Dr. Katie CahillScience 295

The History of ErgonomicsFoundations of ergonomic science observed

in Ancient Greece- Hippocrates- Egyptian Dynasties

Term coined during World War II by Hywel Murell

Continued with the space ageFurther developed during the information

age

What is Ergonomics?AKA Human FactorsDerived from Greek words ergon (work) and

nomos (law)According to the IEA, ergonomics is the

scientific discipline concerned with understanding of interactions among humans and other elements of the system, and the profession that applies theory, principles, data and methods to design, in order to optimize human well being and overall system performance.

What is Ergonomics?Main focus is the safety of the personFactors:

Body posture and movement• Environmental factors• Work Organization

Interdisciplinary approach - biomechanics, physiology, psychology, mechanical engineering, industrial design, information technology and management

So what?Social Value

Human well being, safety, health and comfortReduces accidents at work, at home, etc. by

reducing human errorImproves relationship between operators and

equipmentDecreases absence from work

Diseases of musculoskeletal system (LBP) Psychological illnesses (stress)

User friendly products

So what?Economic Value

Reduction of costs by preventing work related problems

Health care costs for treatmentCosts associated with loss of laborCompanies can improve efficiency, worker

productivity and cost reductionErgonomically designed products deliver

benefits to customers and edge out competition Special situations – short vs. tall, overweight,

handicapped, elderly, pregnant women

Section I: The Human BodyAll humans have similar bodiesBodies of people evolve to meet special circumstances

Unique climates, special diets, athletic trainingDifferences in bodies within the species of mankindRecognize these differences to accommodate

individualityThe following chapters address these differences:

Chapter 1 Body SizesChapter 2MobilityChapter 3 Muscular WorkChapter 4 Body strength and load handling

Body SizesBody sizes differ

Growth cycle: quick growth during childhood, consistency for 20 – 40 years, degenerative changes

Men are normally taller than womenTaller and shorter individualsDiffering body proportions

The Earth’s PopulationsBodies of populations described in height and

weight Table 1.1 Average stature of 20 regionsAnthropometrics – study of the size and

proportion of the bodyWhy is it important to know the variances in

body stature?

How to measureMay need more specific measurements than

just height and weightTraditional method – taking measurements

with hand held devicesEmerging technique records 3D dimensions

of the human bodyFigure 1.1 = most common measurements

takenTable 1.3 use of the measurementsData is missing from many populations due to

its laborious and expensive nature

No “Average Person”Problems with average data

Can’t base designs of the average because too small for some and too large for others

Need to take into account the extremesNeed to understand the “normal” distribution

Statistically analyze a distribution curve“bell cure” or Gaussian curveMajority cluster in the middle and outliers on

either end represent extremes

Normal Distribution Curve

Average and Standard DeviationAverage is the measure of the middle or

expected value of a data setThe standard deviation is a statistic that tells

you how tightly all the various examples are clustered around the mean in a set of data

With tightly bunched data, the bell-shaped curve is steep, the standard deviation is small

With spread apart data, the bell curve is relatively flat, the standard deviation is large

Smaller SD = more reliable data

PercentilesNumerical value of a specific point in a

distribution calculated from the mean and the standard deviation

The mean is normally in the fiftieth percentile range; half the data lies above and half below

Fifth percentile is of design interest: <5% and >95%

p5 is 1.65 SD below the mean and p95 is 1.65 SD above the mean

Table 1.6 Values necessary to calculate percentage points

Hand Size DataFigure 1.3 and Table 1.7Hand measures

LengthBreadth of knucklesMaximal breadthCircumference at knucklesWrist Circumference

Designing to Fit the BodyEven among seemingly similar groups, body

sizes and segments differEx 1 US agriculture workers are shorter by an

average of 2.5 cm than other workersEx 2 Female American agriculture workers

have larger waist circumferences than other occupations

Ex 3Protective Service workers are taller and heavier

Design Principles1. Custom fit each individual2. Have several fixed sizes3. Make it adjustable4. Design for the extreme bodies; assures any

individual can: Operate a gadget Fit through any opening Cannot pass through a dangerous opening

5. Select those persons whose bodies fit the existing design

Fit a RangeSolutions 2 and 3 are the most commonAllows us to select a body size range we

intend to accommodateAim to accommodate the central 90%Exclude the top and bottom 5%; total 10%

extreme sizes

Select Design LimitsMinimum and maximum depend on design

purposeSeveral sizes (solution 2)

Ready made clothingAdjustment features within a range (solution 3)

Shoes with lacesOffice chairs

Statics and dynamicsData collected is often in a static positionMovement must be taken into account with

designs (Table 1.8)

SummaryFitting equipment and tasks to individuals

requires:Anthropometric dataProper procedures

Data is available on many populations, missing data must be estimated

Design procedures often involve selection of middle range of the normal curve to accommodate the majority of the population