| abstract |
The present invention discloses a method of determining the instability of an ultrasonic blade, the method comprising: monitoring the phase angle between the voltage Vg(t) signal and the current Ig(t) signal applied to the ultrasonic transducer The ultrasonic transducer is coupled to the ultrasonic blade via an ultrasonic guide; based on the phase angle to infer the blade temperature; compare the inferred temperature to an ultrasonic blade instability trigger point threshold; and adjust the power level applied to the ultrasonic transducer to modulate the blade temperature. The method may also include determining a frequency/temperature relationship of the ultrasonic blade that exhibits displacement or modal instability, and compensating for thermally induced instability of the ultrasonic blade. The method may be implemented in an ultrasonic surgical instrument or by a control circuit in a power generator for an ultrasonic surgical instrument. |