Estimation of Human Hand Impedance During Maintenance of Posture

The present paper proposes a method to estimate hand impedance characteristics including inertia and viscosity as well as stiffness in multi-joint human arm movement. While subjects maintain a given hand position, small external disturbance to the hand is applied by a manipulandum. Time changes of the hand displacements and forces caused by the disturbance are measured, and the hand impedance are estimated using a second-order linear impedance model.Firstly, accuracy of the estimated impedance is analyzed applying the method to the estimation of mass of the objects and mechanical spring coefficients. Then, the hand impedances of human arm during maintenance of posture are estimated, and the experimental results show the following: 1) the estimated inertia matrices of human hand agree with computed values using a two-joint arm model, 2) the orientations of stiffness fields are almost the same as the experimental results of Mussa-Ivaldi et. al (1985), 3) the amplitude of the estimated stiffnesss is considerably lower than the one of the results of Mussa-Ivaldi et. al (1985), 4) the orientation of viscosity ellipses almost agree with the one of the stiffness ellipses.