Abstract

This paper develops new solution procedures for the order picker routing problem in U-shaped order picking zones with a movable depot, which has so far only been solved using simple heuristics. The paper presents the first exact solution approach, based on combinatorial Benders decomposition, as well as a heuristic approach based on dynamic programming that extends the idea of the venerable sweep algorithm. In a computational study, we demonstrate that the exact approach can solve small instances well, while the heuristic dynamic programming approach is fast and exhibits an average optimality gap close to zero in all test instances. Moreover, we investigate the influence of various storage assignment policies from the literature and compare them to a newly derived policy that is shown to be advantageous under certain circumstances. Secondly, we investigate the effects of having a movable depot compared to a fixed one and the influence of the effort to move the depot.

Highlights

  • The management of warehouse operations has received ample attention over many years

  • This paper addresses two out of the discussed four planning problems, contributing new insights in this research field, namely developing a new heuristic and an exact algorithm based on combinatorial Benders decomposition for the pickerrouting problem within the U-zone and proposing a new radial storage assignment method for this special layout

  • We show that the problem is NP-hard and develop the first exact solution procedure, which is based on combinatorial Benders decomposition

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Summary

Introduction

The management of warehouse operations has received ample attention over many years. Especially order picking, which is commonly described as the retrieval of products from storage locations to fulfill customer orders, is on the top of many research agendas (Van Gils et al 2018). Glock and Grosse (2012), for example, studied order picking in a U-shaped zone and developed procedures for assigning products to shelf locations, for finding a location for the depot of the order picker, and for routing the order picker through the U-zone. Diefenbach and Glock (2019) studied a U-shaped warehouse and optimized the layout and item assignment for single command picking with regard to two different objectives, namely pick efficiency and ergonomics. They did, not study the routing problem since it is not relevant for single command picking. We develop the first exact solution procedure for the picker routing problem in U-shaped order picking zones, namely an algorithm based on combinatorial Benders decomposition.

Literature review
Problem description
Formal description of the picker routing problem
Computational complexity
Algorithms
Logic‐based Benders decomposition for the picker routing problem
Master problem
Slave problem
Combinatorial cuts
Heuristic solution approaches
Sweep algorithm
Heuristic dynamic programming algorithm
Generating instances for the computational tests
Computational performance
Effects of having a movable depot
Effects of storage assignment policies
Random assignment
Horizontal assignment
Vertical assignment
Radial assignment
Findings
Conclusion

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