جستجوی مقالات مرتبط با کلیدواژه "feedback linearization" در نشریات گروه "مکانیک"

This paper proposes a guidance law design for trajectory tracking of a leader UAV and formation flight of pursuer UAVs. According to nonlinear kinematics for both problems, the feedback linearization theory has ben used. Therefore, using this theory, the nonlinear problem has been transferred to a linear one and using the linear control theory the control parameters has been determined to achieve the desired performance. In the trajectory tracking problem, assuming a constant velocity leader, a change of the independent variable from the time to the downrange has been performed and the problem is transferred to a single-input single-output control problem, consequently, the controller is designed. In the formation flight problem, assuming pursuers with the bounded controllable velocity, we have a two-input two-output nonlinear system. Supposing no communications between pursuers and the leader, a second order sliding mode observer is utilized to estimate the required states in formation flight controller. Results show that the settling time of trajectory tracking error of the proposed nonlinear guidance law is almost 30% better than the nonlinear trajectory tracking controller based on the proportional navigation guidance law. Also, the designed formation flight has a good performance in controlling the formation flight. Also, the sliding mode observer is able to estimate the leader states even in the presence of noise.

Quadrotor is an underactuated and nonlinear coupled system. in this paper for controlling the dynamic of the system, feedback linearization (FL) method is used to convert the nonlinear model to a simple linear one. Moreover, a combination of fractional order PID (FOPID) with FL is used to improve the tracking ability. Tuning the parameters of NFOPID, because of two more orders of integral and derivation is a complicated task; therefore neural networks (NNs) method is used to cope with this duty. Back propagation (BP) algorithm is used to train the weights of the NNs. Because of the flexibility and online learning of the NNs, the proposed controller can be robust against uncertainties and disturbances. The fractional order operator has infinite dimension and for practical implementation modified Oustaloup's method is used in this paper. and finally the results of the simulations also validate the effectiveness and robustness of the proposed scheme.

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.

This paper concerned with the performance improvement of quad rotor using by variable pitch control system. The methodology was laid out based on dynamic modeling of six degree of freedom motion, trim calculations, linearization, and robust control system design for a candidate variable pitch quad-rotor at hover. Therefore, a comprehensive mathematical model of rotors was derived based on the blade element-momentum theory (BEMT) at low Reynolds number, and then, the engine and propulsion models were appended to form the real quad-rotor as a whole. Two control loops including of an inner loop for attitude control system and the outer loop for motion control applied with the robust control system, is the main structure of control system design. Linear controller and feedback linearization controller was also implemented to cover the stability of the quad rotor and compensation of fixed and variable pitch control mechanisms.. Variable pitch quad rotor helped the user to made bigger quad rotor with the less problem in control system which prepared from gyroscopic effect in fixed pitch quad rotor.

Nowadays, the need of welding industry's to improve weld quality has led to the consideration of robotic welding. The use of articulated industrial robots for welding has many challenges. Because some robots do not have the capability of online error compensating of the seam track. Therefore, in order to remove the welding seam tracking error, the use of an auxiliary mechanism is proposed in this article. This mechanism is a table with 1-degree of freedom (dof), which produces a continuous motion in workpiece under the welding torch. The rotational motion of the motor is transformed into a translational motion of the workpiece by a ball-screw system, where this linear motion compensates the tracking error. Since in the welding process, relative motion accuracy of the workpiece and the welding torch is crucial, proper control of the interface table ensures the weld quality. In this paper, two different methods for controlling the table with 1-dof are studied. In the first method, due to the complexity of friction model of the ball-screw mechanism and the presence of nonlinear terms, this part of the model is considered as an external disturbance, and, then, a PID controller for the linear part is designed. In the second method, known as feedback linearization, a control law is designed for that the tracking error tends to zero by passing time. Throught a comparison between the simulation results, the second control method demonstrates better precision relating the first controller. While the error of PID controller equals to 3 mm and the second controller’s error does not go beyond 0.5 mm. At last, the experimental cell used for the robotic welding is introduced to evaluate the mentioned results.

Using nonlinear control theories is common for the attitude control problem of spacecraft.Feedback linearization theory is a nonlinear control method which tries to transform nonlinear dynamics of system into linear.In this control theory, outputs choice will have a direct impact on the stability of system.In order to control the spacecraft attitude by this method, parameters that describe the spacecraft attitude are considered as outputs.The aim of this study is to investigate the effect of using quaternion parameters as a conventional representation in the kinematic equations compared with modified Rodrigues parameters.According to designed controller and simulation results, it is evident that in maneuvers with zero scalar part of quaternion, the controller efficiency is reduced due to singularity in the calculations.This is while by using modified Rodrigues parameters, singularity does not occur and in this way the controller, in the same maneuvers as the previous method, is faster and more efficient with less effort.

In this paper, dynamic modeling and position control of a nonlinear servo – hydraulic actuator system under variable loads is proposed. In dynamic model of the under studied system, governing equation of valve, leakage and friction is considered. To achieve to the desired performance of the system under variable loads with extend variation amplitude, a one control method is applied which is robust in the presence of the variation. Also, as a nonlinear servo hydraulic actuator system has a nonlinear dynamics and the extracted dynamic model is not accurate to proposed behavior of the system, one controller can be required which is robust against the nonlinearity and uncertainty effects. The controller should be having an appropriate response, more accuracy and stability. Regarding to position control of the nonlinear servo hydraulic actuator system in presence of variable loads, nonlinear controllers are designed using feedback linearization and sliding mode techniques. In addition, in order to show the robustness of proposed controllers, a time varying disturbance and noise are applied in the simulation and results of the simulation are compared with classical PID controller. Controller parameters is optimized using harmony search algorithm and simulation results show the outperforming of sliding mode control in spite of variable loads against feedback linearization technique and PID controllers.

In this paper a nonlinear controller is going to be designed for micro-beam’s deflections under mechanical shock effects. The micro-beam is supposed to undergo mechanical shocks. Mechanical shocks are one of the failure sources and the controller is to considerably suppress shock’s unfavorable effects. Half-Sine, rectangular and triangular pulses are chosen as reference shock signals to represent true complicated shock signals in nature which consist of different harmonics. Two layers of electrodes are placed in both sides of the micro-beam and they are used to actuate the micro-beam by different voltage levels. Upper layer is specifically meant for control purpose. Nonlinear equations governing micro-beam’s deflection dynamics are derived, discretized by Galerkin method to a set of nonlinear duffing type ODE and used to investigate micro-beams response to each shock input signal. Controller design is based on a simple nonlinear model formed by micro-beam’s first mode shape. Proper second order behavior is generated by feedback linearization method as controller logic. Finally controller performance and shock rejecting capability is evaluated by numerical simulations. Controller is shown to be very effective in diminishing shock unfavorable effects and postponing pull-in instability by numerical simulations.

In this paper, dynamics and control of a Tendon-based continuum robot is investigated. The curvature is assumed that constant in each section of continuum robot. Kinematic equation is established on the basis of the Euler-Bernoulli beam. The dynamic model of the continuum robot is derived by using Lagrange method. In this paper, robot control is performed in two parts: firstly, Dynamic model is assumed to be known and position and velocity tracking control has been by using the feedback linearization method, But uncertainties in the dynamic model, are constantly challenged the control of continuum robots. For unknown parametric quantities such as mass coefficients, one way is simply substitutes a fixed estimate for the unknown parametric quantities. In this case tracking error is not equal to zero but it’s bounded. For many applications, we cannot assume that tracking error vector is not equal to zero. In such cases we use adaptive controller. In this paper the total mass of the primary backbone and secondary backbone are uncertain parameters, therefore, a new adaptive controller is presented to estimate those uncertainties while cause to asymptotically stable for tracking error. Simulation results show good performance in velocity and position tracking.

In this paper, modeling and feedback linearization controller for trajectory tracking of a novel six-rotor UAV (Unmanned Aerial Vehicle) is developed. Because of the very simple structure and high maneuverability, quadrotors are one of the most preferred types of UAVs but the main problem of them is their small payload. In the proposed novel model, two coaxial propellers are added to the center of vehicle to improve the ability of lifting heavier payloads, and to excel anti-crosswind capability of quadrotor, while the dynamic and steering principle is preserved. The dynamic model is obtained via Newton Euler approach. Model is under actuated, nonlinear, and has strongly coupled terms. Also, two types of nonlinear controllers are presented. First one is a conventional input-output feedback linearization controller which involves high-order derivative terms and turns out to be quite sensitive to sensor noise as well as modeling uncertainty. Second controller is a feedback linearization based on the hierarchical control strategy that yields easier controller. To compensate actuator’s dynamic and moreover, to avoid complexity of controller, a two-stage algorithm is utilized. The obtained simulation results confirm that the performance of hierarchical controller is more convenient in terms of position tracking and disturbance rejection than conventional controller.

In this paper, modeling and tow type of nonlinear controller for trajectory tracking of a novel five-rotor UAV (Unmanned Aerial Vehicle) is developed. Because of the very simple structure and high maneuverability, quadrotors are one of the most preferred types of UAVs but the main problem of them is their small payload. In the proposed novel model, one propeller is added to the center of vehicle to improve the ability of lifting heavier payloads, and to excel anti-crosswind capability of quadrotor. The dynamic model is obtained via Newton Euler approach. The model is under actuated, nonlinear, and has strongly coupled terms. Also, two types of nonlinear controllers are presented. First one is a conventional input-output feedback linearization controller which involves high-order derivative terms and turns out to be quite sensitive to sensor noise as well as modeling uncertainty. Second controller is a BackStepping controller based on the hierarchical control strategy that yields easier controller. The obtained simulation results confirm that the performance of BackStepping controller is convenient in terms of stability, position tracking and it is robust in presence of disturbance.

In this paper، a novel adaptive fuzzy control design for a four degrees of freedom single-wheel robot including its electric motors is presented. Another novelty of this paper is to derive a novel model for this robot for using voltage control strategy in the control design. The dynamics of motion is described as a nonlinear multivariable system with couplings between inputs and outputs. Similar to an inverse pendulum، the single-wheeled robot is in the instable equilibrium point. In addition، number of actuators of robot are less than the degrees of freedom of robot. The control design becomes so important due to this complexity. Based on the derived model in this research، a novel feedback linearization controller by using torque control strategy is designed. Then، a novel indirect adaptive fuzzy controller in voltage control strategy is designed. The stability is guaranteed in the presence of uncertainties. The stability of equilibrium point is analyzed by direct method of Lyapunov. Simulation results show the effectiveness of controllers to keep the balance and stability of the single-wheel robot.