The influence of vibration duration and the amount of rest between successive vibrations was addressed in Part I of this study. The relationship between discomfort and Vibration Total Value for different axes of vibration is assessed in Part II. Ten subjects were exposed to repeated single axis, planar, and 6 degree of freedom multi-axial vibrations. We observed statistically significant differences in discomfort between the different axes of vibration for similar ranges of Vibration Total Values. In particular. we observed that discomfort reports for vibrations in the Z axis and XY plane were less than discomfort reports associated with XZ plane and 6 df vibrations when the same range of Vibration Total Values were compared. Furthermore, single axis vertical vibrations were typically associated with less discomfort than multi-axis vibrations when similar ranges of Vibration Total Values were compared. This finding infers that the frequency weighting scheme presented in ISO 2631–1 does not achieve inter-axis equivalence and indicates that a more comprehensive study of multi-axis vibration is required to suggest changes to the ISO 2631–1 weighting factors.
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