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In this article, two dual-loop control methods are proposed for attitude control and reaction wheels momentum management of the spacecraft simulator by assimilating the advantages of sliding mode and model predictive control (MPC). In the first method, by utilizing the high accuracy and constrained features of the MPC, an optimal controller is designed in the inner loop. MPC drives the angular velocity to the desired value while keeping the reaction wheel velocity to a small region near the origin, considering the constraints of the actuators. Furthermore, based on the fixed-time terminal sliding mode (TSM) the proper angular velocity is produced in the outer layer of this composite controller for the MPC part. In the second method, contrary to the first one, in the exterior loop MPC and in the interior loop finite-time TSM have been designed. The incorporated twofold nonlinear controllers’ policy insures a good dynamic and robustness against external disturbances. The high yielding of the control algorithms has been analyzed by simulation and experimental validation utilizing MATLAB software with real-time connection based on LabVIEW. [ABSTRACT FROM AUTHOR]

Differential equation-based hysteresis model is an efficient approach to predict the hysteresis effect with less modeling parameters. Available differential equation-based hysteresis models mainly focus on describing the single-loop hysteresis effect and fail to describe the butterfly hysteresis effect. In this article, a butterfly fractional-order backlash-like hysteresis model is proposed to describe the butterfly hysteretic behavior. To this end, a twist mechanism is developed to transform the single-loop backlash-like hysteresis model into the one that is capable of representing the butterfly hysteresis. To further improve the modeling accuracy, a fractional-order expression is integrated into the butterfly backlash-like hysteresis model. In addition, considering the buckling threshold characteristic of the elastomer membrane in dielectric elastomer actuators, a buckling threshold selector is designed and incorporated into the model as well. Experiments are conducted to validate the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Aerial delivery is becoming a reality due to the development of microelectronics and communication technology. Most existing methods for cable-suspended transportation systems utilize fixed-length cable to connect the unmanned aerial vehicle quadrotor and the payload. Such aerial transportation systems present underactuated property, which is caused by the indirectly controllable payload motion and the underactuation of the quadrotor itself. In practical applications, payload hoisting and lowering motion independent of the quadrotor altitude will further expand the application scope in such areas as limited space crossing and offshore sample collection. To realize the aforementioned objectives, a flexible connection between the quadrotor and the payload is realized by mounting an actuator beneath the fuselage. Suffering from strong nonlinearity and complex dynamic coupling, the control problem becomes extremely challenging and more cumbersome, as the system’s degree of freedom (DOF) increases. To deal with these problems, in this article, a nonlinear control approach is presented by energy-based analysis, which achieves simultaneous quadrotor positioning, payload swing elimination and hoisting/lowering. Lyapunov techniques and LaSalle’s Invariance theorem are utilized to prove the asymptotic convergence of the equilibrium point. Finally, a series of hardware experiments are conducted on a self-built aerial transportation platform. As far as we know, this article provides the first mechanism and control solution for payload hoisting/lowering independent of the quadrotor altitude. [ABSTRACT FROM AUTHOR]

In this article, we propose a switching anti-windup scheme for the aircraft engine control. The linear engine model with asymmetric saturation is first transformed into a switched system, each subsystem of which is subject to symmetric saturation. A state-dependent switching logic is presented to orchestrate the switching among multiple anti-windup compensators. We then establish the sufficient condition to guarantee the regional stability and $\mathcal {L}_{2}$ performance of the resulting closed-loop system. This condition is less conservative since the non-symmetric nature of the saturation nonlinearity can be fully exploited in the control design. Optimization algorithms are further developed for the anti-windup gain design. The theoretical aspect of the proposed method is analyzed rigorously, and the effectiveness is validated through experiments performed on a semi-physical test bed. [ABSTRACT FROM AUTHOR]

When a recloser detects fault currents in electric power distribution lines, it breaks the line and then restores the line after several fault tests. To check whether fault remains, the recloser performs CO operations (opening the contacts after reclosing them for a while). In this operation, the fault currents flow into the line, potentially causing damage to equipment connected to the line. Therefore, reducing the current-carrying time during the fault test is desirable, but this reduction is difficult because of the slow actuation mechanism of reclosers. In this article, a novel actuation mechanism combining a permanent magnetic actuator (PMA) and a solenoid actuator (SA) is proposed. During the CO operations for the fault tests, the proposed mechanism can rapidly break the closed contacts by hitting the moving contact with the SA. To increase the energy efficiency of the actuation mechanism, a distinctive PMA driving method is also proposed; it weakens the strong holding force of the PMA using assistive magneto-motive force (MMF). The structure and configuration of the proposed mechanism are explained. The performance of the mechanism and the effectiveness of the driving method are studied through cosimulations. Finally, a prototype is developed, and its practicality is verified through experiments. [ABSTRACT FROM AUTHOR]

Nanoscale actuators are one of the key technologies in high-precision servo systems. For optical storage systems, the performance of the actuator determines the maximum storage capacity and read/write speed. This article introduces a three-degrees of freedom nanoscale microsuspension actuator. Compared with an actuator from a traditional optical storage system, the proposed actuator can hold dual objective lenses with large apertures, the load capacity of which is increased by 3.14 times. With dual objective lenses operating at the same time, the actuator can achieve a large range of layer jumps. Thanks to the four-sided magnetic circuit and the overall structure, the actuator has an operating bandwidth greater than 10 000 Hz for dynamic performance, can compensate systematic errors in nanoscale, and provides a radial tilt servo direction. We have derived the actuator a unified electromechanical dynamic model, an equivalent stiffness model, an equivalent damping model, and a magnetic circuit analysis model in detail. Compared with other analysis models of microsuspension actuator, the proposed models provide a theoretical guidance for the determination of each key parameter, and can effectively improve design efficiency. The theoretical models and design method of the actuator are also applicable to microactuators design and active vibration isolation design of other high-precision servo systems. The simulation and experimental results verify the good dynamic performance of the actuator and show the effectiveness of the principal analysis and design method. [ABSTRACT FROM AUTHOR]

The improvement of sailing speed and endurance of microunderwater vehicle can be achieved by reducing the wall friction drag. We proposed a piezoelectric drag reducer (PDR), which can be embedded into the wall of the underwater vehicle without affecting the original streamline. We discussed the drag reduction characteristics of the PDR with different arrangement angles based on the simulation analyses, and a maximum friction drag reduction rate of 45.3% can be achieved when the arrangement angle between the direction of PDR and the incoming flow is 60°. The influences of key parameters on the turbulence characteristics are obtained with a view to select control parameters for meeting different drag reduction requirements. In order to verify the simulation results, we carried out experimental tests, the experimental data have been analyzed using turbulence statistical method. The relative errors of friction drag reduction results between simulation and experiment are less than 12%, which proved the effectiveness of the proposed arrangement and control parameter selection methods. Then, the feasibility of achieving high-efficiency active drag reduction of microunderwater vehicle, based on the proposed PDR, is verified to be effective according to the test results of total drag experiments. [ABSTRACT FROM AUTHOR]

Considering a class of nonlinear systems subject to actuator saturation and uncertain control input, this article explored the control capability of an extended-state observer-based active disturbance rejection controller in the presence of disturbances and uncertainties. First, the actuator saturation is handled with the convex hull in the extended-state observer-based control scheme, and an ellipsoid invariant set inside the domain of attraction for control systems is obtained using the Lyapunov method. Second, the enlargement problem of the invariant set is also studied, which illustrates that the convex hull of the ellipsoid invariant sets is also an enlargement invariant set. Finally, comprehensive comparisons with existing methods on a brushless dc motor demonstrate the stronger capability of the designed controller on disturbance rejection and actuator saturation. The results show that the disturbance offset and performance index (integrated time and absolute error and integral absolute error) are about half of the classical proportional–integral–derivative(PID) and double-integral sliding-mode control, or the disturbance rejection capability is about twice in this case. [ABSTRACT FROM AUTHOR]

With simple structure and control, impact inertial piezoelectric actuators are one promising type for precision positioning with large working stroke and high resolution. However, their applications still face some challenges, especially the incompatibility between speed and resolution as well as the motion instability due to the overturning moment. Therefore, innovative design of impact inertial actuators is urgently required. In this article, by designing an asymmetric compliant mechanism with a thick end and a thin end to generate asymmetric friction between the driving feet and U-groove, a novel impact inertial piezoelectric actuator was proposed. Its structure design, working principle, and output performances were addressed in detail. The results indicated that the thick end and thin end had quite different stepping characteristics, and the ideal stepping characteristic with quite small backward motion was achieved at the thick end. The displacement-time curves confirmed the motion stability of the actuator for bidirectional motions, and the small difference in forward and reverse speeds was explored. This actuator achieved the maximum speed of 7311 μm/s, the resolution of 221 nm, vertical and horizontal loading capacities being over 20 N and 1.4 N, respectively. Performance comparison with some previous impact inertial actuators further demonstrated the advancement. [ABSTRACT FROM AUTHOR]

In this article, we consider adaptive output feedback tracking for a class of nonlinear systems with uncertain parameters, multiplicative and additive sensor uncertainties, and external disturbances. A state observer and an adaptive controller are constructed based on gain scaling technique by which a dynamic gain is designed to compensate for the effects of the sensor uncertainties. The adaptive controller is linear-like and, therefore, is simple and easy to implement. It is shown that with this proposed scheme, all states of the closed-loop system are bounded and the real tracking error can converge to an arbitrarily small residual set. Simulation and experiment are presented to illustrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this article, a butterfly-like Prandtl–Ishlinskii (PI) hysteresis model and a novel neural network based adaptive implicit inverse control scheme to describe and control the butterfly-like hysteresis are proposed. The main contributions are: 1) a butterfly-like PI model is developed for the purpose of predicting the hysteresis effects and the model is feasible for controller design; 2) an implicit inverse control scheme especially for mitigating the butterfly-like hysteresis is implemented, which avoids the construction of the direct inverse of the butterfly-like PI model; 3) an adaptive implicit inverse control approach, which integrates the neural network and the implicit inverse technique into the output-feedback control is developed for eliminating the butterfly-like hysteresis and an arbitrarily small $L_{\infty }$ norm of tracking error is achieved. The proposed modeling and control methods are validated experimentally via the dielectric elastomer actuator based motion control platform. [ABSTRACT FROM AUTHOR]

This article studies a single boundary regulator for the flexible tail of an autonomous robotic fish to implement complex oscillating body motions. The dynamic model of the flexible tail is derived by Hamilton’s principle, and conforms to the partial nonuniform Euler–Bernoulli beam with the uneven parameters. Then, a boundary control at the body–tail junction is proposed to manipulate the oscillation of the flexible tail, which is given in the form as a torque. The exponential stability of the error system is deduced by the integral Lyapunov synthesis. For further considering the boundary disturbance at the same point with control and the distributed disturbance, a disturbance observer is proposed. By appropriately choosing the designed parameters, the uniformly ultimate boundedness with disturbances is proved and the tracking error converges to a small neighborhood of 0. Finally, some simulations are presented to illustrate the effectiveness of the proposed control. [ABSTRACT FROM AUTHOR]

This article presents a redundant control strategy of fully-actuated underwater vehicles. The proposed strategy offers vehicles more control flexibility for addressing the position tracking problem under the attitudes and velocities constraints. In kinematics, position tracking is formulated as a convex optimization problem, where the velocity constraints are considered as a feasible region and the attitudes are bounded via a barrier function. Then, a conservative boundary is determined in the context of stability analysis of the dynamic controller with a disturbance observer and an auxiliary system so that kinematic variables lie in the constraints even with the velocity tracking error. Also, it is proven that the position tracking error can converge to a neighborhood about zero, which can be made arbitrarily small. The simulations and experimental results through multiple scenarios have illustrated the efficiency of the proposed strategy. [ABSTRACT FROM AUTHOR]

This article proposes a safety control scheme for quadrotor unmanned aerial vehicle (UAV) to counteract ground effect and blade damage. The impacts of ground effect and blade damage are quantitatively analyzed in the established model. The proposed safety control scheme consists of position and attitude loops. Specifically, a proportional and derivative controller is designed as a baseline control with acceleration feedforward in the position loop. A disturbance observer (DO) using the measured Euler angles is exploited to estimate the lumped disturbance forces. The developed DO can effectively mitigate the estimation deviation caused by the angle tracking error. Subsequently, differential flatness theory is used to obtain the Euler angle references and the derivatives. In the attitude loop, sliding mode control and fixed-time sliding mode observer (SMO) are integrated to deal with ground effect and blade damage promptly. To demonstrate the effectiveness of the proposed safety control scheme, flight experiments are carried out, where the quadrotor UAV flies close to the rugged ground in the presence of blade damage. [ABSTRACT FROM AUTHOR]

Steer-by-wire (SBW) system has been introduced to reduce the number of parts in a vehicle by eliminating the mechanical link between the steering wheel and the road wheel. Even though intensive research has been conducted on the SBW system, the performance of the actuator system that provides the desired steering feel still needs improvement. Therefore, this article presents a compact size torque controllable steering wheel module for the SBW system, where the actuator that provides the steering feel to the driver is modularized with the gear mechanism and the spring. The steering torque sensing mechanism is compactly integrated by placing the spring inside the gear mechanism. Thanks to the advantage in the torque measurement and control ability by the spring mechanism, high gear-ratio transmission can be employed in the proposed module, which can also address the low inherent mechanical impedance problem that may cause fail-safety issues in the SBW system. To enhance the impedance rendering performance of the proposed module, an internal model compensator which is composed of inertia and friction compensation is applied. The kinematics, statics, and dynamics of the proposed module are theoretically analyzed, and a model-based control algorithm is proposed based on this analysis result. Finally, the increase in the inherent impedance and the torque control performance of the proposed module are verified through experiments. [ABSTRACT FROM AUTHOR]

This article addresses a novel adaptive compensation strategy for a flexible manipulator in the presence of unmodeled system dynamics and an infinite number of time-varying actuator faults. Differing from the existing results, the unmodeled system dynamics are represented by a nonlinear time-varying delay function, which is tackled with the aid of neural network technique and Lyapunov–Krasovskii function. By introducing the projection technique and a piecewise Lyapunov function, a fault-tolerant control method is proposed, the uniformly ultimate boundedness of the closed-loop system is ensured, and the number of actuator faults is allowed to be infinite. Simulation and physical experiment results show that the manipulator can track the desired angle and the vibration can be suppressed effectively under the proposed scheme for the system with uncertainties and actuator faults. [ABSTRACT FROM AUTHOR]

This article presents a novel method for enabling energy-efficient and orientation-independent gravity compensation in active vibration isolation systems by taking advantage of the inherent negative stiffness of a hybrid reluctance actuator (HRA). Counteracting the gravitational force acting on the mover of an HRA with the position dependent force of the actuator’s integrated permanent magnet, the gravitational force can be compensated without the need for an additional actuation. An HRA-system with two translational degrees of freedom (DOF) is developed, comprising a permanent magnet for generating a constant biasing flux for both system axes and two actuator coils per axis for actively controlling the position of the mover. The system prototype has an actuation range of $\pm$ 0.7 mm in both DOF, while enabling energy efficient gravity compensation of payloads up to 500 g by an additional current feedback control loop. Experiments demonstrate that the current consumption for compensation of a 500 g payload is reduced from 1.58 A to 10 mA, which corresponds to a reduction of the power consumption by a factor of 25 000. [ABSTRACT FROM AUTHOR]

Focusing on a quadrotor unmanned aerial vehicle (UAV), the presence of unintended actuator faults and external disturbances increases the risk of a crash. Although plenty of efforts have been devoted, how to integrate capability analysis into safety control design is still an open issue. This article presents the design of a safety control system for quadrotor UAVs. Firstly, a system capability analysis method based on a differential flatness algorithm is developed, so that the derivatives (i.e., velocity, jerk, and snap) of flight trajectory can be formulated as flat variables. A tradeoff between system capability and permissible flight maneuverability is made to avoid actuator saturation. Secondly, dual-loop nonlinear disturbance observers are exploited to identify the actuator faults and disturbances, which can thereby be handled by a cascade control scheme. Moreover, the trajectory is regenerated online at the expense of degraded flight maneuverability or even emergency landing, in view of the remaining actuator control authority. When comparing to the existing methods, the gap among safety control, trajectory generation, and system capability analysis is bridged to ameliorate practical flight safety. Finally, flight tests are carried out to demonstrate the unique merits of the proposed system. [ABSTRACT FROM AUTHOR]

The development and characterisation of a piezoelectric actuated high-frequency MEMS scanning mirror with on-chip frequency tuning capability is reported. The resonant scanner operates at frequencies in excess of 140 kHz, generating scan angles of 10° and 6° for two orthogonal movement modes with 40 V actuation. On-chip frequency tuning is achieved through electrothermal actuators fabricated adjacent to the mirror main suspension. The electrothermal actuators produce a global and local temperature increase which changes the suspension stiffness and therefore the resonant frequency. A resonance frequency tuning range of up to 5.5 kHz is achieved, with tuning dominant on only one of the two orthogonal scan movement modes. This opens the possibility for precise tuning of a 2D Lissajous scan pattern using a single resonant MEMS scanner with dual orthogonal resonant modes producing full frame update rates up to 20 kHz while retaining the full angular range of both resonant movement modes. [ABSTRACT FROM AUTHOR]

In this article, a sensorless control method based on signal injection and a high-pass filter (HPF) circuit is presented to control the unsymmetrical bistable multimagnetic circuit permanent magnetic actuator. In this method, a high-frequency sinusoidal signal was indirectly injected into the idle phase via a HPF circuit, and the peak of the high-frequency capacitance current was measured, which was used to calculate the idle phase inductance. Thereafter, the mover position was calculated by the one-to-one relationship between the idle phase inductance and the mover position. Combined with the HPF circuit and the proposed average current peak algorithm, the influences of back-EMF and coil resistance were eliminated. The magnetic saturation effects can also be ignored in the proposed strategy. The estimated noise, caused by measurement noise and signal distortion, was filtered using a simple mathematical filter. The flexibility and accuracy of the presented strategy were verified by simulation and experimental investigation. [ABSTRACT FROM AUTHOR]

Hysteresis nonlinearity is a common issue in nonlinear stiffness compliant actuators. In this type of actuators, the hysteresis effect is obvious and the associated torque curve is nonlinear. Although many mathematical models have been developed for describing hysteresis, they are usually developed with black-box modeling and the model parameters are difficult to tune to match the experimental data well among inputs with different amplitudes. This article presents a novel hysteresis modeling method for a nonlinear stiffness compliant actuator of which the shapes of the associate torque curves vary with amplitudes. In this method, a concept called “virtual deformation” is adopted to transform the nonlinearity curve into a polyline-based model. Then, a modified Maxwell-slip model is developed to estimate the output torque of the actuator according to the “virtual deformation.” Experiments of the proposed hysteresis modeling method applied in a nonlinear stiffness compliant actuator have been conducted and the results showed that the root-mean-square-error of the estimated torque was reduced by 18.6% and the computation cost was reduced to less than one sixteenth using our proposed hysteresis model compared with nonlinear backlash model. [ABSTRACT FROM AUTHOR]

Tactile devices provide an intuitive way for texture display, which allows users to perceive the detailed surface properties of virtual or remote objects. For existing tactile devices that create actual topographical transformations, it remains challenging to render surface textures with high spatial resolution due to the limitation of the size of actuators. To address this challenge, a magnetically responsive soft actuator with a diameter of 1 mm is proposed. Integrating the high-density soft actuator array and a soft membrane bracket, we develop a magnetically responsive soft tactile device (named MRS-Tex) for texture display. When a magnetic field is applied, the magnetic units will sink to form pits, and the soft membrane bracket resists the finger pressure so that users can perceive the rendered surface texture. Thanks to the proposed sunken solution, MRS-Tex is capable of rendering surface textures with millimeter-level resolution (1.5 mm) while providing a sufficient upward holding force. Moreover, we conduct quantitative experiments and two user studies to evaluate the performance of MRS-Tex. Experimental results show that MRS-Tex can generate pits with a depth of more than 0.20 mm, which is sufficient for rendering perceivable surface textures. The average discrimination accuracy of user study can reach up to 82% for both six basic texture patterns and four complex texture patterns. [ABSTRACT FROM AUTHOR]

Modern embedded software includes complex functionalities and routines, often implemented by splitting the code across different tasks. Such tasks communicate their partial computations to their successors, forming a task chain. Traditionally, this architecture relies on the assumption of hard deadlines and timely communication. However, in actual implementations, tasks may miss their deadlines, thus affecting the propagation of their data. This article analyzes a task chain in which tasks can fail to complete their jobs according to the weakly-hard task model. We explore how missing deadlines affect chains in terms of classic latency metrics and valid data paths. Our analysis, based on mixed integer linear programming, extracts the worst-case deadline miss pattern for any given performance metric. [ABSTRACT FROM AUTHOR]

In this article, a novel polarization reconfigurable antenna based on the Moiré effect is proposed. The presented design exploits substantial changes in the overlapped Moiré patterns to minimize the needed actuation for antenna reconfiguration. The novel antenna design is based on stacking two circular FR4 substrates on top of a truncated edge rectangular patch antenna. The top layers of both the substrates are milled into horizontal stripes forming the Moiré patterns. One of these substrates is fixed with respect to the antenna, while the second one rotates with respect to the fixed substrate. Upon rotation, these stripes from the two substrates overlap in pattern, which shapes the antenna. As a result, the antenna design is capable of switching its polarization scheme between vertical, horizontal, and circular with left-hand orientation. In addition, the Moiré patterns can also enhance the directivity and gain of the proposed antenna. The reconfiguration’s mechanical actuation is achieved via a nontraditional ratchet mechanism that uses shape memory alloys (SMAs). This realized actuation system is fast, flexible in its positioning, has low energy expenditure, and minimizes interference with antenna operation. An antenna prototype is fabricated and tested where measured results match the simulated performance. [ABSTRACT FROM AUTHOR]

This article proposes a method to precisely estimate the load force of magnetic lead screw (MLS)-based series elastic actuators (SEAs) in real time. The elastic transmissions of MLS-based SEAs generally comprise permanent magnets (PMs). Owing to the magnetic pole distortion and the characteristic nonlinear force of PMs, conventional force estimation methods are less accurate for MLS-based actuators than for SEAs with mechanical springs. In the proposed method, to precisely estimate force of MLSs, the nonlinear force characteristic of an MLS is modeled with a sinusoidal force model, and the magnetic force hysteresis phenomenon is predicted based on Bouc–Wen-type hysteresis equations. Moreover, a method called the relative displacement normalization method is proposed to detect the magnetic pole distortion and to compensate for the related force estimation error. In addition, the proposed method is applied to a rotary-linear (RotLin) actuator, which is a novel MLS-based linear SEA. The force estimation accuracy is experimentally evaluated by comparison with existing methods. The results demonstrate that the root-mean-square error of the proposed method is less than that of the existing polynomial model by up to 81.2%. Finally, a force controller and a static force control system is designed with the proposed model to prove its feasibility. [ABSTRACT FROM AUTHOR]

This article aims at proposing an adaptive neural control strategy for a class of nonlinear time-delay systems with input delays and unknown control directions. Different from previous researches that investigated delays and constraints separately, the novelty of this article lies in that it simultaneously considers delays (state and input delays) and input constraints (magnitude and rate constraints) for a class of uncertain nonlinear systems. In this article, the uncertain states and input delays are handled by integrating a constructed auxiliary system that functions as an observer with neural networks (NNs), with which the adverse effects caused by the uncertain states and input delays can be approximated and compensated. By involving smooth hyperbolic tangent functions in the designed auxiliary system, the problem of magnitude and rate constraints of the control input is fully addressed. Then, the backstepping technique runs through the entire control designing process, which allows the designed adaptive neural control strategy to handle the input constraints and delays at the same time. Furthermore, Nussbaum functions are employed to resolve the problem of unknown control directions. Due to the introduction of an input-driven filter, only the output of the system is required to be measured as the control feedback, which promotes the applicability of the designed controller. Under the proposed control scheme, semiglobal, uniform, and ultimate boundedness of all signals of the closed-loop system is realized with uncertain control directions, input and state delays, and guaranteed magnitude and rate constraints of control inputs. Finally, simulation results are illustrated to verify the effectiveness of the presented control method. [ABSTRACT FROM AUTHOR]

In recent years, owing to important improvements, the applicability of supervisor synthesis has significantly increased. We discuss notable developments that were pivotal in the application of supervisor synthesis to large infrastructural systems. [ABSTRACT FROM AUTHOR]

Soft actuator is the key component for soft robots to realize flexible motion. But the difficulty of sensing and control of soft actuators seriously restricts their application. Twisted artificial muscles (TAMs) made from together self-coiling of nylon 6,6 fiber and heating wire are potential to address this challenge due to their extremely high actuating stress and self-sensing ability. However, the together coiled twisted artificial muscles (TCTAMs) have a large self-sensing hysteresis because of the small heating area and the self-coiling process restricts their deformation stroke. Besides, the lack of accurate physical models also blocks the development of the TCTAMs. This article presents a new type of tightly wrapped twisted artificial muscles (TWTAMs) to improve the stroke and reduce the hysteresis. Compared with TCTAMs, the hysteresis of TWTAMs is reduced by 76% and the stroke is improved by 35%. Besides, a physical analytical model based on the self-sensing temperature is established and verified by experiments. This article not only provides a new type of TAMs with large stroke and low hysteresis, but also offers an accurate theoretical analysis model for the performance prediction of TWTAM. [ABSTRACT FROM AUTHOR]

Robotic manipulators have been used inindustry for decades. However, their heavy mass and rigidity make them unsuitable for environments where they may coexist with humans. This has spurred interest in robotic arms with compliance in their joints using methods, such as impedance control. However, inherent compliance is safer, less computationally expensive, and does not require complex sensing solutions. In this article, the design of a sensorized hybrid hard-soft articulated joint using inflatable soft rubber bellows for actuation and simple angular potentiometers for angular position sensing is presented. The joint is hybrid in the sense that it combines rigid motion with soft actuation. This design allows for a simple yet effective solution that combines the precise sensing of rigid manipulators with the compliance of soft ones. Closed-loop control of this joint was implemented and it was capable of following a given trajectory while rejecting disturbances. This design was then extended to a two degrees of freedom (DOFs) joint with the path following capability, and then, integrated with a rigid base joint to form a 6-DOFs hybrid robotic manipulator for use in small retail businesses. This manipulator can handle payloads up to 1 kg over a large work area and was tested for pick-and-place operations. [ABSTRACT FROM AUTHOR]

The backward motion is an intrinsic feature of the conventional piezoelectric stick-slip actuator (PSSA), limiting the output speed and applications. Various methods have been proposed for restraining the backward motion. Each method has its pros and cons for the practical application of driving a precision motion stage. A novel method for restraining the backward motion is proposed in this article, in which a passive damping foot is utilized to hold the runner when the active driving foot slips on the runner. An actuator is developed based on this mechanism. The structural dimensions of the actuator are determined with an analytic model and a finite element model. A prototype of the proposed actuator is fabricated and tested by experiments. The experiments validate the operating principle of the actuator for restraining the backward motion, which is eliminated (the backward ratio is less than 1%) when the passive damping foot has an appropriate clamping force. The proposed method is very valuable for designing a PSSA with no backward motion, and it can broaden the applications for precision manipulations. [ABSTRACT FROM AUTHOR]

Long stroke nanopositioning stages with high natural frequency and compact size are demanded in precision engineering. However, in previous researches, the natural frequency of the long stroke nanopositioning stage is normally below 50 Hz because the actuated force, moving mass, stiffness, motion range, and damping ratio are not considered simultaneously and optimized thereafter. To solve this problem, a long stroke nanopositioning stage driven by the self-damping moving magnet actuator (SMMA) and supported by the flexure guide is integrated and designed in this article. The SMMA consists of two identical tooth-slot structure stators and one moving magnet which is embedded inside the flexure guide. Copper plates that functioned as eddy-current dampers are attached on the tooth surfaces to suppress the resonance peak at the natural frequency. An integrated dynamics model that consists of force, damping coefficient, and stiffness is established. The dimensional parameters of the proposed positioning stage are optimized to improve the system performances based on the developed model. Experimental results show that the natural frequency of the positioning stage reaches up to 71 Hz. The stage can achieve 20 nm positioning resolution within a motion range of $\pm$ 5 mm, and the root mean square tracking errors for 1 Hz sinusoidal and triangular commands are below 0.1% of the trajectory amplitudes. [ABSTRACT FROM AUTHOR]

The parallel connection of dc–dc converters requires the development of an appropriate control strategy that regulates load voltage and shares current among participating converters. This article proposes a resilient and robust cooperative distributed control approach that simultaneously ensures voltage regulation and balanced current sharing in parallel dc–dc converters in the presence of false data injection attacks on control input channels. Based on analytical tools from network control and Lyapunov stability theory, concise stability certificates are derived. The proposed cooperative distributed control strategy guarantees resilience against unknown bounded attacks on the actuators of dc–dc converters and the robustness to uncertainties in load parameters and the physical parameters of converters. Furthermore, the control design for each converter does not require any knowledge about the number of participating converters. The detailed simulation and experimental results verify the satisfactory performance of the proposed method in voltage regulation and balanced current sharing in parallel converters, as well as resilience to bounded false data injection attacks. [ABSTRACT FROM AUTHOR]

The Internet of Things (IoT), which describes the equipment of physical objects with sensors, actuators, computing logic, and connectivity, has attracted much attention. Although many facets of the IoT have already been explored, existing works either treat smart things as black box or focus on their technical characteristics. From an engineering management perspective, however, also a profound understanding of nontechnical smart thing characteristics is key. Hence, in this article, we develop and evaluate a corresponding multilayer taxonomy based on the latest IoT literature and a deliberately broad sample of 200 smart things, which covers the diversity of smart things available on the market. Based on 11 dimensions, the taxonomy enables classifying smart things according to the layers of established IoT architectures. Based on our sample, we infer five clusters, each covering a typical combination of nontechnical smart thing characteristics occurring in practice. These results extend our understanding of the IoT by structuring nontechnical characteristics of smart things and by abstracting the diversity of smart things into artefacts with manageable complexity. Our results inspire future research on the adoption, affordances, and design of smart things. Moreover, engineering managers can use our results in early phases of product development and process reengineering projects. [ABSTRACT FROM AUTHOR]

The work has devised a novel fixed-time control scheme for a class of nonlinear systems with output constraints. Two distinctive features are incorporated into the gained results. One is that the upper bound of settling time for the closed-loop system can be estimated without dependence on system initial states, and hence, can be acquired arbitrarily small through tuning control design parameters. The other is that the output constraint can be handled by means of a barrier Lyapunov function (BLF). Via the BLF and the backstepping-like technique, a fixed-time controller, which can cope with a type of nonlinear systems concurrently with and without output constraints, is systematically built. The rigorous analysis on the strength of the Lyapunov theory is given to show that the investigated system under the proposed controller is fixed-time stable, and the violation of a preset output constraint is averted. The case studies of a series elastic actuator system are offered to substantiate the derived theoretical results. [ABSTRACT FROM AUTHOR]

This article focuses on the leader-following consensus problem for a class of high-order uncertain nonlinear multiagent systems (MASs) subject to denial-of-service (DoS) attacks and actuator faults under the directed topology. To reduce the network communication bandwidth resource from the controller to the actuator and mitigate the adverse effect from DoS attacks, a novel event-triggered control strategy is proposed based on the reliable attack detection mechanism. The general attack detection mechanisms depend on the residuals between the values from the systems and observers. Different from the general attack detection mechanisms, a novel attack detection mechanism is proposed based on the logic relationship of voltage level signals which from the outputs of system components. Besides, the controller is designed based on the backstepping method and the controller can guarantee that the Zeno behavior is excluded. Furthermore, by using the Lyapunov stability theory, it proves that the controllers make the MASs achieve consensus. Eventually, a simulation example is presented to demonstrate the effectiveness of the proposed theoretical results. [ABSTRACT FROM AUTHOR]

Locomotion through rolling is attractive compared to other forms of locomotion thanks to uniform designs, high degree of mobility, dynamic stability, and self-recovery from collision. Despite previous efforts to design rolling soft systems, pneumatic and other soft actuators are often limited in terms of high-speed dynamics, system integration, and/or functionalities. Furthermore, mathematical description of the rolling dynamics for this type of robot and how the models can be used for speed control are often not mentioned. This article introduces a cylindrical-shaped shell-bulging rolling soft wheel that employs an array of 16 folded-HASEL actuators as a mean for improved rolling performance. The actuators represent the soft components with discrete forces that propel the wheel, whereas the wheel's frame is rigid but allows for smooth, continuous change in position and speed. We discuss the interplay between the electrical and mechanical design choices, the modeling of the wheel's hybrid (continuous and discrete) dynamic behavior, and the implementation of a model predictive controller (MPC) for the robot's speed. With the balance of several design factors, we show the wheel's ability to carry integrated hardware with a maximum rolling speed at 0.7 m/s (or 2.2 body lengths per second), despite its total weight of 979 g, allowing the wheel to outperform the existing rolling soft wheels with comparable weights and sizes. We also show that the MPC enables the wheel to accelerate and leverage its inherent braking capability to reach desired speeds—a critical function that did not exist in previous rolling soft systems. [ABSTRACT FROM AUTHOR]

Haptic feedback is known to enhance the realism of an individual’s interactions with objects in virtual environments. Wearable haptic devices, such as vibrotactile sleeves or armbands, can provide haptic feedback in a smaller and more lightweight form factor than haptic gloves that can be bulky and cumbersome to the wearer. In this article, we present tactile and squeeze bracelet interface (Tasbi), a multimodal haptic wristband that can provide radial squeeze forces around the wrist along with vibrotactile feedback at six discrete locations around the band. Tasbi implements a squeezing mechanism that minimizes tangential forces between the band’s points of contact with the skin, instead of focusing the motor actuation to predominantly normal forces. Force sensing capacitors enable closed-loop control of the squeeze force, while vibration is achieved with linear resonant actuators. A detailed description of the design and experimental results demonstrating closed-loop control of squeeze cues provided by Tasbi is presented. Additionally, we present the results of psychophysical experiments that quantify user perception of the vibration and squeeze cues, including vibrotactile identification accuracy in the presence of varying squeeze forces, discrimination thresholds for the squeeze force, and an analysis of user preferences for squeeze actuation magnitudes. [ABSTRACT FROM AUTHOR]

Soft actuators are compliant structures that are generally made of elastomers and generates large deformation. The behavior of these structures cannot be estimated accurately using infinitesimal strain theories. The objective of soft robotics applications is the controlled large deformation of these structures. In this article, we propose an analytical model for a pneu-net soft actuator. The model is based on the Euler–Bernoulli finite strain hyperelastic thin cantilever beam theory. The deformation of the air chambers is modeled using finite strain membrane theory. The analytical model is developed for two different states of the actuator: 1) free space; and 2) when the actuator was subjected to tip contact. The proposed theoretical model predicts the deformation and force characteristics of the actuator for the grasping state. The theoretical formulation of the developed model is different from previously developed infinitesimal strain models for the actuator, as it considers the axial stretch and forces applied to the actuator. In addition, it can be theoretically implemented on similar structured actuators for various applications. The theoretically calculated deformation and force characteristics of different actuators are compared with the finite element (FE) model and experimental characteristics. The results suggest that the proposed model can predict the actuator deformation and force characteristics as accurately as the FE model, but the computation time of the proposed model is less than 1% that of the FE model. The proposed model is further implemented on a three-finger gripper to predict the air pressure required for a stable grasp of different objects and is validated experimentally. [ABSTRACT FROM AUTHOR]

We present a self-deformable flexible tweezer capable of simultaneous mechanical handling and electrical measurements. The tweezer has a soft cantilever with the dimensions 2 mm $\times8$ mm $\times $ 75- $100~\mu \text{m}$ , and undergoes self-deformation. The device is shown to be successfully capable of detecting electrical signals by gently touching the surface and grasping a spherical bead. The device demonstrated the lowest working voltage (1.5 VDC), force suitable for soft gripping, and curvature radius of 2 mm, that was one of the smallest values compared to that of similar state-of-the-art devices. The device was fabricated using a unique and highly reliable process that was specifically developed to produce flexible cantilevers with novel ionic polymer-metal composites (IPMCs). The materials used were poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) and an ionic liquid (IL). The PVDF-TrFE/IL gel was prepared using acetone as the solvent and the gel was coated with silver nanowires as the electrodes. The actuator with a length of 8 mm and containing 50 wt% IL yielded the largest bending displacement of 7 mm and minimum curvature radius of 2 mm at 1.5 VDC. [2022-0026] [ABSTRACT FROM AUTHOR]

MEMS based piezoelectrically driven micro-lens actuator experiences resonance frequency shift with changing actuation voltage and exhibits low level of damping. In this paper, we present the design and experimental implementation of a resonant controller, robust against the variation in dynamics, to enhance the damping at the first resonance frequency. The controller is designed using an identified model of the micro-lens actuator from experimental frequency response data at a fixed actuating voltage. The closed-loop stability is guaranteed using the mixed negative-imaginary and small-gain approach. The experimental results demonstrate a damping of 21dB of the first resonance mode. The designed controller achieved the similar level of damping for the shift in resonance frequency due to the change in the actuation voltage. The settling time, due to a step change, of the piezoelectric micro-lens actuator is reduced to 7ms from 120ms. Such quick settling time is necessary for the fast auto-focusing functionality of the piezoelectrically driven micro-lens actuator in a miniaturized camera module. [2022-0137] [ABSTRACT FROM AUTHOR]

This work describes a novel micromechanical structure capable of producing out-of-plane motion from in-plane forces generated by electrostatic microelectromechanical system (MEMS) actuators. The MEMS actuator is fabricated in a commercial silicon-on-insulator (SOI) MEMS process and is anchored at two distinct locations through a pair of beams with a relatively low stiffness in the vertical direction. A comb-drive, whose fixed and moveable fingers are implemented in the same layer with a uniform thickness, is employed to create an attractive electrostatic force. This in-plane electrostatic force rotates the actuator along an axis defined by the anchors, which results in the vertical motion of a suspended platform. Due to the simple structure of the actuator, it can be readily manufactured with standard bulk micromachining processes. Experimental results demonstrate that the actuator can provide $1.02~\mu \text{m}$ of vertical displacement at a resonant frequency of 395 Hz when it is excited in air by a 10 V AC signal, while the displacement can be considerably increased in vacuum. It is further shown that the functionality of the actuator is not dependent on the type of excitation voltage; therefore, it can produce a $3.09~\mu \text{m}$ static out-of-plane motion when excited by a 40 V DC voltage. A comprehensive comparison to the published works in the literature indicates that the proposed actuator is the only SOI electrostatic MEMS actuator with a relatively thick structural layer, i.e., $10~\mu \text{m}$ , that can provide out-of-plane motion at low actuation voltage reported to date. [2022-0069] [ABSTRACT FROM AUTHOR]

This article investigates the prescribed performance control problem associated with attitude stabilization of a rigid body, considering angular velocity constraint, actuator faults, and input saturation. The desired performance specifications in transient and steady-state phases including convergence speed, overshoot, and steady-state value for attitude variable are also provided. To this end, the prescribed performance control methodology is combined with backstepping-based barrier Lyapunov function so as to develop a controller with simple structure compared to the existing constrained controls. The main idea behind the control design is to remove partial differential and complex function terms to considerably decrease complexity of the proposed controller. Moreover, a hyperbolic tangent function and an auxiliary system are employed to develop the constrained virtual rotation velocity control and to consider input saturation. The simulation results carried out on a rigid spacecraft confirm efficiency and success of the proposed constrained attitude control method. [ABSTRACT FROM AUTHOR]

This article reports on the design, modeling, control, and testing of a novel compliant nanopositioning stage driven by a self-developed normal-stressed electromagnetic actuator. To facilitate the parameter selection for the stage to achieve the desired stroke and natural frequency, an analytical model of both the electromagnetic circuit and flexure mechanism is established, which is then systematically verified through finite element analysis. By combining a proportional—integral—differential (PID)-based main controller with a system dynamics inversion-based feedforward compensator, a closed-loop control system for the stage is constructed with the main controller being tuned through Bode’s ideal transfer function-based loop-shaping method. The experimental result shows that a stroke of ${\pm } 95 ~\mu \text{m}$ and a first natural frequency of 743 Hz are achieved for the designed stage. Finally, taking advantage of the constructed control system, the nanopositioning capability is demonstrated by finely tracking the harmonic and nanostair commands. Note to Practitioners—Piezoelectric actuators (PEAs) and voice coil motors (VCMs) are commonly adopted for the actuation of nanopositioning stages. In general, constrained by the inherent small strain, PEA is more suitable for the generation of dynamic motions in dozens of micrometers. Meanwhile, VCM has a theoretically infinite motion range but a slow response due to its low force density nature. Taking advantage of a newly developed normal-stressed electromagnetic actuator (NSEA), we demonstrate the design, modeling, control, and testing of an NSEA-based nanopositioning stage with a relatively long motion range, high bandwidth, and compact size. Considering the high force density and relatively large motion range only constrained by the effective air gap, the NSEA-based stage is demonstrated herein to be very promising to achieve highly dynamic motions within hundreds of micrometers. [ABSTRACT FROM AUTHOR]

This article discusses cooperative control of a mobile dual flexible manipulator system with asymmetric time-varying output constraints and actuator failures. The shift function and a barrier Lyapunov function (BLF) are used to guarantee output constraints when the initial states of the system violate the prescribed constraints. Moreover, an adaptive fault-tolerant control scheme is developed to deal with actuator failures, while suppressing system’s vibration and achieving cooperative operation. Finally, theoretic analysis proves the uniform bounded stability of the system and numerical simulation verifies the effectiveness of the proposed control method. Note to Practitioners—The purpose of this article is to develop a cooperative dual flexible manipulator system with performance limitations and actuator failures. The system can realize the task of stably grasping and moving a rigid object. The existing research on the grasping task of flexible manipulators only focuses on coordinated operation, which limits the application of the dual flexible manipulator system in practical engineering. To further study the problem, this article considers the output constraints and actuator failures of the dual flexible manipulator system in the actual process and proposes a cooperative fault-tolerant control framework. The control framework uses shift function and BLF to deal with output constraints and adopts adaptive technology to deal with actuator failures. In addition, the cooperative operation task of grasping object with dual flexible manipulators is realized. Simulation shows that this control strategy is feasible. [ABSTRACT FROM AUTHOR]

In this article, we propose a redundant fault-tolerant and boundary constraint control in the framework of adaptive method, the neural network approximation, and the barrier Lyapunov function (BLF) with a relaxed initial condition. The actuator failures are compensated by a combination of adaptive methods and redundant actuators when some actuators suffer from partial or even total loss of effectiveness. The radial basis function’s neural network structure is introduced to strengthen the adaptivity in various orientations of the hose and other additionally unmodeled dynamics. To maintain the boundary deflection within a predefined open set after a constraint time, a novel asymmetrical and time-varying BLF is constructed by applying a shifting function to transform the original state into a new state with zero value initially. The performance of the developed adaptive control is demonstrated by numerical simulations. Note to Practitioners—This article is motivated by the limited performances in the existing control designs for flexible unmanned aerial refueling hose systems with failed actuators and boundary constraints. This article considers a redundant actuator case to solve time-varying and partially and totally failed actuator failures that are not settled by adaptive and Nussbaum-based single control. Unlike conventional barrier Lyapunov functions (BLFs), in this article, we resort to a shifting function and propose a novelly asymmetric and time-varying BLF, which is well defined initially and capable to address a deferred constraint control problem. The control design and stability analysis of the actuated system is a Lyapunov-based method rather than relying on semigroup theory or functional analysis, which makes the developed method more engineering orientated. The proposed control strategy is tested to illustrate performances in numerical simulations with the finite difference method. [ABSTRACT FROM AUTHOR]

This article is devoted to real-time optimal attitude reorientation control of rigid spacecraft control. Particularly, two typical practical problems—actuator misalignment and forbidden pointing constraints are considered. Within the framework of adaptive dynamic programming (ADP), a novel constrained optimal attitude control scheme is proposed.In this design, a special reward function is developed to characterize the environment feedback and deal with the pointing constraints. Notably, a novel argument term is introduced to the reward function for overcoming the inevitable difficulty in the actuator misalignment. By virtue of the Lyapunov stability theory, the ultimate boundedness of state error and the optimality of the proposed method can be guaranteed. Finally, the effectiveness and performance of the developed ADP-based controller are evaluated by not only numerical simulations but also experimental tests with a hardware-in-loop platform. [ABSTRACT FROM AUTHOR]

A permanent magnet linear synchronous motor (PMLSM) is susceptible to system uncertainties and external disturbances, resulting in a tracking error that is difficult to eliminate. To effectively reduce the tracking error of a PMLSM, this article presents a novel dynamic microactuation (DMA) method through a microactuation unit (MAU)-assisted dual-stage system. In this article, we reduce the tracking error dynamically through MAU-based actuation and use the PMLSM mover as the working end of the dual-stage system. The proposed DMA method finalizes the actuation mechanism of the MAU. Therefore, the method can dynamically actuate the MAU to act on the PMLSM mover with the appropriate actuation amount, and thus, reduce the tracking error of the motion system. Moreover, to avoid the coupling effect of MAU-based actuation on the PMLSM controller, the DMA method modifies the feedback error of the PMLSM controller by adding the actuation amount to the position error such that it remains unchanged. Thus, the stability of the electromagnetic thrust of the PMLSM can be maintained for its output. After finalizing the actuation mechanism and modifying the feedback error, the tracking error of the PMLSM can be reduced dynamically and the coupling effect of the MAU-based actuation on the PMLSM controller can be avoided. The performance of the proposed DMA method is analyzed theoretically and validated experimentally. The results show that the proposed method can effectively reduce the tracking error of a PMLSM system. [ABSTRACT FROM AUTHOR]

This article proposes a communication-efficient event-triggered time-delay control (ET-TDC) scheme, which is more intelligent, consumes fewer network resources, and is more suitable for practical applications, such as network control systems over bandwidth-limited communication channels. The proposed controller ensures a fast convergence rate and high tracking performance because it is based on TDCs that are well known for achieving high tracking performance. To maintain these properties, the proposed control scheme adopts a performance-preserving ET strategy, whereby the communication effort between the controllers and actuators can be significantly reduced. The ET condition of the proposed controller is devised to ensure system stability by using a Lyapunov function. Finally, the performance of the proposed ET-TDC is demonstrated through a numerical simulation and an experiment using a two-link robot manipulator. [ABSTRACT FROM AUTHOR]

In this letter (Zhu et al. 2011), an adaptive sliding mode controller is proposed for attitude stabilization of spacecraft under inertia uncertainty, external disturbances, and actuator constraints. Some comments on this issue are made here to point out a serious mistake and the untenable main result in the paper. A correction is proposed. [ABSTRACT FROM AUTHOR]

In AC microgrids (MGs), the required high control gain for dealing with control faults would reduce the robustness of the secondary control to communication constraints. To tackle with this problem, the subarea physical infrastructure of AC MGs and the two-layer secondary control framework are designed. For the physical infrastructure, the whole AC MG is divided into several areas, where each area is composed of a distributed generator (DG) and several geographical-close loads. Furthermore, by utilizing the advanced metering infrastructure (AMI), loads transmit the local load change information to the DG in the same area. Based on this physical infrastructure, a distributed event-triggered fixed-time fault-tolerant (ET-FTFT) secondary control framework is proposed in this paper to improve the resilience of the secondary control to sensor and actuator faults/attacks, and communication constraints, simultaneously. The adopted two-layer control framework is to decouple the communication constraints and control faults. The event-based strategy is adopted in the upper layer to reduce the communication burden and Zeno behavior can be evaded. Real-time simulations based on the NI-PXI real-time simulator validate the advantages of the distributed ET-FTFT secondary control framework, which are the better robustness to control faults, and the fixed-time convergence to improve the power quality. [ABSTRACT FROM AUTHOR]