Browsing by Author "Paul I. Ro, Committee Member"

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Advanced Design Techniques in Linear Parameter Varying Control
(2006-08-10) Dong, Ke; Gregory D. Buckner, Committee Member; Stephen L. Campbell, Committee Member; Paul I. Ro, Committee Member; Fen Wu, Committee Chair
To improve the analysis and control synthesis approach of linear fractional transformation (LFT) parameter-dependent systems, two types of non-quadratic Lyapunov function and switching control scheme are introduced and studied in this thesis. A gain-scheduled controller with parameter variation rate, a nonlinear gain-scheduled controller and an online switching linear parameter varying (LPV) controller are derived, and the advantages of proposed LPV control techniques are demonstrated through numerical and physical examples. In the first part of this thesis, we introduce a quadratic LFT parameter-dependent Lyapunov function, which includes affine parameter-dependent functions as special cases. Using full-block S-procedure, new LPV synthesis conditions have been derived in terms of finite number of linear matrix inequalities (LMIs). The constructed controller depends on parameters and their variation rate in general form compared with traditional LFT form. It is shown that the proposed approach can achieve better performance in a ship steering example by exploiting parameter variation rates. In the same spirit of exploiting more general type of Lyapunov function to achieve better controller, an analysis and synthesis algorithm for LPV systems using convex hull Lyapunov function (CHLF) and maximum Lyapunov function is presented. Using duality of LPV systems and conjugate properties of CHLF, sufficient LPV analysis and synthesis conditions have been derived in terms of LMIs with linear search over scalar variables. Because of the special structure of CHLF and maximum Lyapunov function, the output feedback controller turns out to be a nonlinear gain-scheduled controller. A second-order plant is used to demonstrate advantages and benefits of the new approach. The other main contribution in this thesis is the application of switching control to LPV systems with online optimization method. Arbitrary switching among subsystems is achieved, as well as performance improvement using multiple Lyapunov functions. A gain-scheduled controller working for the next switching interval is designed at each switching instant. A bumpless transfer compensator is also designed to minimize the output jump caused by switching. The synthesis conditions for both switching controller and bumpless transfer compensator are formulated as LMIs. The new LPV switching control scheme is applied to an uninhabited combat aerial vehicle (UCAV) problem. All our proposed approaches are efficient in computation, where the conditions are all formulated as LMIs or LMI-like ones. With slightly increased computational complexity, the proposed new approaches for analysis and synthesis of LFT parameter-dependent systems can achieve significant performance improvement comparing to existing approaches.
BATMAV: A Biologically-Inspired Micro-Air Vehicle for Flapping Flight - Kinematic Modeling
(2007-12-04) Bunget, Gheorghe; Paul I. Ro, Committee Member; Gregory D. Buckner, Committee Member; Stefan Seelecke, Committee Chair
The main objective of the BATMAV project is the development of a biologically inspired bat-like Micro-Aerial Vehicle with flexible and foldable wings, capable of flapping flight. This phase of the project starts with an analysis of several small-scale natural flyers from an engineering point of view with the objective to identify the most suitable platform for such a vehicle. Bats are shown to be very agile and efficient flyers with mechanical parameters well-suited to be realized with currently available muscle wire actuators allowing for close bio-inspired actuation. The second part of this thesis focuses on the kinematical analysis of the wing motion with the intent to develop a smart material (shape memory alloy) driven actuator system mimicking the functionality of the bat's relevant muscle groups in the future. In the past decade Micro-Aerial Vehicles (MAV's) have drawn a great interest to military operations, search and rescue, surveillance technologies and aerospace engineering in general. Traditionally these devices use fixed or rotary wings actuated with electric DC motor-transmission, with consequential weight and stability disadvantages. SMA wire actuated flexible wings for flapping flight are promising due to increased energy density while decreasing weight, increased maneuverability and obstacle avoidance, easier navigation in small spaces and better wind gust stability. While flapping flight in MAV has been previously studied and a number of models were realized using light nature-inspired rigid wings, this paper presents a platform that features bat-inspired wings with flexible joints and muscle-wire actuation to allow mimicking the kinematics of the real flyer. The bat was chosen after an extensive analysis of the flight physics of birds, bats and large insects. Typical engineering parameters such as wing loading, wing beat frequency etc. were studied and it was concluded that bats are a suitable platform that can be actuated efficiently using micro-scale Flexinol muscle wires. Also, due to their wing camber variation, they can operate effectively at a large range of speeds and allow remarkably maneuverable flight, avoiding obstacles while flying in small spaces (i.e. search and rescue missions). In order to understand how to implement SMA "mechanical muscles" on a bat-like platform, the analysis was followed by a study of bat flight kinematics. Due to their complexity, from the engineering point of view, only a limited number of muscles were selected to actuate the flexible wing. A computer model of BATMAV platform incorporating SMA wires, wings and platform body, was created using SolidWorks software. The skeleton was subsequently fabricated using rapid prototyping technologies, and a novel joint technology was introduced which, replaces the complicated morphology of the natural flyers by a combination of superelastic SMA wires as flexible hinges. An extended analysis of flight styles in bats coordinated with image processing and inverse kinematics theory for robotic manipulators resulted in a collection of data for joint angles variation of the wing bone structure. These data implemented into the direct kinematics of the "robotic-like wing arm" helped to mimic the wingbeat cycle of the natural flyer.
Design and Control of a Fast Long Range Actuator for Single Point Diamond Turning
(2009-09-16) Chen, Qunyi; Ronald O. Scattergood, Committee Member; Jeffery W. Eischen, Committee Member; Paul I. Ro, Committee Member; Thomas A. Dow, Committee Chair
This dissertation focuses on the design and control of a fast long range actuator to machine non-rotationally symmetric (NRS) optical surfaces with millimeters of sag at high production rates. The goal is to retain the surface quality (form error of less than 200 nm PV and surface finish of less than 5 nm RMS) of existing diamond turning machines while moving the tool over a range of 4 mm at a frequency of 20 Hz. The actuator in this dissertation features a light-weight slide supported by an air bearing, the tool feed motion is controlled by a linear motor, a linear encoder and real-time control platform. The first actuator prototype was built and tested in 2004-2005, but its performance was found to be unacceptable due to various deficiencies. This dissertation research has developed a methodology for the design and control of this type of actuator to optimize its performance. It essentially takes a three-step approach: investigate the characteristics of the tool motion control in the diamond turning in terms of tool motion trajectories, disturbances to the tool motion, and the required tool positioning precision; develop an actuator system to meet motion control requirement; integrate the actuator with a diamond turning machine and conduct precision machining and precision metrology for performance validation. In this research, the original actuator is modified and upgraded with new system components including a linear amplifier, two control platforms, two linear encoders and an add-on counterbalance drive. Effective feedback and feedforward control techniques for profile tracking and disturbance rejection are investigated and implemented. Critical implementation issues for motion planning are resolved to improve the quality of motion trajectory generation and the quality of motion synchronization while machining. Modification of the first prototype has pushed the limits of performance on both tool motion control (Ã‚Â±30 nm for position holding error and Ã‚Â±70 nm for 2 mm 20 Hz sinusoidal tracking error) and machining results (plated copper flat with 7.4 nm RMS surface finish for, non-rotationally symmetric PMMA tilted flat with 50.8 mm diameter and 4 mm excursion with 0.9 ÃŽÂ¼m PV flatness error ii and 17 nm RMS surface finish). Further improvement performance depends on a total redesign of the actuator. The desirable system component characteristics to achieve required tool positioning quality, of the slide piston, the air bearing, the amplifier, the motor and counterbalance, are proposed and analyzed. Critical system configuration issues regarding the amount of moving mass, the size of the motor, the sampling rate of digital control system and the necessity of physical damping are also addressed. Finally, by creating a biconic mirror with fiducial features for kinematic coupling, this dissertation has also proven the feasibility of fabricating real-world optics with this type of actuator.
Development of a Closed-loop MEMS Capacitive Force Sensor
(2009-08-04) Guan, Changhong; Fen Wu, Committee Member; Yong Zhu, Committee Chair; Paul I. Ro, Committee Member
This thesis describes a closed-loop microelectromechanical system (MEMS) based on lumped-parameter modeling. Analytical models are derived for electrostatic comb drive actuator (CDA) under force-controlled actuation, electrothermal actuator (ETA) under displacement-controlled actuation, capacitive position sensor, including parallel plate capacitive sensor (PPCS) and torsional plate capacitive sensor (TPCS), mechanical equation of motion of a suspended shuttle, viscous air damping, folded exure. These models are implemented and simulated in finite element analysis softwares (ANSYS and FEMM). System level simulation, implementing PID difierential feedback loop, is simulated in a numerical simulation program (MATLAB). The MEMS die is fabricated by following the standard PolyMUMPs process by MEMSCAP. A series of MEMS packaging process and storage are done in the lab. All peripheral circuitries are self-made. A commercial capacitive readout IC (MS3110) is first used for open-loop capacitive sensing, which achieves the resolution of 0.05fF, equivalent to 1nm in displacement. Due to the disadvantage of MS3110 in closed-loop, AC bridge capacitance measurement method is then implemented for closed-loop integration. The resolution of AC bridge sensor reaches 0.02fF, equivalent to 0.4nm in displacement. An additional function of AC bridge sensing is accomplished which is simultaneously sensing and actuation of CDA. In the feedback loop, the traditional analog PID controller is designed to transfer the voltage signal of capacitance measurement to the voltage-force transducer which converts feedback voltages to differential feedback force. Since the differential feedback force is limited by clamped voltage, a force-balanced mode is observed under 5V actuation of CDA.
Error Compensation Using Inverse Actuator Dynamics
(2004-11-25) Panusittikorn, Witoon; Gregory D. Buckner, Committee Member; Kenneth P. Garrard, Committee Member; Jeffrey W. Eischen, Committee Member; Thomas A. Dow, Committee Chair; Paul I. Ro, Committee Member
The use of Non-Rotationally Symmetric (NRS) optical surfaces has increased significantly in recent years. These surfaces can be quickly machined using a diamond turning lathe and a Fast Tool Servo (FTS). However, the dynamic response of the actuator influences the output tool motion resulting in form errors. This dissertation describes an open-loop command modification technique, also know as a deconvolution operation, that can significantly reduce tool motion errors. The technique uses knowledge of the gain and phase response of the dynamic system and the information content of the driving command to modify the amplitude, phase and shape of the input command signal. The modified command signal creates the desired tool motion. The research made use of a commercial FTS to demonstrate the error compensation technique and implemented a system identification method using Digital Signal Processing (DSP) to determine the closed-loop transfer function of the actuator. This measurements exposed the physical limits of the FTS which constrained the tool speed to 140 mm/s and the nonlinear dynamic behavior of the FTS as a function of the command amplitude. Initial validation of the inverse dynamics technique for a fixed amplitude tool trajectory employed a single transfer function to modify the entire input command signal. The experiments showed that the excursion of the actuator was identical to the desired path after a start up period. The tool trajectory of an FTS is dependent on the spindle speed and the cross-feed rate which may drift over a long fabrication time and an NRS feature can contain varying amplitude. To address these issues, two adaptive modification schemes using the Short-Time Fourier Transform (STFT) and an equivalent inverse dynamics filter were proposed. These schemes can account for the changing frequency and amplitude content of the driving command using the most recent machining conditions and the appropriate transfer function. The experimental confirmation of the error compensation scheme involved the fabrications of two off-axis features: a sphere and a cosine groove. The adaptive schemes were used to create an off-line modified input command. Measurements of the machined surfaces using a laser interferometer experimentally validated that the deconvolution operation can extend the usable bandwidth of the FTS to produce the proposed surfaces. The measurements across the machined parts indicated that the form fidelity of the deconvoluted features was improved by 2 orders of magnitude over that of the features produced using the unmodified input command signals.
Infrared-based temperature measurement in ceramics grinding and diesel exhaust aftertreatment filters
(2004-02-18) Kong, Jian; John S. Strenkowski, Committee Member; Ronald O. Scattergood, Committee Member; Albert J. Shih, Committee Chair; Paul I. Ro, Committee Member
Non-contact remote-sensing radiation thermometry was used in the applications of temperature measurement in ceramics grinding and diesel exhaust aftertreatment filters. Results of temperature measurements by analysis of the thermal emission spectra generated during grinding and subsequently transmitted through partially stabilized zirconia workpiece are presented. Portions of emitted visible and near-infrared spectra were collected with spectrometers. Source temperatures were determined by fitting the scaled spectrometer output spectra to blackbody curves. Simulations showed that the effective temperatures determined by this method will be strongly biased toward hot-spot (flash) temperatures, which are expected to occur at the grinding grit-workpiece interface. Hot-spot temperatures on the order of 3000 K were obtained for grinding with both SiC and diamond wheels. These high temperatures modify the grinding process and the phase content of grinding chips. The in-situ measurement of the temperature distribution on the cavity wall surface in diesel exhaust aftertreatment filters using the infrared radiation thermometry was developed. The temperature measurement system consists of a sapphire fiber with 45° angled tip, PbS/PbSe two-color sensor, and data conditioning and acquisition device. A calibration technique using the blackbody cavity was developed. Calibration curves were generated between 80 to 400°C, the temperature range of special interest for applications in catalyzed diesel exhaust aftertreatment filters. One-color and two-color radiation thermometry methods were both employed to compare and validate temperature measurement results. The wall surface temperature of a microwave-heated ceramic filter was measured at four locations. This study demonstrates the feasibility of using the infrared thermometry for non-contact temperature measurement at a specific region within the cavity of diesel exhaust aftertreatment filters. Based on the above temperature measurement results, the infrared thermometry method was applied to study the temperature distribution in microwave heating of diesel particulate filters. Temperature measurement tests were conducted in integrated multi-channel fiber optic infrared temperature measurement and microwave heating systems. The silica light-pipes, which are transparent to electromagnetic field, were used to collect the infrared radiation from different locations inside filter cavity. One-color thermometry method was implemented to convert the measured radiation into temperatures. The temporal and spatial distributions of three diesel particulate filters heated by microwave were studied. Experimental results show the non-uniform heating across the filter. The interaction between catalyst, soot loading, and microwave power varies the heating pattern and temperature distribution. During a 600 s heating period, a 1 kW microwave power setting is able to raise the temperatures above 200°C in most area of a catalyzed filter with soot loading.
Intelligent Control Using Confidence Interval Networks: Applications to Robust Control of Active Magnetic Bearings
(2005-04-28) Choi, Heeju; Fen Wu, Committee Member; Gregory D. Buckner, Committee Chair; Richard F. Keltie, Committee Member; Stephen L. Campbell, Committee Member; Paul I. Ro, Committee Member
Robust control synthesis requires an explicit mathematical description of the system dynamics (a model) and uncertainty bounds associated with that model. These uncertainty bounds are usually chosen arbitrarily and conservatively for guaranteed stability, frequently at the expense of controller performance. This research demonstrates the application of Confidence Interval Networks (CINs), unique artificial neural networks that utilize asymmetric bilinear error cost functions, for estimating the bounds of model uncertainty required for robust control synthesis. A highly nonlinear and unstable active magnetic bearing (AMB) system is considered. A high-speed flexible rotor supported by AMBs is modeled using analytical approaches, finite element analysis, and system identification. CINs learn the statistical bounds of model uncertainty resulting from unmodeled dynamics and parameter variations. These bounds are incorporated into the synthesis of multivariable robust controllers based on two approaches, linear time invariant and linear parameter varying. Experimental results on a multivariable AMB test rig reveal the benefits of this combination of intelligent system identification and robust control: significant performance improvements vs. conventional robust control with and without mass imbalance (process disturbances).
Numerical and Theoretical Analysis of Beam Vibration Induced Acoustic Streaming and the Associated Heat Transfer
(2004-02-23) Wan, Qun; Paul I. Ro, Committee Member; Andrey V. Kuznetsov, Committee Chair; Paul D. Franzon, Committee Member; William L. Roberts, Committee Member
The purpose of this research is to numerically and analytically investigate the acoustic streaming and the associated heat transfer, which are induced by a beam vibrating in either standing or traveling waveforms. Analytical results show that the beam vibrating in standing waveforms scatters the acoustic waves into the free space, which have a larger attenuation coefficient and longer propagating traveling wavelength than those of the plane wave. In contrast to a constant Reynolds stress in the plane wave, the Reynolds stress generated by such acoustic wave is expected to drive the free space streaming away from the anti-nodes and towards nodes of the standing wave vibration. The sonic and ultrasonic streamings within the channel between the vibrating beam and a parallel stationary beam are also investigated. The acoustic streaming is utilized to cool the stationary beam, which has either a heat source attached to it or subjected to a uniform heat flux. The sonic streaming is found to be mainly the boundary layer streaming dominating the whole channel while the ultrasonic streaming is clearly composed of two boundary layer streamings near both beams and a core region streaming, which is driven by the streaming velocity at the edge of the boundary layer near the vibrating beam. The standing wave vibration of the beam induces acoustic streaming in a series of counterclockwise eddies, which is directed away from the anti-nodes and towards the nodes. The magnitude of the sonic streaming is proportional to ω²A while that of the ultrasonic streaming is proportional to Ω[superscript 3/2]A². Numerical results show that the acoustic streaming induced by the beam vibrating in either standing or traveling waveforms has almost the same cooling efficiency for the heat source and the heat flux cases although the flow and temperature fields within the channel are different. The hysteresis of the ultrasonic streaming flow patterns associated with the change of the aspect ratio of the channel is numerically investigated. Present research is also extended to a cavity which is driven by a vibrating lid. The ultrasonic streaming induced in the cavity reveals some interesting interactions among the primary eddies, which have never been observed in the classical driven cavity problem.
Simulation-Based Design Strategies for Component Optimization in Steer-by-Wire Applications.
(2009-04-23) Bachmeyer, Paul Joseph; Paul I. Ro, Committee Member; Larry M. Silverberg, Committee Member; Donald L. Margolis, Committee Member; Gregory D. Buckner, Committee Chair
The objective of this thesis is to develop simulation-based design strategies for optimizing the selection of active, semi-active, and passive components for industrial steer-by-wire (SBW) applications. Experimental steering data is collected from an instrumented Honda Accord (1987 model) and used to validate a lateral vehicle model. This model is used to investigate the tactile feedback performance of various SBW configurations at specific driving conditions. Although peak performance is obtained with fully active components (direct-drive electric motors), comparable performance can be obtained using a combination of passive springs, semi-active dampers, and active motors with a 16.3% reduction in cost and an 87.7% reduction in electrical energy required.