IEEE
TRANSACTIONS ON ROBOTICS, VOL. 25, NO. 3, JUNE 2009 539
A
Highly Backdrivable, Lightweight Knee Actuator for Investigating Gait in Stroke
James
S. Sulzer, Ronald A. Roiz, Michael A. Peshkin, Member,
IEEE, and James L. Patton,
Member, IEEE
Abstract—Many
of those who survive a stroke develop a gait disability known as stiff-knee
gait (SKG). Characterized by reduced knee flexion angle during swing, people
with SKG walk with poor energy efficiency and asymmetry due to the compensatory
mechanisms required to clear the foot. Previous modeling studies have shown
that knee flexion activity directly before the foot leaves the ground, and this
should result in improved knee flexion angle during swing. The goal of this
research is to physically test this hypothesis using robotic intervention. We
developed a device that is capable of assisting knee flexion torque before
swing but feels imperceptible (transparent) for the rest of the gait cycle.
This device uses sheathed Bowden cable to control the deflection of a compliant
torsional spring in a configuration known as a Series Elastic Remote Knee
Actuator (SERKA). In this investigation, we describe the design and evaluation
of SERKA, which includes a pilot experiment on stroke subjects. SERKA could
supply a substantial torque (12 N·m)
in less than 20 ms, with a maximum torque of 41 N·m.
The device resisted knee flexion imperceptibly when desired, at less than 1 N·m
rms torque during normal gait. With the remote location of the actuator, the
user experiences a mass of only 1.2 kg on the knee. We found that the device
was capable of increasing both peak knee flexion angle and velocity during gait
in stroke subjects. Thus, the SERKA is a valid experimental device that
selectively alters knee kinetics and kinematics in gait after stroke. Index
Terms—Compliant actuators, gait, orthotics, Series
Elastic Remote Knee Actuator (SERKA), stiff-knee gait (SKG), stroke.
Publishers’ page for this article
This article is part of a special issue on Rehabilitation Robotics