Loading...
Search for:
namvar--m
0.007 seconds
Total 36 records
Observer-free control of satellite attitude using a single vector measurement
, Article IEEE Transactions on Aerospace and Electronic Systems ; Vol. 50, issue. 3 , 2014 , pp. 2070-2081 ; ISSN: 00189251 ; Namvar, M ; Sharif University of Technology
Abstract
The existing methods in attitude control of satellites are based on using the estimate of satellite attitude, which is usually generated by using multiple vector measurements. In this paper we propose an output feedback controller that directly uses a single vector measurement and does not use an attitude estimator. The output feedback gain is computed by solving a generalized Riccati differential equation (GRDE). The existence of a solution to the GRDE depends on a uniform controllability condition
Attitude control of satellites with delay in attitude measurement
, Article 2013 IEEE International Conference on Robotics and Automation, ICRA 2013 ; 2013 , Pages 947-952 ; 10504729 (ISSN); 9781467356411 (ISBN) ; Namvar, M ; Aghili, F ; Sharif University of Technology
2013
Abstract
Time delay in attitude sensors is one of the performance limiting factors in controlling the satellite attitude. In this paper, we investigate attitude control of a fully actuated satellite in presence of constant and known delay in attitude measurement. The proposed controller consists of a matrix gain which is computed by solving a time varying matrix differential equation depending on the time delay. We assume that the moment-of-inertia matrix of the satellite is unknown. The controller guarantees asymptotic convergence of the satellite attitude and angular velocity to their desired values in presence of delay. Finally, a simulation example is presented that illustrates performance of the...
Adaptive compensation of actuator dynamics in manipulators without joint torque measurement
, Article Proceedings of the IEEE Conference on Decision and Contro ; December , 2013 , Pages 2294-2299 ; 01912216 (ISSN) ; 9781467357173 (ISBN) ; Namvar, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2013
Abstract
Neglecting actuator dynamics in control of rigid manipulators can degrade performance and stability of the system. However, consideration of actuator dynamics usually requires measurement of joint torque or armature currents. In this paper, we present an adaptive controller for motion tracking of an n-DOF manipulator without using joint torque measurement. Semi-global convergence of motion and torque tracking errors to zero is proven. We show that the use of non-minimal representation of manipulator dynamics significantly simplifies its linear parametrization. Simulation example shows that avoiding joint torque measurement reduces system sensitivity to sensor failure and noise
Use of PSO in parameter estimation of robot dynamics; part one: No need for parameterization
, Article 2012 16th International Conference on System Theory, Control and Computing, ICSTCC 2012 - Joint Conference Proceedings ; 2012 ; 9786068348483 (ISBN) ; Namvar, M ; Sharif University of Technology
2012
Abstract
Offline procedures for estimating parameters of robot dynamics are practically based on the parameterized inverse dynamic model. In this paper, we present a novel approach to parameter estimation of robot dynamics which removes the necessity of parameterization (i.e. finding the minimum number of parameters from which the dynamics can be calculated through a linear model with respect to these parameters). This offline approach is based on a simple and powerful swarm intelligence tool: the particle swarm optimization (PSO). In this paper, we discuss and validate the method through simulated experiments. In "Part Two" we analyze our method in terms of robustness and compare it to robust...
Robust detection and isolation of failures in satellite attitude sensors and gyro
, Article Robotica ; Volume 30, Issue 7 , 2012 , Pages 1157-1166 ; 02635747 (ISSN) ; Namvar, M ; Sharif University of Technology
2012
Abstract
Summary Reliability of a satellite attitude control system depends on accurate detection of failures in its sensors. This paper presents an observer for robust detection and isolation of a class of failures in satellite attitude sensors. The proposed observer uses measurement of a three-axis gyro together with only one attitude sensor, and generates a residual signal which is sensitive to faults and is simultaneously robust against disturbance and noise. A nonlinear model of satellite kinematics is considered for design of the observer. The structure of the observer is in the form of a delayed continuous-time differential equation ensuring its robustness properties. A realistic simulation is...
Output feedback control of satellite attitude using a single vector measurement
, Article Proceedings of the IEEE Conference on Decision and Control, 10 December 2012 through 13 December 2012, Maui, HI ; 2012 , Pages 490-495 ; 01912216 (ISSN) ; Namvar, M ; Sharif University of Technology
2012
Abstract
The existing methods in attitude control of satellites are based on employing the estimate of satellite attitude which is usually generated by using multiple vector measurements. In this paper we propose an output feedback control law that directly uses a single vector measurement and gyro, and without any need for estimating the satellite attitude. The output feedback gain is computed by solving a generalized Riccati time varying differential equation. We assume the moment-of-inertia matrix of satellite is unknown. The controller guarantees asymptotic convergence of the attitude to its desired value. A realistic simulation is presented where a magnetometer is used to provide the single...
Analysis of gyro noise in non-linear attitude estimation using a single vector measurement
, Article IET Control Theory and Applications ; Volume 6, Issue 14 , 2012 , Pages 2226-2234 ; 17518644 (ISSN) ; Namvar, M ; Sharif University of Technology
IET
2012
Abstract
This study investigates the effect of noisy measurements of the angular rate in a non-linear attitude estimator for satellites. The attitude estimator uses measurement of a single attitude sensor such as Sun, Earth-horizon, star tracker or magnetometer together with a rate gyro, and guarantees exponential convergence of the attitude estimation error to zero under a no-noise condition. In view of a realistic situation where the presence of noise in gyro measurement is not negligible, this study presents stochastic and deterministic upper bounds for the attitude estimation error resulting from noisy angular rate measurement. A realistic simulation is presented to illustrate the results
Rigid body attitude control using a single vector measurement and gyro
, Article IEEE Transactions on Automatic Control ; Volume 57, Issue 5 , 2012 , Pages 1273-1279 ; 00189286 (ISSN) ; Namvar, M ; Sharif University of Technology
2012
Abstract
Most existing methods for satellite attitude control assume that full knowledge of satellite attitude is available by algebraic manipulation of at least two vector measurements from attitude sensors such as Sun, Earth-horizon, Earth-magnetic or star tracker sensors. Kalman filtering is usually used when only one vector measurement is available, however, asymptotic stability of nonlinear and uncertain dynamics of satellite is not guaranteed in this case. This technical note presents a coupled nonlinear estimator-controller for satellite attitude determination and control by using a 3-axis gyro and a single vector measurement for a fully actuated satellite. We assume that the moment-of-inertia...
Noise analysis in satellite attitude estimation using angular rate and a single vector measurement
, Article Proceedings of the IEEE Conference on Decision and Control, 12 December 2011 through 15 December 2011 ; December , 2011 , Pages 7476-7481 ; 01912216 (ISSN) ; 9781612848006 (ISBN) ; Namvar, M ; Sharif University of Technology
Abstract
This paper investigates the effect of noisy measurements of the angular rate in a nonlinear attitude estimator for satellites. The attitude estimator uses measurement of a single attitude sensor such as sun, earth horizon, star tracker or magnetometer together with a rate gyro, and guarantees exponential convergence of the attitude estimation error to zero under no noise condition. This paper presents stochastic and deterministic upper bounds for the attitude estimation error affected by the noise in gyro. A realistic simulation is presented to illustrate the results
Rigid body attitude control with delayed attitude measurement
, Article IEEE Transactions on Control Systems Technology ; Volume 23, Issue 5 , February , 2015 , Pages 1961-1969 ; 10636536 (ISSN) ; Namvar, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Time delay in the evaluation of the attitude of a rigid body can significantly hinder the performance of the attitude control system. In this brief, we propose a dynamically smooth control law that guarantees asymptotic convergence of the rigid body attitude and angular velocity to their desired values in the presence of delayed attitude measurement. We assume that the moment-of-inertia matrix of the body is unknown. The control law includes a matrix gain that is computed by solving a delay-dependent and time-varying matrix differential equation. It is shown that the solvability of the matrix differential equation depends on a uniform controllability condition, which can be verified a priori...
Nonlinear adaptive control of grid-connected three-phase inverters for renewable energy applications
, Article International Journal of Control ; 2015 ; 00207179 (ISSN) ; Namvar, M ; Karimi, H ; Piya, P ; Karimi Ghartemani, M ; Sharif University of Technology
Abstract
Distributed generation (DG) units are often interfaced to the main grid using power electronic converters including voltage-source converters (VSCs). A VSC offers dc/ac power conversion, high controllability, and fast dynamic response. Because of nonlinearities, uncertainties, and system parameters’ changes involved in the nature of a grid-connected renewable DG system, conventional linear control methods cannot completely and efficiently address all control objectives. In this paper, a nonlinear adaptive control scheme based on adaptive backstepping strategy is presented to control the operation of a grid-connected renewable DG unit. As compared to the popular vector control technique, the...
Global adaptive estimation of joint velocities in robotic manipulators
, Article IET Control Theory and Applications ; Volume 4, Issue 12 , December , 2010 , Pages 2672-2681 ; 17518644 (ISSN) ; Namvar, M ; Sharif University of Technology
2010
Abstract
This study presents a method for global estimation of joint velocities in robotic manipulators. The authors consider a non-minimal model of a robotic manipulator and design an adaptive observer capable of handling uncertainties in robot dynamics. Smoothness of the dynamics of the proposed observer allows its easy implementation in comparison with non-smooth observers. Dimension of the proposed observer is shown to be at least 3n where n stands for the manipulator's degrees of freedom. This number is less than the dimension of most existing globally convergent adaptive observers. Global asymptotic convergence of state estimates to their true values is achieved under no persistency of...
Globally exponential estimation of satellite attitude using a single vector measurement and gyro
, Article Proceedings of the IEEE Conference on Decision and Control, 15 December 2010 through 17 December 2010, Atlanta, GA ; 2010 , Pages 364-369 ; 01912216 (ISSN) ; 9781424477456 (ISBN) ; Namvar, M ; Sharif University of Technology
2010
Abstract
This paper presents a dynamically smooth nonlinear observer for satellite attitude determination. The proposed observer uses a 3-axis gyro and a single vector measurement to estimate the attitude of a satellite. The proposed observer preserves orthogonality of the estimated attitude matrix for all time. Almost global and exponential convergence of the estimated attitude to its true value is proven without persistency of excitation conditions. The convergence rate is shown to depend on properties of certain time varying reference vectors expressed in inertial frame. A procedure for maximizing a lower bound of the convergence rate is also presented. Performance of the proposed observer is...
A globally convergent observer for velocity estimation in robotic manipulators with uncertain dynamics
, Article Proceedings - IEEE International Conference on Robotics and Automation, 3 May 2010 through 7 May 2010, Anchorage, AK ; 2010 , Pages 4645-4650 ; 10504729 (ISSN) ; 9781424450381 (ISBN) ; Namvar, M ; Sharif University of Technology
2010
Abstract
We present a method for global estimation of joint velocities in robot manipulators. A non-minimal model of a robotic manipulator is used to design an adaptive observer capable of handling uncertainties in robot dynamics. Dimension of the proposed observer is shown to be at least 3n where n stands for the manipulator degrees of freedom. This number is less than the dimension of most of existing globally convergent adaptive observers. Global asymptotic convergence of system state estimates to their true values is achieved under no persistency of excitation condition. Smoothness of the dynamics of the proposed observer allows its easy implementation in comparison with non-smooth observers....
Adaptive control of robot manipulators including actuator dynamics and without joint torque measurement
, Article 2010 IEEE International Conference on Robotics and Automation, ICRA 2010, Anchorage, AK, 3 May 2010 through 7 May 2010 ; 2010 , Pages 4639-4644 ; 10504729 (ISSN) ; 9781424450381 (ISBN) ; Namvar, M ; Sharif University of Technology
2010
Abstract
Ignoring actuator dynamics in control of rigid manipulators can in practice result in performance degradation or loss of system stability. However, consideration of actuator dynamics usually requires measurement of robot joint torques. This paper addresses motion tracking control of an n-DOF rigid robot by taking into account its actuator dynamics. Joint torque measurement is avoided by using an adaptive observer. The backstepping technique is adopted to develop a dynamically smooth adaptive nonlinear controller dealing with uncertainties in manipulator and actuator dynamics. Semi-global convergence of motion tracking errors as well as torque estimation error are proven without any...
Motion tracking in robotic manipulators in presence of delay in measurements
, Article Proceedings - IEEE International Conference on Robotics and Automation, 3 May 2010 through 7 May 2010, Anchorage, AK ; 2010 , Pages 3884-3889 ; 10504729 (ISSN) ; 9781424450381 (ISBN) ; Namvar, M ; Sharif University of Technology
2010
Abstract
Time-delay in sensor measurements can be a frequent cause of instability and performance degradation in a robotic system. In this paper, motion tracking of rigid manipulators in presence of constant and known delay in sensors is investigated. By using non-minimal model of a manipulator, a dynamically smooth controller based on the Linear Matrix Inequality (LMI) approach is proposed which guarantees asymptotic tracking of desired joint angles and velocities in presence of delayed measurements. For a given controller the maximum amount of delay that preserves system stability is computed by solving an LMI optimization and also by numerical simulations, and the results are compared. Finally, a...
Optimal and robust waveform design for MIMO radars in the presence of clutter
, Article Signal Processing ; Volume 90, Issue 4 , April , 2010 , Pages 1103-1117 ; 01651684 (ISSN) ; Namvar, M ; Behnia, F ; Sharif University of Technology
2010
Abstract
Waveform design for target identification and classification in MIMO radar systems has been studied in several recent works. While the previous works assumed that the noise was independent of the transmission signals, here we extend the results to the signal dependent noise (clutter). We consider two scenarios. In the first scenario it is assumed that different transmit antennas see uncorrelated aspects of the target. In the second scenario, we consider the correlated target. As clutter is dependent to signal, target estimation error cannot vanish only by increasing the transmission power. It can be shown that in the second scenario, MIMO radar receiver can nullify the clutter subspace....
Decentralized adaptive control of robotic systems using uncalibrated joint torque sensors
, Article 2016 IEEE 55th Conference on Decision and Control, CDC 2016, 12 December 2016 through 14 December 2016 ; 2016 , Pages 2689-2694 ; 9781509018376 (ISBN) ; Namvar, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
Standard centralized motion controllers for robotic systems require precise model structure for manipulator dynamics. The controlled robot is also sensitive to sensor failure as each joint in robot receives information from sensors of all other joints. In this paper, we present a dynamically smooth adaptive decentralized controller for robotic manipulators where the control law in each joint depends only on local measurements from that joint. The use of possibly un-calibrated joint torque sensors eliminates the need for modeling link dynamics. Global and asymptotic motion tracking is achieved. Simulation examples demonstrate significant improvement in robustness of the controlled system in...
Port-Hamiltonian control of a brachiating robot via generalized canonical transformations
, Article 2016 American Control Conference, ACC 2016, 6 July 2016 through 8 July 2016 ; Volume 2016-July , 2016 , Pages 3026-3031 ; 07431619 (ISSN); 9781467386821 (ISBN) ; Namvar, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
This paper is devoted to the design of a port Hamiltonian controller for different scenarios of brachiation movement by a two-link bio-inspired robot called brachiating robot. A unified technique for trajectory tracking control problem of nonholonomic (drift-less) port Hamiltonian systems was introduced in the past, which exploits a generalized canonical transformation to form an error system in order to convert the trajectory tracking problem into a stabilization one. Although the method is novel and promising, only fully actuated systems are considered and success of the approach relies on the possibility of solving a set of partial differential equations (PDEs). Considering the fact that...
A predictor-based attitude and position estimation for rigid bodies moving in planar space by using delayed landmark measurements
, Article Robotica ; 2016 , Pages 1-16 ; 02635747 (ISSN) ; Namvar, M ; Sharif University of Technology
Cambridge University Press
Abstract
This paper proposes a globally and exponentially convergent predictive observer for attitude and position estimation based on landmark measurements and velocity (angular and linear) readings. It is assumed that landmark measurements are available with time-delay. The maximum value of the sensor delay under which the estimation error converges to zero is calculated. Synthesis of the observer is based on a representation of rigid-body kinematics and sensor delay, formulated via ordinary and partial differential equations (ODE-PDE). Observability condition specifies necessary and sufficient landmark configuration for convergence of attitude and position estimation error to zero. Finally, for...