A Phase Variable Based Phase Estimation for Stair Descent

Abstract

Accurately estimating the gait phase is essential for controlling a powered lower limb prosthesis. Additionally, for the prosthesis to be practical for daily use, the prosthesis must be able to adapt to different locomotion scenarios, such as level walking, slope walking, and stair walking. Most prosthetic research about level walking utilizes the phase variable, which parametrizes the gait cycle independent of time. However, fewer studies estimate the gait phase for powered prostheses during stair descent. In this study, we developed a phase variable formulating method to estimate the gait phase during stair descent walking. We divided the gait phase into stance and swing phase and showed that we could use hip position and thigh angle to formulate the phase variable for each phase separately. Specifically, we used hip position (x-position of prosthetic hip joint from x-position of prosthetic toe in the sagittal plane) to formulate the phase variable for the stance phase and thigh angle for the swing phase. After formulating phase variables for both phases separately, we integrated them to formulate the phase variable for the entire gait cycle during stair descent walking. By comparing our proposed phase variable with the phase variable for the level walk, the proposed phase variable showed similar performance to the phase variable for the level walk. From this result, we found that our method followed the linear function well enough to estimate the gait phase of stair descent walking. Our future study will validate the proposed phase variable using the powered prosthesis and compare the characteristics of stair descent of males and females.