U.S. patent application number 13/465902 was filed with the patent office on 2012-11-08 for system and method of differential pressure control of a reciprocating electrokinetic pump.
Invention is credited to Kenneth R. Hencken, Robert B. Lewis, Tuan Quoc Mai, Kenneth Kei-ho Nip, Doris Sun-Chia Shieh.
Application Number | 20120282111 13/465902 |
Document ID | / |
Family ID | 47090349 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120282111 |
Kind Code |
A1 |
Nip; Kenneth Kei-ho ; et
al. |
November 8, 2012 |
SYSTEM AND METHOD OF DIFFERENTIAL PRESSURE CONTROL OF A
RECIPROCATING ELECTROKINETIC PUMP
Abstract
A method of controlling the output of an electrokinetic pump to
deliver a target stroke volume includes applying a pump drive
signal to the electrokinetic pump for a pump stroke time duration
and then determining a volume of a delivery fluid pumped. Then,
comparing the volume of the delivery fluid pumped to the target
stroke volume; generate a new time interval for applying the pump
drive signal. Then apply the pump drive signal to the
electrokinetic pump for the new time interval. A system for
delivery of fluid includes an electrokinetic pump under the control
of an electronic controller. The electronic controller contains
computer readable instructions to determine an output of the
electrokinetic pump and then generate a stroke time delivery
adjustment for precise pumping schemes.
Inventors: |
Nip; Kenneth Kei-ho;
(Redwood City, CA) ; Hencken; Kenneth R.;
(Pleasanton, CA) ; Shieh; Doris Sun-Chia; (Santa
Clara, CA) ; Lewis; Robert B.; (Pleasanton, CA)
; Mai; Tuan Quoc; (San Ramon, CA) |
Family ID: |
47090349 |
Appl. No.: |
13/465902 |
Filed: |
May 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61482960 |
May 5, 2011 |
|
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Current U.S.
Class: |
417/48 |
Current CPC
Class: |
F04B 49/06 20130101;
F04B 43/04 20130101; F04B 19/006 20130101; F04B 19/00 20130101 |
Class at
Publication: |
417/48 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Claims
1. A method of controlling the output of an electrokinetic pump to
deliver a target stroke volume, comprising: Applying a pump drive
signal to the electrokinetic pump for a pump stroke time duration
is about one second; Determining a volume of a delivery fluid
pumped during the pump stroke time duration; Comparing the volume
of the delivery fluid pumped to the target stroke volume;
Generating a new time interval for applying the pump drive signal
to the electrokinetic pump based upon the comparing step; and
Applying the pump drive signal to the electrokinetic pump for the
new time interval.
2. The method of controlling the output of an electrokinetic pump
according to claim 1 wherein the difference between the new time
interval and the pump stroke time duration is no more than 100
ms.
3. The method of controlling the output of an electrokinetic pump
according to claim 1 wherein the new time interval is a time
duration that maintains the electrokinetic pump within the
reversible faradaic limits of the electrokinetic pump
components.
4. The method of controlling the output of an electrokinetic pump
according to claim 1 wherein the pump stroke time duration is
selected to remain within the reversible faradic operating
parameters of the electrokinetic pumps.
5. The method of claim 1 wherein the generating a new time interval
is based in part on a temperature compensation related to a
delivery fluid temperature.
6. The method of controlling the output of an electrokinetic pump
according to claim 1 wherein the determining a volume step includes
the use of a differential pressure flow technique.
7. The method of controlling the output of an electrokinetic pump
according to claim 6 wherein the differential pressure flow
technique is based on an input from at least one pressure sensor in
communication with the pump outlet.
8. The method of controlling the output of an electrokinetic pump
according to claim 6 wherein the differential pressure flow
technique uses a flow restrictor and is based on an input from at
least one pressure sensor.
9. The method of claim 6 wherein the determining the volume is
based on a comparison of two differential pressure signals after
the initial applying a pump drive signal step.
10. The method of claim 6 wherein the determining the volume is
based on an integral of a pressure sensor during the applying a
pump drive signal step.
11. The method of claim 6 wherein the determining the volume is
based on an integral a difference between two pressure sensors
during the applying a pump drive signal step.
12. The method of claim 6 wherein the determining the volume is
based on an estimated delivery condition read from a pressure
sensor during the applying a pump drive signal step.
13. The method of claim 12 wherein the duration of the applying a
pump drive signal is adjusted based on the estimated delivery
condition read from a pressure sensor during the applying a pump
drive signal step.
14. The method of controlling the output of an electrokinetic pump
according to claim 6 wherein the differential pressure flow
measurement technique uses input from a pair of pressure
sensors.
15. The method of controlling the output of an electrokinetic pump
according to claim 9 wherein one of the pressure sensors is in
communication with the pump outlet.
16. The method of controlling the output of an electrokinetic pump
according to claim 9 wherein one of the pressure sensors is
positioned to indicate backpressure acting on the output of the
electrokinetic pump.
17. The method of controlling the output of an electrokinetic pump
according to claim 1 further comprising: before the applying a pump
drive signal for the new time interval, applying a pump drive
signal of opposite polarity to the pump drive signal used in the
initial applying a pump drive signal step, wherein the duration of
the applying a pump drive signal of opposite polarity is the same
as the pump stroke time duration.
18. The method of controlling the output of an electrokinetic pump
according to claim 1 further comprising: after applying the pump
drive signal for the new time interval, applying a pump drive
signal of opposite polarity to the pump drive signal used in the
applying a pump drive signal for the new time interval step,
wherein the duration of the applying a pump drive signal of
opposite polarity is the same as the new time interval
duration.
19. The method of controlling the output of an electrokinetic pump
according to claim 1 wherein the pump drive signal during the
applying steps is a constant voltage.
20. The method of controlling the output of an electrokinetic pump
according to claim 1 wherein the pump drive signal during the
applying steps is a constant current.
21. The method of claim 1 wherein the duration of the applying a
pump drive signal is adjusted based on the estimated delivery
condition read from a pressure sensor just prior to the applying a
pump drive signal step.
22. The method of claim 1 further comprising: decrementing a total
volume delivery counter according to the result of the determining
a volume of a delivery fluid pumped step.
23. The method of claim 1 further comprising: incrementing a total
volume delivery counter according to the result of the determining
a volume of a delivery fluid pumped step.
24. The method of claim 23 further comprising: generating a pump
stop signal when the result of the determining a volume of a
delivery fluid pumped step is the last delivery increment of the
total volume delivery counter.
25. The method of claim 23 further comprising: generating a pump
stop signal when the result of the determining a volume of a
delivery fluid pumped step is the last delivery decrement of the
total volume delivery counter.
26. A system for delivery of fluid, comprising: An electrokinetic
pump configured to deflect a diaphragm in an outlet chamber, the
outlet chamber having an inlet and an outlet; A first check valve
in communication with the inlet; A second check valve in
communication with the outlet; A pressure sensor positioned to
indicate a pressure within the system between the first check valve
and the second check valve; and A computer controller in
communication with the electrokinetic pump and the pressure sensor
containing computer readable instructions to determine an output of
the electrokinetic pump based at least in part on a signal from the
pressure sensor and to generate a stroke time delivery adjustment
after each deflection of the diaphragm into the outlet chamber.
27. The system of claim 26 further comprising: another pressure
sensor and a flow restrictor wherein, the pressure sensor is
positioned to indicate the pressure of the outlet chamber, the flow
restrictor is positioned between the outlet chamber outlet and the
second check valve and the another pressure sensor is positioned to
indicate a pressure within the system between the flow restrictor
and the second check valve.
28. The system of claim 26 further comprising: a reservoir
containing a delivery fluid and having an outlet in communication
with the outlet chamber inlet.
29. The system of claim 26 further comprising: a delivery conduit
in communication with the outlet chamber outlet.
30. The system of claim 26 further comprising: a flow restrictor
wherein, the flow restrictor is positioned between the outlet
chamber outlet and the second check valve and the pressure sensor
is positioned to indicate a pressure within the system between the
flow restrictor and the outlet chamber.
31. The system of claim 26 further comprising: another pressure
sensor and a flow restrictor wherein, the flow restrictor is
positioned between the second check valve and a delivery conduit
and the pressure sensor is positioned to indicate the pressure
downstream of the flow restrictor in the delivery conduit.
32. The system of claim 26 the system further comprising: a user
input device in communication with the computer controller wherein
the computer controller is adapted and configured to provide and
receive signals from the user input device.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119 to U.S. Provisional Patent Application No.
61/482,960, filed May 5, 2011, and entitled "SYSTEM AND METHOD OF
DIFFERENTIAL PRESSURE CONTROL OF A RECIPROCATING ELECTROKINETIC
PUMP," incorporated herein by reference in its entirety.
INCORPORATION BY REFERENCE
[0002] All publications and patent applications mentioned in this
specification are herein incorporated by reference to the same
extent as if each individual publication or patent application was
specifically and individually indicated to be incorporated by
reference.
FIELD
[0003] This application relates to electrokinetic pump control
schemes.
BACKGROUND
[0004] Precise pumping systems are important for chemical analysis,
drug delivery, and analyte sampling. However, traditional pumping
systems can be inefficient due to a loss of power incurred by
movement of a mechanical piston. Still further, conventional
systems may not be configured to compensate for errors during
delivery. This is most likely because such pumping systems cannot
precisely deliver small amounts of delivery fluid because the
mechanical piston cannot be accurately stopped mid-stroke.
[0005] Other electrokinetic pumping systems have been described,
however, those pumping systems have not included the flow control
schemes that take full advantage of partial pump stroke control. In
addition, prior pumping systems have not included flow control
measurement systems with accuracy sufficient to provide stroke to
stroke compensation.
[0006] Accordingly, there remains a need for electrokinetic pumping
systems with improved flow control schemes.
SUMMARY OF THE DISCLOSURE
[0007] In one aspect, there is a method of controlling the output
of an electrokinetic pump to deliver a target stroke volume,
including applying a pump drive signal to the electrokinetic pump
for a pump stroke time duration is about one second; determining a
volume of a delivery fluid pumped during the pump stroke time
duration; comparing the volume of the delivery fluid pumped to the
target stroke volume; generating a new time interval for applying
the pump drive signal to the electrokinetic pump based upon the
comparing step; and applying the pump drive signal to the
electrokinetic pump for the new time interval. In performing the
method of controlling the output of an electrokinetic pump the
difference between the new time interval and the pump stroke time
duration is no more than 100 ms. Alternatively, during the method
of controlling the output of an electrokinetic pump and/or the pump
stroke time duration is a time duration selected or constrained so
as to maintain the electrokinetic pump within the reversible
faradaic limits of the electrokinetic pump components or is
selected to remain within the reversible faradic operating
parameters of the electrokinetic pumps.
[0008] In another embodiment, a method of controlling the output of
an electrokinetic pump the determining a volume step includes the
use of a differential pressure flow technique that may, for
example, be based on an input from at least one pressure sensor in
communication with the pump outlet or use a flow restrictor and is
based on an input from at least one pressure sensor.
[0009] In another embodiment, a method of controlling the output of
an electrokinetic pump the process of determining a volume step may
be based on a comparison of two differential pressure signals after
the initial applying a pump drive signal step, be based on an
integral a pressure sensor during the applying a pump drive signal
step, be based on an integral a difference between two pressure
sensors during the applying a pump drive signal step, be based on
an estimated delivery condition read from a pressure sensor during
the applying a pump drive signal step.
[0010] In another embodiment of a method of controlling the output
of an electrokinetic pump the duration of the applying a pump drive
signal is adjusted based on the estimated delivery condition read
from a pressure sensor during the applying a pump drive signal
step. In another aspect of a method of controlling the output of an
electrokinetic pump the differential pressure flow measurement
technique uses input from a pair of pressure sensors. In this
aspect of controlling the output of an electrokinetic pump one of
the pressure sensors is in communication with the pump outlet or
one of the pressure sensors is positioned to indicate backpressure
acting on the output of the electrokinetic pump.
[0011] In another aspect of a method of controlling the output of
an electrokinetic pump, before the applying a pump drive signal for
the new time interval, there is a process of applying a pump drive
signal of opposite polarity to the pump drive signal used in the
initial applying a pump drive signal step. The duration of the
applying a pump drive signal of opposite polarity is the same as
the pump stroke time duration. In another aspect of controlling the
output of an electrokinetic pump after applying the pump drive
signal for the new time interval, there is a process of applying a
pump drive signal of opposite polarity to the pump drive signal
used in the applying a pump drive signal for the new time interval
step. The duration of the applying a pump drive signal of opposite
polarity is the same as the new time interval duration. During any
of the methods of controlling the output of an electrokinetic pump
the pump drive signal during the applying steps may be a constant
voltage or a constant current.
[0012] In another aspect of a control method, the duration of the
applying a pump drive signal is adjusted based on the estimated
delivery condition read from a pressure sensor just prior to the
applying a pump drive signal step. Still further, a method may also
decrementing a total volume delivery counter according to the
result of the determining a volume of a delivery fluid pumped step
or incrementing a total volume delivery counter according to the
result of the determining a volume of a delivery fluid pumped step.
In one aspect, there is a process of generating a pump stop signal
when the result of the determining a volume of a delivery fluid
pumped step is the last delivery increment of the total volume
delivery counter or is the last delivery decrement of the total
volume delivery counter.
[0013] There is also provided a system for delivery of fluid having
an electrokinetic pump configured to deflect a diaphragm in an
outlet chamber, the outlet chamber having an inlet and an outlet.
There is also a first check valve in communication with the inlet
and a second check valve in communication with the outlet. There is
also a pressure sensor positioned to indicate a pressure within the
system between the first check valve and the second check valve and
computer controller. The computer controller is in communication
with the electrokinetic pump and the pressure sensor. The memory of
the computer controller or memory accessible to the computer
controller contains computer readable instructions to determine an
output of the electrokinetic pump based at least in part on a
signal from the pressure sensor and to generate a stroke time
delivery adjustment after each deflection of the diaphragm into the
outlet chamber.
[0014] The system may also include another pressure sensor and a
flow restrictor wherein, the pressure sensor is positioned to
indicate the pressure of the outlet chamber, the flow restrictor is
positioned between the outlet chamber outlet and the second check
valve and the another pressure sensor is positioned to indicate a
pressure within the system between the flow restrictor and the
second check valve. The system may also include a reservoir
containing a delivery fluid and having an outlet in communication
with the outlet chamber inlet. The system may also include a
delivery conduit in communication with the outlet chamber outlet.
The system may also include a flow restrictor wherein, the flow
restrictor is positioned between the outlet chamber outlet and the
second check valve and the pressure sensor is positioned to
indicate a pressure within the system between the flow restrictor
and the outlet chamber. The system may also include another
pressure sensor and a flow restrictor wherein, the flow restrictor
is positioned between the second check valve and a delivery conduit
and the pressure sensor is positioned to indicate the pressure
downstream of the flow restrictor in the delivery conduit. The
system may also include a user input device in communication with
the computer controller wherein the computer controller is adapted
and configured to provide and receive signals from the user input
device.
[0015] In still another aspect of a method of controlling the
output of an electrokinetic pump, the difference between the new
time interval and the pump stroke time duration is between 4 ms and
64 ms. In another, the difference between the new time interval and
the pump stroke time duration is related to an amount of back
pressure acting on the electrokinetic pump. In one embodiment, the
pump stroke time duration is between about 300 milliseconds and
about 500 milliseconds. In another aspect, the pump stroke time
duration is between about 800 milliseconds and about 1 second. In
another aspect, the output of the electrokinetic pump is provided
against a backpressure of between about 3 psi--about 5 psi. In
still another aspect, the method of controlling the output of an
electrokinetic pump has a pump stroke time duration is more than 0
milliseconds and less than 500 milliseconds or the new time
interval is zero or less than one second.
[0016] In still another alternative embodiment, there is a method
of controlling the output of an electrokinetic pump under the
control of a computer controller to deliver a target stroke volume.
This method includes computer readable instructions for the
performance of a number of different processing steps. The
processing steps may include for example, applying a voltage to the
electrokinetic pump for a pump stroke time duration; determining a
volume of a delivery fluid pumped during the pump stroke time
duration using an input from a differential pressure flow meter;
comparing the volume of the delivery fluid pumped during the pump
stroke time duration to the target stroke volume; generating a
stroke time duration adjustment based upon the comparing step;
applying a voltage to the electrokinetic pump in relation to the
pump stroke time duration and the stroke time duration adjustment
and others depending upon the particular configuration of the
pumping system used. In one aspect, the voltage used in both
applying a voltage steps is equal. The method may include
determining a volume of a delivery fluid by measuring flow rates of
a fluid flowing fluid through a differential pressure flow meter
having a venturi flow meter, an orifice flow meter and/or a flow
nozzle flow meter.
[0017] In one aspect, the step of determining a volume of a
delivery fluid relies in part on a pressure sensor reading at the
outlet to a flow restrictor downstream of the delivery chamber of
the electrokinetic pump. In one embodiment, the step of determining
a volume of a delivery fluid may use a pressure sensor reading at
the outlet to a check valve downstream of the delivery chamber of
the electrokinetic pump. In another aspect, the method of
generating a stroke time duration adjustment is based upon a
proportional feedback control scheme programmed into an electronic
memory of the computer controller; a proportional and integral
feedback control scheme programmed into an electronic memory of the
computer controller; a proportional, integral and derivative
feedback control scheme programmed into an electronic memory of the
computer controller, each alone or in any combination.
[0018] In still another aspect, the comparing step includes a
reading of a delivery fluid temperature. In one embodiment, the
stroke time duration adjustment is based on the reading of a
delivery fluid temperature or on a temperature compensation related
to a delivery fluid temperature.
[0019] In another aspect, the steps of the method are repeated
until a total volume delivery counter in the computer controller is
incremented to the total volume delivery. Alternatively, the steps
of the method are repeated until a total volume delivery counter in
the computer controller is decremented to zero from a total volume
delivery. Performance of the method steps may produce an output of
about 3 microliters per stroke or about 0.5 microliters per stroke.
Still further, the method is conducted where the delivery fluid
pumped is a pharmacological agent and the steps of the method are
repeated until a desired volume of is delivered. In the method, the
desired volume is controlled by a value set in the computer
controller to limit delivery of the pharmacological agent. In one
aspect, the pharmacological agent is glucose. In still further
aspect, the steps of the method are repeated to produce an output
of the delivery fluid at a rate of about 0.09 ml/hour, or a rate of
about 0.03 ml/minute. In one embodiment, the stroke time duration
adjustment is completely applied to the immediate next pump
stroke.
[0020] In still another aspect there is a method of controlling an
output of an electrokinetic pump under the control of a computer
controller having computer readable instructions to deliver a
target stroke volume. The instructions include applying a voltage
to the electrokinetic pump for a pump stroke time duration. In
addition, there are instructions for processing a pressure signal
related to the output of the electrokinetic pump; determining a
volume of a delivery fluid pumped during the pump stroke time
duration based at least in part on the result of the processing
step; comparing the volume the delivery fluid pumped during the
pump stroke time duration to the target stroke volume; generating a
stroke time duration adjustment based upon the comparing step; and
applying a voltage to the electrokinetic pump in relation to the
pump stroke time duration and the stroke time duration
adjustment.
[0021] While executing these instructions, the pressure signal
related to the output of the electrokinetic pump is provided by a
pressure sensor in direct communication with the electrokinetic
pump outlet. Alternatively, the pressure signal related to the
output of the electrokinetic pump is provided by a pressure sensor
measuring a pressure reading influenced by the operation of a check
valve. Alternatively, the pressure signal related to the output of
the electrokinetic pump is provided by a pressure sensor measuring
a pressure reading related to a component in a differential
pressure flow meter. In another aspect, instructions used for
performing the method include generating a stroke time duration
adjustment that is based upon a proportional feedback control
scheme; a proportional and integral feedback control scheme; or a
proportional, integral and derivative feedback control scheme. In
still another aspect, the instructions for the method related to
the stroke time duration adjustment are used to select a duration
from one of a plurality of pre-programmed stroke time durations
closest to the result of the comparing step.
[0022] In another alternative embodiment of an electrokinetic pump
fluid delivery system, there is a system having an electrokinetic
pump in communication with an outlet chamber, a reservoir in
communication with the outlet chamber; and a differential pressure
flow control system in communication with the outlet chamber. There
is provided in accordance with the disclosure above a control
system for the delivery system implemented using an electronic
controller. The controller is in communication with the
electrokinetic pump and the differential pressure flow control
system as suited to the specific components thereof. The
instructions in the memory of the controller may also include those
adapted and configured for communication to and from a differential
pressure control system. Such communication includes instructions
for the specific components of a differential pressure system
including power, control, instructions, data, or other signaling
turning components on or off, calibration of said components.
Examples of specific components may include those associated with a
venturi flow meter, an orifice flow meter, or a flow nozzle flow
meter.
[0023] The memory of the controller or suitable memory in
communication with or accessible to the controller contains
computer readable instructions to determine or retrieve data
relating to, for example, a pump drive signal, a constant voltage
value, a constant current value, a pump stroke time based a
correction factor. In one aspect, there is a time based correction
factor is based upon a value in a look up table programmed into or
accessible to an electronic memory of the computer controller.
Still further, a correction factor may be related to a number of
different variables or system conditions as described above. The
correction factor may be, for example, provided or determined in
relation to an input signal to the controller from the
electrokinetic pump and an input signal to the controller from the
differential pressure flow control system. As such, the electronic
memory accessible to the controller may include or be programmed to
include, for example, a time based correction factor is based upon
a feedback control scheme. Additionally or alternatively, the
electronic memory of the computer controller is programmed for or
has access separately or in any combination to: (a) a proportional
feedback control scheme; (b) a proportional and integral feedback
control scheme; and (c) a proportional, integral and derivative
feedback control scheme.
[0024] Those of ordinary skill will appreciate that the various
processing steps, comparisons, methods, techniques, signal
processing and component specific operations performed by a
controller are provided to the controller or contained within
electronic memory accessible to the controller in the form of
appropriate computer readable code. Similarly, the various
diagnostic routines, abnormal condition detectors, functional
indicators and pump control schemes and other operational
considerations described in this patent application are also stored
in an appropriate computer readable code within the memory of or
accessible to the controller. In one specific example, the computer
readable instructions in the memory of the computer controller
implement control schemes for pump cycle duration based on
computations made based at least in part on a differential pressure
flow control (instructions to adjust the pump duration based on a
calculated stroke time adjustment), including techniques described
herein for stroke duration response is calculated, as well as the
tables, files or data relating to those embodiments where the
stroke response adjustment is selected one of a set of pre-selected
stroke durations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The novel features of the invention are set forth with
particularity in the claims that follow. A better understanding of
the features and advantages of the present invention will be
obtained by reference to the following detailed description that
sets forth illustrative embodiments, in which the principles of the
invention are utilized, and the accompanying drawings of which.
[0026] In the drawings:
[0027] FIG. 1 is a schematic view of an embodiment of a
differential pressure control system at the outlet of an
electrokinetic pump having two pressure sensors and a flow
restrictor between two system check valves;
[0028] FIG. 2 is a section view of an embodiment of an
electrokinetic pump block that incorporates differential pressure
control system components described in FIG. 1;
[0029] FIG. 3A is an exemplary method of controlling an
electrokinetic pump using a pump drive signal on duration in a
differential pressure control scheme;
[0030] FIG. 3B is an exemplary method of controlling an
electrokinetic pump using voltage on duration in a differential
pressure control scheme;
[0031] FIG. 4 is an exemplary graph of sensor output in millivolts
versus time in milliseconds for the output of the pressure sensors
PS1 and PS2 (see FIGS. 1 and 2);
[0032] FIG. 5 is an exemplary correlation curve for the
differential pressure control system described in FIG. 1;
[0033] FIGS. 6A, 6B and 6C illustrate alternative differential
pressure control schemes that employ a single pressure sensor and a
single flow restrictor;
[0034] FIG. 7 is a performance graph of an electrokinetic pump
system arranged as in FIG. 6A showing average stroke volume in
microliters (.mu.l) versus differential pressure integral values
for backpressure conditions of 0, 1.7 and 2.7 psi;
[0035] FIG. 8 is a performance graph of an electrokinetic pump
system arranged as in FIG. 6A for delivery flow rate of 8 mL/hour
using a target stroke of 20 mL in a differential pressure control
method under back pressure conditions of 0 psi, about 2.3 psi, and
about 4.2 psi;
[0036] FIG. 9A is a schematic view of an electrokinetic pump using
a differential pressure control system where a system component
(i.e., a check valve) is used as the flow restrictor between the
pressure sensors PS1 and PS2; FIG. 9B is a schematic view similar
to FIG. 9B with a flow restrictor downstream of PS2;
[0037] FIG. 10 is a section view of an embodiment of an
electrokinetic pump block that incorporates differential pressure
control system components described in FIG. 9A;
[0038] FIG. 11 is a schematic view of an embodiment of a
differential pressure control system as in FIG. 1 with a
temperature sensor added to measure incoming fluid temperature for
viscosity correction;
[0039] FIGS. 12 and 13 illustrate, respectively, pump output curves
for using differential pressure controls without and with
temperature compensation for viscosity correction.
[0040] FIG. 14 is an electrokinetic pump pressure response curve
for a single pressure sensor output showing an adjustment in
voltage duration between successive pump strokes;
[0041] FIG. 15 is an electrokinetic pump pressure response curve
for a two pressure sensor output showing an adjustment in voltage
duration between successive pump strokes;
[0042] FIG. 16 is a table showing exemplary values of
electrokinetic pump correction time as related to pump stroke
time;
[0043] FIG. 17 is a table showing exemplary correction values and
corresponding correction times for one illustrative electrokinetic
pump control scheme;
[0044] FIG. 18 is an exploded view of a control module; and
[0045] FIG. 19 is a schematic diagram of the electrical connections
between components of a pump module and components of a control
module.
DETAILED DESCRIPTION
[0046] In one aspect of the present invention, differential
pressure control techniques are used to monitor and control the
output and performance of an electrokinetic pump (EK pump). In
general, readings from pressure sensors at different locations in
the pump system collect pressure information in relation to pump
stroke. This information is then used to determine flow rate.
Pressure curves may be integrated to obtain a flow volume. This
information and technique permits a determination of the amount of
delivery fluid delivered by the pump system. In one aspect of a
control system, subsequent EK pump strokes can be adjusted such as
by lengthening or shortening the pump duty cycle. In terms of an EK
pump, one can lengthen or shorten the duty time by varying the time
which voltage is applied to the pump element in order to adjust the
flow volume.
[0047] The methods and systems described herein are designed to
take advantage of the unique operating characteristics of the
electrokinetic pump. Chief among these characteristics is the
highly responsive nature of EK pumps to a drive signal. The
application of the drive signal leads nearly simultaneously to
movement of fluid from the pump and with that movement useful work
may be performed by the system. A variety of EK system
configurations and differential pressure control schemes are
described herein. Each of these systems take advantage of the
controllable nature of each EK pump stroke that permit the use of
partial strokes or strokes that are less than full pump stroke. As
a result, by using the flow control feedback of each stroke, any
variation in stroke performance may be compensated in the
subsequent stroke. Stroke by stroke error compensation as described
herein provides highly precise flow control. In some embodiments,
the correction of the pump stroke is made in the form of adjusting
the length of time the pump control signal is applied to the EK
pump. The magnitude of a correction value for pump on duration may
be determined using any of a number of techniques. One technique is
to calculate volume at the end of the stroke and then compare to a
target stroke volume. Another technique is to calculate the stroke
during delivery volume as it occurs until the target stroke
delivery volume is reached. Still another technique is to read the
parameters of the pump output (for example, back pressure) and then
estimate, calculate or look up from a table a likely pump stroke
duration to deliver a desired volume at that pump output
condition.
[0048] A reciprocating pumping system driven by electrokinetic
engine (EK engine or EK pump) uses a pressure sensor feedback
scheme to control the amount of fluid delivered. An EK engine
includes a silica porous membrane, two porous electrodes, a
housing, a rear diaphragm, and a front diaphragm. The EK pump is
used to drive a reciprocating pump. A number of alternative
reciprocating pump configurations are described below. Typically
the reciprocating pump includes a reservoir, check valves, pressure
sensors, and some type of a flow restrictor. As will be described
in greater detail below, the working fluid, buffer, and the
delivery fluid (i.e., a pharmacologically active material or drug)
is separated by the front diaphragm. In a different arrangement, a
gel coupling is used in place of the front diaphragm. The gel
coupling is further described in co-pending and commonly owned U.S.
Provisional Patent Application No. 61/482,889, entitled "GEL
COUPLING FOR ELECTROKINETIC DELIVERY SYSTEMS" filed May 5, 2011 and
its corresponding U.S. Non-provisional patent application Ser. No.
______, entitled "GEL COUPLING FOR ELECTROKINETIC DELIVERY
SYSTEMS," filed herewith, each of which are incorporated herein by
reference in its entirety.
[0049] An electronic controller, along with supporting electronic
elements, controls the pump drive signal supplied to the EK engine,
the direction of the current through the EK engine, as well as
receiving and measuring the pressure signals generate by the
pressure sensors. In one aspect, the pump drive signal is a
voltage. The electronic controller may be a microcontroller,
microprocessor or other suitable pump controller. In another
aspect, the pump drive signal is a current. In one aspect, the pump
drive signal maintains a constant amplitude during a pump stroke.
In another aspect, the pump drive signal has one constant amplitude
during one stroke and then a different pump drive signal amplitude
in a subsequent stroke. One example of different pump signal
amplitudes may be appreciated with reference to a voltage drive
signal. In one stroke a 3 v signal may be used. In a subsequent
stroke as a result of an indication of back pressure for example, a
voltage of 6 volts may be used. Thereafter, when the back pressure
condition has cleared the system may return to the 3 v drive
signal. As such, in one aspect of the control system, amplitude of
a pump drive signal may be selected and then the duration of the
application of that pump drive signal controlled and compensated
using the differential pressure techniques described herein.
[0050] The EK engine generates hydrostatic pressure by expanding or
contracting the front diaphragm. Front diaphragm expansion is
achieved by applying a constant forward voltage from rear electrode
to front electrode. Current thus flows through the silica and
generates buffer fluid movement from the rear diaphragm to the
front diaphragm. The front diaphragm collapses by applying a
reverse voltage, from front electrode to the rear electrode.
Current thus flows through the silica and generates buffer fluid
movement from the front to the rear.
[0051] Movement of the delivery fluid is generated by the movement
of the front diaphragm. A negative hydro static pressure is
generated when the front diaphragm is moved (collapsed) toward the
EK element and expands the volume in the chamber. This negative
pressure (pressure below atmospheric) withdraws fluid from the
reservoir, through the inlet check valve, and into the chamber. The
outlet check valve prevents the fluid on the outlet side from
coming back into the chamber. A positive hydro static pressure is
generated as the front diaphragm is moved (expands) away from the
EK element and collapses the volume in the chamber. This positive
pressure (pressure above atmospheric) pushes fluid from the
chamber, through the outlet check valve, and into the delivery
point. The inlet check valve prevents the fluid in the chamber from
going back into the reservoir.
[0052] The amount of delivery fluid being delivered is directly
proportional to the amount of EK buffer being moved. In turn, the
EK buffer moved is directly proportional to the current used. The
delivery fluid can be controlled very precisely using the pressure
sensors as a feedback control. In the different arrangements set
forth below, the pressure sensor or sensors are used to calculate
the delivered volume. Once the delivered volume is determined, the
duration of the time period which the constant forward voltage is
supplied, thus the forward current, is lengthened or shortened as
needed. If the calculated volume is high, the next delivery's
period is shortened. Likewise, if the calculated volume is too low,
the delivery period is lengthened. These adjustments are made until
the desired volume is delivered within prescribed tolerances. The
variations in stroke duration provide a broad range of partial
stroke delivery schemes. In the context of these various
embodiments, a partial stroke is a stroke of a duration that leads
to deflection of the front diaphragm into the delivery chamber that
does not completely empty the delivery fluid in the delivery
chamber. In contrast, a full stroke would be a pump stroke duration
that would deflect the front diaphragm sufficiently into the
delivery chamber such that all or substantially all of the delivery
fluid in the delivery chamber is pumped out. The ability of the
system configurations and methods described herein to provide
partial strokes leads to greater flexibility in both delivery as
well as error correction.
[0053] To prevent hydrolysis of the pump working fluid, the EK pump
is operated with a drive voltage that provides controllable flow
without hydrolysis and resultant gas generation. The charge balance
on the electrodes is maintained such that the exact amount of
charge (current) is charged and then discharged during each EK pump
cycle. The most common technique for this balance is to select
drive currents below the hydrolysis limit and then employ equal
duration reverse and forward drive currents. These and other
details of electrokinetic pump design and operation are described
in commonly owned U.S. Pat. No. 7,235,164, incorporated herein by
reference in its entirety.
[0054] The reciprocating pump by nature is not a continuous pump.
Each pump cycle has a intake stroke and a delivery stroke. There
are inactive periods between each successive stroke. We define the
dwell period as the time between the intake and the delivery
stroke, and the wait period as the time between the delivery stroke
and the intake stroke. The pump operates as wait time, intake
stroke, dwell time, and delivery stroke. To adjust flow rate, we
fix the stroke volume and adjust the wait time: for faster flow
rates the wait time is short; and slower flow rates, the wait time
is long. In one alternative embodiment, an additional wait time or
delay may be used to permit synchronization with one of more EK
pumps when multiple pumps are employed. The control techniques
described herein may be used to control each pump in a multiple
pump configuration as described, for example, in co-pending and
commonly assigned U.S. Provisional Patent Application No.
61/482,949, entitled "GANGING ELECTROKINETIC PUMPS," filed May 5,
2011 and its corresponding U.S. Non-provisional patent application
Ser. No. ______, entitled "GANGING ELECTROKINETIC PUMPS," filed
herewith, each of which are incorporated herein by reference in its
entirety.
[0055] The incorporation of differential pressure control
techniques and information and appropriate correlation curves
provides greater control the amount of fluid being delivered by the
EK pump. There are several alternative methods of using this
information for pump control. Feedback control may include one or
more of: (a) proportional feedback control; (b) proportional and
integral feedback control; or (c) proportional, integral and
derivative feedback control separately or in any combination.
[0056] One method used is the direct control of the EK pump. Using
this method, the drive current or voltage is applied until the
target volume is delivered. The system pressure sensors are sampled
during the application of the drive voltage, integrated and used to
determine volume delivered. Once the targeted delivery volume is
reached, the drive voltage is shut off and the EK pump flow stops.
Put simply, a drive current or voltage is applied to the EK pump
until the integral value reaches the desired or targeted value.
[0057] Alternatively, the EK pump delivery operation could be
operated for an approximated time selected to deliver a targeted
stroke volume. During each EK pump cycle, the pressure sensors are
sampled and used to generate a pressure curve. The pressure curve
integration yields the actual fluid delivered during the stroke.
Comparison of the estimated and actual stroke volumes may then be
used to find the appropriate response to adjust the EK pump
delivery operation. Control responses for the EK pump include one
or more of adjusting drive current, drive voltage or time of drive
stroke, and combinations thereof.
[0058] In a system utilizing a constant drive current or voltage,
the control response may include adjusting the time duration of
each pump stroke. This control response may be accomplished in a
number of ways. One way is to use a look up table. Under this
control scheme, a look up table of pre-generated pump stroke
volumes is used for comparison to the measured stroke volume. Based
on the result of that comparison, the time duration of the next
stroke is adjusted longer or shorter based on the result. If actual
stroke delivery was lower than predicted, the pump time is
increased. If actual stroke delivery was higher than predicted, the
pump on time is decreased. In this method, first estimate a time to
power the EK pump for a targeted stroke delivery target and then
run the EK pump for this estimated time. Sample the pressure
sensors during this time and calculate an integral value for actual
volume delivered. Thereafter, compare the actual and estimate
volumes and adjust the next stroke time as needed.
[0059] In another control method, a function is used to determine
the appropriate response. The function may be a first or higher
order equation used to determine how and to what degree subsequent
pump strokes are adjusted.
[0060] Using information about comparison between
projected/estimated and actual pump delivery, the system may
estimate the time duration for the next pulse sent to the pump.
FIG. 12 illustrates the accuracy of the pump using this control
scheme. The pump is pumping 20 .mu.l per stroke within +/-5% over a
24 hour period. This degree of stability has been demonstrated for
stroke volumes as small at 0.5 .mu.l. The high degree of control is
also illustrated by the fine level of per stroke correction. FIG.
16 relates the per stroke correction amounts to some exemplary flow
rates.
[0061] FIG. 1 is a schematic view of an embodiment of an EK pump
used to deliver fluid using an exemplary differential pressure
control system. The outlet of the EK pump is provided to a pump
chamber between two system check valves. There are two pressure
sensors and a flow restrictor between the two system check valves.
The pressure sensors and the flow restrictor are arranged to
provide a differential pressure flow meter. The system also
includes a reservoir containing a fluid to be delivered by action
of the electrokinetic pump. The electrokinetic pump is connected to
an outlet chamber. An inlet check valve separates the outlet
chamber from the reservoir and the outlet check valve separates the
pump components from the delivery site or outlet.
[0062] FIG. 1 also illustrates a power source 180 and a controller
175 used to operate the EK pump. The controller 175 functions based
on the pump control scheme selected, inputs from the pressure
sensors 152, 154 and desired pump stroke volume or target volume.
The controller 175 includes memory with computer readable
instructions to implement the pump control scheme including for
example receiving and interpreting signals from system components
such as the pressure sensors, perform calculations according to the
control scheme and providing control signals to the EK pump. The
controller can be a microcontroller with sufficient inputs and
outputs depending upon the number of systems components used in a
particular configuration (number of pressure sensors, elements of a
differential pressure system, for example). One commercially
available microcontroller suited to the configurations described
herein is the C8501F310, available from Silicon Laboratories Inc.,
Austin, Tex. In another alternative, the microprocessor or the
computer used as a controller includes a minimum of 4 A-D
converters and 16 digital IOs. Additional details of other suitable
controller types are described below with regard to FIGS. 18 and
19.
[0063] FIG. 1 illustrates a typical differential pressure flow
control arrangement with a pair of pressure sensors 152, 154 on
either side of a flow restrictor 160. In the illustrated schematic,
the pair of pressure sensors PS1 (152) and PS2 (154) are placed on
either side of a flow restrictor 160. The pressure sensors may be
any suitable pressure sensor suited to the range of pressures and
flows used in the system. The system illustrated in FIG. 1 is
typically used for flow applications in the range of 0.01 ml/hr to
50.0 ml/hr at pressures ranging from 0 to 6 psi. In one specific
embodiment, the pressure sensors are commercially available from
Measurement Specialties of Fremont, Calif.
[0064] The flow restrictor 160 may be any suitable flow restrictor
according to the type of measurement scheme being used. For
example, the flow restrictor may be configured as a venturi, an
orifice, a flow nozzle or any other suitable configuration. The
flow restrictor along with one or more pressure sensors may be
arranged for operation as a differential pressure flow meter.
Exemplary differential flow meter configurations include: a Venturi
flow meter, an orifice flow meter or a flow nozzle flow meter.
[0065] The advantage is that most external noise (i.e., outside of
the pump system) is isolated by the outlet check valve 144. In this
configuration, the calculations used to determine pump rate are
simpler because the pressure curve from each pressure sensor is
subjected to any variations caused by the outlet check valve 144.
Since this variable is included in both pressure sensor readings,
the control value of interested is obtained using the difference
between the two pressure curves shown below in FIG. 4 and expressed
as:
.intg.((PS2(t)-PS1(t)))dt*Constant (so called difference area under
the curve or the difference integral)
[0066] Using this scheme produces a good correlation between flow
volume and the difference integral value.
[0067] FIG. 2 is a section view of an embodiment of an
electrokinetic pump block that incorporates differential pressure
control system components described in FIG. 1. The internal
components and arrangement of the EK pump are visible in this view.
In this configuration, the EK engine 103 operates to move front and
rear EK diaphragms placed on either side of the EK engine. The EK
pump diaphragms deflect in response to the movement of the working
or pump fluid as drive current is applied to the EK pump.
Additional details of the operation of EK pumps, diaphragms and
pump system configurations are available in commonly owned,
co-pending U.S. patent application Ser. No. 12/327,568 published as
U.S. Patent Application Publication US 2009/0148308 entitled
"Electrokinetic Pump With Fixed Stroke Volume," the entirety of
which is incorporated herein by reference.
[0068] Referring to FIG. 2, an electrokinetic ("EK") pump assembly
100 includes an EK pump 101 connected to an EK engine 103. The EK
engine 103 includes a first chamber 102 and a second chamber 104
separated by a porous dielectric material 106, which provides a
fluidic path between the first chamber 102 and the second chamber
104. Capacitive electrodes 108a and 108b are disposed within the
first and second chambers 102, 104, respectively, and are situated
adjacent to or near each side of the porous dielectric material
106. The EK engine 103 includes a movable member 110 in the first
chamber 102, opposite the electrode 108a. The moveable member 110
can be, for example, a flexible impermeable diaphragm. A pump fluid
(or "engine fluid"), such as an electrolyte, can fill the EK
engine, such as be present in the first and/or second chambers 102
and 104, including the space between the porous dielectric material
106 and the capacitive electrodes 108a and 108b. The capacitive
electrodes 108a and 108b are in communication with an external
voltage source, such as through lead wires or other conductive
media.
[0069] The EK pump 101 includes a delivery chamber 122 and a
movable member 113 having a first edge 112 contacting the delivery
chamber 122 and a second edge 111 contacting the second chamber
104. In some embodiments, the first and second edges 112, 111 are
flexible diaphragms having a mechanical piston therebetween. In
other embodiments, the first and second edges 112, 111 are flexible
diaphragms having a gel material therebetween. Gel couplings are
described further in U.S. Provisional Patent Application No.
61/482,889, filed May 5, 2011, and entitled "GEL COUPLING FOR
ELECTROKINETIC DELIVERY SYSTEMS," and U.S. patent application Ser.
No. ______, filed herewith, and entitled "GEL COUPLING FOR
ELECTROKINETIC DELIVERY SYSTEMS," the contents of both of which are
incorporated herein by reference. In other embodiments, the first
and second edges 112, 111 are edges of a single flexible member or
diaphragm.
[0070] The delivery chamber 122 can include a delivery fluid, such
as a drug or medication, e.g., insulin or pain management
medications, or a cleansing fluid, such as a wound cleansing fluid,
supplied to the delivery chamber 122 from a fluid reservoir 141. An
inlet check valve 142 between the fluid reservoir 142 and delivery
chamber 122 can control the supply of delivery fluid to the
delivery chamber 122, while an outlet check valve 144 can control
the delivery of delivery fluid from the delivery chamber 122, such
as to a patient. A first pressure sensor 152 and a second pressure
sensor 154 can monitor the flow of fluid from the system. Further,
a flow restrictor 160 can be present in the pump 101 to produce a
pressure differential between sensors 152, 154 so as to provide a
mechanism for measuring the flow of the fluid.
[0071] In use, the electrokinetic assembly 100 works by producing
electrokinetic or electroostmostic flow. A voltage, such as a
positive voltage, is applied to the electrodes 108a, 108b, which
causes the engine fluid to move from the second chamber 104 to the
first chamber 102. The engine fluid may flow through or around the
electrodes 108a and 108b when moving between the chambers 104, 102.
The flow of fluid causes the movable member 110 to be pushed out of
the chamber 102 and the movable member 113 to be pulled into
chamber 104. As a result of the movement of the movable member 113,
delivery fluid is pulled from the reservoir 141 into the delivery
chamber 122. The movement of delivery fluid from the reservoir into
the delivery chamber 122 is called the "intake stroke" of the pump
cycle. When the opposite voltage is applied, such as a negative
voltage, fluid moves from the first chamber 102 to the second
chamber 104. The movement of engine fluid between chambers causes
the movable member 110 to be pulled into the first chamber 102 and
the movable member 113 to expand to compensate for the additional
volume of engine fluid in the second chamber 104. As a result,
delivery fluid in the chamber 122 is pushed out of the chamber 122
and delivered, such as to a patient, through the outlet check valve
144. The delivery of fluid is called the "outtake stroke" of the
pump cycle. Although the exemplary assemblies and systems described
below are configured such that a positive voltage corresponds to
the intake stroke and a negative voltage corresponds to an outtake
stroke, it is to be understood that the opposite configuration is
also possible--i.e., that a negative voltage corresponds to an
intake stroke and a positive voltage corresponds to an outtake
stroke.
[0072] FIGS. 3A and 3B describe exemplary methods of controlling
the operation of an electrokinetic pump system using a differential
pressure flow measurement technique.
[0073] FIG. 3A is an exemplary method 200 of controlling an
electrokinetic pump using pump drive signal on duration in a
differential pressure control scheme. This method determines a pump
drive signal on duration when the pump drive signal amplitude is
maintained constant. A variety of pump drive signals may be used
such as voltage, current or electrode charge, for example.
[0074] First at step 205, the pump drive signal is applied to an
electrokinetic pump for a time duration. The time duration used is
based on a number of factors such as prior pump performance,
calibration curves or experimental information. The time duration
is selected to produce or deliver a target stroke volume which is a
partial stroke of a full stroke.
[0075] Next, at step 210, a differential pressure technique is used
to determine the stroke volume during the time duration selected in
step 205. The result of this process is the determined stroke
volume.
[0076] Next at step 215 the determined stroke volume is compared to
the target stroke volume. Next, at step 222, evaluate whether or
not the total volume has been delivered. This step looks to the
determination of whether the volume calculated in step 210 actually
completed delivery of a total volume. The total volume delivery
could be maintained by any number of techniques. In one aspect, the
total volume delivery is a counter that decrements from a total
volume amount. In another aspect, the total volume delivery is a
counter that increments from zero to the desired total volume
amount. As a result, the step of incrementing or decrementing the
total volume may be performed once the volume of that last stroke
is determined. Thereafter, the decision proceeds based on whether
the total volume was delivered. If YES, then the controller
generates a stop pump command (step 224). In addition, the system
may generate an output or indication that the total volume is
delivered. If the answer in step 222 is NO, the after the counter
is indexed, the method then proceeds.
[0077] Next, evaluate whether or not the target stroke volume has
been delivered (step 220). If the target stroke volume has been
delivered and the answer is YES then no correction is needed (step
225) and the next pump stroke will apply the drive voltage for the
same duration (i.e., returning to step 205 until the total volume
is delivered).
[0078] If however the target stroke volume was not delivered
(answer at block 220 is "no"), then proceed to step 230. In this
step a pump on duration is generated based on the comparison of
determined stroke volume and target stroke volume. The pump
duration adjustment can be positive i.e., an increased duration if
the determined stroke volume is smaller than the target stroke
volume. Conversely, the pump duration adjustment can be negative
i.e., a decreased duration if the determined stroke volume is
greater than the target stroke volume.
[0079] Depending on the result of step 230, the pump drive signal
on duration is then applied to the EK pump on the next pump stroke
(step 235). Thereafter, the process repeats at the determining step
210 to determine the volume of delivery fluid delivered during step
235.
[0080] FIG. 3B is an exemplary method 300 of controlling an
electrokinetic pump using voltage on duration in a differential
pressure control scheme. This method determines the voltage on
duration when drive voltage is maintained constant.
[0081] First at step 305, the drive voltage is applied to an
electrokinetic pump for a time duration. The time duration used is
based on a number of factors such as prior pump performance,
calibration curves or experimental information. The time duration
is selected to produce a deliver a target stroke volume which is a
partial volume of a full stroke volume
[0082] Next, at step 310, a differential pressure technique is used
to determine the stroke volume during the time duration selected in
step 305. The result of this process is the determined stroke
volume.
[0083] Next at step 315 the determined stroke volume is compared to
the target stroke volume. Next, at step 322, evaluate whether or
not the total volume has been delivered. This step looks to the
determination of whether the volume calculated in step 310 actually
completed delivery of a total volume. The total volume delivery
could be maintained by any number of techniques. In one aspect, the
total volume delivery is a counter that decrements from a total
volume amount. In another aspect, the total volume delivery is a
counter that increments from zero to the desired total volume
amount. As a result, the step of incrementing or decrementing the
total volume may be performed once the volume of that last stroke
is determined. Thereafter, the decision proceeds based on whether
the total volume was delivered. If YES, then the controller
generates a stop pump command (step 324). In addition, the system
may generate an output or indication that the total volume is
delivered. If the answer in step 322 is NO, the after the counter
is indexed, the method then proceeds.
[0084] Next, evaluate whether or not the target stroke volume has
been delivered (step 320). If the target stroke volume has been
delivered and the answer is YES then no correction is needed (step
325) and the next pump stroke will apply the drive voltage for the
same duration (i.e., returning to step 305).
[0085] If however the target stroke volume was not delivered
(answer at block 320 is "no"), then proceed to step 330. In this
step an additional pump on duration is generated based on the
comparison of determined stroke volume and target stroke volume.
The pump duration adjustment can be positive i.e., an increased
duration if the determined stroke volume is smaller than the target
stroke volume. Conversely, the pump duration adjustment can be
negative i.e., a decreased duration if the determined stroke volume
is greater than the target stroke volume.
[0086] Depending on the result of step 330, the pump drive signal
on duration is then applied to the EK pump on the next pump stroke
(step 335). Thereafter, the process repeats at the determining step
310 to determine the volume of delivery fluid delivered during step
335.
[0087] As a result of the use of the total volume counter, the EK
pumping system may be used to determine an estimated number of
strokes to deliver a remaining total volume. Consider for example a
pump operations scenario where the operating conditions have
resulted in a lower than expected delivery fluid pumped by the
system. In this instance, the total volume counter will have some
amount of undelivered total volume. The system controller may also
include computer readable instructions to calculate an estimated
number of additional delivery strokes needed to pump the balance of
the total delivery volume. Thereafter, the controller would
continue to operate the cycle pump strokes until the total volume
is delivered.
[0088] FIG. 4 is an exemplary graph of sensor output in millivolts
(mV) versus time in milliseconds for the output of the pressure
sensors PS1 and PS2 (see FIGS. 1 and 2) during a pump stroke. In
this configuration 500 mV equates to a 0 psi reading. Voltage is
applied to the pump at about 8000 ms as the trace crosses the 500
mV line. Next at about 9700 ms and 800 mV, the outlet check valve
cracks and flow begins. After this point, the readings from PS1 and
PS2 separate. The upper solid line comes from PS1 and the lower
dashed line comes from PS2. The drive voltage is turned off at time
10,000 ms where PS1 reads about 890 mV. Shortly thereafter at
approximately 10,500 ms at about 840 mV the curves for PS1 and PS2
converge back into a single trace. The controller evaluates the
readings from PS1 and PS2 to obtain the area between the PS1 and
PS2 curves while they are separated. The area between these curves
then used to control subsequent pump strokes using one or more of
the control schemes described herein. The gradual decrease in the
PS1/PS2 curve is related to the gradual system pressure decrease
between pump strokes.
[0089] FIG. 5 is an exemplary correlation curve generated and used
for a differential pressure control system described in FIGS. 1 and
2. The x axis is the DPI (differential pressure integral) value and
the Y axis is the measure mass delivered during the flow that
generated the DPI. The curve shown has a good linear fit as
illustrated by the solid series 1 fit line. From such a correlation
curve, a delivered mass or volume can be calculated from the DPI
values observed during pumping system operation.
[0090] FIG. 6A illustrates an alternative differential pressure
control scheme. FIG. 6A is similar to FIGS. 1 and 2 in many
respects. The main difference between the system on FIG. 6A and the
earlier described systems is that this system relies on a single
pressure sensor (PS2). There is also a flow restrictor 160 between
the outlet chamber 122 and the pressure sensor 154 (PS2). In
another optional configuration, a single flow restrictor 160 is
positioned between PS2 and the outlet check valve 144 (see FIG.
6B). In this configuration, there is an assumed constant back
pressure on the flow restrictor. The controller scheme used in this
type of system is different since it relies on an assumed constant
back pressure to eliminate the need of a second pressure sensor.
Control of an EK pump in this configuration is simplified as a
result. In still another optional configuration, the flow
restrictor 160 is positioned after the outlet check valve 144 (see
FIG. 6C). Moreover, the electronic memory, routines and computer
readable instructions performed by the controller 175 will be
different and based on performance parameters and curves from a
single pressure reading configuration as well as the specific
component configuration selected (e.g., FIG. 6A, 6B or 6C).
[0091] This so called single pressure sensor method uses a single
pressure sensor to determine pump flow. Assuming that during "off
pump" periods the pump is not delivering any fluid, then during
this time, PS2 is measuring the back pressure applied to the
system. This control scheme assumes as well that the back pressure
does not change during delivery time. For example, for a pump
designed to deliver 0.5 .mu.l to 3 .mu.l per stroke, typically less
than one and half second, for 0.5 .mu.l partial stroke with a 5 psi
back pressure it is in the range from about 0.65 to 1.5 sec., or
for 0.5 .mu.l partial stroke with no back pressure it is 0.30 to
1.5 sec. or in any of the ranges of FIG. 16. As such, when the pump
is powered on, the pump stroke flow rate is equal to the difference
the increase in pressure and the initial pressure. This operation
can be expressed as:
.intg.(PS2(t)-PS2(t0))dt*Constant (so called area under the curve
or the integral)
Whereas the constant is associated with one or more of the
properties of the fluid such as viscosity, density, and/or
friction. One or more of these properties may change depending upon
variations in, for example, the operating temperature of the pump,
temperature of the delivery fluid, or environmental conditions such
as temperature surrounding the reservoir or delivery site.
[0092] To use this scheme, first generate a correlation curve for
each particular system and anticipated stroke length. Here stroke
length refers the length of time that a specific drive signal is
applied to an EK pump. This graph is used to produce the
correlation between the "integral" values and the actual amount for
fluid delivered. The correlation values are generated by operating
the EK pump within the expected performance area during a present
cycle time. The EK pump will be run for a preset number of cycles
with a preset stroke length. The stroke duration (i.e., pump on
signal time or duration of pump drive signal) will be kept constant
for all strokes. The EK pump outlet is configured for delivery to a
scale thereby permitting the mass of fluid delivered to be
measured. Using the appropriate density value for the delivery
fluid, the delivery volume is calculated and then divided into the
number of strokes to yield the per stroke volume for that pump
stroke. The procedure is repeated for two, three, four or more
different pump stroke lengths or pump on or pump drive signal
durations. The correlation curve for that pump is produced by
plotting the results of these various stroke length tests and
applying a suitable curve fit technique. The appropriate
correlation curve is loaded into the controller to control stroke
volume during pump operations. After obtaining the various
correlation values, we then measure this measured pump performance
against a number of exemplary back pressure values to ensure the
accuracy of the correlation curve. A typical graph of one such test
is shown below in FIG. 7. Note that the pump performance against a
variety of back pressures is very linear.
[0093] FIG. 7 is a performance graph of an electrokinetic pump
system arranged as in FIG. 6A showing average stroke volume in
microliters versus differential pressure integral values for
backpressure conditions of 0, 1.7 and 2.7 psi. The correlation
values in this graph would be used to adjust pump performance as
delivery circumstances change.
[0094] Additional experiments reveal that the pressure differential
control schemes described herein produce integral values that are
back pressure independent up to back pressures as high as 6 psi.
The pumping systems and control schemes described herein are
capable of fully compensating for the likely range of back
pressures encountered during delivery to mammals.
[0095] FIG. 8 is a performance graph of an electrokinetic pump
system arranged as in FIG. 6A for delivery flow rate of 8 mL/hour
using a target stroke of 20 .mu.l in a differential pressure
control method as described herein. The typical duty cycle
parameters are 3 volts for 600 ms. The duty cycle may range from
500 ms to about 1 sec. In the example control response illustrated
in FIG. 8 the pump duty cycle was changed using fixed time
intervals of 5 ms, 10 ms, 25 ms and 50 ms according to required
pump response. These additional pump on durations are added or
subtracted from the basic pump duty cycle (see FIG. 3A steps 230,
235 and FIG. 3B steps 330 and 335). In this particular example, the
control system is responding to three back pressure conditions: no
back pressure or 0 psi, a back pressure of about 2.3 psi, and a
back pressure of about 4.2 psi.
[0096] As can be seen from the graph during the 0 psi or no back
pressure scenario from 0-600 seconds, the pump is consistently
delivering the target stroke volume of 20 .mu.l per stroke. At time
600 seconds, a back pressure of about 2 PSI is applied. Note that
the next measured stroke volume immediately drops to about 17
.mu.l. As the control algorithm takes over and pump stroke duration
is adjusted as in FIGS. 3A and 3B, the stroke volume increases over
a few cycles until the stroke target volume of 20 .mu.l is reached.
The pump on time is increased here to provide the added volume to
overcome the impact of the back pressure.
[0097] At time 1000 seconds, the back pressure returns to zero.
With the back pressure removed the stroke volume over delivers as
shown with the spike to about 22 .mu.l at time 1020 seconds.
Thereafter, the controller shortens the pump on time in the
successive strokes. By about time 1100 seconds, the controller has
returned the stoke volume back down to the target stroke volume of
20 .mu.l.
[0098] At time 1300 seconds, a back pressure of about 4 psi is
applied to the system. Note the immediate drop in actual stroke
volume to about 13 .mu.l. The control algorithm then begins
adjusting each subsequent stroke by increasing pump on duration
until by about time 1500 seconds the actual stroke volume is back
on target at 20 .mu.l. At time 1700 seconds another excursion in
pump stroke volume is observed as the 4 psi back pressure is
removed. As before with the 2 psi back pressure, the control system
adjusts (i.e., decreases) the duration of the voltage on during the
pump stroke. As before, the control system quickly returns the
actual pump stroke volume to the target pump stroke volume of 20
.mu.l by about time 1800 seconds.
[0099] In FIG. 8 each point on the graph is a stroke volume
reading. As described above, once a back pressure is applied to the
system, the stroke volume drops. In this exemplary configuration,
the control system feedback will adjust the stroke volume to the
set level after a back pressure is applied or removed without about
7 pump strokes.
[0100] FIG. 9A is a schematic view of another alternative
electrokinetic pump system configured for use with a differential
pressure control scheme. In this configuration, the pump and
components are similar to those previously described. In the
embodiment of FIG. 9, a system component (i.e., a check valve 144)
is used as the flow restrictor between the pressure sensors PS1 and
PS2 (152, 154). Additionally or alternatively, a flow restrictor
may also be placed between the outlet check valve and PS2 or beyond
PS2 (see FIG. 9B).
[0101] FIG. 9A illustrates a pressure sensor (152/PS1) is located
on the pumping chamber 122, and the second pressure sensor
(154/PS2) is located after the outlet check valve 144. A flow
restrictor 160, such as a 26 gage needle (for example), may be
located in front of the pressure sensor (154/PS2) between PS2 and
the outlet check valve 144 or downstream of the pressure sensor
(see FIG. 9B). In this configuration a pressure difference method
may be used to determine the volume produced during a pump stroke.
This control scheme utilizes the difference between the pressure
read at PS1 and PS2. In addition, this control scheme takes into
account the check valve cracking pressure according to:
.intg.(PS1-Check valve cracking pressure-PS2)dt*Constant.
While described in this embodiment, check valve cracking pressure
compensation may be applied to other control schemes described
herein.
[0102] FIG. 10 is a section view of an embodiment of an
electrokinetic pump block that incorporates differential pressure
control system components as described in FIG. 9A.
[0103] FIG. 11 is a schematic view of an embodiment of a
differential pressure control system as in FIG. 1 with a
temperature sensor 185 added to measure incoming fluid temperature
for viscosity correction.
Temperature Compensation for EK Pump Operation
[0104] Adding a temperature sensor to measure the surround
temperature or the fluid temperature, we can compensate for more
effects. Viscosity and density of a fluid changes with temperature.
Also, there are some temperature affects on most pressure sensors.
Thus adding a temperature sensor 185, as shown in FIG. 11, permits
temperature measurements and compensation schemes based on
temperature induced variations to the delivery fluid. The
temperature sensor 185 is shown between the inlet check valve 142
and the pump chamber 122/PS1 152 location. The temperature sensor
185 could be located in any of a number of different locations
along the fluid path shown in FIG. 11.
[0105] It is believed that the use of a temperature sensor permits
pump stroke volume to be adjusted in order to compensate for
delivery liquid viscosity. The result of compensation may well be
within +/-2% as shown in the following figures.
[0106] FIGS. 12 and 13 illustrate, respectively, pump output curves
for using differential pressure controls without and with
temperature compensation for viscosity correction. Without
temperature compensation as shown in FIG. 12, as ambient
temperature decreased overnight (after 5 pm and remaining so after
5 am) the actual pump stroke volume decreased. In contrast, in a
temperature compensated system the stroke volume remains nearly
constant despite the same overnight temperature decreases. This
comparison illustrates how an EK pump with differential pressure
control and temperature compensation may be used to delivery nearly
constant pump stroke volumes even as the temperature of the
delivery fluid changes.
[0107] In one embodiment, temperature compensation is accomplished
according to a method similar to that of FIG. 3 and method 300. If
the temperature reading remains within a selected range then no
compensation is provided. If temperature varies from the
predetermined temperature then the controller will adjust the pump
on duration to compensate as appropriate.
[0108] The information provided by the differential pressure
control system may be used to provide other functions to enhance
the performance of the EK pump. Examples of other functions include
diagnostic analysis of one or more components in the system or
error detection in system operation. This performance information
may be provided from any of a number of sources internal and
external to the pump system. In one specific example, diagnostic
and or error detection information and remedial actions are
obtained from the analysis, comparison or processing of pressure
sensor data (i.e., see FIG. 4). The pressure sensor data may be
analyzed on a per stroke basis, using pump stroke averages, using
intermittent stroke data (i.e., stroke data taken on some time
interval or stroke number interval) or on other circumstances
suited to the diagnostic or error detection sought.
[0109] In terms of a specific example of system component failure,
consider the inlet and outlet check valves. Possible failure modes
for a valve are stuck open or stuck closed. In the case of stuck
open, the peak pressure in the chamber will be less than average.
In this case, the memory of the controller may contain computer
readable instructions for recording and comparing peak chamber
pressure from stroke to stroke, every other stroke or some other
interval or intermediate monitoring rate. If the comparison of peak
pressure indicates repeated lowered peak readings then the
controller may take action to notify a user of the likely
malfunction. Actions the controller make range from alarm
indications with lights, sounds or electronic notifications to
stopping pump operations or inhibiting pump operations until the
condition is cleared. The system may respond in a similar way to
the case of a check valve being stuck closed. In this case, the
system will read chamber peak pressure as higher than normal or
higher than the average peak pressure. In much the same way, the
controller may contain additional instructions in memory for
notifying the user or altering system performance in light of the
component failure.
[0110] In still another embodiment, the pressure sensor data may be
used to detect an occlusion. In this instance, the controller
memory may include instructions in computer readable code for
adjusting pump operations to accommodate or compensate for the
occlusion, adjust pump operations to attempt to clear the
occlusion, notify the user of the possible occlusion, cease pump
operations or combinations of any of the above.
[0111] In one specific example, the output of PS2 (154) in FIG. 9
provides an indication of back pressure acting on the system. The
controller may contain computer readable instructions to add stroke
time in anticipation of pumping against a certain back pressure.
Alternatively, the controller may signal an alarm or cease pump
operations if a back pressure above a threshold value is detected.
A two pressure sensor configuration such as in FIG. 1 may also be
used to detect component failure. If the pump drive signal is on
and there is no difference in the signals from PS1/PS2 then the
controller may contain instructions to indicate this abnormal
condition. The lack of a pressure difference may indicate.
[0112] In another specific example, during application of a reverse
drive voltage to run the pump for charge balance a pressure
sensor(s) on the chamber and/or reading within the system check
valves decreases or becomes negative. Pressure sensor readings such
as these are a likely indication that one or both check valves may
have failed. The controller may contain computer readable
instructions to cease operations or sound an alarm or indication if
this abnormal condition is detected. Back pressure compensation may
be handled as discussed above and most directly by placing one
pressure sensor beyond the outlet check valve (i.e., see the
configuration in FIG. 9) and reading PS2 pressure during the pump
cycle when the outlet check valve 144 is closed. Occlusion
detection may be provided by one or more indications of pump flow
or pump operation with an accompanying increase in chamber pressure
without a corresponding indication of delivery fluid flow.
[0113] In still other alternative embodiments, the result or
outcome of one or more error or diagnostic routines may be used to
adjust the voltage applied to the pump, the time on duration of the
voltage or other suitable operational parameters using methods
similar to those described above and with regard to FIGS. 3A and
3B. In this respect, adjusting the voltage applied to the pump
would occur before or after stroke delivery. This type of adjusting
refers to the use of 4 volts in one stroke and then when
circumstances in the pumping system change a different value other
than 4 volts may be used. For example, one pump delivery profile
may have a number of strokes delivered at 3 volts. Thereafter,
based on a change in system parameters or pump stroke voltage may
be increased to 5 v on a subsequent stroke.
EXAMPLES
[0114] FIG. 14 illustrates a graph of two square wave pump control
signals and a corresponding pressure sensor trace from a single
pressure sensor differential pressure control system. In this
illustrative example, the differential pressure control system
would utilize data from the single pressure sensor output (i.e.,
the integral of the trace curve for a given pump drive signal) to
determine stroke volume. A single pressure sensor system
configuration is illustrated above in FIG. 6. In this example, the
pump drive signal is a constant voltage of about 2.7 volts. The
base line pressure sensor output signal is about 75 mv. The
duration of the first pulse (t1) is 860 ms. In this example, the
pressure sensor output is read every 4 ms. The system controller
includes computer readable instructions to begin integrating the
pressure sensor readings when the pump drive signal is applied and
to continue to integrate until the pressure sensor output voltage
decreases below a determined value. Typically, the value would be
once the output signal indicates that the system has returned to
base pressure (here at a sensor voltage of 75 mv). Thereafter, the
obtained integral values are converted to volume and then compared
to the target flow. It is to be appreciated that the integral
values may be calculated in real-time as the stroke progresses.
This real-time stroke volume calculation may be used as a pump off
trigger signal back to the controller to stop the flow of power to
the EK engine. In this example, the volume delivered during t1 was
calculated tilizing the single sensor output values and determined
to be over the target amount per stroke. As a result, the
subsequent constant voltage pump drive signal is adjusted to be of
shorter duration. In this illustration the amount of correction is
36 ms. In this example, t2--the subsequent pump stroke duration--is
reduced by 36 ms to a new pump on duration of 824 ms.
[0115] FIG. 15 illustrates a graph of two square wave pump control
signals and a corresponding pressure sensor traces from a two
pressure sensor differential pressure control system. In this
illustrative example, the differential pressure control system
would utilize data from the difference between the two pressure
sensor outputs (i.e., the integral of the trace curve for a given
pump drive signal) to determine stroke volume. Two pressure sensor
configurations are illustrated above in FIGS. 2 and 10. In this
example, the pump drive signal is a constant voltage of about 2.7
volts. The base line pressure sensor output signal is about 50 mv.
The duration of the first pulse (t1) is 750 ms. In this example,
the pressure sensor output is read every 4 ms. The system
controller includes computer readable instructions to begin
integrating the differences between the two pressure sensor
readings when the pump drive signal is applied and to continue to
integrate those differences until the pressure sensor output
voltage decreases below a determined value. Typically, the value
would be once the output signal indicates that the system has
returned to base pressure (here at a sensor voltage of 50 mv).
Thereafter, the obtained integral values are converted to volume
and then compared to the target flow. It is to be appreciated that
the integral values may be calculated in real-time as the stroke
progresses. This real-time stroke volume calculation may be used as
a pump off trigger signal back to the controller to stop the flow
of power to the EK engine. It is to be appreciated that the
integral values may be calculated in real-time as the stroke
progresses. This real-time stroke volume calculation may be used as
a pump off trigger signal back to the controller to stop the flow
of power to the EK engine. is to be appreciated that the integral
values may be calculated in real-time as the stroke progresses.
This real-time stroke volume calculation may be used as a pump off
trigger signal back to the controller to stop the flow of power to
the EK engine. The volume delivered during t1 was calculated
utilizing the dual sensor output values and determined to be under
the target amount per stroke. As a result, the subsequent constant
voltage pump drive signal is adjusted to be of longer duration. In
this illustration the amount of correction is 36 ms. In this
example, t2--the subsequent pump stroke duration--is increased by
36 ms to a new pump duration of 786 ms.
[0116] The pressure signal traces in FIGS. 14 and 15 also
illustrate an additional aspect of the EK pump control system. Both
sets of pressure traces indicate that there is a pressure decay
after the pump drive voltage goes to zero (i.e., pump drive signal
is OFF). This decay curve extends from the point where the pressure
output crosses the voltage off line until it reaches the base line
output of 75 mv (FIG. 14) and 50 mv (FIG. 15). The areas in each
are different with FIG. 14 being larger than FIG. 15. Depending
upon the pump system requirements and operating conditions, these
remaining flow indications or additional volumes may or may not be
significant. If not significant, then the system will ignore them.
If significant, then the system can compensate for this type of
error using the techniques described herein. The amount of error
introduced by this part of the pressure trace (and resulting volume
it represents) will result in different outcomes for the determined
stroke volume (see FIG. 3A step 210 and FIG. 3B step 310).
[0117] If the pressure trace information beyond the pump off signal
is not consequential, then the integral period or volume
calculation period may stop when the pump off signal occurs. If the
pressure trace information beyond the pump off signal is
consequential or is to be considered within the stoke compensation
scheme, then there are at least two ways to account for this
condition. One way to compensate for this type of possible
variation is to extend the integral calculation time or volume
calculation time for a time period beyond the end of the pump off
signal. In one exemplary embodiment, the additional integration
time is about 50 ms beyond the pump off signal. Another way to
compensate for this type of possible variation is to extend the
integral calculation or volume calculation period not by time but
instead until the pressure sense voltage drops below a threshold
value. Once the pressure sense voltage reaches or exceeds the
desired threshold value, then the integral calculation or volume
determination time will end.
[0118] FIG. 16 is a table with exemplary correction factors as
applied to a range of stroke durations. This table illustrates the
high degree of precision fluid delivery and correction capabilities
provided by the EK pump control schemes described herein. In this
example, the pump durations are pre-set amounts of 4 milliseconds
(ms), 8 ms, 16 ms and 32 ms. The pump stroke times are selected for
typical values for the exemplary chambers described above. The
stroke times of 300 ms, 500 ms, 800 ms and 1000 ms are listed. The
percentage correction listed corresponds to the amount of
correction time to the total stroke duration. For example, a 16 ms
correction time represents a 5.3% correction of a 300 ms stroke. An
8 ms correction time represents a 0.8% correction of a 1000 ms
stroke.
[0119] FIG. 17 is an exemplary corrections value table for a
typical pumping system as described herein. The information shown
in FIG. 17 may be used as part of the methods 200, 300 described
above such as part of steps 230, 330 respectively. The EK pump
operates as described above with a differential pressure
measurement system utilizing a flow restrictor tube with a length
of about 1 inch and an inner diameter of 0.007 inches. In this
illustrative example, the pump control system is set with a
tolerance of 200 or a value that is 2% of target value. The target
integral value is 5000 based on the pressure curves and signals
used to generate the curves in FIGS. 14 and 15. The correction
value is determined by subtracting the target integral from the
measured DPI and then dividing that value by the tolerance value.
The tolerance value is a number used to represent the accuracy
desired by the system. This is generally set as a percentage value
of a pump stroke volume. In this example, the tolerance value is
200. Measured DPI refers to the measured differential pressure
integral obtained during the pump stroke as an indication of
delivery fluid volume during the stroke. The magnitude of the
correction value determines the amount of stroke duration
adjustment for the subsequent stroke. The sign of the correction
value determines if a subsequent stroke duration is increased
(negative correction value result) or decreased (positive
correction value result). If the correction value is less than 1,
then there is no correction needed. If the correction value is
between 1 and 2, then a 4 ms correction time is used. If the
correction value is between 2 and 3, then an 8 ms correction time
is used. If the correction value is between 3 and 4, then a 16 ms
correction time is used. If the correction value is greater than 4,
then a 32 ms correction time is used.
[0120] Additional details of an exemplary pump controller are
described in co-pending and commonly owned U.S. Provisional Patent
Application No. 61/482,889, entitled "GEL COUPLING FOR
ELECTROKINETIC DELIVERY SYSTEMS," filed May 5, 2012 and its
corresponding U.S. Non-provisional patent application Ser. No.
______, entitled "GEL COUPLING FOR ELECTROKINETIC DELIVERY
SYSTEMS," filed herewith. While described as a modular system
having 1100, 1200, the two may be combined into a single system as
described above. In addition, the EK pump, pressure sensors,
differential pressure system, and controller may be provided in a
single housing having a display 1205. FIG. 18 illustrates a control
module 1200 configured to apply the pump drive signals, receive and
process signals from sensors and other functions to control the
operation of an EK pump system as described herein. The control
module 1200 can include a power source, such as a battery 1203, for
supplying the voltage, and a circuit board 1201 including the
circuitry to control the application of voltage to the pump module.
The control module can further include a display 1205 to provide
instructions and/or information to the user, such as an indication
of flow rate, battery level, operation status, and/or errors in the
system. In addition the display 1205 may be used to provide a GUI
input screen for a user as well as provide information about total
volume delivery progress or system status. An on-off switch 1207
can be located on the control module to allow the user to switch
the control module on and off. The display 1205 also acts as user
input device in communication with the computer controller. The
computer controller is also adapted and configured to provide and
receive signals from the user input device.
[0121] Referring to FIG. 19, the circuit board in the control
module 1200 includes voltage regulators 1301, an H-bridge 1303, a
microprocessor 1305, an amplifier 1307, switches 1309, and
communications 1311. Electrical connections 1310 between the
components of the control module 1200 and components of the pump
module 1100 enable the control module 1200 to run the pump module
1100. While described as separate for purposes of modular design
aspects, it is to be appreciated that the separate, modular aspects
of 1100, 1200 may be combined into a single pumping system. The
control module can provide between 1 and 20 volts, such as between
2 and 15 volts, for example 2.6 to 11 volts, specifically 3 to 3.5
volts, and up to 150 mA, such as up to 100 mA, to the pump module
1100 depending upon pump configuration.
[0122] In use, the batteries 1203 supply voltage to the voltage
regulators 1301. The voltage regulators 1301, under direction of
the microprocessor 1305, supply the required amount of voltage to
the H-bridge 1303. The H-Bridge 1303 in turn supplies voltage to
the EK engine 1103 to start the flow of fluid through the pump. The
amount of fluid that flow through the pump can be monitored and
controlled by the pressure sensors 1152, 1154. Signals from the
sensors 1152, 1154 to the amplifier 1307 in the control module can
be amplified and then transmitted to the microprocessor 1305 for
analysis. Using the pressure feedback information, the
microprocessor 1305 can send the proper signal to the H-bridge to
control the amount of time that a pump drive signal, such as a
constant voltage, is applied to the engine 1103. The switches 1309
can be used to start and stop the engine 1103 as well as to switch
between modes of pump module operation, e.g., from bolus to basal
mode. The communications 1311 can be used to communicate with a
computer (not shown), which can be used for diagnostic purposes
and/or to program the microprocessor 1305. In addition or
alternatively, the communication 1311 may be configured to provide
wired or wireless access to the system 1100/1200.
[0123] As shown in FIG. 19, the pump module 100 and the control
module 1100 can have at least eight electrical connections
extending there between. A positive voltage electrical connection
1310a and a negative voltage electrical connection 1310b can extend
from the H-bridge 1303 to the engine 1103 to supply the appropriate
voltage. Further, an s+ electrical connection 1310c, 1310g and an
s- electrical connection 1310d, 1310h can extend from sensors 1152,
1154, respectively, such that the difference in voltage between the
s+ and s- connections can be used to calculate the applied
pressure. Moreover, a power electrical connection 1310e can extend
from the amplifier 1307 to both sensors 1152, 1154 to power the
sensors, and a ground electrical connection 1310f can extend from
the amplifier 1307 to both sensors 1152, 1154 to ground the
sensors. Sensors in the above description may be any of the
pressure sensors or other appropriate differential pressure sensors
or other control or performance systems utilized in the operation
of the EK pump control schemes described herein.
[0124] In another alternative embodiment of an electrokinetic pump
fluid delivery system, there is a system having an electrokinetic
pump in communication with an outlet chamber, a reservoir in
communication with the outlet chamber; and a differential pressure
flow control system in communication with the outlet chamber. There
is provided in accordance with the disclosure above a control
system for the delivery system implemented using an electronic
controller. The controller is in communication with the
electrokinetic pump and the differential pressure flow control
system as suited to the specific components thereof. The
instructions in the memory of the controller may also include those
adapted and configured for communication to and from a differential
pressure control system. Such communication includes instructions
for the specific components of a differential pressure system
including power, control, instructions, data, or other signaling
turning components on or off, calibration of said components.
Examples of specific components may include those associated with a
venturi flow meter, an orifice flow meter, or a flow nozzle flow
meter.
[0125] The memory of the controller or suitable memory in
communication with or accessible to the controller contains
computer readable instructions to determine or retrieve data
relating to, for example, a pump drive signal, a constant voltage
value, a constant current value, a pump stroke time based a
correction factor. In one aspect, there is a time based correction
factor is based upon a value in a look up table programmed into or
accessible to an electronic memory of the computer controller.
Still further, a correction factor may be related to a number of
different variables or system conditions as described above. The
correction factor may be, for example, provided or determined in
relation to an input signal to the controller from the
electrokinetic pump and an input signal to the controller from the
differential pressure flow control system. As such, the electronic
memory accessible to the controller may include or be programmed to
include, for example, a time based correction factor is based upon
a feedback control scheme. Additionally or alternatively, the
electronic memory of the computer controller is programmed for or
has access separately or in any combination to: (a) a proportional
feedback control scheme; (b) a proportional and integral feedback
control scheme; and (c) a proportional, integral and derivative
feedback control scheme.
[0126] Those of ordinary skill will appreciate that the various
processing steps, comparisons, methods, techniques, signal
processing and component specific operations performed by a
controller are provided to the controller or contained within
electronic memory accessible to the controller in the form of
appropriate computer readable code. Similarly, the various
diagnostic routines, abnormal condition detectors, functional
indicators and pump control schemes and other operational
considerations described in this patent application are also stored
in an appropriate computer readable code within the memory of or
accessible to the controller. In one specific example, the computer
readable instructions in the memory of the computer controller
implement control schemes for pump cycle duration based on
computations made based at least in part on a differential pressure
flow control (instructions to adjust the pump duration based on a
calculated stroke time adjustment), including techniques described
herein for stroke duration response is calculated, as well as the
tables, files or data relating to those embodiments where the
stroke response adjustment is selected one of a set of pre-selected
stroke durations.
[0127] As for additional details pertinent to the present
invention, materials and manufacturing techniques may be employed
as within the level of those with skill in the relevant art. The
same may hold true with respect to method-based aspects of the
invention in terms of additional acts commonly or logically
employed. Also, it is contemplated that any optional feature of the
inventive variations described may be set forth and claimed
independently, or in combination with any one or more of the
features described herein. Likewise, reference to a singular item,
includes the possibility that there are plural of the same items
present. More specifically, as used herein and in the appended
claims, the singular forms "a," "and," "said," and "the" include
plural referents unless the context clearly dictates otherwise. It
is further noted that the claims may be drafted to exclude any
optional element. As such, this statement is intended to serve as
antecedent basis for use of such exclusive terminology as "solely,"
"only" and the like in connection with the recitation of claim
elements, or use of a "negative" limitation. Unless defined
otherwise herein, all technical and scientific terms used herein
have the same meaning as commonly understood by one of ordinary
skill in the art to which this invention belongs. The breadth of
the present invention is not to be limited by the subject
specification, but rather only by the plain meaning of the claim
terms employed.
[0128] It is intended that the following claims define the scope of
the invention and that methods and structures within the scope of
these claims and their equivalents be covered thereby.
* * * * *