Hubert Mitterhofer

On the High Speed Capacity of Bearingless Drives

With soaring raw material costs, the need for smaller drives running at higher speeds is ever increasing. In parallel, magnetic bearings and bearingless drives have outgrown the purely academic level and are the state of the art solution for several industrial processes. All the bearingless drives in industry and most of them in academic research run at relatively low speeds of up to 15 000 r/min. Thus, the suitability for high speed operation remained unclear. Along with a brief introduction to bearingless drives, the criteria for high speed operation and the ability of this topology to fulfill them is discussed in the first part. The second part gives a description of a prototype system, designed to reach speeds of beyond 100 000 r/min. The last section shows the experimental results of the prototype concerning the operational behavior.

Robust Ultrasound-Based Visual Servoing for Beating Heart Intracardiac Surgery

This paper presents a robust visual servoing approach for automatic guidance of an instrument. The visual sensor is an ultrasound probe that observes an instrument which is inserted into the beating heart of a patient and manipulated by a robot. The present paper provides stability analysis, robustification of the control law and an in vivo experiment.

Design aspects and test results of a high speed bearingless drive

Following the trend towards smaller drives operating at increased speeds, the present work examines the suitability of bearingless drives for high speed operation. With rising rotational frequency, the requirements for the drive components differ significantly from a design specification for low speeds. Therefore, the design of the stator, rotor and winding system is described in detail. In order to verify the conducted analytical and FE calculations, a laboratory prototype was constructed reaching - to the knowledge of the authors - a world record speed for bearingless drives of 115.000rpm. Eventually, measurements showing specific losses and operational behavior of the drive are presented.

Comparison of High-Speed Bearingless Drive Topologies With Combined Windings

For high-speed bearingless disk drives, certain topologies seem advantageous. The authors have published works on a bearingless disk drive for high speeds that is characterized by a slotless stator and a toroid winding set. Several different variations of this setup are imaginable. The ones which this paper focuses on are the variation of the number of phases, of the number of coils, and of the applied coil connection. A comparison of the constructed and tested setup with the possible variations is presented in the course of this paper.

Analytical and experimental loss examination of a high speed bearingless drive

Bearingless drives have been intensely researched for over a decade since they represent a compact motor-bearing system fulfilling very special requirements. They provide all advantages of a typical magnetically levitated system, including the absence of mechanical wear and bearing friction. Therefore, an application for high-speed processes seems tempting. Nevertheless, there are no high-speed bearingless drives in industry so far and even in scientific research, their rated speed hardly exceeds 20krpm. One of the main obstacles on the way to rotational speeds of up to 100krpm are the occurring losses in stator, winding and air gap. This work deals with their analytical description, appropriate design steps of the drive system and a concluding experimental verification.

Suitability investigation of a bearingless disk drive for micro turbine applications

Due to several special characteristics of magnetic suspension, bearingless drives may be suitable for turbine application. These characteristics range from operability without lubrication, the absence of mechanical friction and of sliding seals to variable stiffness and damping, inherent bearing diagnostics function, low maintenance and long life time. However, there are several drawbacks which might be critical to turbine operation. Using a bearingless disk drive prototype, experiments with a turbine and compressor wheel at high rotational speeds shall provide conclusive information about the rotor behavior over the entire speed range. The results will show if, and under which assumptions, the use of bearingless disk drives for micro turbine applications seems feasible.

Coaxial tilt damping coil with additional active actuation capabilities

This work presents a tilt stabilization coil inside an exemplary high speed hearingless disk drive. The coil is hased on the passive, electrodynamic “Null-Flux” principle where there are no coil currents and, thus, no losses when the rotor is non-deflected during rotation. The proposed conductor structure is then used as a means of active actuation on the rotor by energizing the coil actively for first producing tilt torque. Modifying the structure geometrically into multiple, coaxial conductor loops which are energized with currents in the same or in equal direction then allows producing additional axial forces and tilt torque with multiple degrees of freedom, depending on the coil design. Simulation and measurement at prototype drives demonstrate the functioning of both, the passive stabilization and the active actuation principles.

Effizienzsteigerung durch die und in der Magnetlagertechnik

ZusammenfassungMagnetlager sind aus etlichen industriellen Anwendungen nicht mehr wegzudenken, in anderen erscheint ein Einsatz in Zukunft vielversprechend. Durch die Magnetlagertechnik werden Effizienzsteigerungen unterschiedlicher Art ermöglicht – sowohl auf direkte Weise durch Verringerung der Lagerverluste im Vergleich zu mechanischen Lagerungen, als auch durch Verbesserungen im industriellen Prozess, die erst durch die besonderen Eigenschaften der Magnetlagerung erzielt werden können.Im ersten Teil dieses Beitrags werden die unterschiedlichen zur Verfügung stehenden Topologien der Magnetlagertechnik vorgestellt. Der zweite Teil stellt effizienzsteigernde Maßnahmen in der Magnetlagertechnik anhand eines lagerlosen Hochgeschwindigkeitsmotors vor. Im abschließenden, dritten Teil, werden Möglichkeiten zur Effizienzsteigerung durch die Magnetlagertechnik präsentiert. Dies geschieht anhand von vier Anwendungsgebieten, in denen Magnetlager bereits wesentlich zur Performance des Gesamtsystems beitragen, gewisse Prozessschritte erst ermöglichen oder dies in Zukunft tun könnten.

Comparison of high speed bearingless drive topologies with combined windings

For high speed bearingless disk drives, certain topologies are advantageous. The authors have published works on a bearingless disk drive for high speeds which is characterized by a slotless stator and a toroid winding set. Several different variations of this setup are imaginable. The ones which this work focuses on are the variation of the number of phases, of the number of coils, and of the applied coil connection. A comparison of the constructed and tested setup with the possible variations is presented in the course of this work.