A roller screw bidirectional axial preloading structure includes a screw, a nut, and a plurality of first and second rollers arranged around the screw in an interleaved manner and respectively having two ends connected to a first and a second retainer. A first gap is formed between the first retainer and one end of each first roller, and a second gap is formed between the second retainer and the other end of each second roller, such that the first and the second gaps are axially spaced while circumferentially interleaved around the screw. Two elastic elements are located outside the first and second retainers to apply two forces, which are transmitted via the first and second retainers to the first and the second rollers to create two directionally opposite axial preloads on the first and second rollers, giving the roller screw good mechanical power transmission accuracy and stability in motion.

A roller screw bidirectional and alternated preloading structure includes a screw, a nut fitted around the screw, a roller unit including first and second rollers alternately arranged between and meshing with the screw and the nut, two preload maintaining units located at two ends of the roller unit and respectively including a retainer including retaining holes for receiving locating ends of the rollers and a metal spring including circumferentially spaced elastic protrusions tilted toward the roller unit and radially offset from the retaining holes, and a retaining unit. Gaps are formed between bottoms of the retaining holes and the locating ends, while the elastic protrusions are pressed against and elastically deformed by pointed ends of the rollers to create two opposite preloads alternately applied to the first and second rollers from two directions. This structure compensates fitting gaps and enables increased transmission accuracy and motion stability of the roller screw.