Cost-optimal deployment of autonomous mobile lockers co-operating with couriers for simultaneous pickup and delivery operations

Abstract

This work is an extension of a study by Li et al. (2021) in which a two-echelon network consisting of multiple depots and a fleet of Autonomous Mobile Lockers (AMLs) co-operating with couriers was examined to address the simultaneous pickup and delivery problem. This work considers the same problem but allows couriers and robots to traverse open routes. Most importantly, couriers can perform multiple missions, allowing them to restart a new mission from any stop. In order to formulate this problem, a mixed-integer linear programming (MILP) model was introduced with the aim of minimizing the total cost. Since the MILP model is not able to solve large-scale problems, an Adaptive Backtracking-Simulated Annealing metaheuristic (ABSM) algorithm was developed whose efficiency was analysed using numerical experimentation. The results show that the ABSM algorithm introduced is able to provide quality solutions within a reasonable amount of time. Also, the proposed algorithm was compared with three variants of the simultaneous pickup and delivery problem and the amount of savings was calculated. Finally, the significant problem parameters were identified and their impact on the value of the objective function was investigated. The results show that significant savings can be achieved when couriers are able to perform multiple open routes in a cooperative system of AMLs and couriers.