The Ins and Outs of Conveyor-Based Zone Picking

Conveyor-based zone picking can dramatically improve operational performance in certain situations. It works by separating an order into two or more distinct picking zones and having the conveyor control system determine what zones the order needs to visit. It is most often used with a shipping carton or tote, traveling on a conveyor system.

Here it is in action:

1) An order is assigned to a carton or a tote via a bar-coded label.
2) The intelligent control system figures out the zone routing required to fill all picks in the order.
3) The tote is routed either sequentially or randomly to each zone requiring picks.
4) When the tote arrives, it must be identified, either automatically or by a picker scan.
5) The picker makes the required picks and then “pushes off” the tote so that it can continue to the next zone with requirements.
6) When the last pick is completed in the last zone, and the order pushed off, the order goes directly to a pack area.

To get the maximum benefit from this sort of system, you need to pay attention to product slotting and order size. Conveyor-based zone picking works best with orders that have a large number of picks for every zone that the order visits. If large orders are not available, it may be possible to slot your product so that orders stay within a single zone—perhaps by keeping product families together or by grouping products by other common characteristics. This way, the pick density in each zone is maximized, and the overhead of handling the tote becomes justified. In both cases, tote handling is minimized relative to the order selection, and therefore the system is used efficiently.

If there are only a couple of picks in each zone, then the carton/tote scanning and walking to and from the locations become substantial portions of the pick process. For this reason, zone routing systems may not be the best choice for small-order environments or in facilities where there is a large assortment of SKUs leading to orders that are cut up into many zones, with only a couple of picks in each.

One way to counter the problem of smaller orders is to increase the density of picks within each zone by batching orders together. In the case of conveyor-based zone picking, this can be done by using a compartmentalized tote that can hold several orders together. The problem with having several compartments in one tote is that it may increase “put errors,” since you have to depend on the picker to select not only the right tote but also the right compartment on the tote.

A nonconveyor alternative to consider is a batch cart. Cart-based systems can sometimes be more efficient because they can substantially reduce the amount of walking. There are two ways to cut walking with a batch cart: 1) Put 10 or more orders together on a single cart, picking to order; 2) create a “superbatch” where all requirements for all orders get picked to a single “grocery” cart. In the second option, the picked items are broken into individual orders on the back end.

Sam Flanders is president of Durham, NH-based operations consultancy Warehouse Management Consultants. He can be reached at