A hybrid algorithm for the input/output scheduling problem of multi-shuttle AS/RSs

This paper proposes a hybrid algorithm for the input/output scheduling problem of multi-shuttle automated storage and retrieval systems (AS/RSs). This problem is to find a minimum travel route of a multi-shuttle storage and retrieval (S/R) machine to process given storage and retrieval requests for a storage rack. The proposed algorithm is based on the exact algorithm previously proposed by the author. In the first stage of the algorithm, a tabu search is used to improve the solutions obtained while column and cut generation is applied to an LP relaxation of the problem. The tabu search solutions are utilized in the second stage as columns of a set-partitioning formulation of the problem, and it is solved by a general MILP solver. The effectiveness of the proposed algorithm is examined by numerical experiments.