This presentation describes the design, manufacturing and testing of an inflatable Dielectric Elastomer Generators (DEGs) with a stadium shape that is intended to be used as integrated prime-mover and power-take-off system of a submerged-membrane pressure-differential Ocean Wave Energy Converter (OWEC). Results highlight the good performances of the developed stadium-shape DEG and its potentialities within the considered OWEC.
Nowadays, several industrial manufacturing processes imply direct cooperation between human operators and robots. This increases production and quality while improving the working conditions. However, the possible presence of physical contact between humans and robots asks for the study and introduction of new technical solutions that aim at guaranteeing a safe Human-Robot Interaction (HRI). Specifically, in recent years, different sensing devices have been developed for collision avoidance monitoring in HRI applications. Generally, common solutions consist of distributed resistive or capacitive sensors networks connected to a central electronic reading board, resulting in a cumbersome layout covering the whole parts of the collaborative robots. In this context, this paper presents an innovative tactile and proximity sensing strategy based on a soft-sensor module that can be installed on the collaborative robot parts or surrounding workspace. The developed module consists of a capacitive sensor based on a silicone elastomer membrane with compliant electrodes attached to the surface, disposed homogeneously on a deformable hemisphere-shape made of silicone. Thanks to the geometrical layout, such a sensor allows multidirectional objects detection resulting in a promising non-invasive solution for collisions avoidance in HRI applications. This work reports the design, manufacturing, and preliminary experimental investigation of such a sensor module, evaluating the electrodes geometry and the most relevant features that optimize objects detection distance and directivity sensing performance.
This paper focuses on the characterisation of the vibroacoustic response of dielectric elastomer (DE) membranes. We set our attention on a circular DE membrane, deformed three-dimensionally and mounted in between fixed frames, which is able to generate sound with no need for any elastic or pneumatic biasing element. We present a finite element model of the system entirely based on commercial software Comsol Multiphysics. The model combines: 1) a mechanical model of the DE membrane, which makes use of suitably defined energy functions that account for electro-elastic coupling; and 2) an acoustic model of the domain surrounding the DE. The model implements a bi-directional coupling between the DE and the acoustic domain. In particular, it accounts for the effect of the acoustic pressure loads applied on the DE membrane, which, given the small thickness and low density of the membrane, play a significant role in the system dynamics. We validate the model against experimental measurements of the DE surface velocity and the sound pressure level (SPL) in the surroundings of the membrane. Despite relying on strong simplifications in the geometry of the system and the viscous response of the material, the model is able to describe the main trends in the device frequency response, and how the SPL varies as a function of the mechanical pre-load and the voltage applied on the membrane.
This paper presents a multi-physics model of an electrostatic loudspeaker system that combines the acoustic diaphragm and the actuator into a lightweight dielectric elastomer (DE) membrane. The focus is set on the so-called cone-shaped DE actuator (DEA) topology, which features a self-standing compact architecture, free from pneumatic loading systems, and is potentially suitable for integration onto complex surfaces and structures. We propose an axial-symmetrical lumped-parameter nonlinear model of the cone DEA structural dynamics, and use it to predict the acoustic pressure field generated by the speaker. We then present a case study in which the model is used to predict the linearised mode shapes of a reference DEA, evaluate their effect on the acoustic frequency response, and compare the harmonic distortions resulting from different driving strategies.
Flexible thin-film Electro-Adhesive Devices (EADs) represent a promising technology with great potential for gripper applications. Generally, the gripping action of an EAD is due to the electrostatic force induced by an electric field produced by applying a voltage across a couple of electrodes that are embedded between dielectric substrates. This paper presents a novel manufacturing process and the experimental characterization of a multilayer electro-adhesive gripper. The proposed device employs highly elastic silicone (PDMS) thin-film as the grasping layer, i.e., the dielectric layer that comes in contact with the grasped object, a carbon-black mixture in a silicone compound for the electrodes, and a rigid polyimide thin-film as the backing layer, i.e., the dielectric layer on the backside of the EAD. A fabrication methodology is illustrated, which starts from a casting of thin conductive electrodes on a polyimide film, followed by a laser-cutting operation to shape the electrodes and a blade casting process to encapsulate the overall system in a PDMS compound. Different prototypes obtained through this manufacturing procedure have been experimentally evaluated through a testing campaign conducted on three groups of specimens, each composed of five identical samples, with a different electrode thickness per group. Samples are tested for electrostatic shear stress and electrical breakdown during the grasping of paper substrates, identifying the best performing EAD group.
Actuators driven by electrostatic force represent a very promising opportunity for the development of advanced robotic systems. Dielectric elastomer actuators have been long investigated and more recently devices based on fluid dielectric have been proposed as a possible alternative that shows remarkable performance.
Here, we present a novel electrostatic actuator that is made of thin polyimide films and liquid dielectric, combined with rigid plates assembled to form a circular actuation unit that undergoes to out-of-plane expansion/contraction. Prototypes of these actuation units have been tested showing a contraction of up to 40%, a maximum power density during contraction of 100 W/kg, a maximum strain rate of 1000% per second, a bandwidth of approximately 10 Hz, and the ability to lift hundreds of times their weight.
Additionally, these units resulted easy to manufacture in different dimensions and can be assembled in arrays and stacks to form an electrostatic bellow muscles (EBM) that can be effectively employed as a contractile artificial muscle, as pump and as electrostatic generator. EBM demonstrated their flexibility in matching a wide range of requirements and scales in terms force-displacement combinations and bandwidth.
The compact 2-D shape, the low-cost of components, the simple assembling procedure, the high level of reliability and the relevant performance make the EBM a possible enabling technology for a variety of high-performance robotic and mechatronic systems.
This demo presents the Electrostatic Bellow Muscle (EBM), a flexible multipurpose
actuator that is obtained by stacking multiple bellow-shaped actuation units. EBM takes
inspiration from previous work on liquid-gap electrostatic actuators introducing a new
architecture. This novel solution makes it possible to implement an actuator that features a
flexible/multipurpose applications such as contractile muscle, pump or energy harvester, while
maintaining performance that are comparable to those of previously developed actuation
systems. Additionally, a very simple manufacturing process makes it possible to scale up force
or displacement by arranging in series or in-parallel actuators.
Specifically, the demo will show an EBM with cylindrical shape with a
diameter of 30 mm and a height sof 14 mm lifting a weight of approximately 300g with a
displacement of 6-7mm at different frequencies.
This paper describes the development of an electro-adhesive gripper with silver interdigitated electrodes that are inkjetprinted on a pre-fabricated flexible dielectric film made of polyether ether ketone (PEEK), which also acts as the gripper adhering surface, and encapsulated in a blade-casted silicone elastomer backing layer. After a description of the manufacturing approach, the paper presents and discusses the results of the electro-mechanical characterization of two fabricated nominally identical electro-adhesive devices, by specifically focusing on: electrically-induced adhesion shear stress, capacitance variation, energy and power consumption.
Dielectric Elastomers (DEs) are deformable dielectrics that can be used as active materials in mechatronic transducers, such as actuators, sensors and generators. Focusing on actuation systems, several kinds of DE actuators have been proposed in the literature, being characterized by various shapes/sizes and disparate performances in terms of efficiency, force/power densities and reliability. In any case, up to date, these devices are mostly based on either silicone or acrylic elastomers. On the other hand, actuator prototypes, which exploit the electromechanical properties of styrenic rubber, have been scarcely considered. Therefore, in this paper, a styrene-based-rubber Lozenge-Shaped DE Actuator (LS-DEA) is proposed and its performance are empirically evaluated. In particular, after material characterization and on the basis of a design procedure previously proposed by the authors, it is practically shown how it is possible to optimize the LS-DEA elastic response in order to tailor the application requirements and also (if needed) to obtain a nearly-zero mechanical stiffness. Several experimental results are henceforth provided, as a basis to highlight advantages and disadvantages of styrenic rubber LS-DEA over similar acrylic or silicone-based devices
Recent research work has shown that dielectric fluids, with specific properties, can be combined with stretchable or flexible shell structures, made of polymeric dielectric/electrode composite films, to implement a novel type of soft electrically-driven fluidic transducers with self-healing and self-sensing capabilities that take the name of Liquid based Electro-Active Polymer transducers (LEAPs). These devices are similar to dielectric elastomer transducers in regards to their electrostatic working principle, but they can potentially produce larger displacements due to their lower mechanical stiffness. In this contribution, we present a new transducer concept in which LEAP actuators are employed to induce out-ofplane deformation of a membrane. Specifically, experimental and theoretical demonstrations are provided for applications as dot actuator for Braille displays or other tactile feedback implementations. Results obtained on a preliminary prototype show that the system is able to provide a perceivable force for a human fingertip, offering potential room for further improvement and optimization. Electrically-induced cyclic actuation can be produced over a wide range of frequencies. The results presented in this paper prove the applicability of the LEAP principle on tactile devices and show new design paradigms for this technology.
Dielectric Elastomer Transducers (DETs) represent an emerging technology with great potential for mechatronic applications. DETs allow to convert electrical energy into mechanical energy and vice-versa, making it possible to design actuators, generators, and sensors. These devices show many advantages like high energy density, silent operations, and low cost, but their practical applicability is strongly affected by their reliability and lifetime, which depend on both environmental conditions and electro-mechanical loads. Theoretical and experimental studies have recently been initiated to investigate the lifetime ranges of such devices for different loading conditions (e.g., mechanical, electrical, electromechanical). At present, the lifetime characterization of DETs has been conducted by means of stochastic models only. In principle, a better understanding of electro-mechanical fatigue mechanism of DETs can be obtained through an appropriate analysis of their underlying physics. In this context, this paper presents a novel modeling approach for electro-mechanical damage evolution of DETs. In order to describe the phenomena involved in the damage process in physically consistent way, a free-energy framework is adopted. Starting from well-established electro-mechanical free-energy functions, additional variables which account for both mechanical and electrical fatigue mechanisms are introduced. Singular models for damage accumulation are developed and integrated within the free-energy conservation principle, in order to dynamically simulate the life status of the dielectric material when subjected to combined electric and mechanical loads. Finally, the kinetic law for damage evolution history due to combination of different failure modes are introduced, and used to assess DETs reliability based on experimental observations.
Dielectric Elastomer Transducers (DETs) are a promising technology for the development of actuators, generators and sensors with high performance and low cost. Practical application and economic viability of DETs is strongly affected by their reliability and lifetime, which depend on the maximum strain and electrical loads that are cyclically applied on such devices. To date, only limited information is available on the fatigue life performances of dielectric elastomer materials and of the transducers made thereof. This paper reports on a first lifetime constant electric-stress test campaign conducted on 38 free-expanding frame-stretched circular DET specimens, made of the silicone elastomer film Elastosil 2030 250/150 by Wacker with blade-casted carbon-black silicone-elastomer electrodes, that have been subjected to nearly square wave electric field signals with 1 Hz frequency, 50% duty cycle and with amplitudes ranging from 65 MV/m to 80 MV/m.
Dielectric fluid transducers (DFTs) are electrostatic devices which alternate solid compliant dielectric layers/electrodes with dielectric fluid layers, and they enable the conversion of electrical energy into mechanical work (and vice versa) through capacitance variations associated with a modification of their shape. Compared to other capacitive transducers, e.g., dielectric elastomer transducers, DFTs feature better tolerance to electrical break-down and larger ratio between converted energy and stored elastic energy. To date, practical DFT topologies have been proposed and demonstrated for both actuation and generation purposes, showing promising performance in terms of converted energy density and efficiency. This paper presents an overview on operating principles/layouts, introduces a simplified analytical modelling approach and proposes some figure of merit to evaluate the performances of this new class of transducers.
Dielectric Elastomer Generators (DEGs) are very promising systems that are able to directly convert oscillating mechanical energy into direct electricity. Their nature and main attributes make them particularly interesting for harvesting energy form ocean waves. In this context, several efforts have been made in the last years to develop effective Wave Energy Converters based on DEG [1-4].
In this contribution, we present a novel Wave Energy Converter (WEC) based on the Oscillating Water Column principle. The device features an inflatable DEG as Power Take Off (PTO) system and collector - i.e. the part of the device that is directly interacting with waves – that possesses a coaxial-ducted shape as described in [5].
Models of the coupled behavior that consider the electro-hyperelastic response of the DEG and the hydrodynamics are presented. It is shown that the dynamic response and the effectiveness of the system can be largely improved through an appropriate dimensioning of the geometry of the device. Specifically, the dynamic response of the system can be designed to match the corresponding harmonic content of water waves achieving an effective conversion of the incoming mechanical energy.
A small/intermediate scale prototype of the system is built and tested in a wave tank facility - i.e. a basin in which artificially controlled waves can be generated - available at Flowave (UK).
Mathematical models are validated against experimental results for monochromatic and panchromatic tests. During the experiments, we obtained peak of estimated power output in the range of 1 W to 4 W with an energy density for the dielectric material of approximately 80-120W/kg.
The achieved results represent a milestone in the study of WEC based on DEG, paving the path toward scaling up of this technology.
Recently, a styrenic rubber membrane (commercialized under the name of “THERABAND YELLOW 11726”) demonstrated excellent electromechanical properties for the development of high power density and highly efficient dielectric elastomer transducers (DETs). In particular, in an experimental application as generator, an inflated circular diaphragm DET based on this material made it possible to consistently convert pneumatic energy into electricity at a maximum energy density per cycle and power density greater than 400 J/kg and 650 W/kg, respectively, with even higher numbers being expected for DETs configured so as to have the material working in uniform states of deformation.
As for any other existing dielectric elastomer material, these experimented performances can however be sustained for a limited number of cycles only, after which the DET will fail irreversibly. To date, very little information is available on the fatigue life performances of dielectric elastomer materials and of the transducers made thereof.
Having identified the electrical breakdown as the most probable mode of DET failure, this paper reports for the first time on a set of lifetime constant-electric-stress tests conducted on the considered styrenic dielectric elastomer membrane.
Specifically, the paper starts with a description of the employed experimental set-up and procedures. Then, it summarizes the obtained experimental results. Finally, it concludes with a discussion on how the acquired data could be used in a design procedure to find optimal tradeoffs between DET performance and lifetime/reliability.
The recent discovery of a new kind of thermo-active coiled polymeric wires has opened new perspectives for the implementation of a novel class of actuators that can be easily and effectively manufactured using low-cost materials such as sewing threads or finishing lines. These new devices feature large displacements in response to temperature variations and show very promising performance in terms of energy and power densities.
With the aim of providing information and data useful for the future engineering applications of polymeric coiled actuators, a custom experimental test-bench and procedure have been developed and employed to characterise their thermo-mechanical response. Such a test-bench has been designed to run isothermal and isometric tensile tests on a set of sample actuators that are fabricated with a repeatable process.
This paper provides technical details on the manufacturing process of such sample actuators and on the design and operation of the test-bench. Preliminary experimental results are finally reported.
Dielectric Elastomers (DE) are incompressible polymeric solids that experience finite elastic deformations and are
electrically non-conductive. Stacking multiple DE films separated by compliant electrodes makes a deformable capacitor
transducer, namely a DE Transducer (DET), which can expand in area while shrinking in thickness and vice versa. DETs
can be used as solid-state actuators, sensors and generators.
The development of an effective DET requires the accurate knowledge of the constitutive behavior of the employed DE
material. In this context, this paper reports the experimental results of the electromechanical characterization of a new
synthetic rubber membrane (TheraBanTM Latex Free Resistance Band Yellow (P/N #11726), or TheraBand LFRB-Y in
short) to be used as elastic dielectric in DETs. Comparison of the obtained results with those of the best quoted Natural
Rubber membrane (OPPO BAND 8003) is also provided that shows the superior performances of TheraBand LFRB-Y
both in terms of reduced mechanical hysteresis and of higher dielectric strength stability to ambient wetness conditions.
KEYWORDS: Prototyping, Dielectrics, Electrodes, Energy harvesting, Water, Energy efficiency, Polymers, Energy conversion efficiency, Electroluminescence, Resistance
Wave energy harvesting is one of the most promising applications for Dielectric Elastomer Generators. A simple and
interesting concept of a Wave Energy Converter based on Dielectric Elastomers is the Polymeric Oscillating Water
Column (Poly-OWC). In this paper, preliminary experimental results on the assessment of a small-scale Poly-OWC
prototype are presented. The scale of the considered prototype is 1:50. Tests are conducted in a wave-flume by
considering sea state conditions with different wave amplitudes and frequencies. The obtained experimental results
confirm the viability of the Poly-OWC device.
Dielectric Elastomer Transducers (DETs) are deformable capacitors that can be used as sensors, actuators and
generators. The design of effective and optimized DETs requires the knowledge of a set of relevant properties of the
employed Dielectric Elastomer (DE) material, which make it possible to accurately predict their electromechanical
dynamic behavior.
In this context, an open-access database for DE materials has been created with the aim of providing the practicing
engineer with the essential information for the design and optimization of new kinds of DET. Among the electrical
properties, dielectric susceptibility, dielectric strength and conductivity are considered along with their dependence on
mechanical strain. As regards mechanical behavior, experimental stress-strain curves are provided to predict
hyperelasticity, plasticity, viscosity, Mullins effect and mechanical rupture. Properties of commercial elastomeric
membranes have been entered in the database and made available to the research community.
This paper describes the instrumentations, experimental setups and procedures that have been employed for the
characterization of the considered DE materials. To provide an example, the experimental data acquired for a
commercially available natural rubber membrane (OPPO Band Red 8012) are presented.
Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce
electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric
and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or
multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of
deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric
Elastomer (DE) material.
This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical
loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE
membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system
is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the
generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes
and used for the experimental verification of the employed numerical models.
Dielectric Elastomers (DE) have been largely studied as actuators and sensors. Fewer researches have addressed their application in the field of energy harvesting. Their light weightiness, low cost, high corrosion resistance, and their intrinsic high-voltage and cyclical-way of operation make DE suited for harvesting mechanical energy from sea waves. To date, the development of cost-effective Wave Energy Converters (WECs) is hindered by inherent limitations of available material technologies. State of the art WECs are indeed based on traditional mechanical components, hydraulic transmissions and electromagnetic generators, which are all made by stiff, bulky, heavy and costly metallic materials. As a consequence, existing WECs result in being expensive, difficult to assemble, sensitive to corrosion and hard to maintain in the marine environment. DE generators could be an enabling technology for overcoming the intrinsic limitations of current WEC technologies. In this context, this paper focuses on Polymer-based Oscillating-Water-Column (Poly-OWC) type WECs, and analyzes the viability of using DE generators as power-take-off systems. Regarding paper structure, the first sections introduce the working principle of OWC devices and discuss possible layouts for their DE-based power-take-off system. Then, a simplified hydraulic-electro-hyperelastic model of a two-dimensional Poly-OWC is described. Finally, preliminary simulation results are shown which provide insights on the potential capabilities of Poly-OWC.
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