Modellbasierte Entwicklung von Methoden, Algorithmen und Werkzeugen zur Analyse und Synthese nachgiebiger Mechanismen. - Ilmenau : Universitätsverlag Ilmenau, 2022. - 1 Online-Ressource (XXI, 184 Seiten, Seite XXIII-LV). - (Berichte der Ilmenauer Mechanismentechnik (BIMT) ; Band 7)
Technische Universität Ilmenau, Dissertation 2022
Nachgiebige Mechanismen sind in technischen Anwendungen weit verbreitet, insbesondere in der Robotik, Präzisions-, Mess- und Medizintechnik. Ihr Verformungsverhalten wird maßgeblich durch die Gestaltung ausgewählter nachgiebiger Strukturabschnitte, beispielsweise durch die gezielte Reduktion der Querschnittsabmessungen, beeinflusst. Die Bewegung des Mechanismus erfolgt vorwiegend durch Biegung dieser Abschnitte. Die Berechnung des Verformungsverhaltens unter dem Einfluss äußerer Belastungen stellt aufgrund von geometrischer Nichtlinearität eine anspruchsvolle Aufgabe bei der Analyse und Synthese nachgiebiger Mechanismen dar. Daher wird in dieser Arbeit ein Beitrag zur analytischen Modellbildung und damit zum Analyse- und Syntheseprozess geleistet. Die Modellgleichungen werden für ebene und räumliche Anwendungsfälle gegeben. Mit Hilfe dieser können nachgiebige Mechanismen mit variierenden Querschnitten, Krümmungen, Werkstoffen und Verzweigungen charakterisiert werden. Für die Betrachtung beliebiger Mechanismen werden die Gleichungen in einer rekursiven Form gegeben. Aufgrund von Strukturabschnitten unterschiedlicher Querschnitte werden, über reine Biegung hinaus, auch Querkraftschub und Querkontraktion im Modell berücksichtigt. Es werden Untersuchungen durchgeführt um zu definieren, wann diese Effekte, in Abhängigkeit der Geometrie, zu berücksichtigen sind. Auf Basis dieser Untersuchungen werden Empfehlungen für die zu verwendende Theorie gegeben. Durch die Formulierung der Gleichungen in einer einheitlichen Form wird ermöglicht, die Theorie für einzelne Abschnitte eines nachgiebigen Mechanismus individuell anzupassen. Weiterhin wird das Modell durch Beispielmechanismen für zwei- und dreidimensionale Anwendungsfälle mit Hilfe der Finiten-Elemente-Methode und experimentellen Untersuchungen validiert. Dabei werden die Empfehlungen der einzusetzenden Theorie angewendet. Daraufhin werden Algorithmen zur Dimensionierung einzelner Festkörpergelenke und nachgiebiger Mechanismen gegeben. Dadurch kann deren Bewegungsverhalten im Hinblick auf konkrete Zielkriterien verbessert werden. Abschließend werden die Methoden in drei eigenständig ausführbare Softwarewerkzeuge implementiert, die frei zur Verfügung gestellt sind. Durch deren Entwicklung wird ein Beitrag zum Entwurf sowie zur Analyse und Synthese von Festkörpergelenken und nachgiebigen Mechanismen geleistet.
https://doi.org/10.22032/dbt.53126
Actuators based on a controlled particle-matrix interaction in magnetic hybrid materials for applications in locomotion and manipulation systems. - In: Magnetic hybrid-materials, (2022), S. 653-680
The paper deals with the investigation of magneto-sensitive elastomers (MSE) and their application in technical actuator systems. MSE consist of an elastic matrix containing suspended magnetically soft and/or hard particles. Additionally, they can also contain silicone oil, graphite particles, thermoplastic components, etc., in various concentrations in order to tune specific properties such as viscosity, conductivity and thermoelasticity, respectively. The focuses of investigations are the beneficial properties of MSE in prototypes for locomotion and manipulation purposes that possess an integrated sensor function. The research follows the principle of a model-based design, i.e. the working steps are ideation, mathematical modelling, material characterization as well as building first functional models (prototypes). The developed apedal (without legs) and non-wheeled locomotion systems use the interplay between material deformations and the mechanical motion in connection with the issues of control and stability. Non-linear friction phenomena lead to a monotonous forward motion of the systems. The aim of this study is the design of such mechanical structures, which reduce the control costs. The investigations deal with the movement and control of 'intelligent' mechanisms, for which the magnetically field-controlled particle-matrix interactions provide an appropriate approach. The presented grippers enclose partially gripped objects, which is an advantage for handling sensitive objects. Form-fit grippers with adaptable contour at the contact area enable a uniform pressure distribution on the surface of gripped objects. Furthermore, with the possibility of active shape adaptation, objects with significantly differing geometries can be gripped. To realise the desired active shape adaptation, the effect of field-induced plasticity of MSE is used. The first developed prototypes mainly confirm the functional principles as such without direct application. For this, besides the ability of locomotion and manipulation itself, further technological possibilities have to be added to the systems.
Magnetoactive elastomers for magnetically tunable vibrating sensor systems. - In: Magnetic hybrid-materials, (2022), S. 625-652
Magnetoactive elastomers (MAEs) are a special type of smart materials consisting of an elastic matrix with embedded microsized particles that are made of ferromagnetic materials with high or low coercivity. Due to their composition, such elastomers possess unique magnetic field-dependent material properties. The present paper compiles the results of investigations on MAEs towards an approach of their potential application as vibrating sensor elements with adaptable sensitivity. Starting with the model-based and experimental studies of the free vibrational behavior displayed by cantilevers made of MAEs, it is shown that the first bending eigenfrequency of the cantilevers depends strongly on the strength of an applied uniform magnetic field. The investigations of the forced vibration response of MAE beams subjected to inplane kinematic excitation confirm the possibility of active magnetic control of the amplitude-frequency characteristics. With change of the uniform field strength, the MAE beam reveals different steady-state responses for the same excitation, and the resonance may occur at various ranges of the excitation frequency. Nonlinear dependencies of the amplification ratio on the excitation frequency are obtained for different magnitudes of the applied field. Furthermore, it is shown that the steady-state vibrations of MAE beams can be detected based on the magnetic field distortion. The field difference, which is measured simultaneously on the sides of a vibrating MAE beam, provides a signal with the same frequency as the excitation and an amplitude proportional to the amplitude of resulting vibrations. The presented prototype of the MAE-based vibrating unit with the field-controlled "configuration" can be implemented for realization of acceleration sensor systems with adaptable sensitivity. The ongoing research on MAEs is oriented to the use of other geometrical forms along with beams, e.g. two-dimensional structures such as membranes.
Design of compliant mechanisms based on rigid-body mechanisms. - In: Romanian journal of technical sciences, ISSN 2601-5811, Bd. 67 (2022), 1, S. 61-78
The design of compliant mechanisms is a much more complicated task than their analysis. Consequently, there are many more methods available for the analysis of compliant mechanisms than for their synthesis. In this article, a contribution to the synthesis of compliant mechanisms is made by presenting a comparison of two different methods for their design. In both methods rigid-body systems are used as a basis for compliant mechanisms. Depending on the task of the compliant mechanism, one of these methods can be selected and applied. The deviations between the results of the used theory and measurement results as well as FEM results are less than 5.5 % for displacements and acting forces. Selected mechanisms for the realization of a straight-line motion of a point and for given relative motions are presented as examples.
Investigations on a torque-compensating adjustment drive for mechanically sensitive devices. - In: Proceedings of the 22nd International Conference of the European Society for Precision Engineering and Nanotechnology, (2022), S. 81-82
Parametric instability of a vertically driven magnetic pendulum with eddy-current braking by a flat plate. - In: Nonlinear dynamics, ISSN 1573-269X, Bd. 109 (2022), 2, S. 509-529
The vertically driven pendulum is one of the classical systems where parametric instability occurs. We study its behavior with an additional electromagnetic interaction caused by eddy currents in a nearby thick conducting plate that are induced when the bob is a magnetic dipole. The known analytical expressions of the induced electromagnetic force and torque acting on the dipole are valid in the quasistatic limit, i.e., when magnetic diffusivity of the plate is sufficiently high to ensure an equilibrium between magnetic field advection and diffusion. The equation of motion of the vertically driven pendulum is derived assuming that its magnetic dipole moment is aligned with the axis of rotation and that the conducting plate is horizontal. The vertical position of the pendulum remains an equilibrium with the electromagnetic interaction. Conditions for instability of this equilibrium are derived analytically by the harmonic balance method for the subharmonic and harmonic resonances in the limit of weak electromagnetic interaction. The analytical stability boundaries agree with the results of numerical Floquet analysis for these conditions but differ substantially when the electromagnetic interaction is strong. The numerical analysis demonstrates that the area of harmonic instability can become doubly connected. Bifurcation diagrams obtained numerically show the co-existence of stable periodic orbits in such conditions. For moderately strong driving, chaotic motions can be maintained for the subharmonic instability.
https://doi.org/10.1007/s11071-022-07555-8
Bending vibration systems which are complementary with respect to eigenvalues. - In: Mechatronics and life sciences, (2022), S. 277-286
In developing prototypes, one fundamental activity is to model appropriate systems which mimic fundamental features of (biological) paradigms. In this way, we set up different models for the investigation of natural frequencies. The aim is to detect object contacts of technical sensors in observing their vibration behavior. For this, we compare the range and the shift of natural frequencies determined from the analysis of the arising two-point boundary-value problems. In particular, we found two systems with complementary spectra of eigenvalues. Considering boundary damping we analyzed these eigenvalues in the first octant of the complex plane. The fundamental result is that these two systems offer no common eigenvalue, they are alternative. This is an interesting and unique observation.
An analytical method for calculating the natural frequencies of spatial compliant mechanisms. - In: Mechanism and machine theory, Bd. 175 (2022), 104939, S. 1-17
Compliant mechanisms are becoming increasingly important in both research and industry. The design and the static analysis of such mechanisms has made much progress in recent years, yet comparatively little research has been done on their dynamic behaviour. The aim of this paper is to advance the dynamic analysis of spatial compliant mechanisms by pursuing the calculation of their natural frequencies. So far, their determination is only possible with time-consuming 3D-FEM simulations or via pseudo-rigid-body models and Lagrangian equations. An analytical method is developed to simplify and accelerate the calculation of the natural frequencies of compliant mechanisms. The method is integrated into an algorithm on which a graphical user interface is developed to allow the design and calculation of the system in the most time efficient and intuitive way. The results are verified by 3D-FEM simulations and validated through an experiment. The evaluation shows good agreement with the reference models. The results of this paper allow a reliable and efficient calculation of natural frequencies and serve to facilitate further work regarding the dynamic analysis of compliant mechanisms.
https://doi.org/10.1016/j.mechmachtheory.2022.104939
Modeling of corner-filleted flexure hinges under various loads. - In: Mechanism and machine theory, Bd. 175 (2022), 104937, S. 1-11
Compliant mechanisms are widely applied in precision engineering, measurement technology and microtechnology, due to their potential for the reduction of mass and assembly effort through the integration of functions into fewer parts and an increasing motion repeatability through less backlash and wear, if designed appropriately. However, a challenge during the design process is the handling of the multitude of geometric parameters and the complex relations between loads, deformations and strains. Furthermore, some tasks such as the dimensioning by means of optimization or the modeling for a controller design require a high number of analysis calculations. From this arises the need for sufficient computational analysis models with low calculation time. Existing studies of analysis models are mostly based on selected load cases, which may limits their general validity. The scope of this article is the comparison of models for the analysis of corner-filleted flexure hinges under various loads, to determine their advantages, disadvantages and application fields. The underlying methods of the study can further be used to evaluate future models based on a broad selection of possible load cases.
https://doi.org/10.1016/j.mechmachtheory.2022.104937
Untersuchung des Feuchtetransportes und dessen Einfluss auf Form- und Eigenspannungsänderungen in Furnieren. - Düren : Shaker Verlag, 2022. - XII, 181 Seiten. - (Berichte aus der Mechanik)
Technische Universität Ilmenau, Dissertation 2021
ISBN 978-3-8440-8523-5
Gegenstand der vorliegenden Arbeit ist, die Untersuchung der Feuchteaufnahme und -weiterleitung in Furnieren, wie sie während der industriellen Verarbeitung vorkommt. Es steht damit die Aufnahme von freiem Wasser einschließlich der damit einhergehenden quellungsbedingten Form- und Eigenspannungsänderungen bei Furnieren im Fokus der Betrachtungen. Hierzu werden, nach Vorstellung ausgewählter Grundlagen aus Forschung und Technik, Konzeption und Realisierung experimenteller Untersuchungen erläutert. Die am Beispiel von Rotbuchenfurnier (Fagus Sylvatica L.) durchgeführten Untersuchungen unterscheiden dabei zwischen Versuchsreihen zur Wasseraufnahme und der damit verbundenen Verformungsentwicklung. Die Randbedingungen der verschiedenen Messreihen berücksichtigen für Holz typische anatomische Eigenschaften (z. B. Faserausrichtung), relevante Befeuchtungsszenarien aus der industriellen Furnierverarbeitung (einseitige, zweiseitige und allseitige Feuchtezufuhr) sowie Einflüsse aus der Furnierherstellung (Unterscheidung rissbehaftete/rissfreie Furniersichtseite). Darüber hinaus ist die mathematische Beschreibung der Feuchtebewegung in Furnieren Gegenstand der Arbeit. So werden auf Basis der Fick’schen Diffusionsgesetze, mit Hilfe der Finite-Elemente-Methode, feuchteabhängige Kennwertverläufe (Transportkoeffizienten) für longitudinalen und radialen Feuchtetransport in Rotbuchenfurnier abgeleitet. Im Ergebnis kann festgehalten werden, dass der Feuchtetransport in Furnier sehr gut mit Hilfe der entwickelten Modelle beschrieben werden kann. Ferner werden, basierend auf den durchgeführten Untersuchungen, ein für Furnier typisches und von Vollholzerzeugnissen abweichendes Verformungsverhalten herausgestellt sowie allgemeine Aussagen zur Formstabilität von Furnieren abgeleitet.