A surgical stapling instrument particularly suited to endoscopic use articulates an end effector (e.g., stapling and severing) that is actuated by a firing bar. An articulation mechanism in an elongate shaft incorporates electrically actuated polymer (EAP) actuators that laterally support the firing bar so that the firing bar is sufficiently constrained to avoid a blow-out, yet is guided without excessive friction and binding. Thereby, effective, consistent firing is accomplished without an undue increase in firing force required when the end effector is articulated.
