Unimorph bending actuators based on dielectric elastomers (DE) are promising components for soft robotic grippers in analogy to the capabilities of the human hand. In a simple manufacturing process of the unimorph actuator, a bendable, but not stretchable passive carrier film is laminated with an active DE film, which expands in the electric field and generates a large bending deformation of the laminated composite film along its length dimension. The actuation performance in terms of the bending angle, actuator tip displacement and blocking force depends not only on the geometrical design of the unimorph actuator, but also on the properties of the used materials such as the Young’s moduli of the passive film and the elastomer film as well as the elastomer’s permittivity. To evaluate the influence of all relevant geometrical and material parameters on the actuation performance, a simple mathematical model was developed. Additionally, DE unimorph actuators were manufactured with silicone elastomer and their performance was experimentally investigated. The results of calculations are compared with those of the corresponding measurements and exhibit a high degree of quantitative agreement. Furthermore, the dependence of the actuator performance on various geometrical and material parameters (thickness of the dielectric and of the carrier film, permittivity and Young’s modulus of the dielectric) is predicted with the mathematical model. These calculations pave the way to a unimorph actuator with strongly improved performance. The key for this high performance is the simultaneous enhancement of the permittivity and the Young’s modulus of the dielectric. Thermoplastic polyurethane (TPU) fulfills these requirements and unimorph actuators based on TPU actually confirm the predicted high performance experimentally. By this way, the simple mathematical model offers a powerful and efficient tool for the optimization of unimorph actuators.
A modified dielectric elastomer strain sensor was developed, in order to enhance the accuracy of the measurement of extremely small strains below 1 %. The new sensor consists of two components, which are connected in series along the sensor length. The shorter component is a stretchable dielectric elastomer strain sensor strip, whereas the longer component exhibits a non-stretchable polymer film. When the whole sensor is stretched, the strain occurs only in the stretchable shorter component. Such sensors with enhanced sensitivity were manufactured and investigated with a self-constructed electro-mechanical testing machine. The results of the measurements of capacitance, electrode resistance and stretch force vs. strain were compared with those of corresponding conventional dielectric elastomer strain sensors. Furthermore, the dependence of the capacitance on the strain was calculated with finite element method (FEM) simulations for both sensor types. The sensor design, the results of the experimental characterization and the comparison with the simulation are described in the paper.
A novel design for dielectric elastomer pressure sensors based on a capacitive measurement principle is introduced. Compared with easily compressible and highly sensitive dielectric elastomer sensors containing internal voids, the new sensors are compact and suitable for an elevated pressure range up to about 2 MPa. In these sensors, a dielectric elastomer film with several dielectric and electrode layers is covered on both surfaces by plates, which exhibit a pattern of openings. When the sensor film is compressed, the elastomer material can expand into these openings, which reduces the film thickness and increases the capacitance. The dielectric elastomer film consists of a soft silicone with carbon black particles in the electrode layers. With this design, the sensitivity of the pressure sensors in terms of the capacitance increase is enhanced in comparison with reference sensors without openings in the plates and the disturbing hysteresis of the capacitance vs. pressure curves is reduced. With FEM Multiphysics simulations, the capacitance enhancement upon pressure increase and the sensor deformation were calculated and compared with experimental data. In a systematic study, different parameters of the sensor design were varied, in order to evaluate their influence on the sensor performance. The results of this study are presented in the paper.
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