CONTROLLING AN ULTRASONIC SURGICAL INSTRUMENT ACCORDING TO TISSUE LOCATION

1 - 24 . (canceled)

25 . A method of determining position of tissue located in an end effector of an ultrasonic surgical instrument comprising an ultrasonic transducer, the end effector comprising an ultrasonic blade acoustically coupled to the ultrasonic transducer, the method comprising:

applying, by a control circuit, a first power level to the ultrasonic transducer;

measuring, by the control circuit, a first impedance measurement of the ultrasonic transducer corresponding to the first power level over a first period of time until the first impedance measurement attains a first plateau value;

applying, by the control circuit, a second power level to the ultrasonic transducer;

measuring, by the control circuit, a second impedance measurement of the ultrasonic transducer corresponding to the second power level over a second period of time until the second impedance measurement attains a second plateau value;

calculating, by the control circuit, a difference in ultrasonic transducer impedance between the first plateau value and the second plateau value;

comparing, by the control circuit, the difference in ultrasonic transducer impedance to a first threshold; and

determining, by the control circuit, a location of the tissue positioned within the end effector based on the first threshold.

26 . The method of claim 25 , wherein the first power level is less than the second power level.

27 . The method of claim 25 , wherein the first power level and the second power level are below a therapeutic power level, wherein the therapeutic power level is sufficient to cause the ultrasonic blade to coagulate and transect the tissue.

28 . The method of claim 25 , further comprising applying, by the control circuit, a therapeutic power level to the ultrasonic transducer based on the location of the tissue within the end effector, wherein the therapeutic power level is sufficient to cause the ultrasonic blade to coagulate and transect the tissue.

29 . The method of claim 25 , further comprising:

comparing, by the control circuit, the difference in ultrasonic transducer impedance to a second threshold; and

determining, by the control circuit, whether tissue positioned within the end effector is at a proximal location, an intermediate location, or a distal location according the difference in ultrasonic transducer impedance relative to the first threshold and the second threshold.

30 . A n ultrasonic surgical instrument connectable to a generator, the ultrasonic surgical instrument comprising:

an end effector comprising an ultrasonic blade;

an ultrasonic transducer acoustically coupled to the ultrasonic blade, the ultrasonic transducer configured to ultrasonically oscillate the ultrasonic blade in response to a drive signal from the generator; and

a control circuit coupled to the ultrasonic transducer, the control circuit configured to:

apply varying power levels to the ultrasonic transducer via the ultrasonic generator;

measure impedances of the ultrasonic transducer over one or more periods of time until the impedances corresponding to the varying power levels attain plateau values; and

determine a location of tissue positioned within the end effector according to a difference between the plateau values relative to a threshold.

31 . The ultrasonic surgical instrument of claim 30 , wherein the control circuit is configured to vary the power levels applied to the ultrasonic transducer between a first power level and a second power level.

32 . The ultrasonic surgical instrument of claim 31 , wherein the first power level and the second power level are below a therapeutic power level, wherein the therapeutic power level is a power level sufficient to cause the ultrasonic blade to coagulate and transect the tissue.

33 . The ultrasonic surgical instrument of claim 30 , wherein the control circuit is further configured to apply a therapeutic power level to the ultrasonic transducer based on the location of the tissue within the end effector, wherein the therapeutic power level is sufficient to cause the ultrasonic blade to coagulate and transect the tissue.

34 . The ultrasonic surgical instrument of claim 30 , wherein the threshold comprises a first threshold, wherein the control circuit is further configured to:

compare the difference between the plateau values to a second threshold; and

determine whether the tissue positioned within the end effector is at a proximal location, an intermediate location, or a distal location according the difference between the impedances of the ultrasonic transducer relative to the first threshold and the second threshold.

35 . A n ultrasonic generator connectable to an ultrasonic instrument comprising an end effector, an ultrasonic blade, and an ultrasonic transducer acoustically coupled to the ultrasonic blade, the ultrasonic generator comprising:

a control circuit couplable to the ultrasonic transducer, the control circuit configured to:

apply varying power levels to the ultrasonic transducer;

measure impedances of the ultrasonic transducer corresponding to the varying power levels for one or more periods of time until the impedances corresponding to the varying power levels attain plateau values; and

determine a location of tissue positioned within the end effector according to a difference between the plateau values of the ultrasonic transducer relative to a threshold.

36 . The ultrasonic generator of claim 35 , wherein the control circuit is configured to vary the power levels applied to the ultrasonic transducer between a first power level and a second power level.

37 . The ultrasonic generator of claim 36 , wherein the first power level and the second power level are below a therapeutic power level, wherein the therapeutic power level is a power level sufficient to cause the ultrasonic blade to coagulate and transect the tissue.

38 . The ultrasonic generator of claim 35 , wherein the control circuit is further configured to apply a therapeutic power level to the ultrasonic transducer based on the location of the tissue within the end effector, wherein the therapeutic power level is a power level sufficient to cause the ultrasonic blade to coagulate and transect the tissue.

39 . The ultrasonic generator of claim 35 , wherein the threshold comprises a first threshold, wherein the control circuit is further configured to:

compare the difference between the plateau values to a second threshold; and

determine whether the tissue positioned within the end effector is at a proximal location, an intermediate location, or a distal location according the difference between the impedances of the ultrasonic transducer relative to the first threshold and the second threshold.