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Showing 4 results for Nonlinear Control
En Mohammad Javad Khosrowjerdi, En Jafar Taheri Kalani,
Volume 1, Issue 1 (9-2013)
Abstract
In this paper, the trajectory tracking problem for a wheeled mobile robot in the presence of kinematic and dynamic uncertainties is considered. A nonlinear control approach based on lyapunove stability theory is proposed for this problem. Uncertainties are modeled as lumped disturbances and are estimated by a generalized disturbance observer using Linear Matrix Inequalities(LMI). These estimates are used for control laws design for compensating disturbances. Simulation results show the effectiveness of the proposed method in the presence of uncertainties generated by sliding velocity.
Mina Ghahestani, Ahmadreza Vali, Mehdi Siahi,
Volume 8, Issue 2 (3-2022)
Abstract
Electromagnetic suspension technology has been developed in recent years due to advantages such as no contact and reduced friction. Of course, ensuring efficiency in these systems requires precise control of the position of the suspended object. Therefore, electromagnetic suspension is considered as a process by control engineers. The dynamics of electromagnetic suspension systems is nonlinear and also include model and parametric uncertainties such as the weight of the suspended object. In this paper, a finite time nonlinear hybrid method is used to stabilize the electromagnetic suspension system. Proof of finite time stability of the proposed method is performed using Lyapunov theory and a relation for calculating the convergence time depends on the controller gains is presented. To ensure the finite time convergence of the system state and output variables, the backstepping algorithm is used and in each step, the finite-time convergence theory is used. The controller designed in this paper is compared with the backsteping method and the superiority of the proposed method in various simulations is shown.
Ali Abooee,
Volume 9, Issue 1 (9-2022)
Abstract
In this paper, the finite-time path tracking problem for a typical fully-actuated unmanned marine vehicle subject to unknown physical constants, modelling uncertainties, and environmental disturbance forces (generated by sea waves) is studied and discussed. To deal and handle the mentioned tracking problem, a novel hybrid control structure (based on the finite-time adaptive-robust approach) is proposed. First, a comprehensive model is extracted and introduced to describe kinematic and dynamic behaviors of the unmanned marine vehicle. In this model, all physical constants of the unmanned marine vehicle are assumed to be unknown. Also, modelling uncertainties and unknown environmental disturbance forces are considered as a lumped vector term added to the right side of the comprehensive model. To overcome with parametric uncertainties, all terms of the left side of the comprehensive model, which include unknown physical constants, are converted to the parametric linear regression form. Second, by developing the terminal sliding mode control method, defining several types of innovative nonlinear sliding manifolds, and designing adaptation laws, a novel adaptive-robust nonlinear control structure is proposed to exactly steer the unmanned marine vehicle (in the existence of aforementioned unwanted factors) to the desired trajectory within an adjustable finite time. Time responses related to the estimation of unknown physical constants will precisely converge to the fixed values after the finite time which are not identical to the nominal values of physical constants. Third, by utilizing mathematical analysis (based on the Lyapunov stability theorem), it is proven that the proposed hybrid control approach is able to both accomplish the path tracking objective and guarantee the global finite-time stability for the closed-loop unmanned marine vehicle. Moreover, the stability analysis demonstrates that the convergence finite time is the summation of two smaller finite time (called reaching and settling times) and these times could be determined by two novel separate inequalities. Finally, by using MATLAB software, the introduced adaptive-robust nonlinear control approach is simulated onto the Cybership II and simulation results demonstrate that the finite-time path tracking aim is appropriately fulfilled and satisfied.
Dr Ali Abooee, Mr Sajad Moradi, Dr Vahid Abootalebi,
Volume 9, Issue 2 (3-2023)
Abstract
ABSTRACT: In this paper, three different finite-time nonlinear controllers are proposed to steer a robotic surgical needle in prostate tissue subject to parametric and modeling uncertainties. The torque generated by each type of these controllers is injected to the surgical needle’s closed-loop structure and, in consequence, the system’s state variable precisely converges to the desired path in prostate tissue within an adjustable finite time. The mentioned controllers are constructed based on the developed terminal sliding mode control method (as the main approach of robust-nonlinear control) incorporated with the adaptive control technique (for designing adaptation laws and estimation of unknown physical constants). It is worth noting that the basic difference between these controllers is in the definition of their nonlinear sliding manifolds. By utilizing the Lyapunov stability theory and several applicable lemmas, it is mathematically proven that all types of the introduced control approaches are able to accomplish the finite-time steering objective and guarantee the global finite-time stability for the needle-tissue dynamical system. Adaptation laws (existing in the proposed nonlinear controllers) continuously estimate the unknown physical constants and it is demonstrated that time responses of these estimations exactly reach the constants values over the finite time. Finally, by using MATLAB software, three types of the proposed controllers are separately simulated onto a second-order needle-tissue system to illustrate their proper performance.
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