Estimation of human finger tapping forces based on a fingerpad-stiffness model

This paper proposes a method of estimating fingertip forces in finger tapping movements based on human fingerpad characteristics. Since the human fingerpad exhibits elasticity, the proposed technique recreates the relationship between the fingertip force and the displacement generated between the thumb and index fingerpads as a fingerpad-stiffness model. Then, using this model, the force between the two fingertips (the fingertip force) can be estimated from the measured fingerpad deformation only. As the method does not require any sensors to be attached to the finger contact surface to measure fingertip force, it can be used to evaluate the tendency of force in natural and unconstrained finger tapping movements conducted by the subject. In the experiments conducted, fingertip forces and the displacement of the two fingerpads generated when the subjects pinched and pushed a force sensor with the thumb and index finger were measured to approximate the relationships between fingerpad force and deformation. The results indicated that human fingerpad characteristics can be expressed using a fingerpad-stiffness function (including an exponential function), and that fingerpad forces can be estimated using the proposed model. Furthermore, comparison between a Parkinson's disease (PD) patient and a healthy subject confirmed differences in the finger tapping forces for each. This implies the possibility of assessing motor function in PD patients using the finger tapping force evaluation method proposed in this paper.