07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8

Browse

Now showing 1 - 20 of 567

Open Access
A 10 V transfer standard based on low-noise solid-state Zener voltage reference ADR1000
(2024) Bülau, André; Walter, Daniela; Zimmermann, André
Voltage standards are widely used to transfer volts from Josephson voltage standards (JVSs) at national metrology institutes (NMIs) into calibration labs to maintain the volts and to transfer them to test equipment at production lines. Therefore, commercial voltage standards based on Zener diodes are used. Analog Devices Inc. (San Jose, CA, USA), namely, Eric Modica, introduced the ADR1000KHZ, a successor to the legendary LTZ1000, at the Metrology Meeting 2021. The first production samples were already available prior to this event. In this article, this new temperature-stabilized Zener diode is compared to several others as per datasheet specifications. Motivated by the superior parameters, a 10 V transfer standard prototype for laboratory use with commercial off-the-shelf components such as resistor networks and chopper amplifiers was built. How much effort it takes to reach the given parameters was investigated. This paper describes how the reference was set up to operate it at its zero-temperature coefficient (z.t.c.) temperature and to lower the requirements for the oven stability. Furthermore, it is shown how the overall temperature coefficient (t.c.) of the circuit was reduced. For the buffered Zener voltage, a t.c. of almost zero, and with amplification to 10 V, a t.c. of <0.01 µV/V/K was achieved in a temperature span of 15 to 31 °C. For the buffered Zener voltage, a noise of ~584 nVp-p and for the 10 V output, ~805 nVp-p were obtained. Finally, 850 days of drift data were taken by comparing the transfer standard prototype to two Fluke 7000 voltage standards according to the method described in NBS Technical Note 430. The drift specification was, however, not met.
Open Access
25jähriges Amtsjubiläum : Feierlichkeiten in Berlin
(1990) Heisel, Uwe
Am 1. Oktober 1990 wurde im Produktlonstechnischen Zentrum (PTZ) Berlin das 125jährige Amtsjubiläum von Professor Dr.-lng. Dres. h. c. Günter Spur in einer Feierstunde begangen, die mit Ansprachen des Präsidenten der Technischen Universität Berlin, Professor Dr.-lng. M. Frlcke und des Prodekans des Fachbereichs Konstruktion und Fertigungstechnik, Professor Dr.-Ing. H. Pucher, im Kreise von Freunden und Schülern des Jubilars eröffnet wurde. Die Laudatio auf den international bekannten und hochgeschätzten Forscher und Hochschullehrer sprach Professor Dr.-Ing. J. Milberg aus München, der als ehemaliger Mitarbeiter G. Spurs und heutiger Kollege das Wlrken und die Verdienste seines Freundes würdigte.
Open Access
3-D-Koordinatenmessung durch optische Triangulation
(1986) Seitz, Günther; Tiziani, Hans J.; Litschel, Reinhold
Das hier vorgestellte Drei-Koordinaten-Meßgerät arbeitet nach dem Prinzip der optischen Triangulation. Einzelne Punkte einer Oberfläche können gezielt angetastet und vermessen werden. Hierbei wurden Meßunsicherheiten von ± 0,1mm bei einer maximalen Meßgeschwindigkeil von 25 Punkten/Sekunde erreicht. Bei einem Meßabstand von 420mm beläuft sich das Antastfeld auf 150 x 150mm. Der optische Aufbau ermöglicht einen Abstandsmeßbereich von ca. 350 mm. Das Gerät eignet sich zur räumlichen Vermessung nichtspiegelnder Werkstückoberflächen. Da das Meßkonzept eine freie Vorgabe der Antastpunkte gestattet, sind Toleranz- und Vollständigkeitsprüfungsaufgaben in der Serienfertigung bevorzugte Anwendungen.
Open Access
3-D-Koordinatenmessung durch optische Triangulation
(1988) Seitz, Günther; Tiziani, Hans J.; Litschel, Reinhold
Das hier vorgestellte Drei-Koordinaten-Meßgerät arbeitet nach dem Prinzip der optischen Triangulation. Einzelne Punkte einer Oberfläche können gezielt angetastet und vermessen werden. Hierbei wurden Meßunsicherheiten von ± 0,1 mm bei einer maximalen Meßgeschwindigkeit von 25 Punkten/Sekunde erreicht. Bei einem Meßabstand von 420 mm beläuft sich das Antastfeld auf 150 x 150 mm. Der optische Aufbau ermöglicht einen Abstandsmeßbereich von ca. 350 mm. Das Gerät eignet sich zur räumlichen Vermessung nichtspiegelnder Werkstückoberflächen. Da das Meßkonzept eine freie Vorgabe der Antastpunkte gestattet, sind Toleranz- und Vollständigkeitsprüfungsaufgaben in der Serienfertigung bevorzugte Anwendungen.
Open Access
3D FEM simulation of titanium alloy (Ti6Al4V) machining with harmonic endmill tools
(2023) Kalu-Uka, Abraham; Ozoegwu, Chigbogu; Eberhard, Peter
Usually, end milling operations have been carried out using conventional uniform helix tools with fixed helix angles. Thus, many studies have been conducted to study the effects of these tools on the thermomechanical properties of a milling process. Recently, there have been works that point to the benefits of using harmonic endmills. Harmonic endmills consist of cutting edge profiles that have continuously harmonically varying helix angles. The variation is described using a harmonic function of axial position (elevation) of points on the cutting edge. In this work, a 3D finite element simulation using ABAQUS, is carried out for the complex milling process of Titanium alloy Ti6Al4V. The envelope of the harmonic tool is first generated using a set of MATLAB codes and stored in a Standard Triangle Language (.stl) format. The machine tool is introduced into an FEM program which has been designed to provide for dynamic effects, thermo‐mechanical coupling, material damage law and the criterion for contact associated with the milling process. A Johnson‐Cook material constitutive equation which combines the effects of strain hardening, strain softening, and temperature softening is used. To account for the chip separation criterion, the Johnson Cook damage evolution equation is used. The milling process simulation for Ti6Al4V is then carried out. In the end, the stress distribution and the cutting forces are obtained.
Open Access
3D printing of colored micro-optics
(2023) Aslani, Valese; Toulouse, Andrea; Schmid, Michael; Giessen, Harald; Haist, Tobias; Herkommer, Alois
Open Access
μ-Suboptimal design of a robustly performing controller for a chemical reactor
(1994) Amann, Notker; Allgöwer, Frank
The design of robustly performing controllers for an important class of control problems is treated. The problem is dealt with in the structured singular value (μ)-framework. The systems considered are characterized by weak nonlinearities and parametric and unstructured uncertainties. Nonlinear effects are taken into account via linearization families. Parametric uncertainty is included in a non-conservative way. Both lead to a μ-synthesis problem with repeated scalar real perturbations. As no direct solution to such a μ-synthesis problem is known to date, an iterative approach comprising both μ-analysis of the actual problem and D-K-iteration for a modified problem is shown. This approach is applied to a realistic continuous stirred-tank reactor for production of cyclopen-tenol to show the applicability to non-trivial MIMO process control problems.
Open Access
Abbildungsqualität photogrammetrischer Objektive unter Berücksichtigung von Umwelteinflüssen
(1983) Tiziani, Hans J.
Hochleistungsobjektive für die Luftbildaufnahmen haben einen hohen Entwicklungsstand erreicht. Umwelteinflüsse machen sich auf die Bildqualität bemerkbar, ja können sie sogar begrenzen. Anstrengungen sind erforderlich, diese Umwelteinflüsse zu erfassen und zu berücksichtigen. Die MTF bietet dazu die Möglichkeit. Bei der Beschreibung der Bildqualität ist die Berücksichtigung des ganzen Bildfeldes wesentlich. Qualitätseinbrüche bei einzelnen Bildwinkeln sind zu vermeiden.
Open Access
Absolutmessender Taster für ein großes Anwendungsspektrum
(1990) Heisel, Uwe
Wenn heute von Meßtastern die Rede ist, so denkt man unwillkürlich an schaltende Taster, die seit langem schon zur integrierten Qualitätssicherung und -überwachung für den automatischen Fertigungsablauf am Markt angeboten werden. Typische Anwendungen in der Praxis reichen von der Prüfung der Werkstückgeometrie am Roh- und Fertigteil über Nullpunktkorrekturen für die Werkstückträger bzw. -aufnahmen bis zur Erfassung von statischen und thermischen Deformationen während des Prozesses. Schon fast in Vergessenheitl geraten ist es, daß am Anfang der Entwicklung auch absolutmessende Taster einen großen Marktanteil hatten.
Open Access
Abstapelvorrichtung für Vierseiten-Hobelmaschine
(1991) Heisel, Uwe; Eggert, Otto Th.; Ozkara, Ali Osman
Vierseiten-Hobelmaschinen (Kehlmaschinen) sind heute in der Holzbearbeitung weit verbreitete Maschinen mit einem universellen Einsatzbereich. Ein bisher noch ungelöstes Problem stellte die preiswerte, funktionelle Handhabung der bearbeiteten Werkstücke dar, besonders dann, wenn es sich dabei um Rundstäbe wie Tisch- und Stuhlfüße handelt. Zusammen mit einem Anwender aus der Möbelindustrie wurde am Institut für Werkzeugmaschinen der Universität Stuttgart eine Einrichtung entworfen und realisiert, mit deren Hilfe es möglich ist, von der Vierseiten-Hobelmaschine bearbeitete Rundstäbe in Paletten abzustapeln. Die im folgenden beschriebene Abstapelanlage ist nun seit etwa einem Jahr im Einsatz und arbeitet seither ohne nennenswerte Störungen.
Open Access
Acceleration-based disturbance compensation for elastic rack-and-pinion drives
(2021) Brenner, Felix; Lechler, Armin; Verl, Alexander
Rack-and-pinion drives are mainly used for large machine tools and are often operated with indirect position control. Due to the lack of state information on the output side, this results in reduced accuracy regarding the table position. In addition, the system can only react inadequately to disturbances outside the control loop, meaning that often insufficient results can be achieved in typical application scenarios such as milling. To meet the increasing dynamic and accuracy requirements of the modern manufacturing industry, this paper presents a highly dynamic acceleration-based disturbance compensation method. For this purpose, the table acceleration is estimated using a dynamical model of the drive train and compared to the signal from an additional acceleration sensor attached to the machine table. Based on the resulting difference, an additional compensation torque is provided, which suppresses the disturbance in counterphase. The approach is tested experimentally on an open control platform with industrial drive components and the behavior is investigated based on compliance frequency responses and externally applied milling forces. At the same time, a standardized parametrization methodology is developed and the robustness is evaluated by varying table masses. In summary, a considerable improvement of the dynamic disturbance behavior can be achieved compared to the conventional system without compensator.
Open Access
Adaptive method for quantitative estimation of glucose and fructose concentrations in aqueous solutions based on infrared nanoantenna optics
(2019) Schuler, Benjamin; Kühner, Lucca; Hentschel, Mario; Giessen, Harald; Tarín, Cristina
In life science and health research one observes a continuous need for new concepts and methods to detect and quantify the presence and concentration of certain biomolecules-preferably even in vivo or aqueous solutions. One prominent example, among many others, is the blood glucose level, which is highly important in the treatment of, e.g., diabetes mellitus. Detecting and, in particular, quantifying the amount of such molecular species in a complex sensing environment, such as human body fluids, constitutes a significant challenge. Surface-enhanced infrared absorption (SEIRA) spectroscopy has proven to be uniquely able to differentiate even very similar molecular species in very small concentrations. We are thus employing SEIRA to gather the vibrational response of aqueous glucose and fructose solutions in the mid-infrared spectral range with varying concentration levels down to 10 g/l. In contrast to previous work, we further demonstrate that it is possible to not only extract the presence of the analyte molecules but to determine the quantitative concentrations in a reliable and automated way. For this, a baseline correction method is applied to pre-process the measurement data in order to extract the characteristic vibrational information. Afterwards, a set of basis functions is fitted to capture the characteristic features of the two examined monosaccharides and a potential contribution of the solvent itself. The reconstruction of the actual concentration levels is then performed by superposition of the different basis functions to approximate the measured data. This software-based enhancement of the employed optical sensors leads to an accurate quantitative estimate of glucose and fructose concentrations in aqueous solutions.
Open Access
Adaptive numerical integration of exponential finite elements for a phase field fracture model
(2021) Olesch, Darius; Kuhn, Charlotte; Schlüter, Alexander; Müller, Ralf
Phase field models for fracture are energy-based and employ a continuous field variable, the phase field, to indicate cracks. The width of the transition zone of this field variable between damaged and intact regions is controlled by a regularization parameter. Narrow transition zones are required for a good approximation of the fracture energy which involves steep gradients of the phase field. This demands a high mesh density in finite element simulations if 4-node elements with standard bilinear shape functions are used. In order to improve the quality of the results with coarser meshes, exponential shape functions derived from the analytic solution of the 1D model are introduced for the discretization of the phase field variable. Compared to the bilinear shape functions these special shape functions allow for a better approximation of the fracture field. Unfortunately, lower-order Gauss-Legendre quadrature schemes, which are sufficiently accurate for the integration of bilinear shape functions, are not sufficient for an accurate integration of the exponential shape functions. Therefore in this work, the numerical accuracy of higher-order Gauss-Legendre formulas and a double exponential formula for numerical integration is analyzed.
Open Access
Additive manufacturing of β-tricalcium phosphate components via Fused Deposition of Ceramics (FDC)
(2020) Eßlinger, Steffen; Grebhardt, Axel; Jäger, Jonas; Kern, Frank; Killinger, Andreas; Bonten, Christian; Gadow, Rainer
Das Paper beschreibt die Compoundierung bioaktiver Keramik (Beta-Tricalciumphosphat) in einer organischen Matrix, die anschließende Extrusion zu Filamenten, die für den FDM-3D-Druck geeignet sind, sowie die Formgebund zu Scaffolds mittels additiver Fertigung. Weiterhin werden fertigungsprozessbegleitende Untersuchungen zur Entbinderung und Sinterung durchgeführt.
Open Access
Additively manufactured porous filling pneumatic network actuator
(2023) Giacoppo, Giuliano A.; Hötzel, Julia; Pott, Peter P.
This research project investigated the additive manufacturing of pneumatic actuators based on the principle of droplet dosing using an Arburg Freeformer 300-3X 3D printer. The developed structure consists of a porous inner filling and a dense, airtight chamber. By selectively varying the filling densities of the porous inner filling, different membrane deflections of the actuator were achieved. By linking the actuators, a pneumatic network actuator was developed that could be used in endorobotics. To describe the membrane deflection of an additively manufactured pneumatic actuator, a mathematical model was developed that takes into account the influence of additive manufacturing and porous filling. Using a dedicated test rig, the predicted behavior of the pneumatic actuators was shown to be qualitatively consistent. In addition, a pneumatic network actuator (PneuNet) with a diameter of 17 mm and a height of 76 mm, consisting of nine chambers with different filling densities, could be bent through 82° under a pressure of 8 bar. Our study shows that the variation of filling densities during production leads to different membrane deflections. The mathematical model developed provides satisfactory predictions, although the influence of additive manufacturing needs to be determined experimentally. Post-processing is still a necessary step to realize the full bending potential of these actuators, although challenges regarding air-tightness remain. Future research approaches include studying the deflection behavior of the chambers in multiple directions, investigating alternative materials, and optimizing the printing process to improve mechanical properties and reliability.
Open Access
Adhesion-induced demolding forces of hard coated microstructures measured with a novel injection molding tool
(2023) Schoenherr, Maximilian; Ruehl, Holger; Guenther, Thomas; Zimmermann, André; Gundelsweiler, Bernd
The demolding of plastic parts remains a challenging aspect of injection molding. Despite various experimental studies and known solutions to reduce demolding forces, there is still not a complete understanding of the effects that occur. For this reason, laboratory devices and in-process measurement injection molding tools have been developed to measure demolding forces. However, these tools are mostly used to measure either frictional forces or demolding forces for a specific part geometry. Tools that can be used to measure the adhesion components are still the exception. In this study, a novel injection molding tool based on the principle of measuring adhesion-induced tensile forces is presented. With this tool, the measurement of the demolding force is separated from the actual ejection step of the molded part. The functionality of the tool was verified by molding PET specimens at different mold temperatures, mold insert conditions and geometries. It was demonstrated that once a stable thermal state of the molding tool was achieved, the demolding force could be accurately measured with a comparatively low force variance. A built-in camera was found to be an efficient tool for monitoring the contact surface between the specimen and the mold insert. By comparing the adhesion forces of PET molded on polished uncoated, diamond-like carbon and chromium nitride (CrN) coated mold inserts, it was found that a CrN coating reduced the demolding force by 98.5% and could therefore be an efficient solution to significantly improve demolding by reducing adhesive bond strength under tensile loading.
Open Access
Adjustment of micro- and macroporosity of ß-TCP scaffolds using solid-stabilized foams as bone replacement
(2023) Dufner, Lukas; Oßwald, Bettina; Eberspaecher, Jan; Riedel, Bianca; Kling, Chiara; Kern, Frank; Seidenstuecker, Michael
To enable rapid osteointegration in bioceramic implants and to give them osteoinductive properties, scaffolds with defined micro- and macroporosity are required. Pores or pore networks promote the integration of cells into the implant, facilitating the supply of nutrients and the removal of metabolic products. In this paper, scaffolds are created from ß-tricalciumphosphate (ß-TCP) and in a novel way, where both the micro- and macroporosity are adjusted simultaneously by the addition of pore-forming polymer particles. The particles used are 10-40 wt%, spherical polymer particles of polymethylmethacrylate (PMMA) (Ø = 5 m) and alternatively polymethylsilsesquioxane (PMSQ) (Ø = 2 m), added in the course of ß-TCP slurry preparation. The arrangement of hydrophobic polymer particles at the interface of air bubbles was incorporated during slurry preparation and foaming of the slurry. The foam structures remain after sintering and lead to the formation of macro-porosity in the scaffolds. Furthermore, decomposition of the polymer particles during thermal debindering results in the formation of an additional network of interconnecting micropores in the stabilizing structures. It is possible to adjust the porosity easily and quickly in a range of 1.2-140 m with a relatively low organic fraction. The structures thus prepared showed no cytotoxicity nor negative effects on the biocompatibility.
Open Access
Adjustment of the geometries of the cutting front and the kerf by means of beam shaping to maximize the speed of laser cutting
(2023) Lind, Jannik; Hagenlocher, Christian; Weckenmann, Niklas; Blazquez-Sanchez, David; Weber, Rudolf; Graf, Thomas
The shape of the laser beam used for fusion cutting significantly influences the geometry of both the cutting front and the cutting kerf. The angle of the cutting front in turn impacts the local absorptivity, while the width of the kerf defines the amount of material, which has to be molten. The kerf’s geometry therefore determines the maximum possible cutting speed at which a successful cut is feasible with a given available laser power. The absorptivity, the width of the kerf, and the maximum possible cutting speed can be estimated from a simple model considering the conservation of energy and rough geometrical approximations. In order to verify the prediction of the model, the geometry of the cutting front and kerf resulting from different processing conditions was observed by means of online high-speed X-ray diagnostics. The geometry of the interaction zone was recorded with a framerate of 1000 Hz during fusion cutting of 10-mm-thick samples of stainless steel. Comparing the results obtained with different shapes of the laser beam, it was found that the absorptivity is increased when the beam’s longitudinal cross-section (parallel to the feed) is enlarged. Reducing the width of the beam in the transversal direction normal to the feed reduces the cross-sectional area of the cutting kerf. The findings show a good agreement with the geometric model which enabled the prediction of the absorptivity and the cross-sectional area of the cutting kerf and hence allows to reliably estimate the maximum cutting speed for different shapes of the laser beam, laser power, and sheet thicknesses.
Open Access
Advantages of holographic imaging through fog
(2023) Gröger, Alexander; Pedrini, Giancarlo; Claus, Daniel; Alekseenko, Igor; Gloeckler, Felix; Reichelt, Stephan
Open Access
Aerodynamics of high-speed trains with respect to ground simulation
(2022) Weidner, Dennis; Stoll, Daniel; Kuthada, Timo; Wagner, Andreas
Wind tunnel testing is commonly used to assess and optimize the aerodynamic characteristics of high-speed trains. The train model is usually mounted above a static ground plane, but a moving ground is necessary for the correct representation of the relative motion between train and ground. This study focuses on the effect of the applied ground simulation on the aerodynamics of a high-speed train. Wind tunnel tests using a stationary and a moving ground were carried out using a 1:20 scale model of a high-speed train’s first car. Numerical simulations for two moving ground configurations are created, and the simulation setup is validated using surface pressure measurements from the wind tunnel tests. It is shown that the ground simulation has a significant effect on the drag in the considered yaw angle range. Additionally, the change in drag due to bogie fairings is evaluated and an impact of the applied ground simulation on the drag reduction is observed. The drag reduction of front and rear bogie fairings is valued similarly using a static ground, however on a moving ground the drag reduction of front bogie fairings is significantly increased. Good agreement between simulations and experiments is achieved.