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Motion

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Motion Main Topics Vibration Acceleration Illusions during Motion Motion Sickness – PowerPoint PPT presentation

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Title: Motion


1
Motion
  • Main Topics
  • Vibration
  • Acceleration
  • Illusions during Motion
  • Motion Sickness

2
Two General Classes of Motions
  • Volitional, Low-Speed
  • Issues Concerned
  • Non-Volitional, High-Speed
  • Issues Concerned
  • Tolerance
  • Safety and protection
  • Impact and acute effects
  • Illusion
  • Vibration a special entity
  • Permanence (S-A trade-off)
  • Strategy to minimize stress
  • Accumulative effects (low force)
  • Acute effect (forceful exertion)

3
Senses Related to Motion
  • Sensory Receptors
  • Exteroceptors
  • Proprioceptors
  • Semicircular Canals
  • Vestibular Sacs
  • postural/balance sensors
  • (Figure 19-1)
  • Conflict between visual perceptions and actual
    gravity

deal with stimuli external to the body
stimulated by bodys own actions
acceleration/deceleration sensors
4
Ways to Describe Vibration
  • Type (Wave Form)
  • Sinusoidal vs. Random
  • Direction
  • Forward-Backward
  • Left-Right
  • Up-Down
  • Frequency
  • Cycles per second
  • Intensity
  • Amplitude (Displacement)
  • Velocity
  • Acceleration
  • Rate of acceleration change

5
Effects of Vibration on the Body
  • 1. Transmission
  • Attenuation
  • Amplification
  • Resonance

3-4 Hz Resonance in cervical (neck
vertebrae) 4 Hz Peak resonance in lumbar
(upper torso) vertebrae 5 Hz Resonance in
shoulder girdle 20-30 Hz Resonance between
head and shoulders 60-90 Hz Resonance in
eyeballs
6
Effects of Vibration
  • 2. Physiological Effects
  • Short-term exposure
  • increased HR
  • increased muscle tension
  • urge to urinate
  • chest pain
  • Long-term exposure
  • increased risk of disc herniation
  • increase risk of low-back pain
  • increased risk of Reynauds Syndrome or Traumatic
    Vasopastic Disease (TVD)

7
Effects of Vibration
  • 3. Performance
  • Visual Performance
  • impaired by vibration of 10-25 Hz
  • minor effect in low frequency range due to
    head/eye compensatory motion
  • Motor Performance
  • vertical sinusoidal vibration of 4-20 Hz most
    detrimental
  • dependent on display and control
  • Neural Process
  • central neural processes (e.g., RT, pattern
    recognition) highly resistant to vibration effect
  • tension in muscle increases vigilance

8
Subjective Responses Whole-Body Vibration
  • Comfort scale
  • mildly uncomfortable
  • annoying
  • very uncomfortable
  • alarming
  • Attempt to link frequency acceleration to
    comfort scales
  • Equivalent-comfort contours
  • Large inter-person variability makes design
    considerations challenging

9
Limits of Exposure to Whole-Body Vibration
  • Criterion-based
  • comfort, task performance, or physiological
    response
  • ISO 2631
  • most applicable for transportation and industrial
    type vibration exposures
  • Fatigue-Decreased Proficiency (FDP)
  • Figure 19-7, page 634

10
Limits of Exposure to Whole-Body Vibration
  • Criticisms of FDP
  • 1. Comfort and FDP limits for short exposures
    maybe too high
  • 2. Appear to be based on mean results
  • 3. Imply the effects of multiple single-axis
    vibrations are additive
  • 4. Similar shaped contours are an
    oversimplification
  • 5. Comfort contours may be inaccurate at extreme
    frequencies
  • 6. Assumes time/intensity trade-off with little
    support

11
Control of Vibration
  • Source Control
  • Reduce intensity
  • Avoid resonance
  • Provide tool balancing
  • Use non- or less vibratory tools
  • Path Control
  • Provide rest period
  • Reduce transmission (attenuate)
  • Use isolator
  • Receiver Control
  • Use isolating or damping apparatus
  • Adopt more resistant postures
  • Reduce grip force
  • Reduce contact area

12
Acceleration
  • Terminology
  • 1. Acceleration
  • Rate of change of motion
  • 2. Linear acceleration
  • Rate of change of velocity
  • 3. Rotational acceleration
  • Rate of change of direction
  • Radial (centrifugal) acceleration
  • Angular (tangential) acceleration
  • Nystagmus

involuntary oscillatory movement of the eyeball
13
Acceleration
  • Direction (Figure 19-8)
  • 1. X-Axis Forward/Backward
  • 2. Y-Axis Left/Right
  • 3. Z-Axis Headward/Footward
  • Follows right-hand rule (RHL)

Look at motion of the eyeballs to determine the
direction of acceleration Eyeballs go opposite
of acceleration, and same direction as
deceleration
14
Acceleration
  • 4. Tumbling
  • 5. Spinning

Head over heels
Around main body axis - spiral nose dive - forces
alternate /-
15
Acceleration Duration
  • Sustained
  • Abrupt

Begins at 2/10 second and continues Effects
are primarily physiological
Shorter acceleration, less than 2/10
second Mainly effects of impact or
rapid deceleration Effects are primarily physical
16
Acceleration Duration
  • Three Categories
  • Short
  • Intermediate
  • Long

- less than 1 second - impact or acute effect
- 1/2 to 2 second duration - very abrupt
- greater than 2 seconds through several minutes
17
Methods of Study
  • Tracks
  • Centrifuges
  • Suicides/Accidents
  • Usually acceleration/deceleration studies
    performed on tracks
  • Slide/ejection tests in impact laboratories
  • Help to study the effect of non-linear
    acceleration
  • Rotary chairs or vehicles
  • Haven - Golden Gate Bridge and Brooklyn Bridge
  • Real field studies if caught on tape
  • Reconstruction or simulation

18
Resulting Forces on the Body
-Gz Eyeballs Up
-Gy Eyeballs Right
Gx Eyeballs In
-Gx Eyeballs Out
Gy Eyeballs Left
Gz Eyeballs Down
19
Effects of Directional Forces
  • Effects of Gz (Figure 19-9)
  • Acceleration headward
  • Increase in weight drooping of face and soft
    tissues
  • Difficult or impossible to raise oneself
  • Blackout loss of consciousness
  • Cardiac output and stroke volume decrease while
    HR, aortic pressure, and vascular resistance
    increase
  • Maximum Tolerance 16 G

20
Effects of Directional Forces
  • Effects of -Gz
  • Acceleration footward
  • facial congestion
  • headache
  • blurring, graying, reddening of vision
  • Limit at -5 G is about 5 s
  • Maximum Tolerance 10 G

21
Effects of Directional Forces
  • Effects of Gx (Fig 19-10, -11)
  • Acceleration sternumward
  • Speech difficult
  • Progressive tightness and pain in chest
  • Difficulty in lifting body parts
  • Blurring of vision
  • Dyspnea
  • Maximum Tolerance 30 G

22
Effects of Directional Forces
  • Effects of -Gx
  • Acceleration spineward
  • Effects the opposite of Gx
  • Tolerance 30G

23
Effects of Directional Forces
  • Effects of /- Gy
  • little information on these effects
  • mainly encountered in an aircraft
  • magnitude is relatively small compared to other
    directions
  • less common in occupational settings

24
Deceleration (Impact)
  • Exposures less than 2/10 second
  • Extremely abrupt
  • Reverse acceleration
  • Mainly in forward/backward direction

25
Deceleration (Impact)
Magnitude
26
Deceleration (Impact)
  • Factors affecting the impact of an impact
  • Rate of Onset
  • Peak G
  • Stopping Distance
  • Angle of Impact

27
Tolerance
  • Survivable
  • limit around 30-40 Gs
  • can only endure for 0.25 seconds
  • Injury
  • Death

60 G with rate of onset 5000 G/sec
200 G with rate of onset 5000 G/sec
28
Protection
  • 1. Restraining Devices
  • seat belt
  • 2. Absorbing Devices
  • air bag
  • 3. Special Contoured Seats
  • secondary collision minimized
  • 4. Body Posture
  • direction-dependent stiffness or resistance
  • 5. Water Immersion
  • damping
  • 6. Anti-G Suits
  • can take up to 9 G

29
Weightlessness
  • Two Aspects
  • absence of weight itself
  • tractionless condition
  • Both remain to be fully investigated
  • Physiological Effects
  • Performance Effects
  • space sickness (space adaptation syndrome)
  • anthropometric change height growth 3
  • relaxed posture assumed
  • (Figure 19-13)
  • exhaustion due to the added third dimension in
    locomotion

30
Illusions During Motion
  • Human senses are not designed for extremely
    dynamic motions and unusual, prolonged forces
    encountered in special settings
  • Disorientation from False Sensations (due to
    inaccurate sensory information)
  • disrupted vestibular-visual coordination
    illusion of spinning in opposite direction
  • Coriolis illusion illusion of roll during
    turning or circling motion
  • oculogravic illusion impression of tilt during a
    sudden increase of forward speed

31
Illusions During Motion
  • Disorientation from Misperception
  • (due to brains misinterpretation or
    misclassification of accurate sensory information
  • Autokinesis
  • fixed light appears to be moving against a dark
    background

32
Motion Sickness
  • Cause incongruities among senses

Vestibular (inner ear tubes)
33
Motion Sickness
  • Head Symptoms
  • drowsiness
  • general apathy
  • Gut Symptoms
  • nausea
  • vomiting
  • Sensory Rearrangement Theory
  • sensory systems provide contradictory information
  • Simulator Sickness
  • exact cause unknown
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