For applications with limited space, the LM 1247 linear servomotor from Micro Mo, Clearwater, Fla. (micromo.com), could be the right fit, measuring 12.5 × 47 mm and weighing 56 grams.
It can exert 9.4 N and standard travel is 20 mm, though an option lets it move loads up to 80 mm. The unit has a threephase self-supporting coil, an analog Hall sensor, a nonmagnetic housing, and it does not require lubrication. It is electronically reversible and uses polymer sleeves as rod bearings. Repeatability and precision are 40 and 120 μm, respectively.