  Recently, many enterprises are facing the difficulties brought out by the
limitation of warehouse land and the increase of loan cost. As a promising
approach to improve space utilization rate, puzzle-based storage systems
(PBSSs) are drawing more attention from logistics researchers. In previous
research about PBSS, concentration has been paid to single target item
problems. However, there are no consensus algorithms to solve load retrievals
route programming in PBSSs with multiple target items. In this paper, a
heuristic algorithm is proposed to solve load retrievals route programming in
PBSSs with multiple target items, multiple escorts and multiple IOs. In this
paper, new concepts about the proposed algorithm are defined, including target
IOs, target position of escorts, number of escorts required, et al. Then, the
decision procedures are designed according to these concepts. Based on Markov
decision process, the proposed algorithm makes the decision of the next action
by analyzing the current status, until all the target items arrive at the IOs.
The case study results have shown the effectiveness and efficiency of the
proposed heuristic algorithm.
