eind 2303: work design and industrial...

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Islamic University of Gaza - Palestine

Department of Industrial Engineering

EIND 2303: Work Design and Industrial Ergonomics


Learning Outcomes

After careful studying this chapter You should be able to

• Explain the term Anthropometry,

• Discuss its importance,

• Distinguish between the types of anthropometric data,

• Describe factors influencing anthropometric measurements,

• Discuss the concept of selection vs. modification,

• Explain the term percentile,

• Measure needed body dimensions,

• Discuss how many sizes and design for population or

person?

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Anthropometry

• Initiative

• Imagination

• Needs

• Dexterity

• Intelligence

• And so forth

• Visual acuity

• Determination

• Upper back strength

• Age

• Leg length

Anthropos (human) + metrein (to measure).

Studying the Dimension of the Human Body

The study of how people vary in


Anthropometry (1)

• Literally, ‘The measure of man’

– quantifies human variability

• What?

– physical measures

– height, weight, reach, length,

width, depth, circumference,

surface area, etc.

– strength, dexterity, range of

motion

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Why?

• We are not all the same size.

– Exclude as few as possible:

•“Let the small person reach, let the large person fit.”

– Poor design for mechanical abilities of the human body can

lead to discomfort or injury, e.g., the height of keyboard for a

computer.

• Sources of Anthropometry Data

– Text

•Ergo disk

– Tables in books


How?

• Populations

• Tools & techniques

• Statistical calculations

– based on central limit theorem

– typical calculations

• mean

• standard deviation

• percentiles

– from ordered data

– estimate for normal distribution

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Engineering Anthropometry

• Physical body size

– Static

• Two dimensional

• Three dimensional

– Functional

Strength

– Isometric

– Dynamic – isotonic, iso-

kinetic, iso-inertial etc.

– MVC joint torques

Biomechanical / inertial properties

– Segment mass

– Segment center of gravity locations

– Muscle attachment sites and lever arms

– Failure stresses of ligaments, tendons, bones etc.


Example Anthropometric Data

• Static Measures

– Passive measures of the dimensions of the human body.

– These measures are used to determine size and spacing

requirements of work space.

– Example Measures

• arm length (e.g., your lab …)

• height

• weight

• wing span

• seat to elbow height.

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Static Anthropometric Measurements

• Static = Fixed or not moving

– Between joint centers

– Body lengths and contours

– Measuring tools: Laser (computer), measuring

tape, calipers

– Resource Examples: NASA Anthropometric Source

Book, Dr. J.T. McConville Anthropology Research

Project (Yellow Springs) , United Nations


Dynamic Anthropometric Measurements

• Dynamic = Functional or with movement

– No exact conversions for static to dynamic

• Kromer (1983) offers some rough estimates for

converting static to dynamic

e.g. Reduce height (stature, eye, shoulder, hip,

etc.) by 3%.

– Somatography

• e.g. A CAD program named SAMMIE

• e.g. A virtual reality program named dv/Maniken

– Scale model mock-up

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More Anthropometric Data

• Dynamic Measures

– Measures of the dynamic properties of the human body,

such as strength and endurance.

– These measures are used to match the dynamic

characteristics of controls to user.

– Measures

• range of motion for various joints

• force of leg pushes

• strength of fingers


Using Anthropometric Data

• Use Recent Data

– Changes in diet and habit lead to changes in size and

fitness of population

– Most size measures are done on nude or lightly clothed

subjects.

• clothes change our sizes

– think of seat belts in summer vs. winter.

• Understand the task

– how will the system or device be used?

– reach, fit, & strength requirements

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Using Anthropometric Data

• Know your population

– If your measures are from a different group than your users

are from problems could result.

• Women are different from men.

• Asians are different from Europeans.

– (“Let the small person reach …”) If you were designing a

console requiring a forward reach to activate a control, what

reach distance would you use to define your maximum

console depth?

– (“Let the large person fit …”) What is the minimum height of

the bottom of the console?


Selection vs. Job Modification

• Two basic strategies:

– Selection—fit the person to the job.

– Job modification—fit the job to the person

• Follow the second strategy: the key to progress

has been to challenge the environment.

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Exclude as Few as Possible

• Minimizes the number of people excluded, which

tends to make the job easier for everyone

• Balance seriousness of exclusion with cost of

inclusion


Population Dimensions

• Define the user population

• Consider the source of population dimensions

• factors influencing anthropometric measurements

– Male/female

– Military/civilian

– Age

– Ethnicity

– (Occupation)

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Excluded Percentile

• May be:

– Upper (a door tall people can’t fit under)

– Lower (a task requiring manual dexterity)

– Both (intelligence test for factory job)

• Designing for the mean may exclude half the population.


Body Position Descriptions

• Planes

– Saggital – divides the body into left and right half (medial/lateral)

– Coronal – divides the body into front and back half (anterior/posterior)

– Transverse – divides the body into top and bottom half (superior/inferior)

• Limbs

– Proximal: close to torso

– Distal: further from torso

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Body Position Descriptions

Saggital – divides the body into left and right half (medial/lateral)

Coronal – divides the body into front and back half (anterior/posterior)

Transverse – divides the body into top and bottom half (superior/inferior)


Wrist/Hand Motions

• Flexion – closes the joint angle from neutral position

• Extension – opens the joint angle from neutral position

• Adduction/ abduction – opens and closes laterally

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Wrist/Hand Motions

• Radial deviation/ulnar deviation


• Pronation / supination

Wrist/Hand Motions

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Body Dimensions

• Sample 95th percentile dimensions (cm) of unclothed U.S. adult civilians.

Female Male

Stature (height) 173.73 186.65

Eye height 162.13 174.29

Thigh height (sitting) 18.02 18.99

Forward reach 79.67 86.70

Hip breadth (sitting) 43.22 41.16

Weight (kg) 84.8 99.3


Variations in body dimensions

• Most body dimensions do not correlate well with stature, coefficient of determination R2 is less than 50%. So be careful when predicting other dimensions from stature

• Individual segment weights are calculated from total body weight

• In absence of data female may be estimated as 93% of male if no data available

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Body Dimensions

% of total body

weight

% of total body

surface area

Head 7.28 8.5

Arm 4.9 9

Leg 16.10 18

Trunk 50.70 38


Variations in Strength

• Females average 63% isometric strength of males

• Strength of specific muscle groups varies depending on

– Limb: Leg approx. 3 times strength of arm

– Direction exerted: Strength may decrease by 50%

– Preferred hand/arm/leg: Strength may vary by 40–50%

• Left and right leg strengths do not differ appreciably.

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Design for Population or Person?

• If for population, what population?

– Current employees?

– Potential employees?

– Everyone in the world?

• If for person, how?

– Adjustability?

– Discrete sizes?


How Many Sizes?

• How much does the population vary?

• How well can a specific size fit part of the population?

• How many dimensions are relevant?

• Sizes and adjustability interact.

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Statistical Calculations

• Normal distribution provides a close approximation

• Mean (average) is 50th percentile

• Normal distribution is symmetrical

• Absolute variability given by standard deviation

• Relative variability given by coefficient of variation


Normal Distribution

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Distribution Calculations

• To Find Percentile

– Find difference from the mean (subtract).

– Convert to standard units (divide by standard deviation).

– Use table to find percentile.


• To Find Dimension

– Use table to find number of standard units from mean.

– Convert to dimension measure (multiply by standard

deviation).

– Add or subtract mean.

Distribution Calculations

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An Example …

A study was performed to determine key anthropometric

measures of school-aged children to be used in the design of

playground equipment. Based on a sample size of 1050, the

vertical reach of 7-year old boys was found to have a mean of

57.1 inches and a standard deviation of 3.3 inches.

– 5th percentile = ___________________ (z = ______)

– 50th percentile = ___________________ (z = ______)

– 95th percentile = ___________________ (z = ______)


Design Principles

• Designing for extreme individuals

– Design for the maximum population value when a

maximum value must accommodate almost everyone.

E.g. Doorways, escape apparatus, ladders, etc.

• This value is commonly the 95th percentile male for the

target population.

– Design for the minimum population value when a

minimum value must accommodate almost

everyone. E.g. Control panel buttons and the

forces to operate them.

• This value is commonly the 5th percentile female for the

target population.

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Design Principles, continued

• Designing for an Adjustable Range

– Designing for the 5th female/95th male of the target

population will accommodate 90% of the population.

• 95% because of the overlap in female/male body

dimensions (if the male/female ratio is 50/50).

• Examples are auto seats, stocking hats

• Designing for the Average

– Use where adjustability is impractical, e.g. auto steering

wheel, supermarket check-out counter, etc.

– Where the design is non-critical, e.g. door knob, snack

machine, etc.


Application of manikins in ergonomic analysis of furniture

Mannequins - a two-

dimensional drawing or

figure which articulates

like ADAM

(Anthropometric Data

Applications Mannequin)

with plastic parts snap

together like clear

moveable paper dolls or

overlay transparencies.

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Common office environment posture measurements



The most common mannequins include the P5, P50,

and P95 models for both males and females.

The 5th% female value for a particular dimension (e.g.

sitting height) usually represents the smallest

measurement for design in a population.

Conversely, a 95th% male value may represent the

largest dimension for which one is designing.

The 5th% to 95th% range accommodates approximately

90% of the population.

To design for a larger portion of the population, one

might use the range from the 1st% female to the 99th%

male.

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When using anthropometric measurements in design,

consider two points:

1. How recently data was collected

2. Type of population measured

First, some data may have been collected over 25 years

ago, and measurements such as height or weight may

have changed in the current population.



The population one is designing for may not be represented by the

anthropometric database being referenced.

For example, ANSUR data may not be applicable in designing a

table used by elderly individuals or children.

Anthropometric measurements should be a guide for design.

(Natick studies or anthropometric survey of military personnel

ANSUR database.)

In 2000, the Civilian American and European Surface

Anthropometry Resource (CAESAR) was compiled by the Society of

Automotive Engineers (SAE) to measure civilian populations.

CAESAR contains anthropometric data and 3D body scans of

over 4,000 individuals from North America and Europe.

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End


Other Characteristics

• Age

• Aisles/corridors/doors

• Personal space

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Age of Workforce

• Birth rate is declining.

• Additional workers must come from

• Immigration

• Longer work hours

• Delayed retirement

• Older workers must be considered.


Aisles

• One-way traffic, people only: 3 ft min

• Door opening into aisle: 6 ft min

• Doors opening on both sides: 8 ft min

• Aisles for people only need not be straight

• Corridors (aisles with walls) must be wider

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Personal Space

• Intimate (0 – 18 in.)

• Personal (18 – 48 in.)

• Social (4 – 12 ft)

• Public (> 12 ft)

• Boundaries vary with gender, familiarity, and culture.


End of Chapter

eind 2303: work design and industrial...

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