Flow rate accuracy of a fluidic delivery system
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 optimized flow rate accuracy over its lifetime, comprising:
a power supply;
charge pump circuitry powered by the power supply;
a piezoelectric actuator charged by the charge pump circuitry, the charge applied across the piezoelectric actuator reaching a predetermined threshold voltage over a rise time; and
a valve transitioning from a CLOSED state to an OPEN state when the piezoelectric actuator exceeds the predetermined threshold voltage; the charge pump circuitry receives as input a PWM charge input signal subdivided into a plurality of PWM units, together comprising a PWM group, each of the plural PWM units having its own associated PWM parameters applied to that PWM unit so as to minimize a valve OPENING time and optimize the flow rate accuracy over the lifetime of the valve.
2. The valve assembly in accordance with claim 1 , wherein each of the plural PWM units in the PWM group are equal in duration.
3. The valve assembly in accordance with claim 1 , wherein the plural PWM units in the PWM group are not all equal in duration.
4. The valve assembly in accordance with claim 1 , wherein the charge pump circuitry comprises a transistor electrically connected to an inductor.
5. The valve assembly in accordance with claim 4 , the PWM charge pump input signal being generated by a processor is received as input to the transistor for establishing transistor ON time when the PWM charge pump input signal is high and transistor OFF time when the PWM charge pump input signal is low.
6. The valve assembly in accordance with claim 5 , wherein when the power supply is substantially constant, among the plural PWM units in a particular PWM group, the transistor ON time remains constant, while the transistor OFF time is varied over time due to increasing charge built up across the piezoelectric actuator.
7. The valve assembly in accordance with claim 6 , wherein with depleting voltage supplied by the power supply over time, among the plural PWM units in a particular PWM group, the transistor OFF time remains constant, while the transistor ON time is varied over time to compensate for the depleting voltage supplied by the power supply.
8. The valve assembly in accordance with claim 5 , wherein with depleting voltage supplied by the power supply over time, among the plural PWM units in a particular PWM group, the transistor OFF time remains constant, while the transistor ON time is varied over time to compensate for the depleting voltage supplied by the power supply.