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.
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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.
6 Citations
7 Claims
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1. A method for improving start up performance of an ultrasonic surgical system under zero load conditions, comprising the steps of:
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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)
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Specification