Abstract: The present disclosure concerns an actuator for converting rotary movement into linear movement. The actuator comprises a prime mover turning a reduction gear assembly which, in turn, drives a mechanical transmission including a linearly moving control element. To achieve precise movement of the control element to a desired position, and to ensure the desired position is retained as exactly as possible, a reduction gear assembly which is self-locking with respect to the maximum back-driving torque exerted on the reduction gear assembly by the mechanical transmission, is combined with a low friction, non-self-locking mechanical transmission. Preferably, the reduction gear assembly is implemented in the form of a strain wave reduction gear set and the mechanical transmission element is implemented in the form of a cooperating ballscrew and ballnut.