Browsing by Author "Ronald O. Scattergood, Committee Member"

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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.
Design and Use of Pre-Stressed Unimorphs for High-Displacement, High-Load Applications
(2004-11-29) Mulling, James Frederick; Angus I. Kingon, Committee Chair; Ronald O. Scattergood, Committee Member; Edward Grant, Committee Co-Chair
The purpose of this research was threefold: to characterize pre-stressed unimorph actuators fabricated by different routes, to investigate 3-D orientation of the polarization vector through the piezoceramic thickness using piezoresponse force microscopy (PFM), and to design a motor to use the strengths of a compliant actuator. Applications such as robotics need high-force, high displacement actuators with potential for scaling. Pre-stressed unimorphs, typified by THUNDER™ actuators by Face International Corporation, provide larger displacement than traditional unimorph or bimorph actuators because pre-stress introduced during fabrication enhances piezoelectric strain. The fact that these are compliant actuators has important implications for use. This research showed that bond material and thickness, as well as end conditions all affect actuator performance. Substrate material and thickness relative to that of the ceramic element were shown to have more subtle effects than previously reported. The likely signature of performance enhanced by pre-stress was found in load-displacement test data, which showed that the effect appears to be modified as displacement under load interacts with the original actuator curvature due to pre-stress. The novel application of PFM showed that orientation of the polarization vector did indeed vary through the actuator thickness. Internal stress bias has a dominant role in determining orientation of the polarization vector, so much so that effects of initial poling were not seen except at a location likely to be a neutral surface. With overall domain orientation generally out of alignment with the poling direction, piezoelectric strain augmented by a large extrinsic contribution can be expected when electric field is applied in the poling direction. Performance of a linear motor using an inchworm cycle was found to be limited by clamp slip. The passive (unpowered) clamps otherwise had the advantage of simplifying operation. A rotary motor of novel design was tested using several configurations of actuators and other parts. Its chief advantage was that resonant behavior was little affected by load, since actuators and load were indirectly coupled. Characterization yielded a range of torque and speed data, with best performance generally provided by the simplest drive signals and configurations of parts. Design principles allow the motor to generate high torque. Experimental results, although promising, imply that ample opportunity exists to identify and ameliorate performance-limiting factors.
Growth and Characterization of ZnO and ZnO-Based Alloys MgxZn1-xO and MnxZn1-xO
(2004-11-19) Jin, Chunming; Robert M. Kolbas, Committee Member; Carl C. Koch, Committee Member; Jagdish Narayan, Committee Chair; Ronald O. Scattergood, Committee Member
The goals of this work were to synthesize ZnO and ZnO based alloy thin films by using PLD and to study the structural, stoichiometric, optical and electrical properties of these films. Epitaxial hexagonal MgZnO thin films have been grown on sapphire (0001) with domain-matching epitaxy by using PLD. The films show the high single-crystalline quality and bright excitonic luminescence. The maximum Mg concentration was found to be 34 at. %, which is almost ten times of the value allowed by the phase diagram. The bandgap of MgZnO alloy film can be tuned from 3.40 eV to 4.19 eV. Epitaxial ZnMgO thin films with cubic (NaCl) structure were also synthesized on MgO (001) sapphire (0001) and TiN/Si(001) by using PLD. The maximum Zn concentration in these cubic alloy films was 18 at. %. The epitaxial growth of cubic ZnMgO on Si(001) substrate is of significant importance for integrating ZnO-based alloys to the Si-based electronics. The phase stability of MgZnO/ZnO/MgZnO superlattice structures was studied using XRD and HRTEM methods. The diffusion of Mg from the MgZnO barrier to the ZnO well was observed by using the HRTEM and optical measurements. The cubic nanoinclusions were also observed with HRTEM. Epitaxial MnZnO thin films were synthesized on sapphire (0001) substrates. The maximum Mn concentration was 35 at. %. The bandgap of these films shifts to the higher energy side with increasing Mn content. Magnetic investigations indicate that these films are paramagnetic. Epitaxial ZnO films have been grown on Si (111) substrates by using PLD with two different heterostructures, ZnO/AlN/Si(111) and ZnO/MgO/TiN/Si(111). These thin films show the excellent single crystalline quality and extremely bright excitonic emission. C-axis orientated ZnO thin films have been grown on the amorphous silica substrates. The PL characteristics of these films are comparable to that of the films grown on the sapphire substrates. An ultraviolet illumination-enhanced luminescence effect was observed. This new phenomenon is attributed to the oxygen desorption on the surface. A phenomenological model was proposed to explain this new effect.
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.
Micromachining Using EVAM (Elliptical Vibration Assisted Machining)
(2005-05-10) Brocato, Brett C; Thomas Dow, Committee Chair; Gregory D. Buckner, Committee Member; Ronald O. Scattergood, Committee Member
The goal of this research is to demonstrate Elliptical Vibration Assisted Machining (EVAM) as a multi-level planar microstructuring tool for MEMS applications. While many MEMS (Micro Electro Mechanical Systems) devices are fabricated using silicon etching techniques developed for the microelectronics industry, micromachining is an attractive alternative because of its low start-up cost, applicability to a wide range of materials, high flexibility of feature geometry, and low prototyping cost. Vibration assisted diamond turning is proposed as an alternative method of fabricating 3D MEMS devices. To demonstrate the capabilities of this technique, a diamond tool holder that moves in an elliptical path at 1000 Hz (the Ultramill) was attached to a 3-axis diamond turning machine (DTM). Using this system, structured surfaces with high accuracy and surface finish were created. Multi-level structures with 15 μm plan-view features, 500 nm elevation features, and 20 nm RMS surface finish have been achieved on a 200 micrometer part scale. In addition, the limits of the fabrication technique in its current form were identified by machining specific features and relating them to the tool, the process and the DTM. Limitations of the current process include a sub-Hertz drift error in the air-bearing third axis, temperature control of the Ultramill, and natural frequencies of the DTM axes in the range of measured error frequencies in machined parts.
Precision Fabrication and Development of Charging and Testing Methods of Fixed-Abrasive Lapping Plates
(2003-07-12) Kametz, David Austin; Jeffrey Eischen, Committee Member; Ronald O. Scattergood, Committee Member; Thomas A. Dow, Committee Chair
The recording head industry is one of the dominant users of advanced ceramics such as alumina, silicon nitride, silicon carbide and AlTiC. The high hardness of these materials makes diamond the optimal abrasive for machining. One challenge when manufacturing recording heads for rigid disk drives is to generate surfaces that are both planar and smooth. Flatness tolerances are in the range of a few tens of nanometers to a few hundred nanometers per millimeter of length [1]. Roughness tolerances are in the range of a few nanometers to the subnanometer range [1]. Fixed-abrasive lapping, sometimes called nanogrinding, is a common method of machining used on ceramics. Fixed-abrasive lapping is generally a two-body abrasive process, with the abrasive grain fixed in the lapping plate that produces an extremely smooth surface due to the controlled depth of cut. The process of fabricating a quality fixed-abrasive lapping plate is a lengthy and sometimes demanding process. The goals of this research are to investigate the current fabrication process for improvements in surface texture quality, charging time and waste reduction of abrasive as well as the development of methods and equipment capable of estimating the lapping qualities of the plate during its fabrication process. The improvement of this process will reduce plate fabrication time and improve lapping performance. Current processes used to fabricate a plate can require 2 hours or more, and often the lapping quality of the plate is unknown until it is used. The research started by analyzing the current process used. The surface texture and charging quality were analyzed by quantifying characteristics such as surface roughness, kurtosis, bearing ratio and diamond concentration. The new process developed at the Precision Engineering Center changed the surface texture from scratches of random geometry to a continuous spiral groove cut by a diamond turning machine. This texture not only has better reproducibility than the random scratches, but the geometry of the individual features can be better controlled. The charging mechanism was also changed from a large charging ring that was half the diameter of the lapping plate to a small rolling cylinder. The cylinder creates higher pressures and the ability to follow the profile of the plate. These changes created a shorter charging time, higher charging quality and reduced abrasive waste during the charging process. A tribometer was developed to test the charging quality of the plate during the charging process. It took advantage of the changing friction coefficient on the surface of the plate with charging time. The mechanism constructed and tested did not perform as designed, but can be used as a prototype for future developments. The use of other equipment for charging verification utilizing friction or other aspects of the charging process is viable.
Precision Replication of Co-Molded Meso and Micro Optics Through Injection Molding
(2002-07-18) Gill, David Dennis; Ronald O. Scattergood, Committee Member; Thomas A. Dow, Committee Chair; Gregory D. Buckner, Committee Member; C. Maurice Balik, Committee Member
The objective of the research reported here is to extend the limits of current optical production techniques for complex, thermally-stable, precise optical components produced in large volume. The goals of this research address the challenges on two fronts 1) injection molding of polymer lenses, and 2) molding of polymer elements directly onto stable substrates. The first goal was addressed through an increased understanding of the injection molding process in the replication of micro optics. Precision molds were produced with optical features of varying size, shape, step height, and aspect ratio. These features included spherical and Fresnel lenses, a blaze diffraction grating, and a wedding cake. Feature pitch was as small as 10um and step heights as small as 1.25um. To gain increased understanding, a partial factorial screening design of experiment was performed to discover the molding factors (process variables) with the greatest effect on the replication of micro optics. These experiments showed mold temperature and screw rotation speed to have the greatest effects on the accurate replication of meso and micro optics. The second challenge, the thermal instability of polymer lenses, has been addressed through research of the co-molding of these optics directly onto thermally stable substrates. Challenges included the modification of properties at the polymer-substrate interface, the large mismatch in coefficients of thermal expansion between the materials, and mold design factors for using substrates in the injection mold. In the experiments, interface adhesion was found to be increased through the use of organofunctional silanes, and co-molding experiments revealed that acrylic lenses had the best adhesion to specially cleaned soda lime glass.