Medical Design Briefs - July 2022 - 21

TECHNOLOGY LEADERS Motors/Motion Control
Advanced Motor Technology Enables Medical
Exoskeleton for Rehabilitation
T
he primary aim for Harmonic Bionics
is to empower patients and
care providers by designing intelligent
technology that facilitated
a data-driven treatment protocol when
dealing with neurological and musculoskeletal
movement impairments. To this
end, the company was responsible for
the complete design and assembly of its
Harmony SHR™ bilateral upper extremity
exoskeleton.
By enabling early intervention, functional
repetition, and intent-based therapy,
Harmony SHR delivers users the ability
to improve the efficiency and
ef fectiveness of upper-body rehabilitation.
As the company's flagship product,
the Harmony SHR is designed to provide
unique value in three areas of practice:
neuroscience and movement science
research, movement disorder
assessment, and rehabilitation.
Harmonic Bionics has selected commercial
off-the-shelf (COTS) components
to integrate into their various robotic
actuators according to each
actu ator's requirements to simplify product
design efforts. The company did
have to make minor trade-offs in the design
phase, at times, such as between actuator
size and load capacity/weight,
and between maximum torque and
torque sensitivity. The end product is
strong enough to assist with physical exercises
while not being too heavy or
cumber some to use.
Typically, in robotic arm applications,
people must be separated from the robotic
arms so that the robot cannot injure
a person while moving. Most robotic
arms on the market are not designed to
interact with humans safely - they cannot
detect a person in their way or move
around a person while performing the
programmed task. Because of this, typical
robots could be very dangerous for
people to interact with, especially in a
physical therapy application. This is not
a problem with the Harmony SHR,
which has been designed to be force sensitive
and to be controlled by force inMedical
Design Briefs, July 2022
puts from users instead of the position
setpoints typical of most robotic arms.
To assist patients with exercises, it is
much more important for the robot to
apply exact forces to patients rather than
to position them accurately (see Figure
1). The robot has been designed with
compliance in mind so that even small
forces applied to the robot can cause the
robot to move out of the way, to slow
down, or to stop completely. This feature
makes the robotic exoskeleton extremely
safe to be in and around.
This force sensitivity necessitated a redesign
of typical robotic actuators. Harmonic
Bionics has developed a patented robotic
actuator, which uses a load cell that is mechanically
isolated from any extraneous
loads. The result is that each load cell can
sense the force exerted by only the joint of
the robot it is mounted to, while being isolated
from the forces being applied to others,
thus maximizing the sensing accuracy
of the load cell. ESCON controllers, manufactured
by maxon, were compact in size
and easy to integrate electrically and physically
(see Figure 2). Harmonic Bionics
found that the software was straightforward
to use. The motors include informative
datasheets, making them simple to
integrate. According to Harmonic Bionics,
motor selection was rarely revised because
the datasheets enabled the company to select
the correct motor the first time.
Fig. 1 - Accuracy is less important for rehabilitation, particularly during exercising.
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Medical Design Briefs - July 2022

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