Search

This paper investigates the problem of robust preview tracking control for uncertain continuous-time interconnected systems. We adopt the technology of decentralized control. The tracking controller for each uncertain isolated subsystem is first designed. With the help of an uncertain error system, the considered tracking problem is converted into a regulation problem. The preview tracking controller for the nominal system is obtained by utilizing existing results. A novel method is proposed to tackle the uncertainty in the systems. In this method, the uncertainty bound is incorporated into the cost function. As a result, the preview tracking controller of the nominal system can be treated as a robust preview controller of the uncertain isolated subsystem. Then, the controllers of the uncertain isolated subsystems are assembled as a robust preview controller of uncertain interconnected systems. Finally, an academic numerical example is presented to show the effectiveness and superiority of the proposed controller. [ABSTRACT FROM AUTHOR]

In this paper, the problem of trajectory tracking for robotic manipulator with input deadzone and time-varying disturbances is investigated using a continuous non-singular terminal sliding mode control (SMC). The robotic manipulator plays a vital role in industrial as well as many other applications. However, it faces numerous problems for accurate and fast trajectory tracking response in the presence of unknown uncertainties and external disturbances, that always have adverse affects on system closed-loop performance. This paper proposes a valid control design scheme to address the aforementioned practical issue. First, a non-singular terminal sliding mode surface is designed. Then, a robust control law is developed to guarantee the finite-time converges of system states to the origin. In addition, the sign function is substituted by saturation function, which can effectively reduce the chattering driven by the high-frequency switching item in the traditional SMC method. Moreover, the Lyapunov stability criterion is used to prove the stability of the closed-loop system. The efficiency of the designed control scheme is validated with numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, a model-free robust adaptive control scheme with finite-time convergence based on time-delay control is proposed for anti-sway and positioning control of two-dimensional underactuated overhead cranes. First, the whole overhead cranes system is simplified to an ultra-local model for time delay estimation (TDE). TDE brings a direct and effective model-free property but also an estimation error. Second, a sliding mode disturbance observer is designed to estimate and compensate for the TDE error. Third, sliding mode control (SMC) is used to enhance the robustness of the controller. An adaptive integral sliding surface is then designed to accelerate the sliding surface convergence rate and shorten the convergence time. To further optimize the selection of parameters, the parameter estimation is integrated to enhance the performance of model-free control. In the final analysis of the simulation, data yield that the introduction of parameter estimation increases the control performance by more than 20% on average, and the above facts verify the effectiveness of the scheme. Finally, the stability of the closed-loop control system is analyzed by using Lyapunov stability theory, and the effectiveness and robustness of the control scheme are verified through computer simulation results. [ABSTRACT FROM AUTHOR]

This paper presents a novel speed control method for an unmanned flight system. A Polytopic Linear Parameter Varying model is generated by linearization of the nonlinear dynamic model around several trim points. As a novelty of this paper, an Integral action over the tracking error is added to a conventional state-feedback to form the proposed control law. Augmenting the proposed control action to the system dynamic, the proposed control law is reassigned as a common state-feedback control problem. An attenuation level for the tracking error under external disturbances is guaranteed by solving the related linear matrix inequalities to compute the control gains. In the end, the designed controller has been implemented for different scenarios in order to maintain the speed in different modes with the ability to control the longitudinal, Lateral, and altitude velocities simultaneously. The simulation results show the effectiveness of the proposed control against the system uncertainties, external disturbances, and the interactions between different channels. [ABSTRACT FROM AUTHOR]

Considering the influence of the magnetorheological damper response time delay on the low-frequency vibration (body vibration) and multi-objective control requirements of the semi-active suspension system, a novel H8/H2 controller (timedelay-dependent H∟/H2 optimal controller) is proposed in this paper. Based on the Lyapunov-Krasovskii function and robust control theory, a time-delay-dependent H∟/H2 controller in consideration of the MR damper response time delay is designed to reduce and remove the effects of time delay on the semi-active suspension system. To obtain better suspension control performances, the optimal selection strategy of anti-interference coefficients in the time-delay-dependent H∟/H2 controller is proposed. Then, the time-delay-dependent H∟/H2 optimal controller is structured built on the optimal selection strategy. With the application of matrix properties and the cone-compensation linearization algorithm, the nonlinear matrix inequality for controller design is linearized, and the feedback gain matrix of the controller is solved iteratively. Finally, comparative simulation and experimental research are conducted to verify the effectiveness and superiority of the designed optimal controller. [ABSTRACT FROM AUTHOR]

This paper puts forward the robust control problem of rail vehicle virtual coupling platoon that is subject to nonlinear and time-varying uncertainties. The uncertainties are caused by external disturbances and parameter variations. To this end, this paper designs a robust controller based on the Udwadia-Kalaba (UK) equation. First, we introduce the concept of virtual coupling and establish the longitudinal dynamics model of the rail vehicle. In order to ensure the control objective of the virtual coupling process, the spatial constraint on position and bidirectional inequality constraints for the spacing error between the marshalling trains are established. After changing the bounded state into the unbounded state through the state transformation, the UK approach can be used. Then, the constraint-following robust controller design is based on the UK approach and Lyapunov stability theory. The controller can render the unbounded state eventual uniform boundedness and uniformultimate boundedness, which also satisfies the spatial constraint and the bidirectional restriction for the spacing error. Moreover, an optimized design scheme for the tunable parameter of this controller is proposed, which minimizes the control cost and comprehensive index of system performance. Finally, numerical simulations are given to illustrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

In this study, a nonlinear absorber that works with a negative stiffness mechanism is suggested to mitigate vibration, and its effect on the reduction of vibration is investigated. The negative stiffness, which is inherently nonlinear, creates internal resonance; therefore, the vibration energy can be transmitted from low-frequency to high-frequency vibrating modes, causing vibration suppression. The nonlinear absorber is added to the primary nonlinear system, and when the main system is subjected to external resonance due to harmonic excitation, the negative stiffness parameter of absorber is so adjusted that autoparametric resonance occurs and vibration is reduced. First, the mathematical model of the system is presented and the governing differential equations of the motion are derived, and then, using the multiple scale method, the equations are solved for the case without, and with the 1:3 internal resonance. The responses and their stability are inspected, discussed, and compared. After that, the effect of negative stiffness and damping parameters on vibration amplitude reduction is investigated and the adequacy of the proposed absorber will be demonstrated by numerical analysis. Finally, the energy exchange between the primary system and the absorber will be demonstrated by plotting the responses in the state space and the displacement response Fourier spectrum. [ABSTRACT FROM AUTHOR]

This paper presents a design framework to obtain a robust multivariable Proportional-Integral-Derivative (PID) controller for second-order linear vibrating systems. A Proportional-Integral-Derivative plus acceleration (PIDA) controller is also proposed to deal with the regularization problem. Relevant control challenges, such as modeling error, regulatory performance optimization, regional pole placement, saturation avoidance, and constant reference tracking are handled within the proposed Linear Matrix Inequality (LMI) design approach. The design strategy is obtained from a linear transformation that can be applied to achieve constant reference tracking for an actuated subspace of underactuated systems. Moreover, the integral action has two additional objectives: (1) to improve regulatory performance in the presence of constant disturbance and (2) to increase the design degree of freedom in order to robustly achieve closed-loop specifications. Three simulation case studies are used to highlight the benefits of the PID and PIDA controllers. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive robust interaction force control algorithm for an underactuated walking lower limb hydraulic exoskeleton. In order to deal with the problem of passive joints (less of control inputs), holonomic constraints from the wearer are considered in system dynamics, which help transform the underactuated exoskeleton dynamics into fully actuated dynamics in Cartesian space. Based on the established dynamic model, adaptive robust interaction force controllers are presented both for the phase of double leg support and single leg support to effectively deal with multiple walking phases, negative effect of high-order nonlinearities of hydraulic systems as well as various model uncertainties and external disturbances. An additional torque allocation method is proposed to deal with the over-actuated characteristic in double leg support phase. Comparative simulations are carried out. The results demonstrate that the proposed force controller can achieve precision and strong robust interaction force control performance to load change and variation of the human trajectory. [ABSTRACT FROM AUTHOR]

This article is concerned with the resilient control problem for cyber-physical power systems. The main difference from the existing works lies in that the proposed resilient control scheme focuses on robust control in consideration of the attack reconstruction. First, power systems under false data injection attacks are modeled as cyber-physical power systems through the characteristics of power systems and attacks. Second, we design a robust adaptive attack estimation observer with a prescribed H ∞ performance index to reconstruct the attack signals. Sufficient conditions for the design of the observer are formulated into matrix inequalities by choosing an appropriate adaptive law for online learning. Third, on the basis of attack estimation, a resilient control strategy by dynamic output feedback is proposed, which avoids the difficulty in designing state feedback resilient control based on the observer. Meanwhile, the attack estimation observer and output feedback resilient control are designed separately, and their performance is considered respectively, which simplifies the design process. Finally, a power system with three generators and six buses is used as an example to verify the feasibility of attack estimation and resilient control scheme. [ABSTRACT FROM AUTHOR]

In this article, a robust adaptive impedance control based on the modified function approximation technique, and augmented with a novel integral nonsingular terminal sliding mode control, is proposed for a surgical haptic system. The haptic device is maneuvered by surgeons, whereby the mode of action, motion path, and haptic dynamics are rendered as unknowns. The inclusion of integral nonsingular terminal sliding mode control leverages the capability of ensuring consistent tracking of system's trajectories performance, fast transient response, finite-time convergence, improved robustness, and reduced chattering. However, the modified function approximation technique strategy allows to estimate model's dynamics regardless of the availability of dynamic uncertainties' lower and upper bounds. In addition, an estimate of the intended motion mode and path is integrated in the evolved adaptive impedance control, via radial basis function neural network, permitting the haptic arm to track the target impedance model. Finally, using the haptic arm, controlled experimental cases and comparative study were done, after which the proposed surgical simulator adopted the results for real-time validation. [ABSTRACT FROM AUTHOR]

When the boom sprayer works in the field, the boom must be parallel to the undulating ground or crop canopy. Aiming at the problem of low control accuracy and poor stability caused by parameter uncertainties and time-varying disturbances in the electro-hydraulic active boom suspension system, this paper proposes an adaptive robust precision control algorithm based on disturbance estimation. Firstly, the dynamic analysis modeling method is adopted to establish the nonlinear dynamic model and mechanism geometric equation of the pendulum active and passive suspension. Then, the controller was designed based on the nonlinear model of the suspension system. The proposed controller uses the backstepping design method to integrate the disturbance observer into the adaptive robust controller, which can effectively deal with the parameter uncertainties and time-varying disturbances in the suspension system model. Finally, a large number of experiments were carried out by taking a 28 m large boom active suspension driven by a single-rod hydraulic pressure as an example. Using an established rapid control prototype of a large boom suspension, a variety of control algorithm comparison experiments were carried out, and a 6-DOF motion platform was used to simulate the motion coupling interference of the sprayer chassis. The experiment results illustrate the high-performance characteristics of the proposed controller and improve the tracking performance of the active pendulum suspension system under various parameter uncertainties and time-varying disturbances. [ABSTRACT FROM AUTHOR]

Legged robots have the advantage of strong terrain adaptability in lunar exploration. A new robust controller is designed for axial flux permanent magnet motors applied on the legged lunar robots to diminish the disturbance from uncertainty and external circumstance. The theoretical verification is carried out through Lyapunov stability theory. The numerical simulation and real-time experiment are carried out to access the stability and dynamic property of the systems adopting the proposed controller. The results are compared with the traditional control strategies to demonstrate the advantages of the proposed controller. The new robust controller contributes to the dynamic stability of legged lunar robots and is also appropriate for the similar mechanical systems. [ABSTRACT FROM AUTHOR]

Gyroelastic solar panel is a kind of flexible solar panel structure with variable-speed control moment gyroscopes distributed inside. The torque generated by these variable-speed control moment gyroscopes can be used for active vibration suppression. This paper addresses the vibration suppression problem of gyroelastic solar panel in the presence of parametric uncertainties and un-modeled dynamic uncertainties. A novel μ-synthesis method based on analytical multiple-input multiple-output weights design is proposed, which relates 2-norm of the vector of regulated outputs, closed-loop modal damping, and relative control ability of actuators to each mode to the weights. Based on the idea of collocated control, the full order state-space model of the constrained gyroelastic plate with angle gyros as measuring devices is derived. After model reduction, modeling of un-modeled dynamic, and designing the multiple-input multiple-output weights, μ-controller is solved by the DK-iteration method. Furthermore, a comparative study of the μ-controller designed by the proposed procedure and the Positive Position Feedback (PPF) controller designed by the non-smooth H∞ synthesis method is also presented. The control methods are compared for their vibration attenuation, energy utilization, robustness performance characteristics, and robustness stability characteristics. Results for both time domain and frequency domain simulations are presented. Simulation results show that the designed μ-controller has better vibration attenuation effect and robustness performance characteristics than the PPF controller, and can achieve a better robust vibration suppression of the constrained gyroelastic solar panel in presence of parametric and un-modeled dynamic uncertainties. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of preview sliding mode control for a class of nonlinear uncertain discrete-time singular systems with time-delays. A difference operator approach is used to deal with the controlled system such that the derived augmented systems including preview information of reference signal can be constructed. A suitable surface is proposed in the sense of admissibility by the free-weighed matrix technique. Based on this, a sliding mode controller with preview information is constructed incorporating with the tracking error to ensure that the closed-loop control system reaches the designed sliding mode surface within finite time. To apply the proposed control scheme to the practical engineering systems, the sliding mode tracking controller with preview information is developed for a DC motor based on the proposed control approach. The comparative experiment results demonstrate that the preview information of reference signal can improve the tracking performance. [ABSTRACT FROM AUTHOR]

The vehicle active suspension has been widely used as it could effectively improve the vehicle ride comfort. To solve the issues of actuator uncertainty and time delay existing in the active suspension system, a multi-objective non-fragile H ∞ control algorithm is proposed in this work. First, to effectively describe the vehicle suspension dynamics, a quarter-car suspension model is constructed first in this study. Second, aiming at improving the ride quality and guarantee the hard constraints of the suspension system, a multi-objective H 2/ H∞ performance index is proposed. Subsequently, the issues of external disturbances, actuator uncertainty and delay are considered in the design process of the suspension controller. Then, a multi-objective non-fragile control algorithm is proposed based on an effective Lyapunov functional. The control gain can be obtained by solving a convex optimization problem in terms of linear matrix inequalities. Finally, numerical simulations are implemented on MATLAB/Simulink platform to show the robustness and superiority of the proposed controller. Experiments are implemented on a quarter-car test rig to validate the practical performance of the designed controller. [ABSTRACT FROM AUTHOR]

In this paper, to obtain ideal dynamic behavior of vibration screen, control synchronization of three eccentric rotors (ERs) driven by motors in space vibration system is investigated by employing the adaptive fuzzy sliding mode control (AFSMC) algorithm. First, the dynamic model of the vibration system is established, and the motion equation of the electromechanical coupling system is derived via Lagrange equation. Then, the synchronization controllers of three ERs are systematically designed with the combination of AFSMC algorithm and master–slave control (MSC) structure, and the stability of the control system is verified by Lyapunov theory. Additionally, in comparison with the conventional sliding mode control (SMC) algorithm, the superiority and feasibility of the proposed AFSMC strategy are confirmed through numerical simulation in MATLAB/Simulink. Moreover, the robustness of the control system is demonstrated in the simulation via changing the motor velocities and structure parameters. The research result shows that the proposed adaptive strategy can effectively control the ERs to implement the desired in-phase synchronization motion, and the control method possesses commendable efficacy in reducing chattering, enhancing control accuracy, eliminating overshoot, and resisting parameter perturbation. [ABSTRACT FROM AUTHOR]

In this article, the formation control problem is investigated for a team of unmanned tail-sitters subject to communication delays. A robust distributed and continuous formation control scheme is developed to achieve the desired aggressive time-varying formation flying in flight mode transitions between forward and vertical flights. The proposed control method consists of a translational controller and a rotational controller for each individual tail-sitter to govern the position and attitude motions, respectively. It is proven that the formation system stability can be guaranteed in the presence of communication delays and multiple uncertainties. Simulation results are presented for a team of tail-sitters to illustrate the advantages of the proposed formation flight control algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we design a novel robust control method to reduce the trajectory tracking errors of the SCARA robot with uncertainties including parameters such as uncertainty of the mechanical system and external disturbance, which are time-varying and nonlinear. Then, we propose a deterministic form of the model-based robust control algorithm to deal with the uncertainties. The proposed control algorithm is composed of two parts according to the assumed upper limit of the system uncertainties: one is the traditional proportional-derivative control, and the other is the robust control based on the Lyapunov method, which has the characteristics of model-based and error-based. The stability of the proposed control algorithm is proved by the Lyapunov method theoretically, which shows the system can maintain uniformly bounded and uniformly ultimately bounded. The experimental platform includes the rapid controller prototyping cSPACE, which is designed to reduce programming time and to improve the efficiency of the practical operation. Moreover, we adopt different friction models to investigate the effect of friction on robot performance in robot joints. Finally, numerical simulation and experimental results indicate that the control algorithm proposed in this paper has desired control performance on the SCARA robot. [ABSTRACT FROM AUTHOR]

This paper investigates nonlinear robust fault-tolerant control for turbofan engines with actuator faults. The nonlinear robust fault-tolerant control method is proposed in this paper, which can guarantee the fault tolerance and robustness of turbofan engines when faults and disturbances occur. The design method is implemented in three steps: Firstly, the dynamic effects caused by actuator faults on turbofan engines are analyzed and then the multivariable polynomial state-space model of turbofan engines with actuator faults is proposed. Secondly, appropriate design parameters are chosen according to fault information. Thirdly, the nonlinear robust fault-tolerant control law for turbofan engines with actuator faults is designed by solving an optimization problem. In addition, stability and L 2 gain-like for turbofan engines with bounded disturbances and actuator faults are guaranteed by the proposed nonlinear robust fault-tolerant control method. The distinctive characteristic of the paper is that the nonlinear robust fault-tolerant control method for turbofan engines against actuator faults is proposed which can relax the accuracy requirements of the fault diagnosis subsystem and improve the fault-tolerant performance of the closed-loop control system. Simulations show that the nonlinear robust fault-tolerant control method has better control performances including transient responses, disturbance rejection, and fault tolerance for the turbofan engine with actuator faults. [ABSTRACT FROM AUTHOR]

This paper presents a robust adaptive sliding mode controller scheme as applied to a class of uncertain nonlinear systems with parametric uncertainties and external disturbances. First, a sliding mode control technique is designed. Then, the proposed robust adaptive control schemes are applied to estimate the parametric uncertainties and the upper bound value of the external disturbances by using adaptive laws, ensure robustness in presence of parametric uncertainties and external disturbances, and reduce chattering problem by introducing an hyperbolic tangent function. Lyapunov stability theory is used to analyze the stability of the closed-loop system. As an exemplar, the schemes have been applied to a quadrotor unmanned aerial vehicle (QUAV) model. Simulation results for the control of the QUAV model are provided to illustrate the performance of the proposed robust adaptive sliding mode control scheme and demonstrate that the proposed method has good tracking performance. The simulation results clearly prove the effectiveness of our approach. [ABSTRACT FROM AUTHOR]

In this paper, trajectory tracking control of an underwater vehicle in three-dimensional (3D) space has been addressed. The assumed underwater vehicle has 6 degrees of freedom and the aim is to control all system rotations and displacements. In this paper, a finite-time sliding mode controller as a robust control method is proposed for an underwater vehicle with 6 degrees of freedom in 3D space using the method without simplifications or decouplings. Therefore, both system positions and orientations are controlled in the presence of disturbances and uncertainties. In previous research works, control of two-dimensional underwater vehicles is commonly studied. In this paper, a novel stable control algorithm is proposed for an underwater vehicle with 6 degrees of freedom. The stability of the closed-loop system is analyzed using the Lyapunov theory. The designed algorithm can cover 3D complicated tasks. Also, the designed algorithm as a robust control approach can attenuate external disturbances. The performance and stability of this approach are compared with the sliding mode controller. The numerical comparison results show that the proposed approach is effective and applicable in practice. [ABSTRACT FROM AUTHOR]

This paper proposes a new robust output-feedback adaptive event-triggered control (AETC) method for linear systems with parametric uncertainties. The proposed event-triggered mechanism (ETM) is obtained based on the L 2 stability condition. In this paper, two design approaches are presented, the emulation approach (pre-designed control gain) and the co-design approach. In the latter, the event-triggering law and the output-feedback controller are designed simultaneously to have a more efficient control system. The proposed adaptive event-triggered mechanism (AETM) in both approaches leads to an increase in the average of inter-event times based on linear matrix inequalities (LMIs). Consequently, in the proposed methods, the stability of the event-based system is ensured, the Zeno phenomenon is avoided, the feasibility margin and the quality of the response are well maintained, and the number of samplings is reduced, considerably. Finally, to indicate the capability of the proposed methods, two numerical simulations are presented. [ABSTRACT FROM AUTHOR]

Restricting transient peaks of contact force in teleoperation systems is undeniably vital, specially in critical applications such as telesurgery. This issue, however, has still remained unsolved in the literature. In order to address this problem, we propose an impedance control scheme using optimal L 1 theory for teleoperation systems encompassing asymmetric randomly time-varying delays and model uncertainties. To this end, an L 1-based state-feedback compensator is designed employing linear matrix inequalities, aiming at minimizing the desired impedance error subjected to human force as exogenous disturbance. A simulation is ultimately conducted in comparison with the sliding-mode-based impedance controller. The results validate that the proposed controller is able to keep the integral of impedance error within the desired bound and, thus, improves the transient response. This is, however, at the expense of imposing a steady-state error for the integral of impedance error, which is normally made zero by the sliding-mode controller. [ABSTRACT FROM AUTHOR]

In addition to the difficulty of system modeling, every physical system faces actuator saturation, making the real control different from the controller output (desired control input). When this occurs, the controller output does not regulate the system properly and errors occur as a result of incorrect updating. This is known as the windup phenomenon. In the event that the controller is configured to override actuator saturation, it can lead to a failure in the controller's performance, such as large overshoots, high response time, and even system instability in the worst case. Therefore, in this paper, a new robust model-free controller method is proposed. It is a combination of four nonlinear control techniques, namely model-free controller, fractional-order sliding mode controller, fractional integral–proportional (PI) controller, and anti-windup compensator, which gives rise to the new model-free controller algorithm called hybrid fractional-order intelligent PI fractional sliding mode controller with an anti-windup compensator termed (MF-FOiPI-FOSMC-AW). However, to illustrate the effectiveness of the new proposed MF-FOiPI-FOSMC-AW method, simulation and experimental results compared to classical PI and iPI controllers (with and without an anti-windup compensator) on a hydraulic system are presented in the presence or absence of external disturbances for different types of references. Finally, simulation is conducted through an experimental comparison of the proposed approach with other strategies such as the classical anti-windup PI controller and the anti-windup intelligent PI controller, which is carried out for this purpose. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive fractional-order (FO) terminal sliding mode control (TSMC) scheme to the robust current control of active power filter (APF) using a recurrent meta-cognitive fuzzy neural network (RMCFNN). An FO TSMC is developed by considering that the parametric perturbations and the external disturbances of APF are bounded. Compared with conventional TSMC approach, the proposed scheme, with an FO sliding surface, can obtain enhanced finite-time high-precision tracking performance due to another degree of freedom. Then, a novel observer-based FO TSMC is derived to achieve an absorbing model-free feature arising from RMCFNN. To improve the capabilities in managing the uncertainties, the specific online updating schemes for the structure and parameters of RMCFNN are designed. Meanwhile, closed-loop stability and finite-time convergence characteristic can be achieved using Lyapunov theory. Finally, simulation and experimental results indicate that the proposed observer-based FO TSMC can be easily implemented by microcontroller and has superior control performance compared with other existing schemes. [ABSTRACT FROM AUTHOR]

The main objective of this article is to solve the trajectory following problem for lower limb exoskeleton robot by using a novel adaptive robust control method. The uncertainties are considered in lower limb exoskeleton robot system which include initial condition offset, joint resistance, structural vibration, and environmental interferences. They are time-varying and have unknown boundaries. We express the trajectory following problem as a servo constraint problem. In contrast to conventional control methods, Udwadia–Kalaba theory does not make any linearization or approximations. Udwadia–Kalaba theory is adopted to derive the closed-form constrained equation of motion and design the proposed control. We also put forward an adaptive law as a performance index whose type is leakage. The proposed control approach ensures the uniform boundedness and uniform ultimate boundedness of the lower limb exoskeleton robot which are demonstrated via the Lyapunov method. Finally, simulation results have shown the tracking effect of the approach presented in this article. [ABSTRACT FROM AUTHOR]

Tuned mass dampers are well-known devices for efficient reduction of structural vibrations; however, they can only control the vibration of a single mode in a narrow frequency range and are not easily retunable. This article presents a semi-active tuned mass damper, consisting of a piezoelectric device connected to an external resistive–inductive electric circuit, which enables multi-modal vibration control, is highly tunable, and introduces high damping. The dynamics of the coupled electromechanical system, which includes the primary and auxiliary masses, the piezoelectric device, and the shunt circuit, are analyzed and the effect of the resistance and inductance is investigated. An experimental prototype using a specialty piezoelectric device is fabricated and tested. The experimental measurements greatly agree with the analytical results, validating the strong electromechanical coupling and the enhanced vibration suppression capabilities of the proposed damper. Moreover, the variation of inductive impedance demonstrates substantial semi-active broadband multi-modal vibration control potential, by introducing an additional highly tunable electromechanical resonant oscillator in the system dynamics, and also by enabling the enhancement of coupling and energy dissipation on targeted modal frequencies. [ABSTRACT FROM AUTHOR]

An Autonomous Underwater Vehicle (AUV) is a nonlinear nonholonomic dynamical system. Tracking control of AUVs in the presence of disturbances and uncertainties is a challenging problem. In this paper, an adaptive passivity-based algorithm is proposed for tracking control of an AUV. Also, a disturbance estimator has been used to attenuate the effects of unknown disturbances. A proper adaptive rule is designed to estimate unknown parameters and disturbances. The stability of the proposed method is analyzed using passivity properties and the Lyapunov theory. Obtained comparative results show the advantages of the proposed Adaptive Computed Torque Method ACTM plus disturbance estimator. [ABSTRACT FROM AUTHOR]

Achieving compliance and flexibility under the premise of ensuring trajectory tracking performance and also reflecting the wearer's movement intention, has not yet been well solved in the field of prosthesis. The aim of this paper is to provide a compliant, robust, and continuous control scheme for robotic knee prosthesis to solve the contradictory problems of trajectory tracking performance and compliance. The proposed scheme are based on the admittance model and radial basis function (RBF) neural network–enhanced nonsingular fast terminal sliding-mode controller (NFTSMC). The desired trajectory of the prosthetic knee joint is driven by humans and reshaped to reference trajectory by an admittance model, so that the prosthetic leg can reflect the human's movement intention and being compliant. RBF neural network is introduced to achieve adaptive approximation of unknown models and ensure that the controller does not depend on the mathematical model of the "human-in-the-loop" prosthesis system. A novel NFTSMC was proposed to deal with the influence of ground reaction forces (GRFs) and fitting errors of the RBF neural network, which make the tracking error converge to zero in a finite time. The adaptive law of the RBF neural network is obtained by the Lyapunov method, and the stability and finite-time convergence of the closed-loop system are rigorously proved and analyzed mathematically. The simulation results prove the feasibility and effectiveness of the propose control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a robust feedback feed-forward proportional-derivative type (PD-type) iterative learning control (ILC) scheme for a class of linear discrete systems with polytopic uncertainty over finite frequency ranges. First, the ILC process is transformed into an equivalent discrete linear repetitive process. Then, with the help of the generalized Kalman–Yakubovich–Popov lemma, the issue of a robust control law design algorithm in the process model is converted into the problem of solutions to the corresponding linear matrix inequality conditions. This procedure not only meets the robust performance specifications along the trial, but also guarantees the monotonic converge of the trial-to-trial error dynamics over finite frequency ranges. Finally, the simulations for a direct current servo motor system are adopted to show the effectiveness and superiority of the proposed method. Compared with previously established works, the new algorithm is more effective in delivering higher performance and achieving better tracking effect. [ABSTRACT FROM AUTHOR]

This paper proposes a neural network-based robust model predictive control (MPC) strategy for visual serving of autonomous vehicles (AVs) with uncertain payloads, ground friction disturbances, and air resistance effects. Based on the dynamics of visual servoing errors and driving of the AV, the quasi-min–max MPC is adopted to calculate the desired velocity of the AV subject to the constraints on the speed, control, and the visual field. The backpropagation (BP) neural network is then used to learn the ground friction disturbances of the AV, which is adopted to compensate the quasi-min–max MPC of the visual servoing system. Finally, the performance of the proposed controller is evaluated and verified by some comparison simulations. [ABSTRACT FROM AUTHOR]

Coupled nonlinear systems are difficult to control due to the adverse effects of uncertainties and coupling effects with increased sensor noise. This paper proposes an improved Lyapunov-based composite controller consisting of fractional-order proportional–integral–derivative (FOPID) and velocity-based disturbance observer to deal with the motion control of uncertain, nonlinear, and coupled system. FOPID utilizes the stable filtered error to facilitate the control development and stability analysis for the multi-input multi-output (MIMO) coupled system. Moreover, a disturbance observer is developed by utilizing the velocity signals to provide robustness against the disturbances and parametric uncertainties. Enhanced infinite order disturbance observer (EIFDOB) structure is used to improve the robustness of the introduced technique despite the high-frequency sensor noise. Stability analysis is provided to verify the introduced controller through the Lyapunov stability theorem, LaSalle’s invariance principle, and Barbalat’s lemma. Signal chasing is also presented to show that all signals are ultimately bounded. Comprehensive numerical simulations are performed on high-fidelity and coupled nonlinear model of the twin rotor MIMO system where the efficiency of the presented technique is examined against the external disturbances, matched uncertainties, and sensor noise. The results presented with different scenarios show that the proposed technique performed better with more robustness than FOPID and integer order proportional–integral–derivative. [ABSTRACT FROM AUTHOR]

In order to tackle the uncertainties encountered in the operation of three-dimensional (3D) overhead crane systems and enhance the overall robustness of the control system, an adaptive sliding mode control (SMC) method based on prescribed performance is proposed in this work. Specifically, an integral sliding mode controller (ISMC) based on prescribed performance is designed for the 3D overhead crane dynamics model with double-pendulum effect, which is used to constrict system error. By considering the case of model uncertainty, time-varying parameters, track friction, and so on, the neural network (NN) is employed to estimate unknown terms in the controller design, and the Lyapunov function is applied to analyze the stability of the close-loop system. The results demonstrated that the proposed method can effectively improve the positioning accuracy and payload swing suppression performance of the overhead crane system, and also improve the robustness of the control system to deal with uncertainties. [ABSTRACT FROM AUTHOR]

Motion control of mechatronic systems with uncertainties and physical constraints, while ensuring robustness and achieving better performance, such as high tracking accuracy and fast response, has always been a hot topic. However, the most current related works only focus on how to guarantee system stability under constraints, and few consider comprehensive performance. This paper investigates gated recurrent unit (GRU)-based compensation adaptive robust control (ARC) for uncertain linear motor–driven stage system with state and input constraints. To achieve rapid and precise motion control, a dual-loop control structure is employed, where GRU and ARC are the outer loop and the inner loop, respectively. First, the ARC control law is used to deal with the parameters uncertainty and external disturbances in the system, which further improves the tracking accuracy. A GRU neural network is then constructed and capable of implementing precise prediction ahead of the actual system output. Through choosing suitable loss function and training model, it can effectively minimize prediction error under state and input constraints. Comparative experiment results demonstrate the superiority and validity of the proposed scheme on the basis of GRU and ARC. [ABSTRACT FROM AUTHOR]

Multi-motor-pendulum vibration systems have been applied to design shale shakers in petroleum drilling engineering. However, synchronization of the multi-motor-pendulum vibration system is instable on account of external load disturbance and systematic parameter restriction, which is a principal factor to decrease screening efficiency of shale shakers. In this work, to maintain stability synchronization of three eccentric rotors driven by three induction motors, a combined synchronous control strategy by tracking velocity and phase among the motors is proposed. First, the dynamic model of the system is deduced based on the Lagrange equation. Second, adjacent cross-coupled control combined with master–slave control is designed to control speed and synchronization between the motors in the multi-motor-pendulum vibration system. Third, to ensure the precision and robustness of the control system, the velocity error, phase error, and coupling error controllers are designed with reaching law algorithm and global sliding mode control; and stability of the controller system is validated by the Lyapunov theorem. Finally, the effectiveness of the control strategy is verified by numerical simulation and compared with previous findings. The results indicate that synchronous state and velocity overshoot of the motors can be controlled with the combined control strategy; and robustness of the control strategy is better than other methods. [ABSTRACT FROM AUTHOR]

In this study, an interval type-2 fuzzy logic controller design method is proposed and validated on the real-time under-actuated nonlinear inverted pendulum system for swing-up and stabilization control problems. The swing-up algorithm is designed to give a faster response and the stabilization controller is designed based on continuity, monotonicity, and smoothness theorems for worst and best cases using the Mamdani fuzzy inference system in order to show the effectiveness of the proposed method. Outstanding type reduction methods are analyzed for the stabilization controller based on the design approach to determine the best type reduction algorithm for the effective and robust control performance. Real-time experiments are conducted to investigate the capability of the proposed controller in terms of adaptation performance and robustness ability. The controller also is able to handle structured and unstructured uncertainties such as measurement noise, external payload, undesirable internal/external disturbances, and parameter uncertainties. The results show that the proposed method clearly improves the control performance of the system in six experimental tasks conducted. [ABSTRACT FROM AUTHOR]

A sliding mode neural network fuzzy control (SMNNFC) method is investigated to suppress the vibration of a translational coupled double flexible beam system, equipped with an AC servomotor and several piezoelectric actuators. Adjacent beams and slider moving frame are connected at the tip by elastic springs. Based on the finite element method, the system model is established to recognize the vibration characteristics. Furthermore, two laser displacement sensors are used to decouple the first two bending modes of the double flexible beam system. In the applied SMNNFC strategy, a neural-fuzzy framework is designed to obtain robust control performance and alleviate the chattering phenomenon. Considering unknown and varying system uncertainty, a parameter updating algorithm is adopted. The stability of SMNNFC is analyzed. The experimental setup is constructed and experiments are conducted, including set-point vibration control and simultaneous translation and vibration control under trapezoidal and sinusoidal trajectories. The experimental results demonstrate that the SMNNFC scheme has advantages in suppressing both the large and low amplitude vibrations of the coupling double flexible beam system. [ABSTRACT FROM AUTHOR]

Position tracking of an autonomous underwater vehicle is not trivial as its accuracy is affected by process noise, measurement noise, and uncertain hydrodynamic parameters. Thus, in this article, we studied the position control of an autonomous underwater vehicle that operates under largely unbounded system uncertainties and large noise levels and proposed a method that reduces the interference and thereby enhances the overall autonomous underwater vehicle position estimation. Our technique extended the ensemble Kalman filter by combining it with a time-delay estimator to compensate against extended uncertainty of the system dynamics which cannot be solved by the traditional ensemble Kalman filter. Our synthetic simulations demonstrated the effectiveness of the proposed controller, highlighting its appealing position-control accuracy under simultaneous noise and uncertain hydrodynamics parameters. In addition, our simulation results showed that the proposed controller outperforms the conventional time-delay controller by a percentage range of approximately 30.8%–92.6% in terms of root-mean-square error and requires on average less than 88.2% calculation time than the conventional model predictive control. [ABSTRACT FROM AUTHOR]

This study investigates the flight longitudinal tracking control problem of hypersonic vehicle in presence of the input saturation, external disturbances, model parametric uncertainties, and actuator faults. First, the velocity and altitude subsystem are established with disturbances based on the feedback linearization model. Second, two robust anti-saturation fault-tolerant controllers are designed for the velocity subsystem and altitude subsystem by the utilization of the tangent function, Nussbaum function, and adaptive nonlinear filter. Finally, Lyapunov stability theory is used to prove that the states of the closed-loop system are bounded. And, the effectiveness and robustness of the control strategy are proved by numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, based on the extended state observer (ESO) and on a fractional order controller (FOC), composed of an integer order PID cascaded with a fractional order filter (FOF), a new control scheme for an n th order integer plant is proposed. The ESO is used to estimate and cancel the unknown internal dynamics and the external disturbance. Afterwards, an FOC is designed to resolve the set-point tracking problem. An analytical and systematic method is proposed to design the FOC. This method is based on the Internal Model Control (IMC) and the Bode's Ideal Transfer Function (BITF). Therefore, the proposed control structure improves the robustness and performance of the traditional linear active disturbance rejection control (LADRC), especially for the open-loop gain variation. In addition, since the system be controlled is an n th order, a general form of the BITF is also proposed. Numerical simulations on a nonlinear model and experimental results on a cart-pendulum system design illustrate the effectiveness of the suggested ESO-PID-FOF scheme for the disturbance rejection, the set-point tracking and robustness. A comparison with the results obtained using the standard LADRC is also presented. [ABSTRACT FROM AUTHOR]

This study aims to develop an advanced integral terminal sliding-mode robust control method using a disturbance observer (DO) to suppress the forced vibration of a large space intelligent truss structure (LSITS). First, the dynamics of the electromechanical coupling of the piezoelectric stack actuator and the LSITS, based on finite element and Lagrangian methods, are established. Subsequently, to constrict the vibration of the structure, a novel integral terminal sliding-mode control (ITSMC) law for the DO is used to estimate the parameter perturbation of the LSITS based on a continuous external disturbance. Simulation results show that, under a forced vibration and compared with the ITSMC system without a DO, the displacement amplitude of the ITSMC system with the DO is effectively reduced. In the case where the model parameters of the LSITS deviate by ±50%, and an unknown continuous external disturbance exists, the control system with the DO can adequately attenuate the structural vibration and realize robust control. Concurrently, the voltage of the employed piezoelectric stack actuator is reduced, and voltage jitter is alleviated. [ABSTRACT FROM AUTHOR]

In this article, a new dynamic non-singular terminal sliding mode control technique for a quadrotor system subjected to external disturbances is evaluated. The offered control approach is based on non-singular terminal sliding mode controller combined with proportional–integral–derivative sliding surface to improve the performance. The proposed controller is formulated using the Lyapunov theory which ensured the existence of the sliding mode surfaces in finite time. Furthermore, the chattering problem, caused by the switching position and attitude laws, has been reduced using the proposed controller. Moreover, a high-precision performance trajectory tracking can be obtained. The problem of the disturbances is addressed using the suggested controller. Simulation results show the feasibility and efficiency of the non-singular terminal sliding mode control-proportional–integral–derivative proposed approach. [ABSTRACT FROM AUTHOR]

In order to reduce the impact of load and system parameter changes on the dynamic performance of collaborative robot joint module, a novel robust control algorithm is proposed in this paper to solve the problem of dynamic control of collaborative robot joint module trajectory tracking. The controller is composed of two parts: one is a nominal control term designed based on the dynamical model, aiming to stabilize the nominal robot system; the other is a robust control term based on the Lyapunov method, aiming to eliminate the influence of uncertainty on tracking performance, where the uncertainties include nonlinear friction, parameter uncertainty, and external disturbances. The Lyapunov minimax method is adopted to prove that the system is uniformly bounded and uniformly ultimately bounded. We performed numerical simulation and experimental validation based on an actual collaborative robot joint module experimental platform and the rapid controller prototype cSPACE. The numerical simulation and experimental results show that the controller has excellent control performance for the collaborative robot joint module and provides more accurate trajectory tracking under the influence of uncertainties. [ABSTRACT FROM AUTHOR]

This paper proposes a novel continuous-time robust direct adaptive controller for the attitude control of the three-dimensional unknown chaotic spacecraft system. It considers that the plant's nonlinear terms, exogenous disturbances, and model uncertainties are unknown and bounded; the controller design is independent of the system's nonlinear terms. These controller attributes flourish the robust performance of the closed-loop and establish smooth state vector convergence to zero. The proposed controller consists of three parts: (1) a linear controller establishes the stability of the closed-loop at the origin, (2) a nonlinear controller component that autonomously adjusts the feedback gain, and (3) a nonlinear adaptive controller compensates for the model uncertainties and external disturbances using the online estimates of bounds and model uncertainties. The output of this part remains within a given upper and lower bound. The feedback controller gain is large when the state variables are away from the origin and become small in the origin's vicinity. This feature is novel and contributes to the synthesis of smooth control effort that establishes robust fast and oscillation-free convergence of the state variables to zero. The Lyapunov direct stability analysis assures the global asymptotic robust stability of the closed-loop. Computer simulations and comparative analysis are included to verify the theoretical findings. [ABSTRACT FROM AUTHOR]

A robust state-feedback H ∞ controller is proposed for an uncertain bilateral teleoperation system having norm-bounded parametric uncertainties on mass and damping coefficients of the considered master/slave system. The proposed method ensures robust stability and successful reference tracking and force reflection performance. While Lyapunov stability is used to ensures asymptotic stability, the H ∞ norm from exogenous input to the controlled output is utilized in satisfying the reference tracking and force reflection. As two performance objectives and robust stability requirement are conflicting with each other, the proposed controller reduces the associated conservatism with dilated linear matrix inequalities. Standard and dilated linear matrix inequality-based robust H ∞ state-feedback controllers are performed with a one degree of freedom uncertain master/slave system under reference signal and environmental-induced exogenous force. Numerical simulation results show that the dilated linear matrix inequality-based H ∞ control satisfies lower H ∞ norm than a standard H ∞ control. Moreover, the proposed controller demonstrates a very successful performance in achieving performance objectives despite the stringent norm-bounded parameter uncertainties. [ABSTRACT FROM AUTHOR]

In this paper, an optimal robust adaptive fuzzy backstepping control is presented to the position control of the electro-hydraulic servo (EHS) system in the presence of structured and unstructured uncertainties. Initially, the robust control using the backstepping technique is presented to overcome the existing uncertainties in the dynamic equations. Mathematical proof demonstrates that the closed-loop system in the presence of uncertainties has a global asymptotic stability. Then, to overcome the chattering problem, a very simple fuzzy approximator is presented where it approximates the bounds of the uncertainties. Although the proposed robust fuzzy backstepping control has a desirable performance, it has no mathematical analysis to prove the stability of the closed-loop system. Therefore, to solve this problem, the proposed fuzzy approximator has been transformed into a one-law adaptive fuzzy approximator with a single-input single-output fuzzy rule. Mathematical analysis illustrates that the closed-loop system in the presence of uncertainties has a global asymptotic stability under the proposed robust adaptive fuzzy backstepping control. Furthermore, a novel modified harmony search algorithm (MHSA) has been developed, by using the original harmony search algorithm (OHSA) as an optimization technique, to achieve the optimal values of the membership functions and the control coefficients. Finally, a comparative study has been conducted between the proposed control scheme under the MHSA and the OHSA, and other existing advanced control approaches to verify the effectiveness of the proposed control. Results show that the proposed control scheme under the MHSA can suppress the chattering problem and reduce the disturbances effectively while ensuring that the performance is tracked. [ABSTRACT FROM AUTHOR]

This paper proposes a predefined-time convergent stabilization controller for a class of nonlinear systems. First, a controller is introduced for linear systems where the convergent time is selected in advance, independent of initial conditions, and can be assigned as a parameter of a control input. The corresponding result is then obtained for a multidimensional system consisting of n nonlinear differential equations. The block control technique is employed to consequently stabilize each state component by a virtual control until the real control appears. Finally, the presented result is applied to a multivariable nonlinear system to design a predefined-time convergent robust controller. To show effectiveness of the proposed convergent controller, numerical simulations have been carried out for a Van-der-Pol system and a 2-degree-of-freedom (2-DOF) helicopter model. [ABSTRACT FROM AUTHOR]

This study investigates the angle tracking control of the electric power steering system, which is underactuated and with (possibly fast) time-varying uncertainties. We design the control based on constraint-following, that is, formulating the tracking goal as servo constraints. To tackle the uncertainty, especially the mismatched uncertainty, a robust control is proposed with two-layer performance: deterministically guaranteed and fuzzily optimized. Particularly, the control design is implemented in three steps. First, without considering uncertainty, a nominal control is designed. Second, an uncertainty decomposition technique is presented to account for uncertainty, which creatively allocates the mismatched uncertainty for the robust control design that also builds on the nominal system control. The robust scheme is deterministic without using any "if–then" rules and guarantees uniform boundedness and uniform ultimate boundedness for the system, that is, the deterministically guaranteed performance. Third, by using fuzzy set theory to describe uncertainty, a fuzzy-based performance index, including system performance and control cost, is introduced. A control parameter optimal design problem is formulated and analytically solved, that is, the fuzzily optimized performance. The effectiveness of the proposed approach is illustrated by rigorous proof and the simulation results on the electric power steering system. [ABSTRACT FROM AUTHOR]

The coupling, nonlinearity, and uncertainty characteristics of vehicle dynamics make the accurate longitudinal and lateral control of an automated and connected vehicle platoon a tough task. Little research has been conducted to fully address the characteristics. By using the ideology of constraint-following control this article proposes an integrated longitudinal and lateral adaptive robust control methodology for a vehicle platoon with a bidirectional communication topology. The platoon control objectives contain the path tracking stability, the platoon internal stability, and the string stability. First, we establish the nonlinear kinematics path tracking model and the coupled vehicle longitudinal and lateral dynamical model that contains time-varying uncertainties. Second, we design a series of nonlinear equality constraints that directly guarantee the control objectives based on the kinematic relations. On this basis, an adaptive robust constraint-following control is proposed. It is shown that the control guarantees the uniform boundedness and the uniform ultimate boundedness of the constraint-following error and the uncertainty estimation error. Finally, simulation results are provided to validate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]