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Chapter 12Chapter 12
Guidelines for Guidelines for Whole-Body Whole-Body and Segmental and Segmental VibrationVibration
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DefinitionDefinition• Vibration is the oscillatory motion
of a body• rapid changes in direction of a body• high acceleration
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DefinitionDefinition• Vibration is the oscillatory motion
of a body• rapid changes in direction of a body• high acceleration
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DefinitionDefinition• Vibration is the oscillatory motion
of a body• rapid changes in direction of a body• high acceleration
• Any body with mass and elasticity may vibrate
• machines• structures• human body
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Two Classifications of Two Classifications of Vibration:Vibration:• Free vibration
• when a system oscillates under the action of internal forces only• Ie water-balloon in the air
• Forced vibration• caused by external forces
• Opera singer and glass• external force: sound waves• glass vibrates
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Quantifying VibrationQuantifying Vibration
• Rate of oscillation • Regular ==> periodic motion
• sine wave• rep time = frequency
• Hertz ==> Hz
• Magnitude of oscillation • size of the force
• Peak value• maximum stress
• Average value• absolute value
Frequency Analysis
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Effects: body & segmentsEffects: body & segments• Primary determinants
• frequency• Magic fingers (1-2Hz) vs “tooth rattling”
• induce sleep
• amplitude• duration
• Secondary determinants• Point of application: buttocks, feet, hands• direction of input --fatigue• orientation of segments -- segment
mass• presence of external supports?
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Mechanical & Mechanical & PsychologicalPsychological
ResponsesResponses• Mechanical effects • strain on different tissues
• energy is absorbed by tissues and organs (muscles)
• voluntary & involuntary contractions of muscles (spindles)
• cause local muscle fatigue
• Psychological effects• stress reactions
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Effects on the spineEffects on the spine
• Research suggests that more low back pain occurs at an earlier age in subjects exposed to prolonged vibration• ie truck drivers, farmers, bus drivers,
pilots
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Effects on segmentsEffects on segments• Vibration on segments typically
• High Hz• Low Amplitude
• Vibration Syndrome (some all, some one)
• Injured blood vessels• Nerves• Bones• Joints• Muscles
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Reynaud’s Syndrome (vibration white finger)
• Cause• Vibration=> blocks finger circulation
• Symptoms• Fingers ==> white, pale, cold, & painful.• Impact on precision work.• Symptoms are intermittent.• 90% of the cases appear in women
• Etiology• Changes in blood vessel walls• Reflex contraction of blood vessel smooth
muscle
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Transmission of vibration Transmission of vibration in UEin UE
• Tools = random vibration over wide Hz • 2-2000 Hz
• Transmission is linear.• Increase in tool vibration = increase
in hand vibration • Greater grip force attenuates
transmission
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Vibration FactorsVibration Factors
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SummarySummary
• Vibration represents high frequency of application of a relatively low force• FIT
• Best avoided• Environment or task modifications• Administrative intervention (ie
rotation)