Sharif Digital Repository

The satellite attitude control problem is to determine the torque that is produced by actuators in such a way that, the satellite reaches to a desired final state from an initial state. If we do not consider the structural and dynamical equations of actuators and its effects in the system’s equations, the control problem is simple and can be solve easily. But, when the dynamic of the actuators and practical constraints associated with them and the equations of the system are to be considered, due to the dependence of these equations, solving the satellite attitude control is not simple like before. That is why, no effective method is presented to solve it. One of the most widely used... 

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... 

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... 

Three-phase voltage source converter (VSC) is vastly utilized in the renewable energy resource and distributed generation (DG) systems interface units due to its high controllability and flexibility. Because of the high nonlinear nature of the system, the gird-connected inverter shows poor performance if the conventional control scheme are used. In this thesis, a new control scheme based on backstepping strategy is presented for control of a grid connected DG systems. The proposed scheme is responsible for regulating the active and reactive power components of the VSC power of the DG system. The VSC of the DG system is connected to a stiff utility grid through an L-type filter. In the first... 

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,... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

One of the important tasks of the customer relationship management of any company is to control the customer churn rate. Because according to research, retaining existing customers for a company costs less than attracting new customers. One of the most important tasks in order to control customer churn is to anticipate customers who intend to leave the company. This thesis proposes new method for customer churn prediction in mobile telecommunication industry. Mobile operators are structured in such a way that they can record and store a lot of data. In this dissertation, the most appropriate operator data was selected using data mining methods and various features related to customer churn... 

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... 

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,... 

In a typical rigid robot manipulator, joint angels and velocities are often considered as system states. Joint angels are usually measured by precise Shaft Encoders. However, lack of velocity measurement sensors “Tachometers” and their undesired characteristics in most of existing robotic systems make it difficult to have access to full system states. As full access to the system states in various applications is inevitable, velocity observers can be used to reconstruct or estimate the unmeasured velocity signals. This thesis presents an observer for global estimation of joint velocities in robot manipulators. A non-minimal model of a robotic manipulator is introduced to design an... 

Nowadays, many researches are inspired by nature and living creatures in order to build various scientific and industrial products such as robots, because of the highest level of creativity which is used in creating them along with their high level of efficiency in power consumption and designing parameters. Underactuated Robots are the type of robots which have more degrees of freedom comparing to the number of operators. As a result their optimum control has a lot of complications. Brachiating robots are designed and built based on an inspiration from long armed apes (Gibbons). This type of monkey is highly skilled in twisting in trees and traversing. This type of movement benefits from... 

The goal of controlling robot manipulators is to perform the mission intended for its end effector. Model-based control is a solution that can achieve the control goal with high speed and accuracy in the presence or absence of environmental obstacles by using the knowledge of the robot model. In this thesis, the Armtin 5 robot model parameters were identified in two steps. In the first step, the gravity and friction parameters and in the second step, the dynamic parameters were estimated. In the estimation of gravity and friction parameters, the non-linear behavior of friction causes the estimated parameters to be accompanied by a large amount of error. Estimation of the parameters was... 

The purpose of this research is to develop a contactless angular sensor based on magnetic methods that in addition to having similar outputs to resistive angle sensors (contact potentiometers) has advantages such as longer lifetime and no sensitivity to contamination, moisture and dust. In this research, an angular GMR sensor is designed and manufactured and tries to present a product that meets the required standards and can be sold in domestic and foreign markets