Claims
- 1. A method for improving start up performance of an ultrasonic surgical system under zero load conditions, comprising the steps of:
exciting a hand piece/blade with a drive current using an ultrasonic generator at an initial drive frequency; setting a frequency of a direct digital synthesis circuit located in the generator to an off-resonance frequency of the hand piece/blade; setting the drive current to a low level; searching for a target 0° impedance phase angle; increasing the drive frequency to a new level; maintaining the target 0° impedance phase angle at a constant value; monitoring impedance and phase angle magnitude values of the drive signal at the new level to calculate a frequency correction value; and correcting the frequency of the direct digital synthesis circuit using the calculated frequency correction value.
- 2. The method of claim 1, wherein the step of setting the drive current to a low level comprises the step of:
applying a drive current having a level of 100 ma.
- 3. The method of claim 1, wherein the step of searching for a target 0° impedance phase angle, comprises the step of:
increasing the drive frequency smoothly in predetermined steps until the target 0° impedance phase angle is located; wherein the drive frequency is smoothly increased to avoid impedance magnitude and impedance phase angle oscillations of the hand piece/blade.
- 4. The method of claim 3, wherein the predetermined step is 20 Hz and applied is applied at a rate of at least 2 kHz.
- 5. The method of claim 1, wherein said calculation of the frequency correction value is performed in accordance with a phase-slope vs. impedance relationship of a hand piece at 0° impedance phase angle.
- 6. The method of claim 5, wherein the phase-slope vs. impedance relationship comprises the relationship:
- 7. The method of claim 6, wherein the scaling factor is a fractional number having a magnitude of less then 1.
RELATED APPLICATIONS
[0001] The present invention relates to, and claims priority of, U.S. Provisional Patent Application Serial No. 60/241,890 filed on Oct. 20, 2000, having the same title as the present invention, which is incorporated herein by reference.
Provisional Applications (1)
|
Number |
Date |
Country |
|
60241890 |
Oct 2000 |
US |
Continuations (1)
|
Number |
Date |
Country |
Parent |
09866372 |
May 2001 |
US |
Child |
10235952 |
Sep 2002 |
US |