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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]

High-speed and highly dynamic hypersonic vehicles demand exceptional safety and reliability during flight. Accurate detection and localization of faults in actuators and reaction control systems are pivotal for controlling and predicting operational states. However, this process encounters challenges such as multiple fault modes, limited data availability, and suboptimal diagnostic accuracy. Our focus is on common fault types in reaction control systems and actuators. We have designed a residual module and an attention module to construct an interpretable fault diagnosis model that extracts deep features from fault residual sequences and state parameter sequences. This model allows for the simultaneous and precise identification of fault type, location, and occurrence time. Furthermore, we visualize the diagnosis process through the use of attention weights and class activation mapping, thereby enhancing the interpretability of the fault diagnosis and bolstering the reliability of the results. Our findings reveal that both the residual module and attention module enhance diagnostic accuracy. In the diagnosis network, shallow attention primarily facilitates feature fusion, whereas deep attention primarily serves to filter features and improve detection capabilities. Without increasing computational complexity, the interpretable fault diagnosis model achieved an accuracy of 96.65%, and the fault time localization error was reduced by 86.15%. The proposed method simplifies model training and elevates fault detection accuracy, offering a reliable approach for isolating and identifying actuator faults. [ABSTRACT FROM AUTHOR]

Nanoporous solids offer a wide range of functionalities for industrial, environmental, and energy applications. However, only a limited number of porous materials are responsive, i.e. the nanopore dynamically alters its size and shape in response to external stimuli such as temperature, pressure, light or the presence of specific molecular stimuli adsorbed inside the voids deforming the framework. Adsorption-induced structural deformation of porous solids can result in unique counterintuitive phenomena. Negative gas adsorption (NGA) is such a phenomenon which describes the spontaneous release of gas from an "overloaded" nanoporous solid via adsorption-induced structural contraction leading to total pressure amplification (PA) in a closed system. Such pressure amplifying materials may open new avenues for pneumatic system engineering, robotics, damping, or micromechanical actuators. In this review we illustrate the discovery of NGA in DUT-49, a mesoporous metal–organic framework (MOF), and the subsequent examination of conditions for its observation leading to a rationalization of the phenomenon. We outline the development of decisive experimental and theoretical methods required to establish the mechanism of NGA and derive key criteria for observing NGA in other porous solids. We demonstrate the application of these design principles in a series of DUT-49-related model compounds of which several also exhibit NGA. Furthermore, we provide an outlook towards applying NGA as a pressure amplification material and discuss possibilities to discover novel NGA materials and other counterintuitive adsorption phenomena in porous solids in the future. [ABSTRACT FROM AUTHOR]

This paper presents a barrier function-based adaptive nonsingular fast terminal sliding mode control (BFANFTSMC) algorithm for the trajectory tracking of a Mecanum-wheeled omnidirectional mobile robot (MWOMR). A four-inputs-three-outputs kinematic-and-dynamic model of the MWOMR is constructed with considerations of parameter uncertainties and unknow external disturbances. To achieve a stable and robust performance, a BFANFTSMC scheme is designed for the MWOMR, while a modified barrier function (MBF) is further proposed with particular consideration of actuator saturation. Stability and robustness of the proposed control methods are analyzed using the Lyapunov theory. Also, real-time experimental results on a MWOMR platform show superior performance on tracking precision and control robustness compared with three existing control schemes. [ABSTRACT FROM AUTHOR]

This paper addresses the joint position regulation of a class of n degrees of freedom torque-driven robot manipulators under a novel practical motivated control objective: Simultaneous Regulation & Prescribed Safe Operating Area (SR&PSOA). More specifically, torque–speed characteristic safe limit functions associated to each actuator are taking into account to ensure that besides of global joint positioning, the requested torque control inputs to robot actuators remain inside user prescribed safe operating torque–speed areas, so avoiding thermal and physical actuator damages. A static smooth nonlinear controller is proposed to achieve global position regulation under prescribed speed-depending bound torque input. Numerical simulations and experimental results are included to illustrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper proposes a two stage anti-windup compensation scheme for systems subject to both input saturation and input quantization. The paper makes two main contributions: (i) it proposes a new partitioning of the saturation/quantization nonlinearity; and (ii) it formulates and solves a two-stage anti-windup problem on the basis of this partitioned nonlinearity. The anti-windup compensator contains two distinct elements: one to assuage the effects of quantization, the other to do the same when saturation occurs. Theoretical results provide conditions which must be satisfied in order for the two-stage anti-windup compensator to bestow stability on the resulting closed-loop system. These results are expressed as linear matrix inequalities and naturally lead to algorithms for anti-windup design. Simulation examples illustrate the effectiveness of the techniques. [ABSTRACT FROM AUTHOR]

In this article, we address the performance output tracking for finite-dimensional systems with infinite-dimensional actuator dynamics and mismatched disturbance. The major difficulties are that the actuator dynamics is covered by an unstable heat equation and it has non-collocated configuration between control input and disturbance. To overcome these difficulties, the trajectory planning technique is first introduced to carry the disturbance to control channel, and then backstepping strategy is applied to cope with the source term of instability in the heat equation. Following, by virtue of system similarity, the recently developed dynamic compensation approach for linear system is utilised to guarantee the performance output tracks reference signal exponentially and closed-loop states are uniformly bounded. Finally, some numerical results are given to support the effectiveness of the theoretical statements. [ABSTRACT FROM AUTHOR]

The use of high-capacity vehicles has been shown to significantly reduce carbon dioxide emissions from heavy goods transport and improve the efficiency of the transport sector. Despite their benefits, current legislations regarding the dimensions and weight of the vehicles have limited the widespread use of heavier and longer vehicles. Long vehicles are less manoeuvrable and often necessitate technological interventions to pass manoeuvrability tests. Various rear-steering systems proposed to solve these issues lead to high costs and mass penalties compared to standard fixed axles. This paper presents a new steering concept which utilises the axles' existing brake actuators to steer, eliminating the need for dedicated actuators on the axle and associated steering hardware. Brakes are individually controlled on each side of a freely steerable axle to generate the necessary torque about the kingpins causing it to steer. A validated vehicle model is used to design a feedback steering strategy based on path-following steering control for low-speed manoeuvring. The proposed system's performance is compared to conventional vehicles and current state-of-the-art active-steering systems through simulations. It demonstrates comparable steering performance to that of electro-hydraulic active-steer systems, with an estimated 50% reduction in both mass and costs. [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced safety‐critical control scheme for hypersonic vehicles (HSVs) with multiple constraints, where both safety constraints (e.g., actuator saturations and time‐varying angle‐of‐attack [AOA] limitation) and transient performance constraints are considered. In this scheme, the extended exponential control barrier function (EECBF) is constructed by incorporating extended states and robust terms to deal with time‐varying constraint boundaries and uncertainties simultaneously. An adaptive programming for optimal transient performance envelopes is conducted to make a trade‐off between safety and transient performance constraints. It is shown that the proposed scheme for HSVs can confine AOA to time‐varying safety boundaries in the presence of uncertainties while the velocity and height tracking errors can always maintain within the desired transient performance envelopes. Simulations and comparisons are provided to verify the effectiveness of our scheme. [ABSTRACT FROM AUTHOR]

This article presents an anti‐disturbance constrained control scheme for the pitch channel of autonomous underwater gliders subject to internal and external disturbances, as well as actuator saturation. First, the integral control technique is employed to develop a disturbance observer to estimate the overall effect of possible uncertainties and disturbances on the nominal vehicle model, which is referred to as the mismatched lumped disturbance. Then, a disturbance rejection control law is constructed based on the disturbance observer. Following that, a straightforward anti‐windup modification is proposed to handle potential input constraints by using the tracking back calculation technique. Specifically, the difference between saturated and unsaturated control input signals is utilized to create a feedback signal that addresses the disturbance observer input, thereby alleviating system windup during actuator saturation events. Furthermore, the stability of the overall closed‐loop system is established in term of the Lyapunov stability theorem, demonstrating that the tracking error is ultimately bounded. Compared with some existing anti‐windup control schemes, the suggested approach offers intuitive design guidelines, resulting in a simple controller that can be easily implemented. Finally, the effectiveness and robustness of the proposed control scheme are verified through simulation results. [ABSTRACT FROM AUTHOR]

Linear quadratic tracker (LQT) is usually employed to solve unconstrained tracking problems but falls short when dealing with systems exhibiting actuator saturation. This paper presents a novel quasilinear quadratic tracking method specifically designed to address this scenario. Firstly, the stochastic linearization (SL) approach is utilized to approximate the saturation nonlinearity with equivalent gains and biases using statistical properties of its input, which are thus incorporated into the system model so as to eliminate the nonlinearity. Then, different time scales are applied in the tracking controller and states in order to improve tracking accuracy. In addition, to reduce computational complexity, two algorithms are provided for approximating the equivalent gains and biases, catering to both scalar and vector control signals. Finally, the proposed algorithms are evaluated through numerical examples, demonstrating their effectiveness and superior tracking performances. [ABSTRACT FROM AUTHOR]

This article investigates anti‐attack stabilization with passivity problem of uncertain singular semi‐Markov jump systems (singular S‐MJSs) with exogenous disturbance and delay. An ingenious non‐fragile observer‐based neural sliding mode control (SMC) scheme is put forward to solve the problem. First, considering unmeasured states, a distinctive non‐fragile and decoupled observer, which does not contain the control input or any auxiliary sliding mode compensator design as in existing observer‐based SMC approaches, is established such that the disadvantages of sliding mode switching in observers in existing literature can be avoided. Then, "only one sliding surface" design and a new system analysis route are presented, and the derived sliding surface is accessibly designed. Next, a new version of stochastic admissibility and passivity sufficient condition is given, and a related algorithm via an optimization problem is proposed to determine the controller gain and the observer gain by linear matrix inequalities (LMIs). Further, a novel observer‐based anti‐attack neural SMC law, which utilizes a neural network‐based approach to approximate actuator attack, is proposed to stabilize the singular S‐MJSs against actuator attack. Finally, simulation and comparison results are presented, which demonstrate the effectiveness and superiority of our method. [ABSTRACT FROM AUTHOR]

The dual ball screw feed mechanism (DBSFM) is commonly employed in high-end machining applications. However, its accuracy is challenging to enhance due to variations in the axial stiffness of the dual actuators under load, making geometric error compensation (GEC) difficult. To address this, our research establishes a comprehensive error model that integrates geometric error and load-induced error (LIE) to improve feeding accuracy. The axial stiffness matrix of the DBSFM is identified using motor current information, and an active prediction error matrix is defined based on the geometric error model, milling force model, and axial stiffness matrix. We propose and analyze the active prediction compensation (APC) strategy as a new method to enhance accuracy under load. Experimental validation using a gantry-type machine tool demonstrates that the APC strategy can reduce the positioning error of the DBSFM to ±2 μm under load, representing significant improvements over the established GEC method. Specifically, the APC strategy achieves a 53.07% and 57.04% enhancement in accuracy along the two axes. This work illustrates the effectiveness of the APC strategy in reducing positioning errors and improving feeding accuracy in DBSFM machining processes. [ABSTRACT FROM AUTHOR]

Civil structures are often overdesigned to meet safety and functionality criteria under rare, strong events. Adaptive structures, however, can modify their response through sensing and actuation to satisfy design criteria more efficiently with better material utilization, which results in lower resource consumption and associated environmental impacts. Adaptation is performed through actuators integrated into the structural layout. Several methods exist for optimal actuator placement to control displacements and internal force flow. In discrete systems like trusses and frames, actuator placement is typically a binary assignment. Most existing methods use bilevel and heuristic formulations, leading to suboptimal solutions without proving global optimality. This paper introduces a Mixed Integer Programming (MIP) method that produces global optimum solutions by optimizing both actuator placement and commands. Two objective functions are used: minimizing the number of actuators and minimizing control energy. The optimization considers structural and serviceability limits and control feasibility. An extensive benchmark compares the new formulation's global optima with solutions from greedy, stochastic, and heuristic methods. Results show that the new method consistently produces higher-quality solutions than all other methods benchmarked in this study. [ABSTRACT FROM AUTHOR]

This article investigates the control of attitude stabilization for a rigid spacecraft using non-singular terminal sliding mode control (NTSMC). A new problem with the traditional NTSMC has been pointed out. This issue is that the mathematical expression of the upper bound of convergence time will approach infinity as the angular velocity approaches zero. In order to address this issue in the traditional NTSMC, a new control method is proposed. This method utilizes the technique of "adding a power integrator" (AAPI), and provides a bounded expression for convergence time. When considering external disturbances, control input limitations, and actuator faults, the attitude and angular velocity can eventually stabilize to a residual set of equilibrium within a finite time. The simulation results demonstrate that the proposed controllers achieve highly accurate and resilient attitude control performance. [ABSTRACT FROM AUTHOR]

To prepare a conductive polymer actuator with decent performance, a self-built experimental platform for the preparation of polypyrrole film is employed. One of the essential goals is to examine the mechanical characteristics of the actuator in the presence of various combinations of process parameters, combined with the orthogonal test method of "four factors and three levels". The bending and sensing characteristics of actuators of various sizes are methodically examined using a self-made bending polypyrrole actuator. The functional relationship between the bending displacement and the output voltage signal is established by studying the characteristics of the actuator sensor subjected to various degrees of bending. The experimental results reveal that the bending displacement of the actuator tip almost exhibits a linear variation as a function of length and width. When the voltage reaches 0.8 V, the bending speed of the actuator tends to be stable. Finally, the mechanical properties of the self-assembled polypyrrole actuator are verified by the design and fabrication of the microgripper. [ABSTRACT FROM AUTHOR]

The demand for safe and flexible actuators has increased as traditional actuators pose safety risks due to their rigid materials, especially in applications requiring human-machine interaction. This study focuses on designing and optimizing a linear fiber-reinforced soft actuator to enhance linear motion performance while maintaining safety and flexibility. Finite element method (FEM) analysis was used to evaluate the effects of varying key design parameters, including core radius, actuator length, and core wall thickness. The analysis revealed that increasing the core radius leads to greater linear extension, while increasing the actuator's length and wall thickness reduces extension. Among the tested designs, the R10 design exhibited the highest linear extension, with a 44.41% increase in length compared to the original design. However, the R10 design also showed undesirable bulging at the free end under pressure, which necessitated further optimization. By increasing the thickness of the sheath wall, the bulging was reduced, and the optimized design achieved a 34.53% increase in extension. This study highlights the significance of parameter optimization in fiber-reinforced soft actuators to achieve superior linear motion performance. Future work will explore further improvements in structural stability, sensor integration for precise control, and advanced fabrication techniques for better customization and durability. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to explore the feasibility and performance of three-dimensional ultrasound (3DUS) imaging in ophthalmology using commercially available ultrasound probes adapted to a slit lamp. Significance: Despite ultrasound's long-standing application in eye care for visualizing ocular components, the evolution of 3DUS technology has remained inactive, with limited development and commercial availability. This study introduces a novel method that could potentially enhance ophthalmic diagnostics and treatment planning by providing comprehensive 3D views of ocular structures using existing ultrasound probes adapted to the conventional slit lamp. Methods: A custom system was designed for mounting a linear actuator to a slit lamp and enabling the horizontal actuation of any ultrasound probe. Ophthalmic and non-ophthalmic ultrasound probes were tested for their ability to reconstruct 3DUS images of the posterior pole. The study involved designing and evaluating three US phantoms ex vivo and performing in vivo imaging on human subjects to assess the system's applicability. Results: The system successfully acquired 3D volume scans of phantoms and live human eyes, demonstrating the system's potential for detailed ocular imaging. The adaptability of the device allowed for compatibility with various ultrasound probes. In vivo imaging revealed the system's capability to produce high-resolution 3D reconstructions of ocular structures, including eyes with pathological conditions. Conclusions: The introduction of a slit lamp-mounted 3DUS system represents a significant advancement in ophthalmic ultrasonography, offering a practical and accessible solution for comprehensive 3D ocular assessments. The device's modularity and compatibility with existing ultrasound probes make it a versatile tool for a wide range of ophthalmic applications. Further research and clinical trials are needed to optimize the system's performance and validate its clinical utility. [ABSTRACT FROM AUTHOR]

[Display omitted] • Automatic color-tunable actuator is from combining photonic crystals with hygroscopic film. • The actuator self-flickers under the natural humidity gradient environment. • The actuator shows continuous upward-downward bending motion and autonomous color switching. • This work offers a new strategy to develop an automatic intelligent actuator. Color-tunable actuators with motion and color-changing functions have attracted considerable attention in recent years, yet it remains a challenge to achieve the autonomous regulation of motion and color. Inspired by Apatura ilia butterfly with dynamic structural color and Pelargonium carnosum plant with moisture responsive bilayer structure, an automatic color-tunable actuator is developed by integrating photonic crystals layer and hygroscopic layer. Taking advantage of the asymmetric hygroscopicity between two layers and the angle-dependent structural color of photonic crystals, this actuator can continuously self-flicker in humid environment by visual switching in structural color due to automated cyclic motion. The actuator is assembled into the self-flapping biomimetic butterfly with switchable color and the self-reporting information array with dynamic visual display, demonstrating its autoregulatory motion and color. This work provides a new strategy for developing automatic color-tunable actuator and suggests its potential in the intelligent robot and optical display. [ABSTRACT FROM AUTHOR]

Over the last few years, the study of adaptable light-driven actuators based on two-dimensional materials has risen to prominence as a pioneering research domain in the field of materials science and engineering. Graphene, transition metal disulfides (TMDs), MXene, and similar two-dimensional materials have shown considerable promise in the realms of nanotechnology and pliable electronics. This is attributed to their ultra-thin atomic layers, expansive specific surface areas, and exceptional electrical and optical characteristics. When these materials are integrated into flexible actuators, they can deform or move by absorbing light of a specific wavelength to change their physical state. Such actuators have shown great application prospects in many fields. At present, there are no review papers on the application of photothermal effects to optical drivers in 2D materials. This article offers a comprehensive review of the characteristics and optical properties of various two-dimensional substances. It delves into the photothermal effects of these materials in a range of sectors, highlighting their targeted deployment in the realm of optical actuation technology. Finally, some challenging problems and prospects in the field of optical drives for two-dimensional materials are proposed. [ABSTRACT FROM AUTHOR]

In this work, a fully actuated system (FAS) control scheme for the quadrotor UAV formation is designed. Deploying the FAS techniques, two controllers are designed for position and angle tracking so that the UAV formation is driven along the given trajectory with enhanced internal stability. Considering the scenario where the environment disturbances and actuator faults affect UAV systems, an extended state observer (ESO) is designed to estimate the uncertainty. Subsequently, the effect of the fault and uncertainty is compensated in the FAS controller to enhance the accuracy. As a result, the proposed formation coordination controller ensures that the UAV team completes the desired flight mission. According to the simulation results, the proposed method is more accurate and robust against the disturbance and fault with the accurate estimation compared with traditional methods. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of event-triggered control (ETC) for vertical take-off and landing (VTOL) aircraft systems under actuator saturation. By introducing the VTOL system with saturated actuators, a composite quadratic Lyapunov function (CQLF) approach is first proposed to describe the problem of the event triggering mechanism. The proposed transfer mechanism not only further saves communication resources, but also further suppresses the conservatism of the attraction domain estimation. Then, sufficient conditions are established via linear matrix inequality (LMI) by incorporating new event triggering mechanism condition and prescribed passive performance metrics under the closed-loop system that is asymptotically stable and strictly passive, respectively. Finally, the method proposed in this paper can effectively reduce the number of triggers and expand the domain of attraction. The validity and feasibility of the obtained results are demonstrated by two example simulations. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of a continuum robot driven by electromagnets and springs, offering enhanced precision in multi-degree-of-freedom bending for diverse applications. Traditional continuum robots, while effective in navigating constrained environments, often face limitations in actuation methods, such as wire-based systems or pre-curved tubes. Our design overcomes these challenges by utilizing electromagnetically driven actuation, which allows each segment of the robot to bend independently at any angle, providing unprecedented flexibility and control. The technical challenges discussed emphasize the goals of this work, with the main aim being to develop a motion control system that uses electromagnets and springs to improve the accuracy and consistency of the robot's movements. By balancing magnetic and spring forces, our system ensures predictable and stable motion in 3D space. The integration of this mechanism into multi-segmented robots opens up new possibilities in fields such as medical devices, search and rescue operations, and industrial inspection. Finite element method (FEM) simulations validate the efficiency of the proposed approach, demonstrating the precise control of the robot's motion trajectory and enhancing its operational reliability in complex scenarios. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper proposes a novel event‐triggered adaptive asymptotic tracking control (ATC) method for stochastic non‐linear systems with unknown hysteresis. Firstly, in order to reduce the depletion of network resources while optimizing the asymptotic tracking performance of the system, a switching threshold mechanism (STM)‐based event‐triggered control (ETC) strategy is adopted. Secondly, a first‐order filter is utilized to address the problem of the contradiction between event‐triggered mechanism (ETM) output and rate‐dependent hysteresis actuator input. By incorporating an enhanced backstepping technique and a bounded estimation method, it is rigorously demonstrate that the system achieves zero tracking error, effectively compensates for unknown hysteresis, and ensures that all closed‐loop signals remain bounded in probability. Meanwhile, the Zeno phenomenon is excluded. Finally, the effectiveness and superiority of the proposed control scheme are verified by the simulation results. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge plasma actuators are flow control devices that can actively induce a flow using electrohydrodynamic force. This Letter proposes a configuration of multi-stage dielectric barrier discharge plasma actuators to accelerate the induced flow velocity. In the proposed configuration, the encapsulated and exposed electrodes between adjacent units of the multi-stage plasma actuator are interconnected and share the same potential, thereby avoiding crosstalk phenomena. The thrusts, cross-sectional flow velocity distributions, discharge images, and electric field distributions are examined for the conventional and proposed multi-stage plasma actuators. The results show that the proposed configuration can increase the thrust and induced flow velocity efficiently compared to the conventional one. The discharge images also show that no crosstalk occurs in the proposed configuration. This is mainly due to the low electric field strength in areas where crosstalk would occur. [ABSTRACT FROM AUTHOR]

This paper presents a coaxial integrated macro–micro composite actuator. The macro-actuator of the macro–micro composite actuator is similar to a moving coil type voice coil motor, and a giant magnetostrictive actuator is installed coaxially inside it as a micro-actuator. In this work, kinetic models are established for both the macro-actuator and micro-actuator, and based on the models, an automatic disturbance rejection controller is adopted to control the macro-actuator, and a fuzzy sliding mode controller is adopted for the micro-actuator. In order to verify the actual performance of the proposed macro–micro composite actuator, a prototype was fabricated, and experimental results show that the macro-actuator can achieve a 10 mm step positioning error of 9 μm and a 30 mm step positioning error of 11 μm under a load of 1 kg. The resolution of the minimum PWM square wave change identification of the controlled micro-actuator is 0.047 μm, and the minimum displacement resolution of the micro-actuator is 0.15 μm. The micro-actuator is capable of achieving 1 μm steps with no displacement overshoot. In addition, when the positioning distance is 5 μm, there is a small amplitude overshoot of 0.18 μm. The final positioning accuracy of macro–micro composite positioning is within 350 nm. [ABSTRACT FROM AUTHOR]

This study investigates the impact of electrode positioning and the amount of energy deposited into the flow on the performance of SparkJet actuators, utilizing computational fluid dynamics (CFD) and modal analysis. The performance metric considered is impulse, defined as the time-integrated thrust. A parametric study was conducted by varying the electrode position from near the cavity bottom to more distant locations to assess the differences in impulse. In addition, the effect of three energy deposition amounts (3.11, 5.14, and 7.17 mJ) on impulse was examined. The results indicate that, for the same energy deposition amount, the impulse can vary by up to approximately 40% depending on electrode positioning. Furthermore, the impulse exhibited a general tendency to decrease as the electrode position moved closer to the orifice, regardless of the energy deposition amount. However, it showed a considerable rebound when the electrode position was near the interface between the cavity and the nozzle. To further analyze these findings, contour analysis of CFD results and modal analysis of the velocity field were conducted. The former revealed that the behavior of the low-density region inside the actuator significantly affects impulse, while the latter demonstrated that a wave with mode 0 and order 1 (an eigenfunction with a single node along the ξ direction) exerts a dominant influence on impulse. Moreover, a new variable related to this eigenfunction was proposed, enabling the prediction of impulse trends with respect to electrode position. Thus, this study successfully analyzed the previously unexplored effect of electrode positioning on SparkJet actuator performance using modal analysis, highlighting the importance of optimizing electrode position for enhanced SparkJet actuator performance. [ABSTRACT FROM AUTHOR]

A plasma actuator with adjustable jet direction based on the combination of dielectric barrier discharge (DBD) and corona discharge is proposed and characterized for turbulent drag reduction applications. The results show that an oblique jet and corresponding vortex series are formed through the interaction of the vertical jet by corona discharge and the horizontal jet by DBD. By changing the power input of DBD and corona discharge, both the velocity amplitude and the deflection angle of the oblique jet can be adjusted swiftly, and the maximum deflection angle of the coupled jet is 66.74°. The maximum velocity of the coupled jet reaches 1.77 m/s at a total power consumption of 23.09 W. Keeping the corona discharge parameters constant and increasing the DBD voltage, the relative distance of the vortex core decreases monotonically. There exists an optimal power ratio, making the total vortex intensity maximized. The actuator can provide combined spanwise and vertical control in a complex turbulent boundary layer to achieve better drag reduction. [ABSTRACT FROM AUTHOR]

To achieve the actuation of silicone-based foamed composites, a liquid–gas phase transition of the liquid captured in its pores is employed. The uncertainty of key parameters for a single or sequential open-air performance of such soft actuators limits their application. To define the main characteristics of the composites, in this work, two functions of the liquid there were separated: the pore-forming agent (FPA) and working liquid (WL). It was demonstrated that the composites can be fabricated using either ethanol or methanol as the PFA, while any of the C1-C4 alcohols can be used as the WL. The results of the sequential actuation tests of the composites revealed that pore formation depends on the composite viscosity during curation, while their expansion in single heat experiments can be approximated by a unified linear relation. Based on a Mendeleev–Clapeyron equation, the qualitative model for predicting the actuator strain is proposed. It was found that the composites with C3–C4 alcohols as the WL outperform ethanol-containing composites on the number of cycles survived under open-air conditions. These findings pave the way to control the operation of soft actuators by manipulating WL variation and PFA content during the composite cure to set the operation temperature and degree of expansion of pre-formed actuators. [ABSTRACT FROM AUTHOR]

This paper introduces a novel Gramian-based quantitative metric to evaluate the disturbance rejection capabilities of linear unstable systems. The proposed metric addresses key limitations of the previously introduced degree of disturbance rejection (DoDR) metrics, including their dependency on the final time and numerical problems arising from differential equation computations. Specifically, this study defines the steady-state solution of the DoDR metric, which avoids numerical issues by relying only on solving four algebraic equations, even when the Gramian matrices diverge. This study further strengthens its contributions by providing rigorous mathematical proofs supporting the proposed method, ensuring a strong theoretical foundation. The derived results demonstrate that the proposed metric represents the sum of the steady-state input energies required to reject the disturbances in the asymptotically stable and anti-stable subsystems. Numerical examples demonstrated that the proposed metric maintained the physical meaning of the original DoDR while offering practical computational advantages. This study represents a significant step toward the efficient and reliable assessment of disturbance rejection capabilities in unstable systems. [ABSTRACT FROM AUTHOR]

This paper investigates the redundant control input problem in the sense of linear quadratic regulator optimal control. Increasing redundant control inputs leads to a decrease in the quadratic performance index. However, in some cases, this also increases the norm of the feedback matrix, resulting in actuator saturation. To solve the problem, a comparative analysis of the latest research results on the redundant control input problem under different conditions is first presented. Secondly, new tighter upper bounds of the positive (semi-)definite solution of the continuous algebraic Riccati equation (CARE) corresponding to the redundant control input problem are studied uniformly in the stabilizable case. Thirdly, based on them, a class of sufficient conditions to guarantee that the norm of the feedback matrix decreases is presented. Finally, numerical experiments demonstrate the effectiveness and superiority of our conclusions. Meanwhile, a simulation experiment demonstrates that systems with redundant control inputs can achieve good control performance. [ABSTRACT FROM AUTHOR]

Millipedes increase the duty ratio and wavelength of their gait to enhance thrust force against resistive load. However, the underlying control mechanisms responsible for generating such adaptive gaits remain elusive. In this study, we proposed a decentralized control law based on the concept of 'discrepancy function'. Our proposed walking controller successfully reproduced the load-adaptive gaits of millipedes on the inclined ground. Furthermore, we evaluated the adaptability of our controller to horizontal resistive forces that hinder forward walking. Our simulation results suggest that the millipede-inspired controller could be beneficial for multi-legged robots equipped with leg actuators operating under limited motor outputs. [ABSTRACT FROM AUTHOR]

Providing new materials with superior properties and discovering usable industrial techniques for these materials has always been a noteworthy issue for manufacturing technologies. In addition, design and manufacturing conditions of existing materials need to be constantly improved. Vaporizing foil actuator welding (VFAW) is a welding method developed for joining dissimilar metals, which is an important issue, especially in industrial and academic fields. In this study, a welding prototype was created and tested in order to improve the applicability of VFAW, which has been introduced to the manufacturing field as a new welding technique, under laboratory conditions. The process of making VFAW using direct current (DC) capacitors has been explained. The study has shown that making VFAW using DC capacitors is possible. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are promising candidates for use in sensors, actuators, or passive dampers. This paper investigates the dynamic response of a superelastic NiTi holed disk to assess its damping performance relative to frequency and temperature for SMA-based damper applications. This study involved several key steps. Initially, the superelastic behavior of the SMA was experimentally characterized through tensile tests. This testing campaign provided the required data to identify material parameters of a thermomechanical constitutive model, already implemented in the finite element code Abaqus. Using the identified parameters, a finite element based structural analysis was conducted to predict the disk's operational range, ensuring it remained within the superelastic domain without incurring potential damage. Following this static analysis, a dynamic mechanical analysis (DMA) was performed on the disk. By employing a complex stiffness approach, we further examined the disk's damping effects. This dynamic method enabled a detailed description of the apparent stiffness and damping characteristics based on solicitation frequency, test temperature, vibration amplitude, and a predefined static displacement. The results indicated a clearly predominant structural effect over the phase transformation effect, despite the disk's substantial damping potential. [ABSTRACT FROM AUTHOR]