High-aspect-ratio homopolar magnetic actuator

• US 8,169,118 B2
• Filed: 09/29/2009
• Issued: 05/01/2012
• Est. Priority Date: 10/09/2008
• Status: Active Grant

• Current Assignee: Calnetix Technologies, LLC (General Electric Company)
• Original Assignee: Calnetix Technologies, LLC (General Electric Company)
• Inventors: Filatov, Alexei V.
• Primary Examiner(s): Leung, Quyen
• Assistant Examiner(s): Truong, Thomas
• Application Number:
  US12/569,559
• Publication Number:
  US 20100090556A1
• Time in Patent Office: 945 Days
• Field of Search: 310/90.5, 310/178, 310/179, 310/181, 310/190, 310/191, 310/112
• US Class Current: 310/178
• CPC Class Codes: F16C 2360/44 Centrifugal pumps in general F04D
• CPC Class Codes: F16C 2380/26 Dynamo-electric machines or combinations therewith, e.g. electro-motors and generators in general H02K
• CPC Class Codes: F16C 32/0465 with permanent magnets provided in the magnetic circuit of the electromagnets
• CPC Class Codes: F16C 32/048 with active support of two degrees of freedom, e.g. radial magnetic bearings

Abstract

A homopolar magnetic actuator is configured to exert controllable radial forces on a body adapted to rotate around an axis. The actuator comprises at least three radial magnetic pole assemblies distributed at some distances from each other along the axis, each including a plurality of poles adjacent to an actuator target on the body. Permanent magnets are used to induce bias magnetic fluxes in the assemblies with polarities alternating from assembly to assembly but remaining the same around the rotational axis. Having several small bias fluxes distributed between several pole assemblies instead of a large single bias flux facilitates designing an actuator with a high aspect ratio. A control coil around each pole can induce a control magnetic flux in the poles. These control fluxes affect magnetic flux distribution around the actuator target, resulting in magnetic forces exerted on the target.

Claims

1. An electromagnetic actuator comprising:

a body having a rotational axis;

at least three radial magnetic pole assemblies, each circumferentially arranged around the rotational axis, separated from the body by radial gaps, and distributed along the rotational axis at fixed distances from each other, each radial magnetic pole assembly comprising;

a plurality of radial poles adjacent and spaced apart from a lateral facing surface of the body and configured to communicate magnetic flux with the lateral facing surface of the body, and

the plurality of radial poles of the respective radial magnetic pole assembly and the body magnetically coupled and defining a radial magnetic control circuit;

an excitation coil around each of the plurality of radial poles configured to produce control magnetic flux in the radial magnetic control circuits; and

a plurality of magnetic elements distributed with alternating polarities along the rotational axis, each of the magnetic elements residing between adjacent radial magnetic pole assemblies and configured to produce bias magnetic fluxes flowing radially within each adjacent radial magnetic pole assembly and axially in the body between adjacent radial magnetic pole assemblies.

2. The actuator of claim 1 wherein two of the at least three radial magnetic pole assemblies are first and second end radial magnetic pole assemblies, the first and second end radial magnetic pole assemblies residing at opposite ends of the electromagnetic actuator of claim 1, the actuator further comprising:

a first end pole circumferentially arranged around the rotational axis, separated from the body by radial gaps and adjacent the first end radial magnetic pole assembly; and

a first end magnetic element configured to produce bias magnetic flux flowing radially within the first end pole in a direction opposite to the bias magnetic flux in the first end radial magnetic pole assembly.

3. The actuator of claim 2 further comprising:

a second end pole circumferentially arranged around the rotational axis, separated from the body by radial gaps and adjacent the second end radial magnetic pole assembly; and

a second end magnetic element configured to produce bias magnetic flux flowing radially within the second end pole in a direction opposite to the bias magnetic flux in the second end radial magnetic pole assembly.

4. The actuator of claim 1 wherein the body comprises a low reluctance target, the target adapted to communicate magnetic flux.

5. The actuator of claim 1 wherein the magnetic fluxes entering the lateral surface of the body exert radial forces on the body.

6. The actuator of claim 5 wherein the radial forces are proportional to the magnetic fluxes in the radial magnetic control circuits.

7. The actuator of claim 1 wherein the magnetic element comprises a permanent magnet.

8. The actuator of claim 7 wherein the permanent magnet comprises at least one of a neodymium iron boron magnet or a samarium cobalt magnet.

9. The actuator of claim 7 wherein the permanent magnet comprises at least one of an axially magnetized permanent magnet or a radially magnetized permanent magnet.

10. The actuator of claim 1 wherein the control magnetic flux is produced by a control current in the excitation coil, the control current controllable to affect a total magnetic flux in the control magnetic circuit.

11. The actuator of claim 1 wherein the excitation coil around each of the plurality of radial poles is energizable with a control current to produce distinct control fluxes in the radial magnetic control circuits of the respective radial magnetic pole assemblies.

12. A method for exerting a radial force on a body, the body configured to rotate about a rotational axis, the method comprising:

communicating a first bias magnetic flux between a first radial pole assembly, the body, and a second radial pole assembly, the first and second radial pole assemblies spaced apart from one another along the rotational axis, the first and second radial pole assemblies each circumferentially arranged around the rotational axis, and the first and second radial pole assemblies separated from the body by an air gap, the first bias magnetic flux propagating through the body in a direction parallel to the rotational axis;

communicating a second bias magnetic flux between the second radial pole assembly, the body, and a third radial pole assembly, the second and third radial pole assemblies spaced apart from one another along the rotational axis, the second and third radial pole assemblies each circumferentially arranged around the rotational axis, and the second and third radial pole assemblies separated from the body by an air gap, the second radial bias magnetic flux propagating through the body in a direction parallel to the rotational axis and opposite from the first bias magnetic flux;

communicating a first radial control magnetic flux between the first radial pole assembly and the body, the first radial control magnetic flux propagating between a first radial pole of the first pole assembly, the body, and a second pole of the first pole assembly, the first radial control magnetic flux propagating in a radial direction orthogonal to the rotational axis;

communicating a second radial control magnetic flux between the second radial pole assembly and the body, the second radial control magnetic flux propagating between a first radial pole of the second pole assembly, the body, and a second pole of the second pole assembly, the second radial control magnetic flux propagating in a radial direction orthogonal to the rotational axis opposite from the first radial control magnetic flux; and

communicating a third radial control magnetic flux between the third radial pole assembly and the body, the third radial control magnetic flux propagating between a first radial pole of the third pole assembly, the body, and a second pole of the third pole assembly, the third radial control magnetic flux propagating in a radial direction orthogonal to the rotational axis opposite from the second radial control magnetic flux.

13. The method of claim 12 wherein communicating the first, second, and third radial control magnetic flux further comprises:

energizing a control coil around each of the first and second radial poles of the first, second, and third radial pole assemblies with a control current.

14. The method of claim 12 further comprising varying a control current to affect a total magnetic flux in the air gaps between the first, second, and third radial pole assemblies and the body.

15. A system comprising:

a body having a rotational axis configured to move relative to a base;

an electromagnetic actuator sub-assembly coupled to the base comprising;

three radial magnetic pole assemblies, each circumferentially arranged around the rotational axis, separated from the body by radial gaps, and distributed along the rotational axis at fixed distances from each other, each radial magnetic pole assembly comprising;

a plurality of radial poles adjacent and spaced apart from a lateral facing surface of the body and configured to communicate magnetic flux with the lateral facing surface of the body, and

the plurality of radial poles of the respective radial magnetic pole assembly and the body magnetically coupled and defining a radial magnetic control circuit,

a control coil around each of the plurality of radial poles configured to produce control magnetic flux in the radial magnetic control circuits, and

a plurality of magnetic elements distributed with alternating polarities along the rotational axis, each of the magnetic elements residing between adjacent radial magnetic pole assemblies and configured to produce bias magnetic fluxes flowing radially within each adjacent radial magnetic pole assembly and axially in the body between adjacent radial magnetic pole assemblies;

one or more position sensors configured to sense a position of the body; and

at least one control electronics package configured to control the magnetic flux in the radial magnetic control circuits.

16. The system of claim 15 wherein the body is coupled to a driven load, the driven load comprising at least one of a flywheel, a compressor, a generator, or an expander.

17. The system of claim 15 wherein the body is coupled to a driver, the driver comprising at least one of a motor, an engine, or a turbine.

18. The system of claim 15 wherein the body is a rotor and the base is a stator of an electric machine.

19. The system of claim 15 wherein the electronic control package is configured to control the magnetic flux in the radial magnetic control circuits by energizing the control coil around each of the plurality of radial poles with a control current.

20. The system of claim 19 wherein the electronic control package is further configured to energize the control coils around each of the plurality of radial poles with a control current to produce distinct control fluxes in the radial magnetic control circuits of the respective radial magnetic pole assemblies.