جستجوی مقالات مرتبط با کلیدواژه « chattering » در نشریات گروه « مکانیک »

In this paper, a robust adaptive hybrid control approach based on a combination of super-twisting and non-singular terminal sliding mode control (STNSMC) approaches for vibration and attitude control of a flexible spacecraft with fully coupled dynamic is developed. The proposed adaptation law eliminates the need for bounds knowledge of external disturbances and uncertainties. Then an ST-based NSMC generates a continuous control signal to reject the Chattering phenomenon, the non-singular terminal switching control law with the ability to generate continuous control commands to eliminate the chattering phenomenon. Moreover, finite-time convergence is achieved, and the singularity problem has been avoided. The overall stability of the system has been demonstrated using the Lyapunov theory. One of the essential features of the proposed control algorithm is to prevent overestimation of control gains and faster convergence rates comparing to conventional ST and non-singular terminal SMC approaches. The simulations in the form of a comparative study for large-angle maneuver reveal the advantage of the proposed approach.

This paper proposes robust hybrid sliding mode control with a time-varying sliding surface and active vibration control for a flexible spacecraft during attitude maneuver. The fully coupled nonlinear dynamic model of the rigid-flexible system includes the three-axis rotation of the rigid body in interaction with the transverse deformation of the smart PZT-mounted flexible appendages. The smooth control signal includes a hyperbolic tangent and a sharpness function to reduce the effects of chattering and high-frequency interactions of the flexible parts and external disturbances in interaction with the rigid body and controller. The structure of the variable sliding surface with time has made it possible to adjust the effect of attitude parameters (quaternions and angular velocities) on the control performance. Also, the residual vibrations during and after the reaching phase are suppressed using a robust active vibration control algorithm. The simulations in the form of a comparative study show the performance and superiority of the proposed approach compared to conventional sliding mode control approaches for systems with structural flexibility in the presence of external perturbations and uncertainties.

In this paper, a robust hybrid control approach for vibration and attitude control of a flexible rotating structure as a fully coupled rigid-flexible system is investigated. Two control algorithms as a combination of second-order super twisting-nonsingular terminal sliding mode control (SMC) considering external disturbances and system uncertainties are developed. The nonlinear dynamic equation of the motion is derived via the Lagrangian approach and the finite element method. The non-singular terminal SMC leads to high accuracy in target tracking, and convergence and the super twisting part significantly reduce the chattering phenomenon. The overall stability of the system has been guaranteed using the Lyapunov theory. The simulations in the form of a comparative study (with agility, accuracy, and high convergence criteria) show the feasibility of performing large-angle maneuvers and significantly reducing the vibrations caused by the flexible parts. Moreover, by controlling the chattering phenomenon, the system performance regarding high-frequency modes excitation is increased.

Quadrotor is one type of unmanned aerial vehicles which it's maneuverability and simple structure has extracted fascination. In spite of this, its highly non-linear behavior can be regarded as one of its disadvantages. The dynamic model of quadrotor is nonlinear with many sources of uncertainty, so in the controller design process, robust control methods such as sliding mode, are required in order to achieve good tracking and stabilization results. In contrast to the high capabilities of sliding mode control approach, high frequency switching of the control signal, is considered as one of its disadvantages, which can be reduced by using higher order techniques. In this paper the behavior of the both first order and second order sliding mode controllers in, trajectory tracking of the position and the yaw angle to their desired values and stabilization of the roll and pitch angles of the quadrotor, under high uncertain conditions, are investigated. The second order sliding mode control was designed based on super twisting algorithm. Considering high parametric uncertainty in quadrotor data, the comparison between the results of the two methods, shows the good performance of the second order sliding mode control, in terms of tracking, stabilization and chattering reduction.

In this paper, optimal integral sliding mode controller with fractional derivative for ¼ active suspension vehicle in order to achievement of safe control and passenger comfort in presence of uncertainty has been designed. Since, hydraulic actuator has nonlinear behavior, controller should be designed robustly. Therefore, sliding mode control as a robust controller is used. In the proposed method, sliding mode controller with fractional integral sliding surface is defined. In order to optimal design, fractional integral sliding surface parameters using particle swarm optimization (PSO) is optimized. Finally accuracy and performance of proposed method is validated by using active and passive method. Simulation results are shown performance of the proposed method in presence of road uncertainty.

An adaptive terminal sliding mode control scheme is presented for Micro-Electro-Mechanical Systems (MEMS) vibrational gyroscope system in this paper. In this approach the dynamics of the vibrational gyroscope system is eliminated by using inverse dynamic method to reduce the bounds of existing uncertainties. the designed terminal sliding mode control vector is provided a global asymptotic stability for close loop system with uncertainties. In this paper, an adaptive estimator is proposed to prevent the occurrence of a chattering problem at the control input, which has only one law. The mathematical proof shows that the closed loop system, with proposed adaptive terminal sliding mode controller with uncertainties has a global asymptotic stability. Four-phase simulations are implemented on the MEMS vibrational gyroscope system to demonstrate the performance of the controller and compare it with other similar controllers. The simulation results show that the proposed adaptive terminal sliding mode controller has desired performance.

Sliding mode control, due to its great robustness, is very effective approach for underwater vehicles. Due to complexity of underwater environment and existence of disturbance, robust controllers such as sliding mode control have appropriate results in experimental tests. In this paper, sliding mode control has been used for depth channel and steering channel. It has been used for linear and nonlinear systems with parametric uncertainty and sensor noise. Kalman filter observer has been applied to estimate the values of state variables of the underwater vehicle dynamic system that is excited by stochastic disturbances and stochastic measurement noise. Simulation results show that the proposed method is effective in control of depth and steering of the AUV and show that this method can obtain high precision tracking control performance.

In this paper, a fuzzy sliding mode controller is presented for controlling a class of underactuated systems. In order to present the proposed method, at first, the sliding mode method for a single input-single output system is expressed. In the following, based on this design method, a sliding mode controller for a class of single input-multi output systems is presented. The mathematical proof shows that the closed loop system, in the presence of structured and un-structured uncertainties, has global asymptotic stability. In the proposed control due to the use of the sign function in the control input, the incidence of chattering is inevitable. For this reason, a fuzzy system is designed and added to the sliding mode controller. The proposed fuzzy sliding mode control eliminates existing problems and its design is done in such a way as to ensure the global asymptotic stability of the closed loop system. Finally, to demonstrate the proposed control performance, three-stage simulations are implemented on the inverse pendulum system. Simulation results show the performance of the proposed control.

Quadrotors are types of Unmanned Aerial Vehicles (UAVs) which have unique features compared to conventional aircrafts because of its vertical take-off and landing capability, flying in small areas and its high maneuverability. Also the relatively simple, economical and easy flight system of quadrotors, makes it to widely used as a good platform for development, implementation and testing a variety of control methods. One of the robust control methods is sliding mode control. In spite of the high capabilities of this approach, it has a main problem which is high frequency switching of the control signal witch is known the chattering phenomenon. In the past several decades, fractional order differential equations have been implemented in engineering application field, including controllers design and provided the possibility of using controllers for improving the performance of system. In this paper, a fractional order sliding surface has been employed for designing sliding mode control rule for quadrotors. The main objective of this study is to improve the performance and reduce the chattering phenomenon in sliding mode method. In this regard, by introducing sliding 〖PD〗^α surface, the control rule is designed in two different modes of 0

In this paper, a robust control law is proposed, based on Lyapunov’s theory and sliding mode control theory, in order to track the angle of attack in nonlinear longitudinal dynamics of a missile. It is assumed that there are unmatched uncertainties in the nonlinear systems. In the proposed algorithm, the controller gains are optimized by Particle Swarm Optimization (PSO) algorithm. For this purpose, a cost function is extracted from the output tracking error. Simulation results show that the proposed algorithm has better performance than conventional Proportional-Integral-Derivative (PID) controller in the presence of unmatched uncertainties.

In this paper, adaptive fuzzy integral sliding mode controller for controlling the position of the mobile robot on wheels in presence of motor’s dynamic, structural and un-structural uncertainties, existing in equations of mobile robot is designed. In the proposed controller, based on kinematic controlling of the back stepping method, the sliding surface dynamic controller the value of integral sliding mode controller is defined by a new method. Furthermore, to overcome undesired chattering phenomena in control input by using the fuzzy logic, a SISO fuzzy approximator is designed in a way to eliminate the chattering phenomena. Then to reduce the tracking error and to prevent, increasing of fuzzy system computational load, the adaptive fuzzy approximator will be presented, to approximate structural and un-structural uncertainties’ bound. Mathematical proof shows that the closed-loop system of kinematic control with adaptive fuzzy integral sliding mode control in the presence of all the uncertainties has global asymptotical stability. To show the performance of proposed controller, a case study of the wheel mobile robot in presence of DC servo motors is performed. Simulation’s results show the desired performance of the proposed controller.

In this paper, a new approach has been presented for dynamic control of active suspension vehicle system subject to the road disturbances. The active suspension system (ASS) which has been considered in this paper is operated by a hydraulic actuator. The input of this hydraulic actuator is a servo valve. In the other word, both mechanical equation of system (related to hydraulic actuator) and its electrical equation (related to servo valve) are considered. Therefore, the equations are complicated and only the input current of servo valve is accessible as the input control signal. The proposed approach is based on dynamic sliding mode control (DSMC).In DSMC chattering is removed due to the integrator which is placed before the input control signal of the plant. However, in DSMC the augmented system (the system plus the integrator) is one dimension bigger than the actual system and then, control of the plant is more complicated. But, its advantage is that the input control signal is obtained from a dynamic system or a low pass filter, while the robust performance (invariance property) of the system is reserved even in the presence of disturbance. Another advantage of proposed approach is that the desired output force of the hydraulic actuator is obtained by the controller.

In this paper, a new procedure for designing the guidance law considering the control loop dynamics is proposed. The nonlinear guidance loop entailing a first order lag as the control loop dynamics is formulated. A new finite time and smooth backstepping sliding mode control scheme is used to guarantee the finite time convergence of relative lateral velocity. Also in the proposed algorithm the chattering is removed and a smooth control signal is produced. Moreover, the target maneuver is considered as an unmatched uncertainty. Then a robust guidance law is designed without requiring the precise measurement or estimation of target acceleration. Simulation results show that the proposed algorithm has better performance as compared to the proportional navigation, augmented PN and the other sliding mode guidance law.

In this paper، guidance laws in the direction and perpendicular to the line-of-sight is designed. The tangential component of missile acceleration is designed for zeroing the LOS rate and the other component is for controlling the closing velocity. In this method، because of using the sliding mode control، the nonlinear equation of motion is used and the acceleration command input is determined considering the target acceleration as an uncertainty. Therefore the guidance laws are robust with respect to target maneuvering and precise measuring or estimating of target acceleration is not required. In these guidance laws there are parameters for adjusting the reaching time to sliding surfaces and for producing smooth command acceleration and removing the chattering phenomenon in control input، continuous approximation method has been applied. Because of using a new sliding condition، the boundary layer is adjust only once and is independent with the designing parameter.