Non-linear viscoelastic models predict fingertip pulp mechanics during voluntary tapping

Devin L. Jindrich

Yanhong Zhou*

Theodore Becker

Jack Tigh Dennerlein 

ABSTRACT

                The mechanical properties of fingertip tissue affect the sensory information available from the finger and the forces transmitted to the finger, hand and arm during manual tasks. We evaluated whether lumped-parameter non-linear viscoelastic models of human fingertip tissue mechanics derived using low-frequency inputs can describe fingertip mechanics during rapid, dynamic tapping tasks. Eight human subjects tapped on the surface of a rigid load cell while an optical system tracked fingertip position using an infra-red LED attached to the fingernail.  Four different tapping conditions were tested:  taps with a relaxed hand, taps with increased velocity, taps with co-contraction of other fingers and high-speed taps when fingers were also co-contracted.  A simple non-linear viscoelastic model comprised of an instantaneous stiffness function and viscous relaxation function was capable of modeling fingertip tissue force response under these four different loading conditions with errors of 10%. The model was able to simultaneously reconstruct very rapid (less than 5 ms) force transients and forces occurring over time periods greater than 100 ms. Viscous properties caused fingertips to dissipate 81% of the energy absorbed when tapping on a stiff substratum. Energy dissipation varied little (<3%) across conditions, despite a 1.5-fold range of energy input.

 

 

Back to Publications

Back to HOB Site