OUTPUT DISPLACEMENT CONTROL USING PHASE MARGIN IN AN ULTRASONIC SURGICAL HAND PIECE

摘要

An ultrasonic surgical hand piece is caused to be driven with an output displacement that is correlated with the phase margin, which is the differen ce of the resonant frequency and the anti-resonant frequency of the hand piece. A frequency sweep is conducted to find the resonant frequency and the anti-resonant frequency for the hand piece. The resonant frequency is measured at a point during the frequency sweep where the impedance of the hand piece is at its minimum. The anti-resonant frequen cy is measured at a point during the frequency sweep where the impedance of the ha nd piece is at its maximum. Using a target or specific output displacement, a drive current is calculated based on the phase margin which is the difference between the resonant frequency and the anti-resonant frequency. The hand piece is caused to be driven with the output displacement, by accordingly controlling the current output from a generator console for driving the hand piece.