WO2004098677A1

WO2004098677A1 - Fluid pump

Info

Publication number: WO2004098677A1
Application number: PCT/AU2004/000600
Authority: WO
Inventors: Daniel Lee Timms
Original assignee: Queensland University Of Technology
Priority date: 2003-05-09
Filing date: 2004-05-07
Publication date: 2004-11-18
Also published as: AU2003902255A0; JP2006525460A

Abstract

The present invention provides a fluid pump including a housing defining a cavity. The cavity includes at least one fluid inlet and outlet, and at least one set of coils for generating a magnetic field. In use, an impeller (3) is positioned in the cavity, which includes a body, a number of vanes (4A, 4B) positioned on the body for urging fluid from the inlet to the outlet, and a number of driver magnets (9). In use, the impeller is suspended within the cavity using an axial coupling and rotated by generating a field using the coils.

Description

FLUID PUMP

Background of the Invention

The present invention relates to a motor, and in particular a fluid pump using an impeller which is suitable for use as a heart assist or heart replacement device, such as an LVAD (left-ventricular device) or BiVAD (Bi-ventricular device).

Description of the Prior Art

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art forms part of the common general knowledge. High speed and maintenance free motors are required for high quality and high productivity machines. Due ^' to their non-contact support, magnetic bearings have been gradually introduced into these machines. However, initial magnetic bearing systems required a separate driving motor. Therefore, when applying this technology to fluid pumps, a seal is required to prevent fluid contacting the driving motor. To overcome this problem, self-bearing motors have been developed. Self bearing motors create magnetic fields that act to suspend and rotate the rotor, thus allowing the capacity for bearing and motor functions from either the same set of coils, or two coil sets occupying the same circumferential location. A number of magnetic principles can achieve this goal, based on so called Reluctance and Lorentz theories. When applied to centrifugal pump technology, self bearing motors eliminate the need for a shaft or seal, as the rotor is completely encapsulated within the pump cavity.

This is particularly relevant in the area of heart transplant surgery, which was developed as a sophisticated response to the problem of life threatening damage to the human heart.

However, with an increasing average age of the general population, the absolute numbers of severe cardiac malfunction are increasing, providing a large number of patients who are candidates for heart transplant surgery. Unfortunately, the availability of suitable replacement organs has always been limited and is becoming increasingly inadequate for general application to patients at serious risk of death from cardiac causes.

One alternative response to the shortage of available heart donors has resulted in various attempts to develop artificial pumps to augment the action of a patient's heart or, ideally, to be suitable for entirely replacing an incompetent heart.

One of the challenges of providing an effective form of such a pump is the need to efficiently harness an available power supply. Given the critical need for such a pump to reliably operate without cessation, it is necessary to supply peak efficiency in the use of a power source. To function other than as an experimental prototype, such a pump must provide a patient with the option to remove themselves from a refuelling or recharging device for considerable periods of time.

Pumps should also minimise the damaging effect of the pumping mechanism on the cells of the blood. Any pump segment generating excessive shear stress will result in traumatic blood cell lyses in that region. Additionally, segments promoting blood stagnation can result in dangerous clots forming within the pump, which can dislodge and travel through the body, potentially blocking vital arteries within the peripheral circulation.

One of the major points of energy loss and blood trauma arises in relation to the method of rotation of a pump rotor or impeller. The use of conventional bearings to support a rotor may lead to increased power consumption and device lifetime issues relating to frictional resistance and consequently wear respectively. Furthermore, this technique promotes blood cell trauma due to excessive heat generation and high shear stress at the contacting bearing site, coupled with stagnation around the rotating shaft. This requires the need for maintenance procedures to eliminate these adverse affects. Various attempts have been made to provide magnetic or hydrodynamic suspension of a pump rotor or impeller to provide a frictionless and seal-less bearing.

US Patent No. 6,609,883 entitled "Rotary Pump with Hydrodynamically Suspended Impeller" describes a seal-less, shaft-less pump featuring open or closed impeller blades with their edges used as hydrodynamic thrust bearings. Rotational torque is provided by the interaction between magnets embedded in the blades and a rotating electromagnetic field generated in coils fixed to the pump housing.

Hydrodynamics bearings require relatively small clearances to provide sufficient bearing force. High shear stress is found in such clearances and is a possible site of haemolysis should blood cells enter this region. Hydrodynamic bearings rely on a passive response to forces imposed on the impeller, that is bearing stiffness cannot be altered for a given condition. Should forces exceed the predetermined bearing stiffness, touchdown is imminent. Additionally, rotors suspended hydrodynamically generate bearing force stiffness in direct proportion to rotor rotational speed. Ventricular assist devices have the potential to collapse the ventricle wall and thus block the inlet canula to the pump when excessive flow is demanded by the circulation system. To prevent this affliction, the rotational speed of the pump must be reduced for a period of time to allow the ventricular wall to detach, a situation not afforded to pumps suspended via hydrodynamic bearings, since a reduction in rotational speed results in reduced bearing stiffness and potential impeller touchdown.

In light of the potential difficulties, of passive hydrodynamic suspension techniques, other configurations centred on magnetic bearing technology to control the position of the rotor within the pumping cavity, have been proposed, as shown for example if US Patent No. 5,326,344 and International Publication No. WO 99/01663.

US Patent No. 5,326,344 entitled "Magnetically Suspended and Rotated Rotor" describes an impeller for a blood pump which is supported by permanent magnets located in the impeller and pump housing respectively and stabilised by an electromagnet on the housing. The configuration of the magnetic suspension system lends itself to low efficiency due to relatively large magnetic "Air Gaps". That is, the distance from rotor magnets to housing magnets is relatively large resulting in excess magnetic flux leakage and thus poor efficiency. Additionally, the magnetic suspension system is separated from the drive mechanism leading to increased size and electronics to provide both functions independently. International Publication No. WO 99/01663 describes an improved rotor for a blood pump which relies on positioning of an impeller to give dynamic balance which is achieved through a combination of hydrodynamic and buoyant forces. The rotor is driven electromagnetically by means of an electromagnetic drive system operating in conjunction with one or more arrays of permanent magnets. The permanent magnets may be enclosed within radial vanes on the surface of the rotor with the drive components being arranged in a brushless motor configuration. In this device rotational movement of the rotor may occur around an axis which varies relative to the pump housing.

The arrangement was provided to attempt to eliminate the need for highly precise axis control and design fabrication. Part of the problem addressed is the need to avoid the introduction of large forces which otherwise are created when the axis of the rotor shifts away from its normally centrally disposed position in a magnetic levitation system. The rotor is fashioned around an internal bore for accommodating inlet fluid and it is provided with a series of external shrouds providing multiple annular flow channels. This arrangement provides a larger surface area to contact blood during normal pumping operation. Erythrocyte fragility becomes a very relevant concern in such a device as shear force and frictional force interaction between the moving components and the blood volume may tend to lysis of red blood cells.

In addition to this, most of the centrifugal heart pumps used for left ventricular assistance to date, feature a conventional single sided impeller. That is, a rotating impeller with one set of vanes used to urge blood from one inlet to one outlet. However, this technique can result in stagnation zones beneath the impeller, as well as unbalanced hydraulic forces experienced by the impeller which must be countered by forces generated from the suspension technique, thus leading to increased bearing power requirements and an overall loss of efficiency. Placement of magnetic material within the rotor required for suspension and/or drive is limited due to the miniature rotor size. By employing the use of a double sided impeller, axial hydraulic forces are balance to a greater degree and potential stagnation zones are eliminated. Furthermore, when these pumps are used to address the application of Bi-ventricular assistance, a current technique is to implant and operate two separate pumps, thus resulting in increased implantation size as well as increased control complexity arising from the need to control two independent pumps for left and right heart assistance. Attempts to create a single rotary centrifugal device BiVAD are troubled by difficulties in altering the output flow of each cavity independently, since the impeller has a common rotational speed, as well as preventing leakage from the high pressure left cavity to the low pressure right cavity.

Summary of the Present Invention

In a first broad form the present invention provides a fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the magnetic field in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity; d) a radial bearing for controlling the position of the impeller in a direction orthogonal to the cavity axis; e) an axial coupling for controlling the position of the impeller in a direction parallel to the cavity axis; and, f) a controller coupled to the sensors and the first and second sets of coils, wherein in use the controller to control the magnetic field to thereby control rotation of the impeller about the impeller axis.

The axial coupling may include: a) a second set of coils for generating a second magnetic field; and, b) a number of axial support magnets provided in the body and positioned in the second magnetic field in use, wherein the controller controls the second magnetic field to thereby control movement of the impeller in a direction parallel to the cavity axis. The axial coupling may include the first set of coils and a number of axial support magnets provided in the body and positioned in the magnetic field in use, wherein the controller controls the magnetic field to thereby control movement of the impeller in a direction parallel to the cavity axis.

The axial coupling may include at least one of: a) a set of magnets coupled to the housing to generate an axial control field; and b) a number of axial support magnets provided in the body and positioned in the axial control magnetic field in use to thereby restrict movement of the impeller in a direction parallel to the cavity axis.

The axial support magnets can be the driver magnets. The axial coupling may include: a) a first bearing member coupled to the housing; and, b) a second bearing member coupled to the impeller, the first and second bearing members cooperating to thereby restrict movement of the impeller in a direction parallel to the cavity axis. The radial bearing may include : a) an inner surface of the housing; and, b) at least a portion of an outer surface of the impeller, the outer surface portion being shaped so as to cooperate with the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis.

The radial bearing may include a second set of coils for generating a second magnetic field, wherein the controller controls the third magnetic field using signals from the sensors to thereby control movement of the impeller orthogonal to the cavity axis.

The fluid pump typically includes at least one sensor positioned at a first end of the cavity and at least two sensors positioned at a second opposing end of the cavity.

The dimensions of the vanes are typically selected to control at least one of the fluid pressure and the flow rate at the outlet.

The dimensions may include at least one of: a) The height of the vanes; b) The diameters of the impellers; c) The length of the vanes; d) The width of the vanes; e) The inlet and outlet vane angles; f) The shape of the vanes; and, g) The number of vanes .

Typically: a) the housing includes: i) at least two fluid inlets; and, ii) at least two fluid outlets; and, b) the impeller includes: i) at least two body portions; and, ii) first and second sets of vanes positioned on the first and second body portions respectively, each set of vanes being for urging fluid from a respective inlet to a respective outlet, in use.

The impeller preferably cooperates with the cavity to define first and second cavity portions, each cavity portion including a respective inlet, outlet, and the impeller and cavity being configured to substantially prevent fluid transfer between the cavity portions.

The first and second sets of vanes may each have substantially identical dimensions to thereby provide fluid at substantially equal pressures and flow rates at the outlets.

The first and second sets of vanes may each have respective different dimensions to thereby provide fluid at respective first and second pressures at the respective outlet.

The first outlet may be coupled to the second inlet.

The cavity can be substantially rotational symmetric around the cavity axis will, with the coils being arranged circumferentially spaced around the cavity.

The body may be substantially rotational symmetric around the impeller axis, the driver magnets being positioned radially outwardly from and circumferentially spaced around the impeller axis.

The driver magnets are preferably positioned radially inwardly of the coils.

The first set of coils may be positioned radially inwardly of the second set of coils. The coils are typically mounted on a yoke.

The yoke may include slots for receiving the coils.

The set of coils can include three pairs of first coils, the first coils in each pair being positioned in circumferential opposition, the controller being adapted to cause current to flow through the coils in corresponding directions, to thereby cause rotation of the impeller. The controller can be adapted to: a) determine a required impeller rotation rate; b) determine a control signal sequence for each pair of first coils; and, c) apply the respective control signal sequence to the respective pair of first coils to urge the driver in a direction predetermined direction thereby causing rotation of the impeller.

The second set of coils can include three pairs of second coils, the second coils in each pair being positioned in circumferential opposition, the controller being adapted to cause current to flow through the coils in counter-corresponding directions, to thereby cause radial movement of the driver member with respect to the cavity axis.

The controller is typically adapted to: a) monitor the sensors; b) determine any movement of the driver axis in a direction radial to the cavity axis; c) select one or more pairs of second magnets; d) generate a control signal for each selected pair; and, e) apply the control signal to the respective selected pair to urge the driver in a direction predetermined direction thereby moving the driver axis toward the cavity axis. The controller may be formed from a processing system having a memory and a processor, the processing system being adapted to generate control signals to control the magnetic field generated by the coils in accordance with a predetermined algorithm stored in the memory.

The processing system can be coupled to a signal generator, the control signal being formed by having the processing system cause the signal generator to apply a predetermined current to the coils. The driver magnets may include eight circumferentially spaced permanent magnets, the poles of the magnets being aligned perpendicularly to the driver axis, and arranged such that the direction of pole alignment is reversed in adjacent magnets.

The body can include: a) two body end portions; and, b) a number of vanes positioned on the end body portions, the vanes extending from a surface of the body end portions in a direction substantially parallel to the driver axis, and being positioned radially outwardly from and circumferentially spaced around the driver axis.

Each body end portion may have a substantially conical shape.

The body can include a substantially cylindrical central body portion positioned between the two body end portions, the driver magnets being positioned in the cylindrical central body portion.

The cavity may include first and second cavity end portions each cavity end portion having: a) an inlet positioned along the cavity axis; and, b) an outlet directed orthogonally with respect to the cavity axis, and arranged radially offset from the cavity axis; and, c) a substantially conical shape for cooperating with the impeller to allow the vanes to urge fluid from the inlet to the outlet in response to rotation of the impeller. The impeller and the cavity typically cooperate to substantially prevent fluid flow from one cavity end portion to the other, the vanes on each body end portion having a respective height or length to thereby control the pressure or rate of fluid flow at the outlet in the respective end portion.

The pump preferably includes at least two sensors positioned in at least one of the cavity end portions to thereby determine the distance between the sensor and the surface of the respective body end portion.

The impeller may include a shroud coupled to the vanes, the sensors being adapted to determine the position of the shroud.

The pump can include at least three sensors positioned radially outwardly from and circumferentially spaced about the cavity axis. The sensors may include a radiation source adapted to emit radiation towards the surface of the respective body end portion and a detector for detecting reflected radiation.

The impeller may include position magnets, the sensors being formed from Hall effect sensors adapted to determine the magnetic field generated by the position magnets. hi this case, the position magnets can be the driver magnets. The support magnets can be substantially cone or frustro-conically shaped.

The impeller and the cavity may have a substantially cylindrical shape.

The impeller can include one or more wedges positioned on an outer circumference of the body to thereby cooperate with the inner surface to hydrodynamically control the position of the impeller in a direction orthogonal to the cavity axis. The wedges may be provided in a central body portion.

The axial support magnets can be formed from a magnetic material positioned in a magnetic field.

The axial support magnets can be formed from soft iron.

The impeller may include a shroud on each body end portion.

Each shroud may include driver magnets. Each shroud can include axial support magnets. The pump can include a set of second magnets provided in each of two cavity end portions. hi a first broad form the present invention provides a fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) first and second sets of coils for generating respective first and second magnetic fields; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first and second magnetic fields in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity; and, d) a controller coupled to the sensors and the first and second sets of coils, wherein in use the controller: i) controls the first magnetic field to thereby control rotation of the impeller about the impeller axis; and, ii) controls the second magnetic field to thereby control movement of the impeller orthogonal to the cavity axis.

The controller can control the second magnetic field to thereby control movement of the impeller parallel to the cavity axis.

The fluid pump can include an axial coupling for restricting movement of the impeller in a direction parallel to the cavity axis. In a first broad form the present invention provides a fluid pump including: a) a housing having an inner surface defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils coupled the housing for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the magnetic field in use; and, iv) an outer surface, at least a portion of the outer surface being shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis; c) an axial coupling for restricting movement of the impeller in a direction parallel to the cavity axis; and, d) a controller for controlling the first magnetic field, to thereby cause rotation of the impeller about the impeller axis.

The axial coupling includes: a) a second set of coils for generating a second magnetic field; and, b) at least two sensors for sensing the position of the impeller within the cavity, the controller being coupled to the sensors and the second set of coils, and wherein in use the controller controls the second magnetic field to thereby confrol movement of the impeller in a direction parallel to the cavity axis. The axial coupling can include at least one of: a) a set of magnets coupled to the housing to generate an axial control field; and b) a number of axial support magnets provided in the body and positioned in the axial control field in use to thereby restrict movement of the impeller in a direction parallel to the cavity axis. The axial coupling may include: a) a first bearing member coupled to the housing; and, b) a second bearing member coupled to the impeller, the first and second bearing members cooperating to thereby restrict movement of the impeller in a direction parallel to the cavity axis. In a first broad form the present invention provides a fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first magnetic field in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity; and, d) a controller coupled to the sensors and the set of coils, wherein in use the controller confrols the magnetic field to thereby control: i) rotation of the impeller about the impeller axis; and, ii) movement of the impeller in a direction parallel to the cavity axis. first broad form the present invention provides a fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils to generate a first magnetic field; iv) a set of magnets to generate an axial control magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first magnetic field in use; and, iv) a number of support magnets positioned in the axial confrol magnetic field to thereby restrict movement of the impeller in a direction parallel to the cavity axis; c) a controller coupled to the set of coils to control the first magnetic field to thereby control rotation of the driver about the driver axis. first broad form the present invention provides a fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; ii) at least one fluid outlet; and, iii) a first bearing member; iv) a set of coils for generating a respective magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets; and, iv) a second bearing member, the first and second bearing members cooperating to thereby restrict movement of the impeller in a direction parallel to the cavity axis; c) a controller coupled to the set of coils, the controller being adapted to confrol the magnetic field generated by the first set of coils to thereby control rotation of the driver about the driver axis.

The fluid pump typically further includes a radial bearing for confrolling movement of the impeller orthogonal to the cavity axis.

The radial bearing may include: a) an inner surface of the housing; and, b) the impeller has an outer surface, at least a portion of the outer surface being shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis.

The radial bearing may include: a) a second set of coils for generating a second magnetic field; b) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity, wherein the controller controls the third magnetic field using signals from the sensors to thereby control movement of the impeller orthogonal to the cavity axis.

The fluid pump can include at least one sensor positioned at a first end of the cavity and at least two sensors positioned at a second opposing end of the cavity.

In a first broad form the present invention provides a fluid pump including: a) a housing having an inner surface defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; ii) at least one fluid outlet; iii) a set of coils coupled the housing for generating a first magnetic field; and, iv) a set of magnets coupled to the housing to generate an axial control magnetic field; b) an impeller positioned in the cavity for urging fluid from the inlet to the outlet, wherein the impeller has: i) a body defining an impeller axis, ii) a number of driver magnets positioned in the first magnetic field in use; iii) an outer surface, at least a portion of the outer surface being shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis; iv) a number of axial support magnets positioned in the axial control magnetic field to thereby restrict movement of the impeller in a direction parallel to the cavity axis; c) a confroller for controlling the magnetic field, to thereby cause rotation of the impeller about the impeller axis. i a first broad form the present invention provides a method of pumping fluid, using a fluid pump having: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) first and second sets of coils for generating respective first and second magnetic fields; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first and second magnetic fields in use; and, c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity, wherein the method includes: i) controlling the first magnetic field to thereby control rotation of the impeller about the impeller axis; and, ii) controlling the second magnetic field to thereby control movement of the impeller orthogonal to the cavity axis. hi a first broad form the present invention provides a method of pumping fluid using a fluid pump having: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first magnetic field in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity, wherein the method includes controlling the magnetic field to thereby control: i) rotation of the impeller about the impeller axis; and, ii) movement of the impeller in a direction parallel to the cavity axis. In a first broad form the present invention provides a computer program product including computer executable code which when executed on a suitable processing system causes the processing system to perform the method of the eighth and ninth broad forms of the invention claim 46 or claim 48.

In a first broad form the present invention provides an impeller for use in a fluid pump, the impeller being mounted in a pump cavity and being adapted to urge fluid from first and second inlets to corresponding first and second outlets, wherein the impeller includes: a) a body defining an impeller axis, the body including first and second body end portions; b) a set of vanes positioned on each body end portion for urging fluid from a respective inlet to a corresponding outlet, in use; c) a number of driver magnets positioned in the first and second magnetic fields in use; and, d) an outer surface portion shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis. The impeller forms part of a fluid pump according to claim 4.

In a first broad form the present invention provides an impeller for use in a fluid pump, the impeller being mounted in a pump cavity and being adapted to urge fluid from first and second inlets to corresponding first and second outlets, wherein the impeller includes: a) a body defining an impeller axis, the body including first and second body end portions; b) a set of vanes positioned on each body end portion for urging fluid from a respective inlet to a corresponding outlet, in use; c) a number of driver magnets positioned in the first and second magnetic fields in use; and, d) at least a first part of an axial coupling for restricting movement of the impeller in a direction parallel to the impeller axis. The axial coupling may include at least one of: a) a second bearing member adapted to cooperate with a first bearing member provided on the housing; and, b) a number of support magnets for positioning in an axial control magnetic field in use.

The dimensions of the vanes typically are typically selected to control at least one of the fluid pressure and the flow rate at the outlet.

The dimensions usually include at least one of: a) The height of the vanes; b) The diameters of the impellers; c) The length of the vanes; d) The width of the vanes; e) The inlet and outlet vane angles; f) The shape of the vanes; and, g) The number of vanes. The impeller can be positioned in a pump cavity in use such that the inlets are aligned parallel to the body axis, with each inlet being positioned to direct fluid along the body axis towards a respective body end portion, the impeller being rotated in use to thereby urge the fluid radially outwardly towards the outlets.

The body may include a substantially cylindrical central body portion positioned between the two end portions, the driver magnets being positioned in the cylindrical central body portion.

The impeller can be adapted to cooperate with the pump cavity to define first and second cavity portions, each cavity portion including a respective inlet, outlet, and end body portion, the impeller being adapted to substantially prevent fluid transfer between the cavity portions.

The impeller can be adapted for use a in heart pump, the first and second sets of vanes being adapted to pump blood for assisting the left and right ventricles respectively.

Brief Description of the Drawings

An example of the present invention will now be described with reference to the accompanying drawings, in which: -

Figures 1A to IE are schematic cross sectional, end, plan, perspective and explored perspective views of an example of a fluid pump incorporating an impeller;

Figures 2A to 2F are schematic plan views of examples of inlet and outlet volutes for use in the pump of Figures lA to IE;

Figures 3A to 3D are schematic perspective and plan views of examples of impellers for use in the pump of Figures lAto IE; Figures 4A to 4J are schematic views of examples of magnets for use in the pump of Figures 1A to IE;

Figures 5 A and 5B are schematic plan views of the fields generated by the coils and the corresponding movement of the impeller in the pump of Figures 1 A to IE;

Figure 6 is a schematic representation of an example of a controller for confrolling the pump of Figures

1A to IE; Figures 7 A to 7C are schematic perspective, plan and side views of examples of sensors for use in the pump of Figures lAto IE;

Figure 8 is a schematic view of an example of the sensing of the position of the impeller of Figure 3 A;

Figure 9 is a schematic view of an example of the sensing of the position of the impeller of Figure 3B;

Figure 10 is a schematic view of an example of a fluid pump having additional axial suspension; Figures 11A and 1 IB are schematic perspective views of an example impeller and a housing for use in a pump having active axial suspension;

Figures 12A to 12L are schematic views of a further example of a fluid pump incorporating an impeller; Figures 13 A to 13J are schematic views of a further example of a fluid pump incorporating an impeller; and, Figure 14 is a schematic cross sectional view of a fluid pump having an axial bearing.

Detailed Description of the Preferred Embodiments

An example of a fluid pump incorporating a double impeller is shown in Figures 1 A to IE. As shown the pump includes a housing 1 having two conically shaped end portions 1A, IB, defining a cavity 2, containing an impeller 3. The impeller is formed from two substantially conically body end portions, 3 A, 3B, each having a number of vanes 4 mounted thereon.

Each housing portion 1A, IB is provided with a respective inlet 5A, 5B, and a respective outlet 6A, 6B.

The housing includes a clearance gap 8 A between a rim 8 and the impeller 3, which cooperate to effectively split the cavity 2, into two cavities cavity end portions forming respective 2A, 2B, and to reduce fluid flow between the two cavities. Thus in this example, the pump effectively includes two pumps defined by the cavities 2 A, 2B. In use, the impeller 3 is rotated about an axis shown generally at 7. This causes fluid at the respective inlets 5A, 5B to be urged towards the respective outlet 6A, 6B, as will be appreciated by persons skilled in the art. In order to improve operating efficiency, the inlets 5A, 5B are preferably aligned with the cavity axis 7, to thereby direct blood flow directly onto the impeller 3 and hence into contact with the vanes 4. This minimises the effect of radial displacement on the impeller 3 caused by fluid flow into the pump. However, to reduce the axial device size, and to improve anatomical compatibility in the heart pump applications, the fluid should enter the cavity from a direction substantially perpendicular to the cavity axis. To achieve this the inlet includes a 90° a turn to align entry of the fluid into the cavity 2 along the cavity axis 7.

It should be noted that despite the anatomical suitability of this arrangement, inlet volutes 5 A, 5B may be replaced with straight canula parallel to the axis of impeller rotation 7.

This may be achieved using inlet volutes 5C, 5D, examples of which are shown in Figures 2A and 2B. Flow enters the inlets rolutes 5C, 5D via respective ports 5E,5F and is provided with a rotational component by the shape of the volute shown at 5G, and the lip 5H at the impeller eye. This lip 5H also reduces recirculation and potential stagnation in the region. Thus, when the fluid enters inlet 5A, 5B inlet 5A, 5B, it has a whirl component which aides the transition into the rotating impeller blades. The inlet volutes 5C, 5D provide additional anatomical compatibility when implanting the fluid pump beneath a subject's heart. In one example the pump the inlet and outlet flow should preferably be in the same plane. Additionally, the axial size of the fluid may be reduced by employing a flattened 'pancake' style inlet volute.

In use, the inlet volutes 5C, 5D direct blood onto the revolving impeller 3. The vanes 4 have the effect of urging blood via respective outlet volutes 37A, 37B, which describe a spiral channel, which leads to a respective one of the outlets 6 A and 6B.

Examples of a number of outlet volutes are shown in Figures 2C to 2F. As shown in Figure 2C, the volutes 37 A, 37B commence with a narrow space between the vanes 4 and an inner surface of the cavity 2, known as the 'cutwater' 38 A. The volute increases in volume and flares out to be continuous with the respective outlet 6A, 6B, or alternatively can further flare out into a vaneless diffuser 38C, as shown in Figure 2E. This volute structure can help decrease turbulent flow and wall friction during flow as the volume of blood is urged towards the outlet, since fluid velocity is kept uniform, thereby reducing shear stress development and preserving the components of the fluid being pumped.

The embodiment shown in Figure 2D implements a split volute. In this example, the radial clearance gap or first volute area 37A between the rotor and the housing increases from the initial point (cutwater) 38A, until it encompasses half or approximately 180° of the impeller. A second cutwater 38B is implemented at 180° as the beginning to the second volute 37B. The split, or 'double' volute encounters a reduced radial thrust and improved efficiency over a larger operating range, which is encountered by a patient with varying levels of heart failure and thus assistance required during the course of their support.

Alternatively, Figure 2F shows a concentric volute. Radial hydraulic thrust is reduced only at the best efficiency point of the single volute, whereas concentric volute encounters the most radial thrust over all operating conditions.

Levitation and rotation of the impeller 3 within the cavity 2 and about the cavity axis may be achieved in a number of manners, h one example this is achieved using two sets of magnets, formed from electrically activated coils 11, 12, provided in the housing, and a set of permanent driver magnets 9 provided in the impeller as shown in Figure 4B, and as will be described in more detail below.

hi this example, the first set of magnets (coils 11) cooperate with the driver magnets 9 embedded in the impeller to provide a rotational torque, with the second set of magnets (coils 12) being used to form a magnetic bearing which can be used to maintain the position of the impeller 3 within the cavity.

However, with a suitable control strategy, only one set of coils is required to provide both the functions of bearing and motor flux generation. Thus, the 1^st and 2^nd set of magnets (coils) can be combined into a single set of magnets (coils) and energised with superimposed currents to produce bearing and motor flux independently.

It will therefore be appreciated that the use of two sets of coils 11, 12 provides redundancy, such that, if one or more coils with a set fail, then functionality can be achieved by a corresponding coil in the other set of coils.

In use, when the impeller is centrally positioned in the cavity 2, the force required to the position is minimal. However the rotor position is inherently unstable due to the negative stiffness, or attractive force of the permanent magnets to the stator. Therefore, the active magnetic bearing provides additional magnetic flux to counteract any disturbance forces. This practice is common to magnetic motor-bearing systems derived from so called Lorentz and Reluctance theory, as described in "Active Magnetic Bearings : Basics, Properties and Applications of Active Magnetic Bearings", Schweitzer, G. Bleuler, H.,Traxler, A, (1994).

This form of pump assembly can provide assistance or replacement of one or more ventricles of a mammalian heart. This is achieved by connecting the inlets 5A, 5B of the pump to either the left ventricle or atrium, imparting energy to the fluid via the double sided centrifugal impeller 3, and connecting the outlets 6A, 6B to the aorta, thus assisting the natural function of the left heart. Additionally or alternatively, the inlets 5A, 5B may be connected to the right ventricle/atrium, with the outlets 6A, 6B connected to the pulmonary artery, thus providing left and right, or right heart assistance respectively.

First Specific Example

A first specific example of a pump will now be described with reference to a pump that can assist or replace the function of the left chambers of the heart (LVAD).

Figure 1A shows a detailed cross section of one example of a pump used as a left ventricular assist device embodiment. As previously described, this configuration includes two volute type inlets, 5C,5D which supply fluid to a double sided centrifugal pump formed by two substantially conical shaped body portions 3A,3B, each having a number of vanes 4A,4B mounted thereon.

The vanes are configured to produce the same pressure at the outlet 6 A, 6B of each cavity 2 A, 2B. This in effect represents two centrifugal pumps operating in parallel, thus output flow rate at a canula 40 is double the flow rate produced at each outlet 6A, 6B, for the specific pressure increase. In this example the cavity 2 is separated into two cavities 2A, 2B by a small clearance gap 8A, which is the site for the radial type magnetic motor bearing. In this example, the coils 11, 12 reside on the outside of the pump housing 1, as shown and couple to the permanent driver magnets 9 embedded in the cylindrical circumference of the impeller. This magnetic bearing provides contact free impeller suspension in the radial (x,y) directions as well as rotational torque. Figure IE is a detailed exploded view of the pump. hilet flow is provided by a single canula 39 from the left ventricle or atrium, and is split into two conduits 39A, 39B, which connect to the inlets 5A, 5B to provide even flows in both of the cavities 2A, 2B. In this arrangement, the variations of left ventricular pressure developed during systole and diastole are transmitted directly to both of the inlets 5A, 5B of the pump via the inlet volutes 5C,5D, acting to balance and therefore minimise axial thrust forces encountered by the impeller 3 which is a feature not significantly afforded in conventional single sided pumps.

Figure 3A is an example of one configuration of the impeller 3 used in this example. In particular, Figure 3A shows that the impeller is formed from three portions, namely end portions 3A, 3B and a central portion 3C, which in one example includes the permanent driver magnets 9. The end portions 3 A, 3B include respective sets of vanes 4A, 5B, as shown.

The configuration of the vanes 4A, 4B allows the characteristics of flow provided at the outlets 6A, 6B to be controlled. This will be effected by a number of factors as discussed in more detail below. It will be appreciated from this however, that a number of different vane arrangements can be used.

For example, another impeller configuration is described by Figure 3B. In this example, a shroud 3D is employed on the vanes 4A, 4B to improve hydraulic efficiency as well as providing a closer proximity sensor target. This situation does however lend itself to potentially higher shear values between the shroud the shroud 3D and the cavity 2, but increase sensor resolution as will be described in more detail below.

Figure 3C shows a 'backward inclined' vane embodiment, with outer and inner blade diameter 4D, 4C, outer vane angle 4E, inlet vane angle 4F and vane height 4G, which can be used to produce the desired flow characteristics. Alternatively, the vanes 4 can be straight radial in nature as shown in Figure 3D, or forward inclined (not shown).^'

Preferably, fluid leaving the impeller 3 is collected by 9 split volute type casing 37 A, 37B and transmitted to outlets 6A,6B, with the angle of spiral corresponding to the relative angle of flow off the vanes 4 at design conditions. Outlet flow is combined by the conduits 40A, 40B to provide the single canula 40 to the aorta.

Alternatively, each output flow 6A, 6B can be directed to different sites of the aorta, eg, the ascending and descending aorta. This may provide additional flow to specific organs otherwise depleted from a single ascending aortic interface, but does not require an additional interface site to the circulatory system.

In designing the configuration of the impeller 3 and housing 1, computational fluid dynamic techniques must ensure the elimination of stagnation zones and the potential for thrombus formation within the split canula, as will be appreciated by persons skilled in the art. In one example, the impeller 3 is suspended and driven by first and second sets of coils 11, 12 which generate respective magnetic fields which couple to the driver magnets 9 provided in the central portion 3C, of the impeller 3, as shown in Figure 4A.

As shown in Figure 4B, the first and second sets of coils 11, 12 are positioned in an outer section of the housing 1 circumferentially surrounding the driver magnets 9, to thereby provide the required magnetic bearing and rotational torque.

The sets of coils 11, 12 are arranged on a common yoke 15, which acts as a stator. The yoke is preferably constructed from a laser or water jet cut laminated or sintered iron core, for the purpose of eddy current loss reduction. The magnetic material can be rare-earth, neodynimum, or any material available to provide sufficient flux, hi one example, six coils are provided in each set, but other numbers amounts could be used.

The coils 11, 12 may be provided flush on the surface of the yoke 15 (known as a "slotless" arrangement), as shown in Figures 4C to 4E. This configuration requires permanent magnet shape 9A, as shown in Figure 4F. Compared to other arrangements this results in a lower production of radial force, though significantly reduces the degree of negative stiffness instability as well as reducing the inductance and therefore allows for greater rotational speed generation as the back EMF generation is lower. Greater impeller mass and larger coil sizes result in a larger volume occupied by this magnetic bearing type.

As an alternative the coils can be located in slots 15A in the yoke (known as a "slot-type"), so that the yoke extends radially inwardly as shown at 15C, 15D in Figure 4G. This configuration prefers the magnet shape 9B shown in Figures 4H and 41 to reduce the degree of cogging torque produced. Greater bearing and torque generation is possible for this stator type, however speed is limited due to the relatively larger inductance, however sufficient rotational speed is possible for this application.

Additionally, or alternatively magnets can be configured in a Halbach array as shown in Figure 4J to improve the flux density. This involves constructing each separate magnet from a plurality of smaller magnets each with slightly changing radial polarity direction.

In use, the driver magnets 9 are arranged with their poles aligned perpendicular to the axis of the impeller 3, with adjacent magnets having poles aligned in opposing directions. This provides alternating magnetic fields around the outside of the impeller 3, as shown by the arrows 10. In particular, in this example, the magnetic fields extend radially outwardly from the permanent magnets 9, with the direction of the field alternating between being directed radially outwardly or radially inwardly, as shown.

An example of the manner in which control of the impeller rotation and position may be achieved will now be described with reference to Figures 5A and 5B which are cross sectional views of the circumference of the coils 11, 12 and yoke 15 to show the directions of the coils 11, 12. hi this example, the first set of coils 11 provide the rotational torque (known as the "motor coils") and the second set of coils 12 provide the bearing action (known as the "bearing coils").

In particular, in Figure 5 A, a pair of opposingly positioned motor coils 11 A, 1 IB in the motor winding are energised with a current flow as shown. This causes the generation of a magnetic field shown by arrows 16A which in turn generates a Lorenz force in the coils as shown by the arrows 16B. As the coils are fixed to the stator, this causes rotation of the impeller body in the direction of arrow 17. Accordingly, by applying appropriate currents to the motor coils, the impeller can be rotated. h Figure 5B, a pair of opposing coils 12A, 12B in the bearing winding are energised with a current flow as shown. This, in turn causes the generation of a Lorenz force in the coils 12 A, 12B as shown by the arrows 16B. As the coils 11, 12 are fixed to the stator yoke 15, this causes lateral movement of the impeller 3 with respect to the cavity axis 7, as shown by the arrow 18. Similarly, by applying appropriate currents to the bearing coils, the impeller can be moved laterally.

Lateral movement is typically achieved using a controller, an example of which is shown in Figure 6. In this example, the controller includes a processing system 20 having a processor 21, a memory 22, and an external interface 23 coupled together via a bus 24. An optional input/output device 25 may also be provided.

The processing system 20 is coupled to three sensors, 26A, 26B, 26C, and a signal generator 27 via the external interface 23. The signal generator 27 is coupled to the motor and bearing coils, to allow pairs of opposing coils to be selectively activated as shown generally for the motor coils 11 A, 11B, 11C, 11D, HE, 11F and the bearing coils 12A, 12B, 12C, 12D, 12E, 12F respectively. As shown the coils are arranged as pairs of opposingly position coils 11 A, 11B; 11C, 11D; HE, 11F and 12A, 12B; 12C, 12D; 12E, 12F.

In use, the processor 21 determines from data stored in the memory 22 the current that must be applied to the motor coils in order to provide a required rotation speed. In the case of a heart pump, a single speed may be pre-set before the device is implanted. It will be appreciated that this may be achieved by storing information defining the pre-set speed in the memory 22, using either the I/O device 25, or a remote processing system coupled to the external interface 23.

Alternatively different speeds may be set whilst the pump is in use. This may be achieved for example using the I/O device 25, or via a wired or wireless connection to the external interface 23, or in response to external impetus, such as an increase in latent heart rate, or the like, through the use of appropriate detection systems. i any event, signals representing the currents to be supplied are provided to the signal generator 27, which operates to generate appropriate currents, which are then supplied to the motor coils HA, 11B, 1 lC. This will typically involve activating the motor coil pairs in a predetermined sequence in order to create the desired movement of the impeller.

In particular, assuming the configuration described above with eight equally spaced permanent magnets 9, and six equally spaced motor and bearings coils 11, 12, as shown. During rotation, the pairs of motor coils 11 are driven by three phase currents. Exact rotational speed can be monitored by a suitably placed hall effect sensor mounted to detect the change in driver magnet position with respect to the sensor fixed to a housing position. Alternatively, the back EMF encountered in the 1^st set of magnets can be related to rotational speed. Once this rate has been determined, it may be fed back to the controller in order for the maintenance of a set rotational speed. hi the case of controlling the lateral position of the impeller, this is achieved by having the processor determine positional information from the sensors 26A, 26B, 26C. In order to achieve this, the sensors are positioned in the housing, as shown in Figures 7A, 7B, 7C, generally by providing appropriate apertures in the housing 1 (not shown), for example in the inner surface of the cavities 2A, 2B.

These figures detail the preferred technique implemented to determine impeller position. A set of apertures are provided in each body potion 1A, IB, evenly circumferentially spaced around the respective cavities 2A, 2B. hi use, it is possible to include only a single set of sensors 26A, 26B, 26C, as only one set of sensors is required in order to determine the lateral (x,y) position of the impeller 3. However, it may be advantageous to also include the sensors 26D, 26E, 26F in all apertures to further resolve the impeller position in all degrees of freedom, as well as providing a degree of position determination redundancy.

In the preferred embodiment, each set of apertures are spaced such that sensors 26A, 26B are arranged along x and y axes having an origin coincident with the cavity axis. The third sensor 26C is positioned mid way between the -x and -y axes. The sensors 26A, 26B, 26C operate by determining the distance "d" between the respective sensor and the surface 33 of the impeller 3, as shown in Figure 8. The determined distance for the three sensors 26A, 26B, 26C is used to determine the position of the impeller body by resolving these distances into the x,y and z planes, as appreciated by anyone skilled in the art. As, in this example, it is only necessary to determine the position of the impeller 3 in the x-y plane, this could theoretically be achieved using the sensors 26A, 26B alone. The third sensor is used in practice to allow for variations in the position of the impeller 3 along the cavity axis. The determination of the distance between the sensors 26A, 26B, 26C and the impeller surface 33 can be achieved in a number of ways. Thus, for example, the sensors 26A, 26B, 26C are preferably Hall effect sensors adapted to detect the magnetic field generated by a permanent magnetic sensor target, which could be formed from the driver magnets 9. The magnitude of the current generated in the Hall effect sensors can then be used by the processor 21 to derive the position of the impeller 3. Alternatively, each sensor 26A, 26B, 26C can be formed from a radiation source such as an LED laser, or the like and corresponding optical detector, as will be appreciated by persons skilled in the art. Other techniques may also be used.

As an alternative to measuring the position of the surface of the impeller 3, a shroud 3D can be mounted on the vanes 34, as shown in Figure 9. In this case, the position of the impeller 3 can be measured by measuring the distance dl between magnetic sensor targets embedded in the shroud 3D and the sensors 26A, 26B, 26C.

This has the advantage that the distance dl between the permanent magnetic sensor targets and the sensors 26A, 26B, 26C is less than distance d between the surface 33 and the sensors 26A, 26B, 26C. In addition to this, when measuring the distance between the surface 33 and the sensors 26A, 26B, 26C, the vanes 4 will periodically pass between the sensors 26A, 26B, 26C and the surface 33, which can affect the measurements. As a result, the use of the shroud 3D tends to allow the processor to determine the position of the impeller faster and more accurately, with a higher degree of resolution. However, the presence of the shroud 3D can reduce the effectiveness of the impeller 3, and generate turbulence within the respective cavity 2 A, 2B. This is undesirable for some applications, such as use of the system as a heart pump.

An alternative method of sensing the position of the impeller within the cavity 2 relates to the so called 'self sensing' technique, whereby the voltage and current waveforms of each motor and/or bearing coil can be monitored by the processing system 20 to sense the position of the impeller. A component of the current waveform is related to the circuit inductance, which in turn varies inversely with movement of the permanent driver magnets 9 in the air gap 8A. Recording and analysing the back EMF voltage generated by the motor achieves rotational position sensing, with signals from the bearing coils determining the position. It will be appreciated that in this example, the bearing coils 12 and the motor coils 11 form the sensors 26. i any event, if the processing system 20 detects movement of the impeller laterally such that the axis of the impeller 3 and the cavity axis 7 are no longer aligned, the processor will use a predetermined algorithm to determine the current that needs to be applied to selected pairs of bearing coils 12. An indication of this is transferred to the signal generator 27, which in turn responds by generating appropriate currents and applying these to the selected ones of the bearing coils 12. The current in the coils 12 causes the impeller body to move, as described above, thereby realigning the impeller body axis with the cavity axis.

It will be appreciated that the sensors 26 can also be adapted to determine the rotational position of the impeller 3, thereby allowing the rate of rotation to be monitored and adjusted by the processing system 3. Additionally, other magnetic bearing techniques may be implemented, such as those based on reluctance type magnetic theory. This configuration requires a slightly different control strategy and slotted stator configuration, with six coils around six iron only cores, as will be appreciated by those skilled in the art. In particular, it is preferable that the impeller is positioned so that the magnets 9 are situated radially inwardly of the motor and bearing coils 11, 12, as this provides optimum coupling between the coils 11, 12 and the permanent magnets 9, thereby providing optimum efficiency and thus stiffness in the radial direction. This can be achieved in a number of ways depending on the specific implementation. hi addition to controlling the position of the impeller 3 laterally, it is also necessary to ensure that the position of the impeller along the cavity axis (the "axial position") is maintained.

In the above example, the permanent driver magnets 9 are attracted to the magnetic fields generated in the motor and bearing coils 11, 12. This provides a degree of restoring action to the axial null position, hi particular, if the impeller is displaced along the cavity axis, the attraction of the coils 11, 12, will urge the impeller back into the optimum position due the effect know as passive stability. This is generally sufficient to maintain alignment in the axial direction in most cases, especially if the fluid pressure is substantially equal in both cavities 2A, 2B. However, additional or alternative axial alignment can be provided through the provision of additional support magnets. In this case, the support magnets can be provided in the housing, with corresponding magnets being provided in the body of the impeller 3. This can be achieved using a variety of magnet configurations. Thus for example, flat (parallel to the radial axes) or frustro-conically shaped permanent magnets 35 can be provided around the circumference of the housing portions 1A, IB as shown in Figure 10. This can be achieved with a single appropriately shaped magnet, or a series of circumferentially spaced magnets 35. In any event, the support magnets 35 A, 35B cooperate with corresponding permanent support magnets 36A, 36B provided in the impeller body 3. If the magnets are configured with like poles facing each other, the support magnets 35 will repel the support magnets 36, thereby urging the impeller body into the centre of the cavity.

Thus, movement of the impeller 3 in a direction parallel to the cavity axis 7 will cause the distance between the support magnets 35 and the corresponding support magnets 36 to be reduced, thereby increasing the resultant repulsive force, and thereby urging the impeller towards the centre of the cavity, which corresponds to the optimum position.

Any tilting, due to gyroscopic effects of the impeller will also lead to increased forces urging the impeller back to a stable position. As an alternative, in this example, the magnets 35 can be replaced by coils. In this case, by configuring the support magnets 36 in a manner similar to the driver magnets 9, this allows the axial bearing to be additionally used to drive the impeller in a manner similar to that described above.

It will be appreciated by persons skilled in the art that some form of active magnetic suspension must be implemented in at least one degree of freedom as described by EARNSHAWS Theorem. This arrangement results in the axes of polarity of the housing magnets and rotor magnets being at an angle to the impeller axis, although the rotor and/or housing magnets may be physically perpendicular to the impeller axis in which case the angle may be suitably 0°, and the magnetic polarity parallel to the impeller axis. Preferably, the angle corresponds to the angle of the cones forming the impeller 3, to provide the smallest gap between rotor and housing permanent magnets, but it may suitably be in the range of 0° - 65°. The angle should be arranged to provide the most counteraction against the varying axial loads imposed by the pumped fluid. This angle may in fact be different from rotor magnets to housing magnets and may be suited to provide one of either radial or axial support.

This therefore provides a self balancing technique for maintaining the position of the impeller in the axial direction. h the above mentioned situation, when permanent magnets 36 are provided on the impeller body, the effectiveness of the magnets is increased if they are closer to the magnets 35 in the housing portions 1A, IB. Accordingly, the magnets 36 may be mounted to a shroud provided on the vanes 4. An example of this is shown in Figure HA. As will be appreciated by a person skilled in the art, this allows the distance measurements obtained by the sensors 26A, 26B, 26C to be obtained by measuring the distance to the magnets 36 mounted on the shroud. The appearance of the housing 1 is shown in Figure 1 IB. hi this example, the housing is adapted to incorporate the support magnets 35. hi any event, the inclusion of additional passive permanent magnets in this system will generally reduce the axial forces applied to the impeller and therefore reduce the current required to maintain axial impeller suspension.

Second Specific Example

In a second specific example the pump is adapted to operate to assist or replace the natural function of the left ventricle, at a reduced rotational speed or impeller diameter as compared to the first example.

This is achieved by utilising the configuration of the double impeller as two pumps in series, rather than parallel as in the first specific example (hereinafter referred to as an XLVAD). Thus, in the above examples, fluid enters directly from the left ventricle/atrium into the first inlet volute 5C. The fluid travels through inlet 5A, with the vanes 4A on the impeller 3A within the cavity 2A acting to urge the fluid to outlet 6A. Fluid then travels from outlet 6A through a cross over volute to the inlet 5B, thus entering the pump cavity 2B. The vanes 4B urge the fluid to the outlet 6B and into the circulatory system via a canula to the aorta. Fluid is separated from the cavities 2A, 2B by the clearance gap 8A.

By operating the pump as two centrifugal pumps in series, the fluid undergoes two stages in pressure increase. Thus, the fluid entering cavity 2A must undergo a rise in pressure in the order of half of the overall required output pressure rise as fluid is transferred from the inlet 5 A to the outlet 6B. Accordingly, the fluid entering the cavity 2B, via the inlet 5B, is already at half the desired overall pressure value, and therefore can undergo the other half of the required overall pressure rise in the cavity 2B.

As a result of this, the impeller rotational speed, can be reduced as compared to the LVAD example described above. The reduction in speed is in the order of LVAD RPM /2. This reduction in rotational speed significantly reduces the level of shear stress within the pump, leading to a potential reduction in hemolysis levels.

Alternatively, the impeller rotational speed may be kept constant, with the impeller outer diameter reducing to achieve the desired pressure rise, as described by Fluid Mechanics Theory. It will be appreciated that this configuration may result in an imbalance in the pressure distribution between the two in cavities 2A, 2B, causing an axial force in the direction of the cavity axis 7 toward the lower pressure cavity 2A. Similarly, a leakage of flow may occur from the cavity 2B to the cavity 2 A, through the clearance gap 8 A, due to the pressure difference between the cavities 2A, 2B.

Accordingly, it is typical to use a method of impeller suspension which counteracts the axial force and therefore reduce the level of generated leakage flow, although this is not essential.

Figures 12A to 12F show a first example configuration for X-LVAD operation. In this example, similar reference numerals to those described above, increased in value by 50, will be used, and each element of the pump will not therefore be described in detail.

In this example, the impeller 53 is completely suspended in the axial direction, and rotated about the cavity axis 57 with the use of an axial magnetic motor bearing. The radial degrees of freedom are restricted by a combination of passive magnetic forces caused by the active axial bearing coupled with a hydrodynamic bearing located at 58. The hydrodynamic bearing requires a minimal clearance gap 58A, which acts to significantly reduce the fluid flow from cavity 52B to 52A. It will be appreciated that the cavity 52 is correspondingly shaped, to accommodate the alternative impeller shape. In this example, the impeller 53 is cylindrical and employs a shroud 53D to improve hydraulic efficiency as well as providing a region for magnet material placement. The vanes 44A are configured, via correct selection of vanes angles, and heights, to produce a pressure rise of half the desired overall pressure rise required by the pump. In one example, the rise in pressure from the inlet 55A to the outlet 56A is in the region of 50mmHg.

The fluid exits the first stage via outlet 56A and enters a 'crossover" volute 56C. This volute transfers the fluid in an efficient manner to the inlet 55B of the second stage. Fluid entering the second stage is at half the overall pressure, and the vanes 54B are required to cause the second half of the overall pressure rise. The vanes 54B may have slightly different profiles to accommodate for the different inlet conditions.

In this example, a magnet system is used to provide both axial suspension and rotation of the impeller 53, with the cavity 52. An example of this will now be described with respect to Figures 12G to 12L. hi this case, two slotted type stators 65 A, 65B are positioned axially above and below the impeller 53. The magnetic fields, which are generated by the coils 61 A, 6 IB wound around cores 65C in the stators 65 A, 65B, couple to specially shaped permanent driver magnets 59 embedded in the shroud 53D, of the impeller 53. hi this example, four driver magnets 59A are provided on the first end 53 A of the impeller, with a corresponding set of driver magnets 59B provided on the second end 53B. However, alternative numbers of magnets may be used.

For motor function, identical currents are applied to the coils 61 A, 6 IB located in the top and bottom stators 65A, 65B. h this example, six coils 61A, 61B are shown, but other numbers may be used.

For bearing function, an increase in the current supplied to the coils 61 A is accompanied by a corresponding decrease in the current applied to the coils 61B, thereby causing an increase in magnetic attraction to the coils 61A, and decreased magnetic attraction to the coils 61B. This results in the generation of a force along the cavity axis 57 towards the coils 61 A, which can therefore be used to alter the position of the impeller 53 along the cavity axis 57. This confrol will again be performed by determining the position of the impeller 53 using appropriate sensors 76, coupled to a processing system 70. Operation will then be performed in a manner similar to that described with respect to Figures 5A, 5B and 6, and will not therefore be described in any detail.

As an alternative to providing two sets of driver magnets 59A, 59B, the stator 65A can be adapted to act solely as a magnetic bearing, coupling to iron on the first end 53 A of the impeller. In this case, the rotational torque is only provided by the bottom stator 65B, which has more iron cores, coupled to a suitable number of driver magnets 59B embedded in the end 53B. hi this example, the sensors 76 can be mounted to target onto the flat impeller shroud 53D, to directly sense motion in the axial direction only, as required for the axial type magnetic bearing. hi an alternative example, the magnetic fields generated by the coils 61 A, 6 IB couple directly to iron embedded within the shroud 55D, at either end 53 A, 53B, of the impeller 53. This provides axial bearing confrol only, and can therefore be used to control the position of the impeller 53 along the cavity axis 57. Rotational torque is provided via similar method described previously, by coupling a three phase motor to magnets 59 embedded in the cylindrical circumference of the impeller 53. This may be achieved using similar arrangements to those described above with respect to Figures 4 to 7.

In one example, the motor has six coils wound around a six core stator located in the housing radially outward from the outer circumference of the impeller. h all of the above examples, movement in a radial direction can be controlled using a number of different manners. For example, this can be achieved by using an appropriate set of coils provided on the housing 51. This can include the driver coils, or an additional set of control coils, as described above with respect to Figures 1 to 11.

Alternatively, movement in the radial direction can be restricted by the use of a hydrodynamic bearing in clearance gap 8 A between impeller 3 and housing 8. hi this case, the cylindrical circumference of the impeller is constructed from a number of small tapered wedges 90, examples of which are shown in Figure 13G.

The wedges 90 preferably have rounded edges to reduce damage to blood elements, however this also compromises the stiffness of the hydrodynamic bearing. The combination of these wedges and a relative rotational speed cause a thrust force due to the squeezing of fluid through the tapered gap, as described by Reynolds' theory of lubrication. This radial thrust force is used to balance any radial forces encountered within the pump.

Third Specific Example

The third specific example, relates to a single pump that can assist or replace the function of both left and right ventricles of a heart, known as a BiVAD. An example of this will now be described with respect to 13A to 13H, in which similar reference numerals increased by 100 will be used to denote similar integers to those shown in the first specific example.

In this example, fluid is drawn from the left ventricle into the cavity 102 A via a canula connected to the inlet 105 A. Fluid passes onto the cylindrical impeller 103, whose vanes 104A urge fluid via the volute 137A to the outlet 106A, returning to the circulatory system via a canula connected to the aorta. This imparts sufficient a flow rate and pressure required by the systemic circulatory system, which in one example includes a pressure rise of lOOmmHg at a flow rate of 5 L/min. Simultaneously, fluid is drawn from the right ventricle into the cavity 102B via the canula connected to the inlet 105B. Fluid passes onto the side 103B of impeller 103, which has vanes 104B that urge the fluid, via the volute 137B, to the outlet 106B. In this case, the vanes 104B are designed to provide a flow rate and pressure suitable for the pulmonary circulatory system, which in one example is a pressure of 20 mmHg at a flow rate of 5 L/min. Fluid is transferred via a suitable canula connected to the pulmonary artery.

In this example, axial suspension and drive of the impeller may be achieved as described above with respect to either the first or second specific example.

In the example shown in Figures 13, the impeller 103 is rotated by coupling magnetic fields generated by the coils 111A, 11 IB, wound on respective stators 115A, 115B, to the driver magnets 109A, 109B embedded in the shroud 103D.

Alternatively, or additional, axial position can be controlled using a pure axial magnetic bearing located at the housing 101B, which couples with an iron only target in the shroud 103D.

It will be appreciated that the provision of alternative means of controlling the position of the impeller along the cavity axis allows different motor and bearing coils to be used, such as those discussed in the previous embodiments.

Again, radial position confrol can be controlled either using appropriate coil configurations which cooperate with driver magnets 109 provided in the central portion 103C of the impeller 103. Alternatively, this can be achieved using hydrodynamic suspension, as described above with respect to the second specific example.

In this later case, the small clearance gap 8A and length of the cylindrical portion in this region acts to reduce the leakage flow from high pressure to low pressure sides by creating a suitable resistance to fluid flow, therefore minor pollution is experienced.

The development of differential pressures and flow characteristics is achieved by utilising respective dimensions for the sets of vanes 104A, 104B, as shown in Figures 13H, to 13J. In particular, since the impeller operates at a single rotational speed, the difference in pressure is achieved by providing different impeller vanes 104A, 104B on the high pressure impeller side 103 A and low pressure side 103B. i this case, the vanes 104B on the impeller portion 103B are of a reduced length, as shown in Figure 13J, when compared to the vanes 104A on the impeller portion 103A.

In one example, with the impeller 103 rotating at 2200rpm, the required flow rates and pressures can be achieved using the following dimensions:

• Vanes 104A Z/ = 22 mm; • Impeller end 103A radius Rl = 25mm

• Vane 104B Xr = l l mm;

• Impeller end 103B radius R = 12.5mm;

It will be appreciated that in this example, the pressure difference may result in minimal blood flow from the left to the right sides of the pump. However, as this represents a flow of oxygenated blood into the unoxygenated blood, this does not represent a problem from a medical perspective.

It will be appreciated from the above that a number of different axial and radial bearings can be provided, together with a number of different rotational drives. These may be used in any combination, together with an impeller having either a cylindrical or double conical shape. Thus, for example, the system can use varying combinations of:

• passive axial suspension provided by magnetically coupling permanent magnets in the pump housing with permanent magnets in the impeller;

• passive axial suspension provided by a physical coupling between the housing and the impeller as shown at 150, 151 in Figure 14; • active axial suspension provided by magnetically coupling coils in the pump housing with permanent magnets or iron in the impeller;

• active radial suspension provided by magnetically coupling coils in the pump housing with permanent magnets in the impeller;

• passive radial suspension provided by hydrodynamic effects between the impeller and the housing; and,

• rotating the impeller by magnetically coupling coils in the pump housing with permanent magnets in the impeller.

It will be appreciated by persons skilled in the art that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope of the invention as broadly hereinbefore described.

Thus, whilst the above description focuses on the use of the fluid pump as a heart assist device, it is possible for the fluid pump to be used for other purposes, and indeed any fluid pumping application where the pressure and flow rates fall within the operating parameters of the device.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1) A fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the magnetic field in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity; d) a radial bearing for confrolling the position of the impeller in a direction orthogonal to the cavity axis; e) an axial coupling for controlling the position of the impeller in a direction parallel to the cavity axis; and, f) a confroller coupled to the sensors and the first and second sets of coils, wherein in use the confroller to confrol the magnetic field to thereby control rotation of the impeller about the impeller axis.

2) A fluid pump according to claim 1, wherein the axial coupling includes: a) a second set of coils for generating a second magnetic field; and, b) a number of axial support magnets provided in the body and positioned in the second magnetic field in use, wherein the controller confrols the second magnetic field to thereby control movement of the impeller in a direction parallel to the cavity axis.

3) A fluid pump according to claim 1, wherein the axial coupling includes the first set of coils and a number of axial support magnets provided in the body and positioned in the magnetic field in use, wherein the controller confrols the magnetic field to thereby control movement of the impeller in a direction parallel to the cavity axis.

4) A fluid pump according to claim 1, wherein the axial coupling includes at least one of: a) a set of magnets coupled to the housing to generate an axial confrol field; and b) a number of axial support magnets provided in the body and positioned in the axial control magnetic field in use to thereby restrict movement of the impeller in a direction parallel to the cavity axis.

5) A fluid pump according to any one of the claims 2 to 4, wherein the axial support magnets are the driver magnets. 6) A fluid pump according to claim 1, wherein the axial coupling includes: a) a first bearing member coupled to the housing; and, b) a second bearing member coupled to the impeller, the first and second bearing members cooperating to thereby restrict movement of the impeller in a direction parallel to the cavity axis.

7) A fluid pump according to any one of the claims 1 to 6, wherein the radial bearing includes: a) an inner surface of the housing; and, b) at least a portion of an outer surface of the impeller, the outer surface portion being shaped so as to cooperate with the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis.

8) A fluid pump according to any one of the claims 1 to 6, wherein the radial bearing includes a second set of coils for generating a second magnetic field, wherein the confroller controls the third magnetic field using signals from the sensors to thereby confrol movement of the impeller orthogonal to the cavity axis.

9) A fluid pump according to any one of claims 1 to 8, wherein the fluid pump includes at least one sensor positioned at a first end of the cavity and at least two sensors positioned at a second opposing end of the cavity.

10) A fluid pump according to any one of the claims 1 to 9, wherein the dimensions of the vanes are selected to confrol at least one of the fluid pressure and the flow rate at the outlet.

11) A fluid pump according to claim 10, wherein the dimensions include at least one of: a) The height of the vanes; b) The diameters of the impellers; c) The length of the vanes; d) The width of the vanes; e) The inlet and outlet vane angles; f) The shape of the vanes; and, g) The number of vanes.

12) A fluid pump according to any one of the claims 1 to 11, wherein: a) the housing includes: i) at least two fluid inlets; and, ii) at least two fluid outlets; and, b) the impeller includes: i) at least two body portions; and, ϋ) first and second sets of vanes positioned on the first and second body portions respectively, each set of vanes being for urging fluid from a respective inlet to a respective outlet, in use. 13) A fluid pump according to claim 12, wherein the impeller cooperates with the cavity to define first and second cavity portions, each cavity portion including a respective inlet, outlet, and the impeller and cavity being configured to substantially prevent fluid transfer between the cavity portions.

14) A fluid pump according to claim 12 or claim 13, wherein the first and second sets of vanes each have substantially identical dimensions to thereby provide fluid at substantially equal pressures and flow rates at the outlets.

15) A fluid pump according to claim 12 or claim 13, wherein the first and second sets of vanes each have respective different dimensions to thereby provide fluid at respective first and second pressures at the respective outlet. 16) A fluid pump according to claim 15, wherein the first outlet is coupled to the second inlet.

17) A fluid pump according to any one of the claims 1 to 16, wherein the cavity is substantially rotational symmetric around the cavity axis, the coils being arranged circumferentially spaced , around the cavity.

18) A fluid pump according to any one of the claims 1 to 17, wherein the body is substantially rotational symmetric around the impeller axis, the driver magnets being positioned radially outwardly from and circumferentially spaced around the impeller axis.

19) A fluid pump according to claim 18, wherein the driver magnets are positioned radially inwardly of the coils.

20) A fluid pump according to claim 2, wherein the first set of coils are positioned radially inwardly of the second set of coils.

21) A fluid pump according to any one of the claims 1 to 20, wherein the coils are mounted on a yoke.

22) A fluid pump according to claim 21, wherein the yoke includes slots for receiving the coils.

23) A fluid pump according to any one of the claims 1 to 22, wherein the set of coils includes three pairs of first coils, the first coils in each pair being positioned in circumferential opposition, the controller being adapted to cause current to flow through the coils in corresponding directions, to thereby cause rotation of the impeller.

24) A fluid pump according to claim 23, wherein the confroller is adapted to: a) determine a required impeller rotation rate; b) determine a control signal sequence for each pair of first coils; and, c) apply the respective confrol signal sequence to the respective pair of first coils to urge the driver in a direction predetermined direction thereby causing rotation of the impeller.

25) A fluid pump according to claim 2, wherein the second set of coils include three pairs of second coils, the second coils in each pair being positioned in circumferential opposition, the controller being adapted to cause current to flow through the coils in counter-corresponding directions, to thereby cause radial movement of the driver member with respect to the cavity axis.

26) A fluid pump according to claim 25, wherein the controller is adapted to: a) monitor the sensors; b) determine any movement of the driver axis in a direction radial to the cavity axis; c) select one or more pairs of second magnets; d) generate a confrol signal for each selected pair; and, e) apply the confrol signal to the respective selected pair to urge the driver in a direction predetermined direction thereby moving the driver axis toward the cavity axis.

27) A fluid pump according to any one of claims 1 to 26, wherein the confroller is formed from a processing system having a memory and a processor, the processing system being adapted to generate confrol signals to control the magnetic field generated by the coils in accordance with a predetermined algorithm stored in the memory. 28) A fluid pump according to claim 27, wherein the processing system is coupled to a signal generator, the control signal being formed by having the processing system cause the signal generator to apply a predetermined current to the coils.

29) A fluid pump according to any one of claims 1 to 28, wherein the driver magnets include eight circumferentially spaced permanent magnets, the poles of the magnets being aligned perpendicularly to the driver axis, and arranged such that the direction of pole alignment is reversed in adjacent magnets.

30) A fluid pump according to any one of claims 1 to 29, wherein the body includes: a) two body end portions; and, b) a number of vanes positioned on the end body portions, the vanes extending from a surface of the body end portions in a direction substantially parallel to the driver axis, and being positioned radially outwardly from and circumferentially spaced around the driver axis.

31) A fluid pump according to claim 30, wherein each body end portion has a substantially conical shape.

32) A fluid pump according to claim 30 or claim 31, wherein the body includes a substantially cylindrical central body portion positioned between the two body end portions, the driver magnets being positioned in the cylindrical central body portion.

33) A fluid pump according to claim 31 or claim 32, wherein the cavity includes first and second cavity end portions each cavity end portion having: a) an inlet positioned along the cavity axis; and, b) an outlet directed orthogonally with respect to the cavity axis, and arranged radially offset from the cavity axis; and, c) a substantially conical shape for cooperating with the impeller to allow the vanes to urge fluid from the inlet to the outlet in response to rotation of the impeller.

34) A fluid pump according to claim 33, wherein the impeller and the cavity cooperate to substantially prevent fluid flow from one cavity end portion to the other, the vanes on each body end portion having a respective height or length to thereby confrol the pressure or rate of fluid flow at the outlet in the respective end portion. 35) A fluid pump according to any one of the claims 30 to 34, wherein the pump includes at least two sensors positioned in at least one of the cavity end portions to thereby determine the distance between the sensor and the surface of the respective body end portion.

36) A fluid pump according to claim 35, wherein the impeller includes a shroud coupled to the vanes, the sensors being adapted to determine the position of the shroud.

37) A fluid pump according to claim 35 or claim 36, wherein the pump includes at least three sensors positioned radially outwardly from and circumferentially spaced about the cavity axis.

38) A fluid pump according to any one of claims 35 to 37, wherein the sensors include a radiation source adapted to emit radiation towards the surface of the respective body end portion and a detector for detecting reflected radiation.

39) A fluid pump according to any one of claims 35 to 37, wherein the impeller includes position magnets, the sensors being formed from Hall effect sensors adapted to determine the magnetic field generated by the position magnets.

40) A fluid pump according to 39, wherein the position magnets are the driver magnets. 41) A fluid pump according to claim 6, claim 9 or claim 15, wherein the support magnets are substantially cone or frusfro-conically shaped.

42) A fluid pump according to any one of the claims 1 to 41, wherein the impeller and the cavity have a substantially cylindrical shape.

43) A fluid pump according to claim 7, wherein the impeller includes one or more wedges positioned on an outer circumference of the body to thereby cooperate with the inner surface to hydrodynamically control the position of the impeller in a direction orthogonal to the cavity axis.

44) A fluid pump according to claim 43, wherein the wedges are provided in a central body portion.

45) A fluid pump according to any one of claims 2 to 5, wherein the axial support magnets are formed from a magnetic material positioned in a magnetic field. 46) A fluid pump according to claim 45, wherein the axial support magnets are formed from soft iron.

47) A fluid pump according to claim 30, wherein the impeller includes a shroud on each body end portion.

48) A fluid pump according to claim 47, wherein each shroud includes driver magnets.

49) A fluid pump according to claim 47, wherein each shroud includes axial support magnets. 50) A fluid pump according to claim 2, wherein the pump includes a set of second magnets provided in each of two cavity end portions. 51) A fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) first and second sets of coils for generating respective first and second magnetic fields; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first and second magnetic fields in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity; and, d) a controller coupled to the sensors and the first and second sets of coils, wherein in use the confroller: i) controls the first magnetic field to thereby control rotation of the impeller about the impeller axis; and, ii) controls the second magnetic field to thereby control movement of the impeller orthogonal to the cavity axis.

52) A fluid pump according to claim 51, wherein the controller controls the second magnetic field to thereby confrol movement of the impeller parallel to the cavity axis.

53) A fluid pump according to claim 51, wherein the fluid pump includes an axial coupling for restricting movement of the impeller in a direction parallel to the cavity axis.

54) A fluid pump including: a) a housing having an inner surface defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils coupled the housing for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the magnetic field in use; and, iv) an outer surface, at least a portion of the outer surface being shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis; c) an axial coupling for restricting movement of the impeller in a direction parallel to the cavity axis; and, d) a confroller for controlling the first magnetic field, to thereby cause rotation of the impeller about the impeller axis.

55) A fluid pump according to claim 53 or 54, wherein the axial coupling includes: a) a second set of coils for generating a second magnetic field; and, b) at least two sensors for sensing the position of the impeller within the cavity, the confroller being coupled to the sensors and the second set of coils, and wherein in use the confroller confrols the second magnetic field to thereby confrol movement of the impeller in a direction parallel to the cavity axis. 56) A fluid pump according to claim 53 or claim 54, wherein the axial coupling includes at least one of: a) a set of magnets coupled to the housing to generate an axial control field; and b) a number of axial support magnets provided in the body and positioned in the axial confrol field in use to thereby restrict movement of the impeller in a direction parallel to the cavity axis.

57) A fluid pump according to claim 53 or claim 54, wherein the axial coupling includes: a) a first bearing member coupled to the housing; and, b) a second bearing member coupled to the impeller, the first and second bearing members cooperating to thereby restrict movement of the impeller in a direction parallel to the cavity axis.

58) A fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first magnetic field in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity; and, d) a confroller coupled to the sensors and the set of coils, wherein in use the confroller controls the magnetic field to thereby control: i) rotation of the impeller about the impeller axis; and, ii) movement of the impeller in a direction parallel to the cavity axis.

59) A fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils to generate a first magnetic field; iv) a set of magnets to generate an axial control magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first magnetic field in use; and, iv) a number of support magnets positioned in the axial confrol magnetic field to thereby restrict movement of the impeller in a direction parallel to the cavity axis; c) a confroller coupled to the set of coils to control the first magnetic field to thereby control rotation of the driver about the driver axis.

60) A fluid pump including: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; ii) at least one fluid outlet; and, iii) a first bearing member; iv) a set of coils for generating a respective magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets; and, iv) a second bearing member, the first and second bearing members cooperating to thereby restrict movement of the impeller in a direction parallel to the cavity axis; c) a confroller coupled to the set of coils, the controller being adapted to control the magnetic field generated by the first set of coils to thereby control rotation of the driver about the driver axis.

61) A fluid pump according to any one of claims 8 to 10, wherein the fluid pump further includes a bearing for controlling movement of the impeller orthogonal to the cavity axis.

62) A fluid pump according to claim 11, wherein the bearing includes: a) an inner surface of the housing; and, b) the impeller has an outer surface, at least a portion of the outer surface being shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis.

63) A fluid pump according to claim 11, wherein the bearing includes: a) a second set of coils for generating a second magnetic field; b) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity, wherein the controller controls the third magnetic field using signals from the sensors to thereby control movement of the impeller orthogonal to the cavity axis. 64) A fluid pump according to any one of claims 1, 5, 8 and 13, the fluid pump including at least one sensor positioned at a first end of the cavity and at least two sensors positioned at a second opposing end of the cavity.

65) A fluid pump including: a) a housing having an inner surface defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; ii) at least one fluid outlet; iii) a set of coils coupled the housing for generating a first magnetic field; and, iv) a set of magnets coupled to the housing to generate an axial confrol magnetic field; b) an impeller positioned in the cavity for urging fluid from the inlet to the outlet, wherein the impeller has: i) a body defining an impeller axis, ii) a number of driver magnets positioned in the first magnetic field in use; iii) an outer surface, at least a portion of the outer surface being shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis; iv) a number of axial support magnets positioned in the axial control magnetic field to thereby restrict movement of the impeller in a direction parallel to the cavity axis; c) a confroller for confrolling the magnetic field, to thereby cause rotation of the impeller about the impeller axis.

66) A method of pumping fluid, using a fluid pump having: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) first and second sets of coils for generating respective first and second magnetic fields; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first and second magnetic fields in use; and, c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity, wherein the method includes: i) confrolling the first magnetic field to thereby confrol rotation of the impeller about the impeller axis; and, ii) confrolling the second magnetic field to thereby control movement of the impeller orthogonal to the cavity axis.

67) A method of pumping fluid using a fluid pump having: a) a housing defining a cavity having a cavity axis, the housing having: i) at least one fluid inlet; and, ii) at least one fluid outlet; iii) a set of coils for generating a magnetic field; b) an impeller positioned in the cavity, the impeller having: i) a body defining an impeller axis, the impeller axis being substantially parallel to the cavity axis in use; ii) a number of vanes positioned on the body for urging fluid from the inlet to the outlet, in use; iii) a number of driver magnets positioned in the first magnetic field in use; c) at least two sensors, the sensors being adapted to detect the position of the impeller within the cavity, wherein the method includes controlling the magnetic field to thereby confrol: i) rotation of the impeller about the impeller axis; and, ii) movement of the impeller in a direction parallel to the cavity axis.

68) A computer program product including computer executable code which when executed on a suitable processing system causes the processing system to perform the method of claim 66 or claim 67. 69) An impeller for use in a fluid pump, the impeller being mounted in a pump cavity and being adapted to urge fluid from first and second inlets to corresponding first and second outlets, wherein the impeller includes: a) a body defining an impeller axis, the body including first and second body end portions; b) a set of vanes positioned on each body end portion for urging fluid from a respective inlet to a corresponding outlet, in use; c) a number of driver magnets positioned in the first and second magnetic fields in use; and, d) an outer surface portion shaped so as to cooperate with a correspondingly shaped portion of the inner surface such that when fluid is pumped in use, a boundary layer is formed between the inner and outer surface portions, to thereby restrict movement of the impeller in a direction orthogonal to the cavity axis.

70) An impeller according to claim 69, wherein the impeller forms part of a fluid pump according to claim 1. 71) An impeller for use in a fluid pump, the impeller being mounted in a pump cavity and being adapted to urge fluid from first and second inlets to corresponding first and second outlets, wherein the impeller includes: a) a body defining an impeller axis, the body including first and second body end portions; b) a set of vanes positioned on each body end portion for urging fluid from a respective inlet to a corresponding outlet, in use; c) a number of driver magnets positioned in the first and second magnetic fields in use; and, d) at least a first part of an axial coupling for restricting movement of the impeller in a direction parallel to the impeller axis. 72) An impeller according to claim 61, wherein the axial coupling includes at least one of: a) a second bearing member adapted to cooperate with a first bearing member provided on the housing; and, b) a number of support magnets for positioning in an axial confrol magnetic field in use.

73) An impeller according to claim 69 to 72, wherein the dimensions of the vanes are selected to confrol at least one of the fluid pressure and the flow rate at the outlet.

74) An impeller according to claim 63, wherein the dimensions include at least one of: a) The height of the vanes; b) The diameters of the impellers; c) The length of the vanes; d) The width of the vanes; e) The inlet and outlet vane angles; f) The shape of the vanes; and, g) The number of vanes.

75) An impeller according to any one of the claims 69 to 74, wherein the impeller is positioned in a pump cavity in use such that the inlets are aligned parallel to the body axis, with each inlet being positioned to direct fluid along the body axis towards a respective body end portion, the impeller being rotated in use to thereby urge the fluid radially outwardly towards the outlets.

76) An impeller according to any one of claims 69 to 75, wherein the body includes a substantially cylindrical central body portion positioned between the two end portions, the driver magnets being positioned in the cylindrical central body portion.

77) An impeller according to any one of the claims 69 to 76, wherein the impeller being adapted to cooperate with the pump cavity to define first and second cavity portions, each cavity portion including a respective inlet, outlet, and end body portion, the impeller being adapted to substantially prevent fluid transfer between the cavity portions. 78) An impeller according to any one of the claims 69 to 77, the impeller being adapted for use a in heart pump, the first and second sets of vanes being adapted to pump blood for assisting the left and right ventricles respectively.