Sequencing unit load retrieval requests has been studied extensively in literature for conventional single-deep automated warehousing systems. A proper sequence can greatly reduce the makespan when carrying out a group of such requests. Although the sequencing problem is NP-hard some very good...

Puzzle-based storage systems (PBSs) can achieve very high utilization of expensive and scarce storage space coupled with fully automated storage and retrieval of unit loads. A PBS system with one empty cell is comparable to the well-known 15-puzzle, in which 15 tiles slide in a 4×4 grid. This...