US Patent 9020632 Storage, retrieval and sortation system

A material handling systems provides efficient storage, retrieval and sortation of articles, utilizing a plurality of carts capable of traveling under storage areas with a three dimensional warehouse system and on multiple levels. The carts may convey items from storage to a goods to operator user interface. The carts may function as decoupled sortation units capable of providing sortation at multiple mobile sortation locations, providing vertical sortation. Carts may include conveying surfaces, and sort articles from between carts. Carts may transport more than one article and a plurality of carts may transport a single article.