U.S. patent application number 13/635582 was filed with the patent office on 2013-03-21 for valveless pump.
The applicant listed for this patent is Jane Kang, David Ku, David Rosen. Invention is credited to Jane Kang, David Ku, David Rosen.
Application Number | 20130071271 13/635582 |
Document ID | / |
Family ID | 44649612 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130071271 |
Kind Code |
A1 |
Rosen; David ; et
al. |
March 21, 2013 |
VALVELESS PUMP
Abstract
A valveless, pulsatile, non-contact, positive displacement,
finger-pump for pumping one or more fluids is disclosed. The pump
can include one or more channels for holding one or more lengths of
flexible tubing. The channels can include an adjustment mechanism
and/or a resilient backing plate to reduce over compression of the
tubing. The pump can utilize a plurality of profiled, pivoting
fingers to sequentially occlude a length of tubing causing a
pumping action. The fingers can be moved from the first position to
the second position by a motor driven camshaft. Cam lobes disposed
on the camshaft can be a modified eccentric design to improve tube
occlusion and pump efficiency. At least one cam lobe can completely
occlude the tubing at all times during operation to prevent
backflow. The fingers can alternatively be moved from the first
position to the second position by a variety of linear
actuators.
Inventors: |
Rosen; David; (Marietta,
GA) ; Ku; David; (Decatur, GA) ; Kang;
Jane; (Atlanta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rosen; David
Ku; David
Kang; Jane |
Marietta
Decatur
Atlanta |
GA
GA
GA |
US
US
US |
|
|
Family ID: |
44649612 |
Appl. No.: |
13/635582 |
Filed: |
March 17, 2011 |
PCT Filed: |
March 17, 2011 |
PCT NO: |
PCT/US11/28885 |
371 Date: |
September 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61314631 |
Mar 17, 2010 |
|
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|
Current U.S.
Class: |
417/477.1 ;
29/888.022 |
Current CPC
Class: |
F04B 43/1292 20130101;
F04B 43/09 20130101; F04B 43/086 20130101; Y10T 29/4924 20150115;
F04B 43/123 20130101 |
Class at
Publication: |
417/477.1 ;
29/888.022 |
International
Class: |
F04B 43/08 20060101
F04B043/08; F04B 43/09 20060101 F04B043/09 |
Claims
1. A pump system for pumping one or more fluids comprising: a
housing comprising: a first tubing holder for holding a length of
flexible tubing; and a first axle disposed in the housing; a
plurality of fingers, each finger comprising an axle hole at a
distal end of each finger, wherein each finger is pivotally coupled
to the first axle; and a drive system configured to move each of
the plurality of fingers sequentially from a first position to a
second position; wherein each of the fingers at least partially
occludes a portion of the flexible tubing in the second
position.
2. The pump system of claim 1, wherein each of the fingers
substantially completely occludes the portion of the flexible
tubing in the second position.
3. The pump system of claim 1, wherein the tubing holder comprises
a channel and a plane surface; and wherein each of the plurality of
fingers compresses the flexible tubing between the finger and the
plane surface when the finger is in the second position.
4. The pump system of claim 3, wherein the plane surface further
comprises a resilient cover to prevent over compression of the
flexible tubing in the second position.
5. The pump system of claim 1, wherein the drive system comprises a
camshaft comprising a central shaft and a plurality of cam lobes;
and a motor for driving the camshaft in a rotary motion.
6. The pump system of claim 5, wherein each of the plurality of cam
lobes is a modified eccentric design.
7. The pump system of claim 5, wherein the motor drives the
camshaft directly.
8. The pump system of claim 5, wherein the motor drives the
camshaft with a belt.
9. The pump system of claim 5, wherein the camshaft further
comprises a driven gear mounted to the central shaft; and wherein
the motor comprises a drive gear mounted to the motor and in
communication with the driven gear to drive the camshaft in a
rotary motion.
10. The pump system of claim 9, wherein the driven gear comprises a
drive gear system comprising two or more gears in communication
with each other and with the driven gear to drive the camshaft in a
rotary motion.
11. The pump system of claim 1, wherein the drive system comprises
a plurality of shape memory alloy (SMA) wires; wherein each of the
plurality of fingers further comprises: a first SMA wire coupled to
the finger above the axle hole; and a second SMA wire coupled to
the finger below the axle hole; and wherein the first and second
SMA wires can be individually activated to move the finger back and
forth between the first position and the second position.
12. The pump system of claim 11, wherein the first SMA wire moves
the finger from the first position to the second position; and
wherein the second SMA wire moves the finger from the second
position to the first position.
13. The pump system of claim 1, wherein at least one of the
plurality of fingers is in the second position at any given time to
prevent backflow in the flexible tubing.
14. The system of claim 1, further comprising an inlet connector
and an outlet connector for connecting the tubes to the length of
flexible tubing; wherein the inlet connector comprises an inlet
port disposed proximate a top portion of the inlet connector; and
wherein the outlet connector comprises an outlet port disposed
proximate a bottom portion of the outlet connector.
15. A system for pumping two or more fluids comprising: a housing,
with a first side, a middle, and a second side, comprising: a first
tubing holder for holding a first flexible tube; a second tubing
holder for holding a second flexible tube; a first axle disposed on
a first side of the housing; and a second axle disposed on the
second side of the housing; a first set of two or more fingers,
each finger comprising an axle hole located on a distal end of each
finger, wherein each finger is pivotally coupled to the first axle;
a second set of two or more fingers, each finger comprising an axle
hole, pivotally coupled to the second axle; a camshaft, comprising
a central shaft and a plurality of cam lobes, disposed in the
middle of the housing; and a motor for driving the camshaft in a
rotary motion; wherein the camshaft sequentially moves the first
set of fingers and the second set of fingers from a first position
to a second position; wherein each of the first set of fingers at
least partially occludes a portion of the first flexible tubing in
the second position; wherein each of the second set of fingers at
least partially occludes a portion of the second flexible tubing in
the second position; and wherein the sequential occlusion of the
first and second flexible tubes by the fingers pumps fluid through
the tubes.
16. The system of claim 15, wherein the first and second tubes each
further comprise an inlet connector and an outlet connector for
connecting the tubes to external tubing; wherein the inlet
connector comprises an inlet port disposed proximate a top portion
of the inlet connector; and wherein the outlet connector comprises
an outlet port disposed proximate a bottom portion of the outlet
connector.
17. The system of claim 16, wherein the inlet connector further
comprises a steeper change in cross-sectional area from a first
side to a second side than the outlet connector.
18. The system of claim 15, wherein each cam lobe has a duration
angle of between approximately 30 degrees and 180 degrees of
rotation.
19. The system of claim 15, wherein each of the fingers further
comprises a first shoulder on a first side of the axle hole and a
second shoulder on the second side of the axle hole to reduce
friction.
20. The system of claim 15, further comprising a washer disposed
between each of the fingers to reduce friction.
21. The system of claim 15, wherein the motor is an electric
motor.
22. A method of manufacturing a pump comprising: providing a
housing with a first end, a second end, a first side, a middle, a
second side, and one or more tubing holders; mounting a first set
of one or more fingers on a first axle; mounting the first axle
proximate the first side of the housing; mounting a camshaft,
comprising one or more cam lobes, in the middle of the housing
proximate the first set of fingers; mounting a motor proximate the
camshaft to rotate the camshaft; wherein each of the one or more
cam lobes is disposed proximate one of the first set of one or more
fingers such that, as the camshaft rotates, each cam lobe activates
a respective finger; and wherein activating the respective finger
comprises moving the respective finger from a first, open position
to a second closed position.
23. The method of manufacture of claim 22, further comprising:
mounting a second set of one or more fingers on a second axle;
mounting the second axle proximate the second side of the housing;
wherein each of the one or more cam lobes is disposed proximate one
of the first set of one or more fingers and one of the second set
of one or more fingers such that, as the camshaft rotates, each cam
lobes activates a respective finger from the first set and a
respective finger from the second set.
24. The method of manufacture of claim 23, wherein the cam lobes
are disposed on the camshaft such that the cam lobes activate the
first and second sets of one or more fingers sequentially.
25. The method of manufacture of claim 22, wherein the cam lobes
are disposed on the camshaft such that the cam lobes activate the
first set of one or more fingers sequentially.
26. The method of manufacture of claim 22, further comprising:
affixing a drive gear to the motor; and affixing a driven gear to
the camshaft; wherein the drive gear rotates the driven gear.
27. The method of manufacture of claim 22, wherein motor is
directly attached to the camshaft.
28. The method of manufacture of claim 22, wherein the motor and
the camshaft are coupled using a drive belt.
29. The method of manufacture of claim 22, wherein the housing
further comprises a first adjustment means to enable the distance
between the tubing holder and the camshaft to be adjusted.
30. The method of manufacture of claim 22, wherein the housing
further comprises a second adjustment means to enable the height of
the camshaft to be adjusted.
31. The method of manufacture of claim 22, wherein the first and
second sides of the housing are coupled to the housing with hinges
to enable insertion of tubing in the tubing holders.
32. The method of manufacture of claim 31, wherein the hinges are
independently adjustable to enable different sizes of tubing to be
inserted in the tubing holders.
Description
CROSS REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIM
[0001] The present application is a national phase entry and claims
the benefit of PCT Patent Application Serial Number
PCT/US2011/028885, and entitled, "Valveless Pump," filed 17 Mar.
2011, which claims the benefit of U.S. Provisional Patent
Application Ser. No. 61/314,631 filed 17 Mar. 2010, and entitled
"Pump Design for a Portable Renal Replacement System," which are
hereby incorporated by reference in their entirety as if fully set
forth below.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention relate to a valveless
pump design, and more specifically to a pulsatile, non-contact,
positive displacement, finger-pump for pumping one or more
fluids.
[0004] 2. Background of the Invention
[0005] Pump designs exist for a variety of applications. Regardless
of design, however, pumps are fundamentally of two types: direct
and indirect (or, "non-contact"). In a direct pump, portions of the
pump are in direct contact with the fluid. An automotive water
pump, for example, uses a motor or belt-driven impeller to pump
cooling fluid throughout the engine. The impeller is connected to
the drive (e.g., a pulley or gear) and is separated from the
cooling fluid by a seal and a housing. In this configuration, the
impeller is in direct contact with the cooling fluid, while the
drive pulley or gear is outside the cooling system.
[0006] In some applications, however, it is desirable to provide a
pump capable of pumping a fluid without contacting the fluid
directly. This can be to prevent, for example, contamination or
clotting of the fluid (e.g., in medical applications). This may
also be desirable to prevent contamination of the pump (e.g., when
pumping radioactive cooling fluid in a nuclear reactor, for
example). An indirect pump may also be desirable when pumping
particularly dirty fluids, such as bilge water, for example, to
prevent fouling and/or clogging of the pump.
[0007] One application for indirect pumps is in the pumping of
fluids for hemodialysis (hereinafter, "dialysis"). End Stage Renal
Disease (ESRD) is a disease afflicting hundreds of thousands of
patients worldwide. Most patients diagnosed with ESRD undergo
dialysis..sup.1 Traditional dialysis generally requires patients to
visit a clinic three times a week for three to five hour treatment
sessions..sup.2 This results in the patients disrupting their
everyday life and restricting activities such as extended travel.
In addition, because the treatments are generally administered
every other day, high waste levels accumulate, which can make
patients experience dizziness and lethargy, amongst other
symptoms..sup.3 Limitations in the current technology have spurred
the development of portable renal replacement systems. A portable
renal system would both free the patients from time required at the
clinic but would also allow more frequent treatments, leading to
lower average waste levels..sup.4 .sup.1A. A. P. B. Kerr, J. L.
Flavier, B. Canaud, C. M. Mion, "Comparison of dialysis and
hemodiafiltration: A long-term longitudinal study," Kidney
International, vol. 41, pp. 1035-1040, 1992..sup.2J. Daugirdas,
"Second generation logarithmic estimates of single-pool variable
volume Kt/V: an analysis of error," Journal of the American Society
of Nephrology, vol. 4, pp. 1205-1213, 1993; I. T. Kjellstrand C M,
"Daily dialysis: history and revival of a superior dialysis
method," ASAIO Journal, vol. 44, pp. 115-122, 1998 May/June; B. F.
Piccoli G. B., Iacuzzo C., Anania P, Iadarola A. M., Mezza E., "Why
our patients like daily dialysis," Dialysis International, vol. 4,
pp. 47-50, 2000..sup.3F. Mastrangelo, et al., "Dialysis with
increased frequency of sessions (Lecce dialysis)," Nephrol Dial
Transplant, vol. 13 Suppl 6, pp. 139-47, 1998..sup.4U. B. Francesco
Locatelli, Bernard Canaud, Hans Kohler, Thierry Petitclerc, Pietro
Zucchelli, "Dialysis dose and frequency," Nephrology Dialysis
Transplantation, vol. 20, pp. 285-296, 2005; L. A. F. Mastrangelo,
M. Napoli, V. DeBlasi, F. Russo and P. Patruno, "Dialysis with
increased frequency of sessions (Lecce dialysis)," Nephrol Dial
Transplant, vol. 13, pp. 139-147, 1998.
[0008] In the case of dialysis system design, maintaining a sterile
path for the blood flow is a critical requirement. Any pump used in
the system must not introduce harmful agents (e.g., bacteria or
viruses) to the blood or the dialysate. Conventional dialysis
systems typically use peristaltic roller pumps, a type of rotary,
positive displacement pump, because they can maintain a sterile
flow path for the blood. These pumps use moving rollers to squeeze
a flexible tube forcing the fluid inside to move in one direction.
When the roller has passed a section of tubing, the tubing
rebounds, or "reinflates," and enables fluid to flow into the void
thus created. Because the flexible tubing is the only component
exposed to the fluid, the pump can maintain sterility.
[0009] These types of pumps rely on relatively stiff tubing,
however, to displace fluid. As a result, these pumps exhibit poor
efficiency primarily due to the energy required to compress the
(not particularly) flexible tubing. In addition, during dialysis,
two pumps are generally used, one for circulating blood and the
other for circulating the dialysate. Additional pumps can be used
is additional drugs or blood products, for example, are to be
administered. Pumps of this type that are capable of producing the
necessary flow rates for efficient dialysis tend to be too large
and heavy to be used as part of a portable renal replacement
system.
[0010] What is needed, therefore, is a small, energy efficient pump
capable of pumping one or more fluids. The pump should be an
indirect pump such that none of the pump components are in direct
contact with the pumped fluid. The pump should be reliable,
serviceable, and economical to produce and maintain. It is to such
a pump that embodiments of the present invention are primarily
directed.
BRIEF SUMMARY OF THE INVENTION
[0011] Embodiments of the present invention relate to a valveless
pump design, and more specifically to a pulsatile, non-contact,
positive displacement, finger-pump for pumping one or more fluids.
In its most basic form, the pump can comprise one or more sets of
fingers sequentially activated by a drive mechanism. Each finger
can have a first, or open, position and a second, or closed
position. When a finger is in this first position, the length of
tubing proximate that finger can be open and uncompressed. When a
finger is in the second position, the length of tubing proximate
that finger can be partially or completely compressed.
[0012] The fingers can be activated, or moved, by a drive mechanism
in a sequential manner. The fingers can act sequentially along the
length of tubing to create positive displacement of the fluid
inside the tubing. As the fingers are sequentially activated, they
alternately compress and release the tubing to create positive
displacement of the fluid in one direction. In some embodiments, in
the closed position, the finger can fully compress the tube such
that no fluid will flow (forward or backward) through that
particular portion of tubing. In a preferred embodiment, at least
one finger in the set of fingers is in the closed position at all
times to substantially prevent backflow in the tubing.
[0013] Embodiments of the present invention can comprise a pump
system for pumping one or more fluids comprising a housing, which
can include a first tubing holder for holding a length of flexible
tubing and a first axle disposed in the housing. The pump system
can further comprise a plurality of fingers, each finger comprising
an axle hole located on a distal end of each finger, wherein each
finger is pivotally coupled to the first axle. The pump system can
further comprise a drive system configured to move each of the
plurality of fingers sequentially from a first position to a second
position. In some embodiments, each of the fingers can at least
partially occlude a portion of the flexible tubing in the second
position. In a preferred embodiment, each of the fingers
substantially completely occludes the portion of the flexible
tubing in the second position.
[0014] In some embodiments, the tubing holder can comprise a
channel and a plane surface and each of the plurality of fingers
can compress the flexible tubing between the finger and the plane
surface when the finger is in the second position. In some
embodiments, the plane surface can further comprise a resilient
cover to prevent over compression of the flexible tubing in the
second position.
[0015] In some embodiments, the drive system can comprise a
camshaft including a central shaft and a plurality of cam lobes,
and a motor for driving the camshaft in a rotary motion. The
plurality of cam lobes can be a modified eccentric design. In some
embodiments, the motor can drive the camshaft directly. In other
embodiments, the motor can drive the camshaft with a belt. In still
other embodiments, the camshaft can further comprise a driven gear
mounted to the central shaft and the motor can comprise a drive
gear mounted to the motor and in communication with the driven gear
to drive the camshaft in a rotary motion. The driven gear can also
comprise a drive gear system comprising two or more gears in
communication with each other and with the driven gear to drive the
camshaft in a rotary motion.
[0016] Embodiments of the present invention can also comprise a
pump system wherein the drive system comprises a plurality of shape
memory alloy (SMA) wires. In this configuration, each of the
plurality of fingers can comprise a first SMA wire coupled to the
finger above the axle hole and a second SMA wire coupled to the
finger below the axle hole. In this configuration, the first and
second SMA wires can be individually activated to move the finger
back and forth between the first position and the second position.
First instance, in some embodiments, the first SMA wire can move
the finger from the first position to the second position and the
second SMA wire can move the finger from the second position to the
first position. In a preferred embodiment, at least one of the
plurality of fingers is in the second position at any given time to
prevent backflow in the flexible tubing.
[0017] Embodiments of the present invention can further comprise a
system for pumping two or more fluids comprising a housing, with a
first side, a middle, and a second side. The housing can further
comprise a first tubing holder for holding a first flexible tube, a
second tubing holder for holding a second flexible tube, a first
axle disposed on a first side of the housing, and a second axle
disposed on the second side of the housing. The system can include
a first set of two or more fingers, while each finger can comprise
an axle hole, and can be pivotally coupled to the first axle and a
second set of two or more fingers, again where each finger can
comprise an axle hole, and can be pivotally coupled to the second
axle.
[0018] The system can include a camshaft, which can comprise a
central shaft and a plurality of cam lobes, and can be disposed in
the center of the housing. In a preferred embodiment, the camshaft
sequentially moves the first set of fingers and the second set of
fingers from a first position to a second position and the fingers
at least partially occludes a portion of the first flexible tubing
in the second position. The sequential occlusion of the first and
second tubes by the fingers can pump fluid through the tubes. In
some embodiments, each cam lobe can have a duration angle of
between approximately 30 degrees and 180 degrees of rotation.
[0019] The system can also include a motor for driving the camshaft
in a rotary motion. In a preferred embodiment, the motor is an
electric motor.
[0020] In some embodiments, the flexible tube can comprise inlet
connectors and outlet connectors for connecting the tubes to
external tubing. The inlet connector can comprise an inlet port
that can be disposed proximate a top portion of the inlet connector
and the outlet connector can comprise an outlet port disposed
proximate a bottom portion of the outlet connector. In some
embodiments, the inlet connector can also comprise a steeper change
in cross-sectional area from a first side to a second side than the
outlet connector.
[0021] In some embodiments, each of the fingers can comprise a
first shoulder on a first side of the axle hole and a second
shoulder on the second side of the axle hole to reduce friction.
the fingers can also be separated by one or more washers disposed
between each of the fingers to reduce friction.
[0022] Embodiments of the present invention can also include a
method of manufacturing a pump. The method can comprise providing a
housing with a first end, a second end, a first side, a middle, a
second side, and one or more tubing holders; mounting a first set
of one or more fingers on a first axle; mounting the first axle
proximate the first side of the housing; mounting a camshaft,
comprising one or more cam lobes, in the middle of the housing
proximate the first set of fingers; and mounting a motor proximate
the camshaft to rotate the camshaft. When mounted each of the one
or more cam lobes can be disposed proximate one of the first set of
one or more fingers such that, as the cam rotates, each cam lobe
can activate a respective finger. Activating can comprise, for
example, moving the respective finger from a first, open position
to a second closed position.
[0023] In some embodiments, the method can further comprise
mounting a second set of one or more fingers on a second axle and
mounting the second axle proximate the second side of the housing.
Again, each of the one or more cam lobes can be disposed proximate
one of the first set of one or more fingers and one of the second
set of one or more fingers such that, as the cam rotates, each cam
lobes can activate a respective finger from the first set and a
respective finger from the second set. In a preferred embodiment,
the cam lobes are disposed on the camshaft such that the cam lobes
activate the first set, the second set, or both sets of one or more
fingers sequentially.
[0024] In some embodiments, the method can further comprise
affixing a drive gear to the motor and affixing a driven gear to
the camshaft. In this configuration, the drive gear rotates the
driven gear. in other embodiments, the motor can be directly
attached to the camshaft. In still other embodiments, the motor and
the driveshaft can be coupled using a drive belt.
[0025] In some embodiments, the housing can further comprise a
first adjustment means to enable the distance between the tubing
holder and the camshaft to be adjusted. In other embodiments, the
housing can further comprise a second adjustment means to enable
the height of the camshaft to be adjusted. In still other
embodiments, the first and second sides of the housing can be
coupled to the housing with hinges that can enable insertion of
tubing in the tubing holder. The hinges can be independently
adjustable to enable different sizes of tubing to be inserted in
the tubing holders.
[0026] These and other objects, features and advantages of the
present invention will become more apparent upon reading the
following specification in conjunction with the accompanying
drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 depicts a side, perspective view of a finger pump, in
accordance with some embodiments of the present invention.
[0028] FIG. 2 depicts a side view of a cam lobe, in accordance with
some embodiments of the present invention.
[0029] FIG. 3 depicts a side, perspective view of a drive system
utilizing shape memory alloy, in accordance with some embodiments
of the present invention.
[0030] FIG. 4a depicts a side, perspective view of a finger, in
accordance with some embodiments of the present invention.
[0031] FIG. 4b depicts an end view of a finger, in accordance with
some embodiments of the present invention.
[0032] FIG. 5 depicts a side, perspective view of a finger pump
with a resilient cover and an adjustment means, in accordance with
some embodiments of the present invention
[0033] FIG. 6 depicts a side view of a tubing connector, in
accordance with some embodiments of the present invention.
[0034] FIG. 7 is a graph depicting the effect of disposal head on
flow rate for pump 1, in accordance with some embodiments of the
present invention.
[0035] FIG. 8 is a graph depicting creatinine levels over time, in
accordance with some embodiments of the present invention.
[0036] FIG. 9 is a graph depicting the oval constant, in accordance
with some embodiments of the present invention.
[0037] FIG. 10 is a graph depicting the effect of disposal head on
flow rate for pump 2, in accordance with some embodiments of the
present invention.
[0038] FIG. 11 is a graph depicting flow rate vs. RPM for pump 3,
in accordance with some embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] Embodiments of the present invention relate to a valveless
pump design, and more specifically to a pulsatile, non-contact,
positive displacement, finger-pump for pumping one or more fluids.
In its most basic form, the pump can comprise one or more sets of
fingers sequentially activated by a drive mechanism. Each finger
can have a first, or open, position and a second, or closed
position. The fingers can be activated in a sequential manner to
create a pumping action through flexible tubing.
[0040] To simplify and clarify explanation, the system is described
below as a pump system for use with a portable renal replacement
system. One skilled in the art will recognize, however, that the
invention is not so limited. The system can be used to in a variety
of fluid pumping applications, especially those applications in
which the fluid is preferably pumped without direct contact with
the fluid. In other applications, the pump could be used for
pumping non-fluids, such as for example, slush, sewage, or in food
processing applications. These applications can include, for
example and not limitation, medical, nuclear, and sewage
applications. In addition, the system is described below for use in
pumping two fluids simultaneously. Obviously, the system can be
adapted to pump one fluid or more than two fluids without departing
from the spirit of the invention.
[0041] The materials described hereinafter as making up the various
elements of the present invention are intended to be illustrative
and not restrictive. Many suitable materials that would perform the
same or a similar function as the materials described herein are
intended to be embraced within the scope of the invention. Such
other materials not described herein can include, but are not
limited to, materials that are developed after the time of the
development of the invention.
[0042] As described above, a problem with conventional fluid pumps
is that pumps with higher efficiency tend to be direct fluid pumps,
i.e., the impeller, or other pump components, are in direct contact
with the fluid being pumped (or, "pumped fluid"). Indirect pumps,
like the roller pumps generally used for dialysis, on the other
hand, tend to be heavy and inefficient. These pumps tend to rely on
stiff-walled tubing, which requires larger, more powerful motors
and increases frictional losses. What is needed is an energy
efficient, compact, indirect pump capable of pumping one or more
fluids that is compatible for use with both flexible and
stiff-walled tubing. It is to such a pump system that embodiments
of the present invention are primarily directed.
[0043] Embodiments of the present invention can comprise a
non-contact fluid pump design that can minimize total pump size
while maximizing pump efficiency. As shown in FIG. 1, embodiments
of the present invention can comprise a pump system 100 comprising
a motor driven camshaft 115, a plurality of fingers 130, and a pump
housing 120. The pump housing 120 can house many of the components
of the pump system 100 and can provide one or more channels 120a
for holding tubing and one or more plane surfaces 120b against
which the tubing can be compressed. The camshaft can comprise a
central shaft 115a and a plurality of cam lobes 115b. Each cam lobe
115b can be mounted on the shaft 115a and can be oriented at
different angles on the shaft 115a such that they can sequentially
actuate the plurality of fingers 130 to compress one or more tubes
150. In other embodiments, the fingers 130 can be actuated in a
non-sequential manner to produce alternative flows. The one or more
tubes 150 can be positioned between the pump housing 120 and the
fingers 130. In a preferred embodiment, two tubes 150 are used
(e.g., one tube 150 on each side of the housing 120).
[0044] In some embodiments, the plurality of fingers 130 can be
positioned between the cam lobes 115b and the tubes 150. The
fingers 130 can be mounted on shafts 145 located on the distal end
of fingers 130 enabling each finger to pivot between a first, open
position and a second, closed position. As each finger 130 is
actuated by its respective cam lobe 115b, the finger 130 pivots
between the first position, in which the tube 150 is open and
flowing and the second position, in which the tube 150 is partially
or completely compressed. In some embodiments, there can be a gap
between each pair of fingers 130 to maximize pumping efficiency
along the tube 150 and reduce friction by preventing direct contact
between the fingers 130 themselves. In a preferred embodiment, a
low friction washer is positioned between each finger 130 to
further minimize friction.
[0045] In some embodiments, a motor 155 can be used to drive the
camshaft 115. The motor 155 can be, for example and not limitation,
an electric, pneumatic, or hydraulic motor. In some embodiments,
the motor 155 can be positioned under the camshaft 115, though
other configurations are contemplated. In some embodiments, a drive
gear on the motor shaft can be used to drive a driven gear on the
camshaft 115 (gears not shown for clarity). In other embodiments,
the motor 155 can be configured to drive the camshaft 115, for
example and not limitation, directly or with a chain or belt.
[0046] As shown in FIG. 2, the cam lobes 115b can be a modified
eccentric design. In some embodiments, the cam lobe 115b can
comprise three regions of cam contour. The first region 205 can be
the rise portion, which can be a substantially circular arc. The
second region 210, or the dwell, can be used to compress the tube
150. In a preferred embodiment, the dwell 210 is configured to
completely occlude the tube 150 for a desired period of time. The
third region 215, or fall region, can enable the finger to release
the tube 150 and, like the first region can be a substantially
circular arc.
[0047] As one would expect, each cam lobe 115b has a different
orientation on the shaft 115a. In a preferred embodiment, the cam
lobes 115b are positioned such that they sequentially compress the
tubing 150 to create a pumping action.
[0048] The eccentric cam design has the advantage of enabling
control of tube 150 occlusion time when compared to, for example, a
conventional eccentric cam design that provides only one instance
of occlusion (i.e., a the top of the lobe). In an exemplary
embodiment, the pump can utilize seven cam lobes 115b that each
actuate a finger 130 on each side of the housing 120 (i.e., each
cam lobe 115b actuates two fingers 130). In this embodiment, the
five middle cam lobes 115b can have 60 degrees of duration, the
first cam lobe 115b can have 90 degrees of duration, and the last
cam lobe 115b can have 180 degrees of duration. This configuration
provides extra time for the tube 150 to refill after compression
and minimizes backflow. Of course, other camshaft 115
configurations can be used for different pumping requirements
(e.g., more even cam lobe 115b duration could provide a
substantially constant flow rate). In some embodiments, for
example, the cam lobe 115b configuration can be changed to provide
a pulsatile flow similar to the natural flow of blood in the body
caused by the heart.
[0049] In some embodiments, as shown in FIG. 3, the drive system
can comprise a plurality of pairs of linear actuators 315. The
linear actuators 315 can comprise, for example and not limitation,
air or hydraulic cylinders, linear solenoids, or shape memory
alloys. As shown, the linear actuators can comprise Flexinol.RTM.
wires 315. Flexinol.RTM. is a trade name for shape memory alloy
actuator wires. Made of nickel-titanium these small diameter wires
contract (typically 2% to 5% of their length) like muscles when
electrically driven or heated..sup.5 .sup.5See, "Introduction to
Flexinol.RTM.", Dynaalloy, Inc., available at
http://www.dynalloy.com/AboutFlexinol.html.
[0050] In this configuration, a first end of both wires 315 can be
anchored to an anchor point on the housing 305. The second end of a
first wire 340a can then be affixed to a finger 330 below the pivot
shaft 335, while the second end of a second wire 340b can be
affixed to the finger above the pivot shaft 335. The wires 340a,
340b can then be activated using an electrical current or heat, as
applicable, which causes the wires 340a, 340b to retract.
[0051] In use, one of the wires 340a, 340b can be activated to pull
a finger 330 into the first position, while the other wire 340a,
340b can be activated to pull the finger 330 into the second
position. The mounting direction, i.e., which side of the housing
120 anchors the wires 340a, 340b, determines which wire 340a, 340b
pulls the finger 330 closed or open. In a preferred embodiment, the
wires 340a, 340b are anchored to the far side of the housing to
maximize their length, thus maximizing their retraction.
[0052] As shown in more detail in FIGS. 4a and 4b, each finger 130
can have a cylindrical hole 405 for pivotally mounting the finger
130 on the pivot shaft 140. In some embodiments, the mounting hole
405 can comprise a bushing or other means for improving durability
and/or reducing friction. In a preferred embodiment, the fingers
130 further comprise steps 410 around the hole 405 to reduce
frictional losses between fingers 130 and/or the spacers between
them, if applicable. In some embodiments, the fingers 130 can be
separated on the pivot shaft 140 by one or more washers 425. The
washers 425 can comprise a low friction material to reduce rubbing
friction between the fingers 130. The washers 425 can comprise, for
example and not limitation, nylon, Teflon, or aluminum.
[0053] In some embodiments, each finger 130 can further comprise a
rounded back profile 415. The rounded profile 415 can reduce the
contact area between the finger 130 and the cam lobes 115b reducing
friction. The fingers 130 can further comprise a longitudinal ridge
420. The ridge 420 can reduces the contact area between the finger
130 and tube 150, which can also reduce friction. Reduced contact
area between the finger 130 and the tube 150 can reduce the area of
the tube 150 that is completely occluded when the finger 130 is in
the second, or closed, position. The use of a small occlusion area
does not affect the flow rate provided the tube 150 is completely
occluded by the contact area 420 and relatively little fluid
remains between the contact areas 420 of each finger 130 during
use. In addition, when used for pumping blood, for example, the
small occlusion area tends to reduce blood cell damage.
Tube Plate Design
[0054] As shown in FIG. 5, due to its configuration, engineering
and material tolerances could be problematic for the pump system
100. Small changes in tube 150 thickness, for example, could
prevent the tube 150 from being completely occluded causing
backflow, which may be undesirable in some applications. If the
tube channel 120a is set at a distance from the plane surface 120b
to correspond to a minimum tube thickness, the tube 150 will be
completely squeezed, thus guaranteeing complete occlusion of the
tube 150. In this configuration, when the tube 150 thickness
increases, however, excessive force will be required to over
compress the thicker tube 150.
[0055] In some embodiments, therefore, an adjustment means 510 can
be provided. The adjustment means can comprise an adjustable
mounting means 510 for the tube channel 120a/plane surface 120b
(collectively, tube holder 505). In other words, the tube holder
505 can be mounted to the pump housing 120 in such a way that its
distance from the camshaft 115 can be adjusted (e.g., using slotted
mounting holes 510). In other embodiments, the pump system 100 can
comprise a resilient cover 515 (e.g., a rubber plate) disposed over
the plane surface 120b. The resilient cover 515 can enable the tube
150 to be completely occluded, while absorbing the over compression
and reducing energy consumption. The adjustment means 510 can
enable individual adjustment to facilitate the use of different
sizes of tubing 150 at the same time (e.g., large tubing on one
side and small tubing on the other).
[0056] In some embodiments, the position of the camshaft 115 can be
adjusted to provide complete occlusion. In other words, the plane
surfaces 120b can be angled such that changing the height of the
camshaft 115 changes the distance between the camshaft 115 and the
plane surfaces 120b. In some embodiments, therefore, the camshaft
115 can be provided with an adjustment slot 520 to enable the
height of the camshaft to be adjusted. In this manner, provided the
tubes 150 are relatively the same size, larger tubes 150 can be
accommodated by raising the camshaft 115 and smaller tubes 150 can
be accommodated by lowering the camshaft 115. This assumes, of
course, that the plane surfaces are angled outward from bottom to
top, but the reverse is also contemplated.
[0057] In still other embodiments, the plane surfaces 120b can be
hinged where they attach to the housing 120. In this configuration,
the plane surfaces 120b can be pivoted away from the camshaft 115
to facilitate insertion of the tubing 150. In some embodiments, the
hinges can have multiple positions to enable the distance between
the plane surfaces 120b and the camshaft 115 to be adjusted. Again,
this provides the ability to accommodate different sizes of tubing.
The hinges can be independently adjustable to facilitate the use of
different sizes of tubing 150 at the same time (e.g., large tubing
on one side and small tubing on the other).
Tube Connector Design
[0058] The pump system 100 is compatible with a variety of tubing
types. In a preferred embodiment, thin-walled, flexible tubing
(e.g., Penrose drain tubing) is used to reduce, among other things,
the compression forces, pump size, and energy consumption. This
flexibility is generally only required, however, for the portion of
the tube 150 that is inserted into the pump 100. For the other
portions of the fluid circuit, using more durable tubing, such as
the tubing commonly used for IVs, may be a better choice. The use
of highly flexible tubing throughout the fluid circuit can cause,
for example, excessive flow rate variation. To enable modularity
and flexibility, tubing connectors can be used to connect the
flexible tubing used at the pump to, for example, standard IV
tubing.
[0059] As shown in FIG. 6, the tubing connectors 605 can comprise
an inlet connector 605a and an outlet connector 605b. The inlet
connector 605a can comprise a high mounted tubing nipple 610 and
can have an abrupt change in cross section. The outlet connector
605b, on the other hand, can comprise a low mounted nipple 615 with
a more gradual profile. This configuration enables fluid to flow
more easily in the flow direction (arrow) and tends to reduce
backflow.
Pump Design
[0060] In some embodiments, the present invention can comprise a
method for efficiently determining pump parameters given a set of
performance requirements (e.g., fluid volume per unit of time). The
performance of a finger pump can be controlled using several design
parameters, such as, for example and not limitation, the
characteristics of the tube and the actuator, which can also affect
the size of the pump. And, while some of these design parameters
have simple relationships when taken separately, many parameters
are inter-related, making it difficult to predict how the pump will
perform for a given configuration and set of actuator
characteristics.
[0061] An understanding of the relationship of these parameters for
the creation of an analytical pump model can nonetheless enable the
systematic pump minimization while providing the desired
performance. Required parameters can represent, for example,
experimental settings, tube and actuator characteristics, design
requirements, power consumption, and pump size information. Several
of those relationships can be embedded in an analytical pump model
and are discussed below.
Relationships Between Parameters
[0062] The flow rate can be calculated by multiplying the effective
cross sectional area of the tube with finger width and the number
of strokes. When the tube is inserted into the pump, its cross
section tends to become a long oval that fits a right trapezoid
space between the fingers and the housing. The oval area can be
calculated by multiplying the shape factor n/4 with tube width and
squeeze distance as the oval area that fits in a rectangle. This is
not, however, the only factor that determines the effective cross
sectional area as peristaltic pumps are subject to head change,
back flow loss, and friction loss, among other things. To consider
these factors, a lumped constant called the oval constant, can be
used to account for pump head changes, back flow loss, friction
loss, and the shape factor shown below in Eq. 1.
effective tube cross section(cm.sup.2)=oval constant.times.tube
width(cm).times.squeeze distance(cm) (1)
[0063] The oval constant can be found by matching the model
prediction with the experimental data (e.g., rpm vs. flow rate). If
the pump is operating with high outlet pressure, for example, the
flow rate will decrease and the oval constant will be smaller than
the default value.
[0064] The efficiency of the pump can be calculated by dividing the
fluid power by the brake power to pump the fluid, as shown in Eq.
2.
efficiency = fluid power ( W ) brake power ( W ) ( 2 )
##EQU00001##
[0065] Fluid power refers to the theoretically calculated power
required to transport the fluid at a given flow rate with a given
flow pressure, as shown in Eq. 3.
fluid power(W)=flow rate.times.flow pressure (3)
[0066] For use in a dialysis application, the flow pressure can be
assumed to be approximately equal to "normal" blood pressure (e.g.,
approximately 100 mmHg). This enables Eq. 3 to be simplified as
shown in Eq. 4.
fluid power ( W ) = 0.0222 ( W min ml ) .times. flow rate ( ml min
) ( 4 ) ##EQU00002##
[0067] Finally, brake power refers to the power required to operate
the pump. Brake power can be calculated, for example, by
multiplying the required battery voltage and current.
[0068] The size of the pump, especially one for portable use can be
an important calculation for the evaluation of a design. The
overall volume of the pump, for example, can be calculated by
multiplying the pump depth, width, and height. Pump depth, for
example, can be defined as the length of the pump in the flow
direction, and is related to the width and number of fingers that
force the flow in the flow direction, as shown in Eq. 5.
pump depth(cm)=no. of fingers.times.finger width(cm)+.alpha.
(5)
Where .alpha. can account for the additional length due to the
housing of the pump. This information can provide useful values,
for example, after designing an actual pump with a given
setting.
[0069] The model can include one or more of the parameters provided
below in Table 1. Each parameter can be designated as either an
input, intermediate calculation, or output. Input parameters
include, among other things, the type of tube, requirements, and
actuator characteristics (shown in normal fonts). Output
parameters, on the other hand, can provide information related to
the pump design specifications (shown in bold). Finally,
intermediate parameters can be used to calculate the output values
from input values (shown in italics).
TABLE-US-00001 TABLE 1 Parameters included in the model
Experimental Oval constant Setting Tube Character Effective tube
cross section tube width (cm) squeeze distance (cm) Force required
to squeeze (N/cm) Design target flow rate (ml/min) Requirements
fluid power (W) Operating time (hr) Required flow velocity (cm/s)
finger width (cm) No. of fingers No. of fingers working at an
instant Flow amount of a finger stroke (ml) No. of cycles per
minute (/min) No. of finger strokes (/min) signal delay (s)
Actuator Required force generation per Character finger (N) Total
required force generation (N) Voltage (V) Resistance (Ohm) Current
(A) Power Ampere hour (Ah) Consumption Watt hour (Wh) Battery size
constant (cm.sup.3/Wh) brake power (W) Efficiency Pump Size pump
width (cm) Information pump height (cm) pump depth (cm) pump body
volume (cm.sup.3) Battery volume (cm.sup.3) Total volume
(cm.sup.3)
Assumptions and Limits of the Analytical Pump Model
[0070] Based on the parameters' relationships, a finger pump model
can be created in a simulation model such as, for example and not
limitation, Simulink.RTM.. The pump model can include quantifiable
design parameters that affect the design of the pump. The model
can, in turn, provide quantifiable design output values including,
but not limited to, the expected power consumption and the overall
size of the pump. In addition, the model can be adapted for
different flow circuits and different design requirements such as,
for example and not limitation, target flow rates.
[0071] For efficiency, the pump model can utilize one or more
assumptions. For example, the compression sequence of the fingers
can be changed by varying the cam design for each finger. For
simplicity, however, the model assumes that no such difference
exists. In use, as long as a suitable average value is used, the
results of the model are sufficiently accurate.
[0072] The model also assumes that the motor fits in the housing in
the space under the camshaft. In other words, if the depth of the
pump is, in reality, shorter than the motor, a portion of the motor
will extend out of the housing. As a result, the size change
according to the change in the force requirement for an actuator is
not embedded in the model, though this could be added by, for
example, comparing the trend of the motor size change due to the
change in the force requirement.
[0073] The relationship between the force generation and power
consumption is not embedded in the model because this is typically
motor dependent. This could nonetheless be added for a known motor
or for a series of motors. Without this information, suitably
accurate information can nonetheless be provided by the model using
average resistance per power output to predict power consumption.
In addition, the force required to squeeze a tube does not increase
linearly when the compression area increases, most notably when the
compression area gets smaller. The model nonetheless assumes a
linear force-compression relationship for simplicity. Thus, a
finger width of greater than 0.4 cm, for example, is
preferable.
Suggestions for the Pump Design
[0074] The creation of analytical pump models with limited number
of design parameters with oval constant allowed an exploration of
all the different parameters associated with pump design. Modeling
suggests that increasing squeeze distance, number of fingers, and
applied voltage while using a flexible tube reduces the size of the
pump. The model is validated experimentally in section 5,
below.
EXPERIMENTAL RESULTS
[0075] To verify the accuracy of the pump model discussed above,
the model was tested while varying pump model parameters. The pump
model can be validated using the pump system 100, as described,
with water experiments. Blood flow results can prove the validity
of the pump system 100 for use in, for example and not limitation,
a portable renal replacement system.
Effect of Cross-Sectional Area Change on the Flow Rate
[0076] To test the effect of the cross-sectional area, one Penrose
drain tube was replaced by two small tubes disposed on the same
side of the pump (i.e., at different heights in the same tube
holder 505). Water was used as the pumped fluid.
[0077] Although the two tubes were the same size, due to their
location in the tubing channel 150 (i.e., one mounted higher than
the other) and the geometry of the pump, the top tube
cross-sectional area was approximately 1.586 times bigger than the
bottom tube. As shown in Table 2, below, when 10.8V was applied to
run the pump at approximately 38 rpm, the flow rate difference
closely matched the area ratio indicating that the cross-sectional
area increases the flow rate linearly.
TABLE-US-00002 TABLE 2 Effect of Cross-Section on Flow Rate Flow
Rate Ratio Top Tube 145 ml/min 1.54 Bottom Tube 94 ml/min
Effect of Inlet Supply Side Head Change on the Flow Rate
[0078] Because flexible tubes are used, a supply side head is
preferably provided to fill the tube (i.e., rather than having the
fingers open the tube). In addition, it is preferable for the pump
to be able to generate stable flow rates regardless of the level of
fluid in the supply source (e.g., a dialysate bag). Experiments
were conducted with water with a dialyzer in the circuit to provide
the same setting as a portable renal replacement system.
[0079] Four different water levels were tested by starting from a
full reservoir (about 550 ml) and running the pump for 1 minute
each time. Resulting flow rates were 132, 127, 125, and 125 ml/min,
respectively. The result validated that in the given system
configuration, the head difference in the supply source had a
negligible effect on flow rate. In addition, the same flow rate is
expected for both single pass mode and recirculation mode.
Effect of Fluid Viscosity Change on the Flow Rate
[0080] The pump 100 can pump two different fluids at the same time.
For a portable renal replacement system, for example, the two
fluids can be blood and dialysate. These fluids may have two
different viscosities, however; thus, the effect of viscosity on
flow rate was also tested. To provide a variety of fluid
viscosities, glycerol mixtures were prepared with different
water-glycerin ratios. Table 3 shows the flow rates for four
separate experiments for each viscosity.
TABLE-US-00003 TABLE 3 Fluid viscosity vs. Flow rate Glycerin
percent Viscosity weight (%) (mPa s) Flow rate (ml/min) 12.6 1.4
132 132 132 132 22.4 1.9 136 136 136 136 30.2 2.5 134 134 134 136
36.6 3.3 138 138 -- -- 41.9 4.1 134 132 134 -- 52.0 6.9 136 136 136
138
[0081] As shown in the table, the flow rate was virtually constant
for different viscosities. Based on the experimental data, a
difference in viscosity of up to 5.5 mPa has little or no effect on
the flow rate. Based on this data, it follows that the flow rate
will be the same for both the blood (1.84 mPa) and dialysate, which
is mostly water (1.005 mPa). It also shows that the oval constant
can be kept the same as long as the fluid viscosity does not vary
too widely (i.e., at least within a 5.5. mPa range).
Example 1
Pump 1
Effect of Changes in Outlet Head Pressure
[0082] The effect of the outlet, or disposal side, head change on
the flow rate was tested using in vitro blood experiments. The
blood flow rate was tested while both dialysate and blood were
running through a dialyzer. Four different disposal side heads (24
cm, 33 cm, 42 cm, and 50 cm) were tested with different motor
speeds (27, 34, and 42 RPM) for each configuration. The test
results for the 50 cm head at 27 rpm are not provided because the
fluid was not able to climb up the height with the slow flow rate.
The results are plotted in FIG. 7.
[0083] As shown, a lower disposal side head yielded higher flow
rates than a higher head. In addition, flow rates increased with
increased rpm. This tends to indicate that the disposal side head
should be considered when designing a pump for use with, for
example and not limitation, a portable renal replacement system
configuration.
[0084] In addition, these results indicate that the head effect has
a considerable effect on the oval constant. Since the oval constant
can be determined according to the flow rate change when all the
other design variables are kept the same, it shows that the oval
constant for 24 cm height, for example, will be about 4 times
larger than that for 50 cm (e.g., 90 ml/min vs. 22 ml/min). The
flow results also can be sensitive to whether or not the tubes are
completely occluded during operation. This indicates that
manufacturing tolerances should be controlled, or, as mentioned
above, means should be provided for adjustment of, or flexibility
in, the tube holders 505 to ensure complete tube occlusion. It
should be noted, however that although the flow rate is affected by
complete occlusion, the system nonetheless yields very repetitive
flow rates at a given setting. In other words, the flow rate is
repeatable whether the tube is completely occluded or not.
Validation of the Pump for the Portable Renal Replacement
System
[0085] Pump 1 was used for in vitro blood experiments to prove that
it can be used for dialysis treatments. The pump was used to
dialyze blood and the results were compared to known dialysis
models that have been proven to match well with both in vitro
experimental data and published patient data..sup.6 .sup.6J. C.
Olson, "Design and modeling of a portable hemodialysis system,"
Master of Science in Mechanical Engineering, Mechanical
Engineering, Georgia Institute of Technology, Atlanta, 2009.
[0086] Porcine blood was obtained during desanguination at a local
abattoir, and Citrate and Heparin were added to the blood
immediately after collection at a ratio of 100:10:890 (35% Citrate
solution: Heparin: blood). The porcine blood was then transported
to the laboratory in a thermally insulated container. Dialysate was
prepared by mixing concentrates with deionized water at a ratio of
22:38:940 (acid concentrate: bicarbonate concentrate: deionized
water).
[0087] The individual solute clearance, K.sub.D, is the typical
measure of clearance of an individual solute. Manufacturers provide
a value of K.sub.DA, the clearance multiplied by the surface area,
in the specifications for their dialyzers. A dialyzer with a small
KoA removes waste more slowly than the one with a larger KoA. Thus,
KoA is an important dialyzer characteristic for the prediction of
the waste level over time. KoA is different, however, for each
solute for different flow rates.
[0088] Unfortunately, a typical manufacturer reports only KoA for
the flow rate around 500 ml/min. This flow rate is consistent with
conventional non-portable dialysis machines designed to treat
dialysis patients quickly at an outpatient dialysis clinic. The use
of a constant, portable dialysis system, on the other hand requires
much lower flow rates. As a result, a single pass mode experiment
was conducted first to find the KoA value. 500 ml of blood was used
with the blood flow rate of 105 ml/min and dialysate flow rate of
100 ml/min. Creatinine levels were measured over time with an iSTAT
analyzer (Abbott). The data points for both single pass mode and
recirculation mode are plotted in FIG. 8 against the prediction of
the simulation package. As shown, the experiment data closely
matches the predicted values for KoA. This result validated the
pump for use as a portable renal replacement system in the single
pass mode.
[0089] A recirculation mode experiment was performed with 450 ml of
blood, with a flow rate of 74 ml/min, and 550 ml of dialysate, with
a flow rate of 75 ml/min. Again, the data points matched the
prediction values closely with the same KoA value found in the
single pass mode, demonstrating that the pump works also well for
the recirculation mode.
Example 2
Finding the Oval Constant
[0090] Since the concept of using a finger pump for a portable
renal replacement system is demonstrated, the effect of rpm change
on the flow rate was tested to find the oval constant that
represents the experimental setting. Pump 2 (a second prototype
pump) was used, which employed a stronger, faster motor. The
experiment results are plotted in FIG. 9 with the model prediction
with an oval constant value of 0.36. The plot depicts a generally
linear increase in flow rate with only minor variations.
[0091] The experimental data was then used to calibrate the model
for the predefined experimental settings. As explained above, the
oval constant is used as a lumped constant to account for head
changes and/or back flow loss. For a given pump design, however,
the oval constant changes substantially linearly with the flow rate
change. Thus, the oval constant can be determined by finding the
value at which the model prediction closely matches experiment
data. Since the main required flow rate for this pump is about 100
ml/min, the oval constant that closely matches that region is
found.
Effect of Changes in Outlet Head Pressure
[0092] As with Pump 1, the effect of outlet, or disposal side, head
change on the flow rate was tested with pump 2, and the results are
plotted in FIG. 10. Four different head values were tested and
compared to the results from pump 1. As shown, the head change did
not have a substantial effect on flow rate. As mentioned above,
when the fingers do not completely occlude the tube, the flow rate
greatly reduces especially when a large outlet head is applied. In
this case, the fingers almost completely occlude the tube, thus the
effect of outlet head is reduced.
OPTIMIZATION OF PUMP DESIGN
[0093] With the oval constant found using pump 2, the pump model
was used to explore the design space and find an optimized pump
design for a portable renal replacement system. The problem is
formulated as below.
TABLE-US-00004 Given: The pump model with the oval constant 0.36.
Find: The input variable combination for the pump design (e.g.,
squeeze distance, motor voltage, etc.). Satisfy: Finger width
>0.4 cm: The finger width is preferably longer than the critical
length to increase efficiency and provide the space for the washer
in between fingers. Objective: 1. Minimize the total volume (i.e.,
size) of the pump and 2. Maximize efficiency of the pump.
[0094] According to the problem formulated above, the design space
was explored in the region where the input variables ranged as
shown in Table 4.
TABLE-US-00005 TABLE 4 Input variables for the design space
exploration inputs Min Increments Max squeeze distance (cm) 0.2 0.1
1.5 Voltage (V) 3 1.5 12
[0095] The maximum squeeze distance was chosen as 1.5 cm because
squeeze distances larger than this tend to cause the flexible tube
to shift out of position. The minimum voltage value was chosen to
ensure that the motor reaches desired minimum operating speed, and
the maximum value is equivalent to the motors nominal voltage. The
increment of the voltage was chosen based on the per cell voltage
(1.5V) of commercially available batteries.
[0096] Other design variables were set to default values. For
example, tube width was set to 2.5 cm since the pump design that
has this motor under the cams yields 2.5 cm space for the tube. The
target flow rate was set to 130 ml/min. The Actual flow rate
required was 100 ml/min, but a 130 ml/min target flow rate was used
to provide a 30% safety margin. As a result of the design space
exploration, many options were found, and five candidate pump
designs are shown in Table 5.
TABLE-US-00006 TABLE 5 Pump design candidates Candidates: 1 2 3 4 5
squeeze 0.5 0.8 0.5 0.4 0.4 distance (cm) Voltage (V) 6.0 6.0 7.5
9.0 12.0 pump body 127.3 117.8 105.7 97.8 78.8 volume (cm.sup.3)
width (cm) 4.4 5.0 4.4 4.2 4.2 depth (cm) 7.1 5.0 5.9 6.0 4.8
height (cm) 4.1 4.7 4.1 3.9 3.9 Efficiency 0.072 0.072 0.046 0.032
0.018 Watt hour 0.8 0.8 1.3 1.8 3.2 (Wh) RPM (/min) 52.9 52.9 67.8
82.7 112.4 finger width 0.78 0.49 0.61 0.62 0.46 (cm) total volume
129.1 119.5 108.5 101.7 85.9 (cm.sup.3)
[0097] Comparing efficiency and total pump volume, we find that the
smaller pump volume tends to yield lower efficiency. As shown, one
can choose any of these designs to achieve a flow rate of 130
ml/min. Thus, the ultimate decision can be based on the predominant
design factor such as, for example and not limitation, overall pump
size, efficiency requirements, or pumping volume. In this case, the
second design yields a relatively small pump volume while retaining
good efficiency.
Example 3
[0098] Pump 3 (a third pump prototype) was built according to the
Candidate 2 design from Table 5 above and tested to determine if
its performance matches model predictions. Since an oval constant
value of 0.36 was used for the optimization in the previous
section, the same value was used in the model for preliminary
validation. A 1.6.times.0.8 cm Penrose drain tube was used for the
experiments and the results are shown in FIG. 11 with model
prediction values.
[0099] The size reduction of the pump yielded an unexpected result
when compared to pump 2. As shown, the flow rate did not increase
linearly but exponentially as rpm increased. Comparison of the
experimental results with the model results [OC=0.3 (1.6.times.0.8
cm) and OC=0.36 (1.6.times.0.8 cm) curves] shows that pump 3
provides flow rates similar to the model with OC=0.3 at low speeds,
similar to the model with OC=0.36 at medium speeds, and greater
than the model with OC=0.36 at higher speeds. As shown, the pump
can achieve a 100 ml/min flow rate at 7.9V (66 rpm, 3.2%
efficiency) and 130 ml/min flow rate at 9V (76 rpm, 3.2%
efficiency). The electrical current varied between 0.05.about.0.12
A.
[0100] The expected performance of the pump with 2.5.times.0.8 cm
tube is also plotted in FIG. 11 [OC=0.3 (2.5.times.0.8 cm) curve]
and generated a 108 ml/min flow rate at 6V. The efficiency is
predicted to be 6% with less than 1 W power consumption. The pump
housing is approximately 5 cm.times.5 cm.times.4.7 cm, and
including the motor and battery compartment, approximately 5
cm.times.6.5 cm.times.4.7 cm (153 cm.sup.3). Pump 3 is compatible
with a variety of tubing sizes, though power consumption changes
with changes in tube size (i.e., larger tubing tends to increase
power consumption). Compared to conventional portable renal
replacement systems, which can be 317 cm.sup.3 and consume
approximately 10 W of power, the proposed pump design achieves a
52% reduction in size and an 89% savings in energy
consumption..sup.7 In addition, no check valves are required
minimizing problems associated with clogging or sticking valves,
for example. .sup.7R. V. B. H. Gura, Edmond, "Dual-ventricle pump
cartridge, pump and method of use in a wearable continuous renal
replacement therapy device," United States patent, 2007
[0101] While several possible embodiments are disclosed above,
embodiments of the present invention are not so limited. For
instance, while several possible configurations have been disclosed
(e.g., a camshaft driven design and a SMA driven design), other
suitable materials and configurations could be selected without
departing from the spirit of the invention. In addition, the
location and configuration used for various features of embodiments
of the present invention can be varied according to, for example,
the intended use of the pump, or a particular pumping volume
requirement, viscosity, or chemical resistance requirement. Such
changes are intended to be embraced within the scope of the
invention.
[0102] The specific configurations, choice of materials, and the
size and shape of various elements can be varied according to
particular design specifications or constraints requiring a device,
system, or method constructed according to the principles of the
invention. Such changes are intended to be embraced within the
scope of the invention. The presently disclosed embodiments,
therefore, are considered in all respects to be illustrative and
not restrictive. The scope of the invention is indicated by the
appended claims, rather than the foregoing description, and all
changes that come within the meaning and range of equivalents
thereof are intended to be embraced therein.
* * * * *
References