U.S. patent number 3,771,694 [Application Number 05/269,707] was granted by the patent office on 1973-11-13 for infusion pump.
Invention is credited to Arthur P. Kaminski.
United States Patent |
3,771,694 |
Kaminski |
November 13, 1973 |
INFUSION PUMP
Abstract
A constant displacement infusion pump for administering
medicinal fluid to a patient and means for controllably operating
the pump such that the pump is caused to intermittently dispense
medicinal fluid with the amount of each dosage dispensation
variable in accordance with a first signal and the duration between
successive dosage dispensations variable in accordance with a
second signal.
Inventors: |
Kaminski; Arthur P. (Utica,
MI) |
Family
ID: |
23028357 |
Appl.
No.: |
05/269,707 |
Filed: |
July 7, 1972 |
Current U.S.
Class: |
222/644;
128/DIG.13 |
Current CPC
Class: |
A61M
5/1456 (20130101); G01F 11/029 (20130101); Y10S
128/13 (20130101) |
Current International
Class: |
A61M
5/145 (20060101); G01F 11/02 (20060101); G01f
011/06 () |
Field of
Search: |
;222/309,70,76
;128/214C,218P,214F,214E,DIG.12,DIG.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tollberg; Stanley H.
Claims
I claim:
1. In infusion pump apparatus for controllably administering the
injection of medicinal fluid into a patient, the combination
comprising infusion pump means for dispensing medicinal fluid,
drive means comprising a D. C. motor, means operatively coupling
said drive means with said pump means, operating means for
operating said drive means, said operating means comprising first
circuit means for alternately and repetitively generating first and
second signals, each of said signals having a variable
characteristic, and second circuit means operatively coupling said
first circuit means and said drive means such that said drive means
is operated in accordance with said first and second signals to
cause the pump means to dispense dosages of medicinal fluid with
the amount of each dosage dispensation variable in accordance with
the characteristic of the first signal and the duration between
successive dosage dispensations variable in accordance with the
characteristic of the second signal, said first circuit means
comprising means for repetitively generating a direct current of
fixed duration and variable amplitude, with said amplitude
representing the variable characteristic of said first signal and
means for varying the duration between successive generations of
said direct current, with said duration between successive
generations of direct current representing the variable
characteristic of said second signal and said second circuit means
comprising means for supplying said direct current to said
motor.
2. In infusion pump apparatus for controllably administering the
injection of medicinal fluid into a patient, the combination
comprising infusion pump means for dispensing medicinal fluid,
drive means comprising a D. C. motor, means operatively coupling
said drive means with said pump means, operating means for
operating said drive means, said operating means comprising first
circuit means for alternately and repetitively generating first and
second signals, each of said signals having a variable
characteristic, and second circuit means operatively coupling said
first circuit means and said drive means such that said drive means
is operated in accordance with said first and second signals to
cause the pump means to dispense dosages of medicinal fluid with
the amount of each dosage dispensation variable in accordance with
the characteristic of the first signal and the duration between
successive dosage dispensations variable in accordance with the
characteristic of the second signal, said first circuit means
comprising means for repetitively generating a direct current of
variable duration and fixed amplitude, with said duration
representing the variable characteristic of said first signal and
means for varying the duration between successive generations of
said direct current, with said duration between successive
generations of said direct current representing the variable
characteristic of said second signal and said second circuit means
comprising means for supplying said direct current to said
motor.
3. In infusion pump apparatus for controllably administering the
injection of medicinal fluid into a patient, the combination
comprising infusion pump means for dispensing medicinal fluid,
drive means, means operatively coupling said drive means with said
pump means, operating means for operating said drive means, said
operating means comprising first circuit means for alternately and
repetitively generating first and second signals, each of said
signals having a variable characteristic, and second circuit means
operatively coupling said first circuit means and said drive means
such that said drive means is operated in accordance with said
first and second signals to cause the pump means to dispense
dosages of medicinal fluid with the amount of each dosage
dispensation variable in accordance with the characteristic of the
first signal and the duration between successive dosage
dispensations variable in accordance with the characteristic of the
second signal, said first circuit means comprising generating
circuit means for generating a waveform alternating between high
and low levels, said first signal corresponding to one of said
levels and said second signal corresponding to the other of said
levels.
4. The combination of claim 3 wherein said drive means comprises a
D. C. motor.
5. The combination of claim 3 wherein said generating circuit means
comprises means for generating a square wave waveform alternating
between said high and low levels, said first signal corresponding
to the duration of said square wave waveform at said one level, and
said second signal corresponding to the duration of said square
wave waveform at said other level.
6. The combination of claim 5 wherein said second circuit means
comprises switching means responsive to one of said levels for
operating said drive means.
7. In an infusion pump apparatus of the type wherein an infusion
pump is controllably operated to controllably dispense fluid the
combination comprising a D.C. motor, a D.C. battery, multivibrator
circuit means for developing a square wave signal, including means
for varying the length of time the square wave signal remains at
one level, switching circuit means operably coupling said motor
with said battery and responsive to said square wave signal for
blocking current flow from the battery to the motor when the square
wave signal is at the one level and for conducting current from the
battery when the square wave signal is at the other level and means
for varying a selected parameter of the current flow from the
battery to the motor.
8. The combination of claim 7 wherein said means for varying a
selected parameter of the current flow from the battery to the
motor comprises means for varying the amplitude of said
current.
9. The combination of claim 7 wherein said means for varying a
selected parameter of the current flow from the battery to the
motor comprises means for varying the duration of said current.
10. The combination of claim 7 wherein said means for varying a
selected parameter of the current flow from the battery to the
motor comprises variable resistance means operatively associated
with said multivibrator circuit means for varying the length of
time the square wave signal remains at the other level.
11. The combination of claim 7 wherein said means for varying a
selected parameter of the current flow from the battery to the
motor comprises variable resistance means operatively associated
with said motor for varying the magnitude of current flow from the
battery to the motor.
12. The combination of claim 7 wherein said means for varying the
length of time the square wave signal remains at the one level
comprises variable resistance means operatively associated with
said multivibrator circuit means.
13. The combination of claim 7 wherein said multivibrator circuit
means comprises first and second transistors, means operatively
coupling the output of the first transistor with the input of the
second transistor, means coupling the output of the second
transistor with the input of the first transistor, said means for
varying the length of time the square wave signal remains at the
one level comprising variable resistance means operatively
associated with one of said coupling means.
14. The combination of claim 13 wherein said means for varying a
selected parameter of the current value from the battery to the
motor comprises variable resistance means operatively associated
with the other of said coupling means.
15. The combination of claim 7 further including a second D.C.
battery, said second battery being operatively coupled with said
multivibrator circuit means for supplying the power requirements of
said multivibrator circuit means, said first battery being isolated
from said multivibrator circuit means.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to infusion pump apparatus of the
type adapted to controllably administer medicinal fluid to a
patient. In apparatus of this type, it is highly important to
control the dispensation of medicinal fluid so that the proper
dosage is administered over a period of time. In view of the
seemingly innumerable types of medicine which can be intravenously
injected into a patient, and the varying needs of individual
patients, it is highly desirable to have a wide range in the
dispensing capability of the pump, yet also ease and simplicity of
adjustment over this range. At the same time, it is important to
maintain accurate control over this range so that the proper dosage
is always administered for the setting to which the unit is
adjusted. Moreover, when the infusion pump is of the portable
battery-operated type, it is also desirable to consume minimum
power so that the unit can operate over relatively long time
periods with assurance that the accuracy in the dispensing rate
will be relatively unimpaired.
Accordingly, among the objects of the present invention are to
provide infusion pump apparatus for controllably administering
medicinal fluid to a patient: which has a wide range of fluid
dispensation rates but which requires at most only two simple
adjustments to deliver fluid at a selected rate; which is accurate
and highly reliable; which when battery operated, consumes minimum
power from the battery thereby prolonging battery life and
maintaining accuracy of delivery; and which is all around a better
unit than previous types of apparatus.
The foregoing objects along with additional objects and advantages
of the invention accrue by providing a constant displacement
infusion pump and means for controllably operating the pump such
that the pump is caused to intermittently dispense dosages of
medicinal fluid with the amount of each dosage dispensation
variable in accordance with a first signal and the duration between
successive dosage dispensations variable in accordance with a
second signal.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing discloses preferred embodiments of the
invention in accordance with the best mode presently contemplated
for carrying out the invention.
FIG. 1 is a semi-schematic plan view of a portion of the infusion
pump apparatus according to the present invention and having
portions broken away.
FIG. 2 is a first form of drive arrangement for the infusion pump
apparatus according to the invention and is to be taken in
conjunction with FIG. 1.
FIG. 3 is a second form of drive arrangement for the infusion pump
apparatus according to the invention and is to be taken in
conjunction with FIG. 1.
FIG. 4 illustrates a waveform useful in understanding the operation
of the drive arrangements of FIGS. 2 and 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows the pumping mechanism 10 of the infusion pump
apparatus of the present invention. A constant displacement
infusion pump in the form of a syringe 12 is arranged to dispense
medicinal fluid 14 via a flexible hose 16 and a needle 18. Hose 16
may be of sufficient length to enable needle 18 to be inserted into
the vein of a patient at a location remote from syringe 12; this
feature allows the infusion pump apparatus to be worn or carried by
the patient as a portable unit with hose 16 being routed from the
unit to the location where needle 18 is inserted into the patient's
vein. Fluid 14 is dispensed from syringe 12 by means of a plunger
20. Plunger 20 is operated by rotating a lead screw 22 to advance a
drive nut 24 axially along the screw. As nut 24 advances along
screw 22, a flange 26 on the nut pushes plunger 20 into syringe 12
to thereby cause the syringe to dispense fluid 14 at a rate
corresponding to the rate of travel of nut 24. Screw 22 is
operatively coupled through a conventional gear reducer 28 and a
conventional reversing clutch 30 to a drive shaft 32. As will be
seen in greater detail hereinafter, shaft 32 is operated by either
of the two forms of drive arrangements shown in FIGS. 2 and 3. Gear
reducer 28 reduces the relatively high rpm of shaft 32 to turn
screw 22 at a relatively low rpm. Clutch 30 permits the direction
of rotation of screw 22 to be reversed so that after nut 24 has
been advanced to discharge the contents of syringe 12, it can be
retracted preparatory to refilling the syringe. From the foregoing
description, it will be apparent that pumping mechanism 10 operates
to administer fluid 14 to the patient at a rate directly
proportional to the speed of shaft 32. Thus, as the speed of shaft
32 increases from zero rpm to maximum rpm, the rate of fluid
delivery increases from zero to a maximum. Stated differently, the
volume of fluid dispensed from syringe 12 with plunger 20 working
against a full charge of fluid is directly proportional to the
distance traveled by nut 24.
A first form of drive arrangement 34 for pumping mechanism 10 is
shown in FIG. 2. Drive arrangement 34 comprises a D.C. motor 36 for
rotating shaft 32 and a D.C. battery 38 for powering motor 36. An
electronic circuit is also operatively associated with motor 36 and
battery 38 for operating motor 36 in a fashion which, as will be
seen later, provides great versatility in regulating the injection
of fluid 14 into the patient. The circuit comprises a multivibrator
stage 40, an emitter follower stage 42 and switching stages 44 and
46.
The circuit is connected across battery 38 through an on-off
control switch 52 and a normally closed limit switch 54. Terminal
52a of switch 52 is connected to the positive terminal 38a of
battery 38 and terminal 52b of switch 52 is connected to terminal
54a of switch 54. Terminal 54b of switch 54 is connected to the
positive supply terminals of stages 40, 42, 44, 46. The negative
terminal 38b of battery 38 is connected via ground to the negative
supply terminals of stages 40, 42, 44 and to the negative armature
terminal 36b of motor 36. Switch 54 is operatively associated with
nut 24, and as can be seen in FIG. 1, is positioned to be tripped
by flange 26 when the contents of syringe 12 have been dispensed.
Accordingly, when switch 52 is operated from its broken line
position to its solid line position, a circuit path is completed
through switches 52 and 54, and the voltage of battery 38 is
applied between terminals 54b of switch 54 and battery terminal 38b
for delivery to the circuit. When switch 54 is tripped by nut 24 to
operate switch 54 from its solid line position to its broken line
position in FIG. 2, or when switch 52 is turned off, the circuit
path is broken so that battery 38 is disconnected from terminals
54b and 38b.
Multivibrator 40 comprises a pair of identical NPN transistors 56,
58 having respective base terminals 56b, 58b, respective emitter
terminals 56e, 58e, and respective collector terminals 56c, 58c.
The positive and negative supply terminals of multivibrator 40 are
designated 40a and 40b respectively. Emitter terminals 56e, 58e are
connected to terminal 40b; collector terminals 56c, 58c through
identical resistors 60, 62 respectively to terminal 40a; and base
terminals 56b, 58b through identical capacitors 64, 66 respectively
to collector terminals 58c, 56c respectively. A resistor 68 is
connected between terminal 56c and terminal 56b. A fixed resistor
70 and a string of switched resistors 72 are serially connected
between terminals 58b and 58c. String 72 consists of serially
connected resistors 72a, 72b, 72c, 72d, 72e which are operatively
connected with a seven position selector switch 74. Switch 74
comprises taps 74a, 74b, 74c, 74d, 74e, 74f, 74g and a wiper 74h
which is connected to a common switch terminal 74j. Wiper 74h is
selectively operable to connect terminal 74j to any of the seven
taps 74a through 74g. Each resistor 72a through 72e is connected
between successive taps 74a through 74f and the last two taps 74f,
74g are connected together and to one terminal of resistor 70. The
other terminal of resistor 70 is connected to terminal 58b, and
terminal 74j is connected to terminal 58c. With this arrangement as
wiper 74h is operated from tap 74a to taps 74f and 74g, the total
resistance between terminals 58c and 58b is selectively reduced
from a maximum value to a minimum value. The maximum resistance
value is equal to the sum of resistor 70 and resistors 72a through
72e; the minimum, the resistance of resistor 70 alone.
A steady state operating cycle of multivibrator 40 is as follows.
With battery 38 connected to multivibrator 40, current flows in a
loop from battery terminal 38a into multivibrator 40 via terminal
40a and from multivibrator 40 via terminal 40b to battery terminal
38b. The division of this current in the various circuit components
of multivibrator 40 is such that transistors 56 and 58 are
alternately conductive. For purposes of description, let it be
assumed that transistor 56 has just become conductive and
transistor 58 non-conductive. With transistor 58 non-conductive,
there is no current flow from terminal 58c to terminal 58e. Upon
conduction of transistor 56, the increasing current flow through
its collector-emitter circuit from terminal 56c to terminal 56e
simultaneously reduces the positive voltage at terminal 56c to just
slightly above ground potential. At this time, there exists a
voltage on capacitor 66 such that plate 66a is positive with
respect to plate 66b. (Why this voltage exists will be seen later.)
Upon conduction of transistor 56, a current path is created from
terminal 40a through capacitor 62, through resistor string 72,
through resistor 70, through capacitor 66, through terminals 56c
and 56e, to terminal 40b. Battery 38 delivers current through this
path in an attempt to reverse the polarity of the charge on
capacitor 66 (i.e., attempts to make plate 66b positive with
respect to plate 66a). The rate at which the voltage of capacitor
66 changes is a function of the capacitance of capacitor 66 and the
resistance of the resistors in the current path through which the
charging current for capacitor 66 flows (i.e., resistor 62,
resistor 70, and the selected resistance of resistor string 72).
Since battery 38 is attempting to charge capacitor 66 to the
battery voltage, the sum of the collector-emitter voltage of
transistor 56 (i.e., the voltage across terminals 56c and 56e) and
the voltage across capacitor 66 reaches a point during charging of
capacitor 66 where the resultant voltage at terminal 58b is
slightly positive with respect to ground and causes transistor 58
to conduct. (For reasons which will soon become apparent, it is
important to note that during the time transistor 56 was
conductive, capacitor 64 has been charged by current flow from
battery 38 through resistor 62 and the base-emitter circuit of
transistor 56 so that plate 64a is positive with respect to plate
64b. ) Now current flow from terminal 58c to terminal 58e increases
rapidly and the positive voltage at terminal 58c drops rapidly to
just slightly above ground potential. However, since capacitor 64
has been charged as indicated above, the rapid fall in voltage at
terminal 58c is coupled through the charged capacitor 64 causing a
negative voltage to be applied to base terminal 56b and rendering
transistor 56 non-conductive. Now with transistor 56 non-conductive
and transistor 58 conductive, a current path is created from
terminal 40a through resistor 60, through resistor 68, through
capacitor 64, through terminals 58c and 58e, to terminal 40b. Since
capacitor 64 at this time is charged with plate 64b negative with
respect to plate 64a, current flows from battery 38 through this
current path is an attempt to reverse the charge on capacitor 64 in
the same fashion as described above in connection with capacitor 66
during the conduction of transistor 56. The rate at which the
voltage of capacitor 64 changes is a function of the capacitance of
capacitor 64 and the resistance of the two resistors 60 and 68 in
the current path through which the charging current for capacitor
64 flows. Since battery 38 is attempting to charge capacitor 64 to
the battery voltage, the sum of the collector-emitter voltage of
transistor 58 and the voltage across capacitor 64 reaches a point
during charging of capacitor 64 where the resultant voltage at
terminal 56b is slightly positive with respect to ground causing
transistor 56 to conduct. The resulting drop in the collector
voltage at terminal 56c is coupled through capacitor 66 to turn off
transistor 58, capacitor 66 having been charged through resistor 60
and the base-emitter circuit of transistor 58 during the time
transistor 58 was conducting so that plate 66a is positive with
respect to plate 66b. This completes one operating cycle of
multivibrator 40. The cycle now repeats itself and continues to do
so until either switch 52 or 54 is opened.
In light of the foregoing description, it is apparent that
multivibrator 40 develops a positive square wave voltage at
terminal 56c whose amplitude is slightly less than battery voltage.
This waveform is illustrated as waveform W in FIG. 4, and it is to
be understood that waveform W is not necessarily to any particular
scale. When transistor 56 is conducting, waveform W is at its low
level (approximately zero volts); and when transistor 56 is not
conducting, at its high level (approximately battery voltage). The
conducting period is designated T.sub.1 while the non-conducting
period is designated T.sub.2. The duration of the time period
T.sub.1 is a function of capacitor 66, resistor 62, resistor 70,
and resistor string 72. The duration of the time period T.sub.2 is
a function of capacitor 64 and resistors 60 and 68. By making
resistor 68 much greater than resistor 60, resistor 70 much greater
than resistor 62 and capacitors 64 and 66 equal, T.sub.1 becomes
essentially a function of resistor 70 and the selected value of
resistor string 72 while T.sub.2 becomes essentially a function of
resistor 68. By making resistor 68 equal to resistor 70, T.sub.1
equals T.sub.2 whenever wiper 74h is operated to either tap 74f or
74g. As wiper 74h is operated away from taps 74g and 74f toward tap
74a, the increasing resistance which is inserted in series with
resistor 70 causes T.sub.1 to increase with the maximum value
thereof occurring when wiper 74h is operated to tap 74a. Because
resistor 68 is fixed, T.sub.2 remains constant for all settings of
switch 74.
Emitter follower stage 42 comprises an NPN transistor 78 whose base
terminal 78b is connected through a resistor 80 to collector
terminal 56c, whose collector terminal 78c is connected to terminal
54b and whose emitter terminal 78e is connected through a resistor
82 to ground. The emitter voltage of transistor 78 at terminal 78e
follows the collector voltage of transistor 56 at collector
terminal 56c to provide power amplification of waveform W without
loading multivibrator 40. Thus, when the voltage at terminal 56c is
high, the voltage at terminal 78e is also high; when the voltage at
terminal 56c is low, the voltage at terminal 78e is also low.
Switching stage 44 comprises a transistor 84 whose base terminal
84b is connected through a resistor 86 to emitter terminal 78e,
whose emitter terminal 84e is connected to ground and whose
collector terminal 84c is connected to a switch 88. Transistor 84
operates as a switch to conduct when the emitter voltage of
transistor 78 at terminal 78e is high, and to not conduct when the
voltage at terminal 78e is low. Switch 88, like switch 74, has
seven operating positions defined by taps 88a through 88g, a wiper
88h and a common terminal 88j. The first six of these taps 88a
through 88f are connected together and collector terminal 84c can
be connected to any tap 88a through 88f. The seventh tap 88g is
connected to ground. When wiper 88h is operated to any one of its
first six positions (i.e., taps 88a through 88f), terminal 84c is
connected to terminal 88j; and when to the seventh position (tap
88g), terminal 88j is connected to ground. Wiper 88h is ganged with
wiper 74h so that the two switches 74, 88 are operated in unison to
corresponding taps.
Switching stage 46 comprises a PNP transistor 90 whose emitter
terminal 90e is connected to terminal 54b, whose base terminal 90b
is connected through a resistor 92 to terminal 88j of switch 88 and
whose collector terminal 90c is connected through the series
combination of a fixed resistor 94 and a variable resistor 96 to
the positive armature terminal 36a of motor 36. With this
arrangement, when switches 74 and 88 are operated to any one of
their first six positions, the base circuit of transistor 90 is
connected to the collector circuit of transistor 84, and transistor
90 conducts whenever transistor 84 conducts. When switches 74 and
88 are operated to their seventh position, transistor 90 is
disconnected from transistor 84 and a ground is applied to the base
of transistor 90 causing the transistor to continuously conduct.
Resistor 94 limits the armature current flow to a maximum selected
value, and hence, limits the motor speed to a corresponding maximum
value. Resistor 96 is variable to vary the armature current
downwardly from its maximum value and hence, vary the speed of
motor 36 downwardly from its maximum value.
The operation of the infusion pump will now be apparent. The output
waveform W developed by multivibrator 40 operates through the
successive stages 42, 44, and 46 to cause transistor 90 to conduct
during the time periods T.sub.2 and to not conduct during the time
periods T.sub.1. The intermittent conduction of transistor 90 in
turn causes current to be intermittently supplied from battery 38
to motor 36 in the form of square wave current pulses. Thus, motor
36 intermittently operates to intermittently dispense dosages of
fluid 14 to the patient. Setting switches 74, 88 to taps 74a, 88a
sets T.sub.1 to maximum. By also setting resistor 96 to maximum
resistance, the speed of motor 36 during time T.sub.2 is a minimum.
Accordingly, with these two adjustment settings, the rate of fluid
dispensation from syringe 12 is a minimum. The rate can be
increased by either operating switches 74, 88 in the direction away
from taps 74a, 88a, by decreasing the resistance of resistor 96, or
by adjusting both switches 74, 88 and resistor 96. When switches
74, 88 are set to taps 74g, 88g, the ground applied to base
terminal 90b overrides the on-off type control of multivibrator 40
causing the motor to run continuously at the speed determined by
resistor 96. By now setting resistor 96 to zero resistance, the
maximum rate of fluid dispensation is achieved. Thus, it will be
appreciated that the various possible settings of switches 74, 88
and resistor 96 cover a wide range in the dispensing capability of
the apparatus with at most only two adjustments being necessary to
select any possible dispensation rate. For example, it is possible
to have the maximum dispensing rate 3,000 times as great as the
minimum dispensing rate so that the present invention has the
advantage of being able to administer medication over a long time
period as well as a short time period.
After the contents of syringe 12 have been exhausted, nut 24 can be
retracted by reversing clutch 30 and operating motor 36 at maximum
speed. Suitable provision could be made for manually actuating
screw 22 if desired.
It is preferable to calibrate the infusion pump apparatus so that
required dispensation rates can be quickly set without need to
empirically determine the dispensing rate for given settings of
switches 74, 88 and resistor 96. The solid state circuit
construction renders the apparatus highly reliable as well as
highly accurate over this wide range of dispensing rates. It will
be noted that the unit is efficiently designed for minimum power
consumption so that when fluid is not being dispensed, motor 36 is
not operated and so that multivibrator 40 draws only very small
current. Moreover, the apparatus may be economically constructed
and readily packaged for portable use by an ambulatory patient.
FIG. 3 discloses a drive arrangement 100 which is very similar to
drive arrangement 34, and hence, need be described only insofar as
it differs from drive arrangement 34. Accordingly, like parts in
both FIGS. 2 and 3 are identified by like numerals. Drive
arrangement 100 differs from drive arrangement 34 in the following
respects. Switch 88 is omitted with terminal 84c of transistor 84
being connected directly to resistor 92. Resistor 96 is omitted
with resistor 94 being connected directly to motor 36. A variable
resistor 102 is connected in series with resistor 68 between
terminals 56c and 56b of transistor 56. Drive arrangement 100
includes an additional battery 104. The way in which batteries 38,
104 are connected to motor 36 and to the electronic circuitry is
somewhat different. Battery 38 is connected through switch 54 and
switch 52 to emitter terminal 90e of transistor 90. Battery 104 is
connected through an on-off switch 106 to terminal 40a of
multivibrator 40 and to terminal 78c of transistor 78. Switch 106
is operative with switch 52, the two switches being either both
closed or both open. With this arrangement, battery 38 powers
essentially only motor 36, while battery 104 powers essentially
only multivibrator 40 and emitter follower 42. Since battery 104 is
thus isolated from motor 36, the voltage delivered by battery 104
to multivibrator 40 is independent of battery voltage drops which
are likely to occur due to motor armature current when only a
single battery is used. For a given adjustment setting, the bwo
battery arrangement maintains high accuracy in the time periods
T.sub.1 and T.sub.2 over a longer operating time.
The operation of drive arrangement 100 further differs from that of
drive arrangement 34 in that resistor 102 replaces resistor 96 to
control the amount of fluid dispensed during each dispensation from
syringe 12. As resistor 102 is increased from zero resistance to
maximum resistance, the duration of time period T.sub.2 is likewise
increased to operate motor 36 for a longer time. Whereas drive
arrangement 34 maintains the operating time of motor 36 constant
while varying the motor speed, drive arrangement 100 varies the
operating time of motor 36 while maintaining constant motor speed.
Preferably, motor 36 is of a type which is relatively insensitive
to variations in the voltage of battery 38 and hence, maintains a
reasonably constant speed over the life of battery 38.
* * * * *