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New Conductive Structure for Electrodynamic Bearings

LAB. DE SYST. ROBOTIQUES. New Conductive Structure for Electrodynamic Bearings. Ding Guoping Wuhan Univ. of Techn. Jan Sandtner Hannes Bleuler. Context: Magnetic Bearings. « Active » M.B. AMB Electromagnets Feedback Control

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New Conductive Structure for Electrodynamic Bearings

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  1. LAB. DE SYST. ROBOTIQUES New Conductive Structure for Electrodynamic Bearings Ding Guoping Wuhan Univ. of Techn. Jan Sandtner Hannes Bleuler

  2. Context: Magnetic Bearings • « Active » M.B. AMB Electromagnets Feedback Control • « Passive » M.B. PMB Unstable equilibrium at rest (Earnshaw)

  3. Context: MagneticBearings • « Active » M.B. AMB Electromagnets Feedback Control • « Passive » M.B. PMB Unstable equilibrium at rest (Earnshaw) Stabilization with additional effect– Gyroscopic– Electrodynamic (eddy currents)

  4. Passive MB: No loss at nominal position possible! Assumptions: • Perfectrotationalsymmetry of magnetic flux • Perfect alignement of geometric, magnetic and intertial axis • No external vibrations • Operation in vacuum

  5. Example: ELECRODYNAMIC PASSIVE MAGNETIC BEARING TEST RIG ASSEMBLY 1.3 kg rotor (wires just for monitoring measmt.) ISMB 9 (2004)

  6. permanent magnet rings as radial bearings (in an attractive mode) ➙ unstable in thrust direction ➙ electrodynamic system as an axial bearing (with two planar Halbach arrays)

  7. Upper touch-down bearing Weight compensation Upper radial bearing Motor magnets Halbach arrays Motor magnets Lower radial bearing Lower touch-down bearing Rotor length ca 40 cm, 1.3 kg

  8. Touch-down bearing Weight compensation Damping discs Radial bearing Damping discs Motor coils Axial bearing coils Motor coils Damping discs Radial bearing Touch-down bearing STATOR ASSEMBLY

  9. THRUST BEARINGS Two stationary sets of four coils are located at the middle of the air gap between the arrays There are two coil plates in a close axial contact, each containing four coils connected with appropriate polarity in series Coils of both plates are connected in series with and then short-circuited.

  10. PLANAR HALBACH ARRAY

  11. AXIAL BEARING COILS

  12. NO THRUST FORCE GENERATED IN AXIALLY CENTERED POSITION

  13. AXIALLY DISPLACED POSITION: CURRENT FLOWS DUE TO ASYMETRIC FLUX DISTRIBUTION, RESULTING IN RESTORING FORCE

  14. RESULTS (ISMB 9 2004): • tested up to 6’000 rpm • robust to shaking or impacts. • The rotor levitates at 4’800 rpm. • Axial clearing 2mm

  15. Further optimization 1: Reduce parasitic losses by approaching rotational symmetry

  16. SIDE VIEW FRONTAL VIEW rotor PM back iron PM rotor conductive structure stator stator axis frontal area conductive structure Example: Stabilization of Thrust direction

  17. copper structure no eddy currents Nominal Rotor Position: Symmetry FEMM open source

  18. copper structure displaced rotor eddy currents

  19. radial magnetic field azimutalcurrent axial force Eddy currents • Azimutal currents in radial magnetic field produce restoring thrust force

  20. Improvements in order to reduce losses • Improve rotational symmetry of magnetic field

  21. Further optimization 2: Restrict eddy currents to desired path

  22. displaced rotor Desired eddy currents at front ends of copper cylinder –> squirrel cage

  23. Proposal: Flexible Printed Circuit 25 sheets wound on cylinder

  24. Measurement of induced voltage @ 1000, 1500, 2000 rpm Displacement

  25. Conclusions • Passive electrodynamic bearing systems with low losses are feasible • Practical issues in basic design and optimization remain open, solutions are proposed • Possible applications: Flywheels, momentum wheels, textile spindles etc.

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