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robotic devices for gait retraining (e.g. Lokomat ®) have
been developed to provide the opportunity for intense
rehabilitation, but their use is limited to the clinical setting
for relatively brief training sessions. A wearable training
orthosis could be used by patients throughout daily activities,
with constant reinforcement of the targeted gait pattern. This
constant reinforcement of gait retraining in a real-world
environment has the potential to provide more effective gait
retraining, improving one's ability to ambulate.
An intelligent programmable actuated knee orthosis
could be used as an alternative to currently available
mechanically-passive braces. Existing options for control of
pathologic knee movement during gait include the use of
short-leg braces (AFO's), long-leg braces (KAFO's), and
stand-alone knee braces (KO's). AFO's provide some
stabilization of knee movement and partially resist knee
hyperextension. However, many patients find that AFO's
are not effective in controlling abnormal knee movements
and frequently adopt maladaptive gait patterns. KAFO's are
more effective at preventing knee hyperextension, but do not
assist with knee flexion, and provide a "hard stop" for knee
hyperextension, rather than providing a graded resistive
force to this movement. The size and weight of KAFO's
interfere with their acceptance by patients. KO's are
similarly unable to assist with knee flexion, and also provide
an abrupt check on knee hyperextension. Long-term use of
KO's by patients with stiff-legged gait and hyperextension is
the exception. These devices lack variable-damping and
torque-actuator characteristics that we see as essential to
restore mobility in stroke patients. The proposed knee brace
would provide such characteristics thus allowing a
significant improvement over existing orthotic interventions.
In this paper, we present the design, control and testing
of a novel, smart and portable Active Knee Rehabilitation
Orthotic Device (AKROD), shown in Figure 1. The main
torque generation component of the device is a resistive
variable damper that is the key to foster training of more
efficient and clinically desirable knee biomechanical
patterns in stroke patients. This component will be relied
upon in order to avoid knee hyperextension and foster re-
learning of a knee flexion pattern during stance. Also, it
will be relied upon to correct stiff-legged pattern, defined as
limited knee flexion during swing.The AKROD is composed of straps and rigid
components for attachment to the leg, with a central hinge
mechanism where a gear system is connected. The key
features of the proposed AKROD include: a compact,
lightweight design with highly tunable resistive torque
capabilities, and sensors (encoder and torque), and real-time
capabilities for closed loop computer control for optimizing
gait retraining. The controllable variable resistance is
achieved through an electro-rheological fluid (ERF) element
that connects to the output of the gear system. Using the
electrically controlled rheological properties of ERFs,
compact brakes capable of supplying high resistive and
controllable torques, have been developed. Concentric
cylinders, acting as electrodes supply the necessary electric
field to activate the fluid. Simultaneously, these plates,
when charged and rotating, act as surfaces upon which the
activated fluid creates a shear force in response to rotation.
This paper presents the detailed design, closed loop control
and initial human testing of AKROD.
II. BACKGROUND
An orthotic by strict definition is a specialized
mechanical device that supports or supplements weakened