Performance Of Actuator Research Articles

Clutchable Fabric Actuator for Energy‐Efficient Wearable Robots

AbstractEnergy‐efficient yet energy‐dense soft actuators are essential for untethered wearable robots. This work reports a fabric‐like actuator, combining shape memory alloy (SMA) springs and electrostatic clutches (ESClutches). The SMA springs provide high force density, with only 18 g of materials generating 40 N of force at actuation strains of over 35%, but requiring 78 W of power to hold that strain. The ESClutches cannot generate motion on their own, but can maintain the force and contraction generated by SMAs consuming only a few mW, thus allowing the SMAs to be turned off. By combining SMAs and ESClutches, a soft wearable fabric actuator is developed with force and stroke suited for an upper‐limb soft exoskeleton, able to lock in any given position using negligible power. The design is scalable: the number and dimensions of the SMA springs and of the ESClutches can be chosen to meet size and actuator performance requirements. This work reports two wearable use cases, where the combined SMAs and ESClutches consume over 70% lower power than SMAs alone.

Modelling and experimentation of failure modes to obtain safe operating range for improved dielectric elastomer actuation performance

Abstract Dielectric elastomers (DEs) possess high energy density, lightweight, and low response time making them suitable material candidatures for electromechanical transducers (ET). Performance enhancement of ET necessitates escalated electrical load making prone to failure and subsequently hindering reliability and life cycle. Existing models towards failure mitigation focus on mechanical and electrical loads individually with constant relative permittivity, whereas DEs undergoes combined loading and stretch-electrostriction in real-time application. This study aims to identify safe design and operating parameters by addressing various modes of failures under combined loads and stretch-electrostriction. Under combined load, pre-strain emerges as a crucial parameter to reduce EMI, while extensive pre-strain leads to diminish thickness which in turn promotes electrical breakdown of elastomer. The optimized design for DEs exhibit substantial failure suppression at a pre-strain value of 1.7 ( λ pre ) under maximum electrical load of 37.66 MV / m ( E max ). The efficacy of optimized parameters for the failure suppression is verified through an in-house fabricated planar actuator. Operation within the identified range of parameters is observed to enhance the reliability and lifespan of DE-actuators, marking a noteworthy advancement in the field of soft robotics.

Multistimuli-Responsive Soft Actuators with Controllable Bionic Motions.

Soft actuators with biomimetic self-regulatory intelligence have garnered significant scientific interest due to their potential applications in robotics and advanced functional devices. We present a multistimuli-responsive actuator made from a carbon nitride/carbon nanotube (CN/CNTs) composite film. This film features a molecular switch based on reversible hydrogen bonds, whose asymmetric distribution endows the film with the ability to absorb water unevenly and convert molecular motion into macroscopic movement. By incorporating carboxylated CNTs, the film demonstrates improved mechanical properties and actuation performance. Under ambient humidity stimuli, the actuator can autonomously generate walking and tumbling motions. The CN/CNTs composite film's actuating behaviors are programmable, enabling diverse deformation modes and complex biomimetic movements. Additionally, the film exhibits excellent photothermal conversion efficiency (74.10 °C/s), allowing for temperature and light-responsive actuation, which can be remotely controlled in real time. These features have enabled the creation of soft robots capable of complex biomimetic actions such as jumping, directional movement, and transporting objects. This research broadens the potential applications of CN-based actuators and paves the way for the development of intelligent soft robots.

Bending and sensing performances of electro-ionic soft actuators based on carboxylated cellulose nanofibers reinforced with graphene nanoplatelets

Abstract Soft robots not only possess greater degrees of freedom and the capability for continuous transformation, but they also offer exceptionally high safety in human-robot interactions, avoiding harm to the human body. Soft actuators are essential for developing high-performance soft robots, offering significant bending deformation, rapid response times, and prolonged operational capabilities. Herein, we present an ionic electroactive soft actuator based on functional cellulose nanofibers, graphene nanoplatelets, and ionic liquid. The proposed actuator achieved a large displacement about ±8 mm under 2.0 V at 0.1 Hz, with long working stability (98% of initial peak displacement maintained after 1260 cycles of cycling). The human-robot interaction applications of this actuator were explored by simulating human fingers. More importantly, the static and dynamic sensing performances of the actuator were investigated, finding that it generated a sensing voltage of 0.37 V at a vibration displacement of only 1.75 mm. The designed actuator provides a promising approach for developing high-performance soft robots, soft actuators, flexible sensors, and flexible active devices.

Modeling and Validation of the Sealing Performance of High-Pressure Vane Rotary Actuator

The EHRA (Electro-Hydraulic Rotary Actuator), using a vane rotary actuator, has the advantages of a high torque density and integration and is expected to become a joint actuator for robots. This research focuses on the sealing characteristics of various parts of a vane rotary actuator. The average Reynolds equation was used to analyze the leakage characteristics at the gap. A detailed theoretical analysis was conducted on the internal leakage mechanism of a vane rotary actuator using an X-ring as the dynamic seal for the rotor vane. According to the path of internal leakage, different sealing forms are considered as a series or parallel, and the Newton iteration method is used to obtain the total internal leakage characteristics of a vane rotary actuator. It was also considered that the deformation of the vane rotary actuator caused a thicker gap, leading to an increase in internal leakage. The calculation results are consistent with the experimental data. The analysis results indicate that when estimating the internal leakage of a vane rotary actuator, it is necessary to take the pressure of the high-pressure chamber and output shaft position as inputs. This research provides a reference for an analysis of the method of internal leakage for vane rotary actuators. It provides theoretical support for designing a vane rotary actuator with more minor internal leakage and a higher volumetric efficiency.

Design and Performance Analysis of A Linear Switched Reluctance Motor Considering End Effects

Introduction: In recent years, linear actuators have gained significant attention due to their ability to provide direct linear movement without the need for motion transformation devices. One significant challenge in the design and modeling of linear actuators is the occurrence of longitudinal end-effects. The finite length of the translator stack in linear actuators causes an unbalanced phase force, leading to discrepancies between the phases at the end and center of the actuator. Neglecting these end-effects can lead to inaccuracies in the actuator's performance and control. Methods: The objective of this study is to develop a comprehensive approach for the design, sizing, and modeling of the actuator to ensure optimal performance. An energy conversion procedure calculates the thrust force and determines the actuator's geometrical parameters. A numerical model based on the finite element method is developed to analyze the actuator's magnetic behavior and establish its characteristics. Furthermore, a thorough analysis of the end effect is conducted using two-dimensional finite element analysis. Results: To accurately capture the actuator's dynamic response and enable precise control, a mathematical model is formulated, incorporating the nonlinear behavior of inductance and incorporating the end effect factor. The proposed model demonstrates high accuracy and provides a solid foundation for the control of the linear switched reluctance actuator. Conclusion: Overall, this study contributes to the advancement of direct drive systems for industrial applications by providing a detailed design procedure and an accurate modeling approach for the linear actuator, enabling more efficient and precise control strategies.

High Cycle Performance of Twisted and Coiled Polymer Actuator

High Cycle Performance of Twisted and Coiled Polymer Actuator

Recyclable Chitosan-Modified Cellulose Fiber Porous Structure for Sensitive and Robust Moisture-Driven Actuators and Automatic Cooling Textiles.

Moisture-driven actuators featuring programmable stimuli-responsiveness and a rapid response have garnered substantial research attention. Cellulose-based actuators face challenges, including prolonged and unstable responsiveness, along with inadequate interfacial bonding. Herein, we developed a bilayer structured moisture actuator by integrating multiscale cellulose fibers with chitosan. The protonated chitosan forms strong electrostatic attractions with negatively charged cellulose nanofibrils (CNF), achieving a robust interfacial interaction. Leveraging the hierarchically porous structure and varying hygroscopicity of microfibrillated cellulose (MFC) and CNF, the film establishes an effective wettability gradient, enabling a stable and rapid moisture actuation performance. The bilayer film exhibits large deformation toward moisture with a bending angle of 60°, a short response time of 12 s, good stability over 50 wetting and drying cycles, and promising recyclability. Harnessing these advantageous properties, the bilayer film was demonstrated for its applications in automatic cooling textiles, contactless electrical switches, and artificial moisture-activated muscles, showing great potential for practical use.

Finite‐Element Analysis of an Antagonistic Bistable Shape Memory Alloy Beam Actuator

A finite‐element (FE) analysis of the active bistability of an antagonistic shape memory alloy (SMA) beam actuator of TiNiCu is presented. The actuator comprises two coupled SMA beams that are clamped at both ends and coupled in their center by a spacer having different memory shapes being deflected in opposite out‐of‐plane directions. The actuator is characterized by two equilibrium positions. To determine bistable behavior as a function of geometrical parameters, a force criterion is defined by the coupling force of the beams in austenitic and martensitic states. Bistable behavior is achieved, if the coupling force does not change sign in the entire displacement range. This implies that the austenitic beam dominates the opposing martensitic beam. Thus, selective heating of the SMA beams results in a snap‐through motion of the coupled SMA beams. Depending on which of the two beams is in austenitic state, either of the two equilibrium positions is reached without the need for an external force. It is demonstrated that geometrical parameters like initial predeflection and spacer length have a crucial effect on the bistable performance. Bistable regions as well as critical limits characterized by geometry‐dependent stability ratios, beyond which the actuator's performance becomes monostable, are identified.

Thermal hysteresis enhancement and dispersion thermal stability in paraffin actuators: Comparison of pan-nanofibers vs metal oxide nanoparticles use

In this research, the possibility of thermal property enhancement of paraffin actuators with nanofiber and metal oxide nanoparticle addition was experimentally evaluated. Besides pure paraffin compound, paraffin mixed with the CuO, Fe3O4, ZnO, Al2O3, and electrospun polyacrylonitrile (PAN) nanofiber nanoparticles were used, and a significant hysteresis improvement at first-level measurement was observed as 24.6, 26.2, 20.0, 29.2, and 30.8 % sequentially for the samples respectively compared with pure paraffin. Thermal dispersion stability of the nanocomposites was comprehended via computer tomographic (CT) investigation. The excessive precipitation of CuO, Fe3O4, and ZnO particles in the paraffin nanocomposite was observed. Precipitation of PAN Nanofiber- and Al2O3-Paraffin nanocomposite was not visually detectable via CT throughputs. The effect of thermal dispersion stability on the hysteresis performance of the nanocomposites was also investigated to ensure long-term consistent hysteresis performance advantages in paraffin actuators. Thermal dispersion stability effect on hysteresis performance of paraffin actuators with CuO, Fe3O4, ZnO, Al2O3, and PAN nanofiber nanocomposite paraffin compounds showed losses as 14.3, 14.6, 5.8, 4.3 and 2.2 % sequentially for the samples respectively.

Environmentally Friendly, Dual-Responsive Actuator Based on Nafion, Carboxylated Multiwalled Carbon Nanotubes, and Polyethylene.

As a type of smart material, flexible stimulus-responsive actuators have become a hot research topic nowadays. However, flexible actuators responding to a single stimulus source are susceptible to external perturbations, which may lead to an unstable function or even failure. Therefore, in this paper, we proposed a bilayer actuator that can be driven by both humidity and light by combining the humidity-sensitive Nafion, carboxylated multiwalled carbon nanotubes (cMWCNT) with excellent photothermal conversion properties, and commercial polyethylene (PE) tape with good humidity insensitivity and thermal expansion. First, the cMWCNT-Nafion film was prepared by a solution casting method and bonded together with PE tape to obtain a bilayer actuator. Then, the effects of the cMWCNT mass fraction and film thickness on the humidity and light response performance of the bilayer actuator were investigated. The optimal ratios of raw materials were obtained for different stimulation sources, respectively. Furthermore, the performance of the bilayer actuator with the optimal ratios was tested; it was verified that the proposed dual-responsive actuator can realize different degrees of bending deformation under different relative humidity (RH) and ultraviolet (UV) light intensity with good stability. Finally, the application potential in multiple scenarios was further verified by applying the prepared cMWCNT-Nafion/PE bilayer actuator to a smart window, crawling robot, and flexible gripper. This paper will provide a meaningful reference for the development and performance optimization of high-performance dual-responsive actuators.

Actuation Performance and Versatility of Photothermally Driven Organic Crystals.

Photomechanical crystals exhibit mechanical motion upon light irradiation and may thus find applications as actuators. Over the last decades, many photomechanical organic crystals have been developed, commonly via photochemical reactions, particularly photoisomerization. However, photochemical crystal actuation is associated with several drawbacks, including a limited number of available crystals, slow actuation speed (< 5 Hz), and narrow wavelength range (< 550 nm). Such constraints have hindered the widespread use of crystals as actuation materials. In this minireview, we focus on crystal actuation by employing more universal physical phenomena (the photothermal effect and photothermally resonated natural vibration) and quantitatively evaluate actuation performance. Both mechanisms, particularly the latter, outperformed conventional photomechanical crystal activation in terms of both speed (maximum: 1,350 Hz) and the useful wavelength range (ultraviolet to near-infrared). The oscillation frequencies of the crystals exceeded those of polymers, efficiently filling the gap between soft and hard materials. Both the photothermal effect and natural vibration can actuate any crystal that absorbs light. These two versatile physical actuation mechanisms could expand 40 years of research on photomechanical crystals-which had been based on photochemical reactions-from the realm of chemistry into engineering and lead to their practical applications in actuators and soft robots.

Actuation Performance and Versatility of Photothermally Driven Organic Crystals

Photomechanical crystals exhibit mechanical motion upon light irradiation and may thus find applications as actuators. Over the last decades, many photomechanical organic crystals have been developed, commonly via photochemical reactions, particularly photoisomerization. However, photochemical crystal actuation is associated with several drawbacks, including a limited number of available crystals, slow actuation speed (&lt; 5 Hz), and narrow wavelength range (&lt; 550 nm). Such constraints have hindered the widespread use of crystals as actuation materials. In this minireview, we focus on crystal actuation by employing more universal physical phenomena (the photothermal effect and photothermally resonated natural vibration) and quantitatively evaluate actuation performance. Both mechanisms, particularly the latter, outperformed conventional photomechanical crystal activation in terms of both speed (maximum: 1,350 Hz) and the useful wavelength range (ultraviolet to near‐infrared). The oscillation frequencies of the crystals exceeded those of polymers, efficiently filling the gap between soft and hard materials. Both the photothermal effect and natural vibration can actuate any crystal that absorbs light. These two versatile physical actuation mechanisms could expand 40 years of research on photomechanical crystals—which had been based on photochemical reactions—from the realm of chemistry into engineering and lead to their practical applications in actuators and soft robots.

Evaluation of fabric-based pneumatic actuator enclosure and anchoring configurations in a pediatric soft robotic exosuit.

Soft robotics play an increasing role in the development of exosuits that assist, and in some cases enhance human motion. While most existing efforts have focused on the adult population, devices targeting infants are on the rise. This work investigated how different configurations pertaining to fabric-based pneumatic shoulder and elbow actuator embedding on the passive substrate of an exosuit for pediatric upper extremity motion assistance can affect key performance metrics. The configurations varied based on actuator anchoring points onto the substrate and the type of fabric used to fabricate the enclosures housing the actuators. Shoulder adduction/abduction and elbow flexion/extension were treated separately. Two different variants (for each case) of similar but distinct actuators were considered. The employed metrics were grouped into two categories; reachable workspace, which includes joint range of motion and end-effector path length; and motion smoothness, which includes end-effector path straightness index and jerk. The former category aimed to capture first-order terms (i.e., rotations and displacements) that capture overall gross motion, while the latter category aimed to shed light on differential terms that correlate with the quality of the attained motion. Extensive experimentation was conducted for each individual considered configuration, and statistical analyses were used to establish distinctive strengths, weaknesses, and trade-offs among those configurations. The main findings from experiments confirm that the performance of the actuators can be significantly impacted by variations in the anchoring and fabric properties of the enclosures while establishing interesting trade-offs. Specifically, the most appropriate anchoring point was not necessarily the same for all actuator variants. In addition, highly stretchable fabrics not only maintained but even enhanced actuator capabilities, in comparison to the less stretchable materials which turned out to hinder actuator performance. The established trade-offs can serve as guiding principles for other researchers and practitioners developing upper extremity exosuits.

Reinforced Magnetic-Responsive Electro-Ionic Artificial Muscles by 3D Laser-Induced Graphene Nano-Heterostructures.

Efficient ion transport and enriched responsive modals via modulating electrochemical properties of conductivity and capacitance are essential for soft electro-ionic actuators. However, cost-effective and straightforward approaches to achieve expedited fabrication of active electrode materials capable of multimodal-responsiveness remain limited. Herein, this work reports the one-step ultrafast laser direct patterning method, to readily synthesize electro- and magneto-active electrode material, derived from the unique cobalt-phosphorus co-doped core-shell heterostructures within 3D graphene frameworks, for fulfilling the dual-mode responsive electro-ionic actuators. The designed nanofiber-structured heterointerfaces across electrodes and electrolytes further promote highly efficient electron/ion transfer. The developed soft actuator exhibits superior actuation performance of peak-to-peak displacement to 13.08mm under an ultra-low ±0.5V, with doubled direct current deflection under 200 mT at 1V, an ultrafast response of 1.38 s and long-term stability (>90% retention for ≈106000 cycles), even detectable bending to ≈280µm under exceptional ±10mV. The promising demonstration of promoting differentiation and proliferation of stem cells under mechanical strain and electrical stimuli, sheds more light as well on the possibility of facilitating biomedical soft robotics with ultrahigh actuation performance.

Water vapor responsiveness of chitosan: An experimental and simulation analysis.

Stimuli-responsive polymers have gained significant research interest in recent years owing to their potential applications in diverse areas. Here, we present a study on the actuation characteristics of chitosan-based free-standing films that exhibit full reversibility and repeatability in response to water vapor exposure. The effect of pH of the water and the degree of cross-linking of the chitosan films on the actuation performance is studied. In the case of free-standing polymer film-based actuators, the primary driving force behind actuation is understood to be the differential strain induced by the gradient in volume changes across the thickness of the film. To understand it further, we conducted full atomistic molecular dynamics simulation studies to explore water absorption and adsorption into the chitosan matrix. Our simulations revealed an accumulation of water molecules in the surface layer that rapidly desorb when shielded from water vapor. Furthermore, estimates of the energy gain resulting from the adsorption of water on the surface suggest that it is adequate to drive the shape change of the actuator when subjected to asymmetric exposure to water vapor. This finding supports the fact that the adsorbed layer of water on the surface of the chitosan film plays a role in actuation.

Improvement of tracking performance of SMA-actuated rotary actuator via thermocouple delay compensation using adaptive predictor

This paper investigates the impact of bounded and unknown delay of a J-type thermocouple sensor on controlling a Shape Memory Alloy (SMA) actuated rotary actuator. To compensate for the delay, a nonlinear adaptive predictor is utilized, which predicts the exact temperature of the present moment using the output of the sensor. A robust sliding mode control is then designed to track the reference input, which is the rotation angle of the pulley. In addition to temperature estimation, the inner system identification algorithm of the predictor identifies the heat transfer coefficients of the experimental setup. Experimental tests demonstrate the precise control of the proposed algorithm. The tracking error of the adaptive predictor with sliding mode control is compared to that of a regular sliding mode controller without temperature delay compensation consideration, showing the superior performance of the proposed control algorithm.

Interfacial modulation of Ti3C2Tx MXene using functionalized cellulose nanofibrils for enhanced electrochemical actuation

Electrochemical actuators (ECAs) with low voltage actuation and large deformation ranges generally require electrode materials with high ion kinetic energy transport, high charge storage, and excellent electrochemical-mechanical properties. However, the fabrication of such actuators remains a major challenge. In the present work, hybrid electroactive films were fabricated by self-assembling one-dimensional functionalized cellulose nanofibrils (CNFs) with two-dimensional MXene (Ti3C2Tx). The obtained ECA actuators fabricated by carboxymethylated cellulose nanofibrils (consisting of -CH2COO−surface groups) with Ti3C2Tx integrate excellent curvature (0.1041 mm−1), mechanical strength (21.68 MPa), a bending strain of 0.50 %, and a good actuation displacement of 9.3 mm at a low voltage range of −0.6 to 0.3 V. This may be attributed to the enlarged layer spacing (15.34 Å), which makes the embedding and transport of H+ easier, and excellent adaptivity of mechanical properties achieved by molecular-scaled strong hydrogen bonding, leading to better actuation performance. This study provides a potential research direction for the preparation of ECAs with large actuation deformation.

Surface charge characteristics in a three-electrode surface dielectric barrier discharge

The surface charge characteristics in a three-electrode surface dielectric barrier discharge (SDBD) are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the most commonly used SDBD structure for airflow control, with an exposed electrode supplied with sinusoidal AC high voltage, a grounded encapsulated electrode and an additional exposed electrode downstream supplied with DC voltage. The ionic wind velocity and thrust can be significantly improved by increasing DC voltage although the plasma discharge characteristics are virtually unaffected. It is found that the negative charges generated by the discharge of the three-electrode structure accumulate on the dielectric surface significantly further downstream in an AC period compared to the actuator with a two-electrode structure. The negative charges in the downstream region increase as the DC voltage increases. In addition, the DC voltage affects the time required for the positive charge filaments to decay. The positive DC voltage expands the ionic acceleration zone downstream to produce a greater EHD force. The amplitude of the DC voltage affects the electric field on the dielectric surface and is therefore a key factor in the formation of the EHD force. Further research on the surface charge characteristics of a three-electrode structure has been conducted using a pulse power to drive the discharge, and the same conclusions are drawn. This work demonstrates a link between surface charge characteristics and EHD performance of a three-electrode SDBD actuator.

Slot‐Die‐Printed Electroactive Polymer Actuators with High‐Strain Sensitivity for Soft Robotic Applications

AbstractIonic electroactive polymer gels are widely employed as actuators in soft robotics due to their ability to undergo rapid mechanical deformation under low‐voltage. How to improve the performance of the ionic electroactive polymer actuators is always the focus of research in this field. Optimizing the migration of ions within the actuator is crucial for enhancing the actuation performance. In this regard, this study innovatively introduces slot‐die‐printing technology to fabricate gel actuation layers characterized by high smoothness and uniform particle distribution, achieving seamless integration between the electrodes and gel actuation layers, while mitigating issues associated with ion accumulation due to polymer clustering. Furthermore, this study attempts to add lactic acid to the traditional CS‐PVA‐IL gel, effectively strengthening the connection between CS and PVA, and promoting smooth ion transport within the gel. The results demonstrate that the actuators prepared in this study achieved a high‐bending‐strain of 0.35%, with a retention rate of 91% for actuation displacement after 10 000 cycles, showcasing superior actuation performance compared to existing research. The fabrication method proposed in this study is simple and highly reproducible, making it suitable for widespread industrial application, and providing a new approach for future industrial production of soft robotics.