Contributions to exact algorithms for picker routing and packing problems
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Abstract
This thesis develops exact solution methods for several combinatorial optimization problems arising in warehouse logistics and packing operations. The primary focus is on picker routing problems in warehouses with scattered storage, where individual articles may be stored at multiple locations, requiring simultaneous decisions on item retrieval locations and routing. Building on dynamic programming-based state-space formulations, the thesis introduces new exact algorithms for the Single Picker Routing Problem with Scattered Storage (SPRP-SS) in both single-block and multi-block warehouse layouts. Contributions include the first exact solution method for the SPRP-SS under heuristic routing policies, two novel mixed-integer programming formulations with linear model size, and a branch-and-cut algorithm for multi-block warehouses. Furthermore, two new routing problems for zoned warehouses—the Multi-Zone Picker Routing Problem (MZPRP) and the Balanced Multi-Zone Picker Routing Problem (BMZPRP)—are introduced, together with efficient exact solution approaches. In addition, the thesis addresses the Skiving Stock Problem (SSP), a packing problem related to the cutting stock problem, by adapting the reflect+ algorithm and its underlying arc-flow formulation. The proposed methods significantly advance the exact optimization of warehouse routing and packing problems and provide effective tools for solving practically relevant large-scale instances.