U.S. patent application number 10/060640 was filed with the patent office on 2003-07-31 for active magnetic bearing assembly using permanent magnet biased homopolar and reluctance centering effects.
Invention is credited to Abel, Stephen G..
Application Number | 20030141773 10/060640 |
Document ID | / |
Family ID | 27610052 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030141773 |
Kind Code |
A1 |
Abel, Stephen G. |
July 31, 2003 |
ACTIVE MAGNETIC BEARING ASSEMBLY USING PERMANENT MAGNET BIASED
HOMOPOLAR AND RELUCTANCE CENTERING EFFECTS
Abstract
An active magnetic bearing assembly includes at least two rotors
and two stator assemblies each having two pole faces. The pole
faces of the stator assemblies are axially offset from the pole
faces of their associated rotors. Thus, axial control of a shaft
that is rotationally mounted using the active magnetic bearing
assembly is provided by a reluctance centering force.
Inventors: |
Abel, Stephen G.; (Chandler,
AZ) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
27610052 |
Appl. No.: |
10/060640 |
Filed: |
January 30, 2002 |
Current U.S.
Class: |
310/90.5 |
Current CPC
Class: |
H02K 7/09 20130101; F16C
32/0444 20130101; F16C 32/0489 20130101 |
Class at
Publication: |
310/90.5 |
International
Class: |
H02K 007/09 |
Claims
We claim:
1. An active magnetic bearing assembly for rotationally mounting a
shaft in a non-contact manner, the bearing assembly comprising: a
first bearing rotor having at least a first pole face and a second
pole face; a first stator assembly spaced radially outwardly of the
first bearing rotor and having at least a first pole face and a
second pole face that are axially offset from the first bearing
rotor first pole face and second pole face, respectively, by a
first predetermined distance in a first direction; a second bearing
rotor having at least a first pole face and a second pole face; and
a second stator assembly spaced radially outwardly of the second
bearing rotor and having at least a first pole face and a second
pole face that are axially offset from the second bearing rotor
first pole face and second pole face, respectively, by a second
predetermined distance and in a second predetermined direction that
is opposite the first predetermined direction.
2. The magnetic bearing assembly of claim 1, wherein: the first
bearing rotor is coupled to the shaft at a first predetermined
position on the shaft; and the second bearing rotor is coupled to
the shaft at a second predetermined position on the shaft.
3. The magnetic bearing assembly of claim 1, wherein the first and
second stator assemblies each comprise: a first stator body having
at least one first coil wound pole extending radially inwardly
therefrom, each first coil wound pole having a first pole face; a
second stator body having at least one second coil wound pole
extending radially inwardly therefrom, each second coil wound pole
positioned parallel to one of the first coil wound poles, and each
having a second pole face; and an axially polarized permanent
magnet interposed between, and coupling together, the first and the
second stator bodies.
4. The magnetic bearing assembly of claim 3, wherein the axially
polarized permanent magnet in each bearing stator assembly supplies
a permanent magnet force bias to its associated bearing rotor.
5. The magnetic bearing assembly of claim 3, wherein the first and
second stator bodies each include eight substantially evenly spaced
coil wound poles.
6. The magnetic bearing assembly of clam 5, wherein selected
adjacent coil wound poles on each of the first stator bodies are
wound together with selected adjacent coil wound poles on their
respective second stator bodies to form a single electromagnetic
actuator.
7. The magnetic bearing assembly of claim 6, wherein the total
number of electromagnetic actuators is four per stator
assembly.
8. The magnetic bearing assembly of claim 1, wherein the first
bearing rotor and first bearing stator, and the second bearing
rotor and second bearing stator are each configured as homopolar
magnetic bearings.
9. The magnetic bearing assembly of claim 1, further comprising: a
first axially polarized permanent magnet coupled to one of the
first and second stator assemblies; and a second axially polarized
permanent magnet coupled to the shaft proximate the first axially
polarized permanent magnet, wherein the first and second axially
polarized permanent magnets are oriented to repel one another.
10. An energy storage flywheel assembly, comprising: a shaft; a
flywheel coupled to the shaft; and an active magnetic bearing
assembly for rotationally mounting the shaft in a non-contact
manner, the magnetic bearing assembly comprising: a first bearing
rotor coupled to the shaft on a first side of the flywheel and
having at least a first pole face and a second pole face; a first
stator assembly spaced radially outwardly of the first bearing
rotor and having at least a first pole face and a second pole face
that are axially offset from the first bearing rotor first pole
face and second pole face, respectively, by a first predetermined
distance in a first direction; a second bearing rotor coupled to
the shaft on a second side of the flywheel, opposite the first
side, and having at least a first pole face and a second pole face;
and a second stator assembly spaced radially outwardly of the
second bearing rotor and having at least a first pole face and a
second pole face that are axially offset from the second bearing
rotor first pole face and second pole face, respectively, by a
second predetermined distance and in a second predetermined
direction that is opposite the first predetermined direction.
11. The energy storage flywheel of claim 10, wherein: the first
bearing rotor is coupled to the shaft at a first predetermined
position on the shaft; and the second bearing rotor is coupled to
the shaft at a second predetermined position on the shaft.
12. The energy storage flywheel of claim 10, wherein the first and
second stator assemblies each comprise: a first stator body having
at least one first coil wound pole extending radially inwardly
therefrom, each first coil wound pole having a first pole face; a
second stator body having at least one second coil wound pole
extending radially inwardly therefrom, each second coil wound pole
positioned parallel to one of the first coil wound poles, and each
having a second pole face; and an axially polarized permanent
magnet interposed between, and coupling together, the first and the
second stator bodies.
13. The energy storage flywheel of claim 12, wherein the axially
polarized permanent magnet in each bearing stator assembly supplies
a permanent magnet force bias to its associated bearing rotor.
14. The energy storage flywheel of claim 12, wherein the first and
second stator bodies each include eight substantially evenly spaced
coil wound poles.
15. The energy storage flywheel of clam 14, wherein selected
adjacent coil wound poles on each of the first stator bodies are
wound together with selected adjacent coil wound poles on their
respective second stator bodies to form a single electromagnetic
actuator.
16. The energy storage flywheel of claim 15, wherein the total
number of electromagnetic actuators is four per stator
assembly.
17. The energy storage flywheel of claim 10, wherein the first
bearing rotor and first bearing stator, and the second bearing
rotor and second bearing stator are each configured as homopolar
magnetic bearings.
18. The energy storage flywheel of claim 10, further comprising: a
motor/generator operably coupled to the shaft.
19. The energy storage flywheel of claim 10, further comprising: a
first axially polarized permanent magnet coupled to one of the
first and second stator assemblies; and a second axially polarized
permanent magnet coupled to one of the first and second sides of
the flywheel, proximate the first axially polarized permanent
magnet, wherein the first and second axially polarized permanent
magnets are oriented to repel one another.
20. An apparatus for imparting rotational motion to a shaft,
comprising: a shaft; a rotational motion imparting device coupled
to the shaft; and an active magnetic bearing assembly for
rotationally mounting the shaft in a non-contact manner, the
magnetic bearing assembly comprising: a first bearing rotor coupled
to the shaft on a first side of the flywheel and having at least a
first pole face and a second pole face; a first stator assembly
spaced radially outwardly of the first bearing rotor and having at
least a first pole face and a second pole face that are axially
offset from the first bearing rotor first pole face and second pole
face, respectively, by a first predetermined distance in a first
direction; a second bearing rotor coupled to the shaft on a second
side of the flywheel, opposite the first side, and having at least
a first pole face and a second pole face; and a second stator
assembly spaced radially outwardly of the second bearing rotor and
having at least a first pole face and a second pole face that are
axially offset from the second bearing rotor first pole face and
second pole face, respectively, by a second predetermined distance
and in a second predetermined direction that is opposite the first
predetermined direction.
21. The apparatus of claim 20, wherein: the first bearing rotor is
coupled to the shaft at a first predetermined position on the
shaft; and the second bearing rotor is coupled to the shaft at a
second predetermined position on the shaft.
22. The apparatus of claim 20, wherein the first and second stator
assemblies each comprise: a first stator body having at least one
first coil wound pole extending radially inwardly therefrom, each
first coil wound pole having a first pole face; a second stator
body having at least one second coil wound pole extending radially
inwardly therefrom, each second coil wound pole positioned parallel
to one of the first coil wound poles, and each having a second pole
face; and an axially polarized permanent magnet interposed between,
and coupling together, the first and the second stator bodies.
23. The apparatus of claim 22, wherein the axially polarized
permanent magnet in each bearing stator assembly supplies a
permanent magnet force bias to its associated bearing rotor.
24. The apparatus of claim 22, wherein the first and second stator
bodies each include eight substantially evenly spaced coil wound
poles.
25. The apparatus of clam 24, wherein selected adjacent coil wound
poles on each of the first stator bodies are wound together with
selected adjacent coil wound poles on their respective second
stator bodies to form a single electromagnetic actuator.
26. The apparatus of claim 25, wherein the total number of
electromagnetic actuators is four per stator assembly.
27. The apparatus of claim 20, wherein the first bearing rotor and
first bearing stator, and the second bearing rotor and second
bearing stator are each configured as homopolar magnetic
bearings.
28. The apparatus of claim 20, wherein the rotational force
imparting device comprises a motor.
29. The apparatus of claim 20, wherein the rotational force
imparting device comprises a turbine wheel.
30. The magnetic bearing assembly of claim 20, further comprising:
a first axially polarized permanent magnet coupled to one of the
first and second stator assemblies; and a second axially polarized
permanent magnet coupled to the shaft proximate the first axially
polarized permanent magnet, wherein the first and second axially
polarized permanent magnets are oriented to repel one another.
31. A satellite, comprising: a housing; at least one component
having a shaft, the component positioned within the housing; and an
active magnetic bearing assembly for rotationally mounting the
shaft in a non-contact manner, the bearing assembly comprising: a
first bearing rotor having at least a first pole face and a second
pole face, a first stator assembly spaced radially outwardly of the
first bearing rotor and having at least a first pole face and a
second pole face that are axially offset from the first bearing
rotor first pole face and second pole face, respectively, by a
first predetermined distance in a first direction, a second bearing
rotor having at least a first pole face and a second pole face, and
a second stator assembly spaced radially outwardly of the second
bearing rotor and having at least a first pole face and a second
pole face that are axially offset from the second bearing rotor
first pole face and second pole face, respectively, by a second
predetermined distance and in a second predetermined direction that
is opposite the first predetermined direction.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to magnetic bearings and, more
particularly, to an active magnetic bearing for use in various
applications, including satellites and other space applications,
that uses a reluctance centering effect to provide axial control of
a rotating shaft.
[0002] Magnetic bearings suspend a rotational body, such as a
rotor, with magnetic force in a non-contact fashion. That is,
instead of the physically supporting the rotor using lubricated
bearings that are in physical contact with the rotor, various
magnets are spaced radially around the rotor and the magnetic
forces supplied by the magnets suspend the rotor without any
physical contact. In order to provide stable support for the rotor,
the magnetic bearing suspends the rotor within five
degrees-of-freedom.
[0003] Generally, there are two categories of magnetic bearings,
passive magnetic bearings and active magnetic bearings. Passive
magnetic bearings are the simplest type, and use permanent magnets
or fixed strength electromagnets to support the rotor. Thus, the
properties of the bearing, such as the magnetic field strength, may
not be controlled during operation. Conversely, active magnetic
bearings are configured such that the magnetic field strength of
the bearing is controllable during operation. To accomplish this,
at least one active magnetic bearing channel is provided for each
degree-of-freedom of the shaft. An active magnetic bearing channel
includes a position sensor, a controller operating according to a
predetermined control law, and an electromagnetic actuator. In
general, the position sensor senses the position of the shaft and
supplies a signal representative of its position to the controller.
The controller, in accordance with the predetermined control law,
then supplies the appropriate current magnitude to the
electromagnetic actuator, which in turn generates an attractive
magnetic force to correct the position of the shaft.
[0004] Various active magnetic bearing assembly configurations are
presently known for controlling a shaft within five
degrees-of-freedom. The active magnetic bearing assembly
configurations used most prominently are: (1) independent radial
and axial bearings; (2) conical bearings; and (3) combination
bearings. Each of these different configurations may have certain
drawbacks. For example, if independent radial axial bearings are
used, then the overall size, or physical package, of the system is
relatively large. Conical bearings may use eight drive channels to
provide control within five degrees-of-freedom, and provide space
savings relative to the use of independent radial and axial
bearings. However, conical bearings may suffer from temperature
sensitivity, and cross-coupling of radial and axial channels.
Finally, while combination bearings may also provide space savings
relative to the use of independent radial and axial bearings, the
assembly of this bearing configuration may be relatively
complex.
[0005] Thus, there is a need for an active magnetic bearing
assembly that provides the space savings and relatively simple
assembly that a conical bearing provides, while simultaneously
exhibiting minimal temperature sensitivity. The present invention
addresses these needs.
SUMMARY OF THE INVENTION
[0006] The present invention provides an active magnetic bearing
assembly that does not require the use of either separate axial
bearing or a combination bearing and thus provides significant
space savings and bearing commonality. The bearing also has minimal
temperature sensitivity.
[0007] In one embodiment of the present invention, and by way of
example onely, an active magnetic bearing assembly for rotationally
mounting a shaft in a non-contact manner includes a first bearing
rotor, a first stator assembly, a second bearing rotor, and a
second stator assembly. The first bearing rotor has at least a
first pole face and a second pole face. The first stator assembly
is spaced radially outwardly of the first bearing rotor and has at
least a first pole face and a second pole face that are axially
offset from the first bearing rotor first pole face and second pole
face, respectively, by a first predetermined distance in a first
direction. The second bearing rotor has at least a first pole face
and a second pole face. The second stator assembly is spaced
radially outwardly of the second bearing rotor and has at least a
first pole face and a second pole face that are axially offset from
the second bearing rotor first pole face and second pole face,
respectively, by a second predetermined distance and in a second
predetermined direction that is opposite the first predetermined
direction.
[0008] In another embodiment of the present invention, an energy
storage flywheel assembly includes a shaft, a flywheel, and an
active magnetic bearing assembly. The flywheel is coupled to the
shaft, and the active magnetic bearing assembly rotationally mounts
the shaft in a non-contact manner. The magnetic bearing assembly
includes a first bearing rotor, a first stator assembly, a second
bearing rotor, and a second stator assembly. The first bearing
rotor has at least a first pole face and a second pole face. The
first stator assembly is spaced radially outwardly of the first
bearing rotor and has at least a first pole face and a second pole
face that are axially offset from the first bearing rotor first
pole face and second pole face, respectively, by a first
predetermined distance in a first direction. The second bearing
rotor has at least a first pole face and a second pole face. The
second stator assembly is spaced radially outwardly of the second
bearing rotor and has at least a first pole face and a second pole
face that are axially offset from the second bearing rotor first
pole face and second pole face, respectively, by a second
predetermined distance and in a second predetermined direction that
is opposite the first predetermined direction.
[0009] In yet another embodiment of the present invention, an
apparatus for imparting rotational motion to a shaft includes a
shaft, a rotational motion imparting device, and an active magnetic
bearing assembly. The rotational motion imparting device is coupled
to the shaft, and the active magnetic bearing assembly rotationally
mounts the shaft in a non-contact manner. The magnetic bearing
assembly includes a first bearing rotor, a first stator assembly, a
second bearing rotor, and a second stator assembly. The first
bearing rotor has at least a first pole face and a second pole
face. The first stator assembly is spaced radially outwardly of the
first bearing rotor and has at least a first pole face and a second
pole face that are axially offset from the first bearing rotor
first pole face and second pole face, respectively, by a first
predetermined distance in a first direction. The second bearing
rotor has at least a first pole face and a second pole face. The
second stator assembly is spaced radially outwardly of the second
bearing rotor and has at least a first pole face and a second pole
face that are axially offset from the second bearing rotor first
pole face and second pole face, respectively, by a second
predetermined distance and in a second predetermined direction that
is opposite the first predetermined direction.
[0010] In still a further embodiment of the present invention, a
satellite includes a housing, a component within the housing having
a shaft, and an active magnetic bearing. The active magnetic
bearing assembly rotationally mounts the shaft in a non-contact
manner and includes a first bearing rotor, a first stator assembly,
a second bearing rotor, and a second stator assembly. The first
bearing rotor has at least a first pole face and a second pole
face. The first stator assembly is spaced radially outwardly of the
first bearing rotor and has at least a first pole face and a second
pole face that are axially offset from the first bearing rotor
first pole face and second pole face, respectively, by a first
predetermined distance in a first direction. The second bearing
rotor has at least a first pole face and a second pole face. The
second stator assembly is spaced radially outwardly of the second
bearing rotor and has at least a first pole face and a second pole
face that are axially offset from the second bearing rotor first
pole face and second pole face, respectively, by a second
predetermined distance and in a second predetermined direction that
is opposite the first predetermined direction.
[0011] Other independent features and advantages of the preferred
sensor will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings
which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a simplified schematic side view representation of
an energy storage flywheel assembly that may utilize the magnetic
bearing assembly of the present invention;
[0013] FIG. 2 is a side view of a particular preferred embodiment
of stator assembly that is used to make the magnetic bearing
assembly of the present invention;
[0014] FIG. 3 is a front view of the stator assembly depicted in
FIG. 2;
[0015] FIG. 4 is a cross section view of the stator assembly
depicted in FIG. 2, taken along line 4-4 in FIG. 2;
[0016] FIG. 5 is a table showing which actuators are activated and
de-activated to produce a desired shaft movement;
[0017] FIG. 6 is a simplified schematic side view representation of
an energy storage flywheel assembly in a vertical orientation that
may utilize another embodiment of the magnetic bearing assembly of
the present invention; and
[0018] FIG. 7 is a perspective view of a satellite that
incorporates, and/or includes one or more components that
incorporate, the system depicted in FIG. 1.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
[0019] Before proceeding with the detailed description of the
invention, it is to be appreciated that the magnetic bearing
assembly of the present invention is not limited to use in
conjunction with a specific type of device. Thus, although the
present invention is, for convenience of explanation, depicted and
described as being implemented in an energy storage flywheel, it
will be appreciated that it can be implemented with other types of
devices. For example, the magnetic bearing assembly may also be
used with various other rotating devices including, but not limited
to, pumps, turbines, gyroscopes, and generators.
[0020] A simplified schematic representation of an energy
conversion device that employs the magnetic bearing assembly
according to an embodiment of the present invention is depicted in
FIG. 1. In the depicted embodiment, the energy conversion device is
an energy storage flywheel assembly 100, which includes a flywheel
102, a rotationally mounted shaft 104, and a motor/generator 106.
The energy storage flywheel assembly 100 works on the principle
that the flywheel 102 spinning at very high speeds can be used to
store energy. The shaft 104 couples the flywheel 102 to the
motor/generator 106, which operates either as an electric motor and
accelerates the flywheel 102 to store rotational kinetic energy, or
as a generator that produces electrical energy from the rotational
kinetic energy stored in the flywheel 102. The flywheel 102 may be
comprised of any one of numerous materials, but is preferably
constructed of a material having a high strength-to-density ratio,
such as filament wound carbon fiber. Additionally, though not
explicitly depicted, it will be appreciated that the energy storage
flywheel assembly 100 may be housed within a vacuum chamber to
minimize aerodynamic losses. It will be additionally appreciated
that if the energy storage flywheel assembly 100 is utilized in a
natural vacuum environment, such as in space applications, then the
housing internals need not be a sealed vacuum.
[0021] The motor/generator 106, as its name implies and as was
alluded to above, is configured to function as either a motor or a
generator. The motor/generator 106 includes a motor/generator
stator 108 and a motor/generator rotor 110. As noted above, when
operating as a motor, electrical energy is supplied to the
motor/generator stator 108 and, via normal motor action, this
electrical energy is converted to mechanical energy in the
motor/generator rotor 110, which rotates the shaft 104 and flywheel
102. Conversely, when it is operating as a generator, mechanical
energy stored in the flywheel 102 is supplied to the shaft 104,
which is in turn supplied to the motor/generator rotor 1 10. This
mechanical energy is converted to electrical energy in the
motor/generator stator 108, via normal generator action, and is
supplied external to the energy storage flywheel assembly 100. It
is to be appreciated that the motor/generator stator 108 and rotor
110 may be any one of numerous stator and rotor designs known in
the art for performing their intended functions. An understanding
of the structure of the motor/generator stator 108 and rotor 110
are not necessary to an understanding of the present invention and,
therefore, will not be further described.
[0022] The shaft 104 is rotationally supported within five
degrees-of-freedom. These five degrees-of-freedom, as illustrated
in FIG. 1, are the three lateral axes (e.g., x, y, and z) and the
two tilt axes (pitch and yaw). This rotational support of the shaft
104 is provided by two separate active magnetic bearings, one
positioned on either side of the flywheel 102. In particular, with
respect to the view depicted in FIG. 1, a first active magnetic
bearing 112 is positioned to the left of the flywheel 102 and a
second active magnetic bearing 114 is positioned to the right of
the flywheel 102. As will be described more fully below, the first
and second active magnetic bearings 112, 114 are preferably
configured as permanent magnet biased homopolar active magnetic
bearings and include, respectively, a first 116 and a second 118
rotor, and a first 120 and a second 122 stator assembly. The
structure of each of these portions of the first and second active
magnetic bearings 112, 114 will now be described in more
detail.
[0023] Beginning first with the rotors, it can be seen that the
first and second rotors 116, 118 are coupled to the shaft 104 at
first and second predetermined locations, respectively, on the
shaft 104. The rotors 116, 118 each have two pole faces, a first
rotor pole face 124 and a second rotor pole face 126. The first and
second rotors 116, 118 are constructed, in whole or in part, of a
magnetically permeable material such as, preferably, a ferrous
material. It is to be appreciated that the first and second rotors
116, 118 may be constructed as separate parts, or as integral parts
of the shaft 104. Preferably, however, the first and second rotors
116, 118 are each constructed as separate parts, and are
subsequently coupled to the shaft 104.
[0024] Turning now to the first and second stator assemblies 120,
122, reference should be made to FIGS. 2, 3 and 4, in combination
with FIG. 1. It should be noted that both of the stator assemblies
120, 122 are substantially identical and, therefore, only one of
the stator assemblies, specifically the first stator assembly 120,
is described and depicted in FIGS. 2-4. The first and second stator
assemblies 120, 122 surround a portion of, and are spaced radially
outwardly from, the first and second rotors 116, 118, respectively,
by a predetermined radial distance. The first and second stator
assemblies 120, 122, as depicted more clearly in FIGS. 2-4, each
include a first main stator body 128, a second main stator body
130, and an axial polarized permanent magnet 132. The permanent
magnet 132 is positioned between the first and second main stator
bodies 128, 130 and, as is generally known, functions to supply a
magnetic force bias to the first and second rotors 116, 118. The
permanent magnet 132 may be comprised of any one of numerous known
magnetic materials including, but not limited to, samarium-cobalt,
and neodymium-iron-boron. Preferably, however, it is comprised of
samarium-cobalt.
[0025] The first and second stator assemblies 120, 122 also include
a plurality of coil wound poles that extend radially inwardly from,
and are spaced evenly around, each of the first and second main
stator bodies 128, 130. Specifically, as depicted more clearly in
FIGS. 3 and 4, in a preferred embodiment, the first main stator
body 128 has eight coil wound poles 302a-302h, each of which has a
pole face, and the second main stator body 130 has eight
corresponding coil wound poles 402a-402h facing radially inwardly,
each having a pole face as well. Thus, the first and second stator
assemblies 120, 122 each have a total of sixteen coil wound poles
302a-302h, 402a-402h. It is noted that although each of the stator
assemblies 120, 122 in the preferred embodiment includes sixteen
total coil wound poles, and thus sixteen total pole faces (e.g.,
eight north pole faces and eight south pole faces), it will be
appreciated that the stator assemblies 120, 122 may each include
other numbers of coil wound poles, and thus other numbers of pole
faces. Non-limiting alternatives include using only four, or six
coil wound poles. It is additionally noted that, similar to the
first and second rotors 116, 118, the first and second main stator
bodies 128, 130 are constructed, in whole or in part, of a
magnetically permeable material such as, preferably, a ferrous
material. This material may be of laminated ferrous construction,
as is common practice in motor and transformer technologies, which
reduces losses and enhances high-speed switching.
[0026] As was noted above, an active magnetic bearing channel
includes a position sensor, a controller, and an electromagnetic
actuator. In accordance with a preferred embodiment of the present
invention, adjacent coil wound poles 302a-302h,402a-402h on each of
the first and second stator bodies 128, 130 are series wound to
create a single electromagnetic actuator. More specifically, poles
302a and 302b on first stator body 128 and poles 402a and 402b on
second stator body 130 are series wound to create a +Y actuator,
poles 302c and 302d on first stator body 128 and poles 402c and
402d on second stator body 130 are series wound to create a +X
actuator, poles 302e and 302f on first stator body 128 and poles
402e and 402f on second stator body 130 are series wound to create
a -Y actuator, and poles 302g and 302h on first stator body 128 and
poles 402g and 402h on second stator body 130 are series wound to
create a -X actuator. The first and the second magnetic bearings
112, 114 are similarly constructed and, therefore, each have +Y,
-Y, +X, -X magnetic actuators. Thus, the actuators associated with
the first magnetic bearing assembly 112 are labeled as +Y1, -Y1,
+X1, -X1, and the actuators associated with the second magnetic
bearing assembly 114 are labeled as +Y2, -Y2, +X2, -X2. For
convenience, these labels are clearly depicted in FIG. 1 below the
appropriate magnetic bearings 112, 114.
[0027] As was additionally described above, the electromagnetic
actuators +Yl, -Y1, +X1, -X1, +Y2, -Y2, +X2, -X2 are each
individually part of a separate active magnetic bearing channel.
Thus, the first and second active magnetic bearing assemblies 112,
114 each have four channels, for a total of eight, to control the
position of the shaft 104 within the five degrees-of-freedom. Shaft
104 position control within the four radial degrees-of-freedom
(e.g., the two tilt axes (pitch, yaw) and two of the lateral axes
(x-axis, y-axis)) is fairly straightforward. Specifically, the
magnitude of the current supplied to the +Y1, -Y1, +X1, -X1, +Y2,
-Y2, +X2, -X2 actuators generates magnetic flux across the radial
clearance gap between the respective pole faces of the actuators
and the first and second rotor pole faces 124, 126, which creates
attractive radial forces on the first and second rotor pole faces
124, 126. These radial forces are translated into appropriate
lateral forces and torques, which are applied to the center of
gravity of the first and second rotors 116, 118, to control the
shaft 104 position in these four degrees-of-freedom.
[0028] Shaft 104 position control in the remaining
degree-of-freedom, meaning the axial direction (e.g., z-axis), is
provided using a different physical phenomenon that does not
require an additional active magnetic bearing channel. In
particular, axial position control is based on the phenomenon that
a force is generated along an axis that serves to reduce the
reluctance of a flux path. To more fully understand how use of this
phenomenon provides axial control, reference should once again be
made to FIG. 1, which illustrates that the actuator pole faces are
axially offset from the first and second rotor pole faces 124, 126
by a predetermined distance. In particular, the actuator pole faces
of the first magnetic bearing 112 are axially offset from the first
and second pole faces 124, 126 of the first rotor 116 by the
predetermined distance in a first direction (e.g., the -z
direction), while the actuator pole faces of the second magnetic
bearing 114 are axially offset from the first and second pole faces
124, 126 of the second rotor 118 by the predetermined distance in a
second direction that is opposite of the first direction (e.g., the
+z direction). It will be appreciated that the actuator pole faces
of the first magnetic bearing assembly 112 and the second magnetic
bearing assembly 114 may also be offset from the first and second
poles faces 124, 126 of their associated rotors 116, 118 by the
predetermined distance in the +z and -z directions,
respectively.
[0029] Since the actuator and rotor pole faces are axially offset
from one another, a force is generated along the z-axis to reduce
the flux path reluctance between the actuators and the rotors.
Because the actuator and rotor pole faces of the first and second
active magnetic bearings 112,114 are axially offset in different
directions from one another, each generates a force in the z-axis
that is opposite from the other. With this arrangement, two effects
serve to center the shaft along the z-axis, one passive and the
other active. With the passive effect, a restoring force is
generated when the shaft 104 is offset along the z-axis such that
the axial offset of one rotor 116 (118) and stator 120 (122) pair
is reduced, thereby reducing its reluctance centering force, while
the offset of the other rotor 118 (116) and stator 122 (120) pair
is increased, thereby increasing its reluctance centering force.
The net effect is a force pulling the shaft 104 back to its center.
It is noted that once the axial offset of a rotor 116 (118) and
stator 120 (122) pair is eliminated, then the reluctance is
maximized, and the centering force vanishes.
[0030] The second, active effect, is brought about by increasing
the current level to all of the actuators in one magnetic bearing
assembly 112 (114) and decreasing it to all the actuators in the
other magnetic bearing assembly 114 (112). This causes a general
increase of axial force in one of the magnetic bearing assemblies
112 (114) and a decrease of axial force in the other 114 (112). The
net effect is a current controlled axial force.
[0031] To more clearly illustrate the position control that is
implemented by the first and second active magnetic bearings 112,
114, FIG. 5 depicts a table that indicates which actuators should
be activated and deactivated in order to provide the desired
action. It is noted that the table is for a shaft 104 that exhibits
no gyroscopic effects while rotating. If gyroscopic effects are
present, then the skilled artisan will appreciate that the desired
action for pitch and yaw control should be advanced 90-degrees,
relative to the spin direction of the shaft 104.
[0032] Up to this point, the invention has been described as being
implemented in a configuration in which the shaft's axial axis (or
z-axis) is generally horizontal. However, it is to be appreciated
that the present invention may also be implemented in a
configuration in which the shaft's axial axis is generally
vertical. Such an implementation is depicted in FIG. 6, which once
again depicts a simplified schematic representation of an energy
storage flywheel assembly 600. In this instance, however, the
flywheel assembly 600 is configured such that the shaft 104 is
oriented in a vertical configuration. It will be appreciated that
the flywheel assembly 600 depicted in FIG. 6 is substantially
identical to the one depicted in FIG. 1 and, therefore, like
reference numerals refer to like parts of the two embodiments. The
only difference between the embodiment of FIGS. 1 and 6 is the
addition of a pair of permanent magnets that provide an axial
weight offsetting function. Specifically, a first axial weight
offset magnet 602 is positioned below, and preferably attached to,
the flywheel 102, and a second axial weight offset magnet 604 is
positioned above, and preferably attached to, the second active
magnetic bearing assembly 114. The first and second axial weight
offset magnets 602, 604 are oriented to repel one another to
thereby create a force that offsets the weight of the flywheel 102.
The first and second active magnetic bearings 112, 114 control the
position of the shaft 104 in identical fashion to the embodiment
described above and depicted in FIGS. 1-5. It will be appreciated
that the axial weight offset magnets 602, 604 may also be included
in a generally horizontal configuration, such as the one depicted
in FIG. 1, without adversely affecting its operation.
[0033] It will be further appreciated that one of the end uses for
the active magnetic bearings described herein is in space
applications, such as the satellite 700 depicted in FIG. 7. The
satellite 700 includes a housing 702 that incorporates, and/or
houses components that include, one or more of the previously
described active magnetic bearings.
[0034] The active magnetic bearing assembly of the present
invention provides significant advantages over presently known
magnetic bearing configurations. For example, it does not require
the use of either a separate axial bearing or a combination bearing
and thus provides significant space savings. The bearing also has
minimal temperature sensitivity, and is less complex to
assemble.
[0035] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt to a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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