Method for improving the start up of an ultrasonic system under zero load conditions
First Claim
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 Assignments
0 Petitions
Accused Products
Abstract
The start up performance of an ultrasonic system under zero load conditions is improved by setting a phase set point in a frequency control loop such that, at start up under zero load conditions, the phase set point intersects a point on a phase-frequency response curve which has a low positive slope. This intersection point on the phase-frequency response curve changes as the load is increased and the system Q is decreased. The controller “seeks” a target 0° impedance phase angle. The frequency of the ultrasonic generator is set to an off-resonance frequency which is lower than the resonance of any known hand piece/blade combination. In order for the drive voltage to not exceed the physical limit of the system, the drive current is set to a low level. The drive frequency is then smoothly increased in steps until the target 0° impedance phase delta is located.
563 Citations
7 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. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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.
- impedance phase angle, comprises the step of;
-
4. The method of claim 3, wherein the predetermined step is 20 Hz and 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.
Specification