Adaptive Control Strategy for Ankle Assistance Using an Actuated Ankle-Foot Orthosis With Selective Adaptive Parameter Convergence
Rami Jradi, Oussama Bey, Hala Rifaï, Yacine Amirat, Samer Mohammed
Abstract
Neuro-muscular injuries affecting the peroneal nerve or ankle joint dorsiflexor muscles can lead to foot-drop (FD), characterized by a difficulty in dorsiflexing the ankle during the gait. This paper introduces mid- and low-level control strategies for providing an adaptive torque assistance at the ankle joint through an actuated ankle-foot orthosis (AAFO). The mid-level control utilizes an inertial measurement unit (IMU) on each foot to estimate the normalized vertical ground reaction forces (NvGRFs) on three points of the foot using a Random Forest Regressor model. The NvGRFs are then used to detect the gait phases and generate an adaptive ankle joint angle and angular velocity reference trajectories. The low-level control features a saturated adaptive active disturbance rejection controller (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sigma$</tex-math></inline-formula>-AADRC), incorporating a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sigma$</tex-math></inline-formula> operator to limit the evolution of the adaptive parameters and ensure a controlled and independent convergence of each parameter. Experimental validation with seven healthy subjects demonstrates accurate NvGRF estimation, reliable gait phase detection, and superior tracking performance compared to previous approaches.
BibTeX
@inproceedings{ral2026_adaptivecontrols,
title = {Adaptive Control Strategy for Ankle Assistance Using an Actuated Ankle-Foot Orthosis With Selective Adaptive Parameter Convergence},
author = {Rami Jradi and Oussama Bey and Hala Rifaï and Yacine Amirat and Samer Mohammed},
booktitle = {RA-L 2026},
year = {2026}
}