An apparatus for operating on tissue, the apparatus comprising: (a) an end effector, wherein the end effector comprises an ultrasonic blade and a clamp arm operable to pivot relative to the ultrasonic blade; (b) a shaft assembly, wherein the end effector is disposed at a distal end of the shaft assembly, wherein the shaft assembly defines a longitudinal axis, wherein the shaft assembly includes an articulation section operable to deflect the end effector away from the longitudinal axis; and (c) an interface assembly, wherein the interface assembly is configured to drive the end effector, wherein the interface assembly comprises: (i) a base, wherein the base is configured to couple with a dock of a robotic control system, and (ii) a plurality of drive shafts (224, 244, 264) oriented perpendicular to the longitudinal axis, wherein a first drive shaft of the plurality of drive shafts is rotatable to pivot the clamp arm toward the ultrasonic blade; wherein the shaft assembly further comprises a translating member (174, 176) coupled between the first drive shaft and the clamp arm; characterized in that the interface assembly further comprises: (iii) an eccentric cam secured to the first drive shaft, and (iv) a rack coupled with the translating member (174, 176), wherein the eccentric cam is operable to drive the rack proximally in response to rotation of the first drive shaft, to thereby pivot the clamp arm toward the ultrasonic blade. (a) an end effector, wherein the end effector comprises an ultrasonic blade and a clamp arm operable to pivot relative to the ultrasonic blade; (b) a shaft assembly, wherein the end effector is disposed at a distal end of the shaft assembly, wherein the shaft assembly defines a longitudinal axis, wherein the shaft assembly includes an articulation section operable to deflect the end effector away from the longitudinal axis; and (c) an interface assembly, wherein the interface assembly is configured to drive the end effector, wherein the interface assembly comprises: (i) a base, wherein the base is configured to couple with a dock of a robotic control system, and (ii) a plurality of drive shafts (224, 244, 264) oriented perpendicular to the longitudinal axis, wherein a first drive shaft of the plurality of drive shafts is rotatable to pivot the clamp arm toward the ultrasonic blade; wherein the shaft assembly further comprises a translating member (174, 176) coupled between the first drive shaft and the clamp arm; characterized in that the interface assembly further comprises: (iii) an eccentric cam secured to the first drive shaft, and (iv) a rack coupled with the translating member (174, 176), wherein the eccentric cam is operable to drive the rack proximally in response to rotation of the first drive shaft, to thereby pivot the clamp arm toward the ultrasonic blade. (i) a base, wherein the base is configured to couple with a dock of a robotic control system, and (ii) a plurality of drive shafts (224, 244, 264) oriented perpendicular to the longitudinal axis, wherein a first drive shaft of the plurality of drive shafts is rotatable to pivot the clamp arm toward the ultrasonic blade; (iii) an eccentric cam secured to the first drive shaft, and (iv) a rack coupled with the translating member (174, 176), wherein the eccentric cam is operable to drive the rack proximally in response to rotation of the first drive shaft, to thereby pivot the clamp arm toward the ultrasonic blade.