A lifting and actuating unit for a planar nanoprecision drive system

Ein wesentlicher Treiber in vielen heutigen Technologiebereichen ist die Miniaturisierung von elektrischen, optischen und mechanischen Systemen. Mehrachsige Geräte mit großen Verfahrbereichen und extremer Präzision spielen dabei nicht nur in der Messung und Qualitätssicherung, sondern auch in der Fabrikation und Manipulation von Nanometerstrukturen eine entscheidende Rolle. Die vertikale Bewegungsaufgabe stellt eine besondere Herausforderung dar, da die Schwerkraft des bewegten Objektes permanent kompensiert werden muss. Diese Arbeit schlägt dafür eine Vertikalhub- und -aktuiereinheit vor und trägt damit zur Weiterentwicklung von Nanometer-Präzisionsantriebssystemen bei. Grundlegende mögliche kinematische Integrationsvarianten werden betrachtet und entsprechend anwendungsrelevanter Kriterien gegenübergestellt. Der gezeigte parallelkinematische Ansatz zeichnet sich durch seine gute Integrierbarkeit, geringe negative Einflüsse auf die umliegenden Systeme, sowie die Verteilung der Last auf mehrere Stellglieder aus. Folgend wird ein konstruktiver Entwicklungsprozess zusammengestellt, um diese favorisierte Variante weiter auszuarbeiten. Im Laufe dieses Prozesses wird die zu entwickelnde Einheit in das Gesamtsystem eingeordnet und ihre Anforderungen, Randbedingungen und enthaltenen Teilsysteme definiert. Die vertikale Aktuierung besteht dabei aus zwei Systemen: Einer pneumatische Gewichtskraftkompensation und einem elektromagnetischen Präzisionsantrieb. Das technische Prinzip der Hubeinheit wird erstellt und die Teilsysteme im verfügbaren Bauraum angeordnet. Daraus wird ein detailliertes Modell des pneumatischen Aktors abgeleitet, dieser dimensioniert und dessen Eigenschaften bestimmt. Die Ausdehnung dieses Teilsystems definiert die räumlichen Grenzen für den umliegenden Präzisionsantrieb. Zur Auslegung dieses Antriebs wird das Kraft-/Leistungsverhältnis als Zielgröße definiert. Mit Hilfe von numerischer Simulation und Optimierung werden Geometrien für verschiedenste Topologien entworfen und bewertet. Die geeignetste Variante wird mit allen Teilsystemen in eine Einheit integriert und auskonstruiert. Abschließend werden zukünftige Schritte für die Integration der Einheit in ein Präzisionsantriebssystem dargestellt und mögliche Anwendungsszenarien in der Nanofabrikation präsentiert.A central driver in many of today's fields of technology is the miniaturization of electrical, optical and mechanical systems. Multi-axis devices with large travel ranges and extreme precision play a decisive role, not only in measurement and quality assurance, but also in the fabrication and manipulation of nanometer structures. The vertical movement task poses a special challenge, since the gravitational load of the moving object must be compensated permanently. This thesis proposes a vertically lifting and actuating unit and thus contributes to the further development of nanometer precision drive systems. Basic possible kinematic integration variants are considered and compared according to application relevant criteria. The presented parallel kinematic approach is characterized by its good integrability, its minimal negative influences on the surrounding systems, as well as the distribution of the load to several actuators. Subsequently, a constructive development process is compiled to further develop this favoured variant. During this process the unit to be developed is integrated into the overall system. Further, its requirements, boundary conditions and subsystems are defined. The vertical actuation consists of two systems: A pneumatic weight force compensation and an electromagnetic precision drive. The technical principle of the lifting unit is developed and the subsystems are arranged in the available design space. Based on this, a detailed model of the pneumatic actuator is created, its dimensions derived and properties obtained. These dimensions define the spatial limits for the surrounding precision actuator. For the design of this actuator, the force-power ratio is chosen as the objective quantity. Using numerical simulations and optimization, geometries for various topologies are created and evaluated. The most suitable variant is designed and integrated with all other subsystems into one unit. Finally, upcoming steps for integrating the unit into a precision drive system are outlined and possible future applications in the field of nanofabrication are presented

Development of an integrated guiding and actuation element for high dynamic nanopositioning systems

In nano precision technology, actuating along the vertical axis is a special challenge because of the permanent gravitational force. In this paper, the development of an integrated guiding and actuation element for the vertical motion is presented. A pneumatic-cylinder-like setup is used with its pressure being load controlled, to compensate the gravitational force of the load. An additional electromagnetic drive creates only dynamic forces for the precision motion, keeping the ohmic heat emission to a minimum. For the vertical guiding an aerostatic bushing is used. The whole setup sits on a planar aerostatic bearing pad. Therefore, translational friction can be neglected. Initial testing results of such a unit are presented and an outlook for future research work is given

Recent advancements in Lorentz force eddy current testing

Lorentz Force Eddy Current Testing (LET) is a non-destructive testing technique based on induced eddy currents due to relative motion between a permanent magnet and a conductive, non-ferromagnetic device under test which has been recently introduced. The Lorentz force acting on the magnet is measured and perturbations in conductivity change the Lorentz force profile along the conductor. The permanent magnet is placed in a lift-off distance above the specimen moving with a constant velocity relative to the magnet. The design of the magnet is the most crucial element to improve the technique. Therefore, we present new developments in LET: the optimization of an innovative magnetic structure enhancing the Lorentz force and an uncertainty analysis to identify most important sources of variance. Futhermore, in a defect depth study a detection limit for LET was determined. A new cylindrical magnetic Halbach structure has been designed to concentrate and magnify the magnetic field below the structure. For internal defects a multi-objective, non-linear optimization to maximize the defect response of the drag force is performed. The optimized magnet shape depends on the geometrical parameters of the experimental setup and therefore the optimal shape is highly problem-specific. Secondly, we investigate the uncertainties in our existing experimental setup quantified by a non-intrusive polynomial chaos expansion to determine the impact of multiple unknown input parameters. The experimentally determined statistics of velocity, magnetic remanence of the permanent magnet, conductivity of the specimen and the lift-off distance are modeled as uniform and beta-distributed random variables. The numerically predicted force profiles were validated by experiments. The included analysis of variance of the Lorentz force enables the enhancement of defect detection capability. Finally, experiments with a specimen containing a quasi-infinite crack were performed. By variation of the defect depth a detection limit for LET for drag- and lift-force components of the Lorentz force was determined. It showed the compatibility of LET compared with traditional eddy current testing

Motion-induced eddy current testing of composite materials

Modern composite materials are gaining more and more importance in mechanical engineering. Due to the complex structure of most of these materials, traditional NDT methods do not satisfy the measurement requirements. In this paper we address the capabilities and limitations of the non-destructive testing method of motion-induced eddy currents for (non-ferromagnetic) composite materials. The specimen moves with constant velocity through a magnetic field, which is created by a fixed permanent magnet. The interaction of induced eddy currents and the primary magnetic field re-sults in the Lorentz force acting on the specimen. Due to the third Newton law, the reaction force acts on the magnet system itself and is measured in all three spatial dimensions. Every force component has a characteristic profile for a certain defect-free specimen. Anomalies in the specimen affect the eddy currents due to variations of local conductivity. These deviations influence the measured force profiles from which the location, size and type of the defect in the specimen may be determined. Two types of magnet systems have been applied: a cylindrical magnet and a radial Halbach array with a ferromagnetic disc. The cylindrical magnet produces a dipole-like field, whereas the Halbach array with the additional disc creates a field concentrated right below the magnet system. Experiments show, that the Halbach array is very well suited for thin speci-mens. The defect response signal is higher due to the stronger eddy currents caused by the focused magnetic field. Two different types of composite materials have been experimentally tested: Carbon fiber reinforced plastic (CFRP) and glass laminate aluminum reinforced epoxy (GLARE). For CFRP four samples were fabricated, whereas one was tested. For GLARE two samples were used with defects in different depth

Tip- and laser-based 3D nanofabrication in extended macroscopic working areas

The field of optical lithography is subject to intense research and has gained enormous improvement. However, the effort necessary for creating structures at the size of 20 nm and below is considerable using conventional technologies. This effort and the resulting financial requirements can only be tackled by few global companies and thus a paradigm change for the semiconductor industry is conceivable: custom design and solutions for specific applications will dominate future development (Fritze in: Panning EM, Liddle JA (eds) Novel patterning technologies. International society for optics and photonics. SPIE, Bellingham, 2021. https://doi.org/10.1117/12.2593229). For this reason, new aspects arise for future lithography, which is why enormous effort has been directed to the development of alternative fabrication technologies. Yet, the technologies emerging from this process, which are promising for coping with the current resolution and accuracy challenges, are only demonstrated as a proof-of-concept on a lab scale of several square micrometers. Such scale is not adequate for the requirements of modern lithography; therefore, there is the need for new and alternative cross-scale solutions to further advance the possibilities of unconventional nanotechnologies. Similar challenges arise because of the technical progress in various other fields, realizing new and unique functionalities based on nanoscale effects, e.g., in nanophotonics, quantum computing, energy harvesting, and life sciences. Experimental platforms for basic research in the field of scale-spanning nanomeasuring and nanofabrication are necessary for these tasks, which are available at the Technische Universität Ilmenau in the form of nanopositioning and nanomeasuring (NPM) machines. With this equipment, the limits of technical structurability are explored for high-performance tip-based and laser-based processes for enabling real 3D nanofabrication with the highest precision in an adequate working range of several thousand cubic millimeters

Structural trends in atomic nuclei from laser spectroscopy of tin

Tin is the chemical element with the largest number of stable isotopes. Its complete proton shell, comparable with the closed electron shells in the chemically inert noble gases, is not a mere precursor to extended stability; since the protons carry the nuclear charge, their spatial arrangement also drives the nuclear electromagnetism. We report high-precision measurements of the electromagnetic moments and isomeric differences in charge radii between the lowest 1/2(+), 3/2(+), and 11/2(-) states in Sn117-131, obtained by collinear laser spectroscopy. Supported by state-of-the-art atomic-structure calculations, the data accurately show a considerable attenuation of the quadrupole moments in the closed-shell tin isotopes relative to those of cadmium, with two protons less. Linear and quadratic mass-dependent trends are observed. While microscopic density functional theory explains the global behaviour of the measured quantities, interpretation of the local patterns demands higher-fidelity modelling. Measurements of the hyperfine structure of chemical elements isotopes provide unique insight into the atomic nucleus in a nuclear model-independent way. The authors present collinear laser spectroscopy data obtained at the CERN ISOLDE and measure hyperfine splitting along a long chain of odd-mass tin isotopes.Peer reviewe

Eye tracking – The overlooked method to measure cognition in neurodegeneration?

Eye tracking (ET) studies are becoming increasingly popular due to rapid methodological and technological advances as well as the development of cost efficient and portable eye trackers. Although historically ET has been mostly employed in psychophysics or developmental cognition studies, there is also promising scope to use ET for movement disorders and measuring cognitive processes in neurodegeneration. Particularly, ET can be a powerful tool for cognitive and neuropsychological assessments of patients with pathologies affecting motor and verbal abilities, as tasks can be adapted without requiring motor (except eye movements) or verbal responses. In this review, we will examine the existing evidence of ET methods in neurodegenerative conditions and its potential clinical impact for cognitive assessment. We highlight that current evidence for ET is mostly focused on diagnostics of cognitive impairments in neurodegenerative disorders, where it is debatable whether it has any more sensitivity or specificity than existing cognitive assessments. By contrast, there is currently a lack of ET studies in more advanced disease stages, when patients’ motor and verbal functions can be significantly affected, and standard cognitive assessments are challenging or often not possible. We conclude that ET is a promising method not only for cognitive diagnostics but more importantly, for potential cognitive disease tracking in progressive neurodegenerative conditions