Electromechanical coupling behavior of dielectric elastomer transducers

Dielectric elastomer transducers with large deformation, high energy output, light weight and low cost have been drawing great interest from both the research and industry communities, and shown potential for versatile applications in biomimetics, dynamics, robotics and energy harvesting. However, in addition to multiple failure modes such as electrical breakdown, electromechanical instability, loss-of-tension and fatigue, the performance of dielectric elastomer transducers are also strongly influenced by the hyperelastic and viscoelastic properties of the material. Also, the interplay among these material properties and the failure modes is rather difficult to predict. Therefore, in order to provide guidelines for the optimal design of dielectric elastomer transducers, it is essential to first develop accurate and reliable models, and efficient numerical methods to investigate their performance. First, this thesis purposes a boundary-constraint method to eliminate the electromechanical instability of dielectric elastomer actuators under voltage-control loading condition and improve their actuation deformation. Second, based on the finite-deformation viscoelasticity model, the natural frequency tuning process of viscoelastic dielectric elastomer resonators is examined in this work. It is found that the tuned natural frequency is highly affected by the material viscoelasticity. Also, it is concluded that the electrical loading rate only influences the tunable frequency range and the safe operation voltage of the resonator, but not the tuned natural frequency when the applied voltage is within the safe range. Third, with the finite-deformation viscoelasticity model, the energy conversion efficiency of dielectric elastomer generators under equi-biaxial loading is also investigated in this work. Simulation results show that increasing the maximum stretch ratio and the rate of deformation, and choosing a proper bias voltage can lead to an improvement of the energy conversion efficiency. Furthermore, the fatigue life of dielectric elastomer devices under cyclic loading is explored in this work for the first time. Simulation results have demonstrated that the energy conversion efficiency of dielectric elastomer generators is compromised by their fatigue life. To tackle the critical challenges for the development and design of dielectric elastomers transducers, this research develops theoretical models and numerical methods that are able to capture the nonlinear electromechanical coupling, the material properties, the typical failure modes and different operating conditions of dielectric elastomer transducers. With more accurate and reliable modeling methods, this work is expected to provide a comprehensive understanding on the fundamentals and technologies of dielectric elastomer transducers and trigger more innovative and optimal design of such devices

Pneumatic Hyperelastic Robotic End-Effector for Grasping Soft Curved Organic Objects

Pneumatically-driven soft robotic grippers can elastically deform to grasp delicate, curved organic objects with minimal surface damage. However, common actuators have complex geometries and are fabricated with ultra-soft hyperelastic elastomers not originally intended for scientific applications. The complexity of the actuator geometry and extreme nonlinearity of their material’s stress-strain behaviour make it difficult to predict the actuator’s deformation prior to experimentation. In this work, a compact soft pneumatic gripper made with polydimethylsiloxane (PDMS) is developed for grasping delicate organic objects, analyzed through computational modelling and experimentally validated. COMSOL Multiphysics is used to simulate the impact of geometrical parameters on the actuator’s behaviour, allowing for the refinement of the proposed geometry prior to fabrication. Optimal parameters are selected for fabrication, with experimental tests matching simulations within ± 1 mm. Gripper performance is evaluated for three actuator wall thicknesses in terms of contact area with target, contact force, and maximum payload before slippage. The comparative assessment between simulations and experiments demonstrate that the proposed soft actuators can be used in robotic grippers tailored for grasping delicate objects without damaging their surface. Furthermore, analysis of the actuators provides additional insight on how to design simple but effective soft systems

The Research on Soft Pneumatic Actuators in Italy: Design Solutions and Applications

Interest in soft actuators has increased enormously in the last 10 years. Thanks to their compliance and flexibility, they are suitable to be employed to actuate devices that must safely interact with humans or delicate objects or to actuate bio-inspired robots able to move in hostile environments. This paper reviews the research on soft pneumatic actuators conducted in Italy, focusing on mechanical design, analytical modeling, and possible application. A classification based on the geometry is proposed, since a wide set of architectures and manufacturing solutions are available. This aspect is confirmed by the extent of scenarios in which researchers take advantage of such systems’ improved flexibility and functionality. Several applications regarding bio-robotics, bioengineering, wearable devices, and more are presented and discussed

Biaxial experimental characterizations of soft polymers: A review

Soft polymeric materials such as elastomers and hydrogels have played a significant role in recent interdisciplinary research. They are subjected to large stretch and high cyclic loading-unloading conditions where the typical loading mode is biaxial rather than simple uniaxial loading thus, necessitating further characterization using biaxial loading conditions and subsequently developing robust and versatile numerical models. Although many standards were prepared for common uniaxial tests in situ elastomers including tensile, shear, and fatigue tests, no specific standardized guidelines were prepared to be employed for the biaxial characterization of elastomers and hydrogels. There existed limited works on the biaxial characterization of soft polymers, thus making it difficult to identify which configurations and results are more reliable. Hence, there were huge discrepancies in the existing literature for biaxial tests in terms of sample configurations (square or cruciform specimens), dimensions, and test setups including strain rate, pre-loading, equi-biaxial and unequi-biaxial tests. Therefore, this paper is aimed at reviewing the published studies on the biaxial characterization of soft polymers in several aspects including (i) sample configurations in terms of geometry and dimension (ii) biaxiality degree of tested specimens where sample should be optimized to reach proper biaxiality, i.e., larger area with homogenous strain distribution in the middle with respect to the edges, (iii) test procedure for the biaxial characterization including strain amplitude, strain rate and loading patterns (iv) a brief review on inflation test of elastomers which was the most common equi-biaxial test studied in the literature. The largest and smallest cruciform samples with the dimensions of 165 × 165 mm2 and 38 × 38 mm2 were used, respectively, while a small sample of 7 × 7 mm2 and large one of 70 × 70 mm2 were also employed for the square specimen. Various test parameters and materials were used for the biaxial characterization. This necessitates the importance of preparing a standardized methodology for the biaxial characterization of elastomers based on intended materials and applications. Hence, a few potential geometries based on the optimization performed in the literature were suggested for future investigations in which numerous examinations using different materials and test parameters shall be conducted to reach an ideal sample configuration and methodology for the biaxial characterization of soft polymeric materials

Buckling Pneumatic Linear Actuators Inspired by Muscle

The mechanical features of biological muscles are difficult to reproduce completely in synthetic systems. A new class of soft pneumatic structures (vacuum-actuated muscle-inspired pneumatic structures) is described that combines actuation by negative pressure (vacuum), with cooperative buckling of beams fabricated in a slab of elastomer, to achieve motion and demonstrate many features that are similar to that of mammalian muscle.Chemistry and Chemical Biolog

Bio-inspired optical components

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references.Guiding electro-magnetic radiation is fundamental to optics. Lenses, mirrors, and photonic crystals all accomplish this task by different routes. Understanding the interaction of light with materials is fundamental to improving and extending optical science and engineering as well as producing novel optical elements. Improvement in this understanding should not only include work to understand the interaction with traditional engineering materials but also should target the understanding of the interaction of electromagnetic radiation with biological structures as millions of years of evolution have sorted out numerous ways to modulate light (e.g. the fish eye or the skin of the octopus). The goal of this thesis work is to fabricate novel optical elements by taking cues from nature and extending the state of the art in light guiding behavior. Here, optical elements are defined as structured materials that guide or direct electromagnetic radiation in a predetermined manner. The work presented in this thesis encompasses biologically inspired tunable multilayer reflectors made from block copolymers and improvements to liquid filled lenses which mimic the human eye.In this thesis a poly(styrene)-poly(2-vinylpyridine) block copolymer was used to create a bio-mimetic, one-dimensional, multilayer reflector. The wavelengths of light reflected from this multilayer reflector or Bragg stack were tuned by the application of stimuli which included temperature, change in the solvent environment, pH, salt concentration in the solvent, and electrochemistry.(cont.) A linear-shear rheometer was also built to investigate the mechanochromic color change brought about through the shearing of a one-dimensional, high molecular-weight, block-copolymer, photonic gel. Biologically inspired lenses were also studied through the construction of a finite element model which simulated the behavior of a liquid-filled lens. Several tunable parameters, such as the modulus, internal residual stress, and thickness of the membrane were studied for their influence on the shape of the lens membrane. Based on these findings, suggestions for the reduction of spherical aberration in a liquid filled lens were made. A gradient in the elastic modulus of the membrane was also investigated for use in the reduction of spherical aberration.by Joseph John Walish.Ph.D

Elastic Inflatable Actuators for Soft Robotic Applications

The 20th century’s robotic systems have been made out of stiff materials and much of the developments in the field have pursued ever more accurate and dynamic robots which thrive in industrial automation settings and will probably continue to do so for many decades to come. However, the 21st century’s robotic legacy may very well become that of soft robots. This emerging domain is characterized by continuous soft structures that simultaneously fulfil the role of robotic link and robotic actuator, where prime focus is on design and fabrication of the robotic hardware instead of software control to achieve a desired operation. These robots are anticipated to take a prominent role in delicate tasks where classic robots fail, such as in minimally invasive surgery, active prosthetics and automation tasks involving delicate irregular objects. Central to the development of these robots is the fabrication of soft actuators to generate movement. This paper reviews a particularly attractive type of soft actuators that are driven by pressurized fluids. These actuators have recently gained substantial traction on the one hand due to the technology push from better simulation tools and new manufacturing technologies including soft-lithography and additive manufacturing, and on the other hand by a market pull from the applications listed above. This paper provides an overview of the different advanced soft actuator configurations, their design, fabrication and applications.This research is supported by the Fund for Scientific Research-Flanders (FWO), and the European Research Council (ERC starting grant HIENA)

Elastic Inflatable Actuators for Soft Robotic Applications

The 20th century’s robotic systems have been made out of stiff materials and much of the developments in the field have pursued ever more accurate and dynamic robots which thrive in industrial automation settings and will probably continue to do so for many decades to come. However, the 21st century’s robotic legacy may very well become that of soft robots. This emerging domain is characterized by continuous soft structures that simultaneously fulfil the role of robotic link and robotic actuator, where prime focus is on design and fabrication of the robotic hardware instead of software control to achieve a desired operation. These robots are anticipated to take a prominent role in delicate tasks where classic robots fail, such as in minimally invasive surgery, active prosthetics and automation tasks involving delicate irregular objects. Central to the development of these robots is the fabrication of soft actuators to generate movement. This paper reviews a particularly attractive type of soft actuators that are driven by pressurized fluids. These actuators have recently gained substantial traction on the one hand due to the technology push from better simulation tools and new manufacturing technologies including soft-lithography and additive manufacturing, and on the other hand by a market pull from the applications listed above. This paper provides an overview of the different advanced soft actuator configurations, their design, fabrication and applications.This research is supported by the Fund for Scientific Research-Flanders (FWO), and the European Research Council (ERC starting grant HIENA)