Most relevant to predicting the behavior of shape-memory-alloy (SMA)-based actuator-sensor applications activated by Joule heating are the electro-mechanical characteristics of the material under consideration. For a comprehensive characterization, a single setup that is able to provide all relevant data and information is desirable. This work covers the design, implementation and validation of such a high-end test bench for the holistic characterization of SMA micro-wires. In addition, the setup provides the possibility of application simulation experiments. Key elements of the design are the clamping mechanism guided on air bearings, a linear direct drive, a high-resolution load cell, a high-precision constant current source and a stress-controlled in-line wire sample installation. All measurements take place inside an isolated, temperature-controlled chamber. With the presented setup, the electro-mechanical and thermal characteristics of SMA wire samples with diameters from 20 µm to 100 µm can be determined. Via hardware-in-the-loop (HiL) implementation, the outputs with different biasing mechanisms and additional end-stops can be simulated even at high ambient temperatures. The generated results facilitate the prediction of the exact characteristics of SMA-driven actuator-sensor systems in a variety of applications and lead to a better general understanding of the alloy's properties. All functionalities and features of the setup are presented by discussing the results of exemplary experiments.

This paper presents a novel design method for high-frequency dielectric elastomer actuator (DEA) applications. A DEA consist of a mechanically pre-stretched elastomer film sandwiched between two compliant electrodes, which expands when subject to a high voltage. While the design of low-frequency DEA applications is generally well understood, up to now there is still a lack of systematic design rules for DEA systems operating in dynamic applications (e.g. pumps, compressors, and acoustics). The goal of this paper is the development of a novel graphical design approach which permits to systematically address the design of high-frequency DEA systems. A pneumatic diaphragm pump driven by a cone DEA is considered as a case study for validation of the new design technique. By means of the proposed method, the actuator performance can be quantitatively predicted at different actuation frequencies by accounting for both static and dynamic effects, as well as external loads, without relying on complex material models and extensive simulation studies. After discussing the design method, experimental validation is presented and performance are evaluated in terms of maximum pressure, maximum flow rate, and energy consumption.

This paper focuses on the electromechanical evaluation of combinations of novel sub-micron metal and carbon thin film electrodes for dielectric elastomers. The thin film electrodes are sputtered either onto 37.5 % biaxially pre-stretched polydimethylsiloxane (PDMS)-foils or on 57.5 % pre-stretched foils under pure shear conditions. The electrodes are wrinkled after relaxing the pre-stretch. The wrinkles in com-bination with the innovative sputtered sandwich-layers of nickel-chromium and carbon, with a total thin film thickness of 10 nm-40 nm, lead to exceptional electromechanical properties. With an initial resistance of only 500 Omega/square, some electrode configurations tolerate high strain up to 100 % without losing conductivity. 10 million cycles of mechanical load do not cause any major degradation of the thin films and their resistances. The capacitance-strain function is linear as long as the test strain is kept below the previously applied pre-stretch. During all the experiments, no delamination of these compliant thin film electrodes was observed. The force-displacement characteristics of the dielectric elastomer can be altered by applying high voltages on the electrodes, and thus, the actuator working principle is demonstrated. Depending on the kind of pre-stretch, some layer sequences are advantageous and others are disadvantageous when a low resistance at high strain is favored. In general, biaxially pre-stretched membranes with a metallic electrode configuration provide the best properties. Hence, this work proves, that sub-micron sandwich-layers of nickel-chromium and carbon are suitable for electrodes of dielectric elastomer actuators and sensors. (c) 2020 Elsevier B.V. All rights reserved.

The structure of dielectric elastomer actuators (DEAs) is based on a thin elastomer layer, which is sandwiched in-between compliant electrodes. This capacitor like structure enables to build lightweight and energy efficient actuators with high design flexibility. An applied high voltage leads to a thickness compression and to a simultaneous area expansion of the elastomer, which can be exploited for actuation. Additionally, due to the capacitive nature of DEAs, the application of a DC voltage allows to maintain a position without consuming energy, making such actuators ideal for, e.g., valves. Despite being relatively easy to manufacture and providing large strokes, membrane DEAs suffer from low force outputs (for single layer systems). This paper presents a novel design concept which permits to retune the stroke-force trade-off of DEAs, by allowing to increase force output of the actuator at the expense of a reduced stroke. This is of particular interest for valve applications, which typically need high closing forces and low strokes in the submillimeter regime. The developed system is based on membrane DEAs biased with linear and non-linear springs. Such systems are typically known for high actuation strain and strokes but low force output, even lower in comparison to a single layer membrane DEA only. By means of the novel design concept, the force output of a single layer membrane DEA can be increased by a factor of 3 to 4. The novel actuator concept is initially illustrated, and subsequently validated via a graphical modeling concept on strip-in-plane DEAs.

Dielectric elastomer actuators (DEA) enable to build compact, silent and lightweight systems capable of a large actuation bandwidth up to the kHz range. They consist of a thin elastomer film between two electrically conductive and flexible electrodes. If a high voltage is supplied to a DEA, the opposing electrical charges on the two electrodes result in electrostatic forces which produce a controllable deformation. This work presents a systematic design approach for the design of DEA driven pneumatic pumps for mobile applications. Due to the combination of large actuation bandwidth and the high compactness, DEA appear as highly suitable for designing pumps for such applications. Silicone based circular out-of-plane membrane DEAs (also referred to as cone DEAs) combined with biasing springs are studied in this work. A commercially available pump mechanism, consisting of a rolling diaphragm and check valves, is used as an experimental platform to validate the design strategy. Based on characterization data of both DEA membrane and pump, a systematic design approach based on graphical method is performed. The proposed design method allows to predict the system performance at high actuation frequencies by accounting for both static and dynamic effects, as well as external loads, without relying on complex material models. The design procedure forms the basis for building the pump by utilizing rapid prototyping. The performance of the pump can then experimentally evaluated in terms of pressure and resulting flow rate to validate the design concept.

This paper presents on finite element (FE) modeling and simulation of dielectric elastomer actuators (DEAs) coupled with articulated structures. DEAs have proven to represent an effective transduction technology for the realization of large deformation, low-power consuming, and fast mechatronic actuators. However, the complex dynamic behavior of the material, characterized by nonlinearities and rate-dependent phenomena, makes it difficult to accurately model and design DEA systems. The problem is further complicated in case the DEA is used to activate articulated structures, which increase both system complexity and implementation effort of numerical simulation models. In this paper, we present a model based tool which allows to effectively implement and simulate complex articulated systems actuated by DEAs. A first prototype of a compact switch actuated by DEA membranes is chosen as reference study to introduce the methodology. The commercially available FE software COMSOL is used for implementing and coupling a physics-based dynamic model of the DEA with the external structure, i.e., the switch. The model is then experimentally calibrated and validated in both quasi-static and dynamic loading conditions. Finally, preliminary results on how to use the simulation tool to optimize the design are presented.

Dielectric elastomer (DE) membrane actuators are known to provide high strokes compared to DE stack actuators. A graphical method can be used to design a membrane actuator system (combination of membrane DEA and biasing elements) for a specific application. This method considers the equilibrium of forces at steady-state, and thus completely neglects the dynamic behavior, such as inertial effects. Since the design is based on low frequencies, the resulting system designed is not expected to provide satisfactory performance in dynamic applications, as well. To overcome this issue, in this work we extend the quasi-static approach by including the effects of inertia force in a strip actuator system design. This allows to design a linear biasing spring in terms of spring rate and pre-compression, in order to tune the system resonance at a desired frequency. It is shown that this approach allows a stroke magnification in a range, which is typically only possible by means of complex non-linear biasing elements. Finally, the extended graphical model is used to predict the dynamic behavior of a DEA-spring-system.

Dielectric elastomers represent a relatively new technology with high potentials for actuators’ applications. Thanks to their lightweight, fast operations, energy efficiency, low power consumption, large deformations, and high scalability, dielectric elastomers permit to develop novel mechatronic systems capable of overperforming standard actuation technologies, such as solenoid valves, in several applications. This article presents a novel design for a dielectric elastomer–driven actuator system which enables closing and opening of a contactor. The design is based on a combination between circular out-of-plane dielectric elastomer membranes and a bi-stable biasing system which allows to increase the out-of-plane stroke. Characterization of the contactor is initially performed in order to establish the actuator requirements in terms of force and stroke. Then, systematic design and manufacturing are carried out for both dielectric elastomer membranes and biasing mechanism. Finally, the effectiveness of the actuator in closing and opening the contactor is validated experimentally. The results show comparable dynamic performance to a conventional electromagnetic drive, with the additional advantage of a significantly lower energy consumption.