Center of Mass Estimation Using Motion Capture System

Abstract

In this paper a center of mass estimation technique that uses the Weighted Segmental method and a motion capture system is presented. Balance is an essential ability needed by all humans for everyday routine activities. Therefore, improving balance ability results in a better and more convenient way of living. There are various major factors and aspects influence on balance, it is important to know which aspects have the greatest effect. And that is the focus of proposed research and experimental testing. The process of estimating the center of mass in a human body depends on the center of pressure of the body, human balance is strongly related to both of them. The center of pressure is the projection of the center of mass onto the XY plane, which can be found using a force plate. In this work, we used a Wii Balance Board with a compatible output program to replace the force plate, which reduced the cost of the system by $5,000-10,000 dollars. Based on the tests, 90% of accuracy was achieved for the center of pressure measurement. The motion capture system is operated from a laptop or desktop computer. Three calibrated cameras detect passive markers attached on the test subject. Weighted Segmental equations are generated and the center of mass of each segment and whole body are calculated and plotted based on recorded 3-dimensional data by the motion capture system and the force plate. Coupled with a passive marker motion capture system, we are able to mathematically determine the center of mass.