United States· Patent [19]
`Bramm et al.
`
`[I.1] Patent Number:
`[45] Date of Patent:
`
`4,944,748
`*Jul. 31, 1990
`
`[54] MAGNETICALLY SUSPENDED AND
`ROTATED ROTOR
`
`[76]
`
`Inventors: Gunter W. Bramm, Luisen Strasse 49,
`8000 Munchen 2, Fed. Rep. of
`Germany; Don B. Olsen, 8832 Blue
`Jay La., Salt Lake City, Utah 84121
`
`[ * ] Notice:
`
`The portion of the term of this patent
`subsequent to May 26, 2004 has been
`disclaimed.
`
`[21] Appl. No.: 193,180
`
`(22] Filed:
`
`May9, 1988
`
`Related U.S. Application Data
`[63] Continuation of Ser. No. 914,486, Oct. 12, 1986, which
`is a continuation of Ser. No. 720,081, Apr. 4, 1985.
`
`Int. Cl.s ............................................... A61M 1/10
`[51]
`[52] U.S. Cl •........................................ 623/3; 417/356;
`416/111
`[58] Field of Search ............................ 623/3; 416/111;
`417/356
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`Re. 27,849 12/1973 Wortman .
`1,105,967 8/1914 Davidson .
`1,711,045 4/1929 Davis .
`2,263,515 11/1941 Pezzillo .
`2,319,730 5/1943 Garraway .
`2,500,400 3/1950 Cogswell .
`2,535,695 12/1950 Pezzillo, Jr ..
`2,827,856 3/1958 Zozulin .
`3,194,165 7/1965 Sorlin .
`3,433,163 3/1969 Sheets .
`3,647,324 3/1972 Rafferty et al ..
`3,846,050 11/1974 Laing .
`3,938,913 2/1976 Isenberg et al ..
`3,957,389 5/1976 Rafferty et al ..
`3,970,408 7/1976 Rafferty et al ..
`4,173,796 11/1979 Jarvik .
`4,213,207 7/1980 Wilson .
`4,382,199 5/1983 Isaacson .............................. 416/111
`4,518,317 5/1985 Inoue .
`4,523,896 6/1985 Lhenry et al ..
`4,688,998 8/1987 Olsen et al. ......................... 417/356
`
`FOREIGN PATENT DOCUMENTS
`1202392 10/1965 Fed. Rep. of Germany .
`2341766 2/1975 Fed. Rep. of Germany .
`2420825 11/1975 Fed. Rep. of Germany .
`2457783 6/1976 Fed. Rep. of Germany .
`2515608 9/1976 Fed. Rep. of Germany .
`2177339 11/1973 France .
`361209 7/1938 Italy .
`
`OTHER PUBLICATIONS
`"An Instrumental Approach to In Vivo Hemocompati(cid:173)
`bility Assessment: Development of the Intravascular
`Magnetic Suspension of A Test Device", by D. M.
`Lederman, R. D. Cumming, H. E. Petschek, T. H.
`Chiu, E. Nyilas, and E. W. Salzman, vol. 283, pp.
`524-535, Feb. 10, 1977, 24894.
`Primary Examiner-Randall L. Green
`Assistant Examiner-Stephanie L. Iantorno
`Attorney, Agent, or Firm-Dunlap, Codding, Peterson &
`Lee
`ABSTRACT
`[57]
`The impellor of a blood pump is supported by perma(cid:173)
`nent magnets on the impellor and pump housing and
`stabilized by an electromagnet on the housing. A con(cid:173)
`trol circuit supplies current to the electromagnet to
`maintain the axial position of the impellor at a control
`position in which the impellor is in mechanical equilib(cid:173)
`rium under permanent magnet forces and static axial
`forces on the impellor to minimize energy consumption
`in the support of the impellor. The impellor is rotated
`magnetically and stator coils in the housing are supplied
`with electric currents having a frequency and amplitude
`adjusted in relation to blood pressure at the pump inlet
`to match the flow characteristics of the pump to physio(cid:173)
`logical characteristics of the natural heart. A cavity is
`formed in the impellor to match the average specific
`gravity of the impellor and portions of the suspension
`and drive systems thereon to the specific gravity of
`blood to further minimize power consumption by the
`pump. A valve member can be formed on the impeller
`to mate with a restriction in the pump inlet for pumps
`used to assist the pumping action of the natural heart.
`
`10 Claims, 14 Drawing Sheets
`
`54
`
`Petitioners' Exhibit 1008, pg. 1
`
`

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`U.S. Patent
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`

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`Jul. 31, 1990
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`

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`U.S. Patent
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`Jul. 31, 1990
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`

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`U.S. Patent
`
`Jul. 31, 1990
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`

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`Petitioners' Exhibit 1008, pg. 12
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`

`

`U.S. Patent
`US. Patent
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`Jul. 31, 1990
`Jul. 31, 1990
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`

`

`U.S. Patent
`US. Patent
`
`Jul. 31, 1990
`
`Sheet 14 of 14
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`Petitioners' Exhibit 1008, pg. 15
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`

`

`1
`
`4,944,748
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`2
`working of the blood causing blood cells to rupture
`Glands which might be used to seal these bearings can(cid:173)
`not solve this problem. Since the impellor will be mov(cid:173)
`ing with respect to the gland, blood in the neighbor-
`5 hood of the gland-impellor interface will be subjected
`to high sheer stresses and friction which can cause the
`rupture of blood cells in much the same manner that
`rupturing of blood cells is occasioned in a bearing.
`Another mechanical effect that can injure blood is the
`IO formation of regions within the pump in which the
`blood is stagnant or in which eddies without sufficient
`blood exchange, equivalent to stagnation, may occur.
`Stagnation tends to result in coagulation of the blood.
`A third effect that can injure blood is excessive heat(cid:173)
`ing as the blood passes through the pump. If the pump
`is inefficient, so that a large part of the energy supplied
`to the pump appears as heat discharged into the blood,
`blood cells may be damaged through overheating or
`coagulation of the blood may occur. In this regard, it
`should be noted that albumen begins to denature at 42°
`C. so that inefficiency of the pump resulting in over-
`heating of the blood can be a serious problem.
`
`MAGNETICALLY SUSPENDED AND ROTATED
`ROTOR
`
`This application is a continuation of Ser. No. 914,486,
`filed Oct. 2, 1986, entitled "MAGNETICALLY SUS(cid:173)
`PENDED AND ROTATED ROTOR" now aban(cid:173)
`doned, which is a continuation of Ser. No. 720,08 i, filed
`Apr. 4, 1985, entitled "MAGNETICALLY SUS(cid:173)
`PENDED AND ROTATED ROTOR" now aban(cid:173)
`doned.
`
`20
`
`BACKGROUND OF THE INVENTION
`The present invention relates· generally to apparatus
`for suspending and rotating rotors and, more particu- 15
`lady, but not by way oflimitation, to the suspension and
`rotation of the impellors of pumps that can be implanted
`in the human body for replacing or assisting the natural
`heart in the pumping of blood through the circulatory
`system.
`It has long been a goal of experimenters to develop a
`pump which can serve as an artificial heart and a variety
`of types of pumps have been designed to either replace
`or assist the natural heart in its function of pumping
`blood through the human body. While these prior art 25
`pumps have met with some degree of success, a number
`of problems associated with them have remained un(cid:173)
`solved so that a practical artificial heart has not previ(cid:173)
`ously been developed. For a pump to be usable as a
`replacement or as an assist for the human heart, the 30
`pump must meet certain practical requirements which
`have been discussed in U.S. Pat. application Ser. No.
`245,007, the teachings of which are hereby specifically
`incorporated herein by reference.
`On a general level, the requirements for a blood pump 35
`are that it must not cause substantial injury to the blood
`and it must not require a large back-up system for its
`operation. Injury to the blood would preclude use of
`the pump over extended periods of time that would be
`required, for example, if the pump were to be a replace- 40
`ment for the natural heart or an assist that is to be im(cid:173)
`planted for the life of the patient. The size of the back-
`up system is a requirement that relates to the quality of
`life; for a pump to be practical, it must not require that
`the recipient be forever tied to an immobile life support 45
`system.
`The requirement that the pump not require a large
`back-up system places certain technical requirements on
`the construction of a practical blood pump. One such
`requirement is that the pump be operable electrically so 50
`that the power supply for the pump can be provided by
`rechargeable batteries. At present, the technology is
`available to implant batteries within the human body
`and to recharge these batteries periodically using an
`induction coil that can be placed against the body as has 55
`been noted in the aforementioned U.S Pat. application
`Ser. No. 245,007. Similarly, it is presently possible to
`build highly efficient, electrically operated pumps in
`which the pumping action is achieved by the rotation of
`an impellor to cause a liquid to be driven through a 60
`chamber in which the impellor is located The problem
`that has not been solved prior to the present invention is
`to provide such a pump which will not cause unaccept(cid:173)
`able injury to blood.
`.
`A pump can injure blood in several ways. If the im- 65
`pellor of the pump is supported by mechanical bearings
`in contact with the blood, relative movement between
`parts of the bearings can result in excessive mechanical
`
`SUMMARY OF THE INVENTION
`The present invention solves the problems that have
`been encountered with earlier blood pumps through a
`novel approach to rotor suspension and rotation, an
`approach which leads not only to a practical blood
`pump but additionally provides an apparatus which, it is
`contemplated, will have a variety of practical applica(cid:173)
`tions in a number of fields. Thus, the rotor can be the
`impeller of a pump and, more specifically, a blood
`pump that can be implanted in the body to replace or
`assist the natural heart. However, the invention is not
`limited to such use; rather, in its most general form, the
`invention is an apparatus for suspending and rotating a
`rotor for any useful purpose. For example, it is contem(cid:173)
`plated that the rotor might be the impellor of a pump
`that is used to pump radioactive, abrasive, or corrosive
`fluids, liquids containing dissolved gases, or the rotor of
`a gyroscope in a missile guidance system where power
`requirements play a role or any suspended rotor in an
`accelerated, moving system in general.
`Nevertheless, it will be useful to consider the appara(cid:173)
`tus of the present invention in a specific context to fully
`bring out the benefits and advantages the invention
`provides. It is in this spirit of complete disclosure that
`the apparatus will be described with particular refer(cid:173)
`ence to the application in which the invention is particu(cid:173)
`larly adapted to the pumping of blood through the
`human body.
`As adapted for use as a blood pump, the apparatus of
`the present invention solves the problems that have
`been encountered with earlier blood pumps by provid(cid:173)
`ing a pump having an impellor that is magnetically
`suspended in a housing and magnetically rotated to
`effect the pumping of blood through the housing. Since
`the impellor is magnetically suspended and rotated, no
`bearings which might mechanically damage blood are
`needed in the pump and no bulky back-up system is
`needed to operate the pump. Rather, a battery pack can
`be utilized for this purpose. Moreover, the apparatus is
`constructed so that very little energy is expended in
`effecting the suspension of the impellor with the result
`that discharge of heat into the blood from the magnetic
`suspension system is held to a minimum level. An ad(cid:173)
`vantage of this construction is that the low power con(cid:173)
`sumption needed to effect the suspension of the impellor
`
`Petitioners' Exhibit 1008, pg. 16
`
`

`

`4,944,748
`
`3
`enables a battery pack which can be used to operate the
`apparatus to be implanted in the body and periodically
`recharged as has been noted above. Thus, the present
`invention provides a heart replacement or assist that is
`capable not only of preserving the life of the user but 5
`one which will make that life meaningful by providing
`only minimal interference with the user's conduct of
`normal human affairs.
`Additionally, the magnetic suspension of the impellor
`solves problems associated with pump lifetime. A se- 10
`vere problem that has been encountered with prior art
`pumps is wear and embrittlement of material of which
`the pumps are constructed and, in the case of blood
`pumps, wear and embrittlement of blood compatible
`materials that are included in the construction of the 15
`pumps. Both wear and embrittlement cause pump fail(cid:173)
`ure or changes in the surface structure of blood compat(cid:173)
`ible materials, reducing the effectiveness of such materi(cid:173)
`als, requiring termination of the use of the pump. The
`use of a magnetic bearing to support the impellor elimi- 20
`nates stresses that might otherwise be exerted on the
`materials, including blood compatible materials, of
`which the pump might be constructed. (A preferred
`construction of the pump of the present invention, when
`used as a blood pump, is the utilization of rigid sub- 25
`strates coated with a blood compatible material. An
`important advantage the magnetic suspension of the
`impellor of the present invention is that it permits all
`surfaces in contact with blood to be composed of mate(cid:173)
`rials which need not have special properties, such as 30
`flexibility, that are not associated with compatibility.)
`Thus, the magnetic suspension of the rotor eliminates
`bending stresses, frictional forces, and heating stresses
`to provide the pump with maintenance free, substan(cid:173)
`tially indefinite lifetime.
`To provide the pump adaptation of the apparatus
`with the capability of meeting these ends, the support of
`the impellor is effected by permanent magnets that are
`located on the impeller and the housing within which
`the impellor is rotated. Since the forces these magnets 40
`exert on the impellor to support it are conservative
`forces, the support of the impeller requires no expendi(cid:173)
`ture of energy which might be degraded into heat and
`discharged into the blood to possibly cause injury to the
`blood. Rather, the only expenditure of energy required 45
`in the suspension of the irnpellor is energy used to stabi(cid:173)
`lize the impeller suspension system and such energy
`expenditure can be minimized by supporting the impel(cid:173)
`lor at a control position at which the impellor is in
`mechanical equilibruim.
`It is well known that a suspension system comprised
`solely of permanent magnets cannot be stable so that no
`object can be supported solely by permanent magnets, a
`fact that is based on Earnshaw's theorem. However, the
`instability in the suspension of an object by permanent 55
`magnets is subject to control. That is, permanent mag(cid:173)
`nets can be used to stably support an object with respect
`to some, but not all, degrees of freedom of movement of
`the suspended object about a selected support position
`and the degree of freedom for which the suspension is 60
`unstable can be selected. The present invention exploits
`this selection capability to provide a suspension system
`for a pump impeller that maximizes permanent magnet
`support forces while requiring very little energy to
`maintain the impellor in position in the pump housing, 65
`thereby minimizing the generation of heat by the sus(cid:173)
`pension system to enable the pump to be used as a re(cid:173)
`placement for, or an assist to, the natural human heart in
`
`4
`the pumping of blood through the circulatory system.
`Such power minimization also permits the use of much
`smaller components in a pump and the use of a highly
`portable power supply for the pump.
`In the pump of the present invention, the permanent
`magnets are mounted on the pump impeller and on the
`pump housing and the magnetization of these perma(cid:173)
`nent magnets is selected so that the permanent magnets
`will tend to align the rotation axis of the impellor with
`a selected support axis on the housing. With such selec(cid:173)
`tion, the permanent magnets will not stably support the
`impeller with respect to axial movement of the impellor
`along the housing support axis. Rather, the permanent
`magnets will tend to drive the impellor away from a
`null position on the housing support axis at which the
`permanent magnet forces cancel. An electromagnet is
`then provided, along with an electromagnet control
`circuit that controls the current through the electro(cid:173)
`magnet in accordance with impeller position, to exert
`axial forces on the pump impellor, via portions of the
`permanent magnet assembly mounted on the pump
`impeller, so that the electromagnet can be used to over(cid:173)
`come the axial instability in the support of the impellor
`by the permanent magnet assembly. Since the electro(cid:173)
`magnet is used only to overcome the instability, as op(cid:173)
`posed to providing support for the impeller, very little
`power is required to operate the electromagnet. More(cid:173)
`over, and as practiced in one preferred embodiment of
`the invention, the current through the electromagnet
`can be continuously monitored and control of the cur(cid:173)
`rent can be effected to maintain power consumption by
`the electromagnet at a minimum in the presence of
`static, or long term, axial forces on the impeller in addi(cid:173)
`tion to the forces arising from the permanent magnets
`35 and the electromagnet of the impellor suspension sys(cid:173)
`tem. In the presence of static axial forces, the electro(cid:173)
`magnet drives the impellor toward a control position
`which is shifted slightly from the null position defined
`by the permanent magnets of the suspension system so
`that the static axial forces are balanced by a force pro(cid:173)
`vided by the permanent magnets of the suspension sys-
`tem. The invention thus provides, by way of example,
`flexibility in pump construction by enabling the perma(cid:173)
`nent magnets of the suspension system to be used to
`counteract reaction forces on the impellor that occur as
`the result of pumping for certain pump designs.
`In a pump constructed using the apparatus of the
`present invention, rotation of the impellor to pump
`blood is effected magnetically by constructing the
`50 pump impeller such that the impeller serves as the rotor
`of an electric motOr. In one preferred construction of
`the irnpellor, a shorting ring is formed about the periph(cid:173)
`ery of the impellor and stator coils are mounted in the
`pump housing about the shorting ring so that the pump
`impellor is also the rotor of an eddy current induction
`motor. Thus, no mechanical connections need be made
`to the pump impellor to suspend and rotate the impeller
`so that construction of a blood pump following the
`teachings of the present invention eliminates any need
`for bearings, glands and the like in contact with blood
`which could cause mechanical damage to the blood.
`Additionally, the stator coils and shorting ring are
`placed in the pump so that the rotation of the impeller
`produces, at most, only negligible forces on the impeller
`that would have to be overcome by the magnetic sus(cid:173)
`pension system of the impellor.
`Another aspect of the present invention is the control
`of current through the stator coils that are provided to
`
`Petitioners' Exhibit 1008, pg. 17
`
`

`

`4,944,748
`
`5
`rotate the impellor of the pump. In the natural heart, a
`relationship known as the Frank-Starling effect exists
`between the flow rate of blood through the heart and
`the blood pressure at the inlet to the heart. The present
`invention contemplates the control of current supplied 5
`to the stator coils that, with the impellor, form an elec(cid:173)
`tric motor so that the pump of the present invention
`mimics the Frank-Starling effect of the natural· heart.
`Such control can readily be adapted to provide for
`rotor speed control in accordance with a selected rela- IO
`tionship to a selected measurable quantity in any appli(cid:173)
`cation of the invention.
`An important object of the present invention is to
`provide a rotor suspension and rotation apparatus
`which can be adapted to a variety of practical applica- 15
`tions.
`Another important object of the present invention is
`to provide a pump which can be implanted in the human
`body to provide a replacement for, or an assist to, the
`natural heart in the pumping of blood through the circu- 20
`latory system.
`Another object of the invention is to provide a blood
`pump which does not require a large back-up system
`that would interfere with the freedom of movement of
`a person in which the pump is implanted.
`Another object of the invention is to provide a blood
`pump which is highly energy efficient so that damage to
`blood through discharge of heat into the blood is sub-
`stantially eliminated.
`Another object of the invention is to provide an en(cid:173)
`ergy efficient rotor suspension and control system that
`can be readily adapted to a variety of pump designs
`without loss of efficiency.
`A further object of the invention is to provide an 35
`apparatus that eliminates the need for glands and bear(cid:173)
`ings in pumps.
`Another object of the invention is to provide a pump
`that avoids flexing and frictional engagement of moving
`parts.
`Yet another object of the invention is to provide an
`apparatus for suspending and rotating a rotor in which
`the rotor speed can be controlled in accordance with
`the value of a selectable physical quantity.
`Other objects, features and advantages of the present 45
`invention will become clear from the following detailed
`description of the invention when read in conjunction
`with the drawings and the appended claims.
`
`25
`
`6
`FIG. 7 is a graphical representation of the axial com(cid:173)
`ponent of the total force on the impellor in the presence
`of a static, axial force on the impellor.
`FIG. 8 is a block diagram of the electromagnet con(cid:173)
`trol circuit for the pump impellor.
`FIG. 9 is the circuit diagram of the astable multivi(cid:173)
`brator of the electromagnet control circuit.
`FIG. 10 is the circuit diagram of the IR transmitter of
`the electromagnet control circuit.
`FIG. 11 is the circuit diagram of one of the IR receiv(cid:173)
`ers of the electromagnet control circuit.
`FIG. 12 is the circuit diagram of the difference ampli(cid:173)
`fier of the electromagnet control circuit.
`FIG. 13 is a circuit diagram for the integrator of the
`electromagnet control circuit.
`FIG. 14 is a circuit diagram of the sample and hold of
`the electromagnet control circuit.
`FIG. 15 is a circuit diagram of the timing circuit of
`the electromagnet control circuit.
`FIG. 16 is a circuit diagram for controller number 1
`of the electromagnet control circuit.
`FIG. 17 is a circuit diagram for controller number 2
`of the electromagnet control circuit.
`FIG. 18 is a circuit diagram of the power amplifier of
`the electromagnet control circuit.
`FIG. 19 is a graphical representation of the electrical
`characteristics of the power amplifier shown in FIG. 18.
`FIG. 20 is a timing diagram illustrating the operation
`of the timing circuit of the electromagnet control cir(cid:173)
`cuit.
`FIG. 21 is an isometric view of one preferred ar(cid:173)
`rangement of stator coils used to rotate the impellor of
`the pump shown in FIG. 1.
`FIG. 22 is a block circuit diagram of a rotation con(cid:173)
`trol circuit used to provide a current through the stator
`coils shown in FIG. 21.
`FIG. 23 is a block diagram of the encoder of the
`rotation control circuit shown in FIG. 22.
`FIG. 24 is a circuit diagram of the oscillator of the
`~
`rotation control circuit shown in FIG. 22.
`FIG. 25 is a circuit diagram of the modulator of the
`rotation control circuit shown in FIG. 22.
`FIG. 26 is a graphical representation of an optimal
`operating characteristic of the impellor of the pump
`shown in FIG. 1.
`FIG. 27 is a side elevational view of a modified impel(cid:173)
`lor for the pump shown in FIG. 1.
`FIG. 28 is an end elevational view of the impellor
`50 shown in FIG. 27.
`FIG. 29 is a cross section in side elevation of another
`modification of the impellor of the pump shown in FIG.
`1.
`
`30
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an isometric view of a pump, suitable for use
`as an implantable blood pump, constructed to employ
`the magnetic rotor suspension and rotation apparatus of
`FIG. 30 is a cross section in side elevation of yet
`the present invention.
`FIG. 2 is a cross section of the pump shown in FIG. 55 another modification of the impellor of the pump shown
`1 taken along line 2-2 of FIG. 1.
`in FIG. 1.
`FIG. 3 is a cross section of the pump shown in FIG.
`FIG. 31 is a cross section in side elevation of a second
`1 taken along line 3-3 of FIG. 1.
`embodiment of a pump employing the magnetic rotor
`FIG. 4 is a cross section of the magnets of the mag-
`suspension and rotation apparatus of the present inven-
`netic suspension system of the present invention illus- 60 tion.
`trating the placement and magnetization of the perma-
`FIG. 32 is a cross section of the pump shown in FIG.
`nent magnet assembly of the suspension system.
`31 along the line 31-31 of FIG. 31.
`FIG. 5 is a graphical representation of the axial com-
`FIG. 33 is a cross section in side elevation of a third
`ponent of permanent magnet forces on the impellor of
`embodiment of a pump employing the magnetic rotor
`the pump shown in FIG. 1.
`65 suspension and rotation apparatus of the present inven-
`FIG. 6 is a graphical representation of the radial
`tion.
`component of permanent magnet forces on the impellor
`FIG. 34 is a cross section in side elevation of a fourth
`of the pump shown in FIG. 1.
`embodiment of a pump employing the magnetic rotor
`
`Petitioners' Exhibit 1008, pg. 18
`
`

`

`7
`suspension and rotation apparatus of the present inven(cid:173)
`tion.
`FIG. 35 is a cross section in end elevation of a second
`preferred arrangement of stator coils in a pump employ(cid:173)
`ing the magnetic rotor suspension and rotation appara(cid:173)
`tus of the present invention and particularly adapted for
`use in the pumps illustrated in FIGS. 31-34.
`FIG. 36 is a block diagram of portions of the rotation
`control system of an apparatus, constructed in accor(cid:173)
`dance with the present invention, having three stator
`coils to rotate a rotor.
`FIG. 37 is an isometric view of two pumps employing
`the apparatus of the present invention illustrating the
`use of such pumps as an artificial heart.
`FIG. 38 is an isometric view of a pump constructed in
`the manner shown in FIG. 34 illustrating the use of such
`pump as an assist to the natural heart.
`
`DESCRIPTION OF FIGURES 1-26
`Referring now to the drawings in general and to 20
`FIGS. 1-3 in particular, shown therein and designated
`by the general reference numeral 40 is an apparatus
`constructed in accordance with the present invention to
`include a magnetically suspended and rotated rotor.
`More specifically, the apparatus 40 is a centrifugal 25
`pump particularly suited for use as a blood pump that
`can be implanted in the human body to replace or assist
`the natural heart in the pumping of blood through the
`circulatory system and, at times, the apparatus 40 will,
`accordingly, be referred to as the pump 40. In this par- 30
`ticular application of the apparatus 40, the rotor thereof,
`indicated at 42 in FIGS. 2 and 3, is configured to act as
`an impellor for the pump 40 and such rotor will, accord(cid:173)
`ingly, also be referred to as the impellor 42.
`The pump 40 is comprised of a housing 44 having a 35
`bore 46 formed therethrough about an impellor support
`axis 48 and central portions of the bore 46 are enlarged
`to form an impellor chamber 50 in which the impellor
`42 is suspended as will be discussed below. Portions of
`the bore 46 to one side of the impellor chamber 50 form 40
`a first inlet passage 52 to the impellor chamber 50 and
`portions of the bore 46 of the other side of the impellor
`chamber 50 form a second inlet passage 54 to the impel(cid:173)
`lor chamber 50. An outlet passage 56 is formed in cen(cid:173)
`tral portions of the housing to extend tangentially from 45
`radially outermost portions of the impellor chamber 50
`as shown in FIG. 3. An ever-widening groove 58 is
`formed in the housing 44 to extend circumferentially
`about the impellor chamber 50 to provide a smooth
`transition from the impellor chamber 50 to the outlet 50
`passage 56 and the impellor cham