Syringe pump abstract
Apparatus for fluid flow control in a parenteral administration
system, utilizing a syringe pump operated by a motor to repetitively
fill and empty a disposable syringe cartridge over a plurality of
operational cycles of successive fill and pump stroke periods. The
syringe cartridge has no valves, and the apparatus repetitively
and sequentially opens and closes, by means of an external pair
of tube pinchers, a pair of intake and output I.V. tubes communicating
with the inlet and outlet nipples of the syringe cartridge. A reference
light source and photoelectric sensor is provided to sense the physical
presence of the syringe cartridge, and an appropriate electrical
signal is generated whenever the reference light beam is interrupted
by one of the syringe nipples, to thereby indicate proper installation
of the syringe cartridge for control over pump operation, while
another reference light source and photoelectric sensor is provided
adjacent one of the syringe nipples as a bubble detector to insure
that all of the air has been removed from the syringe and to prevent
air delivery to the patient.
Syringe pump claims
1. For use in a syringe pump, the combination comprising:
a syringe means having a pair of inlet and outlet nipples projecting
from one end of said syringe;
a fixed reference light source on one side of one of said nipples;
a fixed photosensor on the opposite side of said one of said nipples,
said photosensor adapted to receive the light from said reference
light source only whenever said nipple is not interposed between
said light source and said photosensor.
2. Apparatus as set forth in claim 1 wherein said one of said
nipples is positioned to interrupt the light from said reference
light source only when said syringe is properly installed.
3. Apparatus as set forth in claim 2 wherein said one of said
nipples includes an opaque structure for blocking light which would
otherwise be detected by said photosensor.
4. Apparatus as set forth in claim 2 wherein said one of said
nipples includes a totally reflecting flag member for diverting
the light from said reference light source when said syringe is
5. Apparatus as set forth in claim 4 wherein said flag member
is integral with said one of said nipples.
Syringe pump descriptionBACKGROUND OF THE INVENTION
This invention relates generally to improvements in syringe pumps
and, more particularly, to a new and improved drive system and syringe
for such pumps, wherein a disposible syringe cartridge having no
valves is reliably and precisely mounted, monitored, and driven
through repetitive fill and pump strokes.
The usual medical procedure for the gradual parenteral administration
of liquids into the human body, such as liquid nutrients, blood
or plasma, makes use of apparatus which is commonly referred to
in the medical arts as an intravenous administration set. The intravenous
set usually comprises a bottle of liquid, normally supported in
an inverted position, an intravenous feeding 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
adjustable rate into a transparent drip chamber below the bottle.
The drip chamber serves 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 of the drip chamber to insure that no air enters the main
feeding tube leading to the patient.
While observation of the rate of drop flow via the drip chamber
is a simple way of controlling the amount of liquid fed to a patient
over a period of time, its ultimate effectiveness requires that
a relatively constant vigil be maintained on the drop flow, lest
it cease entirely due to exhaustion of the liquid supplied or become
a continuous stream and perhaps increase the rate of liquid introduction
to the patient to dangerous levels.
By way of example, it has been the general practice in hospitals
to have nurses periodically monitor drop flow rate at each intravenous
feeding or parenteral infusion station. Such monitoring of drop
flow is a tedious, and time consuming process, 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 flow
rate will use a watch to time the number of drops flowing in an
interval of one or more minutes, and she will then mentally perform
the mathematics necessary to convert the observed data to an appropriate
fluid flow rate, e.g., in 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 flow rate.
Obviously, each of the aforedescribed measurements, calculations
and flow rate adjustments usually take several minutes time which,
when multiplied by the number of stations being monitored and the
number of times each station should be monitored per day, can result
in a substantial percentage of total personnel time available. In
addition, under the pressure of a heavy schedule, the observations
and calculations performed by a harried nurse in measuring and adjusting
flow rate may not always prove to be reliable and, hence, errors
do occur resulting in undesired, possibly dangerous infusion flow
In addition to the aforedescribed difficulties, the parenteral
administration of medical liquids by gravity induced hydrostatic
pressure infusion of the liquid from a bottle or other container
suspended above the patient, is very susceptible to fluid flow rate
variation due to changes in the liquid level in the bottle, changes
in temperature, changes in the venous or arterial pressure of the
patient, patient movement, and drift 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, cardiac and pediatric patients, or where rather potent drugs
are being administered, where the desired drop flow rate must be
capable of very precise selection.
It will be apparent, therefore, that some of the most critical
problems confronting hospital personnel faced with an overwhelming
duty schedule and limited time availability are the problems of
quickly, easily, reliably and accurately controlling fluid flow
in the parenteral administration of medical liquids.
In recent years, a number of electrical monitoring systems, drop
flow controllers and infusion pumps have been developed to accomplish
the various tasks of sensing and regulating drop flow rates. However,
while such devices have generally served their purpose, they have
not always proven entirely satisfactory from the standpoint of cost,
complexity, stability, reliability or accuracy. In addition, such
systems have sometimes been subject to drift and substantial flow
rate variations due to changes in temperature, feeding 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.
Even positive pressure pumps of the closed-loop peristaltic type
only serve to maintain accuracy of flow in terms of stabilizing
to a preselected drop flow rate, rather than delivering a precise
preselected volume of fluid, e.g., in cubic centimeters per hour.
The reason for this is that the accuracy of such a system is limited
inherently to the accuracy of the size of the drops produced by
an intravenous administration set, and the actual drops produced
by the latter apparatus can vary rather substantially from its designated
drop size, e.g., due to drip chamber structural variations, by as
much as thirty percent.
More recently, positive pressure infusion pumps of the syringe
type have also been provided, wherein a syringe having a very precise
displacement volume is repeatedly filled and emptied on alternate
syringe piston strokes during a combined "fill" and "pump"
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 over a prescribed period of time. Such syringe pumps
are essentially independent of drop flow inaccuracies introduced
by I.V. administration sets and appear to provide the best overall
solution to accurate and stable fluid volume delivery over long
periods of time, at both high and low flow rates.
At the heart of the syringe pump is the syringe itself. Such syringes
must be sufficiently rugged and reliable to enable repetitive fill
and pump strokes over sustained periods of pump operation without
leaking, or admitting air or pathogens to the interior of the syringe.
Where disposable syringes are involved, the syringe should preferably
be of relatively simple and economical construction, easily handled
for insertion into and removal from the remainder of the pumping
apparatus and should be mounted in such a fashion as to facilitate
removal of air prior to start-up. Unfortunately, however, such syringes
of the prior art have been relatively complex and expensive, have
been prone to leakage and have been relatively difficult to mount
In addition, syringe pumps of the prior art primarily depend on
valving embodied directly within the syringe itself, for switching
from the fill mode to the pumping mode. This not only increases
the cost and complexity of the syringe, particularly where disposable
syringes are employed, but usually also results in reduced reliability
Furthermore, it has been difficult at low flow rates, when the
syringe piston is moving so slowly that its motion is not visually
discernible by the operator, to determine whether or not the syringe
is being driven at all.
Hence, those concerned with the development and use of parenteral
fluid administration systems, and particularly those concerned with
the design of syringe pumps, have long recognized the need for improved,
relatively simple, economical, reliable, stable and accurate syringes,
monitoring and drive systems for such syringe pumps. The present
invention clearly fulfills this need.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides a
new and improved means for accurately controlling fluid flow in
the parenteral administration of medical liquids, wherein a disposable,
valveless syringe cartridge is easily, reliably and precisely mounted,
its state of proper insertion into the pumping apparatus being monitored,
after which the syringe is driven through repetitive fill and pump
strokes. Appropriate valving is provided within the pumping apparatus
external to the syringe cartridge, without the need for providing
relatively complex, expensive and sometimes unreliable valve structures
in the syringe itself.
The syringe cartridge of the present invention is of strong, lightweight,
durable construction and is constructed to minimize the possibility
of fluid leakage, enhance the ease and simplicity of mounting and
removal from the pumping apparatus, facilitate the removal of air
prior to start-up of the pumping apparatus, and to prevent intake
of air or pathogens into the interior of the syringe during repetitive
pumping cycles. A running indicator is provided to indicate visually
to the operator that the pump is cycling, motion of the indicator
being observable even at low flow rates where syringe operation
may not normally be readily discernible by the operator. In addition,
a rotation sensor is provided to monitor the mechanical output of
the motor driving the syringe and detect any stalled motor condition.
More particularly, the present invention provides a new and improved
syringe pump operated by a motor to repetitively fill and empty
a disposable syringe cartridge over a plurality of operational cycles
of successive fill and pump stroke periods. The disposable syringe
cartridge itself embodies no valving structure, but includes a pair
of intake and output I.V. tubes communicating with the inlet and
outlet nipples, respectively, of the syringe. The remainder of the
pumping apparatus drives the syringe and repetitively and sequentially
opens and closes the intake and output I.V. tubes by means of a
pair of tube pinchers external to the syringe cartridge, the I.V.
tubes alternating their opened and closed states, one tube pincher
controlling each I.V. tube.
The disposable syringe cartridge includes a molded plastic cylinder
having inlet and outlet nipples and defining an interior chamber
adapted to slidingly receive a plastic piston and piston rod. A
rubber sealing cap overlies and encases the plastic piston, and
defines a conical piston face. The sealing cap includes a pair of
resilient annular ribs defining piston sealing rings, and further
includes a limp diaphragm conical sealing boot. The dual, spaced
apart sealing rings define two point contact along the longitudinal
axis of the syringe to enhance axial alignment and stability of
the piston and piston rod as the piston slides within the cylinder
of the syringe, whereas the sealing boot at the base of the cylinder
prevents the intake of air or pathogens through the bottom of the
cylinder during repetitive strokes. All plastic cross-sections of
syringe cartridge components are selected to provide maximum strength
for a minimum amount of plastic material.
The inlet and outlet nipples of the syringe cartridge extend parallel
to the longitudinal axis of the syringe, on opposite sides of the
syringe. The interior surface of the cylinder defines, with the
piston, a fluid chamber, and the cylinder surface above the piston
is sloped upwardly towards the base of the outlet nipple, so that,
when the longitudinal axis of the syringe is vertical, gas bubbles
will tend to rise to the highest point of the cylinder and out through
the outlet nipple for easy removal.
The syringe cartridge and associated mounting means are designed
to facilitate simple and easy insertion of the cartridge into the
pump housing, requiring the use of only one hand by the operator.
In this regard, an integral tab extends from the syringe cylinder
and provides an operator handle for mounting and removing the syringe
from the overall pumping apparatus. In addition, the end of the
piston rod remote from the piston head is partially cut-away and
provided with integral, outwardly extending mounting bosses. These
mounting bosses are adapted to engage and be retained by a mounting
shoe secured to the leading end of a linear drive shaft adapted
to be coupled to the piston rod for driving the syringe through
successive fill and pump strokes. The mounting shoe includes a pair
of guide slots adapted to engage the piston rod mounting bosses
so that the syringe cartridge can be inserted into the mounting
shoe horizontally, be rotated so that its longitudinal axis is vertical,
and thereby bring the lower, cut-away end of the syringe piston
rod into a retention slot within the mounting shoe to prevent the
syringe cartridge from being dislodged, either horizontally by virtue
of the retention slot, or vertically by means of the lower end of
the piston rod and the mounting bosses.
A second pair of outwardly extending mounting bosses, parallel
to the first set of mounting bosses on the piston rod, are integral
with the syringe cylinder and are adapted to engage a pair of fixed
guide and retaining slots provided in opposite walls of a syringe
receiving compartment defined in the pump housing. The intake and
output I.V. tubes from the syringe cartridge pass vertically over
a pair of tube pincher blades and are clamped in position by a suitable
tubing compartment access door which is appropriately latched. Thus,
the syringe cartridge is firmly maintained in position during the
operational cycles of the pump. The tubing access door must be unlatched
and opened to enable the syringe cartridge to be rotated from the
vertical position to a horizontal position for removal from the
By controlling the initial location of the mounting shoe, relative
to the guide and retaining slots in the sidewalls of the syringe
compartment, the pumping apparatus can be conditioned to receive
the syringe cartridge only if its piston is in a predetermined position
within the syringe cylinder, i.e., in the top dead center position
adapted to initially perform an intake stroke to fill the syringe
with fluid. The latter is the proper state of the syringe for initial
start-up of the pumping apparatus.
A reference light source and photoelectric sensor is provided within
the syringe compartment to sense the physical presence of the syringe
cartridge, and an appropriate electrical signal is generated whenever
the reference light beam is interrupted by one of the syringe nipples,
to thereby indicate proper installation of the syringe cartridge
for control over pump operation. Another reference light source
and photoelectric sensor is provided adjacent one of the syringe
nipples as a bubble detector to insure that all of the air has been
removed from the syringe and to prevent air delivery to the patient.
A motor rotation sensor is provided, the rotation sensor typically
being in the form of a disc mounted on the motor output shaft for
rotation therewith, the disc having alternate transparent and opaque
sectors. A photocell detects light from a reference light source
passing through the disc, as it rotates, and generates an output
electrical signal capable of indicating any stalled motor condition.
A visual running indicator is also provided, typically in the form
of a rotating disc having index lines uniformly spaced along its
peripheral edge, so that pump operation is visually discernible
by the operator, even at low flow rates where motion of the syringe
piston is so slow as to not be readily discernible by the eye of
The new and improved syringe pump drive system and disposable syringe
cartridge satisfies a long existing need in the medical arts for
improved, relatively simple, economical, reliable, stable and accurate
syringe pumping systems.
The above and other objects and advantages of the present invention
will become apparent from the following more detailed description,
when taken in conjunction with the accompanying drawings of illustrative
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing main components of the interior
structure of a syringe pump embodying the present invention, portions
of the outer pump housing being shown in phantom;
FIG. 2 is a fragmentary, plan view of a rotation sensor in accordance
with the invention;
FIG. 3 is a fragmentary, elevational view, portions being shown
in section, through the syringe pump in the vicinity of the syringe
cartridge compartment, the syringe cartridge being shown in solid
lines in its properly installed position, the cartridge also being
shown in phantom in an intermediate position during the installation
FIG. 3A is a fragmentary sectional view, taken substantially along
the line 3A--3A in FIG. 3 and illustrates the pincher valves external
to the syringe cartridge;
FIG. 4 is a fragmentary sectional view, taken along the line 4--4
in FIG. 3 and illustrates portions of the drive system for the syringe;
FIG. 5 is a perspective view of the mounting shoe for coupling
the drive system to the syringe cartridge;
FIG. 6 is a plan view of the mounting shoe shown in FIG. 5;
FIG. 7 is an elevational view of an assembled syringe cartridge
in accordance with the present invention, portions being shown in
FIG. 8 is a sectional view, taken along the line 8--8 in FIG. 7;
FIG. 9 is an exploded perspective view of the main structural components
of a syringe cartridge constructed in accordance with the present
invention, a portion of the syringe cylinder being shown in section;
FIG. 10 is a fragmentary perspective view of the upper portion
of a syringe cartridge incorporating provisions for monitoring the
physical position of the cartridge and the presence of gas bubbles;
FIG. 11 is a plan view of a syringe nipple embodying the cartridge
position monitoring and bubble detection structure of FIG. 10 and
further illustrating the location of the reference light sources
and photocell sensors relative to the nipple; and
FIG. 12 illustrates an alternate arrangement for monitoring the
physical position of a syringe cartridge.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, there is shown a syringe pump system
for fluid flow control, embodying the features of the present invention.
In the ensuing description, while reference is made to the term
"I.V.", normally connoting intravenous administration,
it is to be understood that this is by way of example only, and
the system of the present invention is suitable for other forms
of parenteral administration as well as intravenous administration.
The system shown in FIG. 1 depicts a syringe pump 20 embodying
a disposable syringe cartridge 21. The syringe cartridge 21 essentially
includes a molded plastic cylinder 22 in which a piston 23 is slidably
received and adapted to be reciprocated back and forth along the
axis of the cylinder by an integral piston rod 24 which is removably
mounted at one end in a coupling shoe 26 carried by a linear drive
shaft 27 which is advanced and retracted by a suitable drive system.
The drive system includes a reversible motor 29 (typically a d.c.
stepping motor) and appropriate gearing 31 to advance and retract
the shaft 27 which is, in turn, coupled to the piston rod 24 of
the syringe cartridge 21. The motor 29 is energized by a pulse train
of motor drive pulses generated by an appropriate electrical control
system (not shown).
The displacement volume of the syringe cartridge 21 is determined
by the volume swept by the piston 23 on each stroke and is identical
for the fill stroke and for the pump stroke. Therefore, an identical
number of discrete steps or motor drive pulses from the electrical
control system to the motor 29 is required for each fill stroke
during which the syringe is filled with liquid, and for each pump
stroke during which the syringe delivers its precise volume of liquid
under positive pressure to a patient.
The syringe cartridge 21 includes an inlet port 21a and an outlet
port 21b. The inlet port 21a communicates through a suitable intake
I.V. tube 33 with any appropriate liquid source (not shown), usually
an I.V. bottle containing appropriate drugs and/or nutrients in
liquid form. Typically, the intake I.V. tube 33 is part of an I.V.
administration set which includes a transparent drip chamber in
the line between the syringe cartridge 21 and the liquid source.
A similar, output I.V. tube 34 is connected at one end to the outlet
port 21b of the syringe cartridge 21 and conveys fluid from the
syringe to a patient.
As best observed in FIGS. 3 and 3A, a pair of syringe pump valves
36 37 external to the syringe cartridge 21 are of the tube pincher
type, and are selectively opened and closed at appropriate times
in the overall pumping cycle, under the control of a suitable valve
control system 40. The valve 36 controls the inlet port 21a and
is open during the fill stroke to enable fluid to be drawn from
the liquid source, through the intake line 33 into the syringe
cartridge 21 the valve 36 being closed during the pump stroke to
prevent fluid from exiting the syringe through the inlet port. The
valve 37 controls the outlet port 21b and is open during the pump
stroke to enable fluid delivery from the syringe cartridge 21 to
the patient through the output line 34 the valve 37 being closed
during the fill stroke.
The valve control system 40 is also driven, through the gearing
31 by the same motor 29 as is used to operate the syringe cartridge
21. In addition, the valve control system 40 includes means (not
shown) for providing information to the electrical control system
controlling the motor 29 and indicating that the syringe cartridge
21 is either in the fill stroke or the pump stroke. This latter
information, in turn, enables the electrical control system to establish
the proper direction of rotation of the motor 29. The electrical
control system may be of conventional design for electrically energizing
the motor 29 and controlling its direction of rotation, or the control
system may be of the form described in copending application, Ser.
No. 554092 entitled Fluid Flow Control System, inventor Heinz
W. Georgi, filed Feb. 28 1975 and assigned to the same assignee
as the present application.
The motor 29 drives, through the gearing 31 and an output camshaft
41 a reversible cam (not shown) in the valve control system 40
which cyclically alternates the open and closed positions of the
syringe pump valves 36 37.
The syringe pump valves 36 37 typically consist of a pair of pivotal
tube pinchers 43 44 which alternately pinch off and open the intake
and output tubes 33 34 respectively, of the syringe cartridge 21.
One face of each of the tube pinchers 43 44 is shaped to define
a pincher blade 43a, 43b, respectively, adapted to cooperate with
the confronting face of a shoulder 45a defined on the interior side
of a syringe pump tubing access door 45 to the syringe compartment.
Together, the pincher blades 43a, 44a and the access door shoulder
45a define a pair of tube clamps between which the intake and output
I.V. tubes 33 34 pass. The access door 45 is held shut, after the
syringe cartridge 21 has been installed, by any suitable latch 45b
The tube pinchers 43 44 are spring biased to the tube shut-off
position and are positively driven open by the valve control system
40 thus allowing full tube closure regardless of normal variations
in I.V. tubing diameter and wall thickness.
The valves 36 37 and valve control system 40 may be of conventional
design or may be of the form described in copending application,
Ser. No. 554091 entitled Syringe Pump Valving And Motor Direction
Control System, inventor Wallace L. Knute, filed Feb. 28 1975 and
assigned to the same assignee as the present application, now U.S.
Pat. No. 3994294 issued Nov. 30 1976.
Referring now more particularly to FIGS. 7-9 of the drawings, the
new and improved syringe cartridge 21 of the present invention is
of strong, lightweight, durable construction and is constructed
to minimize the possibility of fluid leakage from the interior of
the syringe, enhance the ease and simplicity of mounting and removal
from the syringe compartment of the pump, facilitate the removal
of air prior to actual operation of the pumping apparatus, and to
prevent intake of air or pathogens into the interior of the syringe
during repetitive pumping cycles.
The disposable syringe cartridge 21 includes the molded plastic
cylinder 22 having inlet and outlet nipples 51 52 respectively,
at the upper end of the cylinder (with the longitudinal axis of
the syringe in the vertical position as is the case following proper
installation shown in FIG. 1). The cylinder 22 is hollow and thereby
defines an interior chamber adapted to slidingly receive a plastic
piston head 54 which is integral with the piston rod 24. The cylinder
22 and combined piston rod 24 and piston head 54 are typically
injection molded of any suitable thermoplastic material, such as
A rubber sealing cap 56 overlies and encases the piston head 54
to define the piston 23 the sealing cap providing a conical piston
face 23a directed towards the inlet and outlet nipples 51 52 respectively,
of the syringe.
The inlet and outlet nipples 51 52 of the syringe catridge 21
extend parallel to the longitudinal axis of the syringe on opposite
sides of the syringe, diametrically opposed from each other. The
interior surface of the syringe cylinder 22 defines, with the piston
23 a fluid containing chamber, and the uppermost cylinder surface
22a above the piston is sloped upwardly, typically at an angle of
approximately 10.degree., towards the base of the outlet nipple
52. Hence, when the longitudinal axis of the syringe is vertical,
following installation into the pumping apparatus, gas bubbles will
tend to rise to the highest point of the syringe cylinder 22 and
pass out through the outlet nipple 52 for easy removal at some
convenient access point in the output I.V. tube 34. In addition,
the piston face 23a slopes symmetrically downward from its apex
at an angle of approximately 10.degree. to the horizontal, matching
the slope of the interior surface 22a of the cylinder 22 to minimize
the residual volume of the syringe.
The sealing cap 56 which is typically fabricated of a natural
rubber, also includes a pair of resilient, annular ribs 56a, 56b
which fit over and are supported by corresponding annular flanges
54a, 54b in the piston head 54.
The sealing cap ribs 56a, 56b provide a pair of axially spaced
apart piston sealing rings. These dual, spaced apart sealing rings
define two point contact support along the longitudinal axis of
the syringe cartridge 21 to provide improved sealing efficiency,
and to enhance the axial alignment and stability of the piston and
piston rod assembly within the cylinder 22 of the syringe as the
piston 23 reciprocates back and forth within the cylinder during
repetitive pump cycles. Hence, the two point support along the longitudinal
axis of the system prevents rocking of the piston 23 which might
otherwise cause the system to be prone to leakage and might also
provide uneven wear on the sealing rings.
The sealing cap 56 further includes a thin walled conical sealing
boot 56c integral at its frustrum with the rib 56b and terminating
at its base in a thickened wall portion defining a bead 56d. The
sealing boot 56c provides a limp membrane sealing element when the
syringe cartridge 21 is assembled, to prevent the intake of air
or pathogens through the bottom of the cylinder 22 as the piston
assembly reciprocates through repetitive strokes within the cylinder.
The use of the sealing cap to encase the plastic piston head 54
and thereby define the outer surface of the piston 23 including
the sealing rings 56a, 56b, enables the piston head 54 and piston
rod 24 to be fabricated of less expensive materials than would be
required if the piston head were in direct sliding engagement with
the interior walls of the cylinder 22.
The material from which the sealing cap 56 is fabricated is chosen
because of its material properties, e.g., wear resistance on the
seals, compression set resistance so that it will retain its elastic
properties, resistance to tearing on the boot because of the thin
walled membrane, and resistance to the temperatures normally encountered
in the sterilization process. In contrast, the plastic materials
from which the cylinder 22 piston head 54 and piston rod 24 are
fabricated is chosen primarily for low cost of material, ease of
manufacture, and resistance to sterilization temperatures.
All plastic cross-sections of the various components of the syringe
cartridge 21 are selected to provide a maximum of strength for a
minimum amount of plastic material. In this regard, while strength
is required, a thin walled structure is also desirable in order
for plastic molding to be most effective. Hence, a maximum degree
of rigidity with a minimum amount of plastic, in a convenient cross-section,
is selected for the syringe cartridge 21 of the present invention.
In this regard, it will be apparent in FIG. 8 that the piston rod
24 is molded in an "H" cross-section, defined by a pair
of longitudinally extending, parallel flanges 24a, 24b joined by
an integral, coextensive cross-bar 24c.
As previously pointed out, the piston head flanges 54a, 54b retain
the sealing cap 56 and provide adequate support for the piston 23.
The parallel flanges 54a, 54b are, in turn, supported by four integral
ribs 54c which intersect at the longitudinal axis of the piston
head, the uppermost ends of these ribs being tapered to provide
support for the conical face 23a of the sealing cap 56. This prevents
the sealing cap 56 which is not very rigid, from collapsing. The
rib structure defined by the four ribs 54c is selected, instead
of a solid circular cylindrical cross-section, for molding purposes,
to provide adequate strength with a minimal amount of plastic material
In assembling the cylinder 22 sealing cap 56 and combined piston
head 54 and piston rod 24 (the components of FIG. 9) into the syringe
cartridge 21 of FIG. 7 the sealing cap 56 is simply pressed over
the piston head 54 until the flanges 54a, 54b engage internal slots
in the sealing cap adjacent the ribs 56a, 56b, which results in
the sealing cap and piston head snapping together. The resulting
assembly of the sealing cap 56 and piston head 54 (defining the
piston 23) and the piston rod 24 is pushed into the opening in
the base of the cylinder 22. A suitable lubricant may be used to
facilitate insertion of the assembly into the cylinder 22 as well
as subsequent reciprocation within the cylinder. The base of the
sealing boot 56c is then folded over the open base of the cylinder
22 so that the bead 56d, which behaves as an elastic O-ring, grips
the outer surface of the cylinder and holds the sealing boot 56c
in position so that it can't be pealed back easily or tear. In this
regard, the hoop strength of the bead 56d must be sufficient to
resist movement once it has been positioned to grip the outer surface
of the cylinder 22.
The length of the skirt portion of the sealing boot 56c is such
that it is not required to stretch at all during any portion of
the pumping cycle as the piston 23 reciprocates back and forth within
the cylinder 22. Hence, the boot 56c provides a limp membrane as
a seal against admission of air or pathogens to the interior of
the cylinder 22 during repetitive strokes of the syringe. In this
regard, since the limp membrane seal provided by the sealing boot
56c is essentially unstressed, it is both rugged and reliable. In
addition, should sufficient air be trapped in the air gap between
the rib 56b and the sealing boot 56c, during assembly into the cylinder
22 the air volume might be compressed during fill strokes of the
piston 23 when the piston is in its lowermost position. However,
the combination of the additional volume provided by the unfolding
limp membrane of the sealing boot 56c, together with the anchoring
afforded by the bead 56d, resists popping of the sealing boot off
the cylinder 22 even in the event of ballooning of the boot by
any such trapped air.
After the cylinder 22 sealing cap 56 and combined piston 54 and
piston rod 24 have been assembled in the aforedescribed manner,
the intake I.V. tube 33 and output I.V. tube 34 are appropriately
secured to the inlet and outlet nipples 51 52 respectively, to
complete the assembly of the syringe cartridge 21.
The syringe cartridge 21 is constructed to cooperate with associated
mounting means within the syringe compartment of the pump housing
to facilitate simple and easy insertion of the cartridge into the
pump housing while requiring the use of only one hand by the operator.
In this regard, an integral tab 58 projects from the outer surface
of the syringe cylinder 22 near the upper end of the cylinder, and
thereby provides an operator handle for mounting and removing the
syringe cartridge 21 from the pump housing in the manner to be hereinafter
described in further detail.
At the end of the piston rod 24 remote from the piston head 54
the longitudinal flanges 24a, 24b are partially cut-away to define
surfaces 24d and in order to provide clearance for insertion into
the coupling shoe 26. In addition, this same end of the piston rod
24 is provided with a pair of integral, outwardly and oppositely
extending, cylindrical m mounting bosses 59 one boss projecting
perpendicularly outward from the outside face of the flange 24a,
the other boss likewise projecting outward from the flange 24b.
A second pair of outwardly extending mounting bosses 61 parallel
to the first set of mounting bosses 59 on the piston rod 24 are
integral with the syringe cylinder 22 near the upper end of the
As best observed in FIGS. 3 5 and 6 the piston rod mounting bosses
59 are adapted to engage and be retained by the mounting and coupling
shoe 26 which is secured to the leading end of the linear drive
shaft 27 adapted to be coupled to the piston rod 24 for driving
the syringe cartridge 21 through successive fill and pump strokes.
The coupling shoe 26 includes a pair of confronting, wide mouth
guide slots 63 in upstanding flanges 62 disposed on opposite sides
of the coupling shoe, and adapted to engage and guide the mounting
bosses 59 so that the syringe cartridge 21 can be inserted into
the coupling shoe horizontally.
Hence, during the cartridge installation procedure, the tab 58
of the syringe cartridge 21 is gripped by two fingers of one hand
of the operator and, with the longitudinal axis of the syringe cartridge
held horizontally, the piston rod 24 and mounting bosses 59 are
inserted horizontally into the guide slots 63 of the coupling shoe
26 (with the cutaway surfaces 24d of the piston rod directed downward)
and moved to the rear of the coupling shoe which essentially defines
a mounting yoke for the bosses 59. The syringe cartridge 21 is then
rotated upwardly, about an axis of rotation through the mounting
bosses 59 in the coupling shoe 26 so that the longitudinal axis
of the syringe cartridge is brought into a vertical position, as
illustrated by the solid lines in FIG. 3. The latter procedure brings
the cut-away, lower end of the piston rod 24 into a retention channel
64 within the coupling shoe 26. In this regard, the cut-away surfaces
24d of the piston rod are rotated into abutment with a ledge 64a
of the retention channel 64.
When the syringe cartridge 21 has been thus installed, the mounting
bosses 59 in the guide slots 63 prevent the syringe cartridge from
being dislodged vertically, whereas the cut-away surfaces 24d in
the retention channel of the coupling shoe 26 prevent the cartridge
from being dislodged horizontally.
As best observed in FIGS. 1 and 3 the mounting bosses 61 of the
syringe cylinder 22 are adapted to engage a pair of fixed guide
and retaining slots 66 provided in opposite walls of the syringe
receiving compartment of the pump housing. By controlling the initial
location of the coupling shoe 26 relative to the curved, wide mouth
guide and retaining slots 66 the pumping apparatus can be conditioned
to receive the syringe cartridge 21 only if its piston 23 is in
a predetermined position within the syringe cylinder 22 i.e., in
the top dead center position adapted to initially perform an intake
stroke to fill the syringe with liquid. The latter is the proper
state of the syringe for initial start-up of the pumping apparatus.
The intake and output I.V. tubes, 33 34 respectively, from the
syringe cartridge 21 are then passed vertically over the tube pincher
blades 43a, 44a and are clamped in position by the closing of the
tubing compartment access door 45 which is then latched shut by
the latch 45b to firmly anchor and maintain the syringe cartridge
in position during the operational cycles of the pump. The tubing
access door 45 must be unlatched and opened to enable the syringe
cartridge 21 to be rotated from the vertical position to a horizontal
position for removal from the coupling shoe 26 whenever it is desired
to replace the cartridge.
The coupling shoe 26 is, as previously indicated, secured to the
upper end of the linear drive shaft 27 which advances and retracts
the coupling shoe and thereby advances and retracts the piston rod
24 and piston 23 within the cylinder 22 for repetitive fill and
pump strokes. As best observed in FIGS. 3 and 4 the linear drive
shaft 27 is of non-circular cross-section and, in the preferred
embodiment shown, is of rectangular cross-section. The drive shaft
27 passes through and is in sliding engagement with an anti-rotation
bearing 68 having an opening of complimentary cross-section, and
enabling the drive shaft to move along its longitudinal axis while
being keyed against rotation about that axis.
A lead screw 70 is integral with, or otherwise appropriately secured
to, the drive shaft 27 and is advanced and retracted along its longitudinal
axis, to thereby advance and retract the drive shaft 27 by an internally
threaded gear 72 in the gear train 31 driven by the motor 29. The
gear 72 is appropriately supported for rotation in a pair of stationary
gear carriers or thrust bearings 73 74.
As best observed in FIGS. 1 and 3 a visual running indicator is
provided in the form of a rotating disc 76 having a plurality of
visually observable, preferably uniformly spaced, vertical index
lines 77 located along its entire peripheral edge. The disc 76 is
secured to a central bushing 78 (through which the lead screw 70
passes freely) and is journaled for rotation in the upper gear carrier
73. The bushing 78 and disc 76 are driven by the output shaft 29a
of the motor 29 via a belt drive in the form of a simple O-ring
79 which passes around the output shaft of the motor and around
the bushing 78 to provide a simple friction drive.
The peripheral index lines 77 are readily observable through a
window 81 in the pump housing. Hence, when the pumping apparatus
is operating at a very low pumping rate, so that no movement of
the coupling shoe 26 or piston rod 24 is visually discernible by
the operator, the rotation of the running indicator disc 76 will
be apparent through the window 81 to assure the operator that the
system is in operation.
Referring now more specifically to FIGS. 1 and 2 a motor rotation
sensor 83 is provided to insure proper detection of a stalled motor
29 so that, in cooperation with the electrical control system, an
alarm condition can be appropriately generated. Such motor stalling
has a greater probability of occurring when the pump is used with
a downstream filter which may clog and induce high back pressure
on the pumping system.
The rotation sensor 83 comprises a disc 84 mounted on the output
shaft 29a of the motor 29 for rotation therewith, the disc having
alternate transparent and opaque sectors 85 86 respectively. A
photocell 87 detects light passing through the disc 84 from a reference
light source 88 as the disc rotates, and generates electrical pulses
which are appropriately directed to the electrical control system
for monitoring and alarm functions. Hence, the rotation sensor 83
is capable of indicating any stalled motor condition.
As best observed in FIGS. 10 and 11 the pumping system, including
the syringe cartridge 21 may embody appropriate means for indicating
proper installation of the syringe cartridge and for detecting the
presence of gas bubbles. In this regard, the inlet nipple 51 of
the syringe cartridge 21 is surrounded by an integrally molded,
transparent flag member 89. A fixed light source 91 and photoelectric
sensor 92 both located in fixed positions within the syringe compartment
of the pump housing, provide a reference light beam which is selectively
interrupted by the flag member 89 whenever the syringe cartridge
21 has been properly positioned in the syringe compartment of the
pump housing. In this regard, the flag 89 prevents the reference
light beam from reaching the sensor 92 by interposing a totally
reflecting surface 89a in the path of the light beam to deflect
the light beam away from the sensor.
In addition, bubble detection is accomplished in the arrangement
of FIG. 11 by providing a fixed light source 94 and photoelectric
sensor 95 on opposite sides of the inlet nipple 51 so that gas
bubbles passing through the nipple will interrupt the light beam
and generate an appropriate electrical signal. The latter signal
is appropriately transmitted to the electrical control system to
bring about the generation of an alarm state. Hence, the bubble
detection system insures no air bubbles are entering the syringe
through the inlet nipple 51.
An alternative embodiment of a suitable system for monitoring the
proper insertion of the syringe cartridge 21 within the syringe
compartment is shown in FIG. 12. In this embodiment, a syringe nipple
151 is appropriately provided with an opaque, typically black, outer
coating 151a so that, when the cartridge has been properly installed,
a reference light beam from a fixed light source 191 in the pump
housing is interrupted. This causes an appropriate electrical signal
to be generated by a fixed photosensor 192 located in the pump housing
on the opposite side of the nipple 151.
The new and improved syringe pump drive system and disposable syringe
cartridge of the present invention satisfies a long existing need
in the medical arts for improved, relatively simple, economical,
reliable, stable and accurate syringe pumping systems.
It will be apparent from the foregoing that, while particular forms
of the invention have been illustrated and described, various modifications
can be made without departing from the spirit and scope of the invention.
Accordingly, it is not intended that the invention be limited, except
as by the appended claims.