A surgical instrument particularly suited to endoscopic use articulates an end effector by including a laterally sliding member in a proximal portion of a shaft that pivots the end effector to a selected side. Differentially opposing actuating forces (e.g., hydraulic, fluidic, mechanical) act against the laterally sliding member without binding by incorporating guidance mechanisms between the laterally sliding member and a frame of the shaft. A locking member advantageously unlocks automatically as articulation is commanded by resists backdriving of the mechanism.
