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 syringe cartridge over a plurality of operational
cycles of successive fill stroke and pump stroke periods. The apparatus
repetitively and sequentially opens and closes a pair of intake
and output I.V. tubes communicating with a syringe, the tubes alternating
opened and closed states, one tube always being open while the other
is closed, by means of a pair of L-shaped pivotal tube pinchers,
one pincher controlling each I.V. tube, each pincher being normally
spring biased to the tube clamping shut-off state. The tube pinchers
are alternately pivoted to a non-clamping, tube-open position by
a spring biased, intermittent motion, reciprocating slide bar under
the control of a reversible, rotating cam, the cam being driven
by the same motor as that used to drive the piston of the syringe
through its fill and pump strokes. A photoelectric sensor is responsive
to the physical position of one of the tube pinchers and generates
an electrical signal to control the direction of motor rotation
and, hence, determines whether the syringe pump performs a fill
stroke or a pump stroke.
Syringe pump claims
I claim:
1. In a syringe pump having a housing and intake and output I.V.
tubes, the combination comprising:
a pair of movable tube pinchers positioned adjacent the I.V. tubes
to normally pinch off the tubes;
drive means for alternately positioning said tube pinchers to open
and close said I.V. tubes in proper sequence for performance of
fill and pump strokes by the syringe pump;
cam means within the housing in the vicinity of said tube pinchers;
and
cam follower means consisting of a single member positioned by
said cam means for controlling substantially simultaneouus snap
action positioning of both of said tube pinchers so that said positioning
maintains a one tube always open and one tube always closed relationship.
2. A combination as set forth in claim 1 and further comprising:
sensing means responsive to the position of at least one of said
tube pinchers for generating an electrical signal to determine whether
the next stroke performed by the syringe pump will be a fill stroke
or a pump stroke.
3. A combination as set forth in claim 1 and further including:
a tube pincher spring connected between said tube pinchers and
biasing both of said tube pinchers toward the tube closing position.
4. A combination as set forth in claim 1 wherein said cam means
includes a pair of camming surfaces, one of said camming surfaces
conditioning the syringe pump for performance of a fill stroke,
the other of said camming surfaces conditioning the syringe pump
for performance of a pump stroke.
5. In a syringe pump having a housing and intake and output I.V.
tubes, the combination comprising:
a pair of movable tube pinchers positioned adjacent the I.V. tubes;
drive means within the housing for alternately positioning said
tube pinchers to open and close the I.V. tubes in proper sequence
for performance of fill and pump strokes by the syringe pump, said
drive means including a cam and a reciprocating, intermittent motion
slide bar located between said tube pinchers and adapted to alternately
move said tube pinchers, said slide bar being controlled by said
cam.
6. A combination as set forth in claim 5 wherein said slide bar
reciprocates between two positions, and each end of said slide bar
alternately contacts or is spaced away from the adjacent one of
said tube pinchers depending upon which of said two positions is
assumed by said slide bar.
7. A combination as set forth in claim 6 and further including:
means for rotating said cam;
a tube pincher spring connected between said tube pinchers and
biasing both of said tube pinchers toward the tube closing position;
and
a slide bar spring, controlled by said cam, for driving said slide
bar between said two positions.
8. A combination as set forth in claim 1 wherein said cam includes
a pair of camming surfaces for tensioning said slide bar spring
while maintaining said slide bar in one or the other of said two
positions, one of said camming surfaces conditioning the syringe
pump for performance of a fill stroke, the other of said camming
surfaces conditioning the syringe pump for performance of a pump
stroke.
9. A combination as set forth in claim 8 wherein the center of
said slide bar is offset from the center of rotation of said cam
in either of said two positions of said slide bar.
10. A combination as set forth in claim 9 and further including:
tube pincher position sensing means for controlling the direction
of rotation of said cam.
11. In a system for parental administration of liquids from a liquid
source to a patient, apparatus comprising:
a housing;
syringe means supported by said housing for performing alternate
fill and pump strokes to control the flow of liquid to a patient,
said syringe means including intake and output I.V. tubes;
a pair of movable tube pinchers adjacent said I.V. tubes, one for
each of said I.V. tubes, for alternately clamping off and opening
the associated I.V. tube;
motor means within said housing for driving said syringe means
for performance of said fill and pump strokes;
valve control means within said housing for alternately positioning
said tube pinchers to periodically open and close said I.V. tubes
at appropriate times to enable said syringe means to sequentially
perform said fill and pump strokes, said valve control means including
a slide bar adapted to move along a linear path between said tube
pinchers to alternately move one of said tube pinchers and then
the other of said tube pinchers to the tube open position, said
slide bar reciprocating between two positions, each end of said
slide bar alternately contacting or being spaced away from the adjacent
one of said tube pinchers depending upon which of said two positions
is assumed by said slide bar;
a rotary cam adapted to be rotated by said motor means;
a tube pincher spring connected between said tube pinchers and
biasing both of said tube pinchers toward the tube closing position;
and
a slide bar spring, controlled by said cam, for driving said slide
bar between said two positions.
12. Apparatus as set forth in claim 11 wherein said cam includes
a pair of camming surfaces for tensioning said slide bar spring
while maintaining said slide bar in one or the other of said two
positions, one of said camming surfaces conditioning the syringe
pump for performance fo a fill stroke, the other of said camming
surfaces conditioning the syringe pump for performance of a pump
stroke.
13. In a system for parenteral administration of liquids from a
liquid source to a patient, apparatus comprising:
a housing;
syringe means supported by said housing for performing alternate
fill and pump strokes to control the flow of liquid to a patient,
said syringe means including intake and output I.V. tubes;
a pair of spring biased movable tube pinchers adjacent said I.V.
tubes, one for each of said I.V. tubes, for alternately clamping
off and opening the associated I.V. tube;
motor means within said housing for driving said syringe means
for performance of said fill and pump strokes; and
valve control means within said housing for alternately positioning
said tube pinchers to periodically open and close said I.V. tubes
at appropriate times to enable said syringe means to sequentially
perform said fill and pump strokes said valve control means including
a dual surface cam and a single cam follower for controlling substantially
simultaneous snap action positioning of both of said tube pinchers
so that said positioning maintains a one tube always open and one
tube always closed relationship.
14. Apparatus as set forth in claim 13 and further comprising:
a pincher position sensor for generating an output electrical signal
indicating the proper direction of rotation of said motor means
in driving said syringe means.
15. Apparatus as set forht in forth 13 wherein both of said tube
pinchers are biased towards the tube clamping off position and said
valve control means includes a slide bar adapted to reciprocate
along a linear path between said tube pinchers to alternately move
one of said tube pinchers and then the other of said tube pinchers
to the tube open position.
16. Apparatus as set forth in claim 15 wherein said slide bar
reciprocates between two positions, and each end of said slide bar
alternately contacts or is spaced away from the adjacent one of
said tube pinchers depending upon which of said two positions is
assumed by said slide bar.
17. In a system for parenteral administration of liquids from a
liquid source to a patient, apparatus comprising:
a housing;
syringe means supported by said housing for performing alternate
fill and pump strokes to control the flow of liquid to a patient,
said syringe means including intake and output I.V. tubes;
a pair of movable tube pinchers adjacent said I.V. tubes, one for
each of said I.V. tubes, for alternately clamping off and opening
the associated I.V. tube, said tube pinchers being spring biased
towards the tube clamping off point;
motor means within said housing for driving said syringe means
for performance of said fill and pump strokes;
valve control means within said housing for alternately positioning
said tube pinchers to periodically open and close said I.V. tubes
at appropriate times to enable said syringe means to sequentially
perform said fill and pump strokes. said valve control means including
a slide bar adapted to move along a linear path between said tube
pinchers to alternately move one of said tube pinchers and then
the other of said tube pinchers to the tube open position, and slide
bar reciprocating between two positions, each end of said slide
bar alternately contacting or being spaced away from the adjacent
one of said tube pinchers depending upon which of said two positions
is assumed by said slide bar;
a rotary cam driven by said motor means, said cam having an arcuate,
semi-circular ridge defining inner and outer cam surfaces;
a slide bar pin projecting from one face of said slide bar and
engaging one or the other of said inner and outer cam surfaces;
and
a slide bar spring, one end of said slide bar spring being secured
to the center of said slide bar, the other end of said slide bar
spring being secured to said rotary cam.
18. Apparatus as set forth in claim 17 wherein the center of said
slide bar is offset from the center of rotation of said cam in either
of said two positions of said slide bar.
19. Apparatus as set forth in claim 17 and further including:
a reference light source and photoelectric sensor maintained in
a fixed position; and
an opaque member carried by one of said tube pinchers and adapted
to interrupt the light beam from said reference light source in
one position of the tube pincher while being withdrawn from said
light beam in the other position of said tube pincher, whereby an
electrical signal is generated indicating the required direction
of rotation of said motor.
20. Apparatus as set forth in claim 17 wherein said ridge defines
a 180.degree. arc.
21. Apparatus as set forth in claim 17 wherein said other end
of said slide bar spring is secured to said rotary cam adjacent
the outer periphery of said cam.
22. In a syringe pump having a housing and including a syringe
supported within the housing, apparatus comprising:
driving means for driving the syringe through a fill stroke in
which the syringe is filled with fluid through an intake line and
through a pump stroke during which fluid is delivered from the syringe
through an output line;
movable tube pincher means for alternately opening and closing
said intake and output lines in proper sequence for performance
of said fill and pump strokes; and
sensing means responsive to said tube pincher means for determining
the direction of movement of said driving means.
23. Apparatus as set forth in claim 22 wherein said driving means
is an electrical motor and said sensing means generates an electrical
signal for establishing the direction of rotation of said motor.
24. In a syringe pump, apparatus comprising:
an intake pivotal tube pincher for alternately clamping off and
opening an intake I.V. tube;
an output pivotal tube pincher for alternately clamping off and
opening an output I.V. tube;
a pincher spring secured at one end to said intake tube pincher
and at the other end to said output tube pincher, said pincher spring
extending between said tube pinchers and biasing said tube pinchers
towards the tube clamping off position;
a slide bar adapted to reciprocate along a linear path between
said tube pinchers to alternately and sequentially move one of said
tube pinchers and then the other of said tube pinchers to the tube
open position;
a reversible, rotary cam having an arcuate, semi-circular ridge
defining inner and outer camming surfaces, said ridge defining a
180.degree. arc; a slide bar pin projecting from one face of said
slide bar and engaging one or the other of said inner and outer
camming surfaces;
a slide bar spring, one end of said slide bar spring being secured
to the center of said slide bar, the other end of said slide bar
spring being secured to the outer periphery of said rotary cam;
reversible, electrical motor means for rotating said rotary cam
in either of two directions;
a reference light source and photoelectric sensor maintained in
a fixed position; and
an opaque member carried by one of said tube pinchers and adapted
to interrupt the reference light beam from said light source in
one position of the tube pincher while being withdrawn from said
reference light beam in the other position of the tube pincher,
whereby an electrical signal is generated indicating the required
direction of rotation of said motor.
25. Apparatus as set forth in claim 24 wherein said slide bar
reciprocates between two positions, and each end of said slide bar
alternately contacts or is spaced away from the adjacent one of
said tube pinchers depending upon which of said two positions is
assumed by said slide bar.
26. Apparatus as set forth in claim 25 wherein the center of said
slide bar is offset from the center of rotation of said cam in either
of said two positions of said slide bar.
27. Apparatus as set forth in claim 26 wherein each of said tube
pinchers is substantially L-shpaed having a longer arm and a shorter
arm.
28. Apparatus as set forth in claim 27 wherein one edge of said
shorter arm defines a tube pincher blade adapted to clamp off an
I.V. tube.
29. Apparatus as set forth in claim 26 wherein each end of said
slide bar is fitted with a bumper pad through which said slide bar
alternately contacts said tube pinchers.
30. In a syringe pump, the combination comprising;
a housing;
a syringe supported within said housing and having inlet and outlet
ports and a piston slidably received within said syringe, said syringe
having no valves for said inlet and outlet ports;
drive means within said housing for reciprocating said syringe
piston;
an intake I.V. tube coupled to said inlet port;
an outlet I.V. tube coupled to said outlet port; valve means associated
with said tubes; and
valve control means within said housing separate from said syringe
for cyclically opening and closing said valve means and thereby
said intake and output I.v. tubes at appropriate times to enable
said syringe to sequentially perform fill and pump strokes. said
control means including a dual surface cam and a single cam follower
for effecting substantially simultaneous snap action control over
the opening and closing of said intake and output I.V. tubes which
maintains a one tube always open and one tube always closed relationship.
31. In a syringe pump, apparatus comprising:
an intake I.V. tube and output I.V. tube;
an intake tube pincher for alternately clamping off and opening
said intake I.V. tube;
an output tube pincher for alternately clamping off and opening
said output I.V. tube; said pinchers being movably mounted with
respect to one another;
a pincher spring secured at one end to said intake tube pincher
and at the other end to said output tube pincher, said pincher spring
extending between said tube pinchers and biasing said tube pinchers
towards the tube clamping off position;
a tube pincher control means for alternately and sequentially moving
one of said tube pinchers and then the other of said tube pinchers
to the tube open position;
a reversible, rotary cam having an arcuate, semi-circular ridge
defining inner and outer camming surfaces;
a single cam follower coupled to said pincher control means and
engaging one or the other of said inner and outer camming surfaces;
and
reversible, electrical motor means for rotating said rotary cam
in either of two direction.
32. In a syringe pump, apparatus comprising:
a housing;
an intake I.F. tube and output I.V. tube;
an intake tube pincher within said housing for alternately clamping
off and opening said intake I.V. tube;
an output tube pincher within said housing for alternately clamping
off and opening said output I.V. tube; said tube pinchers being
movably mounted with respect to one another;
a pincher spring secured at one end to said intake tube pincher
and at the other end to said output tube pincher, said pincher spring
extending between said tube pinchers and biasing said tube pinchers
towards the tube clamping off position;
a tube pincher control means within said housing for alternately
and sequentially moving one of said tube pinchers and then the other
of said tube pinchers to the tube open position, said tube pincher
control means including a single common member for substantially
simultaneous snap action positioning both of said tube pinchers
so that said positioning maintains a one tube always open and one
tube alwasy closed relationship.
33. Apparatus as set forth in claim 32 and further comprising:
a reversible rotary cam;
a single cam follower coupled to said pincher control means and
engaging said cam; and
reversible, electrical motor means for rotating said rotary cam
in either of two directions.
34. In a syringe pump having a housing and intake and output I.V.
tubes, the combination comprising:
a pair of movable tube pinchers within the housing;
drive means within the housing for positioning said tube pinchers
to open and close said I.V. tubes;
reversible cam means;
cam follower means;
spring means for biasing said cam follower means against surfaces
of said cam means in both directions of said cam control means;
and
a single common member, coupled to said cam follower means for
controlling substantially simultaneous snap action positioning and
repositioning of said tube pinchers so that said positioning maintains
a one tube always open and one tube always closed relationship.
Syringe pump description
BACKGROUND OF THE INVENTION
This invention relates generally to improvements in syringe pumps
and, more particularly, to a new and improved valve control system
for such pumps which reliably and precisely opens and closes the
intake and output I.V. tubes for a syringe at appropriate points
in the pumping cycle and also generates a control signal for establishing
direction of motor rotation.
The usual medical procedure for the gradual parenteral admisistration
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 botttle of liquid, normally supported in
an inverted position, an intravenous feeding tube, trypically 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
rates.
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 monitoring and regulating
flow rates 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 monitoring and drop rate control devices have generally
served their purpose, they have not always proven entirely satisfactory
from the standpoint of cost, complexity, stability, reliability,
accuracy, or precision of adjustment over a wide range of selected
flow rates. 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. Substantial difficulties have
also been experienced particularly in connection with establishing
and maintaining accurate flow at very low flow rates.
Positive pressure pumps of the closed-loop peristaltic type have
been provided which overcome some of the aforementioned difficulties
with regard to drift, and accurate flow at low flow rates. However,
even such closed-loop positive pressure systems 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. However, since
a portion of each operating cycle with such syringe pumps is concerned
with filling the syringe, rather than delivering fluid to the patient
in a pumping mode, there is a need for extremely precise control
over the intake and output syringe valving and the direction of
rotation of the motor driving the syringe. Such valve control must
not only be very positive in its action and extremely accurate in
its timing, but must also be in precise synchronism with the control
over motor direction.
In addition, syringe pumps of the prior art primarily depend on
valving embodied directly within the syringe itself. This not only
increases the cost and complexity of the syringe, particularly where
disposable syringes are employed, but usually also results in reduced
reliability of operation.
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 valving
and motor control 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 system for accurately controlling fluid flow in
the parenteral administration of medical liquids, wherein the repetitive
opening and closing of a pair of intake and output I.V. tubes communicating
with a syringe is automatically accomplished during successive fill
and pump periods by means of cam control of a pair of pivotal tube
pinchers which alternately pinch off and open the intake and output
tubes in proper sequence. In addition, the physical position of
one of the tube pinchers is monitored and controls the direction
of rotation of the pump motor and, hence, determines the fill or
pump mode of operation of the syringe. Such valving and motor direction
control is accomplished with no lost motion or delay, in that the
valving action and motor direction changes are automatically maintained
in precise synchronism. Moreover, valving is provided without the
need for providing relatively complex, expensive and sometimes unreliable
valve structures in the syringe itself.
More particularly, the present invention provides a new and improved
syringe pump embodying a reversible, rotary cam controlled reciprocating
slide bar for alternately moving each of a pair of tube pinchers
to successively clamp off and open the intake and output I.V. tubes
of the syringe to fluid flow, and, further, controlling motor direction
in synchronism with the sequential open and closed states of the
I.V. tubes, to properly enable performance of successive cycles
of fill and pump strokes.
The rotary cam includes an arcuate ridge adjacent its outer periphery
defining semi-circular inner and outer camming surfaces against
which a cam follower is biased, the cam follower being held against
one camming surface during performance of a pump stroke and against
the other camming surface during performance of a fill stroke, the
cam follower typically being in the form of a pin secured to and
projecting from one side of a slide bar which reciprocates intermittently
back and forth in a guide block, along a linear path. Each movement
of the slide bar coincides with a change from a fill stroke to a
pump stroke, or from a pump stroke to a fill stroke, in the overall
operational cycle of the syringe pump.
Both tube pinchers are pivotally mounted and spring biased towards
each other and towards the tube clamping state. The slide bar is
power driven by an extension spring. During performance of each
syringe stroke, the cam surface engaging the slide bar pin holds
the slide bar against the appropriate tube pincher to pivot the
latter and hold it in the tube-open position, thereby relieving
the slide bar spring of the task of overcoming the pincher spring
during performance of each syringe stroke. In addition, during the
transition period between syringe strokes, the slide bar spring
is initially assisted in its movement by the pincher spring, the
slide bar spring only having to work against the pincher spring
in the latter portion of the slide bar stroke when the slide bar
has already acquired some momentum.
The slide bar center is offset from the center of rotation of the
cam, at the end of each slide bar stroke repositioning the pinchers.
In this regard, one end of the slide bar spring is secured to the
center of the slide bar, while the other end is secured to a point
along the outer periphery of the rotary cam. Therefore, as the cam
rotates, with the slide bar held stationary (since the slide bar
pin is biased against either the inner or outer arcuate camming
surface), the slide bar spring is tensioned and suddenly released,
to shift the slide bar longitudinally and reposition the tube pinchers,
only when the slide bar pin cam follower comes to the end of the
arcuate camming surface and drops off to move either from the inner
camming surface to the outer camming surface, or from the outer
surface to the inner surface of the cam, depending upon the particular
syringe stroke just completed. Then the cam begins to turn in the
opposite direction, again trapping the slide bar cam follower pin
to maintain the slide bar in a fixed position while stretching and
rotating the slide bar extension spring. When the latter spring
has been fully stretched and rotated 180.degree. to cock the slide
bar mechanism, the other end of the arcuate ridge on the cam goes
past the slide bar pin, allowing the slide bar to snap over to its
alternate position and begin the entire cycle over again.
A fixed light source and photoelectric sensor arrangement provides
a reference light beam which is selectively interrupted by an opaque
flag carried on one of the tube pinchers. The flag is repositioned
each time the tube pincher on which it is mounted is moved, so that
a control signal is developed indicative of the syringe stroke about
to be performed, the control signal being used to establish the
proper direction of rotation of the motor.
The new and improved syringe pump valving and motor direction control
system of the present invention is extremely accurate and reliable.
The system provides valve control without the need for separate
valves in the syringe itself and provides precise motor direction
control in perfect synchronism with the opening and closing of the
syringe intake and output lines.
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 an illustrative
embodiment.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the interior structure of
a syringe pump embodying the present invention, the outer pump housing
being shown in dashed lines;
FIG. 2 is an enlarged, plan view, of the syringe pump of FIG. 1
with the top plate removed, and illustrates the apparatus during
a pump stroke, sequential positions of the apparatus being shown
in phantom;
FIG. 3 is a fragmentary sectional view, taken along the line 3--3
in FIG. 2;
FIG. 4 is a fragmentary sectional view, taken along the line 4--4
in FIG. 2;
FIG. 5 is a plan view similar to FIG. 2 and illustrates the state
of the apparatus during performance of a fill stroke; and
FIG. 6 is a combined elevational and sectional view, taken along
the line 6--6 in FIG. 5.
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 embodying a syringe
10 which preferably is in the form of a disposable cartridge, but
it will become apparent that all of the features of the present
invention may be practiced independently of whether or not the syringe
10 is disposable. The syringe 10 essentially includes a molded cylinder
10a in which a piston 10b is slidably received and adapted to be
reciprocated back and forth along the axis of the cylinder by an
integral piston rod 10c which is removably mounted at one end in
a coupling shoe 11 carried by a lead screw 12 which is advanced
and retracted by a suitable drive system. The drive system includes
a reversible, d.c. stepping motor 13 and appropriate gearing 14
to drive the lead screw 12 which is, in turn, coupled to the piston
rod 10c of the syringe 10. The motor 13 is energized by a pulse
train of motor drive pulses generated by an appropriate electrical
control system 15.
The syringe 10 includes an inlet port 10d and an outlet port 10e.
The inlet port 10d communicates through a suitable intake I.V. tube
16 with any appropriate liquid source (not shown), usually an I.V.
bottle containing appropriate drugs and/or nutrients in fluid form.
Typically, the intake I.V. tube 16 is part of an I.V. administration
set which includes a transparent drip chamber in the line between
the syringe 10 and the liquid source.
A similar, output I.V. tube 17 is connected at one end to the outlet
port 10e of the syringe 10 and conveys fluid from the syringe to
a patient.
A pair of syringe pump valves 18 19 external to the syringe 10
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 20. The valve 18 controls the
inlet port 10d and is open during the fill stroke to enable fluid
to be drawn from the liquid source, through the intake line 16
into the syringe 10 the valve 18 being closed during the pump stroke
to prevent fluid from exiting the syringe through the inlet port.
The valve 19 controls the outlet port 10e and is open during the
pump stroke to enable fluid delivery from the syringe 10 to the
patient through the output line 17 the valve 19 being closed during
the fill stroke.
The valve control system 20 is also driven, through the gearing
14 by the same drive motor 13 as is used to operate the syringe
10. The valve control system 20 also provides information to the
electrical control system 15 controlling the motor 13 indicating
that the syringe 10 is either in the fill stroke or the pump stroke,
and this information, in turn, enables the electrical control system
to establish the proper direction of rotation of the motor. The
electrical control system 15 may be of conventional design for electrically
energizing the motor 13 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 1965 and assigned to the
same assignee as the present application. A copy of the specification
and drawings for the latter application is attached hereto as Appendix
A.
The motor 13 drives, through the gearing 14 and an output camshaft
21 a reversible, semi-circular rotary cam 22 which controls the
opened and closed positions of the syringe pump valves 18 19.
The gear ratio of the gearing 14 is specifically selected so that
the rotary cam 22 rotates through an angle of approximately 180.degree.
during a pump stroke of the syringe 10 and then reverses and rotates
through another 180.degree. in the opposite direction during an
intake stroke. Hence, the rotary cam 22 is essentially a half-turn
cam. The camshaft 21 rotates the cam 22 which biases a slide bar
23 to alternately hold one syringe pump valve open and then the
other, in proper cyclical sequence.
The syringe pump valves 18 19 consist of a pair of pivotal tube
pinchers 24 25 which alternatively pinch off and open the intake
and output tubes 16 17 respectively, of the syringe 10. The tube
pinchers 24 25 are spring biased to the tube shut-off position
and are positively driven open by the valve control system 20 thus
allowing full tube closure regardless of normal variations in I.V.
tubing diameter and wall thickness.
As best observed in FIGS. 2-5 each of the tube pinchers 24 25
is of substantially L-shape and includes a long arm 24a, 25a, respectively,
and a short arm 24b, 25b, respectively. One face of the short arm
24b is shaped to define a pincher blade 24c adapted to cooperate
with the confronting face of a shoulder 26 defined on the interior
side of a syringe pump access door 27 to the syringe compartment.
Similarly, a pincher blade 25c is defined by the short arm 25b of
the output tube pincher 25. Together, the pincher blades 24c, 25c
and the access door shoulder 26 define a pair of clamping surfaces
between which the intake and output I.V. tubes 16 17 pass. The
access door 27 is held shut, after the syringe has been installed,
by any suitable latch 27a.
The intake tube pincher 24 is pivotally mounted by means of a
pivot pin and bushing at 28. Similarly, the output pincher is pivotally
mounted at 29. Both tube pinchers are spring-biased to the tube
clamping shut-off state by a coil spring 30 extending between the
pinchers and appropriately secured at each end to one of the pinchers,
as by anchor pins 24d, 25d, respectively.
The syringe pump valves 18 19 are selectively opened in proper
cyclical sequence by pivoting the tube pinchers 24 25 one at a
time, via contact with the reciprocating, intermittent motion slide
bar 23 which is power driven by a slide bar extension spring 32.
The slide bar 23 is slidably mounted within a guide block 31 and
contacts the tube pinchers 24 25 by bumper pads 33 mounted at each
end of the slide bar. In order for the slide bar spring 32 to drive
the slide bar 23 in both directions, one end of the slide bar spring
is secured to the slide bar at its center, by an anchor pin 32a,
while the other end of the slide bar spring is secured to the rotary
cam 22 near its outer periphery by an anchor pin 32b. In either
of its two positions at the end of a slide bar stroke, the center
of the slide bar 23 along its longitudinal axis is offset from the
center of rotation of the cam 22.
The slide bar 23 moves only upon completion of a syringe stroke,
either a fill stroke or a pump stroke. The slide bar 23 is maintained
in a fixed position during performance of any syringe stroke by
an arcuate, semi-circular ridge 22a on the cam 22 defining inner
and outer camming surfaces 22b, 22c respectively, adjacent the outer
periphery of the cam, each of these camming surfaces alternately
abutting a slide bar pin 23a secured to and projecting from one
face of the slide bar at the end of the slide bar.
The slide bar pin 23a is a cam follower which is held against one
of the camming surfaces 22b, 22c during performance of each syringe
stroke and switches positions from one of these camming surfaces
to the other camming surface at the end of each stroke. As the cam
22 rotates, the slide bar spring 32 is tensioned to cock the slide
bar mechanism. Since the center of the slide bar 23 does not coincide
with the center of the cam 22 in either of the two positions of
the slide bar, rotation of the cam causes the slide bar spring 32
to stretch becuase the slide bar center is always repositioned to
the opposite side of the cam center when the cam rotates through
a 180.degree. cycle. Hence, the slide bar spring 32 is tensioned
by turning the cam 22 and yet the cam holds the slide bar 23 in
the same position throughout the 180.degree. rotary cycle.
As best observed in FIGS. 2 and 5 wherein mid-cycle positions
of the rotary cam 22 are shown in phantom, when the end of the ridge
22a on the cam 22 is rotated past the slide bar pin 23a, the slide
bar spring 32 snaps the slide bar 23 over from one of its two positions
to the other position in performance of a slide bar stroke, causing
the tube pinchers 24 25 to change position. The tube pincher that
was previously open, now closes, while the tube pincher that was
previously closed now opens. Then the cam 22 begins to turn in the
reverse direction, again trapping the slide bar pin 23a against
one of the camming surfaces 22b, 22c, to maintain the slide bar
23 in a fixed position while tensioning and rotating the slide bar
spring 32. When the slide bar spring 32 has been fully tensioned
and rotated 180.degree., again cocking the slide bar mechanism,
the other end of the semi-circular ridge 22a on the cam 22 goes
past the slide bar pin 23a, allowing the slide bar 23 to briskly
snap over to its alternate position and begin the entire syringe
pump cycle again. The result is extremely precise, positive action
valving.
In the embodiment of the invention illustrated, the slide bar pin
23a rides on the outer surface 22c of the cam 22 during the pump
stroke (FIG. 2) and rides on the inner surface 22b of the cam during
the fill stroke (FIG. 5). As the slide bar 23 moves from one position
to the other, it pushes one or the other of the tube pinchers 24
25 open. The tupe pincher spring 30 is what actually provides the
tube closure force, i.e., the force necessary to close on the I.V.
tubes 16 17. The slide bar extension spring 32 merely provides
a force to drive the slide bar 23 through a slide bar stroke.
One advantage of the valve control system 20 resides in the manner
in which the tube pincher spring 30 always holds one of the tube
pinchers 24 25 against the I.V. tubing. As a result, the slide
bar spring 32 can move the slide bar 23 and both tube pinchers 24
25 without having to overcome the tube pincher spring 30 during
the entire slide bar stroke. The tube pincher spring 30 is stretched
between the pair of tube pinchers 24 25 and, if the I.V. tubing
were not present, it would cause both tube pinchers to rest against
both of the bumper pads 31 of the slide bar 23. However, when the
I.V. tubing is in place, it causes the closed tube pincher to be
spaced a small distance away from the end of the slide bar 23 as
at 34 in FIG. 2 and at 35 in FIG. 5. Because of this gap, when the
slide bar 23 first starts to move at the end of a syringe fill or
pump stroke, the tube pincher spring 30 actually aids the slide
bar spring 32 in initially driving the slide bar. Only near the
end of the slide bar stroke, when the slide bar 23 has already built
up considerable momentum, does the tube pincher spring 30 exert
any force tending to retard the motion of the slide bar.
The position of the tube pinchers 24 25 is sensed by a combined
light source and photoelectric sensor assembly 37 which controls
the direction of rotation of the motor 13. In this regard, the pincher
position sensor assembly 37 is mounted on the underside of the cover
plate 38 (FIG. 6) of the pump housing and is thereby supported in
a fixed position. An opaque flag 39 is carried by the output tube
pincher 25.
As shown in FIG. 2 when the flag 39 interrupts the reference light
beam between the light source and photoelectric sensor, an electrical
signal is generated indicating that the system is either about to
initiate or is already performing a pump stroke, i.e., the output
tube 17 is open. In contrast, as observed in FIG. 5 when the flag
39 is retracted by the tube pincher 25 an electrical signal is
generated indicating that the system is either about to initiate
or is in the performance of a fill stroke, i.e., the intake tubing
16 is open. The motor direction control afforded by such an arrangement
is in precise synchronism with the intake and output tube valving
and the pump can never cause fluid to be taken in through the syringe
output tube 17 or be pumped through the syringe intake tube 16.
Moreover, the motor 13 never reverses until the tube pinchers 24
25 have been actuated. This results in a very precise volume displacement
for each syringe stroke.
In summary, when the slide bar pin 23a arrives at the end of the
inner camming surface 22b at the completion of a fill stroke, the
slide bar pin will drop off the cam 22 because of the force exerted
by the tensioned slide bar spring 32 and the pin will then move
to the outer camming surface 22c for performance of a pump stroke
(FIG. 2). This will reposition the tube pinchers 24 25 to close
the intake tube 16 open the output tube 17 and generate a control
signal via the position sensor 37 to reverse the motor 13. Then
the cam 22 will reverse, because the motor 13 is reversed, and the
cam will rotate while capturing the slide bar pin 23a on its outer
camming surface 23c. The cam 22 will go through another 180.degree.
cycle in the reverse direction while again stretching the slide
bar spring 32 this time because the slide bar center is on the
other side of the cam center. At the end of the 180.degree. cycle,
the slide bar pin 23a will again drop off the outer camming surface
22c, and move to the inner camming surface 22b where it started
(FIG. 5). In this way, the slide bar 23 oscillates intermittently
between its two extreme positions to pivot the tube pinchers 24
25 and open and close the intake and output I.V. tubes 16 17 precisely
and positively at appropriate times in the operational cycle of
the syringe pump.
The syringe pump valving and motor direction control system of
the present invention satisfies a long existing need for improved,
relatively simple, economical, reliable, stable and accurate valving
and motor control systems for such syringe pumps. The system provides
extremely precise valve control without the need for separate valves
in the syringe itself and provides precise motor direction control
in perfect synchronism with the opening and closing of the syringe
intake and output tubes.
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.
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