Integrated magnetic levitation and rotation system

• US 6,049,148 A
• Filed: 10/02/1998
• Issued: 04/11/2000
• Est. Priority Date: 10/26/1995
• Status: Expired due to Term

• Current Assignee: Perfect Galaxy International Limited
• Original Assignee: Satcon Technology Corporation
• Inventors: Gondhalekar, Vijay, Stanton, William, Leary, Kevin, Hockney, Richard, Nichols, Stephen B., Eisenhaure, David, Jagannathan, Shankar, Downer, James
• Primary Examiner(s): Ramirez, Nestor
• Assistant Examiner(s): Waks, Joseph
• Application Number:
  US09/166,064
• Time in Patent Office: 557 Days
• Field of Search: 310/90.5, 310/68 B, 310/86, 310/178, 318/730
• US Class Current: 310/68.00B
• CPC Class Codes: F16C 2380/26 Dynamo-electric machines or combinations therewith, e.g. electro-motors and generators
• CPC Class Codes: F16C 32/0448 by using the electromagnet itself as sensor, e.g. sensorless magnetic bearings
• CPC Class Codes: F16C 32/047 Details of housings; Mounting of active magnetic bearings
• CPC Class Codes: F16C 32/0493 integrated in an electrodynamic machine, e.g. self-bearing motor
• CPC Class Codes: H01L 21/68792 characterised by the construction of the shaft
• CPC Class Codes: H02K 17/12 for multi-phase current
• CPC Class Codes: H02K 21/44 with armature windings wound upon the magnets
• CPC Class Codes: H02K 7/09 with magnetic bearings

Abstract

A rotary motor and a rotary magnetic bearing are integrated in a compact assembly that is contact-less. A stator assembly surrounds a ferromagnetic rotor with an annular air gap which can accommodate a cylindrical wall, e.g. of a chamber for semiconductor wafer processing. The stator assembly has a permanent magnet or magnets sandwiched between vertically spaced magnetic stator plates with plural pole segments. The rotor is preferably a ring of a magnetic stainless steel with complementary pole teeth. The stator assembly (i) levitates and passively centers the rotor along a vertical axis and against tilt about either horizontal axis, (ii) provides a radial position bias for the rotor, and (iii) establishes a motor flux field at the rotor poles. Polyphase coils wound on the stator plates produce a rotating flux field that drives the rotor as a synchronous homopolar motor. A rotor without pole teeth allows operation with an asynchronous inductive drive. A controller energizes control coils wound on each stator pole segment in response to a sensed physical position of the rotor. The control coils provide active radial position control and can actively damp tip and tilt oscillations that may overcome the passive centering.

Claims

1. A method for levitating a mass and rotating the mass about a vertical z-axis with a motor having a stator assembly and a rotor, the rotating occurring without frictional contact between the stator assembly and the rotor, which have an air gap therebetween, said method comprising:

forming the rotor as a ring of ferromagnetic material having a high magnetic permeability, said ring comprising a vertical portion extending along the z-axis and a horizontal portion extending perpendicular to the z-axis,

levitating and centering the rotor with respect to the stator assembly along the z-axis with a stator magnetic flux field comprising a DC flux field, which also centers the rotor against tilt out of a plane orthogonal to the z-axis, said DC flux field originating at the stator assembly,

simultaneously radially biasing the rotor with said stator magnetic flux field,

simultaneously inducing a flux field in said rotor with said stator magnetic flux field applied across an air gap through said horizontal portion of the ring,

driving the rotor to rotate about the z-axis using a rotating electromagnetic field produced by the stator assembly and applied across the air gap, the rotating electromagnetic field interacting with said flux field induced in the rotor by said stator magnetic flux field,

sensing at least a radial position of the rotor with respect to the stator assembly, and

adjusting the stator magnetic flux at angularly spaced regions about the stator assembly in response to said sensing to maintain a spacing between said rotor and said stator assembly during said driving.

2. The method of claim 1, wherein said rotor is a continuous ring of a ferromagnetic material and comprises a portion having a C-shape cross section.

3. The method of claim 1, wherein said step of driving the rotor is synchronous and homopolar.

4. The method of claim 1, wherein said driving is asynchronous and inductive.

5. The method of claim 1, wherein said adjusting step comprises providing coils at each of said regions and altering an excitation current in the coils.

6. The method of claim 1, wherein said adjusting step comprises tuning an AC excited LC circuit at each of said regions where the inductance L is that of a coil in one of said angularly spaced regions whose magnetic field produces said adjusting without an aid of discrete position sensors.

7. The method of claim 1, wherein said adjusting step comprises providing a dynamic estimation of the rotor-to-stator assembly spacing without an aid of discrete position sensors.

8. An integrated magnetic motor and suspension device that rotates a mass about a vertical z-axis that is mutually orthogonal with x and y axes, said device comprising:

a ferromagnetic rotor that lies generally in an x-y plane defined by said x and y axes and is rotatable about the z-axis, said rotor comprising a vertical portion extending along the z-axis and a horizontal portion extending perpendicular to the z-axis,

a stator assembly that extends generally in said x-y plane and is closely spaced from the rotor by an air gap, said stator assembly having an even number of stator pole segments, each of said stator pole segments comprising;

(i) upper and lower pole pieces,

(ii) a permanent magnet coupled between said upper and lower pole pieces to produce a DC magnetic flux field across the air gap, said DC magnetic flux (a) centers the rotor along the z-axis and in an orientation generally orthogonal to the z-axis with a passive reluctance, (b) provides a radial bias force on the rotor, and (c) induces a DC flux field at said rotor,

(iii) windings mounted on said pole pieces to drive the rotor across the air gap to rotate about the z-axis through an interaction with said DC flux field at said rotor, and

(iv) a pair of position control coils, one of said coils located on an upper pole plate and an another one of said coils on a lower pole plate of a stator pole segment between the permanent magnet and the rotor,

wherein a plurality of pairs of position control coils are equiangularly spaced around said stator assembly to produce a magnetic flux that adds and subtracts from the flux field of said DC permanent magnetic field to radially center said rotor with respect to said stator assembly and to supplement a passive tilt control provided by said permanent magnet,

means for sensing at least an actual radial position of the rotor and producing an electrical signal indicative of a sensed radial position, and

means for producing position control currents in each of said plurality of position control coils in response to said electrical signal.

9. The integrated magnetic motor and suspension system of claim 8, wherein said rotor is a continuous ring with plural pole teeth formed at its periphery and wherein said pole pieces have corresponding poles formed on their rotor-facing peripheries to produce a synchronous homopolar drive.

10. The integrated magnetic motor and suspension system of claim 8, wherein said rotor is a continuous ring with no pole teeth and said stator assembly windings produce an asynchronous inductive drive for said rotor.

11. The integrated magnetic motor and suspension system in claim 8, wherein said coils are active coils disposed in diametrically opposed arrays on said pole pieces.

12. The integrated magnetic motor and suspension system of claim 8, wherein said coils are each connected in series with a capacitor and excited by an AC current at a frequency such that the inductance of the associated coil provides a passive radial position control over said rotor.

13. The integrated magnetic motor and suspension system of claim 8, wherein said position control current producing means includes means for sensing the magnitude of said currents and calculating from said sensed magnitudes the radial position of the rotor with respect to the stator assembly.

14. The integrated magnetic motor and suspension system of claim 8, wherein said sensing means comprises a plurality of radial and vertical rotor position sensors.

15. An integrated magnetic support and rotational drive for processing semiconductor wafers in a sealable chamber, comprising,

a rotor with plural poles formed of a ferromagnetic material located in the chamber and adapted to support the wafer in the chamber and rotate it about a vertical z-axis while it extends in an x-y plane orthogonal to said vertical z-axis, said rotor comprising a vertical portion extending along the z-axis and a horizontal portion extending perpendicular to the z-axis,

a stator located in a closely spaced relationship to said rotor with an air gap therebetween and having,

(i) a permanent magnet whose DC flux levitates said rotor, radially biases the position of said rotor, and induces a DC flux field in said rotor across the air gap, and

(ii) upper and lower pole plates that sandwich said permanent magnet and are each divided into plural equiangularly-spaced pole segments,

(a) a polyphase winding wound on said pole plates that produces a rotating electromagnetic field that interacts with said induced DC flux in said rotor to rotate said rotor and the wafer supported on said rotor about said z-axis in said x-y plane, and

(b) a position control coil wound on each of said pole plates at each stator plate segment,

rotor position sensing means that determine at least the radial and vertical positions of said rotor, and

a feedback control circuit responsive to said position sensing means that said position control coils to center said rotor radially and against tilt out of said x-y plane by modulating the DC flux of said permanent magnet acting on said rotor.