U.S. patent application number 09/838699 was filed with the patent office on 2002-06-13 for direct current motor safety circuits for fluid delivery systems.
This patent application is currently assigned to MINIMED INC.. Invention is credited to Causey, James D., Renger, Herman Lee, Sheldon, Moberg.
Application Number | 20020071225 09/838699 |
Document ID | / |
Family ID | 21762628 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020071225 |
Kind Code |
A1 |
Sheldon, Moberg ; et
al. |
June 13, 2002 |
Direct current motor safety circuits for fluid delivery systems
Abstract
A safety circuit system for a DC driven device for use with a
fluid delivery system includes a first voltage potential DC power
line, a second voltage potential DC power line, a controller and a
safety circuit. The first voltage potential DC power line is
coupled to provide a first voltage potential to the DC driven
device, and the second voltage potential DC power line is coupled
to provide a second voltage potential to the DC driven device such
that the second voltage potential is different relative to the
first potential. The controller controls at least the first voltage
potential on the first voltage potential DC power line. The safety
circuit has an enable state and a disable state, in which the
default state is the disable state. The safety circuit is coupled
to the controller, and the controller controls the safety circuit
to place the safety circuit in the enable state independently of
controlling the first voltage potential on the first voltage
potential DC power line. The safety circuit is operatively coupled
to at least one of the first and second voltage potential DC power
lines to inhibit DC flow and operation of the DC driven device when
the safety circuit is in the disable state and to permit DC flow
and operation of the DC driven device when the safety circuit is in
the enable state such that the operation of the DC driven device
will occur when the safety circuit is in the enable state. In one
version the DC driven device is a DC motor in an infusion pump,
while in other versions the DC driven device is a gas generator in
an infusion pump. Preferably, the safety circuit is controlled by
an AC signal from the controller such that the safety circuit is
enabled by the AC signal to permit DC flow and enable the forward
motion of the DC motor while the AC signal is provided by the
controller.
Inventors: |
Sheldon, Moberg; (Granada
Hills, CA) ; Causey, James D.; (Simi Valley, CA)
; Renger, Herman Lee; (Calabasas, CA) |
Correspondence
Address: |
MEDTRONIC MINIMED INC.
18000 DEVONSHIRE STREET
NORTHRIDGE
CA
91325-1219
US
|
Assignee: |
MINIMED INC.
|
Family ID: |
21762628 |
Appl. No.: |
09/838699 |
Filed: |
April 19, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09838699 |
Apr 19, 2001 |
|
|
|
08335008 |
Nov 7, 1994 |
|
|
|
Current U.S.
Class: |
361/23 ; 307/127;
361/58; 361/84 |
Current CPC
Class: |
H02M 1/32 20130101; H02M
3/00 20130101; H02M 7/003 20130101; A61M 5/142 20130101; A61M
2205/18 20130101; A61M 2205/16 20130101; A61M 2205/17 20130101;
B60R 2001/1284 20130101; B60R 1/12 20130101; H02J 7/0042
20130101 |
Class at
Publication: |
361/23 ; 361/58;
361/84; 307/127 |
International
Class: |
H02H 005/04; H02H
009/00 |
Claims
What is claimed is:
1. A safety circuit system for a DC motor for use with a fluid
delivery system, the safety circuit system comprising: a first
voltage potential DC power line coupled to provide a first voltage
potential to the DC motor; a second voltage potential DC power line
coupled to provide a second voltage potential to the DC motor,
wherein the second voltage potential is different relative to the
first potential; a controller that controls at least the first
voltage potential on the first voltage potential DC power line; a
safety circuit having an enable state and a disable state, wherein
a default state is the disable state, wherein the safety circuit is
coupled to the controller, wherein the controller controls the
safety circuit to place the safety circuit in the enable state
independently of controlling the first voltage potential on the
first voltage potential DC power line, and wherein the safety
circuit is operatively coupled to at least one of the first and
second voltage potential DC power lines to inhibit DC flow and
forward motion of the DC motor when the safety circuit is in the
disable state and to permit DC flow and forward motion of the DC
motor when the safety circuit is in the enable state such that the
forward motion of the DC motor will occur when the safety circuit
is in the enable state.
2. The safety circuit system according to claim 1, wherein the
safety circuit is controlled by an AC signal from the controller
such that the safety circuit is enabled by an AC signal to permit
DC to flow and enable the forward motion of the DC motor while the
AC signal is provided by the controller.
3. The safety circuit system according to claim 1, wherein the
safety circuit in the disable state operates to inhibit the forward
motion of the DC motor when the difference of the first voltage
potential relative to second voltage potential is positive.
4. The safety circuit system according to claim 3, wherein the
safety circuit in the disable state is inoperative to inhibit a
reverse motion of the DC motor when the difference of the first
voltage potential relative to second voltage potential is
negative.
5. The safety circuit system according to claim 3, wherein the
safety circuit in the disable state operates to inhibit a reverse
motion of the DC motor when the difference of the first voltage
potential relative to second voltage potential is negative.
6. The safety circuit system according to claim 1, wherein the
safety circuit in the disable state operates to inhibit the forward
motion of the DC motor when the difference of the first voltage
potential relative to second voltage potential is negative.
7. The safety circuit system according to claim 3, wherein the
safety circuit in the disable state is inoperative to inhibit a
reverse motion of the DC motor when the difference of the first
voltage potential relative to second voltage potential is
positive.
8. The safety circuit system according to claim 3, wherein the
safety circuit in the disable state operates to inhibit a reverse
motion of the DC motor when the difference of the first voltage
potential relative to second voltage potential is positive.
9. The safety circuit system according to claim 1, wherein the
fluid delivery device is an infusion pump, and wherein the safety
circuit is used to prevent operation of the DC motor during a
controller failure to prevent accidental delivery of excess
fluid.
10. The safety circuit system according to claim 1, wherein the
safety circuit is integral with the DC motor.
11. The safety circuit system according to claim 1, wherein the
safety circuit is co-located with the controller.
12. A safety circuit system for a DC driven device for use with a
fluid delivery system, the safety circuit system comprising: a
first voltage potential DC power line coupled to provide a first
voltage potential to the DC driven device; a second voltage
potential DC power line coupled to provide a second voltage
potential to the DC driven device, wherein the second voltage
potential is different relative to the first potential; a
controller that controls at least the first voltage potential on
the first voltage potential DC power line; a safety circuit having
an enable state and a disable state, wherein a default state is the
disable state, wherein the safety circuit is coupled to the
controller, wherein the controller controls the safety circuit to
place the safety circuit in the enable state independently of
controlling the first voltage potential on the first voltage
potential DC power line, and wherein the safety circuit is
operatively coupled to at least one of the first and second voltage
potential DC power lines to inhibit DC flow and operation of the DC
driven device when the safety circuit is in the disable state and
to permit DC flow and operation of the DC driven device when the
safety circuit is in the enable state such that the operation of
the DC driven device will occur when the safety circuit is in the
enable state.
13. The safety circuit system according to claim 12, wherein the DC
driven device is a DC motor, and wherein the fluid delivery system
is an infusion pump.
14. The safety circuit system according to claim 12, wherein the DC
driven device is a gas generator, and wherein the fluid delivery
system is an infusion pump.
15. The safety circuit system according to claim 15, wherein the
safety circuit is controlled by an AC signal from the controller
such that the safety circuit is enabled by an AC signal to permit
DC flow and enable the forward motion of the DC motor while the AC
signal is provided by the controller.
Description
FIELD OF THE INVENTION
[0001] This invention relates to direct current (DC) motor safety
circuits in fluid delivery systems and, in particular embodiments,
to safety circuits for DC motors in medication/drug infusion pumps
to inhibit accidental over delivery of medications/drugs due to DC
motor control circuit failures.
BACKGROUND OF THE INVENTION
[0002] Conventional drug delivery systems such as infusion pumps
that deliver insulin over a period of time utilize a variety of
motor technologies to drive an infusion pump. Typical motor
technologies include direct current (DC) motors, stepper motors, or
solenoid motors. Each motor type has various advantages and
disadvantages related to cost, reliability, performance, weight,
and safety.
[0003] In drug delivery using infusion pumps, the accuracy of
medication delivery is critical (such as for insulin, HIV drugs or
the like), since minor differences in medication quantity can
dramatically affect the health of the patient. Thus, safeguards
must be designed into the delivery system to protect the patient
from over or under delivery of medication. For example, in the case
where insulin is administered via an infusion pump to a diabetic
patient, excessive drug delivery could cause complications due to
hypoglycemia, and could possibly even result in death. Therefore,
controlled delivery with safeguards against over delivery of
medications is required for drug delivery systems when over
delivery could result in complications, permanent damage, or death
of the patient.
[0004] In conventional systems, these safeguards against over
delivery have been incorporated into the drive systems of infusion
pumps in varying ways. For example, the motor control electronics
utilize cross checks, encoder counts, motor current consumption,
occlusion detection, or the like, as a form of feedback to guard
against over or under delivery of medication. However, one drawback
to this approach can occur if the control electronics in a DC motor
driven infusion pump were to fail, such that a direct short occurs
from the power source to a DC motor in the infusion pump. For
example, in one failure mode, it would be possible for the DC motor
to drive continuously for an excessive period of time, for example,
until the power source was depleted or removed, or until the short
was removed. This condition is commonly referred to as motor "run
away", and could result in all of the medication contained in the
infusion pump being infused immediately over too short a period of
time resulting in injury or death to the patient.
[0005] To avoid this drawback, some infusion pump manufactures have
avoided the use of DC motors and have instead utilized solenoid or
stepper motor technologies. With these motor types, any short in
the control electronics, would only result in, at most, a single
motor step. Therefore, motor "run away" would not occur. Thus, this
avoids the problem of a "run away" failure. However, a drawback to
the use of solenoid or stepper motor technologies is they generally
have a less efficient performance and tend to cost more as compared
to the DC motors.
SUMMARY OF THE DISCLOSURE
[0006] It is an object of an embodiment of the present invention to
provide improved DC motor safety circuits, which obviate for
practical purposes, the above mentioned limitations.
[0007] According to an embodiment of the invention, a safety
circuit system for a DC driven device for use with a fluid delivery
system includes a first voltage potential DC power line, a second
voltage potential DC power line, a controller and a safety circuit.
The first voltage potential DC power line is coupled to provide a
first voltage potential to the DC driven device, and the second
voltage potential DC power line is coupled to provide a second
voltage potential to the DC driven device such that the second
voltage potential is different relative to the first potential. The
controller controls at least the first voltage potential on the
first voltage potential DC power line. The safety circuit has an
enable state and a disable state, in which the default state is the
disable state. The safety circuit is coupled to the controller, and
the controller controls the safety circuit to place the safety
circuit in the enable state independently of controlling the first
voltage potential on the first voltage potential DC power line. The
safety circuit is operatively coupled to at least one of the first
and second voltage potential DC power lines to inhibit DC flow and
operation of the DC driven device when the safety circuit is in the
disable state and to permit DC flow and operation of the DC driven
device when the safety circuit is in the enable state such that the
operation of the DC driven device will occur when the safety
circuit is in the enable state. In preferred embodiments, the DC
driven device is a DC motor in an infusion pump. Alternatively, the
DC driven device is a gas generator in an infusion pump. In
preferred embodiments, the safety circuit is controlled by an AC
signal from the controller such that the safety circuit is enabled
by the AC signal to permit DC flow and enable the forward motion of
the DC motor while the AC signal is provided by the controller.
[0008] In embodiments that utilize a DC motor, the safety circuit
being in the disable state operates to inhibit the forward motion
of the DC motor when the difference of the first voltage potential
relative to second voltage potential is positive. In addition, the
safety circuit being in the disable state is inoperative to inhibit
a reverse motion of the DC motor when the difference of the first
voltage potential relative to second voltage potential is negative.
Alternatively, or in addition to, the safety circuit being in the
disable state operates to inhibit a reverse motion of the DC motor
when the difference of the first voltage potential relative to
second voltage potential is negative. In addition, the safety
circuit being in the disable state operates to inhibit the forward
motion of the DC motor when the difference of the first voltage
potential relative to second voltage potential is negative.
Further, the safety circuit being in the disable state is
inoperative to inhibit a reverse motion of the DC motor when the
difference of the first voltage potential relative to second
voltage potential is positive. Alternatively, the safety circuit
being in the disable state operates to inhibit a reverse motion of
the DC motor when the difference of the first voltage potential
relative to second voltage potential is positive.
[0009] Preferred embodiments are directed to an infusion pump, in
which the safety circuit is used to prevent operation of the DC
motor during a controller failure to prevent accidental delivery of
excess fluid. In particular embodiments, the safety circuit is
integral with the DC motor. In other embodiments, the safety
circuit is co-located with the controller.
[0010] Other features and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings which illustrate, by way
of example, various features of embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A detailed description of embodiments of the invention will
be made with reference to the accompanying drawings, wherein like
numerals designate corresponding parts in the several figures.
[0012] FIG. 1 is a schematic diagram of a safety circuit in
accordance with a first embodiment of the present invention.
[0013] FIG. 2 is an illustrative schematic diagram of a safety
circuit in accordance with a second embodiment of the present
invention.
[0014] FIG. 3 is a schematic diagram of a safety circuit in
accordance with a third embodiment of the present invention.
[0015] FIG. 4 is a schematic diagram of a safety circuit that is a
variation of the embodiment shown in FIG. 3.
[0016] FIG. 5(a) is a schematic diagram of a safety circuit that is
a further variation of the embodiment shown in FIG. 3.
[0017] FIG. 5(b) is a top view of a pin out diagram for a component
used in the circuit shown in FIG. 5(a).
[0018] FIG. 5(c) is a top view of a pin out diagram for another
component used in the circuit shown in FIG. 5(a).
[0019] FIG. 6 is a schematic diagram of a safety circuit that is
yet another variation of the embodiment shown in FIG. 3.
[0020] FIG. 7 is a perspective view of a motor in accordance with
an embodiment of the present invention.
[0021] FIG. 8 is a simplified schematic of a motor and safety
circuit in accordance with an alternative embodiment of the present
invention.
[0022] FIG. 9 is a waveform diagram illustrating operation of the
safety circuit and power supplied to a DC motor in accordance with
the embodiments of the present invention.
[0023] FIG. 10 is a waveform diagram illustrating operation of the
safety circuit and power supplied to a DC motor that is an enlarged
view of the portion shown in the dashed circle 10-10 of FIG. 9.
[0024] FIG. 11 is a waveform diagram illustrating operation of the
safety circuit and power supplied to a DC motor that is an enlarged
view of the portion shown in the dashed circle 11-11 of FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] As shown in the drawings for purposes of illustration, the
invention is embodied in safety circuits for direct current (DC)
motors used in fluid delivery systems. In preferred embodiments of
the present invention, controllers that provide a signal to the
safety circuit, in addition to providing power for the DC motor in
an infusion pump, that enables the DC motor to operate only when an
enabling signal is provided to the safety circuit. However, it will
be recognized that further embodiments of the invention may be used
to inhibit motor operation with additional signals or by
controlling other aspects of the infusion pump. The safety circuits
are primarily adapted for use in infusion pumps that deliver
medication (or fluid) to subcutaneous human tissue. However, still
further embodiments may be used with infusion pumps for other types
of tissue, such as muscle, lymph, organ tissue, veins, arteries or
the like, and used in animal tissue. The infusion pumps are also
primarily for external use; however, alternative embodiments may be
implanted in the body of a patient. The fluid delivery systems are
also primarily for delivery of medication, drugs and/or fluids to a
patient; however other embodiments may be used with other fluid
delivery systems that require a high degree of confidence that a DC
motor "run away" will not occur, such as in certain manufacturing
techniques or the like. Preferred embodiments are directed to
safety circuits for DC motors. However, alternative embodiments may
be used with other DC driven devices, such as a DC activated gas
generator in an infusion pump or the like.
[0026] Preferred embodiments are directed to circuits and methods
for using DC motor technology in fluid delivery systems with
additional safety circuits to prevent DC motor "run away". Use of
this technology obviates the need for the use of comparatively less
efficient and more expensive stepper motor and solenoid motors. All
of the illustrated embodiments include a DC motor and some DC motor
control electronics, although other components or DC driven devices
may be used. The control electronics may be relatively simple, such
as only including the capability of turning the DC motor on and off
by supplying power for the duration of a key press, or may be more
complex using microprocessors having multiple programmable control
profiles utilizing feedback from an encoder, driving current or the
like.
[0027] FIG. 1 illustrates a safety circuit 110 in accordance with a
first embodiment of the present invention. In this embodiment, a DC
motor 112 is configured to have a nominal voltage winding that is
significantly higher then a supply voltage from a battery 114. To
generate a sufficient voltage to operate the DC motor 112, the
safety circuit 110 utilizes a DC-DC step up converter 116 (or
similar), that includes an integral controller 118, between the
battery 114 and the DC motor 112 to drive the DC motor 112 at its
rated voltage (see FIG. 1). Generally, when a DC motor is supplied
with the rated voltage (and also assuming there is sufficient
current available), the DC motor will provide a known torque. If,
for example, the supply voltage is halved, then the DC motor will
only provide approximately half the full voltage output torque.
However, a two, or more, times DC-DC step up converter could be
utilized between the battery and the DC motor to provide the rated
voltage to the DC motor. Thus, to provide a safety circuit, the
nominal motor voltage winding is selected to be some large multiple
of the supply voltage from the battery, such as ten times, or the
like, higher then the supply voltage from the battery. Therefore,
if the battery 114 is shorted directly to the DC motor 112 (i.e.,
as when there is an control electronics 118 failure and/or DC-DC
step up converter 116), the DC motor's 112 output torque would only
be approximately {fraction (1/10)} of the rated value.
[0028] Generally, if the friction in the complete drive system
(e.g., drive gears, shaft, or the like) is approximately {fraction
(1/10)} of the nominal rated value, the DC motor 112 will not have
enough available torque to drive the system and cause a "run away"
condition. To drive the DC motor 112 with sufficient torque, a
DC-DC step up converter 116 would be required with approximately a
ten times step up capability. For additional safety, alternative
embodiments of the safety circuit 10 would include the DC-DC step
up converter 116 such that it would only be enabled by an
additional internal signal S1 (shown in dashed lines) from the
integral control electronics 118. Thus, if the control electronics
118 were to fail, there would be no enable signal to provide the
required step up voltage to drive the DC motor 12 in a "run away"
condition. Alternative embodiments may utilize different battery
supply voltages to rated nominal motor voltages ratios, with the
choice being based on system friction, tolerance for movement, cost
of control electronics and DC motors, or the like. In further
alternatives, the control electronics 118 may be separated from the
DC-DC step up converter 116 and provided as a discrete element that
is placed before or after the DC-DC step up converter 116.
[0029] FIG. 2 illustrates a safety circuit 200 in accordance with a
second embodiment of the present invention that builds upon the
embodiment shown in FIG. 1. The safety circuit 200 utilizes a DC-DC
step up converter 202 (that includes integral control electronics
210) and a Zener diode 204. The DC-DC step up converter 202
converts the supply voltage from the battery 206 to a value
corresponding to the sum of the rated motor winding voltage of the
DC motor 208 and the Zener diode 204. For instance, if the DC motor
208 has 3.0 volt motor winding and the Zener diode 204 has a
breakdown voltage of 2.0 volts, the DC-DC step up converter 202
must provide 5.0 volts to facilitate operation of the DC motor 208
at its nominal rated voltage, if it is desired to drive the DC
motor 208 at the rated voltage. Thus, in this example, when the
supply voltage from the battery 206 is stepped up to 5 volts as a
positive voltage potential, 2 volts are lost through the Zener
diode 204 and 3 volts are provided for operation of the DC motor
208. In the reverse direction (i.e. a negative voltage potential),
the DC-DC step up converter 202 only needs to step up the 1.5 volts
supply voltage from the battery 206 to 3 volts, since there is
little loss through the Zener diode 204 in the reverse direction.
In an alternative embodiment, a Schottky diode 250 (shown in dashed
lines in FIG. 2) may be placed in parallel with the Zener diode 204
to insure a low and predictable voltage drop in the reverse
direction (i.e., negative voltage potential). Alternatively, if a
higher speed rewind (e.g., more torque) is desired and/or required,
the DC-DC step up converter 202 can still be stepped up to the 5
volts to over drive the 3 volt rated DC motor 208. Alternatively,
the DC-DC step up converter 202 can provide a range of various
voltage values to drive the DC motor 208 at different ratings in
either the forward or the reverse directions.
[0030] In this embodiment, if the integral control electronics 210
failed and caused a direct short between the battery 206 and the DC
motor 208 with the reversed biased Zener diode 202 (or a reversed
biased Zener diode 202 in parallel with a Schottky diode 250), the
DC motor 208 would not operate in the forward direction (i.e.,
there would be no drug delivery), and would have only a fraction of
the rated torque in the rewind direction (or no rewinding if
sufficient friction is present in the drive mechanism). For
additional safety, alternative embodiments of the safety circuit
200 would include the DC-DC step up converter 202 such that it
would only be enabled by an additional internal signal S2 (shown in
dashed lines) from the control electronics 210. Thus, if the
control electronics 210 were to fail, there would be no enable
signal to provide the required step up voltage to drive the DC
motor 208 in a "run away" condition. In preferred embodiments, the
Zener diode 204 is contained within the DC motor package 212 (see
also FIG. 7) so that the DC motor 208 is protected independently of
the type of control electronics 210 to which the DC motor 208 is
connected. In alternative embodiments, the Zener diode 204 could be
contained within the control electronics and the electronics are
then connected to a conventional DC motor (see also FIG. 8). In
alternative embodiments, a second Zener may be used, which is
reversed with respect to the first diode and in series with the
first diode such that the DC motor operates similarly in both
directions. In the event of direct short to the DC motor in the
reverse direction, the battery voltage would not be enough to run
the motor 208 in either direction. In further alternatives, the
control electronics 210 may be separated from the DC-DC step up
converter 202 and provided as a discrete element that is placed
before or after the DC-DC step up converter 202.
[0031] In the first two embodiments, "run away" of the DC motor is
substantially prevented However, if the system were to fail such
that a short were maintained between the stepped up voltage from
the DC-DC converter to the DC motor and/or the Zener diode failed,
then the potential for motor "run away" exists with the above
embodiments.
[0032] FIG. 3 illustrates a safety circuit 300 in accordance with a
third embodiment of the present invention, which includes further
enhancements to provide protection against DC motor 302 "run away".
The safety circuit 300 includes additional electronics added to the
DC motor package (as shown in FIG. 7) that are independent of the
control electronics. Alternatively, the additional electronics may
be included in the control electronics (as shown in FIG. 8) or as a
separate set of control electronics (not shown). In preferred
embodiments, the control electronics must provide a specific signal
(at terminal 3) to the additional electronics to allow the DC motor
302 to operate. As shown in FIG. 3, the rated supply voltage from
the battery (not shown) is supplied to terminals 1 and 2 as a
negative and positive voltage potential, respectively, to control
operation of the DC motor 302 in the forward direction. However,
current will not pass through the DC motor 302 until a specific AC
signal (e.g., a 3 volt Peak-to-Peak Square wave at approximately 32
kHz--see FIGS. 9-11) is provided to terminal 3 and the safety
circuit 300 by the control electronics. This provides a second
independent system to control the operation of the DC motor 302.
For a "run away" to occur the control electronics must short the
battery to the power terminals 1 and 3, and must also provide an AC
signal to terminal 3 of the safety circuit 300. Thus, if a direct
short does occur between the battery and the power terminals 1 and
3 with the safety circuit 300, the DC motor 302 will not operate,
since the required AC signal at terminal 3 is not present.
Preferably, the safety circuit 300 uses two Schottky diodes 304 and
306 (e.g., BAT54SCT-ND from Zetex) and a FET 308 ((e.g., IRMLMS1902
from International Rectifier).
[0033] In operation, when the control electronics provide a
positive DC voltage potential at terminal 2, and a negative voltage
potential at terminal 1, the DC motor 302 will not operate since
the gate G of the FET 308 does not have a positive signal applied
to it derived from the input at terminal 3 of the safety circuit
300. In this situation, the gate G blocks the flow of current from
the drain D to the source S of the FET 308. DC flow through
terminal 3 is blocked by the capacitor C1. Thus, the DC motor 302
will not operate, if there is no AC signal applied to terminal 3 of
the safety circuit 300.
[0034] When an AC voltage potential signal (e.g., a 3 volt Peak to
Peak square wave at a frequency of approximately 32 kHz--see FIGS.
9-11) is applied to terminal 3 of the safety circuit 300, Schottky
diodes 304 and 306 rectify and double the signal to positively bias
the gate G, current then flows from the drain D to the source S of
the FET 308 and to terminal 1. This in turn drives the DC motor
302, which is connected to the positive DC voltage potential at
terminal 2. In alternative embodiments, a different number of
components, such as diodes, capacitors, resistors, or the like, may
be used. In addition, the selection of the type of FET, diode, size
of the voltage potentials on terminals 1, 2 and 3, the AC signal
type (including duration of peaks, waveform and frequency), may be
different, with the selection being dependent on motor nominal
operating voltage, system friction, tolerances, safety issues,
control electronics, or the like.
[0035] In preferred embodiments, the safety circuit 300 uses the
additional AC signal to control the forward operation of the DC
motor 302, since concerns over DC motor "run away" arise mainly
from the possibility of over delivery of a fluid due to the failure
of the safety circuit 300. There is less concern for the situation,
in which the fluid delivery system rewinds, since no fluid would be
delivered in that scenario. However, in alternative embodiments,
the drive system may also use an additional signal to control
operation of the DC motor in the rewind direction.
[0036] FIG. 4 illustrates a safety circuit 400 in accordance with a
fourth embodiment of the present invention. This safety circuit 400
is similar to the embodiment of FIG. 3, but utilizes a BJT 402
(FMMT 491ACT-ND from Zetex) instead of the FET 308, and an
additional Schottky diode 404 (e.g., BAT54CT-ND from Zetex).
[0037] FIGS. 5(a)-(c) illustrate a safety circuit 500 in accordance
with a fifth embodiment of the present invention. This safety
circuit 500 is also similar to the embodiment of FIG. 3, but
utilizes FET 502 (IRLM1902 from International Rectifier) instead of
the FET 308, and an additional Schottky diode 504 (e.g., BAT54CT-ND
from Zetex).
[0038] FIG. 6 illustrates a safety circuit 600 in accordance with a
sixth embodiment of the present invention. This safety circuit 600
is similar to the embodiment of FIG. 3, but utilizes FET 606
(IRLM1902 from International Rectifier) instead of the FET 308, and
an additional Schottky diode (e.g., BAT545CT-ND from Zetex). In
addition, the capacitors and resistors are selected to form a
bandpass filter to provide better noise isolation and circuit
performance. Performance of the safety circuit 600 as it provides
power to the DC motor 604 from a battery 602 is illustrated in
FIGS. 9-11.
[0039] FIG. 7 illustrates a perspective view of a DC motor package
700 that includes a safety circuit 702 within the package 700
holding a DC motor 704. An advantage to this configuration arises
from the fact that the DC motor 704 includes the safety circuit
702, which must be connected, and enabled, or the DC motor 704 will
not operate. This minimizes the possibility that a DC motor 704
will be improperly installed in a fluid delivery device by assuring
that an AC signal must be provided to the terminal input 3 on wire
706 to enable the DC motor 704 to operate. In alternative
embodiments, as shown in FIG. 8, the fluid delivery system 800
includes an additional safety circuit 802 (i.e., in addition to
other switches and controls found in the control circuitry), which
is contained within the control electronics 804. The control
electronics 804 are then connected to a standard, two-input DC
motor 806, without the need for an additional connection to the DC
motor 806. For instance, the safety circuit 802 operates a switch
808 to enable power to pass to and drive the DC motor 806.
[0040] FIGS. 9-11 illustrate operational waveforms for the safety
circuit 600 (see FIG. 6) as DC current is applied to the circuit.
As shown in FIG. 9, when DC current is applied to the DC motor 604
in graph section 902, no current is drawn since the AC enable
signal in graph section 908 is not present. When the AC signal is
applied in graph section 910, the DC current is quickly applied to
the DC motor 604 by the battery 602, as shown by the graph section
904. When the AC enable signal is removed, as shown in graph
section 912, the DC power supplied to the DC motor 604 is cutoff,
as shown in graph section 906. FIGS. 10 and 11 highlight and expand
portions of FIG. 9 to illustrate the AC signal used and the
response of the safety circuit 600. The illustrated AC signal is at
approximately 3 volts peak-to-peak at a frequency of approximately
32 kHz. However, in alternative embodiments, different shape
waveforms, such as saw tooth, sinusoidal, or the like may be used.
In addition, different voltage ranges may be used, with the
selection being dependent on the rated motor output and the
application in which the motor is being used. Further, higher or
lower frequencies may be utilized, with the selection be dependent
on the response characteristics of the safety circuit, noise, or
the like. The delays observed in FIGS. 10 and 11 are a result of
the smoothing and bandpass filters used in the safety circuit 600.
For instance it takes approximately 125 microseconds for the DC
motor 604 to respond after the AC signal is provided, and about 80
microseconds for the DC motor 604 to respond to termination of the
AC signal. One advantage of having the DC current ramp up and down
is that it minimizes the effects of voltage spikes and
electromagnetic interference.
[0041] While the description above refers to particular embodiments
of the present invention, it will be understood that many
modifications may be made without departing from the spirit
thereof. The accompanying claims are intended to cover such
modifications as would fall within the true scope and spirit of the
present invention.
[0042] The presently disclosed embodiments are therefore to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims,
rather than the foregoing description, and all changes which come
within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein.
* * * * *