Piezoelectric devices and methods and circuits for driving same

• US 7,312,554 B2
• Filed: 04/02/2004
• Issued: 12/25/2007
• Est. Priority Date: 04/02/2004
• Status: Expired due to Fees

• Current Assignee: Par Technology Corporation
• Original Assignee: Adaptivenergy, LLC
• Inventors: Vogeley, James
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US10/815,975
• Publication Number:
  US 20050219302A1
• Time in Patent Office: 1,362 Days
• Field of Search: 310/316.01, 310/317
• US Class Current: 310/317
• CPC Class Codes: A61M 2205/0294 Piezoelectric materials
• CPC Class Codes: A61M 5/142 Pressure infusion, e.g. using pumps
• CPC Class Codes: A61M 5/16831 Monitoring, detecting, signalling or eliminating infusion flow anomalies low-level float-valves causing cut-off A61M5/40; indicating or recording presence, absence or direction of flow in general G01P13/0066
• CPC Class Codes: A61M 5/16877 Adjusting flow; Devices for setting a flow rate
• CPC Class Codes: F04B 43/046 with piezoelectric drive
• CPC Class Codes: H10N 30/802 Circuitry or processes for operating piezoelectric or electrostrictive devices not otherwise provided for, e.g. drive circuits

Abstract

A drive circuit (18) senses a parameter of a piezoelectric actuator (14) operating in a device (10) and adjusts a drive signal of the piezoelectric actuator in accordance with the parameter. The drive circuit comprises a controller (100) which controls a drive signal applied to the piezoelectric actuator (14); a feedback monitor (122) which obtains a feedback signal from the piezoelectric actuator while the piezoelectric actuator works; and, a processor (116) which uses the feedback signal to determine the parameter of the piezoelectric actuator. In one example mode, the parameter of the piezoelectric actuator which is determined by the piezoelectric actuator drive circuit is the capacitance or dielectric constant of the piezoelectric actuator. In other example modes, the parameter of the piezoelectric actuator which is determined by the piezoelectric actuator drive circuit is impedance or resonant frequency of the piezoelectric actuator.

Claims

1. A method for determining a parameter for a piezoelectric actuator, the method comprising:

applying a drive signal to the piezoelectric actuator;

controlling the drive signal so that an ascertainable electrical charge is applied to the piezoelectric actuator;

operating the piezoelectric actuator;

obtaining a feedback signal from the piezoelectric actuator;

obtaining a voltage value from the feedback signal;

using the electrical charge and the voltage value from the feedback signal to determine capacitance of the piezoelectric actuator.

2. The method of claim 1 wherein the step of operating the piezoelectric actuator comprises using the piezoelectric actuator to pump fluid in a pump.

3. The method of claim 1, further comprising:

deriving the drive signal from a pulse width modulated signal;

controlling pulse widths of the pulse width modulated signal so that the ascertainable electrical charge is applied to the piezoelectric actuator.

4. The method of claim 1, further comprising subsequently using the capacitance of the piezoelectric actuator to control the drive signal to the piezoelectric actuator.

5. The method of claim 4, further comprising subsequently using the capacitance of the piezoelectric actuator to control pulse widths of a pulse width modulated signal from which the drive signal is derived.

6. A method for determining a parameter for a piezoelectric actuator, the method comprising:

varying a drive signal applied to the piezoelectric actuator;

operating the piezoelectric actuator;

monitoring a feedback signal from the piezoelectric actuator as the drive signal is varied for an “

echo”

;

determining a resonant frequency of the piezoelectric actuator as an inverse of a period of the echo.

7. The method of claim 6, further comprising varying the drive signal through a step function.

8. A drive circuit for sensing capacitance of a piezoelectric actuator operating in a device and for adjusting a drive signal of the piezoelectric actuator in accordance with the capacitance, wherein the drive circuit comprises:

a controller for controlling a drive signal applied to the piezoelectric actuator;

a feedback monitor for obtaining a feedback signal from the piezoelectric actuator while the piezoelectric actuator operates;

a processor for using the feedback signal to determine the capacitance of the piezoelectric actuator;

wherein the controller controls the drive signal so that an ascertainable electrical charge is applied to the piezoelectric actuator;

wherein the feedback monitor obtains a voltage value from the feedback signal; and

wherein the processor uses the electrical charge and the voltage value from the feedback signal to determine the capacitance of the piezoelectric actuator.

9. The drive circuit of claim 8, wherein the device is a pump and wherein the piezoelectric actuator operates to pump fluid in the pump.

10. The apparatus of claim 8, wherein the drive circuit derives the drive signal from a pulse width modulated signal;

and wherein the controller controls pulse widths of the pulse width modulated signal so that the ascertainable electrical charge is applied to the piezoelectric actuator.

11. The apparatus of claim 8, wherein the controller subsequently uses the capacitance of the piezoelectric actuator to control the drive signal to the piezoelectric actuator.

12. The apparatus of claim 11, wherein the controller subsequently uses the capacitance of the piezoelectric actuator to control pulse widths of a pulse width modulated signal from which the drive signal is derived.

13. A drive circuit for sensing a parameter of a piezoelectric actuator operating in a device and for adjusting a drive signal of the piezoelectric actuator in accordance with the parameter, wherein the drive circuit comprises:

a controller for controlling a drive signal applied to the piezoelectric actuator;

a feedback monitor for obtaining a feedback signal from the piezoelectric actuator while the piezoelectric actuator operates;

wherein the feedback monitor obtains the feedback signal as the drive signal is varied for an “

echo”

;

a processor for using the feedback signal to determine the a resonant frequency of the piezoelectric actuator as an inverse of a period of the echo.

14. The apparatus of claim 13, wherein the controller varies the drive signal through a step function.

15. A drive circuit for sensing capacitance of a piezoelectric actuator operating in a device and for adjusting a drive signal of the piezoelectric actuator in accordance with the capacitance, wherein the drive circuit comprises:

means for applying a drive signal to the piezoelectric actuator;

means for obtaining a feedback signal from the piezoelectric actuator while the piezoelectric actuator operates;

means for using the feedback signal to determine a capacitance of the piezoelectric actuator;

wherein the means for applying controls the drive signal so that an ascertainable electrical charge is applied to the piezoelectric actuator;

wherein means for obtaining obtains a voltage value from the feedback signal; and

wherein the means for using uses the electrical charge and the voltage value from the feedback signal to determine the capacitance of the piezoelectric actuator.

16. The apparatus of claim 15, wherein the means for using determines the resonant frequency of the piezoelectric actuator as corresponding to the frequency in the range that had a minimum peak voltage value from the feedback signal.

17. A drive circuit for sensing a parameter of a piezoelectric actuator operating in a device and for adjusting a drive signal of the piezoelectric actuator in accordance with the parameter, wherein the drive circuit comprises:

means for applying and varying a drive signal to the piezoelectric actuator;

means for obtaining a feedback signal from the piezoelectric actuator while the piezoelectric actuator operates;

wherein means for obtaining obtains the feedback signal as the drive signal is varied for an “

echo”

;

means for using the feedback signal to determine a resonant frequency of the piezoelectric actuator as an inverse of a period of the echo.

18. A piezoelectrically-actuated device comprising:

a piezoelectric actuator which is responsive to a drive signal for pumping fluid between the inlet and outlet; and

a drive circuit for sensing a capacitance of the piezoelectric actuator and for adjusting a drive signal of the piezoelectric actuator in accordance with the capacitance, wherein the drive circuit comprises;

a controller for applying a drive signal to the piezoelectric actuator;

a feedback monitor for obtaining a feedback signal from the piezoelectric actuator while the piezoelectric actuator operates;

a processor for using the feedback signal to determine the capacitance of the piezoelectric actuator;

wherein the controller controls the drive signal so that an ascertainable electrical charge is applied to the piezoelectric actuator;

wherein the feedback monitor obtains a voltage value from the feedback signal; and

wherein the processor uses the electrical charge and the voltage value from the feedback signal to determine the capacitance of the piezoelectric actuator.

19. The apparatus of claim 18, wherein the device is a pump having a pump body for at least partially defining a pumping chamber having an inlet and an outlet which communicate with the pumping chamber, and wherein the piezoelectric actuator pumps fluid between the inlet and outlet.

20. The apparatus of claim 18, wherein the drive circuit derives the drive signal from a pulse width modulated signal;

and wherein the controller controls pulse widths of the pulse width modulated signal so that the ascertainable electrical charge is applied to the piezoelectric actuator.

21. The apparatus of claim 18, wherein the controller subsequently uses the capacitance of the piezoelectric actuator to control the drive signal to the piezoelectric actuator.

22. The apparatus of claim 21, wherein the controller subsequently uses the capacitance of the piezoelectric actuator to control pulse widths of a pulse width modulated signal from which the drive signal is derived.

23. The apparatus of claim 18, wherein the controller varies the drive signal through a range of excitation frequencies;

and wherein the output monitor obtains a voltage value from the feedback signal for each of the excitation frequencies; and

wherein the processor determines a resonant frequency of the piezoelectric actuator as corresponding to a frequency in the range that had a minimum voltage value from the feedback signal.

24. The apparatus of claim 23, wherein the processor determines the resonant frequency of the piezoelectric actuator as corresponding to the frequency in the range that had a minimum peak voltage value from the feedback signal.

25. A piezoelectrically-actuated device comprising:

a piezoelectric actuator which is responsive to a drive signal for pumping fluid between the inlet and outlet; and

a drive circuit for sensing a parameter of the piezoelectric actuator and for adjusting a drive signal of the piezoelectric actuator in accordance with the parameter, wherein the drive circuit comprises;

a controller for applying a drive signal to the piezoelectric actuator;

a feedback monitor for obtaining a feedback signal from the piezoelectric actuator while the piezoelectric actuator operates;

a processor for using the feedback signal to determine the parameter of the piezoelectric actuator;

wherein the controller varies the drive signal;

wherein the feedback monitor

obtains the feedback signal as the drive signal is varied for an “

echo”

; and

wherein the processor determines a resonant frequency of the piezoelectric actuator as an inverse of a period of the echo.

26. The apparatus of claim 25, wherein the controller varies the drive signal through a step function.