A surgical stapling and severing instrument particularly suited to endoscopic procedures incorporates a handle that produces separate closing and firing motions to actuate an end effector. In particular, the handle produces multiple firing strokes in order to reduce the required amount of force required to fire (i.e., staple and sever) the end effector. A firing member reciprocates within an elongate shaft to the end effector to transfer this firing motion. A retraction spring retracts the firing member after full firing. Between firing strokes as the firing trigger is released, an anti-backup mechanism activates an electrical actuator (e.g., elecroactive polymer actuator) that is physically grounded to the handle to bind the firing member preventing inadvertent retraction.
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