Patent Grant
9132215
This application is a 35 U.S.C. §371 U.S. National Stage Entry of PCT Application Serial Number PCT/JP2011/050925, filed on 20 Jan. 2011, that claims benefit to Japanese Patent Application Number 2010-031298, filed 16 Feb. 2010, both of are hereby incorporated by reference in their entirety.
The present invention relates to a centrifugal pump apparatus, and particularly to a centrifugal pump apparatus including an impeller for delivering liquid by centrifugal force during rotation.
In recent years, a centrifugal blood pump apparatus in which driving torque from an external motor is transmitted to an impeller in a blood chamber through magnetic coupling has increasingly been used as a blood circulation apparatus of an artificial heart-lung machine. According to such a centrifugal blood pump apparatus, physical contact between the blood chamber and the outside can be eliminated, thus preventing invasion of bacteria and the like into blood.
A centrifugal blood pump in Japanese Patent Laying-Open No. 2004-209240 (PTL 1) includes a housing having first to third chambers partitioned from one another by first and second diaphragms, an impeller rotatably provided in the second chamber (blood chamber), a magnetic element provided in one surface of the impeller, an electromagnet provided in the first chamber to face the one surface of the impeller, a permanent magnet provided in the other surface of the impeller, a rotor and a motor provided in the third chamber, and a permanent magnet provided in the rotor to face the other surface of the impeller. A groove for hydrodynamic bearing is formed in a surface of the second diaphragm facing the other surface of the impeller. Owing to attractive force acting on the one surface of the impeller from the electromagnet, attractive force acting on the other surface of the impeller from the permanent magnet in the rotor, and a hydrodynamic bearing effect of the grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the second chamber and rotates without contacting.
A centrifugal blood pump in Japanese Patent Laying-Open No. 2006-167173 (PTL 2) includes a housing having first to third chambers partitioned from one another by first and second diaphragms, an impeller rotatably provided in the second chamber (blood chamber), a magnetic element provided in one surface of the impeller, a first permanent magnet provided in the first chamber to face the one surface of the impeller, a second permanent magnet provided in the other surface of the impeller, a rotor and a motor provided in the third chamber, and a third permanent magnet provided in the rotor to face the other surface of the impeller. A first hydrodynamic bearing is formed in a surface of the first diaphragm facing the one surface of the impeller, and a second groove for hydrodynamic bearing is formed in a surface of the second diaphragm facing the other surface of the impeller. Owing to attractive force acting on the one surface of the impeller from the first permanent magnet, attractive force acting on the other surface of the impeller from the third permanent magnet in the rotor, and a hydrodynamic bearing effect of the first and second grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the second chamber and rotates without contacting.
A turbo-type pump in FIGS. 8 and 9 of Japanese Patent Laying-Open No. 4-91396 (PTL 3) includes a housing, an impeller rotatably provided in the housing, a first permanent magnet provided in one surface of the impeller, a rotor provided outside the housing, a second permanent magnet provided in the rotor to face the one surface of the impeller, a third permanent magnet provided in the other surface of the impeller, and a magnetic element provided in the housing to face the other surface of the impeller. A first groove for hydrodynamic bearing is formed in the one surface of the impeller, and a second groove for hydrodynamic bearing is formed in the other surface of the impeller. Owing to attractive force acting on the one surface of the impeller from the second permanent magnet in the rotor, attractive force acting on the other surface of the impeller from the magnetic element in the housing, and a hydrodynamic bearing effect of the first and second grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the housing and rotates without contacting.
A clean pump in Japanese Utility Model Laying-Open No. 6-53790 (PTL 4) includes a casing, an impeller rotatably provided in the casing, a first permanent magnet provided in one surface of the impeller, a rotor provided outside the casing, a second permanent magnet provided in the rotor to face the one surface of the impeller, a magnetic element provided in the other surface of the impeller, and an electromagnet provided outside a housing to face the other surface of the impeller. A groove for hydrodynamic bearing is formed in the one surface of the impeller.
The electromagnet is actuated when a rotation speed of the impeller is lower than a prescribed rotation speed, and power supply to the electromagnet is stopped when the rotation speed of the impeller becomes higher than the prescribed rotation speed. Owing to attractive force acting on the one surface of the impeller from the second permanent magnet in the rotor and a hydrodynamic bearing effect of the groove for hydrodynamic bearing, the impeller moves away from an inner surface of the housing and rotates without contacting.
Furthermore, in a centrifugal blood pump in Japanese Patent Laying-Open No. 2007-89972 (PTL 5), a rotation centerline of a rotor is arranged at a position different from that of a centerline of a second chamber such that a rotation centerline of an impeller matches the centerline of the second chamber during rotation of the impeller in the centrifugal blood pump in PTL 2.
The pumps in PTLs 1 to 5 described above are common in the feature of axially (in a direction of a rotation axis of the impeller) supporting the impeller by the grooves for hydrodynamic bearing formed in a portion where the impeller and the housing face each other and radially (in a direction of a radius of the impeller) supporting the impeller by the attractive force between the permanent magnet provided in the impeller and the permanent magnet provided outside the housing.
In such a centrifugal pump apparatus, when rigidity for supporting the impeller (force required for moving the impeller by a unit length) is low, the impeller comes in contact with the inner wall of the blood chamber by application of vibration (accelerated vibration) involved with a user's operation. Therefore, supporting rigidity sufficiently high in each of the axial direction and the radial direction is required.
In order to increase rigidity for supporting the impeller, magnetic coupling force between the permanent magnet in the impeller and the permanent magnet on the housing side should only be increased. It is not easy, however, to increase that magnetic coupling force. Namely, in a hydrodynamic bearing type centrifugal pump apparatus, initially, a flow rate, a pump head (pressure), and a minimum value of an interval between the blood chamber and the impeller are provided as the specifications. Then, a diameter of the impeller determines a rotation speed and a dimension of a groove for hydrodynamic bearing.
When the dimension of the groove for hydrodynamic bearing, the diameter of the impeller, the rotation speed, and the interval between the blood chamber and the impeller are determined, a load capacity is determined and hence magnetic coupling force balanced therewith is determined. When magnetic coupling force is determined, rigidity for supporting the impeller is also determined. Therefore, though it is necessary to increase the load capacity in order to increase rigidity for supporting the impeller, increase in the load capacity is limited, because the load capacity is dependent on viscosity of blood, a rotation speed of the impeller, a dimension of a groove for hydrodynamic bearing, and an interval between the blood chamber and the impeller.
In the centrifugal blood pump in PTL 5, the rotation centerline of the impeller matches the centerline of the second chamber, and thus, the load capacity can be increased. In this centrifugal pump, however, the impeller is rotated, with the rotation centerline of the rotor being arranged at a position different from that of the rotation centerline of the impeller. Therefore, the torque transmission efficiency (motor efficiency) may decrease.
In view of the above, a main object of the present invention is to provide a centrifugal pump apparatus having high torque transmission efficiency and high rigidity for supporting the impeller.
A centrifugal pump apparatus according to the present invention is a centrifugal pump apparatus including a housing having first and second chambers partitioned from each other by a diaphragm, an impeller rotatably provided in the first chamber along the diaphragm, for delivering liquid by centrifugal force during rotation, and a drive unit provided in the second chamber for driving the impeller to rotate with the diaphragm being interposed, including: a first magnetic element provided in one surface of the impeller; a second magnetic element provided in an inner wall of the first chamber facing the one surface of the impeller, for attracting the first magnetic element; and a third magnetic element provided in the other surface of the impeller and attracted by the drive unit. During rotation of the impeller, first attractive force acting on between the first and second magnetic elements and second attractive force acting on between the third magnetic element and the drive unit are balanced with each other substantially in a center of a movable range of the impeller in the first chamber. A first groove for hydrodynamic bearing is formed in one surface of the impeller or in the inner wall of the first chamber facing the one surface and a second groove for hydrodynamic bearing is formed in the other surface of the impeller or in the diaphragm facing the other surface. A sidewall of the first chamber facing a side surface of the impeller is formed cylindrically. A centerline of the second magnetic element is arranged at a position different from that of a centerline of the sidewall of the first chamber such that a rotation centerline of the impeller matches the centerline of the sidewall of the first chamber during rotation of the impeller. Therefore, since the first and second attractive forces are balanced with each other and the first and second grooves for hydrodynamic bearing are provided, rigidity for supporting the impeller in the axial direction can be increased. In addition, since the rotation centerline of the impeller matches the centerline of the sidewall of the first chamber during rotation of the impeller, high torque transmission efficiency can be obtained.
Preferably, when the centerline of the second magnetic element matches the centerline of the sidewall of the first chamber, the rotation centerline of the impeller moves in a prescribed direction by a prescribed distance from the centerline of the sidewall of the first chamber during rotation of the impeller. The centerline of the second magnetic element is arranged at a position distant in a direction opposite to the prescribed direction by the prescribed distance from the centerline of the sidewall of the first chamber.
Further preferably, the centrifugal pump apparatus further includes a liquid outlet port provided to extend in a tangential direction of the sidewall of the first chamber, for allowing the liquid to flow outside the housing from an opening provided in the sidewall of the first chamber. When the centerline of the second magnetic element matches the centerline of the sidewall of the first chamber, the rotation centerline of the impeller moves in a direction of the opening during rotation of the impeller. The centerline of the second magnetic element is arranged on a side opposite to the opening when viewed from the centerline of the sidewall of the first chamber.
Further preferably, assuming that a direction of an end of the opening on an upstream side when viewed from the centerline of the sidewall of the first chamber is defined as 0 degree and an opposite direction is defined as 180 degrees, the centerline of the second magnetic element is arranged within a range of 135 degrees to 225 degrees.
Further preferably, the drive unit includes a plurality of coils provided to face the third magnetic element, for generating rotating magnetic field, and a centerline of the rotating magnetic field matches the centerline of the sidewall of the first chamber.
Further preferably, the drive unit includes a plurality of fourth magnetic elements provided to face the third magnetic element, and a plurality of coils wound around the plurality of fourth magnetic elements, for generating rotating magnetic field, and a centerline of the rotating magnetic field matches the centerline of the sidewall of the first chamber.
Further preferably, the drive unit includes a rotor rotatably provided along the diaphragm in the second chamber, a fourth magnetic element provided in the rotor to face the third magnetic element, for attracting the third magnetic element, and a motor for rotating the rotor, and a centerline of the rotor matches the centerline of the sidewall of the first chamber.
Further preferably, at least one of the first magnetic element and the second magnetic element includes a plurality of first sub magnetic elements aligned annularly.
Further preferably, each of the first and second magnetic elements is a permanent magnet, each of the plurality of first sub magnetic elements is a permanent magnet, and N poles of the plurality of first sub magnetic elements are oriented in a same direction.
Further preferably, at least one of the first magnetic element and the second magnetic element includes a plurality of annular second sub magnetic elements having diameters different from one another.
Further preferably, centerlines of the plurality of second sub magnetic elements match with one another.
Further preferably, each of the first and second magnetic elements includes the plurality of second sub magnetic elements, each of the plurality of second sub magnetic elements is a permanent magnet, and N poles of the plurality of second sub magnetic elements adjacent in a radial direction of the impeller are oriented in a same direction.
Further preferably, a sum of a distance between the centerline of the second magnetic element and the centerline of the sidewall of the first chamber and ½ of a movable distance of the impeller in the radial direction in the first chamber is smaller than ½ of an interval between two adjacent second sub magnetic elements.
Further preferably, each of the first and second magnetic elements includes the plurality of second sub magnetic elements, each of the plurality of second sub magnetic elements is a permanent magnet, and N poles of two second sub magnetic elements adjacent in a radial direction of the impeller are oriented in different directions.
Further preferably, a sum of a distance between the centerline of the second magnetic element and the centerline of the sidewall of the first chamber and ½ of a movable distance of the impeller in the radial direction in the first chamber is smaller than an interval between two adjacent second sub magnetic elements.
Further preferably, the liquid is blood and the centrifugal pump apparatus is used for circulating the blood. In this case, the impeller is smoothly activated to rotate and a distance between the impeller and the housing is secured, thereby preventing occurrence of hemolysis.
As described above, according to the present invention, rigidity of the impeller can be increased, and mechanical contact between the impeller and the housing can be decreased, and the impeller can be levitated in a stable manner. In addition, the torque transmission efficiency from the drive unit to the impeller can be increased, and the energy efficiency of the apparatus can be increased. In addition, hemolysis can be avoided in blood circulation.
As shown in
In housing 2, as shown in
A plurality of (six in this case) blood passages 14 partitioned from one another by the plurality of vanes 13 are formed between two shrouds 11 and 12. As shown in
A sidewall of blood chamber 7 facing a side surface of impeller 10 is formed cylindrically and has an inner diameter larger than an outer diameter of impeller 10. An opening 7a is provided in a part of the sidewall of blood chamber 7. Cylindrical blood outlet port 5 is coupled to opening 7a. Blood outlet port 5 extends in the tangential direction of the cylindrical sidewall 7 of blood chamber 7 so as to allow smooth outflow of blood. 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 it flows out through opening 7a and blood outlet port 5 to the outside of housing 3.
Permanent magnets 15a, 15b are embedded in shroud 11 and permanent magnets 16a, 16b for attracting permanent magnets 15a, 15b respectively are embedded in an inner wall of blood chamber 7 facing shroud 11. Permanent magnets 15a, 15b, 16a, and 16b are provided to attract (in other words, bias) impeller 10 to the side opposite to motor chamber 8, that is, toward blood inlet port 4. When impeller 10 is rotated, impeller 10 is attracted to the opening 7a side. Therefore, in order to attract (in other words, bias) impeller 10 to the side opposite to opening 7a, a centerline L2 of permanent magnets 16a, 16b is arranged on the side opposite to opening 7a when viewed from a centerline L1 of the inner wall of blood chamber 7.
a) and (b) are diagrams showing a structure of permanent magnets 15a, 15b, 16a, and 16b and
As shown in
On the other hand, each of permanent magnets 16a, 16b is formed in an arc shape, and two permanent magnets are aligned in a direction of rotation of impeller 10. An outer diameter and an inner diameter of two permanent magnets 16a arranged annularly are the same as the outer diameter and the inner diameter of permanent magnet 15a, respectively. An outer diameter and an inner diameter of two permanent magnets 16b arranged annularly are the same as the outer diameter and the inner diameter of permanent magnet 15b, respectively. The N-poles of permanent magnets 16a, 16b are oriented in the same direction. The S-poles of permanent magnets 15a, 15b face the N-poles of permanent magnets 16a, 16b. Centerline L2 of permanent magnets 16a, 16b is distant from centerline L1 of the inner wall of blood chamber 7 by a prescribed distance R.
Detailed description will now be given to a reason why centerline L2 of permanent magnets 16a, 16b is distant from centerline L1 of the inner wall of blood chamber 7. When unbalance in pressure in blood chamber 7 is caused in a pump apparatus that does not substantially include a volute, like this centrifugal blood pump apparatus, impeller 10 moves in the radial direction in accordance with the pressure balance in blood chamber 7. Specifically, rotation centerline L3 of impeller 10 moves toward opening 7a, which is a low pressure portion in blood chamber 7.
As shown in
Since the pressure gradient is large and the pressure is low at opening 7a and its surrounding region, impeller 10 is attracted to opening 7a as impeller 10 comes closer to opening 7a. On the other hand, axis torque for providing the hydro-energy from impeller 10 to blood acts on impeller 10 as load during pump operation, and the axis torque increases with increase in rotation speed. In addition, as shown in
Accordingly, in the present invention, centerline L2 of permanent magnets 16a, 16b is arranged on the side opposite to opening 7a when viewed from centerline L1 of the inner wall of blood chamber 7, such that rotation centerline L3 of impeller 10 matches centerline L1 of the sidewall of blood chamber 7 when impeller 10 is rotated at a rated rotation speed, and impeller 10 is attracted (in other words, biased) to the side opposite to opening 7a. Interval R between centerlines L1 and L2 is set depending on operation conditions. In other words, an amount of displacement may be read from
Assuming that a direction of contact point P (the end of opening 7a on the upstream side) is defined as 0 degree and the opposite direction is defined as 180 degrees when viewed from the central point of circle C (centerline L1 of the sidewall of blood chamber 7), centerline L2 of permanent magnets 16a, 16b is arranged at a position displaced from the central point of circle C in the direction of 180 degrees by prescribed amount of eccentricity R.
Movement characteristics of impeller 10 in the radial direction during pump operation vary depending on an area, a shape and the like of opening 7a. Therefore, the position of centerline L2 of permanent magnets 16a, 16b is not necessarily limited to the direction of 180 degrees from the central point of circle C. The position of centerline L2 of permanent magnets 16a, 16b is preferably within the range of 180 degrees±45 degrees (i.e., 135 degrees to 225 degrees) from the central point of circle C.
As shown in
Since two pairs of permanent magnets 15a and 16a and permanent magnets 15b and 16b are thus provided in the radial direction of impeller 10, rigidity for supporting impeller 10 in the radial direction can be increased as compared with a case where only a pair of pet anent magnets is provided in the radial direction of impeller 10.
Instead of providing permanent magnets 15a, 15b and permanent magnets 16a, 16b in shroud 11 and the inner wall of blood chamber 7, respectively, a permanent magnet may be provided in one of shroud 11 and the inner wall of blood chamber 7, and a magnetic element may be provided in the other. Either a soft magnetic element or a hard magnetic element may be used as the magnetic element.
Though
In
As shown in
As shown 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 VU, VV and VW as shown in
When impeller 10 is rotating at a rated rotation speed, attractive force between permanent magnets 15a, 15b and permanent magnets 16a, 16b 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 in a direction of the impeller rotation axis. 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 lowered. 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 pressure is low during low-speed rotation. Accordingly, occurrence of hemolysis due to the relative slide between impeller 10 and housing 2 or occurrence of thrombus due to small damage (projections and recesses) to the surfaces which occurs during the relative slide is avoided.
Centerline L3 of the plurality of permanent magnets 17, centerline L3 of permanent magnets 15a, 15b, and rotation centerline L3 of impeller 10 match with one another. In addition, a centerline of the rotating magnetic field generated by the plurality of coils 20 matches centerline L1 of the sidewall of blood chamber 7.
A plurality of grooves for hydrodynamic bearing 21 are formed in a surface of diaphragm 6 facing shroud 12 of impeller 10, and a plurality of grooves for 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 grooves for hydrodynamic bearing 21, 22 and impeller 10. As a result, drag is generated on impeller 10 from each of grooves for hydrodynamic bearing 21, 22, causing impeller 10 to rotate without contacting in blood chamber 7.
Specifically, as shown in
In
In this manner, owing to the hydrodynamic bearing effect produced between impeller 10 and the plurality of grooves for hydrodynamic bearing 21, impeller 10 moves away from diaphragm 6 and rotates without contacting. Accordingly, a blood flow path is secured between impeller 10 and diaphragm 6, thus preventing occurrence of blood accumulation therebetween and the resultant thrombus. Further, in a normal state, grooves for hydrodynamic bearing 21 perform a stirring function between impeller 10 and diaphragm 6, thus preventing occurrence of partial blood accumulation therebetween.
Instead of providing grooves for hydrodynamic bearing 21 in diaphragm 6, grooves for hydrodynamic bearing 21 may be provided in a surface of shroud 12 of impeller 10.
It is preferable that a corner portion of groove for hydrodynamic bearing 21 be rounded to have R of at least 0.05 mm. As a result, occurrence of hemolysis can further be lessened.
As with the plurality of grooves for hydrodynamic bearing 21, as shown in
Owing to the hydrodynamic bearing effect produced between impeller 10 and the plurality of grooves for hydrodynamic bearing 22, impeller 10 moves away from the inner wall of blood chamber 7 and rotates without contacting. In addition, when pump unit 1 is subjected to external impact or when the hydrodynamic pressure generated by grooves for 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 pressure generated by grooves for hydrodynamic bearing 21 may be different from the hydrodynamic pressure generated by grooves for hydrodynamic bearing 22.
Grooves for hydrodynamic bearing 22 may be provided in a surface of shroud 11 of impeller 10, rather than on the inner surface side of blood chamber 7. It is preferable that a corner portion of groove for hydrodynamic bearing 22 be rounded to have R of at least 0.05 mm. As a result, occurrence of hemolysis can further be lessened.
It is preferable that impeller 10 rotate in a state where a gap between shroud 12 of impeller 10 and diaphragm 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 hydrodynamic force acting on impeller 10, it is preferable that grooves for hydrodynamic bearing 21 and 22 have different shapes, so that the hydrodynamic pressure generated by the grooves for hydrodynamic bearing on the narrower side becomes higher than the hydrodynamic pressure generated by the other grooves for hydrodynamic bearing to make the gaps substantially equal to each other.
While both of grooves for hydrodynamic bearing 21 and 22 have the inward spiral groove shape in
Namely, it is assumed that attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b is set to be smaller than attractive force F2 between permanent magnet 17 and magnetic element 18 and a levitation position of impeller 10 where their resultant force becomes zero is on the diaphragm 6 side relative to the center of the movable range of the impeller. Grooves for hydrodynamic bearing 21, 22 have the same shape.
A horizontal axis of
As can be seen in
In contrast,
Namely, attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force F2 between permanent magnet 17 and magnetic element 18 are set to be substantially equal to each other. In addition, grooves for hydrodynamic bearing 21, 22 have the same shape. In this case, supporting rigidity with respect to the levitation position of impeller 10 becomes higher as compared with the case of
As such, a levitation position of impeller 10 is determined by balance among attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b, attractive force F2 between permanent magnet 17 and magnetic element 18, and hydrodynamic pressures F3, F4 generated by grooves for hydrodynamic bearing 21, 22 during rotation of impeller 10. By making F1 and F2 substantially equal to each other and by forming grooves for hydrodynamic bearing 21, 22 in the same shape, impeller 10 can be levitated substantially in a central portion of blood chamber 7 during rotation of impeller 10. Since impeller 10 has such a shape that vanes are formed between two discs as shown in
In this case, impeller 10 is levitated at the central position of blood chamber 7 and thus held at a position farthest from the inner wall of housing 2. As a result, even if the levitation position of impeller 10 is changed due to application of disturbance force to levitated impeller 10, the possibility that impeller 10 is brought into contact with the inner wall of housing 2 is lowered, thus also lowering the possibility of occurrence of thrombus and hemolysis resulting from such contact.
While grooves for hydrodynamic bearing 21, 22 have the same shape in the examples shown in
Furthermore, when an absolute value of a negative axial supporting rigidity value of impeller 10 which is constituted of attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force F2 between permanent magnet 17 and magnetic element 18 is expressed as Ka, an absolute value of a positive radial rigidity value is expressed as Kr, and an absolute value of a positive rigidity value obtained by two grooves for hydrodynamic bearing 21, 22 in a normal rotation speed range where impeller 10 rotates is expressed as Kg, it is preferable that relation of Kg>Ka+Kr be satisfied.
Specifically, when absolute value Ka of the negative axial rigidity value is 20000 N/m and absolute value Kr of the positive radial rigidity value is 10000 N/m, absolute value Kg of the positive rigidity value obtained by two grooves for hydrodynamic bearing 21, 22 in a rotation speed region where impeller 10 normally rotates is set to a value higher than 30000 N/m.
The axial supporting rigidity for impeller 10 is a value obtained by subtracting negative rigidity due to the attractive force between the magnetic elements and the like from rigidity resulting from the hydrodynamic pressure generated by grooves for hydrodynamic bearing 21, 22. Thus, by satisfying relation of Kg>Ka+Kr, the axial supporting rigidity for impeller 10 can be made higher than the radial supporting rigidity. With such setting, movement of impeller 10 can be suppressed more in the axial direction than in the radial direction when disturbance force acts on impeller 10, thereby avoiding mechanical contact between impeller 10 and housing 2 in a portion where grooves for hydrodynamic bearing 21 are formed.
In particular, since grooves for hydrodynamic bearing 21, 22 are provided as concave portions in planar surfaces as shown in
Whirl occurs in unbalanced impeller 10 during rotation, and this whirl is greatest when a natural frequency determined by the mass of impeller 10 and the supporting rigidity value of impeller 10 matches the rotation speed of impeller 10.
Since the radial supporting rigidity for impeller 10 is smaller than the axial supporting rigidity in pump unit 1, it is preferable to set a maximum rotation speed of impeller 10 to be equal to or lower than the radial natural frequency. Accordingly, in order to prevent mechanical contact between impeller 10 and housing 2, when a radial rigidity value of impeller 10 which is constituted of attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force F2 between permanent magnet 17 and magnetic element 18 is expressed as Kr (N/m), the mass of impeller 10 is expressed as m (kg), and the rotation speed of the impeller is expressed as ω (rad/s), it is preferable that relation of ω<(Kr/m)0.5 be satisfied.
Specifically, when the mass of impeller 10 is 0.03 kg and the radial rigidity value is 2000 N/m, the maximum rotation speed of impeller 10 is set to 258 rad/s (2465 rpm) or lower. Conversely, when the maximum rotation speed of impeller 10 is set to 366 rad/s (3500 rpm), the radial rigidity is set to 4018 N/m or higher.
It is further preferable to set the maximum rotation speed of impeller 10 to 80% or lower of this a). Specifically, when the mass of impeller 10 is 0.03 kg and the radial rigidity value is 2000 N/m, the maximum rotation speed is set to 206.4 rad/s (1971 rpm) or lower. Conversely, when it is desired to set the maximum rotation speed of impeller 10 to 366 rad/s (3500 rpm), the radial rigidity value is set to 6279 N/m or higher. By thus setting the maximum rotation speed of impeller 10, contact between rotating impeller 10 and housing 2 can be suppressed.
It is also preferable to check that impeller 10 is in contact with diaphragm 6 before activating impeller 10 to rotate, and to activate impeller 10 to rotate.
In other words, when impeller 10 is not rotating, noncontact supporting by grooves for hydrodynamic bearing 21, 22 is not achieved, and furthermore, impeller 10 is in contact with housing 2 at a high surface pressure owing to attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force F2 between permanent magnet 17 and magnetic element 18. Activation torque is smaller when impeller 10 is rotated by magnetic interaction between coils 20 and magnetic element 18 in motor chamber 8 and permanent magnet 17 in impeller 10 as with pump unit 1 than when the impeller as shown in FIG. 3 of PTL 2 is driven to rotate by magnetic coupling between the permanent magnets. Therefore, it is difficult to smoothly activate impeller 10 to rotate.
Permanent magnet 17 in impeller 10 is, however, closer to magnetic element 18 in motor chamber 8 when shroud 12 of impeller 10 is in contact with diaphragm 6 than when shroud 11 of impeller 10 is in contact with the inner wall of blood chamber 7. Therefore, rotational torque during activation of impeller 10 can be increased and impeller 10 can be smoothly activated to rotate.
As described above, however, when impeller 10 is rotating, attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force F2 between permanent magnet 17 and magnetic element 18 are set to be balanced with each other around a center of the movable range of impeller 10. Therefore, when impeller 10 stops, impeller 10 is not necessarily in contact with diaphragm 6.
Accordingly, this centrifugal blood pump apparatus is provided with means for moving impeller 10 toward the diaphragm 6 side before activating impeller 10 to rotate. Specifically, a current is fed to the plurality of coils 20 such that attractive force F2 between permanent magnet 17 and magnetic element 18 becomes large, and impeller 10 is moved toward the diaphragm 6 side.
At time t0, voltages VU, VV and VW of any one of the six patterns (0 to 60 degrees, 60 to 120 degrees, . . . , 300 to 360 degrees) shown in
The reason for moving impeller 10 without rotating impeller 10 is that movement of rotating impeller 10 to position PB on the diaphragm 6 side is blocked by the hydrodynamic bearing effect of grooves for hydrodynamic bearing 21. In addition, it is preferable to provide a sensor for detecting a position of impeller 10 in blood chamber 7, and check to see that impeller 10 is in contact with diaphragm 6 before cutting off current I0.
Then, three-phase voltages VU, VV and VW are applied to first to third coils 20 described with reference to
When voltages VU, VV and VW of the six patterns (0 to 60 degrees, 60 to 120 degrees, . . . , 300 to 360 degrees) are applied to first to third coils 20 during activation, respectively, a pattern where the attractive force between permanent magnet 17 and magnetic element 18 becomes maximum varies with positional relation between permanent magnet 17 and magnetic element 18. Thus, instead of applying only voltages VU, VV and VW of the constant patterns to first to third coils 20 during activation, respectively, voltages VU, VV and VW of the six patterns may be successively applied to first to third coils 20 for a predetermined time. In this case, impeller 10 slightly rotates (strictly speaking, equal to or less than a quarter rotation, i.e., rotates equal to or smaller than 360 degrees in electrical angle), and moves to position PB on the diaphragm 6 side.
When voltages VU, VV and VW of the six patterns are applied, a current does not flow through one of first to third coils 20, six of nine magnetic elements 18 become the N-pole or the S-pole, and three remaining magnetic elements 18 do not generate a magnetic polarity. Thus, voltages that cause a current to flow through all of first to third coils 20 and each of nine magnetic elements 18 to become the N-pole or the S-pole may be applied to first to third coils 20, to increase the attractive force between permanent magnet 17 and magnetic element 18.
In this first embodiment, attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b is balanced with attractive force F2 between the plurality of permanent magnets 17 and the plurality of magnetic elements 18, and grooves for hydrodynamic bearing 21, 22 are provided. Therefore, rigidity for supporting impeller 10 in the axial direction can be increased. In addition, since two pairs of permanent magnets 15a and 16a and permanent magnets 15b and 16b are provided in the radial direction of impeller 10, rigidity for supporting impeller 10 in the radial direction can be increased as compared with a case where only a pair of permanent magnets is provided in the radial direction of impeller 10. Therefore, mechanical contact between impeller 10 and housing 2 can be lessened and occurrence of hemolysis or thrombus can be prevented.
In addition, centerline L2 of permanent magnets 15a and 16a is arranged at a position different from that of centerline L1 of the sidewall of blood chamber 7 such that rotation centerline L3 of impeller 10 matches centerline L1 of the sidewall of blood chamber 7 during rotation of impeller 10. Therefore, high torque transmission efficiency can be obtained.
Accordingly, a rotating magnetic field is applied to impeller 10 by current I1. Current I1 is larger than current I0 in
In addition, a diamond-like carbon (DLC) coating may be formed on at least one of the surface of the inner wall of blood chamber 7 and the surface of diaphragm 6, and the surface of impeller 10. As a result, frictional force between impeller 10, and the inner wall of blood chamber 7 and diaphragm 6 can be reduced to smoothly activate impeller 10 to rotate. A fluorine-based resin coating, a paraxylylene-based resin coating or the like may be formed instead of the diamond-like carbon coating.
When the rigidity due to the hydrodynamic pressures by grooves for hydrodynamic bearing 21, 22 becomes higher than the negative axial rigidity value of impeller 10 which is constituted of attractive force F1 between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force F2 between permanent magnet 17 and magnetic element 18, impeller 10 and housing 2 are not in contact with each other. It is thus preferable to minimize this negative rigidity value. In order to keep the negative rigidity value low, it is preferable that the opposing surfaces of permanent magnets 15a and 16a are different in size and the opposing surfaces of permanent magnets 15b and 16b are different in size. For example, as shown in
Alternatively, as shown in
Alternatively, each of yoke 19 and magnetic element 18 in
In addition, in the modification in
As described with reference to
In other words,
As can be seen in
A reason for this is considered as follows. In the case of heteropolar arrangement, in
The plurality of permanent magnets 41 are provided in a surface of a bowl-shaped rotor 42. A plurality of (e.g., eight) permanent magnets 43 are provided at regular angular intervals on an inner side of a circumference of rotor 42. The plurality of permanent magnets 43 are arranged at regular angular intervals along the same circle such that adjacent magnetic polarities thereof are different from each other. In other words, permanent magnet 43 having the N-pole toward the inside of rotor 42 and permanent magnet 43 having the S-pole toward the inside of rotor 42 are alternately arranged at regular angular intervals along the same circle.
A central portion of rotor 42 is rotatably supported by a central axis 45 with a bearing 44 being interposed, and rotor 42 is rotatably provided along diaphragm 6. Central axis 45 is provided to stand in a center of a disc-shaped yoke 46. A plurality of (e.g., nine) magnetic elements 47 are provided at regular angular intervals around central axis 45 on the surface of yoke 46. Tip ends of the plurality of magnetic elements 47 are arranged along the same circle, as facing the plurality of permanent magnets 43 in rotor 42. A coil 48 is wound around each magnetic element 47. The plurality of permanent magnets 43, the plurality of magnetic elements 47, and a plurality of coils 48 constitute a motor for rotating rotor 42. A rotation centerline of rotor 42, a rotation central point of the plurality of permanent magnets 41 and centerline L1 of the sidewall of blood chamber 7 match with one another.
Voltages are applied to nine coils 48 in a power distribution system shifted by 120 degrees, for example. Namely, nine coils 48 are divided into groups each including three coils. Voltages VU, VV and VW shown in
Here, when impeller 10 is rotating at a rated rotation speed, attractive force between permanent magnets 15a, 15b and permanent magnets 16a, 16b and attractive force between the plurality of permanent magnets 40 and the plurality of permanent magnets 41 are set to be balanced with each other substantially around the center of the 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 lowered. In addition, a surface of impeller 10 and a surface of the 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 pressure is small during low-speed rotation.
In addition, as in the first embodiment, a plurality of grooves for hydrodynamic bearing 21 are formed in the surface of diaphragm 6 facing shroud 12 of impeller 10, and a plurality of grooves for 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 grooves for hydrodynamic bearing 21, 22 and impeller 10. As a result, drag is generated on impeller 10 from each of grooves for hydrodynamic bearing 21, 22, causing impeller 10 to rotate without contacting in blood chamber 7.
In addition, as in the first embodiment, centerline L2 of permanent magnets 15a and 16a is arranged at a position different from that of centerline L1 of the sidewall of blood chamber 7 such that rotation centerline L3 of impeller 10 matches centerline L1 of the sidewall of blood chamber 7 during rotation of impeller 10. Therefore, high torque transmission efficiency can be obtained. The same effect as in the first embodiment can be obtained also in this second embodiment.
It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-031298 | Feb 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/050925 | 1/20/2011 | WO | 00 | 8/15/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/102176 | 8/25/2011 | WO | A |
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