(12)
`
`United States Patent
`Watterson et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,227,797 B1
`May 8, 2001
`
`US006227797B1
`
`(54) ROTARY PUMP WITH
`HYDRODYNAMICALLY SUSPENDED
`
`7/1990 Bramm et al. .
`4,944,748
`5,055,005 * 10/1991 Kletschka ....................... .. 415/900 X
`
`IMPELLER
`
`5,195,877 * 3/1993 Kletschka . . . . . . . . . . . .
`
`. . . .. 415/900 X
`
`.
`.
`(75) Inventors‘ PGeteirfAmgeW lwaaters‘lm’ West Ryde’
`90 my 0g as ans 9y’
`Normanhurst> J01“! Campbell
`Woodard, Thorillelgh, all Of (AU)
`
`(73) Assigneer VeHtrASSiSi Pty Ltd and University Of
`Technology, Sydney (AU)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`{gatsmct EYES???) grajj‘slusted under 35
`
`5,322,413 * 6/1994 Vescovini et al. ..
`5,324,177 * 6/1994 Golding et al.
`5,326,344 * 7/1994 Bramm et al.
`5,470,208 * 11/1995 Kletschka
`5,685,700 * 11/1997 IZraelev ..... ..
`5,800,559 * 9/1998 Higham et al
`
`415/206 X
`415/900 X
`417/356 X
`415/900X
`415/900X
`..... .. 623/23
`
`5,924,848 * 7/1999 IZraelev . . . . . . .
`
`. . . .. 417/420
`
`415/206 X
`5,938,412 * 8/1999 IZraelev ............. ..
`415/900 X
`5,947,892 * 9/1999 Benkowski et al.
`415/900 X
`6,015,272 * 1/2000 Antaki et al.
`6,042,347 * 3/2000 Scholl et al. .................. .. 417/423.12
`FOREIGN PATENT DOCUMENTS
`
`(21) APPL No_: 09/281,608
`
`
`
`WO91/19103 WO94/13955
`
`
`
`12/1991 6/1994 (WO) .
`
`(22) Filed:
`
`Mar. 30, 1999
`
`* Cited by examiner
`
`Related US. Application Data
`
`P '' imary Examiner—]0hn E~ RYZniC
`(74) Attorney, Agent, or Firm—Knobbe, Martens, Olson &
`Bear, LLP
`
`(57)
`
`ABSTRACT
`
`This invention relates to rotary pumps adapted, but not
`exclusively, for use as arti?cial hearts or ventricular assist
`devices and, in particular, discloses in preferred forms a
`seal-less shaft-less pump featuring open or closed
`(shrouded) impeller blades With the edges of the blades used
`as hydrodynamic thrust bearing and With electromagnetic
`torque provided by the interaction betWeen magnets embed
`ded in the blades and a rotating current pattern generated in
`coils ?Xed relative to the pump housing.
`
`26 Claims, 19 Drawing Sheets
`
`(63) Continuation of application No. PCT/AU98/00725, ?led on
`S .18 1998.
`ep
`’
`(51) Int. Cl.7 ............................... .. F01D 3/00; B63H 1/26
`(52) US. Cl. ........................ .. 415/107, 415/900; 415/228;
`416/3; 416/228
`415/107 206
`416/3 2,23 R’
`’ 225; 234. 117/420’
`’
`’
`
`’
`
`’
`
`(58) Field of Search
`
`(56)
`
`References Cited
`
`Us PATENT DOCUMENTS
`
`5/1983 Isaacson.
`4,382,199
`4,688,998 * 8/1987 Olsen et al. ....................... .. 417/356
`
`Petitioners' Exhibit 1009, pg. 1
`
`

`

`US. Patent
`
`May 8, 2001
`
`Sheet 1 0f 19
`
`US 6,227,797 B1
`
`
`
`FIG. 1
`
`Petitioners' Exhibit 1009, pg. 2
`
`Petitioners' Exhibit 1009, pg. 2
`
`

`

`U.S. Patent
`US. Patent
`
`May 8,2001
`May 8, 2001
`
`Sheet 2 0f 19
`Sheet 2 0f 19
`
`US 6,227,797 B1
`US 6,227,797 B1
`
`
`
`FIG. 2
`
`Petitioners' Exhibit 1009, pg. 3
`
`Petitioners' Exhibit 1009, pg. 3
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 3 0f 19
`
`US 6,227,797 B1
`
`FIG. 3A
`
`FIG- 3C
`
`Petitioners' Exhibit 1009, pg. 4
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 4 0f 19
`
`US 6,227,797 B1
`
`14
`
`14
`
`FIG. 4A FIG. 43 FIG. 4C
`
`Petitioners' Exhibit 1009, pg. 5
`
`

`

`US. Patent
`
`Ma 8 2001
`
`Sheet 5 0f 19
`
`
`
`FIG. 5
`
`Petitioners' Exhibi00000000 . 6
`
`Petitioners' Exhibit 1009, pg. 6
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 6 0f 19
`
`US 6,227,797 B1
`
`
`
`Petitioners' Exhibit 1009, pg. 7
`
`

`

`U.S. Patent
`US. Patent
`
`May 8,2001
`May 8, 2001
`
`Sheet 7 0f 19
`Sheet 7 0f 19
`
`US 6,227,797 B1
`US 6,227,797 B1
`
`200
`
`Petitioners' Exhibit 1009, pg. 8
`
`Petitioners' Exhibit 1009, pg. 8
`
`

`

`US. Patent
`
`May 8, 2001
`
`Sheet 8 0f 19
`
`US 6,227,797 B1
`
`
`
`Petitioners' Exhibit 1009, pg. 9
`
`Petitioners' Exhibit 1009, pg. 9
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 9 0f 19
`
`US 6,227,797 B1
`
`200
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`200 \
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`
`Petitioners' Exhibit 1009, pg. 10
`
`

`

`U.S. Patent
`US. Patent
`
`May 8,2001
`May 8, 2001
`
`Sheet 10 0f 19
`Sheet 10 0f 19
`
`US 6,227,797 B1
`US 6,227,797 B1
`
`204
`
`
`
`Petitioners‘ Exhibit 1009, pg. 11
`
`Petitioners' Exhibit 1009, pg. 11
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 11 0f 19
`
`US 6,227,797 B1
`
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`
`Petitioners' Exhibit 1009, pg. 12
`
`

`

`U.S. Patent
`
`2 1
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`01,
`
`US 6,227,797 B1
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`Petitioners' Exhibit 1009, pg. 13
`
`

`

`US. Patent
`
`May 8, 2001
`
`Sheet 13 0f 19
`
`US 6,227,797 B1
`
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`Petitioners‘ Exhibit 1009, pg. 14
`
`Petitioners' Exhibit 1009, pg. 14
`
`
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 14 0f 19
`
`US 6,227,797 B1
`
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`
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`Petitioners' Exhibit 1009, pg. 15
`
`

`

`US. Patent
`
`May 8, 2001
`
`Sheet 15 0f 19
`
`US 6,227,797 B1
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`Petitioners‘ Exhibit 1009, pg. 16
`
`Petitioners' Exhibit 1009, pg. 16
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 16 0f 19
`
`US 6,227,797 B1
`
`Outflow
`
`13
`
`Impeller
`
`Concentric Volute
`
`FIG. 16
`
`Petitioners' Exhibit 1009, pg. 17
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 17 0f 19
`
`US 6,227,797 B1
`
`Split Vofute
`
`f2
`
`10B
`
`107
`
`109
`
`Impeller
`
`FIG. 17
`
`Petitioners' Exhibit 1009, pg. 18
`
`

`

`U.S. Patent
`
`May 8,2001
`
`Sheet 18 0f 19
`
`US 6,227,797 B1
`
`302
`
`301
`
`r“ 302
`
`301
`
`FIG. 18
`
`302
`
`306
`
`304\A
`
`309
`
`FIG. 19
`
`309
`
`307
`
`Petitioners' Exhibit 1009, pg. 19
`
`

`

`U.S. Patent
`US. Patent
`
`May 8,2001
`May 8, 2001
`
`Sheet 19 0f 19
`Sheet 19 0f 19
`
`US 6,227,797 B1
`US 6,227,797 B1
`
`‘5\\
`
`314
`
`314
`
`FIG. 20
`FIG. 20
`
`Petitioners‘ Exhibit 1009, pg. 20
`
`Petitioners' Exhibit 1009, pg. 20
`
`

`

`US 6,227,797 B1
`
`1
`ROTARY PUMP WITH
`HYDRODYNAMICALLY SUSPENDED
`IMPELLER
`
`This is a continuation application of PCT Application
`No. PCT/AU98/00725 filed Sep. 18, 1998.
`FIELD OF THE INVENTION
`
`This invention relates to rotary pumps adapted, but not
`exclusively, for use as artificial hearts or ventricular assist
`devices and,
`in particular, discloses in preferred forms a
`seal-less shaft-less pump featuring open or closed
`(shrouded) impeller blades with the edges of the blades used
`as hydrodynamic thrust bearings and with electromagnetic
`torque provided by the interaction between magnets embed-
`ded in the blades and a rotating current pattern generated in
`coils fixed relative to the pump housing.
`BACKGROUND ART
`
`This invention relates to the art of continuous or pulsatile
`flow rotary pumps and, in particular, to electrically driven
`pumps suitable for use although not exclusively as an
`artificial heart or ventricular assist device. For permanent
`implantation in a human patient, such pumps should ideally
`have the following characteristics: no leakage of fluids into
`or from the bloodstream; parts exposed to minimal or no
`wear; minimum residence time of blood in pump to avoid
`thrombosis (clotting); minimum shear stress on blood to
`avoid blood cell damage such as haemolysis; maximum
`efficiency to maximise battery duration and minimise blood
`heating; and absolute reliability.
`Several of these characteristics are very difficult to meet
`in a conventional pump configuration including a seal, i.e.
`with an impeller mounted on a shaft which penetrates a wall
`of the pumping cavity, as exemplified by the blood pumps
`referred to in US. Pat. No. 3,957,389 to Rafferty et al., US.
`Pat. No. 4,625,712 to Wampler, and US. Pat. No. 5,275,580
`to Yamazaki. Two main disadvantages of such pumps are
`firstly that the seal needed on the shaft may leak, especially
`after wear, and secondly that the rotor of the motor providing
`the shaft torque remains to be supported, with mechanical
`bearings such as ball-bearings precluded due to wear. Some
`designs, such as US. Pat. No. 4,625,712 to Wampler and
`US. Pat. No. 4,908,012 to Moise et al., have overcome these
`problems simultaneously by combining the seal and the
`bearing into one hydrodynamic bearing, but in order to
`prevent long residence times they have had to introduce
`means to continuously supply a blood-compatible bearing
`purge fluid via a percutaneous tube.
`In seal-less designs, blood is permitted to flow through the
`gap in the motor, which is usually of the brushless DC type,
`i.e. comprising a rotor including permanent magnets and a
`stator in which an electric current pattern is made to rotate
`synchronously with the rotor. Such designs can be classified
`according to the means by which the rotor is suspended:
`contact bearings, magnetic bearings or hydrodynamic
`bearings, though some designs use two of these means.
`Contact or pivot bearings, as exemplified by US. Pat. No.
`5527159 to Bozeman et al. and US. Pat. No. 5,399,074 to
`Nose et al., have potential problems due to wear, and cause
`very high localised heating and shearing of the blood, which
`can cause deposition and denaturation of plasma proteins,
`with the risk of embolisation and bearing seizure.
`Magnetic bearings, as exemplified by US. Pat. No. 5,350,
`283 to Nakazeki et al., US. Pat. No. 5,326,344 to Bramm et
`al. and US. Pat. No. 4,779,614 to Moise et al., offer
`
`2
`contactless suspension, but require rotor position measure-
`ment and active control of electric current for stabilisation of
`
`the position in at least one direction, according to Earn-
`shaw’s theorem. Position measurement and feedback control
`
`introduce significant complexity, increasing the failure risk.
`Power use by the control current implies reduced overall
`efficiency. Furthermore, size, mass, component count and
`cost are all increased.
`
`US. Pat. No. 5,507,629 to Jarvik claims to have found a
`configuration circumventing Earnshaw’s Theorem and thus
`requiring only passive magnetic bearings, but this is doubt-
`ful and contact axial bearings are included in any case.
`Similarly, passive radial magnetic bearings and a pivot point
`are employed in US. Pat. No. 5,443,503 to Yamane.
`Prior to the present invention, pumps employing hydro-
`dynamic suspension, such as U.S. Pat. No. 5,211,546 to
`Isaacson et al. and US. Pat. No. 5,324,177 to Golding et al.,
`have used journal bearings, in which radial suspension is
`provided by the fluid motion between two cylinders in
`relative rotation, an inner cylinder lying within and slightly
`off axis to a slightly larger diameter outer cylinder. Axial
`suspension is provided magnetically in US. Pat. No. 5,324,
`177 and by either a contact bearing or a hydrodynamic thrust
`bearing in US. Pat. No. 5,211,546.
`A purging flow is needed through the journal bearing, a
`high shear region, in order to remove dissipated heat and to
`prevent long fluid residence time. It would be inefficient to
`pass all the fluid through the bearing gap, of small cross-
`sectional area, as this would demand an excessive pressure
`drop across the bearing. Instead a leakage path is generally
`provided from the high pressure pump outlet, through the
`bearings and back to the low pressure pump inlet, implying
`a small reduction in outflow and pumping efficiency. US.
`Pat. No. 5,324,177 provides a combination of additional
`means to increase the purge flow, namely helical grooves in
`one of the bearing surfaces, and a small additional set of
`impellers.
`US. Pat. No. 5,211,546 provides 10 embodiments with
`various locations of cylindrical bearing surfaces. One of
`these embodiments,
`the third,
`features a single journal
`bearing and a contact axial bearing.
`Embodiments of the present invention offer a relatively
`low cost and/or relatively low complexity means of sus-
`pending the rotor of a seal-less blood pump, thereby over-
`coming or ameliorating the problems of existing devices
`mentioned above.
`
`SUMMARY OF THE INVENTION
`
`According to one aspect of the present invention, there is
`disclosed a rotary blood pump with impeller suspended
`hydrodynamically by thrust forces generated on the edges of
`the impeller blades. The blade edges are shaped such that the
`gap between the edges and the housing at the leading edge
`is greater than at the trailing edge and thus the fluid which
`is drawn through the gap experiences a wedge shaped
`restriction which generates a thrust away from the housing,
`as described in Reynold’s theory of lubrication.
`In preferred embodiments of the invention, the pump is of
`centrifugal or mixed flow type with impeller blades open on
`both the front and back faces of the housing. At least one
`face of the housing is made conical, in order that the thrust
`perpendicular to it has a radial component, which provides
`a radial restoring force to a radial displacement of the
`impeller axis. Similarly, an axial displacement toward either
`the front or the back face increases the thrust from that face
`and reduces the thrust from the other face. Thus the sum of
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Petitioners‘ Exhibit 1009, pg. 21
`
`Petitioners' Exhibit 1009, pg. 21
`
`

`

`US 6,227,797 B1
`
`3
`
`the forces on the impeller due to inertia (within limits),
`gravity and any bulk radial or axial hydrodynamic force on
`the impeller can be countered by a restoring force from the
`thrust bearings after a small displacement of the impeller
`within the housing relative to the housing in either a radial
`or axial direction.
`
`In the preferred embodiment, the impeller driving torque
`derives from the magnetic interaction between permanent
`magnets within the blades of the impeller and oscillating
`currents in windings encapsulated in the pump housing.
`In a second embodiment of the invention, the principle is
`applied in a pump of axial type. Within a uniform cylindrical
`section of the pump housing, tapered blade edges form a
`radial hydrodynamic bearing. If the pump housing is made
`with reducing radius at the two ends, then the end hydro-
`dynamic thrust forces have an axial component which can
`provide the axial bearing. Alternatively, magnetic forces or
`other means can provide the axial bearing.
`In a further broad form of the invention there is provided
`a rotary blood pump having an impeller suspended hydro-
`dynamically by thrust forces generated by the impeller
`during movement in use of the impeller.
`Preferably said thrust forces are generated by blades of
`said impeller or by deformities therein.
`More preferably said thrust forces are generated by edges
`of said blades of said impeller.
`Preferably said edges of said blades are tapered.
`In an alternative preferred form said pump is of axial type.
`Preferably within a uniform cylindrical section of the
`pump housing, tapered blade edges form a radial hydrody-
`namic bearing.
`Preferably the pump housing is made with reducing radius
`at the two ends, and wherein the end hydrodynamic thrust
`forces have an axial component which can provide the axial
`bearing.
`Preferably or alternatively magnetic forces or other means
`can provide the axial bearing.
`In a further broad form of the invention there is provided
`a rotary blood pump having a housing within which an
`impeller acts by rotation about an axis to cause a pressure
`differential between an inlet side of a housing of said pump
`and an outlet side of the housing of said pump; said impeller
`suspended hydrodynamically by thrust forces generated by
`the impeller during movement in use of the impeller.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`invention will now be
`Embodiments of the present
`described, with reference to the accompanying drawings,
`wherein:
`
`50
`
`FIG. 1 is a longitudinal cross-sectional view of a preferred
`embodiment of the invention;
`FIG. 2 is a cross-sectional view taken generally along the
`line Z—Z of FIG. 1;
`FIG. 3A is a cross-sectional view of an impeller blade
`taken generally along the line A—A of FIG. 2;
`FIG. 3B is an enlargement of the blade-pump housing
`interface portion of FIG. 3A;
`FIG. 3C is an alternative impeller blade shape;
`FIGS. 4A, 4B and 4C illustrate various possible locations
`of magnet material within a blade;
`FIG. 5 is a left-hand end view of a possible winding
`geometry taken generally along the line 8—8 of FIG. 1;
`FIG. 6 is a diagrammatic cross-sectional view of an
`alternative embodiment of the invention as an axial pump;
`
`55
`
`60
`
`65
`
`4
`FIG. 7 is an exploded, perspective view of a centrifugal
`pump assembly according to a further embodiment of the
`invention;
`FIG. 8 is a perspective view of the impeller of the
`assembly of FIG. 7;
`FIG. 9 is a perspective, cut away view of the impeller of
`FIG. 8 within the pump assembly of FIG. 7;
`FIG. 10 is a side section indicative view of the impeller
`of FIG. 8;
`FIG. 11 is a detailed view in side section of edge portions
`of the impeller of FIG. 10;
`FIG. 12 is a block diagram of an electronic driver circuit
`for the pump assembly of FIG. 7;
`FIG. 13 is a graph of head versus flow for the pump
`assembly of FIG. 7;
`FIG. 14 is a graph of pump efficiency versus flow for the
`pump assembly of FIG. 7;
`FIG. 15 is a graph of electrical power consumption versus
`flow for the pump assembly of FIG. 7;
`FIG. 16 is a plan, section view of the pump assembly
`showing a volute arrangement according to a preferred
`embodiment;
`FIG. 17 is a plan, section view of a pump assembly
`showing an alternative volute arrangement;
`FIG. 18 is a plan view of an impeller according to a
`further embodiment of the invention;
`FIG. 19 is a plan view of an impeller according to a
`further embodiment of the invention;
`FIG. 20 is a perspective view of an impeller according to
`a further embodiment of the invention.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`The pump assemblies according to various preferred
`embodiments to be described below all have particular,
`although not exclusive, application for implantation in a
`mammalian body so as to at least assist, if not take over, the
`function of the mammalian heart. In practice this is per-
`formed by placing the pump assembly entirely within the
`body of the mammal and connecting the pump between the
`left ventricle and the aorta so as to assist left side heart
`
`function. It may also be connected to the right ventricle and
`pulmonary artery to assist the right side of the heart.
`In this instance the pump assembly includes an impeller
`which is fully sealed within the pump body and so does not
`require a shaft extending through the pump body to support
`it. The impeller is suspended, in use, within the pump body
`by, at least, the operation of hydrodynamic forces imparted
`as a result of the interaction between the rotating impeller,
`the internal pump walls and the fluid which the impeller
`causes to be urged from an inlet of the pump assembly to an
`outlet thereof.
`
`Apreferred embodiment of the invention is the centrifugal
`pump 1, as depicted in FIGS. 1 and 2, intended for implan-
`tation into a human body, in which case the fluid referred to
`below is blood. The pump housing 2, can be fabricated in
`two parts, a front part 3 in the form of a housing body and
`a back part 4 in the form of a housing cover, with a smooth
`join therebetween, for example at 5 in FIG. 1. The pump 1
`has an axial inlet 6 and a tangential outlet 7. The rotating part
`or impeller 100 is of very simple form, comprising only
`blades 8 and a blade support 9 to hold those blades fixed
`relative to each other. The blades may be curved as depicted
`in FIG. 2, or straight, in which case they can be either radial
`
`Petitioners‘ Exhibit 1009, pg. 22
`
`Petitioners' Exhibit 1009, pg. 22
`
`

`

`US 6,227,797 B1
`
`5
`or tilted, i.e. at an angle to the radius. This rotating part 100
`will hereafter be called the impeller 100, but it also serves
`as a bearing component and as the rotor of a motor con-
`figuration as to be further described below whereby a torque
`is applied by electromagnetic means to the impeller 100.
`Note that the impeller has no shaft and that the fluid enters
`the impeller from the region of its axis RR. Some of the fluid
`passes in front of the support cone 9 and some behind it, so
`that the pump 1 can be considered of two-sided open type,
`as compared to conventional open centrifugal pumps, which
`are only open on the front side. Approximate dimensions
`found adequate for the pump 1 to perform as a ventricular
`assist device, when operating at speeds in the range 2,000
`rpm to 4,000 rpm, are outer blade diameter 40 mm, outer
`housing average diameter 60 mm, and housing axial length
`40 mm.
`
`As the blades 8 move within the housing, some of the fluid
`passes through the gaps, much exaggerated in FIGS. 1 and
`3, between the blade edges 101 and the housing front face
`10 and housing back face 11. In all open centrifugal pumps,
`the gaps are made small because this leakage flow lowers the
`pump hydrodynamic efficiency. In the pump disclosed in this
`embodiment,
`the gaps are made slightly smaller than is
`conventional in order that the leakage flow can be utilised to
`create a hydrodynamic bearing. For the hydrodynamic
`forces to be sufficient, the blades must also be tapered as
`depicted in FIGS. 3A and 3B, so that the gap 104 is larger
`at the leading edge 102 of the blade 8 than at the trailing
`edge 103. The fluid 105 which passes through the gap thus
`experiences a wedge shaped restriction which generates a
`thrust, as described in Reynolds’ theory of lubrication (see,
`for example, “Modern Fluid Dynamics, Vol. 1 Incompress-
`ible Flow”, by N. Curle and H. J. Davies, Van Nostrand,
`1968). The thrust is proportional to the square of the blade
`thickness at the edge, and thus thick blades are favoured,
`since if the proportion of the pump cavity filled by blades is
`constant, then the net thrust force will be inversely propor-
`tional to the number of blades. However, the blade edges can
`be made to extend as tails from thin blades as depicted in
`FIG. 3C in order to increase the blade area adjacent the
`walls.
`
`In one particular form, the tails join adjacent blades so as
`to form a complete shroud with wedges or tapers incorpo-
`rated therein. An example of a shroud design as well as other
`variations on the blade structure will be described later in
`
`this specification.
`For manufacturing simplicity, the housing front face 10
`can be made conical, with an angle of around 450 so that it
`provides both axial and radial hydrodynamic forces. Other
`angles are suitable that achieve the functional requirements
`of this pump including the requirements for both axial and
`radial hydrodynamic forces.
`Other curved surfaces are possible provided both axial
`and radial hydrodynamic forces can be produced as a result
`of rotation of the blades relative to the housing surfaces.
`The housing back face 11 can include a roughly conical
`extension 12 pointing into the pump cavity 106, to eliminate
`or minimise the effect of the flow stagnation point on the
`axis of the back housing.
`Alternatively extension 12 can resemble an impeller eye
`to make the flow mixed.
`
`In this preferred embodiment, for manufacturing simplic-
`ity and for uniformity in the flow axial direction RR, the
`housing back face 11 is made flat over the bearing surfaces,
`i.e. under the blade edges. With this the case, a slacker
`tolerance on the alignment between the axes of the front part
`
`6
`3 and back part 4 of the housing 2 is permissible. An
`alternative is to make the back face 11 conical at the bearing
`surfaces, with taper in the opposite direction to the front face
`10, so that the hydrodynamic forces from the back face will
`also have radial components. Tighter tolerance on the axes
`alignment would then be required, and some of the flow
`would have to undergo a reversal in its axial direction. Again
`a roughly conical extension (like 12) will be needed. There
`may be some advantage in making the housing surfaces and
`blade edges non-straight, with varying tangent angle,
`although this will impose greater manufacturing complexity.
`There are several options for the shape of the taper, but in
`the preferred embodiment the amount of material removed
`simply varies linearly or approximately linearly across the
`blade. For the back face, the resulting blade edges are then
`planes at a slight inclination to the back face. For the front
`face, the initial blade edges are curved and the taper only
`removes a relatively small amount of material so they still
`appear curved. Alternative taper shapes can include a step in
`the blade edge, though the corner in that step would repre-
`sent a stagnation line posing a thrombosis risk.
`For a given minimum gap, at the trailing blade edge, the
`hydrodynamic force is maximal if the gap at the leading
`edge is approximately double that at the trailing edge. Thus
`the taper, which equals the leading edge gap minus the
`trailing edge gap, should be chosen to match a nominal
`minimum gap, once the impeller has shifted towards that
`edge. Dimensions which have been found to give adequate
`thrust forces are a tape r of around 0.05 mm for a nominal
`minimum gap of around 0.05 mm, and an average circum-
`ferential blade edge thickness of around 5 mm for 4 blades.
`For the front face, the taper is measured within the plane
`perpendicular to the axis. The axial length of the housing
`between the front and back faces at any position should then
`be made about 0.2 mm greater than the axial length of the
`blade, when it
`is coaxial with the housing, so that
`the
`minimum gaps are both about 0.1 mm axially when the
`impeller 100 is centrally positioned within the housing 2.
`Then, for example, if the impeller shifts axially by 0.05 mm,
`the minimum gaps will be 0.05 mm at one face and 0.15 mm
`at the other face. The thrust increases with decreasing gap
`and would be much larger from the 0.05 mm gap than from
`the 0.15 mm gap, about 14 times larger for the above
`dimensions. Thus there is a net restoring force away from the
`smaller gap.
`for radial shifts of the impeller the radial
`Similarly,
`component of the thrust from the smaller gap on the conical
`housing front face would offer the required restoring radial
`force. The axial component of that force and its torque on the
`impeller would have to be balanced by an axial force and
`torque from the housing back face, and so the impeller will
`also have to shift axially and tilt its axis to be no longer
`parallel with the housing axis. Thus as the person moves and
`the pump is accelerated by external forces, the impeller will
`continually shift its position and alignment, varying the gaps
`in such a way that the total force and torque on the impeller
`100 match that demanded by inertia. The gaps are so small,
`however, that the variation in hydrodynamic efficiency will
`be small, and the pumping action of the blades will be
`approximately the same as when the impeller is centrally
`located.
`
`While smaller gaps imply greater hydrodynamic effi-
`ciency and greater bearing thrust forces, smaller gaps also
`demand tighter manufacturing tolerances, increase frictional
`drag on the impeller, and impose greater shear stress an the
`fluid. Taking these points in turn, for the above 0.05 mm
`tapers and gaps,
`tolerances of around 10.015 mm are
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`Petitioners‘ Exhibit 1009, pg. 23
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`Petitioners' Exhibit 1009, pg. 23
`
`

`

`US 6,227,797 B1
`
`7
`needed, which imposes some cost penalty but is achievable.
`A tighter tolerance is difficult, especially if the housing is
`made of a plastic, given the changes in dimension caused by
`temperature and possible absorption of fluid by plastic. The
`frictional drag for the above gaps produces much smaller
`torque than the typical motor torque. Finally, to estimate the
`shear stress, consider a rotation speed of 3,000 rpm and a
`typical radius of 15 mm, at which the blade speed is 4.7 ms"1
`and the average velocity shear for an average gap of 0.075
`mm is 6.2><104 s'l. For blood of dynamic viscosity 3.5><10'3
`kgm'ls'l, the average shear stress would be 220 Nm'z.
`Other prototype centrifugal blood pumps with closed blades
`have found that slightly larger gaps, e.g. 0.15 mm, are
`acceptable for haemolysis. A major advantage of the open
`blades of the present invention is that a fluid element that
`does pass through a blade edge gap will have very short
`residence time in that gap, around 2x10"3 S, and the fluid
`element will most likely be swept though the pump without
`passing another blade edge.
`To minimise the net force required of the hydrodynamic
`bearings, the net axial and radial hydrodynamic forces on the
`impeller from the bulk fluid flow should be minimised,
`where “bulk” here means other than from the bearing thrust
`surfaces.
`
`One method of minimising the bulk radial hydrodynamic
`force is to use straight radial blades so that pressure acting
`on the blade sides has virtually no radial component. The
`radial force on the impeller depends critically on the shape
`of the output flow collector or volute 13. The shape should
`be designed to minimise the radial impeller force over the
`desired range of pump speeds, without excessively lowering
`the pump efficiency. The optimal shape will have a roughly
`helical perimeter between the “cut water” and outlet. The
`radial force can also be reduced by the introduction of an
`internal division in the volute 13 to create a second output
`flow collector passage, with tongue approximately diametri-
`cally opposite to the tongue of the first passage.
`An indicative plan view of impeller 100 relative to
`housing 2 is shown in FIG. 2 having a concentric volute 13.
`FIG. 17 illustrates the alternative volute arrangement
`comprising a split volute created by volute barrier 107 which
`causes volute 108 in a first hemisphere of the housing 2 to
`split into first half volute 109 and second half volute 110
`over the second hemisphere. The hemispheres are defined
`respectively on each side of a diameter of the housing 2
`which passes through or near exit point 111 of outlet 7.
`In alternative forms concentric volutes can be utilised,
`particularly where specific speed is relatively low.
`In a further particular form a vaneless diffuser may also
`reduce the radial force.
`
`In regard to the bulk axial hydrodynamic axial force, if the
`blade cross-section is made uniform in the axial direction
`
`along the relational axis, apart from the conical front edge,
`then the pressure acting on the blade surface (excluding the
`bearing edges) will have no axial component. This also
`simplifies the blade manufacture. The blade support cone 9
`must then be shaped to minimise axial thrust on the impeller
`and minimise disturbance to the flow over the range of
`speeds, while maintaining sufficient strength to prevent
`relative blade movement. The key design parameter affect-
`ing the axial force is the angle of the cone. The cone is drawn
`in FIG. 1 as having the same internal diameter as the blades,
`which may aid manufacture. However, the cone could be
`made with larger or smaller internal diameter to the blades.
`There may be advantage in using a non-axisymmetric sup-
`port “cone”, e.g. with larger radius on the trailing surface of
`
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`8
`a blade than the radius at the leading surface of the next
`blade. If the blades are made with non-uniform cross-section
`
`to increase hydrodynamic efficiency, then any bulk hydro-
`dynamic axial force on them can be balanced by shaping the
`support cone to produce an opposite bulk hydrodynamic
`axial force on it.
`
`Careful design of the entire pump, employing computa-
`tional fluid dynamics, is necessary to determine the optimal
`shapes of the blades 8, the volute 13, the support cone 9 and
`the housing 2, in order to maximise hydrodynamic efficiency
`while keeping the bulk fluid hydrodynamic forces, shear and
`residence times low. All edges and the joins between the
`blades and the support cone should be smoothed.
`The means of providing the driving torque on the impeller
`100 of the preferred embodiment of the invention is to
`encapsulate permanent magnets 14 in the blades 8 of the
`impeller 100 and to drive them with a rotating magnetic field
`pattern from oscillating currents in windings 15 and 16,
`fixed relative to the housing 2. Magnets of high remanence
`such as sintered rare-earth magnets should be used to
`maximise motor efficiency. The magnets should be aligned
`axially or approximately axially, with alternating polarity for
`adjacent blades. Thus there must be an even number of
`blades. Since low blade number is preferred for the bearing
`force, and since two blades would not have sufficient bearing
`stiffness to rotation about an axis through the bl