Efficient order processing in an inverse order picking system

An inverse order picking system inverts the basic logic of traditional picker-to-parts systems where pickers successively visit all shelves storing requested stock keeping units (SKUs). Instead, the picker successively moves bins each containing a particular SKU along a line of multiple order bins and puts items into all bins that require the current SKU. In this setting, we aim at a synchronization between the batches of picking orders concurrently assembled and the sequence of SKUs moved along the line, such that the number of line passings to be accomplished by the picker is minimized. We formalize the resulting optimization problem, prove computational complexity, and derive suited solution procedures. In our computational study, we also address important managerial aspects, such as the sizing of the picking area that restricts the number of picking orders concurrently processed.