Identification of COM Control Behavior of a Human in Stance as a Dynamical System

Abstract

This paper proposes an identification method of a human's standing stabilization control scheme. The movement of the center of mass (COM) in the motion is focused on rather than that of a couple of joints employed in well-acknowledged ankle/hip strategies in order to understand the human's behaviors in more general situations. It is mathematically represented as a piecewise-affine dynamical system, in which the state space is divided into some regions described by different equations of motions. The representation is based on the authors' previous finding that the COM-ZMP regulator, which was originally designed for humanoid robots to stabilize COM by manipulating the zero-moment point (ZMP), qualitatively models the humans' control scheme. A technical difficulty in the identification of such a piecewise system is that it is a chicken-and-egg problem since the equation of description has to be provided in order to identify system parameters, while the system parameters are required in order to choose the equation of description. The proposed method utilizes K-means method and/or EM algorithm and was applied to motion loci of a human subject in lateral direction measured in the previous study. The result of the identification quantitatively supported the above hypothesis. The differences of the actual human's behavior from the model are additionally discussed.