Cone Dielectric Elastomer Actuators Research Articles

A Soft Mimic Robotic Arm Powered by Dielectric Elastomer Actuator

AbstractGiven the great importance of human‐robot collaboration (HRC), the development of robotic arms tends to prioritize high flexibility, safety as well as low energy consumption. Dielectric elastomer actuators (DEAs), with their high energy density and lightweight characteristics, present a promising alternative for the design of soft robotic arms suitable for HRC setting. Hence, a soft mimic robotic arm powered by dual cone DEA (DCDEA) driver unit is developed that demonstrates high energy density and low energy consumption. The resultant elaborate DCDEA driver unit exhibits a significant bi‐direction actuation stroke with a high load‐to‐weight ratio up to 1,300, ensuring sufficient mechanical power output for powering the robotic arm. The well‐designed efficient transmission mechanism and control system together with DCDEA allow the robotic arm to conduct lifting and twisting action, mimicking the movements of a human arm. During the transportation of a 10 g weight, the robotic arm consumes only ≈35 mJ of energy, while achieving an energy density of 42.1 J kg−1. Encased in soft outer shells, the robotic arm displays full flexibility, high safety, and excellent impact resistance, underscoring its potential as a next‐generation soft robotic arm for HRC setting.

Soft Polymer-Actuated Compliant Microgripper with Adaptive Vibration-Controlled Grasp and Release.

Microgrippers that incorporate soft actuators are appropriate for micromanipulation or microsurgery owing to their ability to grasp objects without causing damage. However, developing a microgripper with a large gripping range that can produce a large force with high speed remains challenging in soft actuation mechanisms. Herein, we introduce a compliant microgripper driven by a soft dielectric elastomer actuator (DEA) called a spiral flexure cone DEA (SFCDEA). The submillimeter-scale SFCDEA exhibited a controllable linear displacement over a high bandwidth and the capability of lifting 100.9 g, which was 670 times higher than its mass. Subsequently, we developed a compliant microgripper based on the SFCDEA using smart composite microstructure technology to fabricate three-dimensional gripper linkages. We demonstrated that the microgripper was able to grasp various millimeter-scale objects with different shapes, sizes, and weights without a complex feedback control owing to its compliance. We proved the versatility of our gripper in robotic manipulation by demonstrating adaptive grasping and releasing of small objects using vibrations owing to its high bandwidth.

A dual cone actuator with high energy density and long fatigue life by developing a nano-silica reinforced dielectric elastomer composite

Dielectric elastomer actuator (DEA) is considered as one of the most promising soft actuators due to its light weight, good flexibility, high actuated strain and energy density. Herein, a novel DEA material is developed by introducing a kind of SiO2 nanoparticles with strong interfacial polarizability into polydimethyl(methylvinyl) siloxane (PMVS). The 7.5 SiO2/PMVS DEA exhibits a high actuated strain of 31.3 % and blocked stress of 68.4 kPa, 2.4 and 2.9 times of pure PMVS DEA. A dual cone DEA (DCDEA) device was self-designed by using 7.5 SiO2/PMVS films, which possesses a high actuated displacement of 1.3 mm, output force of 0.3 N and energy density of 4.7 J/kg. More importantly, because of the high elasticity and strong interfacial interaction, the 7.5 SiO2/PMVS DCDEA exhibits a long fatigue life of 500,000 times, resulting in a full-life energy density of 2.3 × 106 J/kg, 39 times higher than that of the VHB based DCDEA.

The effects of compliant support on the dynamics of a dielectric elastomer actuator: a parametric study

The resonant actuation of dielectric elastomer actuators (DEAs) can greatly amplify the power outputs and energy efficiencies and has facilitated numerous applications in soft robotics. In many circumstances, the DEAs are mounted on robotic bodies that are made of soft materials or compliant structures. Such compliant supports can demonstrate an equivalent stiffness and inertia comparable to the DEAs, thereby complicating the dynamics of the DEAs and threatening the performance and controllability of the soft robots by introducing additional degrees of freedom to the systems. Toward the goal of achieving reliable and controllable resonating actuation of the DEAs on soft robots, the effects of compliant supports on the dynamics of DEAs require dedicated investigations. By adopting a double cone DEA configuration, this work conducts a comprehensive study on the dynamics of a double cone DEA-compliant support system. A nonlinear dynamic model of the double cone DEA-compliant support system is developed. Together with experimental studies, the dynamics of the system in different support configurations are characterized and the influences of the key parameters in the system are clarified. The key findings of this work can potentially guide the designs of future high-performance DEA-driven soft robots.

A parametric study on the subharmonic isolas in a bistable dielectric elastomer actuator

Resonant actuation of dielectric elastomer actuators (DEAs) greatly improves their output power densities and energy efficiencies. However, their outstanding performance usually accompanies complex dynamics which hinder the robust applications of DEAs. Isolated frequency responses, or isolas, are branches of resonant curves that are isolated from the main frequency response curve, hence can be easily overlooked during the dynamic analyses of DEAs. Once triggered, however, isolas can lead to dramatic changes in frequency responses, which pose great threats to system stability. As a critical step towards controlling the isolas within DEAs, this work adopts a bistable cone DEA (BCDEA) configuration and conducts dedicated numerical and experimental parametric studies on its isolas to uncover the physical mechanisms that create them. The effects of potential barriers, equilibrium positions and excitation level on the evolutions of isolas are studied with the aim of finding the critical parameters that determine their evolutions. The outcomes of this paper help to gain more insights into the complex isola phenomena in BCDEAs, which may offer guidelines for eliminating undesired isolas within BCDEAs or for exploiting isolas for applications in, e.g. energy harvesting, soft robotic locomotion and vibro-tactile feedbacks.

Effects of electrostriction on the bifurcated electro-mechanical performance of conical dielectric elastomer actuators and sensors

AbstractDielectric elastomers (DEs) find applications in many areas, particularly in the field of soft robotics. When modeling and simulating DE-based actuators and sensors, a substantial portion of the literature assumes the selected DE material to behave in some perfectly hyperelastic manner, and the vast majority have assumed invariant permittivity. However, studies on simple planar DEs have revealed instabilities and hastened breakdowns when a variable permittivity is allowed. This is partly due to the intertwined electromechanical properties of DEs rooted on their labyrinthine polymeric microstructures. This work focuses on studying the effects of a varying (with stretch) permittivity on the out-of-plane deformation of a circular DE, using a model derived from principles of strain-induced polymer birefringence. In addition, we utilize the Edward–Vilgis model, which attempts to account for effects related to crosslinking, and length extension, slippage, and entanglement of polymer chains. Our approach reveals the presence of “stagnation” regions in the electromechanical behavior of the DE actuator material. These stagnation regions are characterized by both electrical and mechanical critical electrostrictive coefficient ratios. Mechanically, certain values of the electrostrictive coefficient ratio predict cases where deformation does not occur in response to a change in voltage. Electrically, certain cases are predicted where changes in capacitance cannot be measured in response to changes in deformation. Thus, some combined conditions of loading and material properties could limit the effectiveness of DE membranes in either actuation or sensing. Therefore, our results reveal mechanisms that could be useful to designers of actuators and sensors and unveil an opportunity for exploring new theoretical materials with potential novel applications. Furthermore, since there are known analogous formulations between electrical and optical properties, criticality principles studied in this article could be extended to optomechanical coupling.

Influence of loading voltage, domain ratio, and additional load on the actuation of dielectric elastomer

Abstract Dielectric elastomer (DE) is widely used in various fields because of its advantages of large deformation, lightweight, and good flexibility. In this article, based on our previous research work, the actuation performance of the cone dielectric elastomer actuator (DEA) is studied first, and the influence of loading voltage, domain ratio, and additional load on the displacement and output force of DEA is analyzed and discussed. Then, a three-dimensional model of displacement and force of DEA is established. At last, the relationship between the structure and the performance of DE is discussed from the microscopic point of view. The results show that the output displacement and force of the cone DEA increase with the increase of loading voltage and additional load. The three-dimensional model graph of cone DEA can reflect the performance change of DEA well. The design with different domain ratios is the key factor that influences the final DEA actuator, which has a great influence on the cross-link density and chain length in the DE structure. By making clear the regulating function of external environment factors, we can design DEA with different configurations, which lays a good foundation for the further development of DEA and enlarges the potential application scope of DEA.

On the Mechanical Power Output Comparisons of Cone Dielectric Elastomer Actuators

The emerging demand for bioinspired soft robotics requires novel soft actuators whose performance exceeds conventional rigid ones. Dielectric elastomer actuators (DEAs) are a promising soft actuation technology with large actuation strain and fast response. Cone DEAs are one of the most widely adopted DEA configurations for their compact structure and large force/stroke output with several configuration variations developed in recent years. By driving at a resonant frequency, the cone DEAs show a significant amplification in their power outputs, which demonstrates their suitability for highly dynamic robotic applications. However, it is still unclear how the payload conditions could affect the power outputs of cone DEAs and no work has compared the output performance of different variations of cone configurations. In this article, by considering conical configuration DEAs with generalized dissipative payloads, we conduct an extensive study on the effects of payload conditions on the power outputs of the cone DEA family. Additionally, we benchmark the performance of different cone DEA configurations and illustrate the fundamental principles behind these output patterns. The findings reported in this article establish guidelines for designing high-performance cone DEA actuators.

Antagonistic cone dielectric elastomer actuator: Analysis, experiment and application

As a typical electroactive polymer, dielectric elastomer can be used in the research of actuators, sensors, and soft robots. The cone actuator, as a representative dielectric elastomer actuator, suffers from the limitation of deformation range. In this work, an antagonistic cone dielectric elastomer actuator with large deformation range is exhibited. A theoretical model is derived to design geometric parameters and explain the deformation mechanism of the antagonistic cone dielectric elastomer actuator. Comparison between theoretical and experimental results shows that the theoretical model is suitable for the prediction of the performance of the actuator. Inspired by the human heart, the pump is developed by the actuator, and its performance is systematically investigated through experiments. It is hoped that this work can play a guiding role in the development and application of the antagonistic cone dielectric elastomer actuator.

Dimensionless parameter-based numerical model for double conical dielectric elastomer actuators

As the development of soft actuators progresses, new methods for more agile actuator control are required. While there are hardware technologies that can provide such agility (e.g. field-programmable-gate-array electronics), mathematical models tend to slow the controlling processes. For the case of double conical dielectric elastomer actuators (DCDEAs), complex material and physical models are often utilized; however, such models require extended computational time which limits real-time control and prediction, especially in small, portable applications. The foregoing problem is augmented, if agile applications require reprogramming on the fly. In this work, a parameter-based dimensionless model applicable to DCDEAs was developed. The proposed model: (a) relates a dimensionless displacement with a characteristic dimensionless voltage via a power-law equation; (b) is robust enough to accurately describe 5-Degree-of-Freedom motion; (c) is scalable (at least within the range of geometries and parameters used in this study); (d) due to its mathematical simplicity, it could be used for more agile controls. For the development of the model, multiple DCDEAs were manufactured by varying design parameters such as pre-stretch, thickness, dielectric constant, shear modulus, electrode area, and inner and outer radii. By applying the Levenberg-Marquardt best-fit algorithm to experimental data sets containing voltage and (translational and rotational) displacements, a general relationship was found between parameter-based dimensionless quantities and a general dimensionless displacement. The relationship was further simplified via a single dimensionless number related to the actuator design. The model was found to be accurately predictive for VHB4910 and VHB4905. The resulting model is simple and has potential to be used for a wide range of dielectric-elastomer materials.

Dynamic modeling of dielectric elastomer actuator with conical shape.

With desirable physical performances of impressive actuation strain, high energy density, high degree of electromechanical coupling and high mechanical compliance, dielectric elastomer actuators (DEAs) are widely employed to actuate the soft robots. However, there are many challenges to establish the dynamic models for DEAs, such as their inherent nonlinearity, complex electromechanical coupling, and time-dependent viscoelastic behavior. Moreover, most previous studies concentrated on the planar DEAs, but the studies on DEAs with some other functional shapes are insufficient. In this paper, by investigating a conical DEA with the material of polydimethylsiloxane and considering the influence of inertia, we propose a dynamic model based on the principles of nonequilibrium thermodynamics. This dynamic model can describe the complex motion characteristics of the conical DEA. Based on the experimental data, the differential evolution algorithm is employed to identify the undetermined parameters of the developed dynamic model. The result of the model validation demonstrates the effectiveness of the model.

Design and validation of a dielectric elastomer membrane actuator driven pneumatic pump

This paper presents a novel design method for high-frequency dielectric elastomer actuator (DEA) applications. A DEA consist of a mechanically pre-stretched elastomer film sandwiched between two compliant electrodes, which expands when subject to a high voltage. While the design of low-frequency DEA applications is generally well understood, up to now there is still a lack of systematic design rules for DEA systems operating in dynamic applications (e.g. pumps, compressors, and acoustics). The goal of this paper is the development of a novel graphical design approach which permits to systematically address the design of high-frequency DEA systems. A pneumatic diaphragm pump driven by a cone DEA is considered as a case study for validation of the new design technique. By means of the proposed method, the actuator performance can be quantitatively predicted at different actuation frequencies by accounting for both static and dynamic effects, as well as external loads, without relying on complex material models and extensive simulation studies. After discussing the design method, experimental validation is presented and performance are evaluated in terms of maximum pressure, maximum flow rate, and energy consumption.

Linear-Quadratic Regulator for Control of Multi-Wall Carbon Nanotube/Polydimethylsiloxane Based Conical Dielectric Elastomer Actuators

Conventional rigid actuators, such as DC servo motors, face challenges in utilizing them in artificial muscles and soft robotics. Dielectric elastomer actuators (DEAs) overcome all these limitations, as they exhibit complex and fast motions, quietness, lightness, and softness. Recently, there has been much focus on studies of the DEAs material’s non-linearity, the non-linear electromechanical coupling, and viscoelastic behavior of VHB and silicone-based conical DEAs having compliant electrodes that are based on graphite powder and carbon grease. However, the mitigation of overshoot that arises from fast response conical DEAs made with solid electrodes has not received much research focus. In this paper, we fabricated a conical configuration of multi-walled carbon nanotube/polydimethylsiloxane (MWCNT/PDMS) based DEAs with a rise time of 10 ms, and 50% peak overshoot. We developed a full feedback state-based linear-quadratic regulator (LQR) having Luenberger observer to mitigate the DEAs overshoot in both the voltage ON and OFF instances. The cone DEA’s model was identified and a stable and well-fitting transfer function with a fit of 94% was obtained. Optimal parameters Q = 70,000, R = 0.1, and Q = 7000, R = 0.01 resulted in the DEA response having a rise time value of 20 ms with zero overshoot, in both simulations and experiments. The LQR approach can be useful for the control of fast response DEAs and this would expand the potential use of the DEAs as artificial muscles in soft robotics.

Improved Model for Conical Dielectric Elastomer Actuators With Fewer Electrical Connections

Abstract Dielectric elastomers (DEs) exhibit remarkable properties that make them stand out among other electroactive polymers. Various types of actuators based on DEs have been used in applications that include artificial muscles, Braille displays, and robotic joints. In particular, conical dielectric elastomer actuators (CDEAs) are very attractive due to their multiple degrees of freedom (DOF) and easiness of construction. In this study, an energy method is used to derive an improved mathematical model for a double-cone dielectric elastomer actuator (DCDEA) capable of predicting horizontal and rotational displacements. To create the model, a new variable is introduced into the equations, the azimuth angle. In addition, a new pattern of electrodes is proposed as a method for achieving five DOF using only half of the electrode connections of traditional DCDEAs. Experimental tests are carried out and used to validate the proposed model. Results show very close agreement. A limiting aspect of the proposed model is that it relies on two experimental correction coefficients. Nonetheless, the model derived provides a means to more accurately implement automatic control to robotic systems that use DCDEAs (work in progress).

Physic-based and control-oriented modeling based robust control for soft dielectric elastomer actuator

Dielectric elastomer actuators (DEA) have attracted increasing attention in the field of soft robotics for use in generating soft and compliant motions. However, owing to their strong viscoelasticity, nonlinearity, and uncertainty, it is often difficult to gain high-precision tracking control. Here, a physic-based and control-oriented modeling based robust control is proposed to alleviate this difficulty in tracking. First, a conical DEA is designed, along with a physics-based and control-oriented model used to describe its dynamic behaviors. After this, a two-step identification method is proposed to obtain the model’s parameters. Using the model, a robust control approach is then developed to achieve satisfactory control performance—even when tracking multi-frequency and wide-range reference trajectory under uncertain conditions. Its stability is then analyzed and proofed. Finally, we conduct experiments to demonstrate and test the effectiveness of the actuator.

Modeling and Design Optimization of a Rotational Soft Robotic System Driven by Double Cone Dielectric Elastomer Actuators.

Dielectric elastomers (DEs) consist of highly compliant electrostatic transducers which can be operated as actuators, by converting an applied high voltage into motion, and as sensors, since capacitive changes can be related to displacement information. Due to large achievable deformation (on the order of 100%) and high flexibility, DEs appear as highly suitable for the design of soft robotic systems. An important requirement for robotic systems is the possibility of generating a multi degree-of-freedom (MDOF) actuation. By means of DE technology, a controllable motion along several directions can be made possible by combining different membrane actuators in protagonist-antagonist configurations, as well as by designing electrode patterns which allow independent activation of different sections of a single membrane. However, despite several concepts of DE soft robots have been presented in the recent literature, up to date there is still a lack of systematic studies targeted at optimizing the design of the system. To properly understand how different parameters influence the complex motion of DE soft robots, this paper presents an experimental study on how geometry scaling affects the performance of a specific MDOF actuator configuration. The system under investigation consists of two cone DE membranes rigidly connected along the outer diameter, and pre-compressed out-of-plane against each other via a rigid spacer. The electrodes of both membranes are partitioned in four sections that can be activated separately, thus allowing the desired MDOF actuation feature. Different prototypes are assembled and tested to study the influence of the inner radius as well as the length of the rigid spacer on the achievable motion range. For the first experimental study presented here, we focus our analysis on a single actuation variable, i.e., the rotation of the rigid spacer about a fixed axis. A physics-based model is then developed and validated based on the collected experimental measurements. A model-based investigation is subsequently performed, with the aim of studying the influence of the regarded parameters on the rotation angle. Finally, based on the results of the performed study, a model-based optimization of the prototype geometry is performed.

Power optimization of a conical dielectric elastomer actuator for resonant robotic systems

Insects utilize resonant actuation to amplify the flapping stroke and improve the energy efficiency. The inherent elasticity in dielectric elastomer actuators (DEAs) offers the advantage over conventional actuators of achieving resonant actuations with no additional elastic elements required. Despite that the resonant actuation of the DEAs have attracted great research interests, no optimization has been done on the output performance of resonating DEAs. In this work, a double cone DEA (DCDEA) configuration is adopted and a numerical model is developed to characterize its dynamic response. An effective power study framework is developed and the power output of the DCDEA is optimized against its pre-stretch ratios and spacer length. To demonstrate the potential exploitation of resonant DEA performance, a bioinspired flapping wing mechanism driven by the optimized DCDEA design is developed with a peak flapping stroke of 31°at its resonance of 30 Hz.

Towards efficient elastic actuation in bio-inspired robotics using dielectric elastomer artificial muscles

In nature, animals reduce their cost of transport by utilising elastic energy recovery. Emerging soft robotic technologies such as dielectric elastomer actuators (DEAs) offer an advantage in achieving biomimetic energy efficient locomotion thanks to their high actuation strain and inherent elasticity. In this work, we conduct a comprehensive study on the feasibility of using antagonistic DEA artificial muscles for bio-inspired robotics. We adopt a double cone DEA configuration and develop a mathematical model to characterise its dynamic electromechanical response. It is demonstrated that this DEA design can be optimised in terms of the maximum work output by adjusting the strut height design parameter. Using this optimised design, we analyse the power/stroke output and the electromechanical efficiency of the DEA and show how these actuation characteristics can be maximised for different payload conditions, excitation frequencies and actuation waveforms. The elastic energy recovery from the DEA is then demonstrated by reducing the duty ratio of the actuation signal and thus allowing the stored elastic energy in the DEA membranes to contribute to the work output. A bio-inspired three-segment leg prototype driven by the same actuator is presented to demonstrate that the same energy recovery principle is feasible for bio-inspired robotics.

Design of Translational and Rotational Bistable Actuators Based on Dielectric Elastomer

Dielectric elastomer (DE), as a group of electro-active polymers, has been widely used in soft robotics due to its inherent flexibility and large induced deformation. As sustained high voltage is needed to maintain the deformation of DE, it may result in electric breakdown for a long-period actuation. Inspired by the bistable mechanism which has two stable equilibrium positions and can stay at one of them without energy consumption, two bistable dielectric elastomer actuators (DEAs) including a translational actuator and a rotational actuator are proposed. Both the bistable actuators consist of a double conical DEA and a buckling beam and can switch between two stable positions with voltage. In this paper, the analytical models of the bulking beam and the conical DEA are presented first, and then the design method is demonstrated in terms of force equilibrium and moment equilibrium principle. The experiments of the translational bistable DEA and the rotational bistable DEA are conducted, which show that the design method of the bistable DEA is effective.

Toward a Dielectric Elastomer Resonator Driven Flapping Wing Micro Air Vehicle.

In the last two decades, insect-inspired flapping wing micro air vehicles (MAVs) have attracted great attention for their potential for highly agile flight. Insects flap their wings at the resonant frequencies of their flapping mechanisms. Resonant actuation is highly advantageous as it amplifies the flapping amplitude and reduces the inertial power demand. Emerging soft actuators, such as dielectric elastomer actuators (DEAs) have large actuation strains and thanks to their inherent elasticity, DEAs have been shown a promising candidate for resonant actuation. In this work a double cone DEA configuration is presented, a mathematic model is developed to characterize its quasi-static and dynamic performance. We compare the high frequency performance of two most common dielectric elastomers: silicone elastomer and polyacrylate tape VHB. The mechanical power output of the DEA is experimentally analyzed as a DEA-mass oscillator. Then a flapping wing mechanism actuated by this elastic actuator is demonstrated, this design is able to provide a peak flapping amplitude of 63° at the frequency of 18 Hz.