A rivet is inserted into a workpiece by an apparatus that includes an internal roller screw linear actuator in which rotational movement of an internally threaded cylinder is converted into linear movement of a fastener insertion actuator assembly. The cylinder is driven in rotation by a servo-controlled motor. The angular velocity of the cylinder required to deliver the required energy to effect fastener insertion is calculated and the motor is first controlled to accelerate the cylinder up to the calculated angular velocity, the actuator assembly simultaneously being moved by the cylinder towards the workpiece. The motor is then controlled to maintain the angular velocity of the cylinder at not less than the calculated magnitude at least until insertion of the fastener. The cylinder stores kinetic energy by virtue of its inertia. Using this inertia to insert fasteners eliminates the need for position or force feedback control. The process allows for a rapid cycle time and the apparatus is compact.