Unidimensional puzzle-based storage systems

Purpose A paradigm for Puzzle-Based Storage Systems (PBS) is that all grid cells have the capacity to move loads horizontally and vertically. This research challenges this paradigm by considering unidimensional PBS (UPBS), where some grid cells are limited to either horizontal or vertical movements. UPBS simultaneously reduce the investment cost and operational complexity of PBS, at the expense of a potentially lower system throughput. Design/methodology/approach A linear program (LP) formulation is presented to determine the optimal retrieval path for a load using a single escort (i.e. an open cell in the grid that allows load movement) in a UPBS. The LP is solved recursively to understand the tradeoffs of unidimensional designs for a 4 × 4 system. Formulations to solve the single-load multi-escort problem are also proposed. Lastly, an existing decentralized control PBS algorithm was used to develop managerial insights for designing UPBS, considering the simultaneous retrieval of multiple loads using multiple escorts and input/output points. Findings It is concluded that UPBS with three unidimensional cells would reduce the PBS cost by 1.8 times the capital cost of a bidimensional cell, at the expense of an 8.34% average reduction in throughput. It is argued that multi-escort UPBS designs should be similar to the ones empirically produced for single-escort UPBS. Lastly, it is concluded that UPBS may provide a favorable capital investment cost-to-throughput tradeoff. Originality/value This study is a pioneer in considering UPBS. The empirical evidence of a favorable system cost-to-throughput ratio of UPBS improves the business case of implementing PBS in practice.