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Total 26 records

    Robot Control By Port-Hamiltonian Approach

    , M.Sc. Thesis Sharif University of Technology Ebrahimi, Keivan (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    This thesis is devoted to deriving a port Hamiltonian control approach for different scenarios of brachiation movement by a two-link underactuated planar robot called brachiation robot. The port Hamiltonian modeling and control of this type of robot is introduced for the first time and shows promising results in the analysis and simulation as will be showed here. Animals have long inspired roboticists. Their dexterity, versatility, flexibility of motion and great variety of behaviors has made them benchmarks for robot performance. Recently things have begun to change and robots are now capable, to a limited degree, of mimicking the behavior of animals. This paper studies a type of... 

    Rigid Body Asymptotic Attitude & Position Estimation Using Time Delayed Landmark Measurement

    , M.Sc. Thesis Sharif University of Technology Mohammadi Senejohnny, Danial (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    This paper proposes a globally and exponentially convergent predictor 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 representation of the rigid-body kinematics and the sensor delay by a combination of ordinary and partial differential equations (ODE-PDE). An observability condition specifies necessary and sufficient landmark configuration for convergence of attitude and position estimation error to zero.... 

    Nonlinear Geometric Approach to Fault Detection in Mechanical Systems

    , M.Sc. Thesis Sharif University of Technology Mashreghi, Ali (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    The demand for safety operating systems is growing with the new developments in technology. One of the important and critical issues in system monitoring is the capability of the system to detect probable faults and hazards. In model-based fault detection one specific diagnostic signal called residual should be generated for each fault that is only sensitive to a particular fault and independent of other faults and disturbances. In this thesis we try to investigate the nonlinear geometric approach in fault detection of a class of mechanical systems. After a brief introduction to geometric tool for nonlinear inputaffine systems and conditions in which output is decoupled from input, we... 

    Adaptive and Robust Control of Robots Including Actuator Dynamics

    , M.Sc. Thesis Sharif University of Technology Salimi Khaligh, Yahya (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Ignoring actuator dynamics in control of rigid manipulators can in practice result in performance degradation or loss of system stability. However, on the other hand, consideration of actuator dynamics usually requires measurement of robot joint torques that is not cost-effective. This thesis 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 novelty of this thesis is in developing a controller for robot manipulators including non-negligible actuator dynamics in presence of uncertainty in robot dynamics; without using joint torque measurement. Controller design is done... 

    Decentralized Control of Robot Manipulators

    , M.Sc. Thesis Sharif University of Technology Yazdi Almodarresi, Mostafa (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    In this thesis, a decentralized controller for trajectory tracking of robot manipulators is developed. Proposed control scheme use uncalibrated joint torque sensors. Recently, it has been shown that the use of joint torque sensing results in a simplified manipulator model and reduce the need of dynamic model of links for controlling. In this thesis, we use the special lower triangular structure of this simplified model for decentralized control of manipulator. For the first time a smooth decentralized law is designed which makes both position and velocity tracking errors of robot manipulators globally converge to zero. Against most of previous work in decentralized control of manipulators,... 

    Control of Two Degree of Freedom Underactuated Systems

    , M.Sc. Thesis Sharif University of Technology Rahmati, Rahman (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    In robotic, Underactuated systems are interesting subject to study. Underactuated system, is a system that have fewer actuator than degrees of freedom. Underactuated systems are composed of active and passive joints. passive joints are existed, in order to decrease the weight, cost, and energy consumption. Usually, control of these systems are difficult. Underactuated systems have acceleration constraint. This property make the control method have fundamental constraint. So that controller dynamic could not be a smooth function of states of system. So most of standard method in control, such as feedback linearization, are not applicable. Local linearizing methods, because of... 

    Motion Planning & Control of Mobile Robots

    , M.Sc. Thesis Sharif University of Technology Seifi, Sepehr (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Wheeled mobile robots form a subcategory of mobile robots and are usually accompanied with geometric constraints on their velocities. These constraints do not allow the robots to move in any path that only does not collide with obstacles, in order to move from one point to another. On the other hand, the nonlinear nature of these systems make their control difficult. A general approach in motion planning and control for mobile robots is using standard forms equivalent to their state equations; Usually, solving motion planning and control problems for these forms is easier than that of the original system. Also,the mentioned problems are more prospective to have a systematic solution for... 

    Mechanical Systems Using Nonlinear State Feedback

    , M.Sc. Thesis Sharif University of Technology Zade Gharejehdaghi, Elahe (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Disturbance is one of the inseparable components of the mechanical systems which cannot be avoided. In these systems a number of inner and outer sources exist which are the cause of disturbance. Abrupt changes in torque, uncertainty in parameters, mechanical impulses and external forces on robot’s parts all can be mentioned as examples which introduce disturbance that affects the output of mechanical and robotic systems. Therefore, disturbance rejection is considered indispensable in robotic control systems. There are number of problems which are associated with disturbance rejection. In several methods, mostly optimization based methods, system fails to completely reject the disturbance and... 

    Design and Implementation of Nonsmooth Controller for Mechanical Systems under Nonholonomic Constraint

    , M.Sc. Thesis Sharif University of Technology Jafari Harandi, Mohammad Reza (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    This thesis works on certain type of underactuated mechanical systems with nonholonomic constrain, namely wheeled robots.Since this robots has different types, this work focuses specifically on three-wheeled robot. At first we know kinematic characteristics of robot system and equations of motion.To control this system, at first we will change equations to chain form, then control it by using known methods. It will be shown that between the known methods for convergence to a fixed point,irregular transformation is the best way for control systems in chain form.Also, with dynamic feedback linearization we can control robot on a trajectory that has a continuous third order derivatives. Then... 

    Satellite Attitude Determination and Control in Presence of Time Delay

    , Ph.D. Dissertation Sharif University of Technology Bahrami, Somayeh (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Attitude determination and control system (ADCS) design is usually based on using measurements provided by rate gyros or attitude sensors such as Sun, Earth-magnetic, Earthhorizon and star trackers. In many practical scenarios, vector measurements provided by attitude sensors and the corresponding reference vectors are available with time delay while the angular velocity is measured by Gyro without significant delay. Time delay can cause ADCS performance degradation and even instability of the closed-loop system. Due to the nonlinearity of satellite dynamics and kinematics, controller and observer design in presence of measurement delays has its own complexity. Hence, despite its... 

    Path-planning and Control of Space Robots

    , M.Sc. Thesis Sharif University of Technology Nasiri, Mahdi (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Control of many mechanical systems such as satellites lies on the control of space robots. Control of space robots has many theoric complexities because of the presence of non-holonomic constraints due to angular momentum conservation. Unlike fixed-base robots, any movement of space robots manipulator has a reaction on the robot base and moves it. Thus manipulator’s movement toward desired configuration rotates the robot base and as a result appropriate attitude may not be attained. Therefore an appropriate path is required to achieve the desired configuration and the base attitude reaches its desired value. In this thesis, first the dynamic of space robots and the interaction between the... 

    Adaptive Compensation of Effect of Slow Dynamic Actuators in Robots Without Output Torque Measurement

    , M.Sc. Thesis Sharif University of Technology Kazemi, Hadi (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    A motion tracking control design of an n-DOF rigid robot by taking into account its actuator dynamics is proposed in this paper using backstepping technique. neglecting actuator dynamics in control of rigid robot manipulators can degrade the performance and loss of stability. However,consideration of actuator dynamics entails joint torque or armature currents measurement. In this study, torque measurement has been avoided using an torque estimator.. Finally, Semi-global convergence for motion tracking error are proven. In addition, A simulation example of a two-link robotic manipulator is also given to clarify the effectiveness of proposed design method. Considering actuator dynamics entails... 

    Fault Detection and Identification in Robotic Systems

    , M.Sc. Thesis Sharif University of Technology Baghbahari, Masoud (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Fault detection and identification is one of the major issues and challenges in the field of engineering and currently is considered as an active field of research. As the replacement of human in dangerous or inaccessible environments, robotic mechanical systems can be used which exposes to a variety of stresses and actions that causes faults in the actuators or sensors. Accordingly, detection of fault at the earliest possible time after the fault accurence and its identification such that real flaw waveform is being extracted, can prevent more damage to the system without any need to human immediate interference. Model based approach in recent decades has shown their ability to detection... 

    Robot Motion Control In the Presence of Actuator Delay Using Nonlinear Prediction

    , M.Sc. Thesis Sharif University of Technology Tavakoli Kejani, Mohammad (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Time delay usually exists due to different causes in actuator dynamics of robot manipulator. If this time delay is not considered to compensate, we will encounter with instability or oscillation. In this dissertation, we propose a nonlinear predictor feedback to achieve exponentially convergence in the presence of constant and known delay in actuator dynamics of robot manipulator. It is assumed that the dynamics of robot manipulator is known. Since the robot manipulator system is forward-complete, we don’t have explosive instability in dead time and it stays bounded until the control kicks in t=D. Our approach to stability proof of proposed controller employs PDE form to present the delay in... 

    Global Estimation and Control of Rigid-body Attitude and Position Using Single Landmark Measurement

    , M.Sc. Thesis Sharif University of Technology Moeini, Amir (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    The purpose of determining orientation and position of a rigid-body is specifying its attitude and position with respect to a specified reference frame in order to using in controller. Since there is no sensor that can directly measures the attitude and position, we have to estimate those variables by observers. In this thesis we derive a new and explicit neccesary and sufficient condition for observability of the rigid-body kinematic equation. Also we propose a new observer for estimating the attitude and position of the rigid-body. The special feature of the proposed estimator is that it use only a single landmark and is globally and exponentially stable. In the next step we study the... 

    Attitude Control of Satellite Using a Single Vector Measurement and Gyro

    , Ph.D. Dissertation Sharif University of Technology Safaei, Fatemeh (Author) ; Namvar, Mehrzad (Supervisor)

    Position and Attitude Control for a Quadrotor Using Nonsmooth Feedback

    , M.Sc. Thesis Sharif University of Technology Mirshamsi, Alireza (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    In recent years, autonomous unmanned aerial vehicles (UAVs) have attracted considerable amount of interest because of a wide area of applications and a lot of advantages. UAVs have been extensively used for military operations that include tracking, surveillance, active engagement with weapons and airborne data acquisition. UAVs are also in demand commercially due to their advantages in comparison to manned vehicles. These advantages include lower manufacturing and operating costs, flexibility in configuration depending on customer request and not risking the pilot on demanding missions. Quadrotor, which is a kind of rotary wing UAVs, has many advantages such as the vertical take-off and... 

    Control of Robots in Presence of Delay in Measurements

    , M.Sc. Thesis Sharif University of Technology Bahrami, Somayeh (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Time-delay in measurement of the outputs is usually one of the important factors creating complexity in design of a robot controller such that ignoring the delay in controller design can cause instability or significant performance degradation in a robotic system. In this thesis, set-point regulation problem as well as the trajectory tracking problem for a rigid robotic manipulator in presence of constant and known delay in measurements have been investigated and in particular, three dynamically smooth controllers have been proposed:
    1-A controller based on the “minimal” dynamic model of a robot manipulator that satisfies sufficient conditions in the form of Linear Matrix inequalities... 

    Design of Nonlinear Observer and Controller for Satellite Attitude Estimation and Control

    , M.Sc. Thesis Sharif University of Technology Khosravian, Alireza (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    The goal of the attitude determination is to determine the orientation of a satellite with respect to a reference frame. For this purpose, gyroscopes are used to measure the satellite’s angular velocity. Also, the attitude sensors such as magnetometers, Sun sensors, Earth sensors or star trackers are employed to collect vector measurements. The aim of the attitude control is to calculate the torque which is needed to be applied to the satellite such that its orientation and angular velocity converge to their desired values. It is usual to determine the attitude of satellite first and then use it in the attitude control algorithms. When multiple independent vector measurements are available,... 

    Attitude Estimation and Control of Satellite Using Noisy Measurements

    , M.Sc. Thesis Sharif University of Technology Firoozi, Dena (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Satellite attitude determination means specifying its rotation relative to a known reference. To determine satellite attitude, gyroscope is used to measure angular velocity and attitude sensors such as sun sensor, magnetometer, star tracker and earth horizon scanner are used in order to obtain vector measurements. In kinematic control, satellite angular velocity is determined in a way that its attitude converges to desired attitude. Usually, gyroscope and attitude sensors measurements are contaminated by noise which leads to errors in satellite attitude estimation and control. In the literature, gyroscope and at least two vector meaurements are used to estimate and control the...