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Natural resources and technology - on the mitigating effect of green tech
Full text linkThis paper deals with the question as to whether technology can lessen the problem of scarce resources. Focusing on fossil and biomass materials as important resources for production and consumption, the paper empirically investigates whether environmental innovations reduce the material usage in European economies. A dynamic panel model is employed to estimate the effect of environmental innovations on the use of fossil and biomass materials. It shows that there is no continuously mitigating effect of green technology. For biomass, no significant technology effects are found. Fossil materials are saved by innovations in recycling as well as by new production and processing technologies, but not by all categories of relevant green technology
Modular and Analytical Methods for Solving Kinematics and Dynamics of Series-Parallel Hybrid Robots
Full text linkWhile serial robots are known for their versatility in applications, larger workspace, simpler modeling and control, they have certain disadvantages like limited precision, lower stiffness and poor dynamic characteristics in general. A parallel robot can offer higher stiffness, speed, accuracy and payload capacity, at the downside of a reduced workspace and a more complex geometry that needs careful analysis and control. To bring the best of the two worlds, parallel submechanism modules can be connected in series to achieve a series-parallel hybrid robot with better dynamic characteristics and larger workspace. Such a design philosophy is being used in several robots not only at DFKI (for e.g., Mantis, Charlie, Recupera Exoskeleton, RH5 humanoid etc.) but also around the world, for e.g. Lola (TUM), Valkyrie (NASA), THOR (Virginia Tech.) etc.These robots inherit the complexity of both serial and parallel architectures. Hence, solving their kinematics and dynamics is challenging because they are subjected to additional geometric loop closure constraints. Most approaches in multi-body dynamics adopt numerical resolution of these constraints for the sake of generality but may suffer from inaccuracy and performance issues. They also do not exploit the modularity in robot design. Further, closed loop systems can have variable mobility, different assembly modes and can impose redundant constraints on the equations of motion which deteriorates the quality of many multi-body dynamics solvers. Very often only a local view to the system behavior is possible. Hence, it is interesting for geometers or kinematics researchers, to study the analytical solutions to geometric problems associated with a specific type of parallel mechanism and their importance over numerical solutions is irrefutable. Techniques such as screw theory, computational algebraic geometry, elimination and continuation methods are popular in this domain. But this domain specific knowledge is often underrepresented in the design of model based kinematics and dynamics software frameworks. The contributions of this thesis are two-fold. Firstly, a rigorous and comprehensive kinematic analysis is performed for the novel parallel mechanisms invented recently at DFKI-RIC such as RH5 ankle mechanism and Active Ankle using approaches from computational algebraic geometry and screw theory. Secondly, the general idea of a modular software framework called Hybrid Robot Dynamics (HyRoDyn) is presented which can be used to solve the geometry, kinematics and dynamics of series-parallel hybrid robotic systems with the help of a software database which stores the analytical solutions for parallel submechanism modules in a configurable and unit testable manner. HyRoDyn approach is suitable for both high fidelity simulations and real-time control of complex series-parallel hybrid robots. The results from this thesis has been applied to two robotic systems namely Recupera-Reha exoskeleton and RH5 humanoid. The aim of this software tool is to assist both designers and control engineers in developing complex robotic systems of the future. Efficient kinematic and dynamic modeling can lead to more compliant behavior, better whole body control, walking and manipulating capabilities etc. which are highly desired in the present day and future robotic applications
Modellierung des Tribosystems beim trockenen Vollvorwärtsfließpressen mithilfe eines erweiterten Reibmodells
Full text linkWerkzeuge in der Kaltmassivumformung sind hohen Prozessbelastungen ausgesetzt. Zur Reduzierung dieser Prozessbelastung werden Fest- und Flüssigschmierstoffe eingesetzt. Der Einsatz von Schmierstoffen ist jedoch aus ökologischen, ökonomischen und gesetzlichen Gründen nachteilig. Neuartige Ansätze in der Kaltmassivumformung zielen auf die Verwendung von ökologisch unbedenklichen Schmierstoffen oder die vollständige Vermeidung des Einsatzes von Schmierstoffen ab. Dieser Beitrag konzentriert sich auf die Substitution von Schmierstoffen beim Kaltfließpressen durch Oberflächentexturen auf den Halbzeugen und einer selbstschmierenden Beschichtung auf dem Werkzeug. Das Potenzial von Oberflächenstrukturen an Halbzeugen und selbstschmierenden Werkzeugbeschichtungen zur Reduzierung von Reibung und Verschleiß beim trockenen Vollvorwärtsfließpressen wurde in Vorarbeiten durch Analogieuntersuchungen nachgewiesen. Analogieuntersuchungen unter trockenen tribologischen Randbedingungen haben positive Ergebnisse in Vorarbeiten erbracht und im Zuge dieses Beitrags wurden trockene Vollvorwärtsfließpressversuche durchgeführt. Hierbei lag der Schwerpunkt der Untersuchungen auf der Machbarkeit sowie in der Selektion der potenziell besten Kombination aus Oberflächentextur der Halbzeuge und Werkzeugbeschichtung in Bezug auf Reibung und Verschleiß. Zur Untersuchung wurde neben der Presskraft auch die Oberfläche der Fließpresswerkzeuge mittels REM analysiert. Parallel wurde der Prozess durch eine validierte numerische FE-Prozesssimulation mit der Simulationssoftware Forge NxT 2.1 unterstützt. Hierbei wurde ein Ansatz mithilfe eines erweiterten Reibmodells gewählt, um den Kraftverlauf quantitativ genauer ab-zubilden. Der Vollvorwärtsfließpressprozess konnte ohne Schmierstoff durchgeführt werden und die Proben ohne Schädigung ausgeworfen werden. Es wurde beobachtet, dass der höchste Verschleiß der Matrizen nicht in dem Bereich mit der höchsten Werkzeugbelastung, sondern in dem Bereich mit relativ geringer Belastung auftrat. Darüber hinaus wurde gezeigt, dass es bisher kein für das Kaltfließpressen geeignetes Verschleißmodell gibt
Die Rom III-Verordnung und ihre Anwendung auf das Ehescheidungsrecht der Flüchtlingsstaaten Syrien, Afghanistan und Eritrea
Full text linkIn the period of 2015 to 2018 a majority of refugees came from Syria, Afghanistan and Eritrea to Germany. Among the refugees are also families. From the family constellation legal questions can arise in the country of residence, i.e. Germany. In terms of divorce law, the Rome III Regulation, Council Regulation (EU) No 1259/2010 of 20 December 2010, defines the applicable law in connection with a divorce, whether chosen by the disputing parties or by the regulation if a choice of law did not take place. In this context, the law of the country of origin of the refugees could be applicable. The work presents the Rome III Regulation and its application to the divorce law of the countries of Syria, Afghanistan and Eritrea. The marriage-law of Syria, Afghanistan and Eritrea is presented and checked whether the divorce law of these countries could be used before a German court
Robot Learning from Human Demonstrations for Human-Robot Synergy
Full text linkHuman-robot synergy enables new developments in industrial and assistive robotics research. In recent years, collaborative robots can work together with humans to perform a task, while sharing the same workplace. However, the teachability of robots is a crucial factor, in order to establish the role of robots as human teammates. Robots require certain abilities, such as easily learning diversified tasks and adapting to unpredicted events. The most feasible method, which currently utilizes human teammate to teach robots how to perform a task, is the Robot Learning from Demonstrations (RLfD). The goal of this method is to allow non-expert users to a programa a robot by simply guiding the robot through a task. The focus of this thesis is on the development of a novel framework for Robot Learning from Demonstrations that enhances the robotsa abilities to learn and perform the sequences of actions for object manipulation tasks (high-level learning) and, simultaneously, learn and adapt the necessary trajectories for object manipulation (low-level learning). A method that automatically segments demonstrated tasks into sequences of actions is developed in this thesis. Subsequently, the generated sequences of actions are employed by a Reinforcement Learning (RL) from human demonstration approach to enable high-level robot learning. The low-level robot learning consists of a novel method that selects similar demonstrations (in case of multiple demonstrations of a task) and the Gaussian Mixture Model (GMM) method. The developed robot learning framework allows learning from single and multiple demonstrations. As soon as the robot has the knowledge of a demonstrated task, it can perform the task in cooperation with the human. However, the need for adaptation of the learned knowledge may arise during the human-robot synergy. Firstly, Interactive Reinforcement Learning (IRL) is employed as a decision support method to predict the sequence of actions in real-time, to keep the human in the loop and to enable learning the usera s preferences. Subsequently, a novel method that modifies the learned Gaussian Mixture Model (m-GMM) is developed in this thesis. This method allows the robot to cope with changes in the environment, such as objects placed in a different from the demonstrated pose or obstacles, which may be introduced by the human teammate. The modified Gaussian Mixture Model is further used by the Gaussian Mixture Regression (GMR) to generate a trajectory, which can efficiently control the robot. The developed framework for Robot Learning from Demonstrations was evaluated in two different robotic platforms: a dual-arm industrial robot and an assistive robotic manipulator. For both robotic platforms, small studies were performed for industrial and assistive manipulation tasks, respectively. Several Human-Robot Interaction (HRI) methods, such as kinesthetic teaching, gamepad or a hands-freea via head gestures, were used to provide the robot demonstrations. The a hands-freea HRI enables individuals with severe motor impairments to provide a demonstration of an assistive task. The experimental results demonstrate the potential of the developed robot learning framework to enable continuous humana robot synergy in industrial and assistive applications
Alterungsanalyse komplexer analoger integrierter Schaltungen aus Systemsicht
Full text linkThe design of analog circuits ranges from the specifications on system level, the selection of a suitable circuit topology up to the choice of the concrete physical dimensions of components like transistors. The individual steps are performed within computer-aided design environments. These environments are based on a database made available by the semiconductor manufacturers containing process parameters and influences on the components. In particular, the influences to be considered in the design have increased in recent years due to the continuous reduction of the producible structural sizes. Thus, it must be possible to analyze the deviations due to process, temperature, time degradation and, for special applications, radiation influences during the design phase. Conventional approaches regard these additional effects as standing next to the actual design process. As a result, the latter is no longer consistent and it is much more complex to consider different circuits and effects on different abstraction levels within the design flow. The focus of this work lies on the development of a consistent consideration of process, voltage, temperature, aging and radiation influences (PVTAR) during the entire design process of analog circuits to the initial measurement of manufactured circuits. To achieve this goal, a transistor model was extended by the influences to be considered. Thereby, the analysis of the additional effects is seamlessly integrated into conventional design processes and methods. In addition, the possibility of a structured analog design is evaluated. This approach allows the estimation of PVTAR influences on dedicated analog function blocks and their propagation on circuit level. Thus, the enormous simulation effort associated with aging analyses can be reduced. The design and manufacture of circuits is always followed by the measurement of the core properties of these circuits. In the context of this work a method was developed which makes it possible to use all insights from the design of a circuit for the improvement of the measuring results. In addition, the internal parameter sets of individual components can be inferred from the terminal behavior of circuits and systems. Finally, the results of the measurement method can be used for the automated calculation of circuit reliability parameters
Schalldämpfung zur Unterdrückung thermoakustischer Instabilitäten unter Brennkammerbedingungen
Full text linkThe replacement of the Helmholtz resonators currently used for damping thermoacoustic instabilities in stationary gas turbines by ceramic pore absorbers could improve both the efficiency of combustion and the operating range of the gas turbines. In this thesis, the effect of ceramic pore absorbers on thermoacoustic instabilities in a combustion chamber was experimentally investigated. Their sound absorption properties were calculated simulatively under combustion chamber conditions as well as determined experimentally under normal conditions and at ambient pressure increased to 5 bar. The comparison of the results was used to validate the simulation. Finally, the simulation was used to determine acoustic target parameters under specific operating conditions
Response of Southwest Pacific storminess to changing climate
Full text linkMid-latitude island nations of the Southwest Pacific (SWP) region like New Zealand not only host winter mid-latitude storms but also tropical storms that develop during summer and autumn. In recent decades, perhaps under the influence of a changing global climate, such tropical storms are observed to travel longer distances towards the southern mid latitudes. The aim of the current study is to estimate likely changes in future storminess in the SWP region during summer and autumn. It uses a new set up of a regional coupled atmosphere-ocean model (integrated over five years each under historical, 1960-1964, and projected future, 2095-2099, boundary conditions) as a tool that allows for frequent air-sea interaction at a mean horizontal resolution of about 25 km. The role of observed changes in large-scale environmental variables in causing recent changes in storminess is illustrated, and a relationship between the two is established by multiple linear regression. This relationship is used to construct scenarios of likely changes in future storminess using the simulated (projected future minus historical) differences in large-scale environmental conditions
Untersuchung eines magnetischen Lagerungskonzepts einer rotierenden Schleifkugel für achsenlose Mikroschleifwerkzeuge und der auftretenden elektrodynamischen Effekte
Full text linkThe development of ever more compact machine tools for machining smaller pieces and their surfaces is becoming increasingly important, above all in medicine, micro-machining, optics and mechatronics. This work describes the design of a novel concept for the bearing and control of a grinding ball, which is get in rotation by a pneumatic air-driven flow. Particular emphasis is placed on the methodology and parameter studies, which in addition to analytical calculations, a 3D simulation model has been created in addition. The focus of the investigations was the systematic pre-selection of the geometry and the generation of the magnetic field in the correct sections of the calotte, the particular difficulty in the consideration of the three-dimensional force generation and in the decoupling of the magnetic and mechanical quantities.The analytical and the resulting 3D-FEM model of the magnetic bearing with respect to the tensile forces could be confirmed experimentally. The analytical results became more inaccurate as soon as the saturation in the nucleus was reached. For the field guidance in the magnetic bear a ferromagnetic material without sheets was used. Due to the electrical conductivity of the material, the propagation of the eddy currents was high pronounced. The consideration of the electrodynamic effects on the signals was absolutely necessary at high sampling rates (kHz).The investigations have shown that the method of exact linearization is most effective for the nonlinear control of the considered system. Thus, the entire working area within the form and any positions of the ball can be accurately represented. The theory of the control design is based on a nonlinear transformation in the form of tables and calculations as well as the nonlinear decoupling of currents and forces. With the new control method, a clear control structure for the magnetic bearing could be realized. The model and parameter uncertainties could be compensated by the integrator components
Essays on Consumers' Attitudes toward Digital Communication
Full text linkThis cumulative dissertation consists of three research paper. They all aim to give a detailed overview and analysis of the effectiveness of different forms of digital advertising, namely, online touchpoints, mobile advertising, and social media advertising. The construct attitudes toward advertising serves as the central measure of effectiveness