@inproceedings{9891, abstract = {{A measurement method is presented that combines the advantages of the multisine measurement technique with a prediction method for peak bending behavior. This combination allows the analysis of the dynamic behavior of mechanical structures at distinctly reduced measurement durations and has the advantage of reducing high excitation impacts on the structure under test. After a brief presentation of the algorithm, the validity scope of the approach is investigated with emphasis on an exemplary error investigation.}}, author = {{Sprock, Christian and Sextro, Walter}}, booktitle = {{Proceedings of ISMA - International Conference of Noise and Vibration. 2014}}, pages = {{1--8}}, title = {{{Time-efficient analysis of nonlinear peak bending behavior.}}}, year = {{2014}}, } @inproceedings{9892, author = {{Sprock, Christian and Sextro, Walter}}, booktitle = {{Proceedings of 31st Danubia-Adria Symposium. 2014}}, title = {{{Vibration Analysis of Mechanical Structures using Multisine Excitation Techniques}}}, year = {{2014}}, } @inbook{9893, author = {{Trächtler, Ansgar and Hölscher, Christian and Rasche, Christoph and Priesterjahn, Claudia and Zimmer, Detmar and Henning Keßler, Jan and Stahl, Katharin and Flaßkamp, Kathrin and Vaßholz, Mareen and Krüger, Martin and Dellnitz, Michael and Iwanek, Peter and Reinold, Peter and Hartmann, Philip and Meyer, Tobias and Sextro, Walter}}, booktitle = {{Dependability of Self-Optimizing Mechatronic Systems}}, editor = {{Gausemeier, Jürgen and Josef Rammig, Franz and Schäfer, Wilhelm and Sextro, Walter}}, isbn = {{978-3-642-53741-7}}, pages = {{1--24}}, publisher = {{Springer Berlin Heidelberg}}, title = {{{Introduction to Self-optimization and Dependability}}}, doi = {{10.1007/978-3-642-53742-4_1}}, year = {{2014}}, } @inbook{9894, author = {{Trächtler, Ansgar and Kleinjohann, Bernd and Heinzemann, Christian and Rasche, Christoph and Priesterjahn, Claudia and Steenken, Dominik and Wehrheim, Heike and Gausemeier, Jürgen and Flaßkamp, Kathrin and Kleinjohann, Lisa and Krüger, Martin and Iwanek, Peter and Hartmann, Philip and Dorociak, Rafal and Groesbrink, Stefan and Ziegert, Steffen and Meyer, Tobias and Sextro, Walter and Schäfer, Wilhelm}}, booktitle = {{Dependability of Self-Optimizing Mechatronic Systems}}, editor = {{Gausemeier, Jürgen and Josef Rammig, Franz and Schäfer, Wilhelm and Sextro, Walter}}, isbn = {{978-3-642-53741-7}}, pages = {{173--188}}, publisher = {{Springer Berlin Heidelberg}}, title = {{{Case Study}}}, doi = {{10.1007/978-3-642-53742-4_4}}, year = {{2014}}, } @inproceedings{9895, abstract = {{Power semiconductor modules are used to control and switch high electrical currents and voltages. Within the power module package wire bonding is used as an interconnection technology. In recent years, aluminum wire has been used preferably, but an ever-growing market of powerful and efficient power modules requires a material with better mechanical and electrical properties. For this reason, a technology change from aluminum to copper is indispensable. However, the copper wire bonding process reacts more sensitive to parameter changes. This makes manufacturing reliable copper bond connections a challenging task. The aim of the BMBF funded project Itsowl-InCuB is the development of self-optimizing techniques to enable the reliable production of copper bond connections under varying conditions. A model of the process is essential to achieve this aim. This model needs to include the dynamic elasto-plastic deformation, the ultrasonic softening effect and the proceeding adhesion between wire and substrate. This paper focusses on the pre-deformation process. In the touchdown phase, the wire is pressed into the V-groove of the tool and a small initial contact area between wire and substrate arise. The local characteristics of the material change abruptly because of the cold forming. Consequently, the pre-deformation has a strong effect on the joining process. In [1], a pre-cleaning effect during the touchdown process of aluminum wires by cracking of oxide layers was presented. These interactions of the process parameters are still largely unknown for copper. In a first step, this paper validates the importance of modeling the pre-deformation by showing its impact on the wire deformation characteristic experimentally. Creating cross-section views of pre-deformed copper wires has shown a low deformation degree compared to aluminum. By using a digital microscope and a scanning confocal microscope an analysis about the contact areas and penetration depths after touchdown has been made. Additionally, it has to be taken into account that the dynamical touchdown force depends on the touchdown speed and the touchdown force set in the bonding machine. In order to measure the overshoot in the force signals, a strain gauge sensor has been used. Subsequently, the affecting factors have been interpreted independently Furthermore, the material properties of copper wire have been investigated with tensile tests and hardness measurements. In a second step, the paper presents finite element models of the touchdown process for source and destination bonds. These models take the measured overshoot in the touchdown forces into account. A multi-linear, isotropic material model has been selected to map the material properties of the copper. A validation of the model with the experimental determined contact areas, normal pressures and penetration depths reveals the high model quality. Thus, the simulation is able to calculate and visualize the three dimensional pre-deformation with an integrated material parameter of the wire if the touchdown parameters of the bonding machine are known. Based on the calculated deformation degrees of wire and substrate, it is probably possible to investigate the effect of the pre-deformation on the pre-cleaning phase in the copper wire bonding.}}, author = {{Unger, Andreas and Sextro, Walter and Althoff, Simon and Eichwald, Paul and Meyer, Tobias and Eacock, Florian and Brökelmann, Michael}}, booktitle = {{Proceedings of the 47th International Symposium on Microelectronics (IMAPS)}}, keywords = {{pre-deformation, copper wire bonding, finite element model}}, pages = {{289--294}}, title = {{{Experimental and Numerical Simulation Study of Pre-Deformed Heavy Copper Wire Wedge Bonds}}}, year = {{2014}}, } @inproceedings{9896, abstract = {{In power electronics, ultrasonic wire bonding is used to connect the electrical terminals of power modules. To implement a self-optimization technique for ultrasonic wire bonding machines, a model of the process is essential. This model needs to include the so called ultrasonic softening effect. It is a key effect within the wire bonding process primarily enabling the robust interconnection between the wire and a substrate. However, the physical modeling of the ultrasonic softening effect is notoriously difficult because of its highly non-linear character and the absence of a proper measurement method. In a first step, this paper validates the importance of modeling the ultrasonic softening by showing its impact on the wire deformation characteristic experimentally. In a second step, the paper presents a data-driven model of the ultrasonic softening effect which is constructed from data using machine learning techniques. A typical caveat of data-driven modeling is the need for training data that cover the considered domain of process parameters in order to achieve accurate generalization of the trained model to new process configurations. In practice, however, the space of process parameters can only be sampled sparsely. In this paper, a novel technique is applied which enables the integration of prior knowledge about the process into the datadriven modeling process. It turns out that this approach results in accurate generalization of the data-driven model to unseen process parameters from sparse data.}}, author = {{Unger, Andreas and Sextro, Walter and Althoff, Simon and Meyer, Tobias and Brökelmann, Michael and Neumann, Klaus and Reimann, René Felix and Guth, Karsten and Bolowski, Daniel}}, booktitle = {{Proceedings of 8th International Conference on Integrated Power Electronic Systems}}, pages = {{175--180}}, title = {{{Data-driven Modeling of the Ultrasonic Softening Effect for Robust Copper Wire Bonding}}}, volume = {{141}}, year = {{2014}}, } @inproceedings{26973, abstract = {{Self-optimizing mechatronic systems allow the adaptation of the system’s behavior to the current situation. This can be used to actively adapt the behavior to the current degradation state of the system or of some of its components. To this end, the Multi-Level Dependability Concept has been developed. In this contribution, we show how the Multi-Level Dependability Concept has been applied to the active suspension module of an innovative rail-bound vehicle. For this module, the usage of control reconfiguration, which is a novel approach to exploit complex redundancy systems, is required. We show that by combining self-optimization with the possibilities given by control reconfiguration, the dependability of a complex mechatronic system can be greatly improved.}}, author = {{Meyer, Tobias and Kessler, Jan Henning and Sextro, Walter and Trächtler, Ansgar}}, booktitle = {{The Annual Reliability and Maintainability Symposium (RAMS)}}, title = {{{Increasing Intelligent Systems’ Reliability by using Reconfiguration}}}, year = {{2013}}, } @inbook{23139, author = {{Kessler, Jan Henning and Meyer, Tobias and Sextro, Walter and Sondermann-Wölke, Christoph and Trächtler, Ansgar}}, booktitle = {{Dependability of Self-Optimizing Mechatronic Systems}}, pages = {{55--62}}, publisher = {{Springer-Verlag, Heidelberg, Germany}}, title = {{{Increasing the Dependability of Self-Optimizing Systems During Operation Using the Multi-Level Dependability Concept}}}, year = {{2013}}, } @inproceedings{23140, author = {{Meyer, Tobias and Kessler, Jan Henning and Sextro, Walter and Trächtler, Ansgar}}, booktitle = {{The Annual Reliability and Maintainability Symposium (RAMS)}}, title = {{{Increasing Intelligent Systems’ Reliability by using Reconfiguration}}}, year = {{2013}}, } @inbook{23149, author = {{Hölscher, Christian and Kessler, Jan Henning and Meyer, Tobias and Rasche, Christoph and Reinold, Peter and Sextro, Walter and Sondermann-Wölke, Christoph and Zimmer, Detmar}}, booktitle = {{Dependability of Self-Optimizing Mechatronic Systems}}, pages = {{16--22}}, publisher = {{Springer-Verlag, Heidelberg, Germany}}, title = {{{Applications of Self-Optimizing Systems}}}, year = {{2013}}, } @article{9794, abstract = {{A piezoelectric cantilever beam with a tip mass at its free end is a common energy harvester configuration. This article introduces a new principle of designing such a harvester that increases the generated power without changing the resonance frequency of the harvester: the attraction force between two permanent magnets is used to add stiffness to the system. This magnetic stiffening counters the effect of the tip mass on the efficient operation frequency. Five set-ups incorporating piezoelectric bimorph cantilevers of the same type in different mechanical configurations are compared theoretically and experimentally to investigate the feasibility of this principle: theoretical and experimental results show that magnetically stiffened harvesters have important advantages over conventional set-ups with and without tip mass. They generate more power while only slightly increasing the deflection in the piezoelectric harvester and they can be tuned across a wide range of excitation frequencies.}}, author = {{Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Journal of Intelligent Material Systems and Structures}}, number = {{11}}, pages = {{1332--1342}}, title = {{{Increasing the power of piezoelectric energy harvesters by magnetic stiffening}}}, doi = {{10.1177/1045389X13483021}}, volume = {{24}}, year = {{2013}}, } @article{9795, abstract = {{Power and bandwidth of piezoelectric harvesters can be increased by using multiple piezoelectric elements in one harvester. In this contribution, a novel energy harvesting cantilever array with magnetic tuning including three piezoelectric bimorphs is investigated theoretically and experimentally, with a good agreement between model and experiment. Other than harvester designs proposed before, this array is easy to manufacture and insensitive to manufacturing tolerances because its optimum operation frequency can be re-adjusted after fabrication. Using the superposition principle, the Butterworth-Van Dyke model and a mechanical lumped parameters model, the generated voltage and current are determined analytically. Formulas for calculating the power generated by array harvesters with an arbitrary number of piezoelectric elements connected in series or in parallel are derived. It is shown that optimum harvester design must take both the connected load and the operating frequency into account. Strategies for connecting multiple bimorphs to increase the maximum generated power and/or enhance the bandwidth compared to a single bimorph harvester are investigated. For bandwidth enhancement it is essential that individual rectifiers are used for the bimorphs. An example with three bimorphs shows that, depending on the chosen tuning strategy, the power is increased by about 340\% or the bandwidth is increased by about 500\%, compared to one single bimorph.}}, author = {{Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Sensors and Actuators A: Physical}}, keywords = {{Energy harvesting, Cantilever array, Bandwidth, Power increase}}, pages = {{138 -- 146}}, title = {{{Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments}}}, doi = {{10.1016/j.sna.2013.01.008}}, volume = {{200}}, year = {{2013}}, } @inproceedings{9796, abstract = {{A basic autonomous system powered by a piezoelectric harvester contains three components apart from the harvester: a fullwave rectifier, a reservoir capacitor and an electronic device performing the primary task of the system. In this contribution, a model describing the operation of such a system is derived. It is found that in steady-state operation, the piezoelectric harvester experiences two alternating load conditions due to the rectification process. These alternating load conditions can have a significant effect on the operation of the harvester and must be considered in the design of autonomous systems. The results also show that such an autonomous system works efficiently if it is connected to a high impedance load and excited by a frequency matching the anti-resonance frequency of the piezoelectric harvester.}}, author = {{Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013}}, keywords = {{Energy harvesting, harvester modeling, load dependence, generated voltage}}, number = {{05/2013}}, pages = {{159--161}}, title = {{{Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems}}}, year = {{2013}}, } @inproceedings{9797, abstract = {{A model approach for wedge/wedge bonding copper wire is presented. The connection between wire and substrate is based on a variety of physical effects, but the dominant one is the friction based welding while applying ultrasound. Consequently, a friction model was used to investigate the welding process. This model is built up universal and can be used to describe the formation of micro welds in the time variant contact area between wire and substrate. Aim of the model is to identify the interactions between touchdown, bond normal force, ultrasonic power and bonding time. To do so, the contact area is discretized into partial areas where a Point Contact Model is applied. Based on this approach it is possible to simulate micro and macro slip inside the contact area between wire and substrate. The work done by friction force is a main criterion to define occurring micro joints which influence the subsequent welding.}}, author = {{Althoff, Simon and Neuhaus, Jan and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{IMAPS 2013, 46th International Symposium on Microelectronics}}, keywords = {{Wire bonding, friction modeling, wire bond quality, contact element modeling}}, title = {{{A friction based approach for modeling wire bonding}}}, doi = {{10.4071/isom-2013-TA67}}, year = {{2013}}, } @inproceedings{9799, abstract = {{Ultrasonic wire bonding is a common technology for manufacturing electrical interconnects. In the field of power electronics, new thermal and electrical obligations arose due to increasing power density requirements. One approach to achieve these aims is replacing the wire material for heavy wire bonds from aluminum to copper. This material change leads to challenging tasks and problems, for instance the occurring wear of the bond tool. The wear is significantly higher using copper wire instead of aluminum and results in a dramatic loss in the amount of interconnects which can be produced reliable by a single tool. To reduce setting-up time in the production and minimizing costs, an enlarged bonding tool lifetime is desirable. Therefore, the paper discusses the influences of bonding parameters on the wear. The key question is which of the tasks cannot be fulfilled with increased wear of the tool, e.g. loss of process capability. The main functions are fixing the wire in the tool groove, predeformation, applying normal force and transmission of ultrasonic oscillation to the wire. To identify the most affecting factors, four bonding parameters are varied and their influences are investigated. These parameters are: (I) ultrasonic power, (II) tool geometry, (III) the way of tangential force transmission and (IV) loop trajectory.}}, author = {{Eichwald, Paul and Sextro, Walter and Althoff, Simon and Eacock, Florian and Schnietz, Mark and Guth, Karsten and Brökelmann, Michael}}, booktitle = {{15th Electronics Packaging Technology Conference}}, title = {{{Influences of Bonding Parameters on the Tool Wear for Copper Wire Bonding}}}, doi = {{10.1109/EPTC.2013.6745803}}, year = {{2013}}, } @inproceedings{9801, author = {{Hunstig, Matthias and Al-Ashtari, Waleed and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{9. Paderborner Workshop Entwurf mechatronischer Systeme}}, editor = {{Gausemeier, Jürgen and Dumitrescu, Roman and Rammig, Franz and Schäfer, Wilhelm and Trächtler, Ansgar}}, pages = {{359--372}}, publisher = {{Heinz Nixdorf Institut, Universität Paderborn}}, title = {{{Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme}}}, year = {{2013}}, } @inproceedings{9802, abstract = {{It has been shown previously that ``slip-slip'' operation of piezoelectric inertia motors allows higher velocities and smoother movements than classic ``stick-slip'' operation. One very promising driving option is to use a superposition of multiple sinusoidal signals. In this contribution, previous theoretical results are validated experimentally. The results confirm the theoretical result that for a given maximum frequency, usually defined by the actuator characteristics, a signal with high fundamental frequency and consisting of two superposed sine waves leads to the highest velocity and the smoothest motion. This result is of fundamental importance for the further development of high-velocity piezoelectric inertia motors.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop}}, keywords = {{Piezoelectric inertia motor, stick-slip motor, driving signal, velocity, smoothness}}, pages = {{16--18}}, title = {{{High-Velocity Slip-Slip Operation of Piezoelectric Inertia Motors - Experimental Validation}}}, year = {{2013}}, } @article{9803, abstract = {{Piezoelectric inertia motors, also known as stickslip drives or (smooth) impact drives, use the inertia of a body to drive it by a friction contact in small steps, in the majority of motors composed of a stick phase and a slip phase between the friction partners. For optimizing inertia motors, it is important to understand the friction contact correctly and to measure its properties appropriately. This contribution presents experimental set-ups for measuring the contact force, friction force and relative displacement in an actual inertia motor with a dry friction contact and numerical simulations of the motor operation. The motor uses a pre-stressed multilayer actuator with a displacement in the range of 20 $\mu$ m. It is shown that a previously postulated condition for the applicability of simple kinetic friction models is well fulfilled for the investigated motor. The friction contact in the motor is simulated using different kinetic friction models. The input for the friction models is the measured motion of the rod. The models qualitatively reproduce the measured motion but show quantitative deviations varying with frequency. These can be explained by vibrations of the driving rod that are experimentally investigated.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Journal of Intelligent Material Systems and Structures}}, keywords = {{Actuator, friction, motor, piezoelectric}}, number = {{11}}, pages = {{1380--1391}}, title = {{{Modelling the friction contact in an inertia motor}}}, doi = {{10.1177/1045389X12474354}}, volume = {{24}}, year = {{2013}}, } @article{9804, abstract = {{This contribution provides a systematic investigation and performance comparison of different modes of operation for piezoelectric inertia drives. The movement of these motors is classically assumed to consist of steps involving stiction and sliding, resulting in the term ``stick-slip drives''. In the first part of this contribution it has been found that using ideal driving signals, ``slip-slip'' operation without phases of stiction allows very high velocities, while the maximum velocity is limited principally in stick-slip operation. In this part it is shown that slip-slip operation is also suitable for use with real actuators, driven with frequency-limited versions of the ideal signals presented in part I. The motional performance of the motor as well as its wear and the required electric power are investigated for operation with different signals. It is found that for high velocity inertia motors it is recommendable to use actuators with large stroke and to drive them with a signal consisting of two harmonics at a high fundamental frequency, a result that is supported by similar setups implemented experimentally by other authors. Using Lanczos' \sigma factors to calculate the frequency-limited excitation signals instead of standard Fourier series additionally increases the motor performance significantly. The results help motor designers to choose the appropriate mode of operation and to optimise the motor parameters for their individual applications.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Sensors and Actuators A: Physical}}, keywords = {{Inertia motor}}, pages = {{79 -- 89}}, title = {{{Stick-slip and slip-slip operation of piezoelectric inertia drives - Part II: Frequency-limited excitation}}}, doi = {{10.1016/j.sna.2012.11.043}}, volume = {{200}}, year = {{2013}}, } @article{9805, abstract = {{Piezoelectric inertia motors, also known as ``stick--slip drives'', use the inertia of a body to drive it in small steps by means of a friction contact. While these steps are classically assumed to involve stiction and sliding, the motors can also operate in ``slip--slip'' mode without any phase of static friction. This contribution provides a systematic investigation and performance comparison of different stick--slip and slip--slip modes of operation. Different criteria for comparing the motional performance of inertia motors are defined: Steady state velocity, smoothness of motion, and start-up time. Using the example of a translational inertia motor excited by an ideal displacement signal, it is found that the maximum velocity reachable in stick--slip operation is limited principally, while continuous slip--slip operation allows very high velocities. For the investigated driving signals, the motor velocity is proportional to the square root of the actuator stroke. The motor performance with these ideal signals defines an upper boundary for the performance of real motors.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Sensors and Actuators A: Physical}}, keywords = {{Inertia motor, Stick--slip drive, Mode of operation, Performance indicator, Velocity maximization, Actuator stroke}}, pages = {{90 -- 100}}, title = {{{Stick-slip and slip-slip operation of piezoelectric inertia drives - Part I: Ideal Excitation.}}}, doi = {{10.1016/j.sna.2012.11.012}}, volume = {{200}}, year = {{2013}}, }