U.S. patent number 3,731,679 [Application Number 05/081,926] was granted by the patent office on 1973-05-08 for infusion system.
This patent grant is currently assigned to Sherwood Medical Industries Inc.. Invention is credited to Vernon F. Braun, Theodore E. Weichselbaum, Jack L. Wilhelmson.
United States Patent |
3,731,679 |
Wilhelmson , et al. |
May 8, 1973 |
INFUSION SYSTEM
Abstract
A portable infusion system uses a disposable piston type syringe
as a positive displacement pump. The syringe piston is reciprocally
driven by a bidirectional DC motor under control of a battery
powered circuit. Different selectable rates of pumping are
maintained by controlling the width of bidirectional DC pulses
coupled to the DC motor and by monitoring the motor back EMF during
the off-time of the pulses. A disposable two-way valve connects the
syringe pump with a fluid source and a catheter. Safety circuits
protect against deleterious conditions such as the passage of an
air bubble or an over-pressure condition.
Inventors: |
Wilhelmson; Jack L. (Fenton,
MO), Weichselbaum; Theodore E. (St. Louis, MO), Braun;
Vernon F. (Berkeley, MO) |
Assignee: |
Sherwood Medical Industries
Inc. (Hazelwood, MO)
|
Family
ID: |
22167286 |
Appl.
No.: |
05/081,926 |
Filed: |
October 19, 1970 |
Current U.S.
Class: |
604/121;
128/DIG.12; 417/411; 604/152; 128/DIG.1; 128/DIG.13; 417/45;
604/123 |
Current CPC
Class: |
A61M
5/1452 (20130101); F04B 9/02 (20130101); H02P
7/2913 (20130101); A61M 5/16854 (20130101); F04B
49/06 (20130101); F04B 17/03 (20130101); A61M
5/172 (20130101); Y10S 128/12 (20130101); Y10S
128/13 (20130101); A61M 2205/15 (20130101); Y10S
128/01 (20130101) |
Current International
Class: |
A61M
5/172 (20060101); A61M 5/145 (20060101); A61M
5/168 (20060101); F04B 17/03 (20060101); F04B
49/06 (20060101); F04B 9/02 (20060101); H02P
7/18 (20060101); H02P 7/29 (20060101); A61m
005/00 () |
Field of
Search: |
;128/213,214R,214E,214F,214B,214.2,218R,218A,230,234,273,DIG.1,DIG.12
;417/45,411 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Blum et al. "A Method of Continuous Arterial Infusion", Surgery,
1948, pp. 30-35..
|
Primary Examiner: Truluck; Dalton L.
Claims
We claim:
1. In a portable infusion system for transferring fluid from a
fluid source to a catheter, a positive displacement pumping system
having disposable parts, comprising: a self-contained source of DC
power; disposable syringe means having a barrel and a piston
movable in said barrel along a path to move fluid within the
barrel, said barrel having a fluid passage opening; disposable
valve means having a pump port in fluid communication with said
passage opening, input port means connected with said fluid source
for passing fluid to said barrel, and output port means for
connection with said catheter for passing fluid to said catheter;
base means removably holding said syringe means and said valve
means to allow disposal after use with a patient; a holding member
removably connected to said piston and mounted on said base for
reciprocal movement along said path; motor means energized by said
DC power source for reciprocating said holding member and said
piston, said motor means including gear means connected to said
holding member to effect reciprocal movement of said holding member
in response to rotation of said gear means, and a DC motor for
rotating said gear means, means for selecting one of a plurality of
rates of pumping including generator means for generating DC drive
pulses having different duty cycles selectable to effect different
rates of pumping, circuit means for coupling said DC drive pulses
to said DC motor, and voltage variation compensation means
including means responsive to decreasing voltage from said DC power
source for increasing the duty cycle of at least some of said DC
drive pulses.
2. The system of claim 1 wherein said DC motor is a bidirectional
DC motor having an armature shaft rotatable in opposite directions
when opposite polarity current is coupled to the DC motor, said
gear means converting rotational movement of said armature shaft
into translational movement which drives said holding member, and
circuit means for periodically reversing the polarity of current
passed from said DC power source to said DC motor.
3. The system of claim 1 wherein said valve means includes sensing
means for detecting the presence of an air bubble, and safety means
responsive to detection of an air bubble for terminating the
operation of said motor means.
4. The system of claim 1 including over-pressure means for
detecting when the pressure of fluid passed to said catheter
exceeds a predetermined maximum, and indicator means actuated when
said predetermined maximum is exceeded for providing an alarm
indication.
5. In an infusion system for transferring fluid to catheter means,
a pumping system comprising a source of fluid capable of passing
electricity, a valve assembly having a fluid channel with an outlet
adapted for connection with the catheter means for directing the
flow of said fluid to the catheter means, fluid pump means
including a chamber connected in fluid communication with said
fluid source and said fluid channel, and drive means in said
chamber actuable to effect movement of fluid from said fluid source
and pump fluid through said fluid channel to the catheter means,
unidirectional valve means connected in fluid communication with
said fluid channel to permit fluid flow from said fluid channel to
the catheter and prevent fluid flow from the catheter to said fluid
channel, said fluid channel including a fluid passageway having a
fluid opening contiguous with said fluid channel for admitting
fluid into said passageway a distance determined by the pressure of
the fluid in said fluid channel, and a pair of electrode means
located within said fluid channel and having extensions connectable
with an external circuit, at least one of said pair of electrode
means being located in said passageway a predetermined distance
from said fluid opening so that the presence of fluid at said last
named electrode means indicates a predetermined fluid pressure
condition.
6. The pumping system of claim 5 further including third electrode
means in said channel adjacent the other of said pair of
electrodes, and circuit means responsive to the presence of an air
bubble between said third and other electrode means to provide a
signal indicative thereof.
7. The pumping system of claim 5 wherein said fluid passageway has
a closed end opposite said fluid opening for trapping a
compressible gas between said closed end and the fluid admitted
trough said fluid opening, said last named electrode means being
surrounded by said compressible gas when the pressure of fluid in
said fluid channel means is less than said predetermined pressure
condition.
8. In an infusion system for transferring fluid to catheter means,
a pumping system comprising a source of fluid capable of conducting
electricity, a syringe having a barrel and a reciprocal plunger
slidable in said barrel for moving fluid into and out of said
barrel, a valve assembly having a fluid source inlet connected to
said source of fluid, a pressure fluid inlet connected to said
syringe barrel and in fluid communication with said fluid source
inlet, and a channel connected in fluid communication with said
pressure fluid inlet and having an outlet connectable with the
catheter, first valve means connected in fluid communication with
said source of fluid to permit fluid flow from said source to said
syringe barrel and to prevent return fluid flow from said syringe
barrel to said fluid source, second valve means connected in fluid
communication with said channel to permit fluid flow from said
channel to the catheter and prevent return fluid flow from the
catheter to said channel, and means for reciprocating said plunger
to draw fluid from said source into said barrel through said
pressure fluid inlet during movement thereof in one direction and
supply pressurized fluid to said channel from said barrel during
movement thereof in the opposite direction to transfer the fluid to
the catheter, said valve assembly including a pressure chamber
connected at one end in fluid communication with said channel and
closed at the opposite end thereof, an electrode within said
chamber, gas disposed in said chamber normally between said
electrode and said one end to prevent contact between said fluid
and said electrode, said gas being compressible to permit said
fluid to contact said electrode upon the occurrence of fluid
pressure in said channel of a predetermined value, and circuit
means connected with said electrode for detecting the contact
between the fluid and said electrode.
9. The infusion system of claim 8 wherein said circuit means
includes a second electrode disposed in said channel in contact
with the fluid therein.
10. The infusion system of claim 8 further including a pair of
closely spaced electrodes in said channel and normally bridged by
the fluid to normally provide a predetermined value of impedance
between said pair of electrodes, and circuit means connected to
said pair of electrodes and responsive to a change in said value of
impedance upon the occurrence of the presence of an air bubble
between said electrodes to interrupt the reciprocation of said
plunger.
Description
This invention relates to an improved pumping system and an
improved control circuit, particularly adapted for use in an
infusion system.
During typical blood transfusions and intravenous injections, a
solution bottle is usually hung above a patient to allow gravity
feed of fluid through disposable venoclysis tubing to a catheter
inserted in the vein of the patient. Transportation of the patient
is difficult because the solution bottle must always be located
above the patient, requiring an attendant to hold the solution
bottle. Even when the patient is located in a hospital, periodic
monitoring of the process is required, utilizing valuable personnel
time. Despite periodic monitoring, certain malfunctions can occur
which may go unattended for lack of a suitable indication of the
malfunction. For example, during an injection, it is possible for a
needle to become displaced from its position in a vein and become
lodged in a muscle.
In accordance with the present invention, a novel portable positive
displacement pumping system replaces the gravity feed system
typically used for transfusions and injections. As a result, the
solution bottle may be located at any reasonable height with regard
to the patient. A novel battery powered control circuit for the
pump system includes a number of safety circuits which
automatically monitor for deleterious conditions, such as passage
of air bubbles or the dislodgement of the intravenous needle into a
muscle, eliminating the requirement that an attendant periodically
monitor the process. Sterile conditions are easily maintained
because the positive displacement pumping system uses a disposable
syringe and a disposable two-way valve which can be discarded after
use with each patient and replaced with a new sterile syringe and
valve.
Some attempts have been made to use disposable piston type syringes
for pumping fluids at fixed locations. For example, it has been
proposed to drive the piston of a syringe by an AC motor connected
to an external AC line source. To control the rate of pumping,
adjustment is made of the length of the drive stroke for the
piston. Such apparatus is not usable in an infusion system, since
air bubbles may be passed to the patient, and other serious
malfunctions might occur which could not be automatically cured.
Also, such apparatus does not permit priming of the syringe, nor is
accurate control possible, as is essential in an infusion
system.
The applicants' novel control circuit for driving the novel pumping
system includes a unique DC motor drive which can be used to
accurately drive loads other than pumps. The drive automatically
compensates for variations in the load, long term aging of
batteries for powering the control circuit, and detection of
deleterious conditions associated with the driven load.
Bidirectional motor movement is accomplished by a simple reversing
circuit controlled by movement of the motor armature. The control
circuit uses the known techniques of driving the DC motor by
variable width pulses, and monitoring the back EMF across the motor
during the off-time of the pulses to control the on-time width of
the pulses. However, a pair of such circuits has heretofore been
required when driving a motor in both forward and reverse
directions. The applicants' control circuit accomplishes the same
degree of control while substantially simplifying the circuit.
One object of this invention is the provision of an improved
infusion system in which the sterile parts in contact with the
fluid being pumped are disposable and readily replaceable with new
sterile parts.
Another object of this invention is the provision of an improved
control circuit for driving a DC motor through a bidirectional
cycle of operation.
Yet another object of this invention is the provision of improved
pump means driven by a DC motor and feedback means for modifying
the operation of a control circuit in accordance with external
conditions related to the operation of the pump.
Further objects and features of the invention will be apparent from
the following specification, and from the drawings, in which:
FIG. 1 is a perspective illustration of an infusion system
incorporating the pumping system of the present invention;
FIG. 2 is an exploded view of the pumping system, with the syringe
pump being illustrated for clarity as located on the opposite side
of the pump housing shown in FIG. 1;
FIG. 3 is a partly plan and partly sectional view of a disposable
valve with embedded electrodes;
FIG. 4 is a sectional view taken along lines 4--4 of FIG. 3;
FIG. 5 is a plan view taken along lines 5--5 of FIG. 4; and
FIG. 6 is a schematic diagram of the control circuit for the pump
system.
While an illustrative embodiment of the invention is shown in the
drawings and will be described in detail herein, the invention is
susceptible of embodiment in many different forms and it should be
understood that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the invention to the embodiment illustrated.
GENERAL DESCRIPTION
Turning to FIG. 1, a portable infusion system is illustrated for
pumping fluids such as blood from a solution bottle 20 to a
catheter 21 inserted into the vein of a patient. Fluid transfer is
accomplished by a pumping apparatus 24 held by a caddy assembly 26
mounted to a rail 28 of a bed for the patient. The caddy 26 also
removably holds the solution bottle 20, which can be located at any
reasonable altitude with respect to the patient.
Solution bottle 20 is of conventional construction, and includes a
cap 30 having an air valve 31 and an output port 32 for fluid
transfer. Disposable venoclysis tubing 34 couples the port 32 to an
input port 36 in a disposable two-way valve 40 which forms a part
of the pump apparatus 24.
Pump apparatus 24 uses as a pump chamber a conventional disposable
syringe 42 having a slidable piston 44 which can be reciprocated to
pump fluid within a hollow syringe barrel coupled with the two-way
valve 40 which includes an outlet or output port 46 connected by
venoclysis tubing 50 with a conventional Y connector 52 for
medication introduction. The output of the Y connector 52 is
coupled by additional disposable venoclysis tubing 54 to the
catheter 21.
The control circuit for pump apparatus 24, seen in detail in FIG.
3, is completely contained within the housing for the pump
apparatus, and can be either externally or internally powered.
During a back stroke, in which the syringe piston 44 is driven away
from the valve 40, input port 36 admits fluids from solution bottle
20 into the syringe barrel. The valve in output port 46 is closed
at this time. During a forward stroke, in which piston 44 is driven
towards the valve 40, the input port 36 is closed and the output
port 46 is opened, pumping the solution through venoclysis tubing
52 and 54 to the catheter 21.
The novel pumping apparatus 24 is seen in exploded view in FIG. 2.
A sterile, positive displacement pump is economically formed by
using a conventional disposable syringe 42 in combination with a
unique disposable valve 40, to be described. Syringe 42 includes a
gasket 70 fixedly mounted to the piston 44 for movement within a
hollow barrel 72 which has a single fluid opening terminating in a
needle connector 74. The syringe includes extending finger grip
arms 76, which in the present invention are held by base means for
the pump apparatus 24.
Syringe 42 and valve 40 are removably held by housing means in
order to allow disposal after use with each patient and replacement
with a new presteriled syringe and valve. A lower molded case 90
includes a pair of upstanding arms 92 each having a slot channel 94
which slidably receives one of the extensions 76 of the syringe.
Lower case 90 also includes an upstanding post 100 having a concave
surface 102 for holding the valve 40 when it is mated to the
syringe 42, and for making electrical contact with electrodes
embedded in the valve. A pair of female electrical sockets 106 in
surface 102 receive air bubble detector electrodes, as will appear,
and a female socket 108 (not illustrated in FIG. 2), which may be
separate from case 90 or similarly molded in a portion thereof,
receives an over-pressure detector electrode. The sockets 106 and
108 are connected by wires to the circuit of FIG. 3 which is
contained within the hollow case 90.
The mechanical drive arrangement for piston 44 consists of a
bidirectional DC motor 120 having an armature shaft 121 with an
integral motor gear 122. The motor gear 122 meshes with an idler
gear 126 rotatable about an idler shaft 128 rigidly attached to a
pinion gear 130. The pinion gear 130 meshes with a drive gear 132
which is fixedly attached to the shaft of a jackscrew 134. A
syringe cylinder carrier 140 includes a gripping head 142 having an
opening therein for slidably receiving the head 45 of piston 44.
The carrier 140 has an internally threaded central opening for
engaging the threads of the jackscrew 134 to cause the carrier to
act as a drive nut on the jackscrew.
When DC motor 120 is energized by voltage of predetermined
polarity, the two-stage spur reduction gears rotate jackscrew 134
and cause the carrier 140 and attached cylinder 44 to be driven in
a forward stroke. Carrier 140 includes a protrusion 150 with a
permanent magnet which extends downward for magnetically actuating
a sealed forward stroke limit switch 152 and a sealed reverse
stroke limit switch 154, mounted to a circuit board 156 which
contains the circuit of FIG. 3. The carrier 140 is driven in a
forward stroke direction until protrusion 150 is directly over
limit switch 152, at which time the circuit of FIG. 3 reverses the
polarity of voltage to DC motor 120 in order to rotate armature 121
in a reverse direction. The carrier 140 and cylinder 44 are now
longitudinally moved through a back stroke until the protrusion 150
is directly over limit switch 154, at which time the circuit of
FIG. 3 again reverses the polarity of voltage to DC motor 120.
While magnetically actuated proximity switches are preferred, a
mechanical switch arrangement could alternately be used, actuated
by mechanical engagement with protrusion 150.
Power for the DC motor 120 and the control circuit is obtained from
a self-contained DC power source, as a pair of series connected DC
batteries 160. Desirably, batteries 160 are rechargeable, sealed
nickel-cadmium batteries which allow the pump apparatus to be
powered either from an external AC source, or internally powered in
order to allow the unit to be completely portable. If the unit is
constructed for portable use only, the batteries 160 may be
conventional 1.5 volt "D" size. The DC batteries 160 are housed
within a battery retainer cylinder 162 molded in lower case 90.
Electrical connection is made through a battery contact spring 164
and a contact on a battery retainer cap 165 which threads into the
battery retainer cylinder wall to allow replacement of the
batteries when necessary.
An upper case 170 mates with the lower case 90 to enclose the drive
train assembly and the batteries 160. Case 170 includes a window
172 through which indicia on a thumbwheel knob 174 may be observed
in order to allow operator selection of different rates of pumping
fluid. Desirably, the indicia on wheel 174 directly indicate pump
rate, such as one liter of fluid per one, two, three, etc., hours.
A different range of pump rates may be provided by replacing
syringe 42 with a syringe of different capacity, and knob 174 may
be so marked with alternate indicia. A syringe prime switch 176
allows an operator to override the setting selected by wheel 174 in
order to rapidly reciprocate the piston 44 when first priming the
syringe 42 to eliminate air bubbles. During the time the switch 176
is actuated, the air bubble protector circuit is disabled.
Disposable Valve Assembly
The disposable valve assembly 40 is illustrated in detail in FIGS.
3-5. The assembly is economically formed by using a pair of
identically manufactured valve units 190 mated in opposite fluid
flow directions with a central fluid channel unit 192 so that one
valve unit 190 forms input port 36 and the other valve unit 190
forms output port 46.
Each valve unit 190 includes a fluid input port having a tapered
conical wall 194 which directs fluid to a check valve 195 formed of
flexible, resilient material such as rubber. Check valve 195 is
formed by a hollow center portion with an integral tapering nose
196 terminating in a rectangular slit opening 197 which passes
fluid to an output port defined by a tubular wall 200 which also
serves to anchor the hollow center portion of the check valve. The
check valve 195 is of conventional construction and allows fluid
flow in a direction from the input port defined by conical wall 194
to the output port defined by the tubular wall 200, but collapses
to block fluid flow in an opposite direction.
The central fluid channel unit 192 includes an input fluid channel
202 into which is inserted the output port of the valve unit 190
which forms input port 36. Opposite input fluid channel 202 is an
output fluid port or channel 203 having a conical wall which
receives the tapered syringe connector 94. Contiguous with fluid
channels 202 and 203 are an output fluid channel 204 and a closed
fluid channel 206. Channel 204 terminates in a neck portion 208 of
reduced diameter which mates with the input port of the check valve
190 which serves as the output port 46 for passing fluid flow to
the catheter.
To detect the presence of an air bubble in the fluid channel, a
pair of metal rods or electrodes 212 extend through the wall of the
valve assembly and into the fluid channel 204. The electrodes 212
are spaced apart approximately 0.25 inches, and are placed ahead of
the output functioning check valve 195. When fluid of 0.001 percent
salinity or higher is present between the electrodes 212, the fluid
completes a resistance path of sufficiently low impedance to allow
the circuit of FIG. 6 to continue to operate. When an air bubble of
predetermined size passes the electrodes, the impedance rises and
breaks the circuit to cause the forward stroke of the pump to
terminate.
To detect an over-pressure condition, as is caused when the
catheter becomes lodged in a muscle, the closed fluid channel 206
forms a pressure detector. A cap 217 closes the end of fluid
channel 206, trapping air between the cap 217 and the fluid which
enters the channel 206. A single metal rod or electrode 220 is
embedded through the wall of the valve assembly and into the fluid
channel 206. When an over-pressure condition occurs, the pressure
of the fluid within central channel unit 192 further compresses the
trapped air and allows fluid to further enter the closed channel
206 until it contacts the electrode 220, thereby completing a
circuit through the fluid to one of the electrodes 212 in order to
indicate an over-pressure condition.
Desirably, electrodes 212 and 220 are an integral part of the valve
assembly 40, rather than a part of the syringe 42. As a result, a
conventional disposable syringe of low cost may be used as the
pump. The valve assembly itself may be economically molded of
plastic, except for the pair of check valves 190 which may be
molded of rubber. The externally extending ends of the metal
electrodes 212 and 220 are directly inserted in the female sockets
106 and 108, respectively, as previously described.
Control Circuit
The control circuit for the pump assembly is illustrated in detail
in FIG. 5. DC power is provided between a DC potential line 248 and
a source of reference potential or ground 250. When external 115
volt AC is available, a plug 256 may be inserted into the external
AC source so as to couple 115 volt AC to a stepdown transformer
258. The transformer is connected through a full wave diode
rectifier to a line 260 connectable through a socket with line 248.
The rechargeable batteries 160 form a filter capacitor for the full
wave rectified AC voltage, reducing the ripple of the voltage on DC
line 248. If desired, an additional filter capacitor 262 may be
provided. The stepdown transformer 258 and full wave rectifier may
be housed within the plug 256, and connected through a two-line
cord to the socket receptacle on the pump assembly. When the pump
assembly is to be used independent of the external AC source, the
line plug is simply removed from the receptacle on the pump
assembly, allowing the previously recharged batteries 160 to
thereafter power the control circuit.
DC motor 120 is a shunt wound permanent magnet motor which rotates
in a forward direction when current flows from a terminal 260 to a
terminal 262, and rotates in a reverse direction when current flows
from terminal 262 to terminal 260. As will appear, the motor is
driven by pulses having a less than 100 percent duty cycle. During
the off-time of the pulses, the motor 120 acts as a generator or
tachometer, and the back EMF across the terminals is sensed and
stored in order to control the duty cycle of the drive pulses.
An electronic reversing switch, including transistors 265, 266,
267, 268, 269, and 270 forms a double-pole, double-throw switch.
Transistors 265 and 268 are synchronously driven conductive to pass
current in a forward direction through motor 120. Alternatively,
transistors 266 and 267 may be synchronously driven conductive to
complete a reverse current path for motor 120 to drive the motor
through its reverse or back stroke. When transistors 265 and 268
are on, current passes from a positive line 275 through transistor
265 to terminal 260 of motor 120, through motor 120 and out
terminal 262 to transistor 268, and thence to ground 250. When the
forward limit of travel is reached, as indicated by the permanent
magnet on protrusion 150 actuating limit switch 154, a reversing
switch driver, to be described, turns transistors 265 and 268 off
and transistors 266 and 267 on. Current then flows from the
positive line 275 through transistor 266 to terminal 262, and
thence through motor 120 and out terminal 260 to transistor 267 and
thence to ground 250.
The reversing switch driver, consisting of transistors 280, 281,
282, and 283, acts as a regenerative bistable switch useful to
obtain the heavy drive capability which is necessary when using low
supply voltage, such as 3.0 volts from the pair of batteries 160.
Transistors 280 and 283 drive each other into saturation when
magnetic protrusion 150 actuates switch 152 at the end of a back
stroke, grounding the base of transistor 282. Alternatively,
transistors 282 and 281 drive each other into saturation when
magnetic protrusion 150 actuates the switch 154, grounding the base
of transistor 283 at the forward stroke limit of travel.
When transistor 281 saturates, current flows from its emitter to
base and through a resistor 290 to the base of transistor 267 to
provide drive for the reversing switch. At the same time, the
voltage at the collector of transistor 281 rises to the potential
of line 275, back biasing transistors 269 and 265. Transistor 282
is also saturated at this time, causing current to flow through the
emitter-base of transistor 266, through a resistor 292 and via a
line 293 to the collector of transistor 282 and thence to ground
250. This provides drive for the other half of the reversing
switch. Since the collector voltage of transistor 282 is at
approximately ground potential, no current flows through a resistor
295 to transistor 270, nor transistor 268. When the opposite stable
state of the bistable is set by magnetic protrusion 150,
transistors 280 and 283 act similar to the above described
operation for transistors 281 and 282, providing drive for
transistors 265 and 269, and transistors 268 and 270, as will be
explained with reference to the bubble detector circuit.
During the forward stroke, transistor 270 is driven on by pulses
having approximately a 25 percent duty cycle. For one circuit which
was constructed, the drive pulses for minimum motor speed had a
four millisecond on-time out of a sixteen millisecond interval,
producing a sixty hertz frequency. The duty cycle during the
forward stroke is adjustable, as will appear, and is controlled by
a forward stroke control.
The reverse stroke always occurs at maximum speed since transistors
266 and 267 are fully saturated during reverse motor movement. As
the DC voltage from batteries 160 slowly drops with age and use,
lesser voltage is passed through the reverse stroke transistors 266
and 267 to the DC motor 120, resulting in a decreased speed of
movement. As will appear, a battery voltage variation compensation
circuit is responsive to decreased battery voltage to decrease the
off-time of the pulses controlled by the forward stroke control,
thus increasing speed in the forward stroke in order to maintain
the selected rate of pumping.
The forward stroke control includes transistors 300, 301, 302, 303,
and 304, connected basically as an unsymmetrical astable
multivibrator. To allow selection of different rates of pumping,
thumbwheel knob 174 is connected to the wiper 310 of multi-position
switches 312. Wiper 310 is connected to any one of a plurality of
resistors 315 each having a different resistance value. A master
OFF switch 316 when actuated connects the wiper 310 to DC line 248,
via prime switch 176. When the thumbwheel 174 is rotated to cause
the wiper 310 of switch 312 to contact one particular resistor 315,
a path is formed from DC line 248, through actuated switch 316 and
unactuated switch 176 to wiper 310, and thence through the selected
resistor 315 to the emitter of transistor 300. The collector of
transistor 300 is connected through a capacitor 317 and thence
through the collector-emitter of transistor 301 to ground 250. The
duty cycle of the pulse coupled to transistor 270 is determined by
the capacitance of capacitor 317, the selected value of resistor
315, and the voltage at the base of transistor 300 (from the
velocity feedback circuit as will appear).
The on-time of the duty cycle is determined by the time period
transistors 301 and 303 are saturated and transistors 302 and 304
are turned off. Transistor 300 acts as a controlled current source
that discharges capacitor 317 during the time it holds transistor
304 turned off. When transistor 301 turns on, transistor 303 is
turned on by current flowing from its base and through a resistor
320 and conducting transistor 301 to ground 250. Transistor 303
drives transistor 270 of the reversing switch driver through a
resistor 322. Thus, the on-time of the duty cycle which controls
the forward stroke of the motor is determined by saturation of
transistor 303.
The off-time of the duty cycle is controlled by saturation of
transistor 304, at which time transistors 301 and 303 are turned
off. This off-time is determined by the capacitance value of a
capacitor 325, the voltage to which the capacitor 325 is allowed to
charge during the prior on-time, and the resistance values of a
pair of series connected resistors 327 and 328. The allowable
voltage to which capacitor 325 is allowed to charge is set by the
battery voltage variation compensation circuit, to be
explained.
The detailed operation of the forward stroke control circuit is as
follows. Assume transistor 301 has just turned on with capacitor
317 fully charged and capacitor 325 fully discharged. When
transistor 301 saturates, the negative terminal of capacitor 317
has a negative voltage equal to the supply potential. For this
example, it will be assumed that the supply potential from
batteries 160 is at maximum potential, or 3.0 volts. Current now
flows from the +3.0 volt supply and through switches 316, 176 and
310 to the selected resistor 315 and thence through transistor 300
to discharge capacitor 317. When the negative terminal of capacitor
317 reaches 1.2 volts (the base-emitter drop of transistors 302 and
304), transistors 302 and 304 are turned on, turning transistor 301
off and recharging capacitor 317 to supply voltage through a
resistor 330. Capacitor 325 discharges through the series resistors
327 and 328 until the base-emitter voltage of transistor 301 is
reached, at which time transistor 301 turns on and the cycle is
repeated.
During the forward stroke, the pulse coupled to the DC motor has an
approximately 25 percent off-time at the maximum infusion rate
selectable by switch 310. Due to mechanical inertia, the motor
continues to turn and generates a back EMF proportional to the
angular velocity of the armature. This voltage is sensed by a
velocity feedback circuit and stored in order to control transistor
300 and adjust the on-time of the pulses to compensate for
variations in load. Thus, various fluids and syringes may be used
without effecting to any significant extent the calibration of
thumbwheel knob 174.
During the forward stroke, transistor 265 is on, connecting
terminal 260 to the supply voltage at line 275. During the off
portion of the forward stroke pulse, transistor 270 is off,
blocking transistor 268 and disconnecting ground 250 from the motor
terminal 262. The back EMF across the motor terminal is now coupled
through a resistor 335 and a pair of series connected diodes 336
and 337 to a capacitor 340 connected to ground 250. The capacitor
340 charges to a potential that is the sum of the supply voltage
and the voltage generated by the motor.
During the on-time of the forward stroke control, transistor 270 is
driven into conduction, driving transistor 268 into conduction and
hence connecting motor terminal 262 to approximately ground
potential, back biasing the diodes 336 and 337. The voltage charge
across capacitor 340 is now used to control the base drive of
transistors 300, establishing an on-time duration proportional to
the voltage across the capacitor. A resistor 342 allows the voltage
across capacitor 340 to slowly leak off. Since the emitter of
transistor 300 is referenced to the DC supply voltage, the current
through transistor 300 is dependent solely on the back EMF across
the DC motor, eliminating the effect of supply voltage
variations.
The control circuit also includes a number of special circuits
described in the following sections.
Bubble Detector
The bubble detector circuit includes the bubble detector electrodes
212 and transistors 350 and 351. When fluids having a conductivity
equal to a salinity of 0.001 percent or greater are present between
electrodes 212 which are spaced 0.25 inches apart, the resistance
therebetween is on the order of 200 kilohms or lower. This causes
current to flow from the supply line 275, through the emitter-base
of transistor 350, through a resistor 352, as 10 kilohms, to one
electrode 212 and thence through the fluid to the other electrode
212 to charge a capacitor 353, as 1.0 microfarads. Capacitor 353 is
discharged by the forward stroke control circuit through a diode
355. The time constants are chosen such that capacitor 353 is never
charged to more than 0.1 volts unless the forward stroke control
circuit fails. If the forward stroke control circuit fails in such
a way that the forward stroke would be at full supply voltage
across the motor 120, capacitor 353 charges to supply voltage and
turns transistor 350 off. This terminates operation. Thus, the
patient is protected from excessive infusion rates which otherwise
might be caused by failure of critical parts in the circuit. The
current passing through the fluid is on the order of 10 microamps
or less thereby creating no hazard of electrolysis or other hazard
to the patient.
The current that charges capacitor 353 causes a current of at least
200 times magnitude to flow from the supply, through the
emitter-collector of transistor 350, through a resistor 357 and
into the base of transistor 351. This forward biases transistor
351, creating a path to ground through the transistor 351 and a
resistor 358 connected to the base of transistor 269, thereby
allowing drive for transistors 269 and 265 to flow when the
transistors 269 and 265 are turned on by the reversing switch
driver circuit. When an air bubble or cavity is present between the
electrodes 212, the current path is broken and transistor 351 is
biased off. Therefore, the motor 120 stops on the forward stroke.
Prime switch 176 in the forward stroke control circuit is used to
override this shut-off during syringe priming.
The combination of the bubble detector circuit and the placement of
the electrodes 212 and 220 in the two-way valve assembly 40 creates
a fail safe apparatus which detects air leaks caused by a defect in
the pump assembly itself. Referring to FIG. 4, the electrodes 212
are located in the pressure side of the fluid channel, between the
pair of check valves 195. Should the metal electrodes 212 not be
completely surrounded by the plastic material forming the wall of
the valve channel, as might occur due to dropping of the valve
assembly, for example, an air passageway or void would be created
which would allow air to seep from the atmosphere into the fluid
channel 204. If the electrodes 212 were located in input port 36
upstream of the check valve 195, the electrode located furthest
downstream could leak air during a back stroke operation. If the
bubble should pass the check valve 195, it would escape detection
by the bubble detector circuit.
To prevent such an occurrence, the electrodes 212 are located in a
region which has high pressure during a forward stroke. During the
forward stroke, the pressure in channel 204 is in excess of
atmospheric pressure, therefore an air passageway adjacent either
electrode 212 merely causes fluid to seep out of the channel 204,
but does not create an air bubble within the channel. During the
back stroke, a low pressure region is formed in fluid channel 204,
allowing air to seep from the atmosphere into the channel 204.
Regardless of the electrode 212 which leaks air, the bubble will
travel upstream towards the pump port 203, so that the bubble will
again have to pass the electrodes 212 during the forward stroke.
This allows the air bubble to be detected in the same manner as if
the bubble had been drawn in from the fluid supply.
The bubble detector control circuit serves the dual purposes of
providing a safety device to prevent accidental passage of an air
bubble, and also automatically shuts off the pumping apparatus when
all the fluid in the solution bottle is used up. At the end of the
supply of fluid, air is introduced into the solution bottle and is
pumped to the valve assembly 40. When the air reaches the point
where the two sensing electrodes 212 are placed, the current path
is broken and motor operation is terminated, turning off the
pumping system.
Battery Voltage Variation Compensation
This circuit, consisting of transistors 370 and 371, is responsive
to decreases in the battery voltage to decrease the off-time of the
pulses in the forward stroke control. As previously described, the
back stroke is not controlled and will vary in speed with voltage
variations. The time lost on the back stroke is gained by speeding
up the motor on the forward stroke.
Transistor 371 acts as an ideal diode, establishing a reference
voltage of approximately 0.6 volts at its collector, which is
coupled in series through a resistor 376 and a resistor 377 to a
line coupled through switch 316 with the positive potential line
248. In shunt with resistors 376 and 377 and transistor 371 is a
resistor 380 in series with the emitter of transistor 370, and a
resistor 382 in series between the collector of transistor 370 and
ground 250. The collector of transistor 370 is directly coupled to
the junction between transistor 304 and capacitor 325. As the
battery supply voltage lowers, the current through resistor 380
changes linearly. This causes the collector voltage of transistor
370 to rise linearly at a rate established by the ratio of resistor
380 to resistor 382 and a resistor 384 in series between the
collectors of transistors 303 and 304. The voltage at the base of
transistor 370 also varies, but at reduced ratio.
For the particular motor driven mechanism which was constructed,
the circuit constants were chosen so that the voltage on the
collector of transistor 370 and hence also transistor 304 lowered
as the battery voltage lowered by a ratio of 1.5, that is, 0.1 volt
battery variation produced 0.15 volts less charge on capacitor 325.
While this ratio produced the correct compensation, other ratios
may be utilized for other loads driven by the motor. The range of
the battery voltage compensation circuit is such that battery
voltages down to approximately 2.0 volts may be tolerated,
representing a decrease of 33 percent from the full battery voltage
of 3.0 volts.
For the circuit constants disclosed above, a battery supply voltage
of less than 2.0 volts indicates that the batteries must be
replaced or recharged in order to maintain the calibrated accuracy
of the pumping apparatus. A low battery indicator circuit is formed
by integrated circuit NOT gates 390 and 391 for energizing a low
battery indicator lamp 393. When the supply voltage is above 2.0
volts, a divider formed by resistors 395 and 396 in series between
ground 250 and the supply line via switch 316 and line 248 produces
a voltage above 0.8 volts at the junction between resistors 395 and
396 which causes NOT gate 390 to saturate, turning NOT gate 391 off
and thus maintaining the lamp 393 off. When the supply voltage
drops to 2.0 volts, gate 390 turns off, causing gate 391 to turn on
and hence energize the lamp indicator 393. The indicator lamp 393
is desirably located beneath a window in the upper case of the pump
assembly so as to be visible by an operator.
Over-Pressure Detector
This circuit is formed by integrated circuit gates 400, 401 and a
transistor 372. Gates 400 and 401 are connected to form a bistable
multivibrator. During normal operation (no over-pressure
condition), gate 401 is on and transistor 372 is off. To insure
this state, a capacitor 405 is made five times as large as a
capacitor 406. When the control circuit is first energized, the
capacitor 405 holds one input of gate 400 low long enough to set
the bistable with gate 401 saturated and gate 400 off.
When fluid reaches electrode 220, indicating an over-pressure
condition, a circuit path is formed from one input of gate 400 to
the supply voltage line 275 via transistor 350 and the electrode
212 connected through resistor 352 to the base thereof, saturating
gate 400 and turning gate 401 off. This turns transistor 372 on,
turning off transistor 351 which in turn opens the bias path for
transistors 269 and 265. This stops the system on the forward
stroke. The over-pressure detector circuit may be reset by turning
the control circuit off and back on, causing capacitor 405 to again
saturate gate 401.
Bubble and Over-Pressure Indicator
This circuit consists of transistors 310 and 411 which control
energization of a visual indicator, such as a light emitting diode
(LED) 413. Desirably, a light emitting diode is used rather than an
incandescent lamp due to its low power consumption. When an air
bubble or an over-pressure condition is detected by the circuits
previously described, transistor 351 is turned off. This in turn
biases off transistor 410, ungrounding a junction formed between a
resistor 415 and a diode 416 connected in series between the anode
of LED 413 and the base of transistor 411. The transistor 411 is
thus forward biased, creating a current path for the LED 413 to
ground through a resistor 420 and the collector-emitter junction of
the conducting transistor 411. The LED 413 is located adjacent a
jewel lens mounted in case 170 in order to give a visual indication
of a circuit shut-off caused by the detection of an air bubble or
an over-pressure condition.
For some applications, it may be desirable to include less than the
number of individual circuits described above, or to include
various combinations thereof, as will be apparent to one skilled in
the art.
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