Schematic of the proposed ultra-tunable bistable structure. Credit: Li Yingtian
Bistable
structures in nature are unparalleled for their fast response and force
amplification even with the minutest physical stimulation. Harnessing
bistability and instability to rapidly release the stored energy in bistable
structures could improve robot performance in several areas, e.g., high-speed
locomotion, adaptive sensing and fast grasping.
However, current works on bistable
structures mainly focus on their stable states, while intermediate states with
a large range of tunable energy barriers are missing from current studies.
Recently, a research team led by Dr. Li Yingtian from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences has proposed a type of ultra-tunable bistable structure with programable energy barriers and trigger forces of orders of magnitude differences. The structures can also be customized with varied geometric configurations, dimensions, materials, and actuation methods for various robotic applications.
This work was published in Cell Reports Physical Science on April
18.
The reported bistable structure was
fabricated by folding a sheet material to a specific crease pattern. It
possesses a stable state, a metastable state, and enormous intermediate states.
When the bistable structure transitions from its metastable state to the stable
state, there exists a critical point where the stored strain energy reaches its
maximum value and the fast snap-through starts.
Demonstration of ultra-sensitive force detection
and fast response properties. The proposed structure can be triggered by a
droplet and flying bees when adjusted to intermediate states with super-low
energy barriers.
In this work, the enormous
intermediate states with programmable energy barriers before the bistable structure
reaches its critical point were reported.
By reshaping the structure from
the metastable state to any intermediate state, the energy barrier decreases, meaning that smaller external
stimulations are required to trigger the fast snap-through of the bistable
structures. As the energy barrier keeps decreasing, the required external
stimulation gets more and more delicate. That is how the researchers achieved a
large range of adjustable trigger forces for the proposed controllable bistable
structure.
To demonstrate the tunability of
the proposed structure, the researchers conducted a series of experiments and
illustrated that the trigger force of a single structure could be tuned to 0.1%
of its maximum value, while the lifted weight difference was 107 times greater
using grippers fabricated by the proposed structures with different design parameters.
"We can tune the structure to
an ultra-sensitive state so that it will respond to a minute stimulation as
gentle as a touch of a flying bee, while we could also set the structure to an
insensitive state that even a steal ball weighing 110g could not break
its energy barrier," said Dr. LI.
To validate the potentials of the
structure in diverse applications, various prototypes were developed, including
a robotic flytrap, grippers, a jumper, a swimmer, a thermal switch, and a
sorting system. The prototypes demonstrate that the robotic flytrap with a
sensitive "pistil" can be triggered by physical stimulation in 10 ms;
the bistable catcher can capture a high-speed (10 m/s) table tennis ball; and
the minimal jumper reaches a height more than 24 times of its body height, etc.
"We are happy to find out our proposed structure could be used in such a wide range of applications, which demonstrates superior performances," said Dr. Li. "This work could broaden the frontiers of bistable structure design and lead a way to future designs in robotics, biomedical engineering, architecture, and kinetic art."
Provided by Chinese Academy of
Sciences
by Li Yuan, Chinese Academy of Sciences
Source: Researchers develop ultra-tunable bistable structures for universal robotic applications (techxplore.com)
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