Variable Volume, Shape Memory Actuated Insulin Dispensing Pump

Abstract

A portable pumping system provides insulin or other drugs to a user. A shape memory element is used to actuate the pump and an intelligent system controls the actuator in order to minimize stresses within the system and provide accurate and reliable dosage delivery. The control system utilizes various types of feedback to monitor and optimize the position of the pumping mechanisms. Physical design aspects also minimize stress and the combination of the physical design aspects and the intelligent operation of the system results in a lightweight and cost effective pump that may be used in a disposable fashion if desired.

1 . A pumping system comprising:
 a chamber;   a piston within the chamber;   a shape memory element within the chamber that changes length when a current flows through the element,   the element moving the piston between a first and second physical limit, such that when the piston is at the first limit the chamber is occupied with liquid and when the chamber is at the second limit the chamber is substantially discharged of liquid; and   a first switch at the first limit that indicates if the piston is at the first limit.   
     
     
         2 . The pumping system of  claim 1  further comprising a second switch at the second limit that indicates if the piston is at the second limit. 
     
     
         3 . The pumping system of  claim 2  further comprising circuitry that senses the condition of the first and second switches. 
     
     
         4 . The pumping system of  claim 3  wherein the circuitry is operable to detect a pump malfunction if the piston is not at the first or second limit. 
     
     
         5 . A method of dispensing liquid, comprising:
 drawing liquid into a pumping chamber by causing a shape memory material to contract and move a piston;   expelling liquid from the pumping chamber by causing the shape memory material to relax and move the piston;   monitoring the position of the piston; and   controlling the position of the piston based upon the monitored position.   
     
     
         6 . The method of  claim 5  wherein monitoring the position of the piston comprises sensing the condition of one or more switches selectively activated depending upon the position of the piston. 
     
     
         7 . The method of  claim 5  wherein monitoring the position of the piston comprises utilizing encoding indicia provided on the piston. 
     
     
         8 . The method of  claim 5  wherein monitoring the position of the piston comprises measuring the strength of a magnetic field. 
     
     
         9 . The method of  claim 5  wherein monitoring the position of the piston comprises measuring the capacitance between a stationary conductive element and a conductive element that moves with the piston. 
     
     
         10 - 14 . (canceled) 
     
     
         15 . A pump comprising:
 a reservoir having a maximum volume;   an actuator comprising a shape memory alloy that moves a plunger, the plunger displacing liquid from the reservoir; and   a control system that utilizes linear feedback to sense the position of the actuator and to manipulate the actuator to provide doses of variable volume less than the maximum volume.   
     
     
         16 . The pump of  claim 15  wherein the control system comprises a microprocessor. 
     
     
         17 . The pump of  claim 15  wherein the control system comprises means for position detection. 
     
     
         18 . The pump of  claim 15  wherein the control system determines if the pump is primed or not. 
     
     
         19 . The pump of  claim 18  wherein if the pump is not primed the control system creates a warning. 
     
     
         20 - 27 . (canceled)