Masahiro Sekimoto

Analysis of walking skill with trans-femoral prosthesis based on inertia-induced measure

A method to quantify the walking skill with trans-femoral prosthesis will be explored for better gait rehabilitation and design of prosthesis leg. Inertia of the prosthesis plays an important role in natural and smooth gaits during the swing phase. We suppose that goodness of gait is strongly related to effective use of the prosthesis inertia. So far we have proposed the inertia-induced measure as a new method to quantify the effective use of the inertia property of the prosthesis leg in the swing phase based on Riemannian distance. In this paper, we analyzed walking skill with trans-femoral prosthesis leg based on the inertia-induced measure. Gait of a prosthesis leg user was measured at 5th, 8th, and 15th months after amputation. Changes of gait, inertia-induced measure, and subjective evaluation were investigated.

Evaluation of inertia matching of trans-femoral prosthesis based on Riemannian distance

A method to quantify the matching of inertia property of a trans-femoral prosthesis to a given users skill will be explored for better design of the prosthesis. Advancements in the mechanism and the control method of trans-femoral prostheses have drastically improved the gait of amputees. However, realization of a natural gait has not been investigated in detail even though such smooth gait is important to increase the amputees activities of daily living (ADL). Inertia of the prosthesis plays an important role in natural and smooth gaits during the swing phase. We suppose that goodness of gait or easiness of walking is strongly related to effective use of the prosthesis inertia. In this paper, we will attempt to quantify matching of inertia property of the prosthesis to a given users skill / condition from the effective use of the prosthesis inertia during gait in the swing phase. Gaits of an expert prosthesis user will be measured by changing inertia properties. Effective use of inertia property of the prosthesis in gait is evaluated by closeness of the gait to the inertia-induced motion using inertia-induced measure. In addition gait of a novice prosthesis user will be measured to compare with the experts results.

Basis-motion torque composition approach: Generation of motions with different velocity profiles among joints

The basis-motion torque composition (BMC), which generates feedforward torque for precise joint-trajectory tracking of a multi-joint robot arm, has been recently suggested. It is based on four arithmetical operations of time-series torque data of several motions preliminarily obtained by the iterative learning control. The remarkable advantage of BMC is to generate desired feedforward torque without prior information of dynamics parameters. However, the class of torque generated by the BMC has been restricted. The paper presents an enhanced BMC which permits generation of motions with different motion-velocity profiles among joints of a multi-joint robot. The algorithm is presented and the validity of algorithm is confirmed through numerical simulations in the case of a two-joint robot arm under the influence of gravity. Furthermore, a class of applicable systems of BMC approach is discussed.

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.

Realization of turning a screw crank with less control inputs by using redundant degrees of freedom of a manipulator

When a manipulator installing a position controller turns a screw crank, excessive inputs often happen due to installation errors. We solve the issue by using environment adaptation effect of robots redundant degrees of freedom. The experimental results demonstrated that the manipulator specifying the only two control variables has successfully completed the task in the maximum error norms of 0.18[mm] without any excessive control inputs or any unexpected motions of the uncontrolled variables, in comparison with 5.02[mm] in the use of six control variables.

Generation of feedforward torque by reuse of ILC torque for three-joint robot arm in gravity

The disadvantage that the iterative learning control (ILC) requires a learning process again for achieving another motion has been overcome by the basis-motion torque composition (BMTC). However, the increase of robot joints may cause difficulties in motion selections due to the algorithmic issue. We investigated the issue in motions of a three-joint robot arm in gravity and proposed a resolution method using redundant sets of motion torque. The calculation results demonstrated that the five sets of motions were enough for the torque composition though the motion sets which avoid algorithmic singularity were only 5 sets in 50,000 sets. The noise of generated torque was amplified to the signal/noise (S/N) ratio of 14.7[dB] in case of torque inputs of 40.0[dB]. However, the addition of one motion set improved to 29.4[dB].