Seated occupant interactions with seat backrest and pan, and biodynamic responses under vertical vibration

Abstract The relative interactions of the seated occupants with an inclined backrest were investigated in terms of apparent mass (APMS) responses at the two driving-points formed by the buttock–seat pan and the upper body-backrest under exposure to broad-band and road-measured vertical vibration. The measurements were performed using 24 adult subjects seated with full contact with the back support and two different positions of the hands (in lap and on steering wheel), while exposed to three different levels of broad band (0.25, 0.5 and 1.0 m/s 2  rms acceleration) vibration in the 0.5–40 Hz frequency range, and a track-measured vibration spectrum (1.07 m/s 2 rms acceleration). The forces developed on the seat pan and the backrest in directions normal to the supporting surfaces were measured to derive the APMS responses at both the driving-points. The results showed significant interactions of the upper body with the back support in a direction normal to the backrest, even though the vibration is applied along the vertical axis. At low frequencies, the backrest APMS magnitude was smaller than that measured at the seat pan, but it either exceeded or approached that of the seat pan APMS in the vicinity of the primary resonant frequencies. The results also suggested considerable effect of the hands position on the APMS magnitudes measured at both the driving-points. The effects of variations in the excitation type and magnitude, considered in this study, were observed to be small compared to those caused by the hands position and individual body masses. Owing to the strong effects of the body mass on the measured APMS responses at both driving-points, a total of 8 target data sets were identified corresponding to four mass groups ( 80 kg) and two hands positions for formulating mechanical equivalent models. The model parameters identified for the target functions suggested that the models mass, stiffness and damping parameters increase with increasing body mass. The observed variations in the identified parameters could be applied for predicting the APMS responses reflected on the pan as well as backrest of the human occupants with specific body mass.

[1]  Michael J. Griffin,et al.  Effects of posture and vibration magnitude on apparent mass and pelvis rotation during exposure to whole-body vertical vibration , 2002 .

[2]  Subhash Rakheja,et al.  Whole-body vertical biodynamic response characteristics of the seated vehicle driver: measurement and model development , 1998 .

[3]  Michael J. Griffin,et al.  Effect of seat surface angle on forces at the seat surface during whole-body vertical vibration , 2005 .

[4]  M J Griffin,et al.  The apparent mass of the seated human body: vertical vibration. , 1989, Journal of biomechanics.

[5]  David A. Winter,et al.  Biomechanics and Motor Control of Human Movement , 1990 .

[6]  A. Mallik,et al.  STABILITY OF AN ACCELERATING BEAM , 1999 .

[7]  Subhash Rakheja,et al.  Effects of sitting postures on biodynamic response of seated occupants under vertical vibration , 2004 .

[8]  R Lundström,et al.  Mechanical impedance of the human body in vertical direction. , 2000, Applied ergonomics.

[9]  C. H. Lewis,et al.  Evaluating the Vibration Isolation of Soft Seat Cushions Using AN Active Anthropodynamic Dummy , 2002 .

[10]  Subhash Rakheja,et al.  A BODY MASS DEPENDENT MECHANICAL IMPEDANCE MODEL FOR APPLICATIONS IN VIBRATION SEAT TESTING , 2002 .

[11]  B Hinz,et al.  The nonlinearity of the human body's dynamic response during sinusoidal whole body vibration. , 1987, Industrial health.

[12]  Michael J. Griffin,et al.  Tri-axial forces at the seat and backrest during whole-body vertical vibration , 2004 .

[13]  Michael J. Griffin,et al.  Handbook of Human Vibration , 1990 .

[14]  Subhash Rakheja,et al.  SEATED OCCUPANT APPARENT MASS CHARACTERISTICS UNDER AUTOMOTIVE POSTURES AND VERTICAL VIBRATION , 2002 .

[15]  Toshisuke Miwa MECHANICAL IMPEDANCE OF HUMAN BODY IN VARIOUS POSTURES , 1975 .

[16]  Michael J. Griffin,et al.  MATHEMATICAL MODELS FOR THE APPARENT MASS OF THE SEATED HUMAN BODY EXPOSED TO VERTICAL VIBRATION , 1998 .

[17]  C. Bonthoux,et al.  Biodynamic response of the human body in the sitting position when subjected to vertical vibration , 1983 .

[18]  M. Griffin,et al.  Resonance behaviour of the seated human body and effects of posture. , 1997, Journal of biomechanics.

[19]  Michael J. Griffin,et al.  A REVIEW OF THE TRANSMISSION OF TRANSLATIONAL SEAT VIBRATION TO THE HEAD , 1998 .