Hand motion is one of our most expressive abilities. By measuring our interactions with everyday objects, we can create
smarter artificial intelligence that can learn and adapt from our behaviours and patterns. One way to achieve this is to apply
wearable dielectric elastomer strain sensors directly onto the hand.
Applications such as this require fast, efficient and scalable sensing electronics. Most capacitive sensing methods use an
analogue sensing signal and a backend processor to calculate capacitance. This not only reduces scalability and speed of
feedback but also increases the complexity of the sensing circuitry.
A capacitive sensing method that uses a DC sensing signal and continuous tracking of charge is presented. The method is
simple and efficient, allowing large numbers of dielectric elastomer sensors to be measured simulatenously.
One of the great advantages of dielectric elastomers (DE) is their scalability. Large planar DE are quite unique in the
world of actuators. An interesting application of such actuators is the activation of inflatable structures. As research platform
a model airship of 8 m in length was constructed that can move its body and tail fin in a fish-like manner. Unlike
the propulsion with propellers, the fish-like movement is silent and the airflow around the airship is not disturbed. The
bending actuation of the helium-filled hull is realized with planar two-layered DE of 1.6 m2 on either side. The tail fin is
moved by four-layer planar DE of 0.3 m2 on either side. A design for actuators of such dimensions was developed and
the actuators were characterized in terms of their performance.
After having successfully integrated Dielectric Elastomers (DE) in a cross tail for flight control, a novel biologically
inspired propulsion system based on DE is envisaged. The basic idea is to mimic a fish body motion by deforming a) the
envelope of the rear lifting body and b) flapping an aft-tail. In both cases, planar DEs are used, either fully integrated in
the envelope (for a) and/or arranged as an active hinge (for b). In a theoretical study the specifications of a steady-state
horizontal indoor flight of 1 m/s were defined. In an experimental work the concept of an active hull element, which
consists of a balloon hull material and several layers of DE actuators was verified. The specific boundary conditions of a
slightly pressurized elliptical membrane body were simulated in a biaxial test. It could be shown, that the necessary
active strains to reach the specified body deformations were reached. In a second study an aero-elastic fin was designed.
Based on fluid-dynamic similarity principles the size, shape and stiffness of the fin were determined and tested in
preliminary flight test with a three meter long blimp. The main goal of 1 m/s flight velocity could be shown.
In this paper the worldwide first EAP actuated blimp will be presented. It consists of a slightly pressurized Helium filled
body of a biologically inspired form with Dielectric Elastomer (DE) actuators driving a classical cross tail with two
vertical and horizontal rudders for flight control. Two versions of actuators will be discussed: The first version consisted
of "spring-roll" type of cylindrical actuators placed together with the electrical supply and control unit in the pay load
gondola. The second version consisted of a configuration, where the actuators are placed between the control surfaces
and the rudders. This novel type of EAP actuator named "active hinge" was developed and characterized first in the
laboratory and afterwards optimized for minimum weight and finally integrated in the blimp structure. In the design
phase a numerical simulation tool for the prediction of the DE actuators was developed based on a material model
calibrated with the test results from cylindrical actuators. The electrical supply and control system was developed and
optimized for minimum of weight. Special attention was paid to the electromagnetic systems compatibility of the high
voltage electrical supply system of the DE actuators and the radio flight control system. The design and production of
this 3.5 meter long Lighter-than-Air vehicle was collaboration between Empa Duebendorf Switzerland and the Technical
University of Berlin. The first version of this EAP blimp first flew at an RC airship regatta hold on 24th of June 2006 in
Dresden Germany, while the second version had his maiden flight on 8th of January 2007 in Duebendorf Switzerland. In
both cases satisfactory flight control performances were demonstrated.
In this work the electromechanical performance of planar, single- layered dielectric elastomer (DE) actuators was investigated. The mechanical power density and the overall electromechanical efficiency of DE stripe actuators under continuous activation cycles were examined. The viscoelastic behavior of the dielectric film was modeled with a three-dimensionally coupled spring-damper framework. This film model was fitted to the mechanical behavior of the acrylic film VHB 4910 (3M) evaluated in a combination of a uniaxial loading test with holding time and subsequent unloading. In addition the quasielastic film model was derived in order to evaluate the quasistatic behavior of DE actuators under activation.
For the simulation of DE actuators the boundary conditions of the film model were accordingly adapted. By embedding the actuator into an appropriate electrical circuit electrodynamic effects were incorporated as well.
The quasielastic model of a planar DE actuator with free boundary conditions predicted a stable deformation state for activation with constant charge. For activation with constant electrical voltage, however, the model showed a stable and an instable equilibrium state. For activation voltages beyond a critical voltage the film collapses in thickness direction due to the electrostatic forces (Maxwell stresses).
A biaxially prestrained stripe actuator was described with the viscoelastic film model. The stripe actuator was cyclically activated and cyclically elongated with a phase shift (displacement-controlled). A qualitative parameter study showed that the overall electromechanical efficiency as well as the specific power density of such DE actuators strongly depends on the electrical activation and the external mechanical loading.