Date of Award

2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Yi, Sun Dr.

Abstract

High-precision positioning of laser beams has been one of the greatest challenges in industry due to inevitable existence of disturbance and noise. This work addresses this challenge by employing two different control strategies, namely, Proportional Integral Derivative (PID) and State Feedback with an observer for control. Control strategies are intended to stabilize the position of a laser beam on a Position Sensing Device (PSD) located on a Laser Beam Stabilization (laser beam system) equipment. The laser beam system consist of a laser source, a fast steering mirror (FSM), a position sensing device, and a vibrating platform which generates active disturbances. The traditional proportional integral derivative controller is widely used in industry, due to its satisfactory performance, various available tuning methods and relatively straightforward design processes. However, design of filters to obtain the derivative signal is challenging and the filtering can unexpectedly distort the dynamics of the system being controlled. As an alternative, an observer-based state feedback (OBSF) method is proposed and implemented. This method uses the state-space model of the laser beam system, where all the state variables cannot be measured directly. Therefore, an observer is applied to estimate the state of the system. For observer design, eigenvalue assignment and optimal design methods are used and compared in terms of system performance. Also, comparison between the proportional integral derivative and observer-based state xiii feedback controllers for laser beam stabilization are provided. Simulations and experimental results of the two controllers show that the observer-based state feedback controller has a faster response, rejects disturbance better and has a straight forward design procedure.

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