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;

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

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

2. The method of claim 1 , comprising:

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

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

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

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

3. The method of claim 1 , comprising:

resetting, by the generator, a timer when the resonant frequency is greater than the threshold frequency;

comparing, by the generator, a latched time with a minimum latch time; and

resetting, by the generator, the timer when the latched time is greater than the minimum latch time.

4. 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 resonant frequency threshold;

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

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

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

5. The method of claim 4 , 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 not 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.

6. The method of claim 4 , further comprising:

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

7. The method of claim 6 , further comprising:

determining, by the generator, when a condition set latch is set; and

indicating that a predetermined condition set has not been met when the condition set latch is not set.

8. The method of claim 7 , further comprising:

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

receiving, by the generator, an indication that the condition set 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; and

indicating, by the generator, that the predetermined condition set has been met when the latched time of the condition set latch is less than the minimum latch time parameter for the condition set latch.

9. The method of claim 8 , further comprising:

resetting, by the generator, a timer latch; and

indicating, by the generator, that the predetermined condition set has not been met when the latched time of the condition set latch is greater than the minimum latch time parameter for the condition set latch.

10. 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 resonant frequency threshold;

monitor a resonant frequency of the ultrasonic drive system;

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

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

11. The generator of claim 10 , 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 set been met; or

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

12. The generator of claim 10 , wherein the machine executable instructions, when executed by the processor, cause the processor to:

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

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

determine whether the condition set latch is set; and

indicate that a predetermined condition set has not been met when the condition set latch is not set.

14. The generator of claim 13 , 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 an indication that the condition set latch is set;

compare a latched time of the condition set latch with the minimum latch time parameter for the condition set latch; and

indicate that the predetermined condition set has been met when either the latched time of the condition set latch is less than the minimum latch time parameter for the condition set latch.

15. The generator of claim 13 , 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 a latched time of the condition set latch is greater than the minimum latch time parameter for the condition set latch.