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Electro-hydrostatic actuator (EHA) is a type of actuator in more electric aircraft, which is a highly integrated local volume control hydraulic actuator, and can improve the reliability and efficiency. However, the motor heating can hardly be taken out due to the feature of the local closed hydrostatic system, especially under heavy load. In order to solve the problem, direct load sensitive EHA is an effective way to reduce heat, but the dynamic performance is inevitably sacrificed. To achieve the targets of both low heat generation and high dynamic response, a novel active load sensitive EHA (ALS) is proposed in this article. The key characteristic of ALS is that a special pressure following valve (PFV) is added between the load sensitive pressure point and the actuator of the swash plate in the pump. Furthermore, the PFV is actively controlled to adjust the load sensitive pressure. Based on this concept, detailed analysis and design of the system are presented. Following, the load sensitivity is controlled based on the fuzzy algorithm and the main loop is controlled by traditional proportional−integral differential. Finally, compared with the results of simulation and experiments, ALS can effectively reduce motor heating and maintain high dynamic performance, simultaneously. [ABSTRACT FROM AUTHOR]

This article proposes a dynamic model and a tracking control strategy for a dielectric elastomer (DE) actuator based on the model predictive controller (MPC). First, the dynamic model of the DE actuator is established, which can describe its asymmetric hysteresis, creep, and even rate-dependent hysteresis behaviors simultaneously. Then, on the basis of the established dynamic model, an inverse compensation controller (ICC) is designed to compensate the hysteresis and creep nonlinearities of the DE actuator on its tracking control. Moreover, the MPC is designed to cooperate with the ICC, which can overcome the influences of the modeling error and uncertainties on the control precision. Finally, several experiments demonstrate the effectiveness of the proposed dynamic model and control strategy. [ABSTRACT FROM AUTHOR]

Parallel electrical manipulator systems have become prevalent in attitude simulation in recent years to achieve a high precision attitude tracking. However, the attitude tracking performance is affected by internal uncertainty, external disturbances, and uncoordinated performance of the electric actuators. In this article, a coordinated attitude control strategy that combined the distributed active disturbance rejection control (ADRC) framework with a consensus algorithm is proposed for the parallel electrical manipulators. We indicate that the proposed coordinated attitude control strategy solves the uncoordinated problem of the electric actuators, and compensates the disturbances that include internal uncertainty and external disturbances. Meanwhile, a closed-loop control is achieved with a guaranteed stable tracking performance. The control strategy is applied to a 3-DOF parallel electrical manipulator system, and comparative experimental results indicate that the proposed coordinated ADRC consensus control strategy can achieve a better tracking performance than the strategy with only ADRC. [ABSTRACT FROM AUTHOR]

A self-holding three-position electric tubular actuator (SHTPETA) is described in the article. The proposed linear actuator can be applied in a clutch system, where it is necessary to change certain mover positions over time. Other potential applications of such actuators can be shift of gears, coupling (decoupling) of various moving (rotating) mechanisms, or electromagnetic valves. The self-holding force of the proposed SHTPETA is achieved by the reluctance force between the armature and mover cores, where a magnetic flux is excited by a permanent magnet located in the armature and an excitation current is not needed, whereas the moving force is determined by the dc voltage (current) applied to two coils located in the stationary part of the SHTPETA. The article proposes a relatively fast and simple approach for the SHTPETA design process based on the required forces and moved distance. [ABSTRACT FROM AUTHOR]

Thanks to their continuously deformable features, soft bending actuators, including pneumatic and electric actuators, are increasingly used in continuum robots. Further development, however, is limited by the complexity of the multicavity structure in pneumatic actuators and the instability of the electromechanical coupling in dielectric elastomer actuators. In this article, by combining the advantages of the two actuation techniques, a novel hybrid electro-pneumatic bending actuator is proposed that is capable of bending with significantly reduced complexity and improved stability. A timing control method is proposed that enables rapid and significant bending. A low voltage is used for bending guidance with air-pressure concurrently to produce a large bending stroke. The results of experiments indicate that, with increasing air pressure, the bending angle varies in three different stages. These stages are (I) a low-pressure guidance stage, (II) an instability induction stage, and (III) a stable deformation stage. By harnessing the instability at stage II, the driving voltage can be substantially reduced to avoid electric breakdown. By studying the effect of prestretch on bending, the controllability of the bending deformation is improved. The simulation is also used to verify the control method and predict the development path of soft robots. [ABSTRACT FROM AUTHOR]

The integration of cyber and physical domains improves the flexibility and efficiency of industrial systems. However, it also introduces security threats into the physical processes of the systems. More seriously, most of field devices, such as sensors and actuators, in industrial systems are vulnerable to security threats because they are usually not deployed with security countermeasures. Therefore, how to secure the physical processes of these industrial cyber-physical systems becomes an emerging problem. To address this problem, a zoning-based approach is presented in this article for identification and mitigation of actuator attacks in multiple-input multiple-output processes governed by linear time-invariant systems. It partitions the set of actuators into multiple zones that ensures the controllability of the surviving zones when a zone is compromised. When a zone is intruded, the system states of the compromised zone and other zones cooperate to confirm that the detected attack is against actuators. Then, to mitigate the impact of the actuator attack on the system functions, the attacked actuators are isolated. After that, the residual actuators in the surviving zones are used to reconfigure the control loops of the systems. Case studies are conducted to illustrate the effectiveness of the presented approach. [ABSTRACT FROM AUTHOR]

The use of rotary assembly platforms is common in several automation applications, such as in bottle filling and capping systems. One of the problems that designers have to address is how to supply the electric actuators, sensors, and process controllers located on the rotating disk of the machine. The traditional solution is to use slip-ring contacts. However, they suffer from aging, and thus, a scheduled maintenance program is required. In this article, the motion of the platform and the contact-less energy transfer to the auxiliary loads located on the rotating disk is obtained through a direct drive wound-rotor five-phase induction motor. The experimental tests on a scaled prototype demonstrate the practical potential of the machine. [ABSTRACT FROM AUTHOR]

Charge control is a well-known sensorless approach to operate piezoelectric actuators, which has been proposed for more than 30 years. However, it is rarely used in industry because the implemented controllers suffer from the issues of limited low-frequency performance, long settling time, floating-load, and loss of stroke, etc. In this paper, a novel controller circuit dedicated to overcome these issues is presented. In the proposed scheme, a grounded-load charge controller with decoupled configuration is developed, which separates high-frequency and low-frequency paths, thus achieving arbitrarily low transition frequency without increasing the settling time. Based on this, a self-compensating configuration is further proposed and integrated into the controller circuit, which makes full use of controller output to improve its own control performance at low frequencies. Experimental results show that the presented charge controller can effectively reduce more than 88% of the hysteretic nonlinearity even when operating close to the transition frequency. To demonstrate its practical value, we then integrate it into a custom-designed high-speed atomic force microscope system. By comparing images obtained from using voltage drive and charge controller, it is clear that the piezoelectric hysteresis has been significantly reduced in a wide bandwidth. [ABSTRACT FROM AUTHOR]

In this study, we develop a rotary motor using embedded shape memory alloy (SMA) wires, with the aim of realizing a novel compact and modular motor that can generate high-torque bidirectional continuous rotation. Thus, we focus on designing the motion transmission mechanism and torque amplifier of the motor. The designed motion transmission mechanism that functions to convert the contraction/expansion of the SMA wires to rotational motion enables the motor to generate continuous rotation with relatively short-length SMA wires. Additionally, a double-disc cycloidal speed reducer designed as the torque amplifier allows the motor to reliably generate high torque with a compact structure due to its simple configuration, size variability, and torque amplification functionality. One of the advantages of the motor is that an actuating module could be additionally incorporated into the motor to achieve higher torque. In this case, the overall size and weight of the motor are marginally increased although the output torque capacity almost doubles. Hence, the energy density of the motor significantly increases. The study describes the main concept, operating principle, design, and experimental results of the output torque capacity, positioning characteristics, and frequency response of the proposed motor. [ABSTRACT FROM PUBLISHER]

This paper proposes a practically oriented finite-time control design for nonlinear systems under a less ambitious but more practical semiglobal control objective. As one main contribution, the designed finite-time controller can be expressed as a very simple form while the control gain tuning mechanism follows a conventional pole placement manner, which enhances its facility in practical implementations. Moreover, by utilizing a modified nonrecursive homogeneous domination design without preverifying any nonlinearity growth constraints, the control scheme can be directly obtained by totally neglecting the recursive calculations of series virtual controllers. Rigourous semiglobal attractivity and local finite-time convergence analysis are presented to ensure the theoretical justification. A control application and experimental verification to a series elastic actuator demonstrates the control effectiveness and significant performance improvements compared with asymptotical state feedback controllers. [ABSTRACT FROM PUBLISHER]

In this paper, using the state-dependent Riccati equation approach, an event-triggered technique is proposed to solve the tracking problem for a broad class of nonlinear discrete-time networked control systems. It is shown that the proposed tracking controller leads to an asymptotically stable system, while the information exchange between the controller and the actuator can be directly affected with predictable results by changing a parameter of the controller called the triggering factor. The proposed method is experimentally validated on a laboratory three-tank system. The obtained results demonstrate the effectiveness of the proposed event-triggered technique for solving the tracking problem of a nonlinear system in a networked control framework. [ABSTRACT FROM PUBLISHER]

Aircraft transportation holds a tremendous importance in today's society. Considering the international roadmaps for the intensification of the air travel and the targets concerning the environmental impact, aircraft efficiency has been in the spotlight of scientific research for more than two decades. Electrification of the aircraft subsystems and, in the future, of the propulsion appears to be the way forward to reach these ambitious goals. This Special Section collects contributions related to the more electric aircraft (MEA) technologies, from the power systems to the actuation systems. [ABSTRACT FROM AUTHOR]

The micro/nano positioning system discussed in this paper includes a piezoelectric actuator (PEA) and flexure-hinge-based positioning mechanism. Due to the existence of the hysteretic nonlinearity in the PEA and the friction in the system, the accurate positioning of the piezo-actuated positioning system calls applicable control schemes for practical applications. To this end, an implementable adaptive controller is developed in the paper, where a minimized parameterization hysteresis model is employed to reduce the computational load. The formulated adaptive control law guarantees the global stability of the controlled positioning system, and the positioning error can approach to zero asymptotically. The advantages of the proposed method making on-line implementation feasible are that the traditional inversion of the hysteresis does not need to be constructed directly; the real values of the parameters of the positioning system neither need to be identified nor measured; only the parameters in the formulation of the controller are estimated online. Comparison with the feedforward plus proportional-integral feedback control scheme is conducted and experimental results show the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper addresses the transient performance improvement for path-following control of underactuated surface vessels (USVs) in the presence of oceanic disturbances. The traditional practice that chooses the tangent direction of the desired path as the desired heading may deteriorate the tracking performance in the curve following due to the nonzero sideslip angle therein. Also, the disturbances in wave filed greatly affect the transient path-following control. To this end, three contributions are made in this paper: 1) an amendment to the definition of the desired heading using the sideslip-angle compensation is presented to achieve a more accurate path-following maneuver; 2) a novel disturbances observer-based composite nonlinear feedback (DO-CNF) controller is proposed to restrain system overshoots and eliminate steady-state errors while dealing with multiple oceanic disturbances with unknown bounds; and 3) the variation of the yaw-rate reference for path-following objective is handled in the controller design, which can enhance the vessel's robustness to the changing of the path curvature. Comparative simulations verify the reasonability of the desired-heading amendment and the effectiveness of the DO-CNF approach in improving the transient path-following performance of USVs while satisfying actuator saturation considering the unknown disturbances and changing reference. [ABSTRACT FROM PUBLISHER]

Robust motion control for tracking time-varying reference signals and its application to an electrohydraulic camless engine valve actuator is presented. Two challenging issues encountered in many engineering applications, especially reciprocating machines, are addressed: 1) nonlinear system dynamics and 2) time-varying reference signals. Motion control of the electrohydraulic camless engine valve actuator is a typical example. The electrohydraulic actuator has the critical nonlinear dynamic features such as oil flow through the spool valve orifice and friction force exerting on the piston. The reference valve motion is time-varying since its frequency contents change with the engine speed. Prior to studying the time-varying motion control of a nonlinear system, the time-invariant case is investigated by means of internal model principle. Based on the frequency-domain analysis of a nonlinear feedback system, the high-order time-invariant internal model is designed for tracking performance. Motivated by the time-invariant case, the high-order time-varying internal model is designed for robust tracking of time-varying reference signals. The effectiveness of the proposed time-varying internal model is demonstrated by application to the electrohydraulic camless engine valve actuator. [ABSTRACT FROM PUBLISHER]

In this paper, a maximum-power-point-tracking controller for variable-speed wind turbines (VSWTs) is developed, which is shown to be able to account for modeling uncertainties, unexpected disturbances, subsystem failures, and actuation saturation simultaneously. A novel memory-based approach is used to predict wind speed that is used to generate desired rotor speed accordingly. It is shown that the proposed algorithm not only is robust against nonlinear aerodynamics and adaptive to unknown and time-varying inertia/damp/stiffness properties of VSWTs but also is able to accommodate actuator failures under torque constraints. The benefits of the proposed control method are analytically authenticated and demonstrated with Fatigue, Aerodynamics, Structures, and Turbulence code and Simulink. [ABSTRACT FROM PUBLISHER]

This paper deals with a sensorless control approach of a lightweight electric actuator. Force and motion control are necessary to perform manipulation tasks with object interaction of different stiffnesses. The controller must ensure stability in a wide range of rigidity, particularly in soft contact cases. The approach proposed here is based on a force/position control scheme. First, a nonlinear position controller is performed through a linear parameter-varying state feedback. A state observer is added to estimate unmeasurable variables coming from an absence of terminal sensors. Subsequently, an output feedback force control is determined using an \cal H\infty framework. The controller is experimentally applied on a single-acting actuator to demonstrate the efficiency of this approach dedicated to compliant object interaction. [ABSTRACT FROM PUBLISHER]

The tendon-sheath actuation system is capable of providing remote power transmission and greatly simplifying the mechanical design of robotic systems. However, there exist many undesirable nonlinear problems in tendon-sheath transmission, such as hysteresis, dead zone, backlash, and direction-dependent behavior. Unlike most of the existing literature that focus on the analysis of single-tendon-sheath actuation, this paper proposes a general mathematical double-tendon-sheath transmission model suitable for arbitrary types of load conditions. Experimental setups composed of servo motors, tendon-sheath components, and robot joint are established to test the proposed models and gain insights into the transmission processes through sinusoidal input signal experiments. Based on the transmission models, two open-loop control strategies are developed for the friction and deformation compensation, requiring no feedback from the distal end. With the aim of obtaining the complete model parameters, an offline identification method able to calibrate the transmission model using the sensors mounted at the proximal end is developed. The performance of the proposed control methods is evaluated by torque/position-tracking experiments in different kinds of load conditions. Moreover, the frequency characteristics of the actuation system are analyzed, and the controlled bandwidth is about 10 Hz during operation. [ABSTRACT FROM PUBLISHER]

For a novel electric clutch actuator, a nonlinear feedforward–feedback control scheme is proposed to improve the performance of the position tracking control. The design procedure is formalized as a triple-step deduction, and the derived controller consists of three parts: steady-state-like control; feedforward control based on reference dynamics; and state-dependent feedback control. The structure of the proposed nonlinear controller is concise and is also comparable to those widely used in modern automotive control. Finally, the designed controller is evaluated through simulations and experimental tests, which show that the proposed controller satisfied the control requirement. Comparison with proportional–integral–derivative control is given as well. [ABSTRACT FROM PUBLISHER]

This paper presents an overview of motor drive technologies used for safety-critical aerospace applications, with a particular focus placed on the choice of candidate machines and their drive topologies. Aircraft applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. Fault-tolerant motor drives can be achieved by partitioning and redundancy through the use of multichannel three-phase systems or multiple single-phase modules. Analytical methods are adopted to compare caged induction, reluctance, and PM motor technologies and their relative merits. The analysis suggests that the dual (or triple) three-phase PMAC motor drive may be a favored choice for general aerospace applications, striking a balance between necessary redundancy and undue complexity, while maintaining a balanced operation following a failure. The modular single-phase approach offers a good compromise between size and complexity but suffers from high total harmonic distortion of the supply and high torque ripple when faulted. For each specific aircraft application, a parametrical optimization of the suitable motor configuration is needed through a coupled electromagnetic and thermal analysis, and should be verified by finite-element analysis. [ABSTRACT FROM AUTHOR]

This paper deals with the dynamical modeling and posture control of the electromechanical actuator (EMA)-based thrust vector control (TVC) system for aircraft engines. Addressing the issues of the large inertia and low stiffness existing in the TVC system driven by EMA, this paper established a 2-DOF mathematical model to describe the EMA dynamic characteristics. In order to overcome the influence of the motion coupling of the TVC-EMA existing in the pitching and yawing channels, we presented a kind of dual-channel coordinated-control method which realizes the TVC for the swung aircraft engine based on the inverse kinematics. This control strategy uses the command Euler's angle transformation to solve the desired actuator linear lengths and tracks the desired lengths via the compound control law composed of robust PID, with the lead compensation and bang–bang control in the two actuators. The hybrid experimental simulation system based on dSPACE was set up, the control parameters of the compound control methods were confirmed by offline simulation based on MATLAB, and the load experiments of circular motion and step response were implemented on the test system. The simulation and test results show that the designed thrust vector controller can achieve the satisfactory control performances. [ABSTRACT FROM AUTHOR]

An ionic polymer–metal composite (IPMC) is an electroactive material that behaves in an electric field similarly to biological muscles. This intelligent material is leading to a new emerging technology called nonuniformly charged IPMC actuators. This paper introduces first an IPMC analytical modeling approach for its electromechanical characterization. The model considers, for the first time, the action of gravitation force in its electric and mechanic characteristics, which is important for large IPMC actuators. To demonstrate the efficacy of the model, two nonuniformly charged IPMC actuators were fabricated and tested. Experimental results are presented to validate the model and verify its effectiveness in the design of nonuniformly charged IPMC actuators. [ABSTRACT FROM PUBLISHER]