Ultrasonic device for cutting and coagulating with stepped output

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

• generating a first ultrasonic drive signal by a generator coupled to an ultrasonic drive system, wherein the ultrasonic drive system comprises an ultrasonic transducer coupled to a waveguide and an end effector coupled to the waveguide, and wherein the ultrasonic drive system is configured to resonate at a resonant frequency;
• actuating the ultrasonic transducer with the first ultrasonic drive signal for a first period;
• generating a second ultrasonic drive signal by the generator;
• and
• actuating the ultrasonic transducer with the second ultrasonic drive signal for a second period, subsequent to the first period;
• wherein the first drive signal is different from the second drive signal over the respective first and second periods;
• wherein the first and second drive signals define a step function waveform over the first and second periods;
• generating the first ultrasonic drive signal at a first frequency different from the resonant frequency;
• actuating the ultrasonic transducer with the first ultrasonic device signal at the first frequency for the first period to provide a first level of mechanical vibration to the end effector suitable for separating a first tissue from a second tissue;
• generating the second ultrasonic drive signal at the resonance frequency;
• and
• actuating the ultrasonic transducer with the second ultrasonic drive signal at the resonant frequency for the second period subsequent to the first period to provide a second level of mechanical vibration to the end effector suitable for transecting and sealing the first tissue.