Browsing by Author "Dr. Fen Wu, Committee Member"

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Adaptive Fuzzy Modulation for Networked PI Control Systems
(2002-05-30) Al-mutairi, Naif Bejad; Dr. Fen Wu, Committee Member; Dr. H. Joel Trussell, Committee Member; Dr. James J. Brickley, Committee Member; Dr. Mo-Yuen Chow, Committee Chair
Networks and their applications have been evolving substantially in the last two decades. Network-based control systems, also called Networked Control Systems (NCS), are one of the hottest topics in network-based applications. By networked control system we mean controlling the system through the network, i.e., using networks for remote control and automation. One major concern of using networks in remote control and automation is the Quality of Service (QoS) deterioration effects. These QoS deterioration effects such as: network-induced time delays, bandwidth constraints, multiple-packet transmission, and dropping network packets are serious tribulations. Without considering the effect of the QoS deterioration the performance of the NCS closed-loop control system could be degraded and even destabilized. In this thesis, an adaptive fuzzy logic modulation scheme is proposed to compensate for the network-induced time delays in the network-based PI control systems. This scheme is based on modulating the control signal provided by the PI controller and applied to the remote controller via the network. A network-based controlled DC motor is used in this thesis to illustrate the effectiveness of the proposed scheme.
Design Study of an Autonomous Unmanned Air Vehicle Controller
(2005-12-06) Peterson, Joseph Scott; Dr. Sharon Lubkin, Committee Member; Dr. Fen Wu, Committee Member; Dr. Charles Hall, Committee Chair
The purpose of this document is to both quantitatively and qualitatively compare three varying approaches to control of unmanned air vehicles: dynamic inversion, classical gain scheduling, and robust gain scheduling through H∞ synthesis. The quantitative comparisons include robust performance and robust stability measures of the aircraft and controller linearized about a trim operating point. A second study will look at the time response of the system with varying perturbation to the nominal plant dynamics. The qualitative analysis looks at the complexity of the controller and time required to implement, this included comparison of iterative solving methods for system gains both in the frequency and time domains. A full nonlinear form of the dynamic inversion controller was implemented with full non-linear simulation in Simulink and shows comparable results to the linearized studies. The results have shown that a dual loop controller with a dynamic inversion inner loop and H∞ outer loop has the largest robust performance over the flight envelope but one of the more advanced forms of control for implementation.
Modeling and Control of a Magnetostrictive System for High Precision Actuation at a Particular Frequency
(2002-12-05) Mou, Gang; Dr. Gregory D. Buckner, Committee Member; Dr. Fen Wu, Committee Member; Dr. Paul I. Ro, Committee Chair
A magnetostrictive actuator made of Terfenol-D alloy can generate high mechanical strains with broadband response and provide accurate positioning. These characteristics have been employed as controllers and vibration absorbers in industrial and heavy structural applications, such as fast tool servo systems and precision micropositioners. Full utilization of magnetostrictive transducers in these applications requires a suitable controller as well as quantification of the transducer dynamics in response to various inputs. However, at moderate to high drive levels, the output from a magnetostrictive actuator is highly nonlinear and contains significant magnetic and magnetomechanical hysteresis. The control of this nonlinear system is a challenge. In order to simplify this problem, 50Hz is chosen as the working frequency for the actuator in the experiments since it shows near linear property at 50Hz and the approach used at 50Hz could be extended to a broader frequency range in the applications. First, with an optical sensor, the dynamics of the actuator are measured under voltage inputs at different frequencies and amplitudes. Using SAS System V8, a second order dynamic model is obtained at one frequency (50Hz). This model matches the open loop behavior very well. A PID controller is then developed. The control command signal generated through the DSP board is directed to the actuator. A close loop control system is thus formed. As a nonlinear control approach, sliding mode control can offer some ideal properties, such as insensitivity to parameter variations or uncertainties, external disturbance rejection, and fast dynamic response. In order to obtain better tracking performance and robustness, a sliding mode control algorithm is introduced into the system. The experiment results from the sliding mode controller are compared with those from the open loop and PID control. The comparison shows improvement in the displacement tracking performance at this frequency. Further work will involve the modification of the sliding mode controller using a time-varying switching gain and improvement in modeling of the actuator over a broader frequency range.
On Network-based Control and Sensitivity Characterization of Mobile Robot in Intelligent Space
(2008-04-03) Vanijjirattikhan, Rangsarit; Dr. James J. Brickley, Jr., Committee Member; Dr. Griff L. Bilbro, Committee Member; Dr. Fen Wu, Committee Member; Dr. Mo-Yuen Chow, Committee Chair
This dissertation addresses the problem of path-tracking control of a mobile robot, also called an Unmanned Ground Vehicle (UGV), in Intelligent Space, where the controller is located on an entity different from the robot and communicates with the robot over a communication network. The involvement of a communication network leads us to the core of this research, the network time-delay factor. The existence of a network delay presents a challenging problem that might degrade the overall system performance and even destabilize the closed-loop control system. The existing research area for the aforementioned scenario is called Network-based control system (NBC) mostly focused on a general linear system for which the controller must be redesigned so that the overall NBC system can work properly. Distinct from the existing research, and innovative in its own right, the research presented in this dissertation focuses on a specific nonlinear system, the remote UGV path-tracking. More specifically, we focus on the methods that allow the existing workable path-tracking controller to be reused in the NBC environment. In this work, Accumulated effect parameter tuning method is firstly proposed to tune the geometrical path-tracking controller used in UGV before operating over communication network; then sensitivity analysis is introduced to consider how the system is sensitive to noise or perturbation so that the operating condition, such as UGV speed and path curvature, may be changed to limit the effect from noise or perturbation; afterwards, Feedback preprocessor (FP) is proposed to alleviate the effect of network delay by using UGV position estimation through UGV kinematics model; along with FP, UGV response time is proposed to demonstrate the effect of different UGV characteristics on path-tracking performance; finally, the effect of using Gain scheduler (GS) with two-dimensional and one-dimensional gain table is investigated for the capability to alleviate the network delay on remote UGV path-tracking.
Unscented Kalman Filtering for Real-Time Atmospheric Thermal Tracking
(2010-04-09) Hazard, Matthew Wesley; Dr. Charles E. Hall, Committee Chair; Dr. Ashok Gopalarathnam, Committee Member; Dr. Fen Wu, Committee Member
The increasing use of unmanned air vehicles in military and civilian applications has been accompanied by a growing demand for improved endurance and range. These demands have been largely met by advances in aerodynamic and structural efficiency, improved battery technology, and the ongoing miniaturization of onboard computing and payload systems. Recently, more attention has been paid to the extraction of energy from the atmosphere. Aircraft can make use of atmospheric updrafts, or thermals, to gain altitude without expenditure of onboard fuel stores. By intelligently tracking thermals, an unmanned aircraft can extend its range or loiter time without carrying additional fuel or specialized sensors. Prior research has focused on the `big picture' concepts associated with autonomous soaring - determining when to stop and soar in a thermal, what speed to fly, when to return to the desired course, and so on. Finding and tracking thermals is only a single component of the complete soaring system. However, because the high-level decision making tasks rely on estimates of the thermal parameters, the accuracy and computational cost of the thermal tracking algorithm set the upper performance limit of the entire system. So, this research reformulated batch regression thermal finding algorithms used in past efforts into an efficient Unscented Kalman Filter. Open-loop simulation results showed the filter was capable of accurately estimating thermal position, strength, and size with low computational cost for a variety of realistic flight paths. Closed-loop simulation reaffirmed this statement in the presence of realistic aircraft, sensor, and thermal dynamics. Further, the algorithm was embedded into the ALOFT soaring platform (a 4.3m wingspan unmanned glider) for flight testing, which demonstrated its ability to track real-world thermals during cross-country flights exceeding 5 hours flight time over a 70 mile course.