Measurement of standing balance ability by a wire driven parallel mechanism

Abstract

Falls are a major reason for elderly people to require nursing care. Prevention of falls requires evaluation of standing balance ability of human. Thus various measurements were performed and the relation between the results and occurrence of falls was considered. Although these measurements were mainly done under stable upright posture, the measurements of balance ability should be done under near falling. However, from a viewpoint of safety of subjects, the occurrences of falls which may inflict damage on them must be avoided during the measurements. This study, thus, develops a device that can measure standing balance of subjects until falls. The device consists of a three degree of freedom (3DOF) wire driven parallel mechanism, the output link of which is attached to a subject. The device can control 3DOF rotational motion of the output link by wires. Each wire has strain-gages to detect the forces applied to the output link and judge the falling moment. Furthermore, a force-plate is set on the base to measure the center of pressure (COP) of a subject. The device can guide subjects in specified direction at the measurement and support them safely at falling. We measured the COP at the fall moment and the body sways on tilting posture by the proposed device. As a result, it is found that the differences between subjects become clearer as their postures tilt closer to fall moment.