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
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
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.
Investigation of a multistable tensegrity robot applied as tilting locomotion system. - In: 2020 IEEE International Conference on Robotics and Automation (ICRA), (2020), S. 2932-2938
https://doi.org/10.1109/ICRA40945.2020.9196706
Development of a PC program for the analysis of compliant mechanisms for arbitrary motion tasks :
Entwicklung eines PC-Programms zur Analyse von nachgiebigen Mechanismen für beliebige Bewegungsaufgaben. - In: IFToMM D-A-CH Konferenz 2020 der IFTOMM Member Organizations Austria, Germany, Switzerland, (2020), insges. 2 S.
Abhängig von der Bewegungsaufgabe werden nachgiebige Mechanismen mit konzentrierter oder verteilter Nachgiebigkeit in der Feinwerk-, Mess- und Mikrotechnik eingesetzt. Aufgrund von geometrischen Nichtlinearitäten durch große Verformungen und die Querschnittsänderungen entlang des Mechanismus ist eine analytische Beschreibung besonders herausfordernd. Daher werden bisher meist zeitaufwendige FEM-Simulationen für die Analyse eingesetzt. Die Synthese, also die gezielte Anpassung der geometrischen Parameter an ein gewünschtes Bewegungsverhalten ist meist nicht-intuitiv und iterativ. Umfassende Berechnungsprogramme zur Analyse und Synthese nachgiebiger Mechanismen mit konzentrierter und verteilter Nachgiebigkeit sind nicht bekannt. Daher wird ein eigenständiges, in PYTHON entwickeltes PC-Programm zur nichtlinearen analytischen Berechnung von kontinuierlichen nachgiebigen Mechanismen vorgestellt. Die Grundlage für die Berechnung bilden die nichtlineare Theorie großer Verformungen stabförmiger Strukturen und deren Erweiterungen mit Berücksichtigung des Querkraftschubs und der Querkontraktion. Durch die Modellierung des Mechanismus als Kontinuum, liegen im Anschluss an die Lösung des Differentialgleichunggsystems Lösungen für das Schnittmoment, den Neigungsinkel und die Koordinaten x und y für jeden Punkt entlang der Stabachse vor. Diese Ergebnisse werden anschließend verwendet um eine Reihe wichtiger Parameter wie Verschiebungen und Dehnungen zu ermitteln und in der Programmoberfläche für jedes Element anzuzeigen. Es wird eine grafische Benutzeroberfläche präsentiert, mit der über vordefinierte Bausteine ein nachgiebiger Mechanismus elementweise aufgebaut werden kann. Die wichtigsten geometrischen Parameter sowie die Kräfte im Bereich jedes Elements werden über eine umfangreiche Eingabetabelle definiert. Der Nutzer kann zudem die Randbedingungen an beiden Enden des Mechanismus durch Auswahl festlegen. Das Programm bietet zusätzlich die Möglichkeit Parameterstudien durchzuführen. Dies eröffnet die Möglichkeit einen Mechanismus in Bezug auf eine Bewegungsaufgabe oder ein Dehnungsminimum iterativ zu optimieren. Damit leistet das Programm über den detaillierten Analysemöglichkeiten hinaus einen Beitrag zur Synthese nachgiebiger Mechanismen.
https://nbn-resolving.org/urn:nbn:de:hbz:464-20200220-110951-3
Design of a vibration driven motion system based on a multistable tensegrity structure. - In: Informatics in control, automation and robotics, (2020), S. 302-307
Theoretical and experimental investigation of performance characteristics and design aspects of cross-spring pivots. - In: International journal of solids and structures, Bd. 185/186 (2020), S. 240-256
Cross-spring pivots have been widely employed over the last decades in a broad variety of precision engineering applications due to the high motion repeatability achieved thanks to the absence of stick slip and clearance. In this paper, the non-linear effect of the anticlastic curvature of the leaf-springs is considered for the accurate analytical modeling of the elasto-kinematic behavior of cross-spring pivots. Finite element analyses (FEA), based on a non-linear thin-shell model, are carried out in order to compare them with the analytical results for the main performance parameters of this type of device, i.e. center-shift, rotational stiffness and stress in the leaf-springs. Furthermore, an experimental setup is built to assess the applicability limits of both models. Finally, remarkable performance aspects of cross-spring pivots are discussed aiming for design improvements.
https://doi.org/10.1016/j.ijsolstr.2019.08.023
Modellbasierte Untersuchungen der Kraftüberwachung anhand des Verformungsverhaltens einer Matratzenfeder. - In: Tagungsband 13. Kolloquium Getriebetechnik, (2019), S. 191-200
Nichtlinear-analytische Modellbildung nachgiebiger Mechanismen unter Berücksichtigung des Querkraftschubs. - In: Tagungsband 13. Kolloquium Getriebetechnik, (2019), S. 31-40