Transcript Warehouse Zoning - Georgia Institute of Technology

Warehouse Zoning
&
Bucket Brigades
(Chpt. 9 in Bartholdi & Hackman;
also see
http://www.isye.gatech.edu/~jjb/bucket-brigades.html)
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.
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dimensions,
physical characteristics
storage and material handling requirements
throughput,
etc.
– the parallelization of the order-picking activity.
Zone-based order picking
Progressive Zoning / Order assembly
To packing and shipping
Z1
Z2
Z3
Z4
Z5
Order
Parallel/Simultaneous Zoning (typically organized in pick-waves with
downstream sortation)
To sorting and consolidation
Z1
Z2
Z3
Z4
Z5
Order (Batch)
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.
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.
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.