Order Picking

Order Picking is the warehouse operation of retrieving SKUs from their storage locations (shelf, pallet, bin) to fulfil customer orders, typically performed by walking pickers. From an OR viewpoint it contains three sub-problems: (1) **single-order routing** — deciding the aisle sequence and routing algorithm for a single pick list; classical heuristics are S-shape, return, midpoint, largest-gap and combined, compared by Petersen (1997); exact optimisation uses a TSP / Steiner-tree formulation for small SKU counts. (2) **batching** — combining multiple orders into one pick tour; uses clustering plus TSP, savings algorithm or column generation. (3) **zone picking** — splitting the warehouse into zones with one picker per zone and merging at a sort station. The canonical survey by de Koster, Le-Duc and Roodbergen (2007) reports walking as 50-70% of internal warehouse labour cost. Order Picking must be considered jointly with Slot Assignment; together they can cut total pick time by 25-40%.