Transcript VIBRATION - University of Waterloo

VIBRATION
Copyright Catherine M. Burns
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What’s a vibration?
• A vibration is an oscillation of a mass about
a fixed point.
• Can include regular or irregular movements
• Regularity implies periodicity
Copyright Catherine M. Burns
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• In human factors, you are referring to
oscillations of body parts.
– sound is a vibration of cells in the ear.
– jack hammer operation, vibration of arms.
– Vibration may be total body vibration or
individual limbs, or individual cells.
Copyright Catherine M. Burns
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• People analyse point of application of
vibration
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usually main body (seat)
hands
feet
(key is point of contact with external force)
Copyright Catherine M. Burns
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• 2. Direction or vector of vibration
– vertical or perpendicular to body or limb?
• 3.Frequency of oscillation
– low range, high range, or at a resonant
frequency?
• 4.Acceleration of oscillation
– measure of load of oscillation
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• 5. Duration
– how long do they continue?
• 6. Do they match a resonant frequency and
therefore magnify in amplitude
• 7. How well does the body dampen the
oscillation?
– Stats: oscillations at a frequency of 35 Hz are
reduced 1/2 by hands, 1/3 by elbows, 1/10 by
shoulders. Copyright Catherine M. Burns
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Resonant frequencies of the
Human Body
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3-4 Hz cervical vertebrae resonates
3-6 Hz stomach resonates
4-5 Hz hands resonate
4-6 Hz heart resonates
5-20Hz larynx resonates (voice will change pitch)
10-18 Hz bladder resonates (will need to visit
bathroom)
• 20-70 Hz eyeballs resonate (can't see)
Copyright Catherine M. Burns
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Physiological effects of Vibration
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affects visual perception
motor abilities
circulatory and respiratory systems
increased energy consumption as muscles
flex and relax to absorb vibrations
Copyright Catherine M. Burns
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Effects on Vision
• start at about 4 Hz
• mostly at 10-30 Hz
• reductions in visual acuity
Copyright Catherine M. Burns
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Typical complaints with seated
vibration
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difficulty breathing
annoyance
chest pains, teeth rattling 4-10 Hz
back ache 8-12 Hz
muscular tension
Copyright Catherine M. Burns
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Chronic exposure
• seat or feet - degenerative changes in the
spine
• arthritis and discs
• arms and hands - degeneration of joints
tendons and bones in wrist elbow and
shoulder
• bone atrophy leading to fractures
• "dead fingers"
Copyright Catherine M. Burns
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Dead fingers or Raynaud's
disease
• typically caused by 40 to 300 Hz with small
amplitude (0.2-5mm)
• power tools, e.g. pneumatic drills or power saws
• hands dampen the vibration
• blood vessels close reflexively to shunt blood
from vibrating fingers
• fingers go "dead"
• blood returns causing cramping
• starts after aboutCopyright
6 months
Catherine M. Burns
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Repetitive Strain Injuries
• sometimes considered to be a type of
vibration
• keyboard kicks back vibration to fingers.
Copyright Catherine M. Burns
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Design arounds
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Damping elements
suspension systems in vehicles
flexible handgrips
gloves
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