Development of gravity compensator for analysis of walking characteristics under the reduced gravity (verification of its effectiveness with rimless wheel)

For the future manned exploration mission to the other planet, the change of motion characteristics due to the reduced gravity must be studied. Walking, especially, is the basic action of human life, and the efficient walking enables the exploration mission under the limited life-sustaining time and resources. To minimize the risk of injury and damaging of the life-supporting system, the safety of the walking must be studied. To simulate the micro-gravity on the earth, gravity compensation is required, and the wire suspension system is often used for gait analysis. In this system, a subject wears harness and will be suspended by the wire to apply an upward force to the center of mass of the subject. However, pulleys for many systems are fixed at a point and this will lead to inappropriate compensation. While the subject is underneath the pulley, the complete compensation can be achieved with suspension force parallel to the gravity. However, once the subject moved away from the initial position, the unloading force is no longer equal to the suspension force but fluctuate as the subject move. Considering this problem, this paper first represents the effect of force fluctuation to the gait property using the planar rimless wheel, one of the simplest models of locomotion. Gait under lunar gravity and under fixed point suspension is compared, and the effect of restoring force is analyzed. Then, a new gravity compensator with horizontal follower is proposed and its effectiveness is verified through rimless wheel experiment.