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Active control of flexible rotors is a challenging issue in modern industries. This paper focuses on the synthesis of a mixed sensitivity robust controller for a linear parameter-varying (LPV) system. The objective is to control rotor vibration, especially when the rotor is passing the first two bending critical speeds. In the formulation of the problem for the controller, weighting functions are proposed based on the relationship between the desired shape of the open-loop transfer function and sensitivity functions of the closed-loop system. Recent research has highlighted the efficiency of mixed sensitivity robust controllers in stabilizing a wide range of magnetic bearing systems. Here, the method is extended to control the vibration of a piezoelectric bearing system. The experimental rotor features two unbalance-exited resonances within its operating range. Experimental results demonstrate good performance of the vibration reduction and the effectiveness of the design method.

Active control of flexible rotors is a challenging issue in modern industries. This paper focuses on the synthesis of a mixed sensitivity robust controller for a linear parameter-varying (LPV) system. The objective is to control rotor vibration, especially when the rotor is passing the first two bending critical speeds. In the formulation of the problem for the controller, weighting functions are proposed based on the relationship between the desired shape of the open-loop transfer function and sensitivity functions of the closed-loop system. Recent research has highlighted the efficiency of mixed sensitivity robust controllers in stabilizing a wide range of magnetic bearing systems. Here, the method is extended to control the vibration of a piezoelectric bearing system. The experimental rotor features two unbalance-exited resonances within its operating range. Experimental results demonstrate good performance of the vibration reduction and the effectiveness of the design method.

A magnetically levitated spindle was designed for fatigue testing of cylinders made of fiber reinforced plastic. In these fatigue tests, the speed of the cylinders is varied cyclically between 15,000 and 30,000 rpm until their mechanical failure occurs. Several eigenfrequencies have to be passed to reach the operational speed range. During long‐term operation, the rotor of the spindle is prone to overheating due to various losses. One way of reducing the rotor temperature is to decrease the bias current of the radial active magnetic bearings. Since the bias current influences the dynamic behavior of the system, the control of the bearings has to be adapted as well. This article describes a controller design for the system with different bias currents to determine the smallest usable bias current. A detailed model of the plant is developed, which is then used to optimize the parameters of the utilized controller with a predefined structure using the weighted ℋ∞ norm as the objective function. Since the rotor is highly gyroscopic, its eigenfrequencies change with the rotational speed. To ensure that the system meets certain robustness criteria at all rotational speeds, the parameters of the controller are simultaneously optimized for the plant model at different speeds. This approach leads to a controller which can be used in the entire speed range without the need for gain scheduling. The functionality of the controller and the influence of the bias current on the rotor temperature are investigated through measurements.

In der vorliegenden Dissertation wird die Eliminierung von Unwucht erregten Schwingungen von gyroskopischen Rotoren mittels aktiver piezoelektrischer Lager untersucht. Hierzu wird zunächst ein Rotorprüfstand mittels FEM modelliert und anschließend die Ergebnisse experimentell abgeglichen. Bei der Modellierung wird die neue Rotorkoordinate der relativen Auslenkung eingeführt, welche die Differenz zwischen der Rotorauslenkung und einer linearen Interpolation der freien Auslenkung der Piezoaktoren ist. Weiterhin wird ein neuer Ansatz für ein modales Modell für gyroskopische Rotoren präsentiert, welcher zur Black Box Identifikation verwendet werden kann. Nach der Modellierung wird der Least Mean Squares (LMS) Algorithmus in Kombination mit Integral Force Feedback (IFF) zur Regelung des Systems zunächst analytisch untersucht und anschließend experimentell validiert. Durch die kombinierte Minimierung der Lagerkräfte und Auslenkungen der Scheibe können alle Resonanzen des Systems eliminiert werden. Basierend auf der Literatur zum LMS-Algorithmus wird ein rotormodellfreier Regelungsansatz abgeleitet, welcher die Lagerkräfte im aktiven Lager minimiert und für die Implementierung nur die Totzeit des Systems benötigt. Der Ansatz ist hierbei eine Kombination aus LMS und IFF. Weiterhin wird der LMS um einen Transform Domain (TDLMS) Ansatz erweitert, welcher die Schwingungsamplituden als Regelgröße verwendet. Zur Berechnung der Schwingungsamplituden wird die diskrete Fourier-Transformation über eine volle Rotorumdrehung verwendet. Hierdurch werden die Amplituden über eine Umdrehung gemittelt. Zur Kompensation dieses Zeitverzugs wird ein neuer, auf einem Polynom basierender Algorithmus vorgestellt. Die Funktionsfähigkeit der rotormodellfreien Regelung wird in Experimenten nachgewiesen. Der Regelungsansatz wird anschließend verwendet, um ein Modell des Rotors zu schätzen. Hierzu werden zwei Rotorausläufe durchgeführt, bei dem einmal nur IFF verwendet wird und beim anderen IFF in Ko

A magnetically levitated spindle was designed for fatigue testing of cylinders made of fiber reinforced plastic. In these fatigue tests, the speed of the cylinders is varied cyclically between 15,000 and 30,000 rpm until their mechanical failure occurs. Several eigenfrequencies have to be passed to reach the operational speed range. During long‐term operation, the rotor of the spindle is prone to overheating due to various losses. One way of reducing the rotor temperature is to decrease the bias current of the radial active magnetic bearings. Since the bias current influences the dynamic behavior of the system, the control of the bearings has to be adapted as well. This article describes a controller design for the system with different bias currents to determine the smallest usable bias current. A detailed model of the plant is developed, which is then used to optimize the parameters of the utilized controller with a predefined structure using the weighted ℋ∞ norm as the objective function. Since the rotor is highly gyroscopic, its eigenfrequencies change with the rotational speed. To ensure that the system meets certain robustness criteria at all rotational speeds, the parameters of the controller are simultaneously optimized for the plant model at different speeds. This approach leads to a controller which can be used in the entire speed range without the need for gain scheduling. The functionality of the controller and the influence of the bias current on the rotor temperature are investigated through measurements.

A magnetically levitated spindle was designed for fatigue testing of cylinders made of fiber reinforced plastic. In these fatigue tests, the speed of the cylinders is varied cyclically between 15,000 and 30,000 rpm until their mechanical failure occurs. Several eigenfrequencies have to be passed to reach the operational speed range. During long‐term operation, the rotor of the spindle is prone to overheating due to various losses. One way of reducing the rotor temperature is to decrease the bias current of the radial active magnetic bearings. Since the bias current influences the dynamic behavior of the system, the control of the bearings has to be adapted as well. This article describes a controller design for the system with different bias currents to determine the smallest usable bias current. A detailed model of the plant is developed, which is then used to optimize the parameters of the utilized controller with a predefined structure using the weighted ℋ∞ norm as the objective function. Since the rotor is highly gyroscopic, its eigenfrequencies change with the rotational speed. To ensure that the system meets certain robustness criteria at all rotational speeds, the parameters of the controller are simultaneously optimized for the plant model at different speeds. This approach leads to a controller which can be used in the entire speed range without the need for gain scheduling. The functionality of the controller and the influence of the bias current on the rotor temperature are investigated through measurements.

A magnetically levitated spindle was designed for fatigue testing of cylinders made of fiber reinforced plastic. In these fatigue tests, the speed of the cylinders is varied cyclically between 15,000 and 30,000 rpm until their mechanical failure occurs. Several eigenfrequencies have to be passed to reach the operational speed range. During long‐term operation, the rotor of the spindle is prone to overheating due to various losses. One way of reducing the rotor temperature is to decrease the bias current of the radial active magnetic bearings. Since the bias current influences the dynamic behavior of the system, the control of the bearings has to be adapted as well. This article describes a controller design for the system with different bias currents to determine the smallest usable bias current. A detailed model of the plant is developed, which is then used to optimize the parameters of the utilized controller with a predefined structure using the weighted ℋ∞ norm as the objective function. Since the rotor is highly gyroscopic, its eigenfrequencies change with the rotational speed. To ensure that the system meets certain robustness criteria at all rotational speeds, the parameters of the controller are simultaneously optimized for the plant model at different speeds. This approach leads to a controller which can be used in the entire speed range without the need for gain scheduling. The functionality of the controller and the influence of the bias current on the rotor temperature are investigated through measurements.

In der vorliegenden Dissertation wird die Eliminierung von Unwucht erregten Schwingungen von gyroskopischen Rotoren mittels aktiver piezoelektrischer Lager untersucht. Hierzu wird zunächst ein Rotorprüfstand mittels FEM modelliert und anschließend die Ergebnisse experimentell abgeglichen. Bei der Modellierung wird die neue Rotorkoordinate der relativen Auslenkung eingeführt, welche die Differenz zwischen der Rotorauslenkung und einer linearen Interpolation der freien Auslenkung der Piezoaktoren ist. Weiterhin wird ein neuer Ansatz für ein modales Modell für gyroskopische Rotoren präsentiert, welcher zur Black Box Identifikation verwendet werden kann. Nach der Modellierung wird der Least Mean Squares (LMS) Algorithmus in Kombination mit Integral Force Feedback (IFF) zur Regelung des Systems zunächst analytisch untersucht und anschließend experimentell validiert. Durch die kombinierte Minimierung der Lagerkräfte und Auslenkungen der Scheibe können alle Resonanzen des Systems eliminiert werden. Basierend auf der Literatur zum LMS-Algorithmus wird ein rotormodellfreier Regelungsansatz abgeleitet, welcher die Lagerkräfte im aktiven Lager minimiert und für die Implementierung nur die Totzeit des Systems benötigt. Der Ansatz ist hierbei eine Kombination aus LMS und IFF. Weiterhin wird der LMS um einen Transform Domain (TDLMS) Ansatz erweitert, welcher die Schwingungsamplituden als Regelgröße verwendet. Zur Berechnung der Schwingungsamplituden wird die diskrete Fourier-Transformation über eine volle Rotorumdrehung verwendet. Hierdurch werden die Amplituden über eine Umdrehung gemittelt. Zur Kompensation dieses Zeitverzugs wird ein neuer, auf einem Polynom basierender Algorithmus vorgestellt. Die Funktionsfähigkeit der rotormodellfreien Regelung wird in Experimenten nachgewiesen. Der Regelungsansatz wird anschließend verwendet, um ein Modell des Rotors zu schätzen. Hierzu werden zwei Rotorausläufe durchgeführt, bei dem einmal nur IFF verwendet wird und beim anderen IFF in Ko

In der vorliegenden Dissertation wird die Eliminierung von Unwucht erregten Schwingungen von gyroskopischen Rotoren mittels aktiver piezoelektrischer Lager untersucht. Hierzu wird zunächst ein Rotorprüfstand mittels FEM modelliert und anschließend die Ergebnisse experimentell abgeglichen. Bei der Modellierung wird die neue Rotorkoordinate der relativen Auslenkung eingeführt, welche die Differenz zwischen der Rotorauslenkung und einer linearen Interpolation der freien Auslenkung der Piezoaktoren ist. Weiterhin wird ein neuer Ansatz für ein modales Modell für gyroskopische Rotoren präsentiert, welcher zur Black Box Identifikation verwendet werden kann. Nach der Modellierung wird der Least Mean Squares (LMS) Algorithmus in Kombination mit Integral Force Feedback (IFF) zur Regelung des Systems zunächst analytisch untersucht und anschließend experimentell validiert. Durch die kombinierte Minimierung der Lagerkräfte und Auslenkungen der Scheibe können alle Resonanzen des Systems eliminiert werden. Basierend auf der Literatur zum LMS-Algorithmus wird ein rotormodellfreier Regelungsansatz abgeleitet, welcher die Lagerkräfte im aktiven Lager minimiert und für die Implementierung nur die Totzeit des Systems benötigt. Der Ansatz ist hierbei eine Kombination aus LMS und IFF. Weiterhin wird der LMS um einen Transform Domain (TDLMS) Ansatz erweitert, welcher die Schwingungsamplituden als Regelgröße verwendet. Zur Berechnung der Schwingungsamplituden wird die diskrete Fourier-Transformation über eine volle Rotorumdrehung verwendet. Hierdurch werden die Amplituden über eine Umdrehung gemittelt. Zur Kompensation dieses Zeitverzugs wird ein neuer, auf einem Polynom basierender Algorithmus vorgestellt. Die Funktionsfähigkeit der rotormodellfreien Regelung wird in Experimenten nachgewiesen. Der Regelungsansatz wird anschließend verwendet, um ein Modell des Rotors zu schätzen. Hierzu werden zwei Rotorausläufe durchgeführt, bei dem einmal nur IFF verwendet wird und beim anderen IFF in Ko

Modern industry benefits from the automation capabilities and flexibility of robots. Consequently, the performance depends on the individual task, robot and trajectory, while application periods of several years lead to a significant impact of the use phase on the resource efficiency. In this work, simulation models predicting a robot’s energy consumption are extended by an estimation of the reliability, enabling the consideration of maintenance to enhance the assessment of the application’s life cycle costs. Furthermore, a life cycle assessment yields the greenhouse gas emissions for the individual application. Potential benefits of the combination of motion simulation and cost analysis are highlighted by the application to an exemplary system. For the selected application, the consumed energy has a distinct impact on greenhouse gas emissions, while acquisition costs govern life cycle costs. Low cycle times result in reduced costs per workpiece, however, for short cycle times and higher payloads, the probability of required spare parts distinctly increases for two critical robotic joints. Hence, the analysis of energy consumption and reliability, in combination with maintenance, life cycle costing and life cycle assessment, can provide additional information to improve the resource efficiency.

Modern industry benefits from the automation capabilities and flexibility of robots. Consequently, the performance depends on the individual task, robot and trajectory, while application periods of several years lead to a significant impact of the use phase on the resource efficiency. In this work, simulation models predicting a robot’s energy consumption are extended by an estimation of the reliability, enabling the consideration of maintenance to enhance the assessment of the application’s life cycle costs. Furthermore, a life cycle assessment yields the greenhouse gas emissions for the individual application. Potential benefits of the combination of motion simulation and cost analysis are highlighted by the application to an exemplary system. For the selected application, the consumed energy has a distinct impact on greenhouse gas emissions, while acquisition costs govern life cycle costs. Low cycle times result in reduced costs per workpiece, however, for short cycle times and higher payloads, the probability of required spare parts distinctly increases for two critical robotic joints. Hence, the analysis of energy consumption and reliability, in combination with maintenance, life cycle costing and life cycle assessment, can provide additional information to improve the resource efficiency.

Modern industry benefits from the automation capabilities and flexibility of robots. Consequently, the performance depends on the individual task, robot and trajectory, while application periods of several years lead to a significant impact of the use phase on the resource efficiency. In this work, simulation models predicting a robot’s energy consumption are extended by an estimation of the reliability, enabling the consideration of maintenance to enhance the assessment of the application’s life cycle costs. Furthermore, a life cycle assessment yields the greenhouse gas emissions for the individual application. Potential benefits of the combination of motion simulation and cost analysis are highlighted by the application to an exemplary system. For the selected application, the consumed energy has a distinct impact on greenhouse gas emissions, while acquisition costs govern life cycle costs. Low cycle times result in reduced costs per workpiece, however, for short cycle times and higher payloads, the probability of required spare parts distinctly increases for two critical robotic joints. Hence, the analysis of energy consumption and reliability, in combination with maintenance, life cycle costing and life cycle assessment, can provide additional information to improve the resource efficiency.

Modern industry benefits from the automation capabilities and flexibility of robots. Consequently, the performance depends on the individual task, robot and trajectory, while application periods of several years lead to a significant impact of the use phase on the resource efficiency. In this work, simulation models predicting a robot’s energy consumption are extended by an estimation of the reliability, enabling the consideration of maintenance to enhance the assessment of the application’s life cycle costs. Furthermore, a life cycle assessment yields the greenhouse gas emissions for the individual application. Potential benefits of the combination of motion simulation and cost analysis are highlighted by the application to an exemplary system. For the selected application, the consumed energy has a distinct impact on greenhouse gas emissions, while acquisition costs govern life cycle costs. Low cycle times result in reduced costs per workpiece, however, for short cycle times and higher payloads, the probability of required spare parts distinctly increases for two critical robotic joints. Hence, the analysis of energy consumption and reliability, in combination with maintenance, life cycle costing and life cycle assessment, can provide additional information to improve the resource efficiency.

In den letzten Jahren wurde in der deutschen Politikwissenschaft (und darüber hinaus) eine intensive Debatte über die gesellschaftliche und politische Relevanz der Disziplin geführt. Dabei blieb allerdings die faktische politikberatende Rolle mindestens genauso umstritten wie die normative Seite dieser Tätigkeit; und auch innerhalb der vergleichenden Forschung zu Politikberatung wurde der Politikwissenschaft keine gezielte Aufmerksamkeit geschenkt. Dieser Artikel untersucht, wie, für wen und wie häufig Politikwissenschaftler*innen in Deutschland ihre Expertise für die Politik bereitstellen. Die Analyse basiert auf den deutschen Ergebnissen (n=376) einer Umfrage, die 2018 in mehr als 30 europäischen Ländern durchgeführt wurde. Neben ersten empirischen Einblicken in ein bislang wenig untersuchtes Phänomen ist es Ziel des Beitrags, deutsche Politikwissenschaftler*innen in einer Typologie von Beratungsrollen zu verorten. Die Analyse zeigt durchaus umfangreiche und diverse, im Ländervergleich allerdings unterdurchschnittliche politikberatende Tätigkeiten. Der zentrale Unterschied für Art und Ausmaß der Politikberatung scheint zwischen Politikwissenschaftler*innen auf befristeten und unbefristeten Stellen zu bestehen., Recent years have seen intensive debates in German political science (and beyond) on the discipline's societal and political relevance. Yet within this debate, the actual policy-advisory role has been at least as disputed as its normative foundation. Moreover, political science has not been at the focus of policy-advisory research. This article studies how, for whom, and how often political scientists provide expertise for policy-making. The analysis is based on the German responses (n=376) in a survey of political scientists carried out in more than 30 European countries in 2018. Next to empirical insights into a so-far understudied phenomenon, the aim is to locate German political scientists in a typology of policy-advisory roles. The analysis highlights that German political scientists are rather active in a diverse set of policy-advisory activities, though less active than colleagues in other European countries. A key result is that political scientists are more active in policy advice if they are on permanent positions.

Before the UK left the EU, Jens Jungblut (University of Oslo) was one of a team of researchers who asked university staff in Portugal and Germany how they thought Brexit would affect their work. They were confident about the ability to maintain academic partnerships, but concerned about the effect on student mobility – while identifying some opportunities for their own institutions.