Escort analysis in puzzle-based storage systems

Puzzle-Based Storage system (PBS) is an innovative type of high-density Automated Storage/Retrieval System (AS/RS), which is made up of massive adjacent square cells (moveable shelves) arranged in a rectangular grid to allow stored unit-loads to be accessible individually. Previous research mainly focused on reducing retrieval time, designing retrieval algorithms, and improving retrieval performance. Since the lack of research on the impact of the number of unit-load moves from the perspective of escort distribution, this study proposes three escort distribution strategies when retrieving the unit-load in the PBS. Furthermore, the research analyzes the relationship between the number of escorts and the density and conducts simulation experiments in PBS systems of different scales as well. Simulation results show that the increase in the number of escorts would no longer affect the number of movements when the PBS density reached 40%-50%. In summary, the retrieve unit-loads require the minimum number of movements in diagonal distribution, while random distribution is superior to the arrangements in the first line.