Consolidated control framework to control a powered transfemoral prosthesis over inclined terrain conditions

Abstract

For amputees, walking on sloped surfaces is one of the most challenging tasks in their daily lives. Unfortunately, designing a prosthesis that can effectively adapt to varying terrain is an ongoing problem. In this paper, we propose a unified control scheme that enables a powered transfemoral prosthesis to perform human-like walking on sloped terrains regardless of the slope and without any knowledge of the upcoming slope. The control scheme implements impedance control and trajectory tracking during the stance and swing phase, respectively. In the impedance control scheme, properly tuned impedance parameters are used to provide a stable and compliant stance phase that adapts to the slope of the ground. During the swing phase, the system is controlled by a Proportional-Derivative (PD) controller to track the desired trajectories based on cubic Bezier polynomials. These trajectories were obtained by solving an offline optimization problem compared to human slope walking data. Any slope walking trajectories can be generated online by using the optimized Bezier coefficients. At the terminal swing phase, a low gain PD controller is utilized to adapt to the unexpected terrains and smoothly track the generated trajectories. The proposed control framework is implemented on a powered transfemoral prosthesis, AMPRO II, on various slopes. The results validate the controller's ability to adapt to terrain inclinations within the range of ± 10°. © 2019 IEEE.