Development of a Multi-Modal Control Architecture for a Cable-Actuated Ankle Exoskeleton

This work presents a lightweight, cable-actuated ankle exoskeleton with hip-mounted motors and a dual-loop controller (outer PID for joint angle, inner PI for current) to deliver precise, phase-coherent assistance. Smooth reference trajectories are generated via a half-sine interpolation algorithm that ensures continuous velocity/acceleration and limits torque ripple. Control performance was evaluated on bench tests in which joint angles and actuator currents were logged; tracking accuracy was quantified using RMSE for both stepwise (gait-inspired) and sinusoidal commands, with the drive cable kept under constant tension. The architecture achieved sub-degree errors without overshoot or sustained oscillations, confirming stable assistance across dorsiflexion and plantarflexion. A remaining limitation is reduced responsiveness during high-frequency transitions due to inner-loop bandwidth constraints.