Scientific publications without theses

Results: 828
Created on: Thu, 20 Jun 2024 23:10:26 +0200 in 0.0846 sec

Platl, Vivien; Lechner, Leo; Mattheis, Thomas; Zentner, Lena
Free vibration of compliant mechanisms based on Euler-Bernoulli-Beams. - In: Microactuators, Microsensors and Micromechanisms, (2023), S. 1-18

This paper presents an analytical approach for computing the natural frequencies of planar compliant mechanisms consisting of any number of beam segments. The approach is based on the Euler-Bernoulli Beam theory and the transfer matrix method (TMM), which means there is no need for a global dynamics equation, but instead low-order matrices are used which result in high computational efficiency. Each beam segment is elastic, thin, has a different rectangular cross-section or a different orientation and is treated as an Euler-Bernoulli beam. The approach in principle does not differentiate between the flexure hinges, and the more rigid beam sections, both are treated as beams. The difference in stiffness solely results from the changes in the cross sections and length. A finite element analysis (FEA), as often used in practical applications, has been carried out for various geometries to serve as state-of-the-art reference models to which the results obtained by the presented analytical method could be compared. Various test specimens (TS) consisting of concentrated and distributed compliance in various degrees of complexity were produced and measured in free- and forced vibration testing. The results from experiments and the FEA compared to those of the proposed method are in very good correlation with an average deviation of 1.42%. Furthermore, the analytical method is implemented into a readily accessible computer-based calculation tool which allows to calculate the natural frequencies efficiently and to easily vary different parameters.
Henning, Stefan; Zentner, Lena
Analytical characterization of spatial compliant mechanisms using beam theory. - In: Microactuators, Microsensors and Micromechanisms, (2023), S. 61-76

Due to the advantages of compliant mechanisms, they are widely used in technical fields such as precision engineering, measurement and medical technology. The movement of the mostly monolithically designed mechanisms is primarily achieved by bending the individual structural sections. Due to geometric nonlinearities caused by large deflections, the analytical description of the deformation behavior under the influence of external loads is not trivial. While plane compliant mechanisms can be reliably calculated with different models, the analysis of spatial compliant mechanisms is accordingly more difficult. Due to the complexity of the motion, simplifications are often made in the model assumptions, which have a detrimental effect on the precision of the results. Therefore, this paper presents a method to apply nonlinear beam theory to complex spatial structures that can include both curved sections and sections with non-constant cross-sections. Using selected examples of varying complexity, the model is validated using FEM simulations. In addition, a procedure to characterize branched spatial compliant mechanisms with the proposed analytical model and to calculate their deformation is explained. By efficiently solving the analytical model numerically, the deformed state of the mechanism can be obtained in seconds. Therefore, the model is particularly suitable for early stages of development or iterative synthesis tasks.
Zirkel, Marten; Luo, Yinnan; Römer, Ulrich; Fidlin, Alexander; Zentner, Lena
Development of a database to simulate and adapt compliant mechanisms to a given characteristic for improving energy efficiency of a walking robot. - In: Microactuators, Microsensors and Micromechanisms, (2023), S. 46-60

Compliant mechanisms with variable geometric parameters are investigated for the application in a bipedal robot to improve its walking efficiency. These mechanisms have nonlinear torque-angle characteristics and act like torsion springs to change the systems free oscillation frequency. High energy efficiency is achieved if the free oscillation frequency matches the step frequency, meaning the that the robot walks in resonance. For this purpose, the desired characteristic of the optimized elastic coupling is identified via optimization. Then, a database is developed, which consists of boundary conditions and beam elements. In this paper, there are three boundary conditions and three beam elements for demonstration purpose. To simulate a large number of compliant mechanisms with different characteristics, two boundary conditions and a beam element can be combined. The boundary conditions serve as bearing types to connect the beam element to the thighs of a robot. The large deformation behavior is assumed to be simulated by the Euler-Bernoulli beam theory, which is validated by FEM models. Thus, the desired characteristic from the proceeding optimization process is realized by a specific compliant mechanism.
Pandey, Ashok Kumar; Pal, Prem; Nagahanumaiah; Zentner, Lena
Microactuators, Microsensors and Micromechanisms : MAMM 2022. - Cham : Springer International Publishing, 2023. - 1 Online-Ressource (xiii, 364 p. 234 illus., 186 illus. in color.). - (Mechanisms and machine science ; volume 126) ISBN 978-3-031-20353-4

This book brings together investigations which combine theoretical and experimental results related to such systems as flexure hinges and compliant mechanisms for precision applications, the non-linear analytical modeling of compliant mechanisms, mechanical systems using compliance as a bipedal robot and reconfigurable tensegrity systems and micro-electro-mechanical systems (MEMS) as energy efficient micro-robots, microscale force compensation, magnetoelectric micro-sensors, acoustical actuators and the wafer bonding as a key technology for the MEMS fabrication. The volume gathers the contributions presented at the 6th Conference on Microactuators, Microsensors and Micromechanisms (MAMM), held in Hyderabad, India in December 2022. The aim of the conference was to provide a special opportunity for a know-how exchange and collaboration in various disciplines concerning systems pertaining to micro-technology. The conference was organized under the patronage of IFToMM (International Federation for the Promotion of Mechanism and Machine Science).
Luo, Yinnan; Römer, Ulrich J.; Zentner, Lena; Fidlin, Alexander
Improving energy efficiency of a bipedal walker with optimized nonlinear elastic coupling. - In: Advances in nonlinear dynamics, (2022), S. 253-262

A method to improve the energy efficiency of a bipedal walking robot by means of nonlinear elastic couplings between the robot’s thighs is presented. The robot model consists of five rigid segments which are connected by four actuated revolute joints in the hip and knees. The walking movement is generated and stabilized by a nonlinear controller based on the hybrid zero dynamics approach. The optimum walking gaits and the optimum characteristic of the elastic coupling are identified via numerical optimization whereby the energy consumption of locomotion is minimized. Different walking speeds from 0.2 m/s to 1.4 m/s are considered in the study. According to simulations, the optimal nonlinear elastic coupling reduces the mean energy consumption by 78% over the range of investigated speeds. This is significantly better compared to the coupling with optimal linear torsion spring, which saves 62% energy. The free oscillations frequency of the swing leg under influence of the elastic coupling is derived from a simplified pendulum model. This free oscillations frequency closely matches with the double step frequency of the robot at different walking speeds. The nonlinear elastic coupling gives the robot the capability to walk in resonance at different speeds with a very high energy efficiency.
Prem, Nina; Schale, Florian; Sindersberger, Dirk; Zimmermann, Klaus
Thermosensitive elastomers for shape adaption of soft robotic systems. - In: ACTUATOR 2022: International Conference and Exhibition on New Actuator Systems and Applications, (2022), S. 290-293

Recent advances in soft robotics demonstrate robust and versatile performance for dexterous grasping and manipulation. Due to their intrinsically mechanical compliance, soft robots passively adapt their shape to an object during contact. This results in large contact patches and damping of contact dynamics, which compensates for uncertainties in sensing, modeling, and actuation. Therefore, the behavior of soft robots is also determined by contact-based deformations. Building these kinds of compliant structures by using thermosensitive hybrid materials of polydimethylsiloxane and different thermoplastic filler particles as thermosensitive elastomers (TSE) the design could receive a higher versatility and extra functionality. Thermosensitive elastomers (TSE) consist of an addition curing RTV-2 silicone in which different thermoplastic filler particles are embedded. These thermoplastic particles are polycaprolactone (PCL), polyamide-6 (PA6) and polymethylmethacrylat (PMMA) with melting temperatures in the range of 58deg C to 215deg C. In certain examinations, soft magnetic carbonyl iron particles (CIP) are also included to prove the compatibility of the two particle types within the polydimethylsiloxane (PDMS) matrix and to utilize a possible symbiotic effect of the particle mixtures. By means of mechanical tests, the thermosensitive hybrid materials enable shape changes by applying both external heat and stress/force. With a low melting point in the range of 58 deg C to 60 deg C, PCL offers good application potential compared to the other thermoplastic filler particles. One of PCL most important and application-oriented phenomena is the shape memory effect, which results from internal stresses between elastomer molecular chains and PCL particles. Whereby the external shape arises from the equilibrium of all internal forces. Consequently, the material composites can be referred to as both TSE and shape memory polymers (SMP). By adding soft magnetic particles, an accelerated heat distribution within the samples was detected, which results in a faster occurrence of the corresponding effects. Micro computed tomography (mu-CT) and scanning electron microscopy (SEM) examinations indicate that a homogeneous distribution of PCL and CIP within the thermosensitive elastomer prevails. Moreover, the TSE additionally contain CIP can combine the benefits of temperature and magnetic field effects. Due to the material's ability to imprint or adapt to any shape, thermosensitive elastomers as shape memory polymers represent a potential opportunity to modify pre-existing robotic components. Depending on the initial design and force application, the modified systems could adapt to almost any shape under the influence of temperature. This leads to their use in a variety of applications in adaptive sensors, smart actuators, and gripping elements in soft robotics.
Jahn, Hannes; Henning, Stefan; Zentner, Lena
A method for optimising compliant mechanisms :
Eine Methode zur Optimierung nachgiebiger Mechanismen. - In: Getriebetagung 2022, (2022), S. 133-142

In diesem Beitrag wird eine Methode vorgestellt, mit deren Hilfe nachgiebige Mechanismen bezüglich ihres Verformungsverhaltens optimiert werden können. Berechnungsgrundlage der Methode ist die Theorie großer Verformungen stabförmiger Strukturen. Die Berechnung erfolgt mit numerischen Lösungsverfahren in Python. Für die Optimierung werden Festkörpergelenke entlang einer vorgegebenen Balkenachse verschoben. Durch Parameterstudien dreier Mechanismen wird zunächst die Auswirkung der Gelenkposition auf das Verformungsverhalten herausgestellt. Abschließend wird die Berechnungsmethode mit Hilfe von den aus den Parameterstudien resultierenden Ergebnissen erfolgreich verifiziert.

Merker, Lukas;
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.

Becker, Tatiana; Stolbov, Oleg V.; Biller, Armin M.; Borin, Dmitry Yu.; Stolbova, Olga S.; Zimmermann, Klaus; Raikher, Yuriy L.
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.
Henning, Stefan;
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.


... until 2022 from the Technical Mechanics Group

Results: 519
Created on: Thu, 20 Jun 2024 23:10:03 +0200 in 0.0947 sec

Schorr, Philipp; Zentner, Lena; Zimmermann, Klaus; Böhm, Valter
Jumping locomotion system based on a multistable tensegrity structure. - In: Mechanical systems and signal processing, ISSN 1096-1216, Bd. 152 (2021), 107384

All known locomotion principles are limited respective to environmental conditions. Often, the occurrence of obstacles or gaps means the break-off for the operating motion systems. For such circumstances, a controllable jumping locomotion is required to cross these barriers. However, this locomotion demands sophisticated requirements to the actuation. The abrupt actuation is commonly realized by high dynamic actuators or complex mechanisms. In this work, a simple solution utilizing the multistability of a compliant tensegrity structure is described. Therefore, a two-dimensional tensegrity structure featuring four stable equilibria is considered. Based on bifurcation analyses a feasible actuation to control the current equilibrium configuration is derived. Changing between selected equilibrium states enables a great difference in potential energy, which yields a jumping motion of the structure. Based on numerical simulations a suitable actuation strategy is chosen to overcome obstacle and steps by jumping forward or backward, respectively. The theoretical approach is examined experimentally with a prototype of the multistable tensegrity structure.
Schorr, Philipp; Chavez, Jhohan; Zentner, Lena; Böhm, Valter
Reconfiguration of planar quadrilateral linkages utilizing the tensegrity principle. - In: Mechanism and machine theory, Bd. 156 (2021), 104172

The development of reconfigurable planar four-bar linkages by applying the tensegrity principle is considered. Conventional quadrilateral linkages enable two operation modes differing in the kinematic behavior. However, a change between these states is not possible due to the geometric constraints. To enable a reconfiguration between the different modes one-sided limited nonholonomic constraints are introduced in this work. This issue is realized by applying ropes that cannot resist compression. However, to guarantee an appropriate load case in operation a prestress within the mechanism is required. Hence, the linkage is extended to a tensegrity-based mechanism. The structural dynamics are derived using the Lagrange formalism and the structural behavior is evaluated using numerical simulations. Furthermore, a prototype of an exemplary tensegrity-based mechanism is manufactured and experiments regarding the mechanical properties, in particular the reconfiguration, are performed. The results suggest the potential benefit of applying the tensegrity principle within conventional planar four-bar linkages.
Chavez, Jhohan; Ziolkowski, Marek; Schorr, Philipp; Spieß, Lothar; Böhm, Valter; Zimmermann, Klaus
A method to approach constant isotropic permeabilities and demagnetization factors of magneto-rheological elastomers. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 527 (2021), 167742

The use of non-conventional materials is nowadays of much interest in scientific community. Magneto-rheological elastomers are hybrid materials, which in presence of magnetic fields state a change in their mechanical properties. They are composed by an elastomeric matrix with embedded magnetic particles. One of the most attractive features of these materials is that as soon as the magnetic field is removed from the material, the original mechanical properties are completely recovered, with negligible differences in comparison to the original state. This paper focuses on the study of magnetic characteristics of these smart materials, such as relative permeability and demagnetizing factors, for samples with different volume concentration of ferromagnetic particles.
Merker, Lukas; Steigenberger, Joachim; Marangoni, Rafael R.; Behn, Carsten
A vibrissa-inspired highly flexible tactile sensor: scanning 3D object surfaces providing tactile images. - In: Sensors, ISSN 1424-8220, Bd. 21 (2021), 5, 1572, insges. 29 S.

Just as the sense of touch complements vision in various species, several robots could benefit from advanced tactile sensors, in particular when operating under poor visibility. A prominent tactile sense organ, frequently serving as a natural paragon for developing tactile sensors, is the vibrissae of, e.g., rats. Within this study, we present a vibrissa-inspired sensor concept for 3D object scanning and reconstruction to be exemplarily used in mobile robots. The setup consists of a highly flexible rod attached to a 3D force-torque transducer (measuring device). The scanning process is realized by translationally shifting the base of the rod relative to the object. Consequently, the rod sweeps over the object’s surface, undergoing large bending deflections. Then, the support reactions at the base of the rod are evaluated for contact localization. Presenting a method of theoretically generating these support reactions, we provide an important basis for future parameter studies. During scanning, lateral slip of the rod is not actively prevented, in contrast to literature. In this way, we demonstrate the suitability of the sensor for passively dragging it on a mobile robot. Experimental scanning sweeps using an artificial vibrissa (steel wire) of length 50 mm and a glass sphere as a test object with a diameter of 60 mm verify the theoretical results and serve as a proof of concept.
Boeck, Thomas; Sanjari, Seyed Loghman; Becker, Tatiana
Dynamics of a magnetic pendulum in the presence of an oscillating conducting plate. - In: Proceedings in applied mathematics and mechanics, ISSN 1617-7061, Bd. 20 (2021), 1, e202000083, insges. 2 S.

A pendulum with an attached permanent magnet moving near a conductor is a typical experiment for the demonstration of electromagnetic braking. When the conductor itself moves, it can transfer energy to the pendulum. We study a simple but exact analytical model where the conductor is a horizontally unbounded flat plate. For this geometry, eddy currents and induced Lorentz force due to the motion of a magnetic dipole are known analytically in the quasistatic limit. A vertical oscillation of such a horizontal plate located beneath the magnet is considered. In this setup, the vertical position of the pendulum is an equilibrium point when the magnetic moment of the magnet is perpendicular to its plane of motion. Depending on the strength of the magnetic dipole moment, the frequency and amplitude of the plate as well as the distance between plate and magnet, the plate oscillation can destabilize the equilibrium. The stability limits for weak electromagnetic coupling are computed analytically using the harmonic balancing method. For stronger coupling, the stability limits are obtained numerically using Floquet analysis. Chaotic motions with finite amplitudes are also found.
Darnieder, Maximilian; Harfensteller, Felix; Schorr, Philipp; Scharff, Moritz; Linß, Sebastian; Theska, René
Characterization of thin flexure hinges for precision applications based on first eigenfrequency. - In: Microactuators, microsensors and micromechanisms, (2021), S. 15-24

Flexure hinges with small cross-section heights are state of the art in numerous precision engineering applications due to their capability for smooth and repeatable motion. However, the high sensitivity to manufacturing influences represents a challenge. We propose a characterization method for flexure hinges based on the measurement of the free oscillation, to enable the consideration of manufacturing influences in the early stages of the design process. Three semi-circular flexure hinges with different cross-section heights and highly accurate geometry were investigated experimentally to compare them with three theoretical modeling approaches. The results for the three flexure hinge specimens showed small deviations to the predicted values from the models which is in agreement with the results of dimensional measurements. With each modeling approach, a deviation of the minimal notch height from the nominal value can be calculated. This value, in turn, can be used as manufacturing allowance for subsequent manufacturing of compliant mechanisms using the same manufacturing method. An exemplary compliant parallel-crank mechanism proves the applicability of the concept to compliant mechanisms with multiple flexure hinges.
Zimmermann, Klaus; Zeidis, Igor; Lysenko, Victor
Mathematical model of a linear motor controlled by a periodic magnetic field considering dry and viscous friction. - In: Applied mathematical modelling, Bd. 89 (2021), S. 1155-1162

The paper deals with a drive concept that uses the controllable mechanical properties of a magnetorheological fluid (MRF). The biologically inspired operating principle is based on crawling using anisotropic friction, as of worms, and non-Newtonian fluids, as of snails. The MRF located between a slider and two slide-blocks is functionally relevant for the drive system to generate a translational motion. A controlled magnetic field is utilized to change the friction conditions in the drive system by varying the properties of the MRF. An extended friction model takes the dry friction into account, along with the viscous friction. In this case, apart from the ratio of the coefficients of viscous friction, it is necessary to introduce two more parameters: the ratio of the coefficients of dry friction in the absence and presence of the magnetic field, and the ratio of the characteristic forces of viscous and dry frictions. These parameters allow refining the mathematical model that governs the behavior of a linear motor. Using asymptotic methods of non-linear mechanics, an expression for the average velocity of the slider is obtained for the case when the friction force is assumed to be small in comparison with the driving force of the slide-blocks. The theoretical results are verified experimentally on a prototype.
Schorr, Philipp; Carrillo Li, Enrique Roberto; Kaufhold, Tobias; Hernández, Jorge Antonio Rodríguez; Zentner, Lena; Zimmermann, Klaus; Böhm, Valter
Kinematic analysis of a rolling tensegrity structure with spatially curved members. - In: Meccanica, ISSN 1572-9648, Bd. 56 (2021), 4, S. 953-961

In this work, a tensegrity structure with spatially curved members is applied as rolling locomotion system. The actuation of the structure allows a variation of the originally cylindrical shape to a conical shape. Moreover, the structure is equipped with internal movable masses to control the position of the center of mass of the structure. To control the locomotion system a reliable actuation strategy is required. Therefore, the kinematics of the system considering the nonholonomic constraints are derived in this paper. Based on the resulting insight in the locomotion behavior a feasible actuation strategy is designed to control the trajectory of the system. To verify this approach kinematic analyses are evaluated numerically. The simulation data confirm the path following due to an appropriate shape change of the tensegrity structure. Thus, this system enables a two-dimensional rolling locomotion.
Zimmermann, Klaus; Zeidis, Igor
Kinematika koles i koncepcii šassi dlja senapravlennych :
The kinematics of wheels and chassis concepts for omnidirectional robots. - In: Problems of mechanics, ISSN 1512-0740, (2020), No. 4(81), Seite 21-33

Zimmermann, Klaus; Zeidis, Igor
Kinematika sistemy robot-pricep s Mekanum kolesami :
Kinematics of a robot-trailer system with Mecanum wheels. - In: Problems of mechanics, ISSN 1512-0740, (2020), No. 2(79), Seite 13-20