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Characteristics of Recovery Motion Resulting From Side Contact With a Physical Assistant Robot Worn During Gait

Although a wearable assist robot helps to enhance the gait ability of the wearer, it can cause gait instability in an emergency. A collision with an environmental object is one source of such instability. Insufficient adaptation to change by the physical frame, and restriction of joint motion, increases the risk of collision and fall of the wearer owing to the robot. In this article, the reaction motion owing to side contact, which applies a spin moment to the body, is investigated for the wearers of a physical assistant robot. In particular, reaction motions in the horizontal plane, such as body rotation, foot direction, and center-of-mass position, are investigated. Factor analysis and cluster analysis are performed, and two reaction patterns—the rotation group and the straight group—are determined. The motion of these groups suggests an approach for navigation through an obstacle while using an assist robot. Furthermore, the gait phase at collision time is considered as a determinant of the reaction pattern and the reaction pattern is found to affect the fall mode. The results of the article suggest that the joints of the physical assistant robot should be equipped with sufficient degrees of freedom, at least in hip rotation, such that it is capable of rotating the body and feet in the horizontal plane to reduce fall risk.