Upper body center of mass estimation in sitting position with force sensors

Abstract

The seated balance assessment is one of the methods to assess the degree of back pain and balance ability. Although the assessment requires measurement of the center of mass (COM) of the upper body, a method using a 3D motion analysis system is not desirable for the practical use. The purpose of this study was to estimate COM of the upper body in the seated position from data measured by force platforms mounted on seat and underfoot. To achieve the estimation, we assumed that the body consists of five segments and only the upper body has single degree of freedom. Considering the force transfer from the two force platforms, the COM of the upper body was estimated based on the equations of motion. To validate the estimation accuracy of the present method, we implemented three experiments: rest sitting, spontaneous back and force motion, and swaying by an electric cart. Comparing with the COM determined by 3D motion analysis system, fine estimation accuracy was obtained in the rest sitting and the spontaneous moiton. In the swaying by an electric cart, however, we found that the estimation error of the COM became large.