This paper introduces the Twin-Robot Pallet Assignment and Scheduling Problem (TRPASP) in which two robots operating on a rail must be scheduled to pick up and deliver a set of products. The objective is to minimise the makespan, defined as the time taken for the robots to transfer all products from their pickup locations to their delivery locations, and return to their starting positions. Pickup locations are known a priori, while delivery locations must be assigned to minimise the makespan. The robots must respect a safety distance to avoid collisions. The paper presents a mathematical model for the TRPASP before introducing four heuristic algorithms for solving the problem. Computational experiments demonstrate that the best results are returned by a parallel hybrid metaheuristic.

Original languageEnglish
Article number105956
JournalComputers and Operations Research
Early online date22 Jul 2022
Publication statusPublished - 30 Nov 2022


  • Genetic algorithms
  • Makespan
  • Metaheuristics
  • Palletising
  • Scheduling

ASJC Scopus subject areas

  • Computer Science(all)
  • Modelling and Simulation
  • Management Science and Operations Research


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