Syringe pump abstract
A syringe pump comprises a housing with a syringe retainer. The
syringe includes a barrel for liquid medication and a plunger movably
positioned in the barrel for expelling the medication. A driver
is movably mounted on the housing for engagement with the plunger.
A control mechanism within the housing regulates the rate of movement
of the driver and plunger during delivery of medication. A monitoring
circuit connected to receive signals from a potentiometer and a
movable contact associated with the driver indicates driver motion.
A microprocessor with memory includes a preset standard to which
the signal of motion from the driver is compared. An additional
input signal, of motion from a rotary indicator associated with
a part of the driver movement motor assembly, is provided to the
memory and is compared to plunger travel into the barrel.
Syringe pump claims
What is claimed is:
1. A syringe pump comprising:
a housing;
a retainer mounted on the housing for receiving therein a syringe
of the type including a barrel for holding liquid medication and
a plunger movably positioned in the barrel for expelling the liquid
medication therefrom;
a driver movably mounted on the housing for engagement with the
plunger and for pushing the plunger into the barrel to thereby force
the liquid medication out of the barrel;
a motor assembly as part of the driver for providing rotary motion
and for converting the rotary motion to linear driver movement;
control means within the housing for setting the rate of movement
of the driver against the plunger to thereby regulate delivery of
the liquid medication from the barrel;
a potentiometer carried by the housing to provide an input signal
for indicating the position of the driver;
a rotary indicator associated with the motor assembly and responsive
to rotary movement of a part thereof, the rotary indicator providing
an additional input signal indicative of the movement of a part
of the motor assembly; and
a monitoring circuit mounted on the housing and connected with
the potentiometer and the rotary indicator to receive the input
signal from the potentiometer and to receive the additional input
signal from the rotary indicator, the monitoring circuit comprising
a processor for processing and comparing the input signal from the
potentiometer and the additional input signal from the rotary indicator
to detect a malfunction of the syringe pump.
2. The syringe pump of claim 1 wherein the monitoring circuit comprises
a memory, the memory containing data comprising reference values
as standards representative of expected positions of the driver
to which the input signal from the linear potentiometer can be compared
to verify that the motion of the driver during operation of the
pump matches the standards.
3. The syringe pump of claim 2 further comprising a timer for verifying
the rate of movement of the driver.
4. The syringe pump of claim 1 wherein the rotary indicator comprises
means for producing pulses indicative of the rate of rotation of
the motor, the monitoring circuit comprises means to detect the
spacing between the pulses means for comparing the spacing between
the pulses to verify the movement of the part of the motor assembly.
5. The syringe pump of claim 1 wherein the monitoring circuit comprises
a memory, the memory containing a preset function of varying voltage
as a standard to which the input signal from the potentiometer can
be compared to verify the motion of the driver during operation
of the pump.
Syringe pump description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device to deliver or administer
medication to a patient, and more particularly, concerns a syringe
pump monitoring circuit intended for the controlled delivery or
administration of such medications.
2. Background Description
Hospitals typically use intravenous (I.V.) administration sets
to deliver liquid medication to patients. When the patient needs
medication, such as an antibiotic, standard practice until recently
has been to deliver such a drug by a "piggy-back" drip
into the primary infusion line. Recently, however, the procedure
for delivering antibiotics and other drugs to patients on I.V. therapy
has been changing. Mechanically driven syringes, frequently called
or referred to as syringe pumps, are available to hospitals and
other users for the administration of drugs and other liquid medications
which the patient may require.
Indeed, a wide variety of syringe pumps and other liquid medication
delivery devices are becoming available. With particular reference
to a syringe pump, as that term is used herein, such pump employs
a conventional or modified syringe which holds the liquid medication,
the plunger of which is typically driven or pushed by a mechanized
element for the automatic delivery of the liquid contents within
the syringe. These syringe pumps are now available in battery powered
form, include microprocessor technology for programming rates or
times of medication delivery, have digital displays for ease of
viewing by the user or the patient, include alarm circuits in the
event of duty cycle completion, failure, or line occlusion, and
other features to facilitate the operation or performance of the
syringe pump. As these syringe pumps become more sophisticated,
the technological advances frequently have the tendency to increase
the expense of making and using the device, increase the complexity
of use, and increase the opportunities for breakdown and repair
if one or more of the operational elements fail.
For example, many existing syringe pumps include an occlusion circuit
for producing an alarm (visual and/or audible) when the syringe
cycle has been completed, if the I.V. line or syringe is occluded
or if there is a system failure. One common mechanism for activating
the occlusion circuit has been the use of one or more switches which
are tripped after the syringe plunger passes a certain point during
its travel into the syringe barrel. In other instances, the syringe
is mounted on a spring loaded platform which is subject to a small
linear movement after a certain force level has been reached. Thus,
if the plunger being pushed into the syringe barrel either reaches
the bottom of the syringe or cannot expel the liquid contents due
to an occlusion in the line, the force against the plunger causes
the entire spring-mounted syringe to move in linear fashion. This
movement, in turn, either trips a switch or may be sensed by position
sensitive sensors to send a signal to the occlusion circuit so that
the automatic operation of the syringe pump may be terminated.
Improvements in such a plunger movement monitoring circuits are
not only desirable, but are still being sought, in order to reduce
the expense of the elements heretofore needed in such an occlusion
circuit, as well as to eliminate the need for switches or sensing
elements in order to achieve the desired results and make the syringe
pump fail safe.
Rate feedback measurements for syringe pumps have been obtained
from a tachometer gear driven off of the injector drive motor. The
output voltage from the tachometer corresponds to the velocity of
fluid flowing due to the pressure generated in the syringe pump.
In the event that the tachometer became disengaged from the motor
or the motor stopped, the voltage produced could approach zero and
be indistinguishable from noise and interference, thus resulting
in errors and inaccuracies.
In order to overcome the problems of velocity of flow measurement
obtained from a gear driven tachometer, artisans have used a plunger
position feedback signal generated by a potentiometer mechanically
driven by the syringe motor. Such systems have been designed to
use a rotary potentiometer which is drivingly connected to the motor
output, such that as the motor shaft turns a corresponding gear
drives the potentiometer to produce a direct measurement of shaft
rotation. Since the motor is connected through means of a ball nut
to the syringe plunger, the potentiometer should properly read the
position of the plunger. This is not the case however if an overload
conditions occurs or if for some reason the motor gear drive to
the potentiometer fails. Therefore, it is desired that the gear
drive interconnection of the potentiometer be eliminated in order
to be certain that the exact position of the plunger is known.
It is toward such improvements, as mentioned already, as well as
other improvements as will be pointed out, that the present invention
is directed.
SUMMARY OF THE INVENTION
The syringe pump of the present invention comprises a housing and
a retainer mounted thereon for receiving a syringe. The syringe
to be received is of the type including a barrel for holding liquid
medication and a plunger movably positioned in the barrel for expelling
liquid medication therefrom. A driver is movably mounted on the
housing for engagement with the plunger and for pushing the plunger
into the barrel to thereby force the liquid medication out of the
barrel. A control within the housing regulates the rate of movement
of the driver against the plunger to thereby provide the delivery
of the liquid medication from the barrel. Depressible actuation
switches are mounted on the housing for manual access by a user.
The actuation switches are associated with the control to permit
the user to select one or more functions under which the control
operates. The actuation switches are connected to the control when
depressed by the user to electrically energize or de-energize the
control for the operation of the selected function.
In the preferred embodiment of the present invention, the control
includes an electrically powered motor for moving the driver. A
monitoring circuit is provided to assess the motion of the driver
and a part of the motor during delivery of liquid medication from
the barrel. This monitoring circuit is responsive to inputs from
a linear potentiometer. The linear potentiometer with an electrically
conductive strip of resistive material positioned to be engaged
with a contact carried by the driver and in circuit with the control
provides the input signal to the monitoring circuit. A changing
voltage, varying as a function of plunger displacement, provides
the monitoring circuit with an input signal as to plunger position
and movement.
A rotary indicator associated with the motor part and responsive
to its rotary movement signals the monitoring circuit providing
an additional input of a series of pulses to report the position
and movement of the part of the motor assembly such that uniformly
spaced pulses indicate the constant rotation of the part of the
motor. The monitoring circuit is mounted on the housing and connected
to the linear potentiometer and the rotary indicator to receive
the input signal from the linear potentiometer and to receive the
additional input signal from the rotary indicator so the driver
motion relative to rotation of the part of the motor can be compared
to a preset delivery of liquid medication from the barrel.
It is a feature of the present invention that the syringe plunger
movement be automatically measured or sensed so that motion related
information may be provided to a microprocessor part of the monitoring
circuit. The input from the linear potentiometer is in the preferred
embodiment a linearly decreasing voltage which relates directly
to plunger position. That is to say that the voltage starts high
and preferably decreases at a constant rate with respect to plunger
travel. The position and the change is a function of voltage over
time and that is directly related to the rate of medication delivered.
Consequently, motion of the plunger is constantly monitored from
the varying voltage obtained from the linear potentiometer.
A further advantage and improvement is provided by the present
invention in the circuit used to monitor plunger movement as the
driver pushes the plunger into the syringe barrel. In known and
existing syringe pumps, the driver is typically coupled by a half-nut
arrangement to a lead screw which is rotated by the motor and the
occlusion or position responsive devices are connected to provide
information relative to the speed of rotation or the lack of motor
movement. The present monitoring circuit verifies that the lead
screw is rotated a set rate and the plunger is moving at the pre
set rate. The monitoring circuit compares the varying voltage signal
received from the linear potentiometer with a voltage profile in
the memory of the monitoring circuit and with the additional input
of uniformly spaced pulses from the rotary indicator. An alarm is
activated if the comparison of the linear potentiometer voltage
due to plunger movement or the rotation of the motor part are not
as they should be.
In presently known and available syringe pumps, features for detecting
syringe plunger motion were designed to signal occlusion and not
verify programmed motion of the driver and the uniform rotary motion
of the motor part. In the delivery of drugs which are necessary
to maintain life, the importance of monitoring the plunger movement
to verify delivery is needed to maintain life support. The preferred
arrangement minimizes manufacturing steps as well as simplifying
the design and operation of the syringe pump motion monitoring circuit.
Other advantages, improvements and features of the present invention
will be apparent upon reading the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of the preferred embodiment of the syringe
pump of the present invention illustrating the front face thereof
as it appears to a user;
FIG. 2 is a side view of the syringe pump of FIG. 1 looking toward
the side having the driver for moving the plunger and the retainer
for mounting the syringe barrel;
FIG. 3 is a cross sectional view of the interior components of
the syringe pump, particularly illustrating one surface of the printed
circuit board, as these components appear just inside the front
face of the syringe pump of the present invention, taken along line
3--3 of FIG. 2;
FIG. 4 is a cross-sectional view of the interior components of
the syringe pump positioned below the printed circuit board as such
components are positioned inside the back cover of the syringe pump
housing, taken along line 4--4 of FIG. 2;
FIG. 5 is an enlarged cross-sectional view of a driver mechanism
of the present invention taken along line 5--5 of FIG. 1;
FIG. 6 is an enlarged cross-sectional view illustrating the motor
mechanisms and lead screw arrangement inside the syringe housing
taken along line 6--6 of FIG. 1;
FIG. 7 is a graphical representation of the output of the linear
potentiometer in terms of voltage change versus plunger travel according
to the principles of the present invention; and
FIG. 8 is a plan view of the preferred embodiment of the syringe
pump for the present invention illustrating a syringe mounted thereon
as it appears in preparation for use.
DETAILED DESCRIPTION
While this invention is satisfied by embodiments in many different
forms, there is shown in the drawings and will herein be described
in detail a preferred embodiment of the invention; with the understanding
that the present disclosure is to be considered as exemplary of
the the principles of the invention and is not intended to limit
the invention to the embodiment illustrated. The scope of the invention
will be measured by the appended claims and their equivalents.
Turning to the drawings, and FIGS. 1 and 2 in particular, there
is shown a syringe pump 20 in a preferred configuration for purposes
of the present invention. In general, syringe pump 20 is comprised
of a housing 22 a driver mechanism 24 and a syringe retainer 26.
In the preferred configuration, housing 22 is a compact, light-weight
housing which is assembled in two parts, consisting of an upper
(front) cover 28 and a lower (back) cover 29. Each of covers 28
and 29 is preferably formed in tray-like fashion so as to be able
to include the interior components of the syringe pump, as well
as for ease of assembly with a few screws or the like. When assembled,
it is preferred that covers 28 and 29 form housing 22 which is completely
enclosed except for an elongate slot 30 on one side of the housing.
This slot, as will be described more fully hereinafter, permits
driver mechanism 24 to move outside of the housing while being driven
by a motor and drive carried within the housing. A ring 31 is connected
to the housing to provide a place for hanging the syringe pump on
a stand at the location where the patient is to receive the mediation
from the syringe pump.
Upper cover 28 includes a front face 32 with a number of controls
and displays. It is understood that many different controls or displays
may be provided in syringe pump 20 depending upon a variety of factors
and intended functions thereof. For purposes of the present invention,
and while suggesting no limitations, upper face 32 includes five
control mechanisms or buttons, namely, "POWER ON" 34
"INFUSE" 35 "VOLUME DELIVERED" 36 "STOP
INFUSION" 38 and "POWER OFF" 39. Two other buttons
or controls are provided, one such button 40 permitting the user
to increment the rate of medication delivery by "1's."
When buttons 40 and 41 are depressed by the user, a display 42 digitally
indicates the numbers that have been incrementally selected by the
user. Each time buttons 40 and 41 are pushed, the digit in the "1's"
or "10's" columns are incremented by one until the number
selected by the user is displayed. In the embodiment being described,
display 42 usually shows the rate of delivery of medication, in
milliliters per hour, to be selected by the user.
In addition to display 42 INFUSE button 35 has a light display
44 associated therewith so that the light is turned on when the
INFUSE button has been pushed to inform the user that infusion is
taking place. Another panel light 45 is provided to indicate when
the batteries are low. A third panel light 46 is provided as an
ATTENTION indicator serving as a visual alarm to inform the user
that the syringe is empty, the plunger motion is not correct or
that an occlusion has occurred and infusion has been terminated.
The mechanism of actuation of the various controls on the front
face 32 of the upper cover is more clearly seen by referring to
FIG. 3 in conjunction with FIG. 1. The upper cover 28 carries a
number of switches accessed from the front face 32 of cover 28 and
these switches correspond with buttons 34 35 36 38 39 40 and
41 respectively. Similarly, lights 44 45 and 46 appear in FIG.
1 and have access holes.
In FIG. 3 it can be seen that there is a printed circuit board
66 mounted within upper cover 28 so that it is spaced away from
front face 32. This printed circuit board includes the electrical
circuitry for operation of the syringe pump and includes a variety
of electrical components including one or more microprocessors 68
and/or associated integrated circuit chips, a digital readout 69
for display 42 panel lights 44 45 and 46 and other circuits and
components well within the purview of the ordinary artisan for completing
the electrical functions as explained herein. Part of the circuitry
on printed circuit board 66 includes switching circuits for controls
34 35 36 38 and 39 and stepper circuits for controls 40 and
41. These circuits are energized by momentarily closing the circuits
associated therewith, and then are de-energized by momentarily closing
the circuits with the same switching mechanism.
For each control switch on the front panel of the housing, the
printed circuit board includes an electrically conductive contacts
70 in this instance, composed of two electrical elements of the
circuit associated therewith. Each electrically conductive contact
is positioned on the printed circuit board 66 so that they are slightly
spaced and directly across from a switch carried by the housing.
When the user pushes with one of the controls the switch shunt moves
toward electrical contacts 70 so that the circuit is completed energizing
the electrical circuit affected by the control being switched. The
desired operation of the selected function occurs. Similarly, with
respect to control button 40 and 41 successive switching thereof
cause the display to increment to the next higher number in the
column associated with the button being pushed. It is observed that
the electrical actuation mechanism, described above, causes the
electrical circuits and functions to be energized and de-energized
without the need for wire connections between the depressible control
and the printed circuit board on which the circuits are maintained.
Reference is now made to FIGS. 1 2 and 6 in which the details
of syringe retainer 26 are more clearly illustrated. Retainer 26
preferably includes a slidable clamp 74 which has a portion extending
outside of the housing in the form of a depending arm 75 and a portion
extending inside the housing in the form of a relatively flat strip.
A pair of clamp guides 78 and 79 affixed to upper cover 28 hold
clamp 74 in position and serve to guide the movement of the clamp
for holding the syringe barrel in position with respect to the housing.
Inside upper cover 28 are a pair of tracks between which the flat
strip of the clamp is positioned. Thus, guide clamps 78 and 79 and
tracks not only maintain the clamp in position with respect to the
upper cover, but facilitate the sliding movement of the clamp in
and out of the upper cover in a lateral direction across the housing.
Inward bias is maintained on clamp 74 so that when the syringe barrel
is held in place against the housing by virtue of depending arm
75 the inward force applied to the syringe barrel keeps the syringe
barrel securely in place.
FIGS. 4 and 5 along with FIGS. 1 and 2 more clearly illustrate
the details of driver 24 as it is mounted on back cover 29 of housing
22. Driver mechanism 24 is an assembly including a body member 100
to which is attached a slidable latch member 101. Latch member 101
preferably has outwardly protruding finger flanges 102 for easy
grasping by the user. A spring, such as coil spring 104 is preferably
included within body member 100 so that a force is urged against
latch member 101 keeping it biased in an inward direction toward
the housing. Latch member 101 may be moved outwardly by grasping
the finger flanges and applying sufficient outward force to overcome
the biasing force of spring 104. In conjunction with the slidable
movement of latch member 101 there is provided a catch or hook
105 which facilitates the holding of the plunger of the syringe
in position against driver assembly 24. An abutment 106 is provided
on body member 100 serving as a fixed element also for holding the
plunger of the syringe in position against the driver assembly.
Positioning of the syringe, with its extended plunger, will be described
more completely hereinafter.
Body member 100 includes a shank 108 extending through slot 30
of housing 22. On the interior side and connected to shank 108 is
a half-nut mechanism 109 positioned to engage the threads of a lead
screw 110. When half nut 109 is engaged to lead screw 110 rotation
of the lead screw imparts linear movement to driver 24 by virtue
of the half nut threaded engagement. This type of driving arrangement
is well known in the art of syringe pumps and no further details
need be provided for a complete appreciation of the working of such
elements.
In order to provide disengagement between half nut 109 and lead
screw 110 a disengagement rod 112 extends through body member 100
so that is interior end is associated with half nut 109. Although
not shown in FIG. 7 rod 112 is spring-loaded so that its exterior
end extends a short distance beyond the end of body member 100.
A thumb button 114 is preferably included at the exterior end of
rod 112 so that the thumb or finger of the user may depress rod
112 inwardly. Depression of rod 112 inwardly, with sufficient force
to overcome the spring-loading effect thereof, causes half nut 109
to become disengaged from lead screw 110. When disengagement of
these parts occurs, driver mechanism 24 is freely slidable along
slot 30 so that it may be moved to any position along the slot,
such as an initial position for latching onto the plunger rod of
the syringe when the syringe is being loaded. It is preferred that
the depression of rod 112 for disengagement of the half-nut from
the lead screw be independent of the slidable movement of latch
member 101 for making the connection to the plunger rod of the syringe.
Currently available syringe pumps rely on guide rails or the like
for providing bearing support to the driver mechanism as it moves
in linear fashion as a result of rotation of the lead screw. Instead
of guide rails, the present invention relies upon the construction
of housing 22 to provide adequate bearing surfaces for supporting
the driver mechanism during its linear movement along the housing.
Specifically, it can be seen particularly in FIG. 5 that upper cover
28 and back cover 29 are formed so that slot 30 lies between the
two housing portions when joined together. It can be seen that upper
cover 28 includes a raised bearing surface 116 and back cover 29
includes a raised bearing surface 118 with each such bearing surface
extending along the elongate dimension of slot 30 and running substantially
parallel thereto. Bearing surfaces 116 and 118 provide a sliding
support for driver mechanism 24 at portion 119 of body member 100.
This support is provided at this interface when the driver mechanism
is engaged to the lead screw and also when it is disengaged therefrom.
In FIGS. 4 and 5 it can be seen that a small platform 120 is mounted
on the driver mechanism near the half-nut component, on the interior
side of housing 22. Platform 120 is preferably an electrical insulator,
such as rigid plastic or the like. Mounted on platform 120 is an
electrical contact member 121 including one or more electrical contacts
122. These electrical contacts 122 are arranged so that they are
in contact with one side of printed circuit board 66. One or more
electrical pads 124 are provided on the surface of printed circuit
board 66 so that electrical contacts 122 may come in contact therewith.
Electrical pads 124 are preferably positioned on the printed circuit
board at a position near the end of elongate slot 30 where the driver
mechanism will finish its movement when the plunger rod has been
moved all or almost all of the way into the syringe for emptying
the contents thereof. Contact between electrical contacts 122 and
electrical pads 124 is part of an occlusion circuit to be described
more fully hereinbelow.
Turning now to FIG. 4 it can be seen that back cover 29 includes
a compartment 136 which holds one or more batteries 138 to provide
electrical power for operating the motor and electrical circuitry
of the present syringe pump. These batteries provide direct current
(DC) to a motor which is preferably a DC motor 139 for driving
and rotating lead screw 110. Motor 139 includes a shaft 140 which
is also illustrated in FIG. 6 taken in conjunction with FIG. 4.
Attached to shaft 140 is a small gear 141 which rotates when shaft
140 rotates when the motor is operating. Another gear 142 in this
case a larger gear, is connected to lead screw 110 and is in meshing
engagement with smaller gear 140. Accordingly, operation of motor
139 causes the rotation of lead screw 110 by virtue of the rotating
shaft of the motor and the associated gears. Lead screw 110 is maintained
in position within lower housing portion 29 preferably by means
of journal bearings 144 positioned at or near the respective ends
of lead screw 110.
Also connected to drive shaft 140 of DC motor 139 is a wheel 145
which serves as an encoder associated with the timing and the control
circuitry governing the operation of the present syringe pump. Encoder
wheel 145 being connected to drive shaft 140 of the motor, therefore
rotates when shaft 140 rotates. It can be seen, particularly when
viewing FIG. 6 that encoder 145 is divided into a plurality of
equally spaced gaps or segments 146 arranged around the periphery
thereof. These gaps or segments pass in front of a light such as
light emitting diode (LED) 148 connected to printed circuit boards
66 so that the number of segments may be counted for operation
of the control circuit as part of the electrical circuitry hereof.
During operation of DC motor 139 for each passage of a segment
146 of the encoder past LED 148 lead screw 110 rotates to cause
the drive mechanism 24 to move a fixed linear distance if everything
is functioning correctly. In turn, this movement causes the movement
of the syringe plunger into the syringe barrel, as will be pointed
out below. As the syringe plunger is moved into the syringe barrel
by a known, fixed distance, such linear movement of the plunger
may be calculated by the microprocessor 68 to determine the volume
delivered. Thus, it is possible to calculate the volume of liquid
delivery from the syringe in milliliters per segment or increment,
for each passage of a segment of the encoder. For different size
syringes, this volume per increment will vary. This information
of volume per increment for different size syringes, preferably
of the conventional size syringes used in hospital procedures, is
stored in the memory function of microprocessor 68 included in the
electrical circuitry of the control functions of the present syringe
pump. In connection with the microprocessor 68 and the selectable
functions of the present invention, if the desired delivery rate,
in milliliters per hour, is programmed or selected for operation
by a user of the syringe pump, the time between increments may be
determined by dividing the delivery rate (milliliters per hour)
by the volume per increment (milliliters per increment). This calculation
is preformed automatically by the electrical circuitry and is also
storable in the memory function of the microprocessor hereof to
provide the time between increments. Total volume of liquid medication
to be delivered from the syringe may be established or calculated
by multiplying the total number of increments of one rotation of
the motor 139 by the volume per increment of the particular syringe
in use. As pointed out above, each increment of the motor is determined
by the passage of segment 146 of encoder 145 in conjunction with
LED 148. The electrical circuitry of the present invention includes
a timing circuit which is designed to account for the time intervals,
to be calculated as mentioned above, associated with the desired
delivery rates for different size syringes.
At the beginning of the initial timing increment of operation,
DC motor 139 is turned on and a control circuit is set in accordance
with the electrical circuitry thereof. Should there be a line occlusion
or should the end of a cycle be reached, the force to move the plunger
rod into the syringe barrel increases. This, in turn, causes the
torque of the DC motor 139 to increase. Accordingly, the current
increases, and at the current limiting threshold, the motor 139
stalls and stops operation. As a result, the DC motor does not complete
its movement to the next segment 146 of encoder 145. In normal operation,
when motor 139 reaches next encoder segment 146 it activates the
electrical circuitry to turn the motor off and to reset the control
circuitry. However, in the event of an occlusion which causes DC
motor 139 to cease operation, the control circuitry is not reset.
On the other hand, the control circuit receives the next time increment
from a timing circuit in the microprocessor 68 and recognizes that
the last increment has not been completed, and therefore activates
the alarm circuitry. This alarm circuitry lights attention signal
46 on the front face of housing 22 and may also activate an audible
alarm.
If an occlusion occurs because of fluid delivery line blockage
or the like, the audible alarm is programmed to provide a rapid
beeping sound or rapid flashing of light 46 on the face of the panel.
If, however, the occlusion circuit is activated because of end of
cycle and medication delivery from the syringe barrel has been completed,
a different alarm is preferably activated. In the case of end of
cycle, driver mechanism 24 has moved in linear fashion along slot
30 so that that syringe plunger is almost completely pushed within
the syringe barrel. At this location, electrical contacts 122 on
driver mechanism 24 come in contact with electrical pad 124 on printed
circuit board 66. This contact serves as a switch or the like causing
the occlusion detection circuit to issue an alarm different from
the alarm mentioned above with respect to blockage in the delivery
line. The end of cycle alarm may be a slow beeping signal or slow
flashing of light 46 on the front panel of the housing.
It should be appreciated that the passage of segment 146 of the
encoder passed LED 148 as a lead screw 110 rotates provides a signal
when the movement of the segment 146 occurs. That is to say that
should the motor stall or fail, the segment 146 of encoder wheel
145 permit light pass. This arrangement is such that either light
passes or it does not. The microprocessor has no way of knowing
where the plunger is relative to its travel, or if a failure of
the lead screw 110 or half nut 109 has occurred. The only thing
the microprocessor 68 can determine from encoder wheel 145 is whether
or not there is rotation of wheel 145. To supplement the encoder
a monitoring circuit for motion detection of driver mechanism 24
is required. The monitoring circuit is intended to inform the microprocessor
and thus the operator when the medication delivery form the syringe
barrel is not being pumped at the programmed rate. In particular,
if the delivery of medication from the syringe is prevented or the
rate of the delivery has been altered, however slightly, because
of failure of the motor gearing, failure of the lead screw and half
nut, restrictions in the line from the syringe to the patient or
other occlusion, the monitoring circuit provides a warning.
In the specific arrangement of the preferred embodiment best shown
in FIGS. 4 and 5 there is a linear potentiometer 149 carried by
the housing 22 and extending substantially parallel to the lead
screw 110 in the area substantially between a journal bearing 144
each positioned at a respective end of the lead screw 110. The linear
potentiometer 149 is mounted inside the housing 22 on the back cover
29.
Associated with half-nut 109 which engages lead screw 110 is a
contact 150. The contact 150 extends from the half-nut 109 to engage
the linear potentiometer 149 and contact 150 preferably includes
an electrical insulator, such as rigid plastic or the like whereby
the electrically conductive strip of the linear potentiometer 149
is traversed by the contact 150 as the half-nut 109 moves along
the lead screw 110. The contact 150 is connected to carry current
from the conductive strip of linear potentiometer 149. In particular,
the conductive strip of linear potentiometer 149 is a U-shaped path
that provides electrical resistance to the flow of approximately
three (3) volts. The contact 150 completes a circuit through the
linear potentiometer strip such that varying resistance is seen
by the contact 150 as it traverses the linear potentiometer 149.
The varying resistance is directly related to the voltage drop due
to resistance.
FIG. 7 is a graph of the linear relationship of the drop in voltage
and the distance traveled by contact 150 (and thus the plunger)
along linear potentiometer 149. In FIG. 7 it is apparent that a
drop of one (1) volt equals approximately 5 cm. of plunger travel.
The U-shaped potentiometer 149 carries 3 volts across the top end
and movement downwardly along the linear potentiometer 149 by the
contact 150 varies the voltage drop by bridging the legs of the
U thus shunting the potentiometer.
In the preferred embodiment the microprocessor 68 examines periodically
the voltage variation received from the contact 150 and if there
is no change in voltage, the change is inconsistent with the rotation
information from the combination of the wheel 145 segments 146
and LED 148 or the change is less than a pre-programmed profile
of voltage variation, set within the memory of the microprocessor
68 the alarm will be energized, thus warning the operator that
a malfunction has occurred. It can be seen that a faulty drive system
whether it be in the motor, the gear train or the lead screw, will
be immediately noticed by the microprocessor 68 FIG. 5. Similarly,
the combination of the wheel 145 segments 146 and LED 148 provide
an input signal to the memory of the microprocessor 68 which includes
a timer so that the rate at which the pulses of the input signal
can be compared to a preset standard.
The operation of syringe pump 20 will now be described in connection
with FIG. 8. A syringe 152 typically is prepared with liquid medication
to be delivered to a patient at a prescribed delivery rate, such
as in milliliters per hour. Syringe 152 is normally of the conventional
type including a syringe barrel 153 having liquid medication 154
included therein. Distal tip 155 of the syringe barrel 153 is provided
for connection to a delivery line so that the liquid contents of
the syringe may be passed therethrough and delivered to the patient.
At the proximal end of barrel 153 there is usually a finger flange
156 on typical or conventional syringes. Extending out of the proximal
end of syringe barrel 153 is a plunger 157 in the form of an elongate
rod, the proximal end of which preferably terminates in a thumb
disk 158 or the like.
Loaded syringe 152 is mounted onto syringe pump 20 in a few straightforward
steps. The user first assures that driver mechanism clears thumb
disk 158 of the syringe plunger by depressing button 114 inwardly
thereby causing disengagement of the half nut form the lead screw
within the interior of the housing. This disengagement allows the
free movement of driver mechanism 24 to clear the plunger of the
syringe. Mounting of the syringe is then facilitated by the user
grasping clamp 74 and pulling same outwardly so that the clamp slides
linearly between clamp guides 78 and 79. Syringe barrel 153 is then
positioned so that it rests against the protruding surfaces of cradle
160 formed on the outside surfaces of upper housing portion 28 and
lower housing portion 29. Arm 75 of clamp 74 is then allowed to
contact the outside surface of syringe barrel 153. The clamp 74
is biased inwardly thereby holding the syringe barrel snugly and
firmly in the cradle on the outside surface of the housing. At the
same time, finger flange 155 at the proximal end of the syringe
barrel is positioned so that it rests in contact directly on the
outer surface of clamp guide 78. Accordingly, syringe barrel 153
of the syringe is now in a fixed and relatively immovable position
during operation of the syringe pump.
Once the syringe barrel has been positioned as explained and the
rate of delivery has been provided to the microprocessor, the apparatus
is set to operate. Driver mechanism 24 is brought into engagement
with thumb disk 158 by a combination of straightforward steps. Once
again, button 114 may be depressed to release the internal engagement
of the half nut and the lead screw so that the driver 24 may freely
be slid to the position of the extending plunger rod of the syringe.
Once button 114 is released, the internal engagement of the half
nut and lead screw is once again established. Latch member 101 is
then urged slightly outwardly by pulling on finger flanges 102.
Thumb disk 158 of the syringe plunger is then slipped into engagement
with abutment surface 106 on driver mechanism 24. Release of finger
flanges 102 causes latch member 101 to move inwardly so that latch
105 is hooked over the protruding end of thumb disk 158 thereby
capturing same in fixed position. The loaded syringe is now ready
so that its contents may be delivered to the patient.
At this time, syringe pump 20 is typically hanging on a stand or
the like in connection with ring 31. The user starts the procedure
by first depressing POWER ON button 34 thereby activating the electrical
circuitry of the syringe pump in accordance with the elements and
features described. If the battery power is low, light 45 will glow;
if battery power is sufficient, light 45 remains off. If, for example,
the liquid contents of syringe 152 are to be delivered at the rate
of 25 milliliters per hour, the user pushes "tens" button
40 for two successive increments until the number "2"
appears in the tens column of display 42. In similar fashion, the
"ones" button 41 is depressed until it is incremented
five times whereby the number "5" appears in the ones
column of display 42. Once this rate of delivery has been established
and also shown on display 42 the electrical circuitry of the syringe
pump, knowing the size of the syringe mounted on the housing, functions
through its microprocessor capabilities to deliver the contents
of the syringe at the selected rate. The monitoring circuit of the
present invention is programmed to check the movement of the driver
and thereby verify the delivery rate.
Having selected the desired rate of delivery, the user depresses
INFUSE button 35 signaling the initiation of DC motor 139 and subsequent
movement of driver mechanism 24. This movement of the driver mechanism,
in turn, causes plunger 156 to be pushed into syringe barrel 152
causing the liquid medication therein to be delivered through distal
tip 154 into a medication line (not shown). Display 42 may be changed
to show volume delivered from the commencement of operation by depression
of VOLUME DELIVERED button 36. Display 42 will then read a number
in milliliters, and may be programmed to display volume for a period
of a few seconds after the VOLUME DELIVERED button has been depressed.
If an occlusion or decrease in delivery occurs as a result of line
blockage or the like, attention light 46 is lit and an audible alarm
sounds. If, however, the occlusion detection circuit is activated
as a result of end of cycle when medication delivery from the syringe
barrel has been completed, the DC motor stops operation and attention
light 46 comes on. The visual and audible signal corresponding to
end of cycle, however, is different from the signal for line occlusion.
At any time during operation of the syringe pump, the user may stop
the operation of the syringe pump by depressing STOP INFUSION button
38. The unit is turned off by depressing POWER OFF button 39.
Thus, the present invention provides a syringe pump with a number
of significant and notable improvements over presently known and
available syringe pumps. A significant safety feature for assuring
delivery of life nurturing medication has been included. Most significantly,
the present syringe pump may be fabricated with relatively few components
and inexpensive assembly, while providing the user with sophistication
of operation and versatility of performance.
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