tendrils, swapping hard for soft versions, the FAU team found there was an
optimum combination for thrust: with
both top and bottom being made of a
material with floppiness similar to that
of a mouse pad, being pulsed a little
less than once a second.
In addition to the challenges roboti-
cists face with materials and power de-
livery, Josh Bongard, associate professor
at the University of Vermont, says con-
trol presents further problems. “Exploit-
ing the capabilities of soft robots is a
very non-intuitive thing for human engi-
neers to do. The mathematics that we’ve
developed over decades for designing
and controlling traditional robots made
up of rigid links simply doesn’t apply to
[these] systems. In short: it’s hard to de-
sign and control moving blobs.”
In contrast to the inverse kinematics
and closed-loop control that dominate
fixed-function robots, Bongard propos-
es harnessing evolutionary program-
ming coupled with machine learning
to develop novel control methods for
producing movement that take into ac-
count how plastic materials bend and
compress under force.
In these simulations, the design
starts with a basic shape made from
blocks with different levels of stiff-
ness and mobility. Evolutionary
algorithms gradually change the
properties of different blocks until
the robot is able to move. The algo-
rithms tune their response to the
way materials flex under strain in
different positions using machine-
learning algorithms such as neural
networks. Sometimes, the simulat-
ed machines use the equivalent of
body fat to help leverage the effects
of whatever type of motion the robot
adopts. Bongard says, “Our evolution-
ary algorithms often find very non-in-
tuitive designs, such as one that has a
hump on its back and uses it to throw
its weight forward to make movement
more efficient.”
The work tends to agree with re-
sults such as those from FAU: softer
robots perform better under water.
Those simulated on land tended to re-
quire stiffer structures. Bongard now
plans to take the work to physical ro-
bots in a collaboration with Kramer-
Bottiglio and her team on a project
backed by the National Science Foun-
dation. The simulations will help
create configurations for the robotic
skins and the underlying shapes the
skins are wrapped around.
Although soft robots have a long
way to go before becoming autonomous enough to deliver on the promise of lighter, more functional machines, research and development is
gradually bringing together the types
of control and materials science that
will make them work well on Earth
and beyond.
Further Reading
Rus, D., and Tolley, M. T.
Design, Fabrication and Control of Soft
Robots
Nature 521, Number 7553, pp467-475
(2015)
Booth, J. W, Shah, D., Case, J.C.,
White, E.L., Yuen, M.C., Cyr-Choiniere, O.,
and Kramer-Bottiglio, R.
OmniSkins: Robotic Skins That Turn
Inanimate Objects into Multifunctional Robots,
Science Robotics, Vol 3, Issue 22,
eaat1853 (2018)
Frame, J., Lopez, N., Curet, O., and Engeberg, E.D.
Thrust Force Characterization of Free-Swimming Soft Robotic Jellyfish,
Bioinspiration & Biomimetics, Volume 13,
Number 6 (2018)
Corucci, F., Cheney, N., Giorgio-Serchi, F.,
Bongard, J., and Laschi, C.
Evolving Soft Locomotion in Aquatic
and Terrestrial Environments: Effects of
Material Properties and Environmental
Transitions,
Soft Robotics, 5( 4): 475-495 (2018)
Chris Edwards is a Surrey, U.K.-based writer who
reports on electronics, IT, and synthetic biology.
© 2019 ACM 0001-0782/19/4 $15.00
to electronic logic gates to implement components such as oscillators convey the peroxide to reaction
chambers. Each chamber contains
a platinum catalyst, which splits the
molecule into water and oxygen. The
resulting gas drives pneumatic actuators that move the limbs, although
they can do little more than twitch.
Soft robots may overcome the power
problem by operating in environments
where gravity is not as big a problem as
it is on land. The microgravity of space
may be one obvious habitat for them,
but robots made from elastomers and
pumps already find the going much
easier under water.
Former Florida Atlantic University
(FAU) student Jennifer Frame chose
the jellyfish as the biological model
for her thesis. Named JenniFish, the
robot uses stubby plastic tentacles
harnessed to hydraulic pumps powered by a battery to mimic the pulsing action of the invertebrate’s body
as it moves. Able to swim untethered
in the ocean, it is flexible enough to
squeeze through narrow orifices. In
experiments, the robot would collide
with the edges of a hole, then generate enough thrust to push its appendages to its side and squeeze through.
Another situation in which soft robots could perform well is in a different
fluid environment: inside the human
body. In work performed in Europe
before moving to Stanford University
in 2016, Stanford postdoctoral fellow
Giada Gerboni (who works in surgical
robotics) developed a soft endoscopic
camera for surgery. Now Gerboni is focusing on soft robots that can enter the
body, move around, and perform microsurgery operations without direct intervention from human surgeons. She
describes it as a very flexible needle that
can steer around parts of the body and
into organs with minimal disruption.
In further work by the group led by
FAU associate professor Erik Engeberg,
the JenniFish has helped demonstrate
how material choices form a key part
of design for liquid environments. The
algorithm needed to make the robot
swim in different directions is relatively simple: it takes advantage of the
way the polymer limbs are shaped to
bend in on themselves when flexed. By
changing the plastics used for the top
and bottom surface of the JenniFish
Gerboni is focusing
on soft robots
that can enter
the body, move
around, and perform
microsurgery
operations
without direct
intervention from
human surgeons.