Performance Of Actuator Research Articles

Comparative analysis for optimal placement of piezoelectric actuators on smart thin plate

In contemporary smart structures, piezoelectric ceramic (PZT) actuators serve a crucial structural function. To construct a smart thin plate that integrates structural health monitoring (SHM) and active vibration control objectives, many placement methodologies were discussed. In current research, two positioning strategies of the attached PZT actuators are compared. The first strategy is a well-known controllability concept where PZT actuators’ optimum positions are obtained by maximizing the eigenvalues of the controllability Grammian matrix. The second strategy employs the energy concept to strategically position PZT actuators so that the utmost amount of exerted work is accomplished by the actuators. Thus, the optimal performance of actuators to provide energy for mitigating unwanted vibrations is maintained, as is the optimal excitation required for SHM in the designated modes. Kirchoff’s classical laminate plate theory (CLPT) is used to define displacements as well as the normal strains of this coupled electro-mechanical system, and then, using the Ritz solution, the modal eigenvalue problem is solved, and mode shapes are obtained. Consequently, normal strains are transformed into spatially dependent functions used to define both the virtual work and the controllability of the Grammian matrix for the PZT actuators as a function of their locations. Finally, iterative optimization based on a genetic algorithm (GA) is used to find the optimum actuator locations in the desired modes. The best location for the PZT actuator or actuators is explored for two specimen plates with different boundary conditions. The results for the two studied positioning strategies are then compared, showing the superiority of the proposed energy-based strategy. Further, a quantitative variance-based uncertainty analysis reveals a low variance of the output results for the proposed strategy.

Vibration control of membrane structures by piezoelectric actuators considering piezoelectric nonlinearity under strong electric fields

Membrane structures, which are widely used in aerospace and civil engineering, are susceptible to large amplitude vibrations due to their low structural damping and high flexibility, leading to the degradation of their working performance. Strong electric fields are commonly needed for piezoelectric actuators to control larger amplitude vibration of membrane structures. However, the effect of piezoelectric nonlinearity due to strong electric fields on the control performance of membrane structures is still underexplored. Given the importance of piezoelectric nonlinearity due to strong electric fields, the present study aims to investigate the vibration control performance of piezoelectric actuators for membrane structures. First, based on the piezoelectric nonlinear constitutive equation, the actuation equation of the piezoelectric actuator is generated. Then, following D′Alembert's principle, a nonlinear dynamic control model of membrane structure containing actuation force is derived. Finally, active vibration control based on velocity feedback algorithms is realized. The results show that the predicted strain without considering the piezoelectric nonlinearity is 80 % smaller than the finite element structure at 500 V. Meanwhile, the errors of Root Mean Squared (RMS) control displacement without considering the piezoelectric nonlinearity are more than 24 % when vibration amplitudes achieve 10 % of the membrane thickness. The developed model provides theoretical implications for active vibration control of flexible structures with piezoelectric actuators in strong electric field environments.

Development and Application of Shape-Memory Polymer and Alloy Composite Sheets

The authors previously developed a flexible and multi-degree-of-freedom pneumatic artificial rubber muscle that uses shape-memory polymer (SMP) sheets with an embedded electrical heating wire. The bending direction and initial shape of the muscle can be changed by utilizing the large difference in the elastic modulus below and above the glass transition temperature, shape fixity, and shape recovery of SMPs. In this study, to improve performance, we propose a shape-memory composite (SMC) sheet that consists of SMP sheets with an embedded shape-memory alloy (SMA) wire used as an electric heating wire. The mechanical properties of the previously developed SMP sheets and the proposed SMC sheets are compared through shape recovery, bending, and tensile tests using prototypes. The motion of the artificial muscle with various samples attached is evaluated through an isometric test and bending angle measurements. The experimental results confirm that the use of the SMA wire improves the production reproducibility and shape recovery of the SMP sheets without degrading other mechanical properties or actuator performance.

Experimental Validation of Two Types of Force Actuators: A Performance Comparison

This paper experimentally investigates the performance of piezoelectric force actuators. Using the same encapsulated piezoelectric stack, an inertial-type actuator and a frame-type actuator are constructed for performance comparison. The experimental results are also used to validate the recently established actuator models, whilst the mechanical and piezoelectrical parameters of the models are experimentally identified. The performance of the actuators is described by the transmitted force(s) and input power flow from the actuators to the base structure with reference to the same electrical input voltage to the stack. The validation is deemed successful due to the strong agreement observed between the measured and predicted actuator performances. Additionally, it is discovered that the frame-type actuator has the capacity to produce significantly higher transmitted forces and input power flow to the base structure compared to the inertial-type actuator. The mechanism underlying the performance disparity between these two types of actuators is also examined. This paper clarifies the mechanism, shedding light on the design and optimization of piezoelectric actuators.

An Origami-Enabled Soft Linear Actuator and Its Application on a Crawling Robot

Abstract Soft linear actuators have strong deformation ability and good environmental adaptability, which have been widely used in soft robot design. However, little work has focused on designing soft linear actuators with balanced performances, featuring fast driving speed, large output displacement, being lightweight, and miniaturization. Herein, we present a novel soft linear actuator design based on the Kresling origami structure. By driving the Kresling tubes with a servo motor, the soft linear actuator has good compliance and strong environmental adaptability and can achieve a driving speed, large driving force, and high control precision comparable to the traditional electrical motor. The analytical models of the Kresling tubes and the whole actuator are respectively derived to analyze the mechanical properties, determine the optimal geometry of the Kresling tube, and evaluate the driving performance of the whole actuator. The actuator prototype is fabricated by 3D printing, and the actual driving performance is tested. It is shown that the prototype can achieve a maximum output displacement of 18.9 mm without payload or 16 mm under a payload of 30 N. Finally, as a case study, the soft linear actuator is applied to a crawling robot, where the maximum moving speed of 28 mm/s is reached.

Charge-controlled compositional/microstructural regulations and electrochemical actuation performance of bulk nanoporous Ni-Pd alloys

Charge-controlled compositional/microstructural regulations and electrochemical actuation performance of bulk nanoporous Ni-Pd alloys

Comparative Analysis of Peltier Devices and Flexible Heater Strips for Enhancing Bandwidth in Thermo-Active Soft Actuators

Soft actuators are a new generation of robotic actuators designed for safer and more adaptable physical human-robot interaction, that can be triggered by various stimulating mechanisms, including pneumatic, electric, electromagnetic, light, magnetic, and thermal sources. Among the different types of soft actuators, thermoresponsive ones that utilize heat as the stimulus show great potential due to their ability to deliver a relatively high force-to-size ratio without the need for external air pumps, tethers, high voltage sources, or complex designs. However, a major drawback of such actuators is their limited bandwidth. Traditional methods rely on Joule heating for actuation, with the actuator deflating when the heat source is turned off and ambient temperature takes over. Recently, the Peltier mechanism has been introduced as an alternative approach for active heating and cooling. This research paper presents a comparative analysis of the Peltier and flexible heater mechanisms in terms of the bandwidth and energy consumption of phase-change thermo-active soft actuators. The study aims to assess the potential of Peltier-based actuation in addressing the bandwidth limitations observed in traditional soft actuators. The findings reveal that Peltier-based actuation can significantly improve actuation speed in thermoresponsive soft actuators. However, it is important to note that the performance of Peltier-based actuators decreases after a few cycles unless additional measures, such as the use of an external fan, are implemented. This increase in performance comes at the cost of higher energy consumption, which should be carefully considered in practical applications.

Liquid Crystal Elastomer Hollow Fibers as Artificial Muscles with Large and Rapid Actuation Enabled by Thermal‐Pneumatic Enhanced Effect

AbstractLiquid crystal elastomer (LCE) has large and reversible deformation under stimulation, making it an ideal material for artificial muscles. Currently, multi‐stimulus responsive LCE actually responds to each stimulus independently rather than responding to several stimuli simultaneously. Achieving an enhanced effect from concurrent stimuli is still a challenge, which requires a new stimulus‐response mechanism. This work develops a novel and facile solvent evaporation‐assisted template method to prepare LCE hollow fiber (LCEHF) with axial alignment. Taking advantage of the enhanced effect of heat‐induced phase transition and mechanical force‐induced orientation transition of mesogens, the LCEHF under both heat and pressure can produce a large contraction ratio of ≈50%, which is higher than 42% of thermal stimulation or 27% of pneumatic stimulation. It can also enhance the respective response and recovery speed of LCEHF to 300 and 3700 times of pneumatic actuation. Additionally, the enhanced effect lowers the actuation temperature much below the phase transition temperature, imparting LCEHF with high mechanical performance during actuation. Furthermore, the dual thermal‐pneumatic responsive LCEHF can mimic human biceps and cause large and rapid bending of an artificial arm reversibly. This new actuation methodology sheds new light on improving LCE actuation performance and broadens its application scenarios.

Untethered, Dynamic Robotic Fabrics Enabled by Actively‐Rigid Variable Stiffness Fibers

AbstractA robot that uses fabrics as its core body material can be lightweight, compact, and highly flexible. Ideally, the robot's actuation, sensing, and structural support are provided by fiber‐based components, designed to integrate with the fabric's soft and conformable nature while preserving its fiber architecture. Typically, variable stiffness fibers are used for the structural elements, functioning as “bones” that can be turned on and off as needed. However, many variable stiffness fibers are passively‐rigid, only allowing the fabric to become soft when powered, while some require bulky external air or power supplies, making them untenable for untethered robotics. In this work, an electrically‐driven variable stiffness fiber is presented that performs a flat‐to‐curved geometry transition, providing a rigid load‐bearing structure when powered but remaining flexible otherwise. Design principles for pairing the actively‐rigid variable stiffness fiber with a materially compatible fiber‐based actuator are presented, and the actuator performance in different configurations is characterized. The variable stiffness fiber can be arranged into sturdy legs, stable enough for a robotic fabric to lift and hold its own battery pack and onboard electronics. This capability is demonstrated with a first‐of‐its‐kind fully‐untethered locomoting robotic fabric using two different quadruped gaits.

Multifunctional and Electronically Conjugated Triazine Framework for Superior Electro‐Ionic Artificial Muscles

AbstractElectro‐ionic artificial muscles, consisting of a configuration where an electrolyte membrane is flanked by two active electrodes, have emerged as transformative components in the field of soft robotics. Despite this, the current actuation performance falls short for many practical applications, because most existing electrode materials exhibit limitations in terms of their properties. Here, a multifunctional active electrode material is reported for an electro‐ionic artificial muscle, employing a triazine framework that incorporates 6,6′‐Dicyano‐2,2′‐bipyridyl (DCB‐TF). The multifunctional DCB‐TF boasts fully conjugated bonds, facilitating fast electron transfer, high porosity for ion accommodation, a substantial surface area of 1800 m2 g−1 for charge storage, numerous active sites for ion interactions, and complete aromatic rings contributing to stability. The application of DCB‐TF to the active electrodes in the electro‐ionic artificial muscles yields remarkable actuation performance, including a substantial bending displacement of 24 mm at 0.5 V and 0.2 Hz, a rapid response time of 2 s, and outstanding durability sustained over 3.4 million continuous cycles. Consequently, these soft actuators have enabled a dragonfly demonstration as a form of kinetic art.

Optimized Design of a Soft Actuator Considering Force/Torque, Bendability, and Controllability via an Approximated Structure

Abstract This paper introduces a novel design method that enhances the force/torque, bendability, and controllability of soft pneumatic actuators (SPAs). The complex structure of the soft actuator is simplified by approximating it as a cantilever beam. This allows us to derive approximated nonlinear kinematic models and a dynamical model, which is explored to understand the correlation between natural frequency and dimensional parameters of SPA. The design problem is then transformed into an optimization problem, using kinematic equations as the objective function and the dynamical equation as a constraint. By solving this optimization problem, the optimal dimensional parameters are determined. Six prototypes are manufactured to validate the proposed approach. The optimal actuator successfully generates the desired force/torque and bending angle, while its natural frequency remains within the constrained range. This work highlights the potential of using optimization formulation and approximated nonlinear models to boost the performance and dynamical properties of soft pneumatic actuators.

Large eddy simulation study on drag reduction performance of array-based plasma synthetic jet actuators

Large Eddy Simulation (LES) is first used to investigate the drag reduction effect of an array-based configuration of Plasma Synthetic Jet Actuators (PSJAs) on a hemisphere in supersonic inflow, and analyze the effect of energy allocation and array angle on the drag reduction performance of opposing Plasma Synthetic Jet (PSJ) in this paper. Numerical simulation results have been compared with experimental data, confirming the validity of the simulation method. The results show that different energy allocations have a significant effect on the drag of the hemisphere. However, the effect of the change in array angle on the drag of the hemisphere is not as noticeable as the effect caused by energy allocation. Interference regions between the two PSJAs occur, which undermine the effectiveness of drag reduction. High Turbulent Kinetic Energy (TKE) regions primarily concentrate on the core region of the jet and downstream of the bow shock. The influence of the array angle on TKE is most evident in the downstream region of the exits of the PSJs on both sides. Temporal evolution of the coherent structures reveals that as the PSJ intensity decreases, the large-scale vortices progressively break up into smaller-scale vortices, and energy is also transferred from large-scale structures to small-scale structures.

Design and Driving Performance Study of Soft Actuators for Hand Rehabilitation Training.

To address the application requirements of soft actuators in rehabilitation training gloves, and in combination with ergonomic requirements, we designed a segmented soft actuator with bending and elongation modules. This actuator can achieve independent or coupled movements of the finger joints. A finite element model of the joint actuator was established to compare the driving performance of actuators with different structural forms. Numerical calculations were used to analyze the effects of structural size parameters on the bending characteristics and end output force of the actuator. The design was then refined based on these analyses. The joint actuator designed in this study demonstrated a 71% increase in bending angle compared to the standard fast pneumatic network structure. Key factors affecting the driving performance include the thickness of the constraint layer, the inner wall thickness of the chamber, chamber height, chamber width, chamber spacing, chamber length, and the number of chambers. After improvements, the bending angle of the joint actuator increased by 60.6%, and the output force increased by 145.9%, indicating significant improvement. This study designed and improved a soft actuator for hand rehabilitation training, achieving independent and coupled joint movements. The bending angle, bending shape, and joint driving force of the soft actuator meet the requirements for finger rehabilitation training.

Numerical investigations on film cooling effectiveness and heat transfer performance of inclined film hole on the turbine blade squealer tip with plasma actuation

The turbine blade tip frequently encounters elevated thermal loads, necessitating effective protection measures. Conventional film cooling techniques, while employed to mitigate erosion, face challenges in achieving optimal performance due to intricate tip leakage flow dynamics. Thus, the development of advanced film cooling methodologies becomes imperative to ensure the optimal operation of blade tips. In this study, a novel film cooling approach is proposed, leveraging a combination of dielectric barrier discharge (DBD) plasma actuators and inclined film holes. This strategy aims to direct cooling jets towards the tip wall surface, enhancing film cooling efficacy on highly-loaded turbine squealer tips. Numerical investigations are conducted to assess film cooling effectiveness, heat transfer coefficients, and coolant jet flow characteristics across varying actuation strengths (0, 0.6, 0.8, and 1.0) by integrating plasma actuation forces into the Reynolds-Averaged Navier-Stokes equations. Additionally, the impact of different blow ratios (0.5, 1.0, and 1.5) on plasma flow control is examined. Results demonstrate that plasma actuation improves film cooling performance and effectively mitigates tip heat transfer, even in the presence of interfering tip leakage flow. Specifically, at an actuation strength of 1.0, the average blade tip film cooling effectiveness increases by 7.1%, accompanied by a 12.3% reduction in average heat transfer coefficient compared to scenarios without plasma actuation. Furthermore, the blow ratio influences plasma actuation performance, with minimal disparity observed between configurations with and without plasma devices under extreme blow ratio conditions.

Smart versatile hydrogels tailored by metal-phenolic coordinating carbon and polypyrrole for soft actuation, strain sensing and writing recognition

Biomimetic intelligent conductive hydrogels integrating flexibility, signal sensing, and contactless actuation has become ideal candidates for the production of electronic skins, wearable devices, and soft robotics. However, the development of multifunctional smart hydrogels capable of both sensing and actuating simultaneously to enhance intelligent interaction interfaces remains a significant challenge. Herein, a multifunctional hydrogel composite with integrated sensing and actuating capabilities is proposed through the incorporation of Fe3+-tannic acid (TA) coordination compound-coated carbon nanotubes (Fe-TA@SWNT) and the in-situ formation of conductive polymer polypyrrole (PPy) inside the hydrogel networks composed of carboxymethylcellulose (CMC) and a copolymer of acrylic acid (AA) and [2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA). Benefiting from multiple effective dynamic interactions within the internal matrix, the prepared hydrogel exhibits excellent stretchability (1283.42 % elongation) and toughness (1.11 MJ/m3). Additionally, the catechol groups carried by Fe-TA@SWNT, along with the zwitterionic monomer SBMA, provide the hydrogel with repeatable self-adhesion performance. Based on the outstanding photothermal effect of Fe-TA@SWNT and PPy, the hydrogel demonstrates reversible and stable photothermal responsiveness, exhibiting exceptional actuation performance under near-infrared (NIR) radiation. As a strain sensor, the hydrogel shows excellent sensitivity (GF = 3.32), rapid response time, and reliable stability, enabling precise monitoring of various physiological signals in the human body, including joint movements, facial expressions, and heartbeats. Therefore, this work significantly expands the application prospects of multifunctional smart hydrogels in fields of wearable electronics, soft robotics, and remote light-controlled devices.

Enhancing the Performance of Soft Actuators with Magnetic Patterns

AbstractThis study presents a concept for a straightforward method to enhance the actuation performances of magneto‐active elastomer membranes. The concept is based on a characteristic magnetization pattern and offers a solution to two major difficulties in the actuation of thin and mechanically soft magnetic actuators: the localization of actuation forces and the self‐demagnetization. After the magnetization process, the membrane presents two regions with an oppositely oriented out‐of‐plane magnetization. The magnetized regions are separated by a transition zone which is called magnetic pole transition. Experimental investigations reveal a high magnetic flux density near the pole transition—even in the center of bidirectionally magnetized membranes—whereas the magnetic flux density of a uniformly magnetized membrane decreases toward the center. In additional experiments, membranes with both magnetization patterns are actuated by stiff permanent magnets. The resulting out‐of‐plane displacement of the bidirectionally magnetized membrane exceeds the displacement of the unidirectionally magnetized membrane by far. The investigations demonstrate that this enhancement stems from the presence of the magnetic pole transition. All experiments are reproduced using magnetic and magneto‐mechanical numerical models; a good accordance between the results is achieved.

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.