U.S. patent application number 10/177544 was filed with the patent office on 2003-12-25 for method and apparatus for closed-loop flow control system.
This patent application is currently assigned to Baxter International, Inc.. Invention is credited to Bui, Tuan, Garchow, Stephen R., Jacobson, James D., Slepicka, James S., Yardimci, Atif.
Application Number | 20030236489 10/177544 |
Document ID | / |
Family ID | 29734427 |
Filed Date | 2003-12-25 |
United States Patent
Application |
20030236489 |
Kind Code |
A1 |
Jacobson, James D. ; et
al. |
December 25, 2003 |
Method and apparatus for closed-loop flow control system
Abstract
A fluid delivery system having a closed-loop control process for
delivering a medical fluid to a patient. A fluid infusion system
includes a pump for delivering a fluid to a patient via an
administration tube. A flow sensor associated with the
administration tube provides an indication of the actual flow rate
of fluid in the administration tube. Such a flow sensor may
comprise a positive displacement flow sensor constructed using
micro-fabrication and/or micro-molding techniques. A reader reads
the actual flow rate signal and provides an indication to a
controller for controlling the pump. The flow rate information can
also be used for providing status information, such as the
existence of a blockage in the fluid delivery system.
Inventors: |
Jacobson, James D.;
(Lindenhurst, IL) ; Bui, Tuan; (Green Oaks,
IL) ; Garchow, Stephen R.; (Libertyville, IL)
; Yardimci, Atif; (Northbrook, IL) ; Slepicka,
James S.; (Spring Grove, IL) |
Correspondence
Address: |
SENNIGER POWERS LEAVITT AND ROEDEL
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
Baxter International, Inc.
|
Family ID: |
29734427 |
Appl. No.: |
10/177544 |
Filed: |
June 21, 2002 |
Current U.S.
Class: |
604/67 ;
73/861.52 |
Current CPC
Class: |
G05D 7/0676 20130101;
A61M 2205/0244 20130101; A61M 5/16886 20130101; A61M 2205/0294
20130101; A61M 5/14236 20130101; A61M 5/172 20130101 |
Class at
Publication: |
604/67 ;
73/861.52 |
International
Class: |
A61M 037/00 |
Claims
What is claimed is:
1. A system for delivering a fluid at a desired flow rate from a
reservoir to a delivery point associated with a patient, said
system comprising: a delivery channel between the reservoir and the
delivery point through which the fluid is delivered to the patient;
a pump associated with the delivery channel for operatively
delivering the fluid to the delivery point at an adjustable output
rate; a flow sensor located along the delivery channel for sensing
a flow of the fluid in the delivery channel and for generating a
flow rate signal indicative of a rate of flow of the fluid in the
delivery channel, said flow sensor comprising a positive
displacement flow sensor; and a controller for controlling the
pump, said controller causing adjustments to the output rate of the
pump as a function of the flow rate signal whereby the desired flow
rate is substantially achieved.
2. A system as set forth in claim 1 wherein the flow sensor
comprises a passive device having no electrical connections
thereto.
3. A system as set forth in claim 1 wherein the delivery channel
comprises an administration tube and the flow sensor is sized and
shaped for being positioned in fluid communication with the fluid
within the delivery channel.
4. A system as set forth in claim 3 wherein the flow sensor
comprises a MEMS device.
5. A system as set forth in claim 3 wherein the flow sensor
comprises an assembly of micro-molded components.
6. A system as set forth in claim 1 wherein the flow sensor is
capable of detecting flow rates from about 0.1 ml/hr to about 2000
ml/hr.
7. A system as set forth in claim 1 further comprising a reader
associated with the flow sensor for receiving the flow rate signal
and providing a flow control signal indicative of the flow rate
signal, said controller receiving the flow control signal and
adjusting the output rate of the pump in response thereto.
8. A system as set forth in claim 7 wherein the flow sensor
comprises a rotatable impeller for rotating in response to the flow
of the fluid in the administration tube and the flow rate signal
comprises an optical indication generated by a rotation of the
rotatable impeller, and wherein the reader comprises an optical
reader responsive to the optical indication for providing the flow
control signal.
9. A system as set forth in claim 8 wherein: the optical reader
illuminates the flow sensor causing a reflection from the rotatable
impeller; and the optical indication generated by the rotation of
the rotatable impeller comprises a variation in an intensity of the
reflection from the rotation of the rotatable impeller.
10. A system as set forth in claim 7 wherein: the flow sensor
includes a rotatable impeller for rotating in response to the flow
of the fluid in the administration tube; and the reader comprises a
Hall sensor that senses an electrical signal caused by a rotation
of the rotatable impeller and provides the flow control signal in
response thereto.
11. A system as set forth in claim 1 further comprising: a reader
associated with the flow sensor for receiving the flow rate signal;
and a wireless communication channel between the reader and the
controller, said reader providing a flow control signal indicative
of the flow rate signal to the wireless communication channel and
said controller receiving the flow control signal via the wireless
communication channel and causing adjustments to the output rate of
the pump in response thereto.
12. A system as set forth in claim 11 wherein the wireless
communication channel comprises a spread spectrum communication
channel operating in an unlicensed frequency band.
13. A system as set forth in claim 1 wherein the delivery channel
comprises an administration tube and the pump comprises an infusion
pump located along the administration tube.
14. A system as set forth in claim 13 wherein the infusion pump is
a peristaltic pump, a piezoelectric pump or a valve pump.
15. A system as set forth in claim 13 wherein the infusion pump
comprises an ambulatory infusion pump.
16. A system as set forth in claim 13 wherein the infusion pump
comprises a volumetric infusion pump.
17. A system as set forth in claim 1 wherein the delivery channel
comprises an administration tube and the pump comprises an infusion
pump connected to the administration tube, and wherein the
reservoir comprises a syringe barrel having an input opening and an
output orifice operatively connected to the administration tube,
and wherein the infusion pump comprises a syringe plunger slidably
inserted into the syringe barrel through the input opening and a
plunger driver responsive to the controller and operatively
connected to the syringe plunger for causing a positive
displacement of said syringe plunger, whereby the positive
displacement of the plunger operatively delivers the fluid to the
delivery point and the output rate of the infusion pump is adjusted
by adjusting the positive displacement of the plunger caused by the
plunger driver.
18. A system as set forth in claim 1 wherein the desired flow rate
comprises a pulsatile flow profile and the controller adjusts the
output rate of the pump such that the output flow rate has a
generally pulsatile characteristic corresponding to the desired
flow rate.
19. A system as set forth in claim 1 wherein the desired flow rate
comprises a time-varying flow rate and the controller adjusts the
output rate of the pump such that the output flow rate has a
time-varying characteristic corresponding to the desired flow
rate.
20. A system as set forth in claim 1 wherein the controller
provides a flow rate status signal and further comprising a status
monitoring device providing an indication of an operating status of
the desired flow rate in response to the flow rate status
signal.
21. A system as set forth in claim 20 wherein the flow rate status
signal comprises a signal indicative of a blockage in the delivery
channel and wherein the indication of the operating status of
desired flow rate comprises an indication identifying that the
delivery channel has a blockage.
22. A system as set forth in claim 20 further comprising a wireless
communication channel for transmitting the flow rate status signal
from the controller to the status monitoring device.
23. A system as set forth in claim 22 wherein the wireless
communication channel comprises a spread spectrum communication
channel operating in an unlicensed frequency band.
24. A closed-loop fluid delivery system for delivering a fluid from
a reservoir to a delivery point associated with a patient at a
desired delivery rate via an administration tube, said closed-loop
fluid delivery system comprising: fluid delivery means located
along the administration tube for operatively supplying the fluid
to the delivery point at a controllable output rate; positive
displacement flow sensing means located between the fluid delivery
means and the delivery point for sensing an actual flow rate of the
fluid in the delivery channel and for generating a flow rate signal
indicative of the actual flow rate of the fluid in the delivery
channel; and control means associated with the fluid delivery means
receiving and responsive to the flow rate signal for adjusting the
output rate of the fluid delivery means such that the desired
delivery rate at which the fluid is supplied to the delivery point
associated with the patient is substantially achieved.
25. A closed-loop fluid delivery system as set forth in claim 24
wherein the positive displacement flow sensing means is sized and
shaped for being positioned in fluid communication with the fluid
within the administration tube.
26. A closed-loop fluid delivery system as set forth in claim 24
further comprising detector means associated with the positive
displacement flow sensing means for detecting the flow rate signal
and for providing a flow control signal indicative of the flow rate
signal and wherein the control means receives the flow control
signal and adjusts the output rate of the fluid delivery means in
response thereto.
27. A closed-loop fluid delivery system as set forth in claim 26
further comprising a wireless communication path between the
detector means and the control means wherein the detector means
provides the flow control signal to the control means via the
wireless communication channel.
28. A closed-loop fluid delivery system as set forth in claim 24
wherein the desired flow rate comprises a pulsatile flow profile
and the control means adjusts the output rate of the fluid delivery
means such that the output rate has a generally pulsatile
characteristic.
29. A closed-loop fluid delivery system as set forth in claim 24
wherein the control means provides a status signal indicative of
the actual flow rate and said system further comprising monitoring
means receiving the status signal for indicating an operating
status of the fluid delivery system.
30. A closed-loop fluid delivery system as set forth in claim 29
wherein the status signal comprises a signal that is indicative of
a blockage in the administration tube and wherein the operating
status indicated by the monitoring means comprises an indication
identifying that the administration tube is blocked.
31. A system for delivering a fluid from a reservoir to a delivery
point associated with a patient at a desired delivery rate via an
administration tube, said system comprising: a delivery mechanism
operatively connected between the reservoir and the delivery point,
said delivery mechanism being constructed and arranged for
selectively delivering the fluid to the delivery point via the
administration tube at a controllable output flow rate; and a
closed-loop control system controlling the output flow rate of the
delivery mechanism, said closed-loop control system comprising: a
positive displacement flow sensor connected in-line with the
administration tube for determining an actual flow rate of the
fluid in the administration tube and for providing an flow rate
indication reflecting the actual flow rate; a reader associated
with the positive displacement flow sensor for receiving the flow
rate indication and for providing a flow control signal reflecting
the flow rate indication; and a controller associated with the
delivery mechanism receiving and responsive to the flow control
signal for controlling the output flow rate of the delivery
mechanism as a function of the flow control signal such that the
output flow rate is substantially equal to the desired delivery
rate.
32. A system as set forth in claim 31 wherein the positive
displacement flow sensor is sized and shaped for being positioned
within the administration tube in fluid communication with the
fluid.
33. A system as set forth in claim 31 wherein the delivery
mechanism comprises an infusion pump.
34. A system as set forth in claim 33 wherein the infusion pump
comprises a syringe pump, a peristaltic pump, a piezoelectric pump,
or a valve pump.
35. A system as set forth in claim 33 wherein the infusion pump
comprises an ambulatory infusion pump.
36. A system as set forth in claim 33 wherein the infusion pump
comprises a volumetric infusion pump.
37. A system as set forth in claim 31 further comprising a wireless
communication path between the reader and the controller, said
reader providing the flow control signal to the controller via the
wireless communication path.
38. A system as set forth in claim 31 wherein the desired delivery
rate comprises a pulsatile delivery profile and wherein the
controller controls the delivery mechanism such that output flow
rate has a substantially pulsatile characteristic.
39. A system as set forth in claim 31 further comprising a status
monitor and wherein the closed-loop control system provides a
status signal indicating when the actual flow rate is below a flow
rate threshold, said status monitor receiving the status signal and
providing an indication that the actual flow rate is below the flow
rate threshold.
40. A system as set forth in claim 39 wherein the indication that
the actual flow rate is below the flow rate threshold comprises an
audible alarm.
41. A system as set forth in claim 39 wherein the indication that
the actual flow rate is below the flow rate threshold comprises a
visual alarm.
42. A system as set forth in claim 39 wherein the indication that
the actual flow rate is below the flow rate threshold comprises a
vibrating alarm.
43. A method of delivering a medical fluid to a delivery point
associated with a patient at a desired delivery flow rate
comprising: operatively connecting a reservoir to a delivery
mechanism, said reservoir containing the medical fluid to be
delivered to the delivery point; operatively connecting the
delivery mechanism to an administration tube, said administration
tube being in fluid communication with the delivery point, said
delivery mechanism receiving the medical fluid from the reservoir
and supplying the medical fluid to the delivery point via the
administration tube at an output flow rate; sensing the output flow
rate of the medical fluid in the administration tube using a
positive displacement flow sensor; comparing the sensed output flow
rate of the medical fluid with the desired delivery flow rate; and
controlling the delivery mechanism such that the output flow rate
substantially corresponds to the desired delivery flow rate.
44. A method as set forth in claim 43 wherein sensing the output
flow rate of the medical fluid in the administration tube comprises
connecting a flow sensor operatively to the administration tube and
wherein sensing the output flow rate of the medical fluid in the
administration tube comprises sensing a rate of flow through the
flow sensor whereby the generated flow rate signal is a function of
the rate of flow through the flow sensor.
45. A method as set forth in claim 44 wherein the positive
displacement flow sensor is sized and shaped for being positioned
in fluid communication with the medical fluid within the
administration tube.
46. A method as set forth in claim 45 wherein the positive
displacement flow sensor includes a rotatable member and wherein
each rotation of the rotatable member corresponds to a fixed volume
of the medical fluid passing through the positive displacement flow
sensor, and wherein sensing the rate of flow through the positive
displacement flow sensor comprises: sensing a rotation of the
rotatable member; and calculating the rate of flow as a function of
a number of rotations of the rotatable member over a sample
period.
47. A method as set forth in claim 46 further comprising providing
an optical variation based on the rotation of the rotatable member
and wherein sensing the rotation of the rotatable member comprises
sensing the optical variation provided by the rotation of the
rotatable member.
48. A method as set forth in claim 46 wherein the rotation of the
rotatable member causes an electrical variation and wherein sensing
the rotation of the rotatable member comprises sensing the
electrical variation caused by the rotation of the rotatable
member.
49. A method as set forth in claim 44 wherein the delivery
mechanism comprises an infusion pump and supplying the medical
fluid to the administration tube at the output flow rate comprises
pumping the medical fluid through the administration tube such that
desired delivery flow rate is substantially achieved.
50. A method as set forth in claim 49 wherein the administration
tube and flow sensor comprise an administration set constructed and
arranged for disposable use.
51. A method as set forth in claim 49 wherein the desired flow rate
comprises a pulsatile flow profile and wherein controlling the
delivery mechanism comprises controlling the infusion pump such
that the output flow rate has a generally pulsatile
characteristic.
52. A method as set forth in claim 43 further comprising:
determining if the sensed output flow rate is indicative of a
blockage in the administration tube; and providing an alarm signal
if it is determined that the sensed output flow rate indicates a
blockage in the administration tube.
53. A method as set forth in claim 43 wherein comparing the sensed
output flow rate of the medical fluid with the desired delivery
flow rate comprises comparing an average of the output flow rate of
the medical fluid with the output flow rate.
54. A method as set forth in claim 43 wherein comparing the sensed
output flow rate of the medical fluid with the desired delivery
flow rate comprises comparing the sensed output flow rate of the
medical fluid with an acceptability range corresponding to the
output flow rate.
55. A closed-loop flow control system for controlling a medical
fluid delivery system, said medical fluid delivery system
delivering a fluid from a reservoir to a delivery point associated
with a patient at a desired delivery rate via an administration
tube, said medical fluid delivery system including a delivery
mechanism operatively connected between the reservoir and the
delivery point, said delivery mechanism being constructed and
arranged for delivering the fluid to the delivery point via the
administration tube at a controllable output flow rate, said
closed-loop flow control system comprising: a positive displacement
flow sensor connected in-line with the administration tube for
determining an actual flow rate of the fluid in the administration
tube and for providing an flow rate indication reflecting the
actual flow rate; a reader associated with the positive
displacement flow sensor for receiving the flow rate indication and
for providing a flow control signal reflecting the flow rate
indication; and a controller associated with the delivery mechanism
receiving and responsive to the flow control signal for controlling
the output flow rate of the delivery mechanism as a function of the
flow control signal such that the output flow rate is substantially
equal to the desired delivery rate.
56. A closed-loop flow control system as set forth in claim 55
wherein the positive displacement flow sensor is sized and shaped
for being positioned within the administration tube in fluid
communication with the medical fluid.
57. A closed-loop flow control system as set forth in claim 55
further comprising a wireless communication channel between the
reader and the controller, said reader providing the flow control
signal to the controller via the wireless communication
channel.
58. A closed-loop flow control system as set forth in claim 55
wherein the desired delivery rate comprises a pulsatile delivery
profile and wherein the controller controls the delivery mechanism
such that output flow rate includes a substantially pulsatile
characteristic.
59. A method of detecting a blockage in a medical fluid delivery
system arranged for delivering a medical fluid to a delivery point
associated with a patient at a desired flow rate, the method
comprising: operatively connecting a reservoir to a delivery
mechanism, said reservoir containing the medical fluid to be
delivered to the delivery point; operatively connecting the
delivery mechanism to an administration tube, said administration
tube being in fluid communication with the delivery point, said
delivery mechanism receiving the medical fluid from the reservoir
and supplying the medical fluid to the delivery point via the
administration tube at an output flow rate; sensing the output flow
rate of the medical fluid in the administration tube; determining
if the sensed output flow rate is indicative of a blockage in the
administration tube; and providing an alarm signal if it is
determined that the sensed output flow rate indicates that the
administration tube is blocked.
60. A method as set forth in claim 59 wherein determining if the
sensed output flow rate is indicative of a blockage in the
administration tube comprises comparing the sensed output flow rate
to a blockage threshold such that the alarm signal is provided if
the output flow rate is less than the blockage threshold.
61. A method as set forth in claim 60 wherein determining if the
sensed output flow is indicative of a blockage in the
administration tube comprises averaging the sensed output flow rate
of the medical fluid in the administration tube over a time period
and comparing said averaged sensed output flow rate to a blockage
reference such that the alarm signal is provided if the averaged
sensed flow rate is less than the blockage reference.
62. A method as set forth in claim 59 further comprising receiving
the alarm signal at a status monitoring device associated with the
medical fluid delivery system and providing an indication of the
alarm signal at the status monitoring device.
63. A method as set fort hin claim 62 wherein the indication of the
alarm signal comprises an audible alarm.
64. A method as set forth in claim 62 wherein the indication of the
alarm signal comprises a visual alarm.
65. A method as set forth in claim 64 wherein the indication of the
alarm signal comprises a vibrating alarm.
66. An administration set for use in connection with a fluid
delivery system, said fluid delivery system being arranged for
delivering a fluid from a reservoir to a delivery point associated
with a patient at a desired delivery rate, and wherein said fluid
delivery system includes a pump having an output rate for
delivering fluid from the reservoir to the delivery point and a
controller for adjusting the output rate of the pump such that the
desired delivery rate is substantially achieved, the administration
set comprising: an administration tube for providing fluid
communication between the reservoir and the delivery point; and a
positive displacement flow sensor located along the administration
tube being sized and shaped for being positioned in fluid
communication with the fluid within the administration tube, said
positive displacement flow sensor for sensing a rate of flow of the
fluid in the administration tube and for generating a flow rate
signal indicative of the sensed rate of flow of the fluid in the
administration tube whereby the controller adjusts the output rate
of the pump as a function of the flow rate signal.
67. An administration set as set forth in claim 66 wherein the
positive displacement flow sensor is sized and shaped for being
positioned within the administration tube such that substantially
all of the fluid flowing through the administration tube to the
delivery point flows through the flow sensor.
68. A positive displacement flow sensor for use in connection with
a medical fluid infusion system including an administration set
having an administration tube, the positive displacement flow
sensor comprising: a housing having an inlet port and an outlet
port, said ports being operatively connected to the administration
tube; a first rotor positioned within the housing between the inlet
port and the outlet port; a second rotor positioned within the
housing between the inlet port and the outlet port, said second
rotor being positioned adjacent to the first rotor, said first and
second rotors being constructed and arranged to rotate in response
to a flow of medical fluid in the administration tube for detecting
flow of the medical fluid in the administration tube; and a cover
enclosing the housing such that when the medical fluid flows into
the inlet port it causes the first rotor to rotate and thereafter
said medical fluid exits through the outlet port.
69. A positive displacement flow sensor as set forth in claim 68
wherein the first and second rotors each have a plurality of lobes,
said lobes of the first rotor engaging said lobes of the second
rotor in a gearing relationship.
70. A positive displacement flow sensor as set forth in claim 68
wherein the housing and the first and second rotors are fabricated
using micro-fabrication techniques.
71. A positive displacement flow sensor as set forth in claim 68
wherein the housing and the first and second rotors are fabricated
from one or more molds created via a UV-LIGA process.
72. A positive displacement flow sensor as set forth in claim 68
wherein the housing and the first and second rotors are fabricated
using a deep reactive ion etching process.
73. A positive displacement flow sensor as set forth in claim 68
wherein the cover comprises a generally transparent cover allowing
light to pass through a portion of the cover.
74. A positive displacement flow sensor as set forth in claim 73
wherein the first rotor comprises a plurality of lobes, at least
one of said lobes being marked with a marker indication that is
optically detectable through the cover.
75. A positive displacement flow sensor as set forth in claim 73
wherein the cover has a substantially opaque pattern imposed
thereon that substantially prevents light from passing through said
pattern.
76. A positive displacement flow sensor as set forth in claim 75
wherein the pattern imposed on the cover corresponds to a shape and
size of the first rotor.
77. A positive displacement flow sensor as set forth in claim 68
further comprising a reader positioned adjacent the first rotor,
said reader being constructed and arranged for detecting a rotation
of the first rotor and for providing a signal that is indicative of
a rate of the flow of the medical fluid in the administration tube
as a function of the detected rotation of the first rotor.
78. A positive displacement flow sensor as set forth in claim 77
wherein the reader is positioned substantially within the cover.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to delivering fluids to a
patient and, particularly, to closed-loop flow control systems and
methods for delivering medical fluids to a patient at a controlled
delivery rate.
[0003] 2. Description of the Prior Art
[0004] A variety of fluid delivery systems are currently being used
in the medical field for delivering medical fluids (containing
medication, nutrition, saline, and so on) to human and veterinary
patients. It is often desirable to administer such medical fluids
at relatively precise delivery rates. In some cases, the rate of
delivery may be exceptionally important. In recent years, it has
also been found to be advantageous to use various types of infusion
pumps to administer medical fluids automatically, over extended
periods of time. A typical infusion pump delivers the medical fluid
into the patient's venous system using a delivery channel which
usually comprises an administration tube (e.g., a polyvinyl
chloride tube) connected to the patient using some form of
catheter, needle, or the like.
[0005] Heretofore, infusion pumps and similar devices known in the
art have typically not provided closed-loop flow control to achieve
precise delivery rates. Rather, flow control has been open loop
because actual flow rate information has not been used in
controlling the infusion pump. A typical accuracy of such systems,
in terms of flow rate, is normally no better than about +/-5%, and
requires relatively sophisticated (and costly) mechanical
components and tight material/geometry controls (e.g., of the
tubing) to achieve that rate. In fact, ambulatory pumps typically
achieve accuracies of +/-6-8%. Further, non-ambulatory pumps often
do not achieve a five percent accuracy range at low flow rates or
over longer time periods due to modification of the tubing material
over time. For example, a typical peristaltic type pump requires
repeated deformation of the administration tube. This deformation
process changes the elastic recovery properties of the tube,
resulting in changes in the volumetric output of the pump over
time. One volumetric pump available from the assignee of the
present application has a specified rating of +/-5% at 1-1200 ml/hr
and +/-10% at 0.1-1 ml/hr. Another pump available from the assignee
of the present application has a rated accuracy of +/-5% for the
first 24 hours of use and +/-10% thereafter.
[0006] While the foregoing accuracy ranges may be acceptable for
some uses, greater accuracy is desirable for other uses. In some
prior art systems, the pumping mechanism associated with the
infusion pump is monitored and controlled, but the actual flow of
fluid in the administration tube is not. For example, commonly
assigned U.S. Pat. No. 5,533,981 describes a syringe infusion pump
having a sensor for detecting the position and capture of a syringe
plunger for use in controlling the dispensing of fluid from the
syringe. Commonly assigned U.S. Pat. No. 6,078,273 discloses a
variety of known infusion pump systems such as, for example, roller
pump systems, peristaltic-type systems, valve-type systems, and
motor driven systems. Further, commonly assigned U.S. Pat. No.
5,482,841 discloses a volumetric-type infusion pump. An example of
an ambulatory infusion pump is a pump sold under the mark IPUMP by
the assignee of the present application. An example of an
ambulatory pump may also be found in U.S. Pat. No. 5,993,420.
[0007] Some systems have attempted to provide closed-loop control.
For example, commonly assigned U.S. Pat. No. 5,533,412 discloses a
pulsed thermal flow sensor. In such a system, the fluid is heated
by a pulsed heating element. The fluid carries the thermal pulse
through a flow channel to two sensor elements spaced apart,
downstream from the heating element. The transit time of the
thermal pulse between the two sensor elements provides an
indication of the fluid flow velocity. Thus, such an approach
requires the application of a heat pulse to the fluid in order to
determine flow rate information.
[0008] Other prior art systems use information generated by
positional encoders and decoders associated with a motor shaft to
control an infusion pump. For example, the above-mentioned U.S.
Pat. No. 6,078,273 discloses an encoder/decoder for use in
controlling a medical infusion pump. While such systems reflect
improvements in the art, they do not control fluid delivery in view
of actual flow rates. In some circumstances, therefore, such
systems would not provide as accurate information and tight control
based on actual fluid flow rate data.
[0009] Sensors, such as positive displacement (PD) flow rate
sensors, have been in use for many years and directly detect flow
rates. A typical PD sensor includes two complementary rotating
elements that, when exposed to a fluid flow, allow a relatively
well-defined volume of the fluid to transfer from one side of the
sensor to another side of the sensor with each rotation (or partial
rotation) of the rotating elements. One advantage of PD sensors is
that they support a variety of fluids with substantially equal
levels of accuracy. In the prior art, such devices typically
measure large fluid flow rates and the requisite level of precision
is achieved by conventional precision machining and polishing
techniques. In fact, components must sometimes be matched to ensure
minimal clearances of the rotating elements and inner housing
geometry. Such conventional PD sensors, however, are not
well-suited for use in high-precision medical fluid delivery
systems. For example, a commercial infusion pump may require the
ability to deliver fluids over a wide range of delivery rates
(e.g., 4 logs), including very low flow rates. Moreover,
conventional manufacturing techniques tend to be expensive and,
therefore, are not well-suited for use in manufacturing disposable
items.
[0010] In recent years, fabrication techniques have developed that
allow for the manufacture of micro-fabricated devices. Some of such
devices are referred to as micro electromechanical system (MEMS)
devices and micro molded devices. One technique for fabricating
such devices is referred to in the art as LIGA processing. LIGA
(Lithographie Galvanoformung Abormung) was developed in Germany in
the late 1980s and translates roughly to the steps of lithography,
electroplating, and replication. LIGA allows for the formation of
relatively small, high aspect ratio components. Using this
technique, a photoresist layer (e.g., an acrylic polymer such as
polymethyl methacrylate (PMMA)) is applied to a metallized
substrate material. The photoresist layer is selectively exposed to
synchrotron radiation (high-energy X-ray radiation) via a mask
pattern to form the desired high aspect ratio walls. Thus, the
radiation "unzips" the PMMA backbone. The exposed sample is
thereafter placed in a developing solution that selectively removes
the exposed areas of PMMA. One development solution is 20% by
volume of tetrahydro 1,4-oxazine, 5% by volume 2-aminoethanol-1,
60% by volume 2-(2-butoxyethoxy)ethanol, and 15% by volume water.
The sample is thereafter electroplated; metal fills the gaps within
the PMMA to form a negative image. The PMMA is then removed using a
solvent, leaving a metal form for either immediate use or for use
as a replication master. The entire LIGA process is described in
greater detail in chapter 6, page 341 of Marc Madou, "The
Fundamentals of Microfabrication, the Science of Miniaturization,"
Second Edition (CRC Press 2001).
[0011] LIGA has been identified for use in manufacturing
micro-fabricated fluid pumps. It is believed, however, that
LIGA-based micropumps have never been made available commercially.
Cost is one substantial drawback of LIGA; it is believed that there
are relatively few synchrotron devices (e.g., 10-15 devices) in the
world. Accordingly, LIGA is fairly limited in its applicability for
directly manufacturing low cost devices.
[0012] In view of the foregoing, an improved system and method for
delivering a fluid to a patient is desired.
SUMMARY OF THE INVENTION
[0013] In one form, an improved fluid delivery system benefits from
a closed-loop control process that uses flow rate information to
ensure that the desired flow rate is substantially achieved.
Further, in one form, such a system is constructed using one or
more micro-fabrication and/or molding techniques allowing for a
cost-effective, disposable administration set.
[0014] Briefly described, a system for delivering fluid at a
desired flow rate from a reservoir to a delivery point associated
with a patient, embodying aspects of the invention, includes a
delivery channel between the reservoir and the delivery point
through which the fluid is delivered to the patient. A pump is
associated with the delivery channel for operatively delivering the
fluid to the delivery point at an adjustable output rate. A flow
sensor is located along the delivery channel for sensing a flow of
the fluid in the delivery channel and for generating a flow rate
signal indicative of a rate of flow of the fluid in the delivery
channel. The flow sensor comprises a positive displacement flow
sensor. A controller controls the pump. The controller causes
adjustments to the output rate of the pump as a function of the
flow rate signal whereby the desired flow rate is substantially
achieved.
[0015] In another aspect, the invention relates to a closed-loop
fluid delivery system for delivering a fluid from a reservoir to a
delivery point associated with a patient at a desired delivery rate
via an administration tube. The closed-loop fluid delivery system
includes fluid delivery means located along the administration tube
for operatively supplying the fluid to the delivery point at a
controllable output rate. A positive displacement flow sensing
means is located between the fluid delivery means and the delivery
point for sensing an actual flow rate of the fluid in the delivery
channel and for generating a flow rate signal indicative of the
actual flow rate of the fluid in the delivery channel. A control
means associated with the fluid delivery means receives and is
responsive to the flow rate signal for adjusting the output rate of
the fluid delivery means such that the desired delivery rate at
which the fluid is supplied to the delivery point associated with
the patient is substantially achieved.
[0016] In still another aspect, the invention relates to a system
for delivering a fluid from a reservoir to a delivery point
associated with a patient at a desired delivery rate via an
administration tube. The system includes a delivery mechanism
operatively connected between the reservoir and the delivery point.
The delivery mechanism is constructed and arranged for selectively
delivering the fluid to the delivery point via the administration
tube at a controllable output flow rate. A closed-loop control
system controls the output flow rate of the delivery mechanism. The
closed-loop control system includes a positive displacement flow
sensor connected in-line with the administration tube for
determining an actual flow rate of the fluid in the administration
tube and for providing an flow rate indication reflecting the
actual flow rate. A reader associated with the positive
displacement flow sensor receives the flow rate indication and
provides a flow control signal reflecting the flow rate indication.
A controller associated with the delivery mechanism receives and is
responsive to the flow control signal for controlling the output
flow rate of the delivery mechanism as a function of the flow
control signal such that the output flow rate is substantially
equal to the desired delivery rate.
[0017] In yet another aspect, the invention relates to a method of
delivering a medical fluid to a delivery point associated with a
patient at a desired delivery flow rate. The method includes
operatively connecting a reservoir to a delivery mechanism. The
reservoir contains the medical fluid to be delivered to the
delivery point. The delivery mechanism is operatively connected to
an administration tube. The administration tube is in fluid
communication with the delivery point. The delivery mechanism
receives the medical fluid from the reservoir and supplies the
medical fluid to the delivery point via the administration tube at
an output flow rate. The output flow rate of the medical fluid in
the administration tube is sensed using a positive displacement
flow sensor. The sensed output flow rate of the medical fluid is
compared with the desired delivery flow rate. The delivery
mechanism is controlled such that the output flow rate
substantially corresponds to the desired delivery flow rate.
[0018] In another aspect, the invention relates to a closed-loop
flow control system for controlling a medical fluid delivery
system. The medical fluid delivery system delivers a fluid from a
reservoir to a delivery point associated with a patient at a
desired delivery rate via an administration tube. The medical fluid
delivery system includes a delivery mechanism operatively connected
between the reservoir and the delivery point. The delivery
mechanism is constructed and arranged for delivering the fluid to
the delivery point via the administration tube at a controllable
output flow rate. The closed-loop flow control system includes a
positive displacement flow sensor connected in-line with the
administration tube for determining an actual flow rate of the
fluid in the administration tube and for providing an flow rate
indication reflecting the actual flow rate. A reader associated
with the positive displacement flow sensor receives the flow rate
indication and provides a flow control signal reflecting the flow
rate indication. A controller associated with the delivery
mechanism receives and is responsive to the flow control signal for
controlling the output flow rate of the delivery mechanism as a
function of the flow control signal such that the output flow rate
is substantially equal to the desired delivery rate.
[0019] In still another aspect, the invention relates to a method
of detecting a blockage in a medical fluid delivery system arranged
for delivering a medical fluid to a delivery point associated with
a patient at a desired flow rate. The method includes operatively
connecting a reservoir to a delivery mechanism. The reservoir
contains the medical fluid to be delivered to the delivery point.
The delivery mechanism is operatively connected to an
administration tube that is in fluid communication with the
delivery point. The delivery mechanism receives the medical fluid
from the reservoir and supplies the medical fluid to the delivery
point via the administration tube at an output flow rate. The
output flow rate of the medical fluid in the administration tube is
sensed. A determination is made whether the sensed output flow rate
is indicative of a blockage in the administration tube. An alarm
signal is provided if it is determined that the sensed output flow
rate indicates that the administration tube is blocked.
[0020] In yet another aspect, the invention relates to an
administration set for use in connection with a fluid delivery
system that is arranged for delivering a fluid from a reservoir to
a delivery point associated with a patient at a desired delivery
rate. The fluid delivery system includes a pump having an output
rate for delivering fluid from the reservoir to the delivery point
and a controller for adjusting the output rate of the pump such
that the desired delivery rate is substantially achieved. The
administration set includes an administration tube for providing
fluid communication between the reservoir and the delivery point. A
positive displacement flow sensor is located along the
administration tube and is sized and shaped for being positioned in
fluid communication with the fluid within the administration tube.
The positive displacement flow sensor senses a rate of flow of the
fluid in the administration tube and generates a flow rate signal
that is indicative of the sensed rate of flow of the fluid in the
administration tube such that the controller adjusts the output
rate of the pump as a function of the flow rate signal.
[0021] In another form, the invention relates to a positive
displacement flow sensor for use in connection with a medical fluid
infusion system that includes an administration set having an
administration tube. The positive displacement flow sensor
comprises a housing having an inlet port and an outlet port. The
inlet and outlet ports are operatively connected to the
administration tube. A first rotor is positioned within the housing
between the inlet port and the outlet port. A second rotor is
positioned within the housing between the inlet port and the outlet
port. The second rotor is positioned adjacent to the first rotor,
and the first and second rotors are constructed and arranged to
rotate in response to a flow of medical fluid in the administration
tube for detecting flow of the medical fluid in the administration
tube. A cover encloses the housing such that when the medical fluid
flows into the inlet port it causes the first rotor to rotate and
thereafter the medical fluid exits through the outlet port.
[0022] Alternatively, the invention may comprise various other
devices, methods, and systems.
[0023] Other objects and features will be in part apparent and in
part pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates one embodiment of an infusion pump
suitable for use in connection with aspects of the invention.
[0025] FIG. 2 is a block diagram of one embodiment of a closed-loop
flow control system suitable for use in connection with an medical
fluid infusion pump, such as the infusion pump of FIG. 1, according
to aspects of the invention.
[0026] FIG. 3A is a flow chart that illustrates an exemplary method
of delivering a fluid to a patient in accordance with a closed-loop
flow control process, suitable for use in connection with aspects
of the invention.
[0027] FIG. 3B is a flow chart that illustrates an exemplary method
of detecting and reporting a blockage/occlusion in an infusion
system, in accordance with aspects of the invention.
[0028] FIG. 4A is a schematic representation of a top view of one
embodiment of a flow sensor suitable for use in connection with a
closed-loop flow control system, such as the system of FIG. 2.
[0029] FIG. 4B is a schematic representation of a side view of one
embodiment of a flow sensor suitable for use in connection with a
closed-loop flow control system, such as the system of in FIG.
2.
[0030] FIG. 5 illustrates an exemplary process of manufacturing a
positive displacement flow sensor using a high aspect ratio
lithographic process.
[0031] FIG. 6 illustrates an exemplary process of manufacturing a
positive displacement flow sensor using a deep reactive ion etching
sequence.
[0032] FIG. 7 is a top view of a cap piece, suitable for use in
connection with a positive displacement flow rate sensor, in
accordance with aspects of the present invention.
[0033] Corresponding reference characters indicate corresponding
parts throughout the drawings.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0034] Referring now to the drawings, FIG. 1 illustrates one
embodiment of an infusion pump 100 suitable for use in connection
with aspects of the present invention. In the illustrated example,
the infusion pump 100 comprises a syringe-type infusion pump.
Infusion pump 100 includes a housing 102, a display screen 104, and
a control panel 106. The control panel 106 and the display screen
are used to enter set-point data for operating infusion pump 100
and for monitoring the operation of pump 100.
[0035] The infusion pump 100 also includes a syringe barrel 108 for
holding a medical fluid to be administered. A barrel bracket 110
attaches the syringe barrel 108 is attached to the housing 102. A
movable syringe driver 112 is also attached to housing 102 and is
positioned in engagement with a syringe plunger 114. A driving
mechanism within housing 102 is constructed and arranged so that
the movable syringe driver 112 can drive syringe plunger 114 into
(or out of) syringe barrel 108 in a controlled direction along
barrel 108.
[0036] Operationally, a user loads a desired amount of the fluid to
be administered into syringe barrel 108. Syringe barrel 108 is
mounted to housing 102 via bracket 110 and plunger 114 is moved
into position within barrel 108. Infusion pump 100 is attached to a
patient 120 (e.g., a human patient or a veterinary patient) via a
channel such as an intravenous PVC administration tube 122. The
user enters the desired administration program on control panel 106
and infusion pump 100 controls a movement of plunger 114 via driver
112 to deliver the fluid to the patient at a programmed delivery
rate corresponding to the administration program.
[0037] To this point, the description of infusion pump 100 and its
operation in connection with patient 120 has been generally in
accordance with known infusion systems. In other words, fluid
delivery is controlled in an open-loop fashion-based on a desired
set point without regard to actual flow rates. Line 124
diagramatically illustrates a closed-loop information feedback path
from a flow rate sensor 126 that is positioned for detecting a flow
rate in tube 122 at a point between infusion pump 100 and patient
120. Closed loop control using such flow information in a feedback
path is discussed in greater detail in connection with FIG. 2.
Also, and as also discussed in greater detail below, aspects of a
sensed flow information feedback system can be used for occlusion
detection instead of or in addition to flow rate control.
[0038] FIG. 2 is a block diagram that schematically illustrates one
embodiment of a closed-loop flow control system suitable for use in
connection with an medical fluid infusion pump, such as a
volumetric or ambulatory type pump. It should be understood that a
syringe pump does not "draw" from a reservoir. Rather, as shown in
FIG. 1, the plunger of a syringe pump acts upon the reservoir to
output fluid to the patient. For present purposes, such differences
between a syringe type pumps and volumetric and ambulatory type
pumps are not substantial, and aspects of the invention may be
employed with each of these types of infusion pumps.
[0039] In particular, FIG. 2 illustrates a fluid reservoir 202
connected to an administration tube 204. Arrows 206 indicate that a
fluid flows in the administration tube 204 into the patient.
Administration tube 204 is operatively connected to an infusion
pump system 208 that is positioned along the administration tube
204. It should be understood that the position of the infusion pump
system 208 and the nature and type of connection between infusion
pump 208 and administration tube 204 will often depend, at least in
part, on the particular type of infusion pump used. In the
illustrated embodiment, infusion pump 208 includes a pumping
delivery mechanism 210. As will be explained in more detail below,
there are a variety of pumping mechanisms that may be employed. For
example, the pumping mechanism 210 may comprise a syringe driver
driving a syringe plunger in a syringe-type infusion pump. For
present purposes, it is sufficient to note that the pumping
mechanism 210 is controllable/adjustable for controlling/adjusting
a flow rate of the fluid within administration tube 204 to conform
with a desired flow rate.
[0040] A flow rate sensor 212 is located in-line with
administration tube 204 and receives the fluid through pumping
mechanism 210. The flow rate sensor 212 preferably includes an
inlet port 214 and an outlet port 216. The inlet port 214 receives
flowing fluid at the flow rate provided by pumping mechanism 210
and provides flowing fluid at its output port 216. In one
embodiment, administration tube 204 comprises a plurality of IV
tube pieces. A first piece of IV tube connects pumping mechanism
210 to input port 214 and a second piece of IV tube connects output
port 216 to a delivery point associated with a patient 220. Other
flow sensing arrangements are possible. For example, flow rate
sensor 212 could be located entirely within the IV tube.
[0041] It should be understood that, in a typical continuous
infusion pump, fluid runs from a reservoir to an access device
through an administration set, flow rate may be measured at any
convenient point along the path because the flow rate is the
same--upstream or downstream of the pump. For example, the flow
rate in administration tube 204 of FIG. 2 just below fluid
reservoir 202 is equal to the flow rate at input port 214, as well
as at output port 216. Some infusion pumps (e.g., metering and
discontinuous systems), however, fill a defined volume of fluid
from a reservoir, and thereafter pump that fluid out, over time,
according to the delivery profile. Further, an amount of compliance
may exist within a disposable administration set. Therefore, in
many applications there will be value in locating the flow rate
sensor downstream of the pump, and closer to the patient.
[0042] In one embodiment, fluid reservoir 202, tube 204 and flow
rate sensor 212 comprise part of a disposable administration set
that is mounted in infusion pump system 208. It should be
understood that a disposable set could include a variety of
components including, for example, valves (e.g., normally closed
valves), specialized pumping complements, and the like. Further,
the set can include a reservoir; or the reservoir can be separate
and integrated with the set through a spike or other
connection.
[0043] The flow rate sensor 212 provides an indication of an actual
rate of flow within administration tube 204. In one embodiment,
flow rate sensor 212 is a positive displacement flow sensor for
providing a flow rate signal 224 representing the actual flow rate
of fluid flowing in administration tube 204. It is to be understood
that there are a variety of ways that flow rate sensor 212 could
provide the flow rate signal 224. For example, flow rate sensor 212
can be constructed such that a varying optical contrast or
electrical signal is generated by the flow of fluid. Exemplary
structures and methods for providing such a flow rate signal are
discussed in greater detail below. Further, in one embodiment, flow
rate sensor 212 comprises a passive device, having no electrical
connections thereto.
[0044] A reader 230, such as an optical or electrical signal
detector, is preferably positioned adjacent flow rate sensor 212
such that it can receive/detect flow rate signal 224. In turn, the
reader 230 communicates the detected flow rate signal 224 to a
controller 232 via a communication path. In particular, reader 230
receives flow rate signal 224 from flow rate sensor 212 and
supplies a flow control signal 234 to the controller 232. It should
be understood that the flow control signal 234 preferably provides
substantially the same information as the flow rate signal 224--an
indication of the actual flow rate of fluid in tube 204. For
example, in one embodiment, the flow control signal 234 comprises
one or more pulses. In such an embodiment, controller 232 is
programmed to interpret each pulse as corresponding to a fixed
volume of fluid flowing through sensor 216. Accordingly, controller
232 can determine the actual flow rate sensed in the administration
tube as a function of the number of pulses received from reader
230. In such an embodiment, an indication of the cumulative flow
volume delivered is provided by the number of pulses, and an
indication of the instantaneous flow rate is determined by the time
period of the pulses.
[0045] In one embodiment, the communication path between reader 230
and controller 232 comprises a wired communication channel 236. In
another embodiment, the communication path comprises a wireless
(e.g., IR, RF, and/or the like) communication channel 238. The
wireless channel 238 may be advantageous, for instance, in systems
in which flow rate sensor 212 and/or reader 230 are located at a
distance from controller 232 and/or when physical connectivity is
undesirable. One exemplary wireless communication channel uses
Bluetooth.TM. wireless technology. Bluetooth.TM. is a wireless
specification from a trade association, Bluetooth SIG, Inc. In
general, it is a low cost and low power specification, operating in
the unlicensed 2.4 GHz spectrum, and using spread spectrum
frequency hopping techniques.
[0046] The controller 232 is operatively connected for
automatically controlling pumping mechanism 210. This is
illustrated schematically as a pump control signal 240 on line 242
between controller 232 and pump 210. It should be understood that a
wide variety of devices may serve as controller 232. For example,
controller 232 may be embodied by a processor (e.g., a
microprocessor or microcontroller), discrete logic components,
application specific circuitry, programmable logic devices, analog
circuitry, or combinations thereof. Further, a motor-based pump
could be controlled by adjusting the motor rotation rate or a cycle
time associated with the motor. If a certain type of MEMS-based
pump is employed, for example, control may be achieved by adjusting
the frequency of a piezo oscillation.
[0047] The system can also be configured to provide a status
signal. For example, controller 232 provides a status signal, such
as an alarm signal 250, on a line 252 (and/or a wireless channel
256) to a status monitoring device 254. In one form, the status
monitoring device 254 comprises an audible alarm system for
providing an audible alarm in the event of a malfunction. Status
monitoring device 254 may also comprise other audio, visual,
audio-visual, and vibrating devices such as, for example, CRT
monitors, pagers, horns, buzzers, speakers, computers, portable
telephones (e.g, cellular telephones), personal digital assistants
(PDAs), and the like. By way of one specific example, controller
232 provides an alarm signal to cause an audible and/or visual
alarm to be activated if controller 232 is unable to control pump
210 to achieve a desired flow rate. Such a condition can occur if
an occlusion or blockage in administration tube 204 prevents an
adequate flow of fluid to patient 220. Such a blockage may include
complete blockages, as well as partial blockages affecting flow
rate. Alarm conditions can be programmed to occur for a variety of
other reasons, such as when the fluid supply in reservoir 202
becomes depleted to a level at which pump 210 can no longer deliver
the fluid at the desired delivery rate. It should be appreciated,
however, that status indications other than failures or improper
operational conditions may also be provided. For example, a status
signal could be used to provide an indication at a remote
monitoring station of the current sensed flow rate or another
indication regarding the operation of the system. Similarly, sensed
flow rate information can be used to anticipate when the fluid
supply will be depleted, such that a suitable indication is
provided in advance of such event.
[0048] An operational example of the closed-loop flow control
system of FIG. 2 is now described. A patient is operatively
connected to administration tube 204 (e.g., via a catheter inserted
at a desired delivery point associated with the patient). Reservoir
202 contains a fluid to be administered to the patient and is
operatively connected to administration tube 204 and pumping
mechanism 210. A desired delivery rate is entered on a control
panel associated with the pump (see, e.g., FIG. 1). In FIG. 1, for
example, it is to be understood that control panel 106 and display
104 cooperate to provide a user interface to facilitate entering
set-point data for use by pump 100. In the present embodiment,
controller 232 uses set-point data representative of the desired
delivery rate in combination with the flow control signal 234 for
controlling the system.
[0049] As pump 210 causes the fluid to be delivered to patient 220
via tube 204, flow rate sensor 212 senses the flow rate of the
fluid in tube 204 and periodically (or continuously) outputs flow
rate signal 224 which is received/detected by reader 230. For
example, if flow rate sensor 212 is constructed and arranged to
provide an optical signal indication of the actual flow rate of
fluid, reader 230 comprises an optical reader for detecting the
optical signal indication generated by flow rate sensor 212. As a
further example, in one embodiment reader 230 illuminates flow rate
sensor 212 with a light and examines the light reflected by the
flow rate sensor to determine the flow rate signal 224.
[0050] Reader 230 thereafter provides flow control signal 234 to
controller 232. This flow control signal 234 is functionally
related to the flow rate signal 224 and, therefore, provides an
indication of the actual flow rate of fluid into patient 220. As
such, controller 232 is able to monitor the actual flow rate of
fluid in tube 204. With this information, controller 232 is able
complete a closed-loop control path with pump 210. In other words,
controller 232 executes a control scheme for generating the pump
control signal 240 to adjust the pumping action of pump 210 so that
the actual flow rate, as measured by flow rate sensor 212, more
closely matches the desired flow rate. It should be understood that
a variety of control schemes may be employed, depending upon goals.
For example, in some applications it may be desirable to control
the pump to provide a high degree of accuracy in terms of
instantaneous flow rate. In other applications, it may be desirable
to control the pump in terms of the total volume of fluid infused.
In still other applications, it may be desirable to optimize
control in terms of both instantaneous flow rate and total volume.
Other variations are possible.
[0051] The degree of accuracy with respect to controlling flow rate
can be varied, depending upon usage. For example, if gross accuracy
(e.g., +/-15%) is acceptable, the closed-loop feedback control
could be disabled in software (e.g., via a control panel input) or
by eliminating flow rate sensor 212 from the administration set.
Gross accuracy can also be achieved by adjusting control
parameters, such as sample rates and so on. On the other hand, if a
relatively high degree of accuracy is desired (e.g., +/-2%), the
controller is preferably programmed/configured to tightly control
the pumping action of pump 210. It should be appreciated,
therefore, that an infusion pump system, embodying aspects of the
invention can be reconfigured to accommodate a wide variety of
needs, thereby improving the usefulness of such a system.
[0052] As explained above, such a closed-loop flow control system
has been heretofore unknown in the art. Among the advantages of
such a system is the ability to more closely control the flow of
fluid to patient 220. In some situations, a particular precise flow
rate is valuable. Further, flow rate sensor 212 is compatible with
a wide variety of fluid delivery profiles, including constant
profiles, pulsatile profiles, and other time-varying and
non-uniform delivery profiles. With such profiles, including
pulsatile flow profiles, the pump may need to ramp up and/or down
from its running rate faster than with other delivery profiles.
Thus, knowledge of actual flow rate helps to ensure tighter control
of the profile. For example, controller 232 can monitor the actual
flow rate in tube 204 (as detected by flow rate sensor 212) over
time and control the pumping action of pump 210 to ensure that the
actual flow rate conforms to the desired delivery profile.
Moreover, closed-loop control allows infusion pumps to be
manufactured with a greater degree of flexibility in terms of
manufacturing tolerances and the like. In some prior art systems,
delivery accuracy is attempted by tightly controlling the
tolerances of the mechanical pumping components and mechanisms,
which can be expensive. With flow rate feedback control according
to aspects of the invention, on the other hand, infusion pumps can
be made with less precise (and therefore less expensive) components
and mechanisms, yet still achieve a high degree of accuracy in
terms of fluid delivery rate control.
[0053] It should be further appreciated that the tubing would not
need to be as precise and the integration of the pump and
disposable components would be less dependent upon the materials
used in the disposable components. For example, PVC tubing provides
certain advantages in prior art systems, so the design of the
infusion pump may need to be tailored to be compatible with such
tubing. This type of engineering expense may be eliminated if PVC
tubing is no longer necessary.
[0054] Further, knowing the actual rate of flow in tube 204 with a
relatively high degree of precision also allows the system to
provide a highly accurate and fast occlusion detection capability.
It should be appreciated that a blockage--a complete blockage
and/or a partial blockage--between the fluid reservoir and the
delivery point can result in an unacceptably low rate of flow. Such
blockages are sometimes referred to herein as occlusions but may be
caused by a variety of conditions, including a kink in tube 204.
Prior art attempts to detect occlusions rely on pressure sensing,
which requires a relatively large change in the pressure in the
tube to be detected. A disadvantage of pressure sensing is that it
may take a long time for the pressure in the tubing to increase to
a detectable level. This is especially true when delivering fluids
at a relatively low delivery rate. For example, a blockage (e.g., a
complete and/or partial blockage) associated with a 0.1 ml/hour
delivery rate could take two hours or more to be detected with a
typical prior art pump. Further, if the sensitivity of a pressure
sensing system is increased to reduce response times, more false
alarms are likely to be experienced.
[0055] In contrast, a closed-loop flow controller according to
aspects of the present invention is able to rapidly detect
blockages (complete and/or non-complete blockages, even at very low
delivery rates) because flow rate sensor 212 detects an actual flow
rate and does not require a pressure build up. One embodiment of
flow rate sensor 212 is capable of providing accurate measurements
(e.g., better than +/-5%) over four logs of range. For example, a
pump using such a flow sensor supplies fluid from about 0.1 ml/hr
up to about 2000 ml/hr. Thus, flow rate sensing and occlusion
detection is possible at low flow rates, as well as at higher flow
rates.
[0056] For convenience, the foregoing descriptions of FIGS. 1 and 2
have been generally provided in terms of embodiments comprising
syringe-type infusion pumps and ambulatory and volumetric pumps.
One type of prior art syringe pump is more fully described in
commonly assigned U.S. Pat. No. 5,533,981. It should be understood
that, with the benefit of the present disclosure, closed-loop
control systems and methods may be adapted for use with other types
of medical fluid delivery systems. Such systems include, for
example, rotary and linear peristaltic-type pump systems,
valve-type pump systems, piezoelectric pump systems, pressure-based
pump systems, and various motor and/or valve driven systems.
[0057] A peristaltic-type pump manipulates the IV administration
tube to achieve a desired flow rate. In one embodiment, a
peristaltic-type pump employs an array of cams or similar devices
that are angularly spaced from each other. The cams drive cam
followers that are connected to pressure fingers. These elements
cooperate to impart a linear wave motion on the pressure fingers to
apply force to the IV tube. This force imparts motion to the fluid
in the IV tube, thereby propelling the fluid. Other forms of
peristaltic-type pumps use different pressure means such as, for
example, rollers.
[0058] Some valve-type pumps employ pumping chambers and upstream
and downstream valving (e.g., electronically controlled valves) to
sequentially impart a propulsion force to the fluid to be delivered
to the patient. It is also possible to use a valve in connection
with a gravity-fed delivery system in which gravity provides the
motivating force and one or more valves are used to control the
flow rate. Piezoelectric pumps control pumping by varying the
magnitude of an applied voltage step. Pressure-based pumps adjust
flow rate by controlling the pressure applied to a fluid reservoir
(sometimes called "bag squeezer" systems).
[0059] Further, the closed-loop control systems and methods
described herein may be used in ambulatory infusion pump systems
and volumetric infusion pump systems. It should also be understood
that the components illustrated in FIG. 2 are grouped for
convenience. For example, the status monitor device 254 could be
made integral with the rest of the infusion pump system 208.
Likewise, reservoir 202 could be integral with the pump unit or
separate. For example, in a syringe pump, the barrel of the syringe
acts as a reservoir, but is physically mounted to the infusion pump
housing. In other words, with syringe pumps and pressure-based
pumps, the reservoir is typically contained within the pump
boundaries. With a volumetric or ambulatory pump, the reservoir is
generally more external to the pump boundaries.
[0060] FIG. 3A is a flow chart that illustrates an exemplary method
of delivering a fluid to a patient in accordance with a closed-loop
flow control process. As illustrated therein, a fluid reservoir
(e.g., a fluid bag) is connected to an infusion pump which, in
turn, is connected to the patient (blocks 302, 304). After a
desired delivery rate is selected (block 306), fluid delivery
begins (block 308). Periodically (or continuously) the actual flow
rate of fluid to a delivery point associated with the patient is
sensed (block 310). For example, and as explained above, a positive
displacement flow rate sensor located in-line between the patient
and the pump can be used to sense actual fluid flow and provide a
flow rate indication to a control device. The actual flow rate is
compared to the desired delivery rate at block 312. If the actual
flow rate is appreciably greater than desired (block 314), the
infusion pump is adjusted such that its output rate is reduced
(block 316), thereby reducing the actual delivery rate to more
closely match the desired flow rate. If, however, the actual flow
rate is appreciably less than the desired rate (block 318), the
infusion pump is adjusted such that its output rate is increased
(block 320), thereby increasing the actual delivery rate.
[0061] In one embodiment, the method also includes using a
disposable administration set that includes, for example, an
administration tube and an in-line flow rate sensor (e.g., tube 204
and flow rate sensor 212 of FIG. 2) such that, upon completing the
fluid delivery process, the administration set is discarded.
[0062] FIG. 3B is a flow chart that illustrates an exemplary method
of detecting and reporting a blockage/occlusion in an infusion
system, in accordance with aspects of the invention. In the
illustrated example, the process is similar in several aspects to
the method illustrated in FIG. 3A. At block 330, however, the
sensed actual flow rate is compared to an occlusion/blockage
threshold reference. This threshold can be a predetermined value
(e.g., a fixed number or a fixed percentage of the desired delivery
rate), or a dynamically determined value (e.g., a time varying
threshold). In the illustrated embodiment, if the sensed actual
flow rate is less than the occlusion threshold, a blockage is
declared and an alarm condition is triggered (blocks 332, 334). It
should be understood, however, that more complicated comparisons
can also be performed. For example, rather than comparing sensed
flow rate information against a threshold flow rate value, a change
in the sensed flow rate (e.g., a slope) can be determined. If the
slope exceeds a slope threshold, a blockage is declared. Further,
there may be certain infusion protocols in which zero flow is
expected for extended periods of time. In such situations, the
controller preferably accounts for this fact.
[0063] It should be appreciated that flow rate comparisons (e.g.,
block 314 or block 330) need not be referenced to a fixed value.
Rather, other flow rate comparisons are possible. Such comparisons
include comparing the flow rate to an acceptability range and/or a
time varying reference. Further the reference to which the actual
flow rate is compared may be programmed by the user or pre-existing
and used in connection with an algorithm or treatment protocol.
[0064] FIGS. 4A and 4B are schematic representations of one
embodiment of a flow rate sensor 402 suitable for use in connection
with a closed-loop flow control system, such as the pump system 208
illustrated in FIG. 2. Flow rate sensor 402 preferably comprises a
micro-fabricated MEMS device or a similar micro-molded device
(e.g., an assembly of micro-molded components). Exemplary
fabrication techniques for manufacturing such a flow sensor are
discussed below. Flow rate sensor 402 has an inlet port 404 and an
outlet port 406 and is preferably constructed and arranged to fit
in-line with an administration tube (e.g., tube 204 of FIG. 2) such
that the fluid flowing in the tube to the patient also flows
through sensor 402.
[0065] In the illustrated embodiment, flow rate sensor 402
comprises a positive displacement flow sensor. In general, such
sensors operate by allowing known volumes of fluid to be
transferred during each rotation. The particular flow sensor
illustrated comprises a two inter-meshed gears/impellers 408, 410
(sometimes referred to herein as rotors or rotating members). In
the illustrated example, each impeller has six lobes, but other
sizes and shapes may be used. As illustrated, the impellers are
held on pins within a housing 412. The housing is preferably sized
and shaped for being used in-line with an administration tube
(e.g., tube 204 of FIG. 2). In one embodiment, the flow sensor
comprises four components: the first impeller 408; the second
impeller 410; the housing (including the pins on which the
impellers are mounted and rotate); and a cover 416 sized and shaped
for sealing the unit such that entry and exit must be had via inlet
404 and outlet 406, respectively. The cover, housing, and impellers
are also preferably sized and shaped such that substantially all
fluid passing through the sensor passes by operation of first and
second impellers 408 and 410 in a positive displacement
fashion.
[0066] The cover 416 may be clear so that the operation of the
sensor may be monitored by an optical reader. If the flow sensor
402 is constructed primarily out of a silicon or silicon-based
material, cover 416 preferably comprises a flat, clear, and heat
resistant material, such as, for example Pyrex.RTM.. If flow sensor
402 is constructed primarily out of plastic, a flat plastic cover
may be used. Laser welding techniques or ultrasonic welding may be
used to seal the cap to the base. Preferably, in ultrasonic welding
applications, energy directors are also used.
[0067] By way of further example, the alignment pins that hold the
impellers in place could be part of the cap and/or the base.
Further, the base and/or cap could include recessed holes to accept
pins that are part of the impellers (i.e., the impellers have pins
that extrude from their top or bottom).
[0068] In operation, flowing fluid causes impellers 408, 410 to
rotate and to transfer a known volume of fluid from the input port
404 side to the outlet port 406 side. Optical or other techniques
are used to count rotations (or partial rotations). Such
information is indicative of flow rate because each rotation
relates to a known volume of fluid. Therefore, flow rate sensor 402
effectively provides a flow rate signal that is indicative of an
actual rate of fluid flow through the sensor.
[0069] One method of providing an optical indication is to mark one
or more of the lobes of one or both impellers 408, 410 such that an
optical contrast is created. An optical reader then optically
detects when the marked lobe has moved, thereby providing an
indication of a rotation. Similarly, the reader may be configured
to illuminate flow rate sensor 402 (e.g., using an LED) and to
thereafter examine the light reflected to detect the output signal
(e.g., flow rate signal from flow rate sensor 212 in FIG. 2). In
optical detection approaches described herein, the flow sensor
itself is preferably passive; the reader supplies the light and
processes the returned light to provide a signal to the controller.
A controller (e.g., controller 232) can use this information to
determine an actual flow rate through flow rate sensor 402. This is
so because each rotation of the impellers results in a known volume
of fluid passing through the impellers. FIG. 7, which is discussed
in greater detail below, illustrates one embodiment of a rotational
measurement technique that is particularly suited for use when the
flow rate sensor uses a transparent plastic cap.
[0070] Other methods of detecting rotation are possible. For
example, an impeller can include a magnetic component that
generates a detectable magnetic field that changes as the impeller
rotates (e.g., an electrical variation caused by the rotation of
the impeller). Such a changing magnetic field would provide a flow
rate signal that could be detected by, for example, a Hall sensor
or similar device.
[0071] As another alternative, the reader may be made integral with
the flow rate sensor itself. For example, a semiconductor device
may be used (e.g., a semiconductor that forms or is part of the
cap). The rotation rate is detected electronically by the
semiconductor device and the output signal is provided directly to
the controller, without the use of a reader that is separate from
the flow rate sensor.
[0072] In one embodiment, flow rate sensor 402 is constructed using
relatively low-cost, precision MEMS and/or micro-molding techniques
so that the sensor can be used in connection with a cost-effective,
disposable administration set suitable for use in delivering a
medical fluid. Thus, the components that do not come directly into
contact with the fluid and/or patient (e.g., the pump, controller,
and so on) are reusable, while the parts that come into contact
with the fluid and/or patient are disposable. In another
embodiment, the administration set and infusion pump are both
designed to be disposable (e.g., disposed after each use). Two
exemplary manufacturing techniques are discussed in greater detail
below. It should also be understood that other types of flow
sensors and other positive displacement arrangements may be used,
and that the illustrated flow rate sensor 402 is provided for
exemplary purposes. For example, other configurations of positive
displacement flow sensors may use a different number of lobes
and/or impellers, or have impellers of varying sizes and
shapes--including asymmetrical impellers.
[0073] FIGS. 5 and 6 illustrate two exemplary methods of
manufacturing a flow sensor, such as flow rate sensor 402, suitable
for use in connection with aspects of the present invention. More
particularly, FIG. 5 illustrates the pertinent steps of
manufacturing a positive displacement flow sensor using a high
aspect ratio lithographic process which is sometimes referred to
herein as ultra-violet LIGA (UV LIGA) or deep ultra-violet LIGA
(DUV LIGA). FIG. 6 illustrates the pertinent steps of manufacturing
a positive displacement flow sensor using a deep reactive ion
etching sequence (deep RIE).
[0074] UV LIGA typically results in plastic parts. Deep RIE uses
silicon or silicon carbide. Thus, the materials base for each
approach differs. Further, both processes may be used to
manufacture parts. The UV LIGA approach, however, may be more
advantageously practiced if it is used to create replication
masters that are used as molds or mold inserts.
[0075] Referring first to FIG. 5, generally stated, the UV LIGA
approach comprises four steps 502, 504, 506, and 508. Step 502
involves preparation and exposure. Step 504 involves developing.
Step 506 involves electroplating. Step 508 involves removing any
remaining photoresist.
[0076] At step 502, a mask 510 (e.g., a quartz glass mask with
chrome patterns) is placed above a workpiece to be exposed. The
workpiece to be exposed comprises a substrate layer 512 (e.g., a
silicon wafer). Prior to exposure, a seed layer 514 is attached to
the substrate 512 by a deposition process. A photoimageable
material, such as an epoxy-based negative photoresist layer 516
(e.g., SU-8) is added on top of substrate 512 (e.g., deposited from
a bottle and spin coated). The mask 510 comprises a two-dimensional
pattern that is subsequently transferred down to the SU-8 layer.
The seed layer 514 is typically nickel, gold, copper, or
nickel-ferrite (NiFe). Below seed layer 514 there may also be a
"flash" or very thin layer of a refractory metal such as chromium,
titanium, or tantalum to act as an adhesion layer. Typically, the
flash layer is on the order of 50-500A, and the seed layer is about
400-5000A. Additional information regarding this process may be
found at chapter 5 of the "Handbook of Microlithography,
Micromachining, and Microfabrication, Volume 2 Micromachining and
Microfabrication," available from SPIE Press 1997. The photoresist
layer is selectively exposed to deep UV radiation through the
pattern of mask 510.
[0077] At step 504, the exposed photoresist layer 516 is developed.
The developing solution is a solvent and generally depends on the
photoresist being used and whether the photoresist is a positive or
negative tone. This development process removes the portions of
photoresist layer 516 that were exposed to the UV radiation,
leaving structures 530 and 532. At step 506, the remaining
structure is electroplated (up from seed layer 514), filling the
exposed portions 536 removed during the development process. At
step 508, the remaining portions of the photoresist (e.g.,
structures 530, 532) are developed/etched away, leaving the
electroplated structures 540, which may be lifted off of the wafer
substrate.
[0078] It should be appreciated that a number of such electroplated
structures 540, of different sizes and shapes, could be
simultaneously formed. For example, one structure could correspond
to an impeller (e.g., impeller 408 of FIG. 4A), and another
structure could correspond to a housing (e.g., housing 412 of FIGS.
4A and 4B). These structures could thereafter be assembled to form
a flow sensor of an appropriate size and shape for use in
connection with, for example, the various methods and systems
described herein. In other words, structures can be formed for a
flow sensor housing having an inlet port and an outlet port, and
having pins for accepting first and second impellers. In one
embodiment, a clear plastic cover is bonded to the top of the
housing, thereby ensuring that substantially all fluid flowing into
the flow sensor through the inlet port exits the sensor through the
outlet port.
[0079] It should also be appreciated that, rather than directly
using the electroplated structures 540 for construction a desirable
flow sensor, the micro-fabrication processes described herein can
be used for creating molds or mold inserts (e.g., negative images
of the desired structures). One advantage of such a micro-molding
approach is that a large number of molds can be made at once,
thereby allowing for large-scale production of flow sensor
components, without the need for using the UV LIGA process other
than for creating the mold. In one embodiment, components may be
made of a plastic or similar material that is suitable for use in a
medical environment (e.g., disposable). For example, numerous
thermoplastic materials could be used (e.g., polycarbonate or
liquid crystal polymer) to mold flow sensors from the master.
[0080] One advantage of using UV-LIGA is that it does not require
the use of an expensive synchrotron radiation source. As mentioned
above, there are relatively few synchrotrons in the world. In
contrast, UV sources are more readily available and relatively
inexpensive, and masters can be created in most moderately equipped
semiconductor clean room environments.
[0081] Conventional synchrotron LIGA processes require X-Ray masks.
These masks are fabricated by starting with standard quartz/chrome
masks, with the desired patterns thereon. The patterns are
subsequently transferred onto silicon (which is transparent to
synchrotron radiation) in the form of gold or beryllium patterns,
which absorb radiation. DUV LIGA, in contrast, uses the standard
quartz/chrome mask to directly process the SU-8. Therefore, another
advantage of using UV LIGA is that the SU-8 material and mask are
believed to be less expensive than comparable materials used in
conventional synchrotron LIGA.
[0082] Referring next to FIG. 6, illustrated therein at 602, 604,
606, and 608, respectively, are pertinent steps associated with
manufacturing a positive displacement flow sensor using a deep RIE
micro-fabrication process. In general, deep RIE is a silicon-based
process in which deep reactive ion etching is applied to
selectively etch away silicon material from the workpiece. The
selectivity of the etching process is determined by
photolithographic techniques, such as those developed for
manufacturing integrated circuits. By its nature, deep RIE provides
good verticality, allowing 3-dimension structures to be established
from 2-dimension patterns.
[0083] Deep RIE provides a suitable process for manufacturing flow
sensors (either directly or by manufacturing micro-molds) for use
in connection with a closed-loop flow control system and method, in
accordance with aspects of the invention. One such flow sensor may
be created by etching silicon impellers from one substrate, and
etching an accepting housing from another substrate (or from
another part of a single substrate). The housing preferably
includes alignment pins positioned for accepting the impeller gears
so that a positive displacement arrangement is formed. The housing
also preferably includes a base having a landing. The impeller
gears are then placed on their respective rotation pins (either
manually or by an automated process). A coverslip (e.g., a clear,
heat resistant cover material such as Pyrex.RTM.) is thereafter
anodically bonded to the landing on the base. All or part of the
impellers and/or base surface may be oxidized to produce a desired
optical contrast between the respective surfaces. This optical
contrast can be used for sensing rotation of the impellers.
[0084] FIG. 6 illustrates pertinent steps of producing an impeller
and a housing for a flow sensor. Beginning at 602, a workpiece is
prepared comprising a silicon substrate 612 bonded to a base layer
614. The base layer 614 may comprise any number of materials. In
one preferred embodiment, base layer 614 comprises another silicon
wafer. This can also be done with many different types of adhesive
layers, and photoresist may be used as an adhesive layer. Other
substrate materials may be used such as, for example, silicon
carbide. A photoresist material 616 is applied on the silicon
substrate and then patterned using exposure and development steps.
Thus, the photoresist is developed to form a 2-dimensional mask
pattern so that etching selectively occurs only where desirable to
create the part being produced. This pattern is thereafter
transferred down into the base layer (e.g., silicon) using reactive
ion etching. Many commonly available photoresist materials are
suitable. It should be understood that the 2-dimensional mask
pattern could be transferred to an alternate layer, such as a
silicon nitride or silicon oxide layer.
[0085] Further, a deposited metal could serve as the etch mask.
Such a metallic etch mask would be useful in fabricating relatively
tall structures by reactive ion etching techniques. In the etching
process, the base layer (e.g., silicon) may be etched at a higher
rate than the photoresist layer is being etched (e.g., perhaps 100
times greater). Thus, a photoresist mask may be rendered effective
if the etching process is carried out extensively to fabricate tall
structures (e.g., several hundred microns deep). In fabricating
such tall structures, a metallic etch mask (etched even more
selectively than a photoresist) would be useful.
[0086] Referring still to FIG. 6, the photoresist 616 has a
2-dimension shape corresponding to the 3-dimension part being
produced. For example, if an impeller is being produced, the
photoresist has a 2-dimension shape like that of the desired
impeller. The workpiece is selectively exposed and developed so
that the exposed silicon is etched away, leaving the base layer, a
silicon structure of the desired height and shape, and the
photoresist (see 604). Thereafter, the photoresist is stripped
away, leaving the base layer and the silicon structure (see 606).
Finally, the structure is released from the base layer (see
608).
[0087] In one embodiment of a flow sensor (e.g., a positive
displacement flow sensor) manufactured using deep RIE, the silicon
parts are coated with a relatively harder material (e.g., silicon
nitride, carbon, or diamond) before the sensor is assembled.
Silicon is a hard, but brittle material. As such, a coating
improves the strength and integrity of the parts. Also, it should
be understood that, rather than manufacturing parts directly, deep
RIE can be used to fabricate molds for micro-molding flow sensors
in a relatively low-cost, high-volume manner.
[0088] In one embodiment, a micro-molded or micro-fabricated flow
sensor (e.g., a positive displacement flow sensor) is sized and
shaped for being placed in-line with an administration tube (e.g.,
tube 204) as part of a disposable administration set. In another
embodiment, such a flow sensor is integrated into an infusion set
in which the fluid supply, the pump, the administration tube, the
flow sensor, the controller and the reader are all part of a
disposable unit.
[0089] Finally, although UV LIGA and/or deep RIE are believed to be
two preferred methods for manufacturing flow sensors (or molds
therefor), other micro-fabrication techniques may be substituted.
These techniques include, for example, synchrotron LIGA and
techniques that are not yet available for exploitation.
[0090] FIG. 7 is a top view of a cap piece 700, suitable for use in
connection with a positive displacement flow rate sensor, in
accordance with aspects of the present invention. As explained
above, one method of determining flow rate using a positive
displacement flow sensor (e.g., sensor 402 of FIGS. 4A and 4B)
involves optically measuring the rotation of the impellers lobes.
For example, a small optical spot is used to mark one of the lobes.
A reader detects when the marked lobe passes a given point and can
thereby detect the rotation rate of the impeller. Because the flow
rate sensor is a positive displacement-type sensor, knowledge of
the rotation rate corresponds to the actual flow rate. A similar
technique involves a detector focused down, into the sensor, that
looks for a reflection due to an optical contrast between the base
and impeller. If the base is dark and the impeller is relatively
light in contrast to the base, most of the reflected light will
occur when a lobe passes. Such an approach generally allows a
faster detection rate than monitoring a marked lob.
[0091] FIG. 7 illustrates an alternative to using an optical spot.
As illustrated, the cap piece 700 has imposed thereupon a pattern
702 that replicates one position of the two impellers relative to
each other. In one embodiment, pattern 702 is applied to cap piece
700 with additive processes or subtractive processes, creating a
roughened surface. The pattern 702 is selected to provide an
optical contrast between pattern 702 and the impellers 704. For
example, if the impellers are a shade of white, the imposed pattern
702 is a dark shade. A relatively broad light source is applied
from above to illuminate the flow sensor. Light is reflected back
from the relatively light impeller lobes when the impellers are
exposed from behind pattern 702. Thus, as the impellers rotate, the
amount of light reflected back (e.g., to an optical detector)
varies as a function of the amount of the impeller 704 that is
exposed from under pattern 702. Thus, reflection intensity will
rise and fall to denote each partial rotation associated with a
lobe. For example, the reflected light intensity will
increase/decrease at a known number of cycles per revolution,
depending upon the number of lobes, thereby providing an indication
of the rotation rate of the sensor. Such an approach allows a less
precise optical system to be used because the entire filed may be
illuminated.
[0092] It is to be understood that the steps described herein are
not to be construed as necessarily requiring their performance in
the particular order discussed or illustrated. It is also to be
understood that additional or alternative steps may be employed. It
should be further appreciated that the novel principles and
processes disclosed herein are not limited to the particular
embodiments illustrated and described. For instance, flow sensors
having a "dual layer" nature can be fabricated (e.g., impellers
having pins on the bottom). As a more particular example, impellers
having pins fabricated on the bottom can be fabricated using DUV
LIGA by adding another layer (i.e., another SU-layer after step
506), and thereafter, exposing, developing, and electroplating. It
is also possible to reverse the order-fabricate pins first and
impellers second. Similarly, silicon etching can be used to etch
the impellers (or pins). Thereafter, turn the wafer is turned over
and attached to a base to etch pins (or impellers).
[0093] Further, traditional machining fabrication techniques may be
employed in connection with aspects of the present invention. In
particular, machining can be used in connection with DUV LIGA
processing to fabricate features of a mold that are not
dimensionally critical. Such features may include, in some
embodiments, input and output ports of a positive displacement flow
sensor. Similar, in fabricating flow sensors using silicon, a
silicon package (e.g., the silicon components and cover slip) can
be formed to fit inside a plastic housing that is fabricated by
traditional plastic fabrication techniques. Such a plastic housing
can include, for example, input and output ports. Other variations
are possible.
[0094] In view of the above, it will be seen that the several
objects of the invention are achieved and other advantageous
results attained.
[0095] When introducing elements of the present invention or the
preferred embodiment(s) thereof, the articles "a", "an", "the", and
"said" are intended to mean that there are one or more of the
elements. The terms "comprising", "including", and "having" are
intended to be inclusive and mean that there may be additional
elements other than the listed elements.
[0096] As various changes could be made in the above constructions
and methods without departing from the scope of the invention, it
is intended that all matter contained in the above description or
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
* * * * *