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Abstract-In this article, a new stabilizing mechanism for a two wheel robot is proposed. Such systems, due to inherent ‎instability, require dynamic stabilization. The conventional method for stabilizing these robots is moving the base back ‎and forth, to use its inertia effects. Therefore, such strategies drastically depend on the ground surface, besides the ‎robot is not able to reconfigure its manipulator to do any desired task. These limitations reduce the capability of the ‎robot to manipulate objects, and to perform accurate tasks. In order to omit these restrictions, in the developed ‎mechanism, a reaction wheel is used. The proposed mechanism exploits the inertia moment of reaction wheel to ‎stabilize motion of the robot. Therefore, since there is no interaction between the reaction wheel and the ground surface, ‎by using this mechanism there would be no concern about the surface that the robot moves on that. Also, manipulator ‎of the robot can track the given trajectories, without considering stability limitations. In order to show the performance ‎of proposed mechanism, a verified dynamics model of the robot is used and the control algorithm with various initial ‎conditions is simulated.‎

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In this paper, LQG/LTR controller is designed for attitude control of the geostationary satellite at nominal mode. Usage actuator in this paper is the reaction wheel and control torque is determined by the LQR regulator. Usage sensors in this article are sun and earth sensors and EKF are used for estimation of noisy states. LQR controller signal has good performance, if all system's states are considered in system output feedback. But this method is ideal and does not include model noise and sensors noise. Therefore, LQG and LQG/LTR controllers are designed based on the estimated states, and are compared with LQR controller. Controllers gain coefficients are obtained based on linearization about working point. It caused to robustness and similarity of LQG and LQG/LTR response. The results show that control overshoot of LQR is greater than the others.

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Reaction wheels are angular momentum exchange devices used to stabilize the position of the satellite and maneuvering. This actuator can change the momentum of the satellite to change the attitude of the system. During the process of operation, noise and disturbances arisen from the unbalancing of the wheels lead to inconvenient performance of the reaction wheels. Several works have been presented for active noise cancelation in these devices. But, the practical tools of signal processing such as filter banks and wavelets which used for offline de-noising are samples of very useful noise cancellation methods. If these toolboxes are employed for online de-noising these signal processing approaches are applicable for noisy systems such as reaction wheels. The main challenge of this strategy is delay arisen from the signal processing and this is inevitable. In this paper, a strategy of online wavelet de-noising is designed and proposed for noise cancellation in a reaction wheel. In this regards, for considering the delay compensation the method of Smith predictor is used to lead the delay of the process out of the closed loop control system. The accuracy of this algorithm requires an estimate of the system dynamics and the understanding of the delay system. According to the use of the FIR filter delay can be fully calculated. The recursive least squares used for identification reaction wheel as an estimate of the system.

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In the present study, a new attitude stabilization concept has been investigated for a satellite considering failure in one or more reaction wheels. In this approach control torques could be generated using only one thruster mounted on a two axis gimbal mechanism. In the other word, in the absence of reaction wheel(s), control torques are generated by applying a thruster rotating mechanism which can be turned around two axes by thruster vector. If any failure happened in reaction wheels, gimbal angles mechanisms will be added to the system as input controlling. Controller algorithm based on dynamic and kinematic equations of the satellite’s motion, has been developed in the presence of disturbances. Three-axis stabilization of the attitude in a LEO orbit satellites under disturbances has been executed by applying three reaction wheel actuators to produce torque in each direction. Disturbance torques that are commonly applied to the satellites are gravity gradient, solar radiation pressure and aerodynamics. For training the intelligent neuro-fuzzy controller, PID controller is employed. Numerical simulations show that, the recommend controlled method have acceptable results (in the presence of disturbances) and adding of a thruster actuator to the system as a redundancy, could enhance the space missions reliability and if any fault happened in the operation of reaction wheels, thruster mechanisms come in to control system , accurately, and sustained satellite stability at desirability attitude.

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In this paper, a linear dynamic model for a reaction wheel is identified using experimental analysis. To do this, online input-output data of reaction wheel is sent and received by CAN protocol working with the frequency of one mega bit per second. The experimental hardware consists of reaction wheel, processing board, CAN protocol, and LabVIEW monitoring. Modeling assumes the reaction wheel and its inner control circuit as a black box and takes into account the practical considerations. Initially, behavior of the reaction wheel is examined using test signals for velocity and acceleration as inputs. After that, the test signals are replaced by Chirp and PRBS signals and the output results are saved. According the results obtained in the tests, ARMAX and ARX linear dynamic models are assigned to the motor and different orders of these models are compared with each other to reach the appropriate order of the models. Furthermore, a delay is also incorporated in the model and its proper order is determined by the simulations. Finally, to validate the proposed model, the outputs of the model and plant are compared followed by exerting a new test signal. The results indicate a good agreement between the proposed model and the practical behavior.

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The rotational Equations of motion of spacecraft are generally nonlinear, so use of nonlinear control techniques are helpful in real conditions. Feedback linearization theory is a nonlinear control technique which transforms nonlinear system dynamics into a new form that linear control techniques can be applied. Choosing output functions in input-output linearization which is a specific method of feedback linearization, has a significant effect on internal dynamics stability. In this study the kinematic equations of spacecraft motion are expressed by quaternion parameters, these parameters are selected as output functions. Linear quadratic regulator as a linear optimal control law is used to design a controller for linearized system in feedback linearization control and also to design attitude control of spacecraft separately. By considering the actuator constraints on different control methods that are used here, the EULERINT which is the integral of the Euler angles error about the Euler axis, is evaluated. Then, the power and control effort of the actuators are considered for comparison between controllers. The simulation results show that the amount of EULERINT for feedback linearization method is less among the others. Also study of the power and control effort shows that Feedback linearization method is not only quicker but also more efficient and displays better performance of the actuators.

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