جستجوی مقالات مرتبط با کلیدواژه "مقاوم" در نشریات گروه "مکانیک"

In this article, a robust model predictive controller is designed for maintaining the satellite's low earth orbit in the presence of perturbations and uncertainties. The designed control system makes it possible for the satellite to automatically keep the orbital parameters within the allowed range without intervention of the ground station. For this purpose, Hall effect thrusters, which are among the electric thrusters with small size, have been used, and the output of the controller is implemented by continuously commanding these thrusters instead of the traditional impulsive thrust generation algorithms. Based on this, it is possible to modify all orbital parameters simultaneously. In the presented solution, the gain of the controller is calculated online by solving an optimization problem whose objective is to minimize the orbit maintenance error and also the fuel consumption. Also, the optimization problem based on linear matrix inequalities has been developed to ensure the stability of the closed loop system and to be robust against orbital perturbations and unknown parametric uncertainties. Finally, numerical simulations show the effectiveness of the proposed control scheme and the high efficiency of the closed loop system despite uncertainties and perturbations.

The conventional methods for designing autopilots deal conservatively with uncertainties such that the autopilot should be slowed down to the extent in which the system can maintain its desired performance in the presence of a certain uncertainty. However, there will be no guarantee of good performance in the presence of all uncertainties while the capabilities of the system will not be used properly. In the proposed method, using the extended state observer, the lumped uncertainties along with the system’s states will be estimated, and using feedback linearization approach, along with the nonlinear terms will be removed from the control loop. What remains is a simple linear system that is easier to control. In this method, uncertainties is treated without conservatism and consequently performance is improved in different conditions. Finally, for comparing the results of proposed method with linear autopilot a 1000 times Mont Carlo running with specific condition has been used and is shown that the proposed method is better than the conventional method in performance.

Vibration control of large flexible structures in new dynamic systems has significantly encountered with many challenges. In this area, there are several approaches of vibration control implemented on complicated dynamic systems in which the change of vibrational characteristics with the time of process leads to performance violation. In this paper, regarding the estimation of undesired vibration frequency of a flexible structure, input control of the dynamic system is reconstructed. In this regards, the input of the dynamic system is made to minimize the magnitude of the vibration. This strategy in which the control input is constructed by means of undesired vibration frequencies is similar to use of anti-viruses in medicinal approaches. The proposed control strategy is implemented on yaw channel of a flexible sounding rocket in order to reduce the destructive effects of bending vibration. The system responses show the effects of the vibration on the yaw channel of the system are significantly decreased.

In this paper, robust adaptive control is presented for a class of nonlinear systems in strict feedback form with uncertain time delay. It is assumed that time delay is not known, thus terms having delays must not appear in adaptation and control laws. By using the Lyapunov-Krasovskii functional, terms having time delay are deleted from adaptation and control laws. The adaptive backstepping method is used to design a controller and it is shown that this controller guarantees global uniform asymptotic stability of the system. A controller is robust against uncertain time delay and bounded disturbances, which enter the system. Two simulation results are provided to show the effectiveness of the proposed approach.

In most of the researches which has been conducted until now on the robot manipulator tracking control, it has been presumed which the kinematic of robot manipulator or Jacobian Matrix of robot from the joint space to the task space is quite known. However, none of the physical parameters in robot manipulator equations can be calculated by high accuracy. In addition, when the robot manipulator moves something, uncertainties occur in length, direction and point of contact of end-effector. Hence, uncertainties occur on the kinematic of robot manipulator either, and due to the different functions of the robot manipulator, its kinematic is changed as well. Therefore, ensuring stability of the closed-loop system in the presence of uncertainties in the dynamics and kinematics of robot manipulator is quite challenging. In this paper, for overcoming on these uncertainties, we present our simple robust control for tracking the position of robot manipulator in the presence of uncertainties in the dynamics kinematics and Jacobian Matrix of the robot manipulator. The proving of the stability shows the closed-loop system has Global asymptotic stability. Then, to overcome the practical problems of proposed control, amendments will be provided. The closed loop system with improved control has limited uniform stability. Since in many of the operations has been performed by the robot manipulator, transient error plays an important role. Due to this reason, the modified control structure is a changed in a way which could improve the transient error. Finally, for displaying the function of the final controller, a case study is implemented on a two-link elbow robot. Mathematical proof and simulation results confirm the good performance of the proposed control.