#$%^&*AU2014218154A120140918.pdf#####METHOD AND APPARATUS FOR DETERMINING PARAMETERS OF LINEAR MOTION IN A SURGICAL INSTRUMENT ABSTRACT A surgical instrument, comprising a housing (110), an elongated shaft (140) extending distally from the housing and defining a first longitudinal axis. A firing rod (220) disposed at least partially within the elongated shaft. A drive mechanism (200) disposed at least partially within the elongated shaft, the drive mechanism being in mechanical cooperation with the firing rod. A sensor (251) that includes a signal generator that generates a signal that varies with a change in electrical field between the firing rod and the elongated shaft. A measurement unit that measures a characteristic of the signal, and a data processor that computes a signal frequency based on the measured characteristic of the signal and detennines a parameter of the motion of the firing rod based on the signal frequency.
