Modeling, design and prototyping of a pantograph-based compliant mechanism. - In: Microactuators, microsensors and micromechanisms, (2021), S. 76-88
The main task of the compliant mechanism synthesis is to generate a pre-defined motion path as accurately as possible. A general approach to the compliant mechanism synthesis is to develop a compliant mechanism based on the rigid-body model by replacing conventional joints with compliant joints, i.e. flexure hinges. Using the example of a mechanism producing a scissors-like motion, in this paper a more specific and iterative synthesis process is implemented for the design of a compliant path-generating mechanism. Based on two symmetric pantograph mechanisms, a kinematic analysis of the multi-link rigid-body model is performed. The final dimensions and link lengths of the rigid-body model are used to implement a compliant mechanism with different flexure hinges. Therefore, several designs are iteratively investigated by means of FEM simulations in order to improve the path accuracy and the opening angle of the scissors-like motion.
https://doi.org/10.1007/978-3-030-61652-6_7
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.
https://doi.org/10.1016/j.apm.2020.08.021
Non-linear analytical modeling of planar compliant mechanisms. - In: Mechanism and machine theory, Bd. 155 (2021), 104067, insges. 15 S.
Compliant mechanisms are state of the art in technical applications, especially in precision engineering. They mostly achieve their motion due to bending-dominated deformation of their compliant segments, i.e. flexure hinges. Accurately analyzing a compliant mechanism in dependence of specific flexure hinges is still a challenging task due to the monolithic design and non-linearities caused by large deflections. Most existing accurate analytical models are restricted to single hinges. Therefore, this paper presents a non-linear analytical approach to calculate the elasto-kinematic properties of arbitrary planar compliant mechanisms. The approach is based on the theory for large deflections of rod-like structures. As a typical example, a compliant parallel four-bar linkage with varying compliant segments is investigated by means of the proposed analytical approach. The motion and deformation behavior are numerically calculated with the use of MATLAB®. It is shown, that the analytical results are in good correlation with FEM-based simulations and measurements of a manufactured prototype. To demonstrate the generality of the proposed method, two further and more complex mechanism examples are considered. As a result, the implemented modeling approach allows an accurate and fast analysis as well as synthesis of manifold planar compliant mechanisms with distributed or concentrated compliance.
https://doi.org/10.1016/j.mechmachtheory.2020.104067
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.
https://doi.org/10.1007/s11012-020-01199-x
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
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
Arbeitsbuch Technische Mechanik
Unicopy Campus Edition. - Ilmenau : Technische Universität, Fakultät für Maschinenbau, Fachgebiet Technische Mechanik, 2020. - iv, 241 Seiten. - (Ilmenauer Editionen)
Ein Beitrag zur Entwicklung mobiler Roboter basierend auf multistabilen Tensegrity Strukturen. - Ilmenau : Universitätsverlag Ilmenau, 2020. - 1 Online-Ressource (xviii, 135 Seiten)
Technische Universität Ilmenau, Dissertation 2020
In: Universitätsverlag Ilmenau
In dieser Arbeit wird die Anwendung von Tensegrity Strukturen mit mehreren stabilen Gleichgewichtskonfigurationen zur Realisierung von Lokomotionssystemen in der mobilen Robotik untersucht. Diese Strukturen werden unter dem mechanischen Aspekt modelliert und verschiedene Aktuatorstrategien zur Realisierung eines kontrollierten Wechsels zwischen den unterschiedlichen stabilen Gleichgewichtslagen abgeleitet. Zur experimentellen Verifikation der theoretischen Ansätze wird ein Prototyp einer multistabilen Tensegrity Struktur entwickelt. Die experimentellen Ergebnisse bestätigen die vorteilhaften Eigenschaften multistabiler Tensegrity Strukturen sowie die Möglichkeit von kontrollierten Konfigurationswechseln. Infolge von Erweiterungen des mechanischen Modells unter Berücksichtigung von Umwelteinflüssen wird das Bewegungsverhalten von Tensegrity Strukturen simuliert. In dieser Arbeit wird die Fortbewegung durch die Gleichgewichtslagenwechsel der multistabilen Tensegrity Struktur realisiert. Abhängig von der gewählten Aktuierungsstragie kann eine schreitende Lokomotion, eine kriechende Lokomotion sowie eine springende Lokomotion realisiert werden. Experimente mit dem entwickelten Prototyp bestätigen die zuvor untersuchten Lokomotionsformen. Durch Kombination der verschiedenen Bewegungsmodi resultiert ein multimodales Lokomotionssystem. Dieses Lokomotionssystem erlaubt die Anpassung des Lokomotionsprinzips hinsichtlich der gegebenen Umgebungsbedingungen.
https://doi.org/10.22032/dbt.45203
Parametric instability of a magnetic pendulum in the presence of a vibrating conducting plate. - In: Nonlinear dynamics, ISSN 1573-269X, Bd. 102 (2020), 4, S. 2039-2056
A pendulum with an attached permanent magnet swinging in the vicinity of a conductor is a typical experiment for the demonstration of electromagnetic braking and Lenz law of induction. When the conductor itself moves, it can transfer energy to the pendulum. An exact analytical model of such an electromagnetic interaction is possible for a flat conducting plate. The eddy currents induced in the plate by a moving magnetic dipole and the resulting force and torque are known analytically in the quasistatic limit, i.e., when the magnetic diffusivity is sufficiently high to ensure an equilibrium of magnetic field advection and diffusion. This allows us to study a simple pendulum with a magnetic dipole moment in the presence of a horizontal plate oscillating in vertical direction. Equilibrium of the pendulum in the vertical position can be realized in three cases considered, i.e., when the magnetic moment is parallel to the rotation axis, or otherwise, its projection onto the plane of motion is either horizontal or vertical. The stability problem is described by a differential equation of Mathieu type with a damping term. Instability is only possible when the vibration amplitude and the distance between plate and magnet satisfy certain constraints related to the simultaneous excitation and damping effects of the plate. The nonlinear motion is studied numerically for the case when the magnetic moment and rotation axis are parallel. Chaotic behavior is found when the eigenfrequency is sufficiently small compared to the excitation frequency. The plate oscillation typically has a stabilizing effect on the inverted pendulum.
https://doi.org/10.1007/s11071-020-06054-y
An approach to robotic end effectors based on multistable tensegrity structures. - In: New trends in mechanism and machine science, (2020), S. 470-478
In this paper compliant multistable tensegrity structures with discrete variable stiffness are investigated. The different stiffness states result from the different prestress states of these structures corresponding to the equilibrium configurations. Three planar tensegrity mechanisms with two stable equilibrium configurations are considered exemplarily. The overall stiffness of these structures is characterized by investigations with regard to their geometric nonlinear static behavior. Dynamical analyses show the possibility of the change between the equilibrium configurations and enable the derivation of suitable actuation strategies.