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Anthropometry

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Facilitates prediction of a body's response and the design of the workspace interface ... New pliers with span of 11 cm (4.3') USAF women: average ht = 162.1 cm ... – PowerPoint PPT presentation

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Title: Anthropometry


1
Chapter 3
  • Anthropometry

2
Anthropometry
  • Deals with the measure of size, mass, shape and
    inertial properties of the human body segments.

3
Biomechanical Models
  • Facilitates prediction of a bodys response and
    the design of the workspace interface
  • Physical
  • crash test dummies

4
Biomechanical Models
  • Facilitates prediction of a bodys response and
    the design of the workspace interface
  • Physical
  • crash test dummies
  • Mathematical
  • Joint moment of force

5
Biomechanical Models
  • Facilitates prediction of a bodys response and
    the design of the workspace interface
  • Physical
  • crash test dummies
  • Mathematical
  • Joint moment of force

6
Biomechanical Models
  • Facilitates prediction of a bodys response and
    the design of the workspace interface
  • Physical
  • crash test dummies
  • Mathematical
  • Joint moment of force

7
Biomechanical Models
  • Facilitates prediction of a bodys response and
    the design of the workspace interface
  • Physical
  • crash test dummies
  • Mathematical
  • Joint moment of force

8
Measurement of Body-Segment Physical Properties
  • Segments defined by bony prominence (landmarks)
    (fig 3.2)
  • Human body system of rigid links
  • known physical size and form
  • connected at identifiable joints

9
Caveat Body-segment links
  • No joint in the human body is a simple
    single-axis hinge joints, but are considered so
    in many analyses (1 Degree of Freedom)
  • Assume
  • segments are rigid links
  • joints are frictionless and hinged

10
Body-segment links
  • Link lengths can be defined as the distance
    between projected centers
  • Resulting error in link length estimate is lt 5

11
Body-segment links
  • Acceptable degree of model simplification reflect
    analysis goal
  • Assumptions valid for most analyses
  • Crash test dummies require consideration of joint
    structure, ligaments, muscle response, organs,
    etc.
  • Injury risk (Lives!!) depends on the validity of
    the model

12
Average Segment Lengths as Proportion of Total
Body Height (TBH)see Table 3.7
13
Body-segment mass and weight
  • The mass of the body segments adds additional
    stresses to the body beyond those exerted by
    external forces (resistance to acceleration)
  • These weight related stresses can be of
    considerable magnitude in certain postures (a
    force)

14
Inertia
  • Resistance of an object to changing its current
    state of motion.

15
Body-segment inertial properties
  • When a segment can translate and/or rotate during
    activity, the inertial properties of the segment
    must be considered in the analysis

16
Two inertial properties to consider
  • Mass resistance to linear acceleration
  • Moment of Inertia resistance to angular
    acceleration

17
Conversions
  • Mass (kg) to Weight (lbs) multiply by 2.2
    (downward)
  • Mass (kg) to Weight (N) multiply by 9.81
    (downward)
  • Weight (lbs) to Weight (N) multiply by 4.45

18
Body-segment mass and weight
  • Body segment mass (weight) can be expressed as a
    proportion of whole-body mass (weight) without
    great loss of accuracy
  • TBM total body mass
  • Many sources exist (see p41 in text)

19
Table 3.4, p41
  • Recommended Values for Percentage distribution of
    total body weight
  • Grouped segments, of total body wt
  • Head and neck 8.4
  • Torso 50
  • Total arm 5.1
  • Total leg 15.7

20
data from Winter (1989) based on Dempster
(1956) data (overhead)
  • Percent distribution of total body mass
  • Grouped segments of total body wt
  • Head and neck 8
  • HAT 68
  • Total arm 5
  • Total leg 16

One of the most common sources for anthropometric
data.
21
Winter table
22
Winter table (contd)
23
Example
  • TBM of individual is 82 kg (180 lbs)
  • 82 kg x -9.81 804 Newtons
  • What is mass of upper body?
  • from Winter table HAT (head-arms-trunk) 67.8
    of TBM
  • Calculate (82 kg) x (0.678) 55.6 kg
  • 180 lbs x 0.678 122 lbs
  • 804 N x 0.678 545 Newtons

24
Body segmentcenter of mass location
  • Insufficient to know only the mass (weight) of a
    body segment to perform an analysis
  • Must locate the center of mass for each segment
    (and the entire body)
  • single point mass
  • point of application of the gravitational force
  • See Table 3.5 p43, Table 3.13 p.48
  • Better off Winter overhead

25
Winter table
26
Example
  • Arm of individual is 51 cm (20 inches) long
  • 0.51 m long
  • Locate Center of mass
  • from Winter table 0.53 (53 of arm length from
    the proximal end)
  • Calculate (0.51 m) x (0.53) 0.27 m from the
    proximal end of arm

27
Importance
  • Knowledge of
  • mass center location in segment
  • TBM (weight)
  • link length
  • sufficient input for static analysis to calculate
    forces and moments at each joint for a given body
    posture.

28
Draw a FBD of Arm (60 inches, 215 pound person)
29
Angular inertial properties
  • This property is referred to as
  • Inertia (linear motion)
  • moment-of-inertia (angular motion)
  • not only mass, but mass distribution
  • Varies according to Axis
  • Varies according to mass distribution

I m r2
30
Moment of Inertia
  • greater the moment of inertia
  • greater inertial load
  • Greater joint stress

Example flexed vs straight elbow
31
Anthropometric Data for Biomechanics Studies in
Industry
  • anthropometric data defines the reach and space
    requirements of a specified population or
    equipment user
  • modeling and simulation
  • important consideration for workplace design

Making anthropometric measurements in the modern
world
32
Workplace Analyses
  • The book includes tables of PERCENTILE data for
    segment lengths, weights, mass-center location,
    and moment of inertia based on the general
    population.

95
z 1.645
5
z - 1.645
50
33
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34
Example application of Percentile Tables ( Table
3.8 3.9)
  • Table 3.8 Segment lengths as TBH
  • Table 3.9 the mean (50th), 5th and 95th
    percentile population heights.
  • design must strive to accommodate the 5th to 95th
    percentiles (M F)
  • Importance hand tools, workstation surfaces and
    seat design

35
Example Using USAF men and women
  • New pliers with span of 11 cm (4.3)
  • USAF women average ht 162.1 cm
  • USAF men average ht 177.2 cm
  • Calculate average hand length (0.108 x height)
  • Females 162.1 x 0.108 17.5 cm (6.9 )
  • Males 177.2 x 0.108 19.0 cm (7.5)

36
  • Male and female differences
  • Racial differences
  • (US vs Japanese)
  • Specific population
  • (ie source military, NASA, civilians)
  • number of subjects
  • source of variability (SD)
  • (ie NASA vs civilians)

37
Summary
  • Knowledge of anthropometry is important
  • Anthropometrics is basis of models
  • mass, length, and center of mass of segments
  • Design must accommodate 5th to 95th
  • appropriate sex, race, specific population
  • Will use the tables with future analysis
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