A team of California researchers has
developed a robotic gripper that combines
the adhesive properties of gecko toes and
the adaptability of air-powered soft robots
to grasp a much wider variety of objects
than the state of the art.
Researchers will present their findings at
the 2018 International Conference on
Robotics and Automation May 21 to 25 in
Brisbane, Australia.
The gripper that the team developed can lift
up to 45 lbs. and could be used to grasp
objects in a wide range of settings, from
factory floors to the International Space
Station.
Geckos are known as nature’s best climbers
because of a sophisticated gripping
mechanism on their toes. In previous work,
researchers at Stanford University and the
Jet Propulsion Laboratory led by Professor
Aaron Parness recreated that mechanism with
a synthetic material called a gecko-inspired
adhesive. This material was used primarily
on flat surfaces like walls. In the current
work, researchers joined forces with
engineers at the University of California
San Diego. The team coated the fingers of a
soft robotic gripper with the gecko
adhesive, allowing it to get a firmer grasp
on a wide range of objects, including pipes
and mugs, while still being able to handle
rough objects like rocks. The gripper can
also grasp objects in various positions, for
example gripping a mug at many different
angles.
Researchers demonstrated that the gripper
could grasp and manipulate rough, porous and
dirty objects, such as volcanic rocks—a task
that is typically challenging for gecko
adhesives. It also was able to pick up
pieces of large, cylindrical pipe—a task
typically difficult for soft robotic
grippers.
The
gripper can easily manipulate objects like
mugs.
“We realized that these two components, soft
robotics and gecko adhesives, complement
each other really well,” said Paul Glick,
the paper’s first author and a Ph.D. student
in the Bioinspired Robotics and Design Lab
at the Jacobs School of Engineering at UC
San Diego.
The gecko is one of nature’s best climbers,
thanks to millions of microscopic hairs,
with features about 20 to 30 times smaller
than a human hair, that allow it to climb on
virtually any surface. The hairs end in tiny
nanostructures that interact at the atomic
level with molecules on the surface the
gecko is trying to grip. This interaction,
powered by what is called van der Waals
forces, causes the gecko’s toes to easily
attach and detach as needed. Researchers at
JPL use synthetic materials and similar
arrays of microscopic features to harness
the power of van der Waals forces and showed
these adhesives retained many of the same
properties as the toes of animal that
inspired them.
Because gecko adhesives are powered by
molecular interactions between surfaces,
they work best when they have a large
contact surface area. Coating the inside of
the soft robotic fingers with these
adhesives maximizes the amount of surface
area they make contact with, ensuring a
better grip.
The engineering team solves two different
problems in this paper.
First, researchers at UC San Diego set about
making sure that the gripper’s fingers would
maintain constant contact with the surface
of any object. A common problem with
air-powered soft fingers is that they tend
to bulge in the middle when inflated,
reducing this surface contact. Glick found a
study from the 1970s that provided the
equations needed to solve the problem in the
design process. This allowed researchers to
make the gripper apply the correct forces
along the entire length of the fingers.
Secondly, the researchers focused on
distributing forces on surfaces that aren’t
flat to optimize the performance of
gecko-inspired adhesives. The researchers
found a way to distribute force along a
soft, flexible gripper, while maintaining
the manufacturing precision required for the
adhesives.
The
team did this by using a high-strength
fabric embedded in the finger that can
easily bend but resists stretching to
support larger loads. The fingers are
rigidly clamped to a base, which keeps the
easily stretchable silicone from deforming
beyond what is needed. This combination of
soft and stiff materials lets the gripper
conform to many objects while withstanding
large forces.
The gecko adhesives themselves are made in a
three-step process. An original master gecko
adhesive mold with millions of microscopic
structures is made in a clean room using a
photolithography process. Then, wax copies
of the master mold can be made at low cost.
The researchers then can make as many copies
of the adhesive sheets from the wax mold as
they want by using a process called spin
coating. This allows them to make 10 to 20
adhesive sheets in under an hour. Meanwhile,
the soft robotic gripper itself is cast in
3D print molds and is made of silicone-based
rubber.
Next steps in the research include
developing algorithms for grasping that take
advantage of the adhesives, and
investigating the use of this gripper for
zero-gravity and space operations.
The
gripper can also handle porous objects, like
this rock.
Researchers mounted a slightly modified
version of the gripper on a robotic arm at
JPL. They showed it's capable of lifting up
to 45 lbs.
A team of California researchers has
developed a robotic gripper that combines
the adhesive properties of gecko toes and
the adaptability of air-powered soft robots
to grasp a much wider variety of objects
than the state of the art.
The
gripper can easily manipulate objects like
mugs.
