US Patent 10022568 Devices and techniques for cutting and coagulating tissue

Various embodiments are directed to a method of driving an end effector coupled to an ultrasonic drive system of a surgical instrument. In accordance with the method, a generator is configured to generate at least one time varying electrical signal having a resonant frequency, monitor the resonant frequency of the at least one electrical signal, calculate a frequency slope between frequency data points of the time varying electrical signal, where the frequency slope is the change in resonant frequency over time, compare the frequency slope to a threshold frequency slope, and trigger a first response of the generator when the frequency slope crosses the threshold frequency slope.