Performance Of Actuator Research Articles

Liquid Crystalline Elastomers with Tailorable Actuation Performance Based on Orthogonal Click Chemistries

Liquid Crystalline Elastomers with Tailorable Actuation Performance Based on Orthogonal Click Chemistries

Liquid Metal Microdroplet‐Initiated Ultra‐Fast Polymerization of a Stimuli‐Responsive Hydrogel Composite

AbstractRecent advances in composite hydrogels achieve material enhancement or specialized stimuli‐responsive functionalities by pairing with a functional filler. Liquid metals (LM) offer a unique combination of chemical, electrical, and mechanical properties that show great potential in hydrogel composites. Polymerization of hydrogels with LM microdroplets as initiators is a particularly interesting phenomenon that remains in its early stage of development. In this work, an LM‐hydrogel composite is introduced, in which LM microdroplets dispersed inside the hydrogel matrix have dual functions as a polymerization initiator for a polyacrylic acid‐poly vinyl alcohol (PAA/PVA) network and, once polymerized, as passive inclusion to influence its material and stimuli‐responsive characteristics. It is demonstrated that LM microdroplets enable ultra‐fast polymerization in ≈1 min, compared to several hours by conventional polymerization techniques. The results show several mechanical enhancements to the PAA/PVA hydrogels with LM‐initiated polymerization. It is found that LM ratios strongly influence stimuli‐responsive behaviors in the hydrogels, including swelling and ionic bending, where higher LM ratios are found to enhance ionic actuation performance. The dual roles of LM in this composite are analyzed using the experimental characterization results. These LM‐hydrogel composites, which are biocompatible, open up new opportunities in future soft robotics and biomedical applications.

Bistable Actuation Based on Antagonistic Buckling SMA Beams

Novel miniature-scale bistable actuators are developed, which consist of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to have opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snap-through motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography, and systems integration. The stationary force–displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact to a low-temperature heat source in the range of 130–190 °C. The bistable actuation is characterized by a large stroke up to 3.65 mm corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature. The bistable actuation at low-temperature differences provides a route for waste heat recovery.

High-temperature electromechanical actuation of relaxor ferroelectric polymers blended with normal ferroelectric polymer

Soft actuators that can operate at high temperatures are of great interest in emerging research fields such as microfluidics, soft robotics, automotive, aircraft, and bioelectronics. However, most polymer-based flexible actuators suffer from performance degradation at elevated temperatures above 60 °C. In this paper, we present the high-temperature electromechanical actuation of relaxor ferroelectric polymers solution-blended with normal ferroelectric polymers. We conduct a systematic analysis of the electromechanical properties of three unimorph actuators with relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)s [P(VDF-TrFE-CFE)s] containing different amounts of chlorofluoroethylene (CFE) moieties (approximately 1, 3.5, and 9 wt%). In this study, we propose the film stress, given as Young's modulus times strain, as the measure of the electromechanical performance of soft bending actuators under loading, rather than strain or strain energy density. We demonstrate that a relaxor ferroelectric actuator with 1-wt% CFE, which mixes high-modulus ferroelectric crystal domains with an optimized electrostrictive relaxor phase, develops a high film stress of ∼3.5 MPa. When blended with the normal ferroelectric P(VDF-TrFE), the actuator exhibits excellent film stress of approximately 3.1 MPa at an elevated temperature of 60 °C comparable with that at 25 °C. The high-modulus ferroelectric crystals in P(VDF-TrFE) reinforce the mechanical properties of the actuator at elevated temperatures, generating high-temperature electromechanical actuation with a large strain and strain energy density of approximately 1.6% and 23 mJ/cm², respectively. We also demonstrate successful microfluidic pump operation at 60°C with our actuator using a relaxor ferroelectric polymer blended with an intrinsic ferroelectric polymer.

Enhanced performance of electro-responsive PVC gel actuators prepared by advanced rapid thermal melting technique

Polyvinyl chloride (PVC) gel actuators exhibit a contraction-relaxation movement characterized by large strain and rapid response when electrically stimulated, comparable to that of biological muscles, making them attractive for artificial muscles and other actuation purposes. However, the standard fabrication of PVC gel by so-called solution casting has been found to be time-consuming (i.e., typically taking 4–7 days), cost-ineffective, and prone to skin/eyes irritation hazards, limiting its application potential. In this study, a thermal melting method using non-toxic and low-cost stabilizer was proposed to fabricate PVC gel in approximately 10 min. Experimental results show that under the fabrication conditions optimized by Taguchi orthogonal array, the actuation performance of PVC gel is improved, with a contraction strain of 20.62%, an output force of 0.43 N, and a recovery response time of 1.416 s, all of which are superior to that prepared by traditional method. These results open a doorway for fast, affordable, and easily accessible fabrication technology of PVC gel actuators.

Effect of fiber annealing temperature on twisted and coiled UHMWPE actuator performance

Twisted and coiled polymer (TCP) actuators are flexible, wearable, and cost effective. However, the effects of annealing temperature on the properties of these devices are poorly understood. Thus, TCPs were prepared using ultra-high molecular weight polyethylene (UHMWPE) fibers and NiCr string and characterized. High-temperature annealing caused internal crystal-phase transformation, and annealing at 130 °C yielded a coiled fiber with optimized mechanical properties. Electromechanical tests confirmed that TCPs prepared from UHMWPE fibers annealed at 130 °C exhibited the best performance. Additionally, the voltage, displacement, tensile force, and temperature variation in the TCP fibers were recorded under different driving currents and pre-load forces to determine the optimal working conditions, and 1200-cycle life-span tests were carried out for validation. Finally, the driving performance of a TCP array was explored, and the range of motion, pressure, and possibility of lifting weights were tested using a model finger. Overall, the TCP array can be used as a soft actuated dexterous hand robot.

A Novel Cooling Design for an Agonistic–Antagonistic SMA Tendon-Driven Actuator

Shape memory alloys (SMAs) exhibit a unique property that undergoes deformation in response to temperature variation. This characteristic can be utilized via the application of a filiform SMA wire to tendon-driven robotic actuators for biomimetic joint movements. However, due to the inefficiencies in heat dissipation, conventional SMA tendon-driven actuators are characterized by their lower relaxation speeds than other actuators. This paper proposes a novel cooling design for an SMA tendon-driven actuator using thin-fin heat sinks based on a multi-layer wrapped SMA tendon design. In addition, the electric circuit and the controller are refined. Prototype devices are constructed to validate the performance of SMA-based actuators under PID control. The results indicate that the proposed design exceeds previous models in terms of relaxation performance by up to 5.8 times while also being able to stabilize at a target angle within 0.5 s under control.

Digital Light Processing 3D‐Printed Multilayer Dielectric Elastomer Actuator for Vibrotactile Device

AbstractDielectric elastomer actuators (DEAs) have emerged as promising components in the field of soft robotics. Multilayer DEAs can enhance the output performance compared to single‐layer DEAs, but the common layer‐by‐layer stacking methods are time‐consuming and likely susceptible to concerns about frequent dielectric breakdown. Herein, the one‐piece multilayer DEAs are directly fabricated via the digital light processing (DLP) 3D printing method, taking advantage of the precise and intricate printed structure. The study also focuses on the adjustable DLP printable resin formulation, aiming to achieve a DLP printed polyurethane acrylate (PUA)‐based dielectric elastomer (DE) material that exhibits desirable characteristics, such as an appropriate dielectric constant, modulus, and minimal hysteresis loss. The non‐pre‐stretch DLP‐printed cylindrical DEA demonstrates a significant blocked force of 270 mN and maintains 45% actuation performance at a frequency of 100 Hz, attributed to both the printed multilayer structure and the optimized formulation of the DE material. Moreover, the feasibility of DLP‐printed DEAs as vibrotactile devices is demonstrated. This work has advanced the development of rapid and efficient fabrication methods of multilayer DEAs using DLP printing, with enhanced force output and attractive applications in robotics and haptic interfaces.

Application of Modeling and Control Approaches of Piezoelectric Actuators: A Review

Piezoelectric actuators find extensive application in delivering precision motion in the micrometer to nanometer range. The advantages of a broader range of motion, rapid response, higher stiffness, and large actuation force from piezoelectric actuators make them suitable for precision positioning applications. However, the inherent nonlinearity in the piezoelectric actuators under dynamic working conditions severely affects the accuracy of the generated motion. The nonlinearity in the piezoelectric actuators arises from hysteresis, creep, and vibration, which affect the performance of the piezoelectric actuator. Thus, there is a need for appropriate modeling and control approaches for piezoelectric actuators, which can model the nonlinearity phenomenon and provide adequate compensation to achieve higher motion accuracy. The present review covers different methods adopted for overcoming the nonlinearity issues in piezoelectric actuators. This review highlights the charge-based and voltage-based control methods that drive the piezoelectric actuators. The survey also includes different modeling approaches for the creep and hysteresis phenomenon of the piezoelectric actuators. In addition, the present review also highlights different control strategies and their applications in various types of piezoelectric actuators. An attempt is also made to compare the piezoelectric actuator’s different modeling and control approaches and highlight prospects.

The Electrochemical Actuation Performances of Nanoporous Ternary AlCoCu Alloy with a Unique Nanosheet Structure.

Compared to traditional actuators (such as piezoelectric ceramics), metal actuators possess the advantages of a low energy consumption, large strain amplitude, and high strain energy density. However, most of the existing metal actuators with an excellent comprehensive performance are composed of precious metals, which are limited by high costs and have almost no possibility for large-scale production in the future. This study focuses on non-precious metal materials and exploits a one-step chemical dealloying method to prepare bulk nanoporous (NP) CoCuAl actuators (NP-CCA) from Al70Co20Cu10 alloy. The microstructure and actuation properties of the NP-CCA were analyzed in detail. The dense continuous nanoscale pores provide an excellent network connectivity for a large strain response, enabling the NP-CCA to achieve a strain amplitude of up to 1.19% (more than eight and two times that of NP-Pt and NP-Ag, respectively), comparable to precious metal actuators. In addition, the NP-CCA possesses a high strain energy density, which is prominent in many precious metal actuation materials (such as NP-Au, NP-Ag, and NP-Pt).

Research of the Performance of a Hydraulic Actuator Based on an Acoustic Power Analysis

The powered roof support in a mining complex protects machines and people from the harmful effects of the rockmass. The design of the powered roof support should be strictly prepared for adverse working conditions. This especially applies to the construction of the hydraulic actuator, which is designed to transfer uncontrolled load relief. The hydraulic actuators and an adequately selected safety valve determine the requirements for safe work. The study analyses the hydraulic actuators based on the signal obtained from the dynamic impact. The signal obtained from the load of the powered roof support in the bench tests allowed us to determine the opening time of the safety valve, which is not much different than the time of the pressure increase. Until now, the valve’s operation has been primarily analysed regarding pressure increase. This research was intended to determine whether introducing the sound power method for developing powered roof support research in the near future would be helpful. The sub-piston pressure increased during bench testing, generating a dynamic impact signal. The analysed results of the sound power tests in terms of their suitability for the development of standards related to powered roof support. This paper describes a new approach to research on powered roof support. Determining the acoustic power based on bench tests for the hydraulic actuator of a powered longwall support is ground-breaking research. The research results pave the way for new technologies based on acoustic information.

Experimental Study on Double-Joint Soft Actuator and Its Dexterous Hand.

In this paper, we propose a pneumatic double-joint soft actuator based on fiber winding and build a dexterous hand with 11 degrees of freedom. Firstly, soft actuator structural design is carried out according to the actuator driving principle and gives the specific manufacturing process. Then, an experimental analysis of the bending performance of a single soft actuator, including bending angle, speed, and force magnitude, is carried out by building a pneumatic control experimental platform. Finally, a series of dexterous robotic hand-grasping experiments is conducted. Different grasping methods are used to catch the objects and measure the objects' change in height, length, and rotation angle during the experiment. The results show that the proposed soft actuator is more consistent with the bending rule of human fingers, and that the gestures of the dexterous hand are more imaginable and flexible when grasping objects. The soft actuator can carry out horizontal and vertical movements, and rotation of the object in the dexterous hand, thus achieving better human-computer interaction.

Nonlinear position control of electro-hydraulic servo system based on lyapunov robust integral backstepping controller

In electro-hydraulic servo systems (EHSS), high nonlinearity and time-varying features limit the hydraulic actuator performance. In feedback-based systems, linearization reduces nonlinearities. Their cancellation may produce instability when modeling uncertainty exists. This work uses a robust nonlinear controller based on Lyapunov theory to control the nonlinear position of the electro-hydraulic servo system (EHSS). The dynamics of the system were modeled as extensively as possible, and then a simplified mathematical model based on the EHSS dynamics was created for the controller design. Integral backstepping was used to design the nonlinear robust controller utilizing the Lyapunov theory of nonlinear systems. Lyapunov functions theoretically ensured closed-loop stability. Comparative simulation analysis and experimental investigation in real-time with the proportional integral derivative (PID) controller optimized offline for position tracking control were carried out. Besides tracking performance and steady-state error, the mean square error (MSE), the root mean square error (RMSE), the maximum absolute value of tracking errors and the standard deviation of tracking errors (σ) was utilized to evaluate the controllers’ performance. The simulation analysis and experimental verification were accomplished under various sinusoidal trajectories using different testing conditions (amplitudes, frequencies, and external disturbance), in all testing conditions the effectiveness of the robust nonlinear integral backstepping controller was demonstrated.

Largely deformable torsional soft morphing actuator created by twisted shape memory alloy wire and its application to a soft morphing wing

We present a new type of torsional soft morphing actuator designed and fabricated by twisted shape memory alloy (SMA) wires embedded in polydimethylsiloxane matrix. The design and fabrication process of the proposed soft morphing actuator are presented with investigations of its working mechanism. Actuation performance was evaluated with respect to the temporal response, the maximum torsional deformation under an applied electric current, and various design parameters including the twist direction, wire diameter, helical pitch of the SMA wire, and the actuator’s thickness and length. We demonstrate potential applications of the proposed soft morphing actuator as a soft morphing wing and airfoil. The proposed actuator will aid in the development of soft actuators, soft robotics, and other relevant scientific and engineering applications.

Fully 3D-printed tortoise-like soft mobile robot with muti-scenarios adaptability.

Soft robotic systems are well suited to unstructured, dynamic tasks and environments, owing to their ability to adapt and conform without damaging themselves or their surroundings. These abilities are crucial in areas such as human-robot interaction，simplification of control system and weight reduction. However, as the requirements increase, the drawbacks of existing soft mobile robots such as single locomotion mode and application scenarios, manufacturing difficulties and low energy conversion efficiency gradually emerge.
Based on the current shortcomings of soft robots, this paper designs and proposes a fully 3D-printed tortoise-like soft mobile robot with muti-scenarios adaptability. The robot uses a Bionic Tortoise Leg Actuator structure that enables simultaneous bending of the actuator in both directions, simplifying robot control and increasing the maximum bending angle achievable. In addition, a reconfiguration design solution has been proposed to enable the robot to implement two bionic modes for land and sea tortoises, adapting to move on hard and soft surfaces and in water, enabling it to move in amphibious and complex environments. The performance of the pneumatic soft actuators are also improved by an improved Digital Light Processing method that enhances the maximum strain of the 3D printed soft material.
The prototype was tested to give maximum movement speeds for different gaits and environments, demonstrating that the fully 3D printed turtle-like soft-mobile robot designed in this paper is highly adaptable to multiple scenarios. The robot studied in this paper has a wide range of applications, with potential applications including navigation in a variety of domain environments, inspection of large underground oil and gas pipelines, and navigation in high temperature, high humidity and strong magnetic field environments or in military alert conditions.&#xD.

Solvent-exchange triggered hydrogen bond activation strategy toward self-adaptive strong and tough organohydrogel artificial muscle

Hydrogel actuators have aroused tremendous interests in various fields such as artificial muscles, biomedicine and wearable devices. However, hydrogel actuators face persistent challenges due to their intrinsic weak and hydrophilic networks, which result in brittle and weak mechanical properties after swelling. Here, we proposed a solvent-exchange hydrogen bond activation strategy to fabricate a highly strong and tough self-adaptive organohydrogel actuators (SOA). The glycerol releasing and water retention triggers abnormal swelling of SOA due to the cross-linking of tannic acid (TA) and polyvinyl alcohol (PVA) nanofibrillar network. After the hydrogen bond activation between PVA and TA, SOA shows a denser and porous nanofibrillar network with high tensile strength (5.4 ± 0.2 MPa), high fracture energy (134.9 ± 7.6 kJ/m2), and high toughness (18.5 ± 0.7 MJ/m3). Owing to its good processibility, an anisotropic multi-filament twisted fiber actuator that exhibits ultra-high modulus (83.5 ± 2.6 MPa) and humidity-sensitive actuation performance was developed. The proposed solvent-exchange strategy shows great potential for the rational design and fabrication of bionic strong and tough artificial muscles.

From Nature to Technology: Exploring Bioinspired Polymer Actuators via Electrospinning.

Nature has always been a source of inspiration for the development of novel materials and devices. In particular, polymer actuators that mimic the movements and functions of natural organisms have been of great interest due to their potential applications in various fields, such as biomedical engineering, soft robotics, and energy harvesting. During recent years, the development and actuation performance of electrospun fibrous meshes with the advantages of high permeability, surface area, and easy functional modification, has received extensive attention from researchers. This review covers the recent progress in the state-of-the-art electrospun actuators based on commonly used polymers such as stimuli-sensitive hydrogels, shape-memory polymers (SMPs), and electroactive polymers. The design strategies inspired by nature such as hierarchical systems, layered structures, and responsive interfaces to enhance the performance and functionality of these actuators, including the role of biomimicry to create devices that mimic the behavior of natural organisms, are discussed. Finally, the challenges and future directions in the field, with a focus on the development of more efficient and versatile electrospun polymer actuators which can be used in a wide range of applications, are addressed. The insights gained from this review can contribute to the development of advanced and multifunctional actuators with improved performance and expanded application possibilities.

Gold nanowire mesh electrode for electromechanical device

Ionic polymer-metal composite (IPMC) actuators were prepared with Nafion film as the ionic polymer and gold nanowire (Au-NW) mesh film as the metal electrodes by hot-pressing, which shortened preparation time within 1 h. As a reference, IPMC actuator consisting of Nafion film and gold foil (Au-foil) was also prepared. Au-NW mesh film can be an electrode with thinner (about 150 nm) and lower surface resistivity (about 0.5 Ω sq−1) than the conventional electrode prepared by electroless plating. Larger contact area of the Au-NW mesh electrode than the Au-foil electrode resulted in better actuation performance (60% larger peak-to-peak displacement in actuation). It was confirmed that the transformation behavior of Au-NWs differed depending on the external stimuli condition. Namely Au-NWs transformed to Au nanoparticles in the case of the heat stimulus only. Meanwhile, Au-NWs transformed to plates in the case of the heat and pressure stimuli. While higher temperature improved the adhesion of Au-NW mesh electrode to the Nafion surface, it induced the transformation of nanowire to plates. The IPMC actuator that the Au-NW mesh electrodes were hot-pressed at 90 ºC exhibited the highest capacitance and the largest peak-to-peak displacement in actuation. This research expanded the application field of gold nanowires to the electromechanical devices.

Effect of Low-Pass Filtering on Passivity and Rendering Performance of Series Elastic Actuation.

We study the effect of low-pass filtering on the passivity and performance of series elastic actuation (SEA) under velocity-sourced impedance control (VSIC) while rendering virtual linear springs and the null impedance. We analytically derive the necessary and sufficient conditions for the passivity of SEA under VSIC with filters in the loop. We demonstrate that low-pass filtered velocity feedback of the inner motion controller amplifies the noise at the outer force loop, necessitating the force controller also be equipped with low-pass filtering. We derive passive physical equivalents of the closed-loop systems to provide intuitive explanations of the passivity bounds and to rigorously compare the performance of controllers with and without low-pass filtering. We show that, while low-pass filtering improves the rendering performance by decreasing the parasitic damping effects and allowing for higher motion controller gains, it also introduces more strict bounds on the range of passively renderable stiffness. We experimentally verify the passive stiffness rendering bounds and performance improvements for SEA under VSIC with filtered velocity feedback.

Performance of a photothermal actuator based on molecular absorbers dissolved in eicosane

Performance of a photothermal actuator based on molecular absorbers dissolved in eicosane