Browsing by Author "Stefan Seelecke, Committee Member"
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- Automatic Handling Technology for Precision Turning of Two-Sided Parts(2009-04-24) Furst, Stephen Joseph; Jeffrey Eischen, Committee Member; Stefan Seelecke, Committee Member; Thomas Dow, Committee ChairABSTRACT FURST, STEPHEN JOSEPH. Automatic Handling Technology for Precision Turning of Two-Sided Parts. (Under the direction of Dr. Thomas A. Dow.) The fabrication of precision two-sided artifacts is a difficult, time-consuming task. Both sides of such artifacts need to be precision turned on a lathe. Two separate chucks are required to hold the part during machining of the inner contour (IC) and outer contour (OC). Currently, a skilled operator is needed to transfer the part from one chuck to another. To ensure that reference surfaces on both sides are correctly oriented on the machining chuck, the operator must realign the part by measuring run-out with a gage and tapping the part into place. The goal of this study is to develop an automatic transfer and realignment process for a part on a dual-spindle machining center. A hemispherical shell is chosen for demonstration because hemispheres lack “self-aligning†features, and thus require the most complex handling capability. At the moment of transfer, it is desired to have the axial separation between the part and receiving chuck no less than 125 µm (0.005†). Also, the radial gap between an ideal part and the receiving chuck should vary by less than 8 µm (0.0003†), meaning the radial misalignment between the hemispherical part and spindle centerlines is less than 4 µm. A transfer procedure was developed and demonstrated at the Precision Engineering Center (PEC). The demonstration showed that at the moment of part transfer, the radial misalignment between the part surface and receiving pot chuck was less than 1.5 µm (60µin. ) and the axial position of the part will have an uncertainty of 5 µm. In addition to the transfer procedure, a method was developed to realign the part in the event that radial run-out occurs during transfer. This method involves measuring the magnitude and direction of the radial run-out with either a touch probe mounted to the machine slides or an analog electronic gage. The part is then tapped in the appropriate direction by a mass driven with a voice coil until the part and spindle centerlines are within 5 µm (0.0002†) of each other. A procedure was developed to employ this actuator in part realignment. This procedure was successful in repeatedly repositioned a hemispherical part with an initial run-out of 1-2.5 mm (0.3-1†) to within 5 µm of the spindle centerline. This capability shows that the run-out of a part manually placed on a OC chuck or transferred from an IC chuck to an OC chuck can be corrected.
- Biologically Inspired Inteligent Fault Diagnosis for Power Distribution Systems(2006-11-09) Xu, Le; Gianluca Lazzi, Committee Member; James J. Brickely, Jr., Committee Member; Stefan Seelecke, Committee Member; Mo-Yuen Chow, Committee ChairPower distribution systems have been significantly affected by a wide range of faultcausing events; and the current outage restoration procedure may take from tens of minutes to hours. Effective outage cause identification can help to expedite the outage restoration and consequently improve the system reliability. Most current researches are based on system modeling and measurements such as voltage and current; besides, they usually target at a single feeder or a small system due to the difficulty of modeling the large-scale, nonlinear, and time-varying distribution system. In this research, various data mining approaches including statistical methods and artificial intelligence algorithms have been investigated and applied to Duke Energy distribution outage data in order to extract the outage pattern and identify the outage cause; by this means, the additional environmental information recorded in the data can be adopted in the fault diagnosis and the analysis range can be beyond the scope of a single feeder or a small system. Also, the affect of data imperfections such as data noise, data insufficiency, especially the data imbalance issue on the performance of outage cause identification have been investigated. In this work, logistic regression and artificial neural network are firstly compared on their capability in fault diagnosis; then an existing fuzzy classification algorithm is extended to Ealgorithm to alleviate the effect of data imbalance; afterwards, the immune system based Artificial Immune Recognition System (AIRS) algorithm is investigated for its capability in fault diagnosis using real-world data; lastly, a hybrid algorithm based on E-algorithm and AIRS is proposed to embed the rule extraction capability while performing satisfactory fault cause identification.
- Characterization of Stress-Effects in Ferroelectrics with Application to Transducer Design(2006-08-21) Ball, Brian L; Kazifumi Ito, Committee Member; Zhilin Li, Committee Member; Ralph C Smith, Committee Chair; Stefan Seelecke, Committee MemberThe increasing investigation of smart material structures requires a more thorough understanding and characterization of the underlying physics in both the constituent materials and the adaptive structures as a whole. To this end, we focus our efforts on understanding the effects of stress on ferroelectric materials and the transducers which utilize them. This dissertation addresses the development of constitutive models based on homogenized energy principles which characterize the ferroelastic switching mechanisms inherent to ferroelectric materials in a manner suitable for subsequent transducer and control design. Models characterizing the manufactured shape and quantifying the displacements generated in THUNDER (THin layer UNimorph ferroelectric DrivER and sensor) actuators in response to applied voltages for a variety of boundary conditions are developed utilizing the developed ferroelastic switching models. To develop constitutive models, we construct Helmholtz and Gibbs energy relations which quantify the potential and electrostatic energy associated with 90 and 180 degree dipole orientations. Equilibrium relations appropriate for homogeneous materials in the absence or presence of thermal relaxation are respectively determined by minimizing the Gibbs energy or balancing the Gibbs and relative thermal energies using Boltzmann principles. Stochastic homogenization techniques are employed to construct macroscopic models suitable for nonhomogeneous, polycrystalline compounds. Models characterizing the manufactured shape of THUNDER actuators and displacements resulting from applied voltages for fields are constructed using thin shell theory and Newtonian principles. The thermal stresses and strains due to repoling resulting in a prestressing of the PZT layer are also included in the model development. Attributes and limitations of the characterization framework are illustrated through comparison with experimental data.
- Mechanics of Ultrasonic Tube Hydroforming(2008-12-05) Bunget, Cristina Janeta; Gracious Ngaile, Committee Chair; Stefan Seelecke, Committee Member; Kara Peters, Committee Member; Michael Shearer, Committee MemberBUNGET, CRISTINA JANETA. Mechanics of Ultrasonic Tube Hydroforming. (Under the direction of Gracious Ngaile.) Tube hydroforming is a manufacturing process which applies controlled internal pressure and axial feed to expand the tube to desired shapes. The main advantages are: part consolidation, weight reduction, fewer secondary operations, and tighter tolerances. However, it has disadvantages due to many variables, such as loading paths, material formability, and tribological conditions, which limit its applicability and influence parts failure (excessive thinning, wrinkling, buckling or bursting). This research presents ultrasonic technology as a method of improving formability and tribological conditions. The superimposing of ultrasonic oscillations was already proved to have benefits for other metal forming processes, such as reduction in the forming load and frictional stresses. The objectives of this research work are to develop an analytical model to predict the state of stress and strain for the tube expansion under internal pressure and friction conditions, for ultrasonic and non-ultrasonic processes, observe the effects of the vibration on the deformation pattern, design a set of tooling and conduct experiments. An analytical model was derived for both conventional and ultrasonic tube hydroforming processes, using equilibrium of forces, geometric relationships, material flow law and yield criterion. The square dies were chosen for this study, due to the simplicity of plane strain conditions. In conventional process the tube is expanded under internal pressure in the presence of friction. In the ultrasonic process, vibrations are imposed on the die, resulting in alternating gaps at the die/tube interface. The gaps open and close after each oscillation. Two different states of stress alternate during one oscillation in an element of the tube wall. The analytical model was used to predict the internal pressure required, the corner radius, the thickness distribution, and the state of stress and strain. For the conventional process, the influence of some parameters on the deformation pattern and the forming load, such as strain hardening and friction conditions, was studied. Lower friction coefficient is required for more uniform tube wall thickness and lower pressure. In the ultrasonic process, more uniform thickness distribution and state of stress and strain were predicted, as compared to the classical process. When the internal pressure is maintained, the corner radius obtained is smaller. The reduction in the corner radius was between 2.4 and 9%. More uniform thickness and less thinning, as well as smaller corner radius, indicate improvement of the formability of the material. If ultrasonic oscillations are used and the pressure exerted on the tube due to vibration is less than a critical value (equal to the internal pressure), there is a decrease in the maximum internal pressure needed for the same expansion. The most effective ultrasonic pressure is 0.1 MPa. Finite element method was used to approximate the ultrasonic pressure and to design a set of tooling for ultrasonic process at 20 kHz. Four models were proposed and analyzed for three square die sizes. Modal analysis was used to observe the die vibration and the possible useful effects on the forming process. Harmonic response analyses were conducted to evaluate the amplitude of vibration in the deformation zone and the stress in the tooling. Based on the displacement distribution, a method of approximating the ultrasonic pressure was proposed. Most of the average pressure values were found to vary from 5 MPa to 25 MPa. In order to observe the effects of ultrasonic oscillations on tube hydroforming, experiments were conducted with and without vibration. The ultrasonic tests resulted in smaller corner radii as compared to the conventional test, with a reduction of 5.2-7.7%, implying increase in forming capability due to vibration.
- Microforming and Ultrasonic Forming(2007-08-18) Bunget, Cristina Janeta; Gregory Buckner, Committee Member; Stefan Seelecke, Committee Member; Gracious Ngaile, Committee Chair
- Model Development for Shape Memory Polymers(2008-08-01) Siskind, Ryan David; Stefan Seelecke, Committee Member; Hien Tran, Committee Member; Mansoor Haider, Committee Member; Ralph Smith, Committee Chair
- A Point-of-Care Diagnostic Device for Quantifying Estradiol Levels in Human Saliva.(2005-02-06) Lorek, James D; Stefan Seelecke, Committee Member; Kara Peters, Committee Member; M.K. Ramasubramanian, Committee ChairThis study was carried out focusing upon two primary objectives: the first being to investigate experimentally the merit of a photoelectrochemical process for quantifying estradiol by salivary assay and the second to investigate numerically a novel method of accelerated sedimentation for use in sample processing and purification as an alternative to centrifugation. The presented work began initially in pursuit of an improved means of diagnostic testing for estradiol levels in patients undergoing infertility treatment. The validity of using saliva as an alternative diagnostic medium to serum has been investigated and tested experimentally, demonstrating that saliva may be used as a means to quantify estradiol levels. Initial experimental results of the proposed assay technique hold promise, with an observable photocurrent response relative to the presence of E2-[Ru(bpy)3]2+; however, further experimentation is necessary in full development of an assay. Results of a CFD analysis reveal the proposed actuation method for diagnostic sample purification to perform well in comparison to that of a centrifuge and to offer advantages in a potentially compact design well suited to a fully-integrated point-of-care diagnostic device.
- A Transformative Tool for Minimally Invasive Procedures: Design, Modeling and Real-Time Control of a Polycrystalline Shape Memory Alloy Actuated Robotic Catheter(2009-04-24) Veeramani, Arun Shankar; Gregory D. Buckner, Committee Chair; Stefan Seelecke, Committee Member; M. K. Ramasubramanian, Committee Member; Denis R. Cormier, Committee MemberCardiac catheterization is rapidly transforming the diagnosis and treatment of cardiovascular disease. However, the use of catheters is limited to procedures where the target anatomy can be easily accessed via natural vasculature. Robotically controlled catheters have the potential to provide greater access and more precise interaction with internal anatomies. This dissertation presents the development of a shape memory alloy (SMA) actuated robotic catheter: from electromechanical design to the development of novel modeling and control approaches. The robotic catheter is fabricated using conventional manufacturing and rapid prototyping. To analyze the transient characteristics of the catheter, a dynamic model is developed. Its bending mechanics are derived using a circular arc model and are experimentally validated. The effects of outer sleeve thickness on heat transfer and transient response characteristics are studied. SMA actuation is described using the Seelecke-Muller-Achenbach model for single-crystal SMA with experimentally determined parameters. Joule heating is used to generate tip deflections, which are measured in real-time using a dual-camera imaging system. The dynamic characteristics of this active catheter system are simulated and validated experimentally. The direct extension of the Seelecke-Muller-Achenbach model to a catheter with multiple SMA tendons proves difficult because of the computational cost and inherent inaccuracies of the single-crystal modeling assumptions. Moreover, the requisite variable-step solvers are not suitable to real-time control. To facilitate more accurate modeling and effective real-time control of an SMA catheter with multiple tendons, a new modeling technique based on Hysteretic Recurrent Neural Networks (HRNNs) is proposed. Its efficacy is demonstrated experimentally for two- and three-phase hysteretic systems. The HRNN is extended to three-phase SMA actuation and is shown to accurately capture the polycrystalline stress-strain characteristics of SMA tendons at different temperatures. A robotic catheter system consisting of four SMA tendons is then decoupled into two planar bending systems, each consisting of a pair of antagonistic SMA tendons. An HRNN model is developed directly from experimental measurements, and is used to develop a feed-forward controller.
