Control theory

In engineering and mathematics, control theory deals with the behaviour of dynamical systems. The desired output of a system is called the reference. When one or more output variables of a system need to follow a certain reference over time, a controller manipulates the inputs to a system to obtain the desired effect on the output of the system. Rapid advances in digital system technology have radically altered the control design options. It has become routinely practicable to design very complicated digital controllers and to carry out the extensive calculations required for their design. These advances in implementation and design capability can be obtained at low cost because of the widespread availability of inexpensive and powerful digital processing platforms and high-speed analog IO devices

Parameter optimized controller design based on frequency domain identification

Ankara : Department of Electrical and Electronics Engineering and Institute of Engineering and Sciences, Bilkent Univ., 1995.Thesis(Master's) -- Bilkent University, 1995.Includes bibliographical references leaves 51-54.Recently, there has been a great tendency towards the development of iterative design methodologies combining identification with control in a mutually supportive fashion. In this thesis, we develop such an algorithm utilizing nonparametric frequency domain identification methods in order to realize the online iterative design of parameter optimized controllers for a system of unknown dynamics. The control design is based on the minimization of LQG (Linear Quadratic Gaussian) cost criterion with a two-degree of freedom control system. This is achieved by the approximation of an optimality relation, which is derived for a particular parametrization of one of the controllers, using the frequency domain transfer function estimates and application of this together with a numerical optimization algorithm. It is shown that, if the first controller is a FIR filter of length greater than or equal to two times the number of frequencies present in the reference input, the designed control system is optimal independent of the stabilizing second controller.Köroğlu, HakanM.S

Fully probabilistic control for stochastic nonlinear control systems with input dependent noise

Robust controllers for nonlinear stochastic systems with functional uncertainties can be consistently designed using probabilistic control methods. In this paper a generalised probabilistic controller design for the minimisation of the Kullback-Leibler divergence between the actual joint probability density function (pdf) of the closed loop control system, and an ideal joint pdf is presented emphasising how the uncertainty can be systematically incorporated in the absence of reliable systems models. To achieve this objective all probabilistic models of the system are estimated from process data using mixture density networks (MDNs) where all the parameters of the estimated pdfs are taken to be state and control input dependent. Based on this dependency of the density parameters on the input values, explicit formulations to the construction of optimal generalised probabilistic controllers are obtained through the techniques of dynamic programming and adaptive critic methods. Using the proposed generalised probabilistic controller, the conditional joint pdfs can be made to follow the ideal ones. A simulation example is used to demonstrate the implementation of the algorithm and encouraging results are obtained

An Optimal Control Model for Human Postural Regulation

Human upright stance is inherently unstable without a balance control scheme. Many biological behaviors are likely to be optimal with respect to some performance measure that involves energy. It is reasonable to believe that the human is (unconsciously) optimizing some performance measure as he regulates his balance posture. In experimental studies, a notable feature of postural control is a small constant sway. Specifically, there is greater sway than would occur with a linear feedback control without delay. A second notable feature of the human postural control is that the response to perturbations varies with their amplitude. Small disturbances produce motion only at the ankles with the hip and knee angles unchanging. Large perturbation evoke ankle and hip angular movement only. Still larger perturbation result in movement of all three joint angles. Inspired by these features, a biomechanical model resembling human balance control is proposed. The proposed model consists of three main components which are the body dynamics, a sensory estimator for delay and disturbance, and an optimal nonlinear control scheme providing minimum required corrective response. The human body is modeled as a multiple segment inverted pendulum in the sagittal plane and controlled by ankle and hip joint torques. A series of nonlinear optimal control problems are devised as mathematical models of human postural control during quiet standing. Several performance criteria that are high even orders in the body state or functions of these states (such as joint angle, Center of Pressure COP or Center of Mass COM) and quadratic in the joint control are utilized. This objective function provides a trade-off between the allowed deviations of the position from its nominal value and the neuromuscular energy required to correct for these deviations. Note that this performance measure reduces the actuator energy used by penalizing small postural errors very lightly. By using the Model Predictive Control (MPC) technique, the discrete-time approximation to each of these problems can be converted into a nonlinear programming problem and then solved by optimization methods. The solution gives a control scheme that agrees with the main features of the joint kinematics and its coordination process. The derived model is simulated for different scenarios to validate and test the performance of the proposed postural control architecture

LQG/LTR Tilt and Tip Control for the Starfire Optical Range 3.5-meter Telescope\u27s Adaptive Optics System

The Air Force Research Laboratory has sponsored research on the tracking control loop portion of the adaptive optics system in the Starfire Optical Range 3.5-meter telescope at Kirtland Air Force Base. The control loop includes two steering mirrors (Coarse Steering Mirror and Fine Steering Mirror) used to remove wavefront tilt and tip phase distortion from light entering the telescope. The objective of this research is to design a single Linear Quadratic Gaussian controller to control both steering mirrors in order to eliminate wavefront tilt and tip distortions induced by the earth\u27s atmosphere, and to evaluate the stability robustness and performance of the controller through simulation and Monte Carlo analysis. Controller design elements and simulation parameters are varied to examine and compare resulting performance and robustness characteristics. The controller design is limited to the use of linear models even though components within the control loop have some nonlinear characteristics; however, consideration has been given to the nonlinear aspects of the system via the simulation environment in order to observe the linear controller in a near-real-world environment

Design and construction of a STM for use in-situ in a TEM

Since its inception scanning tunneling microscopy (STM) has emerged as a powerful technique in the field of nanoscience, with applications that have provided extremely important insights into the local nano-scale chemical/electrical properties of semiconducting and conducting materials. However, this technique alone is not capable of directly observing the tip and sample during its operation. Direct observation of the dynamic changes of both the tip and sample may help to provide a better understanding of the mechanisms behind some STM applications. Recent developments in this area have successfully combined STM to operate in-situ with imaging techniques such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). This thesis presents a new design for an in-situ STM which can operate within the spatial confines of a TEM – allowing both techniques to be conducted simultaneously. To overcome the spatial constraints of imaging inside a TEM, the design uses a novel coarse approach mechanism; consisting of three parallel hammer-action inertial driving mechanisms that are attached via flexible linkages to a pivot plate that allows the STM tip to be reliably positioned to regions of interest in three dimensions. The operation of STM in a TEM provides numerous advantages that are not available with standard STM techniques; these advantages are discussed and potential applications for this technique are also presented. One such application investigated is the potential for using silver sulphide STM tips for use in in-situ STM manipulation

Design and construction of a STM for use in-situ in a TEM

Since its inception scanning tunneling microscopy (STM) has emerged as a powerful technique in the field of nanoscience, with applications that have provided extremely important insights into the local nano-scale chemical/electrical properties of semiconducting and conducting materials. However, this technique alone is not capable of directly observing the tip and sample during its operation. Direct observation of the dynamic changes of both the tip and sample may help to provide a better understanding of the mechanisms behind some STM applications. Recent developments in this area have successfully combined STM to operate in-situ with imaging techniques such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). This thesis presents a new design for an in-situ STM which can operate within the spatial confines of a TEM – allowing both techniques to be conducted simultaneously. To overcome the spatial constraints of imaging inside a TEM, the design uses a novel coarse approach mechanism; consisting of three parallel hammer-action inertial driving mechanisms that are attached via flexible linkages to a pivot plate that allows the STM tip to be reliably positioned to regions of interest in three dimensions. The operation of STM in a TEM provides numerous advantages that are not available with standard STM techniques; these advantages are discussed and potential applications for this technique are also presented. One such application investigated is the potential for using silver sulphide STM tips for use in in-situ STM manipulation

A history of Averett College

The first school in Danville was established by a Presbyterian minister, the Reverend Mr. J. Matthews, in the year 1802. This school lasted only twelve months and was followed by a procession of others which soon perished for one reason or another. In 1823 the Danville Male Academy was organized and became the forerunner of the modern public education system of Danville. Soon after, a number or schools were established for females. This study is concerned with only one, the school that is now Averett College