Ultrasonic energy device which varies pressure applied by clamp arm to provide threshold control pressure at a cut progression location

Abstract

Surgical instruments and system and methods for using surgical instruments are disclosed. A surgical instrument comprises an end effector comprising an ultrasonic blade and clamp arm, an ultrasonic transducer, and a control circuit. The ultrasonic transducer ultrasonically oscillates the ultrasonic blade in response to a drive signal from a generator. The end effector receives electrosurgical energy to weld tissue. The control circuit determines a resonant frequency measure indicative of a thermally induced change in resonant frequency and a electrical continuity measure; calculates a weld focal point based on the determined measures, controls closure of the clamp arm to vary a pressure applied by the clamp arm to provide a threshold control pressure to the tissue loaded into the end effector, and maintains a gap between the ultrasonic blade and clamp arm at a point proximal to the proximal end of the tissue. Pressure is varied based on corresponding weld focal point.