CA1058996A

CA1058996A - Fluid flow control in a parenteral administration system

Info

Publication number: CA1058996A
Application number: CA229,038A
Authority: CA
Inventors: Heinz W. Georgi
Original assignee: Ivac Medical Systems Inc
Current assignee: Ivac Medical Systems Inc
Priority date: 1975-02-28
Filing date: 1975-06-11
Publication date: 1979-07-24
Also published as: GB1513904A; CA1067781A; GB1513902A; GB1513906A; DE2533314A1; GB1513903A; US4137913A; GB1513905A; JPS51101390A

Abstract

This invention relates generally to improvements in fluid flow control systems for parenteral administration of medical liquids. Positive pressure infusion pumps of the syringe type are known. However, since a portion of each operating cycle with such syringe type pumps is concerned with filling the syringe, rather than delivering fluid to the patient in a pumping mode, the accuracy of such devices tends to fall off, particu-larly at vary high flow rates, where the fill stroke period is of signifi-cantly large duration relative to the pump stroke period. The present invention overcomes this deficiency by providing a system for fluid flow control utilizing a syringe pump operated by a stepping motor to repetitively fill and empty a syringe cartridge over a plurality of operational cycles of successive fill stroke and pump stroke periods. The stepping motor is driven by electrical drive pulses from a digital pulse generation and control system. Means are provided for maintaining a proportional rela-tionship between the preselected pumping rate and the actual fluid flow pumping rate over each complete cycle of successive fill and pump strokes, the motor drive pulse frequency during each pump stroke is automatically increased to compensate for the time lost during each fill stroke.

Description

399~
, ~, This invention relates generally to improvements in fluid flow control ~,ystems and, more particularly, to a new and improved -automatic, highly accurate, positive pressure infusion pump of the syringe pump type, ~or parenteral ad~inistration of medical liquids over a wide range of fluid fl~r rates.
The usual medical procedure for the gradual parenteral administration of liquids into the human body, such as liquid nutrients, .
blood or plasma, makes u~e of apparatus which ii8 commonly referred to in the medical arts as an intravenous admini.stration set. The intra- .
.. 10 venous set usually comprises a bottle of liquid, normally supported ln ~:
an inYerted position, an intravenous ~eeding tube, typically of clear ..
plastic, and a suitable valve mechanism, such as a roll clamp, which ~ allows the liquid to drip out of the bottle at a selectively ad~ustable -::" rate into a transparent drip chamber below the bottle. The drip cham_ ber serve6 the dual function of allowing a nurse or other attendant to observe the rate at which the liquid drips out of the bottle~ and also ~` creates a reservoir for the liquid at the lower end oP the drip chamber `.~ to insure that no air enters the main ~eed.ing tube leading to the patient.
While observation o~ the rate of drop flow via the drip chamber iæ a simple way of controlling the amou~t of liquid fed to a patient over a period of time, its, ultimate e~fectiveness requires that a relatively constant vigil be maintained on the drop flow~ le~,t it ~ t cease entirely due to exhaustion o~ the liquid supply or become a continuous stream and~perhaps increase the r~te of liquid introduction to the patient to dangerous, levels.
~ ~y way of example, it has been the general practice in ;~
- hospitals to haYe nur6es periodically monitor drop flow rate at each ~ :
intravenous ~eeding or parenteral in~usion station. Such monitoring o~ drop ~low is a tedious , nd time consuming proce6s, prone to error `~

and associated, possibly serious consequences, and resulting in a substantial reduction of the available time of qualified medical personnel for other important duties. Typically, the nurse monitoring `:

~':

drop ~low rate will use a watch to time the number of drop3 ~lowing in an interval of one or more minutes, and she will then mentally perform the mathematics necessary to convert the observed d~ta to an appro- -priate ~luid ~low rate~ e.g.~ in cubic centimeters per hour or drops per minute. If the calculated flow rate is substantially different than the prescribed rate, the nurse must manually adjust the roll clamp for a new rate, count drops again~ and recalculate to measure the new : -rate.
Obviously~ each of the aforedescribed measurements and 10 calculation~ and flow rate ad~ustments usually takes several minutes' time which~ when multiplied by the number of stations bein8 monitored and the number of times each station should be monitored per day~ can resu]t in a substantial percentage of total personnel time a~ailable.
In addition~ under the pressure of a hea~y schedule, the observations and calculations performed by a harried nurse in measuring and ad~ust-ing flow rate may not always prove to be reliable; hence~ errors do occur, resulting in undesired, possibly dangerous infusion flow rates. ~ ;
In addition to the aforedescribecl difficultie6, the paren~
teral administration of medical liquids by gravity-induced hydrostatic ¦ 20 pressure infusion of the liquid from a bottle or other container suspended above a patient, i9 very susceptible to fluid flow rate i ~ ~
variation due to changes in the li~uid level in the bottle, changes in , ., temFerature~ changes in the venou~ or arterial pressure of the patient, ~;
patient movement, and drlft in the effective setting of the roll clamp - ;
or other valve mechanism pinching the feeding tube. Moreover~ there are a number of situations~ such as in intensive care~ cardlac and pediatric patientsJ or when rather potent drugs are being administered~
where the desired fluid flow rate must be capable of precise select1on and must not dri~t beyond certain prescribed limit~. In addition) it is extremely important in such situations for medical personnel to be ':. ' ~ :'~
informed o~ undesirable fluctuations i.n ~lcw rate, failure of the fluid delivery system for any reason~ leakage of the system~ or exhaustion of liquid supply when the bottle is emptied.

_2_ - : . ., :: .
. . ., :-: ,. . ' S~6~6 It will be apparent, therefore~ that 60me of the most critical proble~s confronting hospital personnel faced with an over-whelming duty schedule and limlted time availability are the problems of quickly, easily, rellably and accurately maintaining proper fluid flow rates in the parenteral administration of medical liquids.
In recent years, a number of electrical monitoring system3, drop flow controllers a~d infusion pumps have been developed to accom-plish the various tRsks of monitoring and regulating drop flow rates.
Some of these devices have also been capable of activating alarms when a potentially dangerous condition exists~ thus freeing medical per~
sonnel to some extent, for other duties. ~owever, while such monitoring and drop rate control devices have generally served thelr purpose, they have not always proven entirely satlsfactory from the ;
standpolnt of cost, complexity, stability~ reliability, accuracy~ or precision of adJustment over a wide range of selected fluid flow rates.
In addition, such systems have sometimes been subject to drift and substantial flow rate variations due to changes in temperature~ ~eeding tube crimps, variations in venous or arterial pressure of the patient, or variations in the height of the bottle or solution level within the bottle. Substantial difficulties have a:Lso been experienced particu~
larly in connection with establishing and maintainlng accurate flow at very lcw flcw rates.
Positive pressure pumps of the closèd loop peristaltic type ,~. .
~s have been provided which overcome some of the aforementioned difficul- ~
~ ~.
ties with regard to dri~t, and accurate flow at low flcw rates.

cwever~ even such closed loop positive pressure systems only serve to :...................................................................... ; . -maintain accuracy of flow in terms of stabilizing to a preaelected volume of fluld~ e.g., in cubic centimeters per hour. me reason for thls i9 that the accuracy of such systems is limited inherently to the accuracy of the size of the drops produced by an intravenous adminis~
tration set, and the actual drops produced by the latter apparatus can ~ -vary from its designated drop size, e.g., by virtue of drip chamber ;!
structural variations, by as much as 30 percent.

_3_ ~
: ~:
:~ .~: :

5~ 6 Positive pressure infusion pumps of the syringe type have also been provlded, wherein a syringe having a precise displacement ~ volume is repeatedly Pllled and emptied on alternate piston strokesi during a combined fill stroke and pu~p stroke operational cycle, so -that control of the rate at which the syringe is filled and emptied - provides an accurate means for precise fluid volume delivery within a~ prescribed period of time. ~owever, since a portion of each operating . ( - .
- cycle with such syringe type pumps is concerned with ~illing the - syringe9 rather than delivering fluid to the patient in a pumping ; ~`
mode, the accuracy of such devices tends to fall off, particularly at ;`
very high flow rates, where the fill stroke period is of significantly large duration relative to the pump stroke period. Attempts have been made to provide various types of non-linear calibration for such syringe type systems, in an ~ttempt to compensate for the los* time error due to syringe "fill" time in each complete pumping cycle.
I ~ However~ these e$forts, at best, have only reduced the degree of 1 inaccuracy in certain limited flow rate ranges, e.g., at low flow j -rates, and have falled to provide a uniformly high degree of accuracy ~ over a wide range of flow rates~ and particularly at very high fluid `~ 20 flow rates. ' ence, those concerned with the development and use of pa~enteraI fluid administration systems7 and particularly those con~
cerned with the design of automatic fluid flow control systems, have ~ .-long recognized the need for improved, relatively simple, economical, reliable, stable and accurate devices for flu1d flow control which obviate the aforedescribed difficuIties. ~he present invention provides a new and improved fluid flow control system in the form of j ` a syringe pump whlch clearly fulfills this need.
~i ~riefly, and in general terms~ the present invention provides ~ :.
a new &nd improved system for accurately controlling fluid ~low in the ~;
parenteral administration of medical liquids, wherein the frequency of electrical output pulses which energize a stepping motor to drive a syringe cartridge through repetitive cycles of ~uccessive fill and pump , :- :

:10~9~6 strokes, iB automEltically corrected during -the pump stroke of each cycle to compensate ~or tile time lost during the fill stroke o~ each cycle. This is autom~tically accomplished during generation of each individual ~otor drive pulse ~or the pump stroke by accelerating the counting up of the increments defining each pump stroke motor drive pulse period during a portion of each such period equal in duration to a fill stroke motor drive pulse period.
The displacement volume of the syringe cartridge is identical for the fill stroke and ~or the pump stroke. There~ore~ an identical number of discrete steps or motor drive pulses energi~ing the stepping motor (typically 3600 steps) is required for each fill stroke during which the syringe is filled with liquld from a iluid source~ and for each pump stroke during which the syringe is emptied of its contents Emd the precise volume of liquid within the syringe is delivered under positive pressure to a patient. `~
Thie frequency o~ the motor drive pulses during the fill stroke is a fixed~ predetermined frequency selected to fill the syringe as rapidly as possible without creating a vacuum which might suck air into the syringe. Desirably~ the fill period is as short as possible~
80 that its influence on the overall tim~ for each complete operational pump cycle is minîmal. However~ as pump rates increase, the pump ;~ stroke period become~ shorter and~ hence~ the time lost during the ~;
fill stroke period becomes more and more significant in terms of its effect upon the average fluid flow rate actually delivered by the pump. -~
` In accordance with one aspect of the invention, each motor drive pulse generated during the pump stroke is established by a -plurality of smaller increments defined by a counter counted up at a :. , ;: ~ ', pulse frequency which is automatically varied to compensate each ; individual motor drive pulse during the pump stroke for the time lost :., .
ln generating one o~ the motor drive pulses during a corresponding ~ill ~; stroke. In this regard~ the pulse rate counting up the counter iB

. doubled during the generation of each pump stroke drive pulse period~

- for that portion o~ each pump drive pulse period which is equal to a ,. ..

i96 slngle fill stroke drive pulse period.
The system for establishing the frequency of the drive pulses to the stepping motor ia an open loop digital command system embodying a digital pulse generation and rate selection subsystem .: :
wherein a preselected pulse frequency, representing the desired flcw -rate to the counter definine each motor drive pulse period during a pump stroke, is directly proportional to the desired output flow rate, whereas the drive pulses at the output of the counter represent a non_linear compensated functlon corrected for the time lost during the "fill" portion of each combined "fill" and "pump" operational cycle. The compensated output drive pulses are at a frequency which produces an average fluid flow pumping rate over successive pumping ~; cycles equal to the desired flow rate.
In thls regard, while the instantaneous fluid flow pump rate :~ .
~ produced during the pump stroke, in a non-compensated system, would ~ ~
. I .. ,.~ .
be directly proportional to the speed of the stepping motor driving the pump, the average pump rate over longer time periods which includes ~`
, ~:: ,.:
"fill" periods as well as "pumpl' periods would not be proportional to the motor speed because of the time lost for filling the syringe. One poss1ble way of correcting for the 106t "fill'l time in each operational cycle of the syringe pump would be to pump twice as fast as the desired .i ~: ::
average pump rate during a time period equal to a fill stroke, after ~ ;

~ each filling of the syrlnge. The latter procedure is undesirable ., .
' ~ since it would obviously provide pumpin~g periods at twice the desired ~l rate and, consequently, non_uniform dosimetry characteristics which may - not be tolerable with some forms of chemotherapy.
The more desirable approach, in accordance with the present invention, and in contrast to compensation for fill time by pumping twice as fast during the first part of the pump stroke for the same i~ 30 amount of time used to fill the syrinee in the fill stroke~ e.g., nine seconds~ is to spread the frequency correction over the entlre pump stroke period~ in a manner which provides uniform compensa~ion, ` individual motor pulse by individual motor pulse. ~

:. :

~58~96 It takes an equal number of steps of the stepping motor ;
drive to fill and to empty the syringe in the fill and pump stroke periods because the stroke length or travel of the syringe piston is identical in both directions. Instead of running the stepping motor twice as fast for a period equal to the fill stroke, what is done instead is to shorten each pump stroke motor drive pulse period (i.e., increase the motor drive pulse frequency) by the same ratio as the total pumping period would be reduced due to the faster running.

,. . :.
This is accomplished by using a frequency divider or counter to gen-erate the motor drive pulsest The divlder receives an input pulse ~
~ frequency proportional to the desired pumping rate and this defines ~ ~-; the clocking frequency for the counter. m e output frequency of the divider is a pulse train representing the steppi-ng rate of the ~`
motor, with one output pulse for each stepped rota~ional increment ~-`
of the motor. After each step~. the input frequency to the alvider is doubled for a time period equal to the stepping period o~: the motor in the ~ill stroke. ~his causes the divider output period~ and hence the period of each pump stroke motor drive pulse~ to be shortened by the prPper ratio, since each fill step has an equivalent pump step.
` 20 Moreover~ since every motor drive pulse in the pump stroke ls compen-. ~
-~ sated ln the aforedescribed manner for the time lost during the ~
stroke~ the entire ~ill stroke correction is spread over the entire pump stroke rather than distorting the pumping rate excessively over ~ ~ !
.:
~ ~ a lesser portion of the pump stroke.
. ~ , .
More speci~ically~ and by way of example, the electrical output of a high frequency clock is directed to a variable rate multiplier controlled by a bank~of rate selector switches which are adjusted to provide an output pulse train from the rate multiplier proportional to the desired fluid flow rate. The clock also feeds a ;
pulse generation network which provldes an output pulse train at a predesignated, fixed frequency of the motor stepping pulses for the fill stroke. The latter fill frequency pulse generation network may :: :
also be conveniently derived from the same rate multiplier used to -7~

.

,.. . : . . . , . . . . .. . . ~ .

1058~6 select the pump frequency. A divider network, e.g.J a 101 counter, i8 used to divide down and therefore smooth out the output pulse frequency from the rate multiplier, a motor drive pulse being generated each time the counter overflows.
Two systems are provided for counting up the counter, one at the full pulse rate from the rate multiplier, the other at half of the pulse rate from the rate multiplier. ;~
The fill frequency is utiliæed to generate motor drive . .
pulses directly, whenever an appropriate direction sensor indicates that the motor is about to rotate in the directlon defining the fill stroke. When the direction sensor indicates initiation of a pump ~ ~
.. ~':~ - ' .
;~ stroke, the fill frequency motor drive pulses are gated off and the drive pulses generated at the pump frequency determined by the divider `~ network are gated on. However, the frequency of the motor drive pulses produced at the output of the divider is a function not only of the pulse rate output from the rate multiplier, but also is a function of the pulse gating input to the counter which determines the rate at which the counter is counted up, and the latter is exclusi~ely under ~; the control of the fill frequency subsystem. In this connection~ the `; 20 maximum counting rate is ga~ed on to count up the counter twice as fast immedlately after each motor pulse in the pump stroke, for a time period which is equal to the fill frequency pulse period, i.e., ., .
equal to a motor drive pulse in the fill strokè. Upon completion of the time interval deflned by a fill pulse period during the first portion of the counting period defining a pump motor drive pulse period, the maxi~um counting rate is gated off and the half rate is -~
gated on for the remainder of the counting period, thus providing a motor pulse by motor pulse uniform compensation during the entire pump stroke of each operational cycle.

~ence, the pulse frequency out of the divider network is the motor stepping frequency during the pump stroke, and this frequency is increased by counting up the divider network twice as fast for the first portion of each counting cycle for a period equal to a single ' ' ~

96 ~:

motor pulse period during the fill stroke of the operational cycle.
Several additional subsystems are also provided to insure proper operating conditions. In this regard, a start-up subsystem insures that the pumping system is in the proper position for loading ~ -a syringe cartridge, and that the cartridge has been actually installed in the proper manner prior to initiation of a fill and pump cycle.
To this end, a syringe detector indicates absence of a syringe cartridge and brings the syringe piston actuator mechanism to the proper position for loading a syringe cartridge when the power is initially turned "on"~ When the syringe is properly installed, special initializing logic latches out the alarm system and initiates normal fill and pump stroke operation.
In addition, appropriate alarms respond to improper operating conditions such as leakage of fluid from the source during the ~ump .: ~ ., .
stroke, an exhausted fluid source or insufficient fluid flcw during the fill stroke~ a stalled motor, the detection of air bubbles in the -I.V. line~ .lack of fluid flow due to system component failure, or the ~ occurrence of a runaway pumping state due to system component ~ailure.

`~ Leakage detection during the pump stroke is accomplished by - 20 the detection of drop flow between the pump and the fluid source during ... , ~ .
the pump stroke, since such drop flow should be detecte~only during the fill stroke. ~`
: .
~ ~eakage detection during the fill stroke, or the indication ~`

i;~ of an empty bottleJ is accomplished via a drop rate discriminator.
Since the rate of flll of the syringe is fixed~ any indication that the drop rate has fallen belcw a prescribed le~el during the fill stroke would indicate that the fluid source hae either become exhausted, ~ '~
~ or that a leak exists between the fluid source and tbe pump.
- The presence of a stalled motor condition is detected by a rotation sensor which normally resets a counter counting the motor drive pulses.
The existence o~ air bubbles in the I.V. line is detected by a photocell and reference l~ght beam combination, the light beam , , , ~s~9~

being interrupted by the passage o~ bubbles, to generate an output signal from the photocell.
The absence of ~luid ~low due to component failure is accom_ plished by an accumulator-discriminator which is charged up by signals from the drop detector. At the end of the ~ill stroke, the accumu_ lator charge is sensed, and the stepping motor is shut off if the charge is too low.
A high rate alarm, indicative of a runaway pumping state due to system component fallure, is provided by a rate meter-comparator combination which generates a current proportional to the frequency of the motor drive pulses and compares that current with a current ~ ;
representing the high order rate multiplier selection switches. If the cùrrent sensed by the rate meter exceeds the current generated by the setting of the rate selector switches, the system is put into alarm and the stepping motor is shut o~f.
The new and improved ~luid flow control system of the present inrention is extremely accurate, reliable and easy to use. The system provides enhanced precision in selecting and maintaining extremely -accurate -flu1d flow rates over a wide range~ and the system is quick to lnform medical personnel o~ any conditions which might pose a hazard to the patient.
~ ~ These and other ob~ects and advantages of the invention will '~ become apparent ~rom the following more detailed description, when taken in conju~ction with the accompanying dra~ings of illustrative .: ~
embodiments.
FIGURE 1 is a generalized block diagram o~ an overall system for a syringe pump of the type used in practicing the present inven-tion;
;~ FIGURE 2 is a block diagram of an overall electrical system in which some of the basic concepts of the fluid control system of , , the present invention are embodied; ;~
: i :
~ IGURE 3 is a combined block diagram and electrical schematic of a simplified system for compensating motor drive pulses ~enerated 10- ~
, :

'` '' 1~5~
during the pump stroke ~or time lost durin~ the fill stroke;
FIGUR~S 4.and 5 are graphical representations illustrating the basic motor driYe pulse compensation concepts of the present invention;
FlGURES 6a, 6b and 6c are combined block diagrams and -~
electrical schematics of one embodiment of an overall fluid flow control system in accordance with the present invention, FIGURE 6a being primarily directed to the stepping motor drive pulse generation and compensation subsystems, FIGURE 6b being primarily directed to the motor direction and speed control subsystems, and FIGURE 6c being primarily directed to the start-up and alarms subsystems;
FIGURES 7a_7g are waveforms for various portions of the pulse generation and control subfiystems in the overall system of FIGUR~S 6a, 6b and 6c; and FIGURES 8a-8d are graphical representations illustrating Yarious electrical states relating primarily to operation o~ the alarm6 subsystem in the overall system of FIGURES 6a, 6b and 6c.
Referring now to FIGURE 1 of the drawings~ there is shown ` .
.-an overall system for fluid ~low control7 capable of embodying ~eatures ` ~`
of the present invention. In the ensuing description, while reference ~`
is made to the term "I.V.", normally connoting intravenous administra- ;
tion~ it is to be understood tha-t this is by way o~ example only, and ~;
the ~low control system of the present invention is suitable for other forms o-f parenteral administration as well as intravenous administra- :
tion. ~
The system shown in FIG. 1 depicts a syringe pump embodying ;
a syringe 10 which preferably i6 in the ~orm of a disposable cartridge~ ;`
but it will become apparent that many features o~ the pre ent invention ;~
- may be practiced independently o~ whether or not the syringe 10 is disposable. The syringe 10 læ typically fabricated of molded plastic and essentially includes a cylinder lOa in which a piston lOb iB - ~ .
slidably received and adapted to be reciprocated back and forth along the axis of the cylinder by an integral piston rod lOc which is couplçd .

"`~` : ' ' .

to and appropriately driven by a suitable drive subsystem 12. The drive subsyste~n 12 typically includes a reversible d.c stepping motor driving, through appropriate gearing, a lead screw which ls, in turn, coupled to the piston rod lOc of the syringe 10. m e d.c. step-ping motor of the drive subsystem 12 is energized by a pulse train of motor drive pulses generated by an electrical control subsystem 13 and appropriately fed to the drive subsystem.
The syringe 10 includes an inlet port lOd and an outlet port lOe. The inlet port lOd communicates through a suitable I.V.
line 14 with any appropriate fluid source 15, typically an I.V. bottle containing appropriate drugs and/or nutrients in liquid form.
~ypically~ the I.V. line 14 is part of an I.V. administration set which includes a transparent drip chamber (not shown) in the fluid line between the syringe 10 and the fluid source 15.
A similar I.V. line 16 is connected, at one end, to the outlet port lOe of the syringe 10 and conveys fluid from the syringe to a patient. The syringe 10 and drive subsystem 12 may be of con_ ventional design.
A pair of valves 17~ 18, typica].ly of the tube pincher or ;, ;~
clamping type~ are selectively opened and closed ~t appropriate times in the overall pumping cycle, under the control of a suitable valve control subsystem 19. The valve 17 controls the inlet port lOd and f is open during the fill stroke to enable fluid to be drawn from the ~luid source 15, through the line 147 into the syringe 10~ the valve 17 -` being closed during the pump stroke to prevent any fluid from exiting - the syringe through the inlet port. The valve 18 controls the outlet port lOe and is open during the pump stroke to enable fluid delivery from the syringe 10 to the patient through the line 16~ the valve 18 being closed during the fill stroke.
The valve control subsystem 19 is also driven, through `~ ~
appropriate gearing~ by the same drive subsystem 12 used to reciprocate ~ -: .
the piston lOb of the syringe 10. The valve control subsystem 19 also provides information to the electrical control subsystem 13 indicating -12_ .. :
.:
: . . ~ , .
, :, ~l0589~16 that the syringe 10 is either i~ the ~ troke or pump stroke~ and this information, in turn, enables thc electrical control subsystem to establish the proper direction of rotation of the stepping motor in the drive subsystem 12. The valves 17, 18 and valve control subsystem 19 may be of conventional design.
:`
A suitable drop det~ctor 20 monitors drop f1GW in the I.V.
line 14, at the drip chamber (not shown), to insure that drop flow occurs during the fill stroke of the syringe 10 and that drop flcw does not occur during the pump stroke of the syringe. In this regard, 10 drop flow should occur in the drip chamber below the fluid source 15 ~?
during the fill period of the syringe cycle, and the absence o~ such flow is an indication of an exhausted fluid source, e.g., an empty I.Y. bottle, or a leak between the fluid source and the syringe 10.
In contrast~ the absence of such drop ~lcw is a requirement durlng the pump stroke of the syringe cycle, the presence of drops indicating ~;
some Xind of leakage~ such as improper clamping off of the I.V. line 14 -j : .
by the valve 17. ~ i ~he drop detector 20 monitors drop flow in the drip chamber , -`~ of the I.V. administration set and typically may include a sen~or ::, 20 housing (not shown) containing a reference light source located opposite `;~
a photocell to defme an optical æensing gap therebetween, with a ; ;
, reference light beam normally impinging upon the photocell. The housing is appropriately clamped upon the drip chamber of the I.V.
set, with the transparent drip chamber positioned within the sensing gap to intercept the reference beam. A falllng drop of liquid within the drip chamber interrupts the reference beam~ and a variation in ; electrical response of the photocell is directed to appropriate , circuitry indicating the presence of a drop.
- One example of a suitable drop detector 20 is set forth in ;~
- . ~ . . -30 U.S. Patent NO. 3~596~515~ inventor, Richard A. Cramer. ~hile a photo- ;
cell type drop detector 20 has been described, it will be appreciated that any drop sensing device capable of providing an electrical indica-tlon of the detection of a drop mRy be used without departing from the -13_ ., : . . .. ~ . . , .; ., . . - : , : , . . ~ :, ~S~g'~6 spirit and scope of the invention.
The electrical output of the drop detector 20 is directed as an input to the electrical control subsystem 13 in connection with a variety of alarms subsystems (not shown in FIGURE 1).
The displacement volume of the syringe cartridge 10 ls determined by the volume swept by the piston lOb on each stroke and ; is identical for the fill stroke and for the pump stroke. Therefore, an identical number of motor drive pulses from the electrical control subsystem 13 to the drive subsystem 12 is required for each fill stroke during which the syringe is filled with liquid from the fluid source 15, and for each pump stroke during which the syringe delivers ; its precise volume of liquid under positive pressure to a patient.
~ The number of motor drive pulses energi~ing the stepping motor of the .; ., :
~- drive subsystem 12 for a co~plete stroke in either direction, either for the fill stroke or for the pump stroke~ is typically 3600 steps in a presently preferred embodiment of the i~vention.
m e frequency of the motor drive pulses during the fill stroke is a predetermined~ fixed frequency, typically 404 H~.~ selected ;l to rapidly fill the syringe 10 as quickly as possible without creating a vacuum which might suck air into the syringe or which might create a continuous stream (as opposed to flow in discrete drops) in the drip . ~ .
chamber. Preferably~ the time interval for performance of a fill stroke (hereinafter referred to as the fill stroke period) is as short .:, , as possible so that its influence on the overall time for each complete operational cycle of the syringe 10 is minimal. However~ as the desired ., :
fluid output pumping rate increases~ the pump stroke period becomes shorter and, hence, the time lost during the i`ill stroke period becomes -~

more and more sig~iflcant in reducing the actual average fluid flow rate of delivery by the pump. ;~
In accordance with the invention~ the motor drive pulses to the stepping motor of the drive subsystem 12 are increased in frequency during the pump stroke of each operational cycle of the pump to compensate for the time lost during each corresponding fill stroke of ~--14_ : ' , 9~9~

each operational cycle. The entire fill stroke period correction is spread over the ~ull pump stroke period by compensating each and every individual motor pulse during the pump stroke period for a uniform portion of the time lost during the immediately precedlng fill stroke.
To accomplish this~ the electrical control subsystem 13 counts up the increments defining each pump stroke motor drive pulse twice as fast ~ ;~
for the first portion Gf the couNting cycle equal in time to the `
duration of a motor drive pulse period generated during the fill stroke of the operational cycle.
~he compensated output motor drive pulses from the electrical ~ ~
control æubsystem 13 to the drive subsystem 12 are, therefore, at a - ~;
frequency which produces an average pumping rate over successive -pumping cycles equal to the-desired fluid flow rate.
Referring now to FIG. 2, there is shown a new and improved ;~;
electrical control system embodying various features of the present :
invention.

A d.c. stepping motor 22 drives a suitable syringe pump 23, ~` such as that of the general type shown in FIG. 1. The stepping motor 22 is energized by motor drive pulses received from a drive pulse generator subsystem 24~ and the direction of rotation of the stepping motor to produce either a fill stroke or a pump stroke is established ;
:. :
by a direction control subsystem 25. -A suitable high fre~uency clock 27 drives a pump rate determining subsystem 28 and a fill rate determining subsystem 29. `~

The fill rate subsystem 29 feeds the drive pulse generator subsystem ,~
24 directly during the ~ill stroke period of the syringe pump cycle ~`
and~ therefore, produces motor drive pulses at the output of the pulse generator subsystem 24 at a fixed ~ill rate frequency. In contrast~
~ the pump rate subsystem 28 feeds an intermediate drive pulse control v 30 subsystem 31 which, in turn~ energizes the drive pulse generator - subsystem 24.
The drive pulse control subsystem 31 also receives a con-trolling input from the fill rate subsystem 29. In this connection, . . .

3L.~S~

when the syringe pump operational cycle is in the pump stroke period, the drive pulse control subsystem 31 provides a pulse output to the dri-ve pulse generator subsystem 24 which is compensated for the lost time during the fill stroke period to provide an output pulse train from the pulse generator which will maintain an average fluid flow rate equal to the desired fluid flow rate. This is accomplished by having the fill rate subsystem 29 dominate the drive pulse control subsystem 31 for the first portion of each motor drive pulse period of the pump stroke equal to a motor drive pulse period in the fill stroke. -Durine this first time interval of each pump stroke motor drive pulse, ~: the drive pulse control subsystem 31 is counted up at twice the frequency as that which is used to count up the control subsystem for ,~
the remaining portion of the motor drive pulse period. Therefore, the output of the drive pulse control subsystem 31 and, hence, the motor drive pulse output from the pulse eenerator subsystem 24 is at a higher frequency over the entire pump stroke period of the operating cycle than would otherwise be provided if the pump rate subsystem 28 drove the subsystem 24 directly without its output being first compensated for the time lost during each fill stroke.
An alarms subsystem 32 receives input from a drop sensing ~; subsystem 33 for appropriate leakage or empty bottle detection, a rotation sen ing subsystem 34 for detecting a stalled stepping motor 22, ., ,: .
a syringe cartridge detection subsystem 35 to determine whether an appropriate syringe cartridge has been properly installed prior to initiatlon of pump operation, and a bubble detecting subsystem 36 to . , determine if there is air in the I.V. line. The alarms subsystem 32 also receives inputs from the pump rate determining subsystem 28~ the drive pulse generator subsystem 24 and the direction control subsystem 25~ so that other alarm functions can be performed with knowledge of the particular portion of the operational cycle in effect, e.g., fill -stroke~ pump stroke~ or the transient state between either of these . -.
~ strokes. m e alarms subsystem also responds, with the inputs shown in ~ ~
: , FIGURE 2, in the event o~ component failure somewhere in the pumping -16_ .~

: : , , -- : ;, ,. ,: :: ~ , 9Ç;

system which may produce a lack of fluid flcw or induce a runaway pumplng state generating an uncalled-for high pumping rate.
Referring now to FIG. 3, there is shcwn a simplified system for compensating the frequency of stepping motor drive pulses generated during the pump stroke period for the time lost durin~ the fill stroke period.
A stepping motor drive 40 for the syringe pump, typically embodying a d.c. stepping motor (not shown~, receives appropriate incremental drive pulses over line 42 which is the output of a drive , pulse OR gate 43. The stepping motor drive 40 also receives an input over li~e 44-fro~ a suitable direction sensor 45 (typically in the valve control subsystem for the syringe pump) which conditions the ~ ~
stepping motor directlon of rotation so that the drive pulses received ~;
over line 42 will step the motor either in the direction to perform a fill stroke or in the direction to perform a pump stroke. `
e direction sensor 45 also determines whether the output pulses appearing on~line 42 are at the fill frequency or at the pump .~ j . , frequency. In this regard~ the system of-~FIG. 3 includes an AND ~ e `, 4~ which is the control gate for the output of pump frequency mo-tor drive pulses and a second AND gate 48 which is the coDtrol gate for the output o~ fill frequency motor drive pulses.
e pump frequency control gate 47 receives as one input ~;
over line 49 a pump frequency pulse train, and receives as a second -~
enabling input over line 50 the inverted electrical output of the , direction sensor 45. The latter is accomplished by directing the output of the direction sensor 45 through an inverter 51 to the gate 47.
The output of the direction sensor 45 iS al60 directed as an enabling input, over line 52, as one input to the fill frequency con- ;
, trol gate 48, the other input to the gate 48 being the fill frequency : ~ , pulse train over line 53.

Xence, it will be apparent that -the direction sensor 45 selectively enables either the pump frequency control 8ate 47 or the :.I
fill frequency control gate 48, depending upon whether or not a pump -17_ C~6 stroke ~r a fill stroke is about to be performed by the syringe pwmp.
The output pulse6 from the control gates 47 or 48 are directed over lines 54, 55, respectively3 as inputs to the drive pulse gate 43 which, in turn, pas3es motor drive pulses to the stepping motor.
A suitable high frequency clock 60 feeds a pump rate pulse ,:
; generator 61 over line 62 and a fill rate pulse generator 64 over line 63. m e pump rate pulse generator 61 is typically a rate multi_ plier and is under the control of a pump rate selector 65, typically in the form of rate selector switches for the rate multiplier. ~ ~-~he electrical output of the pump rate pulse generator 61, ;~
over line 67, is a pulse train directly proportional to the desired ~`
inst~ntaneous fluid flow rate delivered by the syringe pump during the pump stroke period of the syringe pump operational cycle. However, -as previously inaicated~ the average fluid flow rate delivered by the syringe pump~ in the absence of compensation~ will be less than the . .
desired fluid flow rate and will be a non-linear ~unction of the ; -~

~;` selected pulse rate produced by the pulse generator 61, because of : , the time lost during the fill stroke period of the operational cycle.
;.
~he fill rate pulse generator 64 may be a separate subsystem `
for dividing down the clock frequency to the desired fill freguency or it may conveniently be derived from the appropriate hi8h order decades of the pump rate pulse generator rate multiplier. For purposes of simplicity, however, the fill rate pulse generator 64 is shown as a ,;~ .
separate divider subsystem. The fill frequency pulse train generated by the pulse generator 64 is directed a~ electrical input over line 53 . .
to the fill frequency control gate 48 which passes the pulse train to the drive pulse OR gate 43 whenever the direction sensor 45 calls for performance of a fill stroke.

In order to smooth out the electrical output oP the pump ~, ''. .
rate pulse generator 61~ a divider network is provided which includes a divide-by-two counter 70 and a divide-by-101 counter 71~ thus dividing the output of the pulse generator 61 by a total of "202".
Overflow of the counter 71 at the count of "101" produces a pump -18_ 1~5~C~6 frequency motor drive pulse over line 49 to -the control gate 47 which passes the pump frequency pulse train over line 54 through the drive pulse OR gate 43 whenever the direction sensor 45 calls for performance of a pump stroke. .
The manner in which the pump frequency is compensated for -ti~e lost during the fill stroke period, to make the average M ow rate : equal to the desired flow rate selected by the pump rate selector 65, .:
: is next described. In this regard~ the divide-by-two counter 70 i5 selectively bypassed~ under control of the fill frequency pulse train, ::.
to count up the counter 71 at twice the normal rate during the first portion of each motor drive pulse period for a pump stroke equal in ,.. '' ~:
~ time to a motor drive pulse period for a fill stroke. To this end, `.
the "101" counter 71 is counted up by counting pulses received over .~ line 73 from an OR eate 74 which receives a pair of inputs.over lines ~ 75, 76. ~he pulse rate on line 75 is one-half of the pulse rate on .
:` line 76, the ~or~er pulse rste being the output of the divide-by-two counter 70, whereas the latter count. rate. is the full pulse rate output from the pulse generator 61 with -5he divide-b~_two counter 70 bypassed.

.-; In this regard, the AND gate 77 bypasses the counter 70 and receives .
.~: 20 the output of the pump rate pulse generator 61 over line 78. ~he gate 77 also receives an enabling input over line 79 from a control ~i; flip-~lop 80. The AND gate 77 is enabled each time the Q output of .. ~ the control flip-flop 80 is "true", and the gate 77 is disabled when~
ever tbe ~ output;of the flip_flop 80 is '7false". .; :~`
~ach time the counter 71 overflowsy generating a pump l~ frequency motor drive pulse~ i-t also resets the fill rate pulse gener- :
`-.. ator ~4 and sets the control flip-flop 80, over line 82, so that its ;~
.l Q output is "true". Hence, the output of the pump rate pulse generator ` 67 bypasses the divide-by-two counter 70, through the AND gate 77 ... . 30 and OR gate 74, until such time as the AN~ gate 77 is disabled by ;
-.:, the control flip-flop 80. In this connection, the "reset" lnput of the : ., -: control flip-flop 80 is under the control of the fill rate pulse : `
generator 64~ over line 84. Thus~ the AND gate 77 will be disabled~

~, , ' . .. , ~ ~ .
:: , . , , . . . . , - .. . . .
, ........... . ... . . . : . .. . . , ~:

- ~S~9g~

by the Q output of the control flip-~lop 80 going "false", at the end of a ~ingle fill rate pulse period which resets the flip-flop 80.
In summary, the fill rate pulse generator 64 directly provides output motor drive pulses over`line 53, through gates ~a and 43, during the fill stroke period of the syringe pump operational cycle.
However, during the pump stroke period of the operational cycle, the motor drive pulses are defined by the overflow of a divider network which simultaneously functions to smooth out the pulses from the pump rate pulse generator 61 and also compensates the motor drive pulse frequency for time lost during the fill stroke period. This is accomplished by counting up the "101" counter 71 at twice the rate during the first portion of each pump stroke motor drive pulsé poriod for a time interval equal to a fill stroke motor drive pulse, under the control Or the fill rate pulse generator~ 64, control flip_flop 80 and AND gate 77, a~ter which the gate 77 is disabled and the pulse - rate from the pump rate pulse generator 61 is divided in half by the `
counter 70 prior to being fed through the OR gate 74 to the counter 71.
The result is a uniform, motor pulse by motor pulse compensation for ` time lost during the fill 6troke period~ the compensation being spread over the entire pump stroke period.
: :: : ~
~IGS. 4 and 5 graphically illustrate the basic motor drive pulse frequency compensation technique accomplished by the system o~
::: , , , FIG. 3. In FIG. 4, it will be apparent that the fill stroke period and the pump stroke period are defined by an egual number of motor drive pulse steps~ e.g.~ 3600 steps in a presently preferred embodiment of the invention, since the pump stroke and fill strokes are identical except for direction. ~cwever~ the period of a single motor drive pulse during the pump stroke is at least equal to or greater than the period of a single motor drive pulse during the fill stroke, i.e.~ the fill frequency is equal to or greater than the maximum contemplated pump frequency.
Referring ncw more particularly to FIG. 5, there is shown an enlarged view (on a ti~e scale) o~ the period of a single motor drive :`
:' ~.~13S~

pulse during a pump stroke. The latter period is defined by a total o~ 101 counts into -the counter 71 in the system of FIG. 3. Note that, for the first portion of the counting cycle, equal in time duratlon to a motor drive pulse period during a f.ill stroke, the counter 71 is counted up at twice the counting rate as during the r~mainder of the counting cycle defining -the pump stroke motor drive pulse. Hence, during the first part of the pulse period, the counter 71 is counted up by the full pulse rate output of the pump rate pulse generator 61 -in FIG. 3, whereas for the balance of the counting cycle defining the pump stroke motor drive pulse period, the output of the pulse generator 61 passes through the divide_by_two counter 70, thereby cuttlng the counting frequency in half.
FIGS. 6a, 6b and 6c are combined block diagrams and electrical - ;
schematics of one embodiment of an overall fluid flow control system ~: for accomplishing the aforedescribed motor drive pulse freqùency ` compensation technique and providing a number of additional features regarding proper system conditioning for receipt of a syringe cartridge prior to initiation of an operational cycle, as well as the provision of appropriate alarm safeguards. FIGS. 6a, 6b and 6c are arranged with their respective input and output connections aligned so that ; the three figures can be used as a single drawing for the e~tire fluid flow control system. In this regard~ the various subsystem , electrical connections overlap with each other to such a degree that the system is best described with regard to the combined figures, and the balance of the description will accordingly be made with reference to such a composite drawing.

,:, :
Prior to a detailed description of the operation of the overall system depicted in FIGS. 6a~ 6b and 6c~ the main elements of ~ ~ .
each major subsystem area, and their functions, are first summarized.

~. ~
; 30 FIG. 6a is primarily directed to the frequency generating ~ and compensating sections of the overall system for generating the : stepping frequency of the motor and includes, referring to FIG. 2 previously discussed~ the clock 27~ pump rate determining subsystem 28, _21-::
:
. ., ~ , .
... . , . , . ~ . :

~`

fill rate determinlng subsystem 29, drive pulse control subsystem 31 and portions of the drive pulse generator subsystem 24. The system shown ln FIG. 6a has two primary output frequencies, one being the pump frequency for stepping the syringe pump drive motor in the forward -~ direction during -the pump stroke~ while the other output frequency is the fill frequency which is at a fixed rate and drives the stepping motor drive in the reverse direction during a ~ill stroke. The fill ~requency is slso used to bring tbe piston actuator for the syringe cartridge to its start_up condition ~or easy insertion o~ the syringe cartridge into the pumping apparatus when the overall pump system is ~ `
about to be put into operation.
FIG. 6b relates primarily to the forward-reverse and speed control sectipn o~ the overall system and, referring again to FIG. 2, primarily includes the stepping ~otor 22, the direction control sub_ system 25, and portions of the drive pulse generator subsystem 24.
~IG. 6c i5 directed primarily to the details o~ the alarms subsystem 32 in FIG. 2, and the related input subsystems ~or the alarms, including the drop sensing subsystem 33, rotation sensing subsystem 34, cartridge detection subsygtem 35 and bubble detectlon subsystem 36, ~ 20 as well as inputs from other appropriate portions of the system ,7, necessary to determine the alarm and start-up conditions.
j Re~errlng now to FIGS. 6a, 6b and 6c, as a composite system ` diagramJ a conventional high rre~uency clock generator 100 (FIG. 6a) ;~`
directs digital pulses ~the CLK signal) over line 101 to a conventional digital rate multiplier 102 which embodies a plurality of digital rate selector switches 102a associated therewith for determining the output pulse frequency Or the rate multiplier. The clock 100 is the master clock ~or the entire system and controls the ~re~uencies and timing.
The rate multiplier 102 multiplies the input ~requency by a maximum factor o~ unity. The output of the rate multiplier 102 over line 103 is a digital pulse rate (the RM signal) proportional to the setting of the rate selector switches 102a and, therefore, proportional _22_ : "

5~ 6 to the desired outp~t fluld flow rate to which the overall system i8 intended to stab~lize. The electrical output (RM) of the rate multi~
plier 102 over line 103 is not, however~ a continuous pulse train7 but -rather an irregular burst o~ pulses~ due to the nature of the fractional - multiplication which can occur in the rate r~ultiplier. l'he typically non_uniform pulse train on line 103 i8 directed through AND gates 104~ 106 to a conventional divider network in the form of counters 105 and 107 which serve to smooth out the ~itter in the rate multiplier pulse train. ~`
l'he electrical output of the counter 107 is decoded by an A~D gate 108 to produce an output signal on line 109 each time the ... ~ ,.
;~ counter 107 cou~ts to its 1'101" state. The output pulse train created - - ~
v~ on line 109 by each "101" counts of the counter 107 is at the compenOsated pump ~requency used to generate the motor drive pulses for the pump stroke and corresponds to the output of the drive pulse control ~`
subsystem 31 in FIG. 2.
I'he clock frequency generated b~ bhe clock 100 is, in a ., presentIy preferred embodiment of the inve-~ltion~ selected to be 40.4 kilohertz. The fill frequency is conveniently derived fro-m the high ` 20 order decades of the rate multiplier 102 by dividing the clock fre~uency .~ by a factor of '1100" to produce a fill frequency of ~04 Hz. ~he fill frequency is deplcted schematically as electrical pulse output over line 111 from~the rate multiplier 102. m e latter fill frequency is directed as one input to an AND gate 112 in the drive pulse control ; ~ ;~
subsystem, and 1s alco directed simultaneously over line 113 as an input to the drive pulse generator subsystem (corresponding to the . , .
.' drive pulse generator subsystem 24 in FIG. 2) to control generation .l of motor drive pulses when the overall system is performing a fill stroke.
, 30 The clock frequency (CLK) of the clock 100 is determined by taking into account a number o~ factors such as the number of motor ~: steps to complete a ~troke, the size of the syringe pump chamber i.e.~ syringe volume displacement~ the number of counting pulses -23_ . .
..~ ,.

~S~3~96 de~ining a singl~ motor drive pulse period~ and the maximum frequency at which the selected stepping motor is designed to operate. Using a fill frequency of 404 Hz., a 5 cubic centimeter displacement volume for the syringe, 3600 steps of the stepping motor to accomplish each --syringe stroke and a maximum pump rate of approximately 1000 cc. per hour, a clock frequency of 40.4 kilohertz has been determined to be suitable for the presently preferred embodiment illustrated in FIGURES 6a_6c.
The reason for selecting a count of "101" ior the counter 107 as determinative of the pump frequency is directly related to the relationship of the fill frequency to the clock frequency. ~ince~ aB ~. :
previously pointed out~ it is essential to the basic compensation technique utilized in the present invention that the pump stroke period be equal to or greater than the fill stroke period tsince the compensa~
tion period in each pump stroke motor drive pulse must be equal to a ~-fill stroke motor drive pulse period), the requirement for a count of "101", i.e.~ 101 RM pulses~ insures that the pump stroke motor pulse period will always be at least one percent greater than the fill stroke motor pulse period even at the maximum pumping rate. m is follows logically since~ at the highest pumping rate of approximately 1~000 cc.
j ~
per hour? the output pulse frequency of the rate multiplier 102 will be equal to the full clock frequency (CLK) of the clock 100. Since . ~
the i`ill frequency of 404 ~z. is obtained by dividing the 40.4 kilo~

hert~ clock frequency by a factor of "100"~ the process of limitin~
:, . .
the maximum pump frequency ~~via the counter 107) to the clock frequency `~
d$vided by a factor of "101"~ obviously insure6 that the maximum pump frequency will be less than the fill frequency by approximately one percent and, hence~ the pump stroke period will be longer th~n the fill stroke period by at least that same percentage at all times.
With a fill frequency of 404 ~z. and 3600 step6 of the step~
ping motor to accomplish each syringe stroke~ the fill stroke takes a time period of approximately 9 seconds. The reason for the selection of 9 ~econds for the "fill" period is to make the fill period as _24_ ~`
, ''' ' ~
:. . .: . . ... . .

:ILO$~ f~ `

short as practical, yet avoid pulling so fast as to pull a vacuum ~ ;
on the I.V. tubing and therefore draw air bubbles from the drip chamber into the tubing. In addition, having too high a fill rate can produce a continuous stream in the drip chamber which would cause failure of the drop detection subsystem and, as will sub~
sequently become apparent, would cause the overall system to go into alarm. A further factor involved in determining the fill ; ~
~ rate is the consideration of motor power, in that more battery ~
:i .
; power and a more powerful stepping motor would be required for a higher fill rate. Therefore, it is practical to limit the fill rate to a rate close to the maximum pumping rate required by the ;~ system.
- The rate multiplier 102 is typically a binary coded decimal rate multiplier having three decades, a "hundreds" decade 102b, a ; ` :. .
"tens" decade 102c, and a "units" decade 102d, thus enabling selec-table fluid flow pumping rates of from 1 to 999 cc. per hour. The ;
electrical output from the "tens" decade 102c over line 111 is, as :, .
previously indicated, the fill frequency of 404 Hz. ~ ~
An additional electrical output is provided from the "units" ~-decade 102d, over line 115, and is at a frequency of 40.4 Hz.
obtained by dividing the clock frequency by a factor of "1,000".
The latter 40.4 Hz. frequency is subsequently utilized by the forward-reverse speed control logic as timing pulses to enable the ~ ;~
stepping motor to come to a stop and reverse direction, in going `;~`
from a fill stroke to a pump stroke or from a pump stroke to a fill stroke.
The AND gate 104 controls the feeding of clock pulses, over -. .
line 117, to the flip-flop 105. Essentially, the gate 104 gates the RM pulse output from the rate multiplier 102 to the flip-flop 1 30105, in synchronism with the clock 100. The same RM pulse train :, ' ', :

8¢3~6 i5 also provided, over line 118, as one input to the AND gate 106 which controls the coun-ting input to the counter 107, over line 119. The other inputs -to the AND gate 106 are the CLK signal, ~: over line 101, and the Q state of the flip-flop 105 over line 121.
The flip-flop 105, as well as all of the other flip-flops ., ~'' . ' .

:
: 10 ,-';:' ' ,'. ~.
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:
, '` ,. ,~, ., ' ':
.,. `'~ ~; ,.
~`` `'~

`'~, - '. : ' , ~

, , ~ , ! , ' `"'~ `'" ~''' :, 30 ~:;

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-25a-; .- , S~g~

shown in the system of FIGS. 6a_6c are all conventional D-type flip -~
~ ~lopa which essentially produce at the Q output of the flip-flop, ; after the clock pulse, the signal present at the D input of the flip-flop at the time the clock pulse occurred. Hence, the D-type flip-flop - introduces a delay of one clock period between the input and the output of the flip-flop.
The AND gate 108, as previously indicated, is an AND gate that decodes out the "101" state of the counter 107 for purpose6 of . . .
.: `
generating the compi~nsated pump frequency. The output of the gate 108, on line 109, ls also directed as one input to a NAND gate 125 which forms part of the subsystem for generating reset pulses for the rate multiplier 102, counter 107, flip-flop 105 and a compensation control ,..... i .
~ flip_flop 127. In addition to receiving the "101l' state as input over line 109~ the NAND gate 125 also receives the RM signal over line 128 ~ -.. :, .
''.... ! and the CLK signal over line 129, as additional inputs.
~ he electrical output of the ~AND gate 125 is directed to a dlfferentiator 131 consisting of a capacitor 131a, a resistor 131b ;l and a diode 131c, forming a conventional differentiating c1rcuit and providing the differentiated pulse output on line 132. -The diP~erentiated pulse on line 132 is directed over line 133 as an asynchronous setting input to the co~pensation control ~lip-lop 127. ~ihe fl$p-flop 127 controls the flip-flop 105 since the Q
~output of the flip~flop 127 is the controlling condition on the , : i ; .- .:
- ~ "setting" input of the ~lip-flop 105~ over line 134. This, in turn, . ~ controls the actual counting rate~ over line 119, to the counter 107.
- In this regard, when ~the Q output of the control fllp-f1Op 127 is "true", the fllp-flop 105 1s asynchronously forced into its "true"
state which thereby enables the AND gate 106 to pass the full rate ;~
multiplier pulse rate (RM) to.the counter 107. In contrast, when the Q output of the ~llp-flop 127 is "false", the flip-flop 105 behaves as .. ~
: a divide~by-two binary counter~ and only every other RM pulse from the rate multiplier 102 is passed over line 121, through gate 106 to the counter 107.

_26_ . , . , ~ .,.-~5~ 6 Gate 112 controls the clocking input over line 136, to the control flip-flop 127, the gate 112 having as its three lnputs, the ; CLK signal over line 137, the Q state of the control flip-flop 127 o~er line 138, and the 404 Hz. ~ill frequency over line 111.
A direction sensor 140, forming part of the direc~ion control subsystem for the ~orward-reverse and speed control logic, ;
typically forms part of the mechanical valve control subsystem for the syringe cartridge and typically comprises a light and photocell combination which generates an electrical output indicative of whether or not the valve control subsystem is conditioned for a pump stroke ;~
or a ~ill stroke of the operational c~cle.
The direction senaor 140 i8 schematically illustrated as a switch 140a which provides a "O" input when the syringe has reached the "pump" posi-tion (about to initiate a pump stroke) and provides a "1" input when the syringe has reached the "fill" position (about to ..
initiate a fill ~troke). In other words, when the syringe cartridge has completed a pump stroke, and is about to begin a fill stroke, the switch 140a closes to the "fill" position and enable& the D input of a `
timing ~lip flop 1~1. The flip-flop 141, together with a second timlng ~lip-~lop 142~ are used to synchronize the input ~rom the direc_ tion sensor 140 with the actual clocking of the overall system. The ~ -timing flip_flops 141, 142 are clocked by the 40.4 Hz. frequency output ~ `
~rom the rate multipller 102, on line 115, which provides clocking inputs to these ~lip-flops over lines 143, 144, respectively. ~`~
~` When the pump mechanism reaches the end of its stroke in ,, .
either direction, the tlming flip-flop 141 changes state on the first 40.4 Hertz pulse which occurs on line 143. On the very next 40.4 Hz.
pul6e, the tlming flip_flop 142, which has its D input connected to the ~ output of the flip-flop 141, over line 146, follows the setting o~ the flip~~lop 141, thus providing a pulse period delay of approxi~
mately 24.75 milliseconds during which the pair of flip-flops 141, 142 are not in the same state. m e latter time interval is used to stop the stepplng motor so that it has time to reverse properly, rather than _27 :
,'',' '.......... `' ' ,. '' ''`~.'.' ' ;.:

~S8~9~

callin~ for reverse rotation of the motor without providing adequate time ~or coming to a stop between strokes.
AND gateB 148J 149, 151, 152 and OR gates 154, 155 comprise the gating ~or the speed control subsystem and receive the CLK signal `
over line 101~ the pump frequency signal over 109 and the fill frequency signal over line 113~ to selectively provide output motor drive pulses - of appropriate frequency~ over line 157, depending upon whether a - fill stroke or a pump stroke i5 to be performed, as input to the step-.` ping motor driver 158 for the syringe pump.
Having thus identified the major subsystem components in the pump rate~ f111 rate and motor drive pulse generating and control subsystems, the basic operation of these subsystem areas, particularly as disclosed in FIGS. 6a and 6b are next described.
;; As previously pointed out, the clock 100 ~eeds high frequency .
clocking pulses over line 101 to the rate multiplier 102 and the electrical output (RM) of the rate multiplier~ over line 103, is a ~! pulse frequency proportional to the clock frequency times the r~te selector switch setting established by the switches 102a. For example~
. . . ~
if the rate selector switches have been set to "100"~ representing a ~ ~
. ~ :
desired output pumping flow rate of 100 cc. per hour, the RM output ; frequency would be 100/lOCO or l/lGth of the CLK frequency, whlch ~;
:
is 4.04 kilohertz. If the rate selector switches are set to "10"~
`~i represen~ing 10 cc. per hour~ the RM frequency would be 10/1000 or l/lOOth of the clock frequency~ which is 404 ~z. me RM output fre~
~ quency from the rate multiplier 102~ over line 103, is the normal i! ~requency for driving the flip-flop 105~ assuming the Q output of ;~ :the control flip-flop 127 is "false". In this connection/ the flip-flop 105 has its Q output tied to its D input in a conventlonal toggle arrangeme~t. mls causes the flip-flop 105 to alternate its Q output s~ate with each clock pulse received over line 117~ thus converting the flip-flop 105 into a binary counter with the output frequency on `~
line 121 from the Q output terminal of the flip-flop being half of the input pulse frequency to the clocking input of the flip-flop.

_28_ :~51~ 6 m e same RM frequency passed by the AND gate 104, over line 117~ to the clocking input of the flip-flop 105 is also directed over line 118 as one input to the AND gate 106. The other inputs to the gate 106 are the CLK signal over line 101 and the Q state of the flip_flop 105, over line 121. Hence, the eate 106 is enabled only when the Q output of the flip-~lop 105 is "true". Since the flip-flop 105 is a divide-by_two binary counter, its Q output will be "true" only on every other RM pulse. Hence, the electrical output over l~ne 119 to the counter 107 is half of the frequency of the RM input pulse ~ -train to the 8ate 106.
~he counter 107 counts up to a state of "101" and the latter ~ , counting state is decoded out by the AND gate 108 which receives the "1", "~"~ "32", and "64" states of the counter flip-flops~ over ~; lines 110~ as gate inputs. When the gate 108 goes "true" on the count of "101"~ the electrical output on llne 109, together with the very next RM pulse over line 128~ enables the NAND gate 125 to pass the next CLK pulse which overlaps with the RM pulse. In this regard, ; the electrical output of the NAND gate 125 is normally po~itive and ~-~
goes negative when enabled~ for the period of a single clock pulse. /`
20 The electrical output pulse from the enabled gate 125 is differentiated ;
by the differentia~or 131 and provide~ a reset pul~e output over line 132.
The reset output from the differentiator 131 is fed to the ~ ;~
reset inputs of the high order decades of the rate multiplier 102 over line6 162~ 163, is directed over line 133 to the "set" input of the compensation control flip-flop 127 and is also fed over line 164 to the "resetl' input of the counter 107.
; The reason for resetting the BCD rate multiplier 102 at the "101" state of the counter 107 is that the rate multiplier in the ~ 30 system of ~lG. 6a is also being used to generate the fill frequency -:~ over line 111. Since the "101" counter state of the counter 107 is not necessarily synchronous with the count in the rate multiplier 102 ~` the high order dec~des 102b and 102c of the rate multiplier (used to ~29-:

.. . . .. . . . .. . . . .

l~S~39~6 generate the Eill frequency) must be reset -to "zero" at the be-ginning of each pump stroke motor drive pulse period. This is necessary since the fill frequency output of the rate multiplier 102 is being used, through the AND gate 112, to reset the com-- pensation control flip-flop 127, and the time period between setting and resetting of the latter flip-flop must be exactly equal to a single fill stroke motor drive pulse period, i.e., -1/404 seconds. If the high order decades 102b and 102c of the rate multiplier 102 were not reset at the "101" state of the counter 107, the time period between setting and resetting of the ~ ~, ` control flip-flop 127 would usually be shorter than the desired fill frequency pulse period and would introduce errors into the ` frequency compensation technique.
, ~
The "reset" pulse over line 164 forces the counter 107 to its "zero" state, and simultaneously forces the control flip-flop 127, through its "set" input over line 133, to the "true" state. With -~the flip-flop 127 now set so that its Q output is "true", the divide-by-two flip-flop 105 is also forced into the "true" state ~ through its "set" input over line 134. The flip-flop 105 is thus ;
~ 20 "set" asynchronously and is therefore independent of its clocked input over line 117.
Hence, as long as the Q output of the control flip-flop 127 `~
remains "true", the Q output of the flip-flop 105 also stays "true" -;~`
and enables the AND gate 106, over line 121, continuously as long as these conditions subsist. This results in all of the RM pulses ~-`
from the rate multiplier 102 being fed through the enabled gate 106, over line 119, to the counter 107. Thus, during the entire ~: , ~: .
time period that the flip-flop 127 (and hence the flip-flop 105) remains "true", the counting input over line 119 to the counter 30 107 is at twice the pulse frequency that would otherwise occur. ~`

The counter 107 is thus counted up during this period at twice the normal rate, i~e., at the full RM pulse rate.
:, .

'~:
,, ~ , . , . ~ . ., ~ .. ., :

}39~

Counting a-t -the full RM pulse rate continues, until the rate multiplier output over line 111 completes a single 404 Hz. pulse period t2.475 milliseconds), thus providing a "true" output on line 111 as one input to the AND gate 112, the other inputs to the gate 112 being the CLK signal on line 137 and the "true" Q output of the flip-flop 127. Hence, since all of its inputs are "true", ~ t the clock pulse passes through the AND gate 112 to the clocking input of the control flip-flop 127 and resets the flip-flop 127 so that its Q output goes "false". The reason this change of state `~
occurs is that the Q output of the flip-flop 127 is tied to the D
input of the flip-flop, as in the case of the flip-flop 105, thus establishing the flip-flop 127 as a toggle or binary counter which alternates states each time its clocking input is pulsed. ~ ~
It will be apparent that when the compensation control flip- ~-, - . .
flop 127 goes "false", the "set" input of the flip-flop 105 is also "false", so that the flip-flop 105 resumes operation as a binary counter, whereby the RM pulse train output from the rate multiplier ~ .
..~
102 is again divided by two before being passed through the gate 106 to the counter 107. In -this way, the first portion of the `' 20 counting cycle defining each pump stroke motor drive pulse period ~ ;
`~ is counted up, for a time interval equal to one fill stroke motor drive pulse period, at twice the normal counting rate which pre-~ vails over the balance of the pump stroke motor drive pulse count-- ing cycle. Hence, compensation is accomplished, as in the simpli- `
, ,: -fied system of FIG. 3, and as illustrated graphically in FIGS. 4 and 5 previously discussed. `~
FIGS. 7a through 7g are timing waveforms which further ~. . , amplify the functions and operation of the frequency determination and compensation subsystems described in connection with FIG. 6a.
30 Fig. 7a illustrates the CLK output from the clock 100 which is a ,' `~

~ -31- ~ ;~
':". .' `
'''' '~ "
"' ~, -~58~g6 regularly occurring clock pulse train, the numbe.rs above the : clock pulses representing the counting s-tate of the rate multi-plier 102 (high order decades).
It has been assumed, for purposes of illustration, that . the rate selector switches 102a have been set -to a flow rate of `
300 cc. per hour, which means that the actual counting frequency - out of the ' :~

,. 10 ~

;
, :, :.:

- -, ~ : .

,:~

.

: ' ~ 20 .. .
,~
-~ 30 ~3. -31a- .
", .. .
:
~::

. ' , s~9~6 rate multlplier 102 ls 0.3 time~ the clock frequency (CLK). ~ence~ it will be apparent in FIG. 7b that the RM pulse output from the rate ~ultiplier shows three RM pulse~i for each ten CLK pulses. Howe~er, ~ince the number "10" is not exactly divisible by the number ll3'~
the RM output pulse tr~in i8 not evenly distrlbuted in the groups of ten CLK pulses. Rather, the RM pulses come in non_uniform bunches~
and ~or the particular way illustrated for decoain~ the rate multi-plier~ FI&. 7b shows RM output pulses on the "2", "4" and "7" count~
of the rate multiplier.
FIG. 7c shcws the "Q" output o~ the binary counter flip~flo~
105 whlch constitutes the divide_by-two network. It will be apparent from the le~t half o~ the waveform that the flip-flop 105 i8 dividine the pulse train ~requency RM o~ the rate multiplier 102 in hal~, by -~
producing a single output pulse waveform ~or every two ~M pulses.
FIG. 7d illustrate6 the counting pulses directed as input to the counter 107 and further illustrates the output counting state of the counter 107. ~he left half of the waveform shcws the upper counting state~ ~ga~ through the overflow count of "101" leading up to the "reset" condition where the next RM pul~e resets the counter - 20 107 to its "zero" state. The right half of the waveform 6hows how~
a M er the counte~ 107 has been "reset", the counter is then countea up at twice the rate.
FIG. 7e is a wa~eform of the electrical output of the NAND
~ gate 125 and illustrates the nature of the NAND 8ate output when the .,- '' :
gate is enabled by the coincidence of the "101" count from the counter ; --107 (through AND gate 108) with the RM output from the rate multiplier 102 and the C~K output from the clock 100. In this regard~ the normally positi~e output of the NAN~ gate 125 goes negative. m e RM
output pulse which co~nts the counter 107 to the "101" state does not generate an output pulse from the MAMD ~ate 125. I~stead, the next RM pulse, which does not paB~ as counting input to the counter 107 ; since the Q output o~ the flip-flop 105 is then "false", gates the next clock pulse through the NAND gate 125 (rate multiplier counting .~

'~'''`'' 1~5~g9~ `

state "4") to create a negative pulse out o~ the NAND gate with a perlod equal in duration to the positive clock pulse.
FIG. 7f lllustrates the electrical output of the differentla-tor 131 and shows a "reset" pulse in the form of a positive spikeJ
shorter than the normal CLK period, generated by the positive golng output (trailing edge of the negative pulse) Or the NAND gate 125 ~ -~FIG. 7e). As can be seen from the timing waveforms, the "reset"
pul6e ~rom the differentlator 131 appears at the time that the clock goes from its "true'l state to its "~alse" state, or from a po~itiYe to a negative transition, assuming positive logic.
FIG. 7g illustrates the Q output of the compensation co~trol - flip_flop 127 which enables counting up of the counter 107 at double the count rate (i.e., at the full RM output rate) for the period of ;
100 clock pulses, the latter being the period of a single motor dri~e pulse at the fill frequency o~ l~04 Hz.
Considering now the transition period for the "101" count state of the counter 107, assume that the counter input ha~ Just placed the counter in the "101" state. As a result~ the gate 108 has been enabled and the binary flip_flop 105 has also been "reset". It will be observed that the counting input to the counter 107 is generated by coincidence o~ the "true" state of the ~lip~flop 105 ~nd the occurrence of an RM rate multiplier pulse. m erefore, the same pulse that adYances the counter 107 to its "101" state also always reset~ -~
;~ the flip-flop 105. The very next rate multiplier pulse will now enable the NA~D gate 125, but, as previously indicated, does not count up the counter 107 because of the "false" Q output from the flip-flop - 105 which had been reset. At the end of the clock period, the "reset"
outpu~ appears from the dif~erentiator 131 to force the fllp-flop -;
127 into its "true" state (FIG. 7g) ~hile simultaneously re~etting the rate multiplier to its "zero" state (FIG. 7a). From this point on~
; the flip-flop 127 will remain "true':, which results in the flip-flop 105 being forced into the "true" state through its asynchronous "set"

input. This, in turn, results in enablement of all the RM pulses into . . , -33- `~
:::

the counter 107. All of the changes in counting state of the counter 107 occur at -the same times that the RM pulses appear, with a one-to-one pulse correlation 80 that the RM pulse frequency is no longer divided by two prior to counting up the counter 107.
After 100 clock pulses~ or a period equal to 2.475 milli_ seconds~ at the "9" state of the rate multiplier, the ~ill freguency signal enables gate 112 at the clock transition from "true" to "false"
~` a~d resets the flip-flop 127. The flip-flop 105~ however~ stays "true' for one more RM pulse. miS latter RM pulse will still be paased as a counting pulse to the counter 107~ but the flip-flop 105 will be "reset" at the same time and~ from that poir.t on~ alternate RM pulses will be suppressed by the divide_by-two flip-flop 105.
The reason should n~w also be apparent ~or resetting the high order decades of the rate multiplier 102. Since the decoding provides the divide-by-ten output at the count of "9"~ the rate multipliers could start out at any number other than zero~ just by chance~ if the rate multipliers were not "reset" at the beginning o~
; each counting cycle of the counter 107. Such a random state of the rate multiplier would shorten the period of time during which counting is accomplished at double counting rates ~or compensation puIposes.
~his time for doubling the counting ~requency could vAry randomly ~rom 2ero to 2.475 milliseconds, whereas correct compensation c~lls . . .;:
for double counting rate of the counter 107 ~or exactly 2.475 milli_ seconds during the generation of each pump stroke motor drive pulse.
- Referring now more particularly to FIG. 6b~ forward-reverse speed control, i.e.~ the selection of fill frequency or pump frequency for the motor drive pulses over line 157 to the stepping motor driver ~58, is next described.
` Directional control, as previously indicated, is accomplished with the aid of the timing flip-flops 141~ 142 under the control of the directlon sen60r 140. When the switsh 140a is closed~ indicating that the valve control system i6 at the end of the pump stroke and prepared to initiate a ~ill ætroke~ a non_synchronous enabling signal i6 _34_ ,, ~ ' ,~ ' ' . " ' , . '. , ', , . , . . ~

99~

directed over line 170 to the D input of the flip-flop 141. me clocking input of the flip-flop 141 receives the 40.4 Hz. slgnal from the rate multiplier 102, over line 143, and will set the flip-flop 141 "true" on the very next 40.4 Hz. clock pulse.
me "true" state of the ~lip-flop 141 is directea oYer line 146 to the D input o~ the flip-flop 142 and~ a single 40.4 Hz.
pulse period later, i.e., 24.75 milliseconds later, the flip-flop 142 will also be set "true" on the very next 40.4 Hz. pulse, directed -~
over line 144 to the clocking input o~ the flip-flop 142. ~ence, the flip-flop 142 always foll~rs the flip_~lop 141 by a period of approxi-mately 25 millisecond~ thus providing sufficient time for the stepping motor driver 158 to come to a complete stop after each stroke and reverse direction for the next stroke.
It will be apparent, therefore~ that with the Q outputs of both flip- Mops 141, 142 "true", the system is about to perform a fill stroke to fill the syringe cartridge from a suitable liquld source7 whereas when the Q outputs of both flip-flops are "true", - the system is about to perform a pump stroke. When the flip.flop6 ~;
141, 142 are not set to the same stateJ the ~ystem is in the minimum 25-millisecond transient period bet~reen strokes7 all~tlng the motor to come to a stop and reverse. ~`
It will also be apparent that, while the minimum period for ., ~
; ~witching both of the flip-flops 141, 142 from one state to ~cother is approximately 25 milliseconds, the period can be as long as twice that period. The latter condition would occur if the asynchronous ~ignal over line 170 from the direction sensor 140 occurs immedlately ; ~
after a 40.4 Hz. clocking input on line 143 has just occurred, thus ~ ;
,: ~
requiring an addltional 40.4 ~z. clock perlod (25 milliseconds) -before the first timing Pli~-~lop 141 change6 state. In contrast3 : ~ ~
if the signal over line 170 occurs immediately before such a clocking ~-; pulse on line 143~ the period for motor reversal will be at the minimum -~
time of 25 milli~econds~ since the timing flip-~lop 141 will change state almost immediately.

. ,~ .

.: , ;, ~5~636 The AND gate 148 receives as inputs, over lines 172, 173, the Q outputs of both of the ~lip-flops 141, 142, respectively. The , ~ , output of the AND gate 142, over line 175, will be "true" only when both of its inputs from the timlng flip-flops 141, 142 are "true".
~owever, slnce the Q states of both flip-flops 141, 142 being "true"
defines the "fill'/ state for the system, a "true" output from the --gate 148 over line 175 indicates performance of a fill stroke. The latter output over line 175 passes through the OR gate 154 as enabling input over line 176 to the AND gate 151, the other input to the gate 151 being the 404 ~z. fill frequency over line 113. The fill frequency i9 thus pas6ed by the enabled gate 151, over line 178, through the OR B~te 155, and over line 179 as input to the motor drive pulse AND
gate 152, the other input to the gate 152 being the CLK pulse over line 101 for synchronization purposes. Hence, during the fill stroke of the syringe pump, motor drive pulses to the stepping motor driver 158 are provided on line 157 at the output of the gate 152, at the designated fill frequency of 404 Hz.
When the syringe is completely filled, the valve control subsystem controlling the direct~on sensor 140 causes the switch 140a . -, .
to open to the "pump'~ position and thereby provides a "false" input to the D terminal of the flip flop 141. The next 40.4 Hz. clock pulse, over line 143, reset6 the flip~flop 141 "false" which immediately di~ables AND gate 148 and, consequently, also disables the fill freguency AND gate 151 (through the OR gate 154), so that no further ~:
motor drive pulses are generated at the fill frequency. Indeed, as will become apparent, in the time interval during which the timing flip_flops 141, 142 are in different states from each other, no motor ~ ;~
drive pulses at all are provided to the stepping motor driver 158, thus allowin~ the motor to stop between strokes prior to reversing direction.
Another 24.75 milliseconds later, the timing flip~flop 142 : . . . .
follows the setting of the flip-flop 141 and goes "false", thus establishing the "pump" state where the Q outputs of both flip-flops `~
6 j.

-l~S1~6 141, 142 are "true". The Q outputs o~ the tlming flip-flops 141, 142 are both directed as enabling inputs over lines 181, 182, respectively, to the pump frequency AND gate 149 which receives as a third input over line 109 the pump frequency output from the counter decoding gate 108 (FIG. ~a~. A fourth input to the pump frequency gate 149, over line 183, is normally "truel'7 except when the system i6 being initially started and no syringe cartridge has yet been installed Assuming, for the moment, that the syringe c~rtridge is already installed, all inp~tæ to the pump frequency gate 149 are "true", thus pa~æing the pump frequency over line 185, through OR gate 155, over line 179, through AND gate 152 in synchronism with the CLK
frequency, to provide frequency compensated motor drive pulses on line 157 at the selected pump flow rate in accordance with the setting o~ the rate selector switches 102a (FIG. 6a).
`~ Again, when the pump stroke has been completed, the timing ~lip~flop 141 will again change state, the motor will come to a stop ; during the transition period when the flip~flops 141, 142 are in di~erent states (with all motor drive pulses being gated off) and~
when the flip-flops 141~ 142 assume the san~e state after the tranBition period, motor drive pulses of the appropriate frequency will ~gQin be directed over line 157 to the stepping motor driver 158.
The particular direction in which the stepping motor driver ` ~
158 rotateæ is determined by conventional forward-reverse control ~ ;
logic well known in the art for such stepping motors, and the control signal for such conventional circuitry is directed to the motor driver . - , 158, over line 187, from the Q output of the timing flip-flop 142.
Typically, such stepping motoræ involve a two_phase drive æy~tem with t~o separate windings. m e current is alternately inverted in one of these wlndings at a ~ime. m erefore, to make one step of the motor, ;~-the current is inverted in one of the windings~ while the next step is - accomplished by inverting the current in the other of the pair of ~,:
windings. The forward or reveræe rotation of the motor is dependent merely on the relative phase of the two windings.

, ..

~5~g~6 : ~

e alarm and start up subsystems for the syringe pump will now be more specifically described, reference being made particu-larly to FI~. 6c for the ensuing de~cription.
The alarms subsystem contains a drop detector 190 which i~
e~sentially a combined light beam and photocell detector, as previously descrlbed in connect$on wlth the drop detector 20 in the basic system ~ of FIG. 1.
;~ A drop rate discriminator 191 generates an output signal if ~ the drops sensed by the drop detector 190 are received at below 8 -~ 10 prescribed minimum rate. Since the syringe cartridge is filled durlng the fill stroke at a pre-established~ fixed flow rate of 5 cubic ; centimeters in approximately 9 seconds, the minimum ra~e at which drops should appear ln the drip chamber of the I.V. set i8 readily ascertain- ;
able. If the drop rate i8 below the prescribed minimum, the drop rate di~criminator 191 generates an output signal which is used to place ~`
- : -the system into alarm. m e drop rate discriminator 191 includes a ~`
conventional diode pump rate meter circuit well known in the art, the ~ ;
rate meter feeding an appropriate eate havi~g a threshold representing ;;~
, . ~ . . ~
the minimum drop ~low rate and thereby providing the desired discrimina-tion function.
~ An AND gate 193 is the alarm gate for leak detection during .~ à pump stroke~ i.e., the detection of drop flow in the drip chamber when a pump stroke is being performed~ while & NOR gate 194 is the alarm gate for leak detection or detection of an exhausted 11quid ~; ~ source during the fill stroke. A delay 195, typically a cor~ventional -~;
resistance_capacitance delay circuit~ troduces a delay of approxi~ate~
ly two second~ in the response of the leak detection gste3 193, 194 at the beginning of a pump stroke in the case of the gate 193 and at ~he i beginning of a ~ill stroke in the case of the gate 194.
The reason ~or the in~roduction of the delay 195 is that, - when the syringe is ~ust beginning to be filled~ there is usu~lly no ~ ~-actual drop flcw in the drip chamber ~ince it takes a short period of tlme ~or the pressure to build up when the fill stroke begins.
_38_ " l~S8~96 Therefore, a short delay is needed during this initial "no drop"
period to avoid golng into an lmmediate f`al~e alarm condition. The ~ame delay is also used ~fter the fill stroke has been completed since when the motor ~tops, drops may still fQll through the drip chamber of the I.V. set for a very brie~ interval. These drops~ if detected at the beginning of the pump stroke, would otherwise indicate a leak in the system and, likewise, would produce an immedlate false alarm condition.
An air detector 197, typically comprising a light emitting diode and photocell detector combination, disposed on opposite sides of the I.V. tube or syringe cartridge nipple, detects any air bubble~
passing through the line which interrupt a re~erence light beam and generate an output pulse for placing the system into alarm.
A "power on and reset" subsystem 198, which is essentially a delayed signal produced whenever the main power switch is turned on, provides a "true" signal for a prescribed period of time until all ;~
of the power supplies have reached their normal operating voltages a~d all of the required delays have occurred for the overall system ; :
electronics to initialize to its normal operating state. ~`
The subsystem 198 is used to force the system initlally into !
sn alarm co~aition when the pcwer is ~irst turned "on" and is also used to ~ense the condition when the pcwer is "on" but no syringe cartridge has yet been installed in the pumping apparatus. In this regard, a ~yringe detector 199, which may also be a light beam and ~ photocell sensing arrangement to detect the physicQl presence of a - syringe cartridge, is utilized. ~he detector 199 provides an output , , : .
-, signal which is inverted by an inverter 201 and~ in conjunction with other gating, forces the system to generate a control signal, when the power iæ first turned "on" and no syringe cartridge has been detected. This control signal (GTS) causes the syringe piston actuator (represented by the drive subsystem 12 in ~IG. 1~ to be driven all the way to the end of the pump stroke in preparation ~or subsequent ;~
lnitiation of a fill stroke after a syringe has been properly installed , .
3g ~ .

, , . ~ . . . . . ..

-~L~51~"3~6 and detected.
This is another ~eature o~ the invention, in that it has been determined that a syringe ~hould be comple-tely empty and mounted into the pumping apparatus with ~he syringe piston all the way in (towards the inlet and outlet ports in FIG. 1) as the prescribed format for insertion of the syringe into the apparatus for initial start-up, i~e., it ha6 been determined that system operation should begin with a fill stroke. Hence, the ~yste~ is designed to force the pu~ping apparatus into the condition where the syringe cartridge can be easily inserted prior to sctual operational start_up.
The detection of a stalled stepping motor also forces an ;~
alaxm condition upon the system. The stalled motor alarm compri6es - a rotation senæor 203 directing an appropriate motor rotation signal ; to a counter 204 through an OR gate 205. The counter 20~ counts motor drive pulses snd ls "reset" by the motor rotatlon slgnal. Such motor stalllng has a greater probabllity o~ occurring when the pump is used wlth a downstream filter whlch may clog and induce hiBh back pres6ure on the pumping 6ystem.
m e rotation sensor 203 is typically a disc mounted on the - 20 stepping motor output shaft for rotation therewith, the disc having -; :
alternate transparent and opaque 6ectors. A photocell detects li~ht from a reference light source pas6ing through the disc, as it rotates~
and generates the "re6et" pulses to the counter 204. If the counter reaches a predetermined number of motor drive pul6es without being "reset"~ the sy6tem is put into alarm.
- An OR gate 207, which iB the master alarm gQte~ collects all o~ the various alarm lines from the alarm monitoring subsystem6 pre_ `
viously described. The output of the alarm gate 207 is directed to a pair o~ cross~coupled NOR gates ZO9, 210 defining a latching circuit which latches either in the alarm state or in the normal sy~tem opera- ;~
tion ~tate. A "true" output from the OR gate 207 to the input of the NOR gate 210 will normally force the system into the alarm st~te. -A "start" switch 212 6electively ground~ the input of the ;
_11.0- , ' 1~5~39~;
NOR gate 210 and forces the system into the normal operational s-tate if all o~ the alarm conditions have been removed so that the output of the OR gate 207 i9 "false", thus enabling the system to st~rt.
Another pair of cross-coupled NOR gates 214~ 215 define a "start_up" latch for the system which, in conJunction with the power_on reset subsystem 198 and syrinee detector 199, operate to provide an output "go to start" (GTS) sign~l whicb causes the ~ystem to operate the stepping motor driver at the high fill frequency rate and rapidly ~ move the syringe piston actuator to the position for readily receiving ~;~
.~ 10 a syringe cartridge and initiating a fill stroke. In this regard, an AND gate 216 is used to sense the condition where the syringe actuator has ~irst arrived at the latter position~ which occurs in the transient period between the end of a pump stroke and the beginning of the next fill stroke.
A second or back_up "no drop" alarm which normally does not oper~te~ but assumes control if the normal "no drop" alarm failed to . . .
~` detect a lack of flGw during a fill stroke~ is used in the system to prevent the pumping o~ air into a patient which might otherwise be -~
caused by a single system component failure.
:
; 20 The bac~_up "no drop" alarm system includes an accumulator~
discriminator 218, an AND gate 219 and a latch 220. The accumulator-discriminator 218 is again a conventional diode pump circuit w~lich contains a charging capacitor. ~he latter capacitor gets charged up - by output pulses from the drop detector 190. At the end of the fill stroke, the accumulator charge is sensed and~ if it is too low~ the -`
latch 220 is activated to shut off the stepping motor driver 158.
The back-up "no drop" alarm system is deactivated in the "go to start" mode which occurs when the power is turned "on" and no syringe cartridge has yet been installed. However, the back_up alarm system~ once activated~ cannot be reset by the start switch 212 `~
(as in the case for other alarm conditions) since its activation lndicates a basic system malfunction. ~he back_up alarm sy~tem can be ;~
clear~d only by turning the instrument power lloff'l.

, ~ , , : , . , , , ,, ~ :~ :

~s~
An additional back_up alarm system is provided in the form of a high rate alarm which alarms and deactivate6 the s-tepping motor driver 158 in the ~vent o~ component f~ilure which induces a runaway condition. This condition is manifested by the pump running at maximum pumping rates, even though a low pumping rate has been selected by the -rate selector switches 102a. me high rate alarm subsy6tem includes a rate coMparator 222 which compares the motor drive pulses in the pump stroke with the current from a high order decade rate selection sensing subsy6tem 223 (FIG. ~a), to selectively energi~e the latch 220 whenever the motor drive pulse6 being 6enerated exceed the drive pulse ~ -rate which should be generated in accordance with the 6elected fluid flow rate.
Essentially, the rate comparator 222 is a diode pump rate ;~
motor circuit that generates a current which is counteracted by the ~
current generated by the weighted resistors in the rate selection ;~ ;
; senRing subsystem 223. ~enceJ the rate meter generates a current which ;~
is proportional to the frequency of the motor drlve pulses in the ;~
pump stroke. This current is compared with the current generated by .;~
a series of weighted resistors 223a_223d co~nected to the high order ;`
:, .
rate selector switches 102a. Thus~ when the current senæed by the rate ~; meter exceeds the current generated by the resistors~ the system is put -into alarm by activation of the latch 220 which then prevents the step~
ping motor driver 158 ~rom running. Again, this alarm can be cleared only by turning off the electrical pcwer~ since activation of the alarm ` -indicates a basic system ~Rlfunction.
With the aforedescribed outline of the basic alarms and ,~
~ start~up subsystems components a~d their functional interrelationship~
.:
the various operational sequences for these subsystems are ~urther :
;` detailed in the follcwing description.
A~ previously indlcated~ the NOR gates 20g~ 210 are elec-trically interconnected as a cross_coupled latch which e9sentiallY ;;~
defines a non_synchronous set-reset alarm flip-flop providing an output over line 225 defined as the alarm signal (ALA). The AIA
:
1, ., ~
.... . . .. . .
. .. - ,, ~, . .:, , " - - -: . .. ; . .
: :: . - , , : .. ; , . . :

., . ~, .. .. . . . .. . "

signal is also dlrected over line 226 to the atepping motor driver 158 (FIG. 6b) and thereby provides, by conventional stepping motor cir_ cuitry, a shut-off control signal for turning off the power to the stepping motor.
The NOR gates 214, 215 represent another cross-coupled latch which is the "start_up" latch for syrlnge cartridge loading, and the latter latch gets activated when the system power is first turned "on" and a syringe cartridge has not yet been installed. In thls regard, regardless of the position of the syringe piston actuator in the drive system, when the power i9 first turned "on"~ it will always be driven to its position at the completion of a pump strokeJ 80 that the syringe cartridge can be easily inæerted in preparation ~or a fill stroke.
Assume, for purposes of explanation, that a syringe has not yet been in6talled~ and the syringe piston actuator of the drive sy~tem ;~ ~`
is in some random position between initiation and completion of any stroke. When the electrical power is inl-tially turned "on", the power on reset subsystem 198 provides for a brief period, typically ~ ;
200 milliseconds, a "true" output signal over line 228 which is also , directed over line 22g aB an input to the alarm gate 207J consequently ~ providing a "true" output from the latter gate, over line 230, aB an ~`
- input to the NOR gate 210. This drives the output of NOR gate 210~
over line 231, "~al~e". ~he power on reset signal on line 228 is also directed a~ an input to the ~OR gate 214, thus driving the output of that gate likewise "false" on line 233~
Since a syringe has not yet been installed, the syringe detector 199 provides a "false" output, over line 234, as one input to the NOR gate 215. ~he gate 215 receives a second "false" input, over line 235, from the output of the NOR gate 214 previously di6cussed.
qhe gate 215 receives a third input, over line 236, from the 8ate 216 ` -~
which is normally disabled and therefore provides a normally "false" ~ -output. Hence~ since all of its inputs are "false", the NOR gate 215 is enabled and provides a "true" output on line 237 which i~ defined as ~ 43 ; , ~ . . , ~s~g6 ~

the "8 to start" (GTS) signal.
The "true" output (GTS~ of the gate 215 i8 also directed as an input~ over line 238, to the NOR 8ate 214. The latter input holds the gate 214 disabled to maintain a "false" output~ over line 235~ as input to the gate 215 (even after the power on reset period has pas3ed)~ and therefore Latches the NOR gate 215 in the "true"
(GTS) state.
The "true" output of the gate 215, or GTS signal, is also ~ ;~
directed over lines 240~ 241 as one input to the NOR gate 209~ thus holdlng the output of the gate 209 "false". Although the pcwer on reset subsystem 198~ through the alarm gate 207~ had activated one input of the NOR gate 210 on line 230 and, there~ore, resulted in 8 "false" input to the gate 209 over line 231~ the "true'` GTS 3ignal i ~-on line 241 still holds the output of the gate 209 "fal~e" and there- ~
: ,,~ . , .
- fore prevents the system from going into alarm and shutting off the stepping mo-tor driver 158. Moreover, as soon as the power on reset period has passed~ both of the inputs to the NOR gate 210 will be .. . .
"~al~e"~ since the "false" output o~ the g~te 209 is connected over ~ :
line 243 as the second input to the gate 2:LO~ thus driving the output ;
of the gate 210 "true" on line 231, to again latch the gate 209 80 that ; ;~
its AIA signal output is held "~alse". ~his defines the stable "go to start" or GqS condition.
:: ~
The electrical output o~ the NQR gate 215, or GTS signal~
is directed over line 240 as an input to the OR gate 154 (FIG. 6b) which enables the AND gate 151, over line 176, to pass the 404 ~z.
fill frequency through gates 151, 155 and 152 and thereby provide ~ -fill frequency motor drive pulses over line 157 to the stepping motor -driver 158. Hence~ the gate 151 is enabled by the GTS signal inde~
pendently of the gate 148 and~ therefore, independently o~ the status ., ~
o~ the direction control timing flipoflOps 141, 142.

The fill frequency drive pulses energize the stepping motor driver 158 until the syste~ senses tha-t the syringe piston actuator has been driven to the position which indicates completion of a pump _44_ ' ., :. . . .. .

~C~5~3~96 stroke and transltion to a fill aitroke, the latter condition signaling the end of the "go to start" or GTS .state. The GTS signal over : line 240 is also directed throueh an inverter 242 (FIG. 6b) to disable the AND gate 149 and thereby prevent the pump frequency from being ~:
applied simultaneou~ly with the ~ill frequency while the system is in the GT~ state with no syringe cartridge yet installed.
It is, of course, necessary to disable the stepping motor driver 158 when~ at the end of the GTS state, the desired po~ition of the syringe piston actuator has been reached~ so that a syringe car-tridge can be installed. In this regard~ as the piston actuator i8 .~ ~
.~ moving towards the desired poaition calling for initiation o~ a fill ~.. .
stroke~ the system will be performing a pump stroke, which means that the ~ output of the timing flip-flop 142 will be "true".
. As soon as the pump stroke has been completed~ the direction sensor 140 will be switched to the "fill" position and the tlming flip_flop 141 will be set "true" while the flip-flop 142 remains "~alse" for a period of 24.75 milliseconds~ It will be apparent that~ when the flip-flop 142 is "false"~ its ~ output over line 244 provides a "true" input over line 245 to the AND gate 216. In ~ -,: , .
addition~ while the flip-~lop 141 is "true"~ the other input to the ~ ~.

AND gate 216~ over li~e 246, is likewise "true"~ thus enabling the -~ g~te 216 and providing a "true'7 output over line 236~ as one input to the NOR Bate 215. miB cauæes the output of the gate 215 to go `~
alse"~ thereby terminating the GTS signal and the "go to start~
. ', '' ,: .
state~ the latter state being latched out by the interaction of the NOR

gates 215 and 214. In this regard9 since no syringe cartridge has yet .. ;
. ~", been installed~ a "false" input over line 234 is fed to the NOR gate 215~ but is of no effect in vlew of the "true" input over line 236 from the gate 216.

The "false" output ~rom the gate 215, over line 238~ is .;
.: . . .
directed as one input to the ~OR g&te 214~ the other input to the ;~

:~ gate 214~ over line 228, being also "false" since the power on reset period has long aince passed during the GTS state. This results in .: _45_ 1~5~96 enablement o~ the NOR 8ate 214 and a "true" output, over line 235, as input to the NOR gate 215 to latch the gate 215 in its "false"
output state, thus holding off the GTS signal.
The absence of a syringe cartridge produces a "false" output from the syringe detector 199, the output being inverted by a "true"
signal by the inverter 201 and directed over line 250 as input to the alarm OR gate 207 which results in a "true" output from the gate 207 as input over line 230 to the NOR gate 210, thus driving the output of the gate 210 I'false". Since the GTS signal is now "false" as just describedg both of the inputs to the NOR gate 209 are now "false"~
; thereby enabling the gate 209 and providing a "true" ~utput over line 225 which places the system into the alarm state and shuts off ~
the stepping motor driver 158, via the ALA signal over line 226. ~ -; ~he pair of NOR gates 209~ 210 are latched in this alarm condition and cannot be brought out of this condition until a syringe cartridge has been i~serted and detected b~ the syringe detector 199, to drive the input over line 250 to the alarm gate 207 "false". When ~; this has occurred~ the "start" switch 212 is manually closed and forces the input to the NOR gate 210, over line 243, "false". In this regard, ` 20 the output of the gate 209 is connected to ~round by the "start"
switch 212. A current-limiting series resistor 251 is provided, in --~
view of the high level output from the gate 209. Since all the other alarm lines providing input to the alarm gate 207 should also be -~
: .
- "false"~ the other input to the NOR gate 210, over line 230, should also be "false", which makes the output of gate 210 go "true"~ thereby forcing the output of NOR g~te 209 "false" and removing the alarm ` condition. -~
Hence, the normal "start-up" sequence of events in operating . ........ . .
the overall syringe pump system i8 summ~rized as follows. Turni~g on i ........ . .

-~ 30 the pawer with no syringe cartridge yet installed results in the "go .:, . :, to start" state generating a "true" GTS signal which causes the syringe piston actuator to be driven rapidly at the fill frequency to the position where a fill stroke i5 about to be initiated~ which is the _~6~
. .

. i ", - . , .. .: ..

5~ 91 6, proper po6ition ~or receipt of the syringe cartridge. ~uring the transition period between the completion o~ the pump stroke and - initiation of the fill stroke~ the gate 216 disables the GTS signal and the gate 209 generates the ALA signal which shuts o~ the stepping motor. A syringe cartridge is then inserted and detected. Closlng the "start" switch 212, after the ~yringe cartridge has thus been installed, latches out the alarm condition and enables normal system operation to p~oceed~ with ~illing of the syringe preparatory to a pump stroke and subsequent repetitive operational cycles in the normal mode of sequentlal fill and pump strokes.
~` m e drop detector 190 provides a "true" output signal over line 253 each t$me a drop is detected, to provide a pulse input to the AND gate 193. ~he gate 193 also receives input over line 254 from the Q output of the timing ~lip-Plop 142, and thus receives a "true"
enabllng input whenever the system is in the pump stroke. In addition, the A~D g~te 193 receives a third input~ over line 255, which i8 the ~ ~
pump stroke signaI on line 254 delayed by the delay network 195, and `
which typically introduces a delay o~ approximately two seconds.
~ence~ after the delay has pa~sed~ the input over line 255 to the ~ate ` 20 193 w111 be "true" only while a pump stroke is being performed.-~ Therefore, i~ any drops are detected by the drop detector 190 after this delay period, the output ~of the gate 193 will go "true", over line 257, as an input to the alarm gate 207, putting the NOR gates 209 210 into the alarm condltion. In this regard, no drops should be detected during the normal pump stroke. m e purpose of the delay 195, as previou61y indlcated~ is to avoid going into a false alarm condi_ tion, aince drops may conti~ue just momentarily at the beginning o~
the pump stroke.
~ When the system is performing a fill etroke, the ~ output .~ 30 of the tlming flip-flop 142 will be 1'false"~ disabling gate 193 so .:
that the latter gate cannot possibly place the system into an alarm condition. Xowever, the "false" ~ output of the flip-flop 142 provides an enabling input~ over line 254, to the NOR gate 194 which 47_ ,. . . . . .. .

~5~ >

can go "true" only when all of its inputs are "~alse". Another input to the NOR gate 194, over line 255~ is the delayed Q output signal from the flip_flop 142, which will go "false" only after approximately two seconds. The third input to the NOR gate 194, over line 259, i8 the output of the drop rate discriminator 191.
In the ~ill stroke~ a prescribed minimum drop rats should ~ ~-appear in the drip chamber o~ the I.V. administration set and be detected by the drop rate discriminator 191. If the detected drop ;~
rate is below the prescribed minimum rate, the output of the discrim-;. ~ . :
inator 191 goes "false"! The latter condition, in turn, provides a third "false" input to the NOR gate 194, thus enabling the gate 194 ~ ~ -to provide a "tru~" output, over line 260, as input to the alarm gate i 207 which places the system into an alarm state through the cross_ coupled ~OR gates 209, 210. lf, however, the detected drop rate is above the prescribed minimum rate, then the output of the discriminator x, ~ , 191 will be "true", and the output of the ~OR gate 194 will be "false", ~ ~;

thus avoiding the alarm state.
, The operation of the aforedescribed "no drop" leakage `-~ detection subsystems is further described i~ connection with the wa~e~orms of FIGS. 8a_ & .
FIG. 8a indicates the Q output statu~ of the direction ~ control timing ~lip-flop 142 (FIG. 6b) and lndicates that when Q is f, "true", the system is in a pump stroke~ whereas when Q is i'false"~
i the system is in a fill stroke. .
~' FIG. 8b illustrates the electrical output of the delay 195~
over line 255~ to the AND gate 193 and NOR gate 194. Mote that the ~ -j resistance_capacitance circuitry of the delay 195 builds up voltage ; when~ver the ~ output of the flip-flop 142 is "true"~ and decays through a similar delQy period when the ~ output goes "false".
Referring now to FIGS. 8c and &, the waveforms depict the ; ~-effects of the combination of enabling inputs on the AND gate 193 in ;~
~`~ FIG. 8c, and on the NOR gate 194 in FIG. 8d. The combined gQte inputs are from the ~ output of the timing ~lip-flop 142, over line 254~ and _48_ :'; .

. : : . : , . ., i .: ~

~`~
39~6 the delayed Q output signal from the delay 195, over line 255. In FIG. 8c~ the combined inputs to the AND gate 193 are enabling when the 61gnal is high, and the inputs are disabling ~hen the input is lcw. In FIG. &, the combined inputs to the NOR gate 194 are enabling when the signal i8 low and the inputs are disabling when the sienal i8 :~
high.
In FIG. 8c~ it will be apparent that the input to the gate 193 is enabled with a delay from the time that the system switches from the "fill" state to the "pump" state. However, the gate is disabled immediately in switching from the "pump" state to the "fill"
state. Xence, the gate 193 will not place the system into alarm, ~ ;
even though some drops may be detected during the initial portion of the pump stroke~ so long as no drops are detected a~ter the delay ~ ;
period has been completed and -the gate 193 is enabled to respond to such detected drops. ~ -In contrast~ as observed in FIG. &, the input circuitry ` -~ of the NOR gate 194 is enabled during the fill stroke and is disabled ;;l immediately when the system switches from the fill stroke to the pump stroke. However, the NOR gate 194 input circuitry is not enabled again until after the delay period has passed in switching ~rom the i. . : . , pump state to the fill state. Hence, the gate 194 will not generate ; a false alarm at the beginning of the fill stroke, even though no .: . .
drops have yet been detected, so long as the drop rate has built up to the prescribed minimum level by the time that the delay has passed and the gate 194 is enabled.
The bubble detector alarm includes the air detector 197 which, as previously indicated, typically comprises a photocell and reference light beam combination across some portion o~ the transparent I.Y. line or across one nipple of the syringe cartridge. If the air detector senses bubbles, which are detected by interruption of the ~ -light beamJ a "true" signal is produced by the air detector, over line 262, to the alarm gate 207 which place~ the system into an alarm :~:
condition and shuts off the stepping motor driver 158.

~; ~49-. , .,; . . ., , , . ,, . , , . .,. , ~, , ~ , .

~5~39~6 The back-up "no drop" alarm sub~ystem, comprising the drop `
detector 190, accumulator-discriminator 218, AND gate 219 and latch 220 senses lf a suf~icient number of drops were received during the ~ill stroke. If a su~ficient number of drops were not received, and the primary "no drop" alarm system has not been enabled for some reason, as might occur in the case of a faulty system component, the back~up system will turn of~ the system power to the stepping motor driver 158. The back up "no drop" alarm subsystem is effective only :. :
subsequent to the operation of the normal leakage detection subsystem.
In this regard~ the normal "no drop" alarm system will be activated during the fill stroke, in the manner previously described~ whereas the back_up system will be activated only after the fill stroke has - been completed. ~ ~ -The accumulator_discriminator 218 is also a diode -pump circuit similar to the circuitry used for the drop rate discriminator 191~ and the latch 220 is typically an operatlonal amplifier but could readily be other circuitry such as a set_reset ~lip_flop or a pair o~
, ~
cross_coupled NOR gates similar to the gates 209, 210. When the latch ` 220 is activated~ it provides an electrica]. output9 over line 264, to ;-shut o~f the stepping motor driver ~58. ~;

The electrical output of the accumulator-discriminator 218~
,.'1 ' , ` over Iine 265, i8 normally "true", and is directed as one input to ~ ~
,. ~ '~.. , ~.
the AND gate 219. The gate 219 also receives an input~ over line ` 266, which is the Q state of the timing ~lip-flop 142, and receives ., ~. , .. - an additional input over line 267 from the Q output of the timing `~
flip_flop 141. Both of these inputs over lines 2667 267 will be "true"
at the very end of a fill stroke when the flip-flop 141 has ~ust been ~et "false" to indicate that a pump stroke ls next to be performed.
An additio~al input to the gate 219 is provided,over line 268, ~rom ~;
the output of the NOR gate 214~ the latter input being "true" only when the system is not in the "go to start" state~ during which tlme the alarms should be deactiv~ted.
The Q state of the timing flip-flop 142 is also directed~
, . . .

:

::: . ' - - : ' :
: - :

~58~96 over line 266~ -to the accumulator~discriminator 218 80 that the discriminator iB operative only during the fill stroke. The accumula-tor_discriminator 218 receives an input~ over line 269, from the drop detector 190 and goes "false" when tbe correct number of drops have been detected. Hence, when the system switches from the fill stroke to the pump stroke, the gate 219 will stay disabled if enough drops have been detected to provide a "false" output from the accumulator~
discriminator 218 over line 265. On the other hand, if a sufficient number of drops were not detected by the drop detector 190 during the fill stroke~ the output of the accumulator-discriminator 218 over -line 265 will be "true", the AND gate 21~ will be enabled during the ;~
transition from the fill stroke to the pump stroke, and an output will be dlrected over line 270 to set the latch 220 and shut of~ the step_ 1 ping motor driver 158. ;
i Re~erence is now made to the stalled motor alarm, which ~ includes the rotation sensor 203~ the OR gate 205 and the counter , -' 204. qhe counter 204 is continuously reset over line 272 each time i a pulse is generated by the rotation sensor 203~ over line 273~-~:
through the OR gate 205. me counter 204 is counted up~ over line 274~ by the stepping motor drive pulses from the output of gate 152 ~- (FIG. 6b). An additional input~ over line 275~ is fed to the OR
. , .
gate 205 from the output of the NOR gate 209. The purpo~e of this additional input over line 275 is to reset the counter 204 whenever ;
there is an alarm state~ so that the counter will start out in the "zero" state each time the pcwer is turned "on". Otherwise~ the counter miehk come on in any random state and the next motor drive pulse could put the system into alarm. In this connection, unless the system is in the "go to start" state~ the system alarms whenever the power on reset subsystem 198 is activated, as previously indicated. ~ -However~ when the "start" switch 212 is closed after installation of a syringe~ and the pcwer on reset period has passed, the AIA signal is ~ ;
.. . ~- .
latched out.
me high rate alarm subsystem~ comprising the rate comparator :;
; :

39'9~

222, the high rate selection sensing subsystem 223 (FIG. 6a)~ an AND Bate 277 and the lstch 220J is next described.
The rate comparator 222 is typically a diode pump circuit ` ; ;
: which compares the pulse rate recei~ed over line 278 with the current generated on line 279 by the weighted resistors 223a, 223b, 223c, ~; 223d proportional to the setting of the high order rate selector ; switches 102a. The pulse input, over line 278, i8 the output from the AND gate 277, which is only enabled by the "true" Q output of the timing flip-flop 142 (FIG. 6b) over line 244, indicating th~t the ; 10 system is performing a pump stroke. me gate 277 receives as a second .:~ .
i-nput, over line 274, the stepping motor drive pulse output from `
the AND gate 152 (FIG. 6b). Hence, the rate comparator 222 is opera-tive only during the pump stroke to compare the actual motor drive pulses being generated with the flow ra-te actually selected by the rate selector switches 102a.
If the motor drive pulse rate is higher than the rate that ;~
has been selected, as indicated by the high rate selection sensing subsystem 223, the comparator 222 will generate a signal, over line ;~
., .. ~
280, to set the latch 220 and shut off the motor drive via the latch `~

output on line 264. The latter alar~ state will occur only if a high ~ rate of motor drive pulses is generated while the rate selector switch `~
:. -,~ . -setting calls for a low rate of motor drive pulses. In the event a hi~h flow rate has been called for by the setting of the rate selector switches 102a, the detection of high rate motor drive pulses will not cause the rate comparator 222 to activate the latch 220. ~ence, - the high rate alarm subsystem prevents an extreme runaway pumping condition ~hich might occurJ for example, if a faulty gate were to apply the fill frequency continuously to the stepping motor driver 158 and override the aotual pump frequency being generated~ ~
The aforedescribed fluid flow control system has been set ~orth in suffic~ent detail to readily enable practice of the teachi~gs of the present invention. For purposes of convenience and further .. .
clarification~ a more detailed electrical schematic of such a fluid ~52_ ' . : ~ ' ^~

flow control system ie attach~d hereto as Appendix C.
The new and improved ~luid ~lcw control system of the present lnvention is extremely accurate, reliable and easy to use. The system provides enhanced precision in selecting and maintaining fluid flow rates over a wide range, and the system is quick to inform medical personnel of any conditions which might pose a hazard to the patient.
~ence, the system of the pre~ent invention~minimizes the time-consuming and error~prone aspects of human monitoring and flcw rate adjustment ~nd provides substantial improvement in economy, reliability, stability and accuracy over previous automatic control systems, including peristaltic pumps, syringe pumps and drop flow controllers.
It will be apparent from the foregoing that~ while particular forms of the invention have been illustrated and described~ v~rious modifications can be made without departing from the spirit and ~cope oi~ the invention. Accordingly~ it is not intended that the invention be limited except as by the appended clalms.

.: ~

.;
' '. , . . ~. . .

;' ' `~.,~' `'. ' ` :~

.`, `' ~.~
`~ -53-: ' ', ' ., : :'.' :'. '' ,' ' '. :: :

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for use in a system for parenteral administration of liquids at desired flow rates through a feeding tube from a liquid source to a patient, said apparatus comprising: syringe means for performing alternate fill and pump strokes to control the flow of liquid through the feeding tube; motor means for driving said syringe means; electrical pulsing means for providing output pulses to said motor means at a fill frequency and at a pump frequency to operate said syringe means; and digital means for automatically varying said pump frequency output pulses as a function of said fill frequency output pulses to achieve the desired flow rate.

2. The apparatus as claimed in Claim 1, wherein said digital means compensates each of the pump frequency output pulse periods during a time interval equal to a fill frequency output pulse period.

3. The apparatus as claimed in Claim 1 including: motor means for driving said syringe means through successive fill and pump strokes during which a syringe is first filled with liquid and the liquid is subsequently delivered From the syringe, said electrical pulsing means providing said output pulses to operate said motor means in said fill stroke and said pump stroke and thereby operate said syringe means; and electrical control means in said digital means for automatically varying the pump frequency of said output pulses during said pump stroke, to compensate for the total time lost during said fill stroke and to achieve the desired flow rate.

4. The apparatus as claimed in Claim 3, wherein said electrical control means spreads the compensation for time lost during said fill stroke uniformly over said pump stroke.

5. The apparatus as claimed in Claim 3, wherein said control means includes at least one counter for determining the period between successive pump frequency output pulses.

6. The apparatus as claimed in Claim 5, wherein said control means includes first and second digital counters, said first counter being a divide-by-two counter, said counters together determining the duration of each pump frequency output pulse.

7. The apparatus as claimed in Claim 3 including means for detecting the physical presence of a syringe.

8. The apparatus as claimed in Claim 7, and further includ-ing: a syringe actuator driven by said motor means; means responsive to lack of detection of a syringe for energizing said motor means via said pulsing means to drive said actuator; and means for sensing a prescribed position of said actuator for de-energizing said motor means, whereby said actuator comes to rest in a position designated as proper for syringe installation.

9. The apparatus as claimed in Claim 3, and further com-prising: an intake line through which the syringe is filled with liquid; and means responsive to lack of liquid flow of said intake line during a fill stroke for generating an alarm state.

10. The apparatus as claimed in Claim 3, and further com-prising: means responsive to liquid flow below a prescribed minimum flow rate during a fill stroke for generating an alarm state.

11. The apparatus as claimed in Claim 3, and further com-prising: an intake line through which the syringe is filled with liquid; and means responsive to liquid flow in said intake line during a pump stroke for generating an alarm state.

12. The apparatus as claimed in Claim 3, and further com-prising: alarm means responsive to lack of rotation of said motor means.

13. The apparatus as claimed in Claim 3, and further com-prising: means for detecting drop flow; and means responsive, only at the end of a fill stroke, to a lack of a prescribed number of accumulated drops detected during said fill stroke for generating an alarm state.

14. The apparatus as claimed in Claim 3, and further com-prising: means responsive to a high rate of output pulses in excess of those required to achieve said desired flow rate for generating an alarm state.

15. The apparatus as claimed in Claim 7, and further com-prising: means for preventing energization of said motor means at other than said fill frequency when no syringe is detected.

16. The apparatus as claimed in Claim 3, wherein said control means includes: counting means for counting up at a normal rate the period between successive pump stroke output pulses; and means for counting up said period between successive pump stroke output pulses at twice said normal counting rate, for a time interval equal to the period between successive fill stroke output pulses.

17. The apparatus as claimed in Claim 6, wherein said divide-by-two counter normally controls the counting rate into the other of said pair of counters.

18. The apparatus as claimed in Claim 8, wherein said motor means is a stepping motor, and said stepping motor is energized by said pulsing means at said fill frequency in response to lack of detection of a syringe.

19. The apparatus as claimed in Claim 10, and further com-prising: means for delaying the response to said liquid flow being a prescribed minimum flow rate, for a prescribed period of time at the beginning of each fill stroke.

20. The apparatus as claimed in Claim 11, and further com-prising: means for delaying the response to said liquid flow, for a prescribed period of time at the beginning of each pump stroke.

21. The apparatus as claimed in Claim 12, wherein said alarm means is responsive to lack of rotation within a prescribed number of said output pulses.

22. The apparatus as claimed in Claim 13, and further com-prising: alarm means responsive to said means for detecting for de-energizing said motor means.

23. The apparatus as claimed in Claim 13, wherein said means for detecting drop flow comprises a drop detection means respon-sive to drop flow in the intake line, and including drop rate dis-criminator means, responsive to said drop detection means, for sensing fluid flow below a prescribed drop flow rate through the intake line during said fill stroke.

24. The apparatus as claimed in Claim 3, wherein said electrical pulsing means includes rate multiplier means; means for de-riving from said rate multiplier means a pump frequency proportional to desired fluid flow rate; and means for deriving a fixed fill fre-quency from said rate multiplier means, said fill frequency being in excess of the maximum value of said pump frequency.

25. The apparatus as claimed in Claim 24, and further in-cluding: means for resetting the high order rate multiplier decades at the end of each motor drive pulse in the pump stroke.

26. The apparatus as claimed in Claim 9, and further com-prising: means responsive to detection of gas bubbles in said intake line for generating an alarm state.

27. The apparatus as claimed in Claim 24, wherein: said syringe means has inlet and outlet ports and a piston slidably received within said syringe; said rate multiplier means has a plurality of rate multiplier decades and includes variable rate selector switch means connected to said rate multiplier means for establishing a de-sired output fluid flow rate pump frequency from said rate multiplier means proportional to desired fluid flow rate from said syringe dur-ing a pump stroke in which fluid is delivered from said syringe through said outlet port and an outlet line; said means for deriving is adapted to derive a fixed fill frequency from said rate multiplier means proportional to a specified flow rate during a fill stroke in which said syringe is filled with fluid through said inlet port and an input line, said fill frequency being in excess of the maximum pump frequency; said electrical pulsing means includes means for generat-ing motor drive pulses at said fixed fill frequency during a fill stroke, and means for generating motor drive pulses at a pump fre-quency during a pump stroke, said digital means includes: counting means for counting up the period between successive pump stroke motor drive pulses; means for counting up said period between successive pump stroke motor drive pulses, at twice the normal rate called for by the selected fluid flow rate during the pump stroke, for a time in-terval equal to the period between successive fill stroke motor drive pulses, whereby the frequency of the motor drive pulses to said stepping motor is compensated during said pump stroke for time lost during said fill stroke; and means response to said counting means for resetting the high order rate multiplier decades at the beginning of each motor drive pulse period in the pump stroke.

28. Apparatus as set forth in Claim 17, and further com-prising: means for automatically bypassing said divide-by-two counter during generation of each pump frequency output pulse period for a time interval equal to the period between successive fill stroke out-put pulses.