On the performance mechanisms of Dielectric Elastomer Actuators (original) (raw)
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On the nature of dielectric elastomer actuators and its implications for their design
Proceedings of SPIE, 2006
Dielectric Elastomer (DE) actuators have been studied extensively under laboratory conditions where they have shown promising performance. However, in practical applications, they have not achieved their full potential. Here, the results of detailed analytical and experimental studies of the failure modes and performance boundaries of DE actuators are presented. The objective is to establish fundamental design principles for DE actuators. Analytical models suggest that DE actuators made with highly viscoelastic films are capable of reliably achieving large extensions when used at high speeds (high stretch rates). Experiments show that DE actuators used in low speed applications, such as slow continuous actuation, are subject to failure at substantially lower extensions and also have lower efficiencies. This creates an important reliability/performance trade-off because, due to their viscoelastic nature, highest DE actuators forces are obtained at low speeds. Hence, DE actuator design requires careful reliability/performance trade-offs because actuator speeds and extensions for optimal performance can significantly reduce actuator life.
Large-scale failure modes of dielectric elastomer actuators
International Journal of Solids and Structures, 2006
Dielectric elastomer actuators (DEAs) show promise for robotic and mechatronic applications. However, to date, these actuators have experienced high rates of failure that have prevented their practical application. Here, large scale modes of failure of DEAs and their performance limits are studied. The objective is to provide design guidelines and bound the performance of DEAs that avoid failure. An idealized DEA is modeled and its failure is predicted as a function of film prestretch used during actuator fabrication, actuation voltage, and stretch rate. Three failure modes are considered: pull-in, dielectric strength, and material strength. Each failure mode is shown to dominate for different combinations of pre-stretch and stretch rate. High stretch rates lead to dielectric strength failure while low stretch rates lead to pull-in failure. Material strength failure is less important for most cases. Model predictions are validated experimentally using practical DEAs operating under load. This study suggests that DEAs cannot be operated reliably under load for long periods of time or low stretch rates due to pull-in failure limitations. To be reliable, DEAs must be used for short periods of time with high stretch rates.
Smart Structures and Materials 2006: Electroactive Polymer Actuators and Devices (EAPAD), 2006
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 threedimensionally 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.
Construction Techniques and Statistical Analysis of Dielectric Elastomer Actuators
2018
In this study, a series of experiments were conducted to investigate and improve upon existing construction methods of dielectric elastomer actuators (DEAs). First, a proof of concept was built, which utilized a DEA as an active diaphragm to reproduce sound. Next, two electrode sizes and construction methods were compared via statistical analysis of electrode strain. In an attempt to develop an easier and more efficacious electrode construction method, the substance used for electrodes was then dissolved in six solvents. A commercially available graphite spray was compared against the solutions and determined to be the most promising on the basis of measured surface conductivity and observed particle dispersion. Finally, an actuator was tested with graphite spray electrodes; it was discovered that the spray hardens when dried and was thus not able to produce in-plane deformation.
El-Cezeri Fen ve Mühendislik Dergisi, 2021
Dielectric Elastomer Actuator (DEA) consists of a thin dielectric elastomer membrane sandwiched between two electrode layers. When low current high voltage is applied to the two conductive layers, opposite loads occur on the surface which tends to pull one another. This voltage application causes thinning in width and expansion in surface area. DEAs are the favorite subject of research due to their low-cost advantages, fast response, high energy density, wide deformation, and softness. Due to the rigidity of the electric motors and the metal components of the robot, soft-acting robots using DEA are preferred to perform complex tasks instead of conventional robots. Robots with DEA have higher flexibility and better adaptability. Therefore, soft robots are popular topic in robotics research. DEAs are the best candidate materials for next-generation soft robot actuators and artificial muscles. In this study, simulation of the robotic systems has been realized by using DEAs calculation methods. Simulation results were compared with the data obtained from the application. This study will be the source of future studies on the subject. In the simulation, Matlab 2016 student and Labview Home and Students programs were used.
Modelling of High Output Force Dielectric Elastomer Actuator
International Journal of Mechanical Engineering and Robotics Research, 2017
Restoring the function of a lost limb for an amputee requires the generation of relatively large forces, which remains a challenge in current designs. Dielectric Elastomers (DE) have the desired properties of light weight, low cost, fast response, ease of control and low power consumption. Yet due to the elasticity of the material which requires mechanical support and low output force generation, DEs haven't been suggested for prosthetic devices that mainly require high output forces. This paper proposes a conceptual design for a prosthetic arm, where DE is used as a high output force actuator. A two-bar mechanism was assumed to represent the human arm, with one bar as the Humerus and another for the Radius and the Ulna bones. The flexion action of the mechanism was achieved by a slider-crank mechanism connecting the two bars. A Dielectric Elastomer (DE) was used to actuate the mechanism. In the proposed design, the DE membrane is configured as a planar linear actuator, with about 1000 parallel membranes to maintain the output force and reduce the tensile stress. An Analytic model for the specific configuration of DE materials was developed to analyze the output force of the designed mechanism for a range of input electric fields. The input electric field is below the dielectric strength of the material and induces 97 N of output force which is higher than reported actuator designs.
Modified Electromechanical Model for Dielectric Elastomer Cylindrical Actuators
Advances in Applied Mechanical Engineering, 2020
Dielectric elastomers (DEs)-based electromechanical cylindrical actuators are applicable in the field of biomimetic, robotics, microfluidic pumps and similar instrumental devices. However, to achieve efficient actuation performance, significant attention is requisite towards influences of pre-strain on electromechanical properties. This study shows the effect of pre-strain-induced variation in dielectric permittivity to improve the performance of the existing model for a cylindrical actuator. Modified electromechanical model is proposed for a thin-walled actuator configuration. The hypothesis of linear elasticity for small deformation is used to derive the novel model for voltage-induced axial strain. The analytical results shows improved axial actuation strain with relatively less errors and the values are found in good agreement with experimental results. This may encourage future researchers to identify crucial parameters on the way to design and optimization of soft actuators.
Sensors and Actuators A-physical, 2003
This work intends to extend the electromechanical characterisation of dielectric elastomer actuators. Planar actuators were realised with a 50 m-thick film of an acrylic elastomer coated with compliant electrodes. The isotonic transverse strain, the isometric transverse stress and the driving current, due to a 2 s high voltage impulse, were measured for four electrode materials (thickened electrolyte solution, graphite spray, carbon grease and graphite powder), four transverse prestress values (19.6, 29.4, 39.2 and 49.0 kPa) and different driving voltages (up to the dielectric breakdown voltage). Results showed that the electrode material and prestress strongly influence the electromechanical performances of the devices. Actuators with graphite spray electrodes and transverse prestress of 39.2 kPa exhibited an isotonic transverse strain of 6% at 49 V/m, with a driving current per unit electrode area of 3.5 A/cm 2 , and an isometric transverse stress of 49 kPa at 42 V/m. An electromechanical coupling efficiency of 10% at 21 V/m was calculated for actuators with thickened electrolyte solution electrodes and a transverse prestress of 29.4 kPa. The presented data permits to choose the best electrode material and the best prestress value (among those tested), to obtain the maximum isotonic transverse strain, the maximum isometric transverse stress or the maximum efficiency for different ranges of applied electric field.