Impedance Charactheristics of Human Finger Joints.

Abstract

This paper describes impedance characteristics of human finger joints. Five joints of thumb and index finger are taken into consideration one by one our experiment. While subject keeps the joint angle of the finger to which the moment of rotation is applied as initial condition, small external disturbance is given to the finger joint. From the time trajectories of the joint angle and the moment of rotation caused by the disturbance, impedance parameters of each joint are estimated. Inertia of finger joint depends on position from MP joint or root of finger, and MP joints of thumb and index finger have large viscosity and stiffiness. Especially, MP joint of thumb has very strong stiffness compared with all joints of index finger, and it plays an important roll for stable gripping motions. On the other hand, DIP joint of index finger has small viscosity and stiffness, which is appropriate to perform active probing motion based on touch sense of fingertips. Moreover, we investigate how initial moment of rotation has influence on impedance of the finger joints. It is shown that stiffness of each joint increases in proportion to the initial moment of rotation.