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Lumped-Mass-Modellierung von Förderbändern am Beispiel eines Zwei-Walzensystems mit flexiblen Walzen
(2024)
One major goal of production system design is to decide on space requirements in the plant. In this phase, detailed information about the supply chain network (e.g. which suppliers deliver which parts) is often unavailable. Nevertheless, typical decisions in supply chain management, like the definition of replenishment processes and quantities or make-or-buy decisions, impact space requirements and the capital investment in raw materials and should therefore be considered in factory and production planning. This research article proposes a simulation approach for a production simulation in which raw material replenishment is integrated to evaluate the capital investment and space requirements for raw materials.
Preliminary considerations on the form-finding of a tensegrity joint to be used in dynamic orthoses
(2024)
Isogeometric sheet metal forming simulation is a numerical simulation technique that is used to predict the behavior of sheet metal parts during the forming process [1] and tries to tighten the link with the Computer Aided Design (CAD) description. This technique uses the isogeometric analysis (IGA) approach, which combines the well-established framework of traditional finite element analysis (FEA) and the power of non-uniform rational B-splines (NURBS). In contrast to the approach in a “classical” FEA framework, IGA directly uses the ansatzspace of the CAD geometry for analysis, which opens the possibility to work directly on the exact geometry. Furthermore, the smoothness of the NURBS basis functions results in a more accurate simulation [2].
A powerful method to reduce the computational effort is adaptive mesh refinement, that has been developed and optimized for sheet metal forming applications over several years for standard Finite Elements. However, it remains an open question how an efficient local adaptive mesh refinement strategy can be implemented for complex industrial sheet metal forming simulations based on trimmed NURBS models, which are typically the description in Boundary Representation (B-Rep) CAD-models [3]. First investigations for explicit dynamics have been made in [4].
In this contribution, a detailed comparison between FEA and IGA sheet metal forming applications is conducted. The state of the art for FEA and IGA will be contrasted and the need for an efficient adaptive mesh refinement strategy will be discussed. The goal of our research is to develop an efficient adaptive mesh refinement strategy for isogeometric sheet metal forming simulations in LS-DYNA. This will contribute to closing the efficiency gap between IGA and FEA in explicit dynamics, accelerate the product development process and enable the application of IGA in industrial sheet metal forming simulations.
A factory has to adapt to a future production program and increasing volumes. The planning of new factories must therefore already take expansion stages and reconfigurations into account. This leads to an increase in the complexity of planning, as different variants have to be planned and put into a chronologically reasonable and cost-optimized sequence. A factory data model that covers expansion stages manages the planning data amount and reduces complexity. Based on existing models from the literature, a factory data model was developed and modeled in the Unified Modeling Language standard. The factory data model shows which classes are interdependent and how planning results are stored reusable for other variants. An example is used to explain the developed factory data model and highlighting its advantages. The aim is to enable factory planners to document variant sequences and expansion stages in a comprehensible way, which supports the interdisciplinarity of factory planning projects.
Effects of Deep Rolling on the Fatigue Behavior of Ti-6Al-4V at Ambient and Elevated Temperatures
(2003)
This paper presents a comprehensive analysis of a three-dimensional compliant tensegrity joint structure, examining its actuation, kinematics, and response to external loads. The study investigates a baseline configuration and two asymmetric variants of the joint. The relationship between the shape parameter and the parameters of the tensioned segments is derived, enabling the mathematical description of cable lengths for joint actuation. Geometric nonlinear static finite element simulations are performed to analyze the joint's response under various load conditions. The results reveal the joint's range of motion, the effect of different stiffness configurations, and its deformation behavior under external forces. The study highlights the asymmetric nature of the joint and its potential for targeted motion restriction. These findings advance the general understanding of the behavior of the considered tensegrity joint and provide valuable insights for their design and application in soft robotic systems.
Um die Leistungsfähigkeit von nachgiebigen Robotersystemen („Soft Robotics“) zu verbessern, werden immer neue Möglichkeiten zur Realisierung dieser Systeme gesucht. In vielen Anwendungen ist der Einsatz von mechanisch vorgespannten nachgiebigen Strukturen in diesen Systemen von Vorteil. Die Steifigkeit dieser Strukturen kann gezielt und gegebenenfalls reversibel variabel eingestellt werden. Die Formveränderung kann nur durch wenige Aktuatoren erzeugt werden.
Nachgiebige Tensegrity-Strukturen, die auf hochelastischen Materialien basieren, entsprechen einer speziellen Klasse von mechanisch vorgespannten Strukturen. Sie werden durch druck- und zugbelastete Segmente gebildet, wobei die druckbelasteten Segmente untereinander nicht direkt verbunden sind. Die resultierende Form dieser Strukturen wird durch ihre Vorspannung bestimmt. Weiche Roboter, die auf diesen Strukturen basieren, bieten mehrere vorteilhafte Eigenschaften, wie z. B. Faltbarkeit/Entfaltbarkeit, geringe Masse, hohes Festigkeits-Gewichts-Verhältnis und stoßdämpfende Fähigkeiten [1]. Diese Strukturen haben eine ausgeprägte Fähigkeit, sowohl ihre Form als auch ihre Steifigkeit zu verändern. In den letzten Jahren hat das Interesse an der Erforschung von Robotersystemen, die auf diesen Strukturen basieren, zugenommen. Aktuelle Arbeiten konzentrieren sich auf die Entwicklung von mobilen Robotern [2]–[7] und Manipulatoren, die auf diesen Strukturen basieren [8]–[10]. Tensegrity-Manipulatoren werden typischerweise durch Kaskadierung von gleichartigen elementaren Einheiten gebildet, die nach dem Tensegrity-Prinzip untereinander verbunden werden. Die elementaren Einheiten sind entweder selber konventionelle Tensegrity-Strukturen oder einteilige planare bzw. räumliche Strukturen. In klassischen Tensegrity-Manipulatoren werden starre Drucksegmente und nicht elastische Zugsegmente verwendet. Die Formänderung dieser Systeme wird durch Änderung der Längen ausgewählter Zugsegmente realisiert. Dem gegenübergestellt können nachgiebige Tensegrity-Manipulatoren realisiert werden, indem die Zugsegmente der Struktur eine hohe Nachgiebigkeit aufweisen. Um die mechanische Nachgiebigkeit und Formänderungsfähigkeit von diesen nachgiebigen Manipulatoren zusätzlich
zu erhöhen, ist auch der Einsatz von Tensegrity-Strukturen auf der Basis nachgiebiger Drucksegmente denkbar.
Im vorliegenden Beitrag werden zwei nachgiebige Tensegrity-Manipulatoren vorgestellt und in Hinblick auf ihre mechanischen Eigenschaften und Formänderungsfähigkeit gegenübergestellt. Sie unterscheiden sich in ihrer Topologie, in der Art der Aktuierung und auch in der mechanischen Nachgiebigkeit. Die mechanische Nachgiebigkeit des ersten Systems beruht auf der Elastizität der Zugsegmente, die Drucksegmente sind starr. Die elementaren Einheiten bilden einteilige Strukturen. Das zweite System beruht auf elementaren Einheiten, die selbst räumliche Tensegrity-Strukturen sind. In diesem System sind sowohl die Zug- als auch die Drucksegmente nachgiebig. Die Aktuierung des ersten Systems erfolgt durch Längenänderung der Zugsegmente. Im zweiten System wird die Formänderung des Gesamtsystems durch Änderung der Form der nachgiebigen Drucksegmente realisiert. Die theoretischen Untersuchungen erfolgen unter Anwendung
der statischen geometrisch nichtlinearen FE-Methode. Mit diesen Untersuchungen wird die Formveränderungsfähigkeit der beiden Systeme unter Variation ihrer Vorspannung untersucht und gegenübergestellt. Die experimentellen Untersuchungen an zwei Demonstratoren bestätigen die theoretischen Ergebnisse und zeigen die Anwendbarkeit von Systemen auf Basis dieser Strukturen als Manipulatoren auf.
Theoretical considerations on a 2D compliant tensegrity joint in context of a biomedical application
(2023)
In this paper, a two-dimensional compliant tensegrity joint was investigated for potential biomedical applications such as orthotics or exoskeletons. The structure consists of two compressed members connected by five compliant tensioned members. The concept is based on the tensegrity principle, which allows the realization of dynamic orthoses without conventional hinge joints. Another advantage is the adaptability to the individual needs of the patient through a suitable design of the structure and the careful selection of the characteristics of the elements. Using geometric nonlinear analysis, the mechanical behavior of the structure was investigated, focusing on mechanical compliance. The main objective was to determine the influence of the initial length and stiffness of the tensioned members and the influence of the magnitude of external forces on the overall stiffness of the movable member of the structure. The results highlight the significant impact of member parameters on the structure's stiffness and movability under varying load magnitudes. The research laid the foundation for future development of dynamic orthoses based on this structure.
In diesem Beitrag erfolgt die theoretische Untersuchung einer zweidimensionalen nachgiebigen Tensegrity-Struktur in Hinsicht auf ihre potenzielle Eignung als Basisstruktur für eine dynamische Handorthese. Translatorische und rotatorische relative Bewegungsmöglichkeiten zwischen den Drucksegmenten der Struktur sind möglich, da diese Segmente durch nachgiebige Zugsegmente miteinander verbunden sind. Die Form der Struktur und ihre Vorspannung in einer statisch stabilen Gleichgewichtskonfiguration werden mit Hilfe der Minimierung des Kräfte- und Momentenungleichgewichts, der Betrachtung der potentiellen Energie der Struktur und einem Ansatz mittels statischer Finite-Elemente-Methode (FEM) in Abhängigkeit der Segmentparameter untersucht.
In this paper, the movement behavior of amoeboid locomotion system is investigated and the theoretical proof of the locomotion of the system is provided with the finite element method. It is shown that not only the speed of locomotion but also its direction can be influenced by the drive frequency. Depending on the drive frequency, a movement from the home position and a subsequent movement in opposite directions can be achieved. In addition, high speeds of movement can be achieved in a limited frequency range.
Digital twins enable the digital representation of physical systems and provide comprehensive modelling and analysis capabilities. An online data exchange between the Digital twin and SAP is feasible, through integration of a transport control systems (SAP) via RESTful API. This interface allows decision making in resource allocation and furthermore the adaptation of the digital model if the real system changes. Despite the associated challenges in terms of data synchronisation, the integration has benefits such as a reduction in modelling effort and an increase in the lifetime of the digital twin. In the context of this work, the design of the interface between the simulation software and a SAP transport control system via RESTful API is described.
Current challenges in the planning and control of internal logistics systems are based on permanent changes in the requirements on the system, e.g., due to fluctuating order numbers or changes in their structure. For the representation and planning of in-house logistics processes, digital twins offer the possibility to verify different operational decisions such as predictive workforce scheduling. In this context, the quality of the results and their in-time presentation plays a decisive role. However, both target criteria are influenced by the detail-level of the digital representation. Based on a case study, this paper investigates the influence of the level of detail on the simulation runtime and result divergence to provide an evaluation for detail levels in the modelling of intralogistic transport systems.
Product sounds with clearly audible tonal components are often perceived as unpleasant or annoying. If different simultaneously operating aggregates are present in a system, for example vehicle engines and gearboxes, the interaction of tonal components, similar to music, can evoke additional sensations in human auditory perception. Supplementary to a pronounced tonality, such sounds can also yield distinct degrees of consonance or dissonance between tones. Previous studies showed that the perceived dissonance had a high impact on preference judgements for sounds with similar tonality. In experiments of the present study, sounds that differed in tonality were rated with respect to the auditory sensations sharpness, tonality and dissonance by one group of participants while another group only carried out a preference task. Thereout a model for predicting perceived preference is derived from the subjective judgements of auditory sensations. The performance of the preference predictions based on subjective udgements will be compared against purely model-based predictions using different algorithms for acoustic attributes.
Fused layer modeling (FLM) is widely used and is gaining more acceptance in the industry mainly due to its material variety and low costs. However, the usage is limited by a process-related anisotropy of the produced parts. The strength and ductility of the printed parts are significantly lower in the build-up direction than perpendicular to it. This is caused by insufficient interlayer bonding resulting from a reduced surface temperature in the process zone. To overcome this problem, a diode laser is integrated into the conventional FLM process to increase the surface temperature between the already printed surface and the newly applied substrate directly at the deposition zone. The investigations carried out show a significant improvement in the mesostructure, as well as a clear reduction in the anisotropy of the printed test specimens.
Absorber-free laser transmission welding enables clean and precise joining of plastics without additives or adhesives. It is therefore well suited to produce optical and medical devices, which place high demands on cleanliness and accuracy.
However, the weld usually has an undesirably large vertical expansion, causing bulges and distortion. To improve this, the intensity distribution of the laser beam as well as the processing strategy must be adapted. Due to the complexity, this is aided by process simulation. However, simulation parameter calibration and verification are usually done considering the seam width and height, which is of limited significance. To overcome this, we propose a new method for image processing of microtome sections, determining the spatially resolved geometry of the weld. Thus, the deviation between experiment and simulation can be calculated pixel by pixel. This spatially resolved value is predestined for the calibration of the simulation parameters: For a parameter field with 18 different settings, the total deviation between experiment and simulation is less than 11 % after calibration.
Mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly stressed metallic components. Deep rolling is an especially attractive technique since it is possible to generate deep, near-surface compressive residual stresses and work hardening while retaining a relatively smooth surface finish. Indeed, this technique is best known for increasing the fatigue strength and lifetime of steel components such as crankshafts. Although most work on deep rolling has been on steels, recently it has also been applied with reasonable success to titanium alloys. Accordingly, in this investigation, we examine the effect of deep rolling on the high-cycle fatigue behavior of Ti-6Al-4V, with particular emphasis on the thermal and mechanical stability of the residual stress states and near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. In addition, we examine whether these surface treatments are effective in retaining fatigue strength at the higher temperatures of 300 to 450C. Based on the cyclic deformation and stress/life behavior, together with the X-ray and microstructural observations, it is found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti-6Al-4V at such higher temperatures, despite the almost complete relaxation of the residual stresses at the surface. This clearly implies that, in addition to residual stresses, near-surface microstructures, which in Ti-6Al-4V consist of ultrafine near-surface nanostructures, play a critical role in the enhancement of fatigue lifetimes by mechanical surface treatments.