Amplifying the response of soft actuators by harnessing snap-through instabilities

Engineering actuators with capabilities that match and even exceed those found in nature, is a long-standing challenge. While traditional actuators are built with hard materials, it has been recently shown that elastomeric materials enable the design of fluidic actuators that are lightweight, inexpensive, easy to fabricate, and able to undergo large deformation and complex motions. However, these actuators typically rely on large volumes for their actuation. This requirement limits the performance of soft actuators, since it makes the rate of actuation slow and it requires the system to be in the vicinity of a large reservoir. There is a need for new designs of soft actuators that reduce the amount of fluid needed for actuation, and thus increase their actuation speed and allow for more compact systems.

While instabilities have traditionally been avoided as they often represent mechanical failure, in this work we embrace them to amplify the response of fluidic soft actuators. Besides presenting a robust strategy to trigger snap-through instabilities at constant volume in soft fluidic actuators, we also show that the energy released at the onset of the instabilities can be harnessed to trigger instantaneous and significant changes in internal pressure, extension, shape and exerted force. Therefore, in stark contrast to previously studied soft fluidic actuators, we demonstrate that by harnessing snap-through instabilities it is possible to design and construct systems with highly controllable non-linear behavior, in which small amounts of fluid suffice to instantaneously trigger large outputs.

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Overvelde, J. T. B., Kloek, T., D’haen, J. J. A., Bertoldi, K., (2015) Amplifying the Response of Soft Actuators by Harnessing Snap-through Instabilities. Proceedings of the National Academy of Sciences of the United States of America.