Relative contribution of translational and rotational vibration to discomfort.

Understanding how vibration affects discomfort is an important factor for improving work and travelling experience. Methods of evaluating health effects from whole-body vibration are closely linked to those for evaluating discomfort in ISO 2631-1. The standard includes a method to evaluate discomfort using twelve axes of vibration with a similar approach to that for evaluating health effects; thus using all twelve axes gives a possibility to evaluate both health and discomfort. The full 12-axis method has not been widely used in practice or validated in a multi-axis environment. The standard guidance is not explicit, thus different interpretations are possible especially when determining the method of comparing or combining vibration in different axes. Furthermore there are not enough studies conducted in multi-axis environments to suggest the optimal combination of axes. In this study ISO 2631-1 method was tested and optimised using a multi-axis test bench at Loughborough University, UK. Subjects were exposed to stimuli which represented vibration characteristics from field measurements. Each stimulus, lasting 15 s, was judged using a continuous judgement, cross-modal matching method. The seat translational and rotational and the backrest translational axes were used in the analyses. There was no vibration at the floor, in order to constrain the number of independent variables. Results showed that correlation for discomfort improved with more complex analysis procedures. However a good correlation was also achieved using just seat translational axes with optimised multiplying factors. The results showed that frequency weightings and r.m.s. averaging improved correlation between vibration and subjective ratings of discomfort. Multiplying factors specified in ISO 2631-1 degraded the correlation between objective and subjective measures of discomfort, therefore an improved set of factors were determined. The new factors showed improvement by placing more emphasis on seat fore-and-aft and lateral axes.