Note: Descriptions are shown in the official language in which they were submitted.
326B~
Background of the Invention
The present invention relates generally to
fluid infusion systems, and more particularly to an
improved flow metering apparatus for such systems.
The infusion of fluids into the human body is
usually accomplished by means of an administration set in
conjunction with metering apparatus which controls the rate
of flow of fluid through the set. Peristaltic-type pumps,
which function by repetitively compressing and expanding a
section of tubing, have proven particularly attractive for use
in metering apparatus since they do not introduce the
possibility of leakage or contamination into the system,
while providing positiYe control of fluid flow through the
system.
One form of peristaltic-type pump which is
particularly well adapted for infusion applications is
described in Canadian Patent number 1,088,835
to Thurman S. Jess. Basically, this pump
construction includes indiYidually spring-biased rollers in
the pump rotor which proYide a uniform compression force,
and a spring-biased plunger which restricts the lumen of
the administration set downline of the pump rotor to pro~ide
a back pressuxe against which the pump must work. This
prevents
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the release of dissolved gas in the tubing section, assists
in restoring the tubing to its original shape following com-
pression by the pump, and prevents uncontrolled gravity flow
~ in the event of pump failure.
: 5 In many applications, such as where medication is
being administered, it is necessary that the operation of
the peristaltic pump be precisely controlled to infuse only
a predetermined volume of fluid at a predetermined rate. Thus,
the need has developed for a control system for peristaltic-
type infusion pumps which enables the operator to preset a
quantity and rate of infusion, and which continuously monitors
the performance of the pump to insure compliance with the pre-
set parameters by interrupting operation and alerting the
opexator in the event of a malfunction. Furthermore, it is
desirable that the system be fail-safe, and substantially
unaffected in operation or accuracy ~y power line interruptions
or transients. The metering apparatus of the present invention
provides these features in an integrated unit which is simple
and convenient to use.
Accordingly, it is a general object of the present
invention to provide a new and improved system for infusing
fluid3 into the human body.
It is a more specific object of the present inven-
tion to provide a new and improved metering apparatus for use
in conjunction with an administration s~t for infusing fluids
ll ~Z~Bf~2
into the human body.
It is another object of the present invention to
provide a peristaltic-type pump and control system which
provides for accurate administration of a predetermined
quantity of fluid at a predetermined rate.
It is another object of the present invention to
provide a fluid metering apparatus which provides improved
metering accuracy and prôtection against malfunction.
It is another object of the invention to provide
a self-contained fluid metering apparatus which is simple
and convenient to use.
Summary of the Invention
The invention is directed to metering apparatùs
for controlling the flow of fluid through a fluid infusion
lS set. The metering apparatus includes a housing, a rotor mounted
on the housing for rotation about a fixed axis and having
a plurality of circumferentially-disposed pressure rollers,
and a pressure plate for positioning a ~ubing segment of the
administration set in compressive engagement with the
rollers whereby fluid is pumped through the tubing segment
with rotation of the rotor. Means including a stepper
motor are provided for driving the rotor. The stepper motor
is driven by a source of repetitive clock pulses, and a
pulse divider having a division factor dependent on the count-
ing state of an associated register provides a stepping
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32
signal upon each occurrence of a predetermined
number of the clock pulses. The counting state
of the register may be restricted to limit the
maximum infusion rate of the apparatus.
S
Brief Description of the Drawings
The features of the present invention which are
believed to be novel are set forth with particularity in the
appended claims. The invention, together with the further
objects and advantages thereof, may best be understood by
reference to the following description taken in conjunction
~ with the accompanying drawings, in the several figures of
which like reference numerals identify like elements, and
in which:
Figure 1 is a perspective view of an infusion meter-
ing apparatus constructed in accordance with the invention.
Figure 2 is an exploded perspective view showing
the principal components of the m~tering apparatus housing.
Figure 2a is a cross-sectional view of the metering
apparatus taken along line 2a-2a of Figure 1.
Figure 3 is an enlarged front elevational view of
the peristaltic pump utilized in the metering apparatus of
Figure 1 broken away to show the rotor and downline occlusion
,
~32~
stations thereof,
Figures 3a and 3b show the downline occlusion
station of the pump as seen in Figure 3 in alternate positions.
Figure 4 is a cross-sectional view of the pump taken
S along line 4-4 of Figure 3.
Figures 4a and 4b show the latch member of the down-
line occlusion station as shown in Figure 4 in alternate
positions.
Figure 5 is an enlarged exploded perspective view
of the principal components of the fluid metering station of
the metering apparatus.
Figure 6 is a simplified functional block diagram
; of the control system incorporated in the metering apparatus
of the invention.
Figure 7 is a functional block diagram partially
in schematic form of he control system.
Figure 8 is a simplified schematic diagram of the
bubble detector utilized in the fluid metering apparatus of
the invention.
Figure 9 is a simplified schematic diagram of the
pow~r supplies utilized in the fluid metering apparatus of
~he invention.
Description of the Preferred Embodiment
Referring to the Figures, and particularly to Figure
1, a peristaltic-type flow metering system 10 for use in con-
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~32~8Z
junction with an administration set for controlling the flow
of fluid into a vein or artery includes a generally rectangular
housing 12 having a handle 13 at one end thereof for con-
venient carrying. The front surface of the housing includes
a control panel 14 which allows the operator to control and
monitor the operation of the metering apparatus, and a peri-
staltic-type flow metering head 15 for compressing a section
of tubing 16 of the administration set to effect control of
fluid flow therein. A channel 17 is provided above the
metering head 15 for maintaining a portion of the tubing segment
in a convenient view of the operator whereby flow irregularities
can be more readily observed.
The administration set, o~ which tubing segment 16
is a part, and which may be conventional in design and con-
~ struction, is preferably formed of a plastic material such as
vinyl and packaged in a sterile and non-pyrogenic condition.
To a~oid the danger of contamination, th~ administration set
is normally utilized for one application only, and is disposed
of after use.
The operating mode of the metering apparatus is
controlled by means of a push button STOP switch 20, a push
button START switch 21, and a push button power ON-OFF switch
22. Each of these push button switches includes an internal
indicator lamp which provides a positive indication of the
operating mode of the apparatus.
82
Various abnormal operating conditions are
annunciated by means of indicator lights 23-27 contained on
the control panel to the left (as viewed in Figure 1) of
the mode control push buttons. The operation of these
indicator lights will be explained in conjunction with the
operation of their respective systems within the metering
apparatus.
Control pan~l 14 further includes a digital dis-
play 30 of volume infused, a digital display 31 of volume
to be infused, and a digital display 32 of the fluid flow
rate. The volume displayed by display 30 is the volume
- of fluid actually infused, and can be reset to O by the
operator by means of a push button RESET switch 33. The
volume to be infused by display 31 is preset by the operator
by means of a set of push button switches 34 to indicate a
desired volume of fluid to be infused. Similarly, the
infusion rate display 32 is preset by the operator by means
of a second set of push button swltches 35 to indicate the
rate at which infusion is to take place.
As shown in Figures 2 and 2a, to pxovide an aes-
thetically pleasing front panel surface free of openings which
might harbor contaminants, the front panel 14 is preerably
constructed from a single seamless panel 36 having necessary
transparent sections 37 for viewing readouts 30, 31 and 32.
The push button switches 33-35 associated with these displays
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are preferably pressure-sensitive switches, which respond
to very small deformations of the front panel brought about
by finger pressure from the operator to actuate their re-
spective circuits. The pressure-sensitive switches are
mounted on one side of a printed wiring board 38 behind
panel 36, with connections from the board extending through
apertures in the housing to a printed wiring board 28 within
the housing. Additional individual system wiring boards 29
are plugged into sockets contained on this board. A plurality
of metallic screen panels 39 may be provided between board
38 and housing 12 for the purpose of providing radio fre-
quency interference (RFI) shielding for the electronic
circuitry of the met~ring apparatus.
Referring to Figure 3, the peristaltic metering
head 15 includes a rotor 40 having four pressure rollers
41 disposed in equi-spaced relation about its circumference.
The rollers are each mounted on a shaft 4~ for free rotation
- thereon, and the shafts are carried on carriages 43 and con-
strained to radial movement by respective radial slots 44.
Each carriage 43 is mounted for reciprocation within a
radially aligned recess 45 and spring loaded in a radially
outward direction by a helical spring 46 disposed within the
recess.
The pump also includes a pressure plate 50 having
an arcuate working surface 51 which subs~antially corres-
' ~
ponds in shape to the circumference of the pump rotor and
is positioned to bring the tubing segment 16 into compres-
sive engagement with rollers 41 around at least a portion
of the rotor circumference extending between adjacent
rollers. The pressure plate may be reciprocated toward
and away from rotor 40 to facilitate installation and re-
moval of tubing segment 16 by rotation of an eccentric cam
52, which is constrained to operate within a vertical slot
53 provided on the pressure plate. Rotation of the cam
is accomplished by a shaft 54 and user-actuable lever 55
operatively connected to the cam. When the lever 55 is in
its bottom position, as shown in Figure 3, the pressure
plate is moved sufficiently close to the rotor circumference
to cause tubing segment 16 to be completely occluded by the
rollers. Since each of rollers 41 is individually biased
into engagement with the tubing segment, the pressure
applied by each roller is independent of the number of rollers
engaging the tubing segment.
After passing through the peristaltic metering
station, tubing segment 16 extends between a light source
60 and a photodetector 61, which together comprise a bubble
detector station 62. As will be seen presently, it is the
function of this station to discontinue operation and alert
the operator upon formation of a bubble in the tubing segment.
Referring to Figures 3-5, the tubing next passes
~2~2
;
through a flow restriction station 63. This station in-
cludes a pressure block 66 and a slidably mounted flow re-
striction plunger 67 biased against the sidewall of tubing
segment 16. The end of plunger 67 which engages the tubing
segment includes a generally L-shaped head portion 68
having a wedge shaped working surface 70 and a generally
flat control surface 71. Plunger 67 includes a central
body portion which is slidably received within a stationary
mounting block 73, and which extends through the center
of a helical compression spring 74 provided for biasing
head 68 into engagement with tubing segment 16.
: The working surface 70 of head portion 68 bears
;-~ against the sidewall of tubing segment 16 substantially
perpendiculax to the direction of fluid flow within the
' 15 tubing as the tubing is held in position against pressure
. .,
block 66. As a result, the lumen of the tubing segment
is occluded at the point of engagement, and a downline
~: conduit segment is defined between the point of engagement
of the rollers 41 and the point of engagement of the wedge-
shaped working surface 70. As previously developed, the
. occlusion of the tubing in this way increases the pressure
; of the fluid in the tubing segment and prevents separ-
ation of dissolved gases therein.
:- The control surface 71 of plunger 67 extends
~ 25 suhstantiall~ parallel to the direction of fluid flow
: ' -10-
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and is substantially greater an area than the working
surface 70. The relatively large area of the control
surface 71 renders the plunger mors sensitive to pres-
sures in the tubing lumen when the pump is operative
so that higher pressures can be exerted by spring 74 to
more positively close off the tubing when the pump is
not in operation, without detriment to its ability to
open at lower operating pressures.
Plunger 67 may be opened to facilitate load-
ing or unloading of tubing segment 16 by means of a user-
actuated lever 76 mounted for reciprocation with plunger
670 The plunger is constrained to reciprocation along
a defined operating path by the stationary mounting block
73 which is mounted to the apparatus housing 14. The
helical compression spring bears against this moun~ing
block at one end and against the head of the plunger at
its other ~nd, causing the desired bias of the plunger
against the tubing segment.
Automatic release of the plunger is obtained
by means of a latch member 77 which is pivotably mounted
at 78 to pressure plate 50 and biased by a helical spxing
79 for operation within a plane perpendicular to the
plunger. The plunger includes a slot 80 in which the latch
member 77 is received when the plunger is moved to its
full open position, as shown in Figure 3b. The end 81
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of the plunger may be tapered to facilitate displacement
of the latch member prior to seating in slot 80. Once
the latch member has been received in the slot, the
pllmger is locked open and the tubing segment 16 can
be readily removed
To insure that plunger 67 will be released
when pressure plate 50 is subsequently closed, mounting
block 73 is provided with an actuator pin 82. As shown
in Figures 3 and 4, this actuator pin has a tapered end
surface 83 ~hich serves to displace the pivotably mounted
latch member 77 from slot 80 when the pressure plate
is returned to its closed position by rotation of knob
55. In this way, the plunger is automatically released
so as ~o again become spring-biased against the adminis-
tration set tubing segment 16 as the metering station
is closed. This prevents inadvertent operation o the
system without the back pressure and gravity flow pro-
tection provided by the plunger. Also, when the pres-
sure plate is open, the di~placement of latching member 77
prevents the plunger from being latched open. A gate
member 84 adjacent the control surface 71 of plung~r 67
prevents the ~ubing se~ment from being inadvertently
pulled free of the compression plunger during operation.
By reason of the tubing segment 16 being
held in a highly visible vertical position within
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3Z
channel 17 the flow of fluid therethrough can be readily
monitored, Furthermore, this channel obviates the need
for additional tubing clamps at the inlet and outlet
portions of metering head lS while at the same time
providing an aesthetically pleasing structure on the pump
housing.
Referring now to Figure 6, the control
system for metering apparatus 12 is seen to include
a stepper motor 100 which is rotatably coupled to
rotor 40 so as to drive the rotor one increment for
each step command applied to the motor. To supply
the multi-phase signals required for operation of
the stepper motor the metering apparatus includes
multi-phase motor drive circuits lOl which respond
to an applied control pulse to generate a multi-phase
output signal which steps the motor one increment.
The control pulses are generated by a variable rate di-
vider 102 which produces an output ~ignal aft~r a pre-
determined number of input pulses havP been received from
a continuously running clock 103. The divider, which
may bQ conventional in design and construction, i~
preset by the user to a desired division rate which
iY displayed by an associated display device 104. In
thi way, by setting different division factoxs into
the variable rate diviser 102, ~he stepper motor can
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32
be operated over a wide range of rotational speeds.
To provide a display indicative of the total
volume of fluid infused a register 105 responsive to
the output pulses from divider 102 is provided. The
counting state of register 105, and hence the volume
infused, is displayed by a display device 106. The
output pulses from divider 102 are also applied to
a register 107 having an associated display device
108. This register is a bi-directional register,
which prior to use of the metering appara~us is counted
up to a counting state corresponding to the quantity of
fluid to be infused, and then during use is counted
down with infusion of the fluid until a zero counting
state is reached. At this time the register generates
an output signal which disables a gate 109 to inter-
rupt application of control pulses to motor drive
circuits 101.
The control system of the flow m~tering ap-
paratus 10 is shown in greater detail in Figure 7. Here
the division factor of variable divider 102, and hence
the fluid infusion rate, is seen to depend on the counting
state of a register 11~. This counting state can be con-
veniently set by the user by means of the rate setting
switches 35 which enable respective NOR gates 112 to
supply pulses to the register from a pulse source 113.
~ . ~
1~3Z~i82
In practice, several NOR gates and rate setting switches
are provided to allow each digit of the register to be
independently set. The counting state of register 110
is displayed by display device 104 as an indication of
the metering or infusion rate of the apparatus.
The output of register 110 is applied to a compari-
son circuit 114 wherein the register counting sta~e is com-
pared with a predetermined fixed minimum rate, typically
5 ml. per hour, to determine whether the infusion rate es-
tablished by divider 102 is greater than or less than the
minimum rate. In the event that the desired rate is greater
than the minimum rate, comparison circuit 114 produces an out-
put signal which enables NAND gate 115 to provide for establish-
ment of a minimum "keep open" rate after the desired quantity
of fluid has been infused. To this end, the output of clock
103 is applied to a fixed divider 116 which provides output
pulses at a fixed minimum "keep open" rate. These pulses
are applied to a NOR gate 117 and, dependinq on he sta~
of this gate, to an OR gate 118 for application to the motor
drive circuits 101. The "keep open" mode is operative only
after the desired quantity of fluid has been infused, as
signaled by the ibi-directional register 107 reaching a zero
counting state.
The output signal generated iby register 107 upon
reaching a zero counting s~ate is applied to the remaining
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input of NAND gate 115 and to one input of a NOR gate 119. As
a result, NOR gate 119 is inhibited and the application of
pulses from variable divider 102 is interrupted. Should NAND
gate 115 be enabled as a result of the variable rate being
greater than the predetermined minimum flow rate,the zero
state output signal from register 107 is applied through an in-
verter 120 to a keep open îndicator 24 and to an input of NOR gate
117, wherein it serves as an enabling signal. This gate, when
enabled, allows the fixed rate pulses from the fixed rate
divider 116 to be applied to OR gate 118, and hence to motor
drive circuits 101. In this way, a minimum flow rate is
maintained even after the desired quantity has bePn infused.
To provide start-stop control over stepper motor
100 the remaining inputs of NOR gates 117 and 119 are con-
nected to the output of a start-stop flip-flop 121. This
flip-flop may be conditioned to a start state by actuation
of the push button START switch 21, or to a stop state by
actuation of the push button STOP switch 20, or by occurr~nce
of any one of a numbex of abnormal conditions, including
interruption of power, detection of a bubble in the adminis-
tration set, detection of an occlusion in the administration
set, or the opening of the metering head pressure plate while
the metering apparatus is in operation~
To provide an accurate indication of the volume
of fluid actually infused, the output of OR gate 118 is
-16-
113~iB2
applied to a fixed divider stage 122 wherein a constant
division factor is applied to generate one output pulse for
each milliliter of fluid infused. In practice, where stepper
motor 100 i8 required to step 2,352 times to pump 1 milliliter -~
through tubing segment 16, divider 122 may be set to divide
by 2,352 to obtain the desired volume-indicative output signal.
This output signal is applied to register 105 wherein it
advances the counting state of the xegister so that the in-
stantaneous counting state thereof indicates the volume of
fluid actually infused. As previously stated, this volume
is displayed by display device 106l
The volume-indicative output pulses from divider
122 are also applied through an OR gate 123 to the stepping
input of bi-directional register 107 wherein they cause that
register to count down one step ~oward 2ero with each milli-
liter passing through the system. As stated pre~iously, the
counting state of register 107, and hence the volume of fluid
to be infused, is displayed by display device 108.
Prior to use of the infusion metering apparatus,
the counting state of register 107 is preset by the user by
momentarily applying pulses to the xegister from pulse source
113. This is accomplished through a NOR gate 124 which is
enabled by the operator by actuation of the SET VOLUME switch
34. In practice, one such switch and NOR gate are provid~d
for each decade of the counter. The remaining input of NOR
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gate 124 is connected to the output of the start-
stop flip-flop 121 to prevent the volume display
from being changed while the metering apparatus is
in operation.
Register 107 is capable of counting either up or
down depending on an applied mode control signal. This signal
is developed from the output of start~stop flip-flop 121 by
means of an inverter 125 so as to condition register 107 to
count up with application of set pulses from source 113 when
the apparatus is stopped, and to count down with application
of volume-indicative pulses from divider 122 when the metering
apparatus is in operation.
Prior to initial operation of the metering apparatus
register 105 is reset by the operator by actuation of push
button RESET switch 33. This switch is connected to one in-
put of an AND gate 126, the other input of which is connected
to the output of the start-stop flip-flop 121 to render the
reset switch 33 non-~unctional while the metering apparatus
i5 in operation. The output of AND gate 126 is applied
through an OR gate 127 to the reset inputs of register
106 and divider 122. In this way, the divider and register
are simultaneously reset to a zero counting state prior
to initial operation of the apparatus.
An auto reset state 130 responsive to initial applica-
tion of power to the apparatus is provided to automatically est~blish
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an initial counting state in registers 105, 107 and 110. The
output of the auto reset stage is applied to the remaining
input of OR gate 127 so as to establish a zero counting state
in register 105 and divider 122, and to the xeset input of
register 110 through AND gate 131. Should the operator attempt
to set the most significant digit of register 110 above 4,
a reset circuit coupled to the remaining input of AND gate
131 also resets the register. In this way the setting of
infusion rates in excess of 455 ml. per hour is prevented.
The output of the auto reset stage is also applied to register
107, wherein it establishes a minimum counting state of 1 ml.
to prevent initiation of the "keep open" mode before the
metering apparatus has been placed in operation.
Operation of the infusion metering apparatus is
interrupted upon occurrence of an occlusion within the ad-
- ministration set, as detected by a switch 132 associated
with plunger 67 (Figures 3 and 5). This switch, which may
be a pressure switch similar to switches 33-35, or a magnet-
ically-actuated Hall-effect switch, is actuated by an actuator
lever attached to the plunger when the plunger is allowed
to close against the tubing as a result of an occlusion with-
in the administration set. The switch provides an output
signal which actuates a latch circuit to condition start-stop
flip-flop 121 to a STOP state and illuminate occlusion indi-
cator lamp 25.
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Operation of the apparatus is also interrupted
in the event of a bubble being detected at bubble detector
62. In this event, an output signal is generated by the
bubble detector which actuates a latch circuit to condition
the start-stop flip~flop 121 to interrupt operation of the
metering apparatus. At the same time, BUBBLE indicator
lamp 23 is illuminated to alert the operator.
Operating power for the fluid metering apparatus
is supplied by means of two unidirectional current supplies
135 and 136 which receive operating power from the AC line
through ON-OFF switch 22 A battery 138 is provided as an
~- additional source of operating power in the event of failure
of the AC line. The battery is connected through switch 22
across the output of power supply 135.
Normally, battery 138 is maintained charged by
power supply 135 and the various control circuits of the
infusion metering apparatus are powered by this combined
source, while the stepper motor 100 is powered by the power
supply 136. To guard against interruption of AC line voltage
the output of the power supply 135 is continuously monitored by
a voltage comparator 140. Upon occurrence of a line voltage
interruption an output signal is produced by comparator 140
which simultaneously illuminates a BATTERY ON indicator 26
and actuates a relay 141.
Operation of the metering apparatus is interrupted
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whenever the battery voltage falls below a predetermined
minimum level for a predetermined period of time. To this
end, the battery voltage is continuously monitored by a
voltage comparator stage 133. Upon occurrence of a low
S voltage condition, an output signal is produced which ac-
tivates a latch circuit to illuminate the BATTERY LOW lamp
27 and initiate operation of a timing counter 134. This
counter counts the ~Ikeep open" output pulses developed by
fixed divider 116 to obtain a 10 minute time delay. If the
low voltage condition persists beyond this delay period an
output signal is developed by timing counter 134 which causes
the BATTERY LOW lamp to flash and conditions start-stop flip-
flop 121 to interrupt operation of the metering apparatus.
It should be noted that the operation of comparator 133 is
entirely independent of comparator 140, and serves as a
check on system voltage whether supplied by power supply 135
or battery 138.
Stepper motor 100 is powered by power supply 136
through transfer contacts on relay 141. The purpose of these
contacts is to substitute battery 138 as a source of power
for the stepper motor in the event of an AC line failure as
detected by comparator 140. The various phase windings of
motor 100 are individually supplied from power supply 136 by
means of switching transistors 142-145 connected in series
with the windings.
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In accordance with another feature of the apparatus,
isolation is obtained between stepper motor 100 and the pulse-
sensitive control circuits of the metering apparatus by means
of individual optical isolators 146-149 associated with re-
spective ones of the switching transistors. Each of the
optical isolators includes a light detecting element connected
between the motor current source and a respective one of the
switching transistors, and a light emitting diode (LED) element
connected to the output of a respective one of inverting am-
plifiers 150-153. These amplifiers receive phase control
signals from motor drive circuits 101 through respective
NOR gates 154-157 which serve as a safety shutoff control
means for the metering apparatus.
The NOR gates 154-157 are disabled when the start-
15~ stop flip-flop 121 is conditioned to a stop mode by means
of an OR gate 158 having an output connected to one input
of each of the NOR gates. Also, these NOR gates can be dis-
abled by outputs from bubble detector 62 and occlusion switch
132 through an additional OR gate 159 which provides an
additional input to OR gate 158. Thus, occurrence of an
occlusion, detection of a bubble, or conditioning of the
start-stop flip-flop to a stop state for any reason causes
the interruption of control signals to optical isolators
146~149 and interruption of drive power to stepper motor 100.
In operation, the user initially sets an infusion
, .
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rate by actuating switch 35 to apply a requisite number of
pulses to xegister 110. The counting state of this register
sets the variable divider 102 such that control pulses are
developed at the output thereoE with a repetition rate com-
mensurate with the desired infusion rate. These control
pulses are applied through NOR gate 119 to the motor drive
circuits 101 wherein they are utilized to generate multiple
phase control signals suitable for controlling the operation
of the multi-phase stepper motor 100. Each of the phase
signals developed by drive circuits 101 is applied through
a respective one of NOR gates 154~157 and inverter amplifiers
150-153 to a respective one o optical isolators 146-149.
These isolators in turn control conduction in respective
ones of drive transistors 142-145 to apply current from
power supply 136 to stepper motor 100. In this way, the
stepper motor turns the peristaltic rotor 40 at a rate es-
tablished by the operator.
To provide a continuous readout of fluid volume
infused the drive pulses applied to the drive circuits 101
are also applied to divider 122 to develop pulses indicative
of the number of complete milliliters infused. These pulses
are counted by register 105 to provide a display in device
106 indicative of the actual quantity of fluid lnfused.
Prior to initial operation of the apparatus an
initial counting state is established in register 107 by
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momentary application of pulses from pulse source 113 through
NOR gate 124 and OR gate 123 to establish an initial counting
state indicative of the total volume of fluid to be infused.
Register 10~ is conditioned to count up at this time by
start-stop ~lip-flop 121 through inverter 125.
Once this volume is set, operation is started by
actuat.ion of switch 21 and register 107 is conditioned to
count down by flip-flop 121. Pulses from divider 122 indi-
cative of actual volume infused are now applied through OR
gate 123 to count register 107 down toward zero. When the
register reaches a zero counting state, indicating that the
desired volume of fluid has been infused, an output signal
from register 107 inhibits NOR gate ll9 and prevents further
operation of stepping motor 100 by pulses from the variable
divider 102. However, should the rate established by vari-
able divider 102 be greater than a predetermined minimum
infusion rate, comparison circuit 114 provides an enabling
signal to NAND gate 115 which allows the OUtpl~t signal from
register 107 to enable NOR gate 117 through inverter 120.
This establishes a "keep open" mode of operation wherein
pulses from fixed divider 116 provide motor drive circuits
101 with stepping command signals a~ a frequency which
maintains a desired minimum flow rate through the system.
Registers 106, 107 and 110 are automatically reset
upon initial operation of the system by the auto reset cir-
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cuit 130. Register 105 may also be manually reset by
switch 33 when the ~tart-stop flip~flop 121 is conditioned
to a stop state.
Pxotection against occlusion in the administration
set is provided by switch 132, which conditions flip-flop
121 to a stop state and inhibits AND gates 154-157. Similarly,
protection against the formation of bubbles within the ad-
ministration set is provided by bubble detector 62, which
also conditions flip-flop 121 to a stop state and inhibits
AND gates 154-157. Protection against AC line failure is
provided by voltage comparator 140 which actuates relay 141
to switch stepper motor 100 to battery 138, and by voltage
comparator 133 which interrupts operation of the apparatus
upon occurrence of a low voltage condition for a predetermined
period of time.
Upon occurrence of any one of the above alarm
functions, or upon infusion of the desired fluid volume,
an aural alarm 160 is actuated to aIert the operator that
attention to the apparatus is required. A switch associated
with the pressure plate of the pump head locks out the alarm
when the pump head is opened.
Referring to Figure 8, the bubble detector 62 of
the infusion apparatus includes an AC-powered detection circuit
which offers improved detection sensitivity and stability.
Basically, the detection circuit, as shown in Figure 8,
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comprises a multi-vibrator 161 consisting of three NAND
gates 162, 163 and 164. A capacitor 165 connected to the
output of gate 163 and a potentiometer 166 connected to
the output of gate 164 provide an RC time constant which
determine the frequency of the multi-vibrator output signal
in a manner well known to the art. A diode 167 is connected
between the arm of potentiometer 166 and the output of gate
164 to vary the duty cycle of the oscillator output signal.
~ fixed impedance 168 connected in series with the body of
potentiomèter 156 provides a desired adjustment range.
The AC signal generated by multi-vibrator 161 is
-- applied through an impedance 169 to the base of a transistor
170. The emitter of transistor 170 is connected to ground
and the collector is connected to the cathode of a light
emitting diode (LED) which comprises the light source 60
disposed on one side of the administration set tubing seg-
ment 16. The anode o~ the LED is connected o a source of
positive unidirectional current through a resistor 171. As
a result, the AC signal developed by multi-vibrator 161 is
amplified by transistor 170 and utilized to drive the TED,
causing the LED to produce a light output which varies at
a rate dependent on the output frequency of the multi-vibrator.
The alternating light developed by the LED is
detect~d by photodetector 172 and associated amplifier
transistor 173, which together comprise the light detector
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~3~6~32
61 adjacent tubing segment 16. The collectors of photo-
detector 172 and transistor 173 are connected to the
positive unidirectional current source of the apparatus,
and the emitter of detector 172 is connected to the base of
transistor 173. The emitter of transistor 173 is connected
to ground through a resistor 174 and through respective
diodes 175-177 to respective inputs of a dual Schmitt
trigger 178. The cathodes of diodes 175-177 are connected
to ground by respective ones of capacitors 180-182 and re-
sistors 183-185 in parallel circuit configuration. These
elements serve in conjunction with the diodes a signal de-
tector, generating a DC signal at the inputs of trigger 178
dependent on the amplitude of the AC signal produced by de-
tector 61. Trigger 178, which may be a commercially avail-
able component such as a type MC14583B marketed by Motorola,
produces an output upon reduction below a predetermined
threshold level of the DC signal developed at either of
the inputs associated with diodes 176 and 177. The input
associated with diode 175 functions as an enabling input
for both triggers. The output of Schmitt trigger 178 is
applied to one input of an OR gate 179.
The emitter of transistor 173 is also connected
to ground through series-connected resistors 186 and 187.
The signal developed at the junction of the two resistors
is filtered by a series-connected resistor 188 and a
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~3~3Z
capacitor 189 and parallel-connected resistor connected to
ground and applied to the remaining input of OR gate 179.
In this way OR gate 179 is provided with the output signal
developed by the two Schmitt triggers 178 and a DC control
signal developed across capacitor 189, either of which can
result in a bubble-indicative output from the gate in the
event of a bubble occurring in tubing segment 16. The out-
put of Schmitt triggers 178 and the output of OR gate 179
are also connected to the positive unidirectional current
source of the system by respective resistors.
Since the output of OR gate 179 is dependent on
both the amplitude of the AC signal as rectified and applied
to the parallel-connected Schmitt triggers 178, and on the
DC signal developed across capacitor 189, the bubble de-
tector utilized in the metering apparatus provides two in- -
dependent control channels. The first channel, which
utilizes Schmitt triggers 178, establishes a highly precise
threshold below which an alarm output is produced. The second
channel, which depends only on the input characteristic of
gate 179 and is less precise, serves as a backup in thP
event of failure of the 5chmitt triggers in an active mode.
In order for bubble detector 62 to not provide
an output, it is necessary that the DC signals applied to
the Schmitt triggers as a result of rectification by diodes
176 and 177 be above a predetermined minimum level, which
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~3~32~i82
is possible only when there is fluid within tubing segment
16 which acts as a lens to direct light from light source
60 to detector 172. In the event of failure of the light
source or the detector, or any other component of the system,
the DC signal applied to the Schmitt triggers is removed and
an alarm output is generated~ In the event of failurP of
the Schmitt triggers, an alarm output will be developed by
OR gate 179 upon loss of the DC signal from capacitor 189.
The use of an AC signal eliminates drift in the circuitry as
a factor affecting the threshold level of the Schmitt triggers,
thereby allowing the threshold to be set closer to the normal
operating level of the system for greater detection efficiency.
Transient spikes on the AC line, which are parti-
~ cularly prevalent in institutions such as hospitals where
electrical machinery is in operation, introduce the potential
of spurious counts in the digital registers and gates
utiliæed in the control circuits of the metering apparatus.
For this reason, it is imperative that the greatest possible
isolation be provided by power supplies 135 and 136 between
the control circuits and the AC line, particularly in view
of the possibly critical life-determining nature of the
metering apparatus.
To this end, s~parate power supplies each incor-
porating special transient protection features are provided
in the metering apparatus. Referring to Figure 9, it is
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~Z~8~
seen that the two power supplies 135 and 136 share a common
power transformer 190 which includes individual secondary
windings 191 and 192 each electrostatically shielded from
the line. The output of secondary winding 191 is connected
across a bridge rectifier 193 within power supply 136. The
positive polarity output of bridge rectifier 193 is connected
to the positive polarity input terminal 194 of a first four-
terminal filter capacitor 195. The negative input terminal
196 of this capacitor is connected to the negative polarity
output of the bridge rectifier.
Filter capacitor 195 is an electrolytic type
capacitor which includes four terminals; a first pair of
terminals associated with respective ends of the positive
plate of the capacitor, and a second pair of terminals
associated with respective ends of the negative or foil
side of th~ capacitor.
The output terminals 197 and 198 of capacitor 135
are connected to a conventional voltage regulator circuit
which includes a series-connected regulator transistor 200.
In a manner well kno~n to the art, the conduction state of
transistor 200 is varied in response to the voltage level
existing at the output of power supply 136 so as to maintain
the voltage level constant. To this end, a zener diode 201
and resistor 202 are connected across the output electrodes
of the capacitor to develop a reference voltage. This
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1132G8Z
reference voltage is compared within a comparator amplifier
203 with a portion of the output voltage of the power
supply as developed by a potentiometer 204 connected across
the output terminals of the supply. The output of compara-
tor 203, representing khe deviation of the output voltage
from a reference level, is applied to a transistor 205
which serves to amplify the error signal prior to applica-
tion to the base of transistor 200. Additional regulation
tn compensate for changes in current load is provided by a
series-connected resistor 206 at the emitter of transistor
200. This register develops an additional error signal
which is applied through three series-connected voltage
dropping diodes 207 to the base of the error amplifier
transistor 205. Protection against transient spikes is
provided by reverse-biased diodes:208 and 209 connected
across the input and output leads of the voltage regulator,
respectively.
Power supply 135, which is virtually identical
to power supply 136, includes a bridge rectifier 210 con-
nected across secondary winding 192, and a four terminal
filter capacitor 211 having input terminals 212 and 213
connected across the output of the bridge rectifier. The
output terminals 214 and 215 of the capacitor are connected
to a series regulator circuit similar to that contained in
power suppiy 136, including a series regulator transistor
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82
216, a ~oltage reference zener diode 217 and a differential
amplifier 218 with similar functions. A filter capacitor
220 is connected across the output of the power supply to
provide additional filtering.
The described power supply arrangement has the ad-
vantage of providing a high degree of filtering between the
AC line and the respective power supply busses of the meter-
ing apparatus. The four-terminal filter capacitors are
particularly effective in this respect, in that any transient
currents attempting to enter or leave the respective power
supplies must pass through the electrodes of the capacitor,
since these electrodes are relied upon to complete the
metallic circuit. As a result, the filtering action of the
capacitors is not reduced with transients of higher frequencies,
as in conventional filter capacitors.
The use of separate power supplies, each utilizing
the four-terminal filter capacitor component, provides a very
high degree of isolation between the stepper motor circuit
and the digital control circuitry of the metering apparatus.
This is desirable because of the relatively high switching
transients inherent in the operation of a stepper motor, and
the possibility of these transients affecting the critical
digital control circuitry.
Thus, the invention pro~ides a flow metering appar-
atus for fluid infusion systems which allows the operator to
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directly select fluid flow rate and volume without the need
for calculations. The apparatus is convenient to install
and does not require particular skills on the part of the
operator for its operation. Protection is provided within
the apparatus against malfunctions in the administration set
and with the apparatus itself, in the event of which the
operator is signaled and operation of the apparatus is
terminated. The apparatus is portable and of a construction
which lends itself to convenient use in a hospital environ-
ment.
While a particular embodiment of the invention
has been shown and described, it will be obvious to those
skilled in the art that changes and modifications may be
made therein without departing from the invention in its
broader aspects, and, thereore, the aim in the appended
claims is to cover all such changes and modifications as
fall within the true spirit and scope of the invention.
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