A surgical instrument includes a housing, an end effector and an elongated shaft extending therebetween. The shaft includes a distal portion movable between aligned and articulated configurations. First and second drive cables are coupled to the distal portion such that reciprocal longitudinal motion of the drive cables induces movement of the distal portion between the aligned and articulated configurations. An articulation drive mechanism is operable to induce reciprocal longitudinal motion of the drive cables. The drive mechanism includes an actuator and a pair pulleys operatively coupled to the actuator to rotate about an axle. The first and second drive cables are coupled to the pulleys such that the drive cables extend on opposite lateral sides of the axle. A biasing mechanism is configured to bias the first and second pulleys to at least one discrete orientation to maintain the distal portion of the elongated shaft in a discrete articulated position.
