Integrated magnetic levitation and rotation system
First Claim
1. A process for rotating and levitating a mass within a cylindrical wall 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, and with the cylindrical wall located in an air gap between the stator assembly and the rotor, comprising,forming the rotor as a ring of a ferromagnetic material with a high magnetic permeability and with two flanges mutually spaced along the z-axis and each extending toward the stator assembly,forming the stator assembly as a pair of pole plates that are each vertically aligned with one of said flanges and which sandwich a permanent magnet, said pole plates having a polyphase drive coil and position control coils wound thereon, said position control coils being wound on a plurality of angularly spaced pole segments,passively levitating and centering the rotor in the stator assembly along the z-axis with a DC magnetic flux field, which also centers the rotor against tilt out of a plane orthogonal to the z-axis, said DC flux field originating at said permanent magnet of the stator assembly,simultaneously radially biasing the rotor with said DC magnetic flux field,simultaneously inducing a flux field in said rotor with said DC magnetic flux field applied across the air gap and through the cylindrical wall,driving the rotor to rotate about the z-axis using a rotating electromagnetic field produced by said drive coil at the stator assembly which interacts with said flux field induced in the rotor by said DC magnetic flux field, said rotating electromagnetic field being applied across said air gap and through the cylindrical wall,sensing at least the radial position of the rotor with respect to the stator assembly, andadjusting with said control coils the DC magnetic flux at angularly spaced regions about the stator assembly in response to said sensing to maintain spacing between said rotor and said stator assembly during said driving.
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Accused Products
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.
82 Citations
16 Claims
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1. A process for rotating and levitating a mass within a cylindrical wall 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, and with the cylindrical wall located in an air gap between the stator assembly and the rotor, comprising,
forming the rotor as a ring of a ferromagnetic material with a high magnetic permeability and with two flanges mutually spaced along the z-axis and each extending toward the stator assembly, forming the stator assembly as a pair of pole plates that are each vertically aligned with one of said flanges and which sandwich a permanent magnet, said pole plates having a polyphase drive coil and position control coils wound thereon, said position control coils being wound on a plurality of angularly spaced pole segments, passively levitating and centering the rotor in the stator assembly along the z-axis with a DC magnetic flux field, which also centers the rotor against tilt out of a plane orthogonal to the z-axis, said DC flux field originating at said permanent magnet of the stator assembly, simultaneously radially biasing the rotor with said DC magnetic flux field, simultaneously inducing a flux field in said rotor with said DC magnetic flux field applied across the air gap and through the cylindrical wall, driving the rotor to rotate about the z-axis using a rotating electromagnetic field produced by said drive coil at the stator assembly which interacts with said flux field induced in the rotor by said DC magnetic flux field, said rotating electromagnetic field being applied across said air gap and through the cylindrical wall, sensing at least the radial position of the rotor with respect to the stator assembly, and adjusting with said control coils the DC magnetic flux at angularly spaced regions about the stator assembly in response to said sensing to maintain spacing between said rotor and said stator assembly during said driving.
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8. An integrated magnetic motor and suspension system that rotates a mass about a vertical z-axis that is mutually orthoganal with x and y axes, comprising,
a cylindrical wall, a ring-like rotor formed of a ferromagnetic material with a pair of flanges that each project radially and are mutually spaced along said vertical z-axis, a stator assembly that extends generally in said x-y plane and surrounds the rotor in a closely spaced relationship, said stator assembly having (i) upper and lower pole pieces that are each vertically aligned with one of said rotor flanges in said spacing with said cylindrical wall interposed, (ii) a permanent magnet coupled between said upper and lower pole pieces to produce a DC magnetic flux field across said spacing and through said wall that (a) passively reluctance centers the rotor along the z-axis and in an orientation generally orthogonal to the z-axis, (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 to rotate about the z-axis through an interaction with said DC flux field at said rotor, said driving occurring across said spacing and though said cylindrical wall, and (iv) a plurality of position control coils equiangularly spaced around said stator assembly which produce a magnetic flux that adds and subtracts from the flux field of said DC permanent magnetic field to radically center said rotor with respect to said stator assembly and to supplement the passive tilt control of said permanent magnetic, means for sensing at least the actual radial position of the rotor and producing an electrical signal indicative of the 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 that produce said magnetic flux adding and subtracting.
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16. An integrated magnetic support and rotational drive for processing semiconductor wafers in a sealable chamber, that includes a cylindrical side wall 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 being formed of a ferromagnetic material with a high magnetic permeability and with a pair of vertically spaced flanges, a stator located outside said chamber and surrounding said rotor in a closely spaced relationship having, (i) a permanent magnet whose DC flux, acting across said spacing and through said cylindrical side wall, levitates said rotor, radially biases the position of said rotor, and induces a DC flux field in said rotor, (ii) upper and lower stator plates aligned with said pair of flanges that sandwich said permanent magnet and are each divided into plural equiangularly-spaced pole segments, (a) a polyphase winding wound on said stator that surrounds said rotor and 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, (b) a plurality of position control coils wound on each of said stator plate segments, 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.
Specification