Abstract
The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a three-dimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed.
Highlights
Dielectric Elastomers (DEs) are a type of electro-mechanical transducers which react to an electric voltage with a significant change in shape
We focus on a specific class of DE actuator (DEA) systems, namely a circular out-of-plane DEA (COPDEA)
The polymeric dome serves as a negative-rate bias spring element, which allows to magnify the output stroke of a circular DEA while adding an overall flexibility and deformability to the whole system
Summary
Dielectric Elastomers (DEs) are a type of electro-mechanical transducers which react to an electric voltage with a significant change in shape. The biasing systems used in most of the current DE soft robots, lack the above mentioned NBS principle, they do not allow to exploit the high flexibility of the DE to generate soft actuators with large stroke This is possibly due to the rigid materials commonly used to manufacture the NBS itself, which are mostly based on metal, as well as due to the stiff frames and housings required to implement mechanical clamping and connections. Due to the compliance matching between DE and dome materials, this solution permits in principle to achieve a fully soft and large-stroke actuator system Those types of mechanisms, have not been previously adopted as biasing elements for DE membranes, to the best of our knowledge.
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