135 research outputs found
Sorex thibetanus Kastschenko 1905
No full textSorex thibetanus Kastschenko, 1905. Izv. Tomsk. Univ., 27:93. TYPE LOCALITY: "Tsaidam" [NE Tibet]. DISTRIBUTION: Himalyas and NE Tibet. COMMENTS: The pygmy shrews of the Himalayas are the subject of controversy. The original description of thibetanus (as a subspecies of minutus) is not very helpful and the holotype in the Tomsk Academy was considered to be lost (Yudin, pers. comm. 1977 to the author); Hutterer (1979) therefore regarded thibetanus as a nomen dubium. Dolgov and Hoffmann (1977) and later Hoffmann (1987) used thibetanus to define a Himalayan species in which they included buchariensis, kozlovi, planiceps, and specimens from Nepal and China reported as minutus by various authors. Hutterer (1979) instead recognized three species, buchariensis, planiceps, and minutus as occurring in the Himalayas and regarded kozlovi and thibetanus as indeterminable. Zaitsev (1988) pointed out differences between buchariensis and thibetanus. Surprisingly, the holotype of thibetanus turned up in the Zoological Museum of Moscow (Baranova et al., 1981) and Hoffmann (1987) reported on its measurements. These did not solve the problem but instead matched well with minutus. The controversy still remains unresolved and can be solved presumably only with new material and a more complete data set. Provisionally all the mentioned forms are listed separately.Published as part of Rainer Hutterer, 1993, Order Insectivora, pp. 69-130 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 121, DOI: 10.5281/zenodo.735308
Atelerix algirus Lereboullet 1842
No full textAtelerix algirus Lereboullet, 1842. Mem. Soc. Hist. Nat. Strasbourg, 3(2), art. QQ:4. TYPE LOCALITY: Algeria, "provient de Oran ". DISTRIBUTION: Coastal Western Sahara to Algeria, Tunisia, and N Libya; introduced into Canary Isis, Balearic Isis, Malta, and Mediterranean France and Spain; one historical record from Puerto Rico. SYNONYMS: caniculus, diadematus, fallax, girbaensis, krugi, lavaudeni, vagans. COMMENTS: Authorship is often credited to Duvernoy and Lereboullet, 1842, but Saint-Girons (1972) showed that Lereboullet was the only author. Includes vagans and girbaensis as subspecies, see Hutterer (1983c).Published as part of Rainer Hutterer, 1993, Order Insectivora, pp. 69-130 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on pages 76-77, DOI: 10.5281/zenodo.735308
Robust control of a magnetically stabilized rotor at sub-critical speed
No full textDie vorliegende Arbeit behandelt den Entwurf und Vergleich robuster Positionsregelungen un- terschiedlicher Strukturen für magnetgelagerte unterkritisch laufende Rotoren. Dazu wurde in einem ersten Schritt ein mathematisches Modell hergeleitet, um das dynamische Verhalten eines durch aktive Magnetlager stabilisierten Rotors analysieren zu können. Um dem gyro- skopischen Effekt und der damit einhergehenden Aufspaltung der Eigenmoden des Rotors entgegenzuwirken, wurde eine Reglerstruktur bestehend aus dezentralen PID-Reglern und Querkopplungselementen entwickelt, für deren Elemente drei unterschiedliche Ansätze unter- sucht wurden. Für die Querkopplungen wurden PD-Regler als auch eine geeignete Kombina- tion aus Tief- und Hochpassfiltern eingesetzt. Die Querkopplung ermöglicht die Anordnung an zwei unterschiedlichen Stellen im Regelkreis, wodurch auf unterschiedliche Art und Wei- se auf die Eigenmoden des Rotors eingewirkt werden kann, um somit hohe Rotordrehzahlen zu ermöglichen. Um einen möglichst robusten Regler zu generieren, wurde zur Bestimmung der Parameter die sogenannte H-Infinity-Reglersynthese verwendet. In Simulationen wurden die unterschiedlichen Methoden analysiert und in Hinblick auf die Robustheit des Regelkreises untersucht. Aufbauend auf den theoretischen Ergebnissen wurden die Regler auf einem vor- handenen Magnetlagersystem implementiert und experimentell analysiert.The present diploma thesis deals with the design of a robust controller for a magnetically suspended rotor at under critical speeds. To study the dynamic behaviour of a magnetically levitating rotor, a mathematical model of the magnetic bearing and the rigid body of the rotor has been derived. The gyroscopic effect of a rigid rotor rotating at a very high angular velocity leads to spreading eigenmodes of the rotor. A control structure based on decentralized PID controller and so called cross coupling elements has been developed, to partially counteract the gyroscopic effect. Within the control strategy, three different approaches have been subse- quentialy studied. PD controller as well as a variation of a suitable combination of high- and lowpass filter are used for the cross coupling elements. The cross coupling elements enable the positioning at two different locations withing the control scheme. Through the variation of the positioning, different counteracting effects on the gyroscopic effect and the spreading eigenmodes can be observed, which leads to higher angular velocities. In order to obtain a robust controller, the parameter of the chosen structure are determined with the so called H-Infinity synthesis. The presented strategies have been implemented in simulations in order to examine the robustness of the control loop. Based on the theoretical results, the three control strategies have been implemented and experimentally analysed on an existing magnetic bearing system
Development and Comparison of different Unbalance Control Strategies for a Magnetic Bearing System
No full textDie vorliegende Diplomarbeit behandelt den Vergleich und die Implementierung unterschiedlicher Arten von Unwuchtkompensationen für magnetgelagerte, unterkritisch laufende Rotoren. Dazu wurde zunächst ein mathematisches Modell eines Magnetlagers hergeleitet, welches die statischen und dynamischen Unwuchten des Rotors als Störeingang berücksichtigt. Auf Basis dieses Modells wurden vier Unwuchtkompensationen vorgestellt, verglichen und weiterentwickelt, sodass Unwuchten sowohl im Stromsignal, als auch im Positionssignal effizient unterdrückt werden können. Alle vier vorgestellten Unwuchtkompensationen unterstützen sowohl die Methode "Current Nulling", als auch die Methode "Vibration Nulling". Die Methode "Current Nulling" filtert die Unwuchtschwingung aus den Sensorsignalen und bewirkt dadurch eine Reduktion des Stromes, sodass eine Sättigung der Aktoren vermieden wird und höhere Drehzahlen des Rotors bei verringertem Strom ermöglicht werden. Die Methode "Vibration Nulling" bringt zusätzliche Kräfte über das Magnetlager auf den Rotor auf, sodass dieser um seine geometrische Achse rotiert. In Simulationen wurden die Unwuchtkompensationen analysiert und sowohl deren dynamisches Verhalten als auch deren Robustheit untersucht. Auf Basis dieser Ergebnisse wurden drei ausgewählte Unwuchtkompensationen an einem Versuchsaufbau implementiert und experimentell untersucht.The present diploma thesis deals with the comparison and implementation of four different unbalance compensation strategies for magnetically suspended rotors at under critical speeds. For this purpose, a mathematical model for a magnetic bearing which considers the static and dynamic unbalances of a rotating shaft has been derived in a first step. Subsequently, four different unbalances compensation strategies have been presented, compared and improved in order to suppress the effects of the unbalances in the current signal and in the motion of the rotor. All four approaches support "Current Nulling" as well as "Vibration Nulling". The method "Current Nulling" seperates the unbalance signals from the sensor signals and leads to a reduction of the coil current, which prevents the actuators from saturation and enables high rotational speeds. The method "Vibration Nulling" applies additional forces on the rotor and leads to a reduction of the unbalance motion of the rotor and keeps it rotating about its geometric axis. The presented strategies have been implemented in simulations in order to examine their robustness and their behavior. Based on these results, three unbalance compensation strategies have been implemented on a test rig and the obtained results have been evaluated
Optimization of a sensorless magnetic bearing by means of variable space vector modulation
No full textMagnetlager sind von großer Bedeutung für die reibungsfreie Lagerung von Rotoren. Aufgrund der berührungsfreien Lagerung entstehen weder Verschleiß noch Schmierbedarf des Lagers. Aus diesem Grund können Magnetlager in Bereichen mit hohen Anforderungen an Prozesskontaminierung, wie in der Medizintechnik oder Vakuumtechnik, eingesetzt werden. Im Rahmen dieser Diplomarbeit wird ein radiales Magnetlager untersucht, welches ohne Positionssensoren aufgebaut ist. Die Position der Rotorwelle wird mittels des sogenannten INFORM (Indirect Flux Detection by Online Reactance Measurement) Verfahrens erfasst. In vorausgehenden Arbeiten konnte bereits die Funktion der sensorlosen Positionsregelung an einem Prototyp gezeigt werden. Bislang ist die Positionserfassung jedoch mit unerwünschten Lagerverlusten verbunden. Die Ursache liegt in der Verwendung einer hohen Zwischenkreisspannung des Umrichters, welche für eine hinreichende Positionsauflösung des sensorlosen Verfahrens erforderlich ist. Die Zielsetzung dieser Arbeit besteht darin, die Verlustleistung im Magnetlager zu senken ohne die Lagerperformance zu verringern. Daraus resultiert die Fragestellung, mit welcher Methode die Zwischenkreisspannung gesenkt werden kann, ohne an Positionsauflösung und Regeldynamik zu verlieren. Der Ausgangspunkt zur Lösung dieser Problematik liegt in einer Anpassung der Raumzeigermodulation im Betrieb des Magnetlagers. Die Idee besteht darin, die Raumzeigermodulation so zu gestalten, dass in Abhängigkeit der erforderlichen Lagerkraft eine maximale Positionsauflösung erreicht wird. Dazu erfolgt eine Kombination unterschiedlicher INFORM-Pulsmuster, welche sich hinsichtlich der Regeldynamik und Anzahl der Positionsmessungen unterscheiden. Zur Verifikation der entworfenen Raumzeigermodulation wird diese am Prototyp implementiert und Messungen unterzogen. Das Augenmerk der Messungen liegt auf dem Vergleich der INFORM-Pulsmuster in Hinblick auf die erreichbare Performance des sensorlosen Verfahrens. Zudem wird der Einfluss unterschiedlicher Materialien zur magnetischen Flussführung hinsichtlich der Lagerverluste untersucht.Magnetic bearings are of great significance for contactless stabilization of rotors. Due to the levitation of the rotor no wear occurs and a lubrication of the bearing is not required. For this reason, magnetic bearings can be used in areas with high demands on process contamination, such as medical technology or in vacuum applications. The focus of this diploma thesis is set on a self-sensing radial magnetic bearing. The rotor is levitating without the use of separate position sensors. The position of the rotor is detected by means of the so-called INFORM (Indirect Flux Detection by Online Reactance Measurement) method. In previous work, the function of the sensorless position control could already be shown on a prototype. The sensorless position detection of this prototype has been associated with undesirable bearing losses. The reason for this disadvantage is the use of a high intermediate circuit voltage of the inverter, which is necessary for a sufficient position resolution of the sensorless method. The aim of this thesis is a reduction of the bearing losses without a loss of bearing performance. Therefore, the question is to proof, if the intermediate circuit voltage can be reduced without losing position resolution and actuator dynamics. To solve this problem, an adaptation of the space vector modulation is performed during the operation of the magnetic bearing. This theory is based on designing the space vector modulation in a way, which enables a maximum position resolution as a function of the required bearing force. For this purpose, different INFORM pulse patterns are combined which differ concerning the actuator dynamics and the number of position measurements. In order to verify this theory, the designed space vector modulation is implemented on a prototype and confirming measurements are performed. The measurements emphasize the correlation of INFORM pulse patterns regarding the achievable performance of the sensorless method. Furthermore, the influence of different magnetic flux leading materials is investigated with respect to bearing losses
Inclusion of fluorophores in cyclodextrins: a closer look at the fluorometric determination of association constants by linear and nonlinear fitting procedures
No full textThe author discusses methods for the fluorometric determination of affinity constants by linear and nonlinear fitting methods. This is outlined in particular for the interaction between cyclodextrins and several anesthetic drugs including benzocaine. Special emphasis is given to the limitations of certain fits, and the impact of such studies on enzyme-substrate interactions are demonstrated. Both the experimental part and methods of analysis are well suited for students in an advanced lab
Control of Active Magnetic Bearings in Turbomolecular Pumps for Rotors with Low Resonance Frequencies of the Blade Wheel
No full textRotors with high gyroscopic effects and low resonance frequencies caused by the blade wheel (blade frequencies) can lead to stabilization problems in the application field of turbomolecular pumps. If such a rotor is stabilized by active magnetic bearings, the control structure could be destabilized by the splitting up of the rigid body eigen-frequencies caused by the gyroscopic effect. The control structure of the magnetic bearings can also destabilize the eigen-modes caused by the blade wheel, if the gain of the control structure is too high in the range of the eigen-frequencies of the blade wheel. To deal with the problem of the gyroscopic effect, a decoupling and compensation method was developed based on the inverse dynamics of the rigid body rotor. The gain of the control structure in the range of the blade frequencies is decreased using a Kalman filter. To increase the damping of the system, the predicted states of the linear magnetic bearing model using a Kalman filter are applied instead of the sampled values of the sensors directly. For the decoupled structure, PID controllers are used for stabilization. The functionality of the control structure is verified by a measurement of the current and position signal using the Kalman states and the sensor values. The robustness and performance in the frequency range are verified using the sensitivity and compliance function
Unbalance compensation of a magnetically levitated rotor for the whole operating range
No full textUnbalance vibration of magnetically levitated rotors can lead to instability caused by saturation of the actuators. Further the rotor orbit can increase to not acceptable values. To overcome this problem of the presented paper an unbalance compensation for rotors with a high unbalance even in the low frequency range was developed. The controller consists of two different approaches based on generalized notch filters. The parameters of the filter are dependent on the angular frequency and can be easily evaluated off-line and stored in a look-up table or implemented as a linear approximation. The robustness for different angular velocity ranges is determined in this paper. Also the dependence of the stability on the parameter of the proposed compensation is illustrated. The proposed approach has advantages in terms of calculating the closed loop stability due to the linear nature and in terms of run time and complexity. Experimental results of the developed unbalance compensation on an industrial system are included
Control of a flexible magnetic levitated rotor using the computed torque method in combination with stabilizing filters
No full textAbstract:
Rotors with a high polar moment of inertia cause a high gyroscopic effect dependent on the angular velocity. If such a rotor is stabilized by active magnetic bearings (AMB) the development of the control structure requires often complex control approaches. The split up of the eigen-frequencies, caused by the gyroscopic effect can show stability problems for high speeds. However, for industrial applications the main share is based on conventional PID controllers. To close the gap between the control approaches, this paper uses the computed torque method to decouple the rigid body system
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