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See detailRobotic Trajectory Tracking: Position- and Force-Control
Klecker, Sophie UL

Doctoral thesis (2019)

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a ... [more ▼]

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a freeform surface in a discontinuous manner. Next to resulting switching constraints, disturbances and uncertainties, the case of unknown robot models is addressed. In a second phase, once contact has been established between surface and end effector and the freeform path is followed, a desired force is applied. In order to react to changing circumstances, the manipulator needs to show the features of an intelligent agent, i.e. it needs to learn and adapt its behaviour based on a combination of a constant interaction with its environment and preprogramed goals or preferences. The robotic manipulator mimics the human behaviour based on bio-inspired algorithms. In this way it is taken advantage of the know-how and experience of human operators as their knowledge is translated in robot skills. A selection of promising concepts is explored, developed and combined to extend the application areas of robotic manipulators from monotonous, basic tasks in stiff environments to complex constrained processes. Conventional concepts (Sliding Mode Control, PID) are combined with bio-inspired learning (BELBIC, reinforcement based learning) for robust and adaptive control. Independence of robot parameters is guaranteed through approximated robot functions using a Neural Network with online update laws and model-free algorithms. The performance of the concepts is evaluated through simulations and experiments. In complex freeform trajectory tracking applications, excellent absolute mean position errors (<0.3 rad) are achieved. Position and torque control are combined in a parallel concept with minimized absolute mean torque errors (<0.1 Nm). [less ▲]

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See detailLaser polishing of Aluminum and Polyamide for dissimilar laser welded assemblies
Amne Elahi, Mahdi UL; Koch, Marcus; Plapper, Peter UL

Scientific Conference (2019, June 27)

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See detailLaser overlap joining from copper to aluminum and analysis of failure zone
Mathivanan, Karthik UL; Plapper, Peter UL

Scientific Conference (2019, June 26)

Joining of copper and aluminum sheets are very crucial for battery application. When joining from copper sheet, keyhole mode of welding is essential to overcome the reflectivity and melting threshold of ... [more ▼]

Joining of copper and aluminum sheets are very crucial for battery application. When joining from copper sheet, keyhole mode of welding is essential to overcome the reflectivity and melting threshold of copper. However, in dissimilar material interaction the resulting intermetallic (IMC) phases are brittle, which result in reduced performance.This paper analyses the joint with laser beam irradiated from the copper side (Cu on top). The idea is to distribute the intermetallic compounds inside the joint to obtain a ductile behavior. The zones of failure and the distribution of the intermetallic phase is studied. The microstructural analysis of the fusion zone and mechanical strength of the joint are presented. [less ▲]

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See detailLaser beam joining of copper to aluminum sheet
Mathivanan, Karthik UL; Plapper, Peter UL

Poster (2019, April 04)

Dissimilar metal joining plays a very important role in the battery connections, especially copper and aluminum sheets. The existing literatures for laser research mostly focused on joining from the less ... [more ▼]

Dissimilar metal joining plays a very important role in the battery connections, especially copper and aluminum sheets. The existing literatures for laser research mostly focused on joining from the less reflective aluminum side to bond with copper. In the current research, we explore the joining process from copper side.Finally the optical emission of Cu-Al joint is presented with 394 nm peak as an indication to study the melting of Al. [less ▲]

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See detailEntwicklung eines intelligenten, robotergestützten Assistenzsystems für die Demontage industrieller Produkte
Jungbluth, Jan UL

Doctoral thesis (2019)

Technical assistance systems are used in many aspects of our private environment to simplify our daily lives. Such assistance would also be desirable in our working environment, especially in physically ... [more ▼]

Technical assistance systems are used in many aspects of our private environment to simplify our daily lives. Such assistance would also be desirable in our working environment, especially in physically demanding activities such as dismantling products for maintenance, corrective maintenance, or remanufacturing. However, the use of robot-supported assistance systems is prevented by the imponderabilities in the dismantling process of different products due to the lack of autonomy of the technical systems. In the course of this dissertation, the development of intelligent, robot-supported assistance systems that can support people in such complex processes in a target-oriented manner are considered, and the following research question is posed: What are the technical requirements for such assistance systems and how can they be implemented? In the reviewed scientific literature, no holistic approach has been identified for the development of these systems, but many approaches to partial aspects of such a system have been collected across several research disciplines. In order to address the research question, this dissertation discusses the theoretical fields of technical assistance systems, human-robot systems, and the field of application in order to define technical requirements. A demonstrator for experimental validation is implemented in the form of a multi-agent system in which various technical systems are integrated and interconnected by software. The function of the developed robot-based assistance system could be verified in concrete dismantling processes in conjunction with suitable man-machine communication interfaces. Finally, this dissertation identifies further research questions that must be addressed before such systems can be introduced in the industrial environment. [less ▲]

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See detailElucidation of influencing parameters of the laser butt welding process of dissimilar steel to tungsten alloy sheets
Schiry, Marc UL; Plapper, Peter UL

in Proceedings: International Conference on Competitive Manufacturing COMA'19 (2019, January)

Laser welding of steel - tungsten alloy joints requires deep understanding of the impact of the laser parameters on the welding process. Due to the dissimilar thermal and metallurgical properties of both ... [more ▼]

Laser welding of steel - tungsten alloy joints requires deep understanding of the impact of the laser parameters on the welding process. Due to the dissimilar thermal and metallurgical properties of both materials, a defined heat input and a precise temperature control in the weld interface is required. In the presented work, the influence of different laser parameter (e.g. laser power, focal position, scanner speed etc.) on the joint quality of laser welded steel / tungsten alloy butt-joints were investigated. By using statistical methods, the influencing process parameters were defined and optimized. It is shown that the horizontal focal position is the main parameter for the welding process in a butt-joint configuration. Additionally, manipulation of the heat input leads to modifications of the weld bead profile. By obtaining vertical seam boundaries in the sheet metal, a homogenous temperature profile at the interface of the materials to be welded was achieved. Due to the complete bonding and low amount of intermetallic phases, high shear strength accompanied with a low variance were the result. [less ▲]

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See detailNovel Opportunities by Laser Welding of Dissimilar Materials
Schiry, Marc UL; Plapper, Peter UL

in Proceeding: International Conference on Competitive Manufacturing COMA'19 (2019, January)

The Laser Technology Competence Centre (LTCC) of the University of Luxembourg provides skills in joining material combinations, which are considered being non-weld able with traditional methods or at ... [more ▼]

The Laser Technology Competence Centre (LTCC) of the University of Luxembourg provides skills in joining material combinations, which are considered being non-weld able with traditional methods or at least challenging to join (e.g. Copper and Aluminium, Aluminium and Polyamide (PA), Titanium and PEEK, steel and tungsten hard alloy). Related accomplishments include minimal intermetallic compounds, convincing mechanical and superior electrical properties of the laser-welded specimen. With defined spatial and temporal modulation of the laser beam, an accurately defined temperature profile is created on the lower side of the upper material in the two dimensional directions, which enable joining of dissimilar materials in overlap configurations, despite challenging thermal properties. To weld butt-joint geometries with minimal heat affected volume, the temperature profiles were expanded in the third dimension, which can be achieved through controlled laser energy guidance. The scientific methods to accomplish these convincing results are explained, with selected industrial use cases ranging from automotive industry, energy storage, and medical implants. An outlook with unsolved challenges is intended to ignite discussions about upcoming research topics. [less ▲]

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See detailRobotic trajectory tracking: Bio-inspired position and torque control
Klecker, Sophie UL; Hichri, Bassem UL; Plapper, Peter UL

in Procedia CIRP (2019)

As far as complex contact-based manufacturing tasks are concerned, humans outperform machines. Indeed, conventionally controlled robotic manipulators are limited to basic applications in close to ideal ... [more ▼]

As far as complex contact-based manufacturing tasks are concerned, humans outperform machines. Indeed, conventionally controlled robotic manipulators are limited to basic applications in close to ideal circumstances. However, tedious work in hazardous environments, make some tasks unsuitable for humans. Therefore, the interest in expanding the application-areas of robots arose. This paper employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control in the presence of uncertainties and switching constraints. The robotic manipulators mimicking the human behavior based on bio-inspired algorithms, take advantage of their know-how. Simulations and experiments validate the concept-performance. [less ▲]

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See detailRobotic assistants in factory routines - the ethical implications
Klecker, Sophie UL; Hichri, Bassem UL; Plapper, Peter UL

in RACIR 2019 (2019)

This paper is concerned with the problems which arise when humans are working alongside robotic assistants. The main question which appears is how to define the difference between humans and robots in ... [more ▼]

This paper is concerned with the problems which arise when humans are working alongside robotic assistants. The main question which appears is how to define the difference between humans and robots in terms of characteristics, similarities or differences and how to consequently treat humans and robots in the factory routine. Based on a literature analysis, a common ground for the treatment of human and robotic workforce in the manufacturing industry is established. Subsequently, a framework for their cooperation is deduced and an implementation of the solution suggested. [less ▲]

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See detailRule-Based Supervisory Control-Extension for Automated Manufacturing Processes
Klecker, Sophie UL; Hichri, Bassem UL; Plapper, Peter UL

in International Journal of Mechanical Engineering and Robotics Research (2019)

Before performing a surface finishing process, human operators analyze the workpiece-conditions and react accordingly, i.e. they adapt the contact-situation of the tool with respect to the surface. This ... [more ▼]

Before performing a surface finishing process, human operators analyze the workpiece-conditions and react accordingly, i.e. they adapt the contact-situation of the tool with respect to the surface. This first step is ignored in most suggested automation concepts. Although their performance is satisfactory for the general process thanks to adaptive position- and force-/torque-control algorithms, they are unable to address specific problematic cases as often encountered in practice because of variations in workpiece-dimensions or -positioning. In this work, a human mimicking element is developed to overcome this limitation of current control concepts and to translate human expertise to the robotic manipulator. A rule-based system is designed where human knowledge is encoded as if-then rules. This system is integrated with a previously suggested control strategy in a hierarchical manner. The developed concept is experimentally validated on a KUKA LWR 4+-robotic manipulator. [less ▲]

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See detailLaser welding of dissimilar copper and aluminum sheets by shaping the laser pulses
Mathivanan, Karthik UL; Plapper, Peter UL

in Procedia Manufacturing (2019), 36

Dissimilar metal joining of thin copper and aluminum sheets is very important in the battery connections. The main problem while joining this dissimilar combination is formation of brittle intermetallic ... [more ▼]

Dissimilar metal joining of thin copper and aluminum sheets is very important in the battery connections. The main problem while joining this dissimilar combination is formation of brittle intermetallic phases that degrade the electrical and mechanical properties of the joint. For joining copper and aluminum sheet with laser, very high intensity in the range of 10^7 W/cm^2 is required. Intermixture of copper and aluminum is vital for joint ductility. In this paper, the effect of combined oscillation and shaping of the laser pulses on the overlap welding of copper-aluminum is studied. Precise control of intermixing can be achieved by modifying the laser pulse i.e. the percentage of power with respect to the pulse time. Investigation on different pulse shapes with ramp up and ramp down profile is conducted by cross-section and microstructural analysis. [less ▲]

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See detailDissimilar Laser Micro-Welding of Nickel Wire to CuSn6 Bronze Terminal
Amne Elahi, Mahdi UL; Plapper, Peter UL

in Transactions of the Indian Institute of Metals (2018)

In the present study, the laser welding of wire to flat geometry for miniature electromechanical hybrid components has been investigated. Considering the geometry of parts to be welded and also ... [more ▼]

In the present study, the laser welding of wire to flat geometry for miniature electromechanical hybrid components has been investigated. Considering the geometry of parts to be welded and also requirement of mechanical properties, spatial modulation of the laser beam was needed to be implemented to achieve a sound joint. Tensile-shear test and optical microscopy were employed to represent the mechanical properties and melt pool geometry of the joints. All welds were done by power modulation of the laser beam to better control the energy input at several feed rates and three different beam trajectories. Results showed that the shear load of the joint could be controlled by feed rate and the trajectory of the laser beam. Considering the material combination of the study that were nickel and CuSn6 bronze, which represented solubility in solid state, a joint stronger than base wire metal was achieved by defining a proper spatial modulation and feed rate of the laser beam. [less ▲]

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See detailA survey: The usage of Augmented Reality in Industry
Gallala, Abir UL; Hichri, Bassem UL; Plapper, Peter UL

in Robotix-Academy Conference for Industrial Robotics 2018 (2018, November 01)

Human-Robot-Interaction technologies in industry 4.0 and modern manufacturing are more and more growing. Using off-line robot programming methods such as Augmented Reality (AR) could gain time and money ... [more ▼]

Human-Robot-Interaction technologies in industry 4.0 and modern manufacturing are more and more growing. Using off-line robot programming methods such as Augmented Reality (AR) could gain time and money as well as improve programming and repair tasks. This paper is a study of the use of AR in smart factories. [less ▲]

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See detailRobotix-Academy Conference for Industrial Robotics (RACIR) 2018
Müller, Rainer; Plapper, Peter UL; Brüls, Olivier et al

Book published by Shaker Verlag - 1st ed (2018)

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See detailIndustry 4.0 – Implementation of an automated assembly line in a wooden modular house production plant: The case Leko Labs
de Vincenzo, Vincenzo UL; Hichri, Bassem UL; Plapper, Peter UL

in De vincenzo, Vincenzo; Hichri, Bassem; Plapper, Peter (Eds.) Robotix-Academy Conference for Industrial Robotics (RACIR) 2018 (2018, November)

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See detailFLEXCAP – Cost competitive flexible process for highly aesthetic closures manufacturing
Kakogiannos, Ioannis UL; Hichri, Bassem UL; Plapper, Peter UL

in Kakogiannos, Ioannis; Hichri, Bassem; Plapper, Peter (Eds.) Robotix-Academy Conference for Industrial Robotics (RACIR) 2018 (2018, November)

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See detailAutogenous Laser welding of copper to aluminium
Mathivanan, Karthik UL; Plapper, Peter UL

Poster (2018, September 13)

This work investigates laser joining of copper sheets to aluminium in overlap configuration. Dissimilar Cu-Al connections are widely used in the electrical and electronics applications e.g. battery and ... [more ▼]

This work investigates laser joining of copper sheets to aluminium in overlap configuration. Dissimilar Cu-Al connections are widely used in the electrical and electronics applications e.g. battery and solar panels.Joining these materials is a very critical assembly process. The laser welding from the aluminium surface to copper (Al-Cu) is well described in the literature .But there is no data concerning the laser seam welding from the copper side to join with aluminium i.e Cu-Al.The selection of aluminium surface to irradiate is mainly because of poor absorption of copper to laser in IR region.But high intensities of about 100 MW/cm2 allow for initial vaporization of copper surface.Once the keyhole is generated, absorption of laser light is improved.Thereby high power lasers allow for successful penetration of copper surface to produce a joint with aluminium. The main objective is to investigate the approach of dissimilar laser welding starting from the copper surface to aluminium.The effect of process parameters on the shear force, microstructure and weld pool dimensions are studied.An experimental design is realized to see the effect of laser irradiation of copper surface (Cu-Al) in contrast to aluminium surface(Al-Cu). The selection of aluminium or copper surface is mainly dependent on the laser power.With the high power disk laser the possibility of joining from the copper side was evident and results of joining copper to aluminium and aluminium to copper are comparable.Therefore welding from a highly reflective surface to achive a comparable shear strength is demonstrated. [less ▲]

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See detailLaser micro-welding of wire to flat geometry for dissimilar materials in an electromechanical application
Amne Elahi, Mahdi UL; Plapper, Peter UL

Poster (2018, September 11)

In the presented study, the laser welding of wire to flat geometry for miniature electromechanical hybrid components has been investigated. Laser welding offers variety of advantages compared to the ... [more ▼]

In the presented study, the laser welding of wire to flat geometry for miniature electromechanical hybrid components has been investigated. Laser welding offers variety of advantages compared to the current joining processes for this application however, considering the geometry of parts to be welded also mechanical properties requirement, an accurate spatial modulation of laser beam should be implemented to achieve a sound joint. Tensile shear test and optical microscopy were employed to represent the mechanical properties and melt pool geometry of the joint. All welds were done by power modulation of the laser beam to better control the energy input at several feed rates and three different beam trajectories. Results show that the shear load of the joint can be controlled by feed rate and the trajectory of the laser beam. The material combination of the study (Nickel and CuSn6), represents solubility in solid state therefore, by defining a proper spatial modulation of the laser beam a joint stronger than base wire metal is achievable. Figure 1 represents schematics of weld components. [less ▲]

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See detailInfluence of laser parameter on weld bead shape and process stability of laser welded steel sheets
Schiry, Marc UL; Plapper, Peter UL

in Proceedings of 10th Conference on Photonic Technologies LANE 2018 (2018)

Laser butt-welding of dissimilar heat sensitive materials is one of the most challenging tasks. Significant differences in melting and transition temperatures are typical and occur frequently. Therefore ... [more ▼]

Laser butt-welding of dissimilar heat sensitive materials is one of the most challenging tasks. Significant differences in melting and transition temperatures are typical and occur frequently. Therefore, accurate control of the temperature profile at the interface of the weld is essential. In this paper, the influence of the laser parameter power and velocity, as well as laser spot diameter on the laser process were investigated. It is shown that the beam diameter has a significant impact on the weld bead formation. Further variation of the type of shielding gas showed an effect on the bead geometry depending on the used laser spot diameter. Spectroscopic process observations showed a significant impact of the spot diameter and shielding gas on the energy input and the efficiency of the laser process. A homogeneous damping effect of the laser radiation was obtained by using the larger fiber diameter accompanied with a higher overall intensity of process radiation. [less ▲]

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See detailComposition and phases in laser welded Al-Cu joints by synchrotron x-ray microdiffraction
Schmalen, Pascal Guy UL; Plapper, Peter UL; Peral Alonso, Inmaculada UL et al

in Proceedings of 10th CIRP Conference on Photonic Technologies [LANE 2018] (2018)

This paper presents the characterization of the intermetallic phases of laser-welded Al-Cu joints by synchrotron trough-the-substrate microdiffraction combined with SEM/EDX and etched/non-etched optical ... [more ▼]

This paper presents the characterization of the intermetallic phases of laser-welded Al-Cu joints by synchrotron trough-the-substrate microdiffraction combined with SEM/EDX and etched/non-etched optical micrographs. Transmission microdiffraction offers the spatial resolution and beam flux necessary to study the intermetallic phases, which in conjunction with the excellent contrast of etched micrographs, rendered possible the phase identification. It was found that the major phases are Al2Cu (θ), Al4Cu9 (γ1) and AlCu (η2) were formed. The Al3Cu4 (ζ1) and δ phases where formed in less amount and found to be the primary cause for cracks inside the weld seam and therefore for the failure of the joint. [less ▲]

Detailed reference viewed: 71 (5 UL)