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HUMAN FACTORS IN ENGINEERING & DESIGN

Chapter IV: Workspace & Arrangement

Topics:

AnthropometryUse of anthropometric dataWorkspace dimensionsWork surfacesPrinciples of seat designLocation of components

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AnthropometryImportance: It is the study of human body dimensions

which come in different sizes & builds. Today s requirement makes one to spend

more time sitting at control panels,computer terminals, library, classrooms,Television etc. ill-designed seat results in

life-long injuries.

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AnthropometryEngineering Anthropology is concerned with dimensions, to the

design of things people use

Body measurements of 2 types:- Static dimensions measurements taken when body is fixed /static position sitting, standing.

: varies with age, gender, ethnic divide, occupation &living conditions.

- Dynamic (Functional) dimensions measurements takenwhen body is engaged in some physical activity reaching

across, running.Arm reach is dependent not only on arm length but alsoshoulder movement, trunk rotation, bending of back etc.Somatography studies the front, top & side views of bodymembers in an dynamic act.

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Use of Anthropometric dataPrimary areas of application:

Workspace design Design of Tools, Equipment & Machinery Design of Clothing Consumer Product Design Design of Work Environment

People at large design must accommodate abroad spectrum of people.Design for specific group require collection of

data concerning that group Country, age,h n i

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Principles of applicationof Anthropometric data

1. Design for Extreme Individuals: Design for the maximum (high) value &

minimum (low) value of a design feature to

accommodate almost all ( 5 95 %) personsin the population. Max door height : 7 to allow people to pass

through. Any person beyond 7 comingthrough is very remote 9 door (for 100%) isthus not justifiable.

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Principles of applicationof Anthropometric data

2. Design for Adjustable Range: Certain features of equipment / facilities can

be designed so that they can be adjusted to

the individuals who use them.

To cover 5% females to 95 % males 100 %

may lead to technical difficulties in design.

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Principles of applicationof Anthropometric data

3. Design for the Average: In non-critical features of equipment / facilities can

use average values of anthropometric data on people where extreme adjustability is not possible.

Often this is used to avoid complicity ofanthropometric data.

There is however no average individual

A person may be average only on one or two bodydimensions.

Eg.: Ticket Counters, Height of Anvil in a Forging shop

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Work Space DimensionsWork Space:

Is a 3-dimensional space within which anindividual works called as Work SpaceEnvelope .

Out-of-Reach Requirements:Distance required for preventing a person fromreaching hazardous / barrier.

Clearance Requirements:Minimum space required to move through atight space or perform work in a confined area.

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Work Space Envelope: Seated Personnel

Limit for work space envelope for a seatedpersonnel depends upon the Functional arm reach .

Functional arm reach depends on: Direction of arm reach Any restraint that may be present

Task to be performed

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Work Space Envelope: Seated PersonnelEffect of Direction of Reach & presence of

restraints:Study on persons reasonably representative ofadults in terms of height & weight on reveals

thatThe measured functional arm reach at variouslateral angles from a seated position (- 45 0 left

to +1200

right) and at various levels (- 600 below to +90 0) above from the seated point &

grip center - hand.

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Effect of Direction of Reach & Presence of Restraints:

Traced at 35.4 level; Similarly, such envelopes couldbe drawn at different levels ( 60 0 to + 90 0 levels)

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Work Space Envelope: Seated PersonnelEffect of Manual activity or task:

Envelope boundaries are determined by thenature of the activity

If an individual has to operate the followingtrace are appropriate:

A push-button: Finger tip traceA knob: Thumb-tip trace (reduces by 2 ) A hand-grasp: Palm trace (reduces by 2 ).

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Work Space Envelope: Seated Personnel

Effect of Apparel:

Clothing / apparel restricts the movements and

the distance that they can reach, thus effectingthe size of the envelope.

Winter clothing reduces the envelope by 2 ontruck drivers.

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Work Space Envelope: Standing Personnel Standing Reach is a matter of body

equilibrium. Reach effected by weight carried on the

reaching hand (reduces reach), reach is

increased by increasing the base of feet else one topples over as CG shifts from thebase of support provided by the feet.

Convenient Reach is the distance withinarm s reach without undue exertion (in frontshoulder).

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Work Space Envelope: Standing Personnel Out-of-Reach Requirement: (99% males)

Barrier kept between person & object to prevent person

reaching the object.It depends upon the height of the barrier and the height atwhich the object is placed.Barrier height could be reduced when the object height islessened.

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Work Space Envelope: Standing Personnel Clearance Requirement:

Is the minimum space necessary for aperson to just fit into restricted or awkwardspaces

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Work Space Envelope: Standing Personnel

Clearance Requirement:

Out-of-Reach Requirement:

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Work Surfaces

Are areas within the Workspace envelope Control panels, work tables, desks etc

Generally, studied under 2 categories:1. Horizontal Work surface Area2. Work Surface Height:

a) For Seatedb) For Standingc) For Standing or Sitting

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Work Surfaces1. Horizontal Work surface Area:

This area is used by Seated or Sit-Standpersonnel.Activities lie within the convenient arm s reach(without undue exertion).Certain normal areas & maximum areas wereproposed by Squires (1956) & Barnes (1963):Normal area: Area reached by sweep of forearm

while upper arm hangs in natural position on theside.Maximum area: Area that could be reached byextending the arm from the shoulder.

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1. Horizontal Work surface Area:Barnes (1963) & Squires (1956) model:

Design by Squires is a bit shallow, but reduces the stress onelbow joint.

Wherever feasible it is better to use a slanted surface to reducetrunk movement, better posture lesser bending of neck.

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Work Surfaces - Work Surface Height: a) For Seated Personnel:

Work surface height is the height of the upper surface ofthe table from the floor. Writing on desk

Working Height is the height at one is working from floor.Wash veg in sink (lower than work surface height)

Work surface height if,Too low back to bend too far : Back ache Too high - Shoulders to be raised above relaxed

posture : Discomfort to shoulder & neck.

W k f h i h

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Work surface height Seated Personnel:

Arm posture: Upper arm & elbows at 90 0 is comfortable for repetitive jobs&assembly work.

Table top : 27 30

Thigh clearance: 26.2 from underside of desk

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Work Surfaces - Work Surface Height: a) For Standing Personnel:

Critical features of height for standingpersonnel is same in respect of elbow height &nature of work to be performed.

Table / Work surface to be made adjustable tosuit the requirements by either using platformsfor smaller users or adjust the table

mechanically /hydraulically/electrically.

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Precision Work Light Work Heavy Work(Elec. Circuitry) (Small assembly) (Involving weight & pressure)

WORK SURFACE HEIGHT - STANDING

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Work Surfaces - Work Surface Height: a) For Standing or Sitting Personnel:

It may be desirable to provide an opportunity toperform a job in either standing or sitting or usethe postures alternatively if need be.

Foot rest while sitting

12 0 - 24 0

Desk Top, not longerthan reach

Hand Rest: In levelwith table top

HeightAdjustable

Work surface Angle

P i i l f S D i

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Principles of Seat Design

Chairs to be given importance as improperdesign leads to back strain. Each person finds a specific design most

comfortable chair. Best approach is to provide people a few

good designs to choose from.

P i i l f S D i

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Principles of Seat Design

1. Promote Lumbar Lordosis: While standing erect, the lumbar portion of thespine, (lower back), naturally curved inwards

termed Lordotic . Natural lordosis aligns the vertebrae in almost a

vertical axis through the thigh. A person sitting such that thigh is at 90 0 to axis,the lumbar region is flattened out or evenassumes a outward bend (convex) termed asKyphotic .

Lumbar Kyphosis results in increased pressureon discs.

Discs are between the vertebrae of the spine.

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Promote Lumbar Lordosis:

Kyphotic OutwardArch (Convex)

SittingStanding

Lumbar Support

P L b L d i

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Promote Lumbar Lordosis:

P L b L d i

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Promote Lumbar Lordosis:

Andersson (1979), found that using a 2 thick

lumbar support had a marked impact onmaintaining lumbar Lordosis with a seat backrest angle of 90 0.

When the seat back rest angle was changed to110 0 , & lumbar support used, spine resembledclosely to a curve of standing person.

Lumbar support need not match inward arch ofthe lower back completely.

A forward tilting seat increasing angle betweenhip & upper torso provides relaxed posture.

Inclined tables enhances relaxed postures.

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Promote Lumbar Lordosis:

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Promote Lumbar Lordosis:

P i i l f S t D i

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Principles of Seat Design

2. Minimize Disc Pressure: The discs between the vertebrae can be damageddue to excessive pressure through: Unsupported sitting

Supported sitting upright , erect position (forcedlordosis) increases disc pressure by 40 % thanwhile standing. Unsupported sitting in forward slump increasespressure by 90 % than while standing.

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P i i l f S t D ig

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Principles of Seat Design4. Reduce Postural Fixity: Postural fixity means sitting in one position for long

periods without significant movements.Eg.: Using computer for long hours eyes on screen& hands on keyboard.

Discs between the vertebrae in the spine requirechanges in pressure to receive nutrients & removewaste products they do not require blood supply.

Fixity results in degenerative process in the disc . Swelling in legs, cramps shoulder ache are other

fallouts of restricted blood flow due to postural fixity. Best alternative is provide for standing, stretch outs.

Principles of Se t Design

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Principles of Seat Design5. Provide for Easy Adjustability: Adjustability fundamental for good design. User to be aware of the adjustments for optimum use

Guidelines for increasing ease of making adjustment: Controls to be reachable from seated work position. Adjustments require the use of one hand. Few motion required for use of controls. Tools not necessary. Controls should provide immediate feedback. Operation of controls to be consistent & logical.

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Principles of Seat Design

Body Part Desirable Posture Design Implications

All Small variations of allpostures to bepossible.

Workspace to allowfor these minorchanges

Head,Neck

Head - straight &balanced

Neck vertical,Eye level horizontal.

Main display unitshould be at eye

level or slightlybelow.

Principles of Seat Design

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Principles of Seat DesignBodyPart

Desirable Posture Design Implications

Trunk More or less vertical withnormal spinal curvature tominimize muscle activity ofback.

Provision of backrest & appropriatelocation of display &controls.

UpperLimb

Upper arm verticalForearm horizontalWrist palm downwards &inwards

Provision of arm rest& hand controls.

LowerLimb

Thigh horizontalLower leg obtuse angle tothighFoot 90 0 to lower leg.

Size, height & slopeof seatProvision for:adjustment for footrest & foot controls

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Physical Place & Arrangement Location of Components

Component physical entity such as

controls, articles, equipments, books etc.

lowest level entity being arranged in space. Eg.: While arranging office furniture, desk is a

component. Each to be accommodated in defined area.

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Principles of Arranging Components Every component to be ideally located optimally.

Optimum location is decided by human capabilities& characteristics sensory, anthropometric & bio-

mechanical.

Placing a control in a optimum position mayseparate it from the display to which it is related.Hence a trade-off is required.

Principles of Arranging Components

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Principles of Arranging ComponentsGuidelines in arranging components:

1. Importance Principle:Importance refers to the degree to which thecomponent is vital to the achievement of theobjectives of the system.

Importance is determined by the judgment made byexperts in the operation of the system.

Important components placed in convenientlocations.

Principles of Arranging Components

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Principles of Arranging ComponentsGuidelines in arranging components:

2. Frequency-0f-Use Principle:Frequently used components be placed inconvenient locations.Eg.: Xerox machine near the typist.

3. Functional Principle:Grouping of components according to their functions

grouping of displays, controls or machines which

are functionally related.Eg.: Temperature indicators and temperaturecontrols may be grouped together.

Principles of Arranging Components

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Principles of Arranging ComponentsGuidelines in arranging components:

4. Sequence-0f-Use Principle:Patterns of relationship or sequences occur in theoperation of an equipment or performing a task.The components will be so arranged to take care ofthis sequence.Eg.: Placing of hand tools based on operation ofdismantling sequence.

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Principles of Arranging Components

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Principles of Arranging ComponentsStudy on 200 students by designing Control Panel:

Frequency Of UseImportance

Functional

Sequence Of Use

Level of Principle Application

M e a n

T i m e ,

M i n ( P e r f o r m

a n c e

)

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Principles of Arranging ComponentsStudy on 200 students by designing Control Panel:

Methodologies for Arranging Components

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Methodologies for Arranging Components

Arranging components require relevant data and use ofmethods of applying the data.Step 1: Data collectionBasic data: About human beings anthropometric already discussed.

Environmental Data: Illumination, Noise, Heat etc. Task Analysis data: Work situation.List of components involved.

Includes information relating to:Use of components individuallyRelationship between components as they are used.

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Methodologies for Arranging Components

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Methodologies for Arranging Components

Communicational Links:

Visual: Person to person or Equipment to personAuditory (Voice) : Person to person orEquipment to person orPerson to Equipment

Auditory (Non Voice): Equipment to personControl Links : Person to Equipment Movement Links (One location to another):

Eye MovementManual / Foot movements or both.Body movement.

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Methodologies for Arranging ComponentsStep 2: Summarize Link DataData collected is summarized in the Link Table tounderstand the relationship between components.Link Table cannot picturize the problem at hand.

Printer II

Printer IOperatorDisc IIDisc IComputer IIComputer I

O

OO

O

O

U

U U

U

EE

E

E

E

EE

E

E

E

XX

O Ordinary Closeness

E Essential to be close

U Unimportant, link does not exist

X Undesirable to be placed close by

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Spatial Operational Sequence Diagram (SOS)

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Spatial Operational Sequence Diagram (SOS) SOS graphically / pictorially depicts the actual

sequence of operation at the workspace. Useful when there is a set of a operation.

Methodologies for Arranging Components

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et odo og es o a g g Co po e ts

Step 3: Arranging Components using Link Data:Most common method of arranging components isTrail & Error method more of art than science.

Designer draws scale drawings of components & triesto maximize the criteria that conflict one another.

Keep most frequently used components in the most

advantageous locations.

Quantitative technique like Linear Programmingtechnique helps optimizing the criteria of location.

General Location of Controls & Displays

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p yWithin Workspace

Although optimal location of components generally

depends on situational factors, some generalizationsabout certain classes of components such as Visualdisplays, hand controls, Controls that require force &Foot Controls.

Visual Displays: Normal line of sight is usuallyconsidered to be about 15 0 below the horizon.Moderate eye & head movements permit convenient

visual scanning of an area around the normal line ofsight oval shaped area.

General Location of Controls & Displays

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p yWithin Workspace

Hand Controls:

Optimum location depends on:

Type of control

Mode of operation

Criteria for performance (Speed, accuracy, force)

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General Location of Controls & Displays

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p yWithin Workspace

Controls on Panels:

Control on panels are positioned on locations of reachdepending upon relative priorities, frequency,sequencing of use of controls.

Controls on Panels:

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General Location of Controls & Displays

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p yWithin Workspace

Two-Hand Controls:

Some operations require the simultaneous use ofcontrols by both hands.Eg. Metal Forming presses as operator presses thepush buttons kept on left & right side the ram beginsto descend down for safety reasons.Operators using these push buttons located at eyelevel activate the muscles 4 times faster than when it

is kept at waist level using EMG s Waist level control a better option as it reduces thespeed & enhances operator safety.

General Location of Controls & Displays

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p yWithin Workspace

Foot Controls:

Based on anthropometric data for foot operated (toe &heel) controls certain areas can be considered to beoptimal & maximum .

Maximum location refers to fairly large amount of legmovement avoided for frequent & continuous use.

The area is different when the control is operated withforce termed as optimal area.

General Location of Controls & Displays

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p yWithin Workspace

Foot Controls:

General Location of Controls & Displays

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p yWithin Workspace

Foot Controls:

ASSIGNMENT II

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Last date for submission: 7th June, 20071. Define the following:

Production, Productivity, Partial & Total Productivity, Efficiency & Effectiveness.

2. Explain the factors effecting Productivity.3. What are the methods to improve Productivity?

4. Define Noise and Loss of hearing.5. What are the effects of noise on Performance?6. Explain Noise Control using:

Control at the Source, Control along the path &

Control at the receiver.References:Industrial Engg. Dr. B. KumarHuman factors in Engg & Design Sanders & McCormick