Handbook of Industrial Automationedited - Chapter 7 pdf

Material handling and storage systems planning anddesign are subsets of facilities planning and design.. Third, the arrangement of SPUs sets alarge-scale ¯ow pattern or nonpattern in som

Material handling and storage systems planning and

design are subsets of facilities planning and design

Material ¯ow has both internal and external e€ects

on a site There are in¯uences for the site plan and

the operations space plan Conversely, the material

handling system impacts the facility plans, as

illu-strated inFig 1

In the facilities design process the material

ment determines the ¯ow paths The material

move-ment origins and destinations are layout locations

The storage locations and steps are e€ects of the

opera-tions strategy and thus the organization structure A

lean manufacturing system may have material delivery

direct to point of use replenished daily and a pull

sys-tem cellular manufacturing process that produces to

order with a TAKT* time of 5 min Such a system

could have inventory turns of 300 per year A more

traditional system would have a receiving inspection

hold area, a raw material/purchased parts warehouse,

a single shift functional layout batch manufacturing

system, inspection and test with 90% yield, a separate

packing department, and a policy of one month's

®n-ished goods inventory The space plans for the tional system should be very di€erent from the leanapproach and so should the material handling and sto-rage plans and systems A ``pull '' system also indicatesunnecessary material in the system If it does not pull itshould not be there

tradi-Material handling determines the capacity of a ufacturing plant From the receiving dock to the ship-ping platform the material ¯ow routes are thecirculation system Flow restrictions can act as capa-city limiters The material handling and storage plandetermines handling and storage methods, unit loadsand containerization to support the operations andbusiness strategy

man-The product volume plotÐthe plot of tities of materials by product typically shows a nega-tive exponential distribution, the important few andthe trivial many Pareto distribution The plot can beoverlaid with the most suitable production mode asillustrated in the product volume (PV)/mode curve,Fig 2

volume/quan-We have suggested the following modes:

We ®nd these classi®cations more meaningful than

®xed location, job shop, functional, mass production

line, and process ¯ow

In the manufacture of discrete solid parts their

transportability is improved by placing them in

con-tainers This contained regular shape becomes the unit

load and the material handling method is matched to

the load As material ¯ow volumes increase, the

char-acteristics trend to those of continuous ¯ow, i.e., from

solid discrete parts to bulk (¯owable) solids, liquids,

and gases Solids are handled as pieces or contained

in baskets, cartons etc Ware [1] describes how solids

can also be conveyed by vibratory machines Liquids

and gases are always contained and they conform tothe shape of the container The container may also bethe channel of material transfer, such as a pipeline orduct, particularly for ¯owable bulk solids Bulk solidscan also be transported along pipes or ducts with theaid of a suspension agent, such as a gas or liquid

In just-in-time (JIT)/lean manufacturing the aim ofbatch sizes of one is to emulate continuous liquid

or gaseous molecular ¯ow characteristics to achievesimpli®cation

Designs for material handling in liquids, gases, andbulk solids are an integral part of the process.Examples are chemical and food processes In an oil

Figure 1 Material ¯ow patterns

re®nery the input of raw materials to shipment of

pro-ducts is often totally integrated

In process design it is always desirable to move up

the PV/mode curve Process eciency increases from

project mode to continuous ¯ow This economy was

achieved originally by increasing volumes and thus

increasing inventories More recently, economies of

operations with low volumes have been achieved by a

change of focus/paradigm through rapid added value

to materials yielding increased return on assets

employed The assumption had previously been made

that the economies came from volume only However,

material handling unit volumes and storage

require-ments have shrunk with the use of:

Batch sizes of one

Make to customer order

Mixed product less than full load shipments

Half machines

Lean operations

Material movement dominates the design of many

facilities Conversely, the layout design sets the

loca-tions and origins of each material move Movement

adds cost, time, and complexity to manufacturing

and distribution It adds no ultimate or realized

value until the ®nal moveÐdelivery to the customer

The priority therefore is to reduce material movement

The minimizing of material movement requires an

e€ective layout based on a sound manufacturing

strat-egy The anities and focus approaches which can

reduce both the amount and complexity of handling

are powerful tools They are described in Wrennall [2]

Layout a€ects material ¯ow in three ways First, thespace planning units (SPUs) de®nitions set a patternfor overall material ¯ows.Figure 1, given earlier, illus-trates how production mode impacts both the intensityand complexity of ¯ows Second, the arrangement ofSPUs in the layout can increase or decrease particularroute distances Third, the arrangement of SPUs sets alarge-scale ¯ow pattern (or nonpattern in some cases).Since layout design and material handling are inter-dependent, so is a discussion on the design of either

or both of them

1.2 MATERIAL FLOWANALYSISMaterial ¯ow analysis (MFA) examines the movement

of materials over time It helps develop anities for thelayout and evaluation of layout options, and is basic tothe design of material handling systems Unlike otherreasons for anities, material ¯ow is tangible and mea-surable The use of quantitative methods adds rigor tothe facility layout planning process After rigorousanalysis and simpli®cation, the remaining and neces-sary material moves are economical and timely.Ultimately, all assembly processes are materialhandling This discussion limits the handling of mate-rials to and from a site and from place to place withinthe site Material handling at the workplace and asso-ciated automation is discussed elsewhere

The objectives of material ¯ow analysis (MFA) are

to compute anities based on material ¯ow, evaluatelayout options, and assist handling system design Amacrolayout of 30 SPUs has 435 possible material ¯owroutes In addition, most facilities have many materi-als, processes, handling methods, and multiple move-ment paths with ¯ows in both directions Figure 3illustrates some of the possible material variety.Handling equipment, containers, route structures,and control methods all present additional variety.Therefore, analysis and the subsequent development

of handling systems can be complex and dicult.This chapter explains how to bring order and structure

to the process

The MFA steps, shown inFig 4are:

1 Classify materials

2 De®ne ¯ow unit

3 Determine data source

4 Extract data

5 Format and analyze

6 Calibrate ¯ows

7 Represent graphically

Figure 2 Product volume/mode curve

These seven steps provide an understanding of the

material ¯ows in the facility The calibrated ¯ows are

used to develop anity ratings These initial steps are

also the basis for subsequent evaluation of layout

options and material handling system design

Step 1 Classify Materials Most manufacturing and

warehouse operations have a large variety of products

and materials Situations with 20,000 or more distinct

items are not unusual To analyze ¯ow or design amaterial handling system around so many individualitems is not practical Classi®cation reduces materials

to a manageable number of items so that the classesthen become the basis for determining ¯ow rates, con-tainers, and handling equipment

The initial classi®cations stratify materials for mon handling methods and container design Weight,size, shape, ``stackability,'' and special features are

com-Figure 3 Material varieties

de®ning criteria Figure 5shows a classi®cation based

on handling characteristics for a four-drawer cabinet

In addition, similarities in product, process

sequence, and raw material are bases for grouping

items that move over the same routes

Step 2 Identify Flow Units Material ¯ow is measured

in units of material over a unit of time and the analyst

chooses appropriate units for both parameters The

time unit is usually a matter of convenience and

depends largely on data availability Typical examples

are cases per hour, tons per day, pallets per week

Selection of the material ¯ow unit is more

proble-matic Where only one type of material moves, the

selection is straightforward, for example, the bushel

for a grain mill But few facilities have only a single

material or material type A wide variety of size, shape,

weight, and other handling characteristics must be

con-sidered, as illustrated earlier in Fig 3 For example,

integrated circuits are tiny, delicate, expensive, and

highly sensitive to electrostatic discharge (ESD), but

the operations that use integrated circuits also use

large metal cabinets Between these extremes is a

wide range of diverse items to move

Various items of the same size may have di€erent

handling requirements and costs A resistor and an

integrated circuit (IC) are very close in size But

resis-tors are moved in bulk, in ordinary containers, and

without special precautions The individual IC is sitive to ESD It requires an enclosed, conductive andexpensive container It may have a special tube or bag

sen-to further protect it Humans may sen-touch it only if theywear a grounded wrist strap and a conductive smock.Individual items or materials are seldom handledseparately Most items are in boxes, tote boxes, car-tons, bundles, bales or other containers These contain-ers then are what need to be handled But layout designrequires a standard unit of ¯ow This is the equivalent

¯ow unit (EFU) which should have the following acteristics:

char-Applicable to all materials and routesEasily visualized by the users

Independent of the handling method

The equivalent ¯ow unit should account for weight,bulk, shape, fragility, value, special conditions andother factors:

Weight is a common unit for most materials and isusually available in a central database

Bulk, or density, relates weight and size Overalldimensions determine bulk density

Shape impacts handling diculty Compact regularshapes such as boxes stack and handle mosteasily Round and irregular shapes stack with

Figure 4 Material ¯ow analysis

diculty Long thin shapes (high aspect ratio)

are awkward to handle

Fragility refers to the sensitivity of objects to

damage Fragility in¯uences handling diculty

and expense; 100 lbs of sand and 100 lbs of

glass-ware are very di€erent handling tasks

Value for a wide range of objects and materials has

little in¯uence But high value or special security

items such as gemstones require protection from

theft, damage or loss

Special conditions that a€ect material handling

dif-®culty and expense are stickiness, temperature,slipperiness, hazard, and ESD sensitivity

As material moves through the production system, itsaspects change and the handling e€ort, as measured byequivalent ¯ow units, can change drastically Forexample:

Bulk cellulose acetate ¯ake may be received andplastic ®lm rolls or sheets may be shipped

Figure 5 Material classi®cation summary

Tree trunks may be received and newsprint shipped.

Bulk liquids and gases may be received but

pharma-ceutical intravenous packs or bottles of tablets

Wood pulp and naphtha are received, chemicals,

textiles, and plastics are shipped

What seems a minor change in the item sometimes

brings a dramatic change in the equivalent ¯ow units

Figure 6 is a schematic ¯ow diagram that illustrates

changes in ¯ow intensity as the material is processed

for a four-drawer cabinet

Figure 7is a river diagram illustrating material ¯ow

for all products in an entire plant The diagram shows

how ¯ow intensity increases after the material ispainted and decreases after the parts are assembled.Painted sheet metal parts are easily damaged and di-cult to handle Once assembled and packaged, the unitsbecome protected, compact, and stackable and their

¯ow in equivalent ¯ow units decreases dramaticallyfor the same quantity and weight

When a decision is made on an equivalent ¯ow unit,convenience and familiarity often take precedence overaccuracy The primary purpose of this analysis is torate ¯ow intensities into one of four categories Weuse the vowel letter rating system A, E, I, and O.Accuracy of the order of 20% is therefore sucient.For this level of accuracy, the following procedure isused:

Review potential data sources

Interview production and support personnel

Figure 6 Equivalent unit ¯ow analysis

Observe operations.

De®ne the equivalent ¯ow unit

Some examples of equivalent ¯ow units are pallets,

bales, paper rolls, tote-boxes, letters, tons of steel,

and computer cabinets

The analysis now requires factors to convert all

materials into the equivalent ¯ow unit Conversion

may come from experience, work measurement, or

benchmarking An example from a jet engine overhaul

facility is given inFig 8

The graph converts item size to equivalent ¯ow

units Pallets and pallet-size containers were the most

commonly moved items and the basis for most records

The equivalent pallet was, therefore, the most sensible

equivalent ¯ow unit The pallet container labeled ``PT''

is 1.0 equivalent ¯ow unit on the vertical scale Its

volume is 60 ft3 on the horizontal scale

In this system, volume is the basis for equivalent

¯ow unit conversion Several tote pans of di€erent

sizes are labeled ``2T,'' ``4T,'' ``8T,'' and ``8S.'' An

assembled jet engine has a volume of about 290 ft3

and an equivalent ¯ow unit value of 1.6 equivalent

pallets The relationship between volume and

equiva-lent ¯ow unit is logarithmic rather than linear, which is

not unusual Jet engines are 4.8 times the bulk of a

pallet load On dollies they require only a small tow

tractor or forklift to move The cost and e€ort is about

1.6 times that for moving a pallet load

Additional factors can a€ect the logarithmic volume

relationship This accounts for di€erences in density,

shape or other handling modi®ers

Work standards can be used as conversion factors.The time and cost of moving representative items arecalculated and compared, and become benchmarks forall other items in the facility, or the data might be thebasis for a graphical relationship similar to the oneillustrated previously in Fig 8

Step 3 Determine Data Source Almost every facility

is unique with respect to the material data source.Products, volumes, and mix vary; practices are diverse,

as are recording methods Accuracy may be good, pect, or demonstrably poor, and individuals who con-trol data sources may be co-operative or protective.This diversity necessitates extensive interviews withpeople who collect and compile the data A good selec-tion of data source often makes the di€erence between

sus-a dicult or sus-an esus-asy sus-ansus-alysis Here sus-are some possibledata sources:

Process chartsRouting sheetsMaterial requirements databaseRouting database

Direct observationHandling recordsWork samplingSchedule estimatesInformed opinions

When selecting the data source, the analyst must alsodecide on the range of included items All items should

be used if their number is small or when computerizedrecords make it feasible to do so When a few products

Figure 7 River diagram

represent the largest volumes and are representative of

others, data from the top 20±30% should be used

Where groups of products have similar processes

and ¯ows, a representative item might portray an

entire group When the product mix is very large and

diverse, random sampling may be appropriate Figure

9 illustrates data selection guidelines

Process charts map the sequence of processes

graph-ically; routing sheets often have much the same

infor-mation in text form With either source, each operation

must be examined to determine in which SPU thatoperation will occur This determines the route Fromthe product volume analysis or other information, theraw ¯ow is determined which is then converted toequivalent ¯ow units, as illustrated inFig 10

This procedure is used directly if there are only afew products and where processes and ¯ows are similarand a single item represents a larger product group.For large numbers of items, process charts with arandom sample are used

Figure 8 Equivalent ¯ow units

Figure 9 Data selection guidelines

Most or all of the necessary information may exist

in the databases of manufacturing requirements

plan-ning and other production and scheduling information

systems It may be necessary to change the data to a

format suitable for ¯ow analysis

Material handling records or direct observation are

good sources for data If material is moved by fork

truck, for example, and a central fork truck pool

keeps good records of pickups and deliveries, these

records contain the necessary information In direct

observation, the observer follows products through

various moves and operations In this way both

pro-cess and material ¯ow information are gathered

simul-taneously The from±to chart of Fig 11 documents

¯ows obtained by direct observation

Several sources may be necessary to capture all

¯ows For example, an MRP database may contain

¯ows for production items but not for scrap,

mainte-nance, trash, or empty containers These ancillary

items are often signi®cant and sometimes dominant,

particularly in high-tech industries

Step 4 Acquire the Data After a data source is

determined the data must be acquired

Computer-based data are accessed by information services

Other data sources may require considerable clerical

effort Direct observations or work-sampling derived

data may require weeks to collect and process

Step 5 Format and Analyze the Data Manual ods can suf®ce for the entire material ¯ow analysis.However, computer-aided analysis is necessary forfacilities with a wide product mix, process focus and

meth-a complex process sequence Spremeth-adsheet progrmeth-ams meth-aresuitable for most analyses Database programs aresometimes better than spreadsheets because of theirreporting and subtotaling capabilities

With computerized analysis, data can be entered asthe project progresses Initial data may come fromdownloaded information or manual collection andconsist of product information such as names andpart numbers and perhaps annual volume, weights,and routing The analyst should consider ancillaryuses for the database as well The database may assistlater in developing handling systems or determiningstorage areas It might also be part of a group technol-ogy (GT) study for cell design

Figure 12 is an example of a material ¯ow reportused for the layout of a mail processing facility Datacame from a series of schematic material ¯ow charts, inturn derived from process charts, SPU de®nitions and aproduct volume analysis, as shown earlier in Fig 2.Fields 1 and 2 of Fig 12 are SPU numbers which de®nethe ¯ow path for that entry Fields 3 and 4 are descrip-tors corresponding to the SPU numbers Field 5 is atype code; ®eld 6 is the equivalent ¯ow unit; ®eld 7 is thedaily volume in pieces per day All mail with the same

Figure 10 Equivalent ¯ow units development process

size, type, and class codes uses the same process and

follows the same route Field 8 is the number of

equiva-lent ¯ow units per day for each route and size These

subtotals are the basis for subsequent anity ratings,

stang, and for material-handling-system design

Other possible ®elds might contain information on

the time required per trip, distance for each route and

speed of the equipment From this the database

man-ager can derive the numbers and types of equipment

and containers required

Step 6 Calibrate Flows This step includes the lation of material ¯ow from each route origin to eachdestination It also includes conversion of calculated

calcu-¯ows to a step-function calibration for use in layoutplanning The calibration scale can be alphabetical ornumerical The vowel rating convention AEIO is usedhere The intensities of ¯ow distribution may indicatethe important few and trivial many The calibrationscan be used for relative capacity of material-handling-system selection

Figure 11 Material ¯ows from±to chart

For the calibration the ¯ow rates are ranked on a

bar chart, as shown inFig 13

The breakpoints are a matter of judgment and

should be made near natural breaks Experience from

a range of projects suggests that the following

propor-tions are a useful guideline:

A 5±10%

E 10±20%

I 20±40%

O 40±80%

Transport work Total material handling cost is

roughly proportional to the product of ¯ow intensity

and distance In physics force multiplied by distance

de®nes work For layout planning, material ¯ow

inten-sity I multiplied by distance D equals ``transport

work'' TW:

TW ˆ DI

In an ideal layout all SPUs with anities would be

adjacent Since an SPU occupies ®nite space, proximity

but not necessarily adjacency is possible Placing two

particular SPUs together forces other SPUs fartheraway The theoretical optimum relative locationsoccur with equal transport work on all routes wheretotal transport work is at the theoretical minimum.Transport work, then, is a metric for evaluating thelayout For evaluation, transport work is calculatedalong every path on a layout and the summationmade Layout options may be evaluated by comparingtheir total transport work

Transport work is useful in another way InFig 14distance is plotted on the horizontal axis and ¯owintensity on the vertical axis Each route on the layoutplots as a point As mentioned above, the ideal layoutwould have constant (or iso-) transport work, such acurve being a hyperbola Routes with low intensityhave long distances; those with high intensity, shortdistances The product of distance and intensity foreither is then equal

A ``good'' layout, from strictly a material ¯ow spective, is one which has most or all points close tothe same hyperbolic isotransport work curve Routeswhich are signi®cantly distant from the hyperbola indi-cate an anomaly in the layout

per-Figure 12 Material ¯ow report

Step 7 Graphical Representation Several types of

charts, plots, and diagrams present material ¯ow

infor-mation visually The visual representation assists the

layout designer during the creative portion of the

lay-out project It helps to evaluate laylay-out options and

design the material handling system

Material handling and facility layout are

inextric-ably intertwined Layout determines the distances

materials must be moved Handling methods may

a€ect the total handling and cost on any particular

route

Material ¯ow diagrams and isotransport work grams are used to visualize material ¯ow graphically.They show sequence, distance, intensity, or a combina-tion thereof They assist with evaluation and handling-system design There are at least eight common types

dia-of diagrams:

SchematicQuanti®ed schematicLocational

River

Figure 13 Material ¯ow calibration

Figure 14 Distance±intensity plots

Three-dimensional

Distance±intensity plot

Animated

Figure 15 is a schematic diagram The blocks represent

locations on the layout and the arrows are material

move routes In this example a single arrow represents

all materials But di€erent line styles or colors might

show di€erent materials, or separate diagrams might

represent di€erent material classes Schematic grams are most useful in the early stages of a projectwhen they help the analyst and others to document,visualize, and understand the material ¯ows

dia-Figure 16 is a quanti®ed schematic diagram Inaddition to routes it illustrates ¯ow intensity by thethickness of shaded paths The thicker the path, thehigher the ¯ow intensity The quanti®ed schematicmay derive from the schematic as the project pro-gresses and data become known

Figure 15 Schematic ¯ow diagram

The locational diagrams of Figs 17 and18

super-impose material ¯ows on a layout, showing the

addi-tional variable of distance The layout may be existing

or proposed Locational diagrams illustrate the e€ect

that layout has on ¯ow complexity and transport

work The width of the lines is proportional to ¯ow

intensity Colors or patterns can indicate either

inten-sity or material classes Alternatively, multiple lines

may be used to represent various intensities, as in

Fig 18 These examples show no sequence information

or the direction of ¯ow Location diagrams are

appro-priate for complex situations

The river diagram of Fig 19 presents sequence,

intensity, and distance It is suitable for simple ¯ow

situations with few routes and a ®xed sequence

The string diagram,Fig 20, traces the path of vidual products or items through the plant A separateline for each item illustrates complexity and total dis-tance Where ¯ow paths coincide, the lines are thicker.This diagram shows intensity and possibly sequence.Figure 21 is a locational diagram in three dimen-sions The river and string diagrams can also havethree dimensions when vertical movement is impor-tant

indi-Distance±intensity plots are shown onFigs 14and

27and explained in Step 6, Transport

Computer simulation and animation software sents ¯ow dynamically Arena, Simple‡‡, andWitness VR are popular packages Simulation is animportant tool in demonstrating and selling layouts

Figure 16 Quanti®ed schematic ¯ow diagram

and ¯ow patterns It can also assist in designing certain

types of handling systems, such as automatic guided

vehicles (AGVs)

Macrolevel ¯ow patterns The facility layout

affects sequence and characteristics of material ¯ow

Indeed, the ¯ow pattern dictates the shape or

arrange-ment within a facility.Figure 22 shows the basic ¯ow

patterns: straight-through ¯ow, L-shape, U-shape or

circular, and hybrids

With straight-through or linear ¯ow, material entersand exits at opposite ends of the site or building.Flow deviates little from the shortest straight linepath Material movement is progressive Receivingand shipping areas (entrances and exits) are physicallyseparate

Straight-through ¯ow is simple and encourageshigh material velocity Operations are typicallysequential This ¯ow pattern has been a hallmark of

Figure 17 Locational ¯ow diagram (shaded lines)

Figure 18 Locational ¯ow diagram (multiple lines) Figure 19 River diagram

mass production With this type of ¯ow, material

tracking and handling are relatively simple In fact,

Henry Ford and Charles Sorensen invented the

assembly line to solve a material ¯ow problem

Straight-through ¯ow can also be vertical movement

in a high or multistory building This ¯ow pattern

was used in some of the ®rst water-powered textilefactories in England

L-shape ¯ow has a 908 directional change Thispattern results from multiple material entry pointsalong the ¯ow path and a need for direct access It is

a ¯ow pattern sometimes used in paint shops

U-shape or circular ¯ow is an extension of the shape ¯ow The loop may be open or closed.Materials return to their starting vicinity Thesepatterns combine receiving and shipping docks withshared personnel and handling equipment.Conversely, one set of truck docks in a building cancreate a U or circular ¯ow, for example, morningreceiving and afternoon shipping patterns

L-The use of common receiving and shipping nel is not conducive to good security In pharmaceuti-cal manufacturing regulations may require strictseparation of receiving and shipping facilities.Incoming material handling, storage, and materialphysical characteristic di€erences may also require dif-ferent personnel skills from those required at shipping.Hybrids, such as X, Y, Z, or star, are combinations

person-or variations of the basic ¯ow patterns

Flow complexity Simple material ¯ow patternshave fewer routes, fewer intersections and shorter dis-tances River and locational diagrams show ¯ow com-plexity These can be used to evaluate the relativecomplexity inherent in various layouts

Figure 20 String diagram

Figure 21 Three-dimensional material ¯ow diagram

Figure 23a and 23b shows locational ¯ow diagrams

for two postal facility layouts A visual comparison

indicates that Fig 23b has a more complex ¯ow

pattern than Fig 23a The diagrams illustrate that

the ¯ow from SPU 27 to SPU 2 is the most intense

and yet has the longest distance This is veri®ed by a

comparison of total transport work: 5.323 million

equivalent ¯ow units/day shown in Fig 23a versus

8.097 million equivalent ¯ow units/day for Fig 23b

The option shown in Fig 23b is superior from a

mate-rial ¯ow perspective

1.3 MATERIAL-HANDLING-SYSTEMDESIGN

Optimum material handling requires a macro orplant-wide system design The system approach exam-ines all materials and all routes It ®ts and supportsthe ®rm's manufacturing strategy and considers manyoptions

In the absence of a comprehensive approach, tories usually default to a simple-direct system usingforklift trucks The system designs itself and is quite

fac-Figure 22 Macrolayout basic ¯ow patterns

convenient in that respect However, the convenience

for the designer becomes a high-cost system that

encourages large lots and high inventories It seldom

supports just-in-time and world-class manufacturing

strategies

The macrolevel handling plan speci®es the route,container and equipment for each move It then accu-mulates the total moves by equipment type and calcu-lates equipment requirements To prepare a handlingplan:

Figure 23 Transport work material ¯ow evaluation

(a)

(b)

1 Assemble ¯ow analysis output:

a Routes and intensities

b Material ¯ow diagrams

3 Calculate equipment requirements

4 Evaluate and select equipment

1.3.1 Containers

Materials in industrial and commercial facilities move

in three basic forms: singles, bulk, and contained

Singles are individual items handled and tracked as

such Bulk materials, liquids, and gases assume the

form or shape of their container Fine solids such as

¯owable powders are also bulk In containerized

hand-ling, one or more items are in or on a box, pallet,

board, tank, bottle, or other contrivance The

con-tainer restrains the items within and, for handling

pur-poses, the container then dominates

Some materials take several forms Nails and screws

can move on belt conveyors almost like powders Later

in the process, handling may be individually or in

con-tainers Containers o€er several advantages:

Protecting the contents

Improving handling attributes

Improved use of cube

Standardizing unit loads

Assisting inventory control

Assisting security

Pallet and palletlike containers have in the past been

the most widely used In many industries they still

are

``Tote pans'' and ``shop boxes'' have evolved into

sophisticated container families They are versatile for

internal and external distribution and are an important

feature of kanban systems Because of their wide use

they should be standardized and selected with great

care

Just-in-time, cellular manufacturing and time-based

competition strategies require moving small lot sizes to

point of use, which calls for smaller containers

For broad use in large plants, a family of

inter-modular units is important The International

Organization for Standardization (ISO) and the

American National Standards Institute (ANSI) have

set size standards The most popular families use

48 in:  40 in: and 48 in:  32 in: pallet sizes Figure

24 shows one system

Larger-than-pallet containers are primarily forinternational trade and ISO standardized unit havebeen designed There is, of course, a large variety ofnonstandard loads and containers

The key to container selection is integration.Container, route structure, and equipment are inti-mately connected; they should ®t with and complementeach other Other issues such as process equipmentand lot size also in¯uence container selection.Unfortunately, most container selections occur bydefault Certain containers pre-exist and new products

or items get thrown into them Existing route tures may also dictate container selection

struc-Manufacturing strategy should in¯uence containerselection Conventional cost-based strategies indicatelarge containers corresponding to large lot sizes; con-temporary strategies emphasize variety and responsetime The smallest feasible container corresponding

to small process and movement lot sizes should beselected

Figure 24 Box con®gurations for standard pallets

1.3.2 Route Structure

Route structure in¯uences container and equipment

selection It impacts costs, timing and other design

issues Figure 25 shows the three basic route structures:

direct, channel, and terminal In a direct system,

mate-rials move separately and directly from origin to

desti-nation In a channel system which has a pre-established

route, loads move along it, often comingled with other

loads In a terminal system, endpoints have been

estab-lished where the ¯ow is broken Materials may be

sorted, consolidated, inspected, or transferred at

these terminals In practice, many hybrids and

varia-tions of these basic route structures occur, as Fig 26

shows

1.3.2.1 Direct Systems

Direct systems using fork trucks are common In

operation, a pallet of material needs moving to another

department; the foreman hails a fork truck driver who

moves it to the next department An analogy for a

direct system is how taxis operate, taking their

custo-mers directly from one location to another without

®xed routes or schedules

Direct systems are appropriate for high ¯ow sities and full loads They also have the least transittime and are appropriate when time is a key factor,provided there is no queuing for transit requests.1.3.2.2 Channel Systems

inten-Channel systems use a predetermined path andschedule In manufacturing some automatic guidedvehicle systems work this way Manned trailer trainsand industrial trucks ®t channel systems They follow a

®xed route, often circular At designated points theystop to load and unload whatever is originating orreaching a destination at that point City bus systemsand subway systems use the channel structure.Channel systems are compatible with just-in-time(JIT) and world class manufacturing strategies ManyJIT plants need to make frequent moves of small quan-tities in tote boxes They may use a channel systemwith electric industrial trucks or golf carts Thesecarts operate on a ®xed route, picking up materialand dropping o€ loads as required Externally, overthe road trucks make several stops at di€erent suppli-ers to accumulate a full load for delivery.Simultaneously, they return kanban signals andempty containers for re®ll

Lower ¯ow intensities, less-than-full loads and longdistances with load consolidation bene®t from channelsystems Standardized loads also indicate the use of achannel system

1.3.2.3 Terminal Systems

In terminal systems loads move from origin to ultimatedestination through one or more terminals At the

Figure 25 Basic route structures

Figure 26 Hybrid route structures

terminal material is transferred, consolidated,

inspected, stored, or sorted The United States Postal

Service, Federal Express, and United Parcel Service all

use terminal systems

A single central terminal can control material well

Multiple terminals work well with long distances, low

intensities and many less-than-full loads Airlines use

terminal systems for these reasons

A warning about multistep distribution systems

The characteristics of ultimate demand assume

seaso-nal characteristics and lead to misinterpretations in

production planning

1.4 EQUIPMENT

There are hundreds of equipment types each with

varied capacities, features, options, and brands The

designer chooses a type which ®ts the route, route

structure, containers, ¯ow intensity, and distance

These design choices should be concurrent to assure

a mutual ®t

Any material move has two associated costsÐ

terminal and travel Terminal cost is the cost of

loading and unloading and does not vary with

dis-tance Transport cost varies with distance, usually in

a direct relationship as Fig 27 illustrates Equipment is

suitable for either handling or transporting but seldom

both

1.4.1 Using the Distance±Intensity Plot for

Selection

The distance±intensity (D-I) plot is useful for

equip-ment selection.Figure 28 is a representative D-I plot

with isotransport work curves Each route on a

lay-out plots as a point on the chart Rlay-outes which fall in

the lower-left area have low intensity and short

dis-tances Typically these routes would use elementary,

low-cost handling equipment such as hand dollies or

manual methods Routes in the upper left have short

distances but high intensity These require equipment

with handling and manipulating capabilities, such as

robots, or short-travel equipment, such as conveyors

Routes on the lower-right have long distances and

low intensities Equipment with transport capabilities

like a tractor trailer train is needed here Plots in the

middle area indicate combination equipment such as

the forklift truck In the upper-right area, long

dis-tances and high intensities indicate the need for a

layout revision If substantiated, long routes with

high intensities require expensive and sophisticatedequipment

Figure 29is from a recent study on handling costs

In this study, representative costs for handling palletswith several common devices were calculated Thesecosts included direct, indirect, and capital

Shaded areas on the diagram show regions whereeach type of equipment dominates as the lowest cost.This chart is generic and may not apply to a particularsituation; nor does the chart account for intangiblessuch as ¯exibility, safety or strategic issues

1.4.2 Using Material Flow Diagrams forEquipment Selection

Locational, river and string diagrams also help withequipment selection Here, the ¯ow lines indicate dis-tance, ¯ow intensity and ®xed and variable paths.Figure 30shows how to interpret this information

Figure 27 Terminal/travel cost comparisons

1.4.3 Equipment Selection Guide

The range of equipment choice is broad There is no

substitute for equally broad experience when selections

are being made Nevertheless, Fig 31 can assist the

novice to some extent The chart uses a modi®ed

Bolz [3] classi®cation system for handling equipment

with a three-digit hierarchical code The ®rst digit

represents a primary classi®cation based on design

features:

100ÐConveyors: ®xed-path equipment which

carries or tows loads in primarily horizontal

directions

200ÐLifting Equipment: cranes, elevators, hoists,

and similar equipment designed to move or

posi-tion material in a primarily vertical direcposi-tion

300ÐPositioning/Weighing/Controlling: handling

equipment used for local positioning,

transfer-ring, weighing, and controlling of material

move-ment Included are manipulators, robots,

positioning platforms, and transfers Also

included are scales and weighing equipment,

¯oat controls, bin indicators, counters, and

other control devices

400ÐIndustrial Vehicles: this class includes all types

of vehicles commonly used in and around

indus-trial and commercial facilities Excluded are

``Motor Vehicles'' intended for over-the-road

use Examples are forklift trucks, tow tractors,

trailers, and excavators

500ÐMotor Vehicles: highway passenger and cargovehicles customarily used on public roads.600ÐRailroad Cars: all rolling stock suitable for use

on national railroads Excludes narrow-gage carsand locomotives for in-plant use

700ÐMarine Carriers: all waterborne vessels used

on canals, rivers, oceans and lakes

800ÐAircraft: all types of aircraft used to transport,lift, or position materials

900ÐContainers/Supports: containers, platforms,pallets, coil supports, securement, bulkheads,dunnage, and related items

The second and third digit positions represent ®nerclassi®cations For example, the 100 series indicatesconveyors; the 110 series indicates belt conveyors; the

111 code indicates a bulk material belt conveyor.Similarly, 422 indicates a platform hand truck.The list gives codes that would normally be used in

a commercial or industrial facility It updates the ginal Bolz system to include new types of equipmentand exclude older, rarely used items

ori-To use Fig 31, identify the load characteristics ineach category across the top of the charts These char-actenstics are: Load Unit, Frequency, Distance, Path,Location Moving down the columns note the equip-ment types which match the required characteristics.The columns for Equipment Characteristics showadditional information

While the load characteristics shown are important,other factors impact the decision Moreover, many

Figure 28 Distance±intensity plot equipment classi®cations

types may meet the load requirements Here are some

additional criteria to narrow the selection:

The ®nal task in system design is to calculate

equip-ment requireequip-ments For ®xed-path equipequip-ment this is

straightforward For variable path equipment such as

fork trucks it requires estimating the time and distance

on each route and then applying utilization factors.For sophisticated systems such as automatic guidedvehicles and automatic storage and retrieval systems,

a computer simulation should be used to test thefeasibility

1.4.4 Industrial Forklift TrucksForklift trucks (FLTs) belong to a category of equip-ment which is so common, versatile and useful that itwarrants further discussion

The counterbalanced FLT is the most universal.These trucks come with many options, some of

Figure 29 Equipment handling cost comparisons

Material Handling and Storage Systems 631

Figure 30 Equipment selection guide

Figure 31 Material handling selection guide.

which are: three or four wheel; battery driven or

inter-nal combustion engine; rider, stand-up or walkie;

duplex, triplex or quad mast; and pneumatic,

cush-ioned, or solid tires

The counterbalanced design puts a large force on

the front wheels and can cause ¯oor loading problems

Lifting capacity diminishes with height and there is

some danger of overbalancing Carton clamps, side

shifters and coil handlers are some of the available

attachments

Reach trucks have small wheels near the forward

edge and on each side of the load, thus requiring less

counterbalancing In operation, the forks or the entire

mast extends to pick up or set down a load The truck

does not travel in this extended position Some

char-acteristics of reach trucks as compared with

counter-balanced trucks are:

5%±15% slower

Have nontilting forks

Require better ¯oors

Use smaller batteries

Have poorer ergonomics

Are lighter weight

Work in narrower aisles

Other forklift trucks include the following:

Pallet trucks are small, inexpensive machines which

pick up pallets resting on the ¯oor or on low

stacks Both manual and battery-powered

mod-els are available Pallet trucks cannot handle

double faced pallets and require almost perfect

¯oor conditions

Stackers are small manual or electric machines

simi-lar to pallet trucks Unlike pallet trucks, they can

elevate and thus stack their loads Outriggers or

legs support the weight of the load Outriggers

straddle the load; legs are underneath the forks

Stackers are often used in maintenance or tool

changing

Four-way trucks are useful for carrying long items

lengthwise through relatively narrow aisles They

are variations of the reach truck with rotatable

wheels that allow them to travel in four

direc-tions

Turret trucks have a mast that rotates on a track

without extending beyond the width of the

machine These trucks can operate in an aisle

only 6 in wider than the truck and access pallets

on both sides Turret trucks are used for high rise

storage operations

Side-loader trucks pick up and carry the load on theside The forks are at right angles to the traveldirection, which is useful for long, narrow loadssuch as pipe or lumber The side loader carriessuch loads lengthwise down the aisle

1.4.5 ConveyorsConveyors are ®xed devices which move material con-tinuously on a pre-established route These systemsrange from short, simple lengths of unpowered con-veyor to vast networks of conveyor sections withsophisticated controls

Belt conveyors have a ¯exible belt which rides onrollers or a ¯at bed The belt may be cloth,rubber, plastic, wire mesh, or other material.Most articles can ride a belt conveyor up to 308inclination

With roller and skate-wheel conveyors, objects ride

on rollers or wheels Any objects on the conveyorshould span at least three sets of rollers.Movement can come from powered rollers,gravity, or operators

Chain conveyors carry or push objects with a chain.Many varieties are available

Overhead conveyors use an I-beam or other shape as

a monorail Carriers roll along the monorail withloads suspended underneath A chain connectsthe carriers and pulls them along In a power-and-free system, the chain and carriers are inde-pendent A disconnection mechanism stops thecarrier Power-and-free systems o€er more ¯ex-ibility than standard monorails but at a muchhigher cost Recent designs of power and freeconveyors are inverted and ¯oor mounted.1.4.6 Vibratory Machines

Ware [1] de®nes a vibratory machine as ``any unitintentionally or purposely vibrated in order for it toperform useful work Vibration induces a material tomove instead of forcing it.''

The two distinct categories of vibratory machinesthat are most often used in material handling systemsare those for accomplishing induced vertical ¯ow andinduced conveying

1.4.7 Automatic Guided Vehicle SystemsAutomatic guided vehicle systems (AGVS) use driver-less vehicles to transport materials within an operation

AGV size can vary from small, light-duty vehicles that

carry interoce mail to heavy-duty systems that

trans-port automobiles during assembly Several types of

guidance are available with a range of sophistication

in logic and intelligence

Most AGVs move along a predetermined track

system not unlike a model railroad Optical tracking

systems use re¯ective tape or paint on the ¯oor to

de®ne the track A photosensitive device on the

vehicle detects drift from the track and actuates the

steering mechanism for correction Optical systems

are inexpensive and ¯exible They are sensitive

to dirt, however, and many users consider them

unsatisfactory

Electromagnetic guidance systems follow a

mag-netic ®eld generated by conductors laid in the ¯oor

The frequency of this ®eld can vary in each track

sec-tion and thus identify the vehicle's locasec-tion Sensors on

the vehicle detect the ®eld, its location and perhaps the

frequency The guidance system corrects the vehicles

track accordingly Electromagnetic guidance systems

are somewhat expensive to install or relocate, but

AGV owners generally prefer electromagnetic guidance

systems for their reliability

A newer type of guidance system optically reads

``targets'' placed high on walls and columns The tem then computes vehicle position with triangulation

sys-In the future, guidance systems may use the satellitenavigation systems

Figure 32 illustrates some of the vehicles availablefor AGV systems Tractor±trailer systems use a driver-less tractor to tow one or more trailers, using manual

or automatic coupling Such systems are best for largeloads and long distances Some vehicles serve as assem-bly stations in addition to moving loads

Self-loading vehicles stop at ®xed stations and load

or unload containers These are normally pallet-sizeloads

AGV forklift systems use vehicles similar to pallettrucks They can pick up a pallet, carry it to a newlocation and lower it automatically All or part ofthe cycle may be automatic

Special systems may use ®xtures to carry engines,automobiles or other large products through a produc-tion process

At the lowest level of control vehicles follow a singlepath in a single direction They stop at predeterminedstations, at obstructions or when encountering

Figure 32 Automatic guided vehicles

another Intelligent trucks have preprogrammed

desti-nations, locating their position by sensing the magnetic

frequencies These vehicles can use multiple paths to

navigate to and stop at their assigned destination

Centralized control systems use a computer to track

vehicles and control movement Vehicles broadcast

their current location and the computer sends control

signals back to the vehicle controlling both movement

and route

Towveyors were the precursors to AGVs They are

powered by a cable or chain which moves continuously

in a ¯oor groove A pin or grip mechanism connects

and disconnects the vehicle

1.4.8 System Design and Documentation

When the ¯ow analysis is complete and a layout

selected, it is time to prepare the macrolevel material

handling plan

Now that the handling for each route has been

iden-ti®ed, equipment requirements are estimated In the

case of ®xed-path equipment, such as roller conveyors,

this estimation is simple and straightforward Where

variable-path equipment is used on multiple routes,

estimate the total time required for each route and

material class as well as the e€ective equipment

utiliza-tion In Fig 33 an example estimate is shown for a

bakery ingredients warehouse

1.5 WAREHOUSING AND STORAGE

The most successful manufacturers and distributors

now recognize that inventory often camou¯ages some

form of waste The causes of waste are in the structure

of the inventory systems The ultimate goal is to

restructure and eliminate all storage of products

Restructuring for minimum inventory is usually

more fruitful than pursuing better storage methods,

although compromises must be made and a

require-ment for some storage often exists

1.5.1 Stores Activities

This section explains how to design optimum storage

systems for the inventory which remains after a

suita-ble restructuring e€ort

Storage operations have two main functions:

hold-ing and handlhold-ing Holdhold-ing refers to the stationhold-ing of

materials in de®ned storage positions Handling is the

movement to and from the storage position Ancillary

activities such as inspection, order picking, or receivingare also part of handling

Average turnover is the ratio of annual throughput

to average inventory over the same period.Throughput and inventory may be in dollars, produc-tion units, or storage units ($, pieces, pallets, cartons).Turnover ˆAnnual throughputAverage inventory

The relative importance of holding and handling in aparticular situation guides the analysis With highturnover, handling dominates; with low turnover, hold-ing dominates

Handling-dominated warehouses call for detailedanalysis of procedures and material handling Thesewarehouses use more sophisticated handling devicessuch as automatic storage and retrieval systems(ASRS) and automated conveyors

Holding-dominated warehouses call for simple,inexpensive, and ¯exible handling equipment Thesewarehouses often require high-density storage meth-ods, such as drive-through racking

1.5.2 Storage EquipmentThe types of storage equipment available are almost asdiverse as the types of containers and handling equip-ment The selection of both storage equipment andcontainers is interrelated

1.5.3 Analysis and Design of Storage SystemsThe design of storage systems should co-ordinate withthe layout design of the total facility Layout planninghas four phases: orientation, macrolayout, populatedlayout, and implementation

Orientation Storage planning during this phase is at

a high level In this phase the planners areoriented to the entire scope of the project, forexample, the building size estimates, planningassumptions, project stang, and policies andstrategies to be supported

Macrolayout This is the main planning phase wherethe major storage area SPUs are determined Inaddition to determining storage space these SPUscan include pick and pack areas, docks, andreceiving areas, although some of them may be

in a separate location The designer re®nes mates of storage space and co-ordinates themwith other design and strategic decisions

Populated layouts Populating the layout is

where each piece of equipment is located within

each space planning unit Detail planning of

designated storage occurs during this phase,

which may or may not include the identi®cation

of storage locations for each item number In

situations where handling and picking dominate,

the speci®c storage location may be very

impor-tant for e€ective operation of the overall system

In other situations, assignment of storage tions is considered an operating decision.Implementation In the ®nal phase, equipment ispurchased, installed, and operations initiated.The detailed storage plan should include the following:Populated layout

loca-Material handling planEquipment requirements summary

Figure 33 Calculating requirements

Information systems plan

Stang plan

Populated layouts show the location of all racks, aisles,

doors, oces, and other features The layout should

have sucient information to prepare architectural

and installation drawings

The material handling plan for the storage

opera-tions is similar to that made for the macrolayout of any

facility It shows all origin and destination points for

materials It shows ¯ow rates, equipment, and

contain-ers used on each route For many warehousing

opera-tions, the material handling plan is simple and can be

overlaid on a layout plan

The equipment requirements summary lists the

types and numbers of storage and handling equipment

It should also include a summary speci®cation for each

type of equipment

The information systems plan speci®es the type of

information which is to be available, equipment

required and other data necessary to purchase

equip-ment and set up systems It should include manual as

well as computer-supported systems

Preparing a complete storage plan requires the

fol-lowing steps:

1 Acquire data/information

2 Classify storage materials

3 Calculate material and order ¯ows

4 Calculate storage requirements

5 Select equipment

6 Plan the layout

7 Specify information procedures and systems

Step 1 Acquire Data/Information Information

re-quired for the storage analysis covers products,

volumes, inventory, orders, and current and past

operations

Products and volumes Information on products

includes general orientation material on the

types of products to be stored and any special

characteristics A detailed list or database should

be included with every item number, and

pro-ducts should be included by size, brand, or

other classi®cation Volume information should

include historical sales (or throughput) volumes

for each line item or product group as well as

total sales This is often the same product volume

information used for facility planning and

mate-rial handling analysis A product pro®le showing

items or groups and their volumes on a ranked

bar chart is useful Forecasts by product group

should be obtained or prepared

Inventory Historical inventory information may beavailable when there is a similar existing opera-tion The information should include averageand peak inventory for each item or productgroup over a meaningful period When historicalinformation does not apply, policies or judgnentmust suface A decision to keep ``two months on-hand'' or ``maintain an average 10 turns'' canhelp establish inventory requirements

Orders An order refers to any withdrawal request

It may be a sales order, production order or bal request for incidental supplies An order pro-

ver-®le shows the average line items and line itemquantity per order The pro®le may also includeweekly or seasonal order patterns and shouldinclude forecast trends and changes Identifyingurgency or delivery requirements may be neces-sary in some cases

Current and past operations This informationincludes stang, space usage, procedures, opera-tion sequence, equipment, policies, and any otherpertinent information not included above.Step 2 Classify Materials The classi®cation of mate-rials is similar to classi®cation activities used for mate-rial ¯ow analysis There may be slight differences,however, since the primary concern here is storagecharacteristics Figure 34 shows one classi®cationscheme Categories to select from are function, desti-nation, work-in-process, ®nished goods, high turnoveritems and slow movers

Step 3 Calculate Material and Order Flows Material

¯ows for a storage operation are calculated in the sameway as for any other layout Orders are an additionalparameter Order ¯ows in a storage operation affectthe timing of an order and picking patterns

Step 4 Calculate Storage Requirements For eachstorage class the storage space requirement must becalculated This may be done by using turnover rates,existing data, or computer simulation It is necessary inthis step to con®rm inventory policies and storage areautilization levelsÐrandom storage with high spaceutilization or dedicated locations with lower overallspace utilization

A ``pull'' replenishment system with certi®ed dors requires less space for operating, janitorial, main-tenance, and oce supplies

ven-Step 5 Select Equipment In a warehouse operationhandling and storage equipment are interrelated andshould be selected together Handling equipment typeswere discussed previously Storage equipment types arediscussed in Sec 1.5.3

Step 6 Plan the Layout Planning a storage or

ware-house layout follows the same procedure as planning

factory layouts Figure 35 is helpful for estimating

space for storage

Step 7 Specify Management/Operating Systems.Figure

36illustrates the external ¯ows of material and

informa-tion from and to the warehouse

Figure 37traces the high-level internal ¯ows within

a typical warehousing operation When the storage

system is designed these ¯ows should be re®ned and

speci®ed Operation process charts and information

¯ow charts are useful for this documentation

Information systems require speci®cation For

sim-ple manual systems a notation on the ¯ow chart may

suce; for computer-based systems a more detailed

speci®cation is required.Figure 38illustrates the

over-all operation of a computerized warehouse

informa-tion system

A stang study should also be performed This

study may range from an informal estimate to detailed

work-measurement study.Figure 39is a time standard

for unloading a typical truck The MTM-based EASE

software system was used to generate these data From

such time studies and throughput information an

esti-mate of stang is generated

1.5.4 Pallet StorageFloor stacking is the simplest way to store pallet loads.This method utilizes ¯oor space and building volumee€ectively and can tolerate pallets with overhang Toachieve these advantages requires stacking three to ®vepallets deep which gives a high storage volume peritem In the right location, with access from bothsides, ¯oor stacking can operate on a ®rst-in-®rst-out(FIFO) basis Floor stacking also requires strong,stable, stackable, and unbroken loads, illustrated inFig 40

Pallet racks should be used when loads are able or storage volume is too small for deep ¯oorstacking Double-deep racks achieve higher densitystorage but require a reach truck causing problems ofaccess to the rear pallet

unstack-Flow-through racks are used when FIFO is tant and turnover is high In these racks the pallets orcartons ride on rollers or wheels and ¯ow by gravityfrom the load to the unload end They require high-quality pallets, and the racks are relatively expensive.Drive-in racks should be used for large quantities ofunstackable pallet loads The rack openings must bewide enough for the truck and special narrow trucks

impor-Figure 34 Material classi®cation

Material Handling and Storage Systems 639

Figure 35 Storing space planning guide

Figure 36 External material and information ¯ows

may be necessary Since pallets are supported only on

their edges, pallet quality must be high Limited FIFO

is possible if there is access to both sides

1.5.5 Small Parts Storage

Small parts storage systems are either static or

dynamic Static systems include shelving and drawers

in various con®gurations Dynamic systems are

verti-cal carousels, horizontal carousels, mini-trieves and

movable-aisle systems

Shelving is a basic inexpensive and ¯exible storage

method It often does not use space e€ectively and is

costly for intensive picking operations

Modular drawer systems o€er denser storage than

shelving They are more expensive than shelves and

more dicult for picking

1.5.6 Automatic Storage and Retrieval Systems

Automatic storage and retrieval systems (ASRS) store

materials in a high-density con®guration These

sys-tems use a stacker crane or other mechanical device

to carry each load to its location and place it in

storage The same crane retrieves loads as required

and delivers them to an output station A computer

system controls movements and tracks location The

ASRS computer often is in communication with a

pro-duction control system such as MRP Such systemsusually work with pallet-size loads Mini-trieve systemsare similar in concept to automatic retrieval systemsbut use smaller loads such as tote boxes

1.6 CONCLUSIONMaterials movement is a key consideration in facilityplanning The material ¯ow analysis is necessary forproper facility design and is a prerequisite for thedesign of material handling systems and storageareas It is also an important means of evaluatingdesign options

It is important to select the material handling ment to ®t the determined material ¯ow system Oftenthe ¯ow and handling are forced to ®t the materialhandling methods you have been sold

equip-Even though we want to eliminate material handlingand storage waste product storage may be required foraging, quarantine, or qualifying processes In othercases storage serves as a bu€er in an improperlydesigned and maintained system

Following the step-by-step procedures outlined inthis chapter will support the operating strategy byreducing costs, time and material damage This isbasic to achieving world class and being a time-basedcompetitor

Figure 37 Internal material and information ¯ows

Material Handling and Storage Systems 641

Figure 38 Computerized warehouse information system

1 B Ware Using vibratory machines to convey bulk solids

Chemical Processing, Itasca, IL: Putman Publishing

Company, 1998, pp 74±79

2 W Wrennall, Q Lee, eds Handbook of Commercial

Facilities Management New York: McGraw-Hill, 1994

3 HA Bolz, GE Hagemann, eds Materials Handling

Handbook New York: The Ronald Press, 1958, pp

1.5±1.16

FURTHER READING

CR Asfahl Robots And Manufacturing Automation, New

York: John Wiley, 1985

A Carre Simulation of Manufacturing Systems, Chichester:

NL Hannon Layout Needs: An Integrated Approach Mod

Mater Handling April, 1986

WK Hodson, ed Maynards's Industrial EngineeringHandbook 4th ed New York: McGraw-Hill, 1992

M Hulett Unit Load Handling London: Gower Press, 1970

AL Kihan Plant Services and Operations Handbook NewYork: McGraw-Hill, 1995

Modern Dock Design Milwaukee: Kelly Company, 1997

W MuÈller Integrated Materials Handling in Manufacturing.IFS (Publications), UK: Bedford, 1985

U Rembold Robert Technology and Applications NewYork: Marcel-Dekker, 1990

G Salvendy Handbook of Industrial Engineering 2nd ed.New York: Wiley-Interscience, 1992

ER Sims Planning and Managing Industrial LogisticsSystems Amsterdam: Elsevier, 1991

JA Tompkins, JD Smith The Warehouse ManagementHandbook New York: McGraw-Hill, 1988

W Wrennall Requirements of a Warehouse OperatingSystem In: JA Tompkins, JD Smith, eds TheWarehouse Management Handbook New York:McGraw-Hill, 1988, pp 531±559

W Wrennall, Q Lee Achieving Requisite ManufacturingSimplicity Manufacturing Technology International.London: Sterling Publications, 1989

Figure 39 EaseTMgenerated time standard

Figure 40 Floor stacking

A 20-year-old de®nition of automated storage and

retrieval (AS/R) systems states that the technology is

`` a combination of equipment and controls which

handles, stores, and retrieves materials with precision,

accuracy, and speed under a de®ned degree of

automa-tion'' [1] While basically sound, the de®nition

some-what limits the reader's imagination when it comes to

the entire spectrum of functionality an AS/R system

can o€er to the planner designing a new logistics

process

Using today's ``logistics-speak,'' the AS/R system is

a device which automatically receives material arriving

at an often anomalous rate, securely bu€ers the

mate-rial in a controlled access structure, resequences and

conditionally and responsively releases material out to

points of consumptionÐall under a high degree of

automation so as to eliminate the need for human

resources in the process of performing these

non-value-added functions

2.2 A BRIEF HISTORY

Automated storage and retrieval systems were initially

introduced in the late 1960s, and rose to popularity

between the early 1970s and early 1980s Their primary

use and justi®cation was in the control and automated

handling of pallets or tote pans of material The goal

was to minimize product damage, free ¯oor space,

con-trol and track the inventoryÐprotecting it from age or unauthorized disbursement, and minimize thecost of material handling labor

pilfer-During the ®rst wave of popularity, other logisticspractices were causing a signi®cant demand for storagecapacity For one, MRP (material requirements plan-ning) systems were being introduced that tended tocause large quantities of material to ¯ow into the orga-nization because of errant use of EOQ (economic orderquantity) procedures and faulty forecasting practices.Additionally, problems with the supply chain and theability to track on-hand inventories caused managers

to adopt overly conservative safety stock policieswhich also in¯ated inventory levels It was absolutelyunacceptable to stop production for any reason, letalone for the shortage of material

Systems were large, and new systems were oftensimple extrapolations of requirements based on currentinventory levels without ®rst determining if the processwould actually require the inventory levels this methodprojected

Probably the most infamous story of a distributionwarehouse plan that went wrong is a repair partsdistribution center planned for a large heavy equip-ment manufacturer That system was to have over 90aisles of very tall and very long AS/R systems It wasplanned and a contract was awarded, but the systemwas canceled before it was completed in the mid-1980s Located adjacent to a major interstate high-way, the structural steel for that facility stood foryears Like a skeleton, it silently reminded those

643

that saw it to think about the entire process before

staking your career on a plan that assumes the future

is a simple factor of growth from where one stands

today

In the mid 1980s, an economic recession caused

manufacturers and distributors to pull back plans for

expansion and automation due to a shortage of capital

At that same time, the production philosophies of

just-in-time (JIT) were being introduced to this country

Together, these two events led planners to consider

the AS/R system technology a weapon of

destruc-tionÐespecially if deployed in their own companies

After all, it was a storage technology, and storage of

material was to be avoided at all costs

More on JIT later But to summarize, the

technol-ogy of AS/R systems grew rapidly up until these

events, and then almost disappeared in the United

States until the early 1990s At one time the industry

included nearly 20 companies providing equipment

and automation that meets the classic de®nition of

AS/R systems Today less than a third of them remain,

but the number of systems being planned and installed

is at an all-time high, both in the United States and

worldwide

2.3 A STATE OF MIND

Perhaps the biggest reason for the decline of the

indus-try is the fact that material handling and, more

speci-®cally, storage, have always been regarded as cost

adders to the overall distribution process As a cost

factor, the limit of our interest has been to minimize

the cost

Aside from the fact that proximity can add value to

material, most would respond that the best way to

address material handling is to eliminate it Since it

cannot be eliminated in all cases, however, the next

best thing is to design the systems for handling such

that they are not dependent on scarce resources in

order to function properly, and that they operate

with total control and predictability In other

wordsÐautomate

But automation costs money, and we have been

inclined (or instructed) to not spend money on

non-value-adding functions So another way had to be

found We had little success eliminating these

func-tions We have even tried to pass on (outsource) the

requirements to our suppliers, in the hope that they

would, at least, make the problem go away

The pressure to implement just-in-time

manufactur-ing methods spawned a panic in the 1980s to reduce

inventory below historical levels We forced our pliers to deliver just in time in the belief that reducinginventory was the key to cost reductions and increasedcontrol of the supply chain The price we paid, how-ever, was reduced reliability of supply, higher costs,and reduced quality

sup-One of the interesting ``truths'' to grow out of thisera was the platitude: `` there are three attributes toevery opportunity: Good, Fast, and Cheap You canhave any two of the three '' (see Fig 1) While fewpeople realized that understanding this relationshipwas the beginning of true system-based reasoning,there were underlying causes for the presence of inven-tory that few people could see or address They werenarrowly focused on only one element of a properlydesigned logistics pipeline They tried to ®x the pro-blem by changing the rules under which only a portion

of the system operatedÐwithout re-engineering theentire system to behave in a way consistent with thenew goals

It is quite natural for the human mind to decomposeproblems into components We are taught as beginnersthat we ``eat an elephantÐone bite at a time.'' Theproblem with this approach is that if the ®rst bitedoes not disable the elephant, it will probably react

in a violently defensive way

Systems are no di€erent The diculty with ing systems ``one bite at a time'' is that we often fail

design-to see the impact a decision may have on otheraspects of the system As soon as a portion of thesystem is changed, it may start reacting in unpredict-able ways It is usually at this point that all improve-ment e€orts take a back seat to the e€orts of justtrying to keep the system running and shippingproduct

When components of the system are dealt withindependently, we have very little success reassem-bling the components and making them work in con-cert with the rest of the process It is much liketrying to reassemble a broken mirror in order tosee a true re¯ection The result just never resemblesreality [2]

Figure 1 Conundrum of con¯icting goals

2.4 ``INVENTORY HAPPENS''

Joking about inventory does not make its presence any

less painful The fact is, there are few warehouses in

existence today that are not periodically bursting at the

seams for lack of space to store more material Even in

today's environment where JIT rules, the stories of

hidden inventory, and warehouses on wheels, abound

It is well known that left to the best systems available,

inventory will expand to ®ll the space available

In Japan, where we like to think the concept of JIT

started, the ®rst experiences were not the result of

wanting to reduce the costs of holding an inventory

Just-in-time was developed out of the necessity to free

up space for value-adding manufacturing The result

was near chaos, again, because of the lack of

consid-eration for what the change to JIT did to the overall

system

While it used to be acceptable to ship 100 units of

material on Monday for an entire week's supply, the

new paradigm wants ®ve shipments of 20 units

deliv-ered over the course of 5 days This means that the

ordering and delivery costs are factored up by 5, as

are the number of trucks on the roads to complete

these deliveries In the beginning, Japan was plagued

with a transportation infrastructure that could not

handle the added trac, and lateness and delivery

fail-ures abounded The government even proclaimed that

the reason no one is on time anymore is because of

just-in-time

In summary, most people simply tried to reduce

inventory through edicts The companies that have

succeeded with JIT implementations, however, learned

to use inventory as an asset, not as a waste element in

their process To achieve the goals of inventory

reduc-tion, however, they have turned to the root cause of

inventory, and altered the process in ways that

corre-spondingly reduce a smooth running process's need for

inventory

2.5 THE EQUATIONS OF INVENTORY

But using inventory to your advantage does not mean

a wanton disregard for common sense or economics

Most manufacturing engineering curriculums courses

taught in this country include a healthy dose of the

operations research equations used to compute

eco-nomic lot quantities for production and procurement

Known as ELQ or EOQ, these ancient equations are

based on sound mathematics that are designed to

max-imize the probability of actually having material at the

right place when it is needed, but absolutely ing the cost of material procurement, ownership, andcontrol

minimiz-By and large, these equations have lost popularitybecause of misunderstanding Many inventory plan-ners view them as obsolete, or as inconsistent withmodern logistics techniques As we examine the mathbehind these equations, however, we ®nd they are par-ticularly useful in helping us de®ne system-based plans

To understand them, however, one must realize thatthe inventory a given system will require is totally afunction of that system's theoretical utilization, thevariability of the material supply, and the variability

of the value-adding process itself

As an extremely abstract way of illustrating thispoint, consider the simplest of queues, the M/M/1.This is a single-line queue ahead of a single serverresource The assumptions are that the arrival process

is exponential, and that the trac intensity (arrivalrate/service rate)  < 1 In other words, the number

of items arriving per period of time demanding serviceare always less than the capacity of the server to pro-vide service

If we only look at the work-in-process (WIP)buildup that can develop as a result of equipmentutilization, the length of the line ahead of the server

is estimated by the equation [3]

Lqˆ 2=…1 †

The signi®cance of this example is to show that as theprocess's utilization (i.e., the trac intensity )approaches 100%, the length of the queue waitingfor service grows to an in®nite length (see Fig 2)

At ®rst, it may not be clear how this can occur Itoccurs because there is not enough capacity to accom-modate surges The actual utilization may be below100%, but if the value-adding resource sits idle for

Figure 2 WIP as a function of system utilization

lack of material, that idleness cannot be bought back.

The capacity to add value during the idle period is lost

forever

Add to this the e€ects of variance associated with

scheduling, material availability, and process

down-time, and you begin to get the picture, WIP happens,

even in the best of planned systems

2.6 FUNDAMENTAL DIFFERENCE IN

DESIGN PHILOSOPHIES

The primary focus of re-engineering the logistics

sup-ply chain has been too centered on cost reduction In

today's U.S economy, many of the factors that led the

Japanese manufacturer to embrace JIT and continuous

¯ow technologies are a€ecting domestic

manufac-turers In particular, labor shortages and space

shortages are pushing logistics planners into a new

philosophy of design that tends to favor a new look

at automation

In this excerpt from a JTEC report [4], the required

change in design philosophy is summarized:

In general, automating a task is a way to create

labor by freeing people from non-value added

work While the U.S views labor as a cost to

be minimized, the Japanese seem to view labor

as a resource to be optimized The Unites States

asks, ``Given a speci®c task, what is the lowest

annual cost for performing it?'' The Japanese

ask, ``Given a ®xed number of people, what is

the most value I can add with the best assignment

of skills?'' The Japanese treat human capital the

way we manage ®nancial capital

To this I would add an observation: we tend to design

our systems to utilize our most valuable resource

from the neck down We rarely see systems that take

advantage of the human ability to dynamically

pro-blem solve If we disagree with this view, we should

remember that it has only been a generation since we

commonly referred to our employees as ``hired hands.''

In that same JTEC report, it explains that the

Japanese are between 2 and 5 years ahead of the

United States in deployment of automated

technolo-gies This is not to say that the United States should

run out and try to catch up The pressures have been

di€erent The Japanese have built and automated their

systems based on known shortages of land, labor, and

other resources

With today's sub-4% U.S unemployment levels,

those ``hands'' are becoming scarce Of the people

available to work, many are better educated than inthe past, and will not stay with a job that does not usetheir minds, as well as their backs Additionally, theexisting workforce is gettmg older, and the arrivingreplacements are better educated about ergonomicissues Today's workforce is increasingly resistant tosacri®cing their long-term well-being for the few pre-mium dollars an ergonomically hazardous ``hard-job''o€ers

Finally, as a shortage, land may not seem to be aproblem for most manufacturers For planners that

do not already have available space under roof, ever, the capital to add brick and mortar is almost

how-as unattainable in the United States how-as land is inJapan

2.7 TECHNOLOGY SHIFT

In summary, AS/R systems technology is a tool thatcan automate some of the non-value-added tasks asso-ciated with material management, thus freeing scarceresources (humans) to be directed to value-addingtasks In particular, it eliminates the linear handling

of material from receiving to a storage location, theexpediting function of ®nding the material and moving

it to a point of use, and the process of accounting for,monitoring, and protecting material from unauthor-ized distribution

As mentioned before, the technology took a severehit in the 1980s during the time we were all trying toimplement JIT, and survive an economic recession But

it was not a worldwide demise While the United Statessaw application of the technology stagnate and overhalf its AS/R systems industry suppliers disappear, inthe world market the technology found a new nicheÐspeed

The rest of the world was awakening to the needfor continuous ¯ow manufacturing, which yielded ademand for very responsive systems that could serve

a variety of missions without signi®cant tion Part of the answer was inventory servers thatcould distribute much smaller quantities of material

recon®gura-at very high transaction rrecon®gura-ates This made possiblethe concept of ¯exible manufacturing where theorder, and material requirements to satisfy theorder, were conceivably known only a few minutes

in advance

Obviously, material stocks needed to be kept close

at hand to supply the value-added process, but thesupplies had to be eciently handled, and quicklyavailable to the point of use To make this possible,