#$%^&*AU2011200961B220140529.pdf#####ABSTRACT METHOD AND APPARATUS FOR DETERMINING PARAMETERS OF LINEAR MOTION IN A SURGICAL INSTRUMENT A surgical instrument (10) and method of controlling the surgical instrument are disclosed. The surgical instrument includes a housing (110) and an elongated shaft (140) that extends distally from the housing and defines a first longitudinal axis. The surgical instrument also includes a firing rod (220) disposed in the elongated shaft and a drive mechanism disposed at least partially within the housing. The drive mechanism mechanically cooperates with the firing rod to move the firing rod. A motion sensor (251) senses a change in the electric field (e.g. capacitance, impedance, or admittance) between the firing rod and the elongated shaft. The measurement unit (470) determines a parameter of the motion of the firing rod, such as the position, speed, and direction of the firing rod, based on the sensed change in the electric field. A controller (500) uses the measured parameter of the motion of the firing rod to control the drive mechanism.1/20 ft -A-
