@article{SchaefferHerrmannSchratzenstalleretal., author = {Schaeffer, Leon and Herrmann, David and Schratzenstaller, Thomas and Dendorfer, Sebastian and B{\"o}hm, Valter}, title = {Preliminary theoretical considerations on the stiffness characteristics of a tensegrity joint for the use in dynamic orthoses}, series = {Journal of Medical Robotics Research}, journal = {Journal of Medical Robotics Research}, publisher = {World Scientific}, doi = {10.1142/S2424905X23400081}, abstract = {Early motion therapy plays an important role for effective long-term healing of joint injuries. In many cases, conventional dynamic orthoses fail to address the intricate movement possibilities of the underlying joints, limited by their simplistic joint representations, often represented by revolute joints, enabling rotations by only one axis. In this paper, a two-dimensional compliant tensegrity joint for use in biomedical applications is investigated. It consists of two compressed members and five compliant tensioned members. Relative movement possibilities are realized by the intrinsic compliance of the structure. In the development of these systems, the first step is the determination of the static stable equilibrium. This analysis is conducted in this paper by considering the potential energy approach or by using the geometric nonlinear finite element method. The mechanical behavior of the structure is assessed with a specific emphasis on its mechanical compliance. The primary objective of this study is the investigation of the influence of structural parameters on the overall stiffness and movability of the structure. The results underscore the significant effect of member parameters on the stiffness and movability of the compliant tensegrity joint, particularly under varying load magnitudes. These findings provide insights for optimizing the joint's performance, contributing to its potential application in advanced orthotic and exoskeleton devices.}, language = {en} } @book{RillSchaefferBorchsenius, author = {Rill, Georg and Schaeffer, Thomas and Borchsenius, Fredrik}, title = {Grundlagen und computergerechte Methodik der Mehrk{\"o}rpersimulation}, publisher = {Springer Nature}, doi = {10.1007/978-3-658-41968-4}, pages = {XIV, 260}, abstract = {Dieses Lehr- und {\"U}bungsbuch vermittelt auf anschauliche Weise die Methoden der Mehrk{\"o}rpersimulation und verdeutlicht deren Vor- und Nachteile bei der praktischen Anwendung anhand konkreter Beispiele. Die einzelnen Methoden werden durch Matlab-Skripte und -Funktionen verdeutlicht, wobei die Modellbildung, die mathematische Beschreibung und die numerische Simulation von Systemen starrer K{\"o}rper die Schwerpunkte bilden. Die vorliegende Auflage wurde unter anderem um Matlab-Live-Skripte erweitert, welche kleine Animationen zur Veranschaulichung der Dynamik der Probleme enthalten. Die L{\"o}sungen zu den {\"U}bungsbeispielen und die integrierten Matlab-Skripte sowie weitere Beispiele und Anwendungen stehen {\"u}ber QR-Codes zum Download zur Verf{\"u}gung und erm{\"o}glichen dadurch auch ein effizientes Selbststudium.}, subject = {Mehrk{\"o}rpersystem}, language = {de} } @incollection{RillSchaefferBorchsenius, author = {Rill, Georg and Schaeffer, Thomas and Borchsenius, Fredrik}, title = {Analyse von Mehrk{\"o}rpersystemen}, series = {Grundlagen und computergerechte Methodik der Mehrk{\"o}rpersimulation}, booktitle = {Grundlagen und computergerechte Methodik der Mehrk{\"o}rpersimulation}, publisher = {Springer}, doi = {10.1007/978-3-658-41968-4_5}, pages = {198}, abstract = {Nach dem Aufbau eines Mehrk{\"o}rper-Simulationsmodells muss dieses auf Richtigkeit, Funktionalit{\"a}t und Wirtschaftlichkeit getestet werden. Die Ermittlung der Gleichgewichtslage stellt dabei eine erste Plausibilit{\"a}ts-Kontrolle dar. Eine Linearisierung mit anschließender Analyse der Eigendynamik liefert Aussagen {\"u}ber die Frequenzen und das D{\"a}mpfungsverhalten des Modells. Einfache Erregersignale erm{\"o}glichen einen ersten Einblick in das nichtlineare dynamische Verhalten des Modells. Modell-Parameter, die nicht genau bekannt sind, k{\"o}nnen durch gezielte Variationen plausibel gesch{\"a}tzt oder {\"u}ber eine Optimierung sogar mit optimalen Werten belegt werden. Nach all diesen Tests steht das Mehrk{\"o}rper- Simulationsmodell dann f{\"u}r praktischeUntersuchungen zurVerf{\"u}gung, die neben reinen Zeitsimulationen auch Methoden der Inversen Kinematik und der Inversen Dynamik mit einschließen.}, language = {de} } @article{RillSchaefferSchuderer, author = {Rill, Georg and Schaeffer, Thomas and Schuderer, Matthias}, title = {LuGre or not LuGre}, series = {Multibody System Dynamics}, journal = {Multibody System Dynamics}, publisher = {Springer}, doi = {10.1007/s11044-023-09909-5}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-65653}, pages = {28}, abstract = {The LuGre model is widely used in the analysis and control of systems with friction. Recently, it has even been made available in the commercial multibody dynamics simulation software system Adams. However, the LuGre model exhibits well-known drawbacks like too low and force rate-dependent break-away forces, drift problems during sticking periods, and significant differences in non-stationary situations between the pre-defined friction law and the one produced by the LuGre model. In the present literature, these problems are supposed to come from the model dynamics or its nonlinear nature. However, most of these drawbacks are not simple side effects of a dynamic friction model but are caused in the LuGre approach, as shown here, by a too simple and inconsistent model of the bristle dynamics. Standard examples and a more practical application demonstrate that the LuGre model is not a "what you see is what you get" approach. A dynamic friction model with accurate bristle dynamics and consistent friction force is set up here. It provides insight into the physical basis of the LuGre model dynamics. However, it results in a nonlinear and implicit differential equation, whose solution will not be easy because of the ambiguity of the friction characteristics. The standard workaround, a static model based on simple regularized characteristics, produces reliable and generally satisfactory results but definitely cannot maintain a stick. The paper presents a second-order dynamic friction model, which may serve as an alternative. It can maintain a stick and produces realistic and reliable results.}, language = {en} } @misc{SchudererRillSchaefferetal., author = {Schuderer, Matthias and Rill, Georg and Schaeffer, Thomas and Schulz, Carsten}, title = {Friction modeling from a practical point of view}, series = {MULTIBODY2023: 11th ECCOMAS Thematic Conference on Multibody Dynamics, Tampa, 24th-28th May 2023}, journal = {MULTIBODY2023: 11th ECCOMAS Thematic Conference on Multibody Dynamics, Tampa, 24th-28th May 2023}, language = {en} }