Analysis of inertial motion in swing phase of human gait and its application to motion generation of transfemoral prosthesis

The goal of this study was to develop a transfemoral prosthesis that realizes a natural and smooth gait. To realize such prostheses, the smoothness or goodness of walking in the swing phase should be investigated. So far, many studies have investigated the human gait. However, the goodness of walking has not been clearly defined. Passive walking has drawn much attention because it includes the essence of the gait with higyly energy-efficient walking. The human gait is thought to effectively utilize the dynamics of the body for a smooth gait. Investigating the human gait should help in building smoothly walking robots and realizing prostheses that make it easy to walk. The present paper proposes a method to evaluate the inertial motion of the human gait in the swing phase and a method to generate the joint motion profile of a transfemoral prosthesis that utilizes its inertial motion. First, an inertial motion index is proposed to evaluate the closeness of the given motion to the inertial motion of multilink systems. The gait of healthy participants in the swing phase was analyzed using the proposed index. The results showed that inertial motion is effectively used in the middle of the swing phase. Based on the results, a motion generation method is proposed for the knee joint of a prosthesis that utilizes the inertial motion in the middle of the swing phase. Simulation results with the method showed that a smoother change in torque was realized compared to another method that uses the measured joint motion of human gait as the desired trajectory for the PD controller.