Syringe pump abstract
A syringe pump is disclosed, having a housing, a motor driven pusher
for pushing the plunger of a syringe and various transducers to
determine error conditions in the placement of the syringe in the
syringe pump, the pushing force of the pusher on the syringe and
the engagement of the pusher drive mechanism. The syringe pump is
provided with a clamp for holding the syringe in place and a device
for preventing fluid from being siphoned out of the syringe. There
is also a device for engaging and disengaging the motor drive mechanism.
A position sensor senses the position of the syringe plunger in
the barrel. A display graphically represents the syringe. Indicia
are provided on the display to alert the user of conditions in the
mechanism for holding the syringe in place, antisiphon device, the
syringe drive engagement mechanism and the position of the plunger
in the barrel.
Syringe pump claims
1. A syringe pump for pumping fluid from a syringe having a barrel
and a plunger, the plunger having a flange, the syringe pump comprising:
a pusher for pushing the plunger;
clamp means for engaging the syringe barrel and for holding the
syringe barrel in a stationary position relative to the housing;
clamp detector means for detecting whether or not the syringe is
properly held in position relative to the housing by the clamp means
and for producing an output indicative of whether the syringe is
properly held in position relative to the housing;
antisiphon means for engaging the plunger and holding the plunger
stationary relative to the pusher, thereby preventing the plunger
from moving independently of the pusher;
antisiphon detector means for detecting whether the plunger is
properly engaged by the antisiphon means and for producing an output
indicative of whether the plunger is properly engaged by the antisiphon
a display comprising a graphical representation of the syringe,
the graphical representation comprising a representation of the
syringe barrel and the plunger, first indicium means for indicating
the output of the clamp detector means and located at a point on
the display generally corresponding to the position on the syringe
barrel where the clamp engages the syringe barrel and second indicium
means for indicating the output of antisiphon detector means, and
located at a point on the display generally corresponding to the
position on the plunger where the antisiphon means engages the plunger;
electronic circuitry for transmitting the outputs of the clamp
detector means and the antisiphon detector means respectively to
the first and second indicia means such that the display indicates
whether or not the syringe is properly held relative to the housing
and whether or not the plunger is properly engaged by the antisiphon
2. The syringe pump of claim 1 further comprising:
drive means for driving the pusher;
disengage means for engaging and disengaging the drive means;
disengage detector means for detecting whether the drive means
is engaged or disengaged and for producing an output indicative
of whether the drive means is engaged or disengaged,
wherein the display further comprises a third indicium means for
indicating the output of the disengage detector means, such that
the third indicium means is positioned on the graphical representation
of the syringe corresponding to the syringe plunger; and,
wherein the electronic circuitry further comprises means for transmitting
the output of the third detector means to the third indicium means.
3. The syringe pump of claim 1 wherein the plunger comprises a
stopper and further comprising means for determining whether the
plunger has fully entered the barrel and wherein the display comprises
a fourth indicium for indicating whether the plunger has fully entered
the barrel, the fourth indicium corresponding to the point in the
barrel at which the stopper of the plunger is located when the plunger
has fully entered the barrel.
4. The syringe pump of claim 1 wherein the electronic circuitry
comprises a microprocessor.
5. The syringe pump of claim 2 wherein the third indicium means
is located adjacent a point on the display generally corresponding
to the back of the flange of the plunger.
6. The syringe pump of claim 1 wherein the first indicium means
is activated when the syringe is not properly held in position on
the housing by the clamp means.
7. The syringe pump of claim 1 wherein the second indicium means
is activated when the plunger is not properly engaged by the antisiphon
8. The syringe pump of claim 2 wherein the third indicium is activated
when the drive means is disengaged.
9. The syringe pump of claim 2 wherein the drive means comprises
a lead screw and a half nut, the half nut engaging the lead screw
when the drive means is engaged.
10. The syringe pump of claim 7 wherein the third indicium means
lights up when the half nut does not engage the lead screw.
11. The syringe pump of claim 3 wherein the fourth indicium is
activated when the plunger has fully entered the barrel.
Syringe pump description
1. Field of the Invention
This invention relates to the field of syringe pumps. In particular
it relates to displays for indicating operating conditions in syringe
2. Background of the Invention
A syringe pump is a device for pumping fluid from a syringe into
a patient. It typically comprises a housing to which a syringe is
secured and a mechanism for pushing the plunger of the syringe to
expel the fluid from the syringe, thus infusing the fluid into the
patient. In the course of the operation of the syringe pump, certain
conditions may arise at various parts of the pump. Using this invention,
the user is informed of error conditions in the syringe pump by
means of indicia on a display.
In prior art syringe pumps, the user has been informed of error
conditions by means of messages displayed on the syringe pump control
panel. These messages have been in the form of codes or flashing
indicia. The applicants are unaware of any prior art syringe pump
which has a single graphical representation of a syringe with indicia
of all detected error conditions on that syringe and at points corresponding
to the points at which the error conditions have arisen.
SUMMARY OF THE INVENTION
The invention is made up of a syringe pump having the following
components: The syringe pump is housed in a housing which contains
the drive mechanism for pushing the plunger of the syringe. The
syringe is secured to the housing by means of a syringe clamp. In
order to ensure that the syringe is securely held in place during
the operation of the pump, the clamp is provided with a detector
which detects the position of the clamp. The detector produces an
electrical signal if the clamp is not properly positioned.
The pump also has a mechanism for holding the plunger in place
so that it cannot move independently of the pusher, thus preventing
fluid from being siphoned from the syringe. This antisiphon device
is also provided with an electronic sensor which produces an electrical
signal if the antisiphon device is not properly positioned.
The pusher is driven by means of a motor driven lead screw and
a half nut which engages the lead screw. In order to facilitate
the positioning of the pusher relative to the syringe, the half
nut can be disengaged from the lead screw. A transducer is provided
to detect whether or not the half nut is engaged with the lead screw.
The pump also has a mechanism for detecting the position of the
syringe plunger relative to the barrel. An indicium is activated
when the plunger has fully entered the barrel.
The syringe pump has a display for alerting the user to error conditions
arising at all or some of the points described above. The display
is in the form of a graphical representation of a syringe. The graphical
representation of the syringe has indicia located at the points
on the graphical representation which generally correspond to the
points on the actual syringe at which the error conditions described
above may occur. Thus the display has indicia at all or some the
following points: The point on the syringe barrel at which the clamp
holds the barrel in place; the point on the plunger at which the
antisiphon device engages the plunger; and the point on the plunger
at which the plunger makes contact with the syringe pusher. When
an error condition arises at any of the above identified points
on the actual syringe, the corresponding indicium on the graphical
representation will be activated.
The display also has an indicium at a position on the graphical
representation corresponding to the point at which the stopper of
the syringe plunger resides when the syringe plunger has fully entered
the syringe barrel. When the plunger has fully entered the barrel
of the syringe, the indicium will be activated.
Thus the user is provided with a simple, easy to read means for
identifying the location of error conditions and the end of the
infusion cycle in the syringe pump.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a syringe pump embodying the invention;
FIG. 2 is a perspective view of the drive mechanism of the syringe
FIG. 3 is a perspective view of the lead screw and half nut mechanism
inside pusher block of the syringe pump;
FIG. 4 is a cross sectional view of the pusher mechanism of the
FIG. 5 is a perspective view of the pusher disc and force transducer;
FIG. 6 is a perspective view of the antisiphon catch detector.
FIG. 7 is a block diagram of the electronic components of the invention;
FIG. 8a-m are schematic diagrams of the main electronic components
of the invention.
A syringe pump 8 embodying the invention is shown in FIG. 1. Housing
10 supports syringe barrel 12 pusher 14 and syringe clamp 16. Syringe
clamp 16 holds syringe barrel 12 in place on housing 10. Plunger
18 is pushed by pusher 14 which is driven by an electric motor via
a lead screw (see FIG. 2).
Pusher 14 is provided with antisiphon catch 20 which engages flange
18a of plunger 18 thus preventing plunger 18 from moving independently
of pusher 14. Pusher 14 is also provided with pressure plate 22
for pushing directly against flange 18a thereby pumping fluid from
syringe barrel 12.
FIG. 2 shows the chassis and mechanical components of pump 8. Chassis
226 carries motor 230 and lead screw 222. Motor 230 drives lead
screw 222 via gear assembly 232. Pusher 14 is driven by the interaction
of pusher block 228 with lead screw 222. Pusher block contains half
nuts 322 324 which interact with lead screw 222 (see FIG. 3).
Pusher block 228 carries rack 234 such that rack 234 moves in unison
with pusher block 228. Rack 234 is linked via pinion 233 to rotary
potentiometer 232. Thus as pusher 14 pushes plunger 18 due to the
movement of pusher block 228 the position of pusher block 228 and
hence plunger 14 is sensed by rotary potentiometer 232. The output
of rotary potentiometer 232 indicates the position of plunger 18.
Rotary potentiometer 232 is a five turn rotary potentiometer of
1 Kohm impedance, 0.25 W power rating and a linearity better than
0.25% of full scale.
Display panel 24 contains controls for adjusting various parameters
of the pump. Display panel 24 also contains graphic 26 which is
a graphical representation of syringe barrel 12 and plunger 18.
Graphic 26 is made up of an outline 25 of the syringe, showing the
barrel and the plunger. Graphic 26 also includes indicia 30 32
and 34. Also provided are end of infusion indicator 28 flow direction
arrows 29a, 29c and 29d and occlusion indicator 29b. Indicium 30
is located at a point on graphic 26 corresponding to the point on
syringe barrel 12 at which clamp 16 holds syringe barrel 12 in place.
Indicium 32 is located at a point on graphic 26 which corresponds
to the point on plunger 18 at which antisiphon catch 20 makes contact
with plunger 18. Indicium 34 is located at a point on the graphic
which corresponds to the point at which pusher 14 pushes flange
18a of plunger 18 i.e. pressure plate 22.
Indicia 30 32 and 34 are linked via electronics which will be
described herein to transducers respectively connected to syringe
clamp 16 antisiphon catch 20 and half nut 332. Thus, when an error
condition is detected at any one of the aforementioned, the corresponding
indicium will indicate the error condition on graphic 26. End of
infusion indicator 28 is linked to rotary potentiometer 232. When
plunger 18 has fully entered syringe barrel 12 indicium 28 will
be activated to indicate the end of the infusion cycle.
End of infusion indicator 28 is at a position on graphic 26 corresponding
to the position of syringe plunger 18 when the end of the infusion
is reached. Direction arrows 29a, 29c and 29d represent the flow
of the infusate from syringe barrel 12. Occlusion indicator 29b
points in the direction of the force resulting from the occurrence
of an occlusion in the delivery line.
FIG. 7 is a block diagram showing the main electronic components
of the invention. Five transducers are provided to detect the parameters
of the syringe pump which are displayed. The transducers are: position
sensor 35 force transducer 36 antisiphon catch detector 38 disengage
detector 40 and syringe clamp detector 42. The outputs of these
transducers 62 64 and 66 respectively are fed into central processing
unit 44 via various signal processing or latching modules which
will be described in detail herein.
Schematic diagrams of the various modules are shown in FIGS. 8a-n.
The values and types of the components are indicated on the schematic
Central processing unit 44 comprises microprocessor 46 (FIG. 8a)
with random access memory 53 (FIG. 8a), watchdog 48 (FIG. 8b), EPROM
50 (FIG. 8a) and EEPROM 52 (FIG. 8c). Watchdog 48 monitors microprocessor
46 to ensure its proper operation. EEPROM 52 contains data concerning
the parameters of each of the various types of syringes which may
be used in the pump, such as brand, size and model of syringe, volume
of syringe, number of motor steps per ml infused, "hard-height"
(i.e. the distance from the plunger flange to the open end of syringe
barrel when the plunger has fully entered the barrel, the syringe
frictional force in gF (i.e. Ff) and the syringe pressure under
a 5 kg load in millibars (i.e. Pc). EPROM 50 contains a software
program which controls the operation of the syringe pump.
The output of force transducer 36 is conditioned by signal conditioning
circuit 54 (FIG. 8d), which converts the output of force transducer
36 into a form suitable for input into analog to digital converter
56 (FIG. 8e). Output 61 of position sensor 35 is conditioned by
signal conditioning circuit 55 and is then also fed into analog
to digital converter 56. Analog to digital converter 56 digitizes
the analog outputs 60 and 61 and produces serial output 58 which
is in turn fed into input port 60 of microprocessor 46.
EEPROM 52 contains data representing the outputs of position sensor
(i.e. "hard height" of the syringe) corresponding to the
points at which plunger 18 has fully entered syringe barrel 12 for
various types of syringe.
When antisiphon catch 20 is disengaged, antisiphon catch detector
38 produces digital output 62 (See FIG. 8i). Similarly the opening
of disengage mechanism 44 causes disengage detector 40 to produce
an output 64 (FIG. 8f) and the opening of syringe clamp 16 causes
syringe clamp detector (FIG. 8h) to produce an output 66. Each output
62 64 66 is fed into central processing unit 44 via latch 68 (FIG.
Microprocessor 46 causes error conditions at clamp 16 disengage
mechanism and antisiphon catch 20 to be displayed on display panel
24 (FIG. 8g). Display panel 24 comprises graphical representation
26 which in turn comprises syringe outline 28 indicium 30 indicating
an error condition at syringe clamp 16 indicium 32 which indicates
an error condition at antisiphon catch 20 and indicium 34 which
indicates that disengage 44 mechanism is disengaged.
In FIG. 8j, indicia 30 32 and 34 correspond to light emitting
diodes LD2 LD3 and LD16 respectively. Indicia 30 32 and 34 are
activated under the control of microprocessor 46 when error conditions
arise. Indicia 30 32 and 34 are driven through row and column latches
25 (IC1 and IC6 in FIG. 8m) which in turn activate appropriate driver
transistors (FIG. 8g). LD2 LD3 and LD16 are part of a matrix of
light emitting diodes which are lit up when the row and column of
the matrix corresponding to the position of the particularly light
emitting diode are activated. The remaining light emitting diodes
in the matrix (not shown) are not used in the invention. For simplicity,
the full matrix is not shown. The other diodes in the matrix which
are not shown light up other indicia on the panel of syringe pump
which are not material to the invention.
FIGS. 5 shows force transducer 36 in greater detail. Force transducer
36 is made up of four strain gauges in a wheatstone bridge configuration.
The bridge has an impedance of 350 ohms or 1 Kohm with a tolerance
of .+-.15%. The range of force measurements is 0 to 150N. The bridge
sensitivity is 1.7 mV/V to 2.4 mV/V under a load of 150N at 20 degrees
centigrade. The bridge is powered intermittently under the control
of microprocessor 46 (line CDANA in FIGS. 8a and 8d) in order to
Strain gauges 112 are glued onto beam 114. When force is applied
to pressure plate 22 beam 114 flexes, causing strain gauges 112
to distort and produce output 60.
Output 60 of force transducer 36 is fed into conditioning module
54 (FIG. 8d) and thereafter into analog to digital converter 56
which converts the conditioned output into serial output 58. Serial
output 58 is then fed into input 60 of microprocessor 46.
The output 61 of position sensor 35 is similarly conditioned by
signal conditioning circuit 55 and fed into analog to digital converter
Resident in EPROM 50 is a software program for microprocessor 46
which calculates the pressure inside syringe 12 continuously as
the force on the plunger 18 is measured by force transducer 36.
Certain parameters which are used by the program to calculate the
pressure in the syringe and stored in EEPROM 52. Since syringe pump
8 is programmable to accommodate various types of syringe, a set
of parameters for each type of syringe, is stored in EPROM 52.
The parameters stored in EEPROM 52 include:
Ff=average frictional force between the syringe plunger and the
syringe barrel at null (atmospheric) pressure.
Pc=the pressure in the syringe when a calibration force is applied
to the plunger. The calibration force is typically 5 kgF which leads
to a value of Pc around 0.7 bar, a usual threshold for infusion
Fc=the force with which the plunger is loaded to obtain a pressure
of Pc in the syringe.
The program in EPROM 50 is used by microprocessor 46 to calculate
the pressure in the syringe. Microprocessor 46 then compares the
calculated pressure with the pressure threshold selected by the
user. If the calculated pressure exceeds the threshold, an occlusion
alarm is generated by microprocessor 46.
The algorithm for calculating the pressure in the syringe is: ##EQU1##
where F is the force measured by force transducer 36 and Fc, Ff
and Pc are the parameters defined above.
The main advantages of this formula over the traditional formula
described in the BACKGROUND section above are (1) it is not highly
dependent on the frictional force in the syringe which is known
to vary with pressure and (2) that the cross sectional area of the
syringe need not be determined. Rather, the pressure in the syringe
is calculated using parameters which are easy to determine empirically.
The position of plunger 18 as detected by position sensor 35 is
read by microprocessor 46 and compared with the "hard height"
stored in EEPROM 52 for the particular type of syringe being used.
If the position detected is the same as the hard height, microprocessor
46 actuates indicium 28 (LD14 in FIG. 8j, driven by transistors
Q14 and Q2 in FIG. 8h).
Clamp 16 comprises a spring loaded shaft which enables clamp 16
to be lifted and turned so that the syringe can be placed and removed.
Clamp 16 is provided with a syringe clamp detector 42 (FIG. 8h)
which detects whether or not clamp 16 is properly placed. When clamp
16 is properly placed, output 66 is low. Detector 42 comprises optical
detector 42a, and associated circuitry. Detector 42 is powered by
a sampled power supply controlled by CPU 46.
Disengage mechanism 44 (FIG. 3) comprises half nuts 322 324 which
interact with lead screw 222 so that pusher block 228 which holds
half nuts 322 324 (FIG. 2) may be separated by the rotation of
cam 326. Cam 326 may be rotated by pressing lever 224 (see FIGS.
2 and 4) which in turn rotates shaft 114 and thus cam 326. Half
nut 322 is provided with projection 328 which is linked to disengage
detector switch 330.
When lever 224 is pressed, thus disengaging half nuts 322 324
disengage detector switch 330 is activated. As long as half nut
322 is disengaged from lead screw 222 disengage detector switch
330 will be activated, causing output 64 to be high.
FIG. 7 shows antisiphon catch detector 38 in detail. Antisiphon
catch 20 is attached to shaft 442 which is in turn linked to lever
234 (FIG. 2) via cam 444 so that antisiphon catch 20 can be disengaged.
Also attached to shaft 442 is tab 444. Tab 444 moves in concert
with antisiphon catch 20. Tab 444 is provided with ears 446 and
448 spaced apart by space 450. Detector 452 is an optical detector
available from Optek Technology, Inc. of Carrollton, Tex. under
part number OPB860 or OPB870. When antisiphon catch is correctly
positioned on plunger 18 detector 452 is aligned with space 450
and is inactive. When antisiphon catch is improperly placed, i.e.
is in either position A or position B, ears 446 or 448 interrupt
the light beam in detector 452 and detector is activated and produces
output 62. The electronics of disengage detector are shown in FIG.
Outputs 62 64 and 66 are sequentially latched to microprocessor
46 by latch 68 (FIG. 8f). The latching of outputs 62 64 and 66
provides a power saving since 36 38 40 42 need only be powered
while they are monitored. The sampled power supply and latching
of outputs 62 64 and 66 are controlled by microprocessor 46 by
means of a program stored in EPROM 50. The precise details of how
this is accomplished are not material to this invention.
When the microprocessor detects that any one of outputs 60 62
64 has gone high, it generates a signal to activate the corresponding
indicium on display panel 24. Thus, when output 62 (the antisiphon
catch detector output) goes high, indicium 32 is activated, when
output 64 (the disengage detector output) goes high, indicium 34
is activated and when output 66 (the syringe clamp detector output)
goes high, indicium 34 is activated. The user is thus alerted of
an error condition at any one of antisiphon catch 20 syringe clamp
16 or disengage mechanism 44 by means of a display showing the location
on the syringe at which the error condition occurs.