U.S. patent application number 16/931306 was filed with the patent office on 2020-11-05 for rotary blood pump with opposing spindle magnets, bore and drive windings.
This patent application is currently assigned to TC1 LLC. The applicant listed for this patent is TC1 LLC. Invention is credited to David M. Lancisi, Richard K. Wampler.
Application Number | 20200345908 16/931306 |
Document ID | / |
Family ID | 1000004959949 |
Filed Date | 2020-11-05 |
United States Patent
Application |
20200345908 |
Kind Code |
A1 |
Wampler; Richard K. ; et
al. |
November 5, 2020 |
Rotary Blood Pump With Opposing Spindle Magnets, Bore And Drive
Windings
Abstract
Various "contactless" bearing mechanisms including hydrodynamic
and magnetic bearings are provided for a rotary pump as
alternatives to mechanical contact bearings. In one embodiment, a
pump apparatus includes a pump housing defining a pumping chamber.
The housing has a spindle extending into the pumping chamber. A
spindle magnet assembly includes first and second magnets disposed
within the spindle. The first and second magnets are arranged
proximate each other with their respective magnetic vectors
opposing each other. The lack of mechanical contact bearings
enables longer life pump operation and less damage to working
fluids such as blood.
Inventors: |
Wampler; Richard K.;
(Loomis, CA) ; Lancisi; David M.; (Folsom,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TC1 LLC |
St. Paul |
MN |
US |
|
|
Assignee: |
TC1 LLC
St. Paul
MN
|
Family ID: |
1000004959949 |
Appl. No.: |
16/931306 |
Filed: |
July 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16510707 |
Jul 12, 2019 |
10751454 |
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16931306 |
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16019205 |
Jun 26, 2018 |
10391215 |
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16510707 |
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15811440 |
Nov 13, 2017 |
10034972 |
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16019205 |
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15385364 |
Dec 20, 2016 |
9844617 |
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15811440 |
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14327454 |
Jul 9, 2014 |
9545467 |
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15385364 |
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14047717 |
Oct 7, 2013 |
8807968 |
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14327454 |
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11950328 |
Dec 4, 2007 |
8579607 |
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14047717 |
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10940419 |
Sep 14, 2004 |
7431688 |
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11950328 |
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60504233 |
Sep 18, 2003 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 29/628 20130101;
F04D 29/048 20130101; A61M 1/1017 20140204; F04D 29/047 20130101;
F04D 29/426 20130101; A61M 1/1031 20140204; F04D 29/043 20130101;
F04D 13/06 20130101; A61M 1/101 20130101; F04D 29/22 20130101; F04D
29/0473 20130101; F04D 29/0413 20130101; A61M 1/122 20140204; F16C
32/044 20130101; F04D 1/00 20130101; A61M 1/1015 20140204; F16C
2316/18 20130101; A61M 1/1013 20140204; Y10S 415/90 20130101; A61M
1/1036 20140204; F04D 13/0666 20130101 |
International
Class: |
A61M 1/10 20060101
A61M001/10; F04D 13/06 20060101 F04D013/06; F04D 29/047 20060101
F04D029/047; F04D 29/048 20060101 F04D029/048; F04D 29/041 20060101
F04D029/041; F04D 29/62 20060101 F04D029/62 |
Claims
1. A method of pumping blood comprising: providing a pump having a
housing, a rotor, a spindle, an axial magnetic bearing and at least
one hydrodynamic bearing; adjusting said rotor axially; rotating
said rotor; supporting said rotor with said axial magnetic bearing;
exerting a force in an axial direction via said at least one
hydrodynamic bearing; and, thereby levitating said rotor.
2. A pump comprising: a pump housing defining a pumping chamber;
the pump housing having a spindle extending into the pumping
chamber; a rotor having a bore, the rotor configured to rotate
about the spindle, the rotor including an impeller comprising at
least one blade; a rotor portion of a magnetic bearing disposed
within a non-bladed portion of the rotor; a spindle portion of the
magnetic bearing disposed within the spindle, wherein at least one
of the rotor and spindle portions of the magnetic bearing comprises
a first and a second magnet, wherein the first and second magnets
are arranged proximate each other with their respective magnetic
vectors parallel to each other.
3. A controlled pump system comprising: a control system for
controlling operation of a pump; a pump comprising: housing having
a pumping chamber and a spindle; a rotor positioned around said
spindle; an axial magnetic bearing supportive of said rotor; a
rotor adjustment mechanism; a hydrodynamic bearing generating
forces in an axial direction when said rotor is in a rotating
state; wherein said axial magnetic bearing and said hydrodynamic
bearing combine to levitate said rotor during rotation of said
rotor; a source conduit connected to an inlet of said pump; and, a
destination conduit to an outlet of said pump; said control system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/504,233 of Wampler, et al. filed Sep. 18,
2003.
FIELD OF THE INVENTION
[0002] This invention relates to the field of rotary pumps. In
particular, this invention is drawn to bearings for various rotor
and impeller architectures.
BACKGROUND OF THE INVENTION
[0003] Typical rotary pumps utilize an impeller wherein the
movement of the impeller is constrained in five degrees of freedom
(two angular, three translational) by mechanical contact bearings.
Some working fluids may be damaged by the mechanical contact
bearings. Blood pumped through pumps with contact bearings can
experience hemolysis, i.e., damage to blood cells. In general, a
hydraulically efficient and power efficient pump that can handle
delicate working fluids such as blood is desirable for some
applications.
[0004] U.S. Pat. No. 6,234,772 B1 of Wampler, et al., ("Wampler")
describes a centrifugal blood pump having a repulsive radial
magnetic bearing and an axial hydrodynamic bearing. U.S. Pat. No.
6,250,880 B1 of Woodard, et al. ("Woodard") describes a centrifugal
blood pump with an impeller supported exclusively by hydrodynamic
forces.
[0005] Both blood pumps are based on an axial flux gap motor
design. The pump impeller carries the motor drive magnets thus
serving as a motor rotor. In both cases, the drive magnets are
disposed within the blades of the impeller. Drive windings reside
outside the pump chamber but within the pump housing that serves as
the motor stator. Integration of the motor and pump enables the
elimination of drive shafts and seals for the pumps. The
pump/motors include a back iron to increase the magnetic flux for
driving the impeller.
[0006] Both blood pumps suffer from hydraulic inefficiencies due at
least in part to the large, unconventional blade geometry required
for disposing the magnets within the impeller blades.
[0007] The natural attraction between the magnets carried by the
impeller and the back iron creates significant axial forces that
must be overcome in order for the pump to work efficiently.
Hydrodynamic bearings can damage blood cells as a result of shear
forces related to the load carried by the hydrodynamic bearings
despite the lack of contact between the impeller and the pump
housing. Thus exclusive reliance on hydrodynamic bearings may be
harmful to the blood.
SUMMARY OF THE INVENTION
[0008] In view of limitations of known systems and methods, various
"contactless" bearing mechanisms are provided for a rotary pump as
alternatives to mechanical contact bearings. Various rotor and
housing design features are provided to achieve magnetic or
hydrodynamic bearings. These design features may be combined. The
lack of mechanical contact bearings enables longer life pump
operation and less damage to working fluids such as blood.
[0009] In one embodiment, the pump includes a magnetic thrust
bearing. The pump includes a pump housing defining a pumping
chamber. The pump housing has a spindle extending into the pumping
chamber. A spindle magnet assembly comprising first and second
magnets is disposed within the spindle. The first and second
magnets of the spindle magnet assembly are arranged proximate each
other with their respective magnetic vectors opposing each other.
The pump includes a rotor having an impeller configured to rotate
about the spindle. A rotor magnet assembly comprising first and
second magnets is disposed within a non-bladed portion of the
rotor. The first and second magnets of the rotor magnet assembly
are arranged proximate each other with their respective magnetic
vectors opposing each other. The relative orientations of the
spindle and rotor magnet assemblies are selected so that the
spindle and rotor magnet assemblies attract each other. The rotor
may include a grooved bore. In various embodiments, a hydrodynamic
bearing is included for radial or axial support or both.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention is illustrated by way of example and
not limitation in the figures of the accompanying drawings, in
which like references indicate similar elements and in which:
[0011] FIG. 1 illustrates a cross-section of a pump having a
passive magnetic axial bearing.
[0012] FIG. 2 illustrates one embodiment of the passive magnetic
axial bearing.
[0013] FIG. 3 illustrates center and off-center placement of the
passive magnetic axial bearing.
[0014] FIG. 4 illustrates one embodiment of an impeller.
[0015] FIG. 5 illustrates one embodiment of the pump applied in a
medical application.
DETAILED DESCRIPTION
[0016] FIG. 1 illustrates one embodiment of a centrifugal blood
pump. The pump comprises a housing 110 defining a pumping chamber
112 between an inlet 114 and an outlet 116. Within the pumping
chamber, a rotor 120 rotates about a spindle 130 protruding from a
base of the pump housing. The rotor further comprises a bladed
portion defining an impeller that provides the fluid moving
surfaces. The impeller comprises one or more blades 121 that move
fluids when the impeller rotates.
[0017] The terms "rotor" and "impeller" may be used interchangeably
in some contexts. For example, when the rotor is rotating, the
blade portion of the rotor is inherently rotating such that
reference to rotation of either the impeller or the rotor is
sufficient to describe both. When necessary, however, the term
"non-bladed portion of the rotor" or "rotor excluding the impeller"
may be used to specifically identify portions of the rotor other
than the blades. Each blade of the rotor may separately be referred
to as an impeller, however the term "impeller" is generally used to
refer to a collective set of one or more blades.
[0018] The pump is based upon a moving magnet axial flux gap motor
architecture. In one embodiment, the motor is a brushless DC motor.
Drive magnets 122 carried by the rotor have magnetic vectors
parallel to the rotor axis of rotation 190. In the illustrated
embodiment, the drive magnets are disposed within a non-bladed
portion of the rotor.
[0019] Drive windings 140 are located within the pump housing.
Power is applied to the drive windings to generate the appropriate
time-varying currents that interact with the drive magnets in order
to cause the impeller to rotate. A back iron 150 enhances the
magnetic flux produced by the motor rotor magnets. In one
embodiment, either the face 124 of the bottom of the rotor or the
opposing face 118 provided by the lower pump housing have surfaces
(e.g., 172) contoured to produce a hydrodynamic bearing when the
clearance between the rotor and the housing falls below a
pre-determined threshold. In one embodiment, the pre-determined
threshold is within a range of 0.0002 inches to 0.003 inches.
[0020] The natural attraction between the back iron 150 and the
drive magnets 122 carried by the rotor can create a significant
axial load on the rotor. This axial load is present in centrifugal
pumps based on an axial flux gap motor architecture such as Wampler
or Woodard. Woodard and Wampler both rely on hydrodynamic thrust
bearings to overcome this axial loading force. Despite the lack of
contact, hydrodynamic bearings can still damage blood cells as a
result of shear forces related to the load carried by the
hydrodynamic bearings.
[0021] The repulsive radial magnetic bearing of Wampler exacerbates
the axial loads created by the magnetic attraction between the
drive magnets and the back iron. Although the repulsive radial
magnetic bearing creates radial stability, it introduces
considerable axial instability. This axial instability can
contribute further to the axial loading. This additional axial
loading creates greater shear forces for any axial hydrodynamic
bearing that can cause undesirable hemolysis for blood
applications. In addition, the power required to sustain the
hydrodynamic bearing increases as the load increases. Thus highly
loaded hydrodynamic bearings can impose a significant power
penalty.
[0022] The blood pump of FIG. 1 includes a magnetic axial bearing
that serves to reduce or offset the axial load imposed on the rotor
by the interaction between the drive magnets and the back iron. The
axial magnetic bearing is formed by the interaction between a
spindle magnet assembly 160 disposed within the spindle and a rotor
magnet assembly 180 carried by the rotor. In the illustrated
embodiment, the rotor magnet assembly 180 is disposed proximate the
impeller, but the magnets of the rotor magnet assembly are not
located within the blades. A set screw 134 permits longitudinal
adjustment of the axial position of the axial magnetic bearing by
moving the spindle magnet assembly along a longitudinal axis of the
spindle.
[0023] FIG. 2 illustrates one embodiment of the axial magnetic
bearing. The rotor magnet assembly includes a first rotor bearing
magnet 282 and a second rotor bearing magnet 284 proximately
disposed to each other. The first and second rotor bearing magnets
are permanent magnets. In one embodiment, a pole piece 286 is
disposed between them. A pole piece or flux concentrator serves to
concentrate the magnetic flux produced by rotor bearing magnets 282
and 284. In an alternative embodiment, element 286 is merely a
spacer to aid in positioning the first and second bearing magnets
282, 284 and does not serve to concentrate any magnetic flux. In
other embodiments, element 286 is omitted so that the rotor magnet
assembly does not include a spacer or a pole piece element.
[0024] In one embodiment, elements 282 and 284 are monolithic,
ring-shaped permanent magnets. In alternative embodiments, the
bearing magnets may be non-monolithic compositions. For example, a
bearing magnet may be composed of a plurality of pie-shaped,
arcuate segment-shaped, or other-shaped permanent magnet elements
that collectively form a ring-shaped permanent magnet
structure.
[0025] The rotor axial bearing magnet assembly is distinct from the
drive magnets 222 carried by a portion of the rotor other than the
blades 221. In the illustrated embodiment, the drive magnets are
disposed within the non-bladed portion 228 of the rotor.
[0026] The spindle magnet assembly includes a first spindle bearing
magnet 262 and a second spindle bearing magnet 264. The first and
second spindle bearing magnets are permanent magnets. In one
embodiment, a pole piece 266 is disposed between them. Pole piece
266 concentrates the magnetic flux produced by the spindle bearing
magnets 262 and 264. In an alternative embodiment, element 266 is
merely a spacer for positioning the first and second spindle
bearing magnets and does not serve to concentrate any magnetic
flux. In other embodiments, element 266 is omitted so that the
spindle magnet assembly does not include a spacer or a pole piece
element.
[0027] In the illustrated embodiment, permanent magnets 262 and 264
are cylindrical. Other shapes may be utilized in alternative
embodiments. The ring-shaped rotor magnets rotate with the impeller
about a longitudinal axis of the spindle that is shared by the
spindle bearing magnet assembly.
[0028] The permanent magnets of each of the spindle and rotor
bearing assemblies are arranged such that the magnetic vectors of
the individual magnets on either side of the intervening pole
pieces oppose each other. Each side of a given pole piece is
adjacent the same pole of different magnets. Thus the magnetic
vectors of magnets 262 and 264 oppose each other (e.g., N-to-N or
S-to-S). Similarly, the magnetic vectors of magnets 282 and 284
oppose each other.
[0029] The orientation of the magnets is chosen to establish an
axial attraction whenever the bearings are axially misaligned. Note
that the relative orientations of the spindle and rotor magnet
assemblies are selected so that the spindle and rotor magnet
assemblies attract each other (e.g., S-to-N, N-to-S). The magnet
vector orientation selected for the magnets of one assembly
determines the magnetic vector orientation for the magnets of the
other assembly. Table 292 illustrates the acceptable magnetic
vector combinations for the first and second rotor bearing magnets
(MR1, MR2) and the first and second spindle bearing magnets (MS1,
MS2). Forces such as the magnetic attraction between the back iron
and drive magnets that tend to axially displace the magnet bearing
assemblies are offset at least in part by the magnetic attraction
between the axial bearings that provide an axial force to restore
the axial position of the rotor.
[0030] FIG. 2 also illustrates wedges or tapered surfaces 272 that
form a portion of a hydrodynamic bearing when the clearance between
a face of the non-bladed portion of the rotor (see, e.g., bottom
face 124 of FIG. 1) and the back of the pump housing falls below a
pre-determined threshold. In various embodiments, this
pre-determined threshold is within a range of 0.0002 inches to
0.003 inches. Thus in one embodiment, the pump includes an axial
hydrodynamic bearing. The surface geometry providing the axial
hydrodynamic bearing may be located on the rotor or the
housing.
[0031] Although the spindle magnet assembly is intended to provide
an axial magnetic bearing, the attractive force between the spindle
and rotor magnet assemblies also has a radial component. This
radial component may be utilized to offset radial loading of the
impeller due to the pressure gradient across the impeller. The
radial component also serves as a pre-load during initial rotation
and a bias during normal operation to prevent eccentric rotation of
the rotor about the spindle. Such an eccentric rotation can result
in fluid whirl or whip which is detrimental to the pumping action.
The biasing radial component helps to maintain or restore the
radial position of the rotor and the pumping action, for example,
when the pump is subjected to external forces as a result of
movement or impact.
[0032] Instead of a spindle magnet assembly interacting with a
rotor bearing magnet assembly to form the magnetic bearing, a
ferromagnetic material might be used in lieu of one of a) the
spindle magnet assembly, or b) the rotor bearing magnet assembly
(but not both) in alternative embodiments.
[0033] The magnetic bearing is still composed of a spindle portion
and a rotor portion, however, one of the spindle and the rotor
portions utilizes ferromagnetic material while the other portion
utilizes permanent magnets. The ferromagnetic material interacts
with the magnets to create a magnetic attraction between the rotor
and spindle. Examples of ferromagnetic materials includes iron,
nickel, and cobalt.
[0034] In one embodiment, the ferromagnetic material is "soft
iron". Soft iron is characterized in part by a very low coercivity.
Thus irrespective of its remanence or retentivity, soft iron is
readily magnetized (or re-magnetized) in the presence of an
external magnetic field such as those provided by the permanent
magnets of the magnetic bearing system.
[0035] FIG. 3 illustrates various locations for the placement of
the spindle portion of the magnetic bearing. In one embodiment, the
spindle magnet assembly 360 is axially aligned with a longitudinal
axis 390 of the spindle so that the spindle and spindle magnet
assembly share the same central longitudinal axis. In an
alternative embodiment, the spindle magnet assembly is radially
offset so that the spindle and spindle magnet assembly do not share
the same central axis. In particular, the longitudinal axis 362 of
the spindle magnet assembly 360 is displaced from the longitudinal
axis 390 of the spindle. This latter positioning may be desirable
to provide some radial biasing force. A difference in pressure
across the impeller tends to push the impeller radially towards one
side of the pump housing. This radial load may be offset at least
in part by offsetting the spindle magnet assembly.
[0036] Although the spindle and rotor magnet assemblies are
illustrated as comprising 2 magnetic elements each, the magnet
assemblies may each comprise a single magnet instead. A greater
spring rate may be achieved with multiple magnetic elements per
assembly configured as illustrated instead of a single magnet per
assembly. The use of two magnetic elements per assembly results in
a bearing that tends to correct bi-directional axial displacements
from a position of stability (i.e., displacements above and below
the point of stability) with a greater spring rate than single
magnetic elements per assembly.
[0037] The magnetic force generated by the axial magnetic bearing
will exhibit a radial component in addition to their axial
components. The radial component will tend to de-stabilize the
impeller. In particular, the radial component may introduce radial
position instability for the magnetic bearing of either FIG. 1 or
2.
[0038] This radial instability may be overcome using radial
hydrodynamic bearings. Referring to FIG. 1, the pump may be
designed for a radial hydrodynamic bearing (i.e., hydrodynamic
journal bearing) located between the spindle 130 and the rotor
along the bore of the rotor. The clearances illustrated in FIG. 1
are exaggerated. Hydrodynamic journal bearings require narrow
clearances to be effective. In various embodiments, the
hydrodynamic journal bearing clearances range from 0.0005-0.020
inches. The surface geometries suitable for axial (thrust) or
radial (journal) hydrodynamic bearings may be located on either the
rotor or on an associated portion of the housing (or spindle). In
one embodiment, the surface geometry includes features such as one
or more pads (i.e., a feature creating an abrupt change in
clearance such as a step of uniform height). In alternative
embodiments, the surface geometry includes features such as one or
more tapers.
[0039] FIG. 4 illustrates one embodiment of the rotor 400 including
an impeller. The impeller includes a plurality of blades 420 used
for pumping the working fluid such as blood. The rotor includes a
bore 410. The rotor bore is coaxially aligned with the longitudinal
axis of the spindle within the pump housing. Drive magnets (not
illustrated) are disposed within the non-bladed portion 430 of the
rotor (i.e., within the rotor but not within any blades of the
impeller portion of the rotor). The motor rotor and pump impeller
are thus integrated so that a drive shaft is not required.
Elimination of the drive shaft also permits elimination of shaft
seals for the pump.
[0040] In one embodiment, the rotor has a grooved bore. In
particular, the bore has one or more helical grooves 450. The bore
grooves have a non-zero axial pitch. The groove is in fluid
communication with the working fluid of the pump during operation
of the pump.
[0041] FIG. 5 illustrates the pump 510 operationally coupled to
move a working fluid 540 from a source 520 to a destination 530. A
first working fluid conduit 522 couples the source to the pump
inlet 514. A second working fluid conduit 532 couples the pump
outlet 516 to the destination. The working fluid is the fluid moved
by the pump from the source to the destination. In a medical
application, for example, the working fluid might be blood. In one
embodiment, the source and destination are arteries such that the
pump moves blood from one artery to another artery.
[0042] Various "contactless" bearing mechanisms have been described
as alternatives to mechanical contact bearings for rotary pumps. In
particular, rotor, impeller, and housing design features are
provided to achieve hydrodynamic or magnetic bearings. These design
features may be used in conjunction with each other, if
desired.
[0043] In the preceding detailed description, the invention is
described with reference to specific exemplary embodiments thereof.
Various modifications and changes may be made thereto without
departing from the broader spirit and scope of the invention as set
forth in the claims. The specification and drawings are,
accordingly, to be regarded in an illustrative rather than a
restrictive sense.
* * * * *