Optimal Kinematic Design of a Novel Robotic Knee Device for Gait Rehabilitation with Stance Control

Abstract

In this paper, we have proposed a novel robotic knee device with a five-bar linkage to allow low impedance voluntary knee motions within a specified rotation range during swing phase and to assist knee extension motions during stance phase after reaching the boundary of the rotation range. The proposed device can provide free knee motions through the five-bar linkage with 2-DOF (degree of freedom) actuations by a patient’s shank and a linear actuator, and can assist knee extension at any controlled knee angle during weight bearing by a geared five-bar linkage with 1-DOF actuation of the linear actuator. The kinematic transition between two modes can be implemented by contact mechanism of a circular structure (knee joint) and a linear link (patella), and the resultant knee rotation range can be determined by the linear actuator. A weight optimization scheme with a simple genetic algorithm (SGA) is performed to increase portability of the proposed device and minimize the side-effects of increased link numbers as compared to existing four-bar mechanisms. The cost function is composed of sums of normalized total link lengths and normalized motor powers. The optimization results show that the total link length and motor power were reduced to 47% and 43% respectively, as compared to initial design. The proposed robotic knee device can provide a new rehabilitation mode for a stroke patient to allow safe and self-motivated overground walking with minimum concern of falling down.Keywordskinematicsgenetic algorithmrehabilitationbio-mechanics