2,133 research outputs found
Catastrophic thinning of dielectric elastomers
We provide a clear energetic insight into the catastrophic nature of the
so-called creasing and pull-in instabilities in soft electro-active elastomers.
These phenomena are ubiquitous for thin electro-elastic plates and are a major
obstacle to the development of giant actuators; yet they are not completely
understood nor modelled accurately. Here, in complete agreement with
experiments, we give a simple formula to predict the voltage thresholds for
these instability patterns and model their shape, and show that equilibrium is
impossible beyond their onset. Our analysis is fully analytical, does not
require finite element simulations, and can be extended to include pre-stretch
and to encompass any material behaviour
A Review of Cooperative Actuator and Sensor Systems Based on Dielectric Elastomer Transducers
This paper presents an overview of cooperative actuator and sensor systems based on
dielectric elastomer (DE) transducers. A DE consists of a flexible capacitor made of a thin layer
of soft dielectric material (e.g., acrylic, silicone) surrounded with a compliant electrode, which is
able to work as an actuator or as a sensor. Features such as large deformation, high compliance,
flexibility, energy efficiency, lightweight, self-sensing, and low cost make DE technology particularly
attractive for the realization of mechatronic systems that are capable of performance not achievable
with alternative technologies. If several DEs are arranged in an array-like configuration, new concepts
of cooperative actuator/sensor systems can be enabled, in which novel applications and features
are made possible by the synergistic operations among nearby elements. The goal of this paper is
to review recent advances in the area of cooperative DE systems technology. After summarizing
the basic operating principle of DE transducers, several applications of cooperative DE actuators
and sensors from the recent literature are discussed, ranging from haptic interfaces and bio-inspired
robots to micro-scale devices and tactile sensors. Finally, challenges and perspectives for the future
development of cooperative DE systems are discussed
Control-focused, nonlinear and time-varying modelling of dielectric elastomer actuators with frequency response analysis
Current models of dielectric elastomer actuators (DEAs) are mostly constrained to first principal descriptions that are not well suited to the application of control design due to their computational complexity. In this work we describe an integrated framework for the identification of control focused, data driven and time-varying DEA models that allow advanced analysis of nonlinear system dynamics in the frequency-domain. Experimentally generated input–output data (voltage-displacement) was used to identify control-focused, nonlinear and time-varying dynamic models of a set of film-type DEAs. The model description used was the nonlinear autoregressive with exogenous input structure. Frequency response analysis of the DEA dynamics was performed using generalized frequency response functions, providing insight and a comparison into the time-varying dynamics across a set of DEA actuators. The results demonstrated that models identified within the presented framework provide a compact and accurate description of the system dynamics. The frequency response analysis revealed variation in the time-varying dynamic behaviour of DEAs fabricated to the same specifications. These results suggest that the modelling and analysis framework presented here is a potentially useful tool for future work in guiding DEA actuator design and fabrication for application domains such as soft robotics
Additively Manufactured Dielectric Elastomer Actuators: Development and Performance Enhancement
The recently emerging and actively growing areas of soft robotics and morphing structures promise endless opportunities in a wide range of engineering fields, including biomedical, industrial, and aerospace. Soft actuators and sensors are essential components of any soft robot or morphing structure. Among the utilized materials, dielectric elastomers (DEs) are intrinsically compliant, high energy density polymers with fast and reversible electromechanical response. Additionally, the electrically driven work principle allows DEs to be distributed in a desired fashion and function locally with minimum interference. Thus, a great effort is being made towards utilizing additive manufacturing (AM) technologies to fully realize the potential of DE soft actuators and sensors. While soft sensors have received more attention and development due to their simpler implementation, DE actuators (DEAs) set stricter AM and electrode material requirements. DEAs’ layered structure, compliant nature, and susceptibility to various defects make their manufacturability challenging, especially for non-trivial biomimetic soft robotics geometries. This dissertation comprehensively analyzes DE materials’ transition into a soft actuator using AM to facilitate effective DEA soft actuator fabrication. Closely interrelated fabrication techniques, material properties, and DEA geometries are analyzed to establish a fundamental understanding of how to implement high-quality DEA soft actuators. Furthermore, great attention is paid to enhancing the performance of printed DEAs through developing printable elastomer and electrode materials with improved properties. Lastly, performance enhancement is approached from the design point of view by developing a novel 3D printable DEA configuration that actuates out-of-plane without stiffening elements
Fully Polymeric Domes as High-Stroke Biasing System for Soft Dielectric Elastomer Actuators
The availability of compliant actuators is essential for the development of soft robotic
systems. Dielectric elastomers (DEs) represent a class of smart actuators which has
gained a significant popularity in soft robotics, due to their unique mix of large
deformation (>100%), lightweight, fast response, and low cost. A DE consists of a
thin elastomer membrane coated with flexible electrodes on both sides. When a high
voltage is applied to the electrodes, the membrane undergoes a controllable
mechanical deformation. In order to produce a significant actuation stroke, a DE
membrane must be coupled with a mechanical biasing system. Commonly used
spring-like bias elements, however, are generally made of rigid materials such as
steel, and thus they do not meet the compliance requirements of soft robotic
applications. To overcome this issue, in this paper we propose a novel type of
compliant mechanism as biasing elements for DE actuators, namely a threedimensional polymeric dome. When properly designed, such types of mechanisms
exhibit a region of negative stiffness in their force-displacement behavior. This feature,
in combination with the intrinsic softness of the polymeric material, ensures large
actuation strokes as well as compliance compatibility with soft robots. After presenting
the novel biasing concept, the overall soft actuator design, manufacturing, and
assembly are discussed. Finally, experimental characterization is conducted, and
the suitability for soft robotic applications is assessed
Adhesion modulation In bio-inspired micropatterned adhesives by electrical fields
With steps towards Industry 4.0, it becomes imperative to the development of next-generation industrial assembly lines, to be able to modulate adhesion dynamically for handling complex and diverse substrates. The inspiration for the design and functionality of such adhesive pads comes from gecko’s remarkable ability to traverse rough and smooth topographies with great ease and agility. The emphasis in this thesis was to equip artificial micropatterned adhesives with such functionalities of tunability and devise an on-demand release mechanism. The project evaluates the potential of electric fields in this direction. The first part of this work focusses on integrating electric fields with polymeric micropatterns and studying the synergistic effect of Van der Waals and electrostatic forces. An in-house electroadhesion set up was built to measure the pull-off forces with and without electric fields. As a function of the applied voltage, adhesion forces can be tuned. The second part of the work demonstrates a novel route that exploits the in-plane actuation of the dielectric elastomeric actuators integrated with microstructure to induce peeling in them. Voltage-dependent actuation has been harnessed to generate the requisite peel force to detach the micropatterns. Overall, the findings of this thesis combine disciplines of electroadhesion, electroactuation, and reversible dry adhesives to gain dynamic control over adhesion.Im Einklang mit dem Fortschreiten in Richtung Industrie 4.0, wird es auch für die Entwicklung von industriellen Montagelinien der nächsten Generation unerlässlich sein, die Handhabung komplexer und unterschiedlicher Objekte zu flexibilisieren. Bioinspirierte Haftpads nach dem Vorbild des Gecko könnten zukünftig hierzu wesentlich beitragen. Der Schwerpunkt dieser Arbeit bestand darin, künstliche mikrostrukturierte Haftpads mit einem elektrisch schaltbaren Adhäsions- und Ablösemechanismus zu funktionalisieren, um die Grundlage für einen schnell schaltbaren, intelligenten Greifer zu schaffen. Der erste Teil dieser Arbeit konzentriert sich auf die Kombination elektrischer Felder mit elastomeren Mikrostrukturen und die Untersuchung der synergistischen Wirkung von Van der Waals- und elektrostatischen Kräften. Zur Messung der Adhäsion wurde ein individueller Aufbau realisiert und mit diesem die Feldstärkeabhängigkeit der Haftkräfte nachgewiesen. Der zweite Teil der Arbeit demonstriert einen neuartigen Ablösemechanismus unter Ausnutzung der lateralen Bewegung dielektrischer elastomerer Aktuatoren, um so ein Abschälen der Haftpads vom Substrat zu induzieren. Durch Variation der elektrischen Spannung wurde untersucht, wie sich diese auf die Ablösegeschwindigkeit der Haftpads auswirkt. Insgesamt kombinieren die Ergebnisse dieser Arbeit die Disziplinen Elektroadhäsion, Elektroaktuation und reversible trockene Klebstoffe, um so eine dynamische Kontrolle über die Adhäsion zu erhalten
Design of nematic liquid crystals to control microscale dynamics
Dynamics of small particles, both living such as swimming bacteria and
inanimate, such as colloidal spheres, has fascinated scientists for centuries.
If one could learn how to control and streamline their chaotic motion, that
would open technological opportunities in areas such as the transformation of
stored or environmental energy into systematic motion, micro-robotics, and
transport of matter at the microscale. This overview presents an approach to
command microscale dynamics by replacing an isotropic medium such as water with
an anisotropic fluid, a nematic liquid crystal. Orientational order leads to
new dynamic effects, such as propagation of particle-like solitary waves. Many
of these effects are still awaiting their detailed mathematical description. By
using plasmonic metamask photoalignment, the nematic director can be patterned
into predesigned structures that control dynamics of inanimate particles
through the liquid crystal enabled nonlinear electrokinetics. Moreover,
plasmonic patterning of liquid crystals allows one to command the dynamics of
swimming bacteria, guiding their trajectories, polarity of swimming, and
concentration in space. The patterned director design can also be extended to
liquid crystal elastomers, in which case the director gradients define the
dynamic profile of elastomer coatings. Some of these systems form an
experimental playground for the exploration of out-of-equilibrium active
matter, in which the levels of activity, degree of orientational order and
patterns of alignment can all be controlled independently of each other.Comment: 35 pages, 9 figures, a review based on a lectur
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