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Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive quantized output feedback event‐triggered (ET) distributed consensus control approach for an uncertain nonstrict nonlinear switched fractional‐order (FO) multi‐agent system (SFOMAS) subject to communication limitation is proposed. By relying on the common Lyapunov function method, the switch signals are arbitrarily, and no information regarding the switching instants is required. The consensus error of each agent has its own asymmetric time‐varying constraints (ATCs). By adopting the common barrier Lyapunov function (BLF), violation of these constraints is prevented. For each agent, different input nonlinearities can be considered in different modes, and the controllers need no information about their types and characteristics. The communication burden between outputs sensors and the controllers is reduced by applying uniform‐logarithmic‐hysteresis quantizers to the outputs signals. By using FO filters, which can be considered as a FO version of the dynamic surface control (DSC) method, the so‐called explosion of complexity is avoided and the discontinuity problem of FO derivatives of virtual controllers due to outputs quantization is resolved. Observers are designed to estimate the unmeasured states. Also, function approximators (FAs) are employed to approximate uncertainties. A novel lemma that correlates observer states to consensus errors and their constraints, FO filters errors, adaptive parameters and backstepping error surfaces, has been proposed to establish the observer stability. To reduce the communication burden between the controllers and actuators, relative threshold ET mechanisms have been applied to control signals. The combination problem of unmeasured states with the mentioned input constraints for SFOMASs is coped with another novel lemma. Utilizing the common Lyapunov functions (CLFs) and the backstepping technique, virtual controllers, adaptive law and control signal for each agent have been designed and boundedness of closed‐loop signals and avoidance of Zeno behavior have been proved. The effectiveness of the proposed control scheme is demonstrated through a simulation study. [ABSTRACT FROM AUTHOR]

Er3+-modified (Bi 0.5 Na 0.5) 0.945 Ba 0.055 Ti 0.98 (Fe 0.5 Sb 0.5) 0.02 O 3 (BNBT-FS) lead-free ferroelectric ceramics with large electrostrain and electrostrictive response were fabricated in our work. Results showed that Er3+-doping induced the destruction of ferroelectric order and significantly enhanced the field-induced strain. For 0.2 mol% modified sample, the unipolar strain reached 0.463 % under the electric field of 80 kV/cm, yielding a large normalized strain d 33 * (S max / E max) of 579 pm/V. For 0.4 mol% modified sample, high electrostrictive effect with temperature-insensitive electrostrictive coefficient Q 33 (0.022–0.026 m4/C2 in the temperature range of 25–100°C) was obtained. The large electrostrain and electrostrictive response in the present materials show the great potential of the materials for nonlinear actuators applications. [ABSTRACT FROM AUTHOR]

In material handling, numerous solutions have been proposed to enhance the flexibility and adaptability of transport systems. Among these solutions, smart surfaces stand out as one of the most interesting responses, utilizing an array of actuators for common feeding tasks. The current paper focuses on a novel system within this category, notable for its distinguishing factor of being underactuated. With this characteristic, the concept leads to a simplified cost-effective design and a not actively driven functioning, leveraging gravity or object own velocity to manipulate the material flow maintaining top class performances, as the sorting rate reaches 4000 pcs/h. Specifically, the article begins with an introduction of the concept design and its digital model, followed by a description of the experimental setup built to test the surface's functionality and evaluate the predictions of the virtual counterpart. On top of that, a method to determine the essential parameters for the surface simulation is proposed and applied. As a result, the prototype successfully completed the three main intralogistic tasks experimented, i.e., sorting, slowing, and stopping of packages. Lastly, the digital model outcomes of the same operations were computed and compared with the measured results, demonstrating an accuracy of prediction with displacements and time errors below 7%. [ABSTRACT FROM AUTHOR]

This paper delves into the output feedback control of systems with dual multi‐memoryless channels, where the data packets transmitted from the sensor to the controller (S/C) and from the controller to the actuator (C/A) are suffered from two different multi‐parallel Markovian fading channels. Two new multi‐state Markovian chains are introduced, by which the multiple fading channels system is transformed into a new jumping parameter system. Then a stochastic maximum principle is given along with an optimal state feedback controller for the case that the state is known. When the state is unknown, a Markov jump linear estimator is designed by using the completing square method. In this case, an output feedback controller is obtained by substituting the real system state with its estimation. Meanwhile, the separation principle is shown. Finally, the validity of these methods is verified by simulation examples. [ABSTRACT FROM AUTHOR]

To meet the demand for estimating actuator and sensor faults simultaneously in a class of repetitive nonlinear time‐delay systems, this paper proposes a novel fault estimation strategy based on an iterative learning scheme. Firstly, an iterative‐learning‐based fault estimation law is designed to estimate actuator faults while system is free of sensor failures. Both the fixed initial shift and random one are taken into consideration. Secondly, a novel sensor fault observer is proposed based on an augmented state variable which consists of original system state and sensor fault signal; output compensation strategy is also provided to ensure the iterative‐learning‐based actuator fault estimation method is effective considering the existence of sensor failures. In addition, theorems based on λ$$ \lambda $$‐norm and linear matrix inequality are provided to determine values or ranges of gain matrices and parameters in proposed sensor fault observer and iterative‐learning‐based actuator fault estimation law. Finally, two simulation examples are provided to illustrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper investigates the containment control problem for heterogeneous multi-agent systems with unknown leaders and actuator failures. The dynamics of the leaders are unavailable to all followers and the measurable information of leaders is available to some followers. A model-free adaptive observer for each follower is proposed to estimate the convex hull of the leaders states and the dynamic knowledge of the unknown leaders. The followers may be affected by the actuator failures. Based on the adaptive observer and the adaptive solution of the output regulation equation, an adaptive fault-tolerant control protocol is designed to mitigate the impact of actuator failure on containment performance such that the output containment errors are ultimately uniformly bounded. Two simulation examples are provided to demonstrate the feasibility of the presented control scheme. [ABSTRACT FROM AUTHOR]

In this paper, the problem of reliable bumpless transfer control for switched systems with actuator faults is investigated. A switching law and a class of reliable controllers via output feedback are constructed such that the bumpless transfer performance and H ∞ reliable property of the closed-loop systems are guaranteed. The switching process is divided into two stages, that is, dwell time and state-dependent switching stages. In the dwell time stage, a low bound of the time of the activated subsystem is introduced to restrict the frequent switching and suppress the system bumps. This guarantees the bumpless transfer performance of systems. In the second stage, only the measurable controller states are used to generate the switching signals, which upgrades the feasibility in the frame of output feedback. Finally, to ensure the H ∞ reliable property, the proposed controllers are time-varying, which work in the different switching stages. A simulation example is given to demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper solves the finite-time extended dissipative fault estimate problem for discrete-time Markov jump neural networks based on an event-triggered approach in fully/partially known transition probability cases. Firstly, the systems are expanded into new systems treating sensor faults as states. Based on the proposed event-triggered scheme and an intermediate variable, an event-triggered intermediate observer is designed to estimate states, faults of actuator and sensor, and the intermediate variable, simultaneously. Next, the finite-time stability of error systems with extended dissipativity is analyzed, and the observer gains are shown in fully/partially known transition probability case, respectively, whose existence conditions are given. Finally, an example is given to illustrate the feasibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

The converse flexoelectric effect can be applied to control thin-shell structures. In this paper, the vibration control of a conical shell with multiple flexoelectric actuators is studied. In order to investigate the actuation performance of the flexoelectric patch, this study analyzes the electric field gradient, modal forces, and displacement of a conical shell driven by the flexoelectric patch and their relationships with the design parameters. In the physical model, the AFM probe is positioned on the upper surface of the flexoelectric patch to create a high-intensity non-uniform electric field within the flexoelectric actuator. In turn, generates internal stress in the flexoelectric actuator patch through the converse flexoelectric effect. The case study shows that the high-intensity non-uniform electric field generated by the AFM probe has nearly zero contribution to the electric field in areas far from the contact point. As a result, the stress generated by the converse flexoelectric effect primarily concentrates near the AFM probe, with the size and shape of the flexoelectric patches having minimal influence on the actuation. Based on the assumption of small deformation and linear displacement, considering the vibration control of multiple flexoelectric actuators on the truncated conical shell, the lateral displacement results controlled by multiple flexoelectric actuators can be calculated by the superposition principle. When multiple flexoelectric actuators work together, the same flexoelectric actuator in different positions may induce opposite lateral displacements at a specific point on the surface of the truncated conical shell. This can result in the cancellation of vibrational displacements produced by the flexoelectric actuators. Approximate optimal distribution positions for the multi-channel flexoelectric actuators were determined through experimental simulations. In this study, the superior vibration suppression capabilities of multi-channel flexoelectric actuators are highlighted through a comparative analysis with single-channel configurations, demonstrating their effectiveness in controlling complex vibration modes in conical shell structures. [ABSTRACT FROM AUTHOR]

This paper investigates the stabilization problem of interval type-2 (IT2) Takagi-Sugeno (T-S) fuzzy fractional order systems (FOSs). Firstly, IT2 fuzzy model is constructed to approximate the subject to actuator saturation of systems. Then, the sufficient conditions of output feedback control of IT2 fuzzy FOSs in terms of linear matrix inequalities (LMIs) are presented by using the method involving matrix singular value decomposition (SVD). Furthwemore, we solve optimization problems to estimate stable regions according to the proposed stability conditions. Finally, we proposed a numerical example to demonstrate the availability of theoretical analysis results. [ABSTRACT FROM AUTHOR]

The output force of soft-pneumatic actuators is critical for their applications. However, the hyperelasticity of its material and the high compressibility of the actuation medium, i.e., air, lead to a strong asymmetric hysteresis, which poses a great challenge for its force control. An attention CNN (Convolution Neural Network)–AUPI (Amplitude-dependent Un-parallel Prandtl–Ishlinskii)-based force-position hysteresis modeling method for soft actuators is proposed. Based on the preliminary fitting of the asymmetric hysteresis curve by AUPI, the attention CNN mechanism extracts the global features of the hysteresis information, prevents the model from overfitting, and greatly improves the accuracy and generalization ability of the composite model. Experiments show that the CNN–AUPI model has excellent hysteresis fitting for soft joint actuators, with a maximum relative error of only 6.1% and a goodness-of-fit of more than 0.99. The proposed CNN–AUPI model is also compared with other hysteresis models, and the results show that the CNN–AUPI model not only has a high modeling accuracy but also has a strong prediction capability, which provides a promising method for hysteresis modeling of soft actuators. [ABSTRACT FROM AUTHOR]

This study presents a methodology for applying the three-dimensional actuator disk-RANS technique in modeling tidal energy converters within a regional-scale simulation. Of particular interest are the robustness of the applied momentum source term and its effectiveness in modeling an array of full-sized tidal turbines under realistic hydrodynamic and operational conditions. The Inner Sound region, which is the site of commercial-scale deployment projects of the Pentland Firth in Scotland, is chosen as the study area. While the actuator disk approach had been used in past studies to parameterize the far-wake region of horizontal-axis tidal turbines, details of its three-dimensional implementation have not been thoroughly discussed. Criteria adopted in deciding the array location are presented in this study, along with the actuator disks' detailed setup and constraints. The models are subjected to one operational characteristic that is similar to commercial devices in service to examine the accuracy of the imposed source term under complex flow conditions. The results demonstrate that the thickness of the disk imposed in the source term has a pronounced influence on the model outputs. In addition to accurately modeling flow propagation and wake interactions, the models are also able to replicate the observed asymmetrical tidal currents in the region. Because there is currently limited published material on the detailed application of the actuator disk approach in ocean-scale models, this study is hoped to fill the research gap and provide evidence, guidance, and examples of best practices for future studies. [ABSTRACT FROM AUTHOR]

In fluid dynamics, a flow control device is used to control, manage, or modify the behavior of a fluid flow. Jet actuators work by releasing high-velocity jets of fluid, usually air or gas, into the surrounding environment to control or manipulate the flow of fluids. In this study, the flow control device, which was a dual synthetic jet actuator (DSJA), acted as a lift enhancement device over an optimized NACA 0012 aerofoil with a rounded trailing edge (TE) (Coanda surface approximately 9% of the trailing edge was modified) to enhance the lift at various angles of attack (AOAs). Fluctuating pressure inlets were introduced in two slots. When the dual synthetic jets were in control, the out-of-phase jets from the upper and lower trailing edge jets helped to boost the lift coefficient. The suction stroke from the lower half of the jet made the Coanda effect stronger in the upper half. The upper trailing edge jet deflected downwards merged with the lower one and helped to deflect the flow field closer to the bottom half. An unsteady CFD analysis was performed on optimized airfoils with and without a DSJ, with a driving frequency of 40.6 and a reduced frequency of 0.025 at a Reynolds number of 25000. The results obtained at different angles indicated that the L/D ratio was improved by 13.5% at higher angles of attack in the presence of the DSJA. [ABSTRACT FROM AUTHOR]

Simulating entire wind farms with an actuator line model requires significant computational effort, especially if one is interested in wake dynamics and wants to resolve the tip vortices. A need to explore unconventional approaches for this kind of simulation emerges. In this work, the actuator line method is implemented within a lattice‐Boltzmann flow solver, combined with a sliding mesh approach. Lattice‐Boltzmann solvers have advantages in terms of performance and low dissipation, while the sliding mesh allows for local refinement of the blade and tip vortices. This methodology is validated on a well‐documented case, the NREL Phase VI rotor, and the local refinement is demonstrated on the NREL 5 MW rotor. Results show good agreement with reference Navier–Stokes simulations. Advantages and limitations of the sliding mesh approach are identified. [ABSTRACT FROM AUTHOR]

The intelligent soft robot has received wide attention from both academia and the industry due to its remarkable adaptability. It performs intelligent behavioral learning and evolved morphologies in unpredictable environmental conditions. However, designing a soft robot with a well-adapted morphology involves searching through a large number of possible structures. Furthermore, to learn control tasks in diverse environments, the robot performs computationally intensive numerical simulations, which is time-consuming for evaluating the performance of robots. To address both issues, a multi-fidelity evolutionary algorithm is proposed, which consists of three main components. Firstly, a niching-based fidelity adjustment strategy is introduced to significantly reduce the evaluation cost by training the controller of each robot for only a small number of simulation steps. In particular, considering the estimation errors of the low-fidelity evaluation, the population is divided into multiple subpopulations with different fidelity levels for parallel optimization. Secondly, an effective morphology transfer strategy is proposed to improve the quality of offspring by transferring the local structure of robots in different subpopulations. Finally, a fast local search is developed to enhance the search efficiency of the algorithm without performing additional control simulations. The experimental results on 31 test tasks demonstrate that the proposed algorithm outperforms the SOTA design algorithms on 25 test tasks, especially when the computational budget is limited. Compared to the baseline algorithms, our algorithm reduces the computational cost by 60$\%$% while achieving similar performance. [ABSTRACT FROM AUTHOR]

Electro-hydraulic actuator system (EHAS) has imposed a challenge in the research community for accurate mathematical modeling and identification due to non-linearities. In this paper, autoregressive exogenous (ARX) structure is used for EHAS modeling and identification is performed by exploiting the competency of atomic physics-based chaotic atom search optimization (CASO) that adapts ten chaotic maps (Chebyshev, Circle, Gauss, Iterative, Logistic, Piecewise, Sine, Singer, Sinusoidal and Tent) in position update of atom search optimization (ASO). The fitness/merit function of the EHAS model is developed in mean-square error (MSE) sense between desired and approximated values. Simulations and analysis show that ASO with a chaotic logistic map (CASO5) performs better than the ASO and its other chaotic variants, as well as other recently introduced metaheuristics for diverse variations in the system model. Statistics based on MSE, learning plots, results of autonomous trials and average fitness analyses verify the consistency and reliability of the CASO5 for the identification of the EHAS model. [ABSTRACT FROM AUTHOR]

There are appreciable physical losses to the header of a combine harvester operating in the fields during harvesting. To reduce these losses, it is desirable to effectively control the header height of the combine harvester. In the present study, a soil bund detection system has been developed for the header of the combine harvester using an ultrasonic sensor and tested under field conditions. In the laboratory, the best among five ultrasonic sensors (HC-SR04, US-100, JSN-SR04T, GY-US42 and MB-7092) was selected based on accuracy and response of the sensor operated for 27 treatments of soil bund height, sensor height and stubble density. Consequently, the soil bund detection system was developed using the US-100 sensor, Arduino UNO R3 microcontroller and two relays to control the actuator on prototype. The results showed that during sensor selection, the US-100 sensor had a maximum accuracy of 84.83% in BH3SH1SD1 treatment and a maximum response of 91.38 readings/sec in BH2SH2SD3 treatment. Furthermore, the developed system showed a maximum accuracy of 88.89% and 85.58% without the actuator in the field and with the actuator under laboratory conditions respectively. The highest response of 64.68 and 62.70 readings/sec was recorded for systems without the actuator in the field and with the actuator under laboratory conditions respectively. The study reveals that the increase in stubble density and sensor height causes a decrease in the accuracy, while the increase in bund height significantly increases the accuracy of the system. Moreover, an increase in vehicle speed causes a decrease in the response of the system, whereas with increasing bund height and stubble density, there is an increase in the response. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics with high electro strain are widely used in actuators, sensors, and so on. Here, this work investigates the electro strain of representative piezoelectric materials, and analyzes the influence of electrode type on the electro strain of PZT41 with significant strain anomalies. It is found that the occurrence of abnormally significant strain is not affected by the electrode but caused by intrinsic defects. Therefore, the ceramic samples with and without defects tailoring in Na 0.5 Bi 0.5 TiO 3 (NBT) based and PbZr 0.52 Ti 0.48 O 3 (PZT) based systems were prepared by the solid-state reaction method, and the results show that abnormally ultrahigh electro strains occur in excessively thin samples with diploes due to defects tailoring. Through displacement configuration experiments and comprehensive analysis of polarization switching processes, it is found that the occurrence of asymmetric abnormal significant strains is caused by reversible bending deformation in excessively thin samples. This work provides new support for the emergence of ultrahigh electro strain in piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Modular reconfigurable robots exhibit prominent advantages in the reconnaissance and exploration tasks within unstructured environments for their characteristics of high adaptability and high robustness. However, due to the limitations in locomotion mechanism and integration requirements, the modular design of miniature robots in the aquatic environment encounters significant challenges. Here, a modular strategy based on the synthetic jet principle is proposed, and a modular reconfigurable robot system is developed. Specialized bottom and side jet actuators are designed with vibration motors as excitation sources, and a motion module is developed incorporating the jet actuators to realize three‐dimensional agile motion. Its linear, rotational, and ascending motion speeds reach 70.7 mm s−1, 3.3 rad s−1, and 28.7 mm s−1, respectively. The module integrates the power supply, communication, and control system with a small size of 48 mm × 38 mm × 38 mm, which ensures a wireless controllable motion. Then, various configurations of the multi‐module robot system are established with corresponding motion schemes, and the experiments with replaceable intermediate modules are further conducted to verify the transportation and image‐capturing functions. This work demonstrates the effectiveness of synthetic jet propulsion for aquatic modular reconfigurable robot systems, and it exhibits profound potential in future underwater applications. [ABSTRACT FROM AUTHOR]

Solar energy can be harnessed and converted into heat via the photothermal effect, which can then be utilized to drive many other reactions to produce important resources, such as water, fuel, electricity, and even mechanical actuation in a clean and sustainable manner. Hydrogels and membranes coupled with photothermal materials are particularly suitable for this purpose because they possess advantageous properties, such as porosity and adaptability. These properties allow for the introduction of diverse additives and functionalities, ensuring that photothermal systems can be customized for specific tasks, thereby enhancing their overall performance, functionality and versatility. This review aims to provide an overview of recent developments and the significance of employing photothermal hydrogels and membranes in multiple fields ranging from clean water, fuel production, electricity generation to mechanical actuation, followed by a discussion on key considerations in materials design and engineering. Finally, the review addresses the challenges and future directions of photothermal applications. [ABSTRACT FROM AUTHOR]

Small-scale pumps for controlling microfluidics have promising applications in drug delivery and chemical assays. Liquid metal (LM) demonstrates excellent flow pumping performance due to its simple structure and the electrocapillary effect under an electric field. However, LM droplets risk escaping from constrained structures, which can lead to pump failure. Temperature regulation is also a critical parameter in optimizing chemical reactions in fluidic systems, however, integrating it into a compact system remains challenging. Here, we develop a temperature-triggered gallium-based actuator (TTGA) by introducing a gallium (Ga) droplet wetted on a copper (Cu) plate as the core element for flow actuation. The Cu plate prevents the Ga droplet from escaping the chamber and significantly increases the flow rate. By leveraging the electrochemical method to inhibit the supercooling effect of Ga, the TTGA enables activation/deactivation for flow actuation at different temperatures. We investigate the impact of electrode position, solution concentration, and applied voltage on TTGA’s pumping efficiency. By dynamically tuning the Ga droplet’s temperature to control phase transition, TTGA allows for accurate flow actuation control. Furthermore, placing Ga and eutectic Ga-indium (EGaIn) droplets in different channels enables the expected flow divergence for fluids with different temperatures. The development of TTGA presents new opportunities in microfluidics and biomedical treatment. [ABSTRACT FROM AUTHOR]

Dynamic covalent liquid crystal networks (DCv‐LCNs) with straightforward (re)programmability, reprocessability, and recyclability facilitates the manufacture of sophisticated LCN actuators and intelligent robots. However, the DCv‐LCNs are still limited to heat‐assisted programming and polymer‐to‐polymer reprocessing/recycling, which inevitably lead to deterioration of the LCN structures and the actuation performances after repeated programming/processing treatments, owing to the thermal degradation of the polymer network and/or external agent interference. Here, a totally renewable azobenzene‐based DCv‐LCN with room‐temperature programmability and polymer‐to‐monomers chemical recyclability is reported, which was synthesized by crosslinking the azobenzene‐containing dibenzaldehyde monomer and the triamine monomer via the dynamic and dissociable imine bonds. Thanks to the water‐activated dynamics of the imine bonds, the resultant DCv‐LCN can be simply programmed, upon water‐soaking at room temperature, to yield a UV/Vis light‐driven actuator. Importantly, the reported DCv‐LCN undergoes depolymerization in an acid‐solvent medium at room temperature because of the acid‐catalyzed hydrolysis of the imine bonds, giving rise to easy separation and recovery of both monomers in high purity, even with tolerance to additives. The recovered pure monomers can be used to regenerate totally new DCv‐LCNs and actuators, and their functionalities can be reconfigured by removing old and introducing new additives, by implementing the closed‐loop polymer‐monomers‐polymer recycling. [ABSTRACT FROM AUTHOR]

Soft actuators that mimic the softness and deformability of living organisms have great potential for use in various fields. For most soft actuators, achieving both reprogrammable shape and high work capacity is crucial but challenging. These properties are mutually exclusive for liquid crystal elastomers (LCEs), an important type of soft actuators. Herein, a room‐temperature shape‐programmable LCE capable of high‐energy actuation is developed. Our approach utilizes hydrogen bonds to stabilize the aligned liquid crystal phases. The slow recovery of H‐bonds at room temperature provides a specific processing window, during which the sample shape can be programmed after the thermal treatment. The temperature‐dependent rearrangement of hydrogen bonds allows for fabrication of actuators with customized shapes in a facile do‐it‐yourself manner. Additionally, the integration of strong covalent cross‐links is vital for holding structural integrity. The combination of non‐covalent and covalent cross‐linking significantly improves the mechanical properties, enabling the actuators to perform reversible actuation with a work capacity (440 kJ m−3) higher than that of traditional LCEs (<100 kJ m−3). This study provides a turnkey strategy to address the conflict between shape reprogrammability and work capacity, advancing the development of soft actuators. [ABSTRACT FROM AUTHOR]

The efforts in soft materials actuators that can generate driving deformation under external energy stimulation have promoted the rapid development in miniature sized robotics. Recently, soft actuators with continuous and autonomous actuation behavior under constant stimulation are highly sought after. Light‐fueled self‐oscillators based on self‐shadowing effect triggered by their light‐induced actuation deformation provide an effective scheme. However, grand challenges remain in light‐driven self‐actuators that are multi‐directional controllable and can operate in low power density in air. Here, this study reports a MXene‐based multilayer actuator that generates self‐sustained robotic motion upon low light intensity– 50 mW cm−2 (half Sun). The actuator can self‐track the light sources and continuously oscillate while the incident angle is changed. The self‐sustained actuator exhibits high adaptation to types of light sources, including inherence and coherence light sources with different wavelengths. Diverse applications are demonstrated, including autonomous signal transmitter based on beam reflection, self‐propelled sailboat, light‐to‐mechanical motor, and soft robots with biomimetic movements. The results offer new insights for light‐fueled self‐oscillators with multi‐directional controllability and low‐intensity requirement and its potential application prospect. [ABSTRACT FROM AUTHOR]

Reconfigurable soft robots exhibit superior flexibility and adaptability when coping with complex environments and variable tasks. However, conventional modular design strategy based on soft actuator modules with specific structure and actuation mode as the basic constructing element for reconfigurable soft robots always has limited reprogrammability or scalability. Here, a hierarchical reconfigurable strategy is reported that not only offers conventional module reconfiguration as the first level to build different robot prototypes, but also provides the elastically‐guided multimodal actuation (contraction, bend, and twist) as the second level which can be reprogrammed to construct different actuator modules. This strategy deepens the modularity to a higher dimensionality and provides more choices for robots to adjust various conformations and functions as needed, for example, a peristalsis robot, an omnidirectional crawling robot, and a soft manipulator can be easily constructed using the module‐level reconfiguration. Moreover, soft manipulators with various preprogrammed deformation trajectories based on the mode reconfiguration are proven to dramatically reduce the operation difficulty and cost in potential applications such as environment detection and human‐robot interaction. This work provides a hierarchical framework for reconfigurable soft robots and may open up a new way for modular design. [ABSTRACT FROM AUTHOR]

Liquid crystalline elastomers (LCEs) are a class of shape‐changing polymers with exceptional mechanical properties and potential as artificial muscles/polymer actuators. In this study, multifunctional LCE actuators with strain sensing and joule heating responsivity are developed. LCEs are successfully synthesized using the thiol‐ene two‐staged michael addition polymerization (TMAP) method. The LCE films are further functionalized via sequential polydopamine (PDA) and silver electroless coating. It is found that the PDA coating enabled the anchoring of the Ag particles to the LCE, thereby enabling the electrical conductivity of the Ag‐LCEs (<0.1 Ω cm−1). The studies confirm that the Ag/PDA coated LCEs can sense up to ≈30% strain, sense their own actuation strokes, and actuate at a rate of 1.83% s−1 while lifting a weight ≈50 times its mass in response to a 12 V 2A DC current. [ABSTRACT FROM AUTHOR]

Dynamic covalent organic frameworks (COFs) offer a promising platform for bioinspired soft actuators, yet transitioning their typical microcrystalline or single crystalline morphology to a flexible film suitable for wearable technology applications still remains a grand challenge. Herein, aiming at this issue, this work synthesizes an innovative class of hygrosensitive COF films, denoted as JNU‐hygroCOF, with superior mechanical strength, chemical stability and tunable thickness from nanometer to micrometer scales through solution‐processable sol‐gel method. These JNU‐hygroCOF films display exceptional moisture‐driven actuation capabilities through modulating the intramolecular hydrogen bonds, which act as specific locks that open and close the molecular rotor of N─N bond responding to guest molecules, within the unique azine‐pyridine molecular skeleton. By integrating these new JNU‐hygroCOF films into a portable respiratory monitoring system, a proactive and preventive solution for diagnosing and managing respiratory disorders such as sleep apnea and asthma has been provided. [ABSTRACT FROM AUTHOR]

This paper addresses the co-design of event-triggered dynamic output-feedback (DOF) control for discrete-time linear parameter-varying (LPV) systems. Two independent event-triggering schemes are introduced to determine when to transmit data from the sensor to the controller and from the controller to the actuator channels. Enhanced conditions employing linear matrix inequalities (LMIs) are derived to establish constructive criteria for simultaneously designing the gain-scheduled DOF controller and the triggering mechanisms, ensuring the asymptotic stability of the closed-loop LPV system's origin. Additionally, a convex optimisation problem is proposed to enlarge the inter-event sampling on the independent channels of sensor-to-controller and controller-to-actuator. Numerical examples are provided to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Water constitutes a huge circulation network in solid, liquid and gaseous forms that contains inestimable recyclable energy. Obtaining energy from gaseous moisture is challenging but of great significance to promote the energy upgrading. The emergence of moisture‐driven actuator (MDA) provides an effective way in converting moisture energy to mechanical energy. The MDA can combine with water molecules through hygroscopicity and swell to produce macroscopic deformation. Due to the wide distribution of humidity and the wireless driving mode, MDA shows great application potential in the fields of environmental monitoring, remote control and energy harvesting. This paper comprehensively reviews the research progress of MDA from aspects of hydrophilic materials, structures, preparing methods, multi‐response integration and applications, aiming at providing guidance for the design, preparation and application of MDA. Besides, the challenges faced by MDA are analyzed and corresponding solutions are proposed, which points out the next stage developing direction of MDA. [ABSTRACT FROM AUTHOR]

Unlike conventional rigid robots, soft robots utilize soft materials that allow them to deform based on their structure, enabling safe interaction with humans. Among various pneumatic actuators in soft robotics, pneumatic network (PneuNet) actuators, which consist of bellows‐like chambers, enable bending and repetitive actions with minimal material deformation at low pressures. Given that the performance of PneuNet actuators is affected by their geometric parameters, considering the impact of geometric variations is crucial in this field. Herein, the effect of geometrical parameters on a zig‐zag soft pneumatic actuator, and an improved version of conventional PneuNet actuators designed for enhanced performance are investigated. Finite element analysis (FEA) indicates that smaller gaps between chambers, thinner bottom layers, and taller chamber heights result in greater bending under the same pressure within the tested parameter range. Experimental results reveal a 30.9% larger bending angle than that of conventional actuators with the same parameters. The FEA results are consistent with the experimental data, exhibiting an error of 10.2%. Furthermore, the tip and grip forces are 1.45 times and 1.3 times larger, respectively, compared to conventional actuators. These results provide direction for the design of zig‐zag soft pneumatic actuators, showcasing improved performance over conventional soft actuators. [ABSTRACT FROM AUTHOR]

AbstractThis paper presents the design and optimization process of a Virtual Biomechanical Shoulder Robot Model (VBSRM) based on a 6-4 parallel mechanism. To address the challenges posed by parallel manipulators and the specific biomechanical constraints of the shoulder joint, a comprehensive design analysis is conducted. First, a kinematic model of the VBSRM is developed, followed by an investigation of its geometric model. To obtain an optimal VBSRM design, performance objectives such as condition number, norm of actuator force, and stiffness are identified and optimized. Initially, only condition number of the robot mechanism is optimized using Genetic Algorithm and performance objectives from the optimal design are analyzed. Later, the three objectives are grouped to form a single function and a single objective-based optimization is also conducted. However, further investigation revealed the conflicting nature of the objectives and hence these were simultaneously optimized using the Non-dominated Sorting Genetic Algorithm (NSGA II). The results obtained from various optimization routines are compared and it is found that the results from the NSGA II provide a better tradeoff between the performance objectives. The motion trajectories from the optimal design of the VBSRM are later analyzed vis-à-vis human shoulder motions for its intended use as a robotic model of the human shoulder joint in various applications. [ABSTRACT FROM AUTHOR]

In this work, we investigate short-packet communications in power beacon (PB)-assisted Internet-of-Things (IoT) networks, where an energy-constrained actuator first harvests energy from a dedicated PB, and then transmits confidential signals to a desired controller in the presence of an eavesdropper. We derive a closed-form lower bound approximation expression for the average achievable effective secrecy rate (AESR) over Nakagami-m fading channels. To gain more insights, we also present the asymptotic average AESR in the high signal-to-noise ratio (SNR) regime. Specifically, analytical results indicate that an average AESR floor appears with the increase of SNR. Moreover, a low complexity one-dimensional search method is employed to maximize the average AESR by optimizing the energy harvesting length. Monte-Carlo simulations are provided to corroborate our analysis. [ABSTRACT FROM AUTHOR]

Inflatable pouches are attractive as actuators and structural links in soft robots due to their low deflated profile and high deformation ratio. However, current pouch robot fabrication methods have relatively large minimum feature sizes and multi‐layer fabrication challenges, limiting the integration of mechanisms with many independent degrees of freedom (DoF). A new monolithic prototype fabrication method utilizes inkjet printing of a masking ink layer, which prevents film bonding and thus defines inflatable regions. Multi‐layer inflatable pouches of any planar geometry can be created using thermal fusing, with inter‐layer connections and a minimum feature resolution of 0.3 mm. The multi‐layer fabrication process enables the integration of pouches for bending actuation and structure, pneumatic channels, and external port connections. This high level of integration enables the fabrication of pouch robots with many independent DoFs. Specific examples using four layers of 38 micrometer thick Low‐density polyethylene (LDPE) include 1) a 38 mm‐wide 4‐fingered robot hand with 8 independent DoFs which rotates a cube within its palm and 2) a 138 mm‐long planar continuum manipulator with 10 independent DoFs for pick‐and‐place of a cylinder. These example designs demonstrate the capability of ink‐patterned masking to achieve new levels of functionality for thin‐film pouch robots. [ABSTRACT FROM AUTHOR]

ABSTRACT This article studies the problem of fault estimation (FE) and dynamic output fault‐tolerant control (DOFTC) for a class of Takagi–Sugeno (T–S) fuzzy singularly perturbed systems (SPSs) which subject to time delay, external disturbance and actuator fault. A new fault estimation and fault‐tolerant control scheme was proposed and designed for the influence of the change of perturbation parameter ε$$ \varepsilon $$ on the singularly perturbed system. This scheme adopts the Takagi–Sugeno (T–S) fuzzy model, learning observer and dynamic output feedback fault‐tolerant mechanism, so that the system has multi‐time‐scale dynamic stability. The results show that this method has more accurate estimation effect, faster convergence speed, and very fast steady‐state response of fault‐tolerant control when faults occur. Furthermore, when constructing the Lyapunov function, the improved matrix P(ε)$$ P\left(\varepsilon \right) $$ was selected to ensure that the closed‐loop system is stable for all ε∈(0,ε‾]$$ \varepsilon \in \left(0,\overline{\varepsilon}\right] $$, and at the same time, the conservativeness of the results was reduced. Finally, the feasibility and correctness of the proposed design method were illustrated through two numerical examples. [ABSTRACT FROM AUTHOR]

Recently, soft actuators with the capabilities of stimuli response have attracted great attention and shown potential application prospects in soft robots. The critical factor of soft actuators to realize practical applications is the programmable shape deformations. However, it remains a challenge to develop a simple and versatile method to design a soft actuator with programmable deformations. Herein, we report a programmable graphene oxide (GO)/wax moisture-responsive actuator through water-shaping and heat-welding methods. Diverse actuators with different initial shapes can be achieved by the water-shaping method, which provides the possibility for preparing actuators with various desired shapes. Additionally, more complex 3D configurations of actuators can be programmed by the heat-welding method. As proof-of-concept demonstrations, several soft robots, such as a bionic walking robot, a grasping robot, and a weight-bearing robot, are demonstrated. Certainly, the versatile and simple programming methods of soft actuators hold great potential for intelligent robotics. [ABSTRACT FROM AUTHOR]

Continuum soft-robotic fingers/arms have emerged as a promising solution to realize abilities to delicately manipulate objects, conform to various shapes, and maintain cost-efficiency (i.e. fewer actuators and less computational resource). This paper introduces a novel approach to designing continuum flexible fingers by optimizing the fingers' thickness distribution to achieve specific target force vectors for specific manipulations, enabling actions like pull-in handing (retraction), push-out manipulation, secure grip, and gentle object hold. The proposed method employs a genetic algorithm to optimize the thickness distribution of the continuum finger driven by a single motor, resulting in a highly versatile and cost-effective solution. The proposed method includes physical simulations to validate the approach's effectiveness in applying desired force vectors during manipulation interactions. This work represents a significant advancement in continuum robotic systems, potentially impacting a wide range of applications in human-robot collaboration. [ABSTRACT FROM AUTHOR]

Real-time hybrid testing is a method in which a substructure of the system is realized experimentally and the rest numerically. The two parts interact in real time to emulate the dynamics of the full system. Such experiments, however, are often difficult to realize as the actuators and sensors, needed to ensure compatibility and force-equilibrium conditions at the interface, can seriously affect the predicted dynamics of the system and result in stability and fidelity issues. The traditional approach of using feedback control to overcome the additional unwanted dynamics is challenging due to the presence of an outer feedback loop, passing interface displacements or forces to the numerical substructure. We, therefore, advocate for an alternative approach, removing the problematic interface dynamics with an iterative scheme to minimize interface errors, thus, capturing the response of the true assembly. The technique is examined by hybrid testing of a benchtop four-storey building with different interface configurations, where using conventional hybrid measurement techniques is very challenging. A case where the physical part exhibits nonlinear restoring force characteristics is also considered. These tests show that the iterative approach is capable of handling even scenarios which are theoretically infeasible with feedback control. [ABSTRACT FROM AUTHOR]

This paper investigates the sliding mode control problem for cyber‐physical systems subject to multi‐source disturbances and actuator false data injection attacks simultaneously. Firstly, a series of extended state observers are designed to estimate the unknown multi‐source disturbances. For the actuator false data injection attacks, a sliding mode observer is designed to online estimate the values of attacks. Then, by introducing the disturbance and attack estimations, a dynamic sliding manifold and a composite sliding mode controller are constructed. Under the proposed approach, the unknown disturbances and false data injection attacks can be timely estimated and compensated, which can improve the disturbance rejection ability and guarantee security of the cyber‐physical system. Lyapunov theory is utilized to prove the stability of the closed‐loop system. Finally, simulations of both the numerical example and application to a power converter system demonstrate the effectiveness and superiority of the proposed composite sliding mode control approach. [ABSTRACT FROM AUTHOR]

This article discusses the control problem of marine autonomous surface ships (MASS) under cross‐water scenarios, that is, from open water to restricted water, where several practical facts, such as uncertain dynamic, unknown disturbance and actuator wear suppression, are taken into account. To resolve such a control design challenge, the predefined performance control (PPC)‐based and barrier Lyapunov function (BLF)‐based ideas are employed, and a prespecified performance function (PPF) is designed to implement the transformation of cross‐water design. Under the adaptive backstepping design framework, with aid of PPC‐based and BLF‐based design ideas, an adaptive neural control solution is developed for MASS under cross‐water scenarios. Furthermore, to reduce the actuator wear and tear caused by high‐frequency corresponding control commands and hull vibration, a new multichannel concurrent event‐triggered protocol (ETP) is constructed in the controller‐actuator (C‐A) channel. Finally, a concurrent event‐triggered adaptive neural control scheme is proposed for MASS under cross‐water scenarios. The theoretical analysis indicates that all signals in the control system are ultimately bounded, and the Zeno behavior is avoided. The simulation and comparison results verify the effectiveness and superiority of the developed control scheme. [ABSTRACT FROM AUTHOR]

Actuator constraints, particularly saturation limits, are an intrinsic and long‐standing problem in the implementation of most control systems. Model reference adaptive control (MRAC) is no exception and it may suffer considerably when actuator saturation is encountered. With this in mind, this paper proposes an anti‐windup strategy for model reference adaptive control schemes subject to actuator saturation. A prominent feature of the proposed compensator is that it has the same architecture as well‐known nonadaptive schemes, namely model recovery anti‐windup, which rely on the assumption that the system model is known accurately. Since, in the adaptive case, the model is largely unknown, the proposed approach uses an "estimate" of the system matrices for the anti‐windup formulation and modifies the adaptation laws that update the controller gains; if the (unknown) ideal control gains are reached, the model recovery anti‐windup formulation is recovered. The main results provide conditions under which, if the ideal control signal eventually lies within the control constraints, then the system states will converge to those of the reference model, that is, the tracking error will converge to zero asymptotically. The article deals with open‐loop stable linear systems and highlights the main challenges involved in the design of anti‐windup compensators for model‐reference adaptive control systems, demonstrating its success via a flight control application. [ABSTRACT FROM AUTHOR]

Soft actuators are constituted by a type of intelligent materials, and they can generate reversible mechanical motions under external stimuli. They usually achieve continuous actuation by manual turning on or off the power supply, which significantly increases the operation complexity. In contrast, self-oscillating actuators can achieve autonomous motions under constant stimuli, and have recently attained great advancements, as well as promoted the development of autonomous soft robotics. In this review, the latest achievements of soft oscillators are summarized. First, the self-oscillating mechanisms mainly including oscillating chemical reactions and self-shadowing-induced mechanical negative feedback loops are discussed. The oscillators constructed with various materials and configurations, driven by different stimuli and applied in different fields are then presented in detail. Finally, the difficulties and hopes of oscillators are presented. Overall, self-oscillating actuators are in the stage of vigorous development, and we believe that in the future, they will be used in various fields and make many scenarios more intelligent and autonomous. [ABSTRACT FROM AUTHOR]

Robots with parallel-link structures are generally considered useful for achieving high-speed motion; however, they are typically large in size. Robot size can be reduced by using a serial-link structure. However, their moving parts, typically having a large mass or moment of inertia, are considered unsuitable for high-speed motion. High-speed motion performance can be improved by avoiding mounting actuators on the moving parts using some method to transmit the drive force or motion. In this letter, we propose a model in which a non-pulley musculoskeletal robot, previously studied by us, is modified to avoid mounting actuators on the movable parts. We demonstrate that the robot can be controlled to achieve the target posture using this modified model. We also discuss the feasibility of high-speed motion of a prototype robot using muscular forces computed for several motion patterns based on the minimum muscle-tension change model. [ABSTRACT FROM AUTHOR]

There has been significant interest in the field of bio-inspired robotics, particularly in the development of flapping-wing robots from micro to bird size. Most flapping robots use lever-crank mechanisms or servomotors as wing flapping mechanisms. Servomotor-based flapping has the advantage of being able to generate various flapping patterns according to amplitude, offset, frequency, waveform, and other factors. However, it is not clear how these factors affect thrust generation. Therefore, this study focuses on the force generation and power consumption in different flapping patterns as well as the wing deformation during the flapping motion to provide some insights into the performance improvement. The results showed that the response characteristics of the actuators caused the thrust to saturate at high frequencies, and that sinusoidal pattern could generally achieve good performance and efficiency. [ABSTRACT FROM AUTHOR]

In this work a nanosecond-pulsed dielectric barrier discharge actuator is simulated to investigate the plasma and surface charge behavior during the startup phases of a given pulse sequence. A potential of plus/minus 1.2 kV is applied sinusoidally with a total pulse width of 100 ns over five full pulses. These results show that plasma development changes substantially between the first three pulses, where the distribution of free electrons resulting from the previous pulse influences the development of the plasma sheath and hence the downstream extent of the bulk plasma. Between the third and fifth pulses, a negative surface charge region persists at the downstream extent of the plasma, which generates an electron void, thus inhibiting the development of a strongly ionizing plasma sheath. These results show that by five pulses the plasma has reached its maximum extent and that for the purposes of establishing average values the first two pulses should not be considered representative of the longer-term plasma behavior. [ABSTRACT FROM AUTHOR]

Background: The lack of visual dynamic spray characterization has made the understanding of the physical processes governing atomization and drug particle formation difficult. This study aimed to investigate the changes in the spray plume morphology and aerodynamic particle size of solution-based pressurized metered-dose inhalers (pMDIs) under different conditions to achieve better drug deposition. Methods: Solution-based pMDIs were studied, and the effects of various factors, such as propellant concentration, orifice diameters, and atomization chamber volume, on drug deposition were examined by analyzing the characteristics of spray plume and aerodynamic particle size. Results: Reducing the actuator orifice and spray area led to a concentrated spray plume and increased duration and speed. Moreover, the aerodynamic particle sizes D50 and D90 decreased, whereas D10 remained relatively unchanged. Decreasing the atomization chamber volume of the actuator led to reduced spray area and an increased duration but a decreased plume velocity. D90 exhibited a decreasing trend, whereas D10 and D50 remained relatively unchanged. Reducing the propellant concentration in the prescription, the spray area and the plume velocity first decreased and then increased. The duration initially increased and then decreased. The values of D50 and D90 showed an initial decreasing followed by an increasing trend, whereas D10 remained relatively unchanged. Conclusions: During the development process, attention should be paid to the changes in the spray area, spray angle, duration, and speed of the spray plume. This study recommended analyzing the characteristics of the spray plume and combining the data of two or more aerodynamic particle size detection methods to verify the deposition in vitro to achieve rapid screening and obtain high lung deposition in vivo. [ABSTRACT FROM AUTHOR]

Actuator systems are among the most noteworthy aspects of the rapidly expanding field of smart and multifunctional materials, which is having a substantial impact on a number of application areas. Ionic liquids (ILs) are a particularly relevant option for the development of hybrid materials for actuator applications, because of their simple processing and tailored response. This review work focuses on ionic liquid‐based polymer blends for soft actuator applications. The main properties of IL for these applications are highlighted and the state of the art of actuator devices is presented by the type of polymer matrix. Finally, the main conclusions and future trends are presented, in order to properly tailor the characteristics and functional response of IL‐blends for actuator applications. [ABSTRACT FROM AUTHOR]