Capacitive sensor system for magnetic bearings

Claim 2

A capacitive position sensor located within the confines of a magnetic bearing supporting a rotating shaft comprising a capacitive member disposed proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft.

Claim 3

The capacitive position sensor as recited in claim 1, wherein the magnetic bearing is a radial magnetic bearing including a plurality of teeth supporting a respective plurality of coils, and wherein said capacitive member is disposed in a void space within the radial magnetic bearing bounded by the teeth and the coils.

Claim 4

The capacitive position sensor as recited in claim 2, wherein said capacitive member includes a curved surface having a radius substantially equal to a radius defined by all ends of the teeth proximate to the rotation axis of the rotating shaft.

Claim 5

The capacitive position sensor as recited in claim 1, wherein the magnetic bearing is an axial magnetic bearing including at least one coil whose axis is parallel to the rotation axis of the rotating shaft, and wherein said capacitive member is disposed within the confines of the axial magnetic bearing and between the coil of the axial magnetic bearing and the rotating shaft.

Claim 6

The capacitive position sensor as recited in claim 4, wherein said capacitive member is a ring member.

Claim 7

The capacitive position sensor as recited in claim 5, wherein said ring member includes an exterior surface located substantially parallel with an exterior surface of the axial magnetic bearing located adjacent to the rotating shaft.

Claim 8

A capacitive position sensor located within the confines of a bearing stator of a radial magnetic bearing positioning a rotating shaft, the radial magnetic bearing including an outer ring, N teeth disposed with the outer ring, wherein the N teeth each include a first end coupled to the outer ring and a second end proximate to the axial centerline of the radial magnetic bearing, wherein all of the second ends of the N teeth define a cylindrical surface of predetermined radius, and N coils, each of the N coils surrounding a respective one of the N teeth and each of the N coils being located adjacent to the outer ring and spaced apart from the second ends of the respective N teeth so as to expose an end portion of the respective N teeth proximate to the associated second ends, said capacitive position sensor comprising a capacitive member disposed within a void space defined by respective end portions of adjacent ones of the N teeth and the cylindrical surface and proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft.

Claim 9

A capacitive position sensor located within the confines of a bearing stator of a radial magnetic bearing positioning a rotating shaft, the radial magnetic bearing including an outer ring, N teeth disposed with the outer ring, wherein the N teeth each include a first end coupled to the outer ring and a second end proximate to the axial centerline of the radial magnetic bearing, wherein all of the second ends of the N teeth define a cylindrical surface of predetermined radius, and N coils, each of the N coils surrounding a respective one of the N teeth and each of the N coils being located adjacent to the outer ring and spaced apart from the second ends of the respective N teeth so as to expose an end portion of the respective N teeth proximate to the associated second ends, said capacitive position sensor comprising a capacitive member disposed within a void space defined by respective end portions of adjacent ones of the N teeth and the cylindrical surface and proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft.

Claim 10

A capacitive position sensor located within the confines of a bearing stator of an axial magnetic bearing axially positioning a rotating shaft including a first end surface proximate to a first end of the rotating shaft and perpendicular to the rotation axis of the rotating shaft, the axial magnetic bearing including a cylindrical coil having a coil axis located coaxial with the rotation axis of the rotating shaft, wherein the axial magnetic bearing includes a second end surface perpendicular to the coil axis, wherein the first and second end surfaces are disposed adjacent to one another and wherein the first and second end surfaces are substantially parallel, said capacitive position sensor comprising a capacitive member disposed within the confines of the axial magnetic bearing and between the cylindrical coil and the first end surface of the rotation shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft.

Claim 11

A capacitive position sensor located within the confines of a bearing stator of an axial magnetic bearing axially positioning a rotating shaft including a first end surface proximate to a first end of the rotating shaft and perpendicular to the rotation axis of the rotating shaft, the axial magnetic bearing including a cylindrical coil having a coil axis located coaxial with the rotation axis of the rotating shaft, wherein the axial magnetic bearing includes a second end surface perpendicular to the coil axis, wherein the first and second end surfaces are disposed adjacent to one another and wherein the first and second end surfaces are substantially parallel, said capacitive position sensor comprising a capacitive member disposed within the confines of the axial magnetic bearing and between the cylindrical coil and the first end surface of the rotation shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft.

Claim 12

A capacitive sensor system detecting position of a rotating shaft in a flywheel energy storage system positioned by a magnetic bearing and generating a control signal indicative of the position of the rotating shaft, said capacitive sensor system comprising: a capacitive member disposed proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft; and a sensing circuit, electrically coupled to said capacitive member, receiving a high frequency voltage signal and generating the control signal responsive to the capacitance between said capacitive member and the rotating shaft.

Claim 13

A capacitive sensor system detecting position of a rotating shaft in a flywheel energy storage system positioned by a magnetic bearing and generating a control signal indicative of the position of the rotating shaft, said capacitive sensor system comprising: a capacitive member disposed proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft; and a sensing circuit, electrically coupled to said capacitive member, receiving a high frequency voltage signal and generating the control signal responsive to the capacitance between said capacitive member and the rotating shaft.

Claim 14

The capacitive sensor system as recited in claim 9, wherein said sensing circuit comprises: a signal generator producing said high frequency voltage signal; an envelope detector producing the control signal; an inductor serially connecting said signal generator to said envelope detector, wherein the connection between said inductor and said envelope detector defines a common node; a fixed capacitance coupling said common node to ground; and said capacitive member coupling said common node to ground.

Claim 15

The capacitive sensing system as recited in claim 10, wherein said inductor and said fixed capacitance inductively tune out any stray capacitances.

Claim 16

The capacitive sensing system as recited in claim 11, wherein the inductive tuning and said high frequency voltage signal permit generation of said control signal having a high signal to noise ratio.

Claim 17

The capacitive sensing system as recited in claim 10, wherein said high frequency voltage signal permits a rapid response time for said sensing circuit.

Claim 18

The capacitive sensing system as recited in claim 10, wherein said magnetic bearing is an axial magnetic bearing.

Claim 19

The capacitive sensor system as recited in claim 9, wherein said capacitive member comprises first and second capacitive members, and wherein said sensing circuit comprises: a signal generator producing said high frequency voltage signal; a first envelope detector producing a first output signal; a first inductor serially connecting said signal generator to said first envelope detector, wherein the connection between said first inductor and said first envelope detector defines a first common node; a first fixed capacitance coupling said first common node to ground; said first capacitive member coupling said first common node to ground; a second envelope detector producing a second output signal; a second inductor serially connecting said signal generator to said second envelope detector, wherein the connection between said inductor and said second envelope detector defines a second common node; a second fixed capacitance coupling said second common node to ground; said second capacitive member coupling said second common node to ground; and a subtractor receiving said first and said second output signals and producing the control signal.

Claim 20

The capacitive sensing system as recited in claim 15, wherein said first inductor and said first fixed capacitance and said second inductor and said second fixed capacitance, respectively, inductively tune out any stray capacitances.

Claim 21

The capacitive sensing system as recited in claim 16, wherein said inductive tuning and said high frequency voltage signal permit generation of respective first and second output signals having high signal to noise ratios.

Claim 22

The capacitive sensing system as recited in claim 15, wherein the first and second signal paths including said first and second inductors, respectively, have equal signal path lengths, thereby enhancing accuracy and linearity of the capacitive sensing system.

Claim 23

The capacitive sensing system as recited in claim 18, wherein said high frequency voltage signal permits a rapid response time for said sensing circuit.

Claim 24

The capacitive sensing system as recited in claim 9, wherein the flywheel energy storage system includes a vacuum housing defining a pressure boundary and wherein no part of said sensing circuit crosses the pressure boundary.

Claim 25

The capacitive sensing system as recited in claim 9, wherein said sensing circuit includes: a plurality of branches, each of said branches including a respective inductor; and a high frequency voltage source operatively connected via a single node to all of said branches so as to avoid beat frequencies which could introduce false position signals in said sensing circuit.

Claim 26

The capacitive sensor system as recited in claim 9, wherein said control signal comprises a plurality of control signals, wherein said capacitive member comprises first, second and third capacitive members, and wherein said capacitive sensing circuit comprises: a signal generator producing said high frequency voltage signal; a first envelope detector producing a first of said control signals; a first inductor serially connecting said signal generator to said envelope detector, wherein the connection between said first inductor and said first envelope detector defines a first node; a first fixed capacitance coupling said first node to ground; and said first capacitive member coupling said first node to ground; a second envelope detector producing a first output signal; a second inductor serially connecting said signal generator to said second envelope detector, wherein the connection between said second inductor and said second envelope detector defines a second node; a second fixed capacitance coupling said second node to ground; said second capacitive member coupling said second node to ground; a third envelope detector producing a second output signal; a third inductor serially connecting said signal generator to said third envelope detector, wherein the connection between said third inductor and said third envelope detector defines a third node; a third fixed capacitance coupling said third node to ground; said third capacitive member coupling said third node to ground; and a subtractor receiving said first and said second output signals and producing a second of said control signals.

Claim 27

A capacitive sensor system detecting position of a rotating shaft in a flywheel energy storage system positioned by a magnetic bearing and generating a control signal indicative of the position of the rotating shaft, said capacitive sensor system comprising: a capacitive member disposed proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft; and a sensing circuit, electrically coupled to said capacitive member, receiving a high frequency voltage signal and generating the control signal responsive to the capacitance between said capacitive member and the rotating shaft, said sensing circuit comprising: signal generating means for producing said high frequency voltage signal; envelope detecting means for producing the control signal; and an inductor serially connecting said signal generating means to said envelope detecting means, wherein the connection between said inductor and said envelope detecting means defines a common node, which common node is coupled to ground through both a fixed capacitance and said capacitive member.

Claim 28

A capacitive sensor system detecting position of a rotating shaft in a flywheel energy storage system positioned by a magnetic bearing and generating a control signal indicative of the position of the rotating shaft, said capacitive sensor system comprising: a capacitive member disposed proximate to the rotating shaft, said capacitive member being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft; and a sensing circuit, electrically coupled to said capacitive member, receiving a high frequency voltage signal and generating the control signal responsive to the capacitance between said capacitive member and the rotating shaft, said sensing circuit comprising: signal generating means for producing said high frequency voltage signal; envelope detecting means for producing the control signal; and an inductor serially connecting said signal generating means to said envelope detecting means, wherein the connection between said inductor and said envelope detecting means defines a common node, which common node is coupled to ground through both a fixed capacitance and said capacitive member.

Claim 29

The capacitive sensing system as recited in claim 23, wherein said inductor and said fixed capacitance inductively tune out any stray capacitances.

Claim 30

The capacitive sensing system as recited in claim 24, wherein said inductive tuning and said high frequency voltage signal permit generation of said control signal having a high signal to noise ratio.

Claim 31

The capacitive sensing system as recited in claim 23, wherein said high frequency voltage signal permits a rapid response time for said capacitive sensing circuit.

Claim 32

The capacitive sensing system as recited in claim 23, wherein said magnetic bearing is an axial magnetic bearing.

Claim 33

A capacitive sensor system detecting position of a rotating shaft in a flywheel energy storage system positioned by a magnetic bearing and generating a control signal indicative of the position of the rotating shaft, said capacitive sensor system comprising: first and second capacitive members disposed proximate to the rotating shaft, said first and second capacitive members being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft; and a sensing circuit, electrically coupled to said capacitive member, receiving a high frequency voltage signal and generating the control signal responsive to the capacitance between said capacitive member and the rotating shaft, said sensing circuit comprising: signal generating means for producing said high frequency voltage signal; first envelope detecting means for producing a first output signal; a first inductor serially connecting said signal generating means to said first envelope detecting means, wherein the connection between said first inductor and said first envelope detecting means defines a first common node, and wherein said first common node is electrically coupled to ground by both a first fixed capacitance and said first capacitive member; second envelope detecting means for producing a second output signal; a second inductor serially connecting said signal generating means to said second envelope detecting means, wherein the connection between said inductor and said second envelope detecting means defines a second common node, and wherein said second common node is electrically coupled to ground by both a second fixed capacitance and said second capacitive member; and subtracting means for receiving said first and said second output signals and producing the control signal.

Claim 34

A capacitive sensor system detecting position of a rotating shaft in a flywheel energy storage system positioned by a magnetic bearing and generating a control signal indicative of the position of the rotating shaft, said capacitive sensor system comprising: first and second capacitive members disposed proximate to the rotating shaft, said first and second capacitive members being electrically coupled to the rotating shaft so as to permit sensing of capacitance of said capacitive member with respect to the rotating shaft; and a sensing circuit, electrically coupled to said capacitive member, receiving a high frequency voltage signal and generating the control signal responsive to the capacitance between said capacitive member and the rotating shaft, said sensing circuit comprising: signal generating means for producing said high frequency voltage signal; first envelope detecting means for producing a first output signal; a first inductor serially connecting said signal generating means to said first envelope detecting means, wherein the connection between said first inductor and said first envelope detecting means defines a first common node, and wherein said first common node is electrically coupled to ground by both a first fixed capacitance and said first capacitive member; second envelope detecting means for producing a second output signal; a second inductor serially connecting said signal generating means to said second envelope detecting means, wherein the connection between said inductor and said second envelope detecting means defines a second common node, and wherein said second common node is electrically coupled to ground by both a second fixed capacitance and said second capacitive member; and subtracting means for receiving said first and said second output signals and producing the control signal.

Claim 35

The capacitive sensing system as recited in claim 28, wherein said first inductor and said first fixed capacitance and said second inductor and said second fixed capacitance, respectively, inductively tune out any stray capacitances.

Claim 36

The capacitive sensing system as recited in claim 29, wherein inductive tuning of the capacitive sensing system and said high frequency voltage signal generate respective first and second output signals having high signal to noise ratios.

Claim 37

The capacitive sensing system as recited in claim 28, wherein first and second signal paths including said first and second inductors, respectively, have equal signal path lengths, thereby enhancing accuracy and linearity of the capacitive sensing system.

Claim 38

The capacitive sensing system as recited in claim 28, wherein said high frequency voltage signal produces a rapid response time for said sensing circuit.