Evaluation of whole-body vibration by the category judgment method.

The purpose of this research is to establish a scale for comfort with regard to whole-body vibration by the category judgment method. Experiments were conducted with random signals as stimuli. These stimuli consisted of three types of signal, namely stimulus F, with flat PSD (Power Spectrum Density) ranging from 1 to 100 Hz, stimulus H with PSD, which became 20 dB higher at 100 Hz than at 1 Hz, and stimulus L that had a PSD 20 dB lower at 100 Hz. These signals were modified by Wk frequency weighting in accordance with ISO 2631-1, and the R.M.S. values were adjusted to be equal. In addition, the signal levels were varied over a range of five steps to create 15 kinds of individual stimuli. The subjects sat on a flat, horizontal metal plate mounted directly on the vibrator and were exposed to vertical vibrations before being asked to choose a numerical category to best indicate their perceived level of comfort (or otherwise) during each stimulus. The creation of this assessment scale, including the aforementioned categories, enabled not only clarification of the relationship between the vibration stimuli and the degree of comfort but also discovery of the connection between the frequency-weighted R.M.S. acceleration and the corresponding categories representing each degree of comfort without overlap. Moreover, it became clear that the subjects' assessment of the degree of comfort perceived differed with differences in the vibration spectrum.