A literature survey on
planning and control of
warehousing systems
by JEROEN P. van den BERG
指導老師：林燦煌 博士
報告者：梁士明
2005/4/11
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來自客戶的要求
•Wal-Mart計劃投入30億美
元積極引進RFID，期望這項
新技術能幫助降低控管成本
並提升庫存商品的調度彈性。
•Wal-Mart目前要求前一百
大供應商在2005年的最後期
限前採用RFID，並希望其他
次要廠商也能在2006年底之
前完成RFID的配套措施
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Why RFID ?
Benefit
Revenue(US$)
Saving(process)
6.7 Billion
Out-of-stock
600 M
Shrink
575 M
theft, vendor fraud and admin. error
Tracking
300 M
Product visibility
180 M
8.355 Billion
合計
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Planning and control
• Planning – intermediate term decision (1
or multiple months)
– Inventory management, storage location
assignment
• Control – short term decision (hours or
day)
– Routing , sequencing, scheduling, orderbatching
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大綱
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Introduction
Planning of warehouse operations
Control of warehousing operations
conclusions
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Introduction
• The increasingly busy warehouse
• Warehousing
• Warehouse management
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The increasingly busy
warehouse
• In 1970s, management interest shifted
from productivity to inventory reduction
and introduction of IT made this
possible
– MRP-II(manufacturing resources planning)
– JIT
Low volumes
More frequently
Shorter response time
Significantly wider variety SKU
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The increasingly busy
warehouse
Warehouse managers are forced to
• Minimize product damage
• Establish short and reliable transaction
• Improve order-picking accuracy
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The increasingly busy
warehouse
Current trends – SCM and ECR
• Demend-driven or driven by the sales
downward in sc
Require close cooperation and immediate
feedback of sales data
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Warehousing
Involves all movement of goods in WH and DC
• Receiving
• Storage
• Order-picking
• Accumulation
• Sorting
• Shipping
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Warehousing
Order picking
• Single order-picking
• Batch picking – order sorted and
accumulated
– Sort-while-pick : sort during picking
– Pick-and-sort : sorted afterwards
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Warehousing
Warehousing systems
• Picker-to-product (manual)
• Product-to-picker(AS/RS, carousel)
• Picker-less(robot)
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Warehouse management
Hierarchy of management decisions
• Strategic decisions – long term,policy
– Stochastic model or simulation based on estimates
• Tactical decisions – schedule material and
labor
– Based on historical data to find average
performance
• Operational decisions – short term
– Based on actual data to find high-quality
performance
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Planning of warehouse
operations
• Distribution of products among
warehousing systems
• Clustering of correlated prosucts
• Balancing of workload within a
warehousing system
• Assignment of products to storage
locations
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Distribution of products
among warehousing systems
Warehouse system equipped base on
• Size, weight, shape, perishability, volume,
demand rate, pick size, delivery quantity,
type of storage module
• Forward area(order-picking) and reserve
area(bulk storage) are usually seperated
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Distribution of products
among warehousing systems
Bozer[11] treats problem of spliting a pallet
rack into an upper reserve area and a lower
forward area
• Chebyshev travel time is assumed and a fixed
pick-life for all unit-loads in forward area
• When a separate reserve area is justified
• Case with variable unit-load size and a remote
reserve area
• Derive the break-even value for the pick life
of a unit-load to decide which product to
consider for the forward area
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Distribution of products
among warehousing systems
Hackman and Rosenblatt[12] present a model where
order-picking from the reserve area is possible
• Assume 1 replenishment trip suffices to replenish a
product, q’ty is irrespective
• Which porducts should be picked from forward area
and how much space for these products
• Minimize total cost of order-picking and replenishing
• Derive a expressions for optimal products q’ty as a
function of available storage space
• Present a knapsack-based heuristic that assigns these
q’ty to the forward area in sequence of decreasing
cost saving until full
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Distribution of products
among warehousing systems
Frazelle et al. incorporate the heuristic into a
framework for determining the optimal size of
forward area
• Costs for order-picking in forward area and
for replenishment are related to size of
forward area
• Minimize activity in forward area -> minimize
congestion at the same time
• Project a 20% saving on labor cost by resizing
forward area down to 32% of original size and
by re-allocating products amongforward and
reserve area
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Distribution of products
among warehousing systems
Van den Berg et al.[13] reserve-picking is
possible in WH with busy and idle periods
•Replenish during idle period
•Increase throughput during busy period
•Reduce congestion and accidents
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Clustering of correlated
prosucts
Correlated products - ordered
together(same supplier, color , size)
stored close to each otherin WH
(correlated storage)
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Clustering of correlated
prosucts
Frazelle and Sharp[14] present a simple
rule for identifying correlated products
from a given order set
• A Miniload AS/RS is simulated and 3040% reduction in the number of
retrieval trips is reported
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Clustering of correlated
prosucts
Lee[15] presents a clustering procedure
for an order-picking operation with manboard S/R machines
• 1st, create clusters of correlated
products
• 2nd,provide a sequence of the clusters
and the products in the clusters
according to increasing COI(Cube-perOrder Index, storage volume devided by
the turnover rate of a product)
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Clustering of correlated
prosucts
Rosenwein[16] formulates clustering
problem as a p-median problem
• Cluster median – product has highest
correlation with other products in its
cluster
• p-median – find p clusters with highest
correlation with the cluster medians
• This problem can be solved by branchand-bound algorithm within 1
minute(typical problem)
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Clustering of correlated
prosucts
Van Oudheusden et al.[8] present a WH
operation with man-aboard S/R machines
• Corralted storage is introduced
• Clusters of 2 correlated products are to
be assigned to opposite storage location
so that can be picked in a single stop
• A Weighted Matching Problem
• Simulation shows 46% reduction of
travel time
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Clustering of correlated
prosucts
Van Oudheusden and Zhu[17] same
problem as above with a limited number
of recurrent orders – contain the same
lines that are requested on a regular
basis
• Useful where there is little overlap
among the orders
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Balancing of workload within a
warehousing system
• Oreder-picker are dedicated to zone to
reduce congestion and travel time
• Throughput may be increased by
distributing products among the zones to
balance the mean and peak workload
• Same in an AS/RS system
• No publication awared
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Assignment of products to
storage locations
Storage Location Assignment
Problem(SLAP) - assignment of products
to storage location
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Assignment of products
to storage locations
Hausman et al.[3] presents 3 assignment
policies
• Randomized storage – stored anywhere
• Class-based storage – reserve a region
based on demand
• Dedicated storage – location only used
for specific products
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Unit-load retrieval
systems
• Hardy et al.[18] cross-product of 2
series is minimized if 1 series is nonincreasing and the other is nondecreasing
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Control of warehousing
operations
• Batching of orders
• Routing and sequencing
• Dwell point positioning
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Conclusion
• Few papers present algorithms which
provide optimal solutions
– Need more new models : save more than
optimizing existing one
• Travel time is not the only objective
– Orders often have to meet deadlines
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Conclusion - suggestion
• Flexibilization of labor is important
– Shifted between activityies
– Hire staff from agency temporary
Minimize cost require effective capacity
planning procedures for various activities
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Question & Discussion