A measure to select orientation parameters for spatial impedance control

This paper addresses how to select orientation parameters for rotational impedance control. Since the rotational impedance characteristics are inherently nonlinear, implementation of the rotational impedance control is relatively difficult. As a pragmatic solution to the problem, this paper attempts to maximally approximate the nonlinear impedance characteristics by linear ones. Because the degree of the approximation depends on how to represent the orientation by three independent parameters, selection of the orientation parameters is an important factor to achieve the maximal approximation. In order to select the optimal orientation parameters, this paper proposes a new measure referred to as the nonlinearity measure.