Dielectric Electroactive Polymer Research Articles

Dielectric Electroactive Polymer Membrane Actuator with Ring-type Electrode as Driving Component of a Tactile Actuator

We present a driving concept of a tactile actuator based on a dielectric electroactive polymer using a ring-type electrode. This electrode is located around a deflectable membrane. The fabrication process and tests of the tactile actuator including integration into a hydraulic amplifier design are presented proving the concept of the novel actuation. The tactile actuator exhibits a maximum measured deflection of 124±7μm for an applied voltage of 4200V. The membrane thickness and the total thickness of the actuator including hydraulic amplifier were 30 and about 570μm, respectively.

Bidirectional Resonant DC–DC Step-Up Converters for Driving High-Voltage Actuators in Mobile Microrobots

Electroactive polymer (EAP) actuators have been investigated to convert electrical energy into mechanical deformation in autonomous microrobots. The use of dielectric EAP actuators comes with several challenges to address requirements such as high excitation voltages, explicit driving signals, and low conversion efficiency. External bulky and heavy power sources are used to generate and provide required excitation voltages. The development of a miniature, high voltage gain, and highly efficient power electronic interface is required to overcome such challenges and enable autonomous operation of miniature robots. In this paper, a bidirectional single-stage resonant dc–dc step-up converter is introduced and developed to efficiently drive high-voltage EAP actuators in mobile microrobots. The converter utilizes resonant capacitors and a coupled inductor as a soft-switched LC network to step up low input voltage. High-frequency soft-switching operation owing to LC resonance allows small footprint of the circuit without suffering from switching losses, which in turn increases the efficiency. The circuit is capable of generating explicit high-voltage actuation signals, with capability of recovering unused energy from EAP actuators. A 4-mm × 8-mm, 100-mg, and 600-mW prototype has been designed and fabricated to drive an in-plane gap-closing electrostatic inchworm motor. Experimental validations have been carried out to verify the circuit's ability to step up voltage from 2 to 100 V and generate two 1-kHz, 100-V driving voltages at 2-nF capacitive loads.

A Modulation Strategy for Wide Voltage Output in DAB-Based DC–DC Modular Multilevel Converter for DEAP Wave Energy Conversion

This paper presents an investigation on modulation modes for dual active bridge modules stacked in a 10-kV input parallel output series converter for energy extraction in dielectric electroactive polymer (DEAP) wave energy converters. The converter requirements for energy harvesting with DEAPs are derived, and the operating areas and limitations of each modulation mode are compared. A hybrid modulation strategy consisting of several variable frequency modulation modes is proposed, which is capable of operating over a wide voltage and current range at high-efficiency levels as required by the DEAP harvesting cycles. Through loss calculations using an experimentally validated loss model and by including both material and converter losses in the harvesting cycle, it is shown that the hybrid modulation method increases the energy output of low-strain cycles by 25%.

Actuator design and automated manufacturing process for DEAP-based multilayer stack-actuators

By applying an electric field to a transducer based on dielectric electroactive polymers (DEAP) a relatively high amount of deformation with considerable force generation is achieved. Due to their unique features DEAP-transducers are a promising alternative for conventional actuator systems based on the electromagnetic principle. To maximize the force or absolute deformation of a DEAP-based actuator multilayer technologies are favorable. Although these actuators recently gained a lot of interest, the development of automated manufacturing processes for such transducers are still at a very early stage. Therefore, the authors present the conceptual design and realization of a novel automated process based on pre-fabricated elastomer material for manufacturing DEAP-based multilayer stack-actuators with homogeneous and reproducible properties. For this purpose, the specific design and topology of the conceptualized multilayer stack-actuator from a single layer actuator film towards the encapsulation of the stacked multilayer actuator is explained in a first step. Due to its smart design, advantageous features like safety fuses can be integrated in these multilayer actuators. Furthermore, for its design and optimal integration in various applications a multiphysics FE model is proposed. Afterwards, the manufacturing process consisting of several sub-processes is presented in detail. The quality of the developed process and the proposed FE model is demonstrated by an experimental validation of several manufactured multilayer DEAP stack-actuators made from polyurethane and silicone. Finally, the obtained results are concluded and an outlook concerning an improved actuator characteristic based on a material optimization is given.

Electromechanical characteristic analysis of a dielectric electroactive polymer (DEAP) actuator

To assist in the design and optimization of dielectric electroactive polymer (DEAP) actuators, an analytical model for the electromechanical response of cone DEAP actuators is developed. Using the Yeoh form strain energy potential and the Maxwell stress tensor, the constitutive relationship of the DEAP that accounts for the electromechanical coupling behavior is deduced. The equilibrium equations of DEAP actuators with a cone configuration are derived and an analytical model is then proposed. With this model, the actuation characteristics of the DEAP actuator, including actuation displacement, force output and efficiency can be calculated. Additionally, the principal stresses and principal stretch ratio of the membrane under different actuation voltages can be determined, along with the wrinkling failure mode of DEAP actuators. The experimental results for the DEAP actuator matched the numerical results determined using the proposed model. As such, the proposed work is beneficial as a guide for the design optimization of DEAP actuators.

Analytical modeling and optimization of DEAP-based multilayer stack-transducers

Transducers based on dielectric electroactive polymers (DEAP) use electrostatic pressure to convert electrical into mechanical energy or vice versa. To scale up the actuation or the energy gain, multilayer transducers like DEAP stack transducers are appropriate. Within this contribution, a model of such a stack transducer is derived and experimentally validated. The model is based on a multi-domain approach to describe the mechanical dynamics and the electrical behavior of the DEAP. Since these two domains influence each other they are coupled afterwards by a novel approach using interchanging power flows. To parametrize this model, tensile and compression tests for different polymer materials were performed under static and transient considerations. The results of these experiments show that the parameters obtained from the tensile test sufficiently describe the compression mode and can therefore be used for the model. Based on this transducer model the overall energy and the different parts of the multi-domain are analytically determined for arbitrary operating points. These expressions for the energies are finally used to optimize well-defined coupling coefficients, by which a maximum part of the electrical input energy is converted to mechanical energy, especially mechanical work.

Modeling of the effects of the electrical dynamics on the electromechanical response of a DEAP circular actuator with a mass–spring load

This paper presents a modeling approach of an actuator system based on a dielectric electro-active polymer (DEAP) circular membrane mechanically loaded with a mass and a linear spring. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. A mass and a linear spring are used to pre-load the membrane, allowing stroke in the out-of-plane direction. The development of mathematical models which accurately describe the nonlinear coupling between electrical and mechanical dynamics is a fundamental step in order to design model-based, high-precision position control algorithms operating in high-frequency regimes (up to 150 Hz). The knowledge of the nonlinear electrical dynamics of the actuator driving circuit can be exploited during the control system design in order to achieve desirable features, such as higher modeling accuracy for high-frequency actuation, self-sensing or control energy minimization. This work proposes a physical model of the DEAP actuator system which couples both electrical and mechanical dynamics occurring during the actuation process. By means of numerous experiments, it is shown that the model can be used to predict both actuator current and displacement, and therefore to increase the overall displacement prediction accuracy with respect to actuator models which neglect electrical behavior.

Biohybrid Control of General Linear Systems Using the Adaptive Filter Model of Cerebellum.

The adaptive filter model of the cerebellar microcircuit has been successfully applied to biological motor control problems, such as the vestibulo-ocular reflex (VOR), and to sensory processing problems, such as the adaptive cancelation of reafferent noise. It has also been successfully applied to problems in robotics, such as adaptive camera stabilization and sensor noise cancelation. In previous applications to inverse control problems, the algorithm was applied to the velocity control of a plant dominated by viscous and elastic elements. Naive application of the adaptive filter model to the displacement (as opposed to velocity) control of this plant results in unstable learning and control. To be more generally useful in engineering problems, it is essential to remove this restriction to enable the stable control of plants of any order. We address this problem here by developing a biohybrid model reference adaptive control (MRAC) scheme, which stabilizes the control algorithm for strictly proper plants. We evaluate the performance of this novel cerebellar-inspired algorithm with MRAC scheme in the experimental control of a dielectric electroactive polymer, a class of artificial muscle. The results show that the augmented cerebellar algorithm is able to accurately control the displacement response of the artificial muscle. The proposed solution not only greatly extends the practical applicability of the cerebellar-inspired algorithm, but may also shed light on cerebellar involvement in a wider range of biological control tasks.

Dielectric and magnetic properties of poly (vinylidene fluoride) composites doped with pomegranate-like PPY@NiFe2O4 nanospheres

Pomegranate-like polypyrrole-coated NiFe2O4 ferrite (PPY@NiFe2O4) nanospheres were prepared and used as functional fillers within dielectric electroactive polymer poly(vinylidene fluoride) (PVDF) matrix. The microstructure of PPY@NiFe2O4 ferrite was characterized by Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscope (TEM). The interface interaction of PPY@NiFe2O4 nanofiller and PVDF matrix was stronger than that of pure NiFe2O4 and PVDF matrix. The difference of interface interaction between nanofiller and polymer matrix were simply illustrated by a mechanism schematic. The dielectric and magnetic properties of PVDF composites were investigated. Compared to the pristine NiFe2O4/PVDF composites, the PPY@NiFe2O4/PVDF composites presented enhanced dielectric constant and lower dielectric loss.

Design and modeling of an innovative wave energy converter using dielectric electro-active polymers generator

This paper proposes a design and modeling of an innovative wave energy converter using Dielectric electro active polymer (DEAP). Firstly, an accurate model of conventional DEAP generator is investigated and validated under a specific range of ocean waves. Then, a structure design of an antagonistic DEAP generator so-called energy capture unit (ECU), which consists of two DEAPs in antagonistic connection mode to increase harvested energy efficiency, is modeled and validated by experimental data. A new design of WECs is then developed with array of ECUs to increase the output energy. In addition, by using the linear potential wave theory, the hydrodynamic forces are calculated under regular wave conditions. Consequently, a complete analytical model of the proposed WECs using multiple ECUs under hydrodynamic behavior is then obtained to investigate the performance of energy conversion. Finally, based on the developed analytical model, the stretch ratio known as an important factor to efficiency and output power is investigated under the influence of the floating buoy’s mass. Then, the resonance behavior of the WECs with a typical wave frequ ncy can be tuned by optimizing the floating’s mass to increase the degree of utilization of the device. The simulation results indicate hat the efficiency of wave energy converter can be up to 25% thanks to resonance behavior.

Modeling and experimental investigation on dielectric electro-active polymer generator

Dielectric electro-active polymers (DEAP) have been attracted for the energy harvesting application due to its low cost, lightweight and flexible deformation capability. This paper presents a validated model and experimental investigation on energy conversion of a typical DEAP generator. Firstly, a dynamics model based on Mooney-Rivlin proposition is developed to describe the strain–force relationship of DEAP material. Then, the effect of charging voltages and energy conversion are also taken into account. In addition, identification processes are done separately for stretching and relaxing strokes using an adaptive PSO scheme to find best material parameters for the model. This makes the model be available to describe the sinusoidal strain forms in practical conditions. The validated model is then employed in investigating input mechanical energy, return energy and conversion energy for the DEAP generator. Experimental evaluations show that the developed model can describe the behavior of DEAP material accurately. Finally, analyses based on the energy conversion demonstrate the abilities of DEAP material as wave energy converter.

Experimental assessment of spanwise-oscillating dielectric electroactive surfaces for turbulent drag reduction in an air channel flow

In the present work, wall oscillations for turbulent skin friction drag reduction are realized in an air turbulent duct flow by means of spanwise-oscillating active surfaces based on dielectric electroactive polymers. The actuator system produces spanwise wall velocity oscillations of 820 mm/s semi-amplitude at its resonance frequency of 65 Hz while consuming an active power of a few 100 mW. The actuators achieved a maximum integral drag reduction of 2.4 %. The maximum net power saving, budget of the power benefit and cost of the control, was measured for the first time with wall oscillations. Though negative, the net power saving is order of magnitudes higher than what has been estimated in previous studies. Two new direct numerical simulations of turbulent channel flow show that the finite size of the actuator only partially explains the lower values of integral drag reduction typically achieved in laboratory experiments compared to numerical simulations.

The electrical breakdown strength of pre-stretched elastomers, with and without sample volume conservation

In practice, the electrical breakdown strength of dielectric electroactive polymers (DEAPs) determines the upper limit for transduction. During DEAP actuation, the thickness of the elastomer decreases, and thus the electrical field increases and the breakdown process is determined by a coupled electro-mechanical failure mechanism. A thorough understanding of the mechanisms behind the electro-mechanical breakdown process is required for developing reliable transducers. In this study, two experimental configurations were used to determine the stretch dependence of the electrical breakdown strength of polydimethylsiloxane (PDMS) elastomers. Breakdown strength was determined for samples with and without volume conservation and was found to depend strongly on the stretch ratio and the thickness of the samples. PDMS elastomers are shown to increase breakdown strength by a factor of ∼3 when sample thickness decreases from 120 to 30 μm, while the biaxial pre-stretching (λ = 2) of samples leads similarly to an increase in breakdown strength by a factor of ∼2.5.

Inverse modeling and control of a dielectric electro-active polymer smart actuator

This study focuses on the design of an inverse model for a dielectric electro-active polymer (DEAP) smart actuator using the dynamic nonlinear auto regressive exogenous (NARX) structure and a fuzzy inference system. The unknown parameters of the proposed NARX fuzzy model was identified by the adaptive particle swarm optimization (APSO) algorithm. An augmented proportional-integral-derivative feed-forward inverse (APIDFFI) controller was then developed for position tracking control of the actuator. Finally, an experimental investigation was scrutinized in order to evaluate the effectiveness of the designed inverse model and the proposed controller. The results show that the designed controller based on the inverse model improves the tracking performance of the actuator significantly with the tracking accuracy of about 96% and reduces the tracking errors compared to the conventional proportional-integral-derivative (PID) controller.

Carbon nanotube sheet electrodes for anisotropic actuation of dielectric elastomers

The performance of dielectric electroactive polymer (D-EAP) based actuators depends critically on the electrode characteristics. Among the most challenging issues in the application of D-EAPs is the device-level complexity in producing sufficient directional actuation at acceptably low electric fields. In this work, a simple carbon nanotube (CNT) based electrode for D-EAP actuators is demonstrated that vastly improves directional strain response originating from the mechanical anisotropy of the electrode material. In this novel approach, highly aligned carbon nanotube (CNT) sheet electrodes are applied on acrylate adhesive films show high directed linear actuation strain of greater than 40% at a relatively low electric field (100Vμm−1). The fiber-oriented CNT sheet applied around the D-EAP film, exhibits strong interaction between CNT fibers in the electrode and the D-EAP film to produce a robust conductive-nanolayer at the interface, on actuation cycling. The design paradigm provides a great potential for the fabrication of soft linear actuators.

Modeling, Identification, and Control of a Dielectric Electro-Active Polymer Positioning System

This paper deals with a positioning system based on a dielectric electro-active polymer membrane. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. This paper proposes a detailed electro-mechanical nonlinear model of the system, which is subsequently used to develop (in both time and frequency domains) various model-based feedback control laws. Accurate modeling is useful to compensate the nonlinear behavior of the actuator (caused by the material characteristics and geometry) and obtain PID controllers providing precise tracking of steps or sinusoidal reference signals. The various design strategies are compared on various experimental tests.

Bilaterally Microstructured Thin Polydimethylsiloxane Film Production

Thin PDMS films with complex microstructures are used in the manufacturing of dielectric electro active polymer (DEAP) actuators, sensors and generators, to protect the metal electrode from large strains and to assure controlled actuation. The current manufacturing process at Danfoss Polypower A/S produces films with a one-sided microstructured surface only. It would be advantageous to produce a film with both surfaces microstructured, as this increases the film’s performance efficiency. The new technique introduced herein produces bilaterally microstructured film by combining an embossing method with the existing manufacturing process. In employing the new technique, films with microstructures on both surfaces are successfully made with two different liquid silicone rubber (LSR) formulations: 1) pure XLR630 and 2) XLR630 with titanium dioxide (TiO2). The LSR films (∼70 µm) are cast on a carrier web substrate using a coating blade. The carrier web, which has a sinusoidal corrugation with wave height of 7 µm and a wave period of 7 µm on its surface, imparts corrugations to the bottom surface of the film. The elastomer film on the carrier web is preheated to the gel point, where the elastomer film can retain an imprint made on it. The preheated film at gel point is embossed between the rolls of a gravure lab coater, which corrugates the top surface of the film. The films are then heated, in order to cure completely. For the LSR systems used in this process, the optimum conditions for preheating are 110°C for 4–7 s, while for embossing the temperature is 110°C with 25 psi pressure between the rolls at a speed of 1.4 rpm. Scanning electron microscope (SEM) images confirm the formation of microstructures on both the surfaces of the film.

Foot edema simulation and monitoring using dielectric electro-active polymer sensors

Edema of the lower extremities, nerve damage and circulatory dysfunction, are common symptoms in diabetes and other chronic diseases. These symptoms must be addressed early in the disease process before permanent nerve damages occur. To provide a better understanding of such symptoms and to avoid unnecessary nerve damages, we aim at developing and testing a wearable edema monitoring system. This study addresses a novel method of foot edema simulation and monitoring. Two prototypes based on an artificial foot covered with latex are developed to simulate edema. Dielectric electro-active polymer (DEAP) stretch sensors are employed for continuous monitoring of edema. National Instruments device and LabVIEW are used for data acquisition and analysis. The experimental results indicate that the DEAP sensors are suitable in this application. The edema simulation system provides an efficient method for testing new sensors or techniques, especially in preclinical studies.

A Novel Floor Sensor Network Technology Based on Dielectric Electro-Active Polymers

This study describes a novel floor sensor network being developed to provide a competitive and universal pressure mapping technology for a wide range of medical, research and security applications. The presented sensor network consists of 16 sensor elements distributed in a 4x4 sensor matrix. The sensor elements are made of a special dielectric electro-active polymer film being capable of capacitive sensing of the surface pressure. Each sensor unit is 200x160 mm resulting in an overall sensor matrix size of 800x740 mm. A high precision and high speed sensor interface was realized to provide a differential capacitance measurement method fulfilling the specific measuring requirements of the sensor matrix. Based on the measurement results, the developed sensor network is capable of measuring the distributed weight on their surface with an accuracy of 5 kg, however, this initial measuring accuracy can be significantly increased by improving the manufacturing technology of the sensor elements.

Viscoelastic modelling and experimental results of a dielectric electro‐active polymer diaphragm actuator

AbstractCommon actuating principles e.g. solenoids or piezo‐elements have mostly exploited their potential as electromechanical transducers. A new technology based on Dielectric Electro‐active Polymers (DEAPs) enables major progress in efficiency and functionality for actuators. In order to use the advantages of this new technology in a feasible application, a silicone based DEAP diaphragm actuator was tested experimentally. Here, the mechanical properties of the fundamental parts of the DEAP diaphragm actuator, namely the stressstrain behaviour of an equibiaxially pre‐stretched hyperelastic polymer and the mechanical response of a DEAP diaphragm actuator, were determined by appropriate test benches.The investigated DEAP diaphragm actuator consists of a dielectric, which corresponds to a thin elastic silicone film sandwiched between two compliant electrodes. Furthermore, DEAPs are pre‐stretched, actually up to five times their in‐plane dimensions, in order to improve their performance. In that context, the influence of the pre‐stretched state on the actuator performance was investigated. In addition, a viscoelastic finite‐element model of the electromechanical system has been developed and validated with the experimental results. The mechanical part of the DEAP diaphragm actuator was realized with an incompressible isotropic elastic model, whereas the electrical part was approximated with a circular parallel‐plate capacitor. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)