Abstract: A driving apparatus includes a roller screw that includes a main shaft, a plurality of roller shafts projecting radially outwardly and upwardly at an angle from the radial direction of the main shaft and arranged along a helical line there around, and a plurality of rollers rotatably mounted on the roller shafts. The rollers are tapered to the same angle inwardly toward the main shaft. A rail member, adjacent to and axially oriented with the main shaft, includes a plurality of spaced projections adapted for radial engagement with the tapered rollers. The angle of the tapering is pre-determined to provide a sliding free engagement between the rollers and the projections with the interface there between being oriented to intersect the rotation axis of their respective roller shaft on the rotation axis of the main shaft. The rotation of the main shaft axially moves the roller screw relative to the rail member.