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The problem of finite-time prescribed performance control (PPC) for spacecraft attitude maneuvering is researched. To the best of the authors' knowledge, limited results have been reported. How to achieve the prescribed performance attitude tracking within a preset time interval is still an open problem, especially in the presence of inertia perturbations, external disturbances, actuator saturations, and faults. On account of this, a finite-time performance function is first constructed as the predefined boundary of tracking errors. Second, Chebyshev neural network is utilized to approximate the lumped uncertainties. Then, the Nussbaum gain technique compensating for actuator saturations and faults is incorporated into the backstepping design to develop a new fault-tolerant attitude controller. Both transient and steady-state performances (e.g., the maximum overshoot, steady-state error, and settling time) are guaranteed. Compared with the common PPC or finite-time control achievements on spacecraft attitude tracking, the setting time herein can be set in advance without relying on initial states. Finally, experiments are performed to verify the effectiveness of the solution and comparisons with related works are displayed. National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [61773108]; Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada (NSERC)CGIAR This work was supported in part by the National Natural Science Foundation of China under Grant 61773108, and in part by the Natural Sciences and Engineering Research Council of Canada.

This paper proposes a new design of an event-based dissipative asynchronous controller for the interval type2 (IT2) fuzzy Markov jump systems (MJSs) subject to sensor saturation and actuator nonlinearity. By resorting to a generalized performance index, the $H_{\infty}$, passive, and dissipative fuzzy control problems are solved in a unified framework. The event-based scheme is developed for the IT2 fuzzy MJSs subject to sensor saturation and actuator nonlinearity, and the energy consumption of communication can be reduced. Moreover, the system and controller modes are asynchronous, and a hidden Markov model (HMM) is employed to observe the modes of the original system. The Membership-Function-Dependent (MFD) approach is applied to analyze the stability of the closed-loop system. Finally, two examples are given to demonstrate the effectiveness of the proposed algorithms.

This article contrives a neural-adaptive constrained controller of the cable towed air-ground recovery system subject to terrain obstacles, unmeasurable cable tensions, trailing vortex, wind gust, and actuator saturation. In air-ground recovery system modeling, the towed vehicle's nominal 6 DOF affine nonlinear dynamics and the cable system's finite links-joints dynamics are formulated. To achieve accurate air-ground recovery under terrain obstacles, an asymmetric barrier Lyapunov function-based flight controller of the towed vehicle is proposed, by transforming the terrain obstacles into time-varying constraints on the vehicle's trajectory. Then, to approximate the towed vehicle's lumped unknown dynamics caused by the unmeasurable cable tensions and airflows, several echo state network (ESN) approximators are established for velocity and attitude subsystems. By using the state approximation errors-based neural weights learning strategy and minimal learning parameter technique, these ESNs possess better transient behaviors and lower online computational burden. Furthermore, the actuator saturation is automatically monitored and released, by incorporating a specially designed auxiliary compensating system into the angular rate control law for compensation. The stability of the closed-loop system is analyzed. Finally, numerical simulations under two air-ground recovery scenarios are performed to demonstrate the performance of the proposed controller.

In this short paper, development of an adaptive fault tolerant control (FTC) using a virtual actuator framework is presented for one-sided Lipschitz nonlinear systems subjected to time-varying loss of effectiveness and additive actuator faults. The proposed controller does not require to have a separate unit to detect, isolate, and identify a fault, and it is completely independent from the nominal controller. Due to this important property, the virtual actuator can easily added between the faulty plant and the nominal controller and it can guarantee that the deviation of states from the nominal behavior of the system in the presence of actuator faults can be made arbitrary small. Simulation results are provided to show the efficacy of the proposed adaptive fault tolerant controller. Scopus

To face the demand for applications in which robots have to safely interact with humans and the environment, the research community developed new types of actuators with compliant characteristics. To embody compliance into the actuator, elastic elements with fixed or variable compliance can be used. Among the variable stiffness mechanisms, a popular approach is based on the agonistic-antagonistic (A-A) layout, where two prime movers are elastically connected to the output shaft of the actuator. Notwithstanding the conceptually simple realization of the A-A layout, one limitation is that, due to the nonlinear torque/deflection characteristic of the elastic transmissions and to the limited spring elongation, the stiffness range achievable at the output shaft reduces as the external torque increases. In this work, a novel layout, based on the A-A principle, is proposed to increase the torque/stiffness capability of the actuator. To achieve this result, we combine elastic transmissions with linear and nonlinear torque/deflection characteristics. The mathematical model of the new layout and a possible implementation are analyzed. Then, the design of a novel variable stiffness actuator is presented and experimental validations are shown to compare the new device with the benchmark.

This article deals with trajectory tracking for autonomous cars during evasive maneuvers and in the presence of steering actuator nonlinearities. This article develops an LPV MISO H-infinity controller based on the feedback of the lateral error at the center of gravity and the look-ahead distance. The controller architecture offers a way to cope with the effect of the steering nonlinearities, by scheduling one of the control weighting functions. A detailed experimental validation on three different maneuvers (straight driving, wide bend, and a double-lane change) shows the effectiveness of the proposed LPV solution.

Propeller aircraft are widely used in general aviation. The rotating propeller has a strong effect on the aerodynamic performance of the wing. This paper uses an actuator disc to model the effect of the propeller. A wing optimization method is developed with the actuator disc method. Several wing optimizations with different slipstream settings are studied. The twist angle and airfoils of the wing are used as the design variables. The results show that the propeller slipstream and slipstream directions have a strong influence on the optimization process. Powered-on optimization with a slipstream can obtain better drag reduction results than unpowered optimization. The drag decomposition results show that most of the drag reduction comes from the form drag reduction. The symmetric “inboard-up” slipstream configuration is found to have the highest lift-to-drag ratios, which are 18.87 for the twist angle optimization and 19.15 for the airfoil optimization.

We address the problem of state estimation, attack isolation, and control of discrete-time linear time-invariant systems under (potentially unbounded) actuator and sensor false data injection attacks. Using a bank of unknown input observers, each observer leading to an exponentially stable estimation error (in the attack-free case), we propose an observer-based estimator that provides exponential estimates of the system state in spite of actuator and sensor attacks. Exploiting sensor and actuator redundancy, the estimation scheme is guaranteed to work if a sufficiently small subset of sensors and actuators are under attack. Using the proposed estimator, we provide tools for reconstructing and isolating actuator and sensor attacks; and a control scheme capable of stabilizing the closed-loop dynamics by switching off isolated actuators. Simulation results are presented to illustrate the performance of our tools., arXiv admin note: substantial text overlap with arXiv:1811.10159

This paper addresses the attitude control of nano-spacecraft with three reaction wheels and three magnetorquers in low Earth orbits, and develops algorithms to maintain control when any one of the reaction wheels completely fails. In the event of a reaction wheel failure, it is shown that the key challenge of maintaining accurate autonomous three-axis tracking is a problem of singularity avoidance in control allocation. In particular, control law singularities occur depending on the type of orbit, the environment, and the attitude, where the system is no longer controllable. Two algorithmic singularity avoidance techniques based on singularity prediction and artificial potential functions are proposed. In addition, an optimized reaction wheel configuration is proposed to enhance singularity avoidance capability. To illustrate the effectiveness of the singularity avoidance control laws, they are tested in simulations that include the effects of perturbing environmental torques, reaction wheel jitter, and actuator misalignment.

An accurate understanding of the output power functionality in gas turbines concerning the fuel, inlet valve status and other parameters can provide a general overview of the turbine's performance. In this study, the problem of practical power regulation in gas turbines is investigated in the simultaneous presence of actuator constraints, unknown disturbances, and measurement noises. To this aim, a model predictive controller-based approach is utilized because of its high flexibility combined with a two-layer filtering and anti-filtering procedure to efficiently cope with the measurement noises. Moreover, the proposed structure takes the effects of unknown disturbances into account and thereby it is shown that the proposed controller can efficiently achieve all design objectives while handling actuator constraints, disturbances and measurement noises.

In this article, a fault-tolerant control (FTC) scheme for linear multiagent systems (MASs) subject to time-varying loss of effectiveness and time-varying additive actuator faults as well as external disturbance is investigated. The main objective of the proposed FTC approach is to keep the performance of an MAS after the occurrence of actuator faults similar to the healthy one. The envisaged adaptive virtual actuator for each agent does not require a separate fault detection, isolation, and identification unit nor does it require any information regarding the mission of the MAS. It is shown that the difference between the states of each agent before and after the occurrence of actuator faults can be made arbitrary small and the ultimate bounds of the state error are also obtained. Furthermore, it is shown that for constant actuator faults the state error of each agent converges to zero. Simulation results corresponding to a team of F-8 aircraft and a heterogeneous MAS with the different order demonstrate and illustrate the effectiveness of our proposed FTC scheme. Qatar Foundation; Qatar National Research Fund Scopus

Microfluidic devices and micro-pumps are increasingly necessitated in many fields ranging from untethered soft robots, to pharmaceutical and biomedical technology. While realization of such devices is limited by miniaturization constraints of conventional actuators, these restrictions can be resolved by using smart material transducers instead. This paper proposes and investigates the first ionic polymer metal composite (IPMC) actuator-driven linear peristaltic pump. With the aim of designing a monolithic device, our concept is based on a single IPMC actuator that is etched on both sides and cut with kirigami-inspired slits by laser ablation. Our pump has a planar configuration, operates with low activation voltages (< 5 V) and is simple to manufacture and thus miniaturize. We build proof-of-principle prototypes of an open and closed design of our proposed pump concept, model the closed design, and evaluate both configurations experimentally. Results show the feasibility of the proposed IPMC-driven pump. Without any optimization, the open pump achieved pumping rates of 669 pL/s, while the closed pump configuration attained a 4.57 Pa pressure buildup and 9.18 nL/s pumping rate. These results indicate feasibility of the concept, and future work will focus on design optimization.

Electroactive polymer (EAP) is a kind of smart material, which can change its shape under the stimulation of electric field. Dielectric elastomer (DE) is an important member of the EAP. DE has the characteristics of excellent performance, such as light weight, low noise, low cost, and so on, which guarantee its wide applications in the fields of actuators, generators, sensors. In this review, the principles of energy conversion, the research status and latest development of new technologies for DEs, and the performance characteristics of DEs are summarised. Simultaneously, it points out the development problems and feasible countermeasures. At last, the application prospects of DE are discussed, combined with the research direction of the international frontier.

Selecting actuators for assistive exoskeletons involves decisions in which designers usually face contrasting requirements. While certain choices may depend on the application context or design philosophy, it is generally desirable to avoid oversizing actuators in order to obtain more lightweight and transparent systems, ultimately promoting the adoption of a given device. In many cases, the torque and power requirements can be relaxed by exploiting the contribution of an elastic element acting in mechanical parallel. This contribution considers one such case and introduces a methodology for the evaluation of different actuator choices resulting from the combination of different motors, reduction gears, and parallel stiffness profiles, helping to match actuator capabilities to the task requirements. Such methodology is based on a graphical tool showing how different design choices affect the actuator as a whole. To illustrate the approach, a back-support exoskeleton for lifting tasks is considered as a case study.

Remotely addressable actuators are of great interest in fields like microrobotics and smart textiles because of their simplicity, integrity, flexibility, and lightweight. However, most of the existing actuator systems are composed of complex assemblies and/or offer a low response rate. Here, the actuation performance of a light-driven, highly oriented film based on ultra-high molecular weight polyethylene (UHMW-PE), containing a photo-responsive additive, 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol (BZT), is reported. The material exhibits a fast (

Owing to the non-collocation of actuators and sensors in a flexible-link manipulator (FLM) it becomes difficult to achieve accurate tip position tracking. To resolve this issue, a vision sensor is used for direct measurement of the tip position instead of employing the traditional mechanical sensors. Among the different visual servoing (VS) control schemes, image-based VS (IBVS) is more effective. However, there are many challenges in the IBVS scheme such as singularities in the interaction matrix and local minima in trajectories that affect the system performance in real-time applications. In this study, the moment-based new visual feature is selected to address the aforesaid issues that arise in the IBVS scheme. Furthermore, a new two-time scale IBVS controller is developed for addressing the tip-tracking control problem of the two-link flexible manipulator (TLFM). In the proposed control scheme, the dynamics of the FLM is decomposed into two-time scale models, namely a slow subsystem and a fast subsystem. The performance and robustness of the proposed new two-time scale IBVS controller for TLFM are verified by pursuing simulation studies. It is observed from the obtained results that the proposed controller effectively stabilises the oscillatory dynamics and tracks the reference trajectory accurately.

The performance of a formation control algorithm for a group of autonomous underwater vehicles (AUVs) may be degraded due to communication constraints between the leader and the follower AUVs. Moreover, as the distance between the AUVs change due to ocean waves, the delay in communication also varies. In this study, a modified constrained adaptive controller (CAC) is proposed to resolve the issue of variable-delay as well as actuator saturation. Due to the on-line reduction of the cost function, the gains of the CAC are updated at each sampling time taking into account the effects of communication delay. This improves the path-following accuracy of the leader AUV as well as follower AUVs. The effectiveness of the proposed control algorithm is demonstrated by implementing it on a prototype AUV (ODRA-I) model. The obtained simulation and experimental results show that the follower AUVs maintain a desired distance from the leader AUV to avoid a collision. For the proposed algorithm, the desired path-following performance of the follower AUV is maintained even when the delay is changed from 0 to 5 s. Moreover, the proposed control algorithm is efficient in avoiding actuator saturation.

This paper presents a design optimization framework based on Branch and Bound Algorithm for novel networked electromagnetic soft actuators. The soft actuators work based on the operating principle of solenoids but are made of intrinsically soft materials. We confirmed that by scaling down the size of the soft actuators, their force to volume ratio increases. This suggests that by miniaturizing the actuators size and attaching them as a network based on the arrangement of actin and myosin filaments in skeletal muscles, the output force can be enhanced. In order to achieve the maximum output force, design parameters of a single soft actuator as well as those of a network are considered as design variables. The maximum available volume (thickness, width and length) and deflection range of the network are considered design constraints. The cost function, i.e. the output force is a non-linear mixed-integer function. A Branch and Bound optimization algorithm based on interval analysis is then proposed to solve the optimization problem. Numerical simulations are presented for a representative example of an active soft brace for the human elbow joint. The results suggest that an electromagnetic soft actuator network can provide sufficient torque to be used as a drive train for an active elbow brace for both flexion and extension over a range of around 93 degrees.

In this study, dynamical neural networks (DNNs) are used as an online identifier for a class of non-linear systems with unknown actuator faults. By integrating the designed non-linear FD observer with adaptive regulation algorithm, the parameter coupling problem in DNNs can be successfully solved and the unknown actuator fault can be rejected simultaneously. Based on Lyapunov theory and convex optimisation algorithm, both the observation error and the identification error can be proved to convergent to zero. Finally, simulation examples for the non-linear systems with actuator fault are given to illustrate the effectiveness of the proposed approach.

In this article, a fault tolerant controller (FTC) based on back-stepping sliding mode is proposed for a quadrotor unmanned aerial vehicle (UAV) with single-rotor failure. According to the working mechanism of the quadrotor, the control system of UAV is divided into position subsystem and attitude subsystem. Then, the yaw control is abandoned because of the increased underactuation. The controller is designed by the back-stepping sliding mode control (BSMC). BSMC is robust to system uncertainties and external disturbances. Sliding mode reaching law is designed. Therefore, it can reduce system chattering. Based on the Lyapunov function method, the proposed FTC approach makes the faulty UAV stable and realises position control accuracy. Finally, simulation results show that the quadrotor UAV can reach the desired position and maintain the hover state, which verifies the effectiveness of the proposed method.

Cable-Driven Parallel Robots (CDPRs) use cables arranged in a parallel fashion to manipulate an end-effector (EE). They are functionally similar to several cranes that automatically collaborate in handling a shared payload. Thus, CDPRs share several types of equipment with cranes, such as winches, hoists, and pulleys. On the other hand, since CDPRs rely on model-based automatic controllers for their operations, standard crane equipment may severely limit their performance. In particular, to achieve reasonably accurate feedback control of the EE pose during the process, the length of the cable inside the workspace of the robot should be known. Cable length is usually inferred by measuring winch angular displacement, but this operation is simple and accurate only if the winch transmission ratio is constant. This problem called for the design of novel actuation schemes for CDPRs; in this paper, we analyze the existing architectures of so-called servo-winches (i.e., servo-actuators which employ a rotational motor and have a constant transmission ratio), and we propose a novel servo-winch concept and compare the state-of-the-art architectures with our design in terms of pros and cons, design requirements, and applications.

Wearable fingertip haptic devices aim to deliver somatosensory feedback for applications such as virtual reality, rehabilitation, and enhancing hardware/physical control interfaces. However, providing various kinds of feedback requires several Degrees of Freedom (DoF) and high mechanical complexity which are mechanically difficult to achieve at the mesoscale. Using compliant low-profile transmissions embedded in an origami structure and PCBmotors as actuators, we designed and fabricated a novel 3-DoF fingertip haptic device, called Haptigami. This under-actuated system, measuring 36 x 25 x 26 mm and weighing 13 g, can render vibrotactile and cutaneous force feedback. We tested our device by creating a novel experimental protocol and robotic platform allowing quantitative characterization of mechanical performance. The current prototype of Haptigami produces 678 mN in compression, and 400 mN and 150 mN in shear for the Y and X directions respectively. By virtue of its unique origami-inspired design, Haptigami brings a new direction for future designs of lightweight and compact wearable robots.

Twisted toroidal ribbons such as the one-sided Möbius strip have inspired scientists, engineers and artists for many centuries. A physical Möbius strip exhibits interesting mechanical properties deriving from a tendency to redistribute the torsional strain away from the twist region. This leads to the interesting possibility of building topological actuators with continuous deformations. Here we report on a series of corresponding bi-layered stripe actuators using a photothermally responsive liquid crystal elastomer as the fundamental polymeric material. Employing a special procedure, even Möbius strips with an odd number of twists can be fabricated exhibiting a seamless homeotropic and homogeneous morphology. Imposing a suitable contraction gradient under near-infrared light irradiation, these ribbons can realize continuous anticlockwise/clockwise in-situ rotation. Our work could pave the way for developing actuators and shape morphing materials that need not rely on switching between distinct states., Shape morphing materials are usually difficult to operate in a continuous fashion. Nie et al. fabricate stripes with liquid crystalline elastomers that can be given a Möbius-like morphology with seamless material composition, and perpetually driven under photothermally induced actuation.

The need for faster power switches leads to the following question: Which technical actuation principle has the highest acceleration potential? This study describes the investigation of electrodynamic moving coil (voice coil) actuators. This principle promises no delay for the excitation field because of permanent magnets and a very small electrical time constant of the moving coil. The aim is to find out the limits of the switching time under practicable conditions. In the study, technical limitations of the actuation principle concerning the dynamic behaviour are shown by an analytical approach. It contains the major parameters like stroke or material of the iron poles, the coil, and the permanent magnets. Furthermore, the study discusses thermal aspects and approaches for the mechanical force multiplying by cascaded arrangements. A magnetically optimised elementary unit can be combined parallel or in series. The mechanical load inertial can be divided into a sufficient number of cascaded actuation units. Consequently, only the inherent moving mass determines the acceleration capability. This optimisation was done analytically with the Lorentz force formula and with finite element method simulations. This article describes both approaches, their results, and the experimental verification. The experimental actuator reaches a switching time of 2.7 ms.

Conventional flap and slat high-lift surfaces actuation systems in a commercial aircraft consist of actuators mechanically connected via a transmission system across the wingspan, driven from a centralised power drive unit comprising of a hydraulic, electric, or hybrid hydraulic/electric motor arrangement. The permanent coupling to the shafts makes the entire flap system move in unison, as do the slats. This paper will investigate and discuss different potential system architecture, and present the benefits associated with such architecture. It will also present the advantage that can be linked to a full electric flap configuration.

This paper designs an active fault-tolerant control system for spacecraft attitude control in the presence of actuator faults, fault estimation errors, and control input constraints. The developed fault-tolerant control system is able to detect the actuator fault without false alarms caused by external disturbances, and also estimate the total fault effects accurately through an indirect fault identification approach, in which an auxiliary variable is utilized to build the relation between fault and system states. Once the fault identification is completed with certain degree of reconstruction accuracy, a fault-tolerant backstepping controller using the nonlinear virtual control input is reconfigured to accommodate the detected actuator faults effectively, in spite of actuator saturation limitations and fault estimation errors. Numerical simulation is carried out to demonstrate that the proposed active fault-tolerant control system is successful in fault detection, identification, and controller reconfiguration for handling actuator faults in attitude control systems.

Series Elastic Actuation decouples actuator inertia from the interaction ports and is thus advantageous for force-controlled devices. Parallel or even passive compliance can fulfill a complementary role by compensating for gravitational or periodic inertial forces or by providing passive guidance. Here, these concepts are combined in an underactuated six degree of freedom (DoF) compliant manipulator with one actuated DoF. The mechanism comprises a spring assembly in which each spring serves as an actuation element and simultaneously provides passive compliance in the unactuated DoF. The device is designed to assist weight shifting via controlled lateral forces on a human pelvis during treadmill walking and its eigenfrequencies are tuned to align with normal gait. Six-DoF force and torque sensing are realized via a model of the spring deformation characteristics in combination with low-cost inertial and optical sensors. Experimental evaluation demonstrates that the system can effectively follow physiological weight shifting with low interaction forces and also has little impact on remaining pelvis motions.

This paper reports the concept, design, and development of a pneumatic braided muscle actuator, able to produce bidirectional force and motion. Such a capability can simplify the design and enhance the capabilities of robotic/automation systems using pneumatic muscles as actuators. Finite-element modeling is utilized as a design tool in order to study the feasibility of the concept, where a single braid structure is deformed to produce both contraction and elongation. A three-dimensional finite-element model of the actuator is developed and a number of nonlinear quasi-static simulations are performed using the explicit dynamic solver LS-Dyna to measure the blocked force and free displacement of the actuator. The effect of varying the end-fittings diameter and the length of the inner chamber on the mechanical characteristics of the actuator is also analyzed. The simulation results are validated through mechanical experimentation performed on the functional prototype. With an actuation pressure of 1 bar, the actuator is able to produce a contraction force of around 80 N, extension force of around 40 N, and an overall stroke of >40% of the total length of the actuator. Moreover, the novel actuator has been utilized as a main driver for a one degree of freedom variable stiffness joint, as a case study, to demonstrate the usability of the actuator.

This paper presents a health monitoring approach for Electro-Mechanical Actuators (EMA). We define four different indicators to continuously evaluate the health state of the system. The four indicators are computed by leveraging the output from a Statistical Process Monitoring (SPM) method based on multivariate statistics, such as the Hotelling's T2 statistic and the Q statistic. SPM approaches give a dichotomous answer, i.e. the presence/absence of a fault. In this work, we propose four ways to compute a continuous indicator starting from the discrete SPM output, that is better suited for health monitoring. We test the approach using a dataset collected from a large experimental campaign on a 1:1 scale EMA for primary flight controls of small aircrafts, that led to EMA failure. Results show the effectiveness of the method.

Significance The range of allowed deformation modes currently described for the actuation of microstructures is limited. In this work we introduce magnetic-field–guided encoding of highly controlled molecular anisotropy into 3D liquid-crystalline elastomer microstructures capable of displaying unique multiresponsive, shape-changing behaviors. The richness of the predetermined and self-regulated deformations and region-specific motions in these microstructural arrays gives rise to physicochemical insights, as well as potential applications in controlled adhesion, information encryption, soft robotics, and self-regulated light–material interactions., Dynamic functions of biological organisms often rely on arrays of actively deformable microstructures undergoing a nearly unlimited repertoire of predetermined and self-regulated reconfigurations and motions, most of which are difficult or not yet possible to achieve in synthetic systems. Here, we introduce stimuli-responsive microstructures based on liquid-crystalline elastomers (LCEs) that display a broad range of hierarchical, even mechanically unfavored deformation behaviors. By polymerizing molded prepolymer in patterned magnetic fields, we encode any desired uniform mesogen orientation into the resulting LCE microstructures, which is then read out upon heating above the nematic–isotropic transition temperature (TN–I) as a specific prescribed deformation, such as twisting, in- and out-of-plane tilting, stretching, or contraction. By further introducing light-responsive moieties, we demonstrate unique multifunctionality of the LCEs capable of three actuation modes: self-regulated bending toward the light source at T < TN–I, magnetic-field–encoded predetermined deformation at T > TN–I, and direction-dependent self-regulated motion toward the light at T > TN–I. We develop approaches to create patterned arrays of microstructures with encoded multiple area-specific deformation modes and show their functions in responsive release of cargo, image concealment, and light-controlled reflectivity. We foresee that this platform can be widely applied in switchable adhesion, information encryption, autonomous antennae, energy harvesting, soft robotics, and smart buildings.

A nondeterministic actuator fault model-based reliable control design method is presented for the leader-following consensus of a multiagent system (MAS) subject to input time-varying delay and the nonlinear phenomenon through the observer framework. Notably, a more generalized practical actuator fault model is proposed where the faults of each actuator are assumed to occur randomly and the fault rates are characterized by stochastic variables that satisfy certain probability conditions. To trace the leader dynamics, a reliable observer-based state feedback consensus algorithm is developed for the pursuing agents. After that, in light of graph theory and the Lyapunov–Krasovskii stability theorem, the required conditions are achieved to guarantee the leader-following consensus of the considered MAS, and then the corresponding reliable controller design method is proposed. Furthermore, simulations are eventually conducted to exhibit the efficiency of the newly developed control scheme, where it is shown that the obtained conditions guarantee the consensus of the considered MAS in the case of possible actuator faults.

In this paper, an innovative piezo-hydraulic actuator (PHA) is considered that is intended to realize a fully variable valve control in camless combustion engines. A nonlinear model of the hydraulic system part is presented along with linear models of the remaining system parts. Accurate tracking of desired valve trajectories as well as soft landing despite disturbance forces and measurement noise is achieved using a combined control strategy. It consists of an input–output linearization of the nonlinear part as well as feedforward and linear quadratic integral (LQI) feedback control of the linear system part. Given measurements of the valve spool and engine valve positions, a Cascaded Extended Kalman Filter (CEKF) structure provides estimates for the immeasurable states. Simulation results confirm the effectiveness of the proposed approach.

In this paper, we address the problem of distributed reconfiguration of networked control systems upon the removal of misbehaving sensors and actuators. In particular, we consider systems with redundant sensors and actuators cooperating to recover from faults. Reconfiguration is performed while minimizing a steady-state estimation error covariance and a quadratic control cost. A model-matching condition is imposed on the reconfiguration scheme. It is shown that the reconfiguration and its underlying computation can be distributed. Using an average dwell-time approach, the stability of the distributed reconfiguration scheme under finite-time termination is analyzed. The approach is illustrated in a numerical example.

Summarization: We develop a predictor-based adaptive cruise control design with integral action (based on a nominal constant time-headway policy) for the compensation of large actuator and sensor delays in vehicular systems utilizing measurements of the relative spacing as well as of the speed and the short-term history of the desired acceleration of the ego vehicle. By employing an input-output approach, we show that the predictor-based adaptive cruise control law with integral action guarantees all of the four typical performance specifications of adaptive cruise control designs, namely, 1) stability, 2) zero steady-state spacing error, 3) string stability, and 4) non-negative impulse response, despite the large input delay. The effectiveness of the developed control design is shown in simulation considering various performance metrics. Presented on: IEEE Transactions on Intelligent Transportation Systems

The emerging digital displacement (DD) fluid power technology requires a new class of high-performance valves that can operate in harsh high-pressure conditions. To overcome the switching performance limitations of solenoids and to avoid the mechanical complexity of moving coil actuators, a novel electronically-controlled moving magnet actuated (MMA) annular seat valve is proposed, designed, built, and tested rigorously in the laboratory. The actuator is energized using one coil only, it has bidirectional force capability and it utilizes magnetic latching to keep it open instead of a spring. The annular seat valve has two metering edges; the static pressure drop is 0.11/0.31 bar at -142/108 L/min, respectively. The valve closing time is 4-6 ms depending on the flow rate. The MMA valve is tested experimentally in both standalone test rigs besides in situ tests in a fully operational DD prototype machine. Measurements provided for pumping and motoring operation at 800 r/min/100 bar demonstrate that the proposed MMA valve topology is a promising candidate for energy-efficient digital displacement machines. Key characteristics include little power consumption, good switching performance, and a simple mechanical design.

Magnetic miniature robots (MMRs) are small-scale, untethered actuators which can be controlled by magnetic fields. As these actuators can non-invasively access highly confined and enclosed spaces; they have great potential to revolutionize numerous applications in robotics, materials science, and biomedicine. While the creation of MMRs with six-degrees-of-freedom (six-DOF) represents a major advancement for this class of actuators, these robots are not widely adopted due to two critical limitations: i) under precise orientation control, these MMRs have slow sixth-DOF angular velocities (4 degree s-1 ) and it is difficult to apply desired magnetic forces on them; ii) such MMRs cannot perform soft-bodied functionalities. Here a fabrication method that can magnetize optimal MMRs to produce 51-297-fold larger sixth-DOF torque than existing small-scale, magnetic actuators is introduced. A universal actuation method that is applicable for rigid and soft MMRs with six-DOF is also proposed. Under precise orientation control, the optimal MMRs can execute full six-DOF motions reliably and achieve sixth-DOF angular velocities of 173 degree s-1 . The soft MMRs can display unprecedented functionalities; the six-DOF jellyfish-like robot can swim across barriers impassable by existing similar devices and the six-DOF gripper is 20-folds quicker than its five-DOF predecessor in completing a complicated, small-scale assembly. Nanyang Technological University Submitted/Accepted version G.Z.L. was funded by the start-up grant awarded by Nanyang Technological University.

Self-oscillating systems that enable autonomous, continuous motions driven by an unchanging, constant stimulus would have significant applications in intelligent machines, advanced robotics, and biomedical devices. Despite efforts to gain self-oscillations have been made through artificial systems using responsive soft materials of gels or liquid crystal polymers, these systems are plagued with problems that restrict their practical applicability: few available oscillation modes due to limited degrees of freedom, inability to control the evolution between different modes, and failure under loading. Here we create a phototunable self-oscillating system that possesses a broad range of oscillation modes, controllable evolution between diverse modes, and loading capability. This self-oscillating system is driven by a photoactive self-winding fiber actuator designed and prepared through a twistless strategy inspired by the helix formation of plant-tendrils, which endows the system with high degrees of freedom. It enables not only controllable generation of three basic self-oscillations but also production of diverse complex oscillatory motions. Moreover, it can work continuously over 1270000 cycles without obvious fatigue, exhibiting high robustness. We envision that this system with controllable self-oscillations, loading capability, and mechanical robustness will be useful in autonomous, self-sustained machines and devices with the core feature of photo-mechanical transduction., Self-oscillating systems that enable autonomous motions driven by a constant stimulus find applications in numerous fields but these systems are plagued with problems that restrict their practical applicability. Here, the authors create a photoactive self-winding fiber actuator that possesses a broad range of oscillation modes, controllable evolution between diverse modes, and loading capability.

Significance Over recent years, the increased reporting on mechanically responsive molecular crystals has accumulated an extensive library of organic crystalline materials with diverse nature-like energy-transduction mechanisms. While the chemistry behind the underlying molecular transformations is elaborate, these single crystals' work-producing capacity remains underexplored due to the need for customized testing setups suitable for delicate organic microstructures. Using a simple setup, we lay out a set of performance metrics by which we characterize the light-driven actuation in azobenzene crystals as an exemplary chemical class of dynamic molecular crystals. This work may guide the quantification of responsive molecular crystals' actuation potential and act as an invitation to ramp up interdisciplinary interest to further develop this class of materials into controlled all-organic actuating elements., Dynamic molecular crystals have recently received ample attention as an emerging class of energy-transducing materials, yet have fallen short of developing into fully realized actuators. Through the trans–cis surface isomerization of three crystalline azobenzene materials, here, we set out to extensively characterize the light-to-work energy conversion of photoinduced bending in molecular crystals. We distinguish the azobenzene single crystals from commonly used actuators through quantitative performance evaluation and specific performance indices. Bending molecular crystals have an operating range comparable to that of microactuators such as microelectromechanical systems and a work-generating capacity and dynamic performance that qualifies them to substitute micromotor drivers in mechanical positioning and microgripping tasks. Finite element modeling, applied to determine the surface photoisomerization parameters, allowed for predicting and optimizing the mechanical response of these materials. Utilizing mechanical characterization and numerical simulation tools proves essential in accelerating the introduction of dynamic molecular crystals into soft microrobotics applications.

The regulation of the link positions of compliant robots, damping out undesired link oscillations while preserving the system's inherent elasticity is still a challenging task in practical applications. This task becomes even harder to be tackled in the case of compliant robots driven by agonistic-antagonistic variable stiffness actuators in which there are two motors associated with each joint of the system. In this work, leveraging on the physical realization of the elastic mechanism of such actuators, we propose a novel control law able to simultaneously achieve a good regulation performance and a desired damped behavior at the link, while preserving the elastic structure of the system as well as the possibility of adjusting the passive stiffness at the joints. Simulations on the agonistic-antagonistic actuators of the forearm and wrist joints of the Hand Arm System from the German Aerospace Center (DLR) and experiments on a planar platform with an analogous actuation unit, namely qbMove Advanced, validate the proposed method.

In this paper, we describe how to create simple fluidic systems incorporating soft polymer actuator valves, that can provide highly precise control of flow rates in fluidic channels as an example of a 4D-materials based platform. The particular approach we describe employs photoresponsive gels that swell/contract via a light stimulus, enabling flow behavior to be controlled from outside the fluidic platform in a completely remote and non-contact manner. An improved synthesis of the spiropyran molecular photoswitch that delivers high yields (77%) using scalable green chemistry is described, along with details on how to build the valve structures in custom designed sites within the fluidic system. Fabrication of a demonstrator fluidic system incorporating up to four valves is described, along with electronics and in-house developed PID control software for achieving precise control of flow in the channels using LEDs. The resulting system demonstrates an innovative approach to microfluidics that offers scalability in terms of the number of polymer actuators along with wide variability of actuator form and function.

Lab-on-PCB devices have been developed for many biomedical and biochemical applications. However, much work has to be done towards commercial applications. Even so, the research on devices of this kind is rapidly increasing. The reason for this lies in the great potential of lab-on-PCB devices to provide marketable devices. This review describes the active flow driving methods for lab-on-PCB devices, while commenting on their main characteristics. Among others, the methods described are the typical external impulsion devices, that is, syringe or peristaltic pumps; pressurized microchambers for precise displacement of liquid samples; electrowetting on dielectrics; and electroosmotic and phase-change-based flow driving, to name a few. In general, there is not a perfect method because all of them have drawbacks. The main problems with regard to marketable devices are the complex fabrication processes, the integration of many materials, the sealing process, and the use of many facilities for the PCB-chips. The larger the numbers of integrated sensors and actuators in the PCB-chip, the more complex the fabrication. In addition, the flow driving-integrated devices increase that difficulty. Moreover, the biological applications are demanding. They require transparency, biocompatibility, and specific ambient conditions. All the problems have to be solved when trying to reach repetitiveness and reliability, for both the fabrication process and the working of the lab-on-PCB, including the flow driving system.

Pneumatically-actuated soft robots have advantages over traditional rigid robots in many applications. In particular, their flexible bodies and gentle air-powered movements make them more suitable for use around humans and other objects that could be injured or damaged by traditional robots. However, existing systems for controlling soft robots currently require dedicated electromechanical hardware (usually solenoid valves) to maintain the actuation state (expanded or contracted) of each independent actuator. When combined with power, computation, and sensing components, this control hardware adds considerable cost, size, and power demands to the robot, thereby limiting the feasibility of soft robots in many important application areas. In this work, we introduce a pneumatic memory that uses air (not electricity) to set and maintain the states of large numbers of soft robotic actuators without dedicated electromechanical hardware. These pneumatic logic circuits use normally-closed microfluidic valves as transistor-like elements; this enables our circuits to support more complex computational functions than those built from normally-open valves. We demonstrate an eight-bit nonvolatile random-access pneumatic memory (RAM) that can maintain the states of multiple actuators, control both individual actuators and multiple actuators simultaneously using a pneumatic version of time division multiplexing (TDM), and set actuators to any intermediate position using a pneumatic version of analog-to-digital conversion. We perform proof-of-concept experimental testing of our pneumatic RAM by using it to control soft robotic hands playing individual notes, chords, and songs on a piano keyboard. By dramatically reducing the amount of hardware required to control multiple independent actuators in pneumatic soft robots, our pneumatic RAM can accelerate the spread of soft robotic technologies to a wide range of important application areas.

This paper presents the design, modelling, control, and experimental validation of a novel flapping wing aerial robot built with servo actuators that could be applied in search, rescue, and assistance to injured people. The proposed concept design is intended to facilitate the construction of this kind of aerial robots following a modular and reconfigurable approach, consisting of a series of Servo-Flapping Engine (SFE) modules attached to the carbon fibre tube used as fuselage, and a tail servo, covering the structure with a light nylon cloth. The SFE modules are built with a pair of servos that rotate the wing rods with desired amplitude, frequency, and relative phase. Combining two SFE modules, it is possible to generate different flapping patterns and control the orientation of the aerodynamic surfaces. The paper covers the parametrization of the design, the hardware/software implementation, as well as the modelling and control. The proposed design is validated through gliding and flapping tests in an outdoor environment. Comisión Europea - ERC Advanced Grant GRIFFIN Action 788247 Comisión Europea - Proyecto AERIAL-CORE H2020-2019-871479

Electro-Hydraulic Servo-Actuators (EHSA) are currently the most used actuation technology for primary flight control systems of civil and military aircrafts. Although some alternatives have emerged in the last decade, such as electromechanical or electro-hydrostatic solutions, electrohydraulic systems are still considered the most effective technology in flight-critical application of new commercial aircrafts. Moreover, the vast majority of aircraft currently in service are equipped with this technology. Considering the number of actuators typically employed in a primary flight control system and the expected service life of a commercial aircraft, the development of an effective PHM system could provide significant benefits to fleet operators and aircraft maintenance. This paper presents the results of a feasibility study of such a system for electro-hydraulic actuators used in fly-by-wire primary flight control systems, considering the actuator of a wide body commercial aircraft as use case. Aim of the research is the implementation of a PHM system without the addition of dedicated sensors, solution which would allow for the application of the proposed prognostic solution on both new and existing platforms. This paper describes the methodology and the results of the feasibility study through simulation and experimental activities, which shows how the novel PHM technologies proposed for a PHM system for the EHSAs of primary flight control actuators can allow the migration from scheduled to condition-based maintenance.

In current literature, a number of studies have separately considered path-tracking (PT) control and control allocation (CA) method, but few of studies have integrated them together. This study proposes an integrated PT and CA method for autonomous electric vehicle with independent steering and driving actuators in the limit handling scenario. The high-level feedback PT controller can determine the desired total tire forces and yaw moment, and is designed to guarantee yaw angle error and lateral deviation converge to zero simultaneously. The low-level CA method is formulated as a compact quadratic programming (QP) optimization formulation to optimally allocate individual control actuator. This CA method is designed for a prototype experiment electric vehicle with particularly steering and driving actuator arrangement. The proposed integrated PT controller is validate through numerical simulation based on a high-fidelity CarMaker model on highspeed limit handling scenario.

This work addresses a model based Fault Detection and Isolation problem for the actuators of the Odin Autonomous Underwater Vehicle. The model considered is the nonlinear 6 Dof Fossen model. In this article a new Autonomous Underwater Vehicle Fault Detection and Isolation system, based on the Non Linear Geometric Approach, resulting in a dedicated bank of scalar filters allowing simultaneous Fault Detection and Isolation, is proposed.The structural conditions for actuator fault diagnosability are analytically demonstrated. The results obtained by means of high fidelity simulations demonstrate the effectiveness and the reliability of the proposed methodology. The proposed Health Monitoring system can be successfully applied in Smart Harbour Autonomous Underwater Vehicle applications.

Inflatable soft microactuators typically consist of an elastic material with an internal void that can be inflated to generate a deformation. A crucial feature of these actuators is the shape of ther inflatable void as it determines the bending motion. Due to fabrication limitations, low complex void geometries are the de facto standard, severely restricting attainable motions. This paper introduces wire electrical discharge grinding (WEDG) for shaping the inflatable void, increasing their complexity. This approach enables the creation of new deformation patterns and functionalities. The WEDG process is used to create various moulds to cast rubber microactuators. These microactuators are fabricated through a bonding-free micromoulding process, which is highly sensitive to the accuracy of the mould. The mould cavity (outside of the actuator) is defined by micromilling, whereas the mould insert (inner cavity of the actuator) is defined by WEDG. The deformation patterns are evaluated with a multi-segment linear bending model. The produced microactuators are also characterised and compared with respect to the morphology of the inner cavity. All microactuators have a cylindrical shape with a length of 8 mm and a diameter of 0.8 mm. Actuation tests at a maximum pressure of 50 kPa indicate that complex deformation patterns such as curling, differential bending or multi-points bending can be achieved. ispartof: MICROMACHINES vol:11 issue:7 ispartof: location:Switzerland status: published

Trabajo presentado en la 7th International Conference on Control, Decision and Information Technologies (CoDIT), celebrada en Praga (República Checa), del 29 de junio al 2 de julio de 2020, The intrinsic redundancy of large-scale control systems allows to differentiate between the nominal system configuration, where the dynamics of the plant are controlled through a specific subset of actuators, and the possible configurations that arise from the combination of all the existing actuators (nominal plus back-up ones). After the occurrence of an unexpected event (component fault, isolation of a specific area due to security concerns, etc), some of the back-up system actuators can be used in order to guarantee that the system performance will remain within some admissible margins. Thus, given a scenario that causes a non-admissible system operation with the nominal configuration, the possibility to use back-up actuators in order to improve the system performance expands the traditional fault tolerant control scenario defining a new problem. Accordingly, this work is devoted to the introduction of the problem which is solved by formulating the actuator selection as a mixed-integer programming optimization. A water distribution network is used with the aim to illustrate the new problem implications as well as to demonstrate the validity of the proposed solution.

We here propose the extension of the Arduino Based Embedded Sensory systems Design of a five-parameter single diode estimation method for photovoltaic panels. The first attempt shows how to implement an already proposed algorithm into a micro controller-based system embedded in the PV panel module communicating with a long-range commercial high-frequency radio transmitter. Concerning the five parameter estimation method, it is based on an iterative algorithm, to estimate the parameter of the electrical single-diode model of the panel starting from the panel's datasheet. The proposed very low-cost architecture can be further integrated into a single chip apparatus in order to be implemented directly in the panel embedded electronics.

Limited data is available concerning the safety of active middle ear implants (AMEI) during Magnetic Resonance Imaging (MRI). Measurements in temporal bones are the gold standard for preclinical assessment of device safety. In this study the coupling stability of an actuator as used in a fully implantable AMEI was determined in temporal bones. Eleven temporal bones were implanted with the actuator according to the manufacturer’s surgical guidelines. The actuator was coupled on the incus short process as recommended for sensorineural hearing loss. Temporal bones were exposed 10 times to the MRI magnetic field by entering the MRI suite in a clinically relevant way. Computed Tomography (CT) images were acquired before and after the experiment to investigate the risk of actuator dislocation. Based on the electrical impedance of the actuator, the loading of the actuator to the incus was confirmed. Relative actuator displacement was determined on the CT images by comparing the initial with the final actuator position in 3D space. Impedance curves were analyzed after each exposure to check the loading of the actuator to the ossicles. Analysis of CT images with a 0.30.6 mm in-plane resolution indicate no actuator displacement. The maximum detected change in impedance for all actuators was 8.43 Ω at the actuator’s resonance frequency. Impedance curves measured when the actuator was retracted from the short process after the experiment still indicate the presence of a clear resonance peak. No actuator displacement or dislocation could be detected in the analysis of CT images and the measured impedance curves. Impedance curves obtained when the actuator was retracted from the incus short process still show a clear resonance peak, indicating the device is still functional after the MRI exposures. ispartof: Plos One vol:15 issue:4 ispartof: location:United States status: Published online