Patent ID: 7739934

Claim:
A power tool comprising: a movable blade; and a detection system for detecting contact between the blade and an object, the detection system comprising: an excitation plate capacitively coupling the drive signal to the movable blade; and a circuit in communication with the excitation plate, wherein the circuit is configured to: generate an in-phase component signal and a quadrature component signal from a blade current signal indicative of the instantaneous current drawn by the movable blade; calculate an energy of the blade current signal considering the in-phase component and the quadrature component; and compare the energy of the blade current signal to an adaptive trigger threshold to detect contact between the blade and the object based on whether the energy of the blade current signal is greater than the adaptive trigger threshold, wherein the adaptive trigger threshold is based on a sum of a first plurality of values comprising a fixed direct current (DC) offset, and a mean of the energy of the blade current signal.