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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]

This paper describes the significance of the minimum actuation limit per actuator while controlling the shape of a single-layer frame dome. The algorithms that perform optimum shape controlling allow the user to assign the minimum allowable actuation per actuator, which means the actuators with an actuation of less than the assigned amount are assumed to be passive; thus, they are excluded. In this study, the deformed shape of a numerical model of a single-layer dome is reshaped. At the same time, the minimum limit is assumed to vary between 0.1mm and 1 mm to investigate how the outcomes are affected. The results show that changes in the minimum allowable actuation significantly affect the number of necessary actuators and the final form of the structure in terms of nodal displacements and stresses. The study suggests using the limit of 0.7 mm, which provides the optimum number of actuators while the nodal displacements are controlled.

The remotely controlled shape memory behaviors of a two-dimensional (2D) sheet to controlled helix structure upon external stimuli is of great significance in the field of smart materials. Herein, we devise a strategy to fabricate a series of shape memory polycaprolactone/[W.sub.18][O.sub.49] nanowire film via highly efficient UV-triggered thiol-acrylate click chemistry. The resultant polymer composites exhibited desirable photothermal transfer efficiency and can enable rapid temperature increase over the melting temperature of polymeric matrix, thus remotely actuating shape transformation within 8 s. Owing to the well- defined architecture of the polymer network, the fabricated elastic composite film exhibited a high degree of crystallinity and showed excellent shape memory properties with [R.sub.f] of 93.12% and [R.sub.r] of 95.32%. Remarkably, under a 160 mW/[cm.sup.2] simulated sunlight illumination, the transformation of flat 2D film into 3D chiral actuators is driven by designing anisotropic bilayer thin sheet, and it yields right- and left-handed helix. This work will pave the way for designing biomimetic flexible actuators toward multifunctional shape-shifting devices. Highlights * Shape memory polycaprolactone/[W.sub.18][O.sub.49] nanowires composite film is fabricated via UV-triggered thiol-ene click chemistry. * Polymer composites exhibit light-activated shape memory behaviors. * The composite films show excellent shape fixity and shape recovery ratio based on the well-defined network. * The shape morphing behaviors of a flexible 2D bilayer strip into 3D chiral actuators are achieved. KEYWORDS flexible actuators, polycaprolactone, shape memory polymers, stimuli- responsive polymers, 1 | INTRODUCTION Stimuli-responsive morphing materials belong to one kind of molecules with 'intelligent' behavior, which can generate corresponding response signals upon the stimuli of heat, light, electric field, etc. [...]

In this article, the issue of fixed‐time fault‐tolerant control is studied for a class of nonlinear systems with sensor/actuator faults. The tuning functions and command filters are used to solve the problem of over‐parameterization and differential explosion in traditional backstepping method. The above methods simplify the derivation and reduce the calculation burden of the system respectively. Moreover, the introduction of fixed‐time control further improves the rapidity of the system. Another feature of this design is that the fixed‐time stability is finally realized by introducing a special Lyapunov function, rather than the practical fixed‐time stability. The tracking error can be guaranteed to converge to the origin in a fixed time. Simulation results show that the proposed control strategy is effective even if there are actuator/actuator faults in the system. [ABSTRACT FROM AUTHOR]

This article presents a fault‐tolerant platooning control algorithm for a class of nonlinear homogeneous multi‐vehicle systems under unreliable network communication environment. The considered types of actuator failures in individual vehicle are loss‐in‐effectiveness, and bias faults. Suppose the communication network among vehicles is here described as a switching graph subject to intermittent communications. Unlike the existing results dealing with vehicle platoon under continuous communications, this article develops a hierarchical fault‐tolerant platooning control approach, under which, the multiple vehicle coordination platooning objective is ensured even in the cases of discontinuous communication faults and actuator failures. First, each following vehicle can estimate the desire reference information via cooperative adaptive virtual estimator even in intermittent communications. Second, the local fault‐tolerant controller with adaptive parameter update mechanism can guarantee the practical position and velocity of following vehicles asymptotically track the desire estimations. Finally, a simulation example of a team of autonomous vehicles is given to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Many practical dynamic models always suffer from complex nonlinearities, parameter uncertainties and random noises. Such kind of models are always characterized by uncertain stochastic nonlinear systems. Besides, many factors will lead to dead‐zone actuator, which further adds more challenges to control engineering. This paper studies stabilization issue of stochastic systems with polynomial nonlinear conditions, unknown parameters and dead‐zone actuator. An adaptive control approach is proposed by exploring homogeneous domination control and using dynamic‐gain‐based adaptive design strategy. It shows that all the signals are bounded almost surely and the system states converge to the origin almost surely. The presented method is successfully applied to the mass spring mechanical system. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive fault‐tolerant control (FTC) scheme is proposed for a class of uncertain nonlinear systems with actuator failure, in which a healthy actuator is available as a backup. Instead of monitoring the failure in real‐time, an intermittent monitoring mechanism (IMM) is proposed by designing a set of monitoring functions operating only at discrete time instants, which makes the proposed scheme more applicable for networked control systems for which the actuator status has to be monitored via network. An adaptive backstepping controller is designed with the errors being modified to include shifting functions. Once actuator failure is detected by the monitoring functions, the actuator is switched to its backup and the controller is reconfigured by updating the shifting functions so that the tracking error can be driven into the prescribed performance in a given time. [ABSTRACT FROM AUTHOR]

Microgel-enhanced asymmetric hydrogels containing a thermosensitive layer and a non-thermosensitive layer are constructed. Actuators exhibiting outstanding response properties and multiple mechanosensors possessing high sensitivity are demonstrated. [Display omitted] Thermosensitive hydrogels have found extensive applications in soft devices, but they often suffer from limited functionalities, low response rate and small response amplitude. In this work, double layered asymmetrical hydrogels composed of a thermosensitive layer and a non-thermosensitive layer are developed to simultaneously achieve high-performance mechanosensing and actuating properties in a single hydrogel. In thermosensitive layer, thermosensitive microgels are introduced to construct hierarchical structure, which accounts for the enhanced thermosensitive behaviors by cooperative responsiveness. In non-thermosensitive layer, poly(acrylamide- co -acrylic acid) (P(AM- co -AA)) hydrogel is constructed. KCl is introduced as conductive component. Mechanosensors for monitoring various mechanical stimuli in daily life have been fabricated utilizing such hydrogels and high gauge factors (GF) have been achieved, 0.38 for resistive strain sensors, 9.40 kPa−1 for piezoresistive pressure sensors and 3.92 kPa−1 for capacitive pressure sensors. Because of the asymmetrical structure, such hydrogels also exhibit outstanding actuating properties with a fast response rate of 863°/min and a bending amplitude about 360°. Interestingly, grasping-releasing of target objects utilizing an octopus-shaped hydrogel actuator and temperature alerting based on hydrogel actuator are also demonstrated. Overall, the double layered asymmetrical ionic hydrogels have provided a new clue to construct hydrogel devices with multiple functionalities and enhanced response properties. [ABSTRACT FROM AUTHOR]

Although recent years have seen considerable interest in stimuli‐responsive hydrogels, their strict preparation conditions and narrow applicability limit their use as diverse sensors and soft robots. Herein, a versatile Agar‐Zwirrions hybrid hydrogel actuator (Agar/PSBMA) integrated with simultaneous temperature self‐sensing and wide‐range electrical response is developed. To prepare the Agar/PSBMA hydrogel, a simple and controllable preforming post‐enhancing and mechanical pressing method is used by introducing zwitterions materials into a temperature‐sensitive Agar matrix. Owing to the design, the compact multiplex complementary structure generated by this method and the materials can facilitate the improvement of flexibility, stretchability, and toughness while providing mechanical dissipation and adhesion properties. Importantly, the visible detected temperature self‐sensing ability during 10–40 °C, and quick and wide‐range bending responses of both high‐voltage and low‐voltage electric fields make it unique over other actuators. Furthermore, the electrical response behavior of the hydrogel is found to be impacted by mechanical characteristics and charge polarization based on the finite element Abaqus simulations analysis. The prepared versatile hydrogels show the potential for applications as soft robotics and controlled transportation of adhered substances while simultaneously monitoring their working temperature, which expands the response range of hydrogel actuators and broadens the scope of application. [ABSTRACT FROM AUTHOR]

This paper investigates an event‐triggered adaptive resilient control problem for nonlinear systems against unknown false data injection and actuator saturation. The sensors of the controlled system are subject to unknown false data injection attacks so that all original states can not be directly applied in the controller design process. To address the negative effects of the false data injection attacks, attack compensators are introduced in control design. Simultaneously, a dynamic event‐triggering mechanism is set up to reduce the communication burden of the network. Furthermore, an auxiliary system is constructed to cope with the actuator saturation that commonly exists in practical systems. Based on the Lyapunov stability theory, it is demonstrated that the designed adaptive controller can guarantee the stability of the controlled system and the boundedness of all signals. The validity of the proposed control scheme is evidenced by simulation examples. [ABSTRACT FROM AUTHOR]

This paper aims to develop a robust decomposed system control (RDSC) strategy under input constraints for an electro‐mechanical linear actuator (EMLA) facing model uncertainty and external disturbances. At first, a state‐space model of a complex multi‐stage gearbox EMLA system, driven by a permanent magnet synchronous motor (PMSM), is developed, and the non‐ideal characteristics of the ball screw are presented through the model. The result is a four‐order nonlinear strict‐feedback form (NSFF) system decomposed into three subsystems. As the paper's main result, a novel RDSC strategy with uniform exponential stability for controlling subsystem states is presented. This developed controller avoids the "explosion of complexity" problem associated with backstepping by treating the time derivative of the virtual control input as an uncertain system term. The proposed method, despite assuming load disturbances and input constraints with arbitrary bounds, offers a straightforward control approach for a broader range of applications. Further, the controller's performance is evaluated by simulating two distinct duty cycles, each representing different levels of demand on the actuator facing load disturbances near the rated motor performance. [ABSTRACT FROM AUTHOR]

This article investigates the fault‐tolerant formation containment control of multi‐agent systems with actuator and sensor faults. First, adaptive descriptor observers are proposed for the followers to estimate system states, actuator faults, and sensor faults simultaneously. Then, distributed fault‐tolerant formation containment controllers are designed based on the estimated values and sufficient conditions for the formation containment control are identified using Lyapunov method in the time domain. Finally, the effectiveness and advantages of the proposed method are demonstrated through numerical simulations. [ABSTRACT FROM AUTHOR]

Summary: This article investigates the devise issue of a practical finite‐time output‐tracking control for uncertain nonlinear nonstrict‐feedback systems subject simultaneously to time‐varying output constraints (TVOC), actuator saturation, and bounded unmatched disturbances. An adaptive fuzzy approximator‐based control system is devised using the dynamic surface control (DSC) concept. System output constraints are addressed by employing an appropriate barrier Lyapunov function. Adaptive fuzzy disturbance observers are constructed to practically deal with time‐varying unmatched but bounded disturbances. It is verified via Lyapunov stability analysis and simulation experiments that all closed‐loop signals remain bounded, the output tracking error practically converges in finite time to a tiny but adjustable neighborhood around the origin, and the system output stays within its required time‐varying bounds. [ABSTRACT FROM AUTHOR]

Soft pneumatic actuators (SPAs) hold great promise for simple and effective actuation of soft robots. Multi‐degree‐of‐freedom SPAs are highly desired as they enable diverse motion forms and improve possibility for soft robots to navigate challenging environments and perform complex tasks. Herein, this study proposes two novel origami‐based SPAs (O‐SPAs), namely the Flasher origami‐inspired SPA (FO‐SPA) and the Kresling origami‐inspired SPA (KO‐SPA), which are fabricated entirely from soft silicone without any rigid supports. A finite element model is developed to predict the deformation behavior of O‐SPAs and the deformability and dynamic response of O‐SPAs are characterized through performance tests. Simulation experiments are carried out to investigate the impact of different structural parameters on their performance. These O‐SPAs are highly sensitive to low negative pressure, exhibiting 80% of maximum deformation at −4 kPa. Based on the Flasher and Kresling origami pattern, the actuators are capable of generating compound motions including contraction, twisting, and radial motions. These motions can be used as "building blocks" for the rapid reconfiguration of various soft robots. The study has successfully enriched the types of existing SPAs by providing important multiple motions through origami, with great potential to facilitate the rapid and low‐cost design of soft robots. [ABSTRACT FROM AUTHOR]

With their unique combination of characteristics – an energy density almost 100 times that of human muscle, and a power density of 5.3 kW kg−1, similar to a jet engine's output – Nylon artificial muscles stand out as particularly apt for robotics applications. However, the necessity of integrating sensors and controllers poses a limitation to their practical usage. Here, a constant power open‐loop controller is reported based on machine learning. It shows that the position of a nylon artificial muscle without external sensors can be controlled. To this end, a mapping is constructed from a desired displacement trajectory to a required power using an ensemble encoder‐style feed‐forward neural network. The neural controller is carefully trained on a physics‐based denoised dataset and can be fine‐tuned to accommodate various types of thermal artificial muscles, irrespective of the presence or absence of hysteresis. This neural network effectively endows the artificial muscles with "muscle memory", allowing them to replicate complex movements reliably. [ABSTRACT FROM AUTHOR]

Snap-through instabilities in single and interconnected dielectric elastomer actuators have demonstrated their potential in enabling many functionalities such as large deformation, high-speed actuation, and enhanced flowrates in fluid pumps. However, the nonlinear nature of dielectric elastomers and the complex interplay of mechanics in interconnected inflated actuators, make the modeling of such systems challenging. In this paper, we present a methodology to analytically model the instabilities in a system of three interconnected homogeneous spherical dielectric elastomer actuators through graphical and numerical approaches. The simulation results reveal the presence of a locus of initial stable states that the interconnected actuators can achieve at zero voltage. In specific loading conditions, the system exhibits multiple stable states which can be cyclically transitioned between by selectively applying voltage to specific actuators. In other conditions, the system may undergo two successive instabilities when the voltage applied to a single actuator in the system is increased monotonically. These results retrieve existing experimental results theoretically for the first time and identify a new behavior of cascading instabilities in inflated dielectric elastomer actuators. We hope this work will pave the way for programmable design of multistable systems to unravel new capabilities in dielectric elastomer actuators and soft robotics. [ABSTRACT FROM AUTHOR]

In robotics, finding new structures of parallel robots to achieve higher kinematic and dynamic performance is a great matter. This article describes the introduction, design, and modeling of a novel parallel spatial robot. The name "conjoined twins 3RPRS" (CT-3RPRS) is chosen for the introduced robot as its structure is based on an innovative combination of two 3RPRS robots. Initially, the actuators of the 3RPRS robot were shifted from the base plane to the middle plane of the robot, and then three new links were added to balance the robot. Therefore, CT-3RPRS has six links, three on each side of the middle plane (actuator plane) that are connected to the prismatic actuators with revolute joints. The complete kinematic equations of the robot are extracted. Afterward, the singularity analysis is performed. The results of the simulations showed that CT-3RPRS provides a better reachable workspace feature than 3RPRS. The mentioned advantage is achieved while the size of the two robots is the same and the movement range of CT-3RPRS actuators is less. [ABSTRACT FROM AUTHOR]

In this paper, a distributed observer-based resilient control scheme is proposed to solve the voltage regulation and current sharing problems of islanded direct current (DC) microgrids under actuator faults. First, an observer-based distributed fault estimation design is presented to estimate fault signals with high accuracy. Then, based on the estimated information, a primary decentralized fault-tolerant control layer is designed to ensure accurate voltage reference tracking. A secondary cooperative control layer is employed to achieve the goal of current sharing. Besides, both the fault estimation observers and the fault-tolerant controllers are designed in a plug-and-play fashion, which guarantees the scalability of the DC microgrid. The simulation and experimental results show that the proposed control strategy can efficiently improve the reliability and resilience of the DC microgrid. [ABSTRACT FROM AUTHOR]

The effect of adding texture to increase the deformation of a bilayer actuator by a factor of over 100 was demonstrated. A bilayer actuator is driven by the difference in thermal deformation. Therefore, two films or plates with a large difference in thermal expansion coefficient are required. The newly developed textured film actuator (TFA) obtained large deformation even in a case involving a combination of two films with a small difference in thermal expansion coefficient. The TFA was fabricated by transferring the texture when laminating two PI films with different coefficients of thermal expansion. A TFA with thin‐film electrodes was heated by applying electric power. Thereby, it unfolded from a curled state. The maximum generated force and curvature of the TFA were 7.4 mN and 0.19 mm−1, respectively, at 0.38 W. The manufacturing process for the TFA is simple and convenient, as it does not require adhesives or special materials. In thermal drive bilayer actuator fabrication, the range of material selection is expanded substantially. In addition, large deformations are generated with less energy. Therefore, the energy consumption is likely to be reduced. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This study investigates the system-level performance of variable recruitment (VR) fluidic artificial muscle (FAM) actuator bundles using a model that incorporates FAM interaction effects. A VR bundle combines multiple FAMs to act as one actuator in which the FAMs are sequentially recruited to increase overall efficiency. In a VR bundle, inactive/low-pressure FAMs are compressed beyond their free strains, exerting resistive forces opposing that of active FAMs. A recent model that captures this behavior is used to simulate sinusoidal contraction of a VR bundle with a hanging mass load. The implications of inter-FAM effects on the force-strain space of a VR bundle are discussed and a method of recruitment state transition required to track a sinusoid is proposed. The dynamics of the electrohydraulic subsystems are presented and used to evaluate its system efficiency and bandwidth limits. Three different electrohydraulic configurations are considered: (1) continuous motor operation with constant pump displacement, (2) intermittent motor operation with constant pump displacement, and (3) continuous motor operation with variable pump displacement. Simulation results show the superior bandwidth capabilities of VR bundles by demonstrating its ability to track sinusoids with amplitudes up to 16% strain at frequencies greater than 0.5 Hz, compared to that of a single equivalent cross section area motor unit (SEMU). In addition to increased bandwidth limit, system efficiencies averaged over a range of amplitudes show up to 170% increase when comparing a VR bundle using variable pump displacement to a SEMU using constant pump displacement. [ABSTRACT FROM AUTHOR]

This work presents a finite element framework for simulating the quasi-static response of dielectric elastomer-based minimum energy structure (DEMES). The DEMES is an actuator formed by combining an inextensible frame and pre-stretched dielectric membrane that exhibits the unique shape-morphing characteristics of the actuator. A continuum strain energy-based model is implemented to investigate the impact of the different geometrical parameters on the performance of the DEMES actuator. Finite element analyses are performed using user-defined element (UEL) in ABAQUS for determining the equilibrium shape of the actuators and further investigating their electromechanical response. Experiments are performed using the commercially available VHB-4910 acrylic tape and the PET frames. 3D-printed reinforcements are used to impart anisotropy in the specimen. The findings of the model solutions provide preliminary insights on the alteration of the initial and final configurations of the DEMES affected by different geometrical parameters. It is observed that the shape of the electrode (rectangular, circular and triangular), compliant frame (rectangular, circular and triangular) and implemented stiffeners appreciably alter the attained initial configuration, final configuration and actuation range of the DEMES actuator. In general, this investigation can find its potential use in designing the futuristic DEMES through topological optimization of the compliant electrode and frame geometry together with material anisotropy of the elastomer. [ABSTRACT FROM AUTHOR]

A novel monolithic compliant Lorentz-force-driven XY nanopositioning system (MCLNS) is designed, analyzed, and experimentally assessed with the aim of high-resolution positioning across a large workspace. A double-symmetric Lorentz-force actuator (DSLA) with the benefits of zero friction, high thrust, and large stroke is proposed to generate the actuation force. Correspondingly, a monolithic four-prismatic parallel compliant mechanism (4P-PCM) is exploited to transmit the actuation motion to the central platform and minimize the parasitic motion. The unique integration of four DSLAs and one 4P-PCM make the proposed MCLNS possess compact structure and stable performance. The characterization of the MCLNS is formulated by a specially established analytical model and validated by finite-element analysis simulation and experimental tests. Experimental studies show that the workspace of the MCLNS prototype is large than 0.87 × 0.87 mm2 and the positioning resolution of the MCLNS prototype is better than 9 nm. By means of a nonlinear forward proportional integral derivative control strategy, the maximum contouring error of the MCLNS is maintained within 2.7% while tracking a 1257 μ m s−1 circular trajectory. [ABSTRACT FROM AUTHOR]

This note investigates the adaptive security control issue for uncertain delayed semi-Markov jump systems (DSMJSs) within the framework of sliding mode control (SMC), in which the DSMJSs are affected by generally unknown transition rates (GUTRs), actuator failures (AFs) and cyber attacks. By the virtue of the strong approximation ability of neural network (NN), an adaptive NN-based SMC synthesis is carried out, which could not only force the state trajectories onto the proposed sliding surface but also ensure the DSMJSs operate as demanded in spite of the interference errors, structural uncertainty, hidden AFs, cyber attacks and GUTRs. Then, in view of the reachability of the proposed linear-type sliding mode surface (SMS), linear matrix inequalities (LMIs) and stochastic stability theory, a novel stochastically stable criterion for the resultant DSMJSs is obtained. At last, the single-link robot arm model is offered as an instance with simulation to illustrate the viability of the devised strategy. [ABSTRACT FROM AUTHOR]

This paper addresses the output feedback adaptive resilient control problem for a class of stochastic nonlinear systems under sensor and actuator attacks. By applying a linear state transformation, the original system is transformed into a new one for which output feedback control becomes possible. The Nussbaum function is exploited to overcome the unknown control direction problem generated by uncertain control coefficients and adversary attacks. Based on the available compromised output signal and the states reconstructed by a new extended state observer, an output feedback adaptive resilient control scheme is proposed for such systems by combining the neural-networks-based approximation approach, backstepping technique and some special methods. The proposed controller can guarantee that all signals in the closed-loop system are semiglobally bounded in probability and the stabilisation error variables remain in an adjustable vicinity of origin. Finally, the effectiveness and applicability of the proposed control methodology is verified by two illustrative examples. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of dissipative-based stabilization for fractional-order nonlinear control systems with uncertainties, time-delay, external disturbances, actuator faults, actuator and sensor saturations. Specifically, a non-fragile reliable dynamic output feedback controller is designed for the purpose of stabilization of the addressed system. Due to the effect of saturation phenomena occurring in both the actuator and sensor, the anti-windup loops framed with the help of the observer design are incorporated into the controller design. Some sufficient conditions are formulated in terms of linear matrix inequalities by choosing a suitable Lyapunov function thereby assuring the dissipative-based stabilization. The derived results are thus validated by two numerical examples including the practical model of two-stage chemical reactor. [ABSTRACT FROM AUTHOR]

Multilayer ceramic actuators find extensive utility in applications requiring precise displacement control or force output, due to their advantages of high precision control, rapid response, low driving voltage, low power consumption, and so on. For practical applications, there is a need for high‐performance multilayer ceramic actuators (MLAs) that combine cost‐effectiveness, efficiency, and temperature stability. In this work, 1.5 mol%Sm‐doped 0.25 Pb(Mg1/3Nb2/3)O3–0.36PbZrO3–0.39PbTiO3 piezoelectric ceramics with PbO–CuO as sintering aid were fabricated. The addition of PbO–CuO significantly reduced the sintering temperature by 300°C, while having minimal impact on the piezoelectric properties. The optimized sintering condition, achieved at a low sintering temperature of 950°C with the introduction of a tiny 0.4 wt% sintering aid, yields impressive piezoelectric strain coefficient d33* = 690 pm/V. This substantiates the viability of employing low‐cost Ag/Pd (90/10) as inner electrode, which can be co‐fired with ceramic layer to fabricate MLA. This innovation enables a remarkable displacement of 1 µm at a low driving voltage of 200 V across a 9‐layers piezoelectric actuator, accompanied by high‐temperature stability, exhibiting <20% variation over the temperature range of 30–250°C. These results underscore a great potential for high‐performance piezoelectric actuators over a broad temperature range. [ABSTRACT FROM AUTHOR]

Polymer-based actuators have gained extensive attention owing to their potential applications in aerospace, soft robotics, etc. However, poor mechanical properties, the inability of multi-stimuli response and programmable deformation, and the costly fabrication procedure have significantly hindered their practical application. Herein, these issues are overcome via a simple and scalable one-step molding method. The actuator is fabricated by hot-pressing commercial unidirectional carbon fiber/epoxy prepregs with a commodity PC membrane. Notable CTE differences between the CF and PC layers endow the bilayer actuator with fast and reliable actuation deformation. Benefiting from the high strength of CF, the actuator exhibits excellent mechanical performance. Moreover, the anisotropy of CF endows the actuator with design flexibility. Furthermore, the multifunction of CF makes the actuator capable of responding to thermal, optical, and electrical stimulation simultaneously. Based on the bilayer actuator, we successfully fabricated intelligent devices such as light-driven biomimetic flowers, intelligent grippers, and gesture-simulating apparatuses, which further validate the programmability and multi-stimuli response characteristics of this actuator. Strikingly, the prepared gripper possesses a grasping capacity approximately 31.2 times its own weight. It is thus believed that the concept presented paves the way for building next-generation robust robotics. [ABSTRACT FROM AUTHOR]

This article investigates the robust cooperative fault-tolerant control problem of multi-agent systems subject to mismatched uncertainties and actuator faults. During the design process of the intermediate variable estimator, there is no need to satisfy fault estimation matching conditions, and this overcomes a crucial constraint of traditional observers and estimators. The feedback term of the designed estimator contains the centralized estimation errors and the distributed estimation errors of the agent, and this further improves the design freedom of the proposed estimator. A novel fault-tolerant control protocol is designed based on the fault estimation information. In this work, the bounds of the fault and its derivatives are unknown, and the considered method is applicable to both directed and undirected multi-agent systems. Furthermore, the parameters of the estimator are determined through the resolution of a linear matrix inequality (LMI), which is decoupled by employing coordinate transformation and Schur decomposition. Lastly, a numerical simulation result is used to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we present the design of a fractional-order sliding mode observer (FO-SMO) for actuator fault estimation in a quadrotor unmanned aerial vehicle (QUAV) system. Actuator faults can significantly compromise the stability and performance of QUAV systems; therefore, early detection and compensation are crucial. Sliding mode observers (SMOs) have recently demonstrated their accuracy in estimating faults in QUAV systems under matched uncertainties. However, existing SMOs encounter difficulties associated with chattering and sensitivity to initial conditions and noise. These challenges significantly impact the precision of fault estimation and may even render fault estimation impossible depending on the magnitude of the fault. To address these challenges, we propose a new fractional-order SMO structure based on the Caputo derivative definition. To demonstrate the effectiveness of the proposed FO-SMO in overcoming the limitations associated with classical SMOs, we assess the robustness of the FO-SMO under three distinct scenarios. First, we examined its performance in estimating actuator faults under varying initial conditions. Second, we evaluated its ability to handle significant chattering phenomena during fault estimation. Finally, we analyzed its performance in fault estimation under noisy conditions. For comparison purposes, we assess the performance of both observers using the Normalized Root-Mean-Square Error (NRMSE) criterion. The results demonstrate that our approach enables more accurate actuator fault estimation, particularly in scenarios involving chattering phenomena and noise. In contrast, the performance of classical (non-fractional) SMO suffers significantly under these conditions. We concluded that our FO-SMO is more robust to initial conditions, chattering phenomena, and noise than the classical SMO. [ABSTRACT FROM AUTHOR]

Poly(ionic liquid) (PIL)‐based porous membranes are extensively investigated as soft polymer actuators. While PILs have shown significant advancements in membrane fabrication and stabilization of metal nanoparticles (MNPs), research on integrating MNPs into porous membranes to achieve actuation behavior under multiple stimuli is limited. Herein, this work presents a new paradigm for designing a porous PIL‐polyacrylic acid (PAA) membrane with a distinct MNP gradient via a top‐bottom diffusion approach involving a metal salt precursor solution and NaBH4 as a reducing agent. The strong binding sites provided by PILs, combined with the gradient distribution of ‐COO− groups across the membrane cross‐section, play a significant role in controlling the MNPs' gradient distribution. Interestingly, the MNPs within the membrane display excellent catalytic activity in exothermic reactions such as H2O2 decomposition, dissipating uneven heat that quickly permeates the membrane network. This induces asymmetrical swelling of polymer chains, resulting in rapid membrane bending. Furthermore, such MNP‐loaded membrane could serve as a portable test paper for visually monitoring H2O2. This advancement paves the way for the development of intricate smart actuation materials and expands their practical applications in various real‐life scenarios. [ABSTRACT FROM AUTHOR]

Smart hydrogels responsive to external stimuli are promising for various applications such as soft robotics and smart devices. High mechanical strength and fast response rate are particularly important for the construction of hydrogel actuators. Herein, tough hydrogels with rapid response rates are synthesized using vinyl‐functionalized poly(N‐isopropylacrylamide) (PNIPAM) microgels as macro‐crosslinkers and N‐isopropylacrylamide as monomers. The compression strength of the obtained PNIPAM hydrogels is up to 7.13 MPa. The response rate of the microgel‐crosslinked hydrogels is significantly enhanced compared with conventional chemically crosslinked PNIPAM hydrogels. The mechanical strength and response rate of hydrogels can be adjusted by varying the proportion of monomers and crosslinkers. The lower critical solution temperature (LCST) of the PNIPAM hydrogels could be tuned by copolymerizing with ionic monomer sodium methacrylate. Thermo‐responsive bilayer hydrogels are fabricated using PINPAM hydrogels with different LCSTs via a layer‐by‐layer method. The thermo‐responsive fast swelling and shrinking properties of the two layers endow the bilayer hydrogel with anisotropic structures and asymmetric response characteristics, allowing the hydrogel to respond rapidly. The bilayer hydrogels are fabricated into clamps to grab small objects and flowers that mimicked the closure of petals, and it shows great application prospects in the field of actuators. [ABSTRACT FROM AUTHOR]

The purpose of the Hydracer project is to discuss the system performance of the EHAs (Electro-Hydrostatic Actuators) when integrated into robotic systems. We have developed EHAs focusing on compactness, light-weight, force controllability, and back-drivability. The requirements such as compactness and light-weight lead us to the adoption of high-pressure, which unfortunately contradicts with the other requirements, namely, force controllability and back-drivability. The contradiction indicates the necessity of study to find the balanced specification between them, which was the question we raised when we started the development of Hydracer, a 6-DOF manipulator driven by EHAs. The system design started following the specifications of an industrial standard of small-size manipulators. In the previous paper, we reported on the design and evaluation of actuators, namely, the linear EHA modules for the first three joints from the base and the ceramic-reinforced vane motors for the last three. We could also discuss the preliminary results of force control of the last three (wrist) joints. In this paper, we report on the performance of force-controllability and backdrivability of the first three joints of the manipulator after integrating force controllers and gravity compensation. It provides useful information about the total performance of manipulators driven by EHAs. The RMSEs (root mean square errors) of torques of the first three joints under the gravity compensation were 0.53, 1,7, and 1.2 Nm respectively, while the manipulator could carry 10 kg payload at the horizontally stretched configuration for 5 s. [ABSTRACT FROM AUTHOR]

Flexible-joint manipulators (FJMs) have been attracting much attention in recent decades. However, position control and vibration suppression of single-input (SI) multi-degrees-of-freedom (multi( $ {\geqslant }3 $ ⩾ 3)-DOF) FJM is still a high mountain to climb due to the characteristic that some states of such FJMs cannot be directly controlled by the SI. This paper aims to carry out this challenging research. We present a double-loop frame-based adaptive neural sliding-mode control method for an uncertain horizontal SI 3-DOF FJM, i.e. a two-link FJM with only one actuator at the first joint. Since only the actuator angle can be directly controlled, in the inner loop, we design a torque controller so that the actuator angle tracks a time-varying reference actuator angle, designed in real-time by the outer loop. In the outer loop, we consider the reference actuator angle as a virtual control signal and design it based on the dynamic coupling relationships, aiming to indirectly control the first link to its target position and suppress the vibration of both links. Furthermore, to enhance the transient system performance, we plan the input signal of the outer loop (i.e. the target angle) as a smooth reference-trajectory signal. The validity and superiority of this method are demonstrated in simulations. [ABSTRACT FROM AUTHOR]

To achieve predefined‐time trajectory tracking control of a flexible‐joint space robot(FJSR) with actuator constraints, a nonsingular predefined‐time dynamic surface control scheme is developed. The input saturation caused by actuator constraints is addressed via the designed predefined‐time anti‐saturation compensator. On this basis, two different control laws are designed for such high‐order nonlinear systems by utilizing the backstepping technique, and a novel nonlinear filter is constructed to filter the virtual control signals, thus avoiding the "differential expansion" phenomenon. Moreover, a singularity‐free auxiliary function is designed to solve the singularity issue generated by the derivative of fractional power terms in the predefined‐time control algorithm framework. The closed‐loop system is proven to be semi‐globally predefined‐timely uniformly ultimately bounded (SGPTUUB) via constructing the suitable Lyapunov function. The difference and effectiveness of the two designed control laws are illustrated by the conducted simulations. Both of them allow the FJSR system to track the desired trajectory in a reasonably predefined time. [ABSTRACT FROM AUTHOR]

This article addresses the event‐triggered adaptive consensus control of nonlinear multi‐agent systems with unknown control direction and actuator saturation. A new robust adaptive control algorithm based on an event‐triggered mechanism is designed. The smooth Lipschitz function approximates the saturated nonlinear function, while the Nussbaum function handles unknown control directions and residual terms. The event‐triggered mechanism is designed to determine the time of communication, significantly reducing the communication burden. An additional estimator is utilized to deal with unknown parameters involved in neighbor dynamics and prevent information exchange to consistency errors between connected subsystems. The results show that all the signals of the closed‐loop system are uniformly bounded, and the consensus tracking error converges to a bounded set. Meanwhile, Zeno's behavior is eliminated. Simulation results confirm the superiority of the proposed method. [ABSTRACT FROM AUTHOR]

An adaptive neural network fault‐tolerant control method is proposed for the non‐affine multi‐agent systems with actuator failure and input saturation. Through the transformation of the original multi‐agent systems, an equivalent model is proposed. Considering that the signal input of multi‐agent systems is limited, this article will solve the input saturation problem. But in a real system, the actuator would probably fail. Therefore, a fault tolerant control algorithm is proposed to solve the fault problem in the systems. In this article, an adaptive distributed controller is designed to eliminate the uncertainty of the systems. At the same time, the integral barrier Lyapunov function is selected to verify the stability. Finally, a simulation example is given to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Structurally ordered soft materials that respond to complementary stimuli are susceptible to control over their spatial and temporal morphostructural configurations by intersectional or combined effects such as gating, feedback, shape‐memory, or programming. In the absence of general and robust design and prediction strategies for their mechanical properties, at present, combined chemical and crystal engineering approaches could provide useful guidelines to identify effectors that determine both the magnitude and time of their response. Here, we capitalize on the purported ability of soft intermolecular interactions to instigate mechanical compliance by using halogenation to elicit both mechanical and photochemical activity of organic crystals. Starting from (E)‐1,4‐diphenylbut‐2‐ene‐1,4‐dione, whose crystals are brittle and photoinert, we use double and quadruple halogenation to introduce halogen‐bonded planes that become interfaces for molecular gliding, rendering the material mechanically and photochemically plastic. Fluorination diversifies the mechanical effects further, and crystals of the tetrafluoro derivative are not only elastic but also motile, displaying the rare photosalient effect. [ABSTRACT FROM AUTHOR]

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators. [ABSTRACT FROM AUTHOR]

A porous actuator is prepared using a liquid crystal elastomer (LCE) loaded with metal‐organic framework (MOF) nanoparticles (MIL‐88A). While the swellable MOF additive endows the LCE actuator with nanoscale pores, after its removal by chemical etching, macroporous LCE actuator is obtained. This LCE‐MOF actuator displays several interesting features. 1) Selective etching allows the actuator in water to curl in one direction and then reverse the curling direction owing to differential water absorption of the nano‐ and macroporous layers. 2) The stretching‐induced alignment of mesogens in the actuator is little affected by the presence of MOF and substantially retained after water uptake, so that an actuation deformation can be generated either by water absorption or thermally induced order‐disorder phase transition. 3) Assisted by the UV irradiation used for polymer cross‐linking, magnetic iron oxide FeO appears to be formed after chemical etching, which allows the actuator to gain the ability to move on water surface guided by a magnet. 4) The in situ formation of magnetic iron oxide in the macroporous actuator also provides an enhanced photothermal effect, making light‐driven locomotion of the actuator more effective. The use of active porogen like MOF opens a new way to explore porous LCE actuators. [ABSTRACT FROM AUTHOR]

The load-adaptive behavior of the muscles in the human musculoskeletal system offers great potential for minimizing resource and energy requirements in many technical systems, especially in drive technology and robotics. However, the lack of knowledge about suitable technical linear actuators that can reproduce the load-adaptive behavior of biological muscles in technology is a major reason for the lack of successful implementation of this biological principle. In this paper, therefore, the different types of linear actuators are investigated. The focus is particularly on artificial muscles and rope pulls. The study is based on literature, on the one hand, and on two physical demonstrators in the form of articulated robots, on the other hand. The studies show that ropes are currently the best way to imitate the load-adaptive behavior of the biological model in technology. This is especially illustrated in the context of this paper by the discussion of different advantages and disadvantages of the technical linear actuators, where ropes, among other things, have a good mechanical and control behavior, which is very advantageous for use in an adaptive system. Finally, the next steps for future research are outlined to conclude how ropes can be used as linear actuators to transfer load-adaptive lightweight design into technical applications. [ABSTRACT FROM AUTHOR]

In this work, a problem is formulated and a mathematical model for numerical calculation of the effective piezoelectro-elastic characteristics of macro fiber composite (MFC) structures is developed. At the macrolevel, constitutive relations are obtained for composite under longitudinal and transverse piezoelectric loading taking into account the conductivity of phases. The electromagnetic coupling coefficients of the MFC actuator have been determined depending on the volume fraction of the piezoelectric phase in the form of PZT4 fibers and epoxy matrix. The influence of the design piezo actuator parameters on the MFC piezo actuator efficiency is shown. [ABSTRACT FROM AUTHOR]

Flexible intelligent actuators with the characteristics of flexibility, safety and scalability, are highly promising in industrial production, biomedical fields, environmental monitoring, and soft robots. Nanocomposite hydrogels are attractive candidates for soft actuators due to their high pliability, intelligent responsiveness, and capability to execute large‐scale rapid reversible deformations under external stimuli. Here, the recent advances of nanocomposite hydrogels as soft actuators are reviewed and focus is on the construction of elaborate and programmable structures by the assembly of nano‐objects in the hydrogel matrix. With the help of inducing the gradient or oriented distributions of the nanounits during the gelation process by the external forces or molecular interactions, nanocomposite hydrogels with ordered structures are achieved, which can perform bending, spiraling, patterned deformations, and biomimetic complex shape changes. Given great advantages of these intricate yet programmable shape‐morphing, nanocomposite hydrogel actuators have presented high potentials in the fields of moving robots, energy collectors, and biomedicines. In the end, the challenges and future perspectives of this emerging field of nanocomposite hydrogel actuators are proposed. [ABSTRACT FROM AUTHOR]