IDENTIFICATION OF THE MECHANICAL IMPEDANCE AT THE HUMAN FINGER TIP

Rapid transients were applied to the outstretched human index finger t ip, which resulted in motion primarily at the metacarpophalangeal (MCP ) joint in extension and in abduction. A second-order linear model was fit to approximately 20 milliseconds of the force and displacement da ta to determine the effective mechanical impedance at the finger tip. Ranges of mass, damping, and stiffness parameters were estimated over a range of mean finger tip force (2-20 N for extension, 2-8 N for abdu ction). Effective translational finger tip mass for each subject was r elatively constant for force levels greater than 6 N for extension, an d constant throughout the abduction trials. Stiffness increased linear ly with muscle activation. The estimated damping ratio for extension t rials was about 1.7 times the ratio for abduction.