L12 Order picking - Lunds tekniska högskola

MTTN25 2011‐09‐21

Warehousing and Materials Handling 1

LUNDS UNIVERSITETLUNDS UNIVERSITET

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L11 – Order-pickingMTTN25 – Warehousing and Materials Handling

Joakim KembroEngineering Logistics

Lund University2010-09-21


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Warehousing and Materials Handling

Receiving StoragePut-away Pick Pack, Ship

EquipmentRacks & ShelvesHandling & TransportationAutomationMobile picking

Activity ProfilingMeasurement &Statistical analysis of Warehouse activity / Data Mining

OptimizationmodelsPick-pathsInclusion of SKU in FPALane depth & slotting

LayoutLocation of receiving & shippingAisle configuration,Stack heightForward Pick Area

BenchmarkingPerformancemeasurement

ISIT/WMSSupport the operation withspace allocation, routeplanning, consolidatedpicking and statistics

Labor ManagementSchedulingFT vs. TempsSafety regulationsUnion rules

Tools &Techniques

Processes

Resources

L11

L13

L15L11


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Learning objectives

• Learn what order picking methods that are available• Understand some basic picking ergonomics• Understand advantages and disadvantages of different order

picking methods• Understand the benefits of pick-path optimization and how it is

done


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Content

• Order-picking

• Ergonomics and street-smart

• Picking methods

• Pick-path optimization

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Today’s focus: Order-picking

• Order-picking intensive warehouses:– Amazon.com– Adlibris.com– CDON.com– ICA (fruit & vegetables)– Elektroskandia (e.g. Cylinda)

Receiving StoragePut-away Pick Pack, Ship


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Operating cost distribution in a typical warehouse (CapEx vs. OpEx)

Source: Frazelle, (2002) World-Class Warehousing and Material Handling, Figure 8-1, p.148

Order picking; 50%

Shipping; 15%

Receiving; 15%

Put‐away/ Storage; 20%


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A customer order is picked and packed in order to later ship it

Customer orderCustomer: Store AB

Item Quantity

Screw 3

Cord 5 m

Plug 50

Pick orderNo: A623-432

Pick Item Quantity Aisle Position Shelf1 Screw 3 12 5 B2 Cord 5 m 14 7 A

3 Plug 50 16 3 A


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We have three different types of picking in a warehouse

Receiving

Sorting

Unitizing

Shipping

Crossdock

Carton pick

Pallets

CartonsEach pick

Cartons

Eaches

Pallet reserve

Pallets

Pallets

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Order-picking activities and time?


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Order-picking activities and time

Activity % Order-picking time

Traveling 55%

Searching 15%

Extracting 10%

Paperwork and other activities 20%


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Pick with cart


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Picking small items

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Picking to belt with pick to light


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Pick to pallet


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Picking from the 2nd level


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Content

• Order-picking


• Picking methods


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Ergonomics: Placing the most frequently requested items on the best height

The Golden Zone


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Ergonomics: Pick from pallet2. Pick from side1. Elevated floor


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Warehouse street-smart


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Content

• Order-picking


• Picking methods



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Picking methods

Order picking methods ‐ retrieval

Employing humans Employing machines

Picker‐to‐parts Parts‐to‐picker Automated picking Picking robots


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Description of methods

• Basic order picking:– Operations with a small number of orders and high number of

picks per order• Batch picking / Multi-order picking:

– Operations with a large number of orders and low picks per order

• Zone picking:– Operations with high total numbers of SKUs, high total numbers

of orders, and low to moderate picks per order• Wave picking:

– Operations with high total number of SKUs and moderate/high picks per order

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Full orders / Zone picking

Order picking method

Full order picking Zone picking(Partial order picking)

Buffer

Zon B Zon A


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Basic order picking

• Product stored in fixed locations on shelves or pallet rack • One order at a time following a route up and down each aisle• Design of the picking flow should be such that the order

picker ends up fairly close to the original starting point• Picking document should have the picks sorted in the same

sequence as the picking flow• Work well in operations with a small total number of orders

and a high number of picks per order• Operations with low picks per order will find the travel time

excessive in this type of picking• Operations with large numbers of orders will experience

congestion from many pickers working in the same areas


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Batch picking / Multi-order picking

• Multiple orders are grouped into small batches• Order picker will pick all orders within the batch in one pass

using a consolidated pick list• Usually the picker will use a multi-tiered picking cart

maintaining a separate carton on the cart for each order. • Batch sizes usually run from 4 to 12 orders per batch

depending on the average picks per order in that specific operation.

• Batch picking systems may use extensive logic programmed to consolidate orders with the same items

• Batch picking can greatly reduce travel time by allowing the picker to make additional picks while in the same area


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Picking all the items for one order

Full order picking

Single order picking Batch picking

+

• Fast to pick one order

• Easy to keep track

• Less room for errors

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• Low efficiency (A lot of transport)

+

• High efficiency (Less transport)

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• More room for errors

• Need to keep track of progress

One order at a time

Several orders at a time

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Partial order picking (zone picking)

+• No congestion – Only one picker per zone• Picker learn zone

– Faster routing– Knowledge about details

-• Work with balancing zones• Unbalances always occur between pickers• Buffers between zones are needed• No traceability for finding errors


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Different forms of zone picking

Progressive assembly

A B C

An order passes through zones in a specified order

Downstream sortation

A B C

Sortation

Each zone work independent with its specific items on each order:•It’s fast to get an order through•Requires expensive sorting after the picking•No risk for starvation between zones

Wave picking

A B C

Sortation

Zones are synchronized so that pickers work in a wave:•It’s fast to get an order through•Can reduce the need for sortation•Zones have to wait for each other


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Zone picking in detail

• Picking area is broken up into pick zones (assembly lines)• Order pickers are assigned a specific zone, and only pick

items within that zone• Orders are moved from one zone to the next as the picking

from the previous zone is completed• Conveyor systems are used to move orders from zone to

zone• Important to balance the number of picks per zone to

maintain a consistent flow • Separate zones provide for specialization of picking

techniques (automated handling in one and manual handling in the next)


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Wave picking in detail

• Rather than orders moving from one zone to the next for picking, all zones are picked at the same time

• Items are later sorted and consolidated into individual orders/shipments

• Wave picking is the quickest method (shortest cycle time) for picking multi-item orders

• Wave picking may be used to isolate orders by specific carriers, routes, or zones

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Content

• Order-picking


• Picking methods



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Travel time to retrieve an order is a direct expense

• Largest component of labor in a typical distribution center• Travel time is waste (no value added)• Affects customer service (faster retrieval, better service)• Order picking for only 2–4 SKUs and a few locations:

– Sequence locations to be visited to minimize travel– Solved for each trip an order picker must make into the

warehouse– Unlike the fast-pick area, where the general path of travel is

common and known in advance– Pick-path optimization becomes very important


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The problem of pick-path optimization

• Visiting a given set of locations as quickly as possible: “Traveling Salesman Problem”

• TSP is difficult in several senses:– There is no known fast solution technique that works in general– Randomly-generated instances, even small ones, can be

surprisingly time-consuming to solve– Optimum, or even good solutions can be complex and hard to

describe• NP-hard problem• Solving by complete enumeration


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Traveling salesperson problem (TSP)

• A classic operations research problem• Applies to pick-path optimization• Usually last-mile to customer• Extended version referred to as the Vehicle Routing Problem

(VRP)

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Denoting the TSP

• G = (N,A)– N, set of nodes– A, set of arcs

• Each arc (i,j) in A is associated with:– cij, traveling cost per unit flow (symmetric)– xij, 1 if arc is traversed, otherwise 0


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Example: Pick-path optimization

cij 1 2 3 4

1 0 4 3 4

2 4 0 2 4

3 3 2 0 1

4 4 4 1 0

Distance matrix Network

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22

44

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Beehive

• Shortest path between the different locations• Groups of 2• 2 minutes• Prepare to give an answer


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Example: Short-haul transportation planning

cij 1 2 3 4

1 0 4 3 4

2 4 0 2 4

3 3 2 0 1

4 4 4 1 0

Distance matrix Network

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22

44

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Order-retrieval in a warehouse presents a special case of the TSP

• Travel is constrained by aisles and this special structure makes it possible to find optimal solutions quickly by computer

• Most WMSs do not support pick-path optimization:– Geometric layout of the warehouse (including distances between

all pairs of storage locations)– Time-consuming to gather– Problem of communicating the path to the picker– WMS tells the picker only the sequence of locations, not the

actual path to follow


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Short travel paths that are realizable by an order picker without a detailed warehouse map

• Find an efficient global path to visit all the storage locations of a warehouse

• Sort pick lines on a customer order by storage location so that they appear in the same sequence as the efficient global path

• Global path is efficient => – The sub-path induced on each customer order is likely to be

efficient


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Path outlines

• A good global path should:– Induce short sub-paths on the customer orders, – Help the picker visualize the next location and how to travel

there most directly• Three commonly found path outlines:

– Along a single aisle– Through static shelving is the so-called serpentine pick path– The branch-and-pick, which sequences only the aisles and not

the locations within an aisle• Store popular SKUs close to the path outline, so that they can

be reached with little or no detour• Store SKUs according to affinity


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Pick-path optimization

• Restrict the picker to revisit a previously-visited aisle• Each order-picker can be imagined to follow this rule:

– Pick all the required items from the current aisle and travel forward to the next aisle

• Two ways of traveling to the next aisle:– Travel all the way through the current aisle– Enter the aisle only as far as necessary to pick all required items

therein and then return to the same end of the aisle

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Learning objectives

• Learn what order picking methods that are available• Understand some basic picking ergonomics• Understand advantages and disadvantages of different order

picking methods• Understand the benefits of pick-path optimization and how it is

done


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Thank you for today!

Joakim KembroPhD Candidate

Department of Industrial Management and Logistics

Box 118, SE-221 00 LUND, SwedenVisiting address Ole Römers väg 1, Lund

Phone +46 46 222 33 27Fax +4 46 222 46 15

E-mail [email protected]

Documents

L12 Order picking - Lunds tekniska högskola