System and method of differential pressure control of a reciprocating electrokinetic pump

Abstract

A method of controlling the output of an electrokinetic pump to deliver a target stroke volume includes applying a pump drive signal to the electrokinetic pump for a pump stroke time duration and then determining a volume of a delivery fluid pumped. Then, comparing the volume of the delivery fluid pumped to the target stroke volume; generate a new time interval for applying the pump drive signal. Then apply the pump drive signal to the electrokinetic pump for the new time interval. A system for delivery of fluid includes an electrokinetic pump under the control of an electronic controller. The electronic controller contains computer readable instructions to determine an output of the electrokinetic pump and then generate a stroke time delivery adjustment for precise pumping schemes.

1 . A method of controlling the output of an electrokinetic pump to deliver a target stroke volume, comprising:
 Applying a pump drive signal to the electrokinetic pump for a pump stroke time duration is about one second;   Determining a volume of a delivery fluid pumped during the pump stroke time duration;   Comparing the volume of the delivery fluid pumped to the target stroke volume;   Generating a new time interval for applying the pump drive signal to the electrokinetic pump based upon the comparing step; and   Applying the pump drive signal to the electrokinetic pump for the new time interval.   
     
     
         2 . The method of controlling the output of an electrokinetic pump according to  claim 1  wherein the difference between the new time interval and the pump stroke time duration is no more than 100 ms. 
     
     
         3 . The method of controlling the output of an electrokinetic pump according to  claim 1  wherein the new time interval is a time duration that maintains the electrokinetic pump within the reversible faradaic limits of the electrokinetic pump components. 
     
     
         4 . The method of controlling the output of an electrokinetic pump according to  claim 1  wherein the pump stroke time duration is selected to remain within the reversible faradic operating parameters of the electrokinetic pumps. 
     
     
         5 . The method of  claim 1  wherein the generating a new time interval is based in part on a temperature compensation related to a delivery fluid temperature. 
     
     
         6 . The method of controlling the output of an electrokinetic pump according to  claim 1  wherein the determining a volume step includes the use of a differential pressure flow technique. 
     
     
         7 . The method of controlling the output of an electrokinetic pump according to  claim 6  wherein the differential pressure flow technique is based on an input from at least one pressure sensor in communication with the pump outlet. 
     
     
         8 . The method of controlling the output of an electrokinetic pump according to  claim 6  wherein the differential pressure flow technique uses a flow restrictor and is based on an input from at least one pressure sensor. 
     
     
         9 . The method of  claim 6  wherein the determining the volume is based on a comparison of two differential pressure signals after the initial applying a pump drive signal step. 
     
     
         10 . The method of  claim 6  wherein the determining the volume is based on an integral of a pressure sensor during the applying a pump drive signal step. 
     
     
         11 . The method of  claim 6  wherein the determining the volume is based on an integral a difference between two pressure sensors during the applying a pump drive signal step. 
     
     
         12 . The method of  claim 6  wherein the determining the volume is based on an estimated delivery condition read from a pressure sensor during the applying a pump drive signal step. 
     
     
         13 . The method of  claim 12  wherein the duration of the applying a pump drive signal is adjusted based on the estimated delivery condition read from a pressure sensor during the applying a pump drive signal step. 
     
     
         14 . The method of controlling the output of an electrokinetic pump according to  claim 6  wherein the differential pressure flow measurement technique uses input from a pair of pressure sensors. 
     
     
         15 . The method of controlling the output of an electrokinetic pump according to  claim 9  wherein one of the pressure sensors is in communication with the pump outlet. 
     
     
         16 . The method of controlling the output of an electrokinetic pump according to  claim 9  wherein one of the pressure sensors is positioned to indicate backpressure acting on the output of the electrokinetic pump. 
     
     
         17 . The method of controlling the output of an electrokinetic pump according to  claim 1  further comprising: before the applying a pump drive signal for the new time interval, applying a pump drive signal of opposite polarity to the pump drive signal used in the initial applying a pump drive signal step, wherein the duration of the applying a pump drive signal of opposite polarity is the same as the pump stroke time duration. 
     
     
         18 . The method of controlling the output of an electrokinetic pump according to  claim 1  further comprising: after applying the pump drive signal for the new time interval, applying a pump drive signal of opposite polarity to the pump drive signal used in the applying a pump drive signal for the new time interval step, wherein the duration of the applying a pump drive signal of opposite polarity is the same as the new time interval duration. 
     
     
         19 . The method of controlling the output of an electrokinetic pump according to  claim 1  wherein the pump drive signal during the applying steps is a constant voltage. 
     
     
         20 . The method of controlling the output of an electrokinetic pump according to  claim 1  wherein the pump drive signal during the applying steps is a constant current. 
     
     
         21 . The method of  claim 1  wherein the duration of the applying a pump drive signal is adjusted based on the estimated delivery condition read from a pressure sensor just prior to the applying a pump drive signal step. 
     
     
         22 . The method of  claim 1  further comprising: decrementing a total volume delivery counter according to the result of the determining a volume of a delivery fluid pumped step. 
     
     
         23 . The method of  claim 1  further comprising: incrementing a total volume delivery counter according to the result of the determining a volume of a delivery fluid pumped step. 
     
     
         24 . The method of  claim 23  further comprising: generating a pump stop signal when the result of the determining a volume of a delivery fluid pumped step is the last delivery increment of the total volume delivery counter. 
     
     
         25 . The method of  claim 23  further comprising: generating a pump stop signal when the result of the determining a volume of a delivery fluid pumped step is the last delivery decrement of the total volume delivery counter. 
     
     
         26 . A system for delivery of fluid, comprising:
 An electrokinetic pump configured to deflect a diaphragm in an outlet chamber, the outlet chamber having an inlet and an outlet;   A first check valve in communication with the inlet;   A second check valve in communication with the outlet;   A pressure sensor positioned to indicate a pressure within the system between the first check valve and the second check valve; and   A computer controller in communication with the electrokinetic pump and the pressure sensor containing computer readable instructions to determine an output of the electrokinetic pump based at least in part on a signal from the pressure sensor and to generate a stroke time delivery adjustment after each deflection of the diaphragm into the outlet chamber.   
     
     
         27 . The system of  claim 26  further comprising: another pressure sensor and a flow restrictor wherein, the pressure sensor is positioned to indicate the pressure of the outlet chamber, the flow restrictor is positioned between the outlet chamber outlet and the second check valve and the another pressure sensor is positioned to indicate a pressure within the system between the flow restrictor and the second check valve. 
     
     
         28 . The system of  claim 26  further comprising: a reservoir containing a delivery fluid and having an outlet in communication with the outlet chamber inlet. 
     
     
         29 . The system of  claim 26  further comprising: a delivery conduit in communication with the outlet chamber outlet. 
     
     
         30 . The system of  claim 26  further comprising: a flow restrictor wherein, the flow restrictor is positioned between the outlet chamber outlet and the second check valve and the pressure sensor is positioned to indicate a pressure within the system between the flow restrictor and the outlet chamber. 
     
     
         31 . The system of  claim 26  further comprising: another pressure sensor and a flow restrictor wherein, the flow restrictor is positioned between the second check valve and a delivery conduit and the pressure sensor is positioned to indicate the pressure downstream of the flow restrictor in the delivery conduit. 
     
     
         32 . The system of  claim 26  the system further comprising: a user input device in communication with the computer controller wherein the computer controller is adapted and configured to provide and receive signals from the user input device.