Abstract: A linearly reciprocable actuator is reciprocated by a mechanism which includes a rotatable part which is operably connected to the actuator to produce linear movement of the actuator in response to rotation of the rotatable part. A fine drive motor is operably connected to the rotatable part for rotating the rotatable part in a precisely controlled manner. The fine drive mechanism is operably disconnectable from the rotatable part to permit the latter to be rotatable independently of the fine drive motor. A coarse drive mechanism is connected to the rotatable part independently of the fine drive motor for rotating the rotatable part in a coarser manner than the fine drive motor when the fine drive motor is operably disconnected from the rotatable part.