Title: Motion
1Motion
- Main Topics
- Vibration
- Acceleration
- Illusions during Motion
- Motion Sickness
2Two 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)
3Senses 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
4Ways 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
5Effects 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
6Effects 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)
7Effects 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
8Subjective 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
9Limits 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
10Limits 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
11Control 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
12Acceleration
- 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
13Acceleration
- 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
14Acceleration
Head over heels
Around main body axis - spiral nose dive - forces
alternate /-
15Acceleration Duration
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
16Acceleration 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
17Methods 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
18Resulting Forces on the Body
-Gz Eyeballs Up
-Gy Eyeballs Right
Gx Eyeballs In
-Gx Eyeballs Out
Gy Eyeballs Left
Gz Eyeballs Down
19Effects 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
20Effects 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
21Effects 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
22Effects of Directional Forces
- Effects of -Gx
- Acceleration spineward
- Effects the opposite of Gx
- Tolerance 30G
23Effects 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
24Deceleration (Impact)
- Exposures less than 2/10 second
- Extremely abrupt
- Reverse acceleration
- Mainly in forward/backward direction
25Deceleration (Impact)
Magnitude
26Deceleration (Impact)
- Factors affecting the impact of an impact
- Rate of Onset
- Peak G
- Stopping Distance
- Angle of Impact
27Tolerance
- 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
28Protection
- 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
29Weightlessness
- 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
30Illusions 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
31Illusions 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
32Motion Sickness
- Cause incongruities among senses
Vestibular (inner ear tubes)
33Motion Sickness
- Head Symptoms
- drowsiness
- general apathy
- Gut Symptoms
- nausea
- vomiting
- Sensory Rearrangement Theory
- sensory systems provide contradictory information
- Simulator Sickness
- exact cause unknown