Ultrasonic surgical tool capable of vibrating in plural modes and a drive system that induces non-linear vibrations in the tool tip

1. An assembly for vibrating a tip of an ultrasonic handpiece, the handpiece having a driver to which an AC drive signal is applied to vibrate the tip, the tip being designed to vibrate in plural vibratory modes, the assembly including:

an assembly for generating a variable AC drive signal that is applied to the driver of the handpiece;

an assembly for measuring a voltage of the drive signal applied across the handpiece;

an assembly for measuring a current through the handpiece; and

a processor configured to:

for each vibratory mode of the tip, adjust a first frequency characteristic for the vibratory mode to produce a second frequency characteristic for the vibratory mode based on the measured drive signal voltage and the measured current through the handpiece, wherein the second frequency characteristics for at least two of the vibratory modes are different from each other; and

based on the second frequency characteristics for the vibratory modes, determine a structure of a waveform for the drive signal and assert a command based on the structure of the waveform to the assembly that generates the drive signal so as to cause the assembly to generate a drive signal that contains a component for each of the vibratory modes, each component being based on the second frequency characteristic determined for the vibratory mode.

2. The assembly of claim 1 , wherein the processor is further configured to:

for each vibratory mode of the tip, determine a calculated equivalent of current through mechanical components of the handpiece for the vibratory mode based on the first frequency characteristic for the vibratory mode, the measured drive signal voltage, and the measured current through the handpiece; and

for each vibratory mode of the tip, adjust the first frequency characteristic for the vibratory mode to produce the second frequency characteristic for the vibratory mode based on the calculated equivalent of current through the mechanical components of the handpiece for the vibratory mode.

3. The assembly of claim 2 , wherein the processor is further configured to:

breakdown the measured current through the handpiece into plural components, each component of the measured current representing a measured current through the handpiece associated with a specific one of the vibratory modes of the tip; and

for each vibratory mode of the tip, determine the calculated equivalent of current through the mechanical components of the handpiece for the vibratory mode based on the measured current through the handpiece associated with the vibratory mode.

4. The assembly of claim 3 , wherein the processor is further configured to, for each vibratory mode of the tip, determine the calculated equivalent of current through the mechanical components of the handpiece for the vibratory mode by determining a difference between the measured current through the handpiece associated with the vibratory mode and a current through the driver associated with the vibratory mode.

5. The assembly of claim 4 , wherein the processor is further configured to, for each vibratory mode of the tip, determine the current through the driver associated with the vibratory mode based on a capacitance of the driver, a component of the measured drive signal voltage associated with the vibratory mode, and the first frequency characteristic for the vibratory mode.

6. The assembly of claim 5 , wherein the processor is further configured to read the capacitance of the driver from a memory device included with the tip.

7. The assembly of claim 3 , wherein the processor is further configured to:

for each vibratory mode of the tip:

determine a ratio for the vibratory mode of current through the driver associated with the vibratory mode to the equivalent of current through the mechanical components of the handpiece for the vibratory mode; and

adjust the first frequency characteristic for the vibratory mode to produce the second frequency characteristic for the vibratory mode based on the ratio for the vibratory mode.

8. The assembly of claim 7 , wherein the processor is further configured to:

for each vibratory mode of the tip:

determine if a real part of the ratio for the vibratory mode is substantially equal to a target value; and

adjust the first frequency characteristic for the vibratory mode to produce the second frequency characteristic for the vibratory mode responsive to the real part of the ratio for the vibratory mode not being substantially equal to the target value.

9. The assembly of claim 8 , wherein the target value is zero.

10. The assembly of claim 7 , wherein the processor is further configured to:

for each vibratory mode of the tip:

generate a modified value based on the ratio for the vibratory mode, the first frequency characteristic for the vibratory mode, and a target frequency for the vibratory mode;

determine whether the modified value is substantially equal to a target value; and

adjust the first frequency characteristic for the vibratory mode to produce the second frequency characteristic for the vibratory mode responsive to the modified value not being substantially equal to the target value.

11. The assembly of claim 10 , wherein the processor is further configured to, for each vibratory mode of the tip, generate the modified value by modifying a real part of the ratio for the vibratory mode as a function of a difference between the first frequency characteristic for the vibratory mode and the target frequency for the vibratory mode.

12. The assembly of claim 2 , wherein the processor is further configured to:

breakdown the measured drive signal voltage into plural components, each component of the measured drive signal voltage representing a measured voltage across the handpiece associated with a specific one of the vibratory modes of the tip; and

for each vibratory mode of the tip, determine the calculated equivalent of current through the mechanical components of the handpiece for the vibratory mode based on the measured voltage across the handpiece associated with the vibratory mode.

13. The assembly of claim 1 , wherein as a result of application of the drive signal that contains a component for each of the vibratory modes to the driver, a head of the tip engages in a non-linear path of travel in a single vibratory cycle.

14. The assembly of claim 1 , wherein as a result of application of the drive signal that contains a component for each of the vibratory modes to the driver, a head of the tip travels in a loop in a single vibratory cycle.

15. The assembly of claim 1 , wherein the processor is further configured to establish the first frequency characteristic for each vibratory mode based on data retrieved from a memory device included with the tip.

16. An assembly for vibrating a tip of an ultrasonic handpiece, the handpiece having a driver to which an AC drive signal is applied to vibrate the tip, the tip being designed to vibrate in plural vibratory modes, the assembly including:

an assembly for generating a variable AC drive signal that is applied to the driver of the handpiece;

an assembly for measuring a voltage of the drive signal applied across the handpiece;

an assembly for measuring a current through the handpiece; and

a processor configured to assert a command to the assembly that generates the drive signal based on the measured drive signal voltage and the measured current through the handpiece so as to cause the assembly to generate a drive signal that contains a component for each of the vibratory modes, each component being based on a frequency characteristic determined for the vibratory mode such that the tip moves in a non-linear path of travel in a single vibratory cycle.

17. A method for vibrating a tip of an ultrasonic handpiece, the handpiece having a driver to which an AC drive signal is applied to vibrate the tip, the tip being designed to vibrate in plural vibratory modes, the method comprising:

generating a variable AC drive signal that is applied to the driver of the handpiece;

measuring a voltage of the drive signal applied across the handpiece;

measuring a current through the handpiece;

for each vibratory mode of the tip, adjusting a first frequency characteristic for the vibratory mode to produce a second frequency characteristic for the vibratory mode based on the measured drive signal voltage and the measured current through the handpiece, wherein the second frequency characteristics for at least two of the vibratory modes are different from each other;

based on the second frequency characteristics for the vibratory modes, determining a structure of a waveform for the drive signal; and

based on the structure of the waveform, generating a drive signal that is applied to the driver of the handpiece and contains a component for each of the vibratory modes, each component being based on the second frequency characteristic determined for the vibratory mode.