Gecko is known as one of the
nature’s best climbers, very small in nature but capable of performing several
task
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 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.
"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 often as 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.
Researchers
will present their findings at the 2018 International Conference on Robotics
and Automation May 21 to 25 in Brisbane, Australia. The gripper 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.
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.
Source of Article:
University of California(San Diego).
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