Magnetically levitated pump

Details Magnetically levitated pump Magnetically levitated pump

2000-12-27

2003-06-10

Freay, Charles G. (Department: 3746)

Pumps

Motor driven

Electric or magnetic motor

C417S423120, C310S090500

Reexamination Certificate

active

06575717

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Background Art
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.
8
A.
FIG. 9
is a cross section taken along a line IX—IX of FIG.
8
A.
FIG. 10
is a cross section taken along a line X—X of FIG.
8
A.
Initially, with reference to
FIG. 8
a
through
FIG. 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.
8
B. Casing
21
is formed of a cylindrical, non-magnetic member and impeller
23
includes a non-magnetic member
25
having a permanent magnet
24
configuring a non-controlled 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.
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.
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
.
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.
8
B). 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.
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.
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.
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.
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.
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.
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
Therefore the present invention mainly contemplates a maglev pump capable of miniaturizing a magnetic bearing portion.
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's coil current and enhance the sensitivity of the sensor output.
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.
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

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