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Showing papers on "Actuator published in 2020"


Journal ArticleDOI
TL;DR: The fuzzy control and adaptive backstepping schemes are applied to construct an improved fault-tolerant controller without requiring the specific knowledge of control gains and actuator faults, including both stuck constant value and loss of effectiveness.
Abstract: This paper addresses the trajectory tracking control problem of a class of nonstrict-feedback nonlinear systems with the actuator faults. The functional relationship in the affine form between the nonlinear functions with whole state and error variables is established by using the structure consistency of intermediate control signals and the variable-partition technique. The fuzzy control and adaptive backstepping schemes are applied to construct an improved fault-tolerant controller without requiring the specific knowledge of control gains and actuator faults, including both stuck constant value and loss of effectiveness. The proposed fault-tolerant controller ensures that all signals in the closed-loop system are semiglobally practically finite-time stable and the tracking error remains in a small neighborhood of the origin after a finite period of time. The developed control method is verified through two numerical examples.

210 citations


Journal ArticleDOI
27 Feb 2020
TL;DR: A novel controller which combines feedforward contact forces computed from a kino-dynamic optimizer with impedance control of the center of mass and base orientation is presented, which can regulate complex motions while being robust to environmental uncertainty.
Abstract: We present a new open-source torque-controlled legged robot system, with a low-cost and low-complexity actuator module at its core. It consists of a high-torque brushless DC motor and a low-gear-ratio transmission suitable for impedance and force control. We also present a novel foot contact sensor suitable for legged locomotion with hard impacts. A 2.2 kg quadruped robot with a large range of motion is assembled from eight identical actuator modules and four lower legs with foot contact sensors. Leveraging standard plastic 3D printing and off-the-shelf parts results in a lightweight and inexpensive robot, allowing for rapid distribution and duplication within the research community. We systematically characterize the achieved impedance at the foot in both static and dynamic scenarios, and measure a maximum dimensionless leg stiffness of 10.8 without active damping, which is comparable to the leg stiffness of a running human. Finally, to demonstrate the capabilities of the quadruped, we present a novel controller which combines feedforward contact forces computed from a kino-dynamic optimizer with impedance control of the center of mass and base orientation. The controller can regulate complex motions while being robust to environmental uncertainty.

165 citations


Journal ArticleDOI
TL;DR: A light-powered in-air hydrogel actuator with remarkable performances, including fast motion, speed and rapid response time is reported.
Abstract: Stimuli-responsive hydrogel actuators have promising applications in various fields. However, the typical hydrogel actuation relies on the swelling and de-swelling process caused by osmotic-pressure changes, which is slow and normally requires the presence of water environment. Herein, we report a light-powered in-air hydrogel actuator with remarkable performances, including ultrafast motion speed (up to 1.6 m/s), rapid response (as fast as 800 ms) and high jumping height (~15 cm). The hydrogel is operated based on a fundamentally different mechanism that harnesses the synergetic interactions between the binary constituent parts, i.e. the elasticity of the poly(sodium acrylate) hydrogel, and the bubble caused by the photothermal effect of the embedded magnetic iron oxide nanoparticles. The current hydrogel actuator exhibits controlled motion velocity and direction, making it promising for a wide range of mobile robotics, soft robotics, sensors, controlled drug delivery and other miniature device applications. Actuation of hydrogel actuators relies on slow swelling and de-swelling process which hampers its application in many fields. Here the authors report a light-powered in-air hydrogel actuator with remarkable performances including fast motion, speed and rapid response time.

126 citations


Journal ArticleDOI
TL;DR: A novel event-triggering mechanism is introduced to determine the time instants for communication, which successfully avoids continuous communication and Zeno phenomenon and significantly reduces the communication burden, while providing high reliability and stable, rapid, and accurate response for attitude maneuvers.
Abstract: This paper is devoted to attitude tracking control of fractionated spacecraft with wireless communication. We consider the practical case that the spacecraft suffers from uncertain inertia parameters, external disturbances, and even unknown and time-varying actuator faults. Within the framework of the backstepping method, a novel event-triggered adaptive fault-tolerant control scheme is proposed. In our design, an event-triggering mechanism is introduced to determine the time instants for communication, which successfully avoids continuous communication and Zeno phenomenon. Then, with the aid of a bound estimation approach and a smooth function, the impacts of the actuator faults, as well as the network-induced error, are effectively compensated for. Moreover, by employing the prescribed performance control technique, it is shown that the attitude tracking errors can converge to predefined arbitrarily small residual sets with prescribed convergence rate and maximum overshoot, no matter if there exist unknown actuator faults. Compared with conventional adaptive attitude control schemes, the proposed scheme significantly reduces the communication burden, while providing high reliability and stable, rapid, and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

120 citations


Journal ArticleDOI
TL;DR: Sufficient conditions are developed to guarantee the existence of the reliable SOF controller against actuator faults, and an iterative algorithm is designed to determine the controller gains, which avoids the conservatism brought by the traditional singular value decomposition method.
Abstract: This paper is focused on the static output feedback (SOF) control problem for a class of switched nonlinear systems with actuator faults. By means of the Takagi–Sugeno fuzzy model, the switched nonlinear plant is described by a family of switched fuzzy systems. Considering transmission failures may occur between controller and actuator, a reliable SOF controller against actuator faults is designed. Sufficient conditions are developed to guarantee the existence of the reliable SOF controller. Furthermore, an iterative algorithm is designed to determine the controller gains, which avoids the conservatism brought by the traditional singular value decomposition method. To validate the effectiveness of the proposed approach, a numerical example is exploited and simulation results are also presented.

118 citations


Journal ArticleDOI
TL;DR: This paper investigates the event-triggered adaptive output feedback control problem for a class of uncertain nonlinear systems in the presence of actuator failures and unknown control direction by utilizing the adaptive backstepping technique and develops an event-based output feedback controller together with a time-variant event- Triggered rule.
Abstract: This paper investigates the event-triggered adaptive output feedback control problem for a class of uncertain nonlinear systems in the presence of actuator failures and unknown control direction By utilizing the adaptive backstepping technique, an event-based output feedback controller is developed together with a time-variant event-triggered rule In this design, the radial basis function neural network algorithms are first introduced to identify the unknown terms of the systems Then, a new state observer with adaptive compensation is designed to estimate the state vector The overall control strategy guarantees that the output signal tracks the reference signal and all the signals of the closed-loop systems are bounded Unlike the existing methods, the proposed control scheme can handle the coupling term incurred by the loss of effectiveness fault of the actuator, the event-triggered rule, and unknown control direction Finally, an example is performed to demonstrate the validity of the proposed strategy

117 citations


Journal ArticleDOI
TL;DR: This article concentrates on the output feedback controller design problem for discrete-time nonlinear switched systems with actuator faults, and the developed method is applied to address the control issue of a tunnel diode circuit system model to illustrate its efficiency and applicability.
Abstract: This article concentrates on the output feedback controller design problem for discrete-time nonlinear switched systems with actuator faults. The Takagi–Sugeno fuzzy model is adopted to approximate the nonlinearity of the plant with a set of local linear models. The persistent dwell-time (DT) switching law, which is more general than DT or average DT switching, is introduced to govern the switching among subsystems. In order to alleviate the effects of actuator failures on system stability and performance, a synthesized fault-tolerant output feedback controller ensuring various performance requirements is designed. Intensive attention is focused on establishing sufficient conditions, which can guarantee the exponential mean-square stability as well as the prescribed extended dissipativity property of the closed-loop system. By virtue of the Lyapunov stability theory and appropriate matrix transformation methods, the desired controller gains can be obtained by solving a convex optimization problem. The developed method is finally applied to address the control issue of a tunnel diode circuit system model to illustrate its efficiency and applicability.

113 citations


Journal ArticleDOI
TL;DR: This paper investigates the event-triggered (ET) tracking control problem for a class of discrete-time strict-feedback nonlinear systems subject to both stochastic noises and limited controller-to-actuator communication capacities.
Abstract: This paper investigates the event-triggered (ET) tracking control problem for a class of discrete-time strict-feedback nonlinear systems subject to both stochastic noises and limited controller-to-actuator communication capacities. The ET mechanism with fixed triggering threshold is designed to decide whether the current control signal should be transmitted to the actuator. A systematic framework is developed to construct a novel adaptive neural controller by directly applying the backstepping procedure to the underlying system. The proposed framework overcomes the noncausality problem, avoids the possible controller-related singularity problem, and gets rid of the neural approximation of the virtual control laws. Under the ET mechanism, the corresponding ET-based actuator is put forward by introducing an ET threshold compensation operator. Such a compensation operator (with an adjustable design parameter) is subtly designed based on a hyperbolic tangent function and a sign function. The threshold compensation error is analytically characterized in terms of a time-varying parameter, and the error bound is shown to be relatively small that is dependent on the adjustable design parameter. Compared with the traditional ET-based actuator without the compensation operator, the proposed ET-based actuator exhibits several distinguished features including: 1) improvement of the tracking accuracy (especially at the triggering instants); 2) further mitigation of the communication load; and 3) enlargement of the allowable range of the ET threshold. These features are illustrated by numerical and practical examples.

111 citations


Journal ArticleDOI
TL;DR: Lyapunov theory and Barbalat lemma are adopted to synthesize asymptotic stability of the entire bottom following control system, to tackle the potential unstable control behavior from inherent saturation of control surfaces driven by rudders.
Abstract: This paper addresses the problem of robust bottom following control for a flight-style autonomous underwater vehicle (AUV) subject to system uncertainties, actuator dynamics, and input saturation. First, the actuator dynamics that is approximated by a first-order differential equation is inserted into the AUV dynamics model, which renders a high-order nonlinear dynamics analysis and design in the model-based backstepping controller by utilizing guidance errors. Second, to overcome the shaking control behavior resulted by the model-based high-order derivative calculation, a fuzzy approximator-based model-free controller is proposed, in order to online approximate the unknown part of the ideal backstepping architecture. In addition, the adaptive error estimation technology is resorted to compensate the system approximation error, ensuring that all the position and orientation errors of robust bottom following control tend to zero. Third, to further tackle the potential unstable control behavior from inherent saturation of control surfaces driven by rudders, an additional adaptive fuzzy compensator is introduced, in order to compensate control truncation between the unsaturated and saturation inputs. Subsequently, Lyapunov theory and Barbalat lemma are adopted to synthesize asymptotic stability of the entire bottom following control system. Finally, comparative numerical simulations with different controllers, environmental disturbances and initial states are provided to illustrate adaptability and robustness of the proposed bottom following controller for a flight-style AUV with saturated actuator dynamics.

111 citations


Journal ArticleDOI
TL;DR: Sub-mm thick flexible hydraulically amplified electrostatic actuators are reported here, capable of both out-of-plane and in-plane motion, providing normal and shear forces to the user's fingertip, hand, or arm.
Abstract: The sense of touch is underused in today's virtual reality systems due to lack of wearable, soft, mm-scale transducers to generate dynamic mechanical stimulus on the skin. Extremely thin actuators combining both high force and large displacement are a long-standing challenge in soft actuators. Sub-mm thick flexible hydraulically amplified electrostatic actuators are reported here, capable of both out-of-plane and in-plane motion, providing normal and shear forces to the user's fingertip, hand, or arm. Each actuator consists of a fluid-filled cavity whose shell is made of a metalized polyester boundary and a central elastomer region. When a voltage is applied to the annular electrodes, the fluid is rapidly forced into the stretchable region, forming a raised bump. A 6 mm × 6 mm × 0.8 mm actuator weighs 90 mg, and generates forces of over 300 mN, out-of-plane displacements of 500 µm (over 60% strain), and lateral motion of 760 µm. Response time is below 5 ms, for a specific power of 100 W kg-1 . In user tests, human subjects distinguished normal and different 2-axis shear forces with over 80% accuracy. A flexible 5 × 5 array is demonstrated, integrated in a haptic sleeve.

105 citations


Journal ArticleDOI
TL;DR: This paper proposes a new control design method for high-order servo systems with hydraulic actuator dynamics, where the backstepping scheme is avoided and only the system output is required for the control implementation.
Abstract: Most of the existing control methods for servo systems driven by hydraulic actuators have been developed by using a backstepping scheme and assuming that all system states (including internal hydraulic signals) are measurable. In this paper, we propose a new control design method for high-order servo systems with hydraulic actuator dynamics, where the backstepping scheme is avoided and only the system output (e.g., motion displacement) is required for the control implementation. For this purpose, the system model is first transformed into a canonical form, where the unknown dynamics in the system are lumped as one term. Then, we introduce a simple robust unknown dynamics estimator (UDE) that has only one tuning parameter but achieves exponential error convergence to accommodate the lumped uncertainties. Therefore, the function approximators (e.g., neural network and fuzzy systems) can be avoided, leading to reduced computational costs, simpler parameter tuning, and improved convergence as compared to backstepping methods. Extensive simulations and experiments based on a realistic test rig are conducted to show the efficacy of the proposed control.

Journal ArticleDOI
TL;DR: The closed-loop attitude stabilization system is proved to be fixed-time stable with the convergence time independent of initial states and the attitude stabilization performance is robust to disturbance and uncertainties in inertia and actuators.
Abstract: A robust fixed-time control framework is presented to stabilize flexible spacecraft’s attitude system with external disturbance, uncertain parameters of inertia, and actuator uncertainty. As a stepping stone, a nonlinear system having faster fixed-time convergence property is preliminarily proposed by introducing a time-varying gain into the conventional fixed-time stability method. This gain improves the convergence rate. Then, a fixed-time observer is proposed to estimate the uncertain torque induced by disturbance, uncertain parameters of inertia, and actuator uncertainty. Fixed-time stability is ensured for the estimation error. Using this estimated knowledge and the full-states’ measurements, a nonsingular terminal sliding controller is finally synthesized. This is achieved via a nonsingular and faster terminal sliding surface with faster convergence rate. The closed-loop attitude stabilization system is proved to be fixed-time stable with the convergence time independent of initial states. The attitude stabilization performance is robust to disturbance and uncertainties in inertia and actuators. Simulation results are also shown to validate the attitude stabilization performance of this control approach.

Journal ArticleDOI
TL;DR: It is proved that the proposed approach guarantees output tracking with prescribed accuracy and constraint satisfactions simultaneously, even if actuator faults occur, and a new-type error boundary is introduced to the control design.

Journal ArticleDOI
TL;DR: To improve the transient regulation performance of ASSs when the actuator failure occurs, a novel control scheme with the prescribed performance function is proposed to characterize the tracking error convergence rate and maximum overshoot in ASSs.
Abstract: In this article, we study the control problem of the vehicle active suspension systems (ASSs) subject to actuator failure. An adaptive control scheme is presented to stabilize the vertical displacement of the car-body. Meanwhile, the ride comfort, road holding, and suspension space limitation can be guaranteed. In order to overcome the uncertainty, the neural network is developed to approximate the continuous function with the unknown car-body mass. Furthermore, to improve the transient regulation performance of ASSs when the actuator failure occurs, we propose a novel control scheme with the prescribed performance function to characterize the tracking error convergence rate and maximum overshoot in ASSs. Then, the stability of the proposed control algorithm can be proven based on the Lyapunov theorem. Finally, the comparative simulation results of two actuator failure types (i.e., the float fault and the loss of effectiveness fault) are given to demonstrate the effectiveness of the proposed control schemes.

Journal ArticleDOI
TL;DR: This paper presents a review of SMAs applications in the aerospace field with particular emphasis on morphing wings, tailoring of the orientation and inlet geometry of many propulsion system, variable geometry chevron for thrust and noise optimization, and more in general reduction of power consumption.
Abstract: Shape memory alloys (SMAs) show a particular behavior that is the ability to recuperate the original shape while heating above specific critical temperatures (shape memory effect) or to withstand high deformations recoverable while unloading (pseudoelasticity). In many cases the SMAs play the actuator's role. Starting from the origin of the shape memory effect, the mechanical properties of these alloys are illustrated. This paper presents a review of SMAs applications in the aerospace field with particular emphasis on morphing wings (experimental and modeling), tailoring of the orientation and inlet geometry of many propulsion system, variable geometry chevron for thrust and noise optimization, and more in general reduction of power consumption. Space applications are described too: to isolate the micro-vibrations, for low-shock release devices and self-deployable solar sails. Novel configurations and devices are highlighted too.

Journal ArticleDOI
TL;DR: This paper investigates the finite-time static output feedback control of Markovian switching systems, where quantization effects are taken into consideration from plant to controller and controller to actuator, simultaneously.
Abstract: This paper investigates the finite-time static output feedback control of Markovian switching systems, where quantization effects are taken into consideration from plant to controller and controller to actuator, simultaneously. The resulting system is more general, where asynchronous control, quantization, actuator failure, and external disturbance are covered. Furthermore, a descriptor representation method is employed to eliminate both the coupling term and the quantization effects. Owing to a hidden mode observation approach, sufficient conditions are achieved to guarantee the finite-time stochastic boundedness of the resulting system, and the finite-time output feedback controller is designed. Finally, a vehicle’s throttle actuator is exploited to confirm the feasibility of the proposed method.

Journal ArticleDOI
TL;DR: This paper proposes a finite-time trajectory tracking controller for a space manipulator under model uncertainty, external disturbance, and actuator saturation, and a NN-based adaptive terminal sliding mode controller for trajectory tracking.
Abstract: This paper proposes a finite-time trajectory tracking controller for a space manipulator under model uncertainty, external disturbance, and actuator saturation. The dynamics of space manipulator is derived using Kane's method. Considering the model uncertainty that may exist when the manipulator captures an unknown payload, a radial basis function neural network (NN) is used to estimate the uncertain model of the space manipulator. An auxiliary system is designed to compensate the actuator saturation. Then a NN-based adaptive terminal sliding mode controller is proposed for trajectory tracking of a space manipulator. The stability of the proposed controller is analyzed using Lyapunov theory. Numerical simulations are conducted to verify the effectiveness of the proposed controller.

Journal ArticleDOI
TL;DR: In this paper, a soft bimorph actuator with electrical and visual dual channel signal feedback functions for real-time multiplex motion perception is presented for flexible machines and artificial intelligence robotics to enable an autonomic response to surroundings.

Journal ArticleDOI
TL;DR: This article solves the safe trajectory tracking control problem of robot manipulators with actuator faults, uncertain dynamics, and external disturbance by designing an adaptive control law designed by using the joint position, the estimated velocity, and the reconstructed knowledge of velocity measurement uncertainty.
Abstract: This article solves the safe trajectory tracking control problem of robot manipulators with actuator faults, uncertain dynamics, and external disturbance. Another key issue met in practical robot engineering, i.e., joint velocity measurement uncertainty is also investigated. A robust control framework is presented. In this approach, a novel reconstruction law is preliminarily developed to estimate velocity measurement uncertainty, while the estimation error is finite-time stable. An adaptive control law is, then, designed by using the joint position, the estimated velocity, and the reconstructed knowledge of velocity measurement uncertainty. The key advantage of this methodology is that actual joint velocity and any prior knowledge of actuator faults are not required. The effectiveness of this proposed scheme is experimentally validated on a real robot arm.

Journal ArticleDOI
TL;DR: A new estimator in delta-domain is proposed to estimate the states of the attacked CPS by utilization of a dissipativity approach, estimator-based time-driven controller and self-triggered controller are designed for the enhancement of the estimations and the resource saving.

Journal ArticleDOI
TL;DR: The effectiveness of the proposed active fault-tolerant control strategy is validated through real experiments based on a quadrotor helicopter subject to actuator faults and model uncertainties and its advantages are demonstrated in comparison with a model-based fault estimator and a conventional adaptive sliding mode control.

Journal ArticleDOI
TL;DR: Under the proposed control strategy, the building structure system with uncertain actuator failures can be guaranteed to be stable in finite time.

Journal ArticleDOI
TL;DR: An adaptive fault-tolerant method is proposed to synthesize a compensation controller for the uncertain nonlinear pure-feedback systems possessing dead-zone actuators and stochastic failures to guarantee that the solution of the closed-loop system is a unique and bounded in probability.
Abstract: In this paper, an adaptive fault-tolerant method is proposed to synthesize a compensation controller for the uncertain nonlinear pure-feedback systems possessing dead-zone actuators and stochastic failures. Each actuator’s failure mode is described by a scalar Markovian type function, which is not only much more practical in control engineering but also challenging in control theory. By exploring the adaptive backstepping methodology, a compensation scheme for actuator failure is presented to guarantee that the solution of the closed-loop system is a unique and bounded in probability. Importantly, the proposed control method can achieve arbitrarily small tracking error in the presence of nonlinear actuators with random failures. The case study of active suspension system using the adaptive fault-tolerant compensation controller shows the effectiveness of the presented method.

Journal ArticleDOI
06 Apr 2020
TL;DR: A novel variable-strain parametrization for soft manipulators is proposed, which discretizes the continuous Cosserat rod model onto a finite set of strain basis functions and is shown to be trivialized, providing useful tools for control and actuator routing design.
Abstract: We propose a novel variable-strain parametrization for soft manipulators, which discretizes the continuous Cosserat rod model onto a finite set of strain basis functions. This approach generalizes the recently proposed piecewise-constant strain method to the case of non-constant strain sections. As for its predecessor, the discrete model is based on the relative pose between consecutive cross-sections and is provided in its minimal matrix form (Lagrangian-like). The novel variable-strain model is applied to the static equilibrium of tendon and/or fluidic actuated soft manipulators. It is shown that, for a specific choice of strain basis, exploiting the actuator geometry, the system is trivialized, providing useful tools for control and actuator routing design. Comparisons with the full continuous Cosserat model demonstrate the feasibility of the approach.

Journal ArticleDOI
TL;DR: In this paper, impulsive synchronization of coupled delayed neural networks with actuator saturation is presented and the proposed image encryption system has high security properties.

Journal ArticleDOI
TL;DR: A novel adaptive fault-tolerant sliding-mode control scheme is proposed for high-speed trains, where the longitudinal dynamical model is focused, and the disturbances and actuator faults are considered, to guarantee that the asymptotical convergence of the tracking errors is achieved.
Abstract: In this paper, a novel adaptive fault-tolerant sliding-mode control scheme is proposed for high-speed trains, where the longitudinal dynamical model is focused, and the disturbances and actuator faults are considered. Considering the disturbances in traction force generated by the traction system, a dynamic model with actuator uncertainties modeled as input distribution matrix uncertainty is established. Then, a new sliding-mode controller with design conditions is proposed for the healthy train system, which can drive the tracking error dynamical system to a predesigned sliding surface in finite time and maintain the sliding motion on it thereafter. In order to deal with the actuator uncertainties and unknown faults simultaneously, the adaptive technique is combined with the fault-tolerant sliding-mode control design together to guarantee that the asymptotical convergence of the tracking errors is achieved. Furthermore, the proposed adaptive fault-tolerant sliding-mode control scheme is extended to the cases of the actuator uncertainties with unknown bounds and the unparameterized actuator faults. Finally, the case studies on a real train dynamic model are presented to explain the developed fault-tolerant control scheme. The simulation results show the effectiveness and feasibility of the proposed method.

Journal ArticleDOI
TL;DR: Simulation and experimental results show that the proposed control method can effectively improve the HEV drivability while taking clutch actuator uncertainties into consideration and the time of mode transition process can be shortened and vehicle jerk can be controlled within an acceptable range using the proposed method.
Abstract: Mode transition control problem in a hybrid powertrain has always been a central concern, because many complicated transient dynamics are involved in this process, such as engine-start, clutch engagement, and actuator control, etc. Especially for a parallel hybrid electric vehicle (HEV), the drivability problem during mode transition process is significant yet challenging to solve. In this paper, a new efficient mode transition control method with adaptive dual-loop control framework is proposed for the clutch engagement in a parallel HEV. Firstly, the expected clutch engaging speed can be calculated by two approaches, optimization method via particle swarm optimization algorithm, and practical method by compromising the transient vehicle jerk and the clutch slipping power, respectively. Utilizing the integral transformation, the demand clutch position trajectory for the inner loop can be obtained. Considering the uncertainties and the backlash in the clutch actuator system, an adaptive state feedback controller is designed in the inner loop. Simulation and experimental results show that the proposed control method can effectively improve the HEV drivability while taking clutch actuator uncertainties into consideration. Furthermore, compared with the control method commonly used in practice, the time of mode transition process can be shortened and vehicle jerk can be controlled within an acceptable range using the proposed method.

Journal ArticleDOI
TL;DR: To achieve precision motion control, an adaptive robust control with a backstepping design is proposed for an electrohydraulic system, where the cylinder actuator is direct-driven by a servomotor pump.
Abstract: Pump control hydraulic systems can achieve high efficiency by the advantages of no throttling loss and high power-to-volume ratio. However, low tracking accuracy and slow frequency response are main drawbacks for the applications of pump control hydraulic systems, because of the existing high-order dynamics, uncertainties, and highly nonlinear dynamics. Recently, the advent of servomotor-pump direct-drive electrohydraulic systems shows a good prospect for this issue, and the design of the control algorithm is the key to achieve high motion accuracy. In this article, to achieve precision motion control, an adaptive robust control with a backstepping design is proposed for an electrohydraulic system, where the cylinder actuator is direct-driven by a servomotor pump. Considering the high-order dynamics and nonlinearities of hydraulic systems, the controller is processed in two steps: position tracking step and pressure step. Besides, the pump flow deviation under low speed is another important limitation for good control performance. Thus, a nonlinear pump flow rate mapping is proposed by practical fitting and used into the controller design by the proper nonlinearity compensation of the desired pump flow. Comparative experiment results show that the proposed control strategy achieves high motion control performances in spite of the nonlinearities and uncertainties.

Journal ArticleDOI
TL;DR: A novel fixed-time fault-tolerant control scheme is proposed for trajectory tracking of marine surface vessels (MSVs) and a fixed- time extended state observer (FXESO) is developed to enhance the robustness.

Journal ArticleDOI
TL;DR: A fluid-driven disulfide LCE actuator that can generate large cyclic actuation at a frequency around 1 Hz and can also operate in a wide range of temperature is developed through facile laminate manufacturing enabled by dynamic bonds exchange reaction.
Abstract: Liquid crystal elastomer (LCE) is a newly emerging soft actuating material that has been extensively explored for building novel soft robots and diverse active devices, thanks to its large actuation stress and strain, high work density, and versatile actuation modes. However, there have also been several widely recognized limitations of LCE-based actuators for practical applications, including slow response and narrow range of operation temperature. Herein, we develop fluid-driven disulfide LCE actuators through facile laminate manufacturing enabled by a dynamic bond exchange reaction. Because of the merits of the active heating/cooling mechanism of the fluidic structure, this newly developed disulfide LCE actuator can generate large cyclic actuation at a frequency around 1 Hz and can operate in a wide range of temperatures. The unique combination of the fluidic structure design and the dynamic covalent bonds in the elastomer has also enabled the full recyclability and self-repairability of the actuator. Using the newly developed actuator as building block, we further constructed soft robotic systems that can realize manipulating and programmable movement. The design principle demonstrated in the current work opens a promising avenue for exploring more novel applications of LCE-based soft actuators.