The WCS can mitigate these problems with dynamic pick allocation and workload balancing. Let’s
assume an order requires four SKUs (A, B, C, and D), and all four SKUs are available in the three pick
modules (see diagram left). Now, let’s assume that module 2 is not available because of a conveyor
problem. If the WCS determines the pick location, it would bypass module 2 and pick everything
from modules 1 and 3. If the WMS determines the pick location, either the cartons recirculate and
congestion builds or everything grinds to a halt. In another example, let’s assume that SKU D is only
available in module 3 because the locations in modules 1 and 2 are waiting for replenishment. If the
WCS determines the pick location, it will select module 3, but if the WMS pre-determines the location
and it’s not module 3, then again the cartons will recirculate until the location is replenished.