Use of a portable device for measuring arm´s planar mechanical impedance during motion

This paper proposes the design and use of a portable device for measuring the impedance of human arm during reaching motion. While the device looks and weighs like an ordinary mug, it contains a DC motor, which rotates an eccentric mass, and a 2-axis inertia sensor, which monitors vibration. The centrifugal force due to the rotating eccentric mass applies a perturbing force to the hand; correlation of the acceleration signals with the perturbing force gives the posture dependant mechanical impedance in form of ellipses. The method can configure an impedance ellipse in 0.1 second and can repeat it continuously over the course of reaching; hence for every second of a reaching trial, the device obtains 10 impedance ellipses, which is considerably faster than previous methods. Experimental data collected by the device during reaching motion are also presented.