Source: https://patents.google.com/patent/US20010002234A1/en
Timestamp: 2019-04-23 19:33:16
Document Index: 764304500

Matched Legal Cases: ['art 3', 'art 4', 'art 100', 'art 100', 'art 20', 'art 20']

US20010002234A1 - Rotary pump with exclusively hydrodynamically suspended impeller - Google Patents
US20010002234A1
US20010002234A1 US09/299,038 US29903899A US2001002234A1 US 20010002234 A1 US20010002234 A1 US 20010002234A1 US 29903899 A US29903899 A US 29903899A US 2001002234 A1 US2001002234 A1 US 2001002234A1
US6250880B1 (en
1999-04-23 Application filed by Knobbe Martens Olson And Bear LLP filed Critical Knobbe Martens Olson And Bear LLP
1999-07-13 Assigned to VENTRASSIST PTY. LTD., TECHNOLOGY, SYDNEY UNIVERSITY OF reassignment VENTRASSIST PTY. LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: WATTERSON, PETER A., TANSLEY, GEOFFREY D., WOODARD, JOHN C.
This invention relates to rotary pumps adapted, but not exclusively, for use as artificial hearts or ventricular assist devices and, in particular, discloses in preferred forms a seal-less shaft-less pump featuring open or closed (shrouded) impeller blades with at least parts of the impeller used as hydrodynamic thrust bearings and with electromagnetic torque provided by the interaction between magnets embedded in the blades or shroud and a rotating current pattern generated in coils fixed relative to the pump housing. [0001]
According to one aspect of the present invention, there is disclosed a rotary blood pump for use in a heart assist device or like device, said pump having an impeller suspended in use within a pump housing exclusively by hydrodynamic thrust forces generated by relative movement of said impeller with respect to and within said pump housing. [0012]
In a further broad form of the invention there is provided a rotary blood pump having a housing within which an impeller acts by rotation about an axis to cause a pressure differential between an inlet side of a housing of said pump and an outlet side of the housing of said pump; said impeller suspended exclusively hydrodynamically by thrust forces generated by the impeller during movement in use of the impeller. [0038]
FIG. 15 is a graph of electrical power consumption versus flow for the pump assembly of FIG. 7; [0056]
FIG. 27 illustrates diagramatically the basis of operation of the “deformed surfaces” utilised for hydrodymanic suspension of embodiments of the invention. [0068]
A preferred embodiment of the invention is the centrifugal pump [0071] 1, as depicted in FIGS. 1 and 2, intended for implantation into a human, in which case the fluid referred to below is blood. The pump housing 2, can be fabricated in two parts, a front part 3 in the form of a housing body and a back part 4 in the form of a housing cover, with a smooth join therebetween, for example at 5 in FIG. 1. The pump 1 has an axial inlet 6 and a tangential outlet 7. The rotating part 100 is of very simple form, comprising only blades 8 and a blade support 9 to hold those blades fixed relative to each other. The blades may be curved as depicted in FIG. 2, or straight, in which case they can be either radial or back-swept, i.e. at an angle to the radius. This rotating part 100 will hereafter be called the impeller 100, but it also serves as a bearing component and as the rotor of a motor configuration as to be further described below whereby a torque is applied by electromagnetic means to the impeller 100. Note that the impeller has no shaft and that the fluid enters the impeller from the region of its axis RR. Some of the fluid passes in front of the support cone 9 and some behind it, so that the pump 1 can be considered of two-sided open type, as compared to conventional open centrifugal pumps, which are only open on the front side. Approximate dimensions found adequate for the pump 1 to perform as a ventricular assist device, when operating at speeds in the range 1,500 rpm to 4,000 rpm, are outer blade diameter 40 mm, outer housing average diameter 60 mm, and housing axial length 40 mm.
As the blades [0072] 8 move within the housing, some of the fluid passes through the gaps, much exaggerated in FIGS. 1 and 3, between the blade edges 101 and the housing front face 10 and housing back face 11. In all open centrifugal pumps, the gaps are made small because this leakage flow lowers the pump hydrodynamic efficiency. In the pump disclosed in this embodiment, the gaps are made slightly smaller than is conventional in order that the leakage flow can be utilised to create a hydrodynamic bearing. For the hydrodynamic forces to be sufficient, the blades may also be tapered as depicted in FIGS. 3A and 3B, so that the gap 104 is larger at the leading edge 102 of the blade 8 than at the trailing edge 103 thereby providing one example of a “deformed surface” as described elsewhere in this specification. The fluid 105 which passes through the gap thus experiences a wedge shaped restriction which generates a thrust, as described in Reynolds' theory of lubrication (see, for example, “Modern Fluid Dynamics, Vol. 1 Incompressible Flow”, by N. Curle and H. J. Davies, Van Nostrand, 1968). For blades considerably thinner than their axial length, the thrust is proportional to the square of the blade thickness at the edge, and thus in this embodiment thick blades are favoured, since if the proportion of the pump cavity filled by blades is constant, then the net thrust force will be inversely proportional to the number of blades. However, the blade edges can be made to extend as tails from thin blades as depicted in FIG. 3C in order to increase the blade area adjacent the walls.
For a given minimum gap, at the trailing blade edge, the hydrodynamic force is maximal if the gap at the leading edge is approximately double that at the trailing edge. Thus the taper, which equals the leading edge gap minus the trailing edge gap, should be chosen to match a nominal minimum gap, once the impeller has shifted towards that edge. Dimensions which have been found to give adequate thrust forces are a taper of around 0.05 mm for a nominal minimum gap of around 0.05 mm, and an average circumferential blade edge thickness of around 6 mm for 4 blades. For the front face, the taper is measured within the plane perpendicular to the axis. The axial length of the housing between the front and back faces at any position should then be made about 0.2 mm greater than the axial length of the blade, when it is coaxial with the housing, so that the minimum gaps are both about 0.1 mm axially when the impeller [0080] 100 is centrally positioned within the housing 2. Then, for example, if the impeller shifts axially by 0.05 mm, the minimum gaps will be 0.05 mm at one face and 0.15 mm at the other face. The thrust increases with decreasing gap and would be much larger from the 0.05 mm gap than from the 0.15 mm gap, about 14 times larger for the above dimensions. Thus there is a net restoring force away from the smaller gap.
Similarly, for radial shifts of the impeller the radial component of the thrust from the smaller gap on the conical housing front face would offer the required restoring radial force. The axial component of that force and its torque on the impeller would have to be balanced by an axial force and torque from the housing back face, and so the impeller will also have to shift axially and tilt its axis to be no longer parallel with the housing axis. Thus as the person moves and the pump is accelerated by external forces, the impeller will continually shift its position and alignment, varying the gaps in such a way that the total force and torque on the impeller [0081] 100 match that demanded by inertia. The gaps are so small, however, that the variation in hydrodynamic efficiency will be small, and the pumping action of the blades will be approximately the same as when the impeller is centrally located.
While smaller gaps imply greater hydrodynamic efficiency and greater bearing thrust forces, smaller gaps also demand tighter manufacturing tolerances, increase frictional drag on the impeller, and impose greater shear stress an the fluid. Taking these points in turn, for the above 0.05 mm tapers and gaps, tolerances of around 0.005 mm are needed, which imposes some cost penalty but is achievable. A tighter tolerance is difficult, especially if the housing is made of a plastic, given the changes in dimension caused by temperature and possible absorption of fluid by plastic materials which may be in contact with the blood such as Acrylic of polyurethane. The frictional drag for the above gaps produces much smaller torque than the typical motor torque. Finally, to estimate the shear stress, consider a rotation speed of 3,000 rpm and a typical radius of 15 mm, at which the blade speed is 4.7 ms-[0082] 1 and the average velocity shear for an average gap of 0.075 mm is 6.2×104 s−1. For blood of dynamic viscosity 3.5×10−3 kgm-1s-1, the average shear stress would be 220 Nm−2. Other prototype centrifugal blood pumps with closed blades have found that slightly larger gaps, e.g. 0.15 mm, are acceptable for haemolysis. A major advantage of the open blades of the present invention is that a fluid element that does pass through a blade edge gap will have very short residence time in that gap, around 2×10−3 S, and the fluid element will most likely be swept though the pump without passing another blade edge.
With particular reference to FIGS. 3A and 3B typical working clearances and working movement for the impeller [0083] 8 with respect to the upper and lower housing surfaces 10, 11 is of the order of 100 microns clearance at the top and at the bottom. In use gravitational and other forces will bias the impeller 8 closer to one or other of the housing walls resulting, typically in a clearance at one interface of the order of 50 microns and a corresponding larger clearance at the other interface of the order of 150 microns. In use, likely maximum practical clearances will range from 300 microns down to 1 micron.
Typical restoring forces for a 25 gram rotor mass spinning at 2200 rpm are 1.96 Newtons at a 20 micron clearance extending to 0.1 Newtons at an 80 micron clearance. [0084]
The means of providing the driving torque on the impeller [0093] 100 of the preferred embodiment of the invention is to encapsulate permanent magnets 14 in the blades 8 of the impeller 100 and to drive them with a rotating magnetic field pattern from oscillating currents in windings 15 and 16, fixed relative to the housing 2. Magnets of high remanence such as sintered rare-earth magnets should be used to maximise motor efficiency. The magnets can be aligned axially but greater motor efficiency is achieved by tilting the magnetisation direction to an angle of around 15° to 30° outwards from the inlet axis, with 22.5° tilt suitable for a body of conical angle 45°. The magnetisation direction must alternate in polarity for adjacent blades. Thus there must be an even number of blades. Since low blade number is preferred for the bearing force, and since two blades would not have sufficient bearing stiffness to rotation about an axis through the blades and perpendicular to the pump housing (unless the blades are very curved), four blades are recommended. A higher number of blades, for example 6 or 8 will also work.
A suitable impeller manufacturing method is to die-press the entire impeller, blades and support cone, as a single axially aligned magnet. The die-pressing is much simplified if near axially uniform blades are used (blades with an overhang such as in FIG. 3C are precluded). During pressing, the crushed rare-earth particles must be aligned in an axial magnetic field. This method of die-pressing with parallel alignment direction is cheaper for rare-earth magnets, although it produces slightly lower remanence magnets. The tolerance in die-pressing is poor, and grinding of the tapered blade edges is required. Then the magnet impeller can be coated, for example by physical vapour deposition, of titanium nitride for example, or by chemical vapour deposition, of a thin diamond coating or a teflon coating. [0097]
The winding topologies depicted in FIGS. 5B and C allow the possibility of higher motor efficiency but only if significantly higher coil mass is allowed, and since option FIG. 5A is more compact and simpler to manufacture, it is the preferred option. Material ribs between the coils of option FIG. 5A can be used to stiffen the housing. [0109]
Alternatively, the housing components [0113] 3 and 4 may be made from a biocompatible metallic material of low electrical conductivity, such as Ti-6A1-4V. To minimise the eddy current loss, the material must be as thin as possible, e.g. 0.1 mm to 0.5 mm, wherever the material experiences high alternating magnetic flux densities, such as between the coils and the housing inner surfaces 10 and 11.
FIG. 6 depicts an alternative embodiment of the invention as an axial pump. The pump housing is made of two parts, a front part [0116] 19 and a back part 20, joined for example at 21. The pump has an axial inlet 22 and axial outlet 23. The impeller comprises only blades 24 mounted on a support cylinder 25 of reducing radius at each end. An important feature of this embodiment is that the blade edges are tapered to generate hydrodynamic thrust forces which suspend the impeller. These forces could be used for radial suspension alone from the straight section 26 of the housing, with some alternative means used for axial suspension, such as stable axial magnetic forces or a conventional tapered-land type hydrodynamic thrust bearing. FIG. 6 proposes a design which uses the tapered blade edges to also provide an axial hydrodynamic bearing. The housing is made with a reducing radius at its ends to form a front face 27 and a back face 28 from which the axial thrusts can suspend the motor axially. Magnets are embedded in the blades with blades having alternating polarity and four blades being recommended. Iron in the outer radius of the support cylinder 25 can be used to increase the magnet flux density. Alternatively, the magnets could be housed in the support cylinder and iron could be used in the blades. A slotless helical winding 29 is recommended, with outward bending end-windings 30 at one end to enable insertion of the impeller and inward bending windings 31 at the other end to enable insertion of the winding into a cylindrical magnetic yoke 32. The winding can be encapsulated in the back housing part 20.
With reference to FIGS. [0117] 7 to 15 inclusive there is shown a further preferred embodiment of the pump assembly 200.
With particular reference initially to FIG. 7 the pump assembly [0118] 200 comprises a housing body 201 adapted for bolted connection to a housing cover 202 and so as to define a centrifugal pump cavity 203 therewithin.
The cavity [0119] 203 houses an impeller 204 adapted to receive magnets 205 within cavities 206 defined within blades 207. As for the first embodiment the blades 207 are supported from a support cone 208.
Exterior to the cavity [0120] 203 but forming part of the pump assembly 200 there is located a body winding 209 symmetrically mounted around inlet 210 and housed between the housing body 201 and a body yoke 211.
Also forming part of the pump assembly [0121] 200 and also mounted external to pump cavity 203 is cover winding 212 located within winding cavity 213 which, in turn, is located within housing cover 202 and closed by cover yoke 214.
The windings [0122] 212 and 209 are supplied from the electronic controller of FIG. 12 as for the first embodiment the windings are arranged to receive a three phase electrical supply and so as to set up a rotating magnetic field within cavity 203 which exerts a torque on magnets 205 within the impeller 204 so as to urge the impeller 204 to rotate substantially about central axis TT of cavity 203 and in line with the longitudinal axis of inlet 210. The impeller 204 is caused to rotate so as to urge fluid (in this case blood) around volute 215 and through outlet 216.
The assembly is bolted together in the manner indicated by screws [0123] 217. The yokes 211, 214 are held in place by fasteners 218. Alternatively, press fitting is possible provided sufficient integrity of seal can be maintained.
FIG. 8 shows the impeller [0124] 204 of this embodiment and clearly shows the support cone 208 from which the blades 207 extend. The axial cavity 219 which is arranged, in use, to be aligned with the longitudinal axis of inlet 210 and through which blood is received for urging by blades 207 is clearly visible.
The cutaway view of FIG. 9 shows the axial cavity [0125] 219 and also the magnet cavities 206 located within each blade 207. The preferred cone structure 220 extending from housing cover 202 aligned with the axis of inlet 210 and axial cavity 219 of impeller 204 is also shown.
FIG. 10 is a side section, indicative view of the impeller [0126] 204 defining the orientations of central axis FF, top taper edge DD and bottom taper edge BB, which tapers are illustrated in FIG. 11 in side section view.
FIG. 11A is a section of a blade [0127] 207 of impeller 204 taken through plane DD as defined in FIG. 10 and shows the top edge 221 to be profiled from a leading edge 223 to a trailing edge 224 as follows: central portion 227 comprises an ellipse with centre on the dashed midline having a semi-major axis of radius 113 mm and a semi-minor axis of radius 80 mm and then followed by leading conical surface 225 and trailing conical surface 226 on either side thereof as illustrated in FIG. 11A. The leading surface 225 has radius 0.05 mm less than the trailing surface 226. This prescription is for a taper which can be achieved by a grinding wheel, but many alternative prescriptions could be devised to give a taper of similar utility.
The leading edge [0128] 223 is radiused as illustrated.
FIG. 11B illustrates in cross-section the bottom edge [0129] 222 of blade 207 cut along plane BB of FIG. 10.
The bottom edge includes cap [0130] 228 utilised for sealing magnet 205 within cavity 206.
In this instance substantially the entire edge comprises a straight taper with a radius of 0.05 mm at leading edge [0131] 229 and a radius of 0.25 mm at trailing edge 230.
The blade [0132] 207 is 6.0 mm in width excluding the radii at either end.
FIG. 12 comprises a block diagram of the electrical controller suitable for driving the pump assembly [0133] 200 and comprises a three phase commutation controller 232 adapted to drive the windings 209, 212 of the pump assembly. The commutation controller 232 determines relative phase and frequency values for driving the windings with reference to set point speed input 233 derived from physiological controller 234 which, in turn, receives control inputs 235 comprising motor current input and motor speed (derived from the commutation controller 232), patient blood flow 236, and venous oxygen saturation 237. The pump blood flow can be approximately inferred from the motor speed and current via curve-fitted formulae.
FIG. 13 is a graph of pressure against flow for the pump assembly [0134] 200 where the fluid pumped is 18% glycerol for impeller rotation velocity over the range 1500 RPM to 2500 RPM. The 18% glycerol liquid is believed to be a good analogue for blood under certain circumstances, for example in the housing gap.
FIG. 14 graphs pump efficiency against flow for the same fluid over the same speed ranges as for FIG. 13. [0135]
FIG. 15 is a graph of electrical power consumption against flow for the same fluid over the same speed ranges as for FIG. 13. [0136]
The common theme running through the first, second and third embodiments described thus far is the inclusion in the impeller of a taper or other deformed surface which, in use, moves relative to the adjacent housing wall thereby to cause a restriction with respect to the line of movement of the taper or deformity thereby to generate thrust upon the impeller which includes a component substantially normal to the line of movement of the surface and also normal to the adjacent internal pump wall with respect to which the restriction is defined for fluid located therebetween. [0137]
In order to provide both radial and axial direction control at least one set of surfaces must be angled with respect to the longitudinal axis of the impeller (preferably at approximately 45° thereto) thereby to generate or resolve opposed radial forces and an axial force which can be balanced by a corresponding axial force generated by at least one other tapered or deformed surface located elsewhere on the impeller. [0138]
In the forms thus far described top surfaces of the blades [0139] 8, 207 are angled at approximately 45° with respect to the longitudinal axis of the impeller 100, 204 and arranged for rotation with respect to the internal walls of a similarly angled conical pump housing. The top surfaces of the blades are deformed so as to create the necessary restriction in the gap between the top surfaces of the blades and the internal walls of the conical pump housing thereby to generate a thrust which can be resolved to both radial and axial components.
In the examples thus far the bottom faces of the blades [0140] 8, 207 comprise surfaces substantially lying in a plane at right angles to the axis of rotation of the impeller and, with their deformities define a gap with respect to a lower inside face of the pump housing against which a substantially only axial thrust is generated.
Other arrangements are possible which will also, relying on these principles, provide the necessary balanced radial and axial forces. Such arrangements can include a double cone arrangement where the conical top surface of the blades is mirrored in a corresponding bottom conical surface. The only concern with this arrangement is the increased depth of pump which can be a problem for in vivo applications where size minimisation is an important criteria. [0141]
With reference to FIG. 18 a further embodiment of the invention is illustrated comprising a plan view of the impeller [0142] 300 forming part of a “channel” pump. In this embodiment the blades 301 have been widened relative to the blades 207 of the third embodiment to the point where they are almost sector-shaped and the flow gaps between adjacent blades 301, as a result, take the form of a channel 302, all in communication with axial cavity 303.
A further modification of this arrangement is illustrated in FIG. 19 wherein impeller [0143] 304 includes sector-shaped blades 305 having curved leading and trailing portions 306, 307 respectively thereby defining channels 308 having fluted exit portions 309.
As with the first and second embodiments the radial and axial hydrodynamic forces are generated by appropriate profiling of the top and bottom faces of the blades [0144] 301, 305 (not shown in FIGS. 18 and 19).
FIG. 20 illustrates a perspective view of an impeller [0145] 304 which follows the theme of the impeller arrangement of FIGS. 18 and 19 in perspective view and where like parts are numbered as for FIG. 19. In this case the four blades 305 are joined at mid-portions thereof by a blade support in the form of a conical rim 350 and have edge portions which are shaped so as to have an increased curvature on the trailing edge 351 thereof compared with the leading edge 352.
A fifth embodiment of a pump assembly according to the invention comprises an impeller [0146] 410 as illustrated in FIG. 21 where, conceptually, the upper and lower surfaces of the blades of previous embodiments are interconnected by a top shroud 411 and a bottom shroud 412. In this embodiment the blades 413 can be reduced to a very small width as the hydrodynamic behaviour imparted by their surfaces in previous embodiments is now given effect by the profiling of the shrouds 411, 412 which, in this instance, comprises a series of smooth-edged wedges with the leading surface of one wedge directly interconnected to the trailing edge of the next leading wedge 414.
As for previous embodiments the top shroud [0147] 411 is of overall conical shape thereby to impart both radial and axial thrust forces whilst the bottom shroud 412 is substantially planar thereby to impart substantially only axial thrust forces.
It is to be understood that, whilst the example of FIG. 21 shows the surfaces of the shroud [0148] 411 angled at approximately 45° to the vertical, other inclinations are possible extending to an inclination of 0° to the vertical which is to say the impeller 410 can take the form of a cylinder with surface rippling or other deformations which impart the necessary hydrodynamic lift, in use.
With reference to FIGS. [0149] 22 to 24 a specific example of the concept embodied in FIG. 21 is illustrated and wherein like components are numbered as for FIG. 21.
It will be observed that, with reference to FIG. 24, the blades [0150] 413 are thin compared to previous embodiments and, in this instance, are arcuate channels 416 therebetween which allow fluid communication from a centre volume 417 to the periphery 418 of the impeller 410.
In this arrangement it will be noted that the wedges [0151] 414 are separated one from the other on each shroud by channels 419. The channels extend radially down the shroud from the centre volume 417 to the periphery 418.
In such designs with thin blades, the magnets required for the driving torque can be contained within the top or bottom volute or both, along with the optional soft magnetic yokes to increase motor efficiency. [0152]
A variation of this embodiment is to have the wedge profiling cut into the inner surfaces of the housing and have smooth shroud surfaces. [0153]
In contrast to the embodiments illustrated with respect to FIGS. 3A, 3B and [0154] 3C an arrangement is shown in FIG. 25 wherein the “deformed surface” comprises a stepped formation 510 forming part of an inner wall of the pump housing (not shown). In this instance the rotor including blade 511 includes a flat working surface 512 (and not having a deformed surface therein) which is adapted for relative movement in the direction of the arrow shown with respect to the stepped formation 510 thereby to generate hydrodynamic thrust therebetween.
With reference to FIG. 26 there is shown an arrangement of rotor blade [0155] 610 with respect to stepped formation 611 and wherein the rotor blade 610 includes a deformed surface 612 at a working face thereof. In this instance the deformation comprises curved edges 613, 614. As for the previous embodiment relative movement of the rotor blade 610 in the direction of the arrow with respect to deformed surface 611 forming part of the pump housing (not shown) causes relative hydrodynamic thrust therebetween.
The foregoing describes principles and examples of the present invention, and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope and spirit of the invention. [0156]
With particular reference to FIG. 27 this specification describes the suspension of an impeller [0157] 600 within a pump housing 601 by the use of hydrodynamic forces. In this specification the suspension of the impeller 600 is performed dominantly which is to say exclusively by hydrodynamic forces.
The hydrodynamic forces are forces which are created by relative movement between two surfaces which have a fluid in the gap between the two surfaces. In the case of the use of the pump assembly [0158] 602 as a rotary blood pump the fluid is blood.
The hydrodynamic forces can arise during relative movement between two surfaces even where those surfaces are substantially entirely parallel to each other or non-deformed. However, in this specification, hydrodynamic forces are caused to arise during relative movement between two surfaces where at least one of the surfaces includes a “deformed surface”. [0159]
In this specification “deformed surface” means a surface which includes an irregularity relative to a surface which it faces such that, when the surface moves in a predetermined direction relative to the surface which it faces the fluid located in the gap there between experiences a change in relative distance between the surfaces along the line of movement thereby to cause a hydrodynamic force to arise therebetween in the form of a thrust force including at least a component substantially normal to the plane of the gap defined at any given point between the facing surfaces. [0160]
In the example of FIG. 27 there is a first deformed surface [0161] 603 forming at least part of a first face 604 of impeller 600 and a second deformed surface 605 on a second face 606 of the impeller 600.
The inset of FIG. 27 illustrates conceptually how the first deformed surface [0162] 603 may form only part of the first face 604.
The first deformed surface [0163] 603 faces first inner surface 607 of the pump housing 601 whilst second deformed surface 605 faces second inner surface 608 of the pump housing 601.
In use first gap [0164] 609 defined between first deformed surface 603 and first inner surface 607 has a fluid comprising blood located therein whilst second gap 610 defined between second deformed surface 605 and second inner surface 608 also has a fluid comprising blood located therein.
In use impeller [0165] 600 is caused to rotate about impeller axis 611 such that relative movement across first gap 609 between first deformed surface 603 and first inner face 607 occurs and also relative movement across second gap 610 between second deformed surface 605 and second inner surface 608 occurs. The orientation of the deformities of first deformed surface 603 and second deformed surface 605 relative to the line of movement of the deformed surfaces 603, 605 relative to the inner surfaces 607, 608 is such that the fluid in the gaps 609, 610 experiences a change in height of the gap 609, 610 as a function of time and with the rate of change dependant on the shape of the deformities of the deformed surfaces and also the rate of rotation of the impeller 600 relative to the housing 601. That is, at any given point on either inner surface 607 or 608, the height of the gap between the inner surface 607 or 608 and corresponding deformed surface 603 or 605 will vary with time due to passage of the deformed surface 603 or 605 over the inner surface.
Hydrodynamic forces in the form of thrust forces normal to the line of relative movement of the respective deformed surfaces [0166] 603, 605 relative to the inner surfaces 607, 608 thus arise.
With this configuration it will be noted that the first gap [0167] 609 lies substantially in a single plane whilst the second gap 610 is in the form of a cone and angled at an acute angle relative to the plane of the first gap 609.
Accordingly, the thrust forces which can be enlisted to first gap [0168] 609 and second gap 610 are substantially normal to and distributed across both the predominantly flat plane of first deformed surface 603 and normal to the substantially conical surface of second deformed surface 605 thereby permitting restoring forces to be applied between the impeller 600 and the pump housing 601 thereby to resist forces which seek to translate the impeller 600 in space relative to the pump housing 601 and also to rotate the impeller 600 about any axis (other than about the impeller axis 611) relative to the pump housing 601. This arrangement substantially resists five degrees of freedom of movement of impeller 600 with respect to the housing 601 and does so predominantly without any external intervention to control the position of the impeller with respect to the housing given that disturbing forces from other sources, most notably magnetic forces on the impeller due to its use as rotor of the motor are net zero when the impeller occupies a suitable equilibrium position. The balance of all forces on the rotor, effected by manipulation of magnetic and other external sources, may be adjusted such that the rotor is predominantly hydrodynamically born.
It will be observed that these forces increase as the gaps [0169] 609, 610 narrow relative to a defined operating position and decrease as the gaps 609, 610 increase relative to a defined operating gap. Because of the opposed orientation of first deformed surface 603 relative to second deformed surface 605 it is possible to design for an equilibrium position of the impeller 600 within the pump housing 601 at a defined equilibrium gap distance for gaps 609, 610 at a specified rotor rotational speed about axis 611 and rotor mass leading to a close approximation to an unconditionally stable environment for the impeller 600 within the pump housing 601 against a range of disturbing forces.
Characteristics and advantages which flow from the arrangement described above and with reference to the embodiments includes: [0170]
1. Low haemolysis, hence low running speed and controlled fluid dynamics (especially shear stress) in the gap between the casing and impeller. This in turn led to the selection of radial off-flow and minimal incidence at on-flow to the rotor; [0171]
2. Radial or near-radial off-flow from the impeller can be chosen in order to yield a “flat” pump characteristic (HQ) curve. [0172]
The pump assembly [0173] 1, 200 is applicable to pump fluids such as blood on a continuous basis. With its expected reliability it is particularly applicable as an in vivo heart assist pump.
The pump assembly can also be used with advantage for the pumping of other fluids where damage to the fluid due to high shear stresses must be avoided or where leakage of the fluid must be prevented with a very high degree of reliability—for example where the fluid is a dangerous fluid. [0174]
2. The pump of
wherein at least one of said impeller or said housing includes at least one deformed surface which, in use, moves relative to a facing surface on the other of said impeller or said housing thereby to cause a restriction in the form of a reducing distance between the surfaces with respect to the relative line of movement of said deformed surface thereby to generate relative hydrodynamic thrust between said impeller and said housing which includes everywhere a localized thrust component substantially and everywhere normal to the plane of movement of said deformed surface with respect to said facing surface.
3. The pump of
wherein the combined effect of the localized normal forces generated on the surfaces of said impeller is to produce resistive forces against movement in three translational and two rotational degrees of freedom thus supporting the impeller for rotational movement within said housing exclusively by hydrodynamic forces.
wherein said thrust forces are generated by blades of said impeller.
wherein said thrust forces are generated by edges of said blades of said impeller.
wherein said edges of said blades are tapered or non-planar so that a thrust is created between the edges and the adjacent pump casing during relative movement therebetween.
wherein said edges of said blades are shaped such that the gap at the leading edge of the blade is greater than at the trailing edge and thus the fluid which is drawn through the gap experiences a wedge shaped restriction which generates a thrust.
wherein the pump is of centrifugal type or mixed flow type with impeller blades open on both front and back faces of the pump housing.
wherein the front face of the housing is made conical, in order that the thrust perpendicular to the conical surface has a radial component, which provides a radial restoring force to a radial displacement of the impeller axis during use.
wherein the driving torque of said impeller derives from the magnetic interaction between permanent magnets within the blades of the impeller and oscillating currents in windings encapsulated in the pump housing.
11. The pump of
wherein said blades include magnetic material therein, the magnetic material encapsulated within a biocompatible shell or coating.
12. The pump of
wherein said biocompatible shell or coating comprises a diamond coating or other coating which can be applied at low temperature.
wherein internal walls of said pump which can come into contact with said blades during use are coated with a hard material such as titanium nitride or diamond coating.
14. The pump of
wherein said impeller comprises an upper conical shroud having said taper or other deformed surface therein and wherein blades of said impeller are supported below said shroud.
15. The pump of
wherein said impeller further includes a lower shroud mounted in opposed relationship to said upper conical shroud and whereas said blades are supported within said upper and said lower shroud.
16. The pump of
wherein said deformed surface is located on said impeller.
wherein said deformed surface is located within said housing.
18. The pump of
wherein forces imposed on said impeller in use, other than hydrodynamic forces, are controlled by design so that, over a predetermined range of operating parameters, said hydrodynamic thrust forces provide sufficient thrust to maintain said impeller suspended in use within said pump housing.
US6250880B1 US6250880B1 (en) 2001-06-26
US11/212,227 Active 2019-06-14 US7476077B2 (en) 1997-09-05 2005-08-26 Rotary pump with exclusively hydrodynamically suspended impeller
EP2719403A1 (en) * 2012-10-12 2014-04-16 Abiomed Europe GmbH Centrifugal blood pump
2005-08-26 US US11/212,227 patent/US7476077B2/en active Active
JP2017164503A (en) * 2012-10-12 2017-09-21 アビオメド オイローパ ゲーエムベーハー Centrifugal blood pump
JP2015532146A (en) * 2012-10-12 2015-11-09 アビオメド オイローパ ゲーエムベーハー Centrifugal blood pump