U.S. patent application number 13/243962 was filed with the patent office on 2012-03-08 for optical flow sensor.
This patent application is currently assigned to CareFusion 303, Inc.. Invention is credited to Paul Dewey.
Application Number | 20120059318 13/243962 |
Document ID | / |
Family ID | 41431962 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120059318 |
Kind Code |
A1 |
Dewey; Paul |
March 8, 2012 |
OPTICAL FLOW SENSOR
Abstract
A method for determining a flow rate of a fluid is provided. The
method includes heating an aliquot of the fluid at a first position
of a fluid-delivery channel, illuminating fluid in the
fluid-delivery channel at a second position downstream from the
first position, measuring an amount of light reflected from the
illuminated fluid to determine a change in the amount corresponding
to the heated aliquot passing the second position, and calculating
the flow rate of the fluid based upon a distance between the first
position and the second position and a time between the heating the
aliquot and the heated aliquot passing the second position.
Inventors: |
Dewey; Paul; (Poway,
CA) |
Assignee: |
CareFusion 303, Inc.
San Diego
CA
|
Family ID: |
41431962 |
Appl. No.: |
13/243962 |
Filed: |
September 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12142215 |
Jun 19, 2008 |
8034020 |
|
|
13243962 |
|
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Current U.S.
Class: |
604/113 ;
356/28 |
Current CPC
Class: |
A61M 2205/3306 20130101;
G01F 1/7086 20130101; A61M 5/16886 20130101; A61M 2205/368
20130101; G01F 1/7044 20130101; A61M 2205/3379 20130101 |
Class at
Publication: |
604/113 ;
356/28 |
International
Class: |
A61M 5/44 20060101
A61M005/44; G01P 3/38 20060101 G01P003/38 |
Claims
1. A method for determining a flow rate of a fluid, comprising:
heating an aliquot of the fluid at a first position of a
fluid-delivery channel; illuminating fluid in the fluid-delivery
channel at a second position downstream from the first position;
measuring an amount of light reflected from the illuminated fluid
to determine a change in the amount corresponding to the heated
aliquot passing the second position; and calculating the flow rate
of the fluid based upon a distance between the first position and
the second position and a time between the heating the aliquot and
the heated aliquot passing the second position.
2. The method according to claim 1, wherein the heating the aliquot
comprises heating the aliquot with a laser.
3. The method according to claim 1, wherein illuminating the fluid
in the fluid-delivery channel comprises illuminating the fluid with
an LED optically coupled to the fluid-delivery channel.
4. The method according to claim 1, wherein the measuring the
amount of light reflected comprises measuring the amount of light
reflected with a photodetector optically coupled to the
fluid-delivery channel.
5. The method according to claim 1, wherein the fluid is
opaque.
6. A medicinal fluid administering system, comprising: a fluid
delivery system for administering a fluid to a patient; and an
optical flow sensor for measuring a rate of the fluid administered
to the patient, the optical flow sensor comprising: a laser
configured to heat an aliquot of the fluid in an adjacent
fluid-delivery channel; and a sensor disposed adjacent to the
fluid-delivery channel downstream from the laser, the sensor
configured to illuminate the fluid in the fluid-delivery channel,
to collect reflected light from the illuminated fluid, and to
determine when the heated aliquot passes the sensor based upon an
amount of the reflected light.
7. The medicinal fluid administering system according to claim 6,
wherein the optical flow sensor further comprises a processor
configured to calculate a flow rate of the fluid in the
fluid-delivery channel based upon a time between the laser heating
the aliquot and the sensor determining when the heated aliquot
passes the sensor.
8. The medicinal fluid administering system according to claim 6,
wherein the fluid delivery system comprises a reservoir configured
to store the fluid, a pump configured to pump the fluid from the
reservoir, and delivery path configured to deliver the fluid to the
patient.
9. The medicinal fluid administering system according to claim 8,
further comprising a controller operably coupled to the optical
flow sensor and to the pump, wherein the controller is configured
to adjust a pumping speed of the pump based upon a calculated flow
rate of the fluid in the fluid-delivery channel.
10. The medicinal fluid administering system according to claim 6,
wherein the sensor comprises an LED optically coupled to the
fluid-delivery channel by a first fiber and a photodetector
optically coupled to the fluid-delivery channel by a second
fiber.
11. The medicinal fluid administering system according to claim 10,
wherein the first fiber and the second fiber are disposed on a same
side of the fluid-delivery channel.
12. The medicinal fluid administering system according to claim 6,
wherein the sensor comprises one or more lenses configured to
optically couple an LED with the fluid-delivery channel and a
photodetector with the fluid-delivery channel.
13. The medicinal fluid administering system according to claim 12,
wherein the LED and the photodetector are disposed on a same side
of the fluid-delivery channel.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a divisional of, claims the
benefit of priority under 35 U.S.C. .sctn.121 from, U.S. patent
application Ser. No. 12/142,215 entitled "Optical Flow Sensor,"
filed on Jun. 19, 2008, the disclosure of which is hereby
incorporated by reference in its entirety for all purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
FIELD
[0003] Embodiments of the present invention generally relate to
flow sensors and, in particular, relate to optical flow
sensors.
BACKGROUND
[0004] Intravenous ("IV") fluid delivery systems are used to
deliver fluids (e.g., medicines, transfusions, etc.) to patients at
controlled rates. To accurately control IV fluid delivery, an
open-loop control system may be used. An open-loop control system
includes a processor that varies the speed of a relatively accurate
fluid pump used to infuse a medicinal fluid into a patient based
upon a predefined algorithm and as a function of various
parameters, such as temperature, fluid type, and desired flow rate.
These open-loop, processor-controlled pumping systems are generally
expensive and complex. Moreover, compensation for variations in
pump accuracy must be employed in such systems to achieve an
acceptable level of accuracy. The rate of fluid delivery is also
affected by the precision of disposable components used in the
fluid path that conveys the fluid to the patient. Open-loop control
systems are not capable of compensating for variations in the
internal diameter and material hardness of fluid lines and pumping
components, which may change over time as the components are
repeatedly stressed. As a result, higher cost disposable components
with tight tolerances must be used in such systems to avoid a loss
of accuracy.
SUMMARY
[0005] Embodiments described herein address the foregoing problems
by providing a low-cost, low-complexity system for delivery of
medicinal fluids utilizing a closed-loop control system that
provides high accuracy in the rate of fluid delivery to a patient.
The closed loop system measures fluid flow rate using a low cost
flow sensor and adjusts an inexpensive fluid delivery pump based
upon the measured flow rate to achieve a desired flow rate. An
inexpensive pump can be used in such a system, as the accuracy of
the pump is not important to achieving a desired delivery rate.
Similarly, the tolerance specifications of the disposable
components used in the system can be greatly relaxed, as the
closed-loop system can easily compensate for a lack of precision in
these components. As most of the variables that are considered in
algorithms employed for open-loop control can be ignored in a
closed-loop controlled infusion system, the process control logic
used in a closed-loop infusion system is relatively simple and easy
to implement.
[0006] Certain embodiments provide an optical flow sensor. The
sensor comprises a heater configured to heat an aliquot of fluid in
an adjacent fluid-delivery channel, and a sensor disposed adjacent
to the fluid-delivery channel downstream from the heater. The
sensor is configured to illuminate fluid in the fluid-delivery
channel, to collect reflected light from the illuminated fluid, and
to determine when the heated aliquot passes the sensor based upon
an amount of the reflected light.
[0007] Certain embodiments provide a method for determining a flow
rate of a fluid. The method comprises heating an aliquot of the
fluid at a first position of a fluid-delivery channel, illuminating
fluid in the fluid-delivery channel at a second position downstream
from the first position, measuring an amount of light reflected
from the illuminated fluid to determine a change in the amount
corresponding to the heated aliquot passing the second position,
and calculating the flow rate of the fluid based upon a distance
between the first position and the second position and a time
between the heating the aliquot and the heated aliquot passing the
second position.
[0008] Certain embodiments provide a medicinal fluid administering
system. The system comprises a fluid delivery system for
administering a fluid to a patient, and an optical flow sensor for
measuring a rate of the fluid administered to the patient. The
optical flow sensor comprises a laser configured to heat an aliquot
of the fluid in an adjacent fluid-delivery channel, and a sensor
disposed adjacent to the fluid-delivery channel downstream from the
laser. The sensor is configured to illuminate the fluid in the
fluid-delivery channel, to collect reflected light from the
illuminated fluid, and to determine when the heated aliquot passes
the sensor based upon an amount of the reflected light.
[0009] It is to be understood that both the foregoing summary and
the following detailed description are exemplary and explanatory
and are intended to provide further explanation of the embodiments
as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings, which are included to provide
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
[0011] FIG. 1 is a block diagram illustrating an exemplary optical
flow sensor according to certain embodiments;
[0012] FIG. 2 is a block diagram illustrating an exemplary optical
flow sensor according to certain embodiments;
[0013] FIG. 3 is a block diagram illustrating a medicinal fluid
administering system according to certain embodiments;
[0014] FIG. 4 is a block diagram illustrating a medicinal fluid
administering system according to certain embodiments;
[0015] FIG. 5 is a flow chart illustrating a method for determining
a flow rate of a fluid according to certain embodiments; and
[0016] FIG. 6 is a block diagram illustrating a computer system
upon which certain embodiments may be implemented.
DETAILED DESCRIPTION
[0017] In the following detailed description, numerous specific
details are set forth to provide a full understanding of the
disclosed and claimed embodiments. It will be apparent, however, to
one ordinarily skilled in the art that the embodiments may be
practiced without some of these specific details. In other
instances, well-known structures and techniques have not been shown
in detail to avoid unnecessarily obscuring the disclosure.
[0018] Various approaches to fluid delivery employ different
methods for measuring fluid flow rates. For example, one method,
referred to as a thermal "time of flight" method, involves
measuring the motion of a small heated volume of fluid down a flow
path to determine a flow rate of the fluid. An aliquot of fluid is
heated at a first position in the flow path, and at a predetermined
second position downstream from the first, the passage of the
heated aliquot of fluid is detected by a sensor. The sensor may
measure different parameters of the fluid in the flow path to
determine when the heated portion passes the sensor. For example,
the sensor may shine a light through a fluid-delivery channel
through which the fluid flows to determine when the heated aliquot
passes. Because the temperature of a fluid changes the index of
refraction thereof, the amount of light entering a photodetector
will change as a heated fluid passes. For fluids whose index of
refraction is a function of temperature, a measured change in index
of refraction at the sensor indicates the passage of the heated
aliquot of fluid. Such an approach may not work, however, with
less-than-transparent fluids (e.g., translucent and opaque fluids
such as lipids, packed cells, total parenteral nutrition ("TPN"),
blood, breast milk, etc.).
[0019] According to certain embodiments, an optical flow sensor
provides accurate measurement of flow rate for any fluid, whether
opaque or transparent, at a relatively low cost. A block diagram
illustrating an exemplary optical flow sensor according to certain
embodiments is illustrated in FIG. 1. Optical flow sensor 100
includes a heater 101 configured to heat an aliquot 102 of fluid
103 in a fluid-delivery channel 104 adjacent to heater 101.
According to one exemplary embodiment, heater 101 may be a laser.
In accordance with certain other embodiments, heater 101 may be any
one of a number of other heating devices, including electrical
heaters, resistors, etc. Optical flow sensor 100 further includes a
sensor 105 disposed adjacent to fluid-delivery channel 104
downstream a predetermined distance d from heater 101. Sensor 105
is configured to illuminate fluid 103 in fluid-delivery channel
104. According to certain embodiments, sensor 105 may illuminate
fluid 103 with an LED 106. In accordance with certain other
embodiments, sensor 105 may illuminate fluid 103 with any one of a
number of other light sources, including, for example, a laser, an
incandescent filament, a fluorescent bulb, etc. Moreover, sensor
105 may illuminate fluid 103 with radiation of any wavelength,
including visible light, infrared, ultraviolet, etc.
[0020] Sensor 105 is further configured to collect reflected light
from the illuminated fluid 103, and to determine when heated
aliquot 102 passes sensor 105 based upon an amount of the reflected
light. In this regard, sensor 105 may include a photodetector 107
optically coupled to fluid-delivery channel 104 with a polished
fiber, a lens, a prism, or the like. In the present exemplary
embodiment illustrated in FIG. 1, sensor 105 includes a first
highly polished fiber 108 that optically couples LED 106 to
fluid-delivery channel 104, and a second highly polished fiber 109
that optically couples photodetector 107 to fluid-delivery channel
104. According to certain embodiments, photodetector 107 may be an
optical photodetector. In accordance with certain other
embodiments, photodetector 107 may be any one of a number of other
light or radiation sensors, including a photoresistor, a
photovoltaic cell, a photodiode, etc.
[0021] As can be seen with reference to FIG. 1, both LED 106 and
photodetector 107 are disposed on the same side of fluid-delivery
channel 104. This arrangement allows optical flow sensor 100 to
determine the flow rate of fluids not previously suitable for
time-of-flight rate sensing, such as opaque fluids, non-homogenous
fluids, non-Newtonian fluids and the like.
[0022] FIG. 2 is a block diagram illustrating an optical flow
sensor 200 according to another exemplary embodiment. Optical flow
sensor 200 includes a heater 201 configured to heat an aliquot 202
of fluid 203 in a fluid-delivery channel 204 adjacent to heater
201. Optical flow sensor 200 further includes a sensor 205 disposed
adjacent to fluid-delivery channel 204 downstream a predetermined
distance d from heater 201. Sensor 205 is configured to illuminate
fluid 203 in fluid-delivery channel 204 with an LED 206 optically
coupled to fluid-delivery channel 204 with a lens 208. Sensor 205
is further configured to collect reflected light from the
illuminated fluid 203, and to determine when heated aliquot 202
passes sensor 205 based upon an amount of the reflected light. In
this regard, sensor 205 includes a photodetector 207 optically
coupled to fluid-delivery channel 204 with a lens 209.
[0023] As can be seen with reference to FIG. 2, both LED 206 and
photodetector 207 are disposed on the same side of fluid-delivery
channel 204. This arrangement allows optical flow sensor 200 to
determine the flow rate of fluids not previously suitable for
time-of-flight rate sensing, such as opaque fluids, non-homogenous
fluids, non-Newtonian fluids and the like.
[0024] FIG. 3 illustrates a medicinal fluid administering system in
accordance with one exemplary embodiment. Medicinal fluid
administering system 300 includes a fluid delivery system for
administering a fluid to a patient and optical flow sensor 200,
which is configured to measure a rate at which the fluid is
administered to the patient. The fluid delivery system includes a
fluid reservoir 301, from which fluid 313 is pumped by a pump 302
through a fluid delivery path 303a to the optical flow sensor 310
and on (via delivery path 303b) to the patient. The optical flow
sensor 310 includes a heater 311 configured to heat an aliquot 312
of fluid 313 in a fluid-delivery channel 314 adjacent to heater
311. Optical flow sensor 310 further includes a sensor 315 disposed
adjacent to fluid-delivery channel 314 downstream a predetermined
distance d from heater 311. Sensor 315 is configured to illuminate
fluid 313 in fluid-delivery channel 314 with an LED 316 optically
coupled to fluid-delivery channel 314 with a lens. Sensor 315 is
further configured to collect reflected light from the illuminated
fluid 313, and to determine when heated aliquot 312 passes sensor
315 based upon an amount of the reflected light. In this regard,
sensor 315 includes a photodetector 317 optically coupled to
fluid-delivery channel 314 with a lens.
[0025] FIG. 4 illustrates a medicinal fluid administering system
utilizing a closed-loop control system in accordance with one
exemplary embodiment. Medicinal fluid administering system 400
includes a fluid delivery system for administering a fluid to a
patient and optical flow sensor 200, which is configured to measure
a rate at which the fluid is administered to the patient. The fluid
delivery system includes a fluid reservoir 401, from which fluid
413 is pumped by a pump 402 through a fluid delivery path 403a to
the optical flow sensor 410 and on (via delivery path 403b) to the
patient. The optical flow sensor 410 includes a heater 411
configured to heat an aliquot 412 of fluid 413 in a fluid-delivery
channel 414 adjacent to heater 411. Optical flow sensor 410 further
includes a sensor 415 disposed adjacent to fluid-delivery channel
414 downstream a predetermined distance d from heater 411. Sensor
415 is configured to illuminate fluid 413 in fluid-delivery channel
414 with an LED 416 optically coupled to fluid-delivery channel 414
with a lens. Sensor 415 is further configured to collect reflected
light from the illuminated fluid 413, and to determine when heated
aliquot 412 passes sensor 415 based upon an amount of the reflected
light. In this regard, sensor 415 includes a photodetector 417
optically coupled to fluid-delivery channel 414 with a lens. System
400 further includes a controller 418 configured to calculate a
flow rate of fluid 413 based by dividing the time between heater
411 heating aliquot 412 and heated aliquot 412 being detected by
sensor 415. Controller 418 may be further configured to adjust a
pumping rate of pump 402 based upon a difference between the
calculated flow rate and a desired flow rate (e.g., by reducing or
increasing the pump speed).
[0026] FIG. 5 is a flow chart illustrating a method for determining
a flow rate of a fluid in accordance with one embodiment of the
present invention. The method begins in step 501, in which an
aliquot of fluid is heated at a first position of a fluid-delivery
channel. In step 502, fluid in the fluid-delivery channel is
illuminated at a second position, downstream from the first
position. The amount of light reflected from the illuminated fluid
is measured in step 503 to determine a change in the amount
corresponding to the heated aliquot passing the second position. In
step 504, the flow rate of the fluid is calculated based upon a
distance between the first position and the second position, and
upon a time between heating the aliquot and the heated aliquot
passing the second position.
[0027] FIG. 6 is a block diagram that illustrates a computer system
600 upon which certain embodiments may be implemented. Computer
system 600 includes a bus 602 or other communication mechanism for
communicating information, and a processor 604 coupled with bus 602
for processing information. Computer system 600 also includes a
memory 606, such as a random access memory ("RAM") or other dynamic
storage device, coupled to bus 602 for storing information and
instructions to be executed by processor 604. Memory 606 may also
be used for storing temporary variables or other intermediate
information during execution of instructions by processor 604.
Computer system 600 further includes a data storage device 610,
such as a magnetic disk or optical disk, coupled to bus 602 for
storing information and instructions.
[0028] Computer system 600 may be coupled via I/O module 608 to a
display device (not illustrated), such as a cathode ray tube
("CRT") or liquid crystal display ("LCD") for displaying
information to a computer user. An input device, such as, for
example, a keyboard or a mouse may also be coupled to computer
system 600 via I/O module 608 for communicating information and
command selections to processor 604.
[0029] According to certain embodiments, determining a flow rate of
a fluid is performed by a computer system 600 in response to
processor 604 executing one or more sequences of one or more
instructions contained in memory 606. Such instructions may be read
into memory 606 from another machine-readable medium, such as data
storage device 610. Execution of the sequences of instructions
contained in main memory 606 causes processor 604 to perform the
process steps described herein. One or more processors in a
multi-processing arrangement may also be employed to execute the
sequences of instructions contained in memory 606. In alternative
embodiments, hard-wired circuitry may be used in place of or in
combination with software instructions to implement various
embodiments. Thus, embodiments are not limited to any specific
combination of hardware circuitry and software.
[0030] The term "machine-readable medium" as used herein refers to
any medium that participates in providing instructions to processor
604 for execution. Such a medium may take many forms, including,
but not limited to, non-volatile media, volatile media, and
transmission media. Non-volatile media include, for example,
optical or magnetic disks, such as data storage device 610.
Volatile media include dynamic memory, such as memory 606.
Transmission media include coaxial cables, copper wire, and fiber
optics, including the wires that comprise bus 602. Transmission
media can also take the form of acoustic or light waves, such as
those generated during radio frequency and infrared data
communications. Common forms of machine-readable media include, for
example, floppy disk, a flexible disk, hard disk, magnetic tape,
any other magnetic medium, a CD-ROM, DVD, any other optical medium,
punch cards, paper tape, any other physical medium with patterns of
holes, a RAM, a PROM, an EPROM, a FLASH EPROM, any other memory
chip or cartridge, a carrier wave, or any other medium from which a
computer can read.
[0031] The foregoing description is provided to enable any person
skilled in the art to practice the various embodiments described
herein. While the foregoing embodiments have been particularly
described with reference to the various figures and embodiments, it
should be understood that these are for illustration purposes only
and should not be taken as limiting the scope of the invention.
[0032] There may be many other ways to implement the invention.
Various functions and elements described herein may be partitioned
differently from those shown without departing from the spirit and
scope of the invention. Various modifications to these embodiments
will be readily apparent to those skilled in the art, and generic
principles defined herein may be applied to other embodiments.
Thus, many changes and modifications may be made to the invention,
by one having ordinary skill in the art, without departing from the
spirit and scope of the invention.
[0033] A reference to an element in the singular is not intended to
mean "one and only one" unless specifically stated, but rather "one
or more." The term "some" refers to one or more. Underlined and/or
italicized headings and subheadings are used for convenience only,
do not limit the invention, and are not referred to in connection
with the interpretation of the description of the invention. All
structural and functional equivalents to the elements of the
various embodiments of the invention described throughout this
disclosure that are known or later come to be known to those of
ordinary skill in the art are expressly incorporated herein by
reference and intended to be encompassed by the invention.
Moreover, nothing disclosed herein is intended to be dedicated to
the public regardless of whether such disclosure is explicitly
recited in the above description.
* * * * *