Patent ID: 8186253
Filing Date: 2012-05-29
Classification: B23D,B23Q,B27G,F16P,Y10T

Abstract:
1. A method of sensing contact between an object and a movable blade of a power tool, the power tool comprising an excitation plate positioned proximate and capacitively coupled to the movable blade, the method comprising: providing a drive signal to the excitation plate to capacitively couple the drive signal to the movable blade; sensing a blade current signal indicative of the instantaneous current drawn by the movable blade; generating an in-phase component signal and a quadrature component signal from the blade current signal; calculating, by a circuit in communication with the excitation plate, an energy of the blade current signal considering the in-phase component and the quadrature component; and comparing by the circuit 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.