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In this paper, a fixed-time sliding mode control scheme is developed to fulfill the trajectory tracking task of a marine surface vehicle with unknown dynamics. To restrain the adverse effects of the unknown dynamics including the parameter inaccuracy and exogenous disturbances, a fixed-time disturbance observer is designed to estimate the lumped uncertainties using the bi-limit homogeneous theory without requiring any knowledge of the model uncertainties. Then, a nominal tracking controller is proposed to stabilize the error dynamic model in the sense of fixed-time Lyapunov stability, based on which a novel integral-type sliding mode manifold with bi-limit homogeneity is constructed to drive tracking error convergence in fixed time. To enhance the robustness of the vessel control system, a disturbance observer–based fixed-time integral sliding mode tracking controller is finally proposed, and the chattering phenomenon is effectively alleviated by direct estimation compensations. The analysis of Lyapunov stability indicates that the closed-loop system is fixed-time stable. Numerical simulations on a model vessel are carried out to validate theoretical results of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This article proposes an efficient adaptive robust control for the eight-pole active magnetic bearing based on a heteropolar structure. Due to the uncertain behavior of active magnetic bearing, the mathematical model of active magnetic bearing is considered to be highly nonlinear and uncertain. As the rotor displacement and velocity are the measurable states, sliding mode control is designed to estimate state variables. Also, a matched disturbance term is used to deal with undesirable disturbances in the active magnetic bearing system. The controller is developed for an active magnetic bearing using the event-triggering-based sliding mode control technique. However, the stability of the proposed scheme has been achieved with the help of Lyapunov theory. Furthermore, the adaptive gain scheduling approach based on a neural network has been augmented to adjust the gain of the proposed controller for active magnetic bearing adaptively. The simulation studies have been performed in detail to demonstrate the use of proposed scheme for the robust control of active magnetic bearings. Finally, a comparative analysis of the proposed control design scheme with a conventional controller has been performed to achieve improved performance satisfying the plant constraints. [ABSTRACT FROM AUTHOR]

In this study, a new fixed-time sliding mode control approach for trajectory tracking control of robotic manipulator systems is devised, which provides fixed-time convergence, robust stabilization, and high precision. A novel fixed-time non-singular fast terminal sliding mode surface (FNFTSMS) with fixed-time convergence is provided, and with settling time independent of the initial condition of the system and can be pre-determined using design parameters. Furthermore, using adaptive disturbance observer and the suggested FNFTSMS, a new composite robust control approach is developed. The adaptive disturbance observer is intended to boost control performance and compensate for unpredictably occurring disturbances. The Lyapunov stability theory is used to establish the fixed-time stability of sliding surface and system states under the suggested composite control strategy. Finally, numerical simulations are carried out using PUMA560 robot in order to demonstrate the effectiveness and efficacy of the proposed control method in terms of accuracy of tracking, fast response, and convergent speed. [ABSTRACT FROM AUTHOR]

Aiming at the problem of payload's swing and communication resource saving of the quadrotor-suspended system under external disturbances, this paper proposes a modeling and control scheme of the quadrotor-suspended system with variable cable length at unequal speed. The inner loop adopts adaptive sliding mode control to enhance the robustness of the system and anti-swing feedforward control to suppress the swing angle, and the outer loop uses improved PD control to track the reference trajectory. Meanwhile, an event-triggered strategy based on dynamic threshold is designed in the inner loop controller, which reduces communication resource occupation. The stability of the coupled nonlinear control system is proved, and the event-triggered strategy can avoid Zeno behavior. Simulation results show that the scheme proposed in this paper can make the quadrotor track the desired trajectory, effectively suppress the payload swing, and save communication resources. [ABSTRACT FROM AUTHOR]

Robotic manipulators are nowadays widely used in various underwater scenarios, but their motion control remains a challenging task due to hydrodynamic effects. This article proposes a novel adaptive fuzzy sliding mode control (AFSMC) strategy for precise and robust control of underwater manipulators. To simulate the movement of the robotic manipulators in the underwater environment, the Unified Robot Description Format (URDF) file of a custom-designed electric underwater manipulator is imported into the Simscape Multibody and the hydrodynamic disturbance is modeled according to Morison's equation. Furthermore, the proposed control strategy takes advantage of the universal approximation capability of fuzzy systems to avoid chattering and observe disturbances by adjusting the control gains of classical sliding mode control (CSMC). And adaptive laws are designed to update the parameters of the fuzzy systems. The strong friction caused by the seal is also compensated by actual test data. In the simulation experiments, a special environment of water flow and variable loads is considered. The results demonstrate that the AFSMC strategy can achieve high precision and strong robustness against disturbances for trajectory tracking. More importantly, the chattering caused by CSMC can be eliminated and the hydrodynamic disturbance can be estimated with high precision through the proposed control strategy. [ABSTRACT FROM AUTHOR]

In this study, to reduce the impact that permanent magnet linear synchronous motor (PMLSM) servo system on the sensitivity of external and internal interferences, an adaptive super-twisting-based nonsingular fast terminal sliding mode control (AST-NFTSMC) scheme is put forward. First of all, the mathematical model of PMLSM contains uncertainties is set up, and the control law is established to make position signal converge to given state asymptotically. Second, by introducing the super-twisting algorithm, the chattering caused by nonlinear switching function in traditional method is weakened. However, in actual industrial situations, it is difficult to determine the boundary of lumped disturbance, which makes the switching gains in super-twisting algorithm cannot be accurately selected. Therefore, an adaptive law is introduced to adjust the switching gains online, so that the gains can be dynamically adjusted within a limited range during operation, so as to further weaken chattering. Finally, the practicability of AST-NFTSMC is proved in theory and verified by system experiments. The experimental results prove that AST-NFTSMC can significantly weaken chattering, and result in robust control performance. [ABSTRACT FROM AUTHOR]

In this paper, the autonomous trajectory-tracking problem for an Unmanned Aerial Vehicle (UAV) based on Sliding Mode Control (SMC) algorithms is treated. The control system is implemented in real-time to stabilize a commercial AR.Drone 2.0 quadrotor using monocular vision. The under-actuated mathematical model is based on the Newton-Euler formulation. The algorithm allows the stabilization of the quadrotor in all its states under the simultaneous effect of parametric uncertainties and constant external disturbances. The vision algorithm uses a monocular camera to estimate the vehicle's position. The experimental test results and numerical simulations show the effectiveness and robustness of the proposed controller. [ABSTRACT FROM AUTHOR]

This article presents the design, realization, modelling, and control of an aerial manipulator robot capable of performing tasks considered difficult and dangerous for humans. We propose a manipulation system that consists of two subsystems: an aerial platform represented by a hexacopter and a 3 degree-of-freedom manipulator arm that is light and easy to integrate into our hexacopter. The modelling approach of our aerial manipulation system is inspired by the dynamics of floating base systems with tree structures. This type of system presents many control challenges due to system asymmetry, continuous change of inertia, the centre of gravity, manipulator arm effects, and so on. For these reasons, a robust control technique based on a sliding mode controller is proposed to achieve a three-dimensional trajectory-tracking objective. In order to show the effectiveness of the proposed strategy, numerical simulations have been performed in many scenarios. [ABSTRACT FROM AUTHOR]

In this article, the snake robot having nine links with eight joints is considered for serpentine motion in the underwater environment. The movement of a snake robot occurs due to nonlinear drag forces and fluidic torque in underwater conditions. The uncertainties in drag forces and fluidic torque are considered to track the head angle and tangential velocity in this work. The virtual holonomic constraints are formulated to track all the joints by designing a controller for single joint. The parameters of gait pattern are obtained using the sliding surface. The sliding surface is formulated for head link angle and velocity tracking. Super twisting sliding mode control approach is proposed to deal with uncertainties, and results are compared with sliding mode control and adaptive sliding mode control. The robustness of controller is verified by inputting measurement noise. The significant improvement has been observed in chattering indicator and control effort by using the proposed super twisting sliding mode control. The investigation of this research article focuses on how to get almost chattering free operation in underwater uncertain environmental conditions with minimum control effort. [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 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]

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]

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]

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]

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]

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 paper, the robust trajectory tracking control problem of disturbed quadrotor unmanned aerial vehicles (UAVs) with disturbances, uncertainties and unmodeled dynamics is addressed, by devising a novel compound robust tracking control (CRTC) approach via data-driven cascade control technique. By deploying the data-driven philosophy, a data-based sliding-mode surface is proposed, and thereby contributing to strong adaptability to nonlinearity and model-unknown properties of the UAVs. By utilizing the backstepping technique, virtual control strategy and a novel cascaded compound robust PD control structure, the attitude and position subsystems are efficiently cohered such that a data-driven cascaded compound robust controller containing both PD control and sliding-mode control can be developed to conquer the lumped disturbances induced by uncertainties, disturbances and unmodeled dynamics. Eventually, the asymptotic convergence of the tracking errors with respect to both attitude and position subsystems can be guaranteed rigorously. Simulation studies on a prototype quadrotor UAV are performed to evaluate the efficacy and superiority of the devised CRTC method. [ABSTRACT FROM AUTHOR]

This paper presents a novel robust adaptive dual layer sliding mode control (ADLSMC) for the problem of high accuracy tracking trajectory of robot manipulator in the presence of uncertainties and external disturbances. This new control scheme has a dual layer structure. The first layer drives the robot manipulator system reaches the global nonlinear sliding surface in finite time, and the second layer tackles the values of the two control gains overestimation problem. Moreover, compared with the traditional super-twisting with time delay estimation algorithm, the proposed controller can realize not only set-point tracking but also dynamic tracking, which is very widely used in practice. The stability of the closed–loop system and the finite time convergence are analyzed using Lyapunov techniques. The effectiveness of the proposed method is demonstrated by simulations and experimental studies. [ABSTRACT FROM AUTHOR]

This article proposes a computationally efficient adaptive robust control scheme for a quad-rotor with cable-suspended payloads. Motion of payload introduces unknown disturbances that affect the performance of the quad-rotor controlled with conventional schemes, thus novel adaptive robust controllers with both integer- and fractional-order dynamics are proposed for the trajectory tracking of quad-rotor with cable-suspended payload. The disturbances acting on quad-rotor due to the payload motion are estimated by utilizing adaptive laws derived from integer- and fractional-order Lyapunov functions. The stability of the proposed control systems is guaranteed using integer- and fractional-order Lyapunov theorems. Overall, three variants of the control schemes, namely adaptive fractional-order sliding mode (AFSMC), adaptive sliding mode (ASMC), and classical Sliding mode controllers (SMC)s) are tested using processor in the loop experiments, and based on the two performance indicators, namely robustness and computational resource utilization, the best control scheme is evaluated. From the results presented, it is verified that ASMC scheme exhibits comparable robustness as of SMC and AFSMC, while it utilizes less sources as compared to AFSMC. [ABSTRACT FROM AUTHOR]

This article deals with a novel adaptive robust controller for uncertain nonlinear systems relying on a proportional–integral–derivative-type nonsingular fast terminal sliding mode control. In this nonsingular proportional–integral–derivative-type terminal sliding mode controller nonsingular fast terminal sliding mode control, the nonsingular fast terminal sliding mode control sliding surface is modified with integral to match with the proportional–integral–derivative-type structure to obtain the essential attributes, namely, quick transient response, finite-time convergence, negligible steady-state error, and chattering cancellation. Furthermore, a novel rapid reaching law is also suggested with dynamic proof for providing the robustness during transient phase. The controller stability and convergence is mathematically analyzed using the Lyapunov theory. The overall control structure is simulated on MATLAB® software and tested for trajectory tracking of a two-degree-of-freedom revolute–prismatic joint industrial robotic manipulator. The rigorous test results show the performance efficacy of the innovative controller. [ABSTRACT FROM AUTHOR]

In order to improve the ride comfort of the driver, a higher-order Sliding Mode Controller was proposed in this study for a semiactive magnetorheological (MR) suspension system. The work is mainly focused on improving the ride comfort of the driver with simultaneous improvement in road holding capability of the vehicle and to study the effects of using Super Twisting Sliding Mode Controller (STSMC) in a quarter car with driver seat model. The modified Bouc-Wen model was simulated using MATLAB/Simulink software and the STSMC was adopted to control the voltage variation in MR damper using Continuous State Control (CSC) algorithm. The controller and the suspension system parameters were analysed in time domain with random road inputs. Fast Fourier Transform (FFT) analysis was also carried out to show the effectiveness of the controller towards improving the driver seat comfort. The STSMC-controlled MR damper was used as a primary suspension and the effectiveness of its controllability was compared with passive suspension system. The uncontrolled MR suspension system was also analysed in order to verify the fail-proof advantage of the MR damper. From the results, it was found that the ride comfort was extremely improved when STSMC controller was used than when the uncontrolled MR and passive suspension systems were employed. The uncertainty of the STSMC was verified for different passenger masses and it achieved a robust control over load variation. The selected STSMC was validated with the first-order Sliding Mode Controller and the results were discussed in terms of time-domain analysis. [ABSTRACT FROM AUTHOR]

This paper presents analysis of number of steps required for the consensus in a leader-following discrete multi-agent system (DMAS) with discrete-time sliding mode protocols designed by Gao's reaching law and power rate reaching laws. The DMAS is configured for communication with a fixed, undirected graph topology having one leader and other agents as followers. The sufficient condition for global stability is established using the Lyapunov function in both the cases. The efficacy of both the protocols is compared in simulation for number of steps required for the consensus of a homogeneous multiple two degree of freedom helicopter systems where the pitch angle and its velocity and yaw angle and its velocity are used for consensus. The simulation results reveal that the consensus performance due to protocol with power rate reaching law outperforms the protocol with Gao's reaching law. [ABSTRACT FROM AUTHOR]

High-speed supercavitating vehicles are surrounded by a huge cavity of gas and only a small portion of the nose and the tail of the vehicle are in contact with the water which leads to a considerable reduction in skin friction drag and reaching very high speeds. High-speed supercavitating vehicles are usually controlled by the cavitator at the nose which controls the pitch and depth of the vehicle and the control surfaces or fins which control the roll and heading angle of the vehicle using the bank-to-turn maneuvering method. However, control surfaces have disadvantages such as the high drag force and ineffectiveness due to the supercavity. Therefore, the purpose of the present study is to eliminate the fins from high-speed supercavitating vehicles and propose a new bank-to-turn heading control of this novel finless high-speed supercavitating vehicle which is composed of the cavitator at the nose and an oscillating pendulum as the internal actuator. Sliding mode control as a robust method is used for the six-degrees-of-freedom model of this finless high-speed vehicle against exposed disturbances. Some design criteria for the design of the internal pendulum in this finless supercavitating vehicle are presented for the damping coefficient, pendulum mass, and radius. [ABSTRACT FROM AUTHOR]

This study uses a comprehensive control approach to deal with the trajectory tracking problem of a two-flexible-link manipulator subjected to model uncertainties. Because the control inputs of two-flexible-link manipulators are less than their state variables, the proposed controller should be able to tackle the stated challenge. Practically speaking, there is only a single control signal for each joint, which can be used to suppress link deflections and control joint trajectories. To achieve this objective, a novel optimal robust control scheme, with an updated gain under the adaptive law, has been developed in this work for the first time. In this regard, a nonsingular terminal sliding mode control approach is used as the robust controller and a control Lyapunov function is used as the optimal control law, to benefit from the advantages of both methods. To systematically deal with system uncertainties, an adaptive law is used to update the gain of nonsingular terminal sliding mode control. The advantage of this approach over the existing methods is that it not only can robustly and stably control an uncertain nonlinear system against external disturbances but also can optimally solve a quadratic cost function (e.g. minimization of control effort). The Lyapunov stability theory has been applied to verify the stability of the proposed approach. Moreover, to show the superiority of this method, the computer simulation results of the proposed method have been compared with those of an adaptive sliding mode control scheme. This comparison shows that the presented approach is capable of optimizing the control inputs while achieving the stability of the examined two-flexible-link manipulator in the presence of model uncertainties and external disturbances. [ABSTRACT FROM AUTHOR]

A model reference adaptive sliding mode control for the position control of the permanent magnet synchronous motor is developed in this article. First of all, a fast sliding surface is designed to achieve faster convergence than the ordinary sliding mode control. Then, the adaptive laws are developed to make the control parameters, especially the switching gain, updated online. Therefore, the chattering can be reduced effectively and the disturbance can be rejected well. Finally, a reference model which produces an exponential decay curve is applied for the position error to follow. Thus, not only fast error convergence can be guaranteed, but also the dynamic process of the system response can be controlled easily by modifying the decay rate of the reference model. The proposed model reference adaptive sliding mode control scheme combines the advantages of the sliding mode control and the model reference adaptive control. Simulation and experimental results reveal that faster and more accurate performance with smoother control signal and better robustness is obtained compared with other methods. Also, the model reference adaptive sliding mode control method can maintain good performance when the system inertia or the position reference varies in a wide range. [ABSTRACT FROM AUTHOR]

To alleviate subsynchronous resonance in doubly fed induction generator--based wind farm, this study devises a robust nonlinear control for a rotor-side converter based on a fractional-order sliding mode controller. The designed fractionalorder sliding mode controller is able to realize finite-time control and reduce the control time compared with terminal sliding mode control, which contributes to the faster mitigation of subsynchronous resonance. Impedance-based analysis and transient simulation are carried out to evaluate the performance of the fractional-order sliding mode controller compared with terminal sliding mode control and subsynchronous damping control. Simulation results verify that the fractional-order sliding mode controller is able to damp SSR within shorter time and effectively reduce the fluctuation range of a system's transient responses under various working conditions of compensation degrees and wind speeds. Furthermore, the fractional-order sliding mode controller enhances the robustness under external disturbance and parametric uncertainty, ensuring safe operation of the practical wind farm. [ABSTRACT FROM AUTHOR]

The article applies the robust generalized dynamic inversion control methodology to the problem of stabilizing upright equilibrium configuration of the under-actuated rotary inverted pendulum system while tracking rotary motion of the actuated arm. The proposed robust generalized dynamic inversion control law comprised equivalent and switching control parts. The equivalent control part works to enforce a virtual constraint dynamics of the controlled state variables by means of Moore– Penrose generalized inversion. The switching control part is of the sliding mode type, and it improves robustness against unmodeled system dynamics, parametric uncertainties, and external disturbances. The robust generalized dynamic inversion control design on the linearized model of the under-actuated rotary inverted pendulum is shown to guarantee semi-global asymptotically stable tracking performance. Numerous computer simulations and experiments are conducted on the Quanser rotary inverted pendulum system, revealing that the proposed algorithm has better convergence and tracking performance than conventional sliding mode and generalized dynamic inversion control strategies when both are applied separately. [ABSTRACT FROM AUTHOR]

The aim of this article was to determine control strategy for balance control of rotary double inverted pendulum system, which is highly nonlinear and unstable under-actuated system. The complexities involved in rotary double inverted pendulum dynamics make this system a useful engineering test bed to test and verify newly designed controllers. In this article, a constraint-based control approach titled robust generalized dynamic inversion is designed and implemented for robust stabilization of rotary double inverted pendulum system. The robust generalized dynamic inversion control is designed in two stages; in the first stage, constraint differential equations of the controlled state variables are prescribed, which encompasses the control objectives. To enforce the constraint dynamics, the equivalent control is realized by means of Moore–Penrose generalized inversion. To enhance robustness, the switching (discontinuous) control is introduced in second stage, whose design principle is based on classical sliding mode control theory. Finally, the controllers obtained in two stages are augmented to form the resultant robust generalized dynamic inversion control law. The proposed controller ensures robustness along with improved time domain performance regardless of system nonlinearities, uncertainties, and unwanted disturbances. The stability analysis is presented for guaranteeing semi-global asymptotically stable closed loop performance via Lyapunov stability criteria. Numerical simulation and experimental investigations are carried out along with comparative analysis, to demonstrate the effectiveness of robust generalized dynamic inversion control algorithm over other conventional control methods. [ABSTRACT FROM AUTHOR]

A high-speed supercavitating vehicle is a future underwater vehicle which exploits the supercavitating propulsion technology providing a promising way to increase the vehicle speed. Robust control challenges include complex vehicle maneuvering dynamics caused by factors such as undesired switching, delayed state dependency, and nonlinearities. As effective and applicable controllers, a novel fractional-order sliding mode controller is proposed to robustly control the uncertain high-speed supercavitating vehicle system against external disturbances. The control scheme uses sliding mode control and can produce better control actions than conventional the integer-order counterpart. In this algorithm, the fractional calculus is applied to calculate the noninteger integral or derivative in the sliding mode control algorithm, providing new capabilities for uncertain high-speed supercavitating vehicle control in seeking to operate the underwater vehicle better. The performance of the proposed fractional-order sliding mode controller has been proven through analytic simulation results, which show fast responses with smooth control actions and the ability to deal with nonlinear planing force and external disturbance. One of the interesting features of the fractional-order control system is the time convergence rate of the sliding variable vector, which is greatly improved compared with the integer-order sliding mode control. Finally, the robust control system with a novel fractional-order sliding mode controller algorithm, using high flexibility of controlling undersea vehicles, can provide superior dynamical performance with stability compared with its integer-order counterpart against system uncertainties and disturbances. [ABSTRACT FROM AUTHOR]

Piezoelectric stacks (PS) are wildly used as actuator mechanism for precise instrument in practical engineering. Nevertheless, hysteretic effect that is carried by the piezoelectric materials can degrade the control performance dramatically. For the purpose of improving the control precision, the problem of hysteresis compensation control for PS system is investigated in this paper. First, in order to compensate the hysteretic effect, two kinds of observers are proposed. The design of the observers has considered external disturbance and the creep effect in PS system. By utilizing Lyapunov function and linear matrix inequalities (LMI) technique, the observers can asymptotically estimate the hysteretic output with H ∞ performance. Second, a hysteresis-compensation based back-stepping controller is established. The design of the controller has considered the observation error, and it has a certain robustness. At last, numerical and experimental simulations are carried out to verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Proportional–integral–derivative is one of the most applicable control methods in industry. Although it is simple and effective in most cases, it does not provide robustness against disturbances and may not perform well in cases with uncertainties and nonlinearities. In this study, a fuzzy adaptive robust proportional–integral–derivative controller is used to control a nonlinear 4 degree-of-freedom quadrotor. An adaptation mechanism is submitted to the proportional–integral–derivative controller for updating the proportional, derivative, and integral gains of proportional–integral–derivative control. Furthermore, a sliding surface is generated and submitted to the adaptation mechanism for better regulation of proportional–integral–derivative gains. Afterward, a fuzzy engine is applied to regulate the sliding surface for better performance of the adaptive proportional–integral–derivative when there are disturbance and uncertainties. The multi-objective grasshopper optimization algorithm is implemented on the control system for the regulation of the control system parameters to minimize the error and control effort of the proposed hybrid control system. Finally, the obtained results are presented for a nonlinear 4 degree-of-freedom multi-purpose (for marine, ground, and aerial maneuvers) quadrotor system designed and built in Sirjan University of Technology, Sirjan, Iran, to assure the effectiveness of this technique. [ABSTRACT FROM AUTHOR]

To date, a novel class of smart materials, known as ionic polymer–metal composites, have been intensively studied because of their huge potential applications in robotics, microelectromechanical systems, biomedical devices, and artificial muscles. The position tracking control of the ionic polymer–metal composite actuators is one of the challenging tasks due to the highly nonlinear, uncertain, and unmodeled dynamics. These inaccurate and unmodeled dynamics cause the unwanted disturbances which reduce the control performance. Therefore, a robust feedback controller for position tracking of the ionic polymer–metal composite actuators is necessary. To address this issue, this article presents a super-twisting sliding mode controller combined with integral-chain differentiator as state observer. The main advantage of the proposed method is its potential to estimate the states of the system continuously. As a result, the controller not only eliminates the parameter uncertainties and external disturbance but also it can overcome the chattering problem. The results confirm the feasibility and efficiency of the proposed method both in simulation and experiment. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel problem in control systems area involving the control of a magnetic needle in the presence of an external magnetic field. A magnetic needle when restricted to rotate about a single axis in an external magnetic field, by pivoting its center will produce a stable and unstable equilibrium. Here, we present the detailed mathematical modeling of the 1-D inverted magnetic needle system and its control in the unstable equilibrium point. We use sliding mode controller (SMC) to achieve the control objectives. The simulation results are validated with the experimental results. For achieving a close match, we consider sensor and actuator nonlinearities. Further, its robust performance is compared with proportional-derivative (PD), proportional-integral-derivative (PID) controllers in the presence of system parameter uncertainty, disturbance, and sensor delay. We also study the effect of change in SMC parameters, proportional and derivative gains on the system performance. It is to be noted that the proposed experimental setup can be extended to a much more general and complex system, both in modeling as well as control design leading to a new benchmark problem in the control system. [ABSTRACT FROM AUTHOR]

Position control of piezoelectric actuators is greatly affected by nonlinearities such as hysteresis and creep. Therefore, precise position sensors must be utilized which have high cost and complicated structures in micro scales. Charge-based position estimation is an alternative method which resorts to piezoelectric linear charge-position property to estimate the actuator position, but in low-impedance actuators, there is a charge leakage caused by actuator internal resistance which deteriorates the position estimation and closed-loop control performance. In this article, the leakage is considered as a sensor fault. Therefore, a combination of charge measurement method and an appropriate observer is designed to detect and isolate the mentioned fault and estimate the actuator position properly. In addition, an adaptive sliding mode control procedure is proposed for trajectory tracking in the presence of estimated states. The required analysis is carried out to guarantee the closed-loop stability. Finally, experimental results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Aircraft loss of control is an acute phenomenon that has far reaching consequences irrespective of the class and type of aircraft. In order to ensure safe aircraft operation, loss of control problem has to be addressed efficaciously. This paper investigates various factors that trigger the onset of loss of control events and recovery solutions for the same. Rather than relying on statistics alone, this paper concentrates on simulation-based investigation towards various loss of control scenarios and subsequent recovery schemes. Through bifurcation analysis, distinct abnormal dynamics have been identified and their contributions in driving the aircraft towards loss of control have been examined. The effect of steady wind on aircraft dynamics and the evolution of chaotic dynamics as a precursor to loss of control are presented. Aircraft loss of control under actuator impairment conditions are also probed into. Various loss of control recovery schemes have been investigated and a robust loss of control recovery solution based on sliding mode control is also presented. [ABSTRACT FROM AUTHOR]

The control problem of underactuated systems with external perturbations is investigating in this paper. Using the super-twisting-based global sliding mode control (GSMC) method, an original control law is proposed to guarantee removal of the reaching mode and obtain the robustness and exponential stability of the underactuated systems. Via the offered scheme, a robust control law is designed so that the state trajectories of the underactuated systems are convergent to the global sliding surface in an exponential manner. Moreover, this article develops an adaptive super-twisting algorithm for these systems. The adaptive-tuning controller eliminates the need of the knowledge about upper bound of the exterior disturbance. The discontinuous sign function appears in the controller derivative; as a result, the actual control signal reached after integration is continuous and free of chattering. Demonstrative simulations on a cart–inverted pendulum system as well as an experimental study are presented to show the effectiveness and applicability of the proposed technique. [ABSTRACT FROM AUTHOR]

This paper puts forward a switching rule stabilization design of the robust integral sliding mode control for uncertain switched systems. A kind of common robust integral sliding mode (CRISM) is firstly designed and the system matrices of subsystems under the sliding mode comprise a robust stable matrix set. The stability of the switched system (SS) under the sliding mode is then analyzed by multiple Lyapunov functions (MLF) method. Based on the presented design of CRISM, a sliding mode controller is devised so that the sliding mode can be reached. Finally, the correctness of the proposed method is verified through results of numerical and application simulations. [ABSTRACT FROM AUTHOR]

This paper presents a robust dynamic sliding mode control for electrically driven robot manipulators. The control law computes the motor voltages based on the voltage control strategy. Uncertainties are estimated using the Fourier series expansion and the truncation error is compensated. The Fourier coefficients are tuned based on the stability analysis. The contribution of this paper is designing a robust controller using a novel adaptive Fourier series expansion. In comparison with previous related works based on the Fourier series expansion, the superiority of this paper is presenting an adaptation law for the fundamental frequency of the Fourier series expansion and, consequently, relaxing the need for trial and error procedure in its tuning. The case study is a SCARA (Selective Compliant Articulated Robot for Assembly) robot manipulator actuated by permanent magnet DC electrical motors. The influence of uncertainty estimation based on the Fourier series expansion instead of using sign function is studied. Simulation results verify robust and satisfactory performance of the proposed controller. [ABSTRACT FROM AUTHOR]

Large-scale morphing aircraft can adaptively alter configuration according to the different flight conditions or a variety of missions to ensure the optimal aerodynamic performance. However, this will certainly put forward a higher request to modeling method and controller performance. In this paper, we propose an adaptive sliding mode control strategy with bounded L2 gain performance based on linear-parameter-varying methodology for the robust control of a morphing aircraft with variable span and variable sweep angle. Using the Kane method, the longitudinal dynamic model of the morphing aircraft is derived. Moreover, the linearized linear-parameter-varying model of the aircraft in the wing varying process is formulated for controller synthesis. The adaptive sliding mode control synthesis for this uncertain linear-parameter-varying system consists of two steps. Firstly, based on the full block S-procedure, the sufficient condition in form of linear matrix inequality constrains is derived for the existence of a reduced-order sliding mode dynamics. Then, the synthesized adaptive sliding mode control is proved to drive the linear-parameter-varying system trajectories onto the predefined switching surface without the information of upper bound of external disturbances. The performance and robustness of the proposed controller are verified by the numerical results. [ABSTRACT FROM AUTHOR]

This paper deals with a nonlinear control algorithm based on a sliding mode theory to reach the maximum power point tracking of a variable-speed wind energy conversion system. The proposed method allows us to combine the sliding mode and fractional-order theory. The fractional-order component of the control law is introduced by a sliding surface. In order to validate this controller, fractional and integer sliding modes are developed. The proposed fractional-order sliding mode control law is tested in a Simulink/Matlab environment. The simulation results show the effectiveness of the proposed scheme, suppression of the chattering phenomenon and robustness of the proposed controller compared to the integer sliding mode control law. [ABSTRACT FROM AUTHOR]

This paper studies the finite time spacecraft attitude tracking control problem, while considering modeling uncertainty, external disturbances and control input saturation. A novel integral terminal sliding mode surface (ITSMS) is designed by combining the fast terminal sliding mode surface (FTSMS) with a low pass filter to achieve a fast finite time convergence rate for the control system, without input singularity. An auxiliary signal is used to compensate for the effects of actuator saturation. The basic controller is first formulated based on the ITSMS, fast-TSM-type reaching law and auxiliary system, in the presence of an external disturbance and input saturation. Then, an adaptive control procedure is introduced, which simultaneously handles modeling uncertainty and external disturbance, thereby creating an adaptive attitude tracking controller. The proposed controller provides a fast finite time convergence rate for the control system, based on the newly designed ITSMS, while simultaneously compensating for modeling uncertainty, external disturbances and input saturation, without restricting the parameter selection process nor requiring repeated differentiation of nonlinear functions. Finally, digital simulation results are presented and demonstrate the effectiveness of the proposed controllers. [ABSTRACT FROM AUTHOR]

This paper investigates an adaptive observer-based consensus control strategy for general nonlinear multi-agent systems (MASs). The distributed control of leader–follower MASs is studied in the presence of unknown parts in the dynamical equations of the followers which may be due to model simplification, parameter uncertainties and/or external disturbances. In order to decrease the conservatism of robust analysis, the upper bound of unknown terms are considered as unknown positive constants and are obtained through the adaptation laws. Additionally, it is assumed that all the agents' states are not directly measurable and nonlinear distributed observers are designed. Furthermore, the robust consensus is achieved via distributed adaptive observer-based sliding mode controllers. In this regard, a theorem is given and it is proved that the consensus error converges to zero. Finally, computer simulations are performed and the theoretical results are verified. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical modelling of a wireless power transfer system with a buck circuit is presented. Based on this modelling, an operator-based robust nonlinear control design scheme using sliding mode technology is proposed to consider the uncertain coupling coefficient, which results from an inaccurate distance between the transmit coil and receive coil in the wireless power transfer system. The proposed control design scheme has two advantages. First, in order to tackle the uncertain coupling coefficient, operator-based right coprime factorization is applied to guarantee robust stability of the nonlinear system. Sliding mode technology is also adopted to guarantee the tracking performance of the nonlinear system. Finally, simulations and experiments of the wireless power transfer system are tested using the proposed control design scheme. Results of both the simulations and experiments show the effectiveness of the proposed control design scheme. [ABSTRACT FROM AUTHOR]

This work presents a novel adaptive fuzzy controller based on the inversely fuzzified values associated with the H infinity technique and it is applied to vibration control of a vehicle seat suspension system installed with a magneto-rheological damper. In this work, the fuzzified values are embedded into the Riccati-like equation to achieve enhanced robustness of control function and the sliding surface function of sliding mode control is used for designing the main control function. The synthetic function of controller includes a model of online interval type 2 fuzzy neural network system and a fast calculation for clustering. The combination between the fuzzy model system and the proposed control algorithm can shorten the calculation time and improve control responses of the system in the presence of disturbances and uncertainties. After formulating the controller, the effectiveness is validated through both simulation and experiment. In computer simulation, three different road profiles of random bump, regular bump, and random step wave are adopted to emulate severe external disturbances. It is shown from the simulation that both displacement and acceleration of the driver are remarkably well controlled under three different road conditions. This advantage is also validated in the experimental work. It is demonstrated that vibration control performances under random step wave road are much better than the comparative adaptive fuzzy controller. It is identified from the results that the use of the inversely fuzzified values plays a major role to enhance the robustness and hence better control responses in the presence of the disturbances. [ABSTRACT FROM AUTHOR]

Recently, a great deal of effort has been devoted to the design of robust control techniques that compensate for lumped disturbances in mechanical robots and general electromechanical systems through disturbance observers. In this paper, assuming the Hamiltonian structure of Euler–Lagrange systems subject to a wider class of disturbances, and by exploiting some essential properties of fractional-order integro-differential operators, such as heritage and memory, a disturbance observer that is theoretically exact is proposed based on continuous fractional sliding modes, where exactness is understood in the sense of equality, in contrast to simple equivalence. The novelty of the proposal arises from the fact that the continuous fractional sliding-mode disturbance observer is exact, assuring finite-time disturbance estimation, in contrast with a classical integer-order sliding motion that is equivalent. Consequently, there arises a disturbance observer in finite time, including exact observation of continuous but not necessarily differentiable Hölder disturbances, as well as a clear compromise between regularity and robustness, which stands for a quite important issue overlooked in the conventional integer-order case. Representative simulations are discussed to highlight the reliability of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a fast and accurate robust path-following control approach for a fully actuated marine surface vessel in the presence of external disturbances. The path following is realized by simultaneously converging the yaw rate and sway velocity to their respective desired values, which are generated according to the path-following demand. An improved combined control strategy using an integral terminal sliding mode (ITSM) based composite nonlinear feedback (CNF) technique considering the external disturbances, time-varying tracking reference, input saturations and transient performance improvement is proposed in this study. The proposed ITSM-CNF combines the advantages of the CNF control in improving the transient performance and of the ITSM control in guaranteeing good robustness and finite-time convergence. A continuous and smooth sliding mode controller, based on an integral nonsingular terminal sliding surface, is added to the CNF controller to eliminate chattering. The overall stability of the closed-loop system is strictly proved based on the Lyapunov method. Simulations verify the effectiveness of the ITSM-CNF controller in improving the transient path-following performance, inhibiting overshoots, eliminating steady-state errors, rejecting external disturbances and removing chattering effects, considering input saturations, varying path curvature and finite-time convergence. [ABSTRACT FROM AUTHOR]

An immense body of research has focused on nonlinear vibration energy harvesting systems mainly because of the inherent narrow bandwidth of their linear counterparts. However, nonlinear systems driven by harmonic excitation often exhibit coexisting periodic or chaotic attractors. For effective energy harvesting, it is always desired to operate on the high-energy periodic orbits; therefore, it is crucial for the harvester to move to the desired attractor once the system is trapped in any other coexisting attractor. Here we propose a robust and adaptive sliding mode controller to move the nonlinear harvester to any desired attractor by a short entrainment on the desired attractor. The proposed controller is robust to disturbances and unmodeled dynamics and adaptive to the system parameters. The results show that the controller can successfully move the harvester to the desired attractor, even when the parameters are unknown, in a reasonable period of time, in less than 30 cycles of the excitation force. [ABSTRACT FROM AUTHOR]