Novel Design and Implementation of a Knee Exoskeleton for Gait Rehabilitation with Impedance Control Strategy

Abstract

This paper presents a novel cable-driven robotic joint for a gait exoskeleton robot. We discussed in detail a lightweight, low inertia, and highly back-drivable, 1-DOF tension amplification mechanism based on a pulley system and block-and-tackle technique. The exoskeleton is controlled using an impedance controller under the active-assistive and resistive approaches. Four experiments were conducted to evaluate the proposed exoskeleton’s safety and controller performance: mechanical transparency analysis, active-assistive trajectory tracking, resistance of trajectory tracking, and gait rehabilitation. The exoskeleton demonstrated high transparency with the root mean square (RMS) torque of 0.457 Nm under no-load condition, suggesting that the mechanism is highly back-drivable, has a low moment of inertia, and is mechanically safe to operate. The active-assistive trajectory tracking experiment indicated that the output torque was generated under assist-as-needed approach, as the average robotic-assistance torque was lowered by more than 73% when the user provided assistance force to complete the task on their own.  Additionally, the resistance experiment revealed the feasibility of employing the exoskeleton to strengthen muscles with adjustable resistive torque from 0.94 Nm and 2.25 Nm. Finally, the result of gait rehabilitation experiment demonstrated that the robot was able to provide adequate torque to assist users in completing their gait cycle without causing any negative effects during or after the experiment.