Abstrict A disposable syringe cartridge including a molded plastic cylinder
having an open end and a closed end with inlet and outlet nipples
integrally formed in the closed end, and a plastic piston head slidably
received in the open end of the cylinder and pivotably connected
to a plastic piston rod. The piston head utilizes a quad-type sealing
ring providing a pair of adjacent sealing surfaces with the cylinder,
and includes a square expansion flange rounded at each of its corners
to conform in shape to the cylinder, with a rubber annular sealing
boot extending between the open end of the syringe cylinder and
the piston rod. A flange formed on the outer circumferential edge
of the sealing boot is received over the open end of the cylinder
and is captured by an annular cap that is ultrasonically welded
to the cylinder, while a bead formed on the inner circumferential
edge of the sealing boot is received in a groove defined by a pair
of adjacent annular flanges formed on the piston rod. In an alternative
embodiment, the piston head has two sealing rings, each carried
adjacent an opposite end of the piston head, so that the sealing
boot can be eliminated.
Claims We claim:
1. For use in a syringe pump, a disposable plastic syringe cartridge,
comprising:
a hollow cylinder having an open end and a closed end, said cylinder
having a pair of inlet and outlet nipples projecting from said closed
end of said cylinder, each of said nipples adapted for connection
to an I.V. tube;
a piston head slidably received within said cylinder;
a sealing ring disposed around said piston head for forming a circumferential
sealing relationship with said cylinder;
a piston rod for reciprocating said piston head along the longitudinal
axis of said cylinder;
means for pivotally connecting one end of said piston rod to said
piston head; and
means for engaging the other end of said piston rod to the mounting
means of a piston drive system.
2. Apparatus as set forth in claim 1 and further including an
annular sealing boot formed of a flexible and fluid impervious material,
the outer circumferential edge of said boot affixed to said open
end of said cylinder, and the inner circumferential edge of said
boot affixed to said piston rod, said sealing boot having sufficient
material between its outer and inner circumferential edges to seal
said open end of said cylinder without stretching at any time during
reciprocation of said piston head.
3. Apparatus as set forth in claim 2 and further including:
an annular cap received over and bonded to said open end of said
cylinder with said outer circumferential edge of said boot captured
between said annular cap and said open end of said cylinder to secure
said boot in place.
4. Apparatus as set forth in claim 2 wherein said piston rod further
includes a pair of parallel spaced-apart integral annular flanges
between which said inner circumferential edge of said boot is received.
5. Apparatus as set forth in claim 1 wherein said sealing ring
disposed around the circumference of said piston head comprises
a quad sealing ring having a substantially X-shaped radial cross-section
such that said sealing ring has a pair of adjacent surfaces in sealing
contact with said cylinder.
6. Apparatus as set forth in claim 1 wherein said piston head
and said piston rod are formed as separate parts, and further wherein
said means for pivotally connecting said piston rod to said piston
head comprises an integral hook depending from said piston head
and an integral wrist pin formed in said one end of said piston
rod, said wrist pin receivable in said hook with a snap fit.
7. Apparatus as set forth in claim 1 wherein said piston head
and said piston rod are integrally formed as a unitary structure,
and further wherein said means for pivotally connecting said piston
rod to said piston head comprises an integral connecting member
having at least limited flexibility.
8. Apparatus as set forth in claim 7 wherein said piston head,
said piston rod and said integral connecting member are molded plastic,
and further wherein said integral connecting member includes a relatively
thin portion imparting flexibility to said member.
9. Apparatus as set forth in claim 1 and further including:
an I.V. tube solvent-bonded to each of said nipples.
10. For use in a syringe pump, a disposable plastic syringe cartridge,
comprising:
a hollow cylinder having an open end and a closed end, said cylinder
having a pair of inlet and outlet nipples projecting from said closed
end of said cylinder, each of said nipples adapted for connection
to an I.V. tube;
a piston head slidably received within said cylinder;
a sealing ring disposed about the circumference of said piston
head for forming a circumferential sealing relationship with said
cylinder;
a piston rod for reciprocating said piston head along the longitudinal
axis of said cylinder;
means for pivotally connecting one end of said piston rod to said
piston head;
means for engaging the other end of said piston rod to the mounting
means of a piston drive system; and
means for forming a flexible seal between the open end of said
cylinder and said piston rod to seal said cylinder at all times
during reciprocation of said piston head.
11. Apparatus as set forth in claim 10 wherein the opposite ends
of said piston head are defined respectively by a piston face and
a substantially square expansion flange that is spaced from and
parallel to said piston face, the four corners of said piston face
being rounded for conformance with the shape of said cylinder.
12. Apparatus as set forth in claim 10 wherein said sealing ring
disposed about the circumference of said piston head comprises a
quad sealing ring having a substantially X-shaped radial cross-section
such that said sealing ring has a pair of adjacent surfaces in sealing
contact with said cylinder.
13. Apparatus as set forth in claim 12 wherein said piston head
has a pair of parallel spaced-apart integral annular flanges between
which said sealing ring is disposed.
14. Apparatus as set forth in claim 10 wherein said piston head
and said piston rod are formed as separate parts, and further wherein
said means for pivotally connecting said piston rod to said piston
head comprises an integral hook depending from said piston head
and an integral wrist pin formed in said one end of said piston
rod, said wrist pin receivable in said hook with a snap fit.
15. Apparatus as set forth in claim 10 wherein said piston head
and said piston rod are integrally formed as a unitary structure,
and further wherein said means for pivotally connecting said piston
rod to said piston head comprises an integral connecting member
having at least limited flexibility.
16. Apparatus as set forth in claim 15 wherein said piston head,
said piston rod and said integral connecting member are molded plastic,
and further wherein said integral connecting member includes a relatively
thin portion imparting flexibility to said member.
17. Apparatus as set forth in claim 10 and further including:
an I.V. tube solvent-bonded to each of said nipples.
18. For use in a syringe pump, a disposable plastic syringe cartridge,
comprising:
a hollow cylinder having an open end and a closed end, said cylinder
having a pair of inlet and outlet nipples projecting from said closed
end of said cylinder, each of said nipples adapted for connection
to an I.V. tube;
a piston head slidably received within said cylinder;
a quad sealing ring disposed about the circumference of said piston
head for forming a circumferential sealing relationship with said
cylinder, said quad sealing ring having a substantially X-shaped
radial cross-section such that said sealing ring has a pair of adjacent
surfaces in sealing contact with said cylinder;
a piston rod for reciprocating said piston head along the longitudinal
axis of said cylinder;
means for pivotally connecting one end of said piston rod to said
piston head;
means for pivotally engaging the other end of said piston rod to
the mounting means of a piston drive system; and
an annular sealing boot formed of a flexible and fluid impervious
material, the outer circumferential edge of said boot received over
and affixed to said open end of said cylinder, and the inner circumferential
edge of said boot affixed to said piston rod, said sealing boot
having sufficient material between its outer and inner circumferential
edges to seal said open end of said cylinder without stretching
at any time during reciprocation of said piston head.
19. Apparatus as set forth in claim 18 and further including:
an annular cap received over and bonded to said open end of said
cylinder with said outer circumferential edge of said boot captured
between said annular cap and said open end of said cylinder to secure
said boot in place.
20. Apparatus as set forth in claim 19 wherein said piston rod
further includes a pair of parallel spaced-apart integral annular
flanges between which said inner circumferential edge of said boot
is received.
21. Apparatus as set forth in claim 18 wherein the opposite ends
of said piston head are defined respectively by a piston face and
a substantially square expansion flange that is spaced from and
parallel to said piston face, the four corners of said expansion
flange being rounded for conformance with the shape of said cylinder.
22. Apparatus as set forth in claim 21 wherein said piston head
further includes a pair of parallel spaced-apart integral annular
flanges between which said sealing ring is disposed.
23. Apparatus as set forth in claim 18 wherein said piston head
and said piston rod are formed as separate parts, and further wherein
said means for pivotally connecting said piston rod to said piston
head comprises an integral hook depending from said piston head
and an integral wrist pin formed in said one end of said piston
rod, said wrist pin receivable in said hook with a snap fit.
24. Apparatus as set forth in claim 18 wherein said piston head
and said piston rod are integrally formed as a unitary structure,
and further wherein said means for pivotally connecting said piston
rod to said piston head comprises an integral connecting member
having at least limited flexibility.
25. Apparatus as set forth in claim 24 wherein said piston head,
said piston rod and said integral connecting member are molded plastic,
and said integral connecting member includes a relatively thin portion
imparting flexibility to said member.
26. Apparatus as set forth in claim 18 and further including:
an I.V. tube solvent-bonded to each of said nipples.
27. For use in a syringe pump, a disposable plastic syringe cartridge,
comprising:
a hollow cylinder having an open end and a closed end, said cylinder
having a pair of inlet and outlet nipples projecting from said closed
end of said cylinder, each of said nipples adapted for connection
to an I.V. tube;
a piston head slidably received within said cylinder;
a sealing means disposed around the circumference of the piston
head comprising a quad sealing ring having a substantially X-shaped
radial cross section such that the sealing ring has a pair of adjacent
surfaces in sealing contact with said cylinder;
a piston rod for reciprocating said piston head along the longitudinal
axis of said cylinder;
means for pivotally connecting one end of said piston rod to said
piston head; and
means for engaging the other end of said piston rod to the mounting
means of a piston drive system.
Description BACKGROUND OF THE INVENTION
This invention relates generally to improvements in fluid delivery
systems and, more particularly, to a new and improved disposable
syringe cartridge for a syringe pump.
The administration of parenteral fluids to human patients conventionally
involves use of a solution administration set. The set typically
is a disposable plastic product, and comprises a drip chamber adapted
to be connected to a fluid source, a length of tubing extending
from the chamber to the patient and a valve mechanism, such as a
roller clamp on the tubing.
In recent years, a number of electrical monitoring systems, drop
flow controllers and infusion pumps have been developed to accomplish
the tasks of sensing and regulating the rate of fluid flow into
the human body. One such development has been positive pressure
infusion pumps of the syringe type, 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 provide
an 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 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 startup. A prior disposable syringe cartridge
designed to meet these and other requirements is shown and described
in U.S. Pat. No. 3993061 issued Nov. 23 1976 inventor Stephen
H. O'Leary, which patent is assigned to the same assignee as the
present application.
Basically, the disposable syringe cartridge disclosed in U.S. Pat.
No. 3993061 includes a molded plastic cylinder having inlet and
outlet nipples and defining an interior chamber adapted to slidably
receive a plastic piston and integral 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 enchance 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.
The disposable syringe cartridge of U.S. Pat. No. 3993061 itself
embodies no valving structure, but includes a pair of intake and
output I.V. tubes communicating with 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 inlet and outlet nipples of the syringe cartridge of U.S. Pat.
No. 3993061 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.
With the syringe cartridge of U.S. Pat. No. 3993061 an integral
tab extends from the syringe cylinder and provides an operator handle
for mounting and removing the syringe from the overall pumping apparatus.
The end of the piston rod remote from the piston head is provided
with mounting bosses 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. 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.
Although the aforedescribed disposable syringe cartridge has performed
generally satisfactorily, it was designed under the assumption that
care would be taken by medical personnel to always properly install
the cartridge assembly in the syringe pump. Specifically it was
assumed that the longitudinal axis of the syringe cylinder would
be aligned with the axis of reciprocation of the syringe driving
system of the pump. It has been found, however, in practice that
the syringe cartridge can be subject to misloading, which can result
in misalignment of the syringe cylinder axis relative to the axis
of reciprocation of the driving system. As a consequence, a fulcrum
effect can be created in which the sealing rings of the piston head
are forced away from the cylinder wall and fluid leaks past the
piston head. Air or pathogens, or both can then be introduced into
the syringe pumping chamber, which is of course undesirable.
It has further been found that the aforedescribed syringe cartridge
can be improved in other respects, including the ease with which
the cartridge can be sterilized, the sealing between the piston
head and the cylinder wall, the design and attachment of the flexible
boot, and the connection of the I.V. tubes to the syringe nipples,
which can sometimes become dislodged.
Accordingly, it has been recognized that there is a need for an
improved syringe cartridge that overcomes the foregoing problems,
and yet maintains the desirable characteristics of being relatively
simple, economical, reliable, stable and accurate. The present invention
clearly fulfills this need .
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention resides in
a new and improved syringe cartridge that is relatively insensitive
to misloading in the syringe pump and to resulting misalignment
between the longitudinal axis of the syringe cylinder and the axis
of reciprocation of the syringe drive system. The syringe cartridge
of the present invention accommodates misloading without a fulcrum
effect that leads to fluid leakage between the piston head and the
cylinder. The present invention further allows easier sterilization,
and provides, in various embodiments, improved sealing between the
piston head and the cylinder wall, more secure attachment of a flexible
sealing boot in the syringe assembly, and more secure attachment
of a pair of intake and output I.V. tubes to inlet and outlet nipples,
respectively, of the syringe.
More particularly, the disposable syringe cartridge of the present
invention includes a hollow molded plastic cylinder that slidably
receives a plastic piston head that is pivotally connected to a
piston rod. The pivotal connection between the piston head and the
piston rod prevents any lateral forces caused by misalignment from
being transmitted through the piston rod to the piston head, thereby
avoiding any undesirable fulcrum effect giving rise to fluid leakage.
The piston head can carry a quad annular sealing ring, which has
a substantially X-shaped radial cross-section providing two surfaces
in sealing contact with the syringe cylinder for an improved seal.
The cylinder with its integral nipples is formed from a material
that is readily solvent bondable so that I.V. tubes may be solvent
bonded to the nipples to eliminate any chance that either tube can
become dislodged during use.
In one presently preferred embodiment of the invention, the piston
head is defined at one end by a piston face that carries a first
radially-outwardly extending annular flange and, at the opposite
end, by a substantially square expansion flange having its four
corners rounded for conformance with the shape of the syringe cylinder
wall. The limited four-point contact of the expansion flange allows
an easier exchange of sterilizing gas, while maintaining the piston
head in axial alignment during reciprocation. The piston head further
includes a second radially-outwardly extending annular flange adjacent
to, but spaced from the first annular flange to define therebetween
an annular groove into which the quad sealing ring is received.
An annular sealing boot is affixed between the open end of the syringe
cylinder and the piston rod to seal the bottom of the cylinder against
entry of pathogens.
The piston head and the piston rod can be separate parts, and the
pivotal connection between them can comprise an integral hook that
depends from the bottom of the expansion flange and mates with a
snap fit with a wrist pin that is integrally molded on the end of
the piston rod. Alternatively, the piston head, the piston rod and
the pivotal connection means can be integrally formed as a unitary
structure of molded plastic. In that case, the connecting member
has at limited flexibility, as provided for example by a relatively
thin portion formed therein.
For more secure attachment of the annular sealing boot, its outer
circumferential edge is provided with a flange adapted to be received
over the open end of the syringe cylinder, and then an annular cap
is received over and bonded, such as by ultrasonic welding, to the
open end of cylinder with the boot edge firmly captured therebetween.
A pair of parallel-spaced annular flanges are formed integrally
with the piston rod to define an annular groove into which a bead
on the inner circumferential edge of the sealing boot is received.
The sealing boot is formed of a flexible, fluid impervious material
in a bellows-like configuration, with sufficient material being
provided so that the boot seals the open end of the syringe cylinder
without stretching at any time during reciprocation of the piston
head and the piston rod.
In a second preferred embodiment, the piston head is provided with
two sealing rings, one sealing ring carried adjacent the piston
face as in the first embodiment, and a second sealing ring carried
between another pair of spaced-apart, radially-outwardly extending
annular flanges formed at the bottom of the piston head. With this
embodiment, the second sealing ring acts both as a back-up seal
to the first seal ring and as a seal against pathogens and the like
from the open end of the cylinder, so that no sealing boot is required.
In this regard, this second embodiment is adapted for use with a
syringe pump in which the length of the piston stroke of the piston
drive system is no greater than the distance separating the first
and second sealing rings carried by the piston head, so that the
uppermost location achieved by the second sealing ring during piston
upstroke is never higher than the lowermost location of the first
sealing ring during piston downstroke. The result is maintenance
of a sterile condition within the syringe cartridge, since the portion
of the interior side wall of the cylinder that forms part of the
fluid pumping chamber is never exposed to atmosphere at any time
during reciprocation of the piston head. The amount by which the
stroke is less than the separation between the sealing rings represents
a sterility gap to assure that a sterile condition is maintained.
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
embodiments.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view showing a first preferred embodiment
of a disposable syringe cartridge embodying the present invention,
with a schematic representation being shown of a portion of a syringe
pump drive system into which the syringe cartridge is installed;
FIG. 2 is a fragmentary sectional view, taken substantially along
the line 2--2 in FIG. 1 and illustrates the pincher valves external
to the syringe cartridge;
FIG. 3 is a fragmentary sectional view taken along the line 3--3
in FIG. 1 and illustrates the assembled syringe cartridge;
FIG. 4 is a sectional view taken along the line 4--4 in FIG. 3
and illustrates the pivotal connection between the piston head and
the piston rod, as well as the square expansion flange of the piston
head;
FIG. 5 is an exploded perspective view of the main components of
the first preferred embodiment of the syringe cartridge;
FIG. 6 is an enlarged fragmentary sectional view of the quad sealing
ring carried by the piston head; and
FIG. 7 is an enlarged fragmentary sectional view of the outer circumferential
edge of the sealing boot and the annular cap that affixes the boot
in place over the open end of the syringe cylinder;
FIG. 8 is a perspective view showing an alternative manner of forming
the pivotal connection between the piston head and the piston rod
in the first preferred embodiment of the invention;
FIG. 9 is a fragmentary sectional view of an assembled syringe
cartridge embodying the alternative pivotal connection shown in
FIG. 8;
FIG. 10 is a perspective view of a portion of a second preferred
embodiment of the present invention, such portion comprising a piston
head and a piston rod; and
FIGS. 11a and 11b are fragmentary sectional views of the assembled
syringe cartridge of the second preferred embodiment showing the
piston head in the bottom dead center and top dead center positions,
respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, there are shown, by way of example,
the presently preferred embodiments of the invention. In the ensuing
description, although reference is made to the term "I.V."
normally meaning intravenous administration, it is to be understood
that this is for convenience only, and the disposable syringe cartridge
of the present invention is suitable for other forms of parenteral
administration in addition to intravenous administration.
The system shown in FIG. 1 is a schematic representation of a portion
of a syringe infusion pump 10 having a first preferred embodiment
of a disposable syringe cartridge, indicated generally by reference
numeral 12 installed or loaded therein for operation. The syringe
cartridge 12 basically includes a molded plastic cylinder 13 having
fluid inlet and outlet nipples 14 15 integrally formed in a closed
end, and a piston head 16 slidably received in an open end for reciprocation
up and down along the axis of the cylinder by means of a piston
rod 17 that extends between and is coupled to the piston head and
a linear threaded drive shaft 18. In operation, the drive shaft
will be alternately retracted and advanced by an appropriate motor
drive and control system to first fill the syringe cylinder 13 with
a precise volume of fluid from a source of fluid (not shown) via
a length of I.V. tube 19 mounted over the inlet nipple 14 and to
then pump that same precise volume of fluid from the syringe cylinder
through the outlet nipple 15 and its associated I.V. tube 20 to
the patient, respectively.
As best seen in FIG. 2 the syringe infusion pump has a pair of
tube pincher valves 21 22 which are external to the syringe cartridge,
and are selectively opened and closed at the appropriate times in
the pumping cycle under the control of a suitable valve control
system. Specifically, one valve 22 controls the fluid inlet and
is open during the fill stroke to allow fluid to pass through the
intake tube 19 while the other valve 21 is closed. During the pump
stroke, the valve states are reversed so that the intake tube is
pinched closed by the one valve 22 and the other valve 21 is open
to allow fluid delivery to the patient through the outlet tube 20.
The details of the syringe pump valving and motor control system
do not form a part of the present invention, and will not be described
further herein. Suitable systems are disclosed in U.S. Pat. Nos.
3993061; 3994294; and 4137913 all of which are assigned to
the same assignee as the present application and are incorporated
by reference herein.
Referring now more particularly to FIGS. 3 and 5 it can be seen
that the new and improved syringe cartridge 12 of the present invention
is constructed to avoid any fulcrum effect caused by axial misalignment
between the axis of the syringe cylinder 13 and the axis of reciprocation
of the drive shaft 18 of the pump driving system. In this regard,
the piston rod 17 is not integrally formed with the piston head
16 as a unitary structure, but rather there is a pivotal connection
between the piston rod and the piston head. The piston head is defined
at its oppostie ends by a piston face 23 and a square expansion
flange 24. A coupling hook 25 is integrally formed with the piston
head 16 to depend downwardly from the bottom of the expansion flange
24 and a cylindrical wrist pin 26 is integrally formed on the end
of the piston rod 17 crosswise between a pair of integral spaced-apart,
upstanding flanges 26a, b, and is received within the hook. The
piston head and the piston rod, together with their respective connecting
means, are molded of any suitable thermoplastic material, which
inherently will be somewhat resilient, and this allows the opening
in the hook 25 to be sized to receive the wrist pin 26 with a snap
fit to form a simple, yet reliable coupling, the wrist pin then
being free to pivot within the hook once fully received therein.
By virtue of this pivotal connection, misalignment between the respective
axes of the syringe cylinder and the drive shaft 18 is accommodated
by the pivotal connection without transmitting any lateral misalignment
forces to the piston head tending to skew it relative to the syringe
cylinder and thereby cause fluid leakage.
As best seen in FIGS. 4 and 5 the square expansion flange 24 is
rounded at each of its four corners to conform in shape to the inside
wall of the hollow syringe cylinder 13. The expansion flange 24
which forms the bottom of the piston head 16 and aids in maintaining
it in proper axial orientation within the syringe cylinder, is joined
to the piston force by four integral ribs 16a, which intersect at
the longitudinal axis of the piston head. The limited four-point
contact of the flange 24 with the cylinder 13 allows ETO sterilization
gas to be exchanged more easily during the sterilization cycle,
which results in a savings of both cost and time.
At the piston face 23 a pair of spaced-apart radially-outwardly
extending integral annular flanges 27a, 27b are formed on the piston
head 16 to define a groove 28 immediately below the piston face
into which a sealing ring 29 is received. The sealing ring 29 is
of the quad-type that is substantially X-shaped in radial cross-section
so that the ring presents a pair of surfaces, rather than just a
single surface, in sealing contact with the interior wall of the
syringe cylinder 13 for an improved piston-head-to-cylinder seal
(shown in enlargement in FIG. 6).
An annular sealing boot 30 extends between the open bottom end
of the syringe cylinder 13 and the piston rod 17 to seal the syringe
cylinder against pathogens and the like. The outer circumferential
edge of the sealing boot 30 is provided with a flange 30a to overlie
the open end of the syringe cylinder 13 and an annular cap 32
adapted to be received over the open end of the syringe cylinder,
captures the edge of the sealing boot to firmly secure it in place,
as shown in enlargement in FIG. 7. The cap 32 is designed to compress
the sealing boot flange 31 and is ultrasonically welded to the syringe
cylinder 13 to form a substantially fluid-tight seal.
A pair of spaced-apart radially-outwardly extending annular flanges
33a, b are integrally formed on the piston rod 17 to define an annular
groove 35 into which a bead 30b formed along the inner circumferential
edge of the annular sealing boot 30 is received. The bead 30b does
not form a fluid-tight seal, and in fact is provided with a pair
of gas vents (not shown) for gas sterilization purposes. It will
be appreciated, however, that an effective seal against pathogens
is maintained by virtue of the tortuous path between the annular
flanges 33a, b and the bead 30b. The sealing boot 30 has a bellows-like
configuration and is provided with sufficient material so that it
seals the open end of the syringe cylinder 13 without stretching
at any time during reciprocation of the piston head 16 and piston
rod 17. The sealing boot 30 typically is fabricated of rubber to
create a flexible and fluid impervious barrier.
The material from which the syringe cylinder 13 and integral nipples
14 15 is fabricated is chosen not only for its cost, ease of manufacture
and ability to withstand sterilization techniques, but also for
its ability to take a solvent bond so that the I.V. tubes 19 20
can be solvent welded to the nipples 14 15 respectively. This
ensures that the tubes will not become accidentally dislodged from
the nipples after assembly, and particularly during use. Preferably
the material for the syringe cylinder is a modified acrylic, vinyl,
styrene or polycarbonate, although it will be appreciated that other
materials would be suitable. With solvent bonding, the bond can
be stronger than the tubing itself, so that the tubing would break
before becoming dislodged from the nipple.
As with the prior syringe disclosed in U.S. Pat. No. 3993061
the inlet and outlet nipples 14 15 of the syringe cylinder 13 extend
parallel to the longitudinal axis of the syringe on opposite sides
of the syringe, diametrically opposed from each other. The uppermost
cylinder surface 37 above the piston head 16 is sloped upwardly,
typically at an angle of approximately 10.degree., towards the base
of the outlet nipple 15. 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 13 and pass out through the outlet nipple 15 for easy
removal at some convenient access point in the output I.V. tube
20.
Also in a manner similar to the prior syringe cartridge, the syringe
cartridge 12 of the present invention 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 38 projects
from the outer surface of the syringe cylinder 13 near the upper
end of the cylinder, and thereby provides an operator handle for
mounting and removing the syringe cartridge 12 from the pump housing
in a manner described in further detail in U.S. Pat. No. 3933061.
The piston rod 17 is molded in an H-shaped cross-section, defined
by a pair of longitudinally extending, parallel flanges 17a, 17b,
joined by an integral, coextensive cross-bar 17c. At the end of
the piston rod 17 remote from the piston head 16 the longitudinal
flanges 17a, 17b are partially cut-away to define surfaces 17d in
order to provide clearance for insertion into a coupling shoe 39.
In addition, this same end of the piston rod 17 is provided with
a pair of integral, outwardly and oppositely extending, cylindrical
mounting bosses 40 41 one boss projecting perpendicularly outward
from the outside face of the flange 17a, the other boss likewise
projecting outward from the flange 17b. A second pair of outwardly
extending mounting bosses 42 43 parallel to the first set of mounting
bosses 40 41 on the piston rod 17 are integral with the syringe
cylinder 13 and the tab 38 near the upper end of the cylinder.
As best observed in FIG. 3 the piston rod mounting bosses 40
41 are adapted to engage and be retained by the mounting and coupling
shoe 39 which is secured to the leading end of the linear drive
shaft 18 adapted to be coupled to the piston rod 17 for driving
the syringe cartridge 12 through successive fill and pump strokes.
The coupling shoe 39 includes a pair of confronting, wide mouth
guide slots 44 in upstanding flanges 45 disposed on opposite sides
of the coupling shoe, and adapted to engage and guide the mounting
bosses 40 41 so that the syringe cartridge 12 can be inserted into
the coupling shoe horizontally and then pivoted into a vertical
orientation.
As described in more detail in the aforementioned patent, when
the syringe cartridge 12 has been installed, the mounting bosses
40 41 in the guide slots 44 prevent the syringe cartridge from
being dislodged vertically, whereas the piston rod cut-away surfaces
17d received in the retention channel of the coupling shoe 39 prevent
the cartridge from being dislodged horizontally. The mounting bosses
42 43 of the syringe cylinder 13 are adapted to engage a pair of
fixed guide and retaining slots provided in opposite walls of the
syringe receiving compartment of the pump housing (not shown).
Referring now to FIG. 8 an alternative manner of forming the piston
head, the piston rod and the pivotal connection therebetween is
illustrated. As shown, a piston rod 17' and a piston head 16' are
integrally formed as a unitary structure interconnected by a generally
rectangular upstanding integral connecting plate 50. The connecting
plate 50 is relatively thick at its opposite ends, where it joins
the piston head 16' and the piston rod 17', and includes a reduced-thickness
central portion 50a. The thickness of the central portion 50a is
selected to provide a pivotal connection of at least limited flexibility
to accommodate axial misalignment, while retaining sufficient strength
to resist folding or collapsing in response to the compressive forces
exerted on it during piston upstroke. The advantage of this design
is greater simplicity and reduced cost of manufacture as a result
of one less molding operation and elimination of an assembly step.
It will be appreciated that the thickness chosen for the central
portion 50a of the connecting plate 50 will depend on many factors,
including the material of which it is fabricated, the dimensions
of the piston head and cylinder, and the viscosity of he fluid being
pumped. The integral piston head, piston rod and connecting plate
shown herein is molded of a material comprising polypropylene and
a blowing agent. The connecting plate 50 is 0.100 inches thick at
its thickest end portions and gradually reduces to 0.050 inches
thick in its central portion 50a. Overall the connecting plate 50
is approximately 0.4 inches high and 0.5 inches wide, while the
piston face 23' has a diameter of approximately 0.9 inches.
FIG. 9 shows an assembled syringe cartridge employing the integral
piston head 16', piston rod 17', and connecting plate 50 and except
for the features just described, is identical to the cartridge shown
and described in connection with FIGS. 1-7. Corresponding reference
numerals with prime marks therefore have been applied to the various
elements illustrated in FIG. 9 and further description of its design
and operation is unnecessary.
A second preferred embodiment of the disposable syringe cartridge
of the present invention is shown in FIGS. 10 and 11. A piston head
16" is provided with two sealing rings, one sealing ring 29"
carried adjacent the piston face 23" between a pair of spaced-apart,
radially-outwardly extending integral annular flanges 27a",
b", as with the first preferred embodiment. The second sealing
ring 52 is carried adjacent the bottom of the piston head between
a like pair of spaced-apart, radially-outwardly extending integral
annular flanges 53a, b. The first sealing ring 29" is of the
quad-type, while the second sealing ring 52 is a conventional O-ring.
The second sealing ring 52 functions as both a back-up seal to
the first sealing ring 29" in the event of a fluid leak, and
as a seal against atmosphere through the open end of the cylinder
13". In this regard, referring to FIGS. 11a and 11b, the second
embodiment is adapted for use with a syringe pump in which the length
of the piston stroke is no greater than the distance separating
the first sealing ring 29" and the second sealing ring 52.
As a result, that portion of the interior sidewall of the cylinder
that is part of the fluid pumping chamber is never exposed to atmosphere
at any time during reciprocation of the piston head. That is because
the uppermost location achieved by the second sealing ring 52 during
piston upstroke (FIG. 11b) is never higher than the lowermost location
of the first sealing ring 29" during piston downstroke (FIG.
11a). By making the separation between the sealing rings somewhat
greater than the stroke, a sterility gap is created to provide greater
assurance of maintaining a sterile condition within the fluid pumping
chamber. In the second preferred embodiment, the sterility gap is
a minimum of several thousandths of an inch.
An advantage of this design is again reduced cost as the flexible
sealing boot on the open end of the cylinder may be eliminated,
although an annular retainer cap 54 similar to the sealing boot
cap 32 of the first embodiment, is provided to retain the piston
head 16" in the cylinder 13" of the assembled cartridge.
The syringe cartridge of the second preferred embodiment is otherwise
the same as the first embodiment, and corresponding references with
double-prime marks have been applied so that further description
will not be needed. It should be noted, however, that although the
piston head and the piston rod of the second embodiment are shown
as separate parts, they could be integrally formed with a flexible
connecting member as shown in FIG. 8.
The present invention satisfies the need for an improved and yet
relatively simple, economical, reliable, stable and accurate disposable
syringe cartridge.
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. |