System and method for controlling an ultrasonic tool

1. A method of controlling an ultrasonic surgical tool to reduce presence of a harmonic signal, the ultrasonic surgical tool including a handpiece and a tip coupled to the handpiece, the handpiece including a transducer for vibrating the tip upon receive of a drive signal, the method comprising:

obtaining a value of a capacitance of the handpiece;

driving the ultrasonic surgical tool with a first drive signal;

acquiring at least one characteristics of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the obtained capacitance value;

generating a cancellation signal based on the at least one acquired characteristic of the harmonic signal;

combining the first drive signal and the cancellation signal to produce a second drive signal; and

driving the ultrasonic surgical tool with the second drive signal such that presence of the harmonic signal resulting from driving the ultrasonic surgical tool with the second drive signal is reduced relative to presence of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal.

2. The method of claim 1 , further including

driving the ultrasonic surgical tool with a third drive signal;

generating current samples relating to the third drive signal;

analyzing a fast-Fourier transform of the current samples to acquire a characteristic of a second harmonic signal resulting from driving the ultrasonic surgical tool with the third drive signal;

generating a second cancellation signal based on the at least one acquired characteristic of the second harmonic signal;

combining the third drive signal and the second cancellation signal to produce the first drive signal; and

driving the ultrasonic surgical tool with the third drive signal such that presence of the second harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal is reduced relative to presence of the second harmonic signal resulting from driving the ultrasonic surgical tool with the third drive signal.

3. The method of claim 2 , wherein the current samples include a fundamental frequency of the third drive signal and a harmonic frequency of the second harmonic signal, and the at least one acquired characteristic of the second harmonic signal includes an amplitude of the current samples at the harmonic frequency.

4. The method of claim 3 , further comprising:

comparing the amplitude of the current samples at the harmonic frequency is less than a threshold; and

based on the comparison, acquiring the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the obtained capacitance value.

5. The method of claim 1 , further comprising:

calculating a current through the capacitance of the handpiece based on the capacitance value; and

acquiring the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the current through the capacitance of the handpiece.

6. The method of claim 5 , wherein the first drive signal includes a fundamental frequency, and further comprising:

filtering a harmonic frequency component from the current through the capacitance of the handpiece using the fundamental frequency; and

acquiring the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the harmonic frequency component of the current through the capacitance.

7. The method of claim 6 , further comprising:

measuring a voltage of the first drive signal; and

acquiring the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the harmonic frequency component of the current through the capacitance of the handpiece and the measured voltage.

8. The method of claim 1 , further comprising setting an amplitude of the cancellation signal so that a tip of the ultrasonic surgical tool exhibits desired non-linear vibrational behavior as a result of the ultrasonic surgical tool being driven with the second drive signal.

9. The method of claim 1 , wherein the at least one acquired characteristic includes a phase and a frequency of the harmonic signal.

10. The method of claim 9 , wherein the first drive signal includes a fundamental frequency component corresponding to a first resonant mode of the tip of the ultrasonic surgical tool, and further comprising:

generating the cancellation signal with a first frequency component and a second frequency component, the first frequency component having a first frequency corresponding to the frequency of the harmonic signal and a phase shift based on the phase of the harmonic signal, and the second frequency component having a second frequency corresponding to a second resonant mode of the tip; and

combining the first drive signal and the cancellation signal to produce the second drive signal, the second drive signal reducing the presence of the harmonic signal relative to the presence of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal and causing the tip to simultaneously vibrate in the first and second resonant modes of the tip.

11. A console for controlling an ultrasonic surgical tool to reduce presence of a harmonic signal, the ultrasonic surgical tool including a handpiece and a tip coupled to the handpiece, the handpiece including a transducer for vibrating the tip upon receive of a drive signal, the console comprising:

a controller configured to:

obtain a value of a capacitance of the handpiece;

drive the ultrasonic surgical tool with a first drive signal;

acquire at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the obtained capacitance value;

generate a cancellation signal based on the at least one acquired characteristic of the harmonic signal;

combine the first drive signal and the cancellation signal to produce a second drive signal; and

drive the ultrasonic surgical tool with the second drive signal such that presence of the harmonic signal resulting from driving the ultrasonic surgical tool with the second drive signal is reduced relative to presence of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal.

12. The console of claim 11 , wherein the controller is further configured to:

drive the ultrasonic surgical tool with a third drive signal;

generate current samples relating to the third drive signal;

analyzing a fast-Fourier transform of the current samples to acquire at least one characteristic of a second harmonic signal resulting from driving the ultrasonic surgical tool with the third drive signal;

generate a second cancellation signal based on the at least one characteristic of the second harmonic signal;

combine the third drive signal and the second cancellation signal to produce the first drive signal; and

drive the ultrasonic surgical tool with the first drive signal such that presence of the second harmonic signal resulting from application of the first drive signal is reduced relative to presence of the second harmonic signal resulting from application of the third drive signal.

13. The console of claim 12 , wherein the current samples include a fundamental frequency of the third drive signal and a harmonic frequency of the second harmonic signal, and the at least one acquired characteristic of the second harmonic signal includes an amplitude of the current samples at the harmonic frequency.

14. The console of claim 13 , wherein the controller is further configured to:

compare the amplitude of the current samples at the harmonic frequency is less than a threshold; and

based on the comparison, acquire the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the obtained capacitance value.

15. The console of claim 12 , wherein the controller is configured to:

calculate a current through the capacitance of the handpiece based on the capacitance value; and

acquire the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the current through the capacitance of the handpiece.

16. The console of claim 15 , wherein the first drive signal includes a fundamental frequency, and the controller is further configured to:

filter a harmonic frequency component from the current through the capacitance of the handpiece using the fundamental frequency; and

acquire the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the harmonic frequency component of the current through the capacitance.

17. The console of claim 16 , wherein the controller is configured to:

measure a voltage of the first drive signal; and

acquire the at least one characteristic of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal based on the harmonic frequency component of the current through the capacitance of the handpiece and the measured voltage.

18. The console of claim 12 , wherein the controller is further configured to set an amplitude of the cancellation signal so that a tip of the ultrasonic surgical tool exhibits desired non-linear vibrational behavior as a result of the ultrasonic surgical tool being driven with the second drive signal.

19. The console of claim 12 , wherein the at least one acquired characteristic includes a phase and a frequency of the harmonic signal.

20. The console of claim 19 , wherein the first drive signal includes a fundamental frequency component corresponding to a first resonant mode of the tip of the ultrasonic surgical tool, and comprising:

generating the cancellation signal with a first frequency component and a second frequency component, the first frequency component having a first frequency corresponding to the frequency of the harmonic signal and a phase shift based on the phase of the harmonic signal, and the second frequency component having a second frequency corresponding to a second resonant mode of the tip; and

combining the first drive signal and the cancellation signal to produce the second drive signal, the second drive signal reducing the presence of the harmonic signal relative to the presence of the harmonic signal resulting from driving the ultrasonic surgical tool with the first drive signal and causing the tip to simultaneously vibrate in the first and second resonant modes of the tip.