The Effect of Rotational Vibration In Roll and Pitch Axes on the Discomfort of Seated Subjects

Abstract

An experiment was performed to investigate the effects of vibration level, frequency and foot position on the discomfort of seated persons subjected to sinusoidal vibration in roll and pitch axes. Using the method of category production eight seated subjects adjusted roll and pitch vibrations lo levels described as ‘uncomfortable’ on a given semantic scale. The axes of rotation were located on the same horizontal plane as the ischial tuberosities of the subjects. In each axis subjects assessed the discomfort of six frequencies (1-6, 20, 40. 80, 160, 31-5 Hz) for each of four different heights of a stationary foot-rest and a condition where no foot-rest was used. For all conditions where a foot-rest was present rotational vibration in roll produced greater discomfort than the same level of rotational vibration in pitch. Sensitivity to relational acceleration decreased with increasing frequency in both roll and pitch axes for all foot positions. Subjects became less sensitive lo rotational vibration in roll and especially pitch as foot height was raised. This was attributed lo the decreased contact between the rotating seal and the thighs at higher foot positions.