The thresholds of perception of vibration by recumbent men are a significant index for the governmental agency concerned with regulation of vibration exposure. The thresholds of perception of continuous sinusoidal vibrations and single and multiple bursts of sinusoidal vibrations in the horizontal and vertical directions were investigated in recumbent men. We found that the threshold curves, as a function of the frequency, had different characteristics for vertical vibrations than for horizontal vibrations in the recumbent position. The threshold values for pulsed vibrations became smaller (easier to perceive) as the bursts were elongated until saturation occurred at 4 s duration. Threshold values for pulse durations longer than 4 s were the same as those for continuous vibration. This suggests the existence of temporal integration of sensation of vibrations as in psychoacoustics.
An acceleration measuring apparatus in Z direction with about 50 gr weight and a mechanical hand for simulating the human hand were constructed so as to measure isolation effectiveness of vibration isolation gloves. The glove, the acceleration measuring apparatus and the model hand were pressed in this order by an aircylinder by about 1 kg/cm2 on a vibration table of electro-dynamic type. The vibration frequency was swept from 10 to 1000 Hz in order to measure insertion loss of the glove. tion characteristic of the glove, namely, the gloves were non-effective below this resonance frequency but they showed attenuation near 12 dB/oct above this resonance.
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