STUDY OF HUMAN-SEAT INTERFACE PRESSURE DISTRIBUTION UNDER VERTICAL VIBRATION

The influence of whole-body vertical vibration on the dynamic human-se at interface pressure is investigated using a flexible grid of pressur e sensors. The ischium pressure and the overall pressure distribution at the human-seat interface are evaluated as functions of the magnitud e and frequency of vibration excitation, and seated posture and height . The dynamic pressure at the seat surface is measured under sinusoida l vertical vibration of different magnitudes in the 1-10 Hz frequency range. Two methods based on ischium pressure and ischium force are pro posed to study the influence of seat height, posture and characteristi cs of vibration. The results of the study reveal that the amplitude of dynamic pressure component increases with an increase in the excitati on amplitude in almost entire frequency range considered in this study . The dynamic components of both the ischium pressure and the ischium force reveal peaks in the 4 to 5 Hz frequency band, the range of prima ry resonant frequency of the seated human body in the vertical mode. T he mean values of the dynamic ischium pressure and the ischium force r emain constant, irrespective of the excitation frequency and amplitude . The magnitudes of mean pressure and force at the human-seat interfac e, however, are dependent upon the seat height and the subject's postu re. The inter-subject variability of the static ischium pressure and e ffective contact area are presented as functions of the subject weight and subject weight-to-height ratio, II was found that heavy subjects tend to induce low ischium pressure as a result of increased effective contact area.