Ejector devices, methods, drivers, and circuits therefor
View Patent ↗In a piezoelectric ejector assembly, a piezoelectric actuator is attached to an ejector mechanism, while a drive signal generator and a controller are coupled to the actuator. The drive signal generator is configured to generate a drive signal for driving the actuator to oscillate the ejector assembly. The controller is configured to control the drive signal generator to drive the actuator at a resonant frequency of the ejector assembly, and an auto-tuning circuit is provided to define the optimum drive signal frequency.
1. A piezoelectric ejector device for ejecting droplets of fluid, comprising an ejector mechanism including a piezoelectric actuator and a droplet generator plate, and driver electronics for driving the actuator, the electronics including a microcontroller to perform auto-tuning of the ejector mechanism by identifying and setting an optimum spray frequency; wherein auto-tuning involves the generation of at least one cycle of each of a range of drive signal frequencies over a predefined frequency range and obtaining time-energy product (TEP) feedback from a decay signal emitted by the actuator following each frequency generation.
2. The piezoelectric ejector device of claim 1 , wherein multiple separate cycles are generated for each frequency in quick succession in order to charge a capacitor in an integrating peak detector with the same amplitude coefficient (voltage) for each cycle, the amplitude coefficient being recorded and the procedure repeated at the next frequency.
3. The piezoelectric ejector device of claim 1 , further comprising at least one numerically controlled oscillator (NCO) for incrementing the frequencies over the predefined frequency range.
4. The piezoelectric ejector device of claim 1 , wherein power is supplied to the actuator from at least one battery, the microcontroller being configured to monitor the battery voltage and compensate for gradual depletion of the battery.
5. The piezoelectric ejector device of claim 1 , wherein power is supplied to the actuator from at least one battery and the driver electronics includes a boost circuit for charging a boost rail to a desired voltage for driving the actuator.
6. The piezoelectric ejector device of claim 5 , wherein the boost rail is charged to a constant voltage by using sampling feedback from an analog-to-digital converter (ADC).
7. The piezoelectric ejector device of claim 6 , further comprising at least one inductor to define a resonant tank with the piezoelectric actuator, which acts as a capacitor.
8. The piezoelectric ejector device of claim 2 , wherein the microcontroller is configured to maintain a constant voltage at each drive signal frequency during auto-tuning, using the ADC to monitor the drive voltage to ensure a drive voltage that is high enough to properly drive energy into the piezoelectric actuator while maintaining the voltage at a low enough level to avoid unwanted ejection.
9. The piezoelectric ejector device of claim 7 , wherein the boost circuit is configured to act as a charge pump to raise the piezoelectric actuator voltage to a prescribed voltage after auto-tuning.
10. The piezoelectric ejector device of claim 9 , wherein the driver electronics includes a drive circuit comprising two NCOs, logic for combining signals from the two NCOs to define a combined signal, a complementary waveform generator (CWG) for receiving the combined signal, a level shifter circuit connected to the CWG, and a full bridge connected to the level shifter and operable to drive the piezoelectric actuator with a drive signal for ejecting the fluid.
11. The piezoelectric ejector device of claim 10 , wherein the microcontroller is configured to constantly adjust the boost duty cycle to balance the boost output voltage and thus the amplification in the resonant tank to provide a constant voltage drive.
12. The piezoelectric ejector device of claim 10 , wherein the microcontroller is configured to charge the boost rail up and then turn the drive circuit on causing massive overshoot for high velocity spray to provide an overshoot drive.
13. The piezoelectric ejector device of claim 10 , wherein the microcontroller is configured to keep the drive signal at a constant frequency.
14. The piezoelectric ejector device of claim 10 , wherein the microcontroller is configured to dither the drive signal by sweeping the frequency of the drive signal over a defined bandwidth.
15. The piezoelectric ejector device of claim 10 , wherein the logic combines signals from the two NCO to define a combined signal that disables the CWG periodically to provide two anti-phase square waves with adjustable dead bands to the level shifter circuit.