A multipole magnetoactive elastomer for vibration-driven locomotion. - In: Soft Robotics, ISSN 2169-5180, Bd. 0 (2023), 0
Smart materials such as magnetoactive elastomers (MAEs) combine elastic and magnetic properties that can be significantly changed in response to a magnetic field and therefore offer enormous potential for applications in both scientific research and engineering. When such an elastomer contains microsized hard magnetic particles, it can become an elastic magnet once magnetized in a strong magnetic field. This article studies a multipole MAE with the aim of utilizing it as an actuation element of vibration-driven locomotion robots. The elastomer beam has three magnetic poles overall with the same poles at the ends and possesses silicone bristles protruding from its underside. The quasi-static bending of the multipole elastomer in a uniform magnetic field is investigated experimentally. The theoretical model exploits the magnetic torque to describe the field-induced bending shapes. The unidirectional locomotion of the elastomeric bristle-bot is realized in two prototype designs using magnetic actuation of either an external or an integrated source of an alternating magnetic field. The motion principle is based on cyclic interplay of asymmetric friction and inertia forces caused by field-induced bending vibrations of the elastomer. The locomotion behavior of both prototypes shows a strong resonant dependency of the advancing speed on the frequency of applied magnetic actuation.
https://doi.org/10.1089/soro.2022.0106
Vibrissa-inspired tactile sensing : object shape detection under frictional influences. - Ilmenau, 2022. - x, 154 Seiten
Technische Universität Ilmenau, Dissertation 2022
Die taktile Sensorik birgt große Potenziale für die Weiterentwicklung von technischen Geräten und deren Einsatz in unstrukturierten Umgebungen. Häufig sind taktile Sensorkonzepte von der Natur inspiriert, z.B. durch die mystazialen Vibrissen der Ratte. Diese speziellen Tasthaare dienen als multimodale Sensoren, die Ratten u.a. zur Objektformkennung befähigen. Die vorliegende Arbeit verfolgt einen biomimetischen Ansatz mit dem Ziel der Weiterentwicklung vibrissen-inspirierter Sensoren für die 3D-Objektformerkennung unter Reibungseinflüssen. Das biologische Vorbild Vibrisse besteht im Wesentlichen aus einem hochflexiblen, nicht-sensorischen Haarschaft, welcher in seinen eigenen Follikel-Sinus-Komplex eingebettet ist, der sensorische Komponenten enthält. Diese Struktur wird abstrahiert und auf ein technisches Sensorkonzept übertragen. Zur Realisierung der Objektabtastung wird ein schlanker, einseitig eingespannter, hochflexibler Taster durch lineare Verschiebung der Einspannung entlang des Zielobjekts gestrichen. Die resultierenden Lagerreaktionen dienen als einzige Observablen für die Rekonstruktion von Kontaktpunktfolgen zwischen Taster und Objekt, die schließlich auf die Form des letzteren schließen lassen. Zu diesem Zweck wird das Sensorkonzept mechanisch modelliert und mithilfe von Modellgleichungen beschrieben. Aufbauend auf der Analyse der 2D-Objektabtastung und -Rekonstruktion unter Reibungseinflüssen wird das Modell auf den allgemeinen 3D Fall erweitert. In Simulationen und Experimenten wird die allgemeine Umsetzbarkeit der Objektformerkennung demonstriert. Simulationsbasierte Parameterstudien verdeutlichen zudem den Einfluss der (Coulomb) Reibung auf die Lagerreaktionen und die Rekonstruktionsergebnisse. Während die Lagerreaktionen signifikant von Reibungseffekten beeinflusst werden, ist der Fehler der rekonstruierten Kontaktpunkte reibungsinvariant (unbeeinflusst durch den Reibungskoeffizienten). Diese Erkenntnisse werden im Zusammenhang mit den experimentellen Ergebnissen diskutiert. Darüber hinaus wird für den Fall der 2D-Objektabtastung ein Ansatz zur Rekonstruktion von Reibungsparametern vorgestellt, für den ein erster experimenteller Konzeptnachweis erbracht wird. Schließlich wird das Sensormodell mit Blick auf das biologische Vorbild durch Implementierung einer elastischen Lagerung und einer rotatorischen Abtastkinematik angepasst.
Shape-programmable cantilever made of a magnetoactive elastomer of mixed content. - In: Smart materials and structures, ISSN 1361-665X, Bd. 31 (2022), 10, 105021, S. 1-14
This work presents an approach to the macroscopic field-controlled mechanics of magnetoactive elastomers of mixed content, which are a special type of smart materials made of an elastic composite and a combination of two essentially different ferromagnetic fillers. High-coercive particles of NdFeB-alloy powder for the magnetically hard (MH) filler and carbonyl iron powder particles with nearly zero coercivity for the magnetically soft (MS) filler are usually used. The MH particles are tens-of-micron in size and impart to the elastomer a remanent magnetisation, whereas due to the MS particles of several microns in size, the elastomer acquires a high magnetic susceptibility. Since large MH particles once magnetised in a strong field possess their own fields to which the MS particles are susceptible, the overall elastomer magnetisation as well as its mechanical response greatly depends on the relative concentration of both fillers. This work particularly studies the bending deformation of horizontally fixed magnetoactive cantilevers with the permanent magnetisation along the length axis under the action of gravity and a vertically applied uniform magnetic field. The cantilevers of the same geometry and fixed NdFeB content but different carbonyl iron concentration are considered. The magnetomechanical model is developed based on the finite-strain theory assuming the plane-stress approximation of the two-dimensional cantilever of infinite width. The magnetic energy comprises two magnetic terms, one of which is qualitatively linear and the other one is quadratic in the applied field strength. The numerically calculated field-programmed equilibrium bending shapes of the cantilevers are compared with the experimentally observed shapes. The model provides good agreement with the experiment up to moderate concentrations of the MS filler, when the coefficients of customary interpolation formulas for the concentration dependencies of elastic modulus and magnetic susceptibility are properly adjusted.
https://doi.org/10.1088/1361-665X/ac8f79
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.
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.
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.
Actuators based on a controlled particle-matrix interaction in magnetic hybrid materials for applications in locomotion and manipulation systems. - In: Physical sciences reviews, ISSN 2365-659X, Bd. 7 (2022), 11, S. 1263-1290
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. The first steps are therefore being taken towards integrated MSE based adaptive sensor systems.
https://doi.org/10.1515/psr-2019-0087