Patent Application
20190167876
Conventional heart pumps utilize magnetic elements and/or hydrostatic bearings within a housing of the pump to compensate attractive forces produced by a stator motor to maintain an impeller of the pump in a desired position within a chamber of the pump. Such magnetic attractive forces from the magnetic elements provide negative stiffness. This negative stiffness increases as a distance between the magnetic elements within the housing and magnets on the impeller becomes shorter. Any tilt of the impeller will decrease a gap between the impeller and the wall of the chamber at an outer edge of the impeller. At low impeller speeds, hydrodynamic bearing forces are sufficient to maintain this gap. However, in conventional pump designs, at high speeds the impeller tends to tilt, resulting in a decrease of a size of the gap near the outer edges of the impeller.
In one aspect, a centrifugal blood pump is provided. The pump may include a housing that defines an inlet passage, a chamber, and an outlet passage. The pump may also include an impeller rotatably positioned in the chamber to transfer blood from the inlet passage through the chamber and to the outlet passage. The impeller may include an inner portion and an outer portion. The pump may further include a plurality of impeller magnets embedded in the impeller such that the impeller and the plurality of impeller magnets rotate together within the chamber. The plurality of impeller magnets may include an inner impeller magnet and an outer impeller magnet relative to a central axis of the impeller. The pump may include a motor to control movement of the impeller in the chamber. The motor may be positioned adjacent the chamber and separated from the chamber by a partition member. The pump may also include an inner annular magnetic member embedded in a wall of the housing opposite the partition member and an outer annular magnetic member embedded in the wall of the housing opposite the partition member. A first net magnetic force between the inner annular magnetic member and the inner impeller magnet may exhibit greater attraction than a second net magnetic force between the outer annular member and the outer impeller magnet.
In another aspect, a centrifugal blood pump may include a housing that defines an inlet passage, a chamber, and an outlet passage. The pump may also include an impeller rotatably positioned in the chamber to transfer blood from the inlet passage through the chamber and to the outlet passage. The pump may further include a plurality of impeller magnets embedded in the impeller such that the impeller and the plurality of impeller magnets rotate together within the chamber. The pump may include a motor to control movement of the impeller in the chamber. The motor may be positioned adjacent the chamber and separated from the chamber by a partition member. The pump may further include at least one annular magnetic member embedded in a wall of the housing opposite the partition member. A first net magnetic force between the at least one annular magnetic member and a proximal portion the plurality of impeller magnets may exhibit greater attraction than a second net magnetic force between the at least one annular magnetic member and a distal portion of the plurality of impeller magnets. The proximal portion and the distal portion may be relative to a central axis of the impeller.
In another aspect, a centrifugal blood pump may include a housing that defines an inlet passage, a chamber, and an outlet passage. The pump may also include an impeller rotatably positioned in the chamber to transfer blood from the inlet passage through the chamber and to the outlet passage. The impeller may include an inner portion and an outer portion relative to a central axis of the impeller. The pump may further include at least one impeller magnet embedded in the impeller such that the impeller and at least one magnetic member rotate together within the chamber. The pump may include a motor to control movement of the impeller in the chamber. The motor may be positioned adjacent the chamber and separated from the chamber by a partition member. The pump may also include at least one annular magnetic member embedded in a side of the housing opposite the partition member. A first force exhibited on the inner portion may have a greater attraction than a second force exhibited on the outer portion of the impeller. The first force and the second force may each result from interactions between the at least one impeller magnet and the at least one annular magnetic member.
The ensuing description provides exemplary embodiments only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing one or more exemplary embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth herein.
Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, with regard to any specific embodiment discussed herein, any one or more details may or may not be present in all versions of that embodiment. Likewise, any detail from one embodiment may or may not be present in any particular version of another embodiment discussed herein. Additionally, well-known circuits, systems, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. The absence of discussion of any particular element with regard to any embodiment herein shall be construed to be an implicit contemplation by the disclosure of the absence of that element in any particular version of that or any other embodiment discussed herein.
The present disclosure is directed to, among other things, minimizing or preventing a decrease in gap size at high impeller speeds between the outer edge of the impeller and the inner wall of a chamber of a blood pump. Some aspects of the disclosure are directed to reducing the risk of undesirable tilting of the impeller and/or improving the overall stability of the impeller during operation. Embodiments maintain an appropriately sized gap through all impeller speeds by decreasing the net attractive magnetic force on an outer portion of the impeller, or by having a lower net attractive force on an outer portion of the impeller than an inner portion. Although the feature or aspects of the present disclosure are not limited to a specific type of mechanical blood pump, an example of a blood pump in which embodiments of maintaining an appropriate gap size may be practiced is shown and described in connection with
In
As shown in
As shown in
A plurality (six in this case) of blood passages 14 are formed between two shrouds 11 and 12 and are partitioned from one another by the plurality of vanes 13. As shown in
When impeller 10 is driven to rotate, blood that has flowed in through blood inlet port 4 is delivered by centrifugal force from through hole 10a to an outer circumferential portion of impeller 10 via blood passages 14, and flows out through blood outlet port 5. It is contemplated that the blood inlet port 4 may be configured and/or arranged to minimize or prevent the formation of thrombosis within (i.e., internal) the blood inlet port 4, and also to minimize turbulence at a fluid interface between the blood inlet port 4 and the blood chamber 7.
A plurality of permanent magnets may be embedded in shroud 11. For example, an inner magnet 15 and an outer magnet 16 may be included in shroud 11. One or more annular magnetic members may be embedded in an inner wall of blood chamber 7 facing shroud 11. For example, inner annular magnetic member 30 and outer annular magnetic member may be embedded in the inner wall. The annular magnetic members 30 and 32 may be permanent magnets or may be electromagnetic elements. Either a soft magnetic element or a hard magnetic element may be used as the annular magnetic members 30 and/or 32.
The annular magnetic members 30 and 32 may each be formed as a single permanent magnet or as a plurality of permanent magnets. If a single permanent magnet is provided, the permanent magnet is formed in an annular or ring shape. If a plurality of permanent magnets are provided, the plurality of permanent magnets may be arranged at regular angular intervals along the same circle. While described as annular magnetic members, it will be appreciated that each of the magnetic members described herein may be formed from one or more magnets, and may be in any non-annular arrangement, such as other symmetrical shapes. In some embodiments, the inner annular magnetic member 30 may have a greater net attractive force with the inner magnet 15 than the net attractive force between the outer annular magnetic member 32 and the outer magnet 16. Such a configuration may decrease the tilt of the impeller, especially at high impeller speeds, thus maintaining a size of the gap between the outer edge of the impeller and the housing wall.
As shown in
As shown in
Referring back to
An outline surface surrounding the plurality of magnetic elements 18 (a circle surrounding the peripheries of the plurality of magnetic elements 18 in
Voltages are applied to nine coils 20 in a power distribution system shifted by 120 degrees, for example. That is, nine coils 20 are divided into groups each including three coils. Voltages are applied to first to third coils 20 of each group, respectively. To first coil 20, a positive voltage is applied during a period of 0 to 120 degrees, 0 V is applied during a period of 120 to 180 degrees, a negative voltage is applied during a period of 180 to 300 degrees, and 0 V is applied during a period of 300 to 360 degrees. Accordingly, a tip surface of magnetic element 18 having first coil 20 wound therearound (end surface on the impeller 10 side) becomes the N-pole during the period of 0 to 120 degrees, and becomes the S-pole during the period of 180 to 300 degrees. A Voltage VV is delayed in phase from a voltage VU by 120 degrees, and a voltage VW is delayed in phase from voltage VV by 120 degrees. Thus, rotating magnetic field can be formed by applying voltages VU, VV, VW to first to third coils 20, respectively, so that impeller 10 can be rotated by attractive force and repulsion force between the plurality of magnetic elements 18 and the plurality of permanent magnets 17 in impeller 10.
When impeller 10 is rotating at a rated rotation speed, attractive force between the magnetic elements 15 and 16 and the annular magnetic members 30 and 32 and attractive force between the plurality of permanent magnets 17 and the plurality of magnetic elements 18 are set to be balanced with each other substantially around a center of a movable range of impeller 10 in blood chamber 7. Thus, force acting on impeller 10 due to the attractive force is very small throughout the movable range of impeller 10. Consequently, frictional resistance during relative slide between impeller 10 and housing 2 which occurs when impeller 10 is activated to rotate can be reduced. In addition, a surface of impeller 10 and a surface of an inner wall of housing 2 are not damaged (no projections and recesses in the surfaces) during the relative slide, and moreover, impeller 10 is readily levitated from housing 2 without contacting even when hydrodynamic force is small during low-speed rotation.
A number of grooves of hydrodynamic bearing 21 are formed in a surface of dividing wall X facing shroud 12 of impeller 10, and a number of grooves of hydrodynamic bearing 22 are formed in the inner wall of blood chamber 7 facing shroud 11. When a rotation speed of impeller 10 becomes higher than a prescribed rotation speed, a hydrodynamic bearing effect is produced between each of the grooves of hydrodynamic bearings 21 and 22 and impeller 10. As a result, drag is generated on impeller 10 from each of the grooves of hydrodynamic bearings 21 and 22, causing impeller 10 to rotate without contacting in blood chamber 7.
Specifically, as shown in
In
In some embodiments, alternatively, or in addition to, providing grooves for hydrodynamic bearing 21 in dividing wall 6, grooves for hydrodynamic bearing 21 may be provided in a surface of shroud 12 of impeller 10. The hydrodynamic bearing effect produced between impeller 10 and the grooves of hydrodynamic bearing 21, causes impeller 10 to move away from dividing wall 6 and to rotate without contacting the dividing wall 6. Accordingly, a blood flow path is secured between impeller 10 and dividing wall 6, thus preventing occurrence of blood accumulation therebetween and the resultant thrombus. Further, in a normal state, the grooves of hydrodynamic bearing 21 perform a stirring function between impeller 10 and dividing wall 6, thus preventing occurrence of partial blood accumulation therebetween.
It is preferable that a corner portion of each of grooves for hydrodynamic bearing 21 be rounded to have R of at least 0.05 mm. As a result, occurrence of hemolysis can further be reduced.
As with the grooves of hydrodynamic bearing 21, as shown in
Alternatively, or in addition to, providing the grooves of hydrodynamic bearing 22 in the inner wall of blood chamber 7, the grooves of hydrodynamic bearing 22 may be provided in a surface of shroud 11 of impeller 10. It is preferable that a corner portion of each of grooves of hydrodynamic bearing 22 be rounded to have R of at least 0.05 mm. As a result, occurrence of hemolysis can further be reduced
The hydrodynamic bearing effect produced between impeller 10 and the grooves for hydrodynamic bearing 22 causes impeller 10 to move away from the inner wall of blood chamber 7 and rotates without contacting the inner wall. In addition, when pump unit 1 is subjected to external impact or when the hydrodynamic force generated by hydrodynamic bearing 21 becomes excessive, impeller 10 can be prevented from being in close contact with the inner wall of blood chamber 7. The hydrodynamic force generated by hydrodynamic bearing 21 may be different from the hydrodynamic force generated by hydrodynamic bearing 22.
It is preferable that impeller 10 rotate in a state where a gap between shroud 12 of impeller 10 and dividing wall 6 is substantially equal to a gap between shroud 11 of impeller 10 and the inner wall of blood chamber 7. If one of the gaps becomes narrower due to serious disturbance such as fluid force acting on impeller 10, it is preferable that grooves of hydrodynamic bearing 21 and 22 have different shapes so that the hydrodynamic force generated by the hydrodynamic bearing on the narrower side becomes higher than the hydrodynamic force generated by the other hydrodynamic bearing to make the gaps substantially equal to each other.
While each groove of hydrodynamic bearings 21 and 22 has the inward spiral groove shape shown in
As mentioned above, it is contemplated that the blood inlet port 4 may be configured and/or arranged to minimize or prevent the formation of thrombosis within (i.e., internal) the blood inlet port 4, and also to minimize turbulence at a fluid interface between the blood inlet port 4 and the blood chamber 7. In general, it is contemplated that thrombosis formation may occur due to a vortex forming in or within one or both of blood inlet port 4 and the blood chamber 7 in a location near or adjacent blood inlet port 4, and/or due to stress or forces imparted on blood as it transitions into a spinning motion once it reaches the impeller 10.
In some embodiments, making the distance between the inner magnets smaller than the distance between the outer magnets can be achieved by changing a position of the inner magnet and/or the outer magnet relative to the impeller as shown in
In some embodiments, the gap between the impeller and the housing may be maintained by increasing the attractive force of the inner annular magnetic member while using an opposite polarity magnet as the outer annular magnetic member to create a repulsive force on the outer edge of the impeller and to increase the impeller suspension stiffness. For example,
In some embodiments, reduction of a diameter of an inner annular magnetic member may be used in conjunction with increasing a diameter of an outer annular magnetic member, resulting in an increase in the radial stiffness of the magnetic suspension system of the pump. For example,
In some embodiments, a ferromagnetic ring, such as a steel ring, may be positioned between an inner annular magnetic member and an inner magnetic element when the inner annular magnetic member has a diameter positioned inward of an inner magnetic element on an impeller.
The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the disclosure.
This application is continuation of U.S. patent application Ser. No. 15/042,685, filed Feb. 12, 2016 and entitled “IMPELLER SUSPENSION MECHANISM FOR HEART PUMP,” which claims priority to U.S. Provisional Application No. 62/115,741, filed Feb. 13, 2015 and entitled “IMPELLER SUSPENSION MECHANISM FOR HEART PUMP,” which are hereby incorporated by reference in their entirety, for all purposes, as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 62115741 | Feb 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15042685 | Feb 2016 | US |
| Child | 16268012 | US |
