Effects of whole-body vertical shock-type vibration on human ability for fine manual control

The effects of vertical (z-axis) whole-body shock-type vibration on the ability for fine manual control were examined. The amplitudes and frequency of the shocks was varied, but a constant frequency-weighted acceleration of 1.25 m/s2 r.m.s. was maintained. The examination of the shock's effects was carried out using an experimental system that simulated the actual workplace of earth-moving machinery. Control was measured using a first-order pursuit tracking-test, in which a seated subject was asked to use both hands to direct a cursor on a monitor using a steering wheel. Although the magnitude of shocks (peak amplitude of 6-10 m/s2) and the number of shocks per unit time (shock cycle of 10-40 s) were varied, and two types of shock (symmetric and asymmetric) used, no shock effect could be found by calculating an integrated square of tracking error during the whole exposure time. The tracking error only increased significantly during the moments that the subjects were exposed to a symmetrically shaped shock that reached the highest peak value (for the experiment) of 10 m/s2. The results suggested that shocks with peak amplitudes below defined value induce no evident effect on the steering of vehicles.