Devices and techniques for cutting and coagulating tissue

1. A method of driving an end effector coupled to an ultrasonic drive system of a surgical instrument, the method comprising:

generating, by a generator, at least one time-varying electrical signal having a resonant frequency;

monitoring, by the generator, the resonant frequency of the at least one time-varying electrical signal;

calculating, by the generator, a frequency slope between frequency data points of the time varying electrical signal, where the frequency slope is a change in resonant frequency over time;

comparing, by the generator, the frequency slope to a frequency slope threshold; and

triggering, by the generator, a first response of the generator when the frequency slope crosses the frequency slope threshold.

2. The method of claim 1 , comprising:

comparing, by the generator, the frequency slope to the frequency slope threshold; and

triggering, by the generator, a second response of the generator when the frequency slope crosses the frequency slope threshold.

3. The method of claim 2 , comprising:

determining, by the generator, when the frequency slope is less than the frequency slope threshold;

incrementing, by the generator, a timer when the frequency slope is less than the frequency slope threshold;

determining, by the generator, when the timer is greater than a required trigger time; and

setting a logic condition when the timer is greater than the required trigger time.

4. The method of claim 3 , comprising:

incrementing, by the generator, the timer when the resonant frequency is less than a resonant frequency threshold and the frequency slope is less than the frequency slope threshold.

5. The method of claim 2 , comprising:

comparing, by the generator, the frequency slope to a cross-back frequency slope threshold, wherein the cross-back frequency slope threshold is the frequency slope threshold above which a triggered response stops.

6. A method of driving an end effector coupled to an ultrasonic drive system of a surgical instrument, the method comprising:

receiving, by a generator, a frequency slope threshold;

monitoring, by the generator, a frequency slope of the ultrasonic drive system;

comparing, by the generator, the frequency slope of the ultrasonic drive system with the frequency slope threshold; and

incrementing, by the generator, a timer when the frequency slope is less than the frequency slope threshold.

7. The method of claim 6 , further comprising:

receiving, by the generator, a required time before trigger parameter;

receiving, by the generator, a timer value from the timer;

comparing, by the generator, the required time before trigger parameter and the timer value;

setting, by the generator, a condition set latch when the timer value is greater than the required time before trigger parameter and indicating that a predetermined condition has set been met; or

resetting, by the generator, the condition set latch when the timer value is less than or equal to the required time before trigger parameter.

8. The method of claim 6 further comprising:

resetting, by the generator, the timer when the frequency slope is greater than the frequency slope threshold.

9. The method of claim 8 , further comprising:

determining, by the generator, when a cross-back frequency slope latch is set; and

indicating that a predetermined condition set has not been met when the cross-back frequency slope latch is not set.

10. The method of claim 9 , further comprising:

receiving, by the generator, a minimum latch time parameter for a condition set latch;

receiving, by the generator, a cross-back frequency slope threshold parameter;

receiving, by the generator, an indication that at least one of the condition set latch or the cross-back frequency slope latch is set;

comparing, by the generator, a latched time of the condition set latch with the minimum latch time parameter for the condition set latch;

comparing, by the generator, the frequency slope with the cross-back frequency slope threshold parameter; and

indicating, by the generator, that a predetermined condition set has been met when the frequency slope is less than the cross-back frequency slope threshold parameter.

11. The method of claim 10 , further comprising:

resetting, by the generator, a timer latch; and

indicating, by the generator, that a predetermined condition set has not been met when the frequency slope is greater than the cross-back frequency slope threshold parameter.

12. A generator configured to drive an end effector coupled to an ultrasonic drive system of a surgical instrument, the generator comprising:

a processor;

a timer circuit coupled to the processor;

a timer latch coupled to the processor;

a condition set latch coupled to the processor; and

a memory coupled to the processor, wherein the memory includes machine executable instructions that when executed by the processor cause the processor to:

receive a frequency slope threshold;

monitor a frequency slope of the ultrasonic drive system;

compare the frequency slope of the ultrasonic drive system with the frequency slope threshold; and

increment the timer circuit when the frequency slope is less than the frequency slope threshold.

13. The generator of claim 12 , wherein the machine executable instructions, when executed by the processor, cause the processor to:

receive a required time before trigger parameter;

receive a timer value from the timer circuit;

compare the required time before trigger parameter and the timer value;

set the condition set latch when the timer value is greater than the required time before trigger parameter and indicate that a predetermined condition has not been met; or

reset the condition set latch when the timer value is less than or equal to the required time before trigger parameter.

14. The generator of claim 12 , wherein the machine executable instructions, when executed by the processor, cause the processor to:

reset the timer circuit when the frequency slope is greater than the frequency slope threshold.

15. The generator of claim 14 , wherein the machine executable instructions, when executed by the processor, cause the processor to:

indicate a cross-back frequency slope latch is set; and

indicate that a predetermined condition set has not been met when the cross-back frequency slope latch is not set.

16. The generator of claim 15 , wherein the machine executable instructions, when executed by the processor, cause the processor to:

receive a minimum latch time parameter for the condition set latch;

receive a cross-back frequency slope threshold parameter;

receive an indication that the cross-back frequency slope latch is set;

compare the frequency slope with the cross-back frequency slope threshold parameter; and

indicate that a predetermined condition set has been met when the frequency slope is less than the cross-back frequency slope threshold parameter.

17. The generator of claim 15 , wherein the machine executable instructions, when executed by the processor, cause the processor to:

reset the timer latch; and

indicate that the predetermined condition set has not been met when the frequency slope is greater than the cross-back frequency slope threshold parameter.