Application of Stable Inversion to Flexible Manipulators Modeled by the ANCF

Compared to conventional robots, flexible manipulators offer many advantages, such as faster end-effector velocities and less energy consumption. However, their flexible structure can lead to undesired oscillations. Therefore, the applied control strategy should account for these elasticities. A feedforward controller based on an inverse model of the system is an efficient way to improve the performance. However, unstable internal dynamics arise for many common flexible robots and stable inversion must be applied. In this contribution, an approximation of the original stable inversion approach is proposed. The approximation simplifies the problem setup, since the internal dynamics do not need to be derived explicitly for the definition of the boundary conditions. From a practical point of view, this makes the method applicable to more complex systems with many unactuated degrees of freedom. Flexible manipulators modeled by the absolute nodal coordinate formulation (ANCF) are considered as an application example

On-Line Analytical Processing Accounting: Potentials, Application, and Design Methodology

Most software vendors and business consultants agree that On-Line Analytical Processing (OLAP) tools are needed to derive useful decision support from accounting transaction data. But business solutions can not be created just by installing and integrating some tool(s). To support a selection from the growing number of tools, potentials and applications of OLAP for accounting must be clarified. Moreover, a methodology for designing OLAP applications is needed. Being aware that all research in this brand-new field is still in progress, we address these problems in this paper

Simulation of soft robots with nonlinear material behavior using the cosserat rod theory

For the simulation and model-based control of soft robots accurate models are required. In this contribution the simulation of a simple soft robot with the cosserat rod theory is examined for both linear and nonlinear material models. The soft robot is fabricated out of silicone. Thereby stiffness and damping properties are investigated. In addition to the achievable accuracy, the computation time is also examined

Optimal design of particle dampers for structures with low first eigenfrequency under forced vibration

Lightweight designs are becoming increasingly important these days to reduce energy consumption and natural resources. However, a smaller weight typically causes a decrease in stiffness and non-negligible vibration amplitudes over a wide frequency range. One passive damping technique to reduce such vibrations is the use of particle dampers. Thereby containers attached to a vibrating structure or holes embedded in the vibrating structure are filled with granular material. Due to the structural vibrations, momentum is transferred to the granular material which interacts with each other. As a result, energy is dissipated by impacts and frictional phenomena between the particles. Recently, the rolling attribute of spheres has been used to design efficient particle dampers for low amplitude vibrations. As long as the container’s acceleration stays below the gravitational acceleration, this rolling effect can be used to damp horizontal vibrations efficiently. The description of the damper’s energy dissipation is accurately possible using analytical formulas which are presented here. In this presentation, the workflow for a systematic damper design is presented using the analytical formulas and validated experimentally . A good agreement between analytical and experimental measurements is achieved for an optimized damper, validating the presented approach

Robust Topology Optimization of Static Systems with Unilateral Frictional Contact

In this paper a robust topology optimization algorithm for linear elastic structures in unilateral contact is presented. The deformation of the linear elastic structure is constrained by support structures that are modeled with the help of Signorini's contact conditions. The contact conditions in turn are enforced with the augmented Lagrangian approach. Doing so, the robust optimization considers uncertainties at the support such as manufacturing tolerances and its local friction behavior. Due to high numerical costs in robust optimization, the firstorder second-moment approach is used to approximate the mean and variance of the objective. This approximation results in minimal additional costs to approximate the mean, the variance and their gradients. Consequentially, a gradient-based optimization algorithm can be used to minimize a weighted sum of both. The results show that the presented approach indeed improves the robustness with respect to uncertain contact conditions compared to a deterministic optimization

Christian Ergenzinger

A Discrete Element Approach to Model Breakable Railway Ballast A discrete element approach to assess degradation processes in ballast beds is presented. Firstly, a discrete element model describing strength and failure of strong rock is introduced. For this purpose a granular solid is created by bonding of adjacent particles. A method to define angular ballast stones made from the granular solid is proposed. The strength of these stones is evaluated by compression between parallel platens. Comparing these results to published experimental data yields very good qualitative and reasonable quantitative agreement. Finally, the failure of aggregates of breakable stones is investigated by simulation of oedometric compression tests and indentation of a sleeper into a ballast bed

Beforschung einer eigenen Vorlesung: Effekte von Wahlfreiheit auf Leistung und Konfidenz

Basierend auf Forschung zum Lernen in Vorlesungen und der Selbstbestimmungstheorie wurde der Effekt von Wahlfreiheit auf kognitive Testleistung und metakognitive Konfidenz im Rahmen einer eigenen Vorlesung untersucht. N = 370 Studierende bearbeiteten semesterbegleitend selbst gewählte sowie vorgegebene schriftliche Reflexionen und absolvierten zu zwei Messzeitpunkten Tests mit konfidenzgewichteten Richtig-Falsch-Items. Testitems zu Inhalten der selbstgewählten Reflexionen wurden zu beiden Messzeitpunkten gleich gut bearbeitet (Leistung; kognitives Maß), während die Sicherheit in korrekte und inkorrekte Lösungen abnahm (Konfidenz; metakognitives Maß). Die Leistung bei Testitems zu Inhalten der vorgegebenen Reflexionen nahm zum zweiten Messzeitpunkt ab, während die Konfidenz in inkorrekte Lösungen zunahm. Mögliche Mechanismen und Konsequenzen der Studienergebnisse, aber auch Grenzen der Studie und somit mögliche Implikationen werden diskutiert