Upper-limb impedance adjustment mechanism for dynamic environments

The present paper discusses how human adjusts the mechanical impedance of upper limb in order to perform the reaching task under unstable environments. We identify both the arm stiffness and inertia during horizontal movements using the direct drive manipulator. It is then shown that the stiffness and inertia of the upper limb are cooperatively adjusted such that the dynamic range is kept higher in the direction against the external force during the reaching motion in comparison with the null field.