A STRUCTURAL MODEL OF THE FORCED COMPRESSION OF THE FINGERTIP PULP

The fingertip pulp modulates the force transmitted to the underlying m usculoskeletal system during finger contact on external bodies. A mode l of the fingertip pulp is needed to represent the transmission of for ces to the tendons, muscles, and bone during these contacts. In this s tudy, a structural model of the in vivo human fingertip was developed that incorporates both the material inhomogeneity and geometry. Study objectives were to determine (1) if this fingertip model can predict t he force-displacement and force-contact area responses of the in vivo human fingertip during contact with a flat, rigid surface, and (2) if the stresses and strains predicted by this model are consistent with t he tactile sensing functionality of the in vivo human fingertip. The i n vivo fingertip pulp was modeled as an inflated, ellipsoidal membrane , containing an incompressible fluid, that is quasi-statically compres sed against a flat, Frictionless surface. The membrane was assigned pr operties of skin (Veronda and Westmann, 1970) and when inflated, posse ssed dimensions approximating those of a human fingertip. Finite defor mation was allowed. The model was validated by the gulp force-displace ment relationship obtained by Serina et al. (1997) and by measurements of the contact area when the fingertip was pressed against a rigid su rface with contact forces between 0.25 and 7.0N. Model predictions rep resent the experimental data sufficiently well, suggesting that geomet ry, inhomogeneous material structure, and initial skin tension appear to represent the nonlinear response of the in vivo human fingertip pul p under compression. The predicted response of the fingertip pulp is c onsistent with its functionality as a tactile sensor. (C) 1998 Elsevie r Science Ltd. All rights reserved.