Performance Of Actuator Research Articles

Recent Advances of Soft Actuators in Smart Wearable Electronic‐Textile

AbstractSmart wearable electronic textiles integrate sensing, perception, and control modules, which enhance human adaptability to environmental stimuli and concurrently serve as extensions for limb capabilities. The flexible and programmable nature of soft actuators makes them an indispensable part of smart wearable electronic textiles. These textiles seamlessly combine various components, such as sensors and actuators, through a comprehensive integration of materials manufacturing, circuit control, and transmission design. Exciting applications in various fields such as healthcare, sports, the Internet of Things, and human‐machine interaction have been demonstrated globally. However, there is still a persistent challenge in enhancing the actuation capabilities of soft actuators while maintaining their wearability. A timely and comprehensive review of the progress of this field is provided. Several main aspects are covered: functional materials, stimulus mechanisms, performance improvement strategies, and wearable applications in human‐related areas. Furthermore, the major approaches and challenges for improving the performance of actuators are systematically summarized.

Hygro‐Dynamic and Conductive Actuator That Restructures and Heals by Water

AbstractThe prospects of endowing stimuli‐responsive materials with various life‐like behaviors are promoting the development of intelligent robotic and electronic devices. However, it is challenging to incorporate stimuli‐responsive actuating and healing capabilities into one single material system. Herein, the design and assembly of humidity‐responsive thin films composed of poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and sodium carboxymethyl cellulose (NaCMC) forming a conducting polymer composite through a physically cross‐linked and hydrogen‐bonded supramolecular network are described. Owing to its enhanced dynamics of hydrogen bonding at an elevated humidity, the PEDOT:PSS/NaCMC thin film exhibits a rapid humidity‐responsive actuating performance in an environment with humidity gradient, as well as a repairing function of the structural, mechanical, electrical, and actuating properties after being damaged through a humidifying‐drying cycle. Based on a combined analytical approach, a structural model is proposed for the rearrangement of the thin film when being exposed to stepwise humidity levels at multi‐length scales. Due to the structural rearrangement powered by humidity variations, the film exhibits tunable actuating and healing performance, which makes it a promising candidate material for applications in intelligent soft robotics such as artificial muscles.

Magnetically Active Bicontinuous Polymer Structures for Multiple Controlled Drug Delivery.

The targeted delivery of drugs using wireless navigable magnetic robots allows the delivery of drug molecules to be controlled non only in time but also in space, improving medical outcomes. The main disadvantages behind their use lies in the low amount of drug that can be transported and the single nature of drug that can be loaded (hydrophilic or hydrophobic). These considerations limit their use in co-delivery systems, now recognized to be very promising for many different pathologies. A magnetic bijel-like structure is developed to load and release different types of molecules (hydrophilic and hydrophobic). In this work, the use of ε-caprolactone is explored, which can polymerize, forming hydrophobic domains (oil phase). After mixing with iron oxide nanoparticles (NPs), the water dispersion creates a magnetic biphasic porous structure without phase separation. The resulting device shows good performance both in magnetic actuation and as a drug delivery system.

Experiment and simulation study on the functional fatigue of shape memory alloy beam actuators

The functional fatigue behavior of shape memory alloy (SMA) beam actuators is gaining importance as their utilization in engineering applications becomes more widespread. However, research on the functional fatigue behavior of SMA beam actuators under bending conditions is not as extensive as that on SMA wires. In this paper, an experimental study and theoretical analysis of the functional fatigue behavior of SMA beam actuators were conducted. A measuring method for bending deflection and an automatic thermal cyclic test bench was designed. A series of functional fatigue tests were conducted on SMA beam actuators under different bias load conditions and the functional fatigue patterns were obtained. The material damage factor is defined and calculated through specimen tests. By incorporating the damage factor to modify the existing constitutive model, a model considering functional fatigue and tension-compression asymmetry is obtained. Finite element analysis (FEA) is performed based on this modified model to simulate the actuating performance of SMA beam actuators and to compute the deflection at different numbers of cycles. Additionally, a small parameter study on the actuator shape is conducted using FEA. By comparing the FEA results with functional fatigue experimental data, the effectiveness of the modified model is validated, demonstrating its capability to describe functional fatigue and predict actuator lifespan.

Ionic Liquid Crystal-Polymer Composite Electromechanical Actuators: Design of Two-Dimensional Molecular Assemblies for Efficient Ion Transport and Effect of Electrodes on Actuator Performance.

We present the development of free-standing ionic liquid crystal-polymer composite electrolyte films aimed at achieving high-frequency response electromechanical actuators. Our approach entails designing novel layered ionic liquid-crystalline (LC) assemblies by complexing a mesomorphic dimethylphosphate with either a lithium salt or a room-temperature ionic liquid through the formation of ion-dipole interactions or hydrogen bonds. These electrolytes, exhibiting room-temperature ionic conductivities on the order of 10-4 S cm-1 and wide LC temperature ranges up to 77 °C, were successfully integrated into porous polymer networks. We systematically investigated the impact of ions and electrodes on the performance of ionic electroactive actuators. Specifically, the Li+-based liquid crystal-polymer composite actuator with PEDOT:PSS electrodes demonstrated the highest bending deformation, achieving a strain of 0.68% and exhibiting a broad frequency response up to 110 Hz, with a peak-to-peak displacement of 3 μm. In contrast, the ionic-liquid-based liquid crystal-polymer composite actuator with active carbon electrodes showcased a bending response at a maximum frequency of 50 Hz and a force generation of 0.48 mN, without exhibiting the back relaxation phenomenon. These findings offer valuable insights for advancing high-performance electromechanical systems with applications ranging from soft robotics to haptic interfaces.

A new model of thermo-mechanical actuation for twisted and coiled polymer muscles with initial curvature

The twisted and coiled polymer (TCP) artificial muscle is one type of novel soft actuator for mimicking natural skeletal muscle that can provide large linear and torsional actuation and energy density. Twisting and coiling are the pivotal steps in fabricating TCP muscles. The influence of twisting on the actuation response of TCP muscles has been extensively investigated recently. However, the influence of coiling remains unclear. Based on the finite strain theory, we establish a new thermo-mechanical actuation model for TCP muscles with initial curvature. The theoretical predictions based on the model align well with the finite element simulations, accurately capturing the actuation response of thermally-activated TCP muscles. It is revealed that twisting contributes positively to the actuation, while coiling has a passive effect. Geometrical parameters, such as the helix radius and helix angle, can effectively regulate the actuation performance of TCP muscles. Furthermore, an optimal bias angle is identified that maximizes both the recovery torque and the linear actuation. This study sheds light on the structural optimization design of TCP muscles.

A compound twisted and coiled actuators with payload-insensitive untwisting characteristics

Compound Twisted and Coiled Actuators (CTCAs) are promising candidates for artificial muscles due to their outstanding competences in producing large output forces and long strokes. However, as their thermal actuation performance depends on not only the driving temperature, but also the spandex deformation caused by the payload, it is rather difficult to obtain accurate actuation models for the conventional CTCAs and thus seriously restricts their control performance and application development. To tackle such difficulties, a CTCA with a novel strategic fabrication method is proposed in this work. Motivated by the kinetostatic performance of a stiffening spring with a high preload, the fiber draw ratio of the CTCA is significantly increased through pre-stretching the fiber during the fabrication process, which makes the thermal actuation performance of the CTCA insensitive to the external payload. The effectiveness of the proposed payload-insensitive characteristics of the CTCA is validated through experimental results, which shows that the CTCA has almost the same untwisting strain–temperature curves under different payloads. Consequently, a simplified yet accurate actuation model is obtained such that the displacement of the CTCA is mainly determined by the driving temperature within a meaningful range of payloads. Experiments are conducted to evaluate the accuracy of the actuation model and the model error is less than 7.6%. Such a simplified actuation model is implemented for the pose control of a 2-DOF CTCA-driven continuum robot joint module, in which the average steady-state error of the bending angle is less than 1.0∘.

Bending, electroadhesion and sensing performances of single compliant electrode dielectric elastomer actuator based on SEBS gel

Dielectric elastomer actuators (DEAs) have great potential for application in soft robotics due to their ability to undergo substantial deformations, rapid response times, and high energy density when subjected to external electrical stimuli. However, the application of DEAs in the field of soft grippers is limited by their restricted direct electro-bending capability, output force, self-sensing capacity, and pre-stretching requirement. In this study, we fabricated a single compliant electrode DEA (SCE-DEA) which was made by sandwiching a compliant electrode between two layers of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS)/white mineral oil (WO) dielectric elastomer films. The SCE-SEBS/WO was demonstrated to have the capacities of bending, sensing, and electroadhesion (EA). The SCE-SEBS/WO can be used in various soft actuator modes, such as the unipolar EA actuator, soft gripper, and soft vibrator. The grabbing mechanism of SCE-SEBS/WO-based soft grippers with opposite bipolar configuration is caused by electric field induced bending of SEC-SEBS/WO and subsequent electrostatic attraction between both SEC-SEBS/WO. The SEC-SEBS/WO based soft grippers have rapid response detachment, and ability to grasp various types of objects. Three-layer stacked SCE-SEBS/WO-60 (with 60 wt% of WO) exhibited 531 mN cm−2 of EA stress on the paper at 3.0 kV applied voltage, and the soft gripper made by four SCE-SEBS/WO-60 can successfully grab wood blocks weighing 162.4 g at 5 kV applied voltage. The sensing capacity of SCE-SEBS/WO based soft gripper was based on the bending strain dependent resistance changes of the compliant electrode. Our results provide new insights into the fabrication of DEA based soft grippers.

MXene-Based Soft Humidity-Driven Actuator with High Sensitivity and Fast Response.

Soft actuators possessing notable mechanical deformations, high sensitivity, and fast response speed play a crucial role in various applications, such as artificial muscles, soft robots, and intelligent devices. In this study, a smart humidity-driven actuator was successfully fabricated by utilizing MXene/cellulose nanofiber (CNF)/LiCl (MCL) through vacuum-assisted filtration with fast response speed and high sensitivity. Utilizing the excellent humidity responsiveness of MXene/CNF and the robust hygroscopicity of LiCl, the synergistic effect of these materials enhances the hygroscopic properties and response speed of the actuator. The MCL actuator demonstrates excellent actuation performance, fast deformation, and reliable cyclic stability. To illustrate the extensive potential of the soft actuator, a range of applications, from bionic devices to soft grippers and crawling actuators, are showcased. Remarkably, the crawling actuator demonstrates sustained crawling motion without necessitating a humidity switch, relying on the humidity gradient from water droplets, and exhibits spontaneous directional motions within a certain range, which makes it a promising prospect in the field of soft robotics.

Design and experiment of electromagnetic-hydraulic-rubber integrated vibration isolator

Low-frequency radiated noise, characterized by a distinctive “acoustic fingerprint” is generated when vibrations from marine machinery propagate through a ship’s hull into the ocean. This type of noise travels long distances with concentrated and stable energy, posing a significant threat to a ship’s acoustic stealth capabilities. Active-passive hybrid isolation is the primary method for reducing low-frequency radiated noise from ships; however, technical challenges remain, such as effectively integrating active and passive components, achieving high output force in a compact design, and addressing the poor linearity of actuator output at low frequencies. To address these issues, this paper presented an innovative electromagnetic-hydraulic-rubber integrated vibration isolator. Firstly, the study analyzed the dynamic characteristics of a two-degree-of-freedom isolation system and investigated the influence of active-passive hybrid vibration isolator parameters on control force and vibration reduction performance. Secondly, it was established that the magnetic circuit model and magnetic field strength expressions for the electromagnetic actuator using magnetic circuit analysis derive the analytical relationship between electromagnetic force, current amplitude, and frequency using the energy method. Subsequently, a mathematical model was developed for the rubber-hydraulic suspension component to examine its dynamic characteristics, hydraulic damping, and hydraulic force amplification transmission laws. Lastly, we organically combine the electromagnetic actuator with the rubber-hydraulic suspension and conduct a multi-physics joint simulation of the integrated vibration isolator using Comsol software to verify the effectiveness of the optimized design and vibration isolation control. Experimental research was carried out on the dynamic characteristics, output force properties, and fatigue characteristics of the integrated vibration isolator prototype. Results indicated that the established models and methods can achieve over 90% accuracy in predicting the performance of the electromagnetic actuator’s output force and exhibit good linearity within the 5–400 Hz range. The rubber-hydraulic suspension can achieve an amplification factor of up to 1.5 for the electromagnetic force while reducing the transmission of vibrations to the base. The research findings can enhance the low-frequency vibration isolation performance of marine machinery equipment and improve their acoustic stealth capabilities.

Optimizing Performance of PVC Gel Actuators: Temperature Influence and Characterizations

PVC gels are in high demand for actuators, so choosing the optimal route for preparing PVC gel is crucial. In this study, PVC gel samples were prepared using polymer PVC, plasticizer Di-butyl adipate (DBA), and solvent tetrahydrofuran (THF) at temperatures ranging from 40°C to 70°C. The samples obtained at different temperatures were labeled as PVC40, PVC50, PVC60, and PVC70. Rheological properties of all PVC gel samples were analyzed, revealing, that the rheological behavior of the PVC70 gel sample differed significantly from the others due to THF evaporation at 70°C, resulting in inadequate PVC gel preparation. However, PVC40, PVC50, and PVC60 gel samples were chosen for further characterizations, including scanning electron microscopy (SEM), actuation, and mechanical properties evaluation. Moreover, a self-assembled setup was fabricated using electrodes and PVC gel to test the performance of the planar actuator. The maximum displacement of PVC60 was measured at approximately 0.74 mm, with a response time of 0.75 sec under an applied voltage of 1000V. It was observed that the homogeneity of the gel and the solubility of the raw materials, based on resin were influenced by the reaction temperature, suggesting that uniformity could be achieved through dipole-dipole interactions or hydrogen bonding between PVC and DBA (Cl-H…. O=C). Finally, our findings have the potential to contribute to the development of innovative PVC gel actuators.

Effect of temperature softening on the actuation performance of twisted and coiled polymer muscles

Twisted and coiled polymer (TCP) artificial muscles represent a promising class of actuators capable of emulating natural skeletal muscle, offering substantial linear actuation and energy density. The actuation characteristics of the thermally-activated TCP muscle and twisted fiber are characterized experimentally, emphasizing the influence of the temperature-softening effect. We find that the recovered torque of twisted fiber increases monotonically with temperature while showing a non-monotonical variation with the fiber bias angle. The variations of actuation strain and end torque with three structural parameters of TCP muscles, i.e., fiber bias angle, helical angle, and spring index, are comprehensively investigated. An optimal bias angle and spring index are present. A significant temperature-softening effect of precursor fiber is observed; a polymer becomes softer and more pliable as the temperature increases. A thermo-mechanical model for predicting the effect of temperature-softening on TCP muscle is established and validated with experimental data. This work facilitates precise control and guides the structural optimization design of the thermally-activated TCP muscle.

Optimizing the fatigue‐resistant actuation performance of gel‐based bionic artificial muscles (GBAMs): A comparative study on crosslinking agents

AbstractThe study examined the impact of various calcium salts crosslinking agents on the fatigue‐resistant actuation performance of gel‐based bionic artificial muscles (GBAMs) that exhibited directional bending deflection and generated actuation force when electrically stimulated, thereby converting electrical energy into mechanical energy. Furthermore, a comparative investigation was carried out to examine the mechanical properties, electrochemical characteristics, microstructure, material composition, and actuation lifespan of GBAMs doped with various calcium salts, which were commonly found in biological muscles. Moreover, this research paper offered a comprehensive analysis of the mechanoelectric coupling's contribution towards optimizing the fatigue‐resistant actuation performance of the GBAM. The findings indicated that the GBAM, synthesized through the cross‐linking of calcium iodide doped with a 25% volume fraction of ethanol absolute, exhibited superior mechanical properties, electrochemical characteristics, microstructure, and actuation lifespan when compared to various other calcium salts. Hence, following a comprehensive comparison, it could be deduced that the fatigue‐resistant actuation performance of the GBAM, synthesized using calcium iodide doped with a 25% volume fraction of ethanol absolute as a crosslinking agent, exhibited the highest level of effectiveness when compared to the other four calcium salts.

A multi-point decentralized control for mitigating vibration of flexible space structures using reaction wheel actuators

The vibration with large amplitude and low frequency of the flexible space structures is prone to affect the attitude stability and pointing precision of the spacecraft. To mitigate the vibration of the flexible space structures, a multi-point decentralized control strategy using reaction wheel (RW) actuators is proposed and investigated in this paper. The motion equations of the solar array with multiple RW actuators are derived in modal coordinate representation. To suppress the overall response of the structure, the decentralized control strategy using RW actuators is designed based on the natural frequencies and mode shapes. The stability and the effect of closed-loop dynamic system is theoretically proved. The comparative studies under sun-pointing of the solar array and the rest-to-rest orbital maneuver conditions are presented to show the control performance of the RW actuators. The results indicate that, with 2% increase in total mass from the addition of the actuators, the vibration attenuation time can be decreased by 85.25% and 94.16% for the vibration excited by the sun-pointing and the rest-to-rest orbital maneuver, respectively. The experimental results demonstrate the effectiveness of the proposed decentralized control method. Theoretical analysis, numerical simulation and experimental study are conducted to demonstrate the validity of the proposed vibration mitigation approach and its potential application in the spacecraft design.

Optimizing electrode arrangement in plasma actuators: a study on induced velocity and efficiency

This study investigates the performance of two types of multi-encapsulated electrode (MEE) plasma actuators, compared to typical dielectric barrier discharge (DBD) plasma actuators, in quiescent air. The objective is to determine whether the multiple encapsulated structure can enhance the performance of the plasma actuator. In the present paper, flow characteristics are investigated by using particle image velocimetry (PIV) and Schlieren visualisation. In addition, the distribution of body force over the gas volume based on the Navier–Stokes equations is calculated from velocity measurements. The obtained results demonstrate that the starting vortex behavior is influenced by electrode arrangement. Specifically, it can be observed that when the first encapsulated electrode is positioned closer to the exposed electrode, then a significantly higher induced velocity can be obtained compared to the baseline condition. In fact, the induced velocity can be increased by up to 1.5 times under this optimize configuration. These results highlight the importance of electrode arrangement in the plasma actuator design. Based on body force estimation, MEE plasma actuators exhibit a significantly higher momentum transfer, particularly in the wall normal direction. The investigation on the mechanical efficiency also reveals that the optimized configuration proposed in the present study can significantly enhance the efficiency. In fact, a four-fold increase in maximum efficiency compared to the typical configuration is observed. These results suggest that the proposed configuration could be considered a promising solution for improving the mechanical efficiency of plasma actuators.

Design Optimization of Printed Multi-Layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

Erratum: Optimization of Dynamic Performance of a Solenoid Actuator in a CNG Injector Based on the Effects of Key Design Parameters

Erratum: Optimization of Dynamic Performance of a Solenoid Actuator in a CNG Injector Based on the Effects of Key Design Parameters

Response of Moisture and Temperature Diffusivity on an Orthotropic Hygro-thermo-piezo-elastic Medium

This research explores the complex interaction between piezoelectric waves and heat-moisture diffusion within a semi-infinite piezoelectric material under hygro-thermal conditions. By employing a two-dimensional Cartesian framework, novel governing equations for a thermo-piezoelectrically orthotropic medium influenced by moisture effects are developed. Accurate representations for key parameters are obtained by utilizing normal mode analysis. The investigation examines the influence of critical factors like moisture content, diffusivity, and temperature diffusivity on the spatial distribution of various physical fields. Additionally, a particular scenario of significance is highlighted. These results have the potential to improve sensor, actuator, and energy-harvesting device performance and dependability.

A Solvent-Templated Porous Liquid Crystal Elastomer with Tactile Sensation beyond Reversible Actuation toward Versatile Artificial Muscles.

Liquid crystal elastomers (LCEs), as a classical two-way shape-memory material, are good candidates for developing artificial muscles that mimic the contraction, expansion, or rotational behavior of natural muscles. However, biomimicry is currently focused more on the actuation functions of natural muscles dominated by muscle fibers, whereas the tactile sensing functions that are dominated by neuronal receptors and synapses have not been well captured. Very few studies have reported the sensing concept for LCEs, but the signals were still donated by macroscopic actuation, that is, variations in angle or length. Herein, we develop a conductive porous LCE (CPLCE) using a solvent (dimethyl sulfoxide (DMSO))-templated photo-cross-linking strategy, followed by carbon nanotube (CNT) incorporation. The CPLCE has excellent reversible contraction/elongation behavior in a manner similar to the actuation functions of skeletal muscles. Moreover, the CPLCE shows excellent pressure-sensing performance by providing real-time electrical signals and is capable of microtouch sensing, which is very similar to natural tactile sensing. Furthermore, macroscopic actuation and tactile sensation can be integrated into a single system. Proof-of-concept studies reveal that the CPLCE-based artificial muscle is sensitive to external touch while maintaining its excellent actuation performance. The CPLCE with tactile sensation beyond reversible actuation is expected to benefit the development of versatile artificial muscles and intelligent robots.

Design of an actuator with bionic claw hook–suction cup hybrid structure for soft robot

To improve the adaptability of soft robots to the environment and achieve reliable attachment on various surfaces such as smooth and rough, this study draws inspiration from the collaborative attachment strategy of insects, cats, and other biological claw hooks and foot pads, and designs an actuator with a bionic claw hook–suction cup hybrid structure. The rigid biomimetic pop-up claw hook linkage mechanism is combined with a flexible suction cup of a ‘foot pad’ to achieve a synergistic adhesion effect between claw hook locking and suction cup adhesion through the deformation control of a soft pneumatic actuator. A pop-up claw hook linkage mechanism based on the principle of cat claw movement was designed, and the attachment mechanism of the biological claw hooks and footpads was analysed. An artificial muscle-spring-reinforced flexible pneumatic actuator (SRFPA) was developed and a kinematic model of the SRFPA was established and analysed using Abaqus. Finally, a prototype of the hybrid actuator was fabricated. The kinematic and mechanical performances of the SRFPA and entire actuator were characterised, and the attachment performance of the hybrid actuator to smooth and rough surfaces was tested. The results indicate that the proposed biomimetic claw hook–suction cup hybrid structure actuator is effective for various types of surface adhesion, object grasping, and robot walking. This study provides new insights for the design of highly adaptable robots and biomimetic attachment devices.