Non-linear viscoelastic models predict fingertip pulp force-displacement characteristics during voluntary tapping

Area of Science:

• Biomechanics
• Human Physiology
• Tissue Mechanics

Background:

• Understanding fingertip mechanics is crucial for prosthetics and human-computer interaction.
• Previous models often simplify the complex viscoelastic properties of fingertip tissue.

Purpose of the Study:

• To evaluate lumped-parameter non-linear viscoelastic models for describing human fingertip force-displacement characteristics.
• To assess model performance across various dynamic tapping conditions.

Main Methods:

• Eight subjects performed rapid, dynamic tapping tasks under four conditions (normal/high-speed, relaxed/co-contracted).
• An optical system tracked fingertip position, and a load cell measured forces.
• A non-linear viscoelastic model with instantaneous stiffness and viscous relaxation functions was employed.

Main Results:

• The model accurately predicted fingertip force response (within 10% error) for rapid transients (<5 ms) and longer durations (>100 ms).
• Model parameters showed minimal variation (<20%) across conditions with significant differences in forces and velocities.
• Fingertip energy dissipation averaged 81% with little variation, despite differing energy inputs.

Conclusions:

• Lumped-parameter non-linear viscoelastic models effectively describe fingertip tissue mechanics during dynamic tasks.
• This modeling approach aids in understanding fingertip force transmission and mechanoreceptor stimulation.
• The findings have implications for fields requiring precise fingertip interaction modeling.