Roller screw and method of circulating rollers in roller screw

A roller screw comprising:

• a screw shaft having a spiral roller-rolling surface on an outer peripheral surface thereof;
• a nut having a spiral loaded roller-rolling surface on an inner peripheral surface thereof, the loaded roller-rolling surface being opposed to the roller-rolling surface of the screw shaft;
• a circulation member arranged in the nut and formed to have an unloaded return path connecting one end and the other end of the loaded roller-rolling surface, whose turn number is less than one, of the nut;
• and
• a plurality of rollers arranged in a one-turn roller circulation path composed by a loaded roller-rolling path having less than one turn between the roller-rolling surface of the screw shaft and the loaded roller-rolling surface of the nut and an unloaded return path of the circulation member,
• wherein the circulation member is formed to guide the rollers which have rolled and arrived at one end of the loaded roller-rolling path of less than one turn to the unloaded return path and to return the rollers to the other end of the loaded roller-rolling path of less than one turn, when the screw shaft is relatively rotated to the nut,
• the unloaded return path of the circulation member has a cross section closed to enclose the rollers which is square in conformity with a shape of a side surface of each of the rollers, and having a linear central part and curved end parts,
• the linear central part of the unloaded return path is twisted so as to rotate attitudes of the rollers which move along the unloaded return path,
• the circulation member is formed by combining two split members split at a position of a diagonal line across the full length of the unloaded return path of which cross section is square, and
• mating surfaces of a pair of the two split members are twisted in accordance with the linear central part of the twisted unloaded return path.