Motion planning of two stacker cranes in a large-scale automated storage/retrieval system

Abstract

We propose a method for reducing the computational time of motion planning for stacker cranes. Most automated storage/retrieval systems are only equipped with one stacker crane. However, this is logistically challenging, and higher work efficiency in warehouses, such as those using two stacker cranes, is required. In this paper, a warehouse with two stacker cranes working simultaneously is proposed. Unlike warehouses with only one crane, trajectory planning in those with two cranes is very difficult. Since there are two cranes working together, a proper trajectory must be considered to avoid collision. As transport works in automated storage/retrieval systems are occurring randomly, motion planning cannot be conducted in advance. Planning an appropriate trajectory within a restricted duration would be a difficult task. As a solution, we propose a “free-step” and a method to choose trajectories that are more likely to avoid collision. We thereby address the current problem of motion planning requiring extensive calculation time.