Passive magnetic bearing element with minimal power losses

• US 5,847,480 A
• Filed: 11/03/1995
• Issued: 12/08/1998
• Est. Priority Date: 11/03/1995
• Status: Expired due to Term

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Post, Richard F.
• Primary Examiner(s): LaBalle, Clayton E.
• Assistant Examiner(s): ENAD, ELVIN GENARGUE
• Application Number:
  US08/552,446
• Time in Patent Office: 1,131 Days
• Field of Search: 310/90.5, 310/68 R, 310/156, 310/90, 310/90 J, 415/90
• US Class Current: 310/90.5
• CPC Class Codes: F16C 32/0436 with a conductor on one part movable with respect to a magnetic field, e.g. a body of copper on one part and a permanent magnet on the other part
• CPC Class Codes: H02K 7/09 with magnetic bearings

Abstract

Systems employing passive magnetic bearing elements having minimal power losses are provided. Improved stabilizing elements are shown, employing periodic magnet arrays and inductively loaded circuits, but with improved characteristics compared to the elements disclosed in U.S. Patent No. 5,495,221 entitled "Dynamically Stable Magnetic Suspension/Bearing System." The improvements relate to increasing the magnitude of the force derivative, while at the same time reducing the power dissipated during the normal operation of the bearing system, to provide a passive bearing system that has virtually no losses under equilibrium conditions, that is, when the supported system is not subject to any accelerations except those of gravity.

Claims

1. An apparatus, comprising:

a first spatially periodic permanent magnetic array comprising a first Halbach array;

a second spatially periodic permanent magnetic array comprising a second Halbach array, wherein said second spatially periodic permanent magnetic array is fixedly connected to said first spatially periodic permanent magnetic array and spaced apart from said first spatially periodic permanent magnetic array, wherein said first Halbach array and said second Halbach array are geometrically identical such that they have the same number of magnets and the same pole number so that their fields have the same azimuthal spatial periodicity;

a conductor array movably located between said first Halbach array and said second Halbach array, wherein said conductor array comprises a plurality of inductive circuits;

wherein azimuthal magnetic components of said first Halbach array and azimuthal magnetic components of said second Halbach array add at an equilibrium position between them, wherein said first Halbach array and said second Halbach array together are selected from a group consisting of two concentric cylinders and two planar arrays, wherein said two concentric cylinders are oriented azimuthally with respect to each other such that their radial magnetic components cancel at said equilibrium position, wherein said two planar arrays are oriented azimuthally with respect to each other such they are facing each other and that their axial components cancel at said equilibrium position; and

means for sustaining said at least one rotatable element in stable equilibrium until said rotatable element has exceeded a critical angular velocity, wherein at said equilibrium position between said first Halbach array and said second Halbach array, said conductor array intercepts near zero flux, wherein the resistive power losses in said conductor array are reduced to near zero.

2. The apparatus of claim 1, wherein said first spatially periodic magnetic array and said second spatially periodic magnetic array are both selected from the same group consisting of a planar magnetic array and a cylindrical magnetic array.

3. The apparatus of claim 2,

wherein the axial magnetic components of said first spatially periodic magnetic array of said planar magnetic array and the axial magnetic components of said second spatially periodic magnetic array of said planar magnetic array cancel at said equilibrium position;

and

wherein the radial magnetic components of said first spatially periodic magnetic array of said cylindrical magnetic array and the radial magnetic components of said second spatially periodic magnetic array of said cylindrical magnetic array cancel at a region between them.

4. The apparatus of claim 3, wherein said conductor array is selected from a group consisting of a planar conductor array and a cylindrical conductor array.

5. The apparatus of claim 1, wherein said first Halbach array together with said second Halbach array are rotatable with respect to said conductor array which is stationary.

6. The apparatus of claim 1, wherein said first Halbach array together with said second Halbach array are stationary with respect to said conductor array which is rotatable.

7. An apparatus, comprising:

aa first spatially periodic permanent magnetic array comprising a first Halbach array;

a second spatially periodic permanent magnetic array comprising a second Halbach array, wherein said second spatially periodic permanent magnetic array is fixedly connected to said first spatially periodic permanent magnetic array and spaced apart from said first spatially periodic permanent magnetic array, wherein said first Halbach array and said second Halbach array are geometrically identical such that they have the same number of magnets and the same pole number so that their fields have the same azimuthal spatial periodicity;

wherein said first spatially periodic magnetic array and said second spatially periodic magnetic array are both selected from the same group consisting of a planar magnetic array and a cylindrical magnetic array;

a planar conductor array movably located between said first spatially periodic magnetic array of said planar magnetic array and said second spatially periodic magnetic array of said planar magnetic array, wherein said planar conductor array comprises a plurality of inductive circuits;

a cylindrical conductor array movably located between said first spatially periodic magnetic array of said cylindrical magnetic array and said second spatially periodic magnetic array of said cylindrical magnetic array, wherein said cylindrical conductor array comprises a plurality of inductive circuits;

wherein azimuthal magnetic components of said first spatially periodic magnetic array of said planar magnetic array and azimuthal magnetic components of said second spatially periodic magnetic array of said planar magnetic array add at an equilibrium position between them, wherein axial magnetic components of said first spatially periodic magnetic array of said planar magnetic array and axial magnetic components of said second spatially periodic magnetic array of said planar magnetic array cancel an equilibrium position between them;

wherein azimuthal magnetic components of said first spatially periodic magnetic array of said cylindrical magnetic array and azimuthal magnetic components of said second spatially periodic magnetic array of said cylindrical magnetic array add between them, wherein radial magnetic components of said first spatially periodic magnetic array of said cylindrical magnetic array and radial magnetic components of said second spatially periodic magnetic array of said cylindrical magnetic array cancel at an equilibrium position between them;

at least one rotatable element selected from a first group consisting of said first spatially periodic magnetic array and said second spatially periodic magnetic array, and a second group consisting of said planar conductor array and said cylindrical conductor array; and

means for sustaining said at least one rotatable element in stable equilibrium until said rotatable element has exceeded a critical angular velocity.

8. The apparatus of claim 7, wherein said plurality of inductive circuits comprise inductively loaded circuits.

9. The apparatus of claim 7, further comprising permanent magnet elements fixedly attached to said first spatially periodic magnetic array and said second spatially periodic magnetic array, wherein said permanent magnet elements are arranged so as to reach force equilibrium with external forces (i.e. gravity) at an axial position corresponding to the location where said first and second spatially periodic magnet array lie symmetrically above and below said planar conductor array.

10. The apparatus of claim 7, wherein each said spatially periodic magnetic array may be designed to produce a force derivative ##EQU3## where B₀ is the peak strength of the field at the inner surface of each spatially periodic magnetic array, L₀ is the inductance per said inductive circuit, m is the number of circuits in said planar conductor array, and k is 2π

/λ

where λ

, is the mean azimuthal wavelength of said spatially periodic magnetic array, which are separated by distance 2a, with r₁, and r₂ being the inner and outer radius of the ends of the magnet bars of said spatially periodic magnetic array.

11. The apparatus of claim 7, wherein said inductive circuits comprise in-phase elements that are connected in series.

12. The apparatus of claim 11, wherein said inductive circuits comprise a lumped inductance load.

13. The apparatus of claim 7, wherein said cylindrical magnetic array comprises an outer first concentric cylinder and an inner second concentric cylinder, wherein said first spatially periodic magnetic array is fixedly connected to the inner face of said outer first concentric cylinder, wherein said second spatially periodic magnetic array is fixedly connected to the outer face of said inner second concentric cylinder, wherein said cylindrical conductor array is located at a radius corresponding to the null point for the radial magnetic field that exists between said first spatially periodic magnetic array and said second spatially periodic magnetic array.

14. The apparatus of claim 7, further comprising a pair of radially stable permanent-magnet bearings comprising attracting inner and outer bearing elements, wherein said inner bearing elements are fixedly attached to said first spatially periodic magnetic array and said second spatially periodic magnetic array, and said outer bearing elements, together with said planar conducting array are fixedly attached to a bearing cartridge, wherein each bearing of said pair of radially stable permanent-magnet bearings is disposed on opposite sides of a unit defined by said first spatially periodic magnet array, said planar conductor array and said second spatially periodic magnet array.

15. The apparatus of claim 14, further comprising a plurality of low compliance supporting springs connected to said bearing cartridge and a support structure.

16. The apparatus of claim 14, further comprising a plurality of centering elements fixedly connected to said support structure and configured to provide a centering force on said bearing cartridge.

17. The apparatus of claim 14, wherein said plurality of circuits comprise inductive circuits.

18. The apparatus of claim 14, wherein said plurality of circuits comprise inductively loaded circuits.

19. The apparatus of claim 14, wherein each said spatially periodic magnetic array is rotatable and said planar conductor array is non-rotatable.

20. The apparatus of claim 14, wherein each said spatially periodic magnetic array is non-rotatable and said planar conductor array is rotatable.

21. The apparatus of claim 15, wherein said plurality of low compliance supporting springs are augmented by at least one shock absorber connected to said bearing cartridge and a support structure.

22. The apparatus of claim 16, wherein said plurality of centering elements is selected from a group consisting of a sliding-fit retainer and a slip-fit cylinder.