Flow Rate Accuracy of a Fluidic Delivery System

Abstract

Improving the accuracy of the flow rate of a valve in a fluidic delivery device in which a desired flow rate may be achieved by varying the duty cycle of the valve. The flow rate of fluid delivery from the valve over its lifetime is stabilized by minimizing the voltage OPENING time of the valve to account for valve and piezoelectric actuator drift. Also, the valve OPENING time of one or more fluidic parameters that impact on the flow rate delivery by the valve and differ among fluidic delivery devices is compensated to optimize the flow rate accuracy.

1 . A valve assembly with variable flow rate of fluid delivery, comprising:
 a power supply;   charge pump circuitry powered by the power supply; wherein the charge pump circuitry includes at least one switch, at least one inductor and at least one diode;   a piezoelectric actuator charged by the charge pump circuitry, the charge applied across the piezoelectric actuator reaching a predetermined voltage threshold over a predetermined rise time; and   a valve transitioning from a CLOSED state to an OPENED state when the charge applied across the piezoelectric actuator exceeds the predetermined voltage threshold; the valve transitioning from the OPENED state to the CLOSED state by discharging the applied charge across the piezoelectric actuator; the valve assembly having a duty cycle.   
     
     
         2 . A method for varying a flow rate of fluid delivery, comprising the steps of:
 applying a charge across a piezoelectric actuator via charge pump circuitry powered by a power supply, a valve transitioning from a CLOSED state to an OPENED state when the charge applied across the piezoelectric actuator exceeds a predetermined voltage threshold; wherein the charge pump circuitry includes at least one switch, at least one inductor and at least one diode;   discharging the applied charge across the piezoelectric actuator to transition the valve from the OPENED state to the CLOSED state;   varying the flow rate of the fluid delivery from the valve by adjusting a duty cycle of the valve.   
     
     
         3 . The valve assembly in accordance with claim I, wherein the duty cycle is adjusted to vary the flow rate; and the duty cycle represents a ratio of valve OPENED time to valve CLOSED time. 
     
     
         4 . The method in accordance with  claim 2 , wherein the duty cycle represents a ratio of valve OPENED time to valve CLOSED time. 
     
     
         5 . The valve assembly in accordance with  claim 1 , wherein the at least one switch is a transistor. 
     
     
         6 . The method in accordance with  claim 2 , wherein the at least one switch is a transistor.