Abstract
Head motion has been measured in six axes on twelve subjects exposed to vertical seat vibration in the frequency range 0.5–25 Hz. The subjects sat on a rigid flat seat in two postures: ‘back-off’ (no backrest) and ‘back-on’ (subject's back in contact with the seat backrest). Translational acceleration has been calculated for various locations on the head and transmissibilities between vertical seat vibration and translational head motion determined for each location and all axes. The translational motion of the head was most affected by pitch motion of the head. This caused variations in fore-and-aft motion with position along the vertical axis of the head and variations in vertical motion with position along the fore-and-aft axis of the head. These variations are illustrated for each subject in both postures. The individual data allow the identification of various modes of vibration and show that seat-to-head transmissibility is greatly affected by pitch modes of the head and neck. The magnitude of motion occurring in some modes is dependent on body posture.
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