Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Reexamination Certificate
1999-06-17
2001-07-10
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
C361S033000, C318S434000, C323S276000
Reexamination Certificate
active
06259587
ABSTRACT:
FIELD OF THE INVENTION
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
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.
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.
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.
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
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.
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.
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.
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.
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.
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Causey James D.
Renger Herman Lee
Sheldon Moberg
Huynh Kim
MiniMed Inc.
MiniMed Inc.
Sherry Michael J.
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