Over the last decade, many bio-inspired crawling robots have been proposed by adopting the principle of two-anchor crawling or anisotropic friction-based vibrational crawling. However, these robots are complicated in structure and vulnerable to contamination, which seriously limits their practical application. Therefore, a novel vibro-impact crawling robot driven by a dielectric elastomer actuator (DEA) is proposed in this paper, which attempts to address the limitations of the existing crawling robots. The novelty of the proposed vibro-impact robot lies in the elimination of anchoring mechanisms or tilted bristles in conventional crawling robots, hence reducing the complexity of manufacturing and improving adaptability. A comprehensive experimental approach was adopted to characterize the performance of the robot. First, the dynamic response of the DEA-impact constraint system was characterized in experiments. Second, the performance of the robot was extensively studied and the fundamental mechanisms of the vibro-impact crawling locomotion were analyzed. In addition, effects of several key parameters on the robot's velocity were investigated. It is demonstrated that our robot can realize bidirectional motion (both forward and backward) by simple tuning of the key control parameters. The robot demonstrates a maximum forward velocity of 21.4 mm/s (equivalent to 0.71 body-length/s), a backward velocity of 16.9 mm/s, and a load carrying capacity of 9.5 g (equivalent to its own weight). The outcomes of this paper can offer guidelines for high-performance crawling robot designs, and have potential applications in industrial pipeline inspections, capsule endoscopes, and disaster rescues. 

https://www.mdpi.com/2072-666X/13/10/1660/pdf?version=1666594595

A Dielectric Elastomer Actuator-Driven Vibro-Impact Crawling Robot

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

Generally, a serious practical limitation of dielectric elastomer (DE)-based capacitors is the need for high voltage supply (in the order of 1 kV) to activate them. High voltages require a power level that is currently challenging due to the limit in the operating range of existing function generators. These high voltages are also dangerous for humans, thereby overshadowing many applications of dielectric elastomers. The purpose of this work is to develop a new simple actuation technique to introduce low-voltage driven DE-based capacitors, in which the electrical resonant frequency is syntonized to the mechanical natural frequency by tuning the circuit inductance. This results in extensive voltage amplification across the DE capacitor. In turn, this leads the DE membrane to oscillate with a remarkable large motion using a small voltage which is of one-tenth the magnitude of the input voltage required to drive such systems in the absence of electro-mechanical (EM) resonance syntonization. The efficiency of the proposed approach is demonstrated in the context of nonlinear vibration analysis. The results show that the voltage amplitude across the DE capacitor is amplified substantially while the electrical mode is syntonized with the mechanical one, and as a result, the DE motion’s amplitude is at least two hundred times greater than that of the unmatched system. Furthermore, for unbiased AC voltages with large amplitudes, the electro-mechanical modal interaction causes the system to exhibit the formation of frequency combs in the frequency spectrum of the system’s response. The implementation of this method using a simple electrical circuit just requires adequate matching between the electrical and the mechanical natural frequencies that depends on the inductance value. Our proposal effectively eliminates the need for a high source voltage generator which has been the main limitation in designing DE-based capacitors. 

Low-voltage dielectric elastomer actuators by electro-mechanical resonance syntonization

Soft robotics are attractive to researchers and developers due to their potential for biomimicry applications across a myriad of fields, including biomedicine (e.g., surgery), the film industry (e.g., animatronics), ecology (e.g., physical ‘animats’), human–robot interactions (e.g., social robots), and others. In contrast to their rigid counterparts, soft robotics offer obvious actuation benefits, including their many degrees of freedom in motion and their potential to mimic living organisms. Many material systems have been proposed and used for soft robotic applications, involving soft actuators, sensors, and generators. This review focuses on dielectric elastomer (DE)-based actuators, which are more general electro-active polymer (EAP) smart materials. EAP-based soft robots are very attractive for various reasons: (a) energy can be efficiently (and readily) stored in electrical form; (b) both power and information can be transferred rapidly via electrical phenomena; (c) computations using electronic means are readily available. Due to their potential and benefits, DE-based actuators are attractive to researchers and developers from multiple fields. This review aims to (1) provide non-experts with an “easy-to-follow” survey of the most important aspects and challenges to consider when implementing DE-based soft actuators, and (2) emphasize current solutions and challenges related to the materials, controls, and portability of DE-based soft-actuator systems. First, we start with some fundamental functions, applications, and configurations; then, we review the material models and their selection. After, we outline material limitations and challenges along with some thermo-mechano-chemical treatments to overcome some of those limitations. Finally, we outline some of the control schemes, including modern techniques, and suggest using rewritable hardware for faster and more adaptive controls.

Dielectric Elastomer-Based Actuators: A Modeling and Control Review for Non-Experts

The out-of-plane displacement (OPD) of a circular dielectric elastomer actuator (DEA) membrane has been explored in recent years for a variety of important applications. Circular DEAs consist of an elastomer membrane that is prestretched to a rigid frame and coated with compliant electrodes. Such a simple configuration has found many interesting applications such as in, pumps, pulse tracking, hopping search and rescue robots, dielectric elastomer (DE) generators for renewable energy harvesting, linear actuators, and many others. Here, we present an easy-to-follow implementation of the OPD equations for circular DEAs via a detailed numerical solution using the shooting method (SM) on a system of differential algebraic equations (DAE), based on previous theoretical work. The SM numerical solution to the system of DAEs is applied to a practical range of values based on the reported literature. Analysis of the results and comparison against other studies are provided. The current work provides a go-to framework for implementation in further research and development.

/pdf/a-detailed-solution-framework-for-the-out-of-plane-35h2w1oyao.pdf

A detailed solution framework for the out-of-plane displacement of circular dielectric elastomer actuators

\n 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).

Improved Model for Conical Dielectric Elastomer Actuators With Fewer Electrical Connections

Abstract Dielectric 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.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/90FED89B42656AF2C8E7875A446970AC/S0263574722001254a.pdf/div-class-title-effects-of-electrostriction-on-the-bifurcated-electro-mechanical-performance-of-conical-dielectric-elastomer-actuators-and-sensors-div.pdf

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

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