1,721,293 research outputs found
Roboterbasierte multidirektionale additive Fertigung für das Lichtbogenschweißen mit Drahtzuführung
No full textIncreasing complexity of components and at the same time increasing relevance of sustainable material usage motivate to near-net shape additive manufacturing of cost-intensive alloys. Wire-Arc Additive Manufacturing (WAAM) is also used in this context. The necessary process hardware (welding head with eccentric wire feed, ground cable, substrate plate and sensors) strongly limit the possible movement of the welding head. Rotation around the vertical axis of the welding head, which is necessary for eccentric wire feeding or suitable monitoring by sensors, cannot be enabled for complex paths. The drawbacks and challenges motivate the use of multidirectional additive manufacturing with pure object manipulation (MDAM). In this work, a process chain is developed that specifically ensures the robotic feasibility of a multidirectional welding process. The process chain depends on the specific robot and the position of the welding head in the robot's workspace. To be able to decide about the printable volume before the process starts and to optimize the welding head position on this basis, a corresponding method is developed, implemented and presented. It was shown that specific configurations of robot, substrate plate and welding head influence the printable volume. Not only the pure volume is relevant, but also the manipulability of the robot. Once the configuration has been determined, the process preparation, consisting of slicer, production planning, path planner and trajectory planner, can be carried out. The goal of path planning is to fill the slice with paths that are executable by the robot. The executability can be decomposed into the pure reachability of the necessary robot poses and the manipulability in the speed limits of the robot. To generate reachable paths, a Clustered Hamilton Path (CHP) search is used. This is based on a graph search. For this purpose, the developed path planning approximates and expands the polygon describing the slice. The polygon is then decomposed into convex partial polygons. For each partial polygon different infill structures can be generated. The result is a path that fills the slice with infills that are reachable for the specific robot. In addition to the pure reachability, process influences can also be incorporated via the weights in the graph. Furthermore, a trajectory optimization is developed in the context of this work, which generates executable trajectories tailored to the MDAM. An executability could be achieved by the local adaptation of the path velocity and the deviation from the given rotations. This adaptation of the kinematic parameters can be realized by simultaneous variation of the welding parameters. The developments of this work finally enable the execution of complex welding processes within the MDAM on the part of the robot
Motion design of cam mechanisms by using non-uniform rational B-Spline
No full textThe follower of cam mechanisms may flexibly perform its movement based on the shape of the cam element and the direct contact with the cam. With this feature, it is convenient to design a cam mechanism when an output motion is given by working requirements of machines. The follower motion is characterized by the displacement, velocity, acceleration, and jerk functions. The acceleration is related to inertial forces of the follower. When an acceleration curve has abrupt changes, i.e., peak values, this will lead to large inertial forces. Therefore, contact stresses at the bearing and on the cam surface also change abruptly, which causes noise and surface wear. Additionally, the peak value of the jerk curve is also important in cam design since it determines the tendency of vibration in cam-follower systems. Thus, selecting a mathematic function to describe the motion of the follower is an important step in cam design. In this thesis, Non-Uniform Rational B-Spline (NURBS) is used to describe motion curves of the follower. With the properties of NURBS, the motion curves including peak values of the acceleration and jerk are shown to have advantageous characteristics compared to classical approaches. To do this, the displacement, velocity, acceleration, and jerk functions are represented by NURBS curves. These curves are then determined by solving the system of linear equations under given boundary conditions of the displacement, velocity, acceleration, and jerk. Moreover, the main advantage of NURBS compared with other functions is that the NURBS curve can be controlled by its parameters such as weights and the knot vector. In this thesis, the computation of the knot vector is presented to evaluate its effect on motion curves. Furthermore, finding values of the weight factor to reduce peak values of the acceleration and jerk, the multi-objective functions depended on the weight factor are expressed. For solving this problem, the simulated annealing algorithm is used to get the optimal value of weights. Results of this thesis demonstrate that using NURBS for synthesizing motion curves is robust and effective because this may apply any motion curves of cam-follower systems. In addition, the kinematics of cam mechanisms is improved by controlling NURBS’s parameters
Kombination analytischer und numerischer Berechnungsmethoden als Grundlage eines Softwaresystems zum Getriebeentwurf
No full textKombination analytischer und numerischer Berechnungsmethoden als Grundlage eines Softwaresystems zum Getriebeentwurf
No full textÜbertragungsverhalten von Planetenrollengewindetrieben unterschiedlicher Gewindegangzahl der Spindel und der Mutter
No full textÜbertragungsverhalten von Planetenrollengewindetrieben unterschiedlicher Gewindegangzahl der Spindel und der Mutter
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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