SKU arrangement on a unidirectional picking line

Abstract

An order picking system consisting of independent unidirectional picking lines has been investigated in this study. A picking line forms a type of unidirectional carousel as multiple pickers walk in a clockwise direction around a conveyor belt running down the centre of the picking line. There are three decision tiers in this order picking system, namely the assignment of stock keeping units (SKUs) to different waves, the arrangement of SKUs into locations on a picking line for a wave of picking and the sequencing of orders. Each tier has an objective to minimise the total travel distance of pickers. The focus of this paper is on the arrangement of SKUs on a picking line for a wave of picking. An exact mathematical formulation is introduced which is not solvable to optimality for large real-life instances. Two heuristics known to be optimal for certain carousel systems as well as two further heuristics using SKU correlations are therefore tested. The heuristic approaches are compared against lower bounds generated by relaxing the exact formulation and a set of random solutions. Known algorithms for carousel systems are not optimal in this carousel system and all heuristic approaches perform approximately equally well. It is shown that the gains from addressing the order sequencing decision tier outweighs that of the SKU arrangement decision tier. Moreover, the complexity of addressing the entire system of decision can be reduced by arranging SKUs with a simple heuristic having a negligible impact on solution quality.

Product Variety Management: A Proposal of Metrics and Indicators for the Cosmetic Industry

“…SKU is the identity number of a product through which it is possible to manage the maintenance of the inventory (Matthews et al, 2018). It was created to facilitate and to give agility to the management of the warehouse facility (Hessler & Schwindt, 2017).…”

Route overlap metrics to batch orders

“…An empty carton is registered with the VRS before an order starts. When the carton is full or the order is completed, the cartons are moved to further processing areas via the conveyor belt [21,22].…”

“…Bidirectional movement, as it is frequently implemented in industry for carousel systems, cannot be used in the unidirectional picking line because the minimum span between orders may overlap and thus increase congestion. Furthermore, known optimal picking strategies for bidirectional picking lines are not optimal in the unidirectional case [20,21].…”

A puzzle‐based material handling system for order picking

“…Authors refer to this as dynamic slotting. There are a limited number of studies that evaluate such a system design (Yu and de Koster, 2010; Kim and Smith, 2012; Matthews and Visagie, 2019). The designs in these studies are limited by the reslotting constraints imposed by the technology on hand.…”