Patent ID: 8020742

Claim:
A medical instrument, comprising: a housing having a fixed handle; an elongated shaft extending distally from the housing; a tool assembly coupled to a distal end of the elongated shaft, the tool assembly including a pair of opposing tissue engaging surfaces for clamping tissue therebetween; a movable handle mounted to the housing and selectively movable relative to the fixed handle from a first position in spaced relation relative to the fixed handle to a second position closer to the fixed handle; a firing shaft extending at least partially through the elongated shaft, wherein the firing shaft is operatively coupled to the movable handle such that movement of the movable handle toward the second position advances the firing shaft through the elongated shaft, and wherein the firing shaft is operatively coupled to the tool assembly to induce motion in the tool assembly; a drive assembly including a motor and a controller, wherein the motor is operatively engaged with the firing shaft to supply a longitudinal force thereto, and wherein the controller is configured to variably control a voltage supplied to the motor in response to longitudinal motion of the firing shaft.