Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR
DISPENSE VERIFICATION
BACKGROUND OF THE INVENTION
Embodiments of the present invention generally relate to an
apparatus and a method for verifying dispense of a fluid. More
specifically, the embodiments relate to an apparatus and a
method for verifying fluid dispense in an automated instrument.
Automated instruments are available to perform a number of
tasks. One such automated instrument is an analytical
instrument. An analytical instrument can perform tests, such as
medical diagnostic tests, on a sample. For example, such tests
may identify the AIDS virus in a blood sample or other item of
interest in a biological sample.
To perform such tests, an analytical instrument may mix the
biological sample with a substance, such as a reagent and the
like. In some-embodiments, these reagents may be fluids. The
fluids may be supplied to the biological sample within the
~ medical instrument by a fluid system. The fluid system may
include a source of fluid, a pump, a dispense nozzle and a
conduit fluidly connecting those elements. The source of fluid
may be a c-ont-airier and the like. The pump operates to move
fluid from the container toward the dispense nozzle through the
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conduit. The sample, whichmay be held in a suitable container,
is positioned adjacent the dispense nozzle. When the pump is
operated, fluid from the container leaves the-nozzle and enters
the sample container. Movement of the fluid into the container,
if desired, can cause the fluid and the sample to mix.
Illustrating further by example, a given instrument may
perform a blood analysis. The instrument adds a predetermined
volume of a fluid toa predetermined volume of a blood sample.
The fluid reacts with the blood sample. Because of the reaction
between the sample and the fluid,-an electromagnetic signal or
light is sent from the mixture of sample and fluid. A detector
in the instrument sees or reads the light sent from the mixture.
Appropriate elements of the.instrument, such as a computer and
the like, interpret the information obtained by-the detector and
provide an operator-with information about the blood sample.
In order for this instrument to perform as intended-and to
give accurate results, it is desirable that a specific,
predetermined amount or volume of fluid be mixed with the
sample. If too much--or too-little fluid is added to the sample,
the light sent from-the mixture may be different from the proper
light sent from themixture when the predetermined volume of
fluid is added. The different light sent-from the mixture is
interpreted by the computer in the same, way as-the-proper light.
Therefore, the computer may give inaccurate information to the
operator of the instrument.
The possibilityof inaccurate information being given by an
instrument is a concern. For example, the test performed may be
to see ifa-unit of-blood were infected with the AIDS virus.
Assuming that the blood is infected with the AIDS virus, adding
too little or too much fluid to the blood sampla may result in
the instrumenttellirig the operator that the unit of blood is .
not infected with the AIDS virus.
Many things can cause the wrong amount offluid to be added ,
to the sample. For instance, the conduit may contain a bubble.
The conduit itself may be bent or damaged. T-he pump may not-
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function properly. A drop of fluid may form on an end of
the dispense nozzle. These causes may not be detected by
simply monitoring the length of time of pump operation or
of fluid leaving the dispense nozzle. Accordingly, it
can be appreciated that it is desirable to have an
element in the instrument for verifying that the proper,
predetermined amount of fluid has left the disperse
nozzle during operation of the analytical instrument.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there
is provided A method for verifying dispense of a fluid
from a dispense nozzle, the method comprising the steps
of: (a) providing a source of electromagnetic radiation
and a receiver of the electromagnetic radiation from the
source of electromagnetic radiation operatively
associated with the dispense. nozzle in an analytical
instrument; (b) energizing the source such that the
source produces electromagnetic radiation; (c)
illuminating the receiver with the electromagnetic
radiation; (d) generating with the receiver a first
signal; (e) setting a threshold based on the first
signal; (f) dispensing fluid from the dispense nozzle;
(g) obstructing the electromagnetic signal between the
source and the receiver with the fluid dispensed from the
dispense nozzle; (h) generating with the receiver a
second signal; (i) comparing the threshold and the second
signal to indicate start of a dispense of fluid from the
dispense nozzle; (j) generating with the receiver a third
signal; (k) comparing the third signal and the threshold
to indicate finish of a dispense of fluid from the
dispense nozzle; (1) determining a first time period
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between generation of the second signal and generation of
the third signal; (m) determining a second time period
representing an expected temporal duration between start
and finish of the dispense of fluid from the dispense
nozzle; (n) comparing the first time period and the
second time period to verify the dispense of fluid from
the dispense nozzle; and (o) updating the threshold after
expiration of the second time period.
In accordance with another aspect of the invention
there is provided a method for verifying a dispense of a
fluid from a dispense nozzle, the method comprising the
steps of: (a) providing a source of electromagnetic
radiation and a receiver of the electromagnetic radiation
from the source of electromagnetic radiation operatively
associated with the dispense nozzle in an analytical
instrument for detecting a major volume of fluid,
sufficient to significantly adversely effect dispense of
an intended volume of fluid, hanging from the dispense
nozzle and for ignoring a minor volume of fluid, not
sufficient to significantly adversely affect dispense of
an intended volume of fluid, from the dispense nozzle;
(br setting a threshold relevant to electromagnetic
radiation received by the receiver, the threshold being
sufficient for detection of the major volume and for
ignorance of the minor volume; (c) obstructing the
electromagnetic radiation transmitted between the source
and the receiver with the fluid being dispensed from the
dispense nozzle to generate a signal with the receiver;
and (d) comparing the signal with the threshold to verify
a dispense of the fluid from the dispense nozzle.
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In accordance with still another aspect of the
invention there is provided an apparatus for verifying
dispense of a fluid from a fluid exiting end of a
dispense nozzle, the apparatus comprising: (a) a source
of electromagnetic radiation; (b) a receiver of the
electromagnetic radiation from the source of. the
electromagnetic radiation operatively associated with the
source of the electromagnetic radiation such that the
electromagnetic radiation from the source is received by
the receiver; and (c) a path followed by the electro-
magnetic radiation from the source to the receiver offset
from the fluid exiting end of the dispense nozzle by a
predetermined distance such that dispense of fluid and a
major volume of fluid, sufficient to significantly
adversely effect dispense of an intended volume of fluid,
hanging from the fluid exiting end of the dispense nozzle
obstruct the path and such that a minor volume of fluid,
not sufficient to significantly adversely affect dispense
of an intended volume of fluid, does not obstruct the
path.
Embodiments disclosed herein provide apparatuses and
methods for verifying dispense of a fluid from a dispense
nozzle. According to one method, a path of electro-
magnetic radiation from a source to a receiver is
obstructed with the fluid dispensed from the dispense
nozzle. The intensity of the electromagnetic radiation
received by the receiver is measured. The measured
intensity is compared with a predetermined intensity to
verify the dispense of fluid from the dispense nozzle.
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One apparatus for verifying dispense of a fluid
comprises a source of electromagnetic radiation, and a
receiver of the electromagnetic radiation from the source
of the electromagnetic radiation operatively associated
with the source of the electromagnetic radiation such
that the electromagnetic radiation from the source is
received by the receiver. A path followed by the
electromagnetic radiation from the source to the receiver
is offset from the fluid exiting end of the dispense
nozzle by a predetermined distance such that dispense of
fluid and a major drop of fluid depending from the fluid
exiting end of the dispense nozzle obstruct the path and
such that a minor drop of fluid does not obstruct the
path.
In another method, a source of electromagnetic
radiation and a receiver of the electromagnetic radiation
from the source of electromagnetic radiation are provided
operatively associated with the dispense nozzle. The
source is energized such that the source produces
electromagnetic radiation. The receiver is illuminated
with the electromagnetic radiation. A first signal is
generated with the receiver. A threshold is set based on
the first signal. Fluid is dispensed from the dispense
nozzle. The fluid dispensed from the dispense nozzle
obstructs the electromagnetic signal between the source
and the receiver. The receiver generates a second
signal. The threshold and the second signal are compared
to indicate start of a dispense of fluid from the
dispense nozzle. The receiver generates a third signal
which is compared with the threshold to indicate finish
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of a dispense of fluid from the dispense nozzle. A first
time period between generation of the second signal and
generation of the third signal is determined. A second
time period representing an expected temporal duration
between start and finish of the dispense of fluid from
the dispense nozzle is also determined. The first time
period and the second time period are compared to verify
the dispense of fluid from the dispense nozzle.
According to another method, a source of
electromagnetic radiation and a receiver of the
electromagnetic radiation from the source of
electromagnetic radiation are provided operatively
associated with the dispense nozzle for detecting a major
drop of fluid depending from the dispense nozzle and for
ignoring a minor drop of fluid depending from the
dispense nozzle. A threshold relevant to electromagnetic
radiation received by the receiver is set. The threshold
is sufficient for detection of the major drop and for
ignorance of the minor drop. The electromagnetic
radiation moving between the source and the receiver is
obstructed with the fluid being dispensed from the
dispense nozzle to generate a signal with the receiver.
The signal is compared with the threshold to verify a
dispense of the fluid from the dispense nozzle.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 generically illustrates an apparatus for
verifying dispense of a fluid;
Fig. 2 illustrates another embodiment of the
apparatus shown in Fig. 1;
Fig. 3 is a schematic view of an apparatus for
verifying dispense of a fluid showing relative positions
of elements of the apparatus;
Fig. 4 is a graph of an electronic signal generated
by a receiver responsive to the signal sent by a source
comprising an apparatus of verifying dispense; and
Fig. 5 is a graph similar to Fig. 4 showing an
improper dispense.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Fig. 1 illustrates one embodiment 10 of an apparatus
and a method for verifying dispense of a fluid 12 from a
dispense nozzle 14. dispense verification, as will
become clear herein, refers to obtaining information
about the status of a fluid dispense, detecting a major
hanging drop of fluid, checking temporal duration of a
dispense, etc. In the embodiments discussed herein,
dispense verification utilizes an electromagnetic
radiation intensity measurement, possibly coupled with a
temporal measurement.
For the sake of clarity of understanding, the
embodiments of the apparatus and method will be discussed
with respect to their employment with an analytical
instrument. For instance, the embodiments may be used
with the instruments and methods disclosed in US Pat Nos.
5,006,309; 5,089,424, 5,120,199, 5,185,264, 5,198,368 and
5,244,630.
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However, it is to be recognized that each of the
embodiments may have other employments without department
from the invention.
Furthermore, structures and method steps of one
embodiment may be combined, in any suitable fashion, with
structures and method steps of another embodiment to
arrive at still further embodiments. For instance,
multiple embodiments may be integrated along a processing
path in a single instrument. While the fluid 12 may be
understood to be a reagent, other fluids are also
possible. It may be desirable to locate an apparatus at
every fluid addition location apt to cause a false result
or inaccurate information being given to an instrument
operator. Illustrating by example, in an analytical
instrument, dispense verification apparatus may be
located where particles, conjugate s and/or probes are
added to sample and where washes occur.
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Returning to Fig. l, the embodiment 10 comprises a
source 16 of electromagnetic radiation and a receiver 18
operatively associated with the dispense nozzle 14. The
source 16 and the receiver 18 are disposed with respect
to the dispense nozzle 14 such that flow of fluid 12 from
the nozzle 14 passes through a path 20 of electromagnetic
radiation from the source 16 to the receiver 18. It is
to be noted that the path 20 passes through an ambient
fluid, such as air. No lenses or filters are required.
As will be discussed in further detail later, passage of
fluid 12 through the path 20 allows for dispense
verification.
The source 16 and the receiver 18 are predetermined
such that the receiver 18 generates a signal responsive
to electromagnetic radiation sent from the source 16. In
an exemplary embodiment, the source 16 may be a light
emitting diode and the like. In the specific embodiment,
the source 16 is capable of emitting electromagnetic
radiation of about 900nm (infrared) . The receiver 18, in
an exemplary embodiment, may be a phototransistor and the
like. If the source 16 were a diode
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emitting electromagnetic radiation at about 900nm, then the
receiver 18 would be chosen such that a peak sensitivity of the
receiver 18 would be in substantially the same range of the
electromagnetic spectrum. If the infrared portion of the
electromagnetic spectrum were used in the embodiment 10, then
the amount of energy present in the photons travelling from the
source 16 to the receiver 18 would be reduced. In a specific
embodiment, the source 16 is an SEP8706-002 and the receiver 18
is an SDP8406-003, both being available from Honeywell, MICRO
S4JITCH, Optoelectronics Division of Richardson, Texas.
In the illustrated embodiments, the source 16 and the
receiver 18 are electrically connected by a wire 22 to other
supporting electronics, such as a controller 24 through a
preamplifier 26, for instance. The source 16 is supplied with
power at-a substantially constant level. Thus, if multiple
embodiments 10 were included in a specific instrument, then all
embodiments may be compared against a common threshold,
discussed later.
In the illustrated .embodiment, the preamplifier 26 presents
a relatively high input impedance to match the impedance of the
receiver 18. The preamplifier 26 also presents a relatively low
impedance to match the impedance of the controller 24. The
relatively low impedance facilitates signal transmission along
conduit 22 toward controller 24. In an--exemplary embodiment,
the controller 24 comprises a processor, such as a Motorola
(Schaumburg, Illinois) 68HC11F1 and the like, and a digital-to-
analog converter, such as a 7228A, available from Analog
Devices, Inc. of Norwood, Massachusetts, and the like. If
multiple apparatuses 10 were provided, then the controller 24
can include a multiplexer, such as one handling about six
- outputs and about 12 inputs. The outputs would drive, up to
about 5mA, two source 16/receiver 18 pairs connected
electrically in series. Such a circuit can incorporate current
feedback to provide a substantially linear response. In one
embodiment, the multiplexer is predetermined to have a frequency
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response sufficient for about 98% setting in about 130
microseconds. In this manner, switching of source 16 drives and
multiplexer input signals would be appropriately chosen such
that the 12 inputs could be read, approximately, every 1.6 msec.
In a specific embodiment, the preamplifier 26 drives two
source 16/receiver l8-_pairs selectively with two predetermined
electrical signals. For the sake of clarity, a first pair of
source 16/receiver 1:~_is designated the "A" pair, while the
other pair is designated the "B"pair. The A and B pairs are
electrically connect-ed in series with the preamplifier 26. The
preamplifier 26 drives the A and B pairs at a predetermined
electrical signal appropriate for the A pair. The output of the
receiver 18 in the A pair is monitored. Then, the preamplifier
26 drives the A and B pairs at a predetermined electrical signal
for the B pair. The-output of the B receiver 18_ is monitored.
If a plurality ofA and B pairs were provided,then all of the
pairs would be driven with the A electrical signal, the output
of the A receivers 18 would be monitored sequentially, then all
of the pairs would be driven with the B electrical signal and
the output of all of the B receivers 18 would be monitored
sequentially. -
In this manner, the electrical signaldr-wing all of the
sources 16 is not constant-: The A electrical signal is applied
to the source 16 andthe output of the associated receiver 18 is
monitored after it settles. The B electrical signal is applied
and the output of the B receiver 18 is monitored. This process
can repeat at a rate_ of about 1250 times per second. Thus, each
receiver 18 output is monitored about 625 times each second.
Accordingly,during a dispense cycle, the receiver 18 output can
be monitored about 80 times while the output is below the
threshold. This can result in an error tolerance of about one
percent. -.
In still other=embodiments, the controller 24 may be ,
provided with access-~ such as an RS232 port, to a computer for
monitoring, controlling and trouble shooting"the apparatus 10.
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The computer or other electronic element operatively associated
with the access may provide a feedback signal to an operator
indicative of the status of dispense of fluid12 from the
dispense nozzle 14.
In the embodiment 10 shown in Fig. 1, the source 16 and the
receiver 18 are offset from the path of fluid--12 flow from the
dispense nozzle 14 by screens 28A and 28B, respectively. The.
screens 28A and 28B are constructed and located to reduce the
chance that fluid 12 flowing from the dispense nozzle 14 might
reach the source 16 or the receiver 18. If fluid 12 were to
reach eitherthe source 16 or the receiver 18, then the
embodiment 10 may not operate as intended. The screens 28A and
28B may also be used if it were desired to avoid cleaning the
source 16 and%or the receiver 18. Iri this embodiment, the
screens 28A and 28B could be cleaned instead of the source 16
and receiver 18.
However, fluid 12 reaching the source 16 and/or the
receiver l8 may not always be a concern. This may depend upon
the characteristics of the fluid 12. If fluid 12 reaching the
source 16 or the receiver 18 were not a concern, then one or
both of the screens 28A and 28B may be eliminated. Fig. 2
illustrates an embodiment 30 of an apparatus for verifying
dispense of fluid 12 from dispense nozzle 14 which does not
comprise screens 28A and 28B. The embodiment 30 is
substantially similar to the embodiment 10 of Fig. 1, hence the
like reference numerals for similar structures. Both
embodiments 10 and 30 function substantially the same.
The relative locations of the nozzle 14, the source 16 and
the receiver 18 assist in intended operation ofthe embodiments
10 and 30. These relative locations are illustrated in Fig. 3.
- The dimensions given in the following paragraphs are for the
purposes of illustration only and are not intended to limit the
scope of the claims.
In an exemplary embodiment, the dispense nozzle 14
comprises a bore 32 having a diameter D of about 0.030 inches.
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Therefore, a stream of fluid 12 leaving the dispense nozzle 14
has a diameter of about 0.030 inches.
The source 16, which illuminates relevant portions of the
receiver 18 with electromagnetic radiation, and the receiver 18
5 are mutually exposed through an aperture having a diameter A of
about 0.062 inches. The apertures, in one embodiment, may be
formed by a suitable technique, suchas machining and the like,
in a mounting bracket., formed from a suitable material such as
aluminum and the like, operatively associated with the source 16
10 and the receiver 18. The apertures define dimensions of a
latitudinalcross section of the path 20 of electromagnetic
radiation from the source 16 to the receiver 18. Thus, during
dispense of fluid 12 from the nozzle 14, the fluid 12 will
encounter or block about half of the latitudinal cross section
of the path 20.
A longitudinal-axis of the path 20 is off set from a fluid-
exiting end 34 of the dispense nozzle 14 by a- specific-,
predetermined distance O, shown in Fig. 3. Zn an exemplary
embodiment, the distance O is about 0.10 inches. The distance O
is chosen so that the embodiments 10 and 30 are able to sense a
significantvolume of fluid 12 depending from the end 34 of the
dispense nozzle 14.- Put in another way, the distance O is
chosen such that the embodiments 10 and 30 detect a major drop
of fluid 12 and avoid a minor drop offluid 12 depending or
hanging from the end 34 of-the nozzle 14.
A major drop of fluid 12 contains a volume of fluid 12 -
sufficient to significantly adversely affect dispense of an
intended volume of fluid 12 from the nozzle 14, whereas a minor
drop of fluid 12 does not have sufficient volume of fluid-12 to
significantly adversely affect dispense of an intended volume of
fluid 12'. Thus, it can be appreciated that, by avoiding
detection of minor hanging drops of fluid 12, the likelihood of
sensing a dispense incorrectly can be reduced. However, a
detecting major hanging drops is desirable because a major
hanging drop can significantly affect dispense of fluid 12 from
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the dispense nozzle 14. If the dispense of fluid 12 were
significantly affected, then it is possible that the instrument
associated with the dispense nozzle 14 could give the instrument
operator incorrect information about a sample being tested.
Detection of a major hanging drop is also dependent upon a
threshold applied to a signal generated by the receiver 18. The
threshold is a predetermined percentage of electromagnetic
signal (i.e. electromagnetic intensity) sent from the source 16
and received by the receiver 18. The threshold may be
considered to represent a portion of the electromagnetic signal
sent from the source 16 and blocked from reaching the receiver
18 by fluid12 depending or dispensed from the dispense nozzle
14. The value of the threshold is predetermined such that the
embodiments 10 and 30 can detect-fluid dispense status and a
major hanging drop and ignore a minor hanging drop.
Determination of the threshold will be discussed in detail
later. The embodiments 10 and 30, as well as all supporting
electronics, are constructed to provide feedback dependent upon
a comparison of electromagnetic intensity received by the
receiver 18 with the threshold, thereby indicative of fluid
dispense status and/or hanging drops, to the operator.
For example, if the threshold were set at about 90% of the
source 16 intensity, then the embodiments 10 and 30 could
indicate presence of a hanging drop if the receiver 18 was
illuminated by the source 16 at a level of less than about 900
of the level of illumination of the receiver 18 by the source 16
when no fluid 12 is present (i.e. a quiescent state). Thus, the
embodiments 10 and 30 would indicate an erroneous dispense if
the electromagnetic radiation received by the receiver 18 were
to fall by about 10% from its quiescent state.
If the receiver 18 threshold were set to detect an about
10o drop in electromagnetic intensity sent by the source 16,
then the embodiments 10 and 30 would detect a drop of fluid 12,
having a fluid volume as small as about 10 ~.1, for example,
depending from theend34 of the nozzle 14. In this manner, the
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effects of-things which cause a dispense of fluid 12 from the
nozzle 14 to decrease or trail off relatively slowly at the end
of a dispense cycle,-rather than the dispense cycle ending
abruptly, can bedetected. -
with the construction of the embodiments 10 and 30 being
discussed in detail, a method ofoperation of the embodiment 10
and 30 will now be described. Both of the embodiments 10 and 30
operate in substantially the same manner. Thus, the following
discussion applies equally to both embodiments 10 and 30. It
is to be remembered that the method steps disclosed below may be
performed in any suitable order. Furthermore, steps of
different methods may be combined in any desirable order to
arrive at still other methods.
It is assumed that no fluid 12 has left the dispense nozzle
14 so that no fluid 12 has passed through the nozzle, l4 to form
a hanging drop. The-source 1& is energized to produce an
electromagnetic signal of predetermined characteristics. The
electromagnetic signal travels from the_source 16 along the path
to the receiver 18. The source 16 generatesthis
20 electromagnetic signals substantially continuously during
operation of the embodiments 10 and 30. Ifthe-embodiments 10
and 3~0 were included in an analytical instrument, then, in one
embodiment, the source 16 would generate.the electromagnetic
. signal throughout substantially the entire duration of
analytical instrument operation. At this point, the receiver 18
is at the quiescent state. The electromagnetic signal received
by the rec-ewer 18 at this time is defined as the quiescent or
reference signal.
The substantially continuous operation of -the source 16
allows for substantially fail-safe operation of the embodiments.
Specifically, as will become clear herein, the electromagnetic
signal travels from-the source 16 to the receiver 18
substantially continuously so that any deviation; as determined ,
by the controller24, in transmitted signal intensity, received
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by the receiver 18 can be used to provide feedback indicative of
fluid 12 dispense from the nozzle 14 to the operator.
The intensity of the electromagnetic signal transmitted by
the source 16 and received the receiver 18 is used to determine
the threshold discussed earlier. If there were multiple
embodiments 10 and 30 in a given instrument, then all of the
embodiments may be set to the same threshold. In an exemplary
embodiment, because the flow of fluid 12 from the nozzle 14
during an intended fluid dispense cycle will pass through about
half of the path 20 of electromagnetic radiation from the source
16 to the detector 18, the threshold may be selected to be about
75% of the quiescent state signal. .
Illustrating further by example, in one embodiment, the
source 16 driving signal is adjusted prior to dispense of fluid
12 from the dispense nozzle 14. The source 16 driving signal is
adjusted so that the quiescent signal is at a desired,
predeterminedlevel above the threshold. The-source 16 driving
signal can be adjusted within the range of a maximum and a
minimum source 16 driving signal associated with the relevant
source 16. If it were not possible to adjust the source 16
driving signalsuch that the quiescent signal is above the
threshold by the desired amount, then an error message may be
reported to an operator. Thus, functionality of the associated
source l6/receiver 18 pair is verified.
In some embodiments, it may be desirable to detect a-major
hanging drop. Therefore, in these embodiments, it may be
desirable to set the threshold substantially within the range of
about 80% to about 90% of the quiescent signal. The exact value
of the threshold may depend on a number of factors, such as
physical dimensions of the embodiments 10 and 30,
characteristics of the fluid 12, etc. The threshold value may
be determined by and stored in memory, such as a RAM, ROM,
n EPROM, SRAM arid the like running appropriate routines, present
in or associated with the controller 24. The controller 24 may
update the threshold.as necessary, thereby_possibly allowing for
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obstructions, such as dust, other than fluid 12 in the path 20.
These obstructions may accumulate over time, thereby making ,
updating of the threshold desirable.
With the threshold set, fluid 12 dispense cycles can begin.
As fluid 12 exits the dispense nozzle 14, the fluid 12 passes
through the path 20 and correspondingly reduces the intensity of
the electromagnetic signal reaching the receiver-18. The
electromagnetic intensity received by the receiver 18 is
monitored by the controller 24.
In some embodiments, the controller 24 may contain a timer
to monitor duration of the reduction in received electromagnetic
intensity. In these embodiments, the controller 24 monitors the
time interval during which the electromagnetic intensity
received by the receiver 18 is reduced below the predetermined
threshold. The end of the dispense cycle is determined by the
intensity received by the receiver 18 returning to a value
greater than the threshold. The time between the moment the
received intensity falls below the threshold and the moment the
received intensity rises above the threshold is an actual
temporal duration of-the dispense cycle. This actual temporal
duration is compared to a predetermined, -expected temporal
duration of the dispense cycle, which may be determined
empirically. The expected temporal duration may depend on fluid
12 pump tolerances, conduit length from pump to the end 34 of
the dispense nozzle 14, etc. In an exemplary embodiment, an
expected temporal duration may be about 124 msec. to about 144
msec. If the two temporal durations were substantially the
same, then the controller 24 can cause feedback indicative of a
proper dispense tob~ sent t-o the operator. If the actual and
expected durations were not substantially the same, then the
controller 24 can cause feedback indicative of an improper
dispense to be sent to the operator.
In an exemplary embodiment, an electronic signal generated
by the receiver 18 responsive to the electromagnetic signal sent
by the source 16 during a proper dispense is shown in-Fig. 4.
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In this example, it is assumed that the threshold is set at
about 90% of the quiescent signal Q and the expected temporal
duration for a proper dispense is substantially 'within the range
of 124 and 144 msec.
5 As the graph shows, the dispense cycle begins, labelled "X"
in Fig. 4, and fluid12 flowing from the dispense nozzle 14
blocks a portion of the path 20. The fluid 12 reduces the
intensity of the electromagnetic signal received by the receiver
18. The received intensity is reduced sufficiently such that it
10 falls below the predetermined threshold value. This reduction
in received intensity lasts for about 138 msec (actual temporal
duration). When the dispense cycle ends, indicated by "Y" in
Fig. 4, the received intensity increases, rises above the
threshold value and approaches the quiescent signal Q. The
15 controller 24 compares the actual and expected temporal
durations. Because the two durations are substantially
identical, this dispense is a proper dispense. If desired, the
controller-24 can cause a relevant feedback signal to be sent to
the operator.
Signal transmission from the source 16 to the receiver 18
continues. If desired, it is possible to reset the threshold.
This may be desirable if, for reasons other than a hanging drop,
such as dust and the like, the received intensity were not to
return to the quiescent signal. The embodiments 10 and 30 are
ready for verification of another dispense.
Improper dispenses can have a number of causes. One of. the
causes may be a gas, i.e. air bubble and the like, in the fluid
12 path from a fluid 12 stock container to the end 34 of the
dispense nozzle 14. Many things may cause gas to be present in
the fluid path. For instance, the fluid 12 system may have been
improperly "primed", the fluid 12 stock container may be almost
empty, connections in the fluid 12 system may leak, fluid 12 may
be restricted, there may be effects due,to siphoning, etc.
If a gas were in the fluid line, then the actual temporal
duration may be shortened. This can occur without changing
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16
substantially the volume-of fluid 12 dispensed from the dispense
nozzle 14. The gas in the line may be compressed during initial
activation of a-pump forcing fluid 12 through the line supplying
the dispense nozzle 14, thereby possibly causing a delay in
beginning the dispense. In addition, at-the-end of the dispense
cycle, the velocity of the fluid 12 leaving the end 34 of the
dispense nozzle 14 may be greater than the fluid velocity
generated by the pump. The increased-fluid 12 velocity can
cause the desired volume of fluid 12 to leave the dispense
nozzle 14 before the expiration of the expected temporal
duration. Also, the increased fluid 12 velocity can cause fluid
12 to splash into unintended places.
Build-up of fluid 12 residue, which may be caused by fluid
12 evaporating from the end 34 of,.the nozzle 14,-may direct
fluid 12 from the end- 34 of the dispense nozzle 14 in an
unintended direction. Misdirection of fluid 12 from the end 34
of the dispense nozzla 14 during a dispense cycle may result in
an improper di-spense which is also detectable by the embodiment
10. Thus, the embodiment 10 can also verify that fluid 12 was
dispensed from the dispense nozzle 14 in an intended path or
direction.
Another cause of improper dispenses may be a drop of fluid
12 depending or hanging from the end 34 of the dispense nozzle.
The hanging drop may be formed by fluid pressure being relieved
through the dispense. nozzle 14. This may be caused by a "kink"
or other restriction in the fluid line supplying fluid 12 to the
dispense nozzle 14. ---A hanging drop may become a restriction to
fluid 12 leaving the nozzle 14 through the end 34. Depending
upon the composition of the fluid 12 and the time of duration of
the hanging drop, it. is possible that the fluid 12 comprising
the drop may dry on -the dispense nozzle 14. Also, it is -
possible that fluid 12 hanging from the end34 of the nozzle 14
in the form of a drop may fall off of the end 34 ofthe nozzle ,
14 at an unadvantageous time. The falling drop may cause
erroneous information to be given to the operator. Thus, it is
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recommended that all data associated with tests involving an-
improper dispense be discarded.
To further clarify, in an exemplary embodiment, an
electronic signal generated by the receiver 18 responsive to the
Y
electromagnetic signal sent by the source 16 during an improper
dispense is shown in Fig. 5. For the sake of clarity, the
threshold and the expected temporal durations are assumed to be
the same as described above. During the time period
illustrated,-it is not intended to dispense any fluid 12 from
the nozzle 14. The improper dispense, in this example, is the
result of a major hanging drop. The major hanging drop may have
been caused by fluid 12 slowing leaking from the end 34 of the
dispense nozzle 14. This may be indicative of a defect in the
nozzle 14 or inthe conduit supplying fluid 12 to the nozzle 14.
The received signal, at point A in Fig. 5, is at about the
quiescent signal. As time progresses, more fluid 12 leaks from
the end 34 of -the nozzle 14. A drop begins to form at the end
34. The drop of-fluid 12 directs stray light back into the path
of electromagnetic radiation from the source 16 to the
20 receiver 18. The direction of stray light into the path 20
causes the received intensity to increase, as shown at B.
The received intensity increases until a portion of the
drop of fluid 12 depending from .the end 34 of the nozzle14
begins to obstruct a portion of the path 20 between the source
16 and the receiver 18. At this point C, the received intensity
of electromagnetic intensity begins to decrease. The received
intensity decreases until the drop of fluid 12 is sufficient to
substantially focus or direct electromagnetic radiation from the
source 16 onto the receiver 18. As shown, the received
intensity increases due to the redirection effected by the drop
of fluid 12 hanging from the end 34 of the dispense nozzle 14.
The size of the hanging drop continues to grow as more and
more fluid 12 Leaks from the dispense nozzle 14. The size of
the drop increases until forces of the system, e.g. gravity,
surface tension, adhesion, etc., are insufficient to maintain
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18
the drop of fluid 12 on the end 34 of the dispense nozzle 14.
At this point, label-led E, the drop falls off of the end 34 of -- ,
the dispense nozzle 14. Because there is substantially no fluid
12 depending from the end 34-of the nozzle 14, the path 20 is
substantially unobstructed. The received intensity increases,
labelled F, toward the quiescent signal. Because fluid 12
continues to leak from the end 34 of the nozzle 14, the above-
described behavior repeats.
Given the above examples, it is evident how any conditions
relevant to a fluid_12 dispense from the dispense nozzle 14 can
be monitored by the-embodiments 10 and-30 with appropriate
modifications to thedisclosed structures. For instance, the
distance between the end 34 of the dispense nozzle 14 and the
longitudinal mid line of-the path 20 may be determined to allow,
detection of minor hanging drops. The,threshold may be
predetermined to allow detection of air bubbles, clots,
inhomogeneities, etc. in the dispensed-fluid 12 as it flows from
the end 34 of the dispense nozzle 14.
