Introduction to Human Factors/Ergonomics (HFE)

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Introduction to Human Factors/Ergonomics
(HFE)Engineering Anthropometry

• Hardianto Iridiastadi, Ph.D.

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Introduction

• Variability in physical dimensions
• Studied earlier in Anthoropology (study of
  mankind)
• Interest in physical aspects (beginning of
  anthropometry)
• Later, data are used for biomechanics
  investigations
• The need to design workplaces to accomodate
  differences in body dimensions

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Human variation
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Factors Affecting Anthropometrical Variation

• Age
• Gender
• Race Ethnic
• Socio-economics
• Occupation
• Life style
• Circadian
• Secular trend
• Measurement

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Ergonomic Implications

• International markets
• Different target countries
• Transfer of technology
• Job selection
• Healthy worker effect
• Fit the man to the job

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Engineering Anthropometry

• a branch of science originating from
  anthropology that attempts to describe the
  physical dimensions of the (human) body
• anthropos man
• metron measure

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Types of Anthropometric Data

• Physical (Static) anthropometry which addresses
  basic physical dimensions of the body.
• Functional anthropometry concerned with
  physical dimensions of the body relevant to
  particular activities or tasks.
• Newtonian data body segment mass data and data
  about forces that can be exerted in different
  tasks/postures

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Applications

• Tools design
• Consumer product design
• Workplace design
• Interior design

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Applied Anthropometry
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Measurement Techniques

• Positions
• Standing naturally upright
• Standing stretched to maximum height
• Lean against a wall
• Sitting upright
• Lying (supine posture)
• Anatomical position (see Kroemer et al)

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Measurement Techniques

• Some key measurement terms
• Height
• Breadth
• Depth
• Distance
• Curvature
• Circumference
• Reach

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Measuring Devices
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Newer Measuring Devices

• Photograph
• Use of grids
• Image processing techniques
• Can record all three dimensional aspects
• Infinite number of measurements
• Drawbacks
• Parallax
• Body landmarks cannot be palpated

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Newer Measuring Devices

• Whole body scanner
• Ergonomic center UI
• 50,000 - 400,000
• Hundreds of variables
• Standing and
• seated posture
• Combined with
• modeling software
• (Jack, Mannequin, etc.)

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Sample Anthropometric Data
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Statistics

• Coefficient of variation
• Data diversity sd/mean
• CV 5 (10 for strength data)
• Large CV should be suspected
• Standard error of the mean (se)
• se sd/vn
• Useful for describing confidence interval
• E.g., 95 CI mean 1.96 se

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Statistics

• Means (?) and standard deviations (?) are
  typically reported for anthropometric data (often
  separated by gender)
• Use of these value implicitly assumes a Normal
  distribution. Assumption is reasonable for most
  human data.
• Percentiles can easily be calculated from mean
  and std.dev. using these formulas and/or standard
  statistical tables (usually z).

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Statistics

• Percentile
• Commonly used 5th, 95th, 50th (median)
• Lower-limit dimension the smaller the system,
  the more unusable by the largest user ? Use high
  percentile
• Upper-limit dimension the bigger the system, the
  more unusable by smallest user ? Use low
  percentile

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Statistics - Standard Normal Variate

• Z (y-?)/?
• Normally distributed with mean 0 and variance
  1
• z is N(0,1)
• From tables of normal cumulative probabilities
• Pzz(A) A
• Example if zA 2, A 0.9772 (two std.dev.
  above mean is the 97.7-ile)
• Properties of z
• zA gt 0 above mean (gt50-ile)
• zA 0 at mean (50-ile)
• zA lt 0 below mean (lt50-ile)

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Normal Distribution Table
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Percentile Example

• For female stature (from Table)
• ? 160.5 cm
• ? 6.6 cm
• What female stature represents the 37.5th -ile?
• From normal distribution
• z(37.5) -0.32
• Thus, X(37.5) ? z?
• 160.5 - (0.32)(6.6)
• 158.4 cm

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Anthropometric Data Variances

• To combine anthropometric dimension, need to
  calculate a new distribution for the combined
  measures, accounting also for the covariance
  (Cov) between measures (M mean S std. dev.)

MXY MX MY SXY SX2 SY2
2Cov(X,Y)1/2 SXY SX2 SY2
2(rXY)(SX)(SY)1/2 MX-Y MX - MY SX-Y SX2
SY2 - 2Cov(X,Y)1/2 SX-Y SX2 SY2 -
2(rXY)(SX)(SY)1/2

• Means add, variances do not!

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Class Activity
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Anthropometrical Design Procedures

1. Determine dimensions of product which are
   critical for design (considering effectiveness,
   safety and comfort)
2. Determine the related body dimensions
3. Select user population (who will use the product
   or workplace)
4. Conduct reference study to find secondary data,
   if available (considering population
   characteristics) or conduct measurement
5. Select percentile

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The Average Human

• Anthropometric data for individuals is often
  estimated using stature or body weight in linear
  regression equations.
• Ex average link lengths as a proportion of body
  stature
• Advantages
• Simplicity
• Disadvantages
• relationships are not necessarily linear, nor the
  same for all individuals
• Values represent averages for a portion of a
  specific population

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Anthropometry in Design

• Anthropometric data is most often used to specify
  reach and clearance dimensions.
• The criterion values most often used
• Reach 5 Female
• Clearances 95 Male
• Try to accommodate as large as possible user
  population within constraints

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Design Approaches

• Design for extremes
• emphasize one 'tail' of distribution
• Design for average
• emphasize the center of a population distribution
• Design for adjustability
• emphasize that all potential users/consumers are
  'equal
• Varying ranges of accommodation
• 5th-95th ile typical
• 25th-75 ile less critical functions or
  infrequent use
• 1st - 99th ile more critical functions /- low
  
• 0.01 - 99.99 ile risk of severe outcomes

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Design for Extremes

• Example Door Height
• Assuming a normal distribution
• z (X - ?)/?
• Obtain z gt -ile from stats table
• What height to accommodate? (95th-ile male)
• ? 69 ? 2.8 (from anthropometric table)
• z0.95 1.645 (X - 69)/2.8 gt X 73.6
• Additional allowances?
• Hair
• Hats and shoes
• Gait
• Etc.

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Examples
Which design strategy should be employed?

• leg clearance at a work table
• finger clearance for a recessed button
• height of an overhead conveyor system
• grip size for a power tool
• weight of a power tool
• height of a conveyor
• strength required to turn off an emergency valve

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General Strategies and Recommendations

• Design for Average
• Usually the worst approach both larger and
  smaller users wont be accommodated
• Design for Extremes
• Clearance use 95th percentile male
• Reach use 5th percentile female
• Safety accommodate gt99 of population
• Design for Adjustability
• Preferred method, but range and degrees of
  adjustment are difficult to specify

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Homework

• Working in groups
• Select a workplace near campus. Identify any
  ergonomic mismatch. Suggest how the workplace
  can be better designed from the perspective of
  engineering anthropometry. You should outline the
  design approach.
• Pick a journal paper that discusses the use of
  anthropometric data in design. Submit a one-page
  summary (in Indonesian) of the paper. Also submit
  softcopy of the paper.