Exoskeleton research marches forward with study on fit

Date:
August 20, 2020
Source:
National Institute of Standards and Technology (NIST)
Summary:
Exoskeletons, many of which are powered by springs or motors,
can cause pain or injury if their joints are not aligned with the
user's. To help manufacturers and consumers mitigate these risks,
researchers have developed a new measurement method to test whether
an exoskeleton and the person wearing it are moving smoothly and
in harmony.



FULL STORY ==========================================================================
A shoddily tailored suit or a shrunken T-shirt may not be the
most stylish, but wearing them is unlikely to hurt more than your
reputation. An ill-fitting robotic exoskeleton on the battlefield or
factory floor, however, could be a much bigger problem than a fashion
faux pas.


========================================================================== Exoskeletons, many of which are powered by springs or motors, can cause
pain or injury if their joints are not aligned with the user's. To help manufacturers and consumers mitigate these risks, researchers at the
National Institute of Standards and Technology (NIST) developed a new measurement method to test whether an exoskeleton and the person wearing
it are moving smoothly and in harmony.

In a new report, the researchers describe an optical tracking system
(OTS) not unlike the motion capture techniques used by filmmakers to
bring computer- generated characters to life.

The OTS uses special cameras that emit light and capture what is reflected
back by spherical markers arranged on objects of interest. A computer calculates the position of the labeled objects in 3D space. Here, this
approach was used to track the movement of an exoskeleton and test pieces, called "artifacts," fastened to its user.

"The ultimate goal is to strap these artifacts on to the person,
put on the exoskeleton, compare the difference in the person wearing
these artifacts versus the exoskeleton and see if they move the same,"
said Roger Bostelman, a robotics engineer at NIST and lead author
of the study. "If they move in concert with one another, then it fits correctly. If they move differently, it's not fit correctly, and you could determine adjustments from there." In the new study, the NIST researchers aimed to capture the motion of the knee -- one of the body's relatively
simple joints, Bostelman said. To assess the measurement uncertainty
of their new approach, they constructed two artificial legs as test
beds. One featured an off-the-shelf prosthetic knee, while the other incorporated a 3D-printed knee that more closely mimicked the real thing.

Metal plates were also fastened to the legs with bungee cords to represent exoskeletal limbs or test artifacts attached to the body.



========================================================================== After fixing markers to the legs and plates, the team used the OTS
and a digital protractor to measure knee angles throughout their full
range of motion. By comparing the two sets of measurements, they were
able to determine that their system was capable of accurately tracking
leg position.

The tests also established that their system could calculate the separate motions of the legs and exoskeletal plates, allowing the researchers to
show how closely aligned the two are while moving.

To adapt their method to be used on an actual person's leg, the team
designed and 3D-printed adjustable artifacts that -- like a knee brace --
fit to the user's thigh and shin. Unlike the skin, which shifts due to
its own elasticity and contracting muscles underneath, or skin-tight
clothing that may be uncomfortable for some, these artifacts offer a
rigid surface to stably and consistently place markers on different
people, Bostelman said.

The team mounted the knee artifacts and a full-body exoskeleton garnished
in reflective markers onto Bostelman. With the OTS keeping a close eye
on his legs, he proceeded to perform several sets of squats.

The tests showed that most of the time, Bostelman's leg and the
exoskeleton moved in harmony. But for brief moments, his body moved
while the exoskeleton didn't. These pauses could be explained by the
way in which this exoskeleton works.

To provide extra strength, it uses springs, which engage and disengage as
the person moves. The exoskeleton pauses when the springs shift modes,
however, temporarily resisting the user's movement. By detecting the
nuances of the exoskeleton's function, the new measurement method
demonstrated its attention to detail.

The raw data alone doesn't always reveal whether a fit is adequate. To
improve the accuracy of their method, Bostelman and his team will also
use computational algorithms to analyze the positional data.

"The next steps are to develop artifacts for the arm, for the hip and
basically all the joints this exoskeleton is supposed to be in line with
and then perform similar tests," Bostelman said.


========================================================================== Story Source: Materials provided by National_Institute_of_Standards_and_Technology_(NIST).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Roger V. Bostelman, YaShian Li-Baboud, Karl Van Wyk, Mili Shah.

Development of a Kinematic Measurement Method for Knee
Exoskeleton Fit to a User. Technical Note (NIST TN), 2020 DOI:
10.6028/NIST.TN.2107 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200820143231.htm

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