Abstract:
A pump portion is provided with an impeller internal to a casing. The impeller is coupled with a rotor physically out of contact therewith and it is also supported by a controlled, magnetic bearing portion physically out of contact therewith. The impeller is rotated by a motor to discharge fluid. A position sensor detects the impeller position in levitation and in response to the sensor&#39;s output the magnetic bearing portion is controlled. The magnetic bearing portion is configured of a plurality of electromagnets formed of a magnetic pole, a yoke and a coil. The electromagnet has magnetic S and N poles each with at least yoke and coil arranged circumferentially.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to magnetically levitated (maglev) pumps. More specifically, the present invention relates to those corresponding to a cleanpump employing a magnetic bearing and used for medical equipment, such as artificial heart.  
           [0003]    2. Description of the Background Art  
           [0004]    [0004]FIGS. 8A and 8E, show a conventional maglev pump. More specifically, FIG. 8A is a vertical cross section thereof and FIG. 8B is a cross section taken along a line XIIIB-XIIIB of FIG. 8A. FIG. 9 is a cross section taken along a line IX-IX of FIG. 8A. FIG. 10 is a cross section taken along a line X-X of FIG. 8A.  
           [0005]    Initially, with reference to FIGS.  8 A- 10 , a conventional maglev pump will be described. As shown in FIG. 8A, a maglev pump  1  includes a motor portion  10 , a pump portion  20  and a magnetic bearing portion  30 . In pump portion  20 , a casing  21  accommodates a pump chamber  22  in which an impeller  23  rotates. Impeller  23  has a plurality of vanes  27  spirally provided, as shown in FIG. 8B. Casing  21  is formed of a cylindrical, nonmagnetic member and impeller  23  includes a nonmagnetic member  25  having a permanent magnet  24  configuring a noncontrolled magnetic bearing and a soft magnetic member  26  corresponding to a rotor of a controlled magnetic bearing. Permanent magnet  24  is divided in a circumferential direction of impeller  23  and magnets adjacent to each other are magnetized to have opposite magnetic poles.  
           [0006]    Opposite to the side of impeller  23  provided with permanent magnet  24 , external to pump chamber  22  there is provided a disk rotor  12  supported by a shaft  11 . Rotor  12  is rotatably driven by a motor  13 . Rotor  12  is provided with the same number of permanent magnets  14  as impeller  23  that face permanent magnet  24  of impeller  23  to provide attraction. Adjacent permanent magnets  14  are magnetized to have opposite magnetic poles.  
           [0007]    Furthermore, opposite to the side of impeller  23  provided with soft magnetic member  26 , an electromagnet  31  and a position sensor (not shown) are provided in magnetic bearing portion  30 . Electromagnet  31  and the position sensor allow balance with the attraction of permanent magnets  24  and  14  to hold impeller  23  at the center of pump chamber  22 .  
           [0008]    In maglev pump  1  thus configured, attraction acts between permanent magnet  14  (embedded in rotor  12  and permanent magnet  24  provided in impeller  23 , axially in one direction. This attraction is exploited to provide magnetic-coupling to rotatably drive impeller  23  and obtain radial supporting-stiffness. To match it to this attraction, a flow of current is passed through a coil of C-shaped electromagnet  31 , which in turn attracts impeller  23  axially in the other direction to levitate impeller  23 . As rotor  12  is rotatably driven by motor  13 , permanent magnets  14  and  24  provide magnetic-coupling, impeller  23  rotates and a fluid is sucked through an inlet  60  and discharged through an outlet  70  (see FIG. 8B). Impeller  23  is accommodated in casing  21  and thus isolated from rotor  12  and it is also not contaminated by electromagnet  31 . Thus, maglev pump  1  delivers fluid (blood if it is used as a blood pump) held clean.  
           [0009]    Note that as shown in FIGS. 9 and 10, a conventional maglev blood pump has electromagnet  31  with an arcuate yoke  41  and pairs of magnetic poles  42  and  43 ,  44  and  45 , and  46  and  47  each arranged radially.  
           [0010]    If maglev pump as shown in FIGS. 8A and 8B is used as a blood pump for an artificial heart, it is implanted in a body or used adjacent thereto. As such, it cannot be supplied with energy constantly from an external power supply. Typically, it is supplied with energy obtained from a mobile battery or a battery implanted in the body. As such, to use it for a long term, energy consumption must be minimized. Furthermore, if it is used for human body, it is required to have a small size and it also must be taken great care of to be reliable.  
           [0011]    Conventional maglev pump  1 , however, as shown in FIGS. 9 and 10, has each electromagnet with magnetic poles arranged radially. As such, the space for accommodating the coil cannot be effectively obtained. As such, magnetic bearing portion  30  must be disadvantageously increased in size to provide an additional space for the coil to reduce the power consumption of the electromagnet.  
           [0012]    More specifically, while the power consumption of the electromagnet is reduced by increasing the winding count of the electromagnet coil or increasing the diameter of the wire of the coil, either technique requires increasing magnetic bearing portion  30  in size to ensure a large space for accommodating the coil. Furthermore, conventional maglev pump  1  has electromagnet  31  with an arcuate yoke. This makes it difficult to wind the coil and also hardly ensures insulation resistance between the coil and the yoke.  
           [0013]    Furthermore, as shown in FIGS. 8A and 8B, maglev pump  1  has a partition corresponding to casing  21  of plastic material, ceramic material or nonmagnetic metal material provided between soft magnetic member  26  of impeller  23  in pump chamber  22  and electromagnet  31  of magnetic bearing portion  30  and between soft magnetic member  26  of impeller  23  and position sensor  32  detecting the position of impeller  23 . As such, impeller  23  and electromagnet  31  are spaced far apart from each other. Thus, to levitate impeller  23  electromagnet  31  is required to pass a large amount of current. Furthermore, the sensor sensitivity also degrades as impeller  23  and position sensor  32  are spaced far apart from each other.  
           [0014]    More specifically, if the partition is formed of plastic material, the partition is less durable and can thus not be used for a long term. If the partition is formed of metal material and position sensor  32  is a magnetic sensor, then it has eddy current generated internal thereto to result in a loss and it also degrades the sensor sensitivity as it spaces position sensor  32  apart from a target.  
         SUMMARY OF THE INVENTION  
         [0015]    Therefore the present invention mainly contemplates a maglev pump capable of miniaturizing a magnetic bearing portion.  
           [0016]    The present invention also contemplates a maglev pump capable of reducing the distance between an electromagnet and an impeller and also reducing the distance between a sensor and the impeller to reduce the electromagnet&#39;s coil current and enhance the sensitivity of the sensor output.  
           [0017]    The present invention generally provides a maglev pump wherein a pump portion is provided with a rotative portion internal to a casing, the rotative portion is coupled with a rotation driving portion physically out of contact therewith and it is also supported by a controlled, magnetic bearing portion physically out of contact therewith, the rotative portion is rotated by the rotation driving position to discharge fluid, a position sensor detects the position of the rotative portion in levitation and in response to the output of the position detection portion the controlled magnetic bearing portion is controlled, wherein the magnetic bearing portion is configured of a plurality of electromagnets formed of a magnetic pole, a yoke and a coil and the electromagnet has magnetic S and N poles each with at least the yoke and coil arranged circumferentially.  
           [0018]    As such in an embodiment of the present invention a magnetic bearing includes electromagnets each having a magnetic pole and a yoke that are arranged circumferentially. This ensures a large space for winding a coil without increasing the space for the magnetic bearing portion or increasing the size of the pump. Since the coil can be accommodated in such a large space, the electromagnet coil can have an increased winding count and an increased wire diameter and consequently its power consumption can be reduced. Furthermore, the electromagnet can have a yoke in the form of a cylinder or a prism to facilitate winding a coil and thus readily ensure the insulation withstand voltage between the coil and the yoke.  
           [0019]    More preferably, the electromagnet has a pair of magnetic poles circumferentially arranged and the electromagnet has a pair of magnetic poles radially arranged.  
           [0020]    Still more preferably, the rotative portion is provided in a form of a disk having a side facing the rotation driving portion and provided with a permanent magnet circumferentially arranged and the rotative portion and the rotation driving portion are magnetically coupled together physically out of contact with each other, and the electromagnet has three pairs of magnetic S and N poles.  
           [0021]    Furthermore the present invention in another aspect provides a maglev pump wherein a pump portion is provided with a rotative portion internal to a casing, the rotative portion is coupled with a rotation driving portion physically out of contact therewith and it is also supported by a controlled, magnetic bearing portion physically out of contact therewith, the rotative portion is rotated by the rotation driving portion to discharge fluid, a position sensor detects the position of the rotative portion in levitation and in response to the output of the position detection portion the controlled magnetic bearing portion is controlled, wherein the magnetic bearing portion includes a plurality of electromagnets each directly facing the rotative portion or the position detection portion includes a magnetic sensor directly facing the rotative portion.  
           [0022]    Thus in the present invention the magnetic bearing portion can have a plurality of electromagnets directly facing a rotative portion or a magnetic sensor directly facing the rotative portion to reduce the distance between the rotative portion and the electromagnets or the magnetic sensor corresponding to a plane in which the electromagnetic force of the magnetic bearing acts. Thus, the pump can be levitated with a reduced amount of current flowing through an electromagnet coil for generating electromagnetic force to levitate the same, which is advantageous when the present pump is used as a blood pump since current consumption is one of its significant issues. Furthermore, the position sensor can be enhanced in sensitivity.  
           [0023]    More preferably, the position detection portion includes a core formed of a soft magnetic material and a coil wound around the core.  
           [0024]    Still more preferably, any of the electromagnet and the position detection portion is flipped to the casing by any of welding, brazing, press-fitting, pressure-welding, shrink-fitting and bonding or a combination thereof.  
           [0025]    Still more preferably, the rotative portion is provided in the form of a disk having a side facing the rotation driving portion and having a first permanent magnet circumferentially arranged and the rotation driving portion has a second permanent magnet circumferentially arranged to face the first permanent, magnet, the first and second permanent magnets achieving magnetic-coupling to couple together the rotative portion and the rotation driving portion physically out of contact with each other, and the pump portion has an internal surface coated with heparin.  
           [0026]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    In the drawings  
         [0028]    [0028]FIGS. 1A and 1B show a maglev pump in one embodiment of the present invention;  
         [0029]    [0029]FIG. 2 is a cross section taken along line II-II of FIG. 1A;  
         [0030]    [0030]FIG. 3 is a cross section taken along line III-III of FIG. 1A;  
         [0031]    [0031]FIG. 4 shows anoither embodiment of the present invention, showing an exemplary arrangement of a magnetic pole and a coil;  
         [0032]    [0032]FIG. 5 is a cross section taken along line IV-IV of FIG. 4;  
         [0033]    [0033]FIGS. 6A and 6B show another embodiment of the present invention;  
         [0034]    [0034]FIG. 7 is a block diagram of a controller for driving a maglev pump of the present invention;  
         [0035]    [0035]FIGS. 8A and 8B show a conventional maglev pump;  
         [0036]    [0036]FIG. 9 is a cross section taken along line IX-IX of FIG. 8A; and  
         [0037]    [0037]FIG. 10 is a cross section taken along line X-X of FIG. 8A.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Reference will now be made to FIGS.  1 A- 3  to describe a maglev pump in one embodiment of the present invention. The maglev pump is configured of a motor portion  10 , a pump portion  20  and a magnetic bearing portion  40 . In pump portion  20  a casing  21  houses a pump chamber  22  in which an impeller  23  rotates. Impeller  23  has a plurality of vanes  27  provided spirally, as shown in FIG. 1B.  
         [0039]    Casing  21  is formed of plastic, ceramic, metal or the like, although magnetic material cannot be used for casing  21  corresponding to a partition located between pump portion  20  and motor portion  10  and that located between pump portion  20  and magnetic bearing portion  40  and nonmagnetic material is thus used to form those partitions. Impeller  23  includes a nonmagnetic member  25  having a permanent magnet  24  configuring a noncontrolled magnetic bearing, and a soft magnetic member  26  corresponding to a rotor of a controlled magnetic bearing. Permanent magnet  24  is divided in a circumferential direction of impeller  23  and adjacent permanent magnets are magnetized to have opposite magnetic poles.  
         [0040]    Note that in FIG. 1A a hatched portion corresponds to a soft magnetic material and the remaining portion corresponds to a nonmagnetic material. If the pump is used for transferring a corrosive fluid such as blood, the soft magnetic material is preferably, e.g., highly corrosive-resistant, ferritic stainless steel (corresponding to JIS G4303 SUS447J1 and JIS G4303 SUS444) and the nonmagnetic material is preferably, e.g., highly corrosive-resistant austenitic stainless steel (corresponding to SUS316L or the like), or titanium alloy, pure titanium or the like.  
         [0041]    Opposite to the side of impeller  23  provided with permanent magnet  24 , external to the pump chamber there is provided a rotor  12  supported by a shaft  11 . Rotor  12  is rotatably driven by a motor  13 . Rotor  12  is provided with the same number of permanent magnets  14  as impeller  23  that face permanent magnet  24  of impeller  23  to provide attraction. Permanent magnets  14  adjacent to each other are magnetized to have opposite magnetic poles. Motor portion  10  is a synchronous motor including a DC brushless motor, an asynchronous motor including an induction motor, or the like, although any type of motor may be used.  
         [0042]    Opposite to the side of impeller  23  provided with soft magnetic member  26 , an electromagnet  111  and a position sensor  62  are provided in magnetic bearing portion  40 . Electromagnet  111  and position sensor  62  allow balance with the attraction of permanent magnets  24  and  14  to hold impeller  23  at the center of the pump chamber.  
         [0043]    [0043]FIG. 1A shows a single electromagnet  111  configured of a magnetic pole  51 , an electromagnet yoke  71 , an electromagnet coil  81  and an electromagnet backplate  91 , although magnetic bearing portion  40  has three electromagnets arranged circumferentially. Furthermore, as shown in FIG. 2, sensors  61 ,  62  and  63  are arranged between their respective pairs of magnetic poles  51  and  52 ,  53  and  54 , and  55  and  56 . Sensors  61  to  63  are typically a magnetic sensor, such as an eddy-current sensor, a reluctance sensor, or the like.  
         [0044]    Furthermore, as shown in FIG. 3, electromagnet yokes  71  to  76  each has a cylindrical shape, with electromagnet coils  81  to  86  wound therearound, respectively.  
         [0045]    Circumferentially arranging magnetic poles  51 - 56  can increase a space for accommodating electromagnet coils  81  to  86  that can be housed in magnetic bearing portion  40 . Furthermore, providing electromagnet yokes  71  to  76  in the form of a cylinder can facilitate winding electromagnet coils  81  to  86  around electromagnet yokes  71  to  76 . Furthermore, electromagnet yokes  71  to  76  having a simple shape ensures reliable isolation from electromagnet coils  81  to  86 .  
         [0046]    Although electromagnet yokes  71  to  76  are provided in the form of a cylinder, they may be provided in the form of a prism. Furthermore, while in FIGS. 2 and 3 electromagnet yokes  71  to  76  and electromagnet coils  81  to  86  are arranged on a single circumference, they may not be arranged on a single circumference so that an accommodating space can be effectively ensured.  
         [0047]    [0047]FIGS. 4 and 5 show another embodiment of the present invention, and FIG. 4 shows an exemplary arrangement of a magnetic pole and a coil and FIG. 5 is a cross section taken along line IV-IV of FIG. 4.  
         [0048]    In FIG. 4, electromagnet coils  81  to  86  and electromagnet yokes (not shown) are arranged circumferentially, as similarly in FIG. 3, although pairs of magnetic poles  101  and  102 ,  103  and  104 , and  105  and  106  are each arranged radially. Furthermore, as shown in FIG. 5, magnetic pole  105 , electromagnet yoke  75 , electromagnet backplate  92 , electromagnet yoke  76  and magnetic pole  106  configure a single C-shaped electromagnet. The embodiment shown in FIGS. 4 and 5 also has an electromagnet yoke in the form of a cylinder to facilitate winding electromagnet coils  81  to  86 , although the yoke is not limited to the cylinder and it may for example be a prism.  
         [0049]    The present embodiment is as effective as the embodiment shown in FIGS.  1 A- 3 .  
         [0050]    [0050]FIGS. 6A and 6B show another embodiment of the present invention, and FIG. 6A is a vertical cross section and FIG. 6B is a cross section taken along line XIB-XIB of FIG. 6A.  
         [0051]    In the present embodiment, a magnetic bearing portion  120  includes an electromagnet  121  having a core  122  and a position sensor  124  having a core  125  and cores  122  and  125  are partially buried in casing  21  formed of a nonmagnetic material and providing a partition between magnetic bearing portion  120  and pump portion  20 . Core  122  has a coil  123  wound therearound and core  125  has a coil  126  wound therearound. Furthermore, electromagnet  121  and position sensor  124  have their respective ends exposed in pump chamber  22 . Electromagnet  121  and casing  21  of pump chamber  22  are welded, brazed, press-fit, pressure-welded, shrink-fit or bonded together, or jointed together by a combination of those techniques to seal the interior and exterior of pump chamber  22 . Furthermore, to provide biocompatibility to the portion welded, brazed, press-fit, pressure-welded, shrink-fit or bonded as above, pump chamber  2  can have its interior entirely coated with heparin serving as an anticoagulant to prevent thrombus formation to allow the pump to be used as a blood transporting pump. In this example, heparin coating effectively constrains activation of coagulation system, protects platelets, constrains activation, activation of inflammation system, activation of fibrinolysis system, and the like.  
         [0052]    As has been described above, in the present embodiment, electromagnet  121  and position sensor  124  have their respective ends exposed in pump chamber  22  to directly face impeller  23 . This can reduce the distance between soft magnetic member  25  of impeller  23  in pump chamber  22  and position sensor  124  detecting the position of the impeller. As a result, impeller  23  can be levitated with a small amount of current flowing through the coil of electromagnet  21  and position sensor  124  can also be enhanced in sensitivity.  
         [0053]    [0053]FIG. 7 is a block diagram showing a controller for driving a maglev pump of the present invention. In FIG. 7, a controller  200  includes a function provided to control the position of the impeller, a function provided to control the running torque of the impeller, a function employing the function controlling the impeller position, to alter in pump chamber  22  the position of impeller  23  in levitation, a function provided to measure the current of motor  13 , and a function provided to calculate a fluid viscosity by referring to a variance of the current of motor  13  measured when the position of impeller  23  in levitation is changed via the function controlling the impeller position in levitation.  
         [0054]    More specifically, controller  200  includes a controller body  201 , a motor driver  202 , and a control portion  203  for controlling the impeller position. Motor driver  202  outputs a level of voltage corresponding to a motor rotation rate output from controller body  201 , to rotate motor  13 . Furthermore, control portion  203  for controlling the impeller position maintains the impeller position in levitation output from controller body  201 , by controlling the current or voltage flowing through the FIG. 1A electromagnet  111  or the FIG. 6A electromagnet  121 . The FIG. 2 position sensor  61  to  63  or the FIG. 6A position sensor  24  output a result of detection, which is in turn input to control portion  203  for controlling the impeller position, to control the current flowing through electromagnet  111  or  121 , to control the translation of impeller  23  in the direction of the central axis (an axis z) and the rotation of impeller  23  around axes x and y orthogonal to the central axis (axis z). Note that the position sensor  61 - 63  or  124  output may be input to controller body  201 , which may in turn output a value of voltage or current applied to electromagnet  111  or  121 .  
         [0055]    Controller body  201  includes a storage portion (ROM)  204 , a CPU  205 , a display portion  210  and an input portion  207 . Display portion  210  includes a set delivery rate (SDR) display portion  211 , an executed delivery rate (EDR) display portion  212 , a set delivery output (SDO) display portion  213 , an executed delivery pressure (EDP) display portion  214 , a fluid temperature (FT) display portion  215 , a fluid viscosity (FV) display portion  216 , and an impeller rotation rate (IRR) display portion  217 . Furthermore, input portion  207  includes an SDR input portion  208  and an SDP input portion  209 .  
         [0056]    Controller body  201  includes a data storage portion storing data of a relationship between fluid viscosity and motor current variance, corresponding to a previously obtained relationship between fluid viscosity and motor current variance depending on positional variance of the impeller in levitation (variance in motor drive current), or a relationship expression calculated from the data related to such relationship (for example data of a correlation expression or data of an expression of viscosity calculation), and the function provided for calculation of fluid viscosity calculates fluid viscosity from the data stored in storage portion  24  and the variance of the current through motor  13  obtained when the impeller  23  position in levitation is changed via the function controlling the impeller position in levitation.  
         [0057]    In other words, controller body  201  at storage portion  204  stores data related to a relationship between fluid viscosity and motor current variance corresponding to a previously obtained relationship between fluid viscosity and motor current variance depending on positional change of the impeller in levitation, or correlation data calculated from the data related to such relationship (also serving as data of an expression for viscosity calculation).  
         [0058]    As described above, in the embodiment of the present invention a magnetic bearing includes electromagnets each having a magnetic pole and a yoke that are arranged circumferentially. This ensures a large space for winding a coil without increasing the space for the magnetic bearing portion or increasing the size of the pump. Since the coil can be accommodated in such a large space, the electromagnet coil can have an increased winding count and an increased wire diameter and consequently its power consumption can be reduced. Furthermore, the electromagnet can have a yoke in the form of a cylinder or a prism to facilitate winding a coil and thus readily ensure the insulation withstand voltage between the coil and the yoke.  
         [0059]    Furthermore, the magnetic bearing portion can have a plurality of electromagnets directly facing a rotative portion to reduce the distance between the rotative portion and the electromagnets corresponding to a plane in which the electromagnetic force of the magnetic bearing acts. Thus, the impeller can be levitated with a reduced amount of current flowing through an electromagnet coil for generating electromagnetic force to levitate the impeller, which is advantageous when the present pump is used as a blood pump since current consumption is one of its significant issues.  
         [0060]    Furthermore, the position sensor detecting the impeller position and the impeller can be less distant from each other to enhance the sensitivity of the position sensor.  
         [0061]    Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.