Nowadays, several industrial manufacturing processes imply direct cooperation between human operators and robots. This increases production and quality while improving the working conditions. However, the possible presence of physical contact between humans and robots asks for the study and introduction of new technical solutions that aim at guaranteeing a safe Human-Robot Interaction (HRI). Specifically, in recent years, different sensing devices have been developed for collision avoidance monitoring in HRI applications. Generally, common solutions consist of distributed resistive or capacitive sensors networks connected to a central electronic reading board, resulting in a cumbersome layout covering the whole parts of the collaborative robots. In this context, this paper presents an innovative tactile and proximity sensing strategy based on a soft-sensor module that can be installed on the collaborative robot parts or surrounding workspace. The developed module consists of a capacitive sensor based on a silicone elastomer membrane with compliant electrodes attached to the surface, disposed homogeneously on a deformable hemisphere-shape made of silicone. Thanks to the geometrical layout, such a sensor allows multidirectional objects detection resulting in a promising non-invasive solution for collisions avoidance in HRI applications. This work reports the design, manufacturing, and preliminary experimental investigation of such a sensor module, evaluating the electrodes geometry and the most relevant features that optimize objects detection distance and directivity sensing performance.

Human brain cells are being traumatized using a dielectric elastomer actuator (DEA) cell injury device (CID). The DEAs on the CID share the same membrane as plated human pericytes, delivering an abrupt 20% strain to the cell culture thus producing an insult similar to traumatic brain injury (TBI). In this first phase of the study, we have subjected the pericytes to 50 stretching cycles at 1 Hz. 24 hours after injury, a quantitative real-time polymerase chain reaction has shown a twofold gene change for c-jun, a known inflammation marker. The CID provides a platform for the advancement of TBI pharmacology.

In this study, we investigate the effect of enhancing electrical and ionic conductivity of PEDOT:PSS/PVDF/PEDOT:PSS tri-layer actuators on the speed of charging and of mechanical actuation. We treated the conducting polymer films with methanol, then doped the device with ionic liquid electrolyte. For both treated and untreated tri-layer samples, we measured electrical resistance along the length of the film, ionic resistance through the thickness of the structure, and performed cyclic voltammetry to determine volumetric capacitance and the characteristic time constants. We also measured the mechanical displacement-frequency response of the conducting polymer cantilever beams. Our results showed that methanol treatment increased electrical conductivity by 20x and ionic conductivity by 1.7x. This enhancement did not significantly change the cut-off frequencies of the device. However, at frequencies < 1 Hz, we observed less drop-off in displacement amplitude in the treated samples. For the geometries and conductivities used in this study, improving conductivity of PEDOT:PSS contributed to actuation at frequencies above the cut-off frequency. This may have applications for devices that need to actuate at high frequencies, but not necessarily at maximum strain, such as vibrotactile haptic displays.

Wearable dielectric elastomer actuators (DEAs) have been greatly considered for development of biomedical devices. In particular, a DEA cuff device has the capability of minimizing venous system disorders that occur in the lower limbs such as orthostatic intolerance (OI) and deep-vein thrombosis which are a result of substantial blood pooling. Recent works have shown that DEAs could regulate and even enhance venous blood flow return. This wearable technology orders a new light, low-cost, compliant, and simple countermeasure which could be safely and comfortably worn that includes mobility. In addition, it may supplement or even provide an alternative solution to exercise and medication. This work presents the design, model, and characterization of the DEA cuff device design that is capable of generating significant pressure change. A rolled DEA strip was actuated over a simulated muscle-artery apparatus using a periodic voltage input, and fluid pressure change was directly observed. A force sensitive resistor sensor was used to achieve a more precise pressure measurement. Performance analysis was conducted through frequency response analysis. The results provide a framework for implementing dynamic modelling and control to allow various forms of actuation input.

We report the effect of electric field and of thin encapsulation layers on the lifetime of silicone-based dielectric elastomer actuators (DEAs), for different environmental conditions under DC actuation. The dielectric is Elastosil 2030/20, and the encapsulation layer is a soft silicone elastomer. We conduct our tests from 20°C to 85°C, and from 20% RH to 90% RH. increasing the electric field from 90 V/μm (3.5% actuation strain) to 110 V/μm (7% actuation strain) yields 140x lower lifetimes at 85°C – 85% RH. Encapsulating the DEAs increases DC lifetime of factors up to 30x, with negligible reduction in actuation strain.

Due to their suitability for human-robot interactions the importance of soft robots is increasing in the last years. In this paper, a Soft Robotic tentacle arm element actuated by rolled dielectric elastomer actuators (RDEAs) is presented. A 2D-bending-element has been developed which consists of a central vertical flexible beam and two rigid horizontal platforms onto which two antagonistic RDEA are connected. By exploiting the buckling instability of the beam, high angular deflections can be achieved. We consider this combination of a buckling beam and antagonistic RDEAs an important step towards realizing the full potential of DEAs as artificial muscles.

Dielectric elastomer transducers (DET) are demonstrating exciting potential in many fields, including healthcare, wearable technology, and soft robotics. The electrode layers within these are paramount to their effectiveness, with the demands on these elements likely to increase further as we strive for stretchable electrodes with even greater performance, higher geometric complexity, and greater degrees of actuation or sensing. However, there is a disparity between the demands and ambitions of new DET devices and the capabilities of the current fabrication techniques. Common manufacturing approaches fall into two categories, template-based (e.g screen printing and lithography) and additive methods (e.g. 3D printing). The former limits the design complexity and is poorly suited to low production volumes, prototyping, and device personalization. While the latter overcomes these issues, it is characterized by constraints on printable materials, low material throughput, and limited resolution. We present a novel fabrication approach for DET electrodes, using a micro atmospheric pressure plasma jet to selectively induce hydrophilicity on a silicone elastomer layer. Polar fluids containing dispersed conductive particles self-align with the hydrophilic pattern, removing the need for precise spatially controlled deposition. Furthermore, we demonstrate a dynamically tunable resolution from 45μm to 1200μm through variation driving voltage and frequency. Using a bespoke computer-controlled apparatus we present the opportunity for the rapid and flexible fabrication of the next generation of DETs capable of utilizing a wider range of materials and achieving greater feature resolution, conducted by an automated and scalable process. We showcase the approach by fabricating a functional dielectric elastomer actuator.

We successfully integrated dielectric elastomer switches (DESs) with dielectric elastomer actuators (DEAs) on one flexible dielectric elastomer (DE) membrane via spray painting. The actuator can generate an in-plane compression in the direction of DES, leading to a dramatic reduction in the electric resistance of the switch; while the electric resistance changes back to its initial value when the actuator is off. Therefore, the resultant component exhibits piezoresistive properties and can be further used as DE inverters. This entirely soft inverter can be potentially applied to develop biomimetic robotics in terms of driving, controlling, monitoring, sensing, and self-regulation.

We present a 4-channel multiplexer made with dielectric elastomers (DEs). Multiplexers are fundamental blocks in electronics that allow multichannel communications. Many users/channels can, one at a time, communicate with a shared resource, without the need for building multiple copies of it. After introducing the basic elements of DE-electronics, a DEA-driver, composed of a MUX and a strain sensor, is realized. The experiment shows that a MUX can be used to control the actuation of a DEA in response to an external stimulus.

In this paper, we report a modeling and simulation study based on a 1-by-3 soft array of independently controllable dielectric elastomer actuators (DEAs). Based on collected experimental results, a physics-based model is initially developed, calibrated, and validated. Then, the effects of the system parameters (geometry, DEA spatial distribution, pre-loading of non-actuated elements) on the resulting array stroke, as well as on the coupling among neighbor elements, will be investigated via extensive simulations. The obtained results will serve as guidelines for the optimal design of cooperative DEA microarray systems.

This paper focuses on the characterisation of the vibroacoustic response of dielectric elastomer (DE) membranes. We set our attention on a circular DE membrane, deformed three-dimensionally and mounted in between fixed frames, which is able to generate sound with no need for any elastic or pneumatic biasing element. We present a finite element model of the system entirely based on commercial software Comsol Multiphysics. The model combines: 1) a mechanical model of the DE membrane, which makes use of suitably defined energy functions that account for electro-elastic coupling; and 2) an acoustic model of the domain surrounding the DE. The model implements a bi-directional coupling between the DE and the acoustic domain. In particular, it accounts for the effect of the acoustic pressure loads applied on the DE membrane, which, given the small thickness and low density of the membrane, play a significant role in the system dynamics. We validate the model against experimental measurements of the DE surface velocity and the sound pressure level (SPL) in the surroundings of the membrane. Despite relying on strong simplifications in the geometry of the system and the viscous response of the material, the model is able to describe the main trends in the device frequency response, and how the SPL varies as a function of the mechanical pre-load and the voltage applied on the membrane.

Dielectric elastomer actuators (DEA) exhibit homogeneous driving behavior due to the incompressible material properties of the homogeneous dielectric. This causes the system to expand uniformly in-plane while decreasing its height. In many applications, however, linear actuation is required and the system must be adjusted to operate unidirectionally. For this purpose, different approaches, such as rolling or mechanical stiffening of the actuator, are presented in literature, which aim at adjusting the DEA to work in one direction. In addition, pre-stretching the elastomer film in the required direction can cause the uniaxial motion. Furthermore, there are reports of interpenetrating networks (IPN) forming an anisotropic network that behaves differently depending on the direction. However, these modifications require either external, usually rigid hardware, or additional manufacturing steps that increase the complexity of the process. In the present work, an anisotropic expansion is introduced by our additive manufacturing technique based on aerosol jet printing. By varying the material distribution and the printing of different patterns, the mechanical and electrical properties are changed, resulting in anisotropic driving behavior. In-plane motion is observed with a camera, and the relationship between longitudinal and transverse strain is evaluated using image processing. Systematic design of experiments (DoE) is used to analyze the influencing factors and determine the most promising system design and achievable aspect ratio.

In this contribution, a novel mechanical interface design for multilayer DE stack transducers is presented and compared with alternative connecting approaches. As mechanical interfaces have an impact on the effective actuator performance, an optimized design approach, using a combination of sliding surfaces and hydrostatic power transmission, is proposed. Based on this, an optimized interface design for stack-transducers is carried out and conducting simulations and experiments are performed to investigate the improvement of the static actuation performance.

Dielectric elastomers (DE) are capable of high deformations at fast rates and thus, have inspired many loudspeaker designs. In particular, the previously introduced buckling DE-transducers (BDET) seems promising due to its low structural complexity. Due to electromechanical and geometrical nonlinearities, high total harmonic distortion (THD) in the lower end of the spectrum compromises its capability. Here, a method is developed to be run on an audio DSP to reduce the THD of the BDET by preconditioning the signal. Acoustic measurements are conducted and critically discussed. The study brings down one drawback of the BDET and thus increases its competitiveness.

To advance the field of soft robotics, novel linear actuators that provide high strain, high strain rate, and high specific power are needed. This work deals with a novel, helically self-coiled dielectric elastomer actuator that exhibits such properties. We present the corresponding manufacturing process, the resulting prototypes, and an analytical modeling approach.

The actuator was manufactured by bonding a strip of unidirectional non-crimp carbon fiber fabric to a pre-stretched silicone film. Due to the tension in the silicone, the strip rolls up and forms a helix when released. The unidirectional fabric was used as an electrode with the fibers running perpendicular to the strip. Therefore, the electrode is highly ductile lengthwise, but the cross-section of the strip remains undeformed despite inherent stress due to the pre-strain. A second electrode placed on the outside of the helix results in a contracting actuator when activated. Prototypes showed strains of up to 5.6 % at actuation frequencies of 2 Hz. To aid the design of the prototypes an analytical modeling approach was developed. Theoretical considerations showed that applying a second electrode on the inside of the helix instead of the outside leads to an expanding actuator. Combining these two approaches will further increase the deformation potential.

In this work, we present on the characterization of the mechanical coupling in an array system of independent dielectric elastomer (DE) elements. The target device consists of a 1-by-3 array of silicone-based DE elements on a single silicone membrane. This DE-array is the basis for the development of a future DE-actuator array. To achieve large strokes in this DEA-array, the goal is to bias every DE element with a suitable nonlinear biasing element. A correct design of all biasing elements requires the knowledge of how the biasing of one DE-element influences the others and vice versa. After describing the potential influences of the coupling on the correct actuator design, a possible characterization method for the investigation of the coupling is presented. Furthermore, first results are shown and discussed briefly.

Current robotic sensing is mainly visual, which is useful up until the point of contact. To understand how an object is being gripped, tactile feedback is needed. Human grasp is gentle yet firm, with integrated tactile touch feedback. Ras Labs makes Synthetic Muscle™, which is a class of electroactive polymer (EAP) based materials and actuators that sense pressure from gentle touch to high impact, controllably contract and expand at low voltage (battery levels), and attenuate force. The development of this technology towards sensing has provided for fingertip-like sensors that were able to detect very light pressures down to 0.01 N and even 0.005 N, with a wide pressure range to 25 N and more and with high linearity. By using these soft yet robust Tactile Fingertip™ sensors, immediate feedback was generated at the first point of contact. Because these elastomeric pads provided a soft compliant interface, the first point of contact did not apply excessive force, allowing for gentle object handling and control of the force applied to the object. The Tactile Fingertip could also detect a change in pressure location on its surface, i.e., directional glide provided real time feedback, making it possible to detect and prevent slippage by then adjusting the grip strength. Machine learning (ML) and artificial intelligence (AI) were integrated into these sensors for object identification along with the determination of good grip (position, grip force, no slip, no wobble) for pick-and-place and other applications. Synthetic Muscle™ is also being retrofitted as actuators into a human hand-like biomimetic gripper. The combination of EAP shape-morphing and sensing promises the potential for robotic grippers with human hand-like control and tactile sensing. This is expected to advance robotics, whether it is for agriculture, medical surgery, therapeutic or personal care, or in extreme environments where humans cannot enter, including with contagions that have no cure, as well as for collaborative robotics to allow humans and robots to intuitively work safely and effectively together.

A modified dielectric elastomer strain sensor was developed, in order to enhance the accuracy of the measurement of extremely small strains below 1 %. The new sensor consists of two components, which are connected in series along the sensor length. The shorter component is a stretchable dielectric elastomer strain sensor strip, whereas the longer component exhibits a non-stretchable polymer film. When the whole sensor is stretched, the strain occurs only in the stretchable shorter component. Such sensors with enhanced sensitivity were manufactured and investigated with a self-constructed electro-mechanical testing machine. The results of the measurements of capacitance, electrode resistance and stretch force vs. strain were compared with those of corresponding conventional dielectric elastomer strain sensors. Furthermore, the dependence of the capacitance on the strain was calculated with finite element method (FEM) simulations for both sensor types. The sensor design, the results of the experimental characterization and the comparison with the simulation are described in the paper.

The buddy system, where a pair of divers look out for one another, is used by the diving community to mitigate danger. They inspect each other’s breathing apparatus, monitor remaining air supplies, health status, and can provide emergency support during a dive. Due to buddy unavailability however, some divers dive solo, forgoing the safety aspects of the buddy system. We propose a dedicated dive-buddy robot as a solution to this problem. The robot, an autonomous underwater vehicle, could operate as an assistant, controlled by the diver using hand gesture-based communication; a communication method commonly used amongst divers. To capture the gestures, we have developed a smart dive glove integrated with 5 dielectric elastomer strain sensors. The capacitance of each sensor was measured with on-board electronics, translated into a command using machine learning and transmitted underwater using acoustics. Due to travel restrictions relating to the Covid-19 pandemic, a demonstration with the diver and vehicle in the same pool was not possible. Therefore, here we present a demonstration with the diver performing gestures in a pool in Auckland, New Zealand, sending commands to the robot in a pool in Zagreb, Croatia. The commands were sent through acoustics to a computer in Auckland, over cellular internet to a computer in Zagreb, which then relayed instructions to the robot using acoustics. The robot was sent four commands and successfully completed all manoeuvres. The performance of the communication with regards to time delays is assessed and future improvements are discussed.

Carbon black/silicone rubber composite is a desirable material for highly flexible strain sensors due to its repeatable piezoresistive characteristics, low cost, and simple fabrication process. By customising the conductivity and elastic modulus of the composite, the material can easily be adapted for many human physiological sensing applications. For applications such weight distribution sensors for wheelchair users, it is desirable to have not just a single sensor reading but instead a 2D map of pressure or strain. In this work, after demonstrating that the material can be modelled to give estimated strain value, we have developed a system to give a 2D map of pressure applied to the sensor using Electrical Impedance Tomography (EIT). This method has the advantage that a 2D pressure map can be obtained from a sensor using a homogeneous cast sheet of composite with electrodes around the perimeter only, without requiring complex patterning or a sensor array. Although the design is scalable, our demonstration system was fabricated using a 100 mm diameter pressure pad of carbon black (CB) silicone composite with electrodes evenly spaced around its perimeter. A low-cost circuit was developed to apply current to the material and measure the voltage between electrodes. The voltage measurements were then reconstructed into maps of resistivity and indications of compressive stress. Testing demonstrates that the fabricated pressure sensor can sense localised pressure within the pressure pad. The positional accuracy of the sensor was found to be on average 3.6 mm for the 100 mm diameter circular domain under test.

The Electro-pneumatic Pump (EPP) is a lightweight, flexible electrostatic pump that uses a dielectric-liquidamplified zipping mechanism to control air volume and pressure and generate high air flow rate. In previous studies, the EPP, made of rectangular insulated electrodes, was capable of inflating/deflating pneumatic actuators and operating as a low power soft pump. This article explores a range of designs for the EPP electrodes to increase pressure generation, air transference and flow rate. As a result, the new EPP was able to generate a maximum pressure of 12.24 kPa, or a pressure difference of 11.25 kPa, corresponding to 481% improvement from the previous study. Additional liquid dielectric at 18% of the maximum available volume enabled the EPP to attain maximum EPP performance. The new design of the EPP was developed by combining two identical zipping regions and minimising the inactive region. Different actuator dimensions and actuation frequencies were investigated. The pump was capable of delivering a maximum flow rate of 238 ml/min at atmospheric pressure (48% improvement) at low power consumption of 0.4 Watt, and it could operate up to 4.47 kPa. It was found that the shape of the zipping region and the behaviour of the integrated compliant spring significantly influences the performance of the device. Lastly, approaches to further improve the EPP pump are discussed.

Based on Coulomb forces, electrostatic attraction is a type of actuation that can find many applications for electroactive devices. Electroactive polymers (EAP) are electric responsive materials with specific mechanical and electrical properties that make them promising for an efficient use of this phenomenon. This paper reports on the identification and experimental validation of Figures of Merit (FoM) of electro-adhesion effect for a normal and tangential solicitation. These actuation possibilities are suitable for different kinds of displacement (linear or circular motion) and modulation of shape-shifting designs including origami structures. Several EAP are used to determine the accuracy of experimental benchmarks for the evaluation of these different FoM. The results demonstrate that the developed experimental benchmarks are able to provide accurate values in a range of electric field of [0-5] V/μm. For higher electric fields, different events can occur, at both macroscopic and microscopic scales, leading to a slight decrease of expected performances.

Small-scale soft mobile robots are an attractive solution to gain access to hard-to-reach places. We demonstrate a thin (~4 mm) and flexible mobile robot, 8 cm x 9 cm, mass 4 g, that uses 6 electrostatic zipping actuators with hydraulic coupling, to generate stepwise linear motion. The device is made from laminated films of polymer materials including a high-permittivity layer of a PVDF-HFP/BaTiO₃ composite. Typical operating voltages are around 2 kV, and actuation frequencies range from 1 to 10 steps per second. The HAXELs in the demonstrated device have a side length of 20 mm. Each one is segmented into 4 quadrants that can be independently actuated. This enables each of the robot’s 6 feet to move both front-to-back and side-to-side, allowing for sophisticated motion of the robot (i.e., forward/backward, steering, and sideways movement). We vary several design parameters and investigate different gaits, exploring parts of the large parameter space of possible designs and motion sequences. Locomotion speed up to 2.4 mm/s and a maximum payload capacity of 80 g (20x its own weight) are demonstrated for certain configurations. The actuator scale and other design parameters could be easily adjusted to optimize for movement speed or payload capacity, depending on the intended application.

In recent years, polymer fiber actuators obtained by twisting polymer fibers have attracted much attention. These actuators actuate due to the reversible axial thermal contraction and radial thermal expansion of untwisted fibers. In this study, thermal contraction of the two polyamides, PA6 and PA610, fibers were investigated. The fiber length of both fibers changed reversibly in response to temperature change, but there was no initial load dependence on the amount of contraction. These results indicate that this thermal contraction is not due to the entropic elasticity effect seen in rubber. In addition, the thermal contraction was larger for PA610, which has a larger thermal expansion coefficient in the amorphous state. This suggests that the thermal expansion of the amorphous state was converted by its fiber structure into expansion in the diameter direction and contraction in the fiber axial direction [Kimura et al., Sens. Actuators B Chem., 2021].

In this paper, tensegrity structures with active cables made of ribbon-like dielectric elastomer actuators (DEAs) are presented. The deformation of structure can be controlled by applying high voltages to the DEAs. The DEA-tensegrities proposed here are expected to function as a building block for soft robotic systems. For the DEAs, an acrylic elastomer (3M, VHB4905) and a conductive elastomer (Adhesives Research, Arcare90336) are used as a dielectric and an electrode material, respectively. For the rods, acrylic (poly(methyl methacrylate)(PMMA)) plate is employed. In the paper, the experimental results obtained through characterization of DEA-tensegrities are shown and discussed.

Due to their favorable characteristics, including high permselectivity and chemical stability, ionic membranes are widely adopted in electrochemical applications, including electrochemical cells and electrophoresis devices. Their ability to operate in wet environments, compliance, and biocompatibility have also made these membranes attractive for the development of soft actuators and sensors. Ionic membranes comprise a negatively charged polymeric backbone and a saturating solution with positive cations that neutralize the fixed charges of the membrane. Despite extensive literature about these membranes, our understanding of their electrochemomechanical behavior remains limited. Here, we illustrate a counterintuitive phenomenon that has been heretofore neglected. Specifically, we show that the motion of the solvent in the membrane can be opposite to the motion that one would expect from typical osmosis. We attribute such a phenomenon to the finite volume of mobile ions in the membranes, which is routinely neglected, on the basis of traditional practice in the study of biological mixtures and geological porous media. Starting from a simple one-dimensional continuum model for the mechanics and electrochemistry of the membrane, we theoretically demonstrate the inversion of the migration of solvent for large mobile ions. The inversion occurs at a spatial scale comparable to the Debye screening length, which measures the thickness of electric double layers in ionic membranes and is of the order of nanometers in standard, commercial membranes. This phenomenon could be exploited for concentration and dilution at a nanoscale level, paving the way for new applications in the fields of electrochemistry and micro-/nano-fluidics.

Space-resolved stimulation of active hydrogel layers can be achieved for example by using a micro-heater array. In the current work, we present the interaction of (i) such a rigid array of heating elements that can be selectively activated and (ii) an active thermo-responsive hydrogel layer that responds to the local stimulus change. Due to the respective local actuation, (iii) the surface form of a passive top-layer can be manipulated. We present continuum-based simulative predictions based on the Temperature Expansion Model and compare them to experimental outcomes for the system.

Within the family of electroactive polymers, ionic polymer metal composites (IPMCs) stand out for their low driving voltage, operability in water, and biocompatibility. These characteristics make them attractive as soft actuators for applications in underwater robotics and biomedical engineering. However, their use is currently limited by the lack of predictability of their chemoelectromechanical behavior. Part of this unpredictability is associated with the complex microstructure of the ionic membrane forming the core of the IPMC. The membrane consists of a porous, negatively charged polymer network, which is neutralized by a solution of mobile counterions. In the literature, migration of counterions in the membrane is typically described through the Poisson-Nernst- Planck system of equations. To the best of our knowledge, non-ideal behaviors of the ionic saturating solution have never been considered in the IPMC literature. Here, we make a first step toward studying the effect of non-idealities on the mechanics and electrochemistry of IPMCs. We investigate four non-ideal behaviors of ionic solutions: 1. solvation (that is, the interaction between solute and solvent molecules due to ionic or dipole bonds); 2. electrostatic interactions that affect the mixing of ions in the solution, causing ions of one sign to be surrounded by ions of the opposite sign; 3. physical interactions between ions of opposite signs; and 4. steric effects associated with the finite volume of the membrane pores. Through numerical simulations, we demonstrate the role of each of these contributions on the formation of an electric double layer in a charged membrane near to an electrode, toward developing more realistic models to describe the mechanics and electrochemistry of IPMCs.

This contribution proposes a vaporization and recovery system for the contactless printing of solvent-based electrodes. The developed system prevents swelling effects, which frequently occur when solvent-based electrode material interacts with the elastomer film. In addition, this novel system features recovery of the vaporized solvent by extraction. For this purpose, the heat transport and vaporization process is theoretically analyzed to design and realize the system. Finally, various tests are conducted with the integrated jetting system to evaluate the functions and performance of the developed system.

In this contribution, 3D printing of elastomer layers is investigated. 3D printing gains emerging interest due to its versatility in geometry as well as the ability of producing thin layers and therefore is a promising fabrication method for dielectric elastomer transducers (DETs). Direct Ink Writing (DIW) is a specific type of 3D printing based on the extrusion of fluidic elastomer with middle viscosity, which is the used printing technology in this work. The printing requirements for DETs are defined and by varying the process parameters, printing tests are conducted. Finally, the layers are analyzed and the results are discussed. The main results are printing of a single layer elastomer with 40 µm thickness and three elastomer layers printed on top of each other.

Efficient and flexible fabrication is critical to facilitate experimental research of dielectric elastomer actuators (DEAs). As a rapid prototyping technique, additive manufacturing enables autonomous fabrication of DEAs with controlled geometry and distributed actuation. Contact dispensing is currently the most utilized additive manufacturing method for fully printed DEAs due to its capability to utilize a wide range of materials. However, modest contact dispensing printers produce DEAs with reliable actuation by fabricating thicker dielectric layers. There is an evident need for other approaches to increase actuation performance and lower the driving voltage. While utilization of particulate dielectric composites is a known technique to increase DEA performance, it is not widely applied for 3D printed DEAs. Adverse effects of 3D printed dielectric particulate composites, such as stiffening and material flow interruption, can be diminished with lower operational strains and thicker layers, respectively. Additionally, composite DEAs with improved performance often possess lower driving voltage due to lower breakdown strength. In this study, various dielectric composites properties, such as compressive Young’s modulus, permittivity, and breakdown strength, were examined to evaluate the electromechanical performance of unimorph DEAs through the figures of merit (FOMs). Breakdown strength of both blade-casted films and 3D printed actuators were compared. Particle distribution was monitored using a scanning electron microscope. Unimorph DEAs with plain silicone and dielectric composites were fabricated using HYREL 30M printer. Printed actuators showed improved electromechanical performance and lowered the driving voltage.

This paper reports on a novel measurement method to characterize piezoelectric thin layer (~ 20 μm) through a four-point bending (4PB) setup. Polymer-based piezoelectric composite is directly screen printed onto the surface of host structure, which is assimilated to an instrumented steel substrate. Because of electromechanical coupling properties, a voltage signal can be generated through the piezoelectric sensor when subjected to mechanical strain in its film plane. As the typically sensor layer is very thin in comparison to the underlying substrate, the mechanical properties of the whole system are mainly determined by the characteristics of the steel-type material. Furthermore, the piezoelectric layer properties strongly depend on underlying substrate, electrodes, and the processing route of the layered sensor structure. Therefore, the method developed here enables to reliably extract characteristics such as the effective piezoelectric behavior of the thin composite. In combination with a strain gage coated onto the back side of the substrate, the developed setup allows the determination of the effective piezoelectric sensitivity. The homogeneous strain distribution in the sensing layer is verified by finite element simulations. Furthermore, analytical model is investigated to predict the mechanical behavior of the 4PB structure. The results demonstrate that the developed sensing setup is capable to provide a direct strain/stress measurement instead of traditional techniques through interpolation, and thus offers an efficient method for on-line and in situ structural health monitoring of bearing.

Dielectric elastomers (DEs) have shown a significant potential for actuation applications such as artificial muscles, due to their low weight, fast response, silent operation, and high efficiency. DEs with large actuation strain or low driving voltages are usually incorporated with high permittivity fillers. Ionic liquid (IL) presents a promising improvement on relative permittivity of DEs, however, its aggregation in the elastomer matrix by the physical blending modification has limited the improvement on actuating performances. In this study, a new strategy is developed to prepare high-performance PDMS elastomers by the formation of bis(1-ethylene-imidazole-3-ium) bromide between the PDMS backbones, after which the actuation performance of the IL-modified elastomer is investigated.

Piezoelectric poly(vinylidene fluoride-co-trifluoroethylene), or PVDF-trFE, has enabled unprecedented flexible and dynamic force sensors due to its mechanical robustness and biocompatibility. This study focuses on additive manufacturing of PVDF-trFE thin film sensors using an nScrypt micro-dispenser. PVDF-trFE ink composition, substrate treatment, and printer settings were first investigated to ensure consistent and uniform printing. Post-processing procedures, including curing and electrical poling, were then analyzed experimentally. The effectiveness of the manufacturing procedure was quantified in terms of piezoelectric coefficients. By using commercially-available electrically conductive silver inks, a force sensor consisting of a PVDF-trFE film sandwiched by silver electrodes were prototyped.

Electroactive polymers are a major component of dielectric elastomer actuators (DEA). The performance of DEAs depends on the Young’s modulus, dielectric constant and film thickness of the electroactive polymer as well as the compliance of the electrodes and the applied voltage. In literature mostly experiments on silicone- and acrylic-based DEAs are reported. However, better actuator performance can be expected with materials that have a higher dielectric constant. Therefore, unconventional electroactive polymers, such as polyurethane, chloroprene, or nitrile rubber, are currently attracting increasing interest for DEA applications. Besides their inherent dielectric properties, ferroelectric fillers embedded in the electroactive polymer can increase the dielectric constant even further. Provided that the filler concentration does not significantly increase the Young’s modulus, ferroelectrically filled polymers can be expected to have a better actuator performance than standard materials. In this work, barium titanate particles with different concentrations were embedded in crosslinked polyurethane elastomer films. The hyperelastic material behavior of the polyurethane elastomer is represented by a Mooney-Rivlin model. Impedance spectroscopy is used to determine the dielectric constant of the electroactive compounds. Planar DEAs are designed from both unfilled and barium titanate-filled polyurethane films and compared with respect to their mechanical, dielectric, and actuator properties. The electric field response of unfilled and barium titanate-filled polyurethane-based DEAs is investigated experimentally and compared to an analytical solution of the actuator deformation. Additionally, a comparison between experimental DEA operation and an FEA prediction is carried out and discussed.

Most of the current market demand is for EAP (Electro Active Polymers) power suits, EAP motors, EAP muscles for robots, and systems that drive them in reverse to generate electricity efficiently. We believe that Dielectric Elastomer (DE) transducers are the most suitable for those purposes. To meet these demands, the elasticity of the elastomer is extremely important. We conducted SS (strain stress) curves and viscoelasticity tests on several DE materials (including HNBR: Hydrogenated nitrile rubber) to examine DE’s elongations and their relationships. We discuss important factors (such as cross-linking agents and double bond cleavage) in this paper, based on the research results. In addition, recent attempts have been made to use new carbon foam materials such as single-wall carbon nanotubes (SWCNTs) and multi-wall nanotubes (MWCNTs) as electrodes for DEs. These electrodes could bring a higher performance for DEs. Those possibilities are also discussed in the paper.

Twisting-coiled Actuator (TCA) have numerous appealing properties such as huge energy density, large stroke, and large contractions. Thermally incited muscles manufactured from nylon/polymer can be utilized in robotics, biomedical gadgets, and energy harvesting devices. To optimally make it a promising artificial muscle for robotic and medical applications, it is important to fabricate and characterize them effectively. TCA can exhibits the adaptability of the artificial muscles behavior in general. Notwithstanding, this flexibility accompanies a need to see how the unique ways of the fabrication can be accomplished with these novel actuators and how they compromise in execution. In this work, we propose a Twisting-coiled Actuator to create an artificial muscles. The proposed actuator consists of fishing line in 0.6mm diameter. The fishing line is coiled into coils to create a twisting-coiled actuator. Experimental are conducted with a hot water to characterize the actuator. The findings of our experiments highlight essential results related to the response of these artificial muscles such as large displacement, stored elastic energy, and repeatability

Electroactive polymers (EAP) and their related dielectric elastomers (DE) belong to a very performant and emerging class of functional materials. While being compliant and light-weight, they can be utilized to serve as integrated actuators for soft robotics. By combining EAP with the well-developed class of textile materials and their excellent capability to directly manipulate the local mechanical behavior of structures, compound materials with outstanding properties can be created. In this work a bending structure based on a fiber-elastomer compound is presented. By integrating uniaxially oriented carbon fibers under defined fiber angles in an elastomer matrix, a structure with highly anisotropic bending stiffness is achieved. By attaching dielectric layers with different pre-stretch ratios on both outer sides, an initial elastic stress state is introduced to the structure leading to an anisotropic bending deformation. An attached electrode to the outer side, together with an electrical connection of the textile layers to act as ground electrode, enables the dielectric layers to serve as driving element. Applying a voltage of up to 5000 V leads to an anisotropic bending deflection of up to 1.2 mm at the tips of the structure and 1 mm at the upper edge. Tailoring the geometrical conditions will enable the concept to serve as a gripping mechanism for arbitrarily shaped objects.

In general, materials for dielectric elastomer (DE) transducers, i.e. elastomer and electrode materials, are characterized by their electromechanical behavior. Whereas previous works frequently focus on the mechanical characterization of the elastomer material, this contribution deals with the mechanical characterization of two electrode materials, ELASTOSIL ® LR 3162 (EL 3162) and POWERSIL® 466 (PS 466), as well as the elastomer material ELASTOSIL ® 2030 (EL 2030). The mechanical behavior of the elastomer and electrode materials is determined by elastic and viscous properties such as creep and relaxation. In addition, the electrode materials, exhibit a significant rate-independent hysteresis, which is well-known for filled elastomer materials. A material model based on rheological, mechanical elements is introduced to describe these material properties, and experimental investigations are done to perform a parameter identification for the material model. Experimental investigations show a higher Young’s modulus, higher viscous losses, and an additional rate-independent hysteresis for the electrode materials compared to the elastomer material. In conclusion, the impact of the material properties of the electrode materials on the DE-transducer performance by thinning the elastomer film is discussed.

Dielectric elastomer transducers (DET) progressively attract attention in research and industry. One major reason is their diverse use as actuator, sensor or generator. For manufacturing a DE stack-transducer for example, first, multilayer DE laminates consisting of several DE layers are produced. The submodules are cut out from the DE laminate and can then be stacked to a DE stack-transducer. In order to minimize the scrap rate, increase the productivity, and monitor the manufacturing process testing of multilayered composites during manufacturing process could be favorable. The proposed test approach within this contribution is capacitancebased, versatile applicable, and can be used to test DE laminates or DE submodules. An electrical voltage vtest is applied to additionally added external electrodes (anode and cathode), exposing the multilayer composite to an electric field per layer of EDE. The testing voltage is chosen in such a way that the testing electric field strength holds the relation EDE < E_test < E_crit. Hence, it is selected in between the operation field strength EDE and the critical field strength E_crit. If two electrode layers inside the DET are conductively connected due to a defect in production, a breakdown may occur. The production quality of the DE composite can be determined by measuring the capacitive behavior before and after applying the high voltage as well as compare these to the analytical calculated capacitance. In this way, faulty DE submodules may be detected by scanning the DE laminate at multiple positions. A test procedure to prove the dielectric properties, to improve the production quality, and thus to reduce the scrap rate is proposed. Methodologically, an analytical approach and FEM-based simulation are used to compare various concepts and to design a test approach. First measurements prove the developed testing approach.

Although traditional vibrotactile devices have dominated the global haptic market, they still suffer from poor spatial resolution, poor flexibility, low stretchability, safety issues, and high weight. Emerging electroactive polymer technologies including conducting polymers (CPs) may be suitable to drive thin, compliant haptic devices that can operate at safe and accessible voltages (~ 2 V in the case of conducting polymers). However, optimal sensitivity is achieved at frequencies between 150 and 300 Hz – a frequency range that is difficult to reach in conducting polymers while also producing significant displacement. In this work we develop finite element model that helps explore the trade-off between frequency, displacement, and force, relating these to actuator dimensions and material properties. We developed a finite element analysis (FEA) numerical simulation of CP-based haptic devices, which works based on a combination of the diffusive elastic model (DEM) and modified linear elastic constitutive equations for large deformation. Unlike many previous, analytical models, this simulation paves the way to complete device modeling as it enables geometrically non-linear formulation to be modeled. The novelty of this simulation compared to the previous work is the consideration of the mass and damping effects of the device, which play important roles in describing the resonance frequency response. The model is able to predict frequency responses of tri-layer conducting polymer actuators made from spray coated poly(3,4-ethylenediodythiopehe) polystyrene sulfonate, abbreviated PEDOT:PSS, on poly (vinylidene fluoride) (PVDF) porous membranes. The model employs measured material properties including electronic conductivity, ionic conductivities, elastic modulus, volumetric capacitance, and strain to charge ratio. Frequency responses follow in amplitude from 0.01 to 150 Hz, including through resonance, with some significant differences near resonance. The results extend previous simulation work to include the effects of mass and damping.

Electroactive polymer-based sensors are subjected to repeated loading and unloading cycles under variable applied strains and estimation of the tear strength plays a critical role in determining durability. A trouser type of specimen made from conducting and stretchable freestanding films consisting of SEBS rubber and dodecyl benzenesulfonic acid (DBSA) doped polyaniline composite was used for fabricating the capacitive strain sensor and tear strength estimation. Strain energy density for the composite film was calculated from the tear test data aiming towards the prediction of the life of the specimen. Our results revealed a very high value (150 newton/mm) of tear strength, leading to the sustainability of the film up to millions of cycles.

Low-cost, highly versatile thermally driven coiled nylon actuators have demonstrated great tensile stress (>10 MPa) and large stroke (>5%). The work density of this material is 100 times greater than mammalian muscle, which makes coiled nylon actuators good candidates for applications in soft robotics. Similar to other thermally driven actuators, heat transfer rate limits their frequency response and benefits from extensive cooling. The cooling time for these actuators is dependent on heat conduction and convection. For instance, an 860 µm multi-stranded coiled nylon actuator is limited to 0.2 Hz frequency of actuation, above which tensile stroke drops due to heat accumulation. We analyzed the thermal behavior of silver-coated nylon actuators and investigated the actuation under air flow, in hydrogel, and in water, to improve the frequency response. An improved frequency response was observed under air flow (compressed air) in relation to still air. The measured heat transfer coefficient under air flow reaches 137 W/m² /K enabling 5% strain at 0.8 Hz. The fastest frequency responses were observed in water and within hydrogel, where the nylon actuators demonstrated ~10% strain at 1 Hz (add water and hydrogel heat transfer coefficient). The application of a hydrogel coated actuator is demonstrated through an actuated 3D printed finger, which makes use of antagonistic coiled nylon actuators.

Silver-coated nylon actuators - a form of artificial muscle - are potential candidates in biomedical applications, , as they yield a large strain (5-20%+), high force (>20 MN/m² ), are compact and low-cost. But the on skin or internal application of these thermal actuators is limited by the heat released and the high activation temperatures (typically >80°C), which could cause tissue damage. We present a hybrid coating that reduces the temperature at the interface of the nylon actuator and surrounding tissue/skin, while maintaining the inner nylon actuator activation temperature. By taking advantage of the high heat capacity of water-swollen polyacrylamide (PAAm) hydrogel and the low thermal conductivity of silicone elastomer, we develop a hybrid coating for nylon actuators that provides effective heat dissipation and encapsulation without impacting strain. Hydrogel is used to absorb and dissipate heat. Using it alone dissipates heat quickly, and in turn, excess power is needed to achieve full strain. Therefore, silicone is used as a thin, inner insulating layer to retain the heat, so full strain can be achieved without excess power. We examined the strain and temperature of uncoated nylon fibres (control), single-layered silicone-coated nylon fibres, single-layered hydrogel nylon fibres and hybrid-coated (inner layer of silicone, outer layer of hydrogel) nylon fibres. At a constant current of 0.55 A, the mean strains of hybrid coated nylon fibres (6.0 %), and silicone coated nylon fibres (5.5%) were comparable to uncoated nylon fibres (5.3%). The mean strain for the hydrogel-coated nylon fibres was considerably lower (1.4%). The hybrid coating effectively maintains the fibre temperature (80-87°C) while cooling the outer surface (hydrogel) of the hybrid-coated nylon fibre (30-35°C). This provides a possible solution for use of these actuators in temperature sensitive applications.