Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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PowerGrasp: Development Aspects for Arm Support Systems

2022 , Goppold, J.-P. , Kuschan, J. , Schmidt, H. , Krüger, J.

Exoskeletons can support workers on physically demanding tasks, but in industry they lack of acceptance. This contribution gives an insight into design aspects for upper body exoskeletons, especially how active exoskeletons for industrial applications differ from military and medical use-cases. To overcome typical rigid exoskeleton problems, we suggest the use of modular soft-exosuit support systems and therefore checked different types of soft actuation principles for their eligibility for the use on upper body joints. Most promising approach is using two-layered actuators sting of robust fabric with embedded rubber tubes as pressure chambers. By inflating the tubes, it is possible to vary the stiffness of the chambers, which can be effectively used to generate assisting forces and moments at human joints (shoulder, elbow, wrist, finger).

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Investigation of the gap bridgeability at high-power laser hybrid welding of plasma-cut thick mild steels with AC magnetic support

2021 , Üstündag, Ö. , Bakir, N. , Gumenyuk, A. , Rethmeier, M.

One of the challenges of the high-power hybrid laser welding of thick steels is the sensitivity of the process of the process to manufacturing tolerances. This usually leads to a time-consuming preparation of the welding edges, such as milling. The study deals with the influence of the edge quality of milled and plasma-cut steel made of S355J2 with a wall thickness of 20 mm on the laser hybrid welded seam quality. Furthermore, the gap bridgeability and the tolerances towards edge misalignment was investigated. An AC magnet was used as backing support to prevent sagging and positioned under the workpiece, to generate an upwards directed electromagnetic pressure. The profiles of the edges and the gap on the top and root side were measured using a digital camera. Single-pass laser hybrid welds of plasma-cut edges could be welded using a laser beam power of just 13.7 kW. A gap bridgeability up to 2 mm and misalignment of edges up to 2 mm could be achieved successful. Additionally, the independence of the cutting side and the welding side was shown, so that samples were welded to the opposite side to their cutting. For evaluation of internal defects or irregularities, X-ray images were carried out. Charpy impact strength tests were performed to determine the toughness of the welds.

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Cutting edge preparation of monolithic ceramic milling tools

2021 , Uhlmann, Eckart , Polte, Mitchel , Polte, Julian , Hocke, Toni

Due to international competition, continuous increases in productivity, product quality and reduction of production costs are required. Especially, the development of milling tools made of innovative cutting materials and application-specific tool geometries for the machining of brittle materials are in focus to overcome these challenges. One approach to improve the performance and the tool behaviour concerning milling of graphite is the use of monolithic ceramic milling tools. Unfortunately, the high brittleness of the ceramic leads to breakouts on the cutting edge during the grinding process. This results in an increased maximum chipping of the cutting edge, which has a significant influence on the milling process. To improve the breakout behaviour, a cutting edge preparation with the immersed tumbling process was applied. To enable a process reliable cutting edge preparation, a suitable lapping medium, the influence of the processing time as well as the depth of imme rsion were investigated. Besides the maximum chipping of the cutting edge, the rounded cutting edge radius was also analysed. The results show that a process reliable cutting edge preparation of monolithic ceramic milling tools with a maximum chipping of the cutting edge RS,max ⤠3 µm and a rounded cutting edge radius of rβ ⤠7 µm could be realised. In future investigations, the experimental applicability of monolithic ceramic milling tools will be proved.

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Particle contact conditions for cutting edge preparation of micro-milling tools by the immersed tumbling process

2021 , Uhlmann, Eckart , Polte, Julian , Kuche, Yves , Landua, Fabian

For increasing tool life and cutting length of micro-milling tools the cutting edge preparation was successfully established. Using the immersed tumbling process, a reproducible cutting edge preparation with constant cutting edge radii as well as low chipping of the cutting edges can be realised. For a profound understanding of the preparation process and the process mechanisms further knowledge about the particle interactions with cutting tools as well as the particle flow mechanisms needs to be obtained. In this investigation the preparation process of micro-milling tools was analysed and the contact-mechanisms as well as the resulting pressures were investigated by simulation studies. Using the discrete element method (DEM) with the software ROCKY DEM from the company ESSS, Florianópolis, Brasil, the immersed tumbling process could be modelled and particle contacts, particle traces as well as particle interactions with the micro-milling tool can be visualized. Especially the particle-tool interactions were more accurately investigated by analysing the stresses and particles shear work as well as correlations between these parameters to prove the comparability between the process simulation and the real preparation process.

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Simulating flow behaviour of wet particles within the immersed tumbling process

2021 , Uhlmann, Eckart , Polte, Julian , Kuche, Yves , Landua, Fabian

For many production chains, it is mandatory to involve special finishing of the manufactured parts for the chipping of the edges as well as the polishing of surfaces. One commonly used method is the immersed tumbling process, where any workpiece is dragged through a particle filled container. In many cases, the immersed tumbling process operates in environments with added liquids, leading to changes in particle-tool interaction and general flow behaviour of the used particles. Whilst the discrete element method for simulating particles is mainly limited to dry particles, the used software ROCKY DEM from ESSS, Florianópolis, Brasil, comes with a built-in liquid-bridge model to simulate water-covered particles and granulate and furthermore an extension for system couplings with Ansys Fluent of the company ANSYS, INC., Canonsburg, Pennsylvania. The latter can be used to create from both software one three-phase-model with higher amounts of actually simulated water. In thi s study, small amounts of water were added to differently shaped particles using the build-in liquid-bridge model, to analyse and compare the particles flow characteristics in both, wet and dry environments. To gather significant information leading towards precise comparisons, the particles trajectories, velocities and resulting forces against the workpieces can be specifically observed and analysed, whilst this kind of process knowledge could previously never been taken into account without simulation.

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Concept for an actuated variable tool electrode for use in sinking EDM

2021 , Uhlmann, Eckart , Streckenbach, Jan , Thißen, Kai , Schulte Westhoff, Bela , Masoud, Abd Elkarim , Maas, Jürgen

Typically, a large number of individual tool electrodes has to be used in sinking electrical discharge machining (sinking EDM) to successfully machine a single workpiece. Due to non-uniform wear and insufficient flushing of the working gap electrode geometries have a significant effect on the process efficiency. This paper discusses the use of an actuated variable tool electrode for sinking EDM to reduce the number of required tool electrodes and to increase the overall process efficiency. A miniaturised linear actuator was developed to individually move electrode segments to form the target shape for the tool electrode. The coordinated actuation of bundled electrode segments introduces new methods for the active flushing within the working gap, which cannot be implemented in conventional sinking EDM. Intelligent sinking strategies can further improve process efficiency by creating and sinking sub-geometries into the workpiece offering improved flushing conditions compa red to the original geometry.

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Photocatalytic effect of TiO2-coated surfaces on the pathogenic microorganisms E.coli and S.aureus

2021 , Uhlmann, Eckart , Hein, Christoph , Brehmer, Annika

The use of titanium dioxide as a strong photocatalytic substance can have a large effect in combating the spread of pathogens through heavily contaminated surfaces. For this purpose, various materials, such as metal, glass, and polymer were coated with rutile- and anatase-rich titanium dioxide by sol-gel method. The contact angle and photocatalytic activity of the coated surface were measured under UV irradiation. The anatase-rich titanium dioxide showed higher photocatalytic activity, which further increased with the coating thickness. The process temperature had an effect on the photocatalytic activity due to the temperature-dependent conversion of anatase to rutile crystal conformation. The coated surfaces had strongly reduced contact angles compared to the uncoated material. In particular, the anatase-rich surfaces resulted in superhydrophilic properties. Photocatalytically induced antibacterial activity against pathogenic microorganisms in liquid environments was d emonstrated, especially for gram-negative Escherichia coli bacteria.

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How Pedestrians Perceive Autonomous Buses: Evaluating Visual Signals

2021 , Brandenburg, Elisabeth , Kozachek, Diana , Konkol, Kathrin , Woelfel, Christiane , Geiger, Andreas , Stark, Rainer

With the deployment of autonomous buses, sophisticated technological systems are entering our daily lives and their signals are becoming a crucial factor in human-machine interaction. The successful implementation of visual signals requires a well-researched human-centred design as a key component for the new transportation system. The autonomous vehicle we investigated in this study uses a variety of these: Icons, LED panels and text. We conducted a user study with 45 participants in a virtual reality environment in which four recurring communication scenarios between an autonomous driving bus and its potential passengers had to be correctly interpreted. For our four scenarios, efficiency and comprehension of each visual signal combination was measured to evaluate performance on different types of visual information. The results show that new visualization concepts such as LED panels lead to highly variable efficiency and comprehension, while text or icons were well ac cepted. In summary, the authors of this paper present the most efficient combinations of visual signals for four reality scenarios.

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A contribution to the interpretation of organizational resilience (Or) based on the analysis of key drivers and conceptual elements

2021 , Hecklau, Fabian , Kidschun, Florian , Kohl, Holger , Hizal, Gamze Gül

Organizations are increasingly confronted with unexpected events, which can occur within or outside the organization and relate to various dimensions or aspects. The significance and extent of its impact on the organization can be quite surprising (Duchek 2020). Despite the fact that academic interest in this subject area has grown steadily in recent years, its conceptualization is not yet fully developed. There is no consensus on the meaning of resilience and the elements it contains. This paper contributes to the understanding and need for organizational resilience (OR) and also reveals gaps in its conceptualization. Resilience is understood as the ability of an organization to repel, prepare for, consider, absorb, recover from and adapt ever more successfully to actual or potential adverse events. Those events are either catastrophes or processes of change with catastrophic outcome which can have human, technical or natural causes.(Thoma 2014) In order to survive in an uncertain environment and promote future success, organizations must be able to deal with all these manifestations of the unexpected and catapult themselves out of the crisis. They have to develop a capacity for resilience that enables them to react appropriately to unexpected events and to make capital from events that could potentially threaten the survival of an organization (Lengnick-Hall et al. 2011; Duchek 2020; Denyer 2017; Aguilar 1967). In literature and practice, there are various approaches to OR, which consist of phase models that also allow an assessment of an organization as resilience using a maturity model. From the examined methods in this paper it follows that the resilience capability is questioned only after occurrence of an adverse event and no "preparation phase" according to the Fraunhofer resilience cycle exists. This ex post approach endangers not only the competitive position, but also the existence of an organization.

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Business model development in European aerospace start-ups: The case of the spaceup project

2021 , Steinhöfel, Erik , Singer, Katrin

In their quest for market establishment and organizational maturity, business model development (BMD) plays a crucial role for start-ups. After foundation, primary focus is no longer on generating promising business ideas, but on commercializing a start-upâs inherent potential. This particularly applies to innovative, technology-based start-ups. Here, superior functions in relation to existing solutions resulting from advancements in technologies and the value associated with such functional superiority are center of entrepreneurial activity and BMD. This study presents the BMD methodology applied for supporting 60 technology-based, aerospace-related start-ups on their path to becoming leading companies in their field and the results of its application in the frame of the SpaceUp project. The methodology was carried out in a two-stage process. First, a questionnaire was provided to the start-ups to capture and assess their business model (BM). In a second step, based on the information provided, a detailed evaluation of the start-upsâ BM was carried out and starting points for further development were generated. In order to assess the relevance and usefulness of the results generated by applying the methodology, a quantitative survey was conducted among the start-ups. The survey showed that the generated results were perceived as beneficial by the start-ups and that the application of the methodology therefore proved successful in the project.

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