Mechatronics Methods for Mitigating Undesirable Effects of Pre-motion Friction in Nanopositioning Stages with Mechanical Bearings

Nanopositioning (NP) stages are used to for precise positioning in a wide range of nanotech processes, ranging from substrate patterning to micro additive manufacturing. They are often used for point-to-point (P2P) motions, where the stage is commanded to travel to and settle within a pre-specified window of the target position, and for tracking motions, where the stage is commanded to follow a reference trajectory. The settling time, in-position stability and tracking accuracy of NP stages directly affects productivity and quality of the associated processes or manufactured products. NP stages can be constructed using flexure, fluidic, magnetic or mechanical bearings (i.e., sliding and, especially, rolling-element bearings). Of these choices, mechanical bearings are the most cost-effective, and are currently the only commercially viable option for a growing number of NP applications that must be performed in high vacuum environments. However, mechanical-bearing-guided NP stages experience nonlinear pre-motion (i.e., pre-sliding/pre-rolling) friction which adversely affects their precision and speed. Control-based compensation methods, commonly used to address this problem, often suffer from poor robustness and limited practicality due to the complexity and extreme variability of friction dynamics at the micro scale. Therefore, this dissertation proposes three novel mechatronics methods, featuring a combination of mechanical design and control strategy, as more effective and robust solutions to mitigate the undesirable effects of pre-motion friction. The first approach is vibration assisted nanopositioning (VAN), which utilizes high frequency vibration (i.e., dither) to mitigate the low speed (slow settling) of mechanical-bearing-guided NP stages during P2P motions. VAN allows the use of dither to mitigate pre-motion friction while maintaining nanometer-level positioning precision. P2P positioning experiments on an in-house built VAN stage demonstrates up to 66% reductions in the settling time, compared to a conventional mechanical bearing NP stage. A major shortcoming of VAN is that it increases the cost of NP stages. To address this limitation, a friction isolator (FI) is proposed as a simple and more cost-effective method for mitigating pre-motion friction. The idea of FI is to connect the mechanical bearing to the NP stage using a joint that is very compliant in the motion direction, thus effectively isolating the stage from bearing friction. P2P positioning tests on a NP stage equipped with FI prototypes demonstrate up to 84% reductions in the settling time. The introduction of FI also enables accurate and robust reductions of motion errors during circular tracking tests, using feedforward compensation with a simple friction model. One pitfall of FI is that it causes increased error of the stage during in position. Therefore, a semi-active isolator (SAI) is proposed to mitigate the slow settling problem using the FI, while maintaining the benefits of friction on in-position stability. The proposed SAI, which connects the bearing and NP stage, is equipped with solenoids to switch its stiffness from low, during settling, to high once the stage gets into position. P2P experiments demonstrate up to 81% improvements in the settling time without sacrificing in-position stability. The proposed mechatronics methods are compared and FI stands out as a result of its simplicity, cost-effectiveness and robust performance. Therefore, the influence of design parameters on the effectiveness of FI are investigated to provide design guidelines. It is recommended that the FI should be designed with the smallest stiffness in the motion direction, while satisfying other requirements such as in-position stability and off-axis rigidity.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155296/1/terrydx_1.pd

Volume 1 – Symposium: Tuesday, March 8

Group A: Digital Hydraulics Group B: Intelligent Control Group C: Valves Group D | G | K: Fundamentals Group E | H | L: Mobile Hydraulics Group F | I: Pumps Group M: Hydraulic Components:Group A: Digital Hydraulics Group B: Intelligent Control Group C: Valves Group D | G | K: Fundamentals Group E | H | L: Mobile Hydraulics Group F | I: Pumps Group M: Hydraulic Component

Modeling and robust adaptive tracking control of a planar precision positioning system

Precision positioning systems constitute an essential prerequisite for modern production processes in the diverse applications of micro- and nanotechnology. Associated with the control of these systems there are high demands with respect to bandwidth, accuracy, robustness and stability. The most important requirement, however, is dynamic tracking of complex reference trajectories with highest precision. To achieve these objectives, usually a good knowledge of system parameters is necessary, whereby their identification is mostly laborious and expensive. In addition, depending on the production process or plant, parameters may change with time which may endanger the achievement of these goals. From an economic perspective, it is therefore desirable that parameter identification is carried out during operation, within the control scheme. This reduces the effort for system identification and also ensures that the controller may also adapt to parametric changes. Based on this motivation, the present thesis deals with the development of an adaptive tracking control concept for the planar precision positioning system PPS1405 build by the motor manufacturer Tetra. The development and identification of detailed system models of the most important components of the PPS1405 is the foundation for this. The developed model serves firstly as a basis for model-based control design and secondly as a realistic simulation environment for testing and evaluation of the controllers designed. Furthermore, the model gives insights about the potential applicability of adaptive control which is confirmed throughout the analysis. Following this, the aspired tracking control design is based on the idea of a two-stage approach, comprising a nominal tracking controller and an adaptive augmentation exploiting ideas from $\mathcal{L}_1$ adaptive control. The latter seems promising in view of remarkable performance and robustness properties. For the adaptive tracking controller, both, state and output feedback schemes are developed, whereas in view of the available measurement signals only the output feedback scheme is implemented at the test rig. Experimental results confirm the efficiency of the proposed control scheme. It meets all specifications with regard to tracking errors and yields tracking performance that has not been obtained by any of the existing controllers so far.Präzisionspositioniersysteme bilden eine wesentliche Grundvoraussetzung für moderne Produktionsprozesse in den vielschichtigen Anwendungen der Mikro- und Nanotechnologie. An die Regelung dieser Systeme werden hohe Anforderungen bzgl. Bandbreite, Genauigkeit, Robustheit und Stabilität gestellt. Die wichtigste Anforderung jedoch, bildet die dynamische Verfolgung komplexer Referenztrajektorien mit höchster Präzision. Zur Erreichung dieser Ziele ist zumeist eine möglichst genaue Kenntnis der wesentlichen Systemparameter erforderlich, deren Identifikation in der Regel aufwändig und teuer ist. Zudem können sich je nach Produktionsprozess oder Anlage Parameter mit der Zeit verändern, was die Erreichung dieser Ziele gefährdet. Aus betriebswirtschaftlicher Sicht ist es daher erstrebenswert, die Parameteridentifikation während des Betriebs innerhalb der Regelung durchzuführen. Dies reduziert den Aufwand bei der Systemidentifikation und stellt zudem sicher, dass die Regelung sich auch gegenüber Veränderungen anpassen kann. Aus dieser Motivation heraus beschäftigt sich die vorliegende Dissertation mit der Entwicklung eines adaptiven Folgeregelungskonzepts für das planare Präzisionspositioniersystem PPS1405 der Firma Tetra. Die Grundlage hierfür bildet die Entwicklung sowie die Identifikation detaillierter Systemmodelle der wesentlichen Komponenten des PPS1405. Das entwickelte Modell dient zum einen als Grundlage für modellbasierte Regelungsentwürfe und zum anderen als realistische Simulationsumgebung zur Erprobung und Bewertung dieser Verfahren. Aufbauend darauf, basiert der angestrebte Folgeregelungsentwurf auf der Idee eines zweistufigen Ansatzes, bestehend aus einem nominellen Folgeregler und einer adaptiven Erweiterung mittels L1 adaptiver Regelung. Letztere erscheint im Hinblick auf herausragenden Performance- und Robustheitseigenschaften vielversprechend. Für die adaptive Folgeregelung werden sowohl Ansätze für Zustands- als auch Ausgangsrückführungen entwickelt, wobei aufgrund der zur Verfügung stehenden Messsignale nur letztere am Versuchsstand implementiert werden. Experimentelle Ergebnisse bestätigen die Leistungsfähigkeit der entwickelten Regelung. Diese erfüllt alle gestellten Anforderungen hinsichtlich der Positionsabweichung und erzielt Regelgüten, die mit existierenden Reglern bisher nicht erreicht wurden

Third International Symposium on Magnetic Suspension Technology

In order to examine the state of technology of all areas of magnetic suspension and to review recent developments in sensors, controls, superconducting magnet technology, and design/implementation practices, the Third International Symposium on Magnetic Suspension Technology was held at the Holiday Inn Capital Plaza in Tallahassee, Florida on 13-15 Dec. 1995. The symposium included 19 sessions in which a total of 55 papers were presented. The technical sessions covered the areas of bearings, superconductivity, vibration isolation, maglev, controls, space applications, general applications, bearing/actuator design, modeling, precision applications, electromagnetic launch and hypersonic maglev, applications of superconductivity, and sensors

Design, control, and application of piezoelectric actuator: External-sensing and self-sensing actuator

Ph.DDOCTOR OF PHILOSOPH

MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

Research reports: 1991 NASA/ASEE Summer Faculty Fellowship Program

The basic objectives of the programs, which are in the 28th year of operation nationally, are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA Centers. The faculty fellows spent 10 weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague. This is a compilation of their research reports for summer 1991

Passive devices for terahertz frequencies

Terahertz technology is a relatively new field of electromagnetic study and interest is rapidly growing in the wake of dramatic imaging demonstrations. Other applications are expected to follow, and they will need passive devices with functionality already found in more familiar microwave and visible regions of the electromagnetic spectrum, but presently missing in the terahertz region. Two fundamental devices in particular are variable polarisation compensators, and tunable frequency-selective filters. This work represents the first demonstration of a variable polarisation compensator using subwavelength patterned features (artificial dielectrics). Following on from the original proposal, this work contains a complete and thorough investigation including the development of a bulk silicon micromachining fabrication process, full characterisation of the device performance in the W-band (70 – 110GHz) and comprehensive simulations of the device, including detailed simulation of three distinct new designs with improved performance (continuously-variable retardance with maximum in excess of quarter- and half wave). The third of the three designs is capable of extremely low insertion loss (<0.6 dB) and overcomes a difficulty of the original design that prevented zero retardance in a practical device. Secondly, a new tunable photonic crystal filter is proposed and demonstrated. Easily accessible external control surfaces integrated into the interlocking plates of a layer-by-layer photonic crystal allow unprecedented contol over the number and type of defects within the structure, all of which may be tuned "on-the-fly". Devices are initially investigated with a full-vector electromagnetic finite-difference time-domain technique, to reveal the influence of the design dimensions on the band gap as well as the effect of the defects. A two-plate metal device having four layers of rods is constructed and measured in the W-band. In good agreement with the simulations, it is experimentally determined that a moveable passband is centered at 81 GHz, with a quality factor of 11, and a tuning shift of 1.7 GHz for a plate movement of 450 µm