Method and device for driving a piezoelectric device

1. A driving device comprising:

a sense load, the sense load being operably couplable to a piezoelectric device operable by a switching voltage, the sensed voltage across the sense load having a phase corresponding to a phase of the piezoelectric device,

the driving device being configured to:

determine whether the sensed voltage is in phase or out of phase relative to the switching voltage;

responsive to the sensed voltage being in phase relative to the switching voltage when the switching voltage is provided at an operating frequency, make a change to the operating frequency by a predetermined first value; and

responsive to the sensed voltage being out of phase relative to the switching voltage when the switching voltage is provided at the operating frequency, make a change to the operating frequency by a predetermined second value,

wherein if the predetermined first value corresponds to an increase in value of the operating frequency, the predetermined second value corresponds to a decrease in value of the operating frequency, and

wherein if the predetermined first value corresponds to a decrease in value of the operating frequency, the predetermined second value corresponds to an increase in value of the operating frequency.

2. The driving device as recited in claim 1 , further configured to perform the following repeatedly:

determine whether the sensed voltage is in phase or out of phase relative to the switching voltage; and

make a corresponding change to the operating frequency by one of the predetermined first value and the predetermined second value.

3. The driving device as recited in claim 2 , further configured to make the corresponding change to the operating frequency periodically according to a sampling frequency, such that the operating frequency fluctuates within a target frequency band, wherein the target frequency band is a predefined range of frequencies including at least one resonant frequency of the piezoelectric device.

4. The driving device as recited in claim 3 , wherein the sampling frequency is defined by selected transitions of the switching voltage.

5. The driving device as recited in claim 4 , further comprising:

an alternator coupled to the piezoelectric device, the alternator being configured to provide the switching voltage to drive the piezoelectric device; and

an analog digital converter configured to convert the switching voltage to a switching voltage digital signal; and

a logic device configured such that the selected transitions between two states of the switching voltage digital signal triggers the sensing of the sensed voltage and the corresponding change to the operating frequency by one of the predetermined first value and the predetermined second value.

6. The driving device as recited in claim 5 , wherein the alternator comprises a full-bridge configured to produce the switching voltage in the form of a square waveform.

7. The driving device as recited in claim 5 , wherein the alternator is configured in a push-pull configuration such that the switching voltage is a square waveform.

8. The driving device as recited in claim 7 , wherein the sense load is a resistive element.

9. The driving device as recited in claim 1 , further configured to:

determine a first occurrence when the operating frequency is within a target frequency band, the target frequency band being a predefined range of frequencies including at least one resonant frequency of the piezoelectric device;

responsive to the first occurrence, repeatedly perform the following:

determine whether the sensed voltage is in phase or out of phase relative to the switching voltage; and

make a corresponding change to the operating frequency by one of the predetermined first value and the predetermined second value.

10. The driving device as recited in claim 9 , further configured to make the corresponding change to the operating frequency such that the operating frequency fluctuates within the target frequency band.

11. The driving device as recited in claim 10 , wherein the corresponding changes to the operating frequency are made at times corresponding to selected transitions of the switching voltage.

12. The driving device as recited in claim 11 , wherein each of the predetermined first value and the predetermined second value is smaller than a range of the target frequency band.

13. The driving device as recited in claim 12 , wherein during operation of the driving device, each of the predetermined first value and the predetermined second value is independent of a difference in value between the operating frequency and either one of an upper limit of the target frequency band and a lower limit of the target frequency band.

14. The driving device as recited in claim 12 , wherein during operation of the driving device, each of the predetermined first value and the predetermined second value is independent of a difference in value between the operating frequency and the at least one resonant frequency.

15. The driving device as recited in claim 1 , wherein if an initial operating frequency of the switching voltage is higher than a target frequency of the piezoelectric device, the predetermined first value corresponds to the increase in value of the operating frequency, and the predetermined second value corresponds to the decrease in value of the operating frequency.

16. The driving device as recited in claim 1 , wherein if an initial operating frequency of the switching voltage is lower than a target frequency of the piezoelectric device, the predetermined first value corresponds to the decrease in value of the operating frequency, and the predetermined second value corresponds to the increase in value of the operating frequency.

17. An apparatus, comprising:

a piezoelectric device, the piezoelectric device being operable by the operating frequency; and

the driving device as recited in any one of claims 1 to 16 , the sense load of the driving device being coupled to the piezoelectric device, the driving device being configured to operate the piezoelectric device at the operating frequency, wherein the operating frequency is configured to be responsive to whether the sensed voltage is in phase or out of phase with the switching frequency.

18. The apparatus as recited in claim 17 , wherein the driving device is configured to operate the piezoelectric device at the operating frequency to track a target frequency.