A move-and-hold pneumatic actuator enabled by self-softening variable stiffness materials

Materials exhibiting variable stiffness properties have great potential for use in the growing field of soft robotics. Soft structural materials allow a robot to fit into enclosed spaces, resist shock and vibration, or even reconfigure its geometry and adapt to various environments. Rigid structural materials on the other hand allow environmental interactions through application of force and load-bearing capabilities. Materials that can be selectively switched between these two extremes could greatly expand the functionality of a robot that requires the properties of both. In this paper, we introduce a conductive epoxy composite that is self-softening through Joule heating via direct application of electrical current. The polymer can then become load-bearing and rigid again after being formed into a new shape. We demonstrate the capabilities of this material by attaching a pneumatic actuator and showing that the resulting variable stiffness device can be softened from its initial rigid state, reshape itself using the pneumatic actuator, then become rigid again and hold this new position without additional power being supplied to the actuator.