Characteristics of threshold vibration tangible to the tips of fingers have been observed over a range from 5 cps to 1000 cps with a vertical vibration generator. It is found that the thershold amplitude of vibration φ is proportional to
d2φ/
dt2 in the range of 5_??_150 cps, to φ in the range of 200_??_400 cps and to ∫∫φ(
dt)
2 in the range of 500_??_1000 cps where φ is the displacement and is represented approximately by
_??_
where
φ: the threshold vibration amplitude in μ,
K: the minimum value of φ in μ,
ƒ: the frequency per sec,
h: a damping constant,
n1 : the first order natural frequency of the vibration,
n2: the second order natural frequency of the vibration.
Actually the values of the constants
n1,
n2 and
K were
n1=160 cps,
n2=500 cps and
K=0.2μ.
It is concluded that the human body can be represented by a fine vibrograph, its magnification coefficient being equal to the product of that of displacement vibrograph and that of accelerometer.
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