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Dielectric elastomer actuators (DEAs) consist of thin and highly stretchable dielectric membranes coated with compliant electrodes, which react to an applied high voltage with a controllable mechanical deformation. DEAs are lightweight, stretchable, flexible, and soft, and thus they are suitable for the development of soft robots, wearable actuators, and smart skins. To increase the actuation stroke, DEAs are commonly combined with negative-stiffness mechanical biasing mechanisms, such as pre-compressed metal beams. These beams are subjected to high inherent stresses, and thus they are not well suited for miniaturization and integration into soft structures. Alternative negative-stiffness solutions based on buckling silicone domes, on the other hand, are affected by limited reproducibility, complex manufacturability, and large hysteresis. To overcome these issues, this work proposes novel biasing mechanisms based on thermoplastic polymers, which exhibit negative stiffness and thus are well suited for miniaturized and fully-polymeric DEA systems. In comparison to silicone-based domes and metal beams, they exhibit less hysteretic losses while maintaining high softness and flexibility. The new type of bias is also designed in a simple beam shape with stress-free configuration, due to the adopted thermoforming process. Their mechanical characteristics can be shaped by changing the thermoforming process parameters, as well as on their shape and dimensioning. This paper presents the thermoforming manufacturing process, and demonstrates its reproducibility by experimentally characterizing and comparing the force-displacement behavior of several biasing elements with various geometries. In this way, the suitability of the new bias in DEA applications can be assessed.
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