Feasibility analysis of low-cost flexible resistive sensors for measurements of driving point mechanical impedance of the hand-arm system

Abstract This study explored the feasibility of the flexible resistive (FlexiForce) force sensors for measurement of the hand-arm biodynamic response. Two FlexiForce sensors were installed on an instrumented handle to measure the palm-handle and finger–handle interface dynamic forces. The measurements were performed with six subjects grasping a 38 mm diameter instrumented handle with nine different combinations of grip (10, 30 and 50 N) and push (25, 50 and 75 N) forces and two levels of broad-band random vibration (1.5 and 3.0 m/s 2 weighted rms acceleration) in the 4–1000 Hz frequency range. The data acquired from the instrumented handle was analyzed to determine the palm and finger impedance responses, which served as the reference values to evaluate feasibility of the FlexiForce sensors. The comparisons revealed very similar trends, while the impedance magnitude responses obtained from the FlexiForce sensors were substantially lower in the entire frequency range than the reference values, except at very low frequencies. A correction function was subsequently developed and applied to the FlexiForce measured data, which resulted in similar hand-arm impedance response trends compared to the reference values. It was concluded that the low-cost FlexiForce sensors could be applied for measurements of biodynamic responses of the hand-arm system in real tool handles in the field. Due to the physiological risks associated with prolonged exposure to tool vibration the applicability of a low-cost biodynamic response measurement system can be used as a preventative measure for such risks. Relevance to industry The measurement of hand–handle interface forces is vital for assessing the hand-transmitted vibration exposure and the biodynamic responses of the hand-arm system to vibration. The low cost and flexible sensors, proposed in the study, could be conveniently applied to the curved surfaces of real power tool handles in the field. The most significant benefit of the sensors lies with its negligible mass and thereby the instrumented handle inertia-induced errors in the biodynamic responses can be eliminated.

[1]  Subhash Rakheja,et al.  Development of a low-cost system to evaluate coupling forces on real power tool handles , 2011 .

[2]  L Burström.  The influence of biodynamic factors on the mechanical impedance of the hand and arm , 1997, International archives of occupational and environmental health.

[3]  Thomas W. McDowell,et al.  Analysis of handle dynamics-induced errors in hand biodynamic measurements , 2008 .

[4]  Pierre Marcotte,et al.  Effect of handle size and hand–handle contact force on the biodynamic response of the hand–arm system under zh-axis vibration , 2005 .

[5]  R G Dong,et al.  Hand-transmitted vibration and biodynamic response of the human hand-arm: a critical review. , 2001, Critical reviews in biomedical engineering.

[6]  C.M.A. Ashruf,et al.  Thin flexible pressure sensors , 2002 .

[7]  Subhash Rakheja,et al.  Influence of hand–arm posture on biodynamic response of the human hand–arm exposed to zh-axis vibration , 2006 .

[8]  D. E. Welcome,et al.  Contact pressure distribution at hand–handle interface: role of hand forces and handle size , 2005 .

[9]  C. Hall,et al.  External pressure at the hand during object handling and work with tools , 1997 .

[10]  R G Dong,et al.  Distribution of mechanical impedance at the fingers and the palm of the human hand. , 2005, Journal of biomechanics.

[11]  S. K. Patra,et al.  Comparisons of apparent mass responses of human subjects seated on rigid and elastic seats under vertical vibration , 2013, Ergonomics.

[12]  D. E. Welcome,et al.  An investigation on the relationship between grip, push and contact forces applied to a tool handle , 2004 .

[13]  Steve Rothberg,et al.  Evaluation of thin, flexible sensors for time-resolved grip force measurement , 2007 .

[14]  S. Rakheja,et al.  Mechanical impedance and absorbed power of hand-arm under x(h)-axis vibration and role of hand forces and posture. , 2005, Industrial health.

[15]  Subhash Rakheja,et al.  On the discrepancies in the reported human hand–arm impedance at higher frequencies , 2008 .

[16]  Subhash Rakheja,et al.  Distributed occupant-seat interactions as an objective measure of seating comfort , 2014 .