Helical Dielectric Elastomer Actuator

A helical dielectric elastomer actuator (HDEA) can include a first dielectric region comprising an elastomer defining a helix. In an example, a dielectric material can be deposited, and a compliant conductive material can be deposited, such as using an additive manufacturing approach, to provide an HDEA. In an example where the HDEA has multiple mechanical degrees of freedom, at least two compliant conductive regions can be located on a first surface of the first dielectric region and at least one compliant conductive region can be located on an opposite second surface of the first dielectric region. For such an example, the at least two compliant conductive regions can be arranged to be ener­gized with respect to the at least one compliant conductive region in a manner providing at least two mechanical degrees of freedom for operation of the HDEA

Elastomeric actuator devices for magnetic resonance imaging

The present invention is directed to devices and systems used in magnetic imaging environments that include an actuator device having an elastomeric dielectric film with at least two electrodes, and a frame attached to the actuator device. The frame can have a plurality of configurations including, such as, for example, at least two members that can be, but not limited to, curved beams, rods, plates, or parallel beams. These rigid members can be coupled to flexible members such as, for example, links wherein the frame provides an elastic restoring force. The frame preferably provides a linear actuation force characteristic over a displacement range. The linear actuation force characteristic is defined as .+-.20% and preferably 10% over a displacement range. The actuator further includes a passive element disposed between the flexible members to tune a stiffness characteristic of the actuator. The passive element can be a bi-stable element. The preferred embodiment actuator includes one or more layers of the elastomeric film integrated into the frame. The elastomeric film can be made of many elastomeric materials such as, for example, but not limited to, acrylic, silicone and latex

Large Deformable Soft Actuators Using Dielectric Elastomer and Origami Inspired Structures

There have been significant developments in the field of robotics. Significant development consists of new configurations, control mechanisms, and actuators based upon its applications. Despite significant improvements in modern robotics, the biologically inspired robots has taken the center stage. Inspired by nature, biologically inspired robots are called ‘soft robots’. Within these robots lies a secret ingredient: the actuator. Soft robotic development has been driven by the idea of developing actuators that are like human muscle and are known as ‘artificial muscle’. Among different materials suitable for the development of artificial muscle, the dielectric elastomer actuator (DEA) is capable of large deformation by applying an electric field. Theoretical formulation for DEA was performed based upon the constitutive hyperelastic models and was validated by using finite element method (FEM) using ABAQUS. For FEM, multistep analysis was performed to apply pre-stretch to the membrane before applying actuation voltage. Based on the validation of DEA, different configurations of DEA were investigated. Helical dielectric elastomer actuator and origami dielectric elastomer actuator were investigated using theoretical modeling. Comparisons were made with FEM to validate the model. This study focus on the theoretical and FEM analysis of strain within the different configuration of DEA and how the actuation strain of the dielectric elastomer can be translated into contraction and/or bending of the actuator

4D Printing Dielectric Elastomer Actuator Based Soft Robots

4D printing is an emerging technology that prints 3D structural smart materials that can respond to external stimuli and change shape over time. 4D printing represents a major manufacturing paradigm shift from single-function static structures to dynamic structures with highly integrated functionalities. Direct printing of dynamic structures can provide great benefits (e.g., design freedom, low material cost) to a wide variety of applications, such as sensors and actuators, and robotics. Soft robotics is a new direction of robotics in which hard and rigid components are replaced by soft and flexible materials to mimic mechanisms that works in living creatures, which are crucial for dealing with uncertain and dynamic tasks. However, little research on direct printing of soft robotics has been reported. Due to the short history of 4D printing, only a few smart materials have been successfully 4D printed, such as shape memory and thermo-responsive polymers, which have relatively small actuation strains (up to ~8%). In order to produce the large motion, dielectric elastomer actuator (DEA), a sheet of elastomer sandwiched between two compliant electrodes and known as artificial muscle for its high elastic energy density and capability of producing large strains (~200%), is chosen as the actuator for soft robotics. Little research on 3D printing silicone DEA soft robotics has been done in the literature. Thus, this thesis is motivated by applying the advantages in 3D printing fabrication methods to develop DEA soft robotics. The ultimate research goal is to demonstrate fully printed DEA soft robots with large actuation. In Chapter 1, the research background of soft robotics and DEAs are introduced, as well as 3D printing technologies. Chapter 2 reports the rules of selecting potentially good silicone candidates and the printing process with printed material characterizations. Chapter 3 studies the effects of pre-strain condition on silicone material properties and the performance of DEA configurations, in order to obtain large actuation strain. In Chapter 4, two facial soft robots are designed to achieve facial expressions as judged by a smiling lip and expanding pupils based on DEA actuation. Conclusions and future developments are given in chapter 5 and 6, respectively

Characterization, fabrication, and analysis of soft dielectric elastomer actuators capable of complex 3D deformation

Inspired by nature, the development of soft actuators has drawn large attention to provide higher flexibility and allow adaptation to more complex environment. This thesis is focused on utilizing electroactive polymers as active materials to develop soft planar dielectric elastomer actuators capable of complex 3D deformation. The potential applications of such soft actuators are in flexible robotic arms and grippers, morphing structures and flapping wings for micro aerial vehicles. The embraces design for a freestanding actuator utilizes the constrained deformation imposed by surface stiffeners on an electroactive membrane to avert the requirement of membrane pre-stretch and the supporting frames. The proposed design increases the overall actuator flexibility and degrees-of-freedom. Actuator design, fabrication, and performance are presented for different arrangement of stiffeners. Digital images correlation technique were utilized to evaluate the in-plane finite strain components, in order to elucidate the role of the stiffeners in controlling the three dimensional deformation. It was found that a key controlling factor was the localized deformation near the stiffeners, while the rest of the membrane would follow through. A detailed finite element modeling framework was developed with a user-material subroutine, built into the ABAQUS commercial finite element package. An experimentally calibrated Neo-Hookean based material model that coupled the applied electrical field to the actuator mechanical deformation was employed. The numerical model was used to optimize different geometrical features, electrode layup and stacking sequence of actuators. It was found that by splitting the stiffeners into finer segments, the force-stroke characteristics of actuator were able to be adjusted with stiffener configuration, while keeping the overall bending stiffness. The efficacy of actuators could also be greatly improved by increasing the stiffener periodicity. The developed framework would aid in designing and optimizing the dielectric elastomer actuator configurations for 3D prescribed deformation configuration. Finally, inspired by the membrane textures of bat wings, a study of utilizing fiber reinforcement on dielectric elastomer actuators were conducted for the mechanical and the coupled electromechanical characteristics. Woven fibers were employed on the surface of actuator membrane with different pre-deformed configurations. Experimentally, actuator stiffness changes were measured for up to four orders of magnitude. The orientation of embedded fibers controlled the level and the triggered phase of stiffness changes. A trade-off between the actuator stiffness and stroke could be controlled during the fabrication stage by the fiber orientation and the prestretch level of the base elastomer membrane. A simplified model using small-strain composite laminate theory was developed and accurately predicted the composite actuator stiffness. Additionally, compliant edge stiffeners were found had to present a marked overall effect on actuator electromechanical response. The developed simplified analytical solutions using Timoshenko-bimaterial laminate solution and composite laminate theory, as well as the developed finite element framework can be utilized in addressing more complex 3D deformation patterns and their electromechanical response

Dynamic Modeling of Soft Robotic Dielectric Elastomer Actuator

Dielectric elastomers actuators (DEAs) are among the preferred materials for developing lightweight, high compliance and energy efficient driven mechanisms for soft robots. Simple DEAs consist mostly of a homogeneous elastomeric materials that transduce electrical energy into mechanical deformation by means of electrostatic attraction forces from coated electrodes. Furthermore, stacking multiple single DEAs can escalate the total mechanical displacement performed by the actuator, such is the case of multilayer DEAs. The presented research proposes a model for the dynamical characterization of multilayer DEAs in the mechanical and electrical domain. The analytical model is derived by using free body diagrams and lumped parameters that recreate an analogous system representing the multiphysics dynamics within the DEA. Hyperelasticity in most elastomeric materials is characterized by a nonlinear spring capable of undergoing large deformation; thus, defining the isostatic nonlinear relationship between stress and stretch. The transient response is added by employing the generalize Kelvin-Maxwell elements model of viscoelasticity in parallel with the hyperplastic spring. The electrostatic pressure applied by the electrodes appears as an external mechanical pressure that compress the material; thus, representing the bridge between the electrical and mechanical domain. Moreover, DEAs can be represented as compliant capacitors that change their capacitance as it keeps deforming; consequently, this feature can be used for purposes of self-sensing since there is always a capacitance value that can be mapped into the actual displacement. Therefore, an analytical model of an equivalent circuit of the actuator is also derived to analyze the changes in the capacitance while the actuator is under duty. The models presented analytically are then cross-validated by finite element methods using COMSOL Multiphysics® as the software tool. The results from both models, the analytical and FEM model, were compared by virtually recreating the dynamics of a multilayer DEA with general circular cross section and material parameters from VHB4905 3M commercially available tape. Furthermore, this research takes the general dynamical framework built for DEAs and expand it to model the dynamical system for helical dielectric elastomer actuators (HDEAs) which is a novel configuration of the classical stack that increases the nonlinearity of the system. Finally, this research present a complementary study on enhancing the dielectric permittivity for DEAs, which is an electrical material property that can be optimized to improve the relationship between voltage applied and deformation of the actuator

Dielectric Elastomer Actuator biased by Magnetorheological Elastomer with Permanent Magnet

Dielectric elastomer actuators have become one of the most important smart material transducers in recent times. One of the crucial aspects in this field is the application of bias to find the best operating conditions. The basic task is to find the proper bias configuration to obtain a wide range of displacements in the actuator. In the literature, various biases, such as mechanical springs, permanent magnets, or pneumatic springs, are studied. In our work, the magnetorheological elastomer is applied to build a novel bias that ensures a wide range of displacement. Because of the softness and the compliant chemical structure, the magnetorheological elastomer can be easily integrated with the dielectric elastomer actuator. The magnetorheological elastomer as a bias for a dielectric elastomer actuator is verified in the series of experiments. Finally, the discussion on the advantages and disadvantages of the new bias type is performed

Transparent dielectric elastomer actuator used as tunable optical grating

In this work, a transparent dielectric elastomer actuator is integrated into a tunable transmission grating. A 13 micron-thick silicone membrane has been sandwiched between two 750 nanometer-thick transparent ionogel electrodes to fabricate a transparent dielectric elastomer actuator. By structuring the top transparent ionogel electrode into a sinusoid grating profile, with 2 µm period, the transparent dielectric elastomer actuator is transformed into a tunable transmission grating. The structured stretchable electrode plays both the role of electrical conductor and optical grating. When 1300V is applied between the two stretchable ionogel electrodes, the actuator presents a linear strain of 12.8 percent, which correspond to a 1.4 degree change in the first diffraction angle for green light. The transparent ionogel electrode also present the self-clearing property, thus further extending the lifetime of the actuator at high drive voltages. The ionogel electrodes maintain the accurate grating shape for several weeks, and could be patterned into the shape of any diffractive element