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Chapter 9Chapter 9Storage & Warehouse SystemsStorage & Warehouse Systems

1. 1. Warehouse Layout ModelWarehouse Layout Model

3. 3. Automated Storage & Retrieval SystemAutomated Storage & Retrieval System

FACILITIES PLANNING & DESIGNAlberto Garcia-DiazJ. MacGregor Smith

2. 2. Storage EquipmentStorage Equipment

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Dedicated StorageA set of storage locations assigned to a specific product

Decision variablexjk = 1 or 0 for assigning or not assigning product j to location k

Measure of effectivenessMinimize total expected distance traveled

Dedicated & Random StorageDedicated & Random StorageSection 9.3Section 9.3

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Input DataInput Dataq = number of storage locationsn = number of productsm = number of input/output points (docks)Sj = number of storage locations required by

product jTj = number of trips in/out of storage for

product jpi = percentage of travel in/out of storage

to/from point idik = distance or time required to travel from

point i to location k

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Mathematical ModelMathematical Model

∑∑∑===

m

ijkiki

q

kST

n

j

x )d p(Minj

j

111

∑=

=≤n

jjk q,...,k,x

1

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∑=

==q

kjjk n,...,j,Sx

1

1

q,...,k;n,...,jfor,x jk 1110 ===

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5

fk = pi dik

i

m

=∑

1

Minj

n

=∑

1

TS

j

j

( k

q

=∑

1

fk xjk ) = j

n

=∑

1

TS

j

j

( f1 xj1 + f2 xj2 + … + fq xjq )

∑∑∑===

m

ijkiki

q

kST

n

j

x )d p(Minj

j

111

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(a) Relabel the products according to the decreasing order of their Tj / Sj values

(b) Find the values of fk (expected distance traveled between location k and docks)

(c) Assign the locations to products according to their f-values from lowest to highest

Solution ProcedureSolution Procedure

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Warehouse’s dimensions: 40 x 40 ftStorage Location: 10 x 10 ftOne receiving dock at the northeast corner of the layoutOne shipping dock at the midpoint of the west sideTwo products A and BProduct A: 100 pallets per week (TA=100)Product B: 80 pallets per week (TB=80)Product A requires 10 storage bays (SA=10)Product B requires 4 storage bays (SB=4)

1 2 3 4

5 6 7 8

9 10 11 12

13 14 15 16

p1 = 180/360=0.5

p2 = 180/360=0.5

ExampleExample 9.19.1

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1 2 3 4

5 6 7 8

9 10 11 12

13 14 15 16

p1 = 0.5

p2 = 0.5

30 30 30 30

30 30 30 30

35 35 35 35

45 45 45 45

TA=100SA=10TA/SA=10

TB=80SB=4TB/SB=20

Consider Consider Product BProduct B first first and and Product AProduct A second.second.

B B B B

A A A A

A A A A

A A

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STORAGE STORAGE SYSTEMSSYSTEMS

RACK STORAGERACK STORAGE

CAROUSELSCAROUSELS

AS/RS (Automated Storage Retrieval AS/RS (Automated Storage Retrieval

Systems)Systems)

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RACK STORAGE SYSTEMSRACK STORAGE SYSTEMS

One of the primary methods of material storage

Utilizes the vertical space in the warehouse

Highly cost efficient

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RACK TYPESRACK TYPES

Walk Through RacksPush Back RackVery Narrow Aisle RacksDrive-in RacksGravity Flow RacksMobile Racks

Double Deep RacksRollout Shelf RacksReel RacksCantilever RacksStacker SystemsWire Coil RacksSheet Storage Racks

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WALK THROUGH RACKSWALK THROUGH RACKS

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FEATURESFEATURES

Provides easy accessibility to the adjacent aisles

Pickers time is greatly reduced

Allows more lighting into aisles

Higher utilization of vertical space

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PUSH BACK RACKSPUSH BACK RACKS

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FEATURESFEATURES

Pallet loads are literally pushed back into the rack

When pallet is retrieved, the deeper pallet load automatically advance to the aisle

High density and high accessibility

Used to store large number of pallets for a long time and then remove and ship them as seasonal products

Used mostly in combination with drive-in racks

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VERY NARROW AISLE RACKSVERY NARROW AISLE RACKS

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FEATURESFEATURES

Permits aisle widths less than 5 feet

Provide significant floor space reduction

Used at heights of 40 feet to 50 feet

Provides 100% selective storage

Pallets are accessed with turret or side loader lift trucks

Sometimes racks are designed with top and bottom monorails

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DRIVEDRIVE--IN RACKSIN RACKS

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FEATURESFEATURES

Used for bulky and light weight parts

Parts are mainly in cartons

Fork lift is the material handling device used

Parts are typically stacked one over the other in large numbers

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GRAVITY FLOW RACKSGRAVITY FLOW RACKS

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FEATURESFEATURES

Used for parts in cartons

Parts are supported on rollers in the rack system

Material transfer is done with ease

Easy to move parts along the same row as less effort

is required due to the presence of rollers

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MOBILE RACKSMOBILE RACKS

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FEATURESFEATURES

High density storage systems

100% utilization of pallet positions

Number of rows of racks mounted on mobile bases

Storage carriages are driven by electric motors

Used mainly in cold or ultra-cold warehouses where aisle space is at a premium

Used when speed of product movement is not a major concern

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DOUBLE DEEP RACKSDOUBLE DEEP RACKS

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FEATURESFEATURES

It is like placing two rows of racks together

Uses a deep reach lift truck for storage and retrieval

Increases floor space usage to about 60% to 65%

Used for high throughput operations

Low initial cost

High productivity

Less equipment damage

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ROLLOUT SHELF RACKSROLLOUT SHELF RACKS

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FEATURESFEATURES

Specialized storage

Mainly for delicate and costly parts

Used for dies, measurement tools

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REEL RACKSREEL RACKS

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FEATURESFEATURES

Special type of storage

Mainly for cables and wires in reels

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CANTILEVER RACKSCANTILEVER RACKS

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FEATURESFEATURES

Used to store long pipes and wood

Parts are stored using the fork lifts

Highly economical

Can be used till heights of 22 feet

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STACKER SYSTEMSSTACKER SYSTEMS

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FEATURESFEATURES

Provided with an integral crane

Easy handling of heavy items

High storage and retrieval speeds

Eliminates fork lift usage

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WIRE COIL RACKSWIRE COIL RACKS

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FEATURESFEATURES

Used to store wire coils

Used to house rubber hoses and hose assemblies

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SHEET STORAGE RACKSSHEET STORAGE RACKS

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FEATURESFEATURES

Store material in the form of sheets

Can be used to store glass

Permits a height of 10 feet

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CAROUSELS STORAGECAROUSELS STORAGE

ADVANTAGES

High pick rates

Motorized, computer controlled and independent rotating aisles of shelving

Parts are carried to the picker rather than the picker going to the parts like in the case of racks

Mostly set up in pods of 2 or 3

Pick rates vary from 80-200 picks/person hour

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CAROUSELS STORAGECAROUSELS STORAGE

DISADVANTAGE

Adding more people cannot significantly increase pick rate

Only one picker can operate at a given time

Thus reduces the ability of the warehouse to respond to surges in demand

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TYPES OF CAROUSELS TYPES OF CAROUSELS STORAGESTORAGE

Horizontal Carousels

Vertical Carousels

Independent Rack Carousels

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HORIZONTAL CAROUSELHORIZONTAL CAROUSEL

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FEATURESFEATURES

It is a series of rotating bins of adjustable shelves driven on the top or bottom by a motor

Rotation takes place on an axis perpendicular to the floor at about 80 feet/minute

Horizontal lengths vary from 15 feet to 100 feet

Height varies from 6 feet to 25 feet

Prices start from $5000 and increases with the number of bins and weight capacity

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VERTICAL CAROUSELVERTICAL CAROUSEL

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FEATURESFEATURES

It is a horizontal carousel placed on its end and enclosed in sheet metal

Height ranges from 8 feet to 35 feet

They include excellent item protection and security

Only one shelf of items is exposed at a time

All items cannot be looked at, at the same time

Prices range form $10,000 onwards

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INDEPENDENT RACK CAROUSELS INDEPENDENT RACK CAROUSELS FEATURESFEATURES

They are multiple one level horizontal carousel stacked on top of one another

Order picker accesses several pick locations at any time

Each levels operate independently and have their own power and communication link

Hence they are very costly

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AUTOMATED STORAGE AND AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS)RETRIEVAL SYSTEMS (AS/RS)

Improved Space Utilization

75 % of rack space can be recovered

High saving in pickers time

Allows quick access to goods via a system of shelves operating on a shuttle mechanism

It brings the exact pick/store location to the operator

Increases retrieval productivity by more than 2.5 times

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AUTOMATED STORAGE AND AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS)RETRIEVAL SYSTEMS (AS/RS)

Access area of the system is ergonomically designed to present stored items at an ideal height for picking

High employee safety and improved throughput

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AUTOMATED STORAGE AND AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS)RETRIEVAL SYSTEMS (AS/RS)

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WAREHOUSE DESIGN STRATEGYWAREHOUSE DESIGN STRATEGY

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Automated Storage & Retrieval SystemAutomated Storage & Retrieval System

W

H

L

Unit LoadUnit Load: W x L x H

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• Bay: A vertical stack of unit loads from floor to ceiling

• Row: A series of bays located side by side • Aisles: Spaces between rows • The aisles are used for stacker cranes to

move up and down between rows• Each crane serves both sides of an aisle• Light loads of less than 2500 pounds

require a 6- inch clearance for rack supportand crane entry

• Heavier loads require 9 inches

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Bay

Crane

Aisle Unit

AisleRack

Length

Bay

Width

Rack

Bay Height

Crane

Clearance

W

HL

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• Racks may be 80-90 feet high• Served by computer-controlled stacker cranes carrying 3000-4000-pound loads• Can travel at speeds of 500 feet per minute in aisles that are only 6 inches wider than the cranes• Savings of as much as 20 percent of the inventory cost• Fully mechanized system requiring little labor to operate• Single operator can handle a warehouse with 1000’s of parts• Minimizes need of material handling equipment and material handling operations

Some facts Some facts ……

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1. Dimensions and weight of the load to be stored2. Number of units to be stored3. Throughput rate per hour4. Number of cranes needed5. Number of rows required6. Building height and load height7. Number of bays8. System length9. System width

Design ProcessDesign Process

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Number of cranes =iency)ur)x(effic(cycles/ho

hourperthroughput

Bays per row = number of units to be stored(number of rows)x(number of loads vertically stacked per bay)

Loads stacked per bay = height of storage building

(load height + clearance between stacks) - 1

System width = (aisle unit) x (number of cranes)

System length = (width of bay + clearance) x (bays/row)+ (crane clearance)

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• Unit load: 36”x48”x24” pallet having a weight of 1400 lb• 75 dual cycles per hour• Total storage is 18,000 unit loads• Height of the building is 80’• Clearances of 4.5’ from the ceiling and 6” from the floor for rack support• Clearance equal to 6” between stacks• Availability factor of 85% for cranes

ExampleExample

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1. Loads stacked per bay = [80 – (4.5 + 0.5)]/[2 + 0.5] = 30

2. Number of dual cranes = 75/(22 x 0.85) = 4.01 = 5

3. Number of rows = 10

4. Bays per row = 18,000/(10 x 30) = 60

5. Width = (aisle unit) x (cranes) = [3(4)+2](5) = 70 feet

6. Length = (3 + 0.5) x 60 + 25 = 235 feet

7. Height = 80 feet

SolutionSolution

W=3’

H=2’

L=4’