Warehouse Zoning & Bucket Brigades

1. Warehouse Zoning &Bucket Brigades (Chpt. 9 in Bartholdi & Hackman; also see http://www.isye.gatech.edu/~jjb/bucket-brigades.html)

2. The two main concepts of zoning in contemporary warehousing Warehouse zoning: The physical and/or logical segmentation of the warehouse / picking area, through • the employment of different storage modes and practices due to the product differentiation w.r.t. • dimensions, • physical characteristics • storage and material handling requirements • throughput, • etc. • the parallelization of the order-picking activity.

3. To packing and shipping Z1 Z2 Z3 Z4 Z5 Order Zone-based order picking Progressive Zoning / Order assembly Parallel/Simultaneous Zoning (typically organized in pick-waves with downstream sortation) To sorting and consolidation Z1 Z2 Z3 Z4 Z5 Order (Batch)

4. The problem and the problems of establishing effective logical zones in Warehouse operations • The problem: Try to achieve maximum utilization of the picking resources, by distributing “equally” the total (picking) workload among the defined zones. • The problems: • The warehouse picking environment usually is a very dynamic environment; workload profiles are constantly changing. • Existing zoning systems seek to balance the average workloads across zones, based on some hypothetical order work-content and worker behavioral models. • Furthermore, constant zone redefinition requires a lot of effort from, both, the warehouse management (who must keep track of all the workload changes and re-establish the zones) and the warehouse pickers (who must adjust to the new policies). • The results: Very limited scientific literature.

5. Bucket Brigades( c.f. Bartholdi & Hackman, Chpt. 10) • A dynamic self-balancing scheme for progressive zoning. • The three main requirements of bucket brigades: • Carry work forward, from station to station, until someone takes over your work. • If a worker catches up to his successor, he remains idle until the station is available (i.e., no overpassing is allowed) • Workers are sequenced from slowest to fastest.

6. The self-balancing property of bucket brigades • Theorem: Letting v_i denote the working rate of the i-th worker, • the line operation under the three main requirements of bucket • brigades, converges to a balanced partition of the effort, wherein • the fraction of work performed by the i-th worker is equal to • v_i / _{j=1}^n v_j • and the line production rate is equal to • _{j=1}^n v_j • items per unit time.