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 method comprising:

driving the ultrasonic surgical tool with a first drive signal;

increasing a mechanical current of the ultrasonic surgical tool;

determining whether the increased mechanical current causes the harmonic signal to reach a predetermined level;

responsive to determining that the increased mechanical current does not cause the harmonic signal to reach the predetermined level, continuing to drive the ultrasonic surgical tool with the first drive signal; and

responsive to determining that the increased mechanical current causes the harmonic signal to reach the predetermined level:

acquiring characteristics of the harmonic signal resulting from the increased mechanical current, the characteristics being at least a frequency and a phase of the harmonic signal;

generating a cancellation signal with a frequency similar to the frequency of the harmonic signal and a phase that is shifted in relation to the phase of the harmonic signal;

combining the first drive signal and the cancellation signal to produce a second drive signal, the second drive signal being sinusoidal; 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 wherein acquiring the characteristics of the harmonic signal is further defined as generating current and voltage samples relating to the first drive signal, wherein the characteristics of the harmonic signal are present in the generated current and voltage samples.

3. The method of claim 2 wherein acquiring the characteristics of the harmonic signal is further defined as analyzing a fast-Fourier transform of the generated current and voltage samples to determine the characteristics of the harmonic signal.

4. The method of claim 1 wherein the predetermined level is based on an amplitude of a fundamental frequency component of the first drive signal.

5. The method of claim 1 wherein generating the cancellation signal is further defined as generating the cancellation signal with the phase being shifted by any odd multiple of 180 degrees in relation to the phase of the harmonic signal.

6. The method of claim 1 wherein generating the cancellation signal is further defined as generating the cancellation signal with an amplitude being equal to or greater than the amplitude of the harmonic signal.

7. The method of claim 6 wherein generating the cancellation signal is further defined as generating the cancellation signal with the amplitude being twice the amplitude of the harmonic signal.

8. The method of claim 6 wherein generating the cancellation signal is further defined as adjusting the amplitude of the cancellation signal, monitoring how adjusting the amplitude of the cancellation signal affects the harmonic signal, and selecting the amplitude of the cancellation signal having maximum cancelling effect on the harmonic signal relative to other amplitudes.

9. The method of claim 1 further including:

driving the ultrasonic surgical tool with the second drive signal;

acquiring a characteristic of a second harmonic signal resulting from driving the ultrasonic surgical tool with the second drive signal;

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

combining the second drive signal and the second cancellation signal to produce a third drive signal, the third drive signal being sinusoidal; 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 third drive signal is reduced relative to presence of the second harmonic signal resulting from driving the ultrasonic surgical tool with the second drive signal.

10. A console for controlling an ultrasonic surgical tool to reduce presence of a harmonic signal, the console comprising:

a controller configured to:

drive the ultrasonic surgical tool with a first drive signal;

increase a mechanical current of the ultrasonic surgical tool;

determine whether the increased mechanical current causes the harmonic signal to reach a predetermined level;

responsive to determining that the increased mechanical current does not cause the harmonic signal to reach the predetermined level, continue driving the ultrasonic surgical tool with the first drive signal; and

responsive to determining that the increased mechanical current causes the harmonic signal to reach the predetermined level:

acquire characteristics of the harmonic signal resulting from the increased mechanical current, the characteristics being at least a frequency and a phase of the harmonic signal;

generate a cancellation signal with a frequency similar to the frequency of the harmonic signal and a phase that is shifted in relation to the phase of the harmonic signal;

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

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

11. The console of claim 10 wherein the controller is configured to acquire the characteristics of the harmonic signal by generating current and voltage samples relating to the first drive signal, wherein the characteristics of the harmonic signal are present in the generated current and voltage samples.

12. The console of claim 11 wherein the controller is configured to acquire the characteristics of the harmonic signal by analyzing a fast-Fourier transform of the generated current and voltage samples to determine the characteristics of the harmonic signal.

13. The console of claim 10 wherein the predetermined level is based on an amplitude of a fundamental frequency component of the first drive signal.

14. The console of claim 10 wherein the controller is configured to generate the cancellation signal with the phase being shifted by any odd multiple of 180 degrees in relation to the phase of the harmonic signal.

15. The console of claim 10 wherein the characteristics further include an amplitude of the harmonic signal, and the controller is further configured to generate the cancellation signal with an amplitude being equal to or greater than the amplitude of the harmonic signal.

16. The console of claim 15 wherein the controller is configured to generate the cancellation signal with the amplitude being twice the amplitude of the harmonic signal.

17. The console of claim 15 wherein the controller is configured to generate the cancellation signal by adjusting the amplitude of the cancellation signal and monitoring how adjusting the amplitude of the cancellation signal affects the harmonic signal and selecting the amplitude of the cancellation signal having maximum cancelling effect on the harmonic signal relative to other amplitudes.

18. The console of claim 10 wherein the controller is configured to:

drive the ultrasonic surgical tool with the second drive signal;

acquire a characteristic of a second harmonic signal resulting from application of the second drive signal to the ultrasonic surgical tool;

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

combine the second drive signal and the second cancellation signal to produce a third drive signal, the third drive signal being sinusoidal; and

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