For the BepiColombo mission, the extreme thermal environment around Mercury requires good heat shields for the instruments. The BepiColombo Laser altimeter (BELA) Receiver will be equipped with a specular reflective baffle in order to limit the solar power impact. The design uses a Stavroudis geometry with alternating elliptical and hyperbolic vanes to reflect radiation at angles >38° back into space. The thermal loads on the baffle lead to deformations, and the resulting changes in the optical performance can be modeled by ray-tracing. Conventional interfaces, such as Zernike surface fitting, fail to provide a proper import of the mechanical distortions into optical models. We have studied alternative models such as free form surface representations and compared them to a simple modeling approach with straight segments. The performance merit is presented in terms of the power rejection ratio and the absence of specular stray-light.
Adaptive structures are capable to change their shape in a smart way in order to "adapt" to variable external conditions.
Active shell structures with large out-of-plane deformation potential may be used to generate an interaction between the
structural shape and the environment. Exemplarily, such shell-like actuators may be utilized for the propulsion of
vehicles through air or water. Among the electroactive polymers (EAPs) especially soft dielectric EAP are promising for
driving shell-like actuators due to their huge active strain potential and intrinsic compliancy.
The challenging task of this study was to explore the potential of the DE actuator technology for the design of shell-like
actuators with the ability to perform complex out-of-plane deflections. We present and evaluate concepts for the design
of active shell structures driven by soft dielectric EAP. Preliminary experiments were conducted for selected approaches
in order to basically verify their principle of operation and to quantify their active out-of-plane deformation potential.
These experiments showed that the so-called agonist-antagonist configuration, where pre-strained DE films are attached
on both sides of a hinged backbone structure, holds good performance in terms of active out-of-plane deflections and
Miniature spring roll dielectric elastomer actuators for a novel
kinematic-free force feedback concept were manufactured and experimentally characterized. The actuators exhibited a maximum blocking force of 7.2 N and a displacement of 5 mm. The
theoretical considerations based on the material's incompressibility
were discussed in order to estimate the actuator behavior under
blocked-strain activation and free-strain activation. One prototype
was built for the demonstration of the proposed force feedback
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.
On March 7, 2005, the first arm wrestling match of an EAP robotic arm against a human was held during the EAP-inaction
session of the EAPAD conference in San Diego. The primary object was to demonstrate the potential of the EAP
technology for applications in the field of robotics and bioengineering. The Swiss Federal Laboratories for Materials
Testing and Research (Empa), Switzerland, was one of the three participating organizations in this competition. The
presented Empa robot was driven by a system of dielectric elastomer actuators. More than 250 rolled actuators were
arranged in two groups according to the human agonist-antagonist operating principle in order to achieve an arm-like
rotation movement in both directions. The robot was powered by a computer-controlled high voltage amplifier. The
rotary motion of the arm was performed by electrical activation respectively deactivation of the corresponding actuator