Data from: A rapid-response soft end effector inspired by the hummingbird beak

Biology is a wellspring of inspiration in engineering design. This paper
delves into the application of elastic instabilities-commonly used in
biological systems to facilitate swift movement as a power-amplification
mechanism for soft robots. Specifically, inspired by the nonlinear
mechanics of the hummingbird beak and shedding further light on it, we
design, build, and test a novel, rapid-response, soft end effector. The
hummingbird beak embodies the capacity for swift movement, achieving
closure in less than 10 ms. Previous work demonstrated that rapid movement
is achieved through snap-through deformations, induced by muscular
actuation of the beak's root. Using nonlinear finite element
simulations coupled with continuation algorithms, we unveil a
representative portion of the equilibrium manifold of the beak-inspired
structure. The exploration involves the application of a sequence of
rotations as exerted by the hummingbird muscles. Specific emphasis is
placed on pinpointing and tailoring the position along the manifold of the
saddle-node bifurcation at which the onset of elastic instability triggers
dynamic snap-through. We show the critical importance of the intermediate
rotation input in the sequence, as it results in the accumulation of
elastic energy that is then explosively released as kinetic energy upon
snap-through. Informed by our numerical studies, we conduct experimental
testing on a prototype end effector fabricated using a compliant material
(thermoplastic polyurethane). The experimental results support the trends
observed in the numerical simulations and demonstrate the effectiveness of
the bio-inspired design. Specifically, we measure the energy transferred
by the soft end effector to a pendulum, varying the input levels in the
sequence of prescribed rotations. Additionally, we demonstrate a potential
robotic application in scenarios demanding explosive action. From a
mechanics perspective, our work sheds light on how pre-stress fields can
enable swift movement in soft robotic systems with the potential to
facilitate high input-to-output energy efficiency.