There are two major categories of dielectric elastomer actuators (DEAs), which differ from the way in which the actuation is exploited: stack DEAs, using the thickness compression, and membrane DEAs, which exploit the expansion in area. In this work we focus on a specific type of membrane DEAs, i.e., silicone-based strip-in-plane (SIP) DEAs with screen printed electrodes. The performance of such actuators strongly depends on their geometry and on the adopted mechanical biasing system. Typically, the biasing is based on elastomer pre-stretch or on dead loads, which results in relatively low actuation strain. Biasing systems characterized by a negative rate spring have proven to significantly increase the performance of circular out-of-plane DEAs. However, this kind of biasing has never been systematically applied to silicone SIP DEAs. In this work, the biasing design based on negative rate springs is extended to strip DEAs as well, allowing to improve speed, strain, and force of the resulting actuator. At first, the DEAs are characterized under electrical and mechanical loading. Afterwards, two actuator systems are studied and compared in terms of actuation strain, force output, and actuation speed. In a first design stage, the DEA is coupled with a linear spring. Subsequently, the membrane is loaded with a combination of linear and nonlinear spring (working in a negative stiffness region). The resulting stroke output of the second systems is more than 9 times higher in comparison to the first one. An actuation strain of up to 45% (11.2 millimeter) and a force output of 0.38 Newton are measured. A maximum speed of 0.29 m s−1 is achieved, which is about 60 times faster than the one typically measured for similar systems based on VHB.

In this work, we develop a coreless rolled dielectric elastomer actuator (CORDEA) to be used as artificial muscles in soft robotic structures. The new CORDEA concept is based on a 50 µm silicone film with screen-printed electrodes made of carbon black suspended in polydimethylsiloxane. Two printed silicone films are stacked together and then tightly rolled in a spiral-like structure. Readily available off-the-shelf components are used to implement both electrical and mechanical contacts. A novel manufacturing process is developed to enable the production of rolled actuators without a hollow core, with a focus on simplicity and reliability. In this way, actuator systems with high energy density can be effectively achieved. After presenting the design, an experimental evaluation of the CORDEA electromechanical behavior is performed. Finally, actuator experiments in which the CORDEA is pre-loaded with a mass load and subsequently subject to cycling voltage are illustrated, and the resulting performance is discussed.

Due to their large deformation, high energy density, and high compliance, dielectric elastomer actuators (DEAs) have found a number of applications in several areas of mechatronics and robotics. Among the many types of DEAs proposed in the literature, rolled DEAs (RDEAs) represent one of the most popular configurations. RDEAs can be effectively used as compact muscle-like actuators for soft robots, since they allow eliminating the need for external motors or compressors while providing at the same time a flexible and lightweight structure with self-sensing capabilities. To effectively design and control complex RDEA-driven systems and robots, accurate and numerically efficient mathematical models need to be developed. In this work, we propose a novel lumped-parameter model for silicone-based, thin and tightly rolled RDEAs. The model is grounded on a free-energy approach, and permits to describe the electro-mechanically coupled response of the transducer with a set of nonlinear ordinary differential equations. After deriving the constitutive relationships, the model is validated by means of an extensive experimental campaign, conducted on three RDEA specimens having different geometries. It is shown how the developed model permits to accurately predict the effects of several parameters (external load, applied voltage, actuator geometry) on the RDEA electro-mechanical response, while maintaining an overall simple mathematical structure.

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