According to Koster, Tho, and Kees (2007),
order picking systems can be classified as picker-to-parts systems,
parts-to-picker systems, put systems,automated picking systems,
and picking robot systems. Pickerto-parts systems are systems
that order-pickers walk or drive along the aisles to pick items,
whereas parts-to-picker systems are vice versa.
Put systems are systems that consist of retrieval
and distribution processes. Automated picking and picking robot systems are systems that employ machines for order picking.