Deformation Of Actuators Research Articles

Effect of Electrode Morphology on Performance of Ionic Actuators Based on Vat Photopolymerized Membranes.

Bucky gel electrodes are composed of morphology-determining polyvinylidene difluoride (PVDF) filled with carbon nanotubes (CNT). The electrodes are commonly fabricated via the casting of a CNT dispersion containing PVDF and ionic liquid. In this study, several pore-forming additives such as polyethylene glycol (PEG), dibutyl phthalate (DBP), and the common ionic liquid BMIMBF4 were used to control the morphology of the bucky gel electrodes. The crystalline phase type and content of PVDF in the electrodes were determined by FT-IR and DSC, respectively. SEM revealed a sponge-like structure in the case of the use of BMIMBF4 and a spherulite structure if PEG and DBP were used as additives. A strong influence of morphology on the anisotropic increase in the volume of electrodes upon impregnation with electrolyte was observed. The PEG-based electrode elongated more than the others, while the BMIMBF4-based electrode thickened to a greater extent. Ionic actuators were fabricated to experimentally reveal the effect of electrode morphology on their electromechanical efficiency. A high-precision vat photopolymerization technique was used to fabricate identical ionic membranes and minimize their influence on the properties of the actuators. The electrodes were characterized by the same porosity and electrical capacitance, while the actuators differ significantly in performance. As a result, a simple method of using pore-forming additives made it possible to increase the maximum deformation of bucky gel ionic actuators by 1.5 times by changing the morphology of the electrodes.

Analytical Modeling of a Soft Pneu-Net Actuator Subjected to Planar Tip Contact

Soft actuators are compliant structures that are generally made of elastomers and generates large deformation. The behavior of these structures cannot be estimated accurately using infinitesimal strain theories. The objective of soft robotics applications is the controlled large deformation of these structures. In this article, we propose an analytical model for a pneu-net soft actuator. The model is based on the Euler–Bernoulli finite strain hyperelastic thin cantilever beam theory. The deformation of the air chambers is modeled using finite strain membrane theory. The analytical model is developed for two different states of the actuator: 1) free space; and 2) when the actuator was subjected to tip contact. The proposed theoretical model predicts the deformation and force characteristics of the actuator for the grasping state. The theoretical formulation of the developed model is different from previously developed infinitesimal strain models for the actuator, as it considers the axial stretch and forces applied to the actuator. In addition, it can be theoretically implemented on similar structured actuators for various applications. The theoretically calculated deformation and force characteristics of different actuators are compared with the finite element (FE) model and experimental characteristics. The results suggest that the proposed model can predict the actuator deformation and force characteristics as accurately as the FE model, but the computation time of the proposed model is less than 1% that of the FE model. The proposed model is further implemented on a three-finger gripper to predict the air pressure required for a stable grasp of different objects and is validated experimentally.

Electrically actuated soft actuator integrated with an electrochemical reactor

The soft actuators integrated with the reversible proton exchange membrane fuel cell (RPEMFC) structure exhibit the potential to serve in portable and untethered soft robots with advantages of electric actuation, and compact and lightweight structure. But their performances in actuation strain, load capacity, controllability, and robustness are expected to be further improved. Here, a soft electrochemical actuator (SECA) that is integrated with an electrochemical reactor (ECR) designed based on the RPEMFC structure is reported. The ECR works as a pneumatic source that provides regulated pneumatic pressure through the water electrolysis reaction and hydrogen–oxygen fuel cell reaction. With the designed water-containing structure, the ECR has an improved performance of robustness to pose variations. The SECA can reach controllable deformation by the proposed actuation and deformation control methods which require a low-voltage (<3 V) and simple electrical system. With the new structural design, the SECA achieves excellent performances of large actuation deformation (150% actuation strain) and a high load-to-weight ratio (25:1) with a lightweight, compact, and easy-to-fabricate structure.

Feed-forward Control of Vortices Using Real-Time Particle Image Velocimetry

Active flow control (AFC) is a topic with enormous potential for improving a wide array of technologies. This work presents the use and evaluation of a novel AFC system to apply feed-forward control to vortices formed in the wake of a wall-mounted spherical cap. A real-time particle image velocimetry (RT-PIV) system served as the sensor for the AFC system. The RT-PIV system produced 7.35 vector fields per second, each consisting of a two-dimensional grid of 5 × 37 velocity vectors. The actuator system consisted of a rubber surface that could deform using 16 independently controlled linear actuators. The actuators were controlled to apply wall-normal surface deformation at velocities proportional to wall-normal velocities measured by the RT-PIV system upstream of each of the 16 actuators. Analysis of the RT-PIV measurements in comparison to those from an offline PIV system run in parallel indicated that the RT-PIV system produced accurate flow measurements. As well, it was found that the RT-PIV system had a delay of approximately 0.09 seconds. The evaluation of the actuator system indicated that the actuator displacements were consistently damped by 20-25% and lagged the control signal by approximately 0.1 seconds relative to the input signal to the actuators. Therefore, the AFC system had a total delay of approximately 0.2 seconds and applied slightly weaker than specified actuations. These results were within anticipated values and, overall, the AFC system functioned adequately. The impacts of the flow control included disruption of the coherent ejection and sweep structures formed in the wake of the spherical cap and the formation of numerous smaller turbulent structures. As well, several of the control cases showed altered wall-normal velocity fluctuation variance fields in comparison to that of the unforced wake. This is a promising result for AFC using deformable surface actuators as it shows that the active control had a significant effect on an average quantity of the flow.

Modular Origami Soft Robot with the Perception of Interaction Force and Body Configuration

Bio‐inspired soft robots provide a promising solution for robots working in human‐centered scenarios and interacting with unstructured environments. However, the functional versatility and multimodal sensing of soft robots still need improvements. On one hand, the configuration of a soft robot is predefined during manufacturing; on the other hand, the multimodal perception of the deformable soft actuator is challenging. In this work, a reconfigurable and proprioceptive soft origami module is presented, where two kinds of basic actuation modes (i.e., extension and bending) are realized, and multimodal perception is enabled using a novel foldable self‐inductance sensor. As a result, the origami module can be reconfigured to assemble multifunctional robots that can measure interaction force, body configuration, and other environmental information. Dedicated experiments are performed to validate the performance of the proposed origami module. An intelligent gripper assembled using three origami modules is designed with the capabilities of grasping mode adjustment, grasping force measurement, and the grasping target's size measurement. An intelligent jellyfish is assembled using five origami modules, and equipped with buoyancy adjustment and underwater grasping capabilities. The proposed proprioceptive modular soft origami provides an effective solution for versatile and intelligent soft robot design.

Multicoating Nanoarchitectonics for Facile Preparation of Multi-Responsive Paper Actuators.

Stimuli-responsive actuators (SRAs) that can harvest environmental energies and convert them to mechanical works without additional energy-supplying systems have revealed great potential for robotic applications. However, at present, the practical usage of SRAs is significantly limited due to the problems with respect to solo responsiveness, simple deformation, and the difficulties for large-scale and cost-effective production. In this paper, multi-responsive paper actuators with multicoating nanoarchitectonics that enable complex deformation have been fabricated through a very simple painting process on common papers. The resultant paper actuator permits large-scale and low-cost production (A4 size: ∼0.5 dollar). The paper actuators that consist of a paper/graphite/polydimethylsiloxane sandwich structure can be actuated by multi-form stimuli, including moisture, temperature, light, and volatile organic compounds. More importantly, the bending deformation of the paper actuators can be further programmed by controlling the pencil drawing orientation, providing the feasibility of performing more complex deformations. Several multi-responsive paper actuators, including organic compound-responsive smart devices working in the liquid environment, moisture-enabled terrestrial crawling actuator, and a light-responsive attitude-control actuator integrated with an airplane model, have been demonstrated. The development of multi-responsive yet cost-effective paper actuators may hold great promise for a wide range of practical applications, for instance, soft micro-electromechanical systems, lab-on-a-chip systems, smart homes, and robotics.

Evoking the snap-through instability in hard-magnetic soft materials: Rapid actuation and giant deformation

In this paper, we break into an appropriate strategy for achieving a rapid actuation and giant deformation in hard magnetoactive elastomers (MAEs). We devise a flat arch with a properly distributed residual magnetic flux field and realize the large deformation by harnessing the snap-through instability. With an ingenious design of the residual magnetic flux field within the arch that has a large slenderness ratio, the applied magnetic field for inducing the onset of instability can be relatively small. Even if the size of the flat arch is up to millimeter level, the applied magnetic field is as small as hundreds of oersted. We also develop a theoretical model for revealing the mechanism of the magnetic-driven instability in hard magnetoactive elastomers. The stress, induced by the coupling between the external magnetic field and the residual magnetic flux field, is transformed into a surface load. We formulate the total energy of the magneto-mechanical system and carry out the first and second variations to study the equilibrium states and their stability. To verify our theoretical predictions, we fabricate the corresponding MAE specimen and observe the tantalizing magneto-mechanical behaviors in the lab. Our theoretical predictions agree with the experimental observations in the case of flat arches of MAEs. This paper is desirable to open new ways of designing multifunctional MAE devices with rapid actuation and giant deformation.

Magnetic Actuator with Programmable Force Distribution and Self‐Sensing for Bidirectional Deformation Control

AbstractThe realization of bidirectional deformation function is an important symbol of most natural creatures and intelligent flexible robots. Currently, most soft actuators are developed on the basis of transition between two different states, which means difficulties of control during the whole movement. In this work, variable distribution positions of hard magnetorheological elastomers (H‐MREs) in the matrix are used to achieve different magnetic force distributions. The programmable force distribution promotes different deformations of the magnetic actuators, which enlarges the deformation range by 51.69% under the same magnetic field. Pre‐magnetizing the H‐MREs makes them have a certain residual magnetization. Due to the residual magnetization property of H‐MREs, the magnetized actuator can not only be attracted but also be repelled by the applied magnetic field. This bidirectional deformation capability gives the actuators a wider deformation range and greater clamping force, such as the smart gripper for pinching up object. In addition, the actuators are integrated with a flexible sensing layer with high resolution and strong stability for self‐sensing. This kind of force distribution programmable technology and self‐sensing performance have the potential to broaden the application of actuators in medical equipment requiring high control accuracy.

Morphable three-dimensional electronic mesofliers capable of on-demand unfolding

Development of miniaturized three-dimensional (3D) fliers with integrated functional components has important implications to a diverse range of engineering areas. Among the various active and passive miniaturized 3D fliers reported previously, a class of 3D electronic fliers inspired by wind-dispersed seeds show promising potentials, owing to the lightweight and noiseless features, aside from the stable rotational fall associated with a low falling velocity. While on-demand shape-morphing capabilities are essential for those 3D electronic fliers, the realization of such miniaturized systems remains very challenging, due to the lack of fast-response 3D actuators that can be seamlessly integrated with 3D electronic fliers. Here we develop a type of morphable 3D mesofliers with shape memory polymer (SMP)-based electrothermal actuators, capable of large degree of actuation deformations, with a fast response (e.g., ∼1 s). Integration of functional components, including sensors, controllers, and chip batteries, enables development of intelligent 3D mesoflier systems that can achieve the on-demand unfolding, triggered by the processing of real-time sensed information (e.g., acceleration and humidity data). Such intelligent electronic mesofliers are capable of both the low-air-drag rising and the low-velocity falling, and thereby, can be used to measure the humidity fields in a wide 3D space by simple hand throwing, according to our demonstrations. The developed electronic mesofliers can also be integrated with other types of physical/chemical sensors for uses in different application scenarios.

Bionic Soft Multimodal Actuators for Fast, Large Deformation under Ultralow Magnetic Conditions

AbstractVery recently, magnetically driven soft actuators have prompted increasing interest due to their programmable deformation, swift response, and remote actuation. However, it is still challenging to trigger strong and fast actuating performances with an extremely weak magnetic field due to the difficult task of in situ programming of magnetic domains and the limited mechanical structures. Here, first a bionic sandwich structure is proposed for designing soft magnetic actuators with a specific threshold value. The crab‐like jointed structure of PDMS‐embedded NdFeB upper/lower layers is essential for generating the desirable threshold effect, while a flytrap‐inspired soft interlayer is further implemented to decrease the driving magnetic field. Theoretical analysis and numerical simulations are implemented to optimize the actuating performances of soft actuators (deformation rate, deformation angle) by modulating the structural parameters. Experimental results show that the biomimetic features yield a promptly switchable bistable state, a superior strong deformation rate of 1.93, and a maximum deformation angle of 25.5° under an ultralow magnetic field of 1 mT. Two demonstrative applications of soft actuators are investigated, including threshold switching and soft grippers, suggesting their broad applications in engineering fields. Remarkably, the magnetic soft grippers associated with the gecko‐inspired adhesion surface exhibit an improved and stable grasping ability. This work focuses on designing highly deformable actuators and functions in emerging areas of soft robotics.

Development of an inertial piezoelectric pump with separable chamber.

This paper presents an inertial pump with rectangular piezoelectric actuators. The mass block adhered at the free end of the actuator increases the actuator deformation, and the pump chamber is separable. Theoretical and experimental analyses are conducted. The different drive modes with the mass block, different excitation electric signals, and their influence on the performance of the piezoelectric pump are investigated. The drive mode is divided into the mass block adhered with two rectangular piezoelectric actuators, one of the actuators, and actuators without mass blocks. The square wave, sine wave, and triangle wave constitute different excitation electric signals. The experimental results prove that the pump with the mass block adhered with two rectangular piezoelectric actuators and driven by the square wave has a wide working frequency range and high performance. The highest flow rate reached is 72 ml/min at 160V, 20Hz. The pump with the mass block adhered with one of the actuators and driven by the square wave generates the loudest noise of 97.6 dB at 160V, 35Hz.

Highly Tough, Stretchable, and Solvent-Resistant Cellulose Nanocrystal Photonic Films for Mechanochromism and Actuator Properties.

Cellulose nanocrystals (CNCs)-derived photonic materials have confirmed great potential in producing renewable optical and engineering areas. However, it remains challenging to simultaneously possess toughness, strength, and multiple responses for developing high-performance sensors, intelligent coatings, flexible textiles, and multifunctional devices. Herein, the authors report a facile and robust strategy that poly(ethylene glycol) dimethacrylate (PEGDMA) can be converged into the chiral nematic structure of CNCs by ultraviolet-triggered free radical polymerization in an N,N-dimethylformamide solvent system. The resulting CNC-poly(PEGDMA) composite exhibits impressive strength (42MPa), stretchability (104%), toughness (31MJm-3 ), and solvent resistance. Notably, it preserves vivid optical iridescence, displaying stretchable variation from red, yellow, to green responding to the applied mechanical stimuli. More interestingly, upon exposure to spraying moisture, it executes sensitive actuation (4.6°s-1 ) and multiple complex 3D deformation behaviors, accompanied by synergistic iridescent appearances. Due to its structural anisotropy of CNC with typical left-handedness, the actuation shows the capability to generate a high probability (63%) of right-handed helical shapes, mimicking a coiled tendril. The authors envision that this versatile system with sustainability, robustness, mechanochromism, and specific actuating ability will open a sustainable avenue in mechanical sensors, stretchable optics, intelligent actuators, and soft robots.

Soft magnetic composites for highly deformable actuators by four-dimensional electrohydrodynamic printing

Soft magnetic composites have been orderly deposited using an advanced four-dimensional electrohydrodynamic printing process to build deformable actuators that have favorable attributes in fast response, untethered control, and harmless human-machine interactions under low-strength magnetic fields. To effectively deliver the magnetic composites ink with a high viscosity, a rotating needle is utilized to induce the microscale Weissenberg effect (MWE) and help ejecting the polymer solution. The magnetic polarities of microparticles in the resulting structure can be controlled via a permanent magnet structure which is designed and added into the printing system. The main process parameters have been investigated for obtaining optimal options of the motor rotational speed (2000 rpm), electrostatic field strength (2.0 kV), and the ratio (0.732) of the needle diameter to nozzle diameter. Prototype actuators with different magnetization orientations and profiles have been designed and tested, including magnetically powered electrical switches and bionic soft robots to emulate the operations of inchworms and dragonflies. As such, this printing process offers a facile and effective path to fabricate soft magnetic composites toward potential applications.

Experimental and numerical investigations on cooling performance of chemical-vapor-deposited SiC deformable mirror for adaptive optics system in high-power laser radiation environments

• A large-diameter CVD SiC U-WDM for use in AO systems utilizing an HPLR system was presented. • The cooling performance of the CVD SiC U-WDM was investigated under HPLR conditions. • Fluid-thermal-structural coupling characteristics of the CVD SiC U-WDM were analyzed. • The CVD SiC U-WDM dramatically decreased the thermal deformation to submicron scale. In an adaptive optics system combined with a high-power laser radiation (HPLR) system, the thermal deformation of a deformable mirror (DM), which is induced by high-energy irradiation, is a significant factor influencing the optical performance of the system. In particular, the thermal deformation of the DM with a large diameter of more than a few hundred millimeters should be controlled to be on the order of 1 μm in various HPLR environments. To satisfy these challenging criteria, we experimentally and numerically investigated the cooling performance of a large-diameter water-cooled DM (WDM) with U-shaped cooling microchannels (U-WDM) made of chemical-vapor-deposited SiC, which was designed first in our previous research. The fluid-thermal-structural coupling characteristics of the U-WDM were verified and analyzed through the verification process. In addition, the fluid-thermal-structural coupling characteristics of the DM and U-WDM were compared and analyzed by applying four different HPLR conditions: annular, circular, holed-square, and square beams. Under all the HPLR conditions, the comparative study demonstrated that the U-WDM had dramatic cooling performance, reducing the thermal deformation by more than 85% compared to that of the DM and achieving submicron-scale thermal displacement, which was lower than the targeted actuator deformation limit of 1.3 μm.

Rapid Preparation of Dual Cross-Linked Mechanical Strengthening Hydrogels via Frontal Polymerization for use as Shape Deformable Actuators

The hydrogel artificial muscle has demonstrated enormous potential in various applications, such as soft robotics and actuators. However, the poor mechanical properties have always limited the practical applications of hydrogels. Here, we designed a Zr4+ coordinated and vinyl hybrid silica nanoparticle (VSNP) grafted poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (VSNP@poly(AM-co-AMPS)-Zr4+) via frontal polymerization (FP). Benefiting from the synergistic effect of the polymer–nanocomposite interaction (VSNP nanocomposite) and metal ion–ligand interactions (Zr4+–sulfonate group coordination), the mechanical properties of hydrogels can be extremely improved. In addition, a deformable hydrogel with gradient structure and swelling ratio was designed through introducing Zr4+ to one side of the hydrogel, which can serve as an artificial muscle to accomplish multiple moving activities, such as bending and grabbing. This work offers an easy-to-perform strategy to construct mechanically strong hydrogels, which might promote the development of artificial muscle materials.

Large Torsional Rotation and Rotational Inversion Coupling with Linear Deformation of Electromechanical Actuators Based on Conductive Micro-/Nano-Helices

Large Torsional Rotation and Rotational Inversion Coupling with Linear Deformation of Electromechanical Actuators Based on Conductive Micro-/Nano-Helices

Semicrystalline polymer networks with a swelling-enhanced water-triggered two-way shape-memory effect for programmable deformation and smart actuation

A simple, effective and universal strategy is proposed to fabricate a water-triggered two-way shape-memory polymer with the highest angle reversibility of 45.2%, which can be applied as a soft gripper and water level monitor.

Modeling Fabric-Type Actuator Using Point Clouds by Deep Learning

Flexible actuators are popular in the consumer and medical fields because of their flexibility and compliance. However, they are typically difficult to model because of their viscoelasticity and nonlinearity. This letter proposes a method for correcting the deformation of the simulated flexible robots to make it similar to the deformation of real robots using point clouds by deep learning. Long short-term memory (LSTM) can simulate the next frame of actuator deformation from the previous frames of deformations. In this study, we presented the robots with four different muscle structures. We found that using an encoder–LSTM–decoder network can improve the similarity between the deformation of a learned muscle structure and the real deformation and is also effective in correcting the deformation of the unlearned structures. Our correction method reduced the average Chamfer distance of the simulated point clouds of the basic-type structure actuator from 15.89 to 7.81. This research can provide a new concept for future flexible robot modeling using point clouds.

Magnetic field assisted fabrication of asymmetric hydrogels for complex shape deformable actuators

Our work provides a facile yet universal strategy to fabricate programmable hydrogel actuators with asymmetric structures.

A Virtual Work Model for the Design and Parameter Identification of Cylindrical Pressure-Driven Soft Actuators

Abstract In this paper, we derive a model based on the principle of virtual work to describe the deformations of cylindrical pressure-driven soft actuators with four types of fiber reinforcement and with externally applied forces. Such cylindrical actuators are often used as the basis for multi-chamber soft robotic systems, for example, bending actuators. In the virtual work model, each type of reinforcement leads to particular geometric constraints; the energy of the stretched material is determined by the Yeoh material model. Finally, the stretch of the actuator is solved numerically by a minimization problem. The virtual work model yielded only little deviations of the predicted stretch relative to finite element simulations in abaqus. The key contribution of the virtual work model is improved parameter identification for the modeling of cylindrical soft actuators, as it illustrates the possibility to distinguish between material-dependent behavior and geometry-dependent behavior of these actuators. Also, the virtual work model is applicable in the design process of the investigated actuators. We demonstrate that an optimization of the actuator’s inner and outer radii and of its fiber angle, respectively, is possible and we derive design rules including criteria for the choice of fiber reinforcement.