U.S. patent application number 13/897107 was filed with the patent office on 2013-12-12 for magnetically suspended pump.
This patent application is currently assigned to HEARTWARE, INC.. The applicant listed for this patent is Jeffrey A. LaRose, Charles R. Shambaugh, JR.. Invention is credited to Jeffrey A. LaRose, Charles R. Shambaugh, JR..
Application Number | 20130330219 13/897107 |
Document ID | / |
Family ID | 49584347 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130330219 |
Kind Code |
A1 |
LaRose; Jeffrey A. ; et
al. |
December 12, 2013 |
MAGNETICALLY SUSPENDED PUMP
Abstract
An axial now blood pump includes a pump housing and first and
second stator permanent magnets fixed to the pump housing. A rotor
assembly is disposed within the pump housing and includes first and
second rotor permanent magnets. The first fixed permanent magnet
may be axially offset from the first rotor permanent magnet and the
second fixed permanent magnet may be axially offset from the second
rotor permanent magnet. The permanent magnets act as passive radial
bearings with maintain the rotor coaxial with the housing, and also
exert axial forces on the first and second rotor permanent magnets
to urge the rotor towards an equilibrium axial position relative to
the housing. The rotor may be suspended and positioned within the
housing solely by operation of the permanent magnets.
Inventors: |
LaRose; Jeffrey A.;
(Parkland, FL) ; Shambaugh, JR.; Charles R.;
(Coral Gables, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LaRose; Jeffrey A.
Shambaugh, JR.; Charles R. |
Parkland
Coral Gables |
FL
FL |
US
US |
|
|
Assignee: |
HEARTWARE, INC.
Miami Lakes
FL
|
Family ID: |
49584347 |
Appl. No.: |
13/897107 |
Filed: |
May 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61648289 |
May 17, 2012 |
|
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|
Current U.S.
Class: |
417/420 |
Current CPC
Class: |
F04D 13/06 20130101;
A61M 1/122 20140204; F04D 29/041 20130101; F16C 2316/18 20130101;
F16C 32/0429 20130101; A61M 1/1015 20140204; A61M 1/101 20130101;
F04D 29/048 20130101; F16C 32/0408 20130101; F04D 29/058 20130101;
A61M 1/1031 20140204; F04D 29/051 20130101 |
Class at
Publication: |
417/420 |
International
Class: |
F04D 13/06 20060101
F04D013/06 |
Claims
1. A blood pump comprising: a housing having an axis; first and
second stator permanent magnets fixed relative to the housing at
axially-spaced locations; a rotor having an axis disposed within
the pump housing including a first rotor permanent magnet
associated with and magnetically interacting with the first stator
permanent magnet and a second rotor permanent magnet associated
with and magnetically interacting with the second stator permanent
magnet, so that the interacting magnets urge the rotor into an
alignment coaxial with the housing, wherein the first stator
permanent magnet exerts a first axial force on the first rotor
permanent magnet in a first axial direction and the second stator
permanent magnet exerts a second axial force on the second rotor
permanent magnet in a second axial direction opposite to the first
axial direction.
2. A blood pump as claimed in claim 1, wherein, over an operating
range of axial positions of the rotor relative to housing, the
first axial force decreases and the second axial force increases
upon movement of the rotor relative to the housing in the first
axial direction, whereas the first axial force increases and the
second axial force decreases with movement of the rotor relative to
the housing in the second axial direction, whereby the first and
second axial forces urge the rotor towards an equilibrium position
within the operating range.
3. A blood pump as claimed in claim 2, wherein, in operation, the
rotor is suspended and positioned within the housing without
contact between the rotor and the housing.
4. A blood pump as claimed in claim 3, wherein, in operation, the
rotor is suspended and positioned within the housing without
feedback control of the axial position of the rotor.
5. A blood pump as claimed in claim 3, wherein, in operation, the
rotor is suspended and positioned within the housing solely by the
permanent magnets.
6. A blood pump as claimed In claim 2, wherein each stator
permanent magnet is generally tubular and symmetrical about the
axis of the housing and defines a plurality of opposite magnetic
poles axially spaced from one another.
7. A blood pump as claimed in claim 6, wherein each rotor permanent
magnet is symmetrical about the axis of the rotor and defines a
plurality of opposite magnetic poles axially spaced from one
another, and wherein the first rotor permanent magnet is at least
partially disposed within the first stator permanent magnet, the
second rotor permanent magnet being at least partially disposed
within the second stator permanent magnet.
8. A blood pump as claimed in claim 7, wherein the first stator
permanent magnet has poles disposed at first axial locations and
the first rotor permanent magnet has identical poles disposed at
the same first axial locations, plus a first offset distance in the
first axial direction, and wherein the second stator permanent
magnet has poles disposed at second axial locations and the second
rotor permanent magnet has identical poles disposed at the same
second axial locations, plus an second offset distance in the
second axial direction.
9. A blood pump as claimed in claim 8, wherein the first offset
distance is less than an axial spacing distance between any two
opposite poles of the first stator permanent magnet and the second
offset distance is less than an axial spacing distance between any
two opposite poles of the second stator permanent magnet.
10. A blood pump as claimed in claim 2, wherein each stator
permanent magnet includes at least one magnetic ring element
coaxial with the axis of the housing and each rotor permanent
magnet includes at least one magnetic disc or ring element coaxial
with the axis of the rotor.
11. A blood pump as claimed in claim 10, wherein each stator
permanent magnet includes a plurality of magnetic ring elements
having like magnetic poles facing axially toward one another and
each rotor permanent magnet includes a plurality of magnetic ring
or disc elements having like magnetic poles facing axially toward
one another.
12. The blood pump of claim 1, wherein the pump housing has an
inflow end and an outflow end, the axis of the housing extends
between the inflow and outflow ends, and the rotor includes
impeller surfaces arranged to impel blood toward the outflow end
upon rotation of the rotor about the axis of the rotor.
13. The blood pump of claim 12, wherein the first rotor permanent
magnet is positioned closer to the inflow end than the first stator
permanent magnet and the second rotor permanent magnet is
positioned closer to the outflow end than second stator permanent
magnet, the first stator permanent magnet exerts an axial force on
the first rotor permanent magnet toward the inflow end, and the
second stator permanent magnet exerts an axial force on the second
rotor permanent magnet toward the outflow end.
14. The blood pump of claim 12, wherein the first rotor permanent
magnet is positioned further from the inflow end than the first
stator permanent magnet, the second rotor permanent magnet is
positioned further from the outflow end than the second stator
permanent magnet, the first stator permanent magnet exerts a force
on the first rotor permanent magnet toward the outflow end, and the
second stator permanent magnet exerts a force on the second rotor
permanent magnet toward the inflow end.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of the filing
date of U.S. Provisional Patent Application No. 61/648,289 filed
May 17, 2012, the disclosure of which is hereby incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] Clinical applications of ventricular assist devices to
support patients with end-stage heart disease, as a bridge to
cardiac transplantation, or as an end stage therapeutic modality
have become an accepted clinical practice in cardiovascular
medicine. It is estimated that greater than 35,000 persons
suffering from end stage cardiac failure are candidates for cardiac
support therapy.
[0003] Ventricular assist devices may utilize a blood pump for
imparting momentum to a patients blood thereby driving the blood to
a higher pressure. One example of a ventricular assist device is a
Left Ventricular Assist Device (LVAD). The blood inlet of the LVAD
is connected to the left ventricle of the patient's heart, whereas
the blood outlet of the LVAD is connected to the patient's aorta.
Oxygenated blood from the ventricle enters the LVAD and is pumped
by the LVAD into the patient's aorta.
[0004] Certain LVADs use rotary pumps. A rotary pump includes a
rotor that spins about an axis within the housing of pump and
imparts momentum to the blood. Rotary blood pumps may be either
centrifugal or axial, In a radial flow or centrifugal blood pump,
blood enters the pump along its axis of rotation and exits the pump
remote from the axis of rotation. In an axial flow blood pump,
blood enters the pump along its axis of rotation and exits the pump
along the axis of rotation.
[0005] Certain rotary blood pumps use mechanical bearings to
support and position in the axial and radial directions. Mechanical
bearings in contact with the blood can cause of thrombosis.
Moreover, mechanical bearings that have contact between a part
fixed to the housing and a part fixed to the rotor are subject to
wear. This can pose a considerable problem, particularly in a blood
pump that must remain implanted within the patient for many
years.
[0006] To avoid these problems, non-contact bearings have been
employed. These bearings utilize magnetic or hydrodynamic forces to
suspend the rotor within the housing. For example, certain
embodiments in U.S. Pat. No. 5,695,471 to Wampler, the disclosure
of which is hereby incorporated by reference herein, utilize a
magnetic bearing including a multipole, rod-like permanent magnet,
such as an assemblage of magnetic discs, on the rotor. The rotor
permanent magnet is disposed within a multi-pole generally tubular
permanent magnet, such as an assemblage of magnetic rings, on the
housing. Repulsion forces between like poles of these magnets help
to maintain the rotor coaxial with the housing. Stated another way,
these permanent magnets act as a radial bearing with constrains the
rotor in radial directions. These permanent magnets also produce an
axial thrust on the rotor. The axial position of the rotor relative
to the housing is maintained by magnetic or hydrodynamic thrust
bearings separate from the radial bearing. Because bearings that
rely only on permanent magnets do not require an external source of
power and do not require any control circuitry, they are commonly
referred to as "passive" magnetic bearings.
[0007] U.S. Pat. No. 6,234,772, to Wampler et al. (the '772
Patent), hereby incorporated by reference herein, discloses certain
embodiments using a passive magnetic radial bearing incorporating a
permanent magnet on a spindle fixed to the pump housing. The
spindle is received within a bore in the rotor. The rotor has a
tubular permanent magnet surrounding the spindle. In certain
preferred embodiments, the '772 Patent uses hydrodynamic thrust
bearings to control axial position of the rotor.
[0008] It has been suggested in the past that passive magnetic
radial bearings alone cannot keep an impeller suspended in both the
axial and radial directions. For example, U.S. Patent Publication
No. 2011/0237863 (the '863 Publication), the entire contents of
which are hereby incorporated by reference herein, discloses an
axial flow blood pump with passive magnetic bearings to radially
support the pump impeller. This pump uses an electromagnetic coil,
referred to as a "voice coil" energized by an electrical drive
circuit, to axially support the pump impeller. The pump also
includes sensors that monitor the axial position of the rotor
relative to the housing, and the drive circuit is arranged to vary
the current supplied to the voice coil responsive to the detected
axial position. The use of a voice coil, drive circuit, and sensors
makes the design of the pump more complex and more difficult to
miniaturize. Such an arrangement is commonly referred to as an
"active" magnetic bearing.
[0009] Despite these efforts in the art, further improvement would
be desirable.
BRIEF SUMMARY OF THE INVENTION
[0010] One aspect of the invention provides a blood pump which
includes a housing having an axis and first and second stator
permanent magnets fixed relative to the housing at axially-spaced
locations. The pump according to this aspect of the invention
desirably also includes a rotor having an axis disposed within the
pump housing including a first rotor permanent magnet associated
with and magnetically interacting with the first stator permanent
magnet and a second rotor permanent magnet associated with and
magnetically interacting with the second stator permanent magnet,
so that the interacting magnets urge the rotor into an alignment
coaxial with the housing.
[0011] Most preferably, the magnets are constructed and arranged so
that first stator permanent magnet exerts a first axial force on
the first rotor permanent magnet in a first axial direction and the
second stator permanent magnet exerts a second axial force on the
second rotor permanent magnet in a second axial direction opposite
to the first axial direction. The rotor and stator permanent
magnets desirably are arranged so that, over an operating range of
axial positions of the rotor relative to housing, the first axial
force decreases upon movement of the rotor relative to the housing
in the first axial direction, whereas the second axial force
decreases upon movement of the rotor relative to the housing in the
second axial direction. Thus, the first and second axial forces
urge the rotor towards an equilibrium position within the operating
range.
[0012] In particularly preferred embodiments, the rotor can be
suspended and positioned within the housing entirely by
interactions between the aforementioned rotor and stator permanent
magnets. Preferred embodiments of the present invention can provide
simple and compact pumps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional view of an axial flow blood pump
according to the prior art.
[0014] FIG. 2A is a schematic view of an axial flow blood pump
according to one embodiment of the invention.
[0015] FIG. 2B is a schematic view of the interaction of magnetic
bearings in the axial flow blood pump of FIG. 2A.
[0016] FIG. 3 is a schematic view of an alternate embodiment of an
axial flow blood pump according to a further embodiment of the
invention.
DETAILED DESCRIPTION
[0017] FIG. 1 illustrates a cross sectional view of a portion of
the axial blood pump disclosed in the '863 Publication. Although
incorporated by reference, certain portions of the '863 Publication
are reproduced below to more fully explain that disclosure.
[0018] As shown, blood flow is designed to flow in the direction
from inflow lumen 37 to outflow lumen 38 and thereby respectively
guide the blood flow into and out of pump. The rotor assembly 60
spins and pumps blood via attached impeller blades 62. Stationary
stator blades 102 direct the flow at the outlet end 22 of the blood
pump 20. The rotor assembly 60 is rotated via a 4-pole motor
assembly 124 forming stator components including motor iron 125,
motor windings 126, and potting material 127 and rotor components
including motor magnets 70.
[0019] FIG. 1 also shows radial support to the rotor assembly
provided by fore and aft PM magnetic bearings. The fore PM magnetic
bearing includes rotor PM rings 68a and 68b and corresponding
stator PM rings 121a and 121b. Similarly, the aft PM magnetic
bearing includes rotor PM rings 68c and 68d and corresponding
stator PM rings 121c and 121d. The magnetization directions of the
various PM components are indicated with arrows.
[0020] While the fore and aft PM magnetic bearings provide a radial
magnetic spring force that stabilizes and centers the rotor
assembly 60 with a positive spring characteristic, the PM magnetic
bearings also create a negative spring characteristic in the axial
direction which makes the rotor axially unstable. To compensate for
the axial negative spring characteristic, a feedback-controlled
voice-coil actuator acts on the rotor assembly 60 in the axial
direction.
[0021] The voice-coil actuator is comprised of voice coils 129a and
129b wired such that current flows in opposite directions in the
two coils 129a, 129b and thus interacts with magnets 71, 72, and 73
to produce an axial force in response to an
electronically-controlled current in the coils 129a, 129b. Magnet
68b also contributes to the function of the voice-coil actuator, as
it is proximal to voice coil 129a and contributes to the radial
magnetic field in voice coil 129a.
[0022] Feedback control of the voice-coil actuator in FIG. 1 is
accomplished by using fore and aft position sensor coils 135 and
136. As the rotor assembly 60 moves fore and aft, the impedance of
coils 135 and 136 change and the impedance change is interpreted as
positional change by electronics external to the blood pump 20. A
feedback control algorithm such as virtually zero power control is
applied to the position signal to determine the voltage or current
applied to the voice coils 129a and 129b.
[0023] With further regard to FIG. 1, the stator housing 81 extends
for a large fraction of the length of the blood pump 20. Stator
housing 81 forms the outside wall of annular flow gap 39, which is
a large part of the blood flow path through the pump. Additionally,
the stator housing 81 supports the stator PM rings 121a, 121b,
121c, 121d, the voice coils 129a, 129b, the motors coils 126, and
motor iron 125.
[0024] As pointed out above, the requirement for a voice coil and
the associated sensors and circuitry in the pump of FIG. 1
increases the complexity and size of the pump.
[0025] Now referring to FIG. 2A, an embodiment of a blood pump 220
according to an aspect of the invention is shown. Pump 220 includes
a hollow housing having an inflow end 237, an outflow end 238, and
a housing axis 201 extending between these ends.
[0026] The pump further includes a rotor 260 having a rotor axis
203, the rotor being disposed within the housing. The rotor
includes a first set of cylindrical rotor PM rings 268a-c disposed
adjacent the inflow end 237 of the pump 220. The first set of rotor
PM rings have like magnetic poles of mutually-adjacent rings facing
axially toward one another. For example, the north pole of ring
268a faces toward the north pole of ring 268b. The south pole of
ring 268b faces toward the south pole of ring 268c. The first set
of rotor PM rings thus cooperatively constitute a first rotor
permanent magnet 269 that is symmetrical about the rotor axis 203,
and which has opposite magnetic poles axially spaced apart from one
another in an alternating arrangement. For example, there is a
south pole 271a at the end of the magnet defined by ring 268a, a
north pole 271b at the juncture between rings 268a and 268b, a
south pole 271c at the juncture of rings 268b and 268c, and a south
pole 271d at the end of the magnet defined by ring 268c. In this
embodiment, the rings are of uniform thickness, so that the each
pole 271 of magnet 269 is spaced apart from the next adjacent pole
of this magnet by a uniform spacing distance DS1. The rotor further
includes a second set of rotor PM rings 268d-f, which cooperatively
constitute a second rotor permanent magnet 273 disposed adjacent
the outflow end 238 of the pump. The second rotor permanent magnet
is similar to the first rotor permanent magnet. Thus, magnet 273 is
symmetrical about the rotor axis 203 and defines poles 275a-275d in
alternating north pole and south pole sequence along axis 203. Here
again, the mutually-adjacent poles of magnet 273 are spaced apart
from one another along the axis by a uniform spacing distance
DS2.
[0027] A first set of cylindrical stator PM rings 321a-c is fixed
to the housing 281 of the pump 220 adjacent the inflow end 237 of
the housing. The first set of stator rings cooperatively
constitutes a first stator permanent magnet 323. This magnet is
tubular and symmetrical about the housing axis 201 and has poles
371a-371d in the same alternating sequence of south and north poles
as the first rotor permanent magnet 269. Thus, magnet 323 has a
south pole 371 at the end closest to the inflow end 237 of the
housing, followed by a north pole 371b, and so on. Mutually
adjacent poles of first stator permanent magnet 323 are spaced
apart from one another by the same spacing distance DS1 as the
poles of the first rotor permanent magnet 269.
[0028] A second set of stator PM rings 321d-f is fixed to the
housing 281 of the pump 220 adjacent outflow end 238. These rings
cooperatively define a second stator permanent magnet 325. Magnet
325 is also tubular and symmetrical about the housing axis 201 and
has alternating north and south poles 373a-373d in a sequence
corresponding to the sequence of poles 275a-275d in the second
rotor permanent magnet 273. Adjacent poles of the second stator
permanent magnet 325 are axially spaced from one another at the
same spacing distance DS2 as the poles of the second rotor
permanent magnet 273.
[0029] However, in the illustrated embodiment of pump 220, the
axial distance between stator permanent magnets 323 and 325 is
slightly greater than the axial distance between the rotor
permanent magnets 269 and 273.
[0030] Rotor 260 also has motor permanent magnets schematically
depicted at 207. A set of motor coils 209 is mounted to the housing
281. The motor magnets and motor coils may be of conventional
construction and are arranged to spin the rotor around its axis
when the coils are energized by an appropriate drive circuit. The
rotor is also equipped with surfaces such as the vanes
schematically depicted at 211, arranged to impel blood in the
downstream direction indicated by arrow Q, from the inflow end 237
to the outflow end 238, upon rotation of the rotor about its
axis.
[0031] The magnetic interactions between the first rotor magnet 269
and first stator magnet 323, and between second rotor magnet 273
and second stator magnet 325, levitate the rotor 260 within the
housing 281 in the operating position shown. In this operating
position, the rotor axis 203 is coaxial with the housing axis 201.
First rotor PM magnet 269 is largely received within the tubular
first stator PM magnet 323, but the rotor magnet 269 is offset in a
first axial direction from the stator magnet by an offset distance
DO1, so that pole 271d of the rotor magnet protrudes beyond pole
371d of the stator magnet. In this embodiment, the first axial
direction is the downstream direction indicated by arrow Q in FIG.
2A. Preferably, the first offset distance D01 is less than the
spacing distance DS1 between adjacent poles of the first rotor
magnet, and typically D01 is less than one-half DS1. Second rotor
magnet 273 is received within second stator magnet 325, but is
offset therefrom by a second offset distance DO2 in the second
axial direction, opposite to the first axial direction. Thus, the
second rotor magnet is offset from the stator rotor magnet in the
upstream direction, opposite to arrow Q in FIG. 2A. Preferably, the
second offset distance D02 is less than the spacing distance DS2
between adjacent poles of the first rotor magnet, and typically D02
is less than one-half DS2.
[0032] FIG. 2B illustrates the interactions between the bearings.
The magnetic forces exerted by the poles of the stator magnets on
the corresponding poles of the rotor magnets are depicted by the
inclined arrows in FIG. 2. Because each pole of the rotor magnet is
disposed closer to a like pole of the associated stator magnet,
repulsive forces predominate over attractive forces. In the radial
direction, the repulsive forces tend to hold each rotor magnet
coaxial with the associated stator magnet. Because the poles of the
first rotor magnet 269 are offset in the first axial direction (to
the right in FIG. 2B) from the like poles of the first stator
magnet 323, the first stator magnet imparts a first axial force FA1
on the first rotor magnet 269 and thus on rotor 260. This axial
force is in the first axial direction, and thus in the downstream
direction indicated by arrow Q. Similarly, the second stator magnet
325 imparts a second axial force FA2 on the second rotor magnet
273, and thus on rotor 260 in the second axial direction.
[0033] In the equilibrium position depicted, these axial forces
balance one another. Moreover, within an operating range of rotor
axial positions near the equilibrium position, the axial forces
will urge the rotor toward the equilibrium position. Within this
operating range, displacement of the rotor in the downstream or
first axial direction (to the right in FIG. 2B, and toward the
outflow end 238 of the housing in FIG. 2A) causes the first axial
force to decreases and the second axial force to increase, so that
the second axial force FA2 becomes greater than the first axial
force FA. This yields a net force in the second axial direction,
which urges the rotor back toward the equilibrium position. The
opposite effects occur upon displacement of the rotor from the
equilibrium position in the second axial direction. In this case,
FA1 increases and FA2 decreases. Stated another way, the
interactions between the rotor and stator magnets cause the axial
forces exerted on the rotor to vary with axial displacement of the
rotor in such a way as to restore the rotor to the equilibrium
position.
[0034] Although the axial forces result from interaction of all of
the poles of the interacting magnets, the changes in axial forces
with displacement of the rotor can be appreciated with reference to
the projecting poles 271d and 275a of the rotor magnets. Movement
in the first axial direction increases the first offset distance
DO1, and thus moves pole 271d away from the adjacent pole 371d of
the first stator magnet and reduces the repulsive force on pole
271d. Rotor movement in the first axial direction also reduces the
second offset distance DO2 and thus moves pole 275d closer to the
adjacent pole and increases the repulsion force exerted on pole
275a by pole 373a of the second stator magnet.
[0035] Thus, the rotor permanent magnets 269, 273, and stator
permanent magnets 323, 325 tend to keep the rotor 260 not only in
radial alignment with the housing 281 of the pump 220, but also in
axial alignment.
[0036] FIG. 3A shows an alternate embodiment of a blood pump 420.
Similar to blood pump 220 of FIG. 2A, pump 420 includes first and
second sets of rotor PM rings 468a-c and 468d-f constituting first
and second rotor permanent magnets 402 and 404 on the rotor 460.
Corresponding first and second stator permanent magnets 406 and 408
are formed by first and second sets of stator PM rings 521a-c and
521d-f on the housing 481 of the pump 420. These permanent magnets
may have the same configurations as the rotor and stator permanent
magnets discussed above. In pump 420, however, the rotor permanent
magnets 402 and 404 are disposed farther from one another than the
stator permanent magnets 406 and 408. Thus, offsets between rotor
and stator permanent magnets are the reverse of those shown in FIG.
2A. In pump 420, the first rotor permanent magnet 402 is largely
received within the first stator permanent magnet 406, but is
offset therefrom by an offset distance DO1 in a first direction
toward the inflow or upstream end 437 of the housing, i.e., to the
left as seen in FIG. 3A. The second rotor permanent magnet 404 is
largely received within the second stator permanent magnet 408, but
magnet 404 is offset from magnet 408 by an offset distance DO2 in a
second direction, toward the outflow or downstream end 438 of the
housing. Here again, the two offset directions are opposite to one
another. Pump 420 also includes motor magnets and coils (not shown)
for rotating rotor 460 about its axis 401, as well as surfaces (not
shown) on the rotor for impelling blood in a downstream direction
toward the outflow end 438 of the housing upon rotation of the
rotor.
[0037] In this configuration, the magnetic interactions of first
rotor permanent magnet 402 with first stator permanent magnet 406,
and of second rotor permanent magnet 404 with second stator
permanent magnet 408, levitate the rotor within housing 408 and
provide both radial and axial positioning. Repulsion of first rotor
magnet 402 by first stator magnet 406 produces an first axial force
FA1 in the first direction, whereas second stator magnet 408 and
second rotor magnet 404 apply a second axial force FA2 in the
second, opposite direction on the rotor. In the equilibrium
position depicted, these forces balance one another. If the rotor
460 moves in the first direction (toward the inflow end 437 of the
pump) from the equilibrium position depicted in FIG. 3A, first
axial force FA1 decreases and second axial force FA2 increases, so
that there is a net restoring force in the second axial direction,
toward the outflow end 438 of the pump 420. The opposite effects
occur upon movement of the rotor in the second axial direction from
the equilibrium position.
[0038] In the embodiments discussed above, the rotor is levitated
within the housing and maintained in radial and axial position
without the use of any other bearings or position control elements.
For example, active position control elements such as a voice coil
and feedback control circuitry are not used in this embodiment.
Also, there is no need for separate magnetic or hydrodynamic thrust
bearings to maintain rotor position during operation. Thus, the
pump can be simple and compact. In other embodiments, the magnetic
bearing arrangements discussed above can be used in conjunction
with additional magnetic, hydrodynamic, or other bearings, in
conjunction with active position control elements, or both.
[0039] The number of poles in each of the first and second rotor
permanent magnets can be varied. Also, the rotor permanent magnets
may be formed from plural discs rather than from plural rings as in
the embodiments discussed above. Moreover, each of the rotor
permanent magnets and the stator permanent magnets may be formed as
a unitary body of magnetic material with magnetization as required
to provide the plural poles of each magnet, rather than from
separate rings or discs. The stator permanent magnets may be formed
integrally with other elements of the rotor and stator.
[0040] Patterns of magnetization different from those discussed
above can be used in the magnetic bearings as long as the magnets
provide radial and axial forces that urge the rotor towards axial
and radial equilibrium positions. For example, the arrangement of
magnets can be modified so long as one pair of rotor and stator
magnets provides an axial force on the rotor in a first direction
that decreases upon movement of the rotor in the first direction,
whereas another pair of rotor and stator magnets provides an axial
force in a second, opposite direction, and that axial force
decreases upon movement of the rotor in the second axial direction.
The rotor and stator magnets need not be cylindrical, as in the
embodiments discussed above. For example, these magnets may be
conical or frustoconical. The poles of the rotor and stator
permanent magnets need not be disposed at uniform spacing
distances, and the spacing distances between a rotor permanent
magnet need not be the same as the spacing distances between poles
of the associated stator permanent magnet. Still further, the
magnetic intensity may vary from magnet type to magnet type and,
therefore, the specific shape and size may vary from the specific
embodiment shown.
[0041] The bearing arrangements can be used in pumps other than the
axial flow pumps depicted herein. For example, the bearing
arrangements can be using to support the rotor of a blood pump
having radial flow or mixed axial and radial flow.
[0042] In the embodiments discussed above, the stator permanent
magnets are tubular and the rotor permanent magnets are received
within the stator permanent magnets. However, the reverse
arrangement can be used. For example, where the spindle is fixed to
the housing and the rotor surrounds the spindle, the rotor
permanent magnets may be tubular, and the stator permanent magnets
may be mounted on the spindle and received within the rotor
permanent magnets.
[0043] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications, including combinations of
features illustrated in different embodiments of the disclosure,
may be made to the illustrative embodiments and that other
arrangements may be devised without departing from the spirit and
scope of the present invention as defined by the appended
claims.
* * * * *