim 6 , wherein:

the first vertical portion comprises an overlapping zone and a first exclusive zone above the overlapping zone; and

the second vertical portion comprises the overlapping zone and a second exclusive zone below the overlapping zone.

8. The vertical lift of claim 7 , wherein the first carriage and the second carriage are positionable to service at least one in-feed conveyor and at least one out-feed conveyor that are adjacent to a level of the overlapping zone.

9. The vertical lift of claim 7 , wherein:

the first carriage is positionable to service at least one in-feed conveyor and at least one out-feed conveyor that are adjacent to a level of the first exclusive zone; and

the second carriage is positionable to service at least one in-feed conveyor and at least one out-feed conveyor that are adjacent to a level of the second exclusive zone.

10. The vertical lift of claim 6 , wherein:

the first vertical portion is coextensive with a first exclusive zone and spaced apart from the second vertical portion that is coextensive with a second exclusive zone; and

the processor subsystem selectively positions the first carriage within the first exclusive zone and selectively positions the second carriage within the second exclusive zone to prevent colliding.

11. A method comprising:

conveying an article on an in-feed conveyor to a storage rack having more than one vertically-spaced level, each level having a plurality of storage locations accessible from an adjacent aisle;

receiving a selected storage location for the article;

selecting a first carriage of a vertical lift to receive the product from the in-feed conveyor based at least in part on a corresponding level of the storage rack associated with the selected storage location, the vertical lift having a vertical support structure positioned proximate to the storage rack, the first carriage vertically aligned with a second carriage of the vertical lift and independently positionable along a respective first vertical portion and a second vertical portion of the vertical support structure, wherein at least a portion of the first vertical portion and the second vertical portion of the vertical support structure overlap;

activating a first vertical drive system to position the first carriage at the in-feed conveyor;

receiving the article on the first carriage;

activating the first vertical drive system to position the first carriage at the corresponding level to deposit the article for put away by a shuttle vehicle that is servicing the adjacent aisle; and

activating a second vertical drive system to position the second carriage to avoid any collision with the first carriage during movement to receive and deposit the article, such that the first carriage is activated to receive and to deposit articles at a selected level and the second carriage is concurrently positioned out of a path of the first carriage to avoid collision between the first carriage and the second carriage.

12. The method of claim 11 , further comprising:

receiving a command to remove the article from the selected storage location;

selecting the first carriage to receive the article at the corresponding level and to deposit the article at an out-feed conveyor; and

activating the corresponding vertical drive systems to transfer the article on the first carriage and concurrently positioning the second carriage out of a path of the first carriage.