Some problems with the measurement of 6-DOF head motion in low frequency range were investigated in this study. To measure the 6-DOF head motion for a long time run, the roller-blade helmet was used. This causes a problem that a relative motion between the human head and the helmet may distort signals from the human head motion. The 12-axis bite bar, which was used frequently in earlier researches, was employed to compare with the helmet. Finally, it was concluded that the helmet could be applied for measuring and estimating of the 6-DOF head motion in low frequency range.
The next problem is the angular-velocity terms that exist in the kinematic equation of motion for the 6-DOF head motion. These terms would possibly cause an inconvenience of estimating the 6-DOF head motion. To examine these angular-velocity terms addressed here, experiments on a bus, a car and a ship were conducted. Their effects on the estimation of the 6-DOF head motion were done that they cannot be ignored, but should be considered carefully.
